Method for charging secondary battery

Abstract

The present invention provides a power storage system which has high energy density. The present invention provides a power storage system which has high safety. The present invention provides a secondary battery which has high energy density. The present invention provides a secondary battery which has high safety. A battery charger which has a function of controlling the start and stop of charging of a secondary battery and a function of controlling the charging current of a secondary battery. The secondary battery comprises a positive electrode; the positive electrode comprises positive electrode active material particles; and the positive electrode active material particles are formed of lithium cobaltate to which magnesium has been added. The battery charger has a function of controlling charging of a secondary battery with use of a first step in which constant current charging of a secondary battery is started at a time point t1 and a second step in which the charging is stopped at a time point t2. At the time point t2, the crystal structure of lithium cobaltate as determined by powder X-ray diffractometry is represented by the space group R-3m.

Description

Secondary battery charging method

[0001] One embodiment of the present invention relates to a power storage system, a method for operating the power storage system, a secondary battery, and a method for operating the secondary battery. Another embodiment of the present invention relates to a method for charging the secondary battery. Another embodiment of the present invention relates to a semiconductor device and a method for operating the semiconductor device. Another embodiment of the present invention relates to a battery control circuit, a battery protection circuit, a power storage device, an electric device, and methods for operating them.

[0002] Note that one embodiment of the present invention is not limited to the above technical field. The technical field of the invention disclosed in this specification and the like relates to an object or a method. Alternatively, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Therefore, more specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a display device, a light-emitting device, a power storage device, an imaging device, a memory device, a driving method thereof, or a manufacturing method thereof.

[0003] Energy storage devices (also called batteries or secondary batteries) are now used in a wide range of fields, from small electronic devices to automobiles. As the range of applications for batteries expands, applications using multi-cell battery stacks, in which multiple battery cells are connected in series, are also increasing.

[0004] The battery storage device is equipped with a circuit for detecting abnormalities during charging and discharging, such as over-discharge, over-charge, over-current, or short circuit. Such a circuit acquires data such as voltage and current, and based on that data, performs control such as stopping charging and discharging or cell balancing. This allows for battery protection and control.

[0005] Patent Document 1 discloses a protection IC that functions as a battery protection circuit. Specifically, Patent Document 1 discloses a protection IC that has multiple internal comparators and compares a reference voltage with the voltage at the terminal to which the battery is connected to detect abnormalities during charging and discharging.

[0006] Furthermore, Patent Document 2 discloses a battery state detection device for detecting a micro-short circuit in a secondary battery, and a battery pack incorporating the same.

[0007] Furthermore, Patent Document 3 discloses a protective semiconductor device that protects a battery pack in which secondary battery cells are connected in series.

[0008] U.S. Patent Application Publication No. 2011-267726 JP 2010-66161 A JP 2010-220389 A

[0009] An object of one embodiment of the present invention is to provide a power storage system with high energy density. Another object of one embodiment of the present invention is to provide a power storage system with high safety. Another object of one embodiment of the present invention is to provide a charging method for a power storage system with high energy density. Another object of one embodiment of the present invention is to provide a charging method for a power storage system with high safety. Another object of one embodiment of the present invention is to provide a secondary battery with high energy density. Another object of one embodiment of the present invention is to provide a secondary battery with high safety. Another object of one embodiment of the present invention is to provide a novel charging method for a secondary battery. Another object of one embodiment of the present invention is to provide a power storage system using a highly reliable positive electrode active material. Another object of one embodiment of the present invention is to provide a highly reliable positive electrode active material. Another object of one embodiment of the present invention is to apply the positive electrode active material of one embodiment of the present invention to the power storage system of one embodiment of the present invention to provide an excellent power storage system. Another object of one embodiment of the present invention is to estimate the state of a secondary battery. Another object of one embodiment of the present invention is to estimate the depth of charge of a secondary battery.Another object of one embodiment of the present invention is to estimate the capacity at which a secondary battery can be fully charged and to estimate the deterioration state of the secondary battery.Another object of one embodiment of the present invention is to estimate the dischargeable capacity of the secondary battery.

[0010] Another object of one embodiment of the present invention is to provide a novel charger, a charge control circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, a vehicle, an electronic device, etc. Another object of one embodiment of the present invention is to provide a low-power charger, a charge control circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, a vehicle, an electronic device, etc. Another object of one embodiment of the present invention is to provide a highly integrated charger, a charge control circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, a vehicle, an electronic device, etc.

[0011] The problems of one embodiment of the present invention are not limited to the problems listed above. The problems listed above do not preclude the existence of other problems. The other problems are problems not mentioned in this section, which will be described below. Problems not mentioned in this section can be derived by a person skilled in the art from the description in the specification or drawings, and can be appropriately extracted from these descriptions. One embodiment of the present invention solves at least one of the problems listed above and / or other problems.

[0012] The charger of one embodiment of the present invention can be particularly advantageously used in combination with a secondary battery using the positive electrode active material of one embodiment of the present invention. The charger of one embodiment of the present invention has a function of measuring the charging voltage and charging current of the secondary battery and detecting a change in the crystal structure of the positive electrode active material of one embodiment of the present invention during charging by analyzing the measured charging voltage and charging current.

[0013] In a secondary battery, the charge capacity can be increased by maximizing the charge voltage during repeated charge and discharge. Furthermore, to realize a secondary battery with a long life, it is preferable that the change in the crystal structure of the positive electrode active material is generally reversible even at an elevated charge voltage. A charging method according to one embodiment of the present invention is a charging method in which the change in the crystal structure of the positive electrode active material is generally reversible, thereby suppressing the collapse of the crystal structure of the positive electrode active material during charging and achieving a high-capacity, long-life secondary battery.

[0014] The positive electrode active material of one embodiment of the present invention can make the change in the crystal structure of the positive electrode active material approximately reversible even at an elevated charging voltage. By suitably using the positive electrode active material of one embodiment of the present invention for a secondary battery, the charger of one embodiment of the present invention has a function of detecting the change in the crystal structure of the positive electrode active material and controlling charging in a range where the charging voltage is high and the change in the crystal structure is approximately reversible, using the charger of one embodiment of the present invention.

[0015] The positive electrode active material of one embodiment of the present invention changes from an O3-type crystal structure to an O3'-type crystal structure, which will be described later. This change in crystal structure occurs when the secondary battery is in a deep state of charge. The charger of one embodiment of the present invention has a function of detecting the change from the O3-type crystal structure to the O3'-type crystal structure and controlling charging.

[0016] One aspect of the present invention is a method for charging a secondary battery using a charger that has a function of controlling the start and stop of charging of the secondary battery and a function of controlling the charging current of the secondary battery, the secondary battery having a positive electrode, the positive electrode having positive electrode active material particles, the positive electrode active material particles being lithium cobalt oxide with added magnesium, the method comprising: a first step of starting charging of the secondary battery at a constant current at time t1; and a second step of stopping charging at time t2, wherein the crystal structure of the lithium cobalt oxide determined by powder X-ray diffraction at time t2 is a crystal structure represented by the space group R-3m. Note that "determined by X-ray diffraction" can also be expressed as "identified by X-ray diffraction."

[0017] In the above configuration, when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation at time t2, it is preferable that the positive electrode has diffraction peaks at 2θ = 19.35 ± 0.10° and 2θ = 45.55 ± 0.20°, respectively. It is also preferable that the depth of charge of the lithium cobalt oxide is 70% or more at time t2.

[0018] Alternatively, one embodiment of the present invention is a method for charging a secondary battery using a charger including a control circuit and a voltage measurement circuit. The control circuit has a function of controlling start and stop of charging of the secondary battery and a function of controlling a charging current of the secondary battery. The control circuit has a function of calculating a time change in voltage of the secondary battery and a function of detecting a maximum time change in voltage of the secondary battery. The voltage measurement circuit has a function of measuring a charging voltage of the secondary battery. The control circuit starts charging of the secondary battery at time t3. The voltage measurement circuit measures a voltage V(t) of the secondary battery at time t. This is a charging method for a secondary battery in which the voltage V(t-Δt1) of the secondary battery at time t minus time Δt1 is measured and the control circuit analyzes a second curve with time t on the horizontal axis and the vertical axis on the change in voltage of the secondary battery over time [voltage V(t) - voltage V(t-Δt1)] to detect a time tq at which the second curve has a first minimum, and the control circuit stops charging at time t4, a predetermined time after time tq, and charging of the secondary battery is performed at a constant current from time t3 to time t4, so that the voltage V(tq) of the secondary battery at time tq is 4.25 V or higher.

[0019] In the above configuration, it is preferable that the control circuit has an analog-to-digital conversion circuit, which has a function of converting the measured charging voltage from an analog value to a digital value, and that the resolution of the analog-to-digital conversion circuit is 12 bits or less.

[0020] In the above configuration, the secondary battery preferably has a positive electrode, the positive electrode containing lithium and cobalt, and at time tq, the crystal structure determined by powder X-ray diffraction is preferably a crystal structure represented by space group R-3m.

[0021] In the above configuration, it is preferable that the charger has a memory circuit, data according to the environmental temperature is stored in the memory circuit, and the time tq is detected using the data.

[0022] In the above configuration, it is preferable that the charger has a memory circuit, data corresponding to the positive electrode active material of the secondary battery is stored in the memory circuit, and the time tq is detected using the data.

[0023] One aspect of the present invention is a method for charging a secondary battery using a charger having a control circuit, a voltage measurement circuit, and a current measurement circuit. The control circuit has a function of controlling the start and stop of charging of the secondary battery and a function of controlling the charging current of the secondary battery. The control circuit has a function of calculating a voltage derivative of a quantity of electricity of the secondary battery and a function of detecting a local maximum of the voltage derivative of the quantity of electricity. The voltage measurement circuit has a function of measuring the charging voltage of the secondary battery, and the current measurement circuit has a function of measuring the charging current of the secondary battery. The method starts charging of the secondary battery at time t1, calculates a quantity of electricity Q(t) using a current I(t) at time t, analyzes a first curve with voltage V(t) on the horizontal axis and voltage derivative [dQ(t) / dV(t)] of the quantity of electricity Q(t) on the vertical axis, detects a time tp at which the first curve has a first local maximum, and stops charging at time t2, a predetermined time after time tp, and the voltage V(tp) at time tp is 4.25 V or higher.

[0024] In the above configuration, it is preferable that charging is performed at a constant current.

[0025] In the above configuration, the secondary battery preferably has a positive electrode, the positive electrode containing lithium and cobalt, and the crystal structure determined by powder X-ray diffraction analysis at time tp is a crystal structure represented by space group R-3m.In the above configuration, the positive electrode preferably has lithium cobalt oxide, and the crystal structure determined by powder X-ray diffraction at time tp is a crystal structure represented by space group R-3m.

[0026] In the above configuration, it is preferable that the charger has a memory circuit, data corresponding to the environmental temperature is stored in the memory circuit, and the time tp is detected using the data.

[0027] In the above configuration, it is preferable that the charger has a memory circuit, and the memory circuit stores data corresponding to the positive electrode active material of the secondary battery, and the time tp is detected using the data.

[0028] One embodiment of the present invention is a method for charging a secondary battery using a charger having a control circuit, a voltage measurement circuit, and a current measurement circuit, in which the control circuit has a function of controlling the start and stop of charging of the secondary battery and a function of controlling the charging current of the secondary battery, the control circuit has a function of calculating a time change in voltage of the secondary battery and a function of detecting a maximum of the time change in voltage, the voltage measurement circuit has a function of measuring the charging voltage of the secondary battery, and the current measurement circuit has a function of measuring the charging current of the secondary battery, the control circuit starts charging the secondary battery at time t3, and the voltage measurement circuit has a function of measuring the charging current of the secondary battery at time t The control circuit measures the voltage V(t) of the secondary battery at time t, and the voltage V(t-Δt1) of the secondary battery at time t minus a time Δt1 (t-Δt1), and analyzes a second curve with time t on the horizontal axis and the vertical axis showing the change in voltage of the secondary battery over time [voltage V(t)-voltage V(t-Δt1)] to detect a time tq at which the second curve has a first minimum, and the control circuit stops charging at time t4, a predetermined time after time tq, and charges the secondary battery at a constant current from time t3 to time t4, so that the voltage V(tq) of the secondary battery at time tq is 4.25 V or higher.

[0029] In the above configuration, the secondary battery preferably has a positive electrode, the positive electrode containing lithium and cobalt, and the crystal structure determined by powder X-ray diffraction analysis at time t3 is a crystal structure represented by space group R-3m.In the above configuration, the positive electrode preferably has lithium cobalt oxide, and the crystal structure determined by powder X-ray diffraction at time tq is a crystal structure represented by space group R-3m.

[0030] In the above configuration, it is preferable that the charger has a memory circuit, data according to the environmental temperature is stored in the memory circuit, and the time tq is detected using the data.

[0031] In the above configuration, it is preferable that the charger has a memory circuit, data corresponding to the positive electrode active material of the secondary battery is stored in the memory circuit, and the time tq is detected using the data.

[0032] A method for charging a secondary battery using a charger having a function for controlling the start and stop of charging of the secondary battery and a function for controlling the charging current of the secondary battery, wherein the secondary battery has a positive electrode, the positive electrode containing lithium and cobalt, and the method includes a first step of starting charging of the secondary battery with a constant current at time t1 and a second step of stopping charging at time t2, and the crystal structure determined by X-ray diffraction at time t2 is a crystal structure expressed by the space group R-3m.

[0033] In the above configuration, when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation at time t2, it is preferable that the positive electrode has diffraction peaks at 2θ=19.35±0.10° and 2θ=45.55±0.20°.

[0034] In the above structure, the positive electrode preferably contains lithium cobalt oxide.

[0035] In the above configuration, the positive electrode is LiMO ２ (M is a metal), and the metal M is preferably two or more metals including cobalt.

[0036] One aspect of the present invention is a method for charging a secondary battery using a charger having a control circuit and a voltage measurement circuit, wherein the control circuit has a function of controlling the start and stop of charging of the secondary battery and a function of controlling the charging current of the secondary battery, the control circuit has a function of calculating a time change in voltage of the secondary battery and a function of detecting a maximum of the time change, and the voltage measurement circuit has a function of measuring the charging voltage of the secondary battery, and the method includes a first step in which the control circuit starts constant current charging of the secondary battery, a second step in which the voltage measurement circuit measures a voltage V of the secondary battery, and the control circuit compares the voltage V with a predetermined voltage V1, and if the voltage V is equal to or greater than the voltage V1, proceeds to a fourth step, and if the voltage V is less than V1, returns to the second step. a fourth step in which the control circuit accumulates paired data of dt / dV and time t and calculates [dt / dV]mean, which is a moving average of dt / dV, and [dt / dV]max, which is the maximum value of the accumulated dt / dV; a fifth step in which the control circuit compares [dt / dV]mean with a value obtained by multiplying [dt / dV]max by a constant Rt, and proceeds to a sixth step if [dt / dV]mean is smaller than the value obtained by multiplying [dt / dV]max by the constant Rt, and returns to the fourth step if [dt / dV]mean is equal to or greater than the value obtained by multiplying [dt / dV]max by the constant Rt; and a sixth step in which the control circuit stops constant current charging of the secondary battery.

[0037] In the above configuration, it is preferable that the voltage V1 is 4.25 V or more, and the constant Rt is 0.6 or more and 0.9 or less.

[0038] According to one embodiment of the present invention, a power storage system with high energy density can be provided. According to one embodiment of the present invention, a power storage system with high safety can be provided. According to one embodiment of the present invention, a secondary battery with high energy density can be provided. According to one embodiment of the present invention, a secondary battery with high safety can be provided. According to one embodiment of the present invention, a novel charging method for a secondary battery can be provided. According to one embodiment of the present invention, a power storage system using a highly reliable positive electrode active material can be provided. According to one embodiment of the present invention, a highly reliable positive electrode active material can be provided. According to one embodiment of the present invention, an excellent power storage system can be provided by applying the positive electrode active material of one embodiment of the present invention to the power storage system of one embodiment of the present invention. According to one embodiment of the present invention, the state of a secondary battery can be estimated. According to one embodiment of the present invention, the depth of charge of a secondary battery can be estimated. According to one embodiment of the present invention, the fully chargeable capacity of a secondary battery can be estimated, and the deterioration state of the secondary battery can be estimated. According to one embodiment of the present invention, the dischargeable capacity of a secondary battery can be estimated.

[0039] One embodiment of the present invention can provide a novel charger, a charge control circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, a vehicle, an electronic device, etc. One embodiment of the present invention can provide a low-power charger, a charge control circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, a vehicle, an electronic device, etc. One embodiment of the present invention can provide a highly integrated charger, a charge control circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, a vehicle, an electronic device, etc.

[0040] The effects of one embodiment of the present invention are not limited to the effects listed above. The effects listed above do not preclude the existence of other effects. The other effects are described below and are not mentioned in this section. Effects not mentioned in this section can be derived by a person skilled in the art from the description in the specification or drawings, and can be extracted as appropriate from these descriptions. One embodiment of the present invention has at least one of the effects listed above and / or other effects. Therefore, one embodiment of the present invention may not have the effects listed above in some cases.

[0041] FIG. 1A is a block diagram showing an example of a power storage system. FIG. 1B is a block diagram showing an example of a power storage system. FIG. 2A is a block diagram showing an example of a power storage system. FIG. 2B is a block diagram showing an example of a power storage system. FIG. 3A is a block diagram showing an example of a power storage system. FIG. 3B is a block diagram showing an example of a power storage system. FIG. 4A is a block diagram showing an example of a power storage system. FIG. 4B is a block diagram showing an example of a power storage system. FIG. 5 is a flow diagram illustrating a method for charging a secondary battery. FIG. 6 is a flow diagram illustrating a method for charging a secondary battery. FIG. 7A is a block diagram showing an example of a power storage system. FIG. 7B is a block diagram showing an example of a power storage system. FIG. 7C is a block diagram showing an example of a power storage system. FIG. 8A is a cross-sectional view of a positive electrode active material, and FIGS. 8B to 8E are partial cross-sectional views of the positive electrode active material. FIGS. 9A and 9B are cross-sectional views of the positive electrode active material, and FIGS. 9C and 9D are partial cross-sectional views of the positive electrode active material. FIG. 10 is a cross-sectional view of the positive electrode active material. FIG. 11 is a cross-sectional view of the positive electrode active material. FIG. 12 is a diagram illustrating the crystal structure of a positive electrode active material. FIG. 13 is a diagram illustrating an example of a method for manufacturing a positive electrode active material. FIG. 14 is a diagram illustrating an example of a method for manufacturing a positive electrode active material. FIGS. 15A and 15B are diagrams illustrating an example of the appearance of a secondary battery. FIGS. 16A and 16B are diagrams illustrating a method for manufacturing a secondary battery. FIGS. 17A and 17B are diagrams illustrating a method for manufacturing a secondary battery. FIG. 18 is a cross-sectional view showing an example of a secondary battery. FIG. 19A is a diagram illustrating an example of a secondary battery. FIGS. 19B and 19C are diagrams illustrating an example of a method for manufacturing a stack. FIGS. 20A to 20C are diagrams illustrating an example of a method for manufacturing a secondary battery. FIGS. 21A and 21B are cross-sectional views showing an example of a stack. FIG. 21C is a cross-sectional view showing an example of a secondary battery. FIGS. 22A and 22B are diagrams illustrating an example of a secondary battery. FIG. 22C is a diagram illustrating the interior of a secondary battery. FIGS. 23A to 23C are diagrams illustrating an example of a secondary battery. FIG. 24 is a block diagram showing an example of a vehicle having a motor. Figures 25A to 25E are diagrams showing an example of a transportation vehicle. Figure 26A is a diagram showing an electric bicycle, Figure 26B is a diagram showing a secondary battery for the electric bicycle, and Figure 26C is a diagram explaining an electric motorcycle.FIGS. 27A and 27B are diagrams showing an example of a power storage device. FIGS. 28A to 28E are diagrams showing an example of an electronic device. FIGS. 29A to 29F are diagrams explaining an example of an electronic device. FIGS. 30A to 30C are diagrams explaining an example of an electronic device. FIG. 31 is a diagram explaining an example of an electronic device. FIGS. 32A to 32C are diagrams explaining an example of an electronic device. FIGS. 33A to 33D are diagrams showing an example of an electronic device. FIGS. 34A and 34B are dQ / dV-V curves. FIGS. 35A and 35B are dQ / dV-V curves. FIG. 36A is a V-C curve. FIG. 36B is a ΔV-t curve. FIGS. 37A and 37B are dQ / dV curves. FIG. 38A is a diagram showing the relationship between the number of charge / discharge cycles and discharge capacity. FIG. 38B is a diagram showing the relationship between the number of charge / discharge cycles and discharge capacity retention rate. FIGS. 39A and 39B are diagrams showing the relationship between charge time and voltage, and the relationship between charge time and charge capacity. FIG. 40A shows the relationship between charge time and voltage, and the relationship between charge time and charge capacity. FIG. 40B shows the number of charge / discharge cycles and the maximum charge voltage. FIGS. 41A and 41B show SEM images. FIGS. 42A and 42B show SEM images. FIGS. 43A and 43B show SEM images. FIG. 44A shows a transmission electron image. FIG. 44B shows a Z-contrast image. FIG. 44C shows a transmission electron image. FIG. 45A shows a transmission electron image. FIG. 45B shows a Z-contrast image. FIG. 45C shows a transmission electron image. FIG. 46A shows a transmission electron image. FIG. 46B shows a Z-contrast image. FIG. 46C shows a transmission electron image. FIG. 47A shows a transmission electron image. FIG. 47B shows a Z-contrast image. FIG. 47C shows a transmission electron image. FIGS. 47D to 47F show the results of EDX area analysis. FIG. 48A shows a transmission electron image. Fig. 48B shows a Z-contrast image. Fig. 48C shows a transmission electron image. Figs. 48D to 48F show the results of EDX area analysis. Fig. 49A shows a transmission electron image. Fig. 49B shows a Z-contrast image. Fig. 49C shows a transmission electron image. Figs. 49D to 49F show the results of EDX area analysis. Figs. 50A to 50C show the results of EDX ray analysis. Fig. 51 is a flow chart showing a charging method for a secondary battery. Fig. 52 shows the results of the cycle characteristics of the secondary battery.Fig. 53 shows the relationship between the end-of-charge voltage of a secondary battery and the charge / discharge cycle. Fig. 54A to Fig. 54C show the dQ / dV curve of the secondary battery. Fig. 55A and Fig. 55B show the dQ / dV curve of the secondary battery.

[0042] Hereinafter, embodiments will be described with reference to the drawings. However, it will be readily understood by those skilled in the art that the embodiments can be implemented in many different ways and that various changes in form and details can be made without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the following description of the embodiments.

[0043] In this specification, the ordinal numbers "first," "second," and "third" are used to avoid confusion between components. Therefore, they do not limit the number of components. Furthermore, they do not limit the order of the components. For example, a component referred to as "first" in one embodiment of this specification may be a component referred to as "second" in another embodiment or in the claims. For example, a component referred to as "first" in one embodiment of this specification may be omitted in another embodiment or in the claims.

[0044] In the drawings, the same elements or elements having similar functions, elements made of the same material, or elements formed at the same time may be given the same reference numerals, and repeated explanations thereof may be omitted.

[0045] Furthermore, in order to facilitate understanding of the invention, the position, size, range, etc. of each component shown in the drawings, etc. may not represent the actual position, size, range, etc. Therefore, the disclosed invention is not necessarily limited to the position, size, range, etc. disclosed in the drawings, etc.

[0046] In addition, in top views (also called "plan views") or perspective views, illustration of some components may be omitted to make the drawings easier to understand.

[0047] Furthermore, the terms "electrode" and "wiring" used in this specification and the like do not limit the functionality of these components. For example, they may be used as part of an "electrode" or "wiring," and vice versa. Furthermore, the terms "electrode" and "wiring" also include cases where multiple "electrodes" or "wirings" are integrally formed.

[0048] In this specification, a "terminal" may refer to, for example, a wiring or an electrode connected to a wiring. In this specification, a part of a "wiring" may be called a "terminal."

[0049] In this specification, the terms "above" and "below" do not limit the positional relationship of components to being directly above or below, and being in direct contact with each other. For example, the expression "electrode B on insulating layer A" does not require that electrode B be formed on insulating layer A in direct contact with it, and does not exclude the inclusion of other components between insulating layer A and electrode B.

[0050] In addition, the functions of the source and drain are interchangeable depending on operating conditions, such as when transistors of different polarities are used or when the direction of current flow changes during circuit operation, making it difficult to define which is the source and which is the drain. For this reason, the terms source and drain can be used interchangeably in this specification.

[0051] Furthermore, in this specification, "electrically connected" includes both direct connection and connection via "something that has some kind of electrical effect." Here, "something that has some kind of electrical effect" is not particularly limited as long as it allows electrical signals to be transmitted and received between the connected objects. Therefore, even when the expression "electrically connected" is used, in an actual circuit, there may be no physical connection and only wiring may be extended.

[0052] Furthermore, in this specification and elsewhere, "parallel" refers to, for example, a state in which two straight lines are arranged at an angle of -10° or more and 10° or less. Therefore, cases in which the angle is -5° or more and 5° or less are also included. Furthermore, "perpendicular" and "orthogonal" refer to, for example, a state in which two straight lines are arranged at an angle of 80° or more and 100° or less. Therefore, cases in which the angle is 85° or more and 95° or less are also included.

[0053] In this specification and elsewhere, when referring to counting values ​​and measurement values, terms such as "identical," "same," "equal," or "uniform" are used, unless otherwise specified, and include an error of plus or minus 20%.

[0054] Furthermore, voltage often refers to the potential difference between a certain potential and a reference potential (for example, a ground potential or a source potential). Therefore, voltage and potential can often be used interchangeably.

[0055] It should be noted that even when written as "semiconductor," if the conductivity is sufficiently low, it will have the properties of an "insulator." Therefore, it is also possible to use "semiconductor" instead of "insulator." In this case, the boundary between "semiconductor" and "insulator" is vague, and it is difficult to strictly distinguish between the two. Therefore, "semiconductor" and "insulator" described in this specification may be read interchangeably.

[0056] Furthermore, even when written as "semiconductor," if the conductivity is sufficiently high, it will have the properties of a "conductor." Therefore, it is also possible to use "semiconductor" instead of "conductor." In this case, the boundary between "semiconductor" and "conductor" is vague, and it is difficult to strictly distinguish between the two. Therefore, "semiconductor" and "conductor" described in this specification may be read interchangeably.

[0057] In this specification and the like, the "on state" of a transistor refers to a state in which the source and drain of the transistor are considered to be electrically short-circuited (also referred to as a "conductive state"). The "off state" of a transistor refers to a state in which the source and drain of the transistor are considered to be electrically disconnected (also referred to as a "non-conductive state").

[0058] In this specification, the term "on-state current" may refer to a current that flows between the source and drain of a transistor when the transistor is on, and the term "off-state current" may refer to a current that flows between the source and drain of a transistor when the transistor is off.

[0059] In this specification and the like, a high power supply potential VDD (hereinafter simply referred to as "VDD" or "H potential") refers to a power supply potential that is higher than a low power supply potential VSS. A low power supply potential VSS (hereinafter simply referred to as "VSS" or "L potential") refers to a power supply potential that is lower than the high power supply potential VDD. A ground potential can also be used as VDD or VSS. For example, when VDD is a ground potential, VSS is a potential lower than the ground potential, and when VSS is a ground potential, VDD is a potential higher than the ground potential.

[0060] In this specification and the like, a gate refers to a gate electrode and a part or all of a gate wiring, and a gate wiring refers to a wiring for electrically connecting the gate electrode of at least one transistor to another electrode or another wiring.

[0061] In this specification, the term "source" refers to a source region, a source electrode, and part or all of a source wiring. The term "source region" refers to a region of a semiconductor layer whose resistivity is equal to or less than a certain value. The term "source electrode" refers to a conductive layer connected to the source region. The term "source wiring" refers to wiring that electrically connects the source electrode of at least one transistor to another electrode or wiring.

[0062] In this specification, the term "drain" refers to a part or all of the drain region, drain electrode, and drain wiring. The term "drain region" refers to a region of the semiconductor layer whose resistivity is equal to or less than a certain value. The term "drain electrode" refers to a conductive layer connected to the drain region. The term "drain wiring" refers to wiring that electrically connects the drain electrode of at least one transistor to another electrode or another wiring.

[0063] In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially distributed non-uniformly in a solid composed of a plurality of elements (for example, A, B, C).

[0064] In this specification, the surface layer of a particle of active material or the like refers to a region extending from the surface to the interior, extending up to approximately 10 nm perpendicular or nearly perpendicular from the surface. Alternatively, it refers to a region within 50 nm. Alternatively, it refers to a region within 5 nm. The surface layer is synonymous with near-surface, near-surface region, or shell. Nearly perpendicular refers to an angle of 80° to 100°. Surfaces caused by cracks or fissures may also be considered the surface. The region deeper than the surface layer is referred to as the interior. In EDX line analysis, the surface of a positive electrode active material refers to the measurement point where the transition metal exhibits a measurement value closest to 50% of the average detected amount of the bulk. Alternatively, in the tangent method, it refers to the intersection of a tangent drawn to the intensity profile of the EDX line analysis of the transition metal and the depth axis. In STEM images, the surface of a positive electrode active material refers to the boundary between the region where an image derived from the crystalline structure of the positive electrode active material is observed and the region where it is not observed, and is the outermost region where atomic columns derived from the nuclei of metal elements with atomic numbers greater than that of lithium are observed. Alternatively, the surface is defined as the intersection of a tangent drawn to the brightness profile from the surface to the bulk in an STEM image and the axis in the depth direction. The surface in an STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.

[0065] In this specification, the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Furthermore, strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice structure.

[0066] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately, and it is also possible for there to be a deficiency of cations or anions.

[0067] In this specification and the like, the O3'-type crystal structure (also referred to as a pseudospinel-type crystal structure) possessed by a composite oxide containing lithium and a transition metal refers to a crystal structure that is in the space group R-3m and is not a spinel-type crystal structure, but in which ions of cobalt, magnesium, etc. occupy oxygen hexacoordination positions and in which the arrangement of cations has a symmetry similar to that of the spinel type. Note that in the O3'-type crystal structure, light elements such as lithium may occupy oxygen tetracoordination positions, and in this case, the arrangement of ions also has a symmetry similar to that of the spinel type.

[0068] The O3' type crystal structure has randomly interlayered Li atoms, but the CdCl ２ It can be said that this crystal structure is similar to that of the CdCl type. ２ A similar crystal structure to the Li-type is lithium nickel oxide. ０．０６ NiO ２ However, it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0069] The anions in the layered rock salt crystal and the rock salt crystal have a cubic close-packed structure (face-centered cubic lattice structure). It is estimated that the anions in the O3'-type crystal also have a cubic close-packed structure. When they contact, there is a crystal plane where the orientation of the cubic close-packed structure formed by the anions is aligned. However, the space group of the layered rock salt crystal and the O3'-type crystal is R-3m, which is different from the space group of the rock salt crystal, Fm-3m (the space group of a general rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt crystal and the O3'-type crystal and the rock salt crystal. In this specification, when the orientation of the cubic close-packed structure formed by the anions is aligned in the layered rock salt crystal, the O3'-type crystal, and the rock salt crystal, the crystal orientation may be said to be approximately aligned.

[0070] A secondary battery has, for example, a positive electrode and a negative electrode. A material constituting the positive electrode is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may partially contain a substance that does not contribute to the charge / discharge capacity.

[0071] In this specification and the like, the positive electrode active material used in one embodiment of the present invention may be referred to as a positive electrode material, a positive electrode material for a secondary battery, or the like. In this specification and the like, the positive electrode active material used in one embodiment of the present invention preferably includes a compound. In this specification and the like, the positive electrode active material used in one embodiment of the present invention preferably includes a composition. In this specification and the like, the positive electrode active material used in one embodiment of the present invention preferably includes a composite.

[0072] In this specification, Miller indices are used to represent crystal planes and crystal directions. Individual planes representing crystal planes are represented using ( ). In crystallography, crystal planes, crystal directions, and space groups are represented by a superscript bar. However, due to formatting constraints, in this specification, instead of a bar above the number, a minus sign (-) may be placed before the number. Individual orientations indicating directions within a crystal are represented using [ ], collective orientations indicating all equivalent directions are represented using < >, individual planes indicating crystal planes are represented using ( ), and collective planes with equivalent symmetry are represented using {}. Trigonal crystals represented by the space group R-3m are generally represented as a hexagonal composite hexagonal lattice for ease of understanding the structure, and Miller indices such as (hkl) and (hkil) are sometimes used. Here, i is -(h+k).

[0073] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated. ２ The theoretical capacity of LiNiO is 274 mAh / g. ２ The theoretical capacity of LiMn is 274mAh / g. ２ O ４ The theoretical capacity of the battery is 148 mAh / g.

[0074] In this specification, the depth of charge is a value that indicates how much capacity is charged based on the theoretical capacity of the positive electrode active material, in other words, how much lithium has been released from the positive electrode. For example, lithium cobalt oxide (LiCoO ２ ) and lithium nickel-cobalt-manganese oxide (LiNi ｘ Co ｙ Mn ｚO ２ In the case of a positive electrode active material having a layered rock salt structure such as (x+y+z=1), based on the theoretical capacity of 274 mAh / g, a charge depth of 0 refers to a state in which no Li has been released from the positive electrode active material, a charge depth of 0.5 refers to a state in which lithium equivalent to 137 mAh / g has been released from the positive electrode, and a charge depth of 0.8 refers to a state in which lithium equivalent to 219.2 mAh / g has been released from the positive electrode. ａ CoO ２ When expressed as (0≦a≦1), when the charge depth is 0, a is 1, LiCoO ２ When the charge depth is 0.5, a is 0.5 Li ０．５ CoO ２ When the charge depth is 0.8, a is 0.2. ０．２ CoO ２ It is written as follows.

[0075] Embodiment 1 In this embodiment, a charger according to one embodiment of the present invention and a power storage system including the charger according to one embodiment of the present invention will be described.

[0076] 1A shows an example of a power storage system 100. The power storage system 100 includes a charger 101 and a secondary battery 121. The charger 101 is electrically connected to the positive electrode and the negative electrode of the secondary battery 121.

[0077] The charger 101 includes a control circuit 153, a current measurement circuit 152, and a voltage measurement circuit 151. The charger 101 also preferably includes a temperature sensor TS. The temperature sensor TS can measure the ambient temperature of the secondary battery. The temperature sensor TS is set, for example, to be in contact with the exterior body or housing of the secondary battery. Charging control using temperature will be described later.

[0078] The current measuring circuit 152 has a function of measuring the current of the secondary battery 121. In particular, it is preferable that the current measuring circuit 152 has a function of measuring the charging current of the secondary battery 121. The current measuring circuit 152 can provide the measured current value to the control circuit 153.

[0079] The voltage measurement circuit 151 has a function of measuring the voltage of the secondary battery 121. In particular, it is preferable that the voltage measurement circuit 151 has a function of measuring the charging voltage of the secondary battery 121. The voltage measurement circuit 151 can provide the measured voltage value to the control circuit 153.

[0080] The control circuit 153 has a function of controlling the start and stop of charging of the secondary battery 121. The control circuit 153 also has a function of controlling the charging conditions of the secondary battery 121. Specifically, for example, the control circuit 153 has a function of controlling the charging current of the secondary battery 121.

[0081] The control circuit 153 may be a CPU (Central Processing Unit), an MCU (Micro Controller Unit), or the like.

[0082] The control circuit 153 also has a function of calculating the time change in the voltage of the secondary battery 121 provided by the voltage measurement circuit 151. The calculation of the time change in voltage refers, for example, to acquiring multiple sets of data of voltage values ​​and time and performing calculations using the acquired sets of data. Specifically, the control circuit 153 has a function of calculating a time derivative, for example. The control circuit 153 preferably has an analog-to-digital conversion circuit. If the acquired voltage value of the secondary battery is an analog value, the control circuit 153 can convert it to a digital value using the analog-to-digital conversion circuit. If an MCU is used as the control circuit 153, the control circuit 153 can also be configured to include the voltage measurement circuit 151 and an analog-to-digital conversion circuit unit. The analog-to-digital conversion circuit may also be provided separately from the control circuit 153.

[0083] The control circuit 153 also has a function of calculating the amount of electricity of the secondary battery using the voltage value of the secondary battery 121 given from the voltage measurement circuit 151 and the current value of the secondary battery 121 given from the current measurement circuit 152. The control circuit 153 also has a function of calculating the voltage differential (dQ / dV) of the amount of electricity of the secondary battery.

[0084] The control circuit 153 also includes a memory circuit. The memory circuit functions as, for example, a register of a CPU or an MCU, or a cache memory. The memory circuit also has a function of storing, for example, various programs used in the power storage system 100 and data necessary for the operation of the power storage system 100.

[0085] 1B shows an example in which charger 101 has, in addition to the configuration shown in FIG. 1A, detection circuit 185, detection circuit 186, short detection circuit SD, micro-short detection circuit MSD, transistor 140, and transistor 150. Details of detection circuit 185, detection circuit 186, short detection circuit SD, micro-short detection circuit MSD, transistor 140, and transistor 150 will be described later.

[0086] 2A and 2B show an example in which the current measuring circuit 152 includes a resistive element 152a and a circuit 152b.

[0087] The resistor element 152a functions as a shunt resistor, and the circuit 152b functions to measure the voltage across the resistor element 152a.

[0088] 3A and 3B , the power storage system 100 may also include a DC-DC converter 157. The DC-DC converter 157 includes a voltage conversion circuit and a control circuit. The DC-DC converter 157 has a function of converting and outputting the voltage of the secondary battery 121.

[0089] The power storage system 100 may also include a circuit 158, as shown in FIGS. 3A and 3B . The circuit 158 ​​preferably functions as an AC adapter. For example, the circuit 158 ​​has a function of converting AC power to DC power. The circuit 158 ​​may also have a function of converting voltage. The circuit 158 ​​also has a function of supplying the converted DC power to the secondary battery. The circuit 158 ​​may also have a function of controlling the current value and voltage value to be supplied when supplying power to the secondary battery. Alternatively, the circuit 158 ​​may have a function of controlling the current value and voltage value to be supplied to the secondary battery based on a signal supplied from the control circuit 153.

[0090] 3A and 3B , in the power storage system 100, a diode 159 may be provided between the circuit 158 ​​and the charger 101. The diode 159 has a function of suppressing a reverse current from the charger 101 to the circuit 158.

[0091] In a secondary battery, as the depth of charge increases (the charge capacity increases), the crystalline structure of the positive electrode active material of the secondary battery changes. If this change in crystalline structure is irreversible, repeated charging may result in a decrease in the chargeable capacity of the secondary battery.

[0092] Therefore, in order to realize a secondary battery with high capacity and long life, it is necessary to increase the depth of charge of the secondary battery and keep the depth of charge of the secondary battery so that the change in the crystal structure is within a range that is approximately reversible.

[0093] For example, by charging a secondary battery at a predetermined voltage, the state of the secondary battery can be controlled so that the change in the crystal structure is within a roughly reversible range. However, because the state of a secondary battery changes with repeated charging and discharging, it becomes difficult to maintain the same state of charge of the secondary battery as the number of charge and discharge cycles increases, even when charging is performed at the same upper voltage. Therefore, a means for monitoring the charging process is required to control the state of charge of a secondary battery within a roughly reversible range of the crystal structure.

[0094] By using the charger of one embodiment of the present invention, the charging process can be monitored, and the charge depth of the secondary battery can be controlled so that the charge depth is deep and within a substantially reversible range of the crystal structure. In addition, it is preferable to apply the positive electrode active material of one embodiment of the present invention to the secondary battery.

[0095] A charger according to one embodiment of the present invention can suppress the collapse of the crystal structure of a positive electrode active material of a secondary battery by controlling the charging conditions of the secondary battery. More specifically, for example, the charger according to one embodiment of the present invention can maximize the charging voltage of the secondary battery within a range in which the collapse of the crystal structure can be suppressed, thereby improving the reliability of the secondary battery and achieving a high energy density by utilizing the secondary battery to its limit.

[0096] In addition, the charger of one embodiment of the present invention can particularly suppress the collapse of the crystal structure of a positive electrode active material having a layered crystal structure. In a positive electrode active material having a layered crystal structure, for example, metals serving as carrier ions are arranged in a layered structure. For example, in lithium cobalt oxide, CoO ２ Lithium exists in layers between the layers. In a positive electrode active material having a layered crystal structure, when carrier ions are released during charging, distortion of the crystal, changes in the crystal structure due to the release of carrier ions, etc. may occur. For example, in the case of lithium cobalt oxide, when lithium ions are released during charging, CoO ２ Layer misalignment, CoO ２ Changes such as a decrease in the interlayer distance may occur. If such changes are reversible in the crystal structure of the positive electrode active material, the decrease in charge capacity and discharge capacity during repeated charge and discharge can be suppressed. On the other hand, if the charge voltage is too high, the depth of charge becomes deep and the amount of carrier ions released increases. As the depth of charge becomes deep, the change in the crystal structure accompanying charging becomes irreversible, and there is a concern that the charge capacity and discharge capacity will decrease during repeated charge and discharge.

[0097] Furthermore, excessively high charging voltages may cause components of the positive electrode active material to leach into the electrolyte, leading to the breakdown of the crystalline structure of the positive electrode active material. Charging at high voltages may also cause decomposition reactions of the elements that make up the electrolyte.

[0098] A charger according to one embodiment of the present invention uses a simple method to detect changes in the crystal structure, increase the charging voltage to the maximum extent possible while ensuring high reliability, and efficiently utilize the charge / discharge capacity of the secondary battery to the maximum extent possible.

[0099] The secondary battery 121 to which the charger of one embodiment of the present invention is applied is preferably a secondary battery capable of determining an upper limit voltage for charging based on a waveform acquired during charging. Here, the waveform can have various shapes, such as a curve, a straight line, or a combination of a curve and a straight line. The waveform is not limited to a periodic wave. Examples of waveforms acquired during charging include a dQ / dV-V curve or a ΔV-t curve created from data on the voltage, time, and current during charging. That is, in the secondary battery 121, it is preferable that an extreme value resulting from a change in the crystal structure of the positive electrode active material is detected in the waveform acquired during charging. Furthermore, in the secondary battery 121, it is preferable that the charging voltage during repeated charging and discharging be maximized, and that the change in the crystal structure of the positive electrode active material is generally reversible even at the increased charging voltage. Here, "approximately reversible" refers to extremely small deterioration due to repeated crystal structure changes, even if the change is reversible or irreversible. The positive electrode active material of one embodiment of the present invention changes from an O3-type crystal structure to an O3'-type crystal structure, which will be described later, when the SOC (State of Charge) of the secondary battery is approximately 80% or close to that value. Furthermore, when this change occurs, an extreme value is observed in the dQ / dV curve, etc. The charger of one embodiment of the present invention has a function of detecting this extreme value and controlling charging.

[0100] Furthermore, in order to utilize the secondary battery 121 as efficiently as possible within a range in which the change in the crystal structure is approximately reversible, it is preferable that the peak caused by the change in the crystal structure be near the upper limit voltage of charging in the secondary battery 121. For example, it is preferable that the peak caused by the change in the crystal structure be lower than the upper limit voltage of charging, and that the difference between the voltage at which the peak is detected and the upper limit voltage of charging be 0.15 V or less.

[0101] Furthermore, in the secondary battery 121, it is preferable that the crystal structure of the positive electrode active material can be changed substantially reversibly during charging and discharging, even if charging is performed for a predetermined time beyond the voltage at which the extreme value is detected. When the secondary battery 121 has such characteristics, a charger according to one embodiment of the present invention can easily control the upper limit voltage of charging for marginal use by using the extreme value.

[0102] The extreme value caused by the change in the crystal structure is detected, for example, in a time change curve of the voltage of the secondary battery, or in a time derivative curve (dV / dt curve) of the voltage of the secondary battery.

[0103] Furthermore, the extreme value resulting from the change in the crystal structure is detected, for example, in the voltage differential curve (dQ / dV curve) of the quantity of electricity of the secondary battery.

[0104] Constant current-constant voltage charging (CC-CV charging) is sometimes used to charge secondary batteries. CC-CV charging involves constant current charging, and then constant voltage charging after the upper limit voltage of charging has been reached during constant current charging. In CC-CV charging, for example, constant voltage charging is performed at the upper limit voltage of constant current charging, allowing charging to be performed over a long period of time at the upper limit voltage, making the charge capacity less susceptible to changes in impedance due to deterioration of the secondary battery, and enabling the achievement of charge capacity with little variation.

[0105] Increasing the charging voltage can increase the charge capacity. However, depending on the performance of the positive electrode active material, charging at a high voltage may cause the crystal structure of the positive electrode active material to collapse and may cause decomposition reactions of elements constituting the electrolyte. Therefore, constant voltage charging at the upper limit voltage may increase the deterioration of the secondary battery. Constant current charging is preferable because it reduces the charging time at the upper limit voltage and extends the life of the secondary battery. In particular, under high-temperature conditions where the environmental temperature of the secondary battery exceeds 40°C, constant voltage charging at the upper limit voltage may significantly deteriorate the secondary battery. Therefore, when the environmental temperature of the secondary battery is high, it is more preferable to perform constant current charging. Furthermore, when the environmental temperature of the secondary battery is high, it is preferable to avoid constant voltage charging at a high voltage or to shorten the time of constant voltage charging at a high voltage as much as possible.

[0106] Here, the chemical formula AM ｙ O Ｚ (y>0, z>0), more specifically, for example, a positive electrode active material represented by the chemical formula AMO ２ Charging will be described when using a positive electrode active material represented by the chemical formula AM ｙ O Ｚ The details of the positive electrode active material represented by (y>0, z>0), as well as the element A and the metal M, will be described later. ２ However, the A:M:O composition is not limited to 1:1:2. Lithium cobalt oxide is LiCoO ２ Lithium nickel oxide is sometimes expressed as LiNiO ２ It may be expressed as:

[0107] Using the charger of one embodiment of the present invention, a secondary battery is charged at a temperature of 35° C. or higher and 55° C. or lower so that the state of charge (SOC) is 85% or lower, 80% or lower, or 77% or lower.

[0108] The degree of charge is determined by determining how much intercalable lithium remains in the positive electrode active material, for example, by determining x in the composition formula, Li ｘ CoO ２In the case of a positive electrode active material in a secondary battery, x = (theoretical capacity - charging capacity) / theoretical capacity. For example, LiCoO ２ When a secondary battery using as a positive electrode active material is charged at 219.2 mAh / g, Li ０．２ CoO ２ Or we can say x = 0.2. ｘ CoO ２ The small value of x in the formula means, for example, 0.1<x≦0.24.

[0109] In the power storage system of one embodiment of the present invention, charging may be performed so that x is 0.2 or less, 0.24 or less, or 0.3 or less.

[0110] The theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated. For example, LiCoO ２ The theoretical capacity of LiNiO is 274 mAh / g. ２ The theoretical capacity of LiMn is 274mAh / g. ２ O ４ The theoretical capacity of the battery is 148 mAh / g.

[0111] Li ｘ CoO ２ It is preferable that the charge capacity and / or discharge capacity used to calculate x in the above should be measured under conditions where there is no or minimal influence of short circuit and / or electrolyte decomposition. For example, data from a secondary battery that has experienced a sudden change in capacity that is considered to be due to a short circuit should not be used to calculate x.

[0112] In such a case, for example, at temperatures between 35° C. and 55° C., the upper limit voltage of charging is the lithium potential (Li / Li ＋ ) as a reference, charging is performed so that the potential of the positive electrode is preferably 4.8 V or less, more preferably 4.75 V or less, even more preferably 4.7 V or less, and even more preferably 4.65 V or less.

[0113] In such a case, for example, charging is performed at a temperature of 40°C or higher and 55°C or lower, with a charge rate (also called C rate or capacity rate) of preferably 0.35C or higher, more preferably 0.45C or higher, even more preferably 0.7C or higher, and even more preferably 0.9C or higher. Here, "C" is the unit of rate. In particular, during charging, the lithium potential (Li / Li ＋ ) as a reference, charging is performed so as to achieve this charge rate at a voltage at which the potential of the positive electrode is 4.2 V or higher, or 4.3 V or higher, or 4.4 V or higher. Here, a charge rate of 1 C is, for example, a current density at which, assuming that the amount of electricity required for the charge reaction of the entire amount of element A (in the case of lithium cobalt oxide, element A is lithium) contained in the positive electrode active material is 1, charging is performed with about 0.7 times that amount of electricity in 1 hour.

[0114] Although a shallower depth of charge can extend the life of the secondary battery, a too low depth of charge reduces the capacity of the secondary battery. Therefore, the depth of charge is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 73% or more. The depth of charge may also be higher than 75%.

[0115] Here, the SOC is normalized using the capacity per weight of the positive electrode active material, and the state in which all of the lithium contained in the positive electrode active material has been released is defined as SOC=100%.

[0116] The method for calculating the SOC of a secondary battery is not limited to the example shown above. For example, a charge corresponding to the rated capacity of the secondary battery may be set as SOC = 100%. Furthermore, the normalization of the capacity used for the SOC is not limited to the example shown above. Normalization may be performed using the volume of the secondary battery, the internal volume of the secondary battery, the volume of a portion of the secondary battery, the weight of the secondary battery, the weight of the contents of the secondary battery, or the weight of a portion of the secondary battery, etc.

[0117] In the charger of one embodiment of the present invention, an extreme value due to a change in the crystal structure of the positive electrode active material can be detected in a dQ / dV curve or the like, and constant-current charging can be performed. Furthermore, constant-current charging using the detected extreme value is simple and easy to control. Therefore, by using the charger of one embodiment of the present invention, a secondary battery with small variation in charge capacity and suppressed deterioration due to high-voltage charging can be realized.

[0118] Details of secondary batteries that can be used as the secondary battery 121 will be described later.

[0119] The voltage measurement circuit 151 may measure the voltage Vb1 between the positive and negative electrodes of the secondary battery as shown in Fig. 4A, or may measure a voltage obtained by resistively dividing the voltage Vb1 as shown in Fig. 4B. In this specification and the like, the voltage of the secondary battery refers to, for example, the voltage between the positive and negative electrodes of the secondary battery.

[0120] In FIG. 4B, voltage Vb1 is divided into voltages Vb2 and Vb3 by resistor elements 122 and 123, and voltage measurement circuit 151 measures voltage Vb3.

[0121] When the voltage measurement circuit 151 measures the voltage obtained by resistively dividing the voltage between the positive and negative electrodes of the secondary battery, the voltage measurement circuit 151 or the control circuit 153 may estimate the voltage between the positive and negative electrodes of the secondary battery from the resistively divided voltage.

[0122] The charger of one embodiment of the present invention preferably has a function as a coulomb counter. For example, the charger of one embodiment of the present invention has a function of calculating the charge capacity and discharge capacity of the secondary battery 121 by calculating the integrated charge amount of the secondary battery 121 using the current measurement circuit 152 and the control circuit 153. The charger of one embodiment of the present invention may also have a function of analyzing the state of charge (SOC) using the calculated charge capacity and discharge capacity.

[0123] <Example 1 of Charging Method> Next, an example of a charging method using the charger of one embodiment of the present invention will be described with reference to the flow chart in FIG. 5 .

[0124] First, in step S100, the process starts.

[0125] Next, in step S101, constant current charging of the secondary battery is started at time t1, and the constant current charging is continued until charging is stopped in step S107.

[0126] Next, in step S102, the voltage measurement circuit 151 starts measuring the voltage of the secondary battery. Also, the current measurement circuit 152 starts measuring the current of the secondary battery. The voltage measurement circuit 151 provides the measured voltage value to the control circuit 153. The current measurement circuit 152 provides the measured current value to the control circuit 153.

[0127] Next, in step S103, the control circuit 153 stores the voltage values ​​measured by the voltage measurement circuit 151 and the current values ​​measured by the current measurement circuit 152 after step S102 as data pairs, along with the time. A memory circuit or the like included in the control circuit 153 can be used to store the data. For example, the time from the start of charging can be used as the time associated with the voltage value and the current value.

[0128] Next, in step S104, the control circuit 153 calculates a voltage differential curve (dQ / dV curve) of the quantity of electricity of the secondary battery using the group data of voltage values, current values, and time that are accumulated as needed. Here, in step S103, the voltage differential curve of the quantity of electricity of the secondary battery may be calculated after accumulating group data of voltage values, current values, and time for a predetermined period of time. For example, the group data may be accumulated for a period sufficient to detect extreme values.

[0129] Next, in step S105, the control circuit 153 analyzes and determines a curve (hereinafter, dQ / dV-V curve) with the horizontal axis representing the voltage V and the vertical axis representing the voltage derivative dQ / dV of the quantity of electricity Q. If an extreme value (also called a peak), for example, a maximum (also called an upwardly convex peak) is detected in the dQ / dV-V curve, the process proceeds to step S106. If no extreme value is detected, the process returns to step S103. Note that multiple extreme values ​​may be detected in the dQ / dV-V curve. In such a case, the highest extreme value among the multiple extreme values ​​is detected. Alternatively, the top r extreme values ​​(r is an integer greater than or equal to 2) among the multiple extreme values ​​may be detected, and one of the r extreme values ​​may be selected.

[0130] Here, the top extreme value refers to the highest extreme value among those determined based on a predetermined condition. For example, it may be sorted in descending order of the height of the extreme value.

[0131] It is preferable that the control circuit 153 continuously accumulates data sets of voltage values, current values, and time while repeating steps S103 to S105. That is, when steps S103 to S105 are repeated n times, the dQ / dV-V curve can be calculated using all of the data from the n times. Alternatively, only the most recent one or the most recent few of the n times may be used.

[0132] Next, in step S106, if the voltage V of the secondary battery is equal to or greater than voltage V2, the process proceeds to step S107. If voltage V is less than voltage V2, the process returns to step S103. Here, voltage V2 is, for example, 4.25 V or greater, or 4.25 V or greater but less than 4.8 V.

[0133] Alternatively, the determination in step S006 may be made based on the charge depth of the secondary battery. For example, if the charge depth of the secondary battery is S1% or greater, the process proceeds to step S007. If the charge depth is less than S1%, the process returns to step S003. Here, S1 is 60% or greater, or 60% or greater but 95% or less.

[0134] The control circuit 153 can continuously accumulate group data of voltage values, current values, and time from the first of the multiple repetitions of step S103 until the process proceeds to step S107.

[0135] Next, in step S107, the time tp at which the dQ / dV-V curve reaches an extreme value is detected by analysis, and charging is stopped at time t2, which is a predetermined time after time tp. Here, the predetermined time is, for example, the time required for control circuit 153 to stop charging. Alternatively, as time t2, for example, a region having a desired voltage range centered on the voltage at the extreme value on the dQ / dV-V curve may be determined, and the time corresponding to the voltage at the upper end of that region may be set as time t2. Note that if no extreme value is detected in step S107, charging may be stopped when a predetermined charging voltage is reached.

[0136] Furthermore, although the detection of an extreme value is cited here as a condition for stopping charging in step S107, for example, an inflection point may be detected, and stopping of charging may be controlled based on the elapsed time from the detected inflection point.

[0137] The curve to be analyzed may be smoothed, for example, by using a moving average.

[0138] Here, the inflection point detected at time tp is, for example, an inflection point caused by a change in the crystal structure of the positive electrode active material of the positive electrode of the secondary battery.

[0139] For example, by using the positive electrode active material of one embodiment of the present invention as the positive electrode active material, if charging of the secondary battery is stopped around time tp, collapse of the crystalline structure of the positive electrode active material due to repeated charging and discharging can be suppressed.

[0140] As a specific example of the inflection point detected at time tp, by using a positive electrode active material according to one embodiment of the present invention, an inflection point corresponding to the change in the crystal structure of the positive electrode active material from an O3-type crystal structure to an O3'-type crystal structure can be used. Here, the positive electrode active material is, for example, lithium cobalt oxide. Furthermore, the charge voltage or depth of charge at time t2 is preferably lower than the charge voltage at which the crystal structure of the positive electrode active material changes to an H1-3-type crystal structure, or shallower than the charge depth. The O3-type crystal structure, the O3'-type crystal structure, and the H1-3-type crystal structure will be described in detail below. This change from the O3-type crystal structure to the O3'-type crystal structure may be referred to as a phase change.

[0141] In the power storage system of one embodiment of the present invention, for example, the crystal structure of the positive electrode active material of the secondary battery at time t2 can be controlled to be an O3′-type crystal structure, which can suppress the breakdown of the crystal structure of the positive electrode active material due to repeated charging and discharging of the secondary battery.

[0142] When the positive electrode is analyzed by X-ray diffraction in a charged state corresponding to time t2, the determined crystal structure is preferably represented by the space group R-3m.More preferably, the determined crystal structure is represented by the space group R-3m and suggests an O3'-type crystal structure.

[0143] For example, when a positive electrode obtained by disassembling a secondary battery that was charged with the power storage system of one embodiment of the present invention in a charged state corresponding to time t2 is evaluated by X-ray diffraction, a spectrum corresponding to the space group R-3m is observed. For the measurement conditions, the measurement method, and the like, see the description below.

[0144] Furthermore, even before charging the secondary battery, when the positive electrode is analyzed by X-ray diffraction, the determined crystal structure is preferably represented by the space group R-3m.

[0145] In the power storage system of one embodiment of the present invention, when the positive electrode is analyzed by X-ray diffraction at time t2 and before charging, the determined crystal structure is represented by the space group R-3m, and thus the secondary battery can have a small decrease in discharge capacity during charge and discharge cycles.

[0146] Consider a case where steps S101 to S107 are repeated s times, where s is an integer equal to or greater than 2. In this case, the times tp and t2 determined based on the extreme values ​​detected in steps S102 to S106 may be used in the next charging cycle. Specifically, the times tp and t2 determined in the (s-1)th charging may be used as conditions for stopping charging in step S107 of the sth charging.

[0147] Next, in step S199, the process ends.

[0148] In the above description, an example has been given in which constant current charging is performed continuously from the start of charging in step S101 to the stop of charging in step S107. In this case, the current value of constant current charging is set to a constant value, for example, from the start of charging in step S101 to the stop of charging in step S107. Alternatively, the current value of constant current charging may be changed in stages from the start of charging in step S101 to the stop of charging in step S107. As a specific example, when steps S103 to S105 are repeated n times, the current value may be changed after a certain number of times.

[0149] A charger according to one embodiment of the present invention analyzes the charging characteristics of a secondary battery in steps S103 to S106, and can change the charging conditions of the secondary battery in step S107 based on the analysis results. Specifically, for example, charging of the secondary battery can be stopped. The charging characteristics analyzed in steps S103 to S106 change depending on the ambient temperature during charging and discharging of the secondary battery, deterioration of the secondary battery due to charge and discharge cycles, and the like. The charger according to one embodiment of the present invention can suppress deterioration of the secondary battery by changing the charging conditions of the secondary battery, such as the charging voltage of the secondary battery, in accordance with such changes in the charging characteristics.

[0150] Furthermore, by analyzing charging characteristics, the charger of one embodiment of the present invention can charge the secondary battery to the maximum extent possible within a range in which deterioration of the secondary battery is suppressed.

[0151] Alternatively, in step S107, after time t4, constant voltage charging may be performed at a voltage lower than the upper limit charging voltage of constant current charging at time t4.

[0152] <Example 2 of Charging Method> An example of a charging method using a charger of one embodiment of the present invention will be described with reference to the flow diagram in Fig. 6. Note that in the charging method shown in Fig. 6, the calculation performed by the control circuit 153 is simpler than in the charging method shown in Fig. 5, and the charging method can be performed with a smaller circuit scale in some cases.

[0153] dQ / dV can be expressed by the following formula:

[0154] dQ / dV=(dQ / dt)×(dt / dV)

[0155] During constant current charging, dQ / dt is constant, so dQ / dV is proportional to dt / dV. Therefore, by evaluating the dt / dV characteristics during constant current charging, it is possible to obtain information similar to that of the dQ / dV characteristics.

[0156] Below, an example of evaluating the dt / dV characteristic in the region where constant current charging is performed is shown. The dt / dV characteristic can be obtained without having to obtain the current value of the secondary battery each time, and can be performed more easily than dQ / dV in some cases. Furthermore, since only two parameters, voltage and time, are required to be obtained, the calculation is simple and the circuit scale can be reduced in some cases. Furthermore, since the amount of data to be obtained can be reduced, the scale of the memory circuit can be reduced in some cases.

[0157] Furthermore, dQ / dV in constant current charging may change more slowly than dQ / dV in constant voltage charging.

[0158] In view of the above, in the power storage system of one embodiment of the present invention, sufficient evaluation can be performed even if the voltage resolution of a circuit that acquires dt / dV characteristics during constant current charging is, for example, 12 bits or less. In particular, in a secondary battery using the positive electrode active material of one embodiment of the present invention, extrema are stably observed in the dQ / dV curve during constant current charging. Therefore, charging can be controlled with high accuracy even with a simpler measurement system.

[0159] First, in step S000, the process starts.

[0160] Next, in step S001, constant current charging of the secondary battery is started at time t3, and the constant current charging is continued until charging is stopped in step S007.

[0161] Next, in step S002, the voltage measurement circuit 151 starts measuring the voltage of the secondary battery. The voltage measurement circuit 151 provides the measured voltage value to the control circuit 153.

[0162] Next, in step S003, the control circuit 153 stores the voltage values ​​measured by the voltage measurement circuit 151 after step S002 as data paired with the time. The data can be stored using a memory circuit or the like included in the control circuit 153. For example, the time from the start of charging can be used as the time associated with the voltage value.

[0163] The acquired voltage value is converted from an analog value to a digital value in the control circuit 153. Alternatively, the control circuit 153 may use the acquired analog value for calculation without converting it to a digital value. Here, an example will be described in which an MCU is used as the control circuit 153 and an analog-to-digital conversion circuit installed in the MCU is used to convert the voltage value.

[0164] Here, an MCU equipped with an analog-to-digital conversion circuit having a voltage resolution of 12 bits is used as an example.

[0165] When the change in voltage value or the absolute value of the change in voltage value reaches or exceeds a predetermined value, paired data of the voltage value and time is acquired and stored. The predetermined value can be, for example, the minimum value of the voltage resolution of the analog-to-digital conversion circuit, or it can be a value greater than that.

[0166] If the change in voltage value or the absolute value of the change in voltage value is less than a predetermined value, a set of data of the voltage value and time is acquired and stored after a predetermined time has elapsed since the previous acquisition of the set of data.

[0167] Next, in step S004, the control circuit 153 calculates the time change in the voltage of the secondary battery using the paired data of voltage values ​​and times accumulated as needed. The time change in voltage can be expressed as voltage [V(t)-V(t-Δt1)], for example, using voltage V(t) at time t and voltage V(t-Δt1) at time (t-Δt1). The curve of the time change in voltage is sometimes called a ΔV-t curve. Alternatively, for example, the time derivative of voltage (dV / dt) may be used to represent the time change in voltage. The calculation of the time change is performed after time t becomes Δt1. Here, in step S003, the time change may be calculated after accumulating paired data of voltage values ​​and times for a predetermined period of time. For example, the paired data may be accumulated for a period sufficient to detect extreme values.

[0168] Next, in step S005, the control circuit 153 analyzes the time change curve of the secondary battery voltage (e.g., a ΔV-t curve) and makes a determination. If an extreme value, for example, a minimum (also called a downwardly convex peak) is detected in the time change curve, the process proceeds to step S006. If no extreme value is detected, the process returns to step S003. Note that multiple extreme values ​​may be detected in the ΔV-t curve. In such a case, the highest extreme value among the multiple extreme values ​​is detected. Alternatively, the top r extreme values ​​(r is an integer equal to or greater than 2) may be detected from the multiple extreme values, and one of the r extreme values ​​may be selected.

[0169] It is preferable that the control circuit 153 continuously accumulates data pairs of voltage values ​​and time while repeating steps S003 to S005. That is, when steps S003 to S005 are repeated n times, all of the data from the n times can be used to calculate a time change curve. Alternatively, only the most recent one or the most recent few of the n times may be used. Here, n is an integer equal to or greater than 1.

[0170] Next, in step S006, the control circuit 153 makes a determination based on the voltage of the secondary battery. If the voltage V of the secondary battery is equal to or greater than voltage V1, the process proceeds to step S007. If the voltage V is less than voltage V1, the process returns to step S003. Here, voltage V1 is, for example, equal to or greater than 4.25 V, or equal to or greater than 4.25 V and less than 4.8 V. Here, if the voltage measurement circuit 151 measures a voltage obtained by resistively dividing the voltage between the positive and negative electrodes of the secondary battery, it is preferable to use, as voltage V1, an estimated value of the voltage between the positive and negative electrodes of the secondary battery estimated from the resistively divided voltage.

[0171] Alternatively, the determination in step S006 may be made based on the charge depth of the secondary battery. For example, if the charge depth of the secondary battery is S1% or greater, the process proceeds to step S007. If the charge depth is less than S1%, the process returns to step S003. Here, S1 is 60% or greater, or 60% or greater but 95% or less.

[0172] The control circuit 153 can continuously accumulate paired data of voltage values ​​and times from the first step S003 among the multiple repetitions of step S003 until the process proceeds to step S007.

[0173] Next, in step S007, the time tq at which the ΔV-t curve reaches an extreme value is detected by analysis, and charging is stopped at time t4, which is a predetermined time after time tq. Alternatively, as time t4, for example, a region of the ΔV-t curve with a desired time width centered around the time at which the extreme value is reached may be determined, and the time at the top of that region may be set as time t4. Here, the predetermined time may be, for example, the time required for control circuit 153 to stop charging. Note that if no extreme value is detected in step S007, charging may be stopped when a predetermined charging voltage is reached.

[0174] Furthermore, although the detection of an extreme value is cited here as a condition for stopping charging in step S007, for example, an inflection point may be detected, and stopping of charging may be controlled based on the elapsed time from the detected inflection point.

[0175] Consider a case where steps S001 to S007 are repeated w times, where w is an integer equal to or greater than 2. In this case, times t3 and t4 determined based on the extreme values ​​detected in steps S002 to S006 may be used in the next charging cycle. Specifically, times tq and t4 determined in the (w-1)th charging may be used as conditions for stopping charging in step S007 of the wth charging.

[0176] Next, in step S099, the process ends.

[0177] In the above description, an example has been described in which constant current charging is performed continuously from the start of charging in step S001 to the stop of charging in step S007. In this case, the current value of constant current charging is set to a constant value, for example, from the start of charging in step S001 to the stop of charging in step S007. Alternatively, the current value of constant current charging may be changed in stages from the start of charging in step S001 to the stop of charging in step S007. As a specific example, when steps S003 to S005 are repeated n times, the current value may be changed after a certain number of times.

[0178] <Example 3 of Charging Method> An example of a charging method using the charger of one embodiment of the present invention will be described with reference to the flow chart in FIG. 51 .

[0179] First, in step S000, the process starts.

[0180] Next, in step S001, constant current charging of the secondary battery is started, and the constant current charging is continued until charging is stopped in step S006.

[0181] Next, in step S002, the voltage measurement circuit 151 starts measuring the voltage of the secondary battery. The measured voltage V is provided from the voltage measurement circuit 151 to the control circuit 153.

[0182] Next, in step S003, the control circuit 153 compares the measured voltage V with a predetermined voltage V1. If the voltage V is equal to or greater than the voltage V1, the process proceeds to step S004, and if the voltage V is lower than the voltage V1, the process returns to step S002.

[0183] In step S004, the control circuit 153 evaluates dQ / dV. Here, since the charging current is constant, the value of dt / dV is measured. The value of dt / dV can be accumulated at any time during the charging process. Using the accumulated paired data of voltage V and time t, the moving average [dt / dV]mean and maximum value [dt / dV]max of dt / dV are calculated.

[0184] Alternatively, the value corresponding to dt / dV may be calculated as the time required for the voltage to change by a predetermined value, which may be set to, for example, 0.5 mV or more and 10 mV or less.

[0185] Next, in step S005, the moving average [dt / dV]mean is compared with the value obtained by multiplying the maximum value [dt / dV]max by the constant Rt. If the moving average [dt / dV]mean is smaller than the value obtained by multiplying the maximum value [dt / dV]max by the constant Rt, the process proceeds to step S006. If the moving average [dt / dV]mean is equal to or greater than the value obtained by multiplying the maximum value [dt / dV]max by the constant Rt, the process returns to step S004.

[0186] The time when the moving average [dt / dV]mean becomes smaller than the maximum value [dt / dV]max multiplied by the constant Rt corresponds to the time when the dt / dV curve decreases from a maximum value near the voltage V1 to (Rt x 100) [%] of the maximum value. Here, Rt is, for example, 0.6 to 0.9. By setting Rt in the range of 0.6 to 0.9, for example, it is possible to distinguish between minute decreases due to measurement noise and extreme values ​​of the dt / dV curve (or dQ / dV curve), thereby improving measurement accuracy. Furthermore, by setting Rt in the range of 0.6 to 0.9, it is possible to detect changes in the crystalline structure of the positive electrode active material, and to make the change in the crystalline structure of the charged positive electrode active material approximately reversible.

[0187] In step S006, charging of the secondary battery is stopped.

[0188] Next, in step S099, the process ends.

[0189] Although the flow chart shown in FIG. 51 shows an example of constant current charging, when the charging current is not constant, for example, instead of comparing the moving average of dt / dV [dt / dV]mean with the value obtained by multiplying the maximum voltage [dt / dV]max by the constant Rt, it is sufficient to compare the average value at the time of measurement of the quantity of electricity Q and times around that time with the value obtained by multiplying the maximum value of the quantity of electricity Q by a constant.

[0190] <SOH Estimation> A charger according to one aspect of the present invention preferably has a function for estimating the SOH (State of Health) of a secondary battery. The SOH is an index that indicates the capacity that can be fully charged at a certain point in time, based on the capacity that can be fully charged when the secondary battery is new. The SOH is expressed in percentages, with the fully chargeable capacity of a new secondary battery being 100, and becomes smaller as the secondary battery deteriorates.

[0191] In the dQ / dV-V curve analyzed in the above example, the intensity of the extreme value (e.g., the height of the upwardly convex peak) may decrease. This decrease in intensity may be caused by the phase change corresponding to the extreme value becoming less likely to occur in the positive electrode active material, and may be correlated with, for example, the SOH.

[0192] The charger according to one embodiment of the present invention preferably has a function of estimating the SOH by observing the intensity of an extreme value in the dQ / dV-V curve.

[0193] Furthermore, regarding the extreme values ​​of the dQ / dV-V curve analyzed in the above example, the voltage at which the extreme value occurs may be correlated with the full discharge capacity after charging (the capacity that the secondary battery can discharge). Preferably, the charger of one embodiment of the present invention has a function of estimating the discharge capacity of the secondary battery by observing the intensity of the extreme value of the dQ / dV-V curve.

[0194] <Charging Control Using Temperature> The charger 101 preferably controls charging using temperature.

[0195] It is preferable that the control circuit 153 change the charging conditions in accordance with the environmental temperature of the secondary battery measured by the temperature sensor TS.

[0196] The memory circuit included in the control circuit 153 preferably has, for example, a table in which the ambient temperature of the secondary battery is linked to the charging conditions.

[0197] Furthermore, it is preferable that the memory circuit of the control circuit 153 stores charging characteristics linked to the ambient temperature of the secondary battery. The charging characteristics may be past measurements of the secondary battery 121, measurements of other secondary batteries having similar characteristics, or waveforms obtained by calculation. Furthermore, in the flow charts shown in FIGS. 5 and 6, these measurements may be used to estimate extreme values ​​(peaks). For example, machine learning or the like may be used for the estimation.

[0198] The control circuit 153 may use the charging characteristics of the secondary battery stored in the memory circuit to analyze the extreme values ​​in the differential curves of the voltage and the quantity of electricity. Here, examples of the charging characteristics that can be used include a capacity-voltage curve, a voltage-dQ / dV curve, a ΔV-t curve, and impedance characteristics.

[0199] <Example 2 of Power Storage System> FIG. 1B shows an example in which charger 101 has, in addition to the configuration shown in FIG. 1A , detection circuit 185 having a function of detecting overcharging and overdischarging, detection circuit 186 having a function of detecting charging overcurrent and discharging overcurrent, short circuit detection circuit SD, micro-short circuit detection circuit MSD, transistor 140, and transistor 150.

[0200] The charger 101 shown in Figure 1B has the function of suppressing overcharging, overdischarging, charging overcurrent, discharging overcurrent, short circuit, micro-short circuit, etc., and can function as a protection circuit for the secondary battery. Here, a micro-short circuit refers to a minute short circuit inside the secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and render the battery in a charging-disabled state, but refers to a phenomenon in which a small short-circuit current flows at a minute short-circuited point. Even a relatively short-term, small-area short circuit can cause a large voltage change.

[0201] For example, transistors called power MOSFETs can be used as the transistors 140 and 150 .

[0202] The control circuit 153 has a function of cutting off the current flowing to the secondary battery 121 by supplying signals to the gates of the transistors 140 and 150 .

[0203] The detection circuit 185 monitors the voltage of the secondary battery, and when it detects overcharging or over-discharging, it can send a signal indicating the detection to the control circuit 153. The control circuit receives the signal and sends a signal to at least one of the gates of the transistors 140 and 150, thereby cutting off the current flowing to the secondary battery 121.

[0204] The detection circuit 186 monitors the current of the secondary battery 121, and when it detects an overcurrent during charging or discharging, it can send a signal indicating the detection to the control circuit 153. The control circuit receives the signal and sends a signal to at least one of the gates of the transistors 140 and 150, thereby cutting off the current flowing to the secondary battery 121.

[0205] The overcharge detected by the detection circuit 185 may be detected using the extreme value of the charge voltage time change curve (e.g., ΔV-t curve) or the extreme value of the voltage differential curve of the charged quantity of electricity (dQ / dV curve) described above. Alternatively, the overcharge detected by the detection circuit 185 may be detected by comparing the charge voltage with a predetermined voltage value using a comparison circuit. The predetermined voltage value may vary depending on the ambient temperature of the secondary battery. The voltage value depending on the ambient temperature of the secondary battery is stored, for example, in a memory circuit included in the control circuit 153.

[0206] The power storage system 100 shown in Figures 7A, 7B, and 7C shows an example in which a charger 101 is connected to each of m secondary batteries 121 connected in series. Figure 7A shows an example of the power storage system 100 when m is an integer greater than or equal to 4, and of the m secondary batteries 121, secondary battery 121(1), secondary battery 121(2), secondary battery 121(3), and secondary battery 121(m) are shown as the first, second, third, and mth secondary batteries 121, with the other secondary batteries omitted. Figure 7B shows an example of the power storage system 100 when m is 3, and Figure 7C shows an example of the power storage system 100 when m is 2.

[0207] Some functions may be shared among the m chargers 101. For example, the detection circuit 185 included in the charger 101 may detect overcharging of the voltage between the terminal 124 electrically connected to the positive electrode of the secondary battery 121(1) and the terminal 125 electrically connected to the negative electrode of the secondary battery 121(m). Also, for example, the detection circuit 186 and the short-circuit detection circuit SD included in the charger 101 may detect overcharging or a short circuit based on the current between the terminal 124 and the terminal 125.

[0208] Furthermore, the energy storage system 100 can independently control the m secondary batteries 121 (121(1) to 121(m)) using the chargers 101 connected to each of them. At this time, for the secondary battery 121 that is to be completed charging first among the m secondary batteries 121, after the charging is completed, current flows through a path connected in parallel to the secondary battery 121, for example, a transistor, a resistive element, or a diode connected in parallel to the secondary battery 121. Therefore, it is preferable that the charger 101 has a switch that switches between the secondary battery 121 and the path as a current path.

[0209] Furthermore, the power storage system 100 may control charging of m secondary batteries 121 connected in series using the total voltage of the m secondary batteries (for example, in FIG. 7A , the voltage between the positive electrode of secondary battery 121(1) and the negative electrode of secondary battery 121(m)). In such a case, the voltage used to control charging can be m times the voltage value.

[0210] This embodiment mode can be combined with the descriptions of other embodiment modes as appropriate.

[0211] Embodiment 2 In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described.

[0212] The secondary battery of one embodiment of the present invention preferably includes a positive electrode, a negative electrode, and an electrolyte.

[0213] <Positive Electrode> A positive electrode according to one embodiment of the present invention includes a positive electrode active material.

[0214] [Positive Electrode Active Material] As the positive electrode active material, it is preferable to use a compound containing a metal M (M is, for example, a metal). Furthermore, for example, a transition metal can be used as the metal M. Furthermore, the metal M may contain an element that does not change valence and can have the same valence as the metal M, more specifically, for example, a trivalent typical element. For example, cobalt, nickel, manganese, iron, vanadium, chromium, niobium, aluminum, etc. can be used as the metal M. For example, the positive electrode active material of one embodiment of the present invention contains one or more of cobalt, nickel, and manganese as the metal M, particularly cobalt. Furthermore, sulfur may be used in addition to or instead of the metal M. For example, oxides, fluorides, sulfides, phosphates, sulfates, borates, silicates, fluorophosphates, fluorosulfates, etc. can be used as the compound.

[0215] The positive electrode active material preferably contains element A in addition to the metal M. Element A can be, for example, one or more selected from alkali metals such as lithium, sodium, and potassium, and Group 2 elements such as calcium, beryllium, and magnesium. Element A is preferably an element that functions as a carrier metal. During charging and discharging of the secondary battery of one embodiment of the present invention, element A is desorbed from and inserted into the positive electrode active material.

[0216] The positive electrode active material can have a layered rock salt crystal structure. Alternatively, a composite oxide having a spinel crystal structure can be used. Alternatively, a polyanion-based positive electrode material can be used. Examples of polyanion-based positive electrode materials include materials having an olivine crystal structure and Nasicon-based materials.

[0217] The positive electrode active material of one embodiment of the present invention is represented by the chemical formula AM ｙ O Ｚ (y>0, z>0). More specifically, for example, the positive electrode active material of one embodiment of the present invention may be represented by the chemical formula AMO ２ It may also be expressed as AMO ２However, the A:M:O composition is not limited to 1:1:2. Lithium cobalt oxide is LiCoO ２ Lithium nickel oxide is sometimes expressed as LiNiO ２ It may be expressed as:

[0218] The positive electrode active material of one embodiment of the present invention preferably contains an element X. Examples of the element X include magnesium, calcium, barium, zirconium, lanthanum, titanium, and yttrium. Examples of the element X include nickel, aluminum, manganese, cobalt, vanadium, iron, chromium, and niobium. Examples of the element X include potassium, sodium, copper, zinc, chlorine, fluorine, hafnium, silicon, sulfur, phosphorus, boron, and arsenic. Two or more of the above elements may be used in combination as the element X. For example, one or more elements selected from magnesium, calcium, and barium and one or more elements selected from nickel, aluminum, and manganese may be used as the element X.

[0219] For example, the element X may be partially substituted at the position of the element A. Alternatively, the element X may be partially substituted at the position of the metal M.

[0220] In the positive electrode active material of one embodiment of the present invention, the concentration of element X in the surface layer portion may be higher than the concentration of element X in the interior portion. Furthermore, in the positive electrode active material of one embodiment of the present invention, element X may be uniformly dissolved in the entire positive electrode active material.

[0221] The positive electrode active material of one embodiment of the present invention is represented by chemical formula A １−ｗ X ｗ M ｙ O Ｚ (y>0, z>0, 0<w<1). ｙーｊ X ｊ O Ｚ (y>0, z>0, 0<j<y). １−ｗ X ｗ M ｙーｊ X ｊ OＺ It may be expressed as (y>0, z>0, 0<w<1, 0<j<y).

[0222] The positive electrode active material of one embodiment of the present invention preferably contains a halogen, such as fluorine or chlorine. When the positive electrode active material of one embodiment of the present invention contains the halogen, substitution of the element X at the position of the element A may be promoted.

[0223] [Positive Electrode Active Material Structure 1] Fig. 8A is a cross-sectional view of a positive electrode active material 200 that can be used in a secondary battery of one embodiment of the present invention. Figs. 8B and 8C are enlarged views of the vicinity of A-B in Fig. 8A. Figs. 8C and 8D are enlarged views of the vicinity of C-D in Fig. 8A.

[0224] 8A to 8E, positive electrode active material 200 has surface layer 200a and interior 200b. In these figures, the boundary between surface layer 200a and interior 200b is indicated by a dashed line. Also, in Fig. 8A, part of crystal grain boundary 201 is indicated by a dashed-dotted line.

[0225] In this specification and the like, the region extending from the surface of the positive electrode active material to a depth of 10 nm toward the inside is referred to as the surface layer 200a. Surfaces formed by cracks and / or fissures may also be referred to as the surface. The surface layer 200a may also be referred to as the near-surface or near-surface region. The region deeper than the surface layer 200a of the positive electrode active material is referred to as the interior 200b. The interior 200b may also be referred to as the interior region.

[0226] The surface layer 200a preferably has a higher concentration of an additive element (described later) than the inner layer 200b. The additive element preferably has a concentration gradient. When multiple additive elements are present, the depths of the concentration peaks from the surface preferably differ depending on the additive element.

[0227] Furthermore, the concentration of the additive element in the surface layer 200a is preferably higher than the average concentration in the entire particle.

[0228] The concentration of the added element can be measured by XPS, ICP-MS, EDX area analysis, or the like.

[0229] For example, it is preferable that a certain additional element X1 has a concentration gradient that increases from the interior 200b toward the surface, as shown by the gradation in Fig. 8B. The additional element X1 that preferably has such a concentration gradient can be one or more selected from the above-mentioned additional elements X, and more specific examples include magnesium, fluorine, titanium, silicon, phosphorus, boron, and calcium.

[0230] The additional element X2 preferably has a concentration gradient as shown by the gradation in FIG. 8C and a concentration peak in a region deeper than that in FIG. 8B. The concentration peak may be present in the surface layer 200a or may be deeper than the surface layer 200a. It is preferable that the additional element X2 has a concentration peak in a region other than the outermost surface layer. For example, it is preferable that the peak be in a region of 5 nm to 30 nm from the surface toward the interior. The additional element X2 preferably having such a concentration gradient can be one or more selected from the additional elements X described above, and more specifically, aluminum and manganese can be mentioned, for example.

[0231] Furthermore, it is preferable that the crystal structure continuously changes from the interior 200b toward the surface due to the concentration gradient of the added element as described above.

[0232] In the positive electrode active material 200 according to one embodiment of the present invention, the surface layer 200 a having a high concentration of the added element, i.e., the outer periphery of the particle, is reinforced so that the layered structure consisting of the transition metal M and oxygen octahedra is not destroyed even when lithium is released from the positive electrode active material 200 due to charging.

[0233] However, the additive element does not necessarily have to have the same concentration gradient throughout the entire surface layer portion 200a of the positive electrode active material 200. For example, if some additive elements are designated as X1 and other additive elements are designated as X2, an example of the distribution of additive element X1 near C-D in Fig. 8A is shown in Fig. 8D, and an example of the distribution of additive element X2 near C-D is shown in Fig. 8E.

[0234] Here, the vicinity of C-D has an R-3m layered rock salt type crystal structure, and the surface is (001) oriented. The (001) oriented surface may have a different distribution of additive elements than the other surfaces. For example, the (001) oriented surface and its surface layer 200a may have at least one of the additive elements X1 and X2 distributed shallower from the surface than the other orientations. Alternatively, the (001) oriented surface and its surface layer 200a may have a lower concentration of at least one of the additive elements X1 and X2 than the other orientations. Alternatively, the (001) oriented surface and its surface layer 200a may have at least one of the additive elements X1 and X2 below the lower detection limit.

[0235] In the layered rock salt type crystal structure of R-3m, cations are arranged parallel to the (001) plane. This is MO consisting of transition metal M and oxygen octahedra. ２ The structure is composed of alternately stacked layers and lithium layers parallel to the (001) plane, and the diffusion path of lithium ions is also parallel to the (001) plane.

[0236] MO consisting of transition metal M and oxygen octahedra ２ The layer is relatively stable, so MO ２ The (001) plane on which the layer exists is relatively stable, and the diffusion path of lithium ions is not exposed on the (001) plane.

[0237] On the other hand, the diffusion paths of lithium ions are exposed on surfaces other than those with the (001) orientation. Therefore, the surfaces other than those with the (001) orientation and the surface layer portion 200a are important regions for maintaining the diffusion paths of lithium ions, and at the same time, they are regions from which lithium ions are first released and are therefore prone to instability. Therefore, reinforcing the surfaces other than those with the (001) orientation and the surface layer portion 200a is extremely important for maintaining the crystal structure of the entire positive electrode active material 200.

[0238] Therefore, in positive electrode active material 200 of another embodiment of the present invention, it is important that the distribution of the additive element in the plane other than the (001) plane and its surface layer portion 200a is as shown in Figures 8B and 8C . On the other hand, in the (001) plane and its surface layer portion 200a, as described above, the peak position of the additive element may be shallow, the concentration of the additive element may be low, or the additive element may be absent.

[0239] As will be described later, high-purity LiMO ２ In the manufacturing method of manufacturing the above, and then mixing the additive elements therein and heating the mixture, the additive elements spread mainly through the diffusion paths of lithium ions, and therefore it is easy to make the distribution of the additive elements in the planes other than (001) and in the surface layer portion 200 a thereof fall within a preferred range.

[0240] High purity LiMO ２ After the (001) plane is fabricated, the additive elements are mixed in and heated, thereby making it possible to achieve a more preferable distribution of the additive elements in the other planes and the surface layer 200a thereof than in the (001) plane. ２ It is expected that the magnesium atoms and other additive elements will be more easily distributed in high concentrations in the surface layer.

[0241] Furthermore, while it is preferable that the surface of the positive electrode active material 200 is smooth and has few irregularities, this is not necessarily the case for the entire positive electrode active material 200. A composite oxide having an R-3m layered rock salt crystal structure is prone to slippage on a plane parallel to the (001) plane, for example, on a plane where lithium was arranged. When the (001) plane is horizontal, as shown in Figure 9A , horizontal slippage may occur as indicated by the arrows in Figure 9B after undergoing a process such as pressing, resulting in deformation.

[0242] In this case, the surface newly formed as a result of the slip and its surface layer 200a may be free of the additional element or may contain an amount below the detection limit. E-F in FIG. 9B is an example of the surface newly formed as a result of the slip and its surface layer 200a. Enlarged views of the vicinity of E-F are shown in FIGS. 9C and 9D. Unlike FIGS. 8B to 8E, FIGS. 9C and 9D do not contain a gradation of the additional element X1 and the additional element X2.

[0243] However, since slippage tends to occur parallel to the (001) plane, the newly formed surface and its surface layer 200a have a (001) orientation. The (001) plane does not expose the diffusion path of lithium ions and is relatively stable, so there is almost no problem even if the added element is absent or below the detection limit.

[0244] As mentioned above, the composition is LiMO ２ In the composite oxide having a layered rock salt type crystal structure of R-3m, the transition metal M is arranged parallel to the (001) plane. ２ Among these, the transition metal M with the largest atomic number has the highest brightness. Therefore, in the HAADF-STEM image, the arrangement of atoms with high brightness can be considered to be the arrangement of the transition metal M. The repetition of this arrangement with high brightness can also be called crystal fringes or lattice fringes. Furthermore, when the crystal structure is an R-3m layered rock salt type, the crystal fringes or lattice fringes can be considered to be parallel to the (001) plane.

[0245] The positive electrode active material 200 may have recesses, cracks, dents, V-shaped cross sections, etc. These are defects, and repeated charge and discharge may cause elution of the transition metal M, collapse of the crystalline structure, cracking of the body, and oxygen desorption. However, if the embedded portion 202 is present so as to embed these defects, elution of the transition metal M, etc., can be suppressed. Therefore, the positive electrode active material 200 can have excellent reliability and cycle characteristics.

[0246] The positive electrode active material 200 may have protrusions 203 as regions where the additive element is unevenly distributed.

[0247] If the additive element contained in the positive electrode active material 200 is excessive, it may adversely affect the insertion and extraction of lithium. Furthermore, when used as a secondary battery, it may also lead to an increase in internal resistance and a decrease in charge / discharge capacity. On the other hand, if the additive element is insufficient, it may not be distributed throughout the entire surface layer portion 200a, and the effect of suppressing deterioration of the crystal structure may be insufficient. Thus, the additive element needs to be present at an appropriate concentration in the positive electrode active material 200, but adjusting this concentration is not easy.

[0248] Therefore, if the positive electrode active material 200 has a region where the additive element is unevenly distributed, a portion of the excess additive element is removed from the interior 200b of the positive electrode active material 200, and an appropriate additive element concentration can be achieved in the interior 200b. This makes it possible to suppress an increase in internal resistance and a decrease in charge / discharge capacity when the resulting secondary battery is formed. The ability to suppress an increase in internal resistance of a secondary battery is an extremely desirable characteristic, particularly in high-rate charge / discharge, for example, charge / discharge at 2C or higher.

[0249] Furthermore, in the positive electrode active material 200 having a region where the additive element is unevenly distributed, it is permissible to mix an excess amount of the additive element to some extent during the manufacturing process, which is preferable because it widens the margin in production.

[0250] In this specification and the like, uneven distribution refers to the concentration of an element in a certain region being different from that in other regions, and may also be referred to as segregation, precipitation, non-uniformity, bias, or the presence of a mixture of high-concentration and low-concentration regions.

[0251] Magnesium, one of the additive elements X1, is divalent and is more stable at the lithium site than at the transition metal site in the layered rock-salt crystal structure, and therefore more likely to enter the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer portion 200a facilitates the maintenance of the layered rock-salt crystal structure. Furthermore, the presence of magnesium can suppress the desorption of oxygen around the magnesium at high depths of charge. The presence of magnesium is also expected to increase the density of the positive electrode active material. At an appropriate concentration, magnesium is preferable because it does not adversely affect the intercalation and deintercalation of lithium during charge and discharge. However, excessive magnesium may adversely affect the intercalation and deintercalation of lithium. Therefore, as described below, it is preferable that the concentration of the transition metal M in the surface layer portion 200a be higher than that of magnesium.

[0252] Aluminum, one of the additive elements X2, is trivalent and can exist at the transition metal site in the layered rock salt crystal structure. Aluminum can suppress the elution of surrounding cobalt. Furthermore, because aluminum has a strong bond with oxygen, it can suppress the release of oxygen from the surrounding area of ​​aluminum. Therefore, the presence of aluminum as an additive element can result in a positive electrode active material 200 whose crystal structure is less likely to collapse even after repeated charge and discharge.

[0253] Fluorine is a monovalent anion, and when part of the oxygen in the surface layer portion 200a is substituted with fluorine, the lithium desorption energy is reduced. This is because the valence of the cobalt ion changes with lithium desorption, from trivalent to tetravalent in the absence of fluorine, and from divalent to trivalent in the presence of fluorine, resulting in different oxidation-reduction potentials. Therefore, when part of the oxygen in the surface layer portion 200a of the positive electrode active material 200 is substituted with fluorine, it can be said that desorption and insertion of lithium ions near the fluorine is more likely to occur smoothly. Therefore, when used in a secondary battery, charge / discharge characteristics, rate characteristics, etc. are improved, which is preferable.

[0254] Titanium oxide is known to have superhydrophilicity. Therefore, by providing the cathode active material 200 with titanium oxide in the surface layer portion 200a, it is possible that the cathode active material 200 has good wettability with a highly polar solvent. When used in a secondary battery, this improves the contact at the interface between the cathode active material 200 and a highly polar electrolyte, which may prevent an increase in internal resistance.

[0255] As the charging voltage of a secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in a charged state can suppress a decrease in charge / discharge capacity due to repeated charge / discharge.

[0256] Furthermore, a short circuit in a secondary battery not only causes problems in the charging and / or discharging operations of the secondary battery, but may also lead to heat generation and fire. To achieve a safe secondary battery, it is preferable that a short circuit current be suppressed even at a high charging voltage. The positive electrode active material 200 of one embodiment of the present invention suppresses a short circuit current even at a high charging voltage. Therefore, a secondary battery that achieves both high charge / discharge capacity and safety can be obtained.

[0257] The concentration gradient of the added element can be evaluated using, for example, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like. Among EDX measurements, EDX area analysis is performed by scanning an area and evaluating the area two-dimensionally. EDX area analysis is performed by linearly scanning the area and evaluating the distribution of atomic concentration within the positive electrode active material particles. Furthermore, data extracted from a linear area of ​​EDX area analysis may be called line analysis. Measurement of a certain area without scanning is called point analysis.

[0258] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentration of the added element in the surface layer 200a, the interior 200b, and near the grain boundary 201 of the positive electrode active material 200. Furthermore, EDX ray analysis can analyze the concentration distribution and maximum value of the added element. Furthermore, analysis that thins the sample, such as STEM-EDX, is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the particle in a specific region without being affected by the distribution in the depth direction.

[0259] When EDX ray analysis is performed on the positive electrode active material 200 having magnesium as an added element, the peak of the magnesium concentration in the surface layer portion 200 a is preferably present at a depth of up to 3 nm from the surface toward the center of the positive electrode active material 200, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.

[0260] In addition, in the cathode active material 200 having magnesium and fluorine as additive elements, the distribution of fluorine preferably overlaps with the distribution of magnesium. Therefore, when EDX ray analysis is performed, the peak of the fluorine concentration in the surface layer 200 a is preferably present at a depth of 3 nm from the surface of the cathode active material 200 toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm.

[0261] It should be noted that not all additive elements need have the same concentration distribution. For example, when the positive electrode active material 200 contains aluminum as an additive element, it is preferable that the distribution be slightly different from that of magnesium and fluorine, as described above. For example, when EDX-ray analysis is performed, it is preferable that the magnesium concentration peak be closer to the surface than the aluminum concentration peak in the surface layer portion 200a. For example, the aluminum concentration peak is preferably present at a depth of 0.5 nm to 50 nm from the surface toward the center of the positive electrode active material 200, and more preferably at a depth of 5 nm to 30 nm. Alternatively, it is preferable that it be present at a depth of 0.5 nm to 30 nm. Alternatively, it is preferable that it be present at a depth of 5 nm to 50 nm.

[0262] Furthermore, when linear or area analysis is performed on the positive electrode active material 200, the ratio of the number of atoms of the additive element I to the transition metal M in the surface layer portion 200a (I / M) is preferably 0.05 or more and 1.00 or less. Furthermore, when the additive element is titanium, the ratio of the number of atoms of the titanium to the transition metal M (Ti / M) is preferably 0.05 or more and 0.4 or less, and more preferably 0.1 or more and 0.3 or less. Furthermore, when the additive element is magnesium, the ratio of the number of atoms of the magnesium to the transition metal M (Mg / M) is preferably 0.4 or more and 1.5 or less, and more preferably 0.45 or more and 1.00 or less. Furthermore, when the additive element is fluorine, the ratio of the number of atoms of the fluorine to the transition metal M (F / M) is preferably 0.05 or more and 1.5 or less, and more preferably 0.3 or more and 1.00 or less.

[0263] The surface of the positive electrode active material 200 in the EDX ray analysis results can be estimated, for example, as follows.

[0264] For an element that is uniformly present in the interior 200b of the positive electrode active material 200, for example, oxygen or a transition metal M such as cobalt, the point where the detected amount is half that of the interior 200b is defined as the surface.

[0265] Since the positive electrode active material 200 is a composite oxide, it is preferable to estimate the surface using the detected amount of oxygen. Specifically, first, the average oxygen concentration O ａｖｅ At this time, oxygen O, which is thought to be due to chemical adsorption or background, is found in the area that can be clearly determined to be outside the surface. ｂａｃｋｇｒｏｕｎｄ If detected, O ｂａｃｋｇｒｏｕｎｄ The average oxygen concentration O ａｖｅ This average value O ａｖｅ Half the value of, that is, 1 / 2O ａｖｅ The measurement point showing the measurement value closest to this can be assumed to be the surface of the positive electrode active material.

[0266] The surface can also be estimated using the transition metal M contained in the positive electrode active material 200. For example, if 95% or more of the transition metal M is cobalt, the surface can be estimated in the same manner as above using the detected amount of cobalt. Alternatively, the surface can be estimated in the same manner using the sum of the detected amounts of multiple transition metals M. The detected amount of transition metal M is suitable for estimating the surface because it is less susceptible to the influence of chemical adsorption.

[0267] Furthermore, when the positive electrode active material 200 is subjected to linear or area analysis, the ratio of the number of atoms of the added element I to the transition metal M (I / M) in the vicinity of the crystal grain boundary 201 is preferably 0.020 or more and 0.50 or less. It is further preferably 0.025 or more and 0.30 or less. It is further preferably 0.030 or more and 0.20 or less. It is also preferably 0.020 or more and 0.30 or less. It is also preferably 0.020 or more and 0.20 or less. It is also preferably 0.025 or more and 0.50 or less. It is also preferably 0.025 or more and 0.20 or less. It is also preferably 0.030 or more and 0.50 or less. It is also preferably 0.030 or more and 0.30 or less.

[0268] For example, when the additive element is magnesium and the transition metal M is cobalt, the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg / Co) is preferably 0.020 or more and 0.50 or less. It is further preferably 0.025 or more and 0.30 or less. It is further preferably 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less. Or it is preferably 0.030 or more and 0.30 or less.

[0269] In addition, when the positive electrode active material 200 is charged under conditions of a high depth of charge, such as charging at 4.5 V or higher, or when it is charged and discharged at high temperatures (45°C or higher), progressive defects (also called pits) may occur in the positive electrode active material. Furthermore, defects such as fissures (also called cracks) may occur due to expansion and contraction of the positive electrode active material caused by charging and discharging. Figure 10 shows a schematic cross-sectional view of a positive electrode active material 51. In the positive electrode active material 51, the pits are illustrated as holes in pits 54 and 58, but the opening shape is not circular but has a deep, groove-like shape. The source of the pits may be point defects. Furthermore, in the vicinity of where the pits are formed, LiMO ２ It is believed that the crystal structure of the layered rock salt structure is disrupted, resulting in a crystal structure different from that of the layered rock salt structure. When the crystal structure is disrupted, it may hinder the diffusion and release of lithium ions, which are carrier ions, and the pits are thought to be a cause of deterioration in cycle characteristics. In addition, in the positive electrode active material 51, cracks are shown as cracks 57. The crystal plane parallel to the arrangement of cations is shown as crystal plane 55, the recesses are shown as recesses 52, and the regions where the added element is present are shown as regions 53 and 56.

[0270] The positive electrode active materials of lithium-ion secondary batteries are typically LCO (lithium cobalt oxide) and NMC (lithium nickel-manganese-cobalt oxide), which can also be considered composite oxides containing multiple metal elements (e.g., cobalt, nickel, etc.). At least one of the multiple positive electrode active material particles may have defects, and the defects may change before and after charging and discharging. When used in secondary batteries, the positive electrode active material may be chemically or electrochemically eroded by the environmental substances (e.g., electrolyte) surrounding the positive electrode active material, or the material may deteriorate. This deterioration does not occur uniformly on the surface of the positive electrode active material, but occurs in a locally concentrated manner. Repeated charging and discharging of the secondary battery can cause defects to form deep inside, for example, from the surface.

[0271] The phenomenon in which defects progress to form holes in a positive electrode active material may be called pitting corrosion, and the holes formed by this phenomenon are also referred to as pits in this specification.

[0272] In this specification, cracks and pits are different. Even if cracks are present immediately after the preparation of the positive electrode active material, pits are not. Pits can be considered as holes formed by the loss of several layers of cobalt and oxygen due to charging and discharging under conditions of high depth of charge, such as charging at a high voltage of 4.5 V or higher, or at high temperatures (45°C or higher), and can also be considered as locations where cobalt has dissolved. Cracks refer to new surfaces formed by the application of physical pressure, or fissures caused by grain boundaries 201. Cracks can also occur due to the expansion and contraction of the positive electrode active material caused by charging and discharging. Pits can also occur from cracks.

[0273] The positive electrode active material 200 may have a coating film on at least a part of its surface. FIG. 11 shows an example of a positive electrode active material 200 having a coating film 204.

[0274] The coating 204 is preferably formed, for example, by the deposition of decomposition products of the electrolyte solution during charge and discharge. In particular, when repeated charging to a high depth of charge is performed, having a coating derived from the electrolyte solution on the surface of the positive electrode active material 200 is expected to improve charge and discharge cycle characteristics. This is due to reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing the elution of the transition metal M. The coating 204 preferably contains, for example, carbon, oxygen, and fluorine. Furthermore, a high-quality coating is easily obtained when LiBOB and / or SUN (suberonitrile) are used as part of the electrolyte. Therefore, a coating 204 containing at least one of boron, nitrogen, sulfur, and fluorine may be a high-quality coating and is therefore preferable. Furthermore, the coating 204 does not have to cover the entire positive electrode active material 200.

[0275] [Relationship between Charging Conditions and Positive Electrode Active Material] Furthermore, by repeatedly charging and discharging a secondary battery using the power storage system of one embodiment of the present invention, elution of the elements X1 and X2 from the positive electrode active material during charging and discharging can be suppressed. Since the elements X1 and X2 contained in the positive electrode active material remain even after repeated charging and discharging, the power storage system of one embodiment of the present invention can achieve excellent cycle characteristics of the secondary battery.

[0276] For example, when a secondary battery including the positive electrode active material of one embodiment of the present invention is charged and discharged using the power storage system of one embodiment of the present invention, the element X1 and the element X2 are preferably detected in a surface portion of the positive electrode active material even after 30 to 100 charge-discharge cycles at 40° C. or higher and 55° C. or lower. Furthermore, even after 30 to 100 charge-discharge cycles at 40° C. or higher and 55° C. or lower, the concentrations of the element X1 and the element X2 in the surface portion of the positive electrode active material are preferably higher than the concentrations in the interior. Furthermore, even after 30 to 100 charge-discharge cycles at 40° C. or higher and 55° C. or lower, when the positive electrode active material is subjected to EDX linear analysis or EDX area analysis, the atomic ratio (I / M) of the additive element I to the transition metal M in the surface portion is preferably 0.03 or higher, more preferably 0.05 to 1.00.

[0277] [Positive Electrode Active Material Structure 2] In a positive electrode active material represented by space group R-3m and having a layered rock salt structure, when the depth of charge is 0.8 or more, ions of a metal M (e.g., cobalt), an element X (e.g., magnesium), or the like may occupy oxygen hexacoordinate positions. This structure is referred to as an O3'-type crystal structure in this specification. In the O3'-type crystal structure, light elements such as lithium may occupy oxygen tetracoordinate positions. The O3'-type crystal structure is a structure that can maintain high stability despite the elimination of lithium and the like during charging.

[0278] The O3' type crystal structure has randomly interlayered Li atoms, but the CdCl ２ It can be said that this crystal structure is similar to that of the CdCl type. ２ A crystal structure similar to the type was observed when lithium nickel oxide was charged to a charge depth of 94% (Li ０．０６ NiO ２ ) crystal structure is similar to that of

[0279] The anions in layered rock salt-type crystals and rock salt-type crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is estimated that the anions in O3'-type crystals also have a cubic close-packed structure. When they contact, there is a crystal plane where the orientation of the cubic close-packed structure formed by the anions is aligned. However, since the space group of layered rock salt-type crystals and O3'-type crystals is R-3m, which is different from the space group Fm-3m (the space group of general rock salt-type crystals) of rock salt-type crystals, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt-type crystals and O3'-type crystals and rock salt-type crystals. In this specification, when the orientation of the cubic close-packed structure formed by the anions is aligned in layered rock salt-type crystals, O3'-type crystals, and rock salt-type crystals, the crystal orientations may be said to be roughly aligned.

[0280] FIG. 12 shows an example of the crystal structure of lithium cobalt oxide containing magnesium. The crystal structure at a charge depth of 0 (discharged state) in FIG. 12 is R-3m(O3). The positive electrode active material shown in FIG. 12 has an O3'-type crystal structure when the charge depth is fully charged. Note that, in the diagram of the O3'-type crystal structure shown in FIG. 12, lithium can be present at any lithium site with a probability of about 20%, but this is not limited to this. It may be present only at a specific portion of the lithium sites. In both the O3-type crystal structure and the O3'-type crystal structure, CoO ２ It is preferable that element X is present in a dilute form between the layers, i.e., at the lithium sites, and it is also preferable that halogen such as fluorine is present randomly and dilutely at the oxygen sites.

[0281] In the positive electrode active materials shown in Fig. 12, the change in the crystal structure when a large amount of lithium is released by charging at a high voltage is suppressed. For example, as shown by the dotted line in Fig. 12, in these crystal structures, CoO ２ There is almost no layer misalignment.

[0282] More specifically, the positive electrode active material of one embodiment of the present invention has high structural stability even at high charge voltages. For example, the R-3m(O3) crystal structure can be maintained even at charge voltages of about 4.6 V relative to the potential of lithium metal. Even at higher charge voltages, for example, voltages of about 4.65 V to 4.7 V relative to the potential of lithium metal, the positive electrode active material of one embodiment of the present invention can adopt an O3'-type crystal structure. When the charge voltage is further increased above 4.7 V, H1-3 crystals may be observed in the positive electrode active material of one embodiment of the present invention. Furthermore, even at lower charge voltages (for example, when the charge voltage is 4.5 V or more and less than 4.6 V relative to the potential of lithium metal), the positive electrode active material of one embodiment of the present invention may adopt an O3'-type crystal structure.

[0283] Note that when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery is lower than the above by the potential of the graphite. The potential of graphite is approximately 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, even when the voltage of a secondary battery using graphite as the negative electrode active material is 4.3 V or higher and 4.5 V or lower, the positive electrode active material of one embodiment of the present invention can maintain the R-3m(O3) crystal structure. Furthermore, even when the charge voltage is increased, for example, when the voltage of the secondary battery is higher than 4.5 V and lower than 4.6 V, the positive electrode active material of one embodiment of the present invention can also have the O3'-type crystal structure. Furthermore, even when the charge voltage is lower, for example, when the voltage of the secondary battery is 4.2 V or higher but lower than 4.3 V, the positive electrode active material of one embodiment of the present invention may have the O3' structure.

[0284] In addition, in a positive electrode active material according to one embodiment of the present invention, the difference in volume per unit cell between the O3-type crystal structure at a charge depth of 0 and the O3'-type crystal structure at a charge depth of 80% is 2.5% or less, more specifically 2.2% or less. Note that the O3'-type crystal structure can have the coordinates of cobalt and oxygen in the unit cell expressed in the ranges of Co(0,0,0.5), O(0,0,x), where 0.20≦x≦0.25.

[0285] The lattice constant of the unit cell is 2.814 × 10 for the a-axis. −１０ m is greater than 2.817 x 10 −１０ m, and the c-axis is 14.05 × 10 −１０ m or larger, 14.07 x 10−１０ It is preferable that the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is greater than 0.20000 and smaller than 0.20049.

[0286] The above-mentioned positive electrode active material, whose crystal structure during charging is represented by an O3'-type crystal structure, may have diffraction peaks at 2θ = 19.35 ± 0.10° and 2θ = 45.55 ± 0.20° when analyzed by powder X-ray analysis using CuKα1 rays during charging.

[0287] In the positive electrode active material shown in Fig. 12, by setting the upper charge voltage to a voltage lower than the voltage at which H1-3 type crystals are observed, it is possible to suppress the collapse of the crystal structure due to repeated charge and discharge. That is, at time t2 in Fig. 5 or time t4 in Fig. 6, it is preferable that the positive electrode active material has the O3 type crystal structure or the O3' type crystal structure.

[0288] A positive electrode active material according to one embodiment of the present invention changes from an O3-type crystal structure to an O3'-type crystal structure, which will be described later. This change in crystal structure occurs when the secondary battery is in a deep state of charge, and the change in crystal structure is generally reversible. A charger according to one embodiment of the present invention has a function of detecting the change from the O3-type crystal structure to the O3'-type crystal structure and controlling charging. This change in crystal structure occurs when the secondary battery is in a high state of charge, and therefore the charger according to one embodiment of the present invention is capable of charging at a high capacity.

[0289] CoO ２ Magnesium, which exists randomly and dilutely between the layers, i.e., at the lithium sites, turns into CoO when charged at a high voltage. ２ This has the effect of suppressing layer misalignment. ２ When magnesium is present between the layers, the O3' type crystal structure is easily formed.

[0290] Therefore, magnesium is preferably distributed throughout the particles of the positive electrode active material 200 of one embodiment of the present invention. In order to distribute magnesium throughout the particles, heat treatment is preferably performed in the manufacturing process of the positive electrode active material 200 of one embodiment of the present invention.

[0291] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that additives, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site is ineffective in maintaining the R-3m structure at high depths of charge. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium transpiration.

[0292] Therefore, it is preferable to add a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. Adding a fluorine compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium throughout the particles at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0293] Note that increasing the magnesium concentration above the desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of atoms of the transition metal M, more preferably more than 0.01 to less than 0.04 times, and even more preferably about 0.02 times. Alternatively, it is preferably 0.001 to 0.04 times. Alternatively, it is preferably 0.01 to 0.1 times. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition during the production process of the positive electrode active material.

[0294] The transition metals M, such as nickel, and aluminum are preferably present at the cobalt site, but may be partially present at the lithium site. Magnesium is preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0295] As the magnesium concentration in the positive electrode active material of one embodiment of the present invention increases, the charge / discharge capacity of the positive electrode active material may decrease. For example, this may be due to magnesium entering the lithium site, reducing the amount of lithium contributing to charge / discharge. Excess magnesium may also produce magnesium compounds that do not contribute to charge / discharge. When the positive electrode active material of one embodiment of the present invention contains nickel in addition to magnesium, the charge / discharge capacity per weight and per volume may be increased. When the positive electrode active material of one embodiment of the present invention contains aluminum in addition to magnesium, the charge / discharge capacity per weight and per volume may be increased. When the positive electrode active material of one embodiment of the present invention contains nickel and aluminum in addition to magnesium, the charge / discharge capacity per weight and per volume may be increased.

[0296] Hereinafter, the concentrations of elements such as magnesium, nickel, and aluminum contained in the positive electrode active material of one embodiment of the present invention will be expressed in terms of the number of atoms.

[0297] The number of nickel atoms in the positive electrode active material 200 of one embodiment of the present invention is preferably more than 0% and 7.5% or less of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Alternatively, more than 0% and 4% or less is preferable. Alternatively, more than 0% and 2% or less is preferable. Alternatively, 0.05% to 7.5% or less is preferable. Alternatively, 0.05% to 2% or less is preferable. Alternatively, 0.1% to 7.5% or less is preferable. Alternatively, 0.1% to 4% or less is preferable. The nickel concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0298] The presence of divalent nickel in the inner portion 200b may allow divalent additive elements, such as magnesium, present randomly and dilutely at lithium sites nearby to exist more stably. This can suppress the elution of magnesium even after charging and discharging to a high depth of charge. This can improve charge-discharge cycle performance. Thus, combining the effects of nickel in the inner portion 200b and magnesium, aluminum, titanium, fluorine, and the like in the surface portion 200a is extremely effective in stabilizing the crystal structure at high depths of charge.

[0299] The number of aluminum atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferred. Alternatively, 0.1% to 4% is preferred. The aluminum concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0300] The positive electrode active material of one embodiment of the present invention preferably further contains phosphorus as an additional element, and more preferably contains a compound containing phosphorus and oxygen.

[0301] When the positive electrode active material of one embodiment of the present invention contains a compound containing phosphorus, short circuits can be suppressed in some cases when a state of high depth of charge is maintained.

[0302] When the positive electrode active material of one embodiment of the present invention contains phosphorus, the hydrogen fluoride generated by decomposition of the electrolyte solution may react with the phosphorus, resulting in a decrease in the concentration of hydrogen fluoride in the electrolyte solution.

[0303] The electrolyte is LiPF ６When the electrolyte solution has the above structure, hydrogen fluoride may be generated by hydrolysis. Hydrogen fluoride may also be generated by a reaction between PVDF, which is used as a component of the positive electrode, and an alkali. By reducing the hydrogen fluoride concentration in the electrolyte solution, corrosion of the current collector and / or peeling of the coating 204 may be suppressed. Furthermore, a decrease in adhesion due to gelation and / or insolubilization of PVDF may be suppressed.

[0304] When the positive electrode active material of one embodiment of the present invention contains phosphorus in addition to magnesium, the stability at a high state of charge is extremely high. When phosphorus is contained, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. Alternatively, 1% to 10% is preferred. Alternatively, 1% to 8% is preferred. Alternatively, 2% to 20% is preferred. Alternatively, 2% to 8% is preferred. Alternatively, 3% to 20% is preferred. Alternatively, 3% to 10% is preferred. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and even more preferably 0.7% to 4%. Alternatively, 0.1% to 5% is preferred. Alternatively, 0.1% to 4% is preferred. Alternatively, 0.5% to 10% is preferred. Alternatively, 0.5% to 4% is preferred. Alternatively, 0.7% to 10% is preferred. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS or the like, or may be based on values ​​of the composition of raw materials in the process of producing the positive electrode active material.

[0305] The positive electrode active material may have cracks. The presence of phosphorus, more specifically, a compound containing phosphorus and oxygen, in the positive electrode active material having the cracks on the surface, for example, in the embedded portion 202, may inhibit the progression of the cracks.

[0306] Magnesium is preferably distributed throughout the entire particle of the positive electrode active material 200 of one embodiment of the present invention, and in addition, the magnesium concentration in the surface layer 200 a is preferably higher than the average throughout the particle. Alternatively, the magnesium concentration in the surface layer 200 a is preferably higher than the concentration in the interior 200 b.

[0307] Furthermore, when the positive electrode active material 200 of one embodiment of the present invention contains an additive element, for example, one or more metals selected from aluminum, nickel, manganese, iron, and chromium, the concentration of the additive element in the surface layer 200a is preferably higher than the average throughout the particle. Alternatively, the concentration of the metal in the surface layer 200a is preferably higher than that in the interior 200b. While some of the additive elements, particularly magnesium, nickel, and aluminum, are preferably present in the surface layer 200a at a higher concentration than in the interior 200b, they are also preferably present randomly and dilutely in the interior 200b. The presence of magnesium and aluminum at appropriate concentrations at the lithium sites in the interior 200b can facilitate the maintenance of a layered rock-salt crystal structure, as described above. The presence of nickel at an appropriate concentration in the interior 200b can also suppress the shift of the layered structure consisting of octahedra of the transition metal M and oxygen, as described above. Furthermore, when magnesium and nickel are present together, a synergistic effect of suppressing magnesium elution can be expected, since divalent magnesium may be more stable near divalent nickel.

[0308] Unlike the inner portion 200b, which maintains its crystalline structure, the surface portion 200a is in a state where bonds are broken, and since lithium is released from the surface during charging, the surface portion 200a is prone to have a lower lithium concentration than the inner portion. Therefore, this portion is prone to becoming unstable and the crystalline structure is prone to collapse. If the magnesium concentration in the surface portion 200a is high, changes in the crystalline structure can be more effectively suppressed. Furthermore, if the magnesium concentration in the surface portion 200a is high, it can be expected that the corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte will be improved.

[0309] Furthermore, the fluorine concentration in the surface layer 200 a of the positive electrode active material 200 according to one embodiment of the present invention is preferably higher than the average concentration in the entire particle. Alternatively, the fluorine concentration in the surface layer 200 a is preferably higher than the concentration in the interior 200 b. The presence of fluorine in the surface layer 200 a, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0310] As described above, the surface layer portion 200a of the cathode active material 200 of one embodiment of the present invention preferably has a different composition from the interior portion 200b, i.e., a higher concentration of additive elements, such as magnesium and fluorine, than the interior portion 200b. Furthermore, the composition preferably has a stable crystal structure at room temperature (25°C). Therefore, the surface layer portion 200a may have a different crystal structure from the interior portion 200b. For example, at least a portion of the surface layer portion 200a of the cathode active material 200 of one embodiment of the present invention may have a rock salt crystal structure. Furthermore, when the surface layer portion 200a and the interior portion 200b have different crystal structures, it is preferable that the crystal orientations of the surface layer portion 200a and the interior portion 200b are approximately the same.

[0311] The layered rock salt crystal and the anions of the rock salt crystal have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3' type crystal also have a cubic close-packed structure.

[0312] The fact that the crystal orientations of the two regions roughly coincide can be seen from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-Angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron diffraction patterns, and FFT (Fast Fourier transform) images of TEM images, etc. The determination can be made from a Transform pattern, etc. XRD (X-ray diffraction), neutron diffraction, etc. can also be used as materials for the determination.

[0313] <Grain Boundary> In addition to the above-described distribution, the additive element contained in the positive electrode active material 200 of one embodiment of the present invention is preferably partially distributed unevenly in the grain boundary 201 and its vicinity.

[0314] More specifically, the magnesium concentration at and near the grain boundary 201 of the positive electrode active material 200 is preferably higher than that in other regions of the interior 200b. Also, the fluorine concentration at and near the grain boundary 201 is preferably higher than that in other regions of the interior 200b.

[0315] The grain boundaries 201 are one type of planar defect. Therefore, like the grain surfaces, they are prone to become unstable and changes in the crystal structure are likely to occur. Therefore, if the magnesium concentration at and near the grain boundaries 201 is high, changes in the crystal structure can be more effectively suppressed.

[0316] Furthermore, when the magnesium concentration and fluorine concentration are high at and near the grain boundary, even if cracks occur along the grain boundary 201 of the particles of the positive electrode active material 200 of one embodiment of the present invention, the magnesium concentration and fluorine concentration become high near the surface where the cracks occur. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after the cracks occur.

[0317] In this specification, the vicinity of the grain boundary 201 refers to the region up to 10 nm from the grain boundary. The grain boundary refers to a surface where there is a change in the atomic arrangement, and can be observed in an electron microscope image. Specifically, the term refers to a portion where the repetition of bright and dark lines in an electron microscope image becomes discontinuous, a portion containing many crystal defects, or defects observable in a cross-sectional STEM image, i.e., a structure where other elements have entered between the lattice, cavities, etc.

[0318] <Particle size> If the particle size of the positive electrode active material 200 of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to a current collector may occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector and excessive reaction with the electrolyte may occur. Therefore, the median diameter (D50) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Alternatively, 1 μm or more and 40 μm or less is preferable. Alternatively, 1 μm or more and 30 μm or less is preferable. Alternatively, 2 μm or more and 100 μm or less is preferable. Alternatively, 2 μm or more and 30 μm or less is preferable. Alternatively, 5 μm or more and 100 μm or less is preferable. Alternatively, 5 μm or more and 40 μm or less is preferable.

[0319] <Analysis Method> Whether a certain cathode active material is the cathode active material 200 of one embodiment of the present invention that exhibits an O3'-type crystal structure at a high depth of charge can be determined by analyzing a cathode having a cathode active material with a high depth of charge using XRD, electron beam diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred in that it can analyze the symmetry of transition metals such as cobalt contained in the cathode active material with high resolution, can compare the level of crystallinity and crystal orientation, can analyze lattice periodic distortion and crystallite size, and can provide sufficient accuracy even when measuring a cathode obtained by disassembling a secondary battery.

[0320] As described above, the cathode active material 200 of one embodiment of the present invention is characterized by minimal change in crystal structure between a high state of charge and a discharged state. Materials in which 50% or more of the crystal structure exhibits significant changes from the discharged state at a high state of charge are undesirable because they cannot withstand charge and discharge cycles that result in a high state of charge. It should be noted that the desired crystal structure may not be achieved simply by adding an additive element. For example, even if lithium cobalt oxide containing magnesium and fluorine has a common feature, at a high state of charge, the O3'-type crystal structure may account for 60% or more, or the H1-3-type crystal structure may account for 50% or more. Furthermore, at a certain voltage, the O3'-type crystal structure may be nearly 100%, and further increasing the voltage may result in the H1-3-type crystal structure. Therefore, to determine whether a material is the cathode active material 200 of one embodiment of the present invention, analysis of the crystal structure, including XRD, is required.

[0321] However, when a positive electrode active material is in a highly charged or discharged state, its crystal structure may change when exposed to air. For example, it may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0322] <<XRD>> The apparatus and conditions for XRD measurement are not particularly limited. For example, measurement can be performed using the following apparatus and conditions. XRD apparatus: D8 ADVANCE manufactured by Bruker AXS X-ray source: CuKα ray Output: 40 KV, 40 mA Slit width: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0323] X-ray photoelectron spectroscopy (XPS) can analyze a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less), allowing quantitative analysis of the concentration of each element in a region about half the depth of the surface layer 200a. Furthermore, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is often about ±1 atomic %, and the lower detection limit is about 1 atomic %, depending on the element.

[0324] When XPS analysis was performed on the positive electrode active material 200 of one embodiment of the present invention, the number of atoms of the additive element was preferably 1.6 to 6.0 times, and more preferably 1.8 to less than 4.0 times, the number of atoms of the transition metal M. When the additive is magnesium and the transition metal M is cobalt, the number of magnesium atoms is preferably 1.6 to 6.0 times, and more preferably 1.8 to less than 4.0 times, the number of cobalt atoms. Furthermore, the number of atoms of the halogen such as fluorine is preferably 0.2 to 6.0 times, and more preferably 1.2 to 4.0 times, the number of atoms of the transition metal M.

[0325] When performing XPS analysis, for example, monochromated aluminum Kα can be used as the X-ray source. The take-off angle can be set to, for example, 45°. Measurement can be performed, for example, using the following equipment and conditions. Measurement equipment: PHI Quantera II X-ray source: monochromated Al Kα (1486.6 eV) Detection area: 100 μmφ Detection depth: approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: wide scan, narrow scan of each detected element

[0326] Furthermore, when the positive electrode active material 200 of one embodiment of the present invention is subjected to XPS analysis, the peak representing the bond energy between fluorine and another element is preferably equal to or greater than 682 eV and less than 685 eV, and more preferably approximately 684.3 eV. This value is different from both the bond energy of lithium fluoride (685 eV) and the bond energy of magnesium fluoride (686 eV). In other words, when the positive electrode active material 200 of one embodiment of the present invention contains fluorine, the bond is preferably other than that of lithium fluoride or magnesium fluoride.

[0327] Furthermore, when the positive electrode active material 200 of one embodiment of the present invention is subjected to XPS analysis, the peak representing the bond energy between magnesium and another element is preferably greater than or equal to 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This value is different from the bond energy of magnesium fluoride, 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 200 of one embodiment of the present invention contains magnesium, the bond is preferably other than that of magnesium fluoride.

[0328] The concentrations of additive elements, such as magnesium and aluminum, which are preferably present in large amounts in the surface layer 200a, measured by XPS or the like are preferably higher than the concentrations measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0329] When a cross section of magnesium and aluminum is exposed by processing and analyzed using TEM-EDX, the concentration of magnesium and aluminum in the surface layer 200a is preferably higher than the concentration in the interior 200b. For example, in TEM-EDX analysis, the magnesium concentration preferably decays to 60% or less of the peak at a point 1 nm deep from the peak top. Also, it preferably decays to 30% or less of the peak at a point 2 nm deep from the peak top. Processing can be performed using, for example, a focused ion beam (FIB).

[0330] In an XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms, while in an ICP-MS analysis, the ratio of the number of magnesium atoms, Mg / Co, is preferably 0.001 to 0.06.

[0331] On the other hand, it is preferable that nickel contained in the transition metal M is not unevenly distributed in the surface layer portion 200a but is distributed throughout the positive electrode active material 200. However, this does not apply when there is a region where the additive element is unevenly distributed as described above.

[0332] <<ESR>> As described above, the positive electrode active material of one embodiment of the present invention preferably contains cobalt and nickel as the transition metal M and magnesium as the additive element. ３＋ Ni ３＋ and some Li ＋ is Mg ２＋ It is preferred that Li be substituted with ＋ is Mg ２＋ With the substitution of ３＋ is reduced to Ni ２＋ In addition, some Li ＋ is Mg ２＋ is replaced by Mg ２＋ Nearby Co ３＋ is reduced to Co ２＋ In addition, some Co ３＋ is Mg ２＋ is replaced by Mg ２＋ Nearby Co ３＋ is oxidized to Co ４＋ This may occur.

[0333] Therefore, the positive electrode active material according to one embodiment of the present invention is ２＋ , Ni ３＋ , Co ２＋ and Co ４＋ It is preferable that the positive electrode active material contains at least one of the following: ２＋ , Ni ３＋ , Co ２＋ and Co ４＋ The spin density due to one or more of the above is 2.0 × 10 １７ spins / g or more 1.0×10 ２１ It is preferable that the spin density is 1 / 2 spins / g or less. By using a positive electrode active material having the above spin density, the crystal structure becomes stable, especially in the charged state, which is preferable. Note that if the magnesium concentration is too high, Ni ２＋ , Ni ３＋ , Co ２＋ and Co ４＋ The spin density may be reduced due to one or more of the above.

[0334] The spin density in the positive electrode active material can be analyzed using, for example, electron spin resonance (ESR).

[0335] <EPMA> EPMA (Electron Probe Microanalysis) allows for the quantification of elements. Area analysis allows for the distribution of each element to be analyzed.

[0336] EPMA analyzes a region from the surface to a depth of approximately 1 μm. Therefore, the concentration of each element may differ from the measurement results obtained using other analytical methods. For example, when performing a surface analysis of the positive electrode active material 200, the concentration of the additive present in the surface layer may be lower than the result obtained by XPS. Furthermore, the concentration of the additive present in the surface layer may be higher than the result obtained by ICP-MS or the value obtained by the raw material composition during the production process of the positive electrode active material.

[0337] When EPMA surface analysis is performed on a cross section of the positive electrode active material 200 of one embodiment of the present invention, the concentration of the added element preferably has a concentration gradient that increases from the interior toward the surface. More specifically, as shown in FIG. 8C1, magnesium, fluorine, titanium, and silicon preferably have a concentration gradient that increases from the interior toward the surface. Furthermore, as shown in FIG. 8C2, aluminum preferably has a concentration peak deeper than the concentration peaks of the above elements, i.e., in a region closer to the interior. The aluminum concentration peak may be present in the surface or may be deeper than the surface.

[0338] The surface and surface layer of the positive electrode active material of one embodiment of the present invention are assumed to be free of carbonates, hydroxyl groups, and the like chemically adsorbed after the preparation of the positive electrode active material. They are also assumed to be free of electrolyte, binder, conductive material, and compounds derived therefrom that adhere to the surface of the positive electrode active material. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, and the like that can be detected by surface analysis such as XPS and EPMA. For example, XPS can separate the types of bonds by analysis, and corrections may be made to exclude C—F bonds derived from the binder.

[0339] Furthermore, before subjecting the sample to various analyses, the sample of the positive electrode active material and the positive electrode active material layer may be washed to remove the electrolyte, binder, conductive material, or compounds derived therefrom that adhere to the surface of the positive electrode active material. In this case, lithium may dissolve in the solvent used for washing, but even in this case, the added element is unlikely to dissolve, and therefore the atomic ratio of the added element is not affected.

[0340] <Surface Roughness and Specific Surface Area> The positive electrode active material 200 of one embodiment of the present invention preferably has a smooth surface with few irregularities. A smooth surface with few irregularities is one factor indicating that the distribution of the additive element in the surface layer portion 200 a is good.

[0341] Whether the surface is smooth and has few irregularities can be determined from, for example, a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 200, the specific surface area of ​​the positive electrode active material 200, or the like.

[0342] [Method for manufacturing positive electrode active material] An example of a method for manufacturing a compound including an element A, a metal M, and an element X as a positive electrode active material of one embodiment of the present invention will be described below. The example of the manufacturing method will be described with reference to a flowchart shown in FIG.

[0343] In step S11 of FIG. 13, a material of element A and a material of metal M are prepared.

[0344] As the source of element A (referred to as A source in FIG. 13 ), an oxide, carbonate compound, halogen compound, or the like having element A can be used. When element A is lithium, lithium carbonate, lithium fluoride, or the like can be used.

[0345] As the metal M source (referred to as M source in FIG. 13 ), a compound containing the metal M can be used. When the positive electrode active material is an oxide, for example, an oxide, hydroxide, or the like can be used as the M source.

[0346] Next, in step S12, the element A source and the metal M source are mixed. In addition to mixing, crushing may be performed. Crushing and mixing can be performed by a dry method or a wet method.

[0347] Next, in step S13, the mixed materials are heated.

[0348] Through the above steps, a compound 901 containing the element A and the metal M can be produced (step S14).

[0349] Here, lithium is used as the element A, and an oxide or hydroxide of metal M is used as the metal M source, the ratio of the lithium source to the metal M source is 1:1, and the compound represented by the chemical formula LiMO ２ It is possible to obtain a lithium composite oxide represented by the formula: ２ The composition is not strictly limited to Li:M:O=1:1:2, so long as it has a crystalline structure of a lithium composite oxide represented by the formula:

[0350] Next, in step S20, an element X source is prepared. A compound containing element X can be used as the element X source (referred to as X source in FIG. 13 ). When multiple elements are used as element X, compounds containing each of the elements may be prepared separately. Alternatively, a single compound containing multiple elements may be used. Note that by using a halogen compound as the element X source, for example, a positive electrode active material containing a halogen can be obtained.

[0351] The source of element X may be crushed. When a plurality of compounds are used as the source of element X, they are preferably mixed.

[0352] Next, in step S31, the compound 901 obtained in step S14 is mixed with a source of element X.

[0353] Next, in step S32, the mixed materials are collected to obtain a mixture 902.

[0354] Next, in step S33, the mixture 902 is heated. Note that it may be preferable that the heating temperature in step S33 is lower than the heating temperature in step S13.

[0355] Next, the heated material is recovered to obtain positive electrode active material 903 (step S34).

[0356] The flow chart shown in FIG. 14 differs from FIG. 13 in that step S15 is provided between step S14 and step S31.

[0357] In step S15 shown in FIG. 14, the compound 901 obtained in step S14 is heated. Because this is the first heating of compound 901, the heating in step S15 is sometimes called initial heating. After initial heating, the surface of compound 901 becomes smooth. A smooth surface refers to a state in which the surface of compound 901 has few irregularities, is rounded overall, and has rounded corners. Furthermore, a state in which there is little foreign matter adhering to the surface is called smooth. Foreign matter is thought to be a cause of irregularities, so it is preferable that it does not adhere to the surface.

[0358] The initial heating is performed after the compound 901 is completed, and the initial heating is performed for the purpose of smoothing the surface, which may reduce deterioration after charge and discharge. The initial heating for smoothing the surface does not require the preparation of a lithium compound source.

[0359] Alternatively, the initial heating to smooth the surface does not require the provision of a source of the additive element.

[0360] Alternatively, initial heating to smooth the surface does not require the use of a fluxing agent.

[0361] The initial heating is performed before step S31 and may be called preheating or pretreatment.

[0362] At least one of the lithium source and the transition metal source prepared in step S11 etc. may contain impurities. The initial heating can reduce the amount of impurities in the compound 901 completed in step S14.

[0363] The heating conditions in this step may be any conditions that result in a smooth surface of compound 901. For example, the heating conditions may be selected from those described in step S13. Regarding the heating conditions, the heating temperature in this step may be lower than the temperature in step S13 in order to maintain the crystal structure of compound 901. Furthermore, the heating time in this step may be shorter than the time in step S13 in order to maintain the crystal structure of compound 901. For example, heating may be performed at a temperature of 700° C. or higher and 1000° C. or lower for 2 hours or longer.

[0364] The heating of compound 901 in step S13 may cause a temperature difference between the surface and the interior of compound 901. The temperature difference may induce a shrinkage difference. It is also believed that the temperature difference causes a difference in fluidity between the surface and the interior, resulting in a shrinkage difference. The energy associated with the shrinkage difference causes a difference in internal stress in compound 901. The difference in internal stress is also referred to as strain, and this energy is sometimes referred to as strain energy. It is believed that the internal stress is removed by the initial heating in step S15; in other words, the strain energy is homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in compound 901 is relaxed. Therefore, the surface of compound 901 may become smooth after step S15. This is also referred to as an improved surface. In other words, it is believed that the shrinkage difference that occurred in compound 901 is relaxed after step S15, resulting in a smoother surface of compound 901.

[0365] Furthermore, the shrinkage difference may cause microscopic deviations in compound 901, such as deviations in crystals. This step is preferably carried out to reduce such deviations. This step makes it possible to equalize the deviations in compound 901. Equalizing the deviations may result in a smoother surface for compound 901. This is also referred to as crystalline grain alignment. In other words, it is believed that step S15 reduces deviations in crystals and other components in compound 901, resulting in a smoother surface for compound 901.

[0366] When the compound 901 having a smooth surface is used as a positive electrode active material, deterioration during charge and discharge as a secondary battery is reduced, and cracking of the positive electrode active material can be prevented.

[0367] The smooth surface of compound 901 can be expressed as having a surface roughness of at least 10 nm or less when surface roughness information is quantified from measurement data on a cross section of compound 901. The cross section is, for example, a cross section obtained when observing with a scanning transmission electron microscope (STEM).

[0368] Note that a compound 901 containing lithium, a transition metal, and oxygen that has been synthesized in advance may be used in step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on the compound 901 that has been synthesized in advance, a compound 901 with a smooth surface can be obtained.

[0369] It is conceivable that the initial heating reduces the amount of lithium in compound 901. The lithium from the reduced amount of added elements, which will be explained in the next step S20, may be more likely to enter compound 901.

[0370] <Negative Electrode> A negative electrode according to one embodiment of the present invention includes a negative electrode active material.

[0371] As the negative electrode active material, it is preferable to use a material capable of reacting with carrier ions of the secondary battery, a material capable of inserting and desorbing carrier ions, a material capable of alloying with a metal that becomes a carrier ion, a material capable of dissolving and precipitating a metal that becomes a carrier ion, or the like.

[0372] As the negative electrode active material, for example, carbon materials such as graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene can be used.

[0373] As the negative electrode active material, for example, a material containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used.

[0374] Furthermore, impurity elements such as phosphorus, arsenic, boron, aluminum, and gallium may be added to silicon to lower its resistance.

[0375] Examples of silicon-containing materials include SiOｘ (x is preferably smaller than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0376] As a silicon-containing material, for example, a form having multiple crystal grains within a single particle can be used. For example, a form having one or multiple silicon crystal grains within a single particle can be used. Furthermore, the single particle may have silicon oxide around the silicon crystal grain. Furthermore, the silicon oxide may be amorphous.

[0377] Examples of compounds containing silicon include Li ２ SiO ３ and Li ４ SiO ４ Li can be used. ２ SiO ３ and Li ４ SiO ４ may each be crystalline or amorphous.

[0378] The silicon-containing compound can be analyzed using NMR, XRD, Raman spectroscopy, or the like.

[0379] Examples of materials that can be used for the negative electrode active material include oxides containing one or more elements selected from titanium, niobium, tungsten, and molybdenum.

[0380] As the negative electrode active material, a combination of the above-mentioned metals, materials, compounds, etc. can be used.

[0381] The negative electrode active material of one embodiment of the present invention may have fluorine in the surface layer portion. The negative electrode active material having a halogen in the surface layer portion can suppress a decrease in charge / discharge efficiency. It is also believed that the reaction with the electrolyte on the active material surface is suppressed. Furthermore, the negative electrode active material of one embodiment of the present invention may have at least a portion of its surface covered with a region containing a halogen. The region may be, for example, in the form of a film. Fluorine is particularly preferred as the halogen.

[0382] <Electrolyte> The electrolyte preferably contains a solvent and a metal salt that serves as a carrier ion. The solvent for the electrolyte is preferably an aprotic organic solvent, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone, or any combination and ratio of two or more of these.

[0383] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the electrolyte solvent, it is possible to prevent the secondary battery from exploding or catching fire even if the internal temperature of the secondary battery rises due to an internal short circuit, overcharging, or the like. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0384] The salt to be dissolved in the solvent is, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ These lithium salts may be used alone or in any combination and ratio of two or more of them.

[0385] The electrolyte used in the secondary battery is preferably a highly purified electrolytic solution with a low content of granular dust and elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0386] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the added material may be, for example, 0.1 wt % to 5 wt % of the total solvent. VC and LiBOB are particularly preferred because they easily form a good coating.

[0387] A solution containing a solvent and a salt that serves as carrier ions may be called an electrolyte.

[0388] A polymer gel electrolyte in which a polymer is swollen with an electrolytic solution may also be used.

[0389] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0390] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0391] Examples of polymers that can be used include polymers having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, and polyacrylonitrile, as well as copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0392] In addition, a solid electrolyte containing an inorganic material can be used as the electrolyte. For example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc. can be used. A solid electrolyte containing a polymer material such as PEO (polyethylene oxide) can also be used. When a solid electrolyte is used, the installation of a separator and spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0393] The sulfide-based solid electrolytes include thiolithium-based (Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ etc.), sulfide glass (70Li ２ S・30P ２ S ５ , 30Li ２S・26B ２ S ３ ・44LiI, 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４ SiO ４ , 50Li ２ S・50GeS ２ etc.), sulfide crystallized glass (Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0394] The oxide-based solid electrolyte includes a material having a perovskite crystal structure (La ２／３−ｘ Li ３ｘ TiO ３ etc.), materials having a NASICON type crystal structure (Li １−Ｘ Al Ｘ Ti ２−Ｘ (P.O. ４ ) ３ etc.), materials having a garnet-type crystal structure (Li ７ La ３ Zr ２ O １２ etc.), materials having a LISICON type crystal structure (Li １４ ZnGe ４ O １６ etc.), LLZO (Li ７ La ３ Zr ２ O １２ ), oxide glass (Li ３ P.O. ４ -Li ４ SiO ４ , 50Li ４ SiO ４ ・50Li ３ BO ３ etc.), oxide crystallized glass (Li １．０７ Al ０．６９ Ti１．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0395] Halide-based solid electrolytes include LiAlCl ４ , Li ３ InBr ６ , LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as the solid electrolyte.

[0396] Also, different solid electrolytes may be mixed and used.

[0397] Among them, Li having a NASICON type crystal structure １＋ｘ Al ｘ Ti ２−ｘ (P.O. ４ ) ３ Since (0[x[1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that may be contained in the positive electrode active material used in the secondary battery of one embodiment of the present invention, a synergistic effect can be expected in improving cycle characteristics, which is preferable. In addition, an improvement in productivity due to a reduction in the number of steps can also be expected. Note that in this specification and the like, the NASICON-type crystal structure refers to a structure in which M ２ (A.O. ４ ) ３ (M: transition metal, A: S, P, As, Mo, W, etc.), ６ Octahedron and AO ４ It refers to a structure in which tetrahedrons are arranged three-dimensionally with their vertices shared.

[0398] <Voltage of secondary battery> The secondary battery uses a positive electrode active material of the chemical formula LiCoO ２and containing 70 wt % or more of graphite as the negative electrode active material, the upper limit charging voltage of the secondary battery is preferably higher than 4.2 V, and more preferably higher than 4.3 V. In addition, the upper limit charging voltage of the secondary battery is, for example, 4.8 V or lower, or 4.7 V or lower, or 4.65 V or lower.

[0399] The secondary battery uses a positive electrode active material with the chemical formula LiMO ２ In the case where the secondary battery contains a compound in which 40 mol % or more of M is nickel and contains 70 wt % or more of graphite as the negative electrode active material, the upper limit charging voltage of the secondary battery is preferably higher than 4.1 V, and more preferably higher than 4.2 V. In addition, the upper limit charging voltage of the secondary battery is, for example, 4.8 V or lower, or 4.7 V or lower, or 4.65 V or lower.

[0400] <Capacity of Secondary Battery> In the case of charging using the charger of one embodiment of the present invention, the charge capacity is, for example, preferably 200 mAh / g or more, more preferably 210 mAh / g or more, and still more preferably 215 mAh / g or more (at 45° C. and a charge rate of 0.5 C) per weight of the positive electrode active material.

[0401] This embodiment mode can be combined with the descriptions of other embodiment modes as appropriate.

[0402] Embodiment Mode 3 In this embodiment mode, a method for manufacturing a secondary battery will be described.

[0403] <Method 1 for manufacturing laminated secondary battery> Here, an example of a method for manufacturing a laminated secondary battery whose external views are shown in Figures 15A and 15B will be described with reference to Figures 16A and 16B and Figures 17A and 17B. A secondary battery 500 shown in Figures 15A and 15B has a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. Note that, as a cross-sectional view of the laminated secondary battery shown in Figure 15A etc., for example, a structure in which a positive electrode, a separator, and a negative electrode are stacked and surrounded by an outer casing can be used, as shown in Figure 18 described later.

[0404] First, a positive electrode 503, a negative electrode 506, and a separator 507 are prepared. Fig. 16A shows an example of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode active material layer 502 on a positive electrode current collector 501. The positive electrode 503 preferably has a tab region where the positive electrode current collector 501 is exposed. The negative electrode 506 has a negative electrode active material layer 505 on a negative electrode current collector 504. The negative electrode 506 preferably has a tab region where the negative electrode current collector 504 is exposed.

[0405] Next, negative electrodes 506, separators 507, and positive electrodes 503 are stacked. Fig. 16B shows the stacked negative electrodes 506, separators 507, and positive electrodes 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a stack consisting of negative electrodes, separators, and positive electrodes.

[0406] Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0407] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are arranged on the outer casing 509 .

[0408] Next, as shown in Fig. 17A, the exterior body 509 is bent at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for the joining. At this time, an area (hereinafter referred to as an inlet 516) that is not joined is provided in a part (or one side) of the exterior body 509 so that the electrolyte 508 can be introduced later.

[0409] 17B , electrolyte 508 is introduced into exterior body 509 through inlet 516 provided in exterior body 509. The introduction of electrolyte 508 is preferably performed under a reduced pressure atmosphere or an inert atmosphere. Finally, inlet 516 is joined. In this manner, laminated secondary battery 500 can be fabricated.

[0410] In the above, the positive electrode lead electrode 510 and the negative electrode lead electrode 511 are led out of the exterior of the outer casing from the same side to produce the secondary battery 500 shown in Fig. 15A. The positive electrode lead electrode 510 and the negative electrode lead electrode 511 can also be led out of the exterior of the outer casing from opposite sides to produce the secondary battery 500 shown in Fig. 15B.

[0411] <Another Secondary Battery and Manufacturing Method 1> An example of a cross-sectional view of a stack of one embodiment of the present invention is shown in Fig. 18. A stack 550 shown in Fig. 18 is manufactured by placing one separator between a positive electrode and a negative electrode while folding the separator.

[0412] In the laminate 550, one separator 507 is folded multiple times so as to be sandwiched between the positive electrode active material layers 502 and the negative electrode active material layers 505. In Fig. 18, six layers of positive electrodes 503 and six layers of negative electrodes 506 are stacked, and therefore the separator 507 is folded at least five times. The separator 507 may not only be provided so as to be sandwiched between the positive electrode active material layers 502 and the negative electrode active material layers 505, but also may have its extending portion further folded so as to bind the multiple positive electrodes 503 and negative electrodes 506 together with tape or the like.

[0413] In the method for manufacturing a secondary battery of one embodiment of the present invention, after the positive electrode 503 is disposed, an electrolyte can be dropped onto the positive electrode 503. Similarly, after the negative electrode 506 is disposed, an electrolyte can be dropped onto the negative electrode 506. Furthermore, in the method for manufacturing a secondary battery of one embodiment of the present invention, an electrolyte can be dropped onto the separator 507 before folding the separator or after folding the separator 507 and overlapping it with the negative electrode 506 or the positive electrode 503. By dropping the electrolyte onto at least one of the negative electrode 506, the separator 507, and the positive electrode 503, the negative electrode 506, the separator 507, or the positive electrode 503 can be impregnated with the electrolyte.

[0414] 19A has a stack 972 inside a housing 971. A terminal 973b and a terminal 974b are electrically connected to the stack 972. At least a portion of the terminal 973b and at least a portion of the terminal 974b are exposed to the outside of the housing 971.

[0415] The stacked body 972 can have a structure in which a positive electrode, a negative electrode, and a separator are stacked. Alternatively, the stacked body 972 can have a structure in which a positive electrode, a negative electrode, and a separator are wound, or the like.

[0416] For example, the laminate 972 may be a laminate having a structure in which separators are folded back as shown in FIG.

[0417] An example of a method for manufacturing the stacked body 972 will be described with reference to FIGS. 19B and 19C.

[0418] First, as shown in FIG. 19B , a strip-shaped separator 976 is placed on top of a positive electrode 975a, and then a negative electrode 977a is placed on top of the positive electrode 975a with the separator 976 sandwiched between them. The separator 976 is then folded back and placed on top of the negative electrode 977a. Next, as shown in FIG. 19C , a positive electrode 975b is placed on top of the negative electrode 977a with the separator 976 sandwiched between them. In this way, by folding back the separator and arranging the positive electrode and negative electrode in order, a stack 972 can be produced. A structure including a stack produced in this way is sometimes called a "zigzag structure."

[0419] Next, an example of a method for manufacturing the secondary battery 970 will be described with reference to FIGS. 20A to 20C.

[0420] 20A , a positive electrode lead electrode 973a is electrically connected to the positive electrode of the laminate 972. Specifically, for example, a tab region may be provided on each positive electrode of the laminate 972, and each tab region may be electrically connected to the positive electrode lead electrode 973a by welding or the like. In addition, a negative electrode lead electrode 974a is electrically connected to the negative electrode of the laminate 972.

[0421] One stack 972 or a plurality of stacks 972 may be arranged inside the housing 971. Fig. 20B shows an example in which two sets of stacks 972 are prepared.

[0422] Next, as shown in FIG. 20C , the prepared laminate 972 is housed in a housing 971, terminals 973b and 974b are attached, and the housing 971 is sealed. It is preferable that a conductor 973c is electrically connected to each positive electrode lead electrode 973a of the plurality of laminates 972. It is also preferable that a conductor 974c is electrically connected to each negative electrode lead electrode 974a of the plurality of laminates 972. The terminal 973b is electrically connected to the conductor 973c, and the terminal 974b is electrically connected to the conductor 974c. The conductor 973c may have a conductive region and an insulating region. The conductor 974c may have a conductive region and an insulating region.

[0423] A metal material (for example, aluminum) can be used for the housing 971. In the case where a metal material is used for the housing 971, the surface of the housing 971 is preferably covered with resin or the like. Alternatively, a resin material can be used for the housing 971.

[0424] It is preferable to provide a safety valve, an overcurrent protection element, or the like in the housing 971. The safety valve is a valve that releases gas when the pressure inside the housing 971 reaches a predetermined level in order to prevent the battery from exploding.

[0425] <Another Secondary Battery and Manufacturing Method 2> Fig. 21C shows an example of a cross-sectional view of a secondary battery of another embodiment of the present invention. A secondary battery 560 shown in Fig. 21C is manufactured using the stack 130 shown in Fig. 21A and the stack 131 shown in Fig. 21B. Note that for clarity, Fig. 21C only shows the stack 130, the stack 131, and the separator 507.

[0426] As shown in FIG. 21A , the laminate 130 includes a positive electrode 503 having positive electrode active material layers on both sides of a positive electrode current collector, a separator 507, a negative electrode 506 having negative electrode active material layers on both sides of a negative electrode current collector, the separator 507, and a positive electrode 503 having positive electrode active material layers on both sides of a positive electrode current collector laminated in this order.

[0427] As shown in FIG. 21B , the laminate 131 includes a negative electrode 506 having a negative electrode active material layer on both sides of a negative electrode current collector, a separator 507, a positive electrode 503 having a positive electrode active material layer on both sides of a positive electrode current collector, the separator 507, and a negative electrode 506 having a negative electrode active material layer on both sides of a negative electrode current collector laminated in this order.

[0428] The method for manufacturing a secondary battery according to one embodiment of the present invention can be applied to manufacturing a stack. Specifically, when the negative electrode 506, the separator 507, and the positive electrode 503 are stacked to manufacture a stack, an electrolyte is dropped onto at least one of the negative electrode 506, the separator 507, and the positive electrode 503. By dropping multiple drops of the electrolyte, the negative electrode 506, the separator 507, or the positive electrode 503 can be impregnated with the electrolyte.

[0429] As shown in FIG. 21C, the plurality of stacks 130 and the plurality of stacks 131 are covered with a wound separator 507 .

[0430] In addition, in the method for manufacturing a secondary battery of one embodiment of the present invention, after the stack 130 is arranged, an electrolyte can be dropped onto the stack 130. Similarly, after the stack 131 is arranged, an electrolyte can be dropped onto the stack 131. Furthermore, before the separator 507 is folded, or after the separator 507 is folded and overlapped with the stack, an electrolyte can be dropped onto the separator 507. By dropping multiple drops of the electrolyte, the stack 130, the stack 131, or the separator 507 can be impregnated with the electrolyte.

[0431] 22A to 22C and 23A to 23C , a secondary battery according to another embodiment of the present invention will be described. The secondary battery described here can be called a wound secondary battery, or the like.

[0432] The secondary battery 913 shown in FIG. 22A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 22A , for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0433] 22B, the housing 930 shown in Fig. 22A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 22B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0434] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0435] 22C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that multiple layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0436] In a method for manufacturing a secondary battery according to one embodiment of the present invention, when the negative electrode 931, the separator 933, and the positive electrode 932 are stacked, an electrolyte is dropped onto at least one of the negative electrode 931, the separator 933, and the positive electrode 932. That is, the electrolyte is preferably dropped onto at least one of the negative electrode 931, the separator 933, and the positive electrode 932 before the laminate sheet is wound. By dropping multiple drops of the electrolyte, the negative electrode 931, the separator 933, or the positive electrode 932 can be impregnated with the electrolyte.

[0437] 23A to 23C may be used as a secondary battery 913 having a wound body 950a. The wound body 950a shown in Fig. 23A includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0438] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable because of its high safety and productivity.

[0439] 23B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0440] 23C , the wound body 950a and the electrolyte are covered by the housing 930 to form the secondary battery 913. It is preferable to provide the housing 930 with a safety valve, an overcurrent protection element, etc. The safety valve opens temporarily only when the internal pressure of the housing 930 exceeds a predetermined value to prevent the battery from exploding.

[0441] 23B, the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the secondary battery 913 can have a larger charge / discharge capacity.

[0442] This embodiment mode can be combined with other embodiment modes as appropriate.

[0443] Embodiment 4 In this embodiment, application examples of a power storage system of one embodiment of the present invention will be described with reference to FIGS.

[0444] In the following application examples, the power storage system preferably includes a charger according to one embodiment of the present invention. The charger according to one embodiment of the present invention preferably includes the components included in the charger described in the above embodiment. The charger according to one embodiment of the present invention may also include a circuit that has a function of converting the voltage, current, or the like of supplied power. Examples of circuits that have a function of converting the voltage, current, or the like of power include a regulator, a step-down circuit, a step-up circuit, a circuit that converts AC power to DC power, a modulation circuit, a demodulation circuit, an amplifier circuit, and the like.

[0445] [Vehicle] First, an example in which the power storage system of one embodiment of the present invention is applied to an electric vehicle (EV) will be described.

[0446] 24 shows a block diagram of a vehicle having a motor. The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery or starter battery. The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0447] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0448] In addition, in a secondary battery for vehicle use, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a in order to cut off power from multiple secondary batteries.

[0449] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V system (high voltage system) on-board components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0450] In addition, the second battery 1311 supplies power to 14V (low voltage) in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0451] The first batteries 1301a and 1301b mainly supply power to in-vehicle devices of the 42V system (high voltage system), and the second battery 1311 supplies power to in-vehicle devices of the 14V system (low voltage system). A lead-acid battery is often used as the second battery 1311 because of its cost advantage.

[0452] In this embodiment, an example is shown in which lithium ion secondary batteries are used as both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0453] Furthermore, regenerated energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 or the battery controller 1302. Alternatively, the first battery 1301a is charged from the battery controller 1302. Alternatively, the first battery 1301b is charged from the battery controller 1302. In order to efficiently charge the regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0454] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the secondary battery used, and can perform rapid charging.

[0455] The charger of one embodiment of the present invention can be used as the battery controller 1302. Note that a circuit having a function of converting the voltage, current, and the like of power may be provided between the motor 1304 and the battery controller 1302. By using the charger of one embodiment of the present invention as the battery controller 1302, the charge capacity of the first batteries 1301a and 1301b can be increased and the reliability of the first batteries 1301a and 1301b can be improved. Since the charge capacity of the first batteries 1301a and 1301b can be increased, the traveling distance of the electric vehicle can be increased. Furthermore, since deterioration of the first batteries 1301a and 1301b can be suppressed, the frequency of battery replacement in the electric vehicle can be reduced. Furthermore, since the reliability of the first batteries 1301a and 1301b can be increased, the safety of the electric vehicle can be improved.

[0456] Next, an example in which the power storage system of one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0457] By installing the power storage system of one embodiment of the present invention in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, the secondary battery can also be installed in agricultural machinery such as electric tractors, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes or planetary probes, and spacecraft. A large secondary battery can be manufactured by using the manufacturing method of the secondary battery according to one embodiment of the present invention. Therefore, the secondary battery of one embodiment of the present invention can be suitably used in transportation vehicles.

[0458] 25A to 25E illustrate a transportation vehicle using the power storage system of one embodiment of the present invention. The automobile 2001 illustrated in FIG. 25A is an electric automobile using an electric motor as a power source for traveling. Alternatively, the automobile 2001 is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, the secondary battery is installed in one or more locations. The automobile 2001 illustrated in FIG. 25A includes the power storage system of one embodiment of the present invention. The power storage system includes the charger of one embodiment of the present invention and the first battery 1301a illustrated in FIG. 24A . The power storage system may also include a plurality of secondary batteries connected in series as a battery pack. The battery pack is electrically connected to the charger of one embodiment of the present invention.

[0459] The power storage system of the automobile 2001 can receive power from an external power supply facility using a plug-in system, a contactless power supply system, or the like. A predetermined connector standard and power supply system, such as CHAdeMO (registered trademark) or Combo, can be used for power supply. Power may be supplied from a charging station installed in a commercial facility or from a home power source.

[0460] When the charger of one embodiment of the present invention determines that charging should be stopped, a signal informing the charging station of the stop of charging can be sent via a control circuit included in the charger of one embodiment of the present invention. Alternatively, the charger of one embodiment of the present invention may be applied to a charging station. For example, the charging station may include at least some of the components of the charger of one embodiment of the present invention, such as the control circuit of the charger of one embodiment of the present invention.

[0461] Furthermore, the automobile 2001 preferably has a function of converting AC power into DC power via a conversion device such as an AC-DC converter. In such a case, for example, the converted DC power is supplied to the power storage system.

[0462] Although not shown, a power receiving device can be mounted on a vehicle to receive power from a ground-based power transmitting device in a contactless manner. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, power can be supplied not only when the vehicle is stopped but also when the vehicle is moving. This contactless power supply method may also be used to transmit and receive power between two vehicles. Furthermore, solar cells may be provided on the exterior of the vehicle to receive power when the vehicle is stopped or moving. Electromagnetic induction or magnetic resonance methods can be used for such contactless power supply.

[0463] 25B illustrates a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 includes, for example, a four-cell unit including secondary batteries of 3.5 V to 4.7 V, with 48 cells connected in series to achieve a maximum voltage of 170 V. The power storage system 2201 includes a charger of one embodiment of the present invention and a secondary battery module. Except for the number of secondary batteries included in the secondary battery module, the power storage system 2201 has the same functions as those in FIG. 25A , and therefore description thereof will be omitted.

[0464] 25C illustrates, as an example, a large transport vehicle 2003 having an electrically controlled motor. The transport vehicle 2003 includes a power storage system 2202. The power storage system 2202 includes a charger of one embodiment of the present invention and a secondary battery module. The secondary battery module has, for example, a maximum voltage of 600 V, in which one hundred or more secondary batteries with a voltage of 3.5 V or higher and 4.7 V or lower are connected in series. Except for the number of secondary batteries constituting the secondary battery module, the transport vehicle 2003 has the same functions as those in FIG. 25A , and therefore description thereof will be omitted.

[0465] 25D illustrates, as an example, an aircraft 2004 having an engine that burns fuel. The aircraft 2004 illustrated in Fig. 25D has wheels for takeoff and landing, and therefore can also be considered a part of a transportation vehicle. The aircraft 2004 includes a power storage system 2203 including a secondary battery module formed by connecting multiple secondary batteries and the secondary battery module and a charger of one embodiment of the present invention.

[0466] The secondary battery module of the aircraft 2004 is, for example, eight 4 V secondary batteries connected in series to produce a maximum voltage of 32 V. Apart from the number of secondary batteries constituting the secondary battery module of the power storage system 2203, the secondary battery module has the same functions as those shown in Fig. 25A, and therefore a description thereof will be omitted.

[0467] FIG. 25E illustrates a transport vehicle 2005 for transporting cargo as an example. The transport vehicle 2005 includes a power storage system 2204. The power storage system 2204 includes a charger of one embodiment of the present invention and a secondary battery module. The transport vehicle 2005 has an electrically controlled motor and performs various tasks by receiving power from a secondary battery constituting the secondary battery module of the power storage system 2204. The transport vehicle 2005 is not limited to being driven and operated by a human driver, and can also be unmanned via CAN communication or the like. Although a forklift is illustrated in FIG. 25E , the present invention is not limited to this. The power storage system of one embodiment of the present invention can be installed in industrial machinery that can be operated via CAN communication or the like, such as an automatic transporter, a work robot, or a small construction machine.

[0468] 26A is an example of an electric bicycle using the power storage system of one embodiment of the present invention. The power storage system of one embodiment of the present invention can be applied to an electric bicycle 2100 shown in Fig. 26A. A power storage system 2102 shown in Fig. 26B includes, for example, a plurality of secondary batteries and the charger of one embodiment of the present invention.

[0469] The electric bicycle 2100 includes a power storage system 2102. The power storage system 2102 can supply electricity to a motor that assists the rider. The power storage system 2102 is portable and is shown detached from the bicycle in FIG. 26B . The power storage system 2102 also includes multiple built-in secondary batteries 2101, and a display unit 2103 can display the remaining battery charge and other information. The power storage system 2102 also includes a charger 2104. The charger 2104 is electrically connected to the positive and negative electrodes of the secondary batteries 2101. A small solid-state secondary battery may also be provided in the charger 2104. Providing a small solid-state secondary battery in the charger 2104 can also supply power to retain data in the memory circuit of the charger 2104 for a long period of time. Using the charger 2104 can improve the safety of the secondary battery and significantly contribute to preventing accidents such as fires. Using the charger 2104 can also increase the mileage of the bicycle.

[0470] 26C shows an example of a two-wheeled vehicle using the power storage system of one embodiment of the present invention. A scooter 2300 shown in FIG. 26C includes a power storage system 2302, a side mirror 2301, and a turn signal light 2303. The power storage system 2302 can supply electricity to the turn signal light 2303.

[0471] 26C is capable of storing the power storage system 2302 in the under-seat storage compartment 2304. The power storage system 2302 can be stored in the under-seat storage compartment 2304 even if the under-seat storage compartment 2304 is small.

[0472] [Building] Next, an example in which the power storage system of one embodiment of the present invention is mounted in a building will be described with reference to FIGS.

[0473] 27A includes a power storage system 2612 and a solar panel 2610. The power storage system 2612 includes, for example, a battery pack including a plurality of secondary batteries. The power storage system 2612 is electrically connected to the solar panel 2610 via wiring 2611 and the like.

[0474] The power storage system 2612 includes a charger according to one embodiment of the present invention. The power storage system 2612 can be charged with power obtained by the solar panel 2610 via the charger.

[0475] The power storage system 2612 may be electrically connected to a ground-mounted charging device 2604. When a charger included in the power storage system 2612 determines that charging should be stopped, a signal informing the charging device 2604 of the stop of charging can be sent via a control circuit included in the charger. Alternatively, the charger of one embodiment of the present invention may be applied to the charging device 2604. For example, the charging device 2604 may include at least some of the components of the charger of one embodiment of the present invention, for example, a control circuit of the charger of one embodiment of the present invention.

[0476] The power stored in the power storage system 2612 can be charged into a secondary battery of the vehicle 2603 via a charging device 2604. The power storage system 2612 is preferably installed in an underfloor space. By installing the power storage system 2612 in an underfloor space, the space above the floor can be used effectively. Alternatively, the power storage system 2612 may be installed on the floor.

[0477] The power stored in the power storage system 2612 can also be supplied to other electronic devices in the home. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the power storage system 2612 can be used as an uninterruptible power supply, making it possible to use electronic devices.

[0478] 27B illustrates an example of a power storage system according to one embodiment of the present invention. As illustrated in FIG. 27B , a power storage system 791 including a large secondary battery and a charger according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799.

[0479] The power storage system 791 is equipped with a control device 790, which is electrically connected to a distribution board 703, a power storage controller 705 (also referred to as a control device), a display 706, and a router 709 via wiring.

[0480] Electric power is sent from commercial power source 704 to distribution board 703 via service line attachment portion 710. Electric power is also sent to distribution board 703 from power storage system 791 and commercial power source 704, and distribution board 703 supplies the sent electric power to general loads 707 and power storage loads 708 via outlets (not shown).

[0481] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0482] The power storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during one day (e.g., from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage system 791 and the amount of power supplied from the commercial power source 704. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage system 791 based on the amount of power demand predicted by the prediction unit 712.

[0483] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electrical device such as a television or a personal computer via the router 709. It can also be confirmed on a portable electronic device such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical device, or the portable electronic device.

[0484] The secondary battery of one embodiment of the present invention can be used in, for example, one or both of an electronic device and a lighting device, such as a mobile phone, a smartphone, a portable information terminal such as a laptop computer, a portable game console, a portable music player, a digital camera, or a digital video camera.

[0485] A personal computer 2800 shown in FIG. 28A includes a housing 2801, a housing 2802, a display unit 2803, a keyboard 2804, a pointing device 2805, and the like. A power storage system 2807 is provided inside the housing 2801, and a power storage system 2806 is provided inside the housing 2802. The power storage system 2806 includes a secondary battery and a charger electrically connected to the secondary battery. The power storage system 2807 includes a secondary battery and a charger electrically connected to the secondary battery. A touch panel is applied to the display unit 2803. As shown in FIG. 28B, the housings 2801 and 2802 can be removed from the personal computer 2800, and the personal computer 2800 can be used as a tablet terminal using only the housing 2802.

[0486] By applying a flexible film or the like to the exterior of the secondary battery included in the power storage systems 2806 and 2807 and forming the exterior to fit the shape of the housings 2801 and 2802, the capacity of the secondary battery can be increased and the usage time of the personal computer 2800 can be extended. In addition, the weight of the personal computer 2800 can be reduced.

[0487] A flexible display is applied to the display portion 2803 of the housing 2802. The power storage system 2806 includes a secondary battery and a charger electrically connected to the secondary battery. The secondary battery included in the power storage system 2806 can be made bendable by using a flexible film for the exterior body. This allows the housing 2802 to be folded for use, as shown in FIG. 28C. In this case, part of the display portion 2803 can also be used as a keyboard, as shown in FIG. 28C.

[0488] The housing 2802 can be folded so that the display portion 2803 faces inward as shown in FIG. 28D, or can be folded so that the display portion 2803 faces outward as shown in FIG. 28E.

[0489] FIG. 29A shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 built into a housing 7401, as well as operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 also includes a power storage system. The power storage system includes a secondary battery 7407 and a charger 7408 electrically connected to the secondary battery 7407. The charger 7408 can receive power from an external power source via the external connection port 7404. The external connection port 7404 receives power from, for example, an AC adapter. The AC adapter has a function of converting AC power into DC power and providing the power to the external connection port 7404. Alternatively, the mobile phone 7400 may have a function of converting AC power into DC power via a conversion circuit such as an AC-DC converter. The charger 7408 may also have a circuit for converting AC power into DC power.

[0490] Furthermore, power may be supplied to the mobile phone 7400 from an external power source by wireless power supply. The Qi standard or the like may be used as a standard for wireless power supply. A signal transmitted to the mobile phone 7400 by wireless power supply is provided to the charger 7408 via, for example, a demodulation circuit. Alternatively, the charger 7408 may have a circuit for wireless communication, such as a modulation circuit, a demodulation circuit, or the like.

[0491] When the mobile phone 7400 includes the charger of one embodiment of the present invention as the charger 7408, the safety of the mobile phone 7400 can be improved. Furthermore, since the discharge energy density of the secondary battery can be increased, the volume and weight of the secondary battery can be reduced, thereby enabling the size and weight of the mobile phone 7400 to be reduced. Furthermore, since the life of the secondary battery can be extended, the mobile phone 7400 can be used for a long time without having to replace the secondary battery.

[0492] Furthermore, the charger of one embodiment of the present invention has the functions of both a charge control circuit and a protection circuit, and therefore can reduce the area or number of chips included in the mobile phone 7400. Therefore, the mobile phone 7400 can be made smaller and lighter, and the reliability of the mobile phone 7400 can be improved.

[0493] 29B shows a bent state of the mobile phone 7400. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 provided inside is also bent.

[0494] FIG. 29C shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a power storage system. The power storage system includes a secondary battery 7104 and a charger 7105 electrically connected to the secondary battery 7104. When the secondary battery 7104 included in the power storage system is bent and worn on a user's arm, the housing deforms, causing a change in the curvature of part or all of the secondary battery 7104. Note that the degree of curvature at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surfaces of the housing or secondary battery change within a range of a radius of curvature of 40 mm to 150 mm. High reliability can be maintained if the radius of curvature of the main surface of the secondary battery is within a range of 40 mm to 150 mm.

[0495] 29D shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0496] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0497] The display surface of the display portion 7202 is curved, and display can be performed along the curved display surface. The display portion 7202 also includes a touch sensor, and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0498] The operation button 7205 can have various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the portable information terminal 7200.

[0499] The portable information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is possible by communicating with a wirelessly enabled headset.

[0500] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0501] The display portion 7202 of the portable information terminal 7200 has a power storage system. The secondary battery 7104 and the charger 7105 shown in FIG. 29C can be incorporated into the housing 7201 in a curved state or into the band 7203 in a bendable state.

[0502] The portable information terminal 7200 preferably has a sensor. For example, a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is preferably mounted as the sensor.

[0503] 29E shows an example of a wristband-type display device. The display device 7300 includes a display portion 7304 and a power storage system. The secondary battery 7104 and the charger 7105 shown in FIG. 29C can be incorporated into the display device 7300. The display device 7300 can also include a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0504] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0505] The display device 7300 also includes an input / output terminal, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal. Note that charging may be performed by wireless power supply without using the input / output terminal.

[0506] An example in which the power storage system of one embodiment of the present invention is mounted on an electronic device will be described with reference to FIGS. 29F, 30, and 31. FIG.

[0507] FIG. 29F is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 29F, the electronic cigarette 7500 is composed of an atomizer 7501 including a heating element, a power storage system 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle or a sensor. The power storage system 7504 includes a secondary battery and a charger electrically connected to the secondary battery. The power storage system 7504 shown in FIG. 29F has external terminals that allow connection to an external power source of the electronic cigarette 7500. Because the power storage system 7504 forms the tip of the device when held, it is desirable that the secondary battery included in the power storage system 7504 be short in total length and lightweight.

[0508] Next, Figures 30A and 30B show an example of a foldable tablet terminal. The tablet terminal 7600 shown in Figures 30A and 30B includes a housing 7630a, a housing 7630b, a movable portion 7640 connecting the housings 7630a and 7630b, a display portion 7631 having display portions 7631a and 7631b, switches 7625, 7626, and 7627, a fastener 7629, and an operation switch 7628. Using a flexible panel for the display portion 7631 allows for a tablet terminal with a larger display area. Figure 30A shows the tablet terminal 7600 in an open state, and Figure 30B shows the tablet terminal 7600 in a closed state.

[0509] The tablet terminal 7600 also includes a secondary battery 7635 inside the housing 7630a and the housing 7630b. The secondary battery 7635 passes through the movable portion 7640 and is provided across the housing 7630a and the housing 7630b.

[0510] All or part of the display portion 7631 can be a touch panel area, and data can be input by touching an image including an icon, text, an input form, etc. displayed in the area. For example, keyboard buttons may be displayed on the entire surface of the display portion 7631a on the housing 7630a side, and information such as text and images may be displayed on the display portion 7631b on the housing 7630b side.

[0511] A keyboard may be displayed on the display portion 7631b of the housing 7630b, and information such as text and images may be displayed on the display portion 7631a of the housing 7630a. A keyboard display switch button of a touch panel may be displayed on the display portion 7631, and the keyboard may be displayed on the display portion 7631 by touching the button with a finger, a stylus, or the like.

[0512] In addition, touch input can be simultaneously performed on the touch panel area of ​​the display portion 7631a on the housing 7630a side and the touch panel area of ​​the display portion 7631b on the housing 7630b side.

[0513] Furthermore, the switches 7625 to 7627 may be interfaces capable of switching various functions in addition to interfaces for operating the tablet terminal 7600. For example, at least one of the switches 7625 to 7627 may function as a switch for turning the tablet terminal 7600 on and off. For example, at least one of the switches 7625 to 7627 may have a function for switching the display orientation, such as portrait or landscape, or a function for switching between black and white and color display. For example, at least one of the switches 7625 to 7627 may have a function for adjusting the brightness of the display unit 7631. The brightness of the display unit 7631 can be optimized depending on the amount of external light detected by an optical sensor built into the tablet terminal 7600 during use. The tablet terminal may also have built-in not only an optical sensor but also other detection devices, such as a gyroscope, an acceleration sensor, or other sensors for detecting tilt.

[0514] 30A shows an example in which the display areas of the display portion 7631a on the housing 7630a and the display portion 7631b on the housing 7630b are substantially the same, the display areas of the display portion 7631a and the display portion 7631b are not particularly limited, and the sizes of one and the other may be different, and the display qualities may also be different. For example, one display panel may be capable of displaying at a higher resolution than the other.

[0515] 30B illustrates a tablet terminal 7600 in a folded state, and the tablet terminal 7600 includes a housing 7630, a solar cell 7633, and a power storage system 7634. ​​The power storage system 7634 includes the charger described in the above embodiment. The power storage system 7634 also includes a DC-DC converter 7636.

[0516] As described above, the tablet terminal 7600 can be folded in half, so that the housing 7630a and the housing 7630b overlap each other when not in use. By folding, the display portion 7631 can be protected, thereby improving the durability of the tablet terminal 7600.

[0517] In addition, the tablet terminal 7600 shown in Figures 30A and 30B can have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date or time on the display unit, a touch input function for touch input operations or editing information displayed on the display unit, and controlling processing using various software (programs).

[0518] A solar cell 7633 attached to the surface of the tablet terminal 7600 can supply power to a touch panel, a display unit, a video signal processor, or the like. The solar cell 7633 can be provided on one or both surfaces of the housing 7630, and can be configured to efficiently charge the secondary battery 7635. Use of a lithium-ion battery as the secondary battery 7635 has advantages such as miniaturization.

[0519] The configuration and operation of the power storage system 7634 shown in FIG. 30B are described with reference to a block diagram in FIG. 30C . FIG. 30C illustrates a solar cell 7633, a secondary battery 7635, a DC-DC converter 7636, a converter 7637, a charger 7638, switches SW1 to SW3, and a display unit 7631. The secondary battery 7635, the DC-DC converter 7636, the converter 7637, and the switches SW1 to SW3 correspond to the power storage system 7634 shown in FIG. 30B . The charger of one embodiment of the present invention can be used as the charger 7638. The charger 7638 has a function of applying a signal S1 to one or more of the switches SW1 to SW3. The charger 7638 has a function of measuring the current and voltage of the secondary battery 7635, for example. The secondary battery 7635 has a function of determining charging conditions and controlling the switch SW2 according to the determined charging conditions.

[0520] An example of operation when power is generated by the solar cell 7633 using external light will be described. The power generated by the solar cell is increased or decreased by a DC-DC converter 7636 to a voltage for charging the secondary battery 7635. When power from the solar cell 7633 is used to operate the display portion 7631, a switch SW1 is turned on, and the converter 7637 increases or decreases the voltage to a voltage required for the display portion 7631. When no display is to be performed on the display portion 7631, the switch SW1 may be turned off and the switch SW2 may be turned on to charge the secondary battery 7635.

[0521] Note that the solar cell 7633 is shown as an example of a power generating means, but is not particularly limited thereto, and a configuration may be adopted in which the secondary battery 7635 is charged by other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a configuration in which a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging, or a combination of other charging means may be adopted.

[0522] 31 illustrates an example of another electronic device. In FIG. 31 , a display device 8000 is an example of an electronic device including a power storage system 8004 of one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display portion 8002, a speaker portion 8003, a power storage system 8004, and the like. The power storage system 8004 is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or can use power stored in the power storage system 8004. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the display device 8000 can be used by using the power storage system 8004 of one embodiment of the present invention as an uninterruptible power supply.

[0523] The display portion 8002 can be a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a semiconductor display device such as a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0524] The display device includes all display devices for displaying information, such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

[0525] 31 , a stationary lighting device 8100 is an example of an electronic device including a power storage system 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a power storage system 8103, and the like. Although FIG. 31 illustrates the case where the power storage system 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed, the power storage system 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or can use power stored in the power storage system 8103. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the power storage system 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0526] Note that although the lighting device 8100 in FIG. 31 is a stationary lighting device provided on the ceiling 8104, the power storage system of one embodiment of the present invention can also be used in a stationary lighting device provided on a surface other than the ceiling 8104, such as a side wall 8105, a floor 8106, or a window 8107, or can also be used in a tabletop lighting device.

[0527] Furthermore, an artificial light source that artificially obtains light using electric power can be used as the light source 8102. Specifically, examples of the artificial light source include a discharge lamp such as an incandescent lamp or a fluorescent lamp, an LED, and / or an organic EL element.

[0528] 31 , an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a power storage system 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a power storage system 8203, and the like. Although FIG. 31 illustrates the case where the power storage system 8203 is provided in the indoor unit 8200, the power storage system 8203 may be provided in the outdoor unit 8204. Alternatively, the power storage system 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or can use power stored in the power storage system 8203. In particular, when the power storage system 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be used by using the power storage system 8203 of one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power source due to a power outage or the like.

[0529] Note that although FIG. 31 illustrates an example of a separate-type air conditioner including an indoor unit and an outdoor unit, the power storage system of one embodiment of the present invention can also be used for an all-in-one air conditioner in which the functions of the indoor unit and the outdoor unit are combined in one housing.

[0530] 31 , an electric refrigerator-freezer 8300 is an example of an electronic device including a power storage system 8304 according to one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a power storage system 8304, and the like. In FIG. 31 , the power storage system 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or can use power stored in the power storage system 8304. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the power storage system 8304 according to one embodiment of the present invention as an uninterruptible power supply.

[0531] Among the electronic devices described above, electronic devices such as high-frequency heating devices such as microwave ovens and electric rice cookers require a large amount of power for a short period of time. Therefore, by using the power storage system according to one embodiment of the present invention as an auxiliary power source for supplementing the power that cannot be supplied by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0532] Furthermore, by storing power in the power storage system during time periods when electronic devices are not in use, particularly during time periods when the ratio of the amount of power actually used to the total amount of power that can be supplied by the commercial power supplier (referred to as the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of these time periods. For example, in the case of an electric refrigerator-freezer 8300, power is stored in the power storage system 8304 during the night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened or closed. Then, during the daytime when the temperature is high and the refrigerator door 8302 and the freezer door 8303 are opened and closed, the power storage system 8304 is used as an auxiliary power source, thereby preventing the daytime power usage rate from increasing.

[0533] 32A shows an example of a wearable device. The wearable device uses a power storage system as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector is desired.

[0534] For example, the power storage system of one embodiment of the present invention can be mounted on an eyeglasses-type device 9000 as shown in FIG. 32A . The eyeglasses-type device 9000 includes a frame 9000a and a display portion 9000b. By mounting the power storage system on temple portions of the curved frame 9000a, the eyeglasses-type device 9000 can be lightweight, well-balanced in weight, and has a long continuous use time. By providing the power storage system of one embodiment of the present invention, the energy density of the power storage system can be increased, and a configuration that can accommodate space-saving due to a smaller housing can be realized.

[0535] Furthermore, the power storage system according to one embodiment of the present invention can be mounted on a headset device 9001. The headset device 9001 includes at least a microphone unit 9001a, a flexible pipe 9001b, and an earphone unit 9001c. The power storage system can be provided in the flexible pipe 9001b or the earphone unit 9001c. By providing the power storage system according to one embodiment of the present invention, a configuration that can accommodate space saving due to a miniaturized housing can be realized.

[0536] Furthermore, the power storage system according to one embodiment of the present invention can be mounted on a device 9002 that can be directly attached to a body. A power storage system 9002b can be provided in a thin housing 9002a of the device 9002. By providing the power storage system according to one embodiment of the present invention, a space-saving configuration can be realized that can be achieved by miniaturizing the housing.

[0537] Furthermore, the power storage system according to one embodiment of the present invention can be mounted on a device 9003 that can be attached to clothing. A power storage system 9003b can be provided in a thin housing 9003a of the device 9003. By providing the power storage system according to one embodiment of the present invention, a structure that can achieve space saving due to miniaturization of the housing can be realized.

[0538] Furthermore, the power storage system of one embodiment of the present invention can be mounted on a belt-type device 9006. The belt-type device 9006 includes a belt portion 9006a and a wireless power receiving portion 9006b, and the power storage system can be mounted inside the belt portion 9006a. By including the power storage system of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of a housing can be realized.

[0539] Furthermore, the power storage system of one embodiment of the present invention can be mounted on a wristwatch-type device 9005. The wristwatch-type device 9005 has a display portion 9005a and a belt portion 9005b, and the power storage system can be provided on the display portion 9005a or the belt portion 9005b. By providing the power storage system of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0540] The display portion 9005a can display not only the time but also various information such as incoming emails and phone calls.

[0541] Furthermore, since the wristwatch-type device 9005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise amount and health can be accumulated to manage the user's health.

[0542] FIG. 32B shows a perspective view of the wristwatch-type device 9005 removed from the wrist.

[0543] 32C shows a side view of the display device 9005. The display device 9005 includes a power storage system 9011 according to one embodiment of the present invention. The power storage system 9011 is provided so as to overlap with the display portion 9005a, and is small and lightweight.

[0544] 33A shows an example of a cleaning robot. The cleaning robot 9300 includes a display portion 9302 arranged on the top surface of a housing 9301, a plurality of cameras 9303 arranged on the side surface, a brush 9304, operation buttons 9305, a power storage system 9306, various sensors, and the like. Although not shown, the cleaning robot 9300 is provided with tires, a suction port, and the like. The cleaning robot 9300 can move by itself, detect dust 9310, and suck up the dust from a suction port arranged on the bottom surface.

[0545] For example, the cleaning robot 9300 can analyze an image captured by the camera 9303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 9304, such as a wire, is detected through image analysis, the cleaning robot 9300 can stop the rotation of the brush 9304. The cleaning robot 9300 includes a power storage system 9306 according to one embodiment of the present invention and a semiconductor device or an electronic component therein. By using the power storage system 9306 according to one embodiment of the present invention in the cleaning robot 9300, the cleaning robot 9300 can be a highly reliable electronic device with a long operating time.

[0546] Fig. 33B shows an example of a robot. The robot 9400 shown in Fig. 33B includes a power storage system 9409, an illuminance sensor 9401, a microphone 9402, an upper camera 9403, a speaker 9404, a display unit 9405, a lower camera 9406, an obstacle sensor 9407, a moving mechanism 9408, a computing device, etc.

[0547] The microphone 9402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 9404 has a function of emitting sound. The robot 9400 can communicate with the user using the microphone 9402 and the speaker 9404.

[0548] The display portion 9405 has a function of displaying various information. The robot 9400 can display information desired by a user on the display portion 9405. The display portion 9405 may be equipped with a touch panel. The display portion 9405 may be a detachable information terminal, which can be installed in a fixed position on the robot 9400 to enable charging and data transfer.

[0549] The upper camera 9403 and the lower camera 9406 have the function of capturing images of the surroundings of the robot 9400. In addition, the obstacle sensor 9407 can detect the presence or absence of obstacles in the direction of travel when the robot 9400 moves forward using the movement mechanism 9408. The robot 9400 can recognize the surrounding environment and move safely using the upper camera 9403, the lower camera 9406, and the obstacle sensor 9407.

[0550] The robot 9400 includes a power storage system 9409 according to one embodiment of the present invention and a semiconductor device or an electronic component inside the robot 9400. By using the power storage system according to one embodiment of the present invention in the robot 9400, the robot 9400 can be a highly reliable electronic device with a long operating time.

[0551] Fig. 33C shows an example of an air vehicle. The air vehicle 9500 shown in Fig. 33C includes a propeller 9501, a camera 9502, a power storage system 9503, and the like, and has a function of flying autonomously.

[0552] For example, image data captured by the camera 9502 is stored in the electronic component 9504. The electronic component 9504 can analyze the image data and detect the presence or absence of an obstacle when moving. Furthermore, the electronic component 9504 can estimate the remaining battery charge from a change in the power storage capacity of the power storage system 9503. The flying object 9500 includes the power storage system 9503 according to one embodiment of the present invention therein. By using the power storage system according to one embodiment of the present invention in the flying object 9500, the flying object 9500 can be an electronic device with long operating time and high reliability.

[0553] 33D shows an example of an artificial satellite 6800. The artificial satellite 6800 has a body 6801, a solar panel 6802, an antenna 6803, and a secondary battery 6805.

[0554] When sunlight is irradiated onto the solar panel 6802, the power required for the operation of the satellite 6800 is generated. However, for example, in a situation where sunlight is not irradiated onto the solar panel or where the amount of sunlight irradiating the solar panel is small, the generated power is small. Therefore, there is a possibility that the power required for the operation of the satellite 6800 will not be generated. In order to operate the satellite 6800 even in a situation where the generated power is small, it is preferable to provide a secondary battery 6805 in the satellite 6800.

[0555] The satellite 6800 can generate a signal. The signal is transmitted via an antenna 6803 and can be received, for example, by a receiver installed on the ground or by another satellite. By receiving the signal transmitted by the satellite 6800, for example, the position of the receiver that received the signal can be measured. As described above, the satellite 6800 can constitute, for example, a satellite positioning system.

[0556] Alternatively, the artificial satellite 6800 may be configured to include a sensor. For example, by including a visible light sensor, the artificial satellite 6800 may have the function of detecting sunlight reflected from an object on the ground. Alternatively, by including a thermal infrared sensor, the artificial satellite 6800 may have the function of detecting thermal infrared rays emitted from the earth's surface. As described above, the artificial satellite 6800 may function as, for example, an earth observation satellite.

[0557] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0558] In this example, a secondary battery was fabricated and its characteristics were evaluated.

[0559] <Preparation of Positive Electrode Active Material> A positive electrode active material was prepared.

[0560] As the lithium cobalt oxide, commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) was prepared. Next, the prepared lithium cobalt oxide was heated at 850° C. for 2 hours in an oxygen atmosphere.

[0561] Lithium fluoride and magnesium fluoride were weighed and mixed in a molar ratio of lithium fluoride:magnesium fluoride = 1:3 to obtain a magnesium source. Next, magnesium in the magnesium source was weighed out so that the amount of magnesium in the lithium cobalt oxide was 1 at % of the cobalt in the lithium cobalt oxide, and the magnesium was mixed with heated lithium cobalt oxide to obtain a mixture A1.

[0562] Next, the mixture A1 was heated at 900° C. for 20 hours in an oxygen atmosphere to obtain a composite oxide B1.

[0563] Next, nickel hydroxide was prepared as the nickel source, and aluminum hydroxide was prepared as the aluminum source. Each was weighed out so that the nickel content of the nickel hydroxide was 0.5 at% of the cobalt content of the composite oxide B1, and the aluminum content of the aluminum hydroxide was 0.5 at% of the cobalt content of the composite oxide B1, and then mixed with the composite oxide B1 to obtain a mixture C1.

[0564] Next, the mixture C1 was heated at 850° C. for 10 hours in an oxygen atmosphere to prepare a sample Sa1.

[0565] <Preparation of Positive Electrode> Sample Sa1, acetylene black (AB), polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) were mixed to prepare a slurry, with the ratio of Sample Sa1, AB, and PVDF being Sample Sa1:AB:PVDF=95:3:2 (weight ratio).

[0566] The prepared slurry was applied to one side of an aluminum foil, and then heated at 80° C. to volatilize the NMP. After heating, the aluminum foil was pressed to obtain a positive electrode.

[0567] <Preparation of Negative Electrode> Graphite, VGCF (registered trademark), carboxymethyl cellulose sodium salt (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed to prepare a slurry, where the ratio of graphite, VGCF, CMC-Na, and SBR was graphite:VGCF:CMC-Na:SBR=96:1:1:2 (weight ratio).

[0568] The prepared slurry was applied to one side of a copper foil, which was then heated at 50° C. to obtain a negative electrode.

[0569] <Preparation of Secondary Battery> A secondary battery was prepared using the positive electrode and negative electrode prepared above. The electrolyte solution used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ) was used as the lithium salt. ６) was used, and the concentration of lithium salt in the electrolyte was 1.00 mol / L. Polypropylene was used as the separator. A film in which a polypropylene layer, an acid-modified polypropylene layer, an aluminum layer, and a nylon layer were laminated in this order was used as the film serving as the exterior body. One negative electrode having a negative electrode active material layer formed on one side and one positive electrode having a positive electrode active material layer formed on one side were prepared, and the negative electrode active material layer and the positive electrode active material layer were arranged so that they faced each other with the separator sandwiched between them.

[0570] Through the above steps, a secondary battery was fabricated.

[0571] <dQ / dV-V curve> A charge / discharge cycle test was performed on the secondary battery thus prepared. The ambient temperature during the measurement was 45° C. The charging conditions were a constant current charge of 0.5 C with an upper limit voltage of 4.55 V. The discharging conditions were a constant current discharge of 0.5 C with a lower limit voltage of 3.0 V.

[0572] Fig. 34A shows the dQ / dV-V curves for the first charge cycle, Fig. 34B shows the dQ / dV-V curves for the third charge cycle, and Fig. 35A shows the dQ / dV-V curves for the 40th charge cycle. Fig. 35B shows a five-point moving average curve for the data in Fig. 35A. Note that the data acquisition interval during charging was approximately 2 minutes.

[0573] In the charger of one embodiment of the present invention, for example, the location indicated by the arrow in FIG. 35A can be determined to be the maximum.

[0574] Furthermore, Fig. 36A shows the voltage V-capacity C curve during the 40th charging cycle, and Fig. 36B shows the change in voltage over time (ΔV-t curve) during the 40th charging cycle. The vertical axis represents ΔV, and the horizontal axis represents time from the start of charging. ΔV is the difference from the voltage obtained one time previously. The locations corresponding to those indicated by arrows in Fig. 35A are indicated by arrows in Figs. 36A and 36B, respectively.

[0575] In this example, a secondary battery was fabricated and its characteristics were evaluated.

[0576] <Preparation of Secondary Battery> A secondary battery was prepared using the positive electrode and negative electrode prepared in Example 1. However, the negative electrode was prepared by applying the slurry to both sides of the current collector, not just one side. EMI-FSA (1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide) was used as the solvent for the electrolyte. LiFSA (lithium bis(fluorosulfonyl)amide) was used as the lithium salt, and the concentration of the lithium salt in the electrolyte was 2.15 mol / L. A 50 μm-thick solvent-spun regenerated cellulose fiber (TF40, manufactured by Nippon Kodoshi Kogyo Co., Ltd.) was used as the separator. A film consisting of a polypropylene layer, an acid-modified polypropylene layer, an aluminum layer, and a nylon layer laminated in this order was used as the exterior film. One negative electrode having a negative electrode active material layer formed on both sides and two positive electrodes having a positive electrode active material layer formed on one side were prepared, and the negative electrodes were arranged so that the positive electrode active material layers faced each other with a separator sandwiched therebetween.

[0577] Through the above steps, a secondary battery was fabricated.

[0578] <dQ / dV characteristics> A charge / discharge cycle test was performed on the fabricated secondary battery. The ambient temperature during the measurement was 45° C. The charging conditions were a constant current charge at 0.5 C with an upper limit voltage of 4.55 V. The discharging conditions were a constant current discharge at 0.5 C with a lower limit voltage of 3.0 V.

[0579] Next, the dQ / dV characteristics were evaluated. Verification was performed in the region where constant current charging was performed. dQ / dV can be calculated from (dQ / dt) x (dt / dV). During constant current charging, dQ / dt is constant, so dQ / dV is proportional to dt / dV. Therefore, for ease of evaluation, the dt / dV characteristics were used for the evaluation.

[0580] Figure 37A shows the dt / dV-V curve for the first cycle, and Figure 37B shows the dt / dV-V curve for the tenth cycle. Note that in Figures 37A and 37B, data is plotted each time the voltage changes by a predetermined value, or, if no change in voltage is observed, each time the time changes by a predetermined value.

[0581] In the charger of one embodiment of the present invention, for example, the location indicated by the arrow in FIG. 37A can be determined to be the maximum.

[0582] In this example, a secondary battery was fabricated and its characteristics were evaluated.

[0583] <Preparation of Positive Electrode Active Material> A positive electrode active material was prepared.

[0584] The lithium cobalt oxide was heated to 850° C. for 2 hours in an oxygen atmosphere.

[0585] Lithium fluoride and magnesium fluoride were weighed and mixed in a molar ratio of lithium fluoride:magnesium fluoride = 1:3 to obtain a magnesium source. Next, magnesium in the magnesium source was weighed out so that the amount of magnesium in the lithium cobalt oxide was 1 at % of the cobalt in the lithium cobalt oxide, and the magnesium was mixed with the heated lithium cobalt oxide to obtain a mixture A2.

[0586] Next, the mixture A2 was heated at 900° C. for 20 hours in an oxygen atmosphere to obtain a composite oxide B2.

[0587] Next, nickel hydroxide was prepared as the nickel source, and aluminum hydroxide was prepared as the aluminum source. Each was weighed out so that the nickel content of the nickel hydroxide was 0.5 at% of the cobalt content of the composite oxide B2, and so that the aluminum content of the aluminum hydroxide was 0.5 at% of the cobalt content of the composite oxide B2, and then mixed with the composite oxide B2 to obtain a mixture C2.

[0588] Next, the mixture C2 was heated at 850° C. for 10 hours in an oxygen atmosphere to prepare a sample Sa2.

[0589] <Preparation of Positive Electrode> Sample Sa2, acetylene black (AB), polyvinylidene fluoride (PVDF), and NMP were mixed to prepare a slurry, with the ratio of Sample Sa2, AB, and PVDF being Sample Sa2:AB:PVDF=95:3:2 (weight ratio).

[0590] The prepared slurry was applied to one side of an aluminum foil, and then heated at 80° C. to volatilize the solvent. After heating, the aluminum foil was pressed at a pressure of 210 kN / m to obtain a positive electrode.

[0591] <Preparation of Secondary Battery> Using the positive electrode prepared above, a coin-shaped battery cell of CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0592] Lithium metal was used as the counter electrode.

[0593] The electrolyte used was a solvent made of a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, to which 2 wt% vinylene carbonate (VC) was added, and lithium hexafluorophosphate (LiPF ６ The concentration of the lithium salt in the electrolyte was 1.00 mol / L.

[0594] A porous polypropylene film was used as the separator.

[0595] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0596] <Cycle Characteristics> Next, the cycle characteristics of the fabricated secondary batteries were evaluated. Three different charging conditions were used, and a secondary battery was prepared for each condition. No different discharging conditions were used. Measurements were performed at 45°C. Note that 200 mA / g was converted into a 1C rate for charging and discharging. The capacity and charge / discharge current values ​​were normalized using the weight of the positive electrode active material.

[0597] In the following, the depth of charge was calculated by setting the charge amount corresponding to the capacity at which all lithium is desorbed from the lithium cobalt oxide as 100%. The charge amount corresponding to the capacity at which all lithium is desorbed from the lithium cobalt oxide was determined to be 274 mAh / g.

[0598] As a first charging condition, constant current charging was performed at a rate of 0.5C up to an upper limit of 4.7V, and then constant voltage charging was performed at 4.7V down to a rate of 0.05C.

[0599] As a second charging condition, constant current charging was performed at a rate of 0.5 C up to an upper limit of 4.7 V, and then charging was stopped.

[0600] As a third charging condition, the battery was charged at a rate of 0.5 C to a charge depth of 75%, i.e., to a charge capacity of 205.5 mAh / g. After charging, a rest period of 10 minutes was provided.

[0601] The battery was discharged at a constant current of 0.5 C to a lower limit of 2.5 V. After the discharge, a rest period of 10 minutes was provided.

[0602] Figures 38A and 38B show the cycle characteristics of the secondary battery. In Figures 38A and 38B, the first charging condition is indicated as "CCCV," the second charging condition is indicated as "CC," and the third charging condition is indicated as "CC, 75%." The horizontal axis of Figure 38A indicates the number of charge / discharge cycles, and the vertical axis indicates the discharge capacity. The horizontal axis of Figure 38B indicates the number of charge / discharge cycles, and the vertical axis indicates the discharge capacity retention rate.

[0603] Figure 39A shows the relationship between charge time and voltage, and between charge time and charge capacity under the first charge condition. The curves shown in Figure 39A are the results for the fourth charge cycle. The charge depth at the completion of constant current charge was 78.8%. That is, charging was performed up to a charge capacity of 215.9 mAh / g. The charge depth at the completion of constant voltage charge was 82.1%.

[0604] Figure 39B shows the relationship between charging time and voltage, and between charging time and charge capacity under the second charging condition. The curves shown in Figure 39B are the results for the 11th charging cycle. The state of charge at the completion of constant-current charging was 80.2%.

[0605] Figure 40A shows the relationship between charging time and voltage, and between charging time and charge capacity under the third charging condition. The curves shown in Figure 40A are the results for the 38th charging cycle. The charge depth at the completion of charging was 75.0%.

[0606] FIG. 40B shows the relationship between the number of cycles and the maximum charging voltage under the third charging condition.

[0607] Under the condition of constant voltage charging, the discharge capacity decreased significantly with the number of cycles.

[0608] <SEM Observation> Next, the secondary battery that had undergone the charge-discharge cycle test was disassembled, and a cross section of the positive electrode was observed under an SEM.

[0609] The cross section of the positive electrode active material layer was exposed by ion milling and observed with an SEM (Scanning Electron Microscope) SU8030 manufactured by Hitachi High-Technologies Corporation at an acceleration voltage of 1 kV.

[0610] The results of SEM observation are shown in Figures 41A, 42A, and 43A. In each figure, positive electrode active material 701 and conductive agent 702 were observed. In each figure, arrows indicate locations where pits are suggested in positive electrode active material 701, and open arrows indicate locations where cracks are suggested in positive electrode active material 701.

[0611] Fig. 41A shows the observation results of the positive electrode after 50 cycles of charge-discharge testing under the first charging condition, and Fig. 41B is an enlarged view of the boxed area shown in Fig. 41A.

[0612] Fig. 42A shows the observation results of the positive electrode after 50 cycles of charge-discharge testing under the second charging condition, and Fig. 42B is an enlarged view of the boxed area shown in Fig. 42A.

[0613] Fig. 43A shows the observation results of the positive electrode after 50 cycles of charge-discharge testing under the third charging condition, and Fig. 43B is an enlarged view of the boxed area shown in Fig. 43A.

[0614] Under the condition of constant voltage charging, many pits were observed.

[0615] <STEM Observation> Next, a cross-sectional STEM observation of the positive electrode of the secondary battery disassembled after the charge-discharge cycle test was performed. The cross section was exposed by FIB processing. For the STEM observation, a Hitachi High-Tech HD-2700 was used, and the accelerating voltage was set to 200 kV.

[0616] FIG. 44A shows a cross-sectional STEM TE image (transmission electron image) of the positive electrode after 50 cycles of charge-discharge testing using the first charging condition. In FIG. 44A, the positive electrode active material 701 and the protective layer 729 applied for observation were observed. FIG. 44B shows an enlarged image of the area enclosed by a square in FIG. 44A. The image shown in FIG. 44B is a ZC image (Z-contrast image).

[0617] Figure 44C shows an enlarged image of the area surrounded by a square in Figure 44B. The image shown in Figure 44C is a TE image. Lattice fringes were observed in Figure 44C. The area where the lattice fringes were observed suggests that the material has crystallinity. Cracks were also observed along the lattice fringes, and there were also areas around the cracks where the lattice fringes were unclear. The area where the lattice fringes were unclear may have low crystallinity.

[0618] FIG. 45A shows a cross-sectional STEM TE image (transmission electron image) of the positive electrode after 50 cycles of charge-discharge testing using the second charging condition as the charging condition. In FIG. 45A, the positive electrode active material 701 and the protective layer 729 coated for observation were observed. FIG. 45B shows a ZC image of the area surrounded by a square in FIG. 45A, and FIG. 45C shows a TE image of the area surrounded by a square in FIG. 45B. Lattice fringes were observed in FIG. 45C. The area where the lattice fringes could be observed suggests that the material has crystallinity. Cracks along the lattice fringes were also observed, and there were also areas where the lattice fringes were unclear around the cracks. Areas where the lattice fringes were unclear may have low crystallinity.

[0619] FIG. 46A shows a cross-sectional STEM TE image (transmission electron image) of the positive electrode after 50 cycles of charge-discharge testing using the third charging condition. In FIG. 46A, the positive electrode active material 701 and the protective layer 729 coated for observation were observed. FIG. 46B shows a ZC image of the area surrounded by a square in FIG. 46A, and FIG. 46C shows a TE image of the area surrounded by a square in FIG. 46B. Lattice fringes were observed in FIG. 46C. The area where lattice fringes can be observed suggests that the positive electrode active material has crystallinity. Furthermore, no significant cracks were observed in FIG. 46C. This suggests that charging and discharging using the third charging condition can suppress a decrease in the crystallinity of the positive electrode active material.

[0620] <EDX analysis> Next, the secondary batteries disassembled after the charge-discharge cycle test were subjected to area analysis (element mapping) of the positive electrode by STEM-EDX. The thickness of the thinned sample was approximately 100 nm. STEM-EDX was acquired using a Hitachi High-Tech HD-2700 at an acceleration voltage of 200 kV.

[0621] Fig. 47A shows a cross-sectional STEM TE image (transmission electron image) of the positive electrode after 50 cycles of charge-discharge testing using the first charging condition as the charging condition. Fig. 47C shows a ZC image of the area enclosed by the square in Fig. 47A, and Fig. 47B shows a TE image of the area enclosed by the square in Fig. 47C.

[0622] Figures 47D, 47E, and 47F show the results of EDX area analysis corresponding to the ZC image shown in Figure 47C. Figure 47D shows the results of area analysis of cobalt, Figure 47E shows the results of area analysis of magnesium, and Figure 47F shows the results of area analysis of aluminum.

[0623] Fig. 48A shows a cross-sectional STEM TE image (transmission electron image) of the positive electrode after 50 cycles of charge-discharge testing under the second charging condition. Fig. 48C shows a ZC image of the area enclosed by the square in Fig. 48A, and Fig. 48B shows a TE image of the area enclosed by the square in Fig. 48C.

[0624] Figures 48D, 48E, and 48F show the results of EDX area analysis corresponding to the ZC image shown in Figure 48C. Figure 48D shows the results of area analysis of cobalt, Figure 48E shows the results of area analysis of magnesium, and Figure 48F shows the results of area analysis of aluminum.

[0625] Fig. 49A shows a cross-sectional STEM TE image (transmission electron image) of the positive electrode after 50 cycles of charge-discharge testing under the second charging condition. Fig. 49C shows a ZC image of the area enclosed by the square in Fig. 49A, and Fig. 49B shows a TE image of the area enclosed by the square in Fig. 49C.

[0626] Figures 49D, 49E, and 49F show the results of EDX area analysis corresponding to the ZC image shown in Figure 49C. Figure 49D shows the results of area analysis of cobalt, Figure 49E shows the results of area analysis of magnesium, and Figure 49F shows the results of area analysis of aluminum.

[0627] Fig. 50A shows the results of EDX ray analysis of the area indicated by the arrow in Fig. 47C, Fig. 50B shows the results of EDX ray analysis of the area indicated by the arrow in Fig. 48C, and Fig. 50C shows the results of EDX ray analysis of the area indicated by the arrow in Fig. 49C. Note that the results of the linear analysis shown in Fig. 50B and Fig. 50C are the results of extracting data of a linear region from the EDX area analysis.

[0628] The results of EDX area analysis and EDX ray analysis confirmed that magnesium and aluminum were present in the surface layer of the positive electrode active material in the secondary battery that underwent charge-discharge cycles under the second or third charge conditions, while the results suggested that the amount of magnesium and aluminum present in the surface layer of the positive electrode active material particles was small or not detectable in the secondary battery that underwent charge-discharge cycles under the first charge conditions.

[0629] It is believed that constant-voltage charging causes magnesium and aluminum from the surface layer of the positive electrode active material particles to leach out of the positive electrode active material into the electrolyte. This leach-out may be due to the longer charging time at high voltages and the deeper charge depth. Furthermore, this leach-out may prevent the collapse of the crystalline structure associated with charge-discharge cycles, resulting in a decrease in discharge capacity. Furthermore, the occurrence of pits in the positive electrode active material may be due to the leach-out of magnesium and aluminum into the electrolyte.

[0630] In this example, a secondary battery was charged using a charger of one embodiment of the present invention, and characteristics of the secondary battery were evaluated.

[0631] <Preparation of Positive Electrode Active Material> A positive electrode active material was prepared.

[0632] The lithium cobalt oxide was heated to 850° C. for 2 hours in an oxygen atmosphere.

[0633] Lithium fluoride and magnesium fluoride were weighed and mixed in a molar ratio of lithium fluoride:magnesium fluoride = 1:3 to obtain a magnesium source. Next, magnesium in the magnesium source was weighed out so that the amount of magnesium in the lithium cobalt oxide was 1 at % of the cobalt in the lithium cobalt oxide, and mixed with heated lithium cobalt oxide to obtain a mixture A3.

[0634] Next, the mixture A3 was heated at 900° C. for 20 hours in an oxygen atmosphere to obtain a composite oxide B3.

[0635] Next, nickel hydroxide was prepared as the nickel source, and aluminum hydroxide was prepared as the aluminum source. Each was weighed out so that the nickel content of the nickel hydroxide was 0.5 at% of the cobalt content of the composite oxide B3, and so that the aluminum content of the aluminum hydroxide was 0.5 at% of the cobalt content of the composite oxide A, and then mixed with the composite oxide B3 to obtain a mixture C3.

[0636] Next, the mixture C3 was heated at 850° C. for 10 hours in an oxygen atmosphere to prepare a sample Sa3.

[0637] <Preparation of Positive Electrode> Sample Sa3, acetylene black (AB), polyvinylidene fluoride (PVDF), and NMP were mixed to prepare a slurry, with the ratio of Sample Sa3, AB, and PVDF being Sample Sa3:AB:PVDF = 95:3:2 (weight ratio).

[0638] The prepared slurry was applied to one side of an aluminum foil, which was then heated at 80° C. to volatilize the solvent. After heating, the aluminum foil was pressed to obtain a positive electrode.

[0639] <Preparation of Negative Electrode> Graphite, VGCF (registered trademark), carboxymethyl cellulose sodium salt (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed to prepare a slurry, where the ratio of graphite, VGCF, CMC-Na, and SBR was graphite:VGCF:CMC-Na:SBR=96:1:1:2 (weight ratio).

[0640] The prepared slurry was applied to one side of a copper foil, which was then heated at 50° C. to obtain a negative electrode.

[0641] <Preparation of Secondary Battery> A secondary battery was prepared using the positive electrode and negative electrode prepared above. The electrolyte solution used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ) was used as the lithium salt. ６ ) was used, and the concentration of lithium salt in the electrolyte was 1.00 mol / L. Polypropylene was used as the separator. A film in which a polypropylene layer, an acid-modified polypropylene layer, an aluminum layer, and a nylon layer were laminated in this order was used as the film serving as the exterior body. One negative electrode having a negative electrode active material layer formed on one side and one positive electrode having a positive electrode active material layer formed on the other side were prepared, and the negative electrode active material layer and the positive electrode active material layer were arranged so that they faced each other with the separator sandwiched between them.

[0642] The area of ​​the positive electrode active material layer is 20.493 cm ２ The weight of the positive electrode active material layer was 0.11995 g. The area of ​​the negative electrode active material layer was 23.841 cm ２The positive electrode and the negative electrode were arranged so as to minimize the area where the positive electrode active material layer did not face the negative electrode active material layer. The amount of the positive electrode active material layer was approximately 10.6 mg / cm ２ The film thickness was 54 μm or more and 56 μm or less. The amount of the negative electrode active material layer supported was 7.8 mg / cm ２ More than 7.9 mg / cm ２ The film thickness was 83 μm or more and 85 μm or less.

[0643] The secondary batteries were fabricated by the above steps. Four secondary batteries were fabricated by the above steps.

[0644] <Method for Charging Secondary Battery> A secondary battery was charged using the charger of one embodiment of the present invention based on the flow shown in FIG. 51 .

[0645] First, in step S000, the process starts.

[0646] Next, in step S001, constant current charging of the secondary battery was started at a current value of 20 mA.

[0647] Next, in step S002, the voltage of the secondary battery was measured by the voltage measurement circuit. The voltage value was acquired at 100 ms intervals. The measured voltage was converted into a 16-bit digital value by an analog-to-digital conversion circuit and provided to the control circuit. An MCU (Micro Controller Unit) was used as the control circuit.

[0648] Next, in step S003, the control circuit compares the voltage measured by the voltage measurement circuit with a predetermined voltage (set to 4.4 V in this example).

[0649] Based on the result of the comparison in step S003, if the measured voltage is lower than 4.4V, the process returns to step S002, and if it is 4.4V or higher, the process proceeds to the next step (step S004).

[0650] In step S004, the value of dt / dV was obtained. Here, the time required for the voltage to change by 1 mV was calculated as a value equivalent to dt / dV. The moving average of the measured dt / dV and the maximum value of dt / dV measured from the start of charging in step S001 to the current time were multiplied by a constant (0.8 in this case). The moving average was calculated using a total of three points: the measurement point at which the calculation was performed, the measurement point immediately before that measurement point, and the measurement point two points before that measurement point.

[0651] In step S005, the moving average of dt / dV was compared with a value 0.8 times the maximum value of dt / dV.

[0652] If the moving average of dt / dV is equal to or greater than 0.8 times the maximum value of dt / dV, steps S004 and S005 are repeated.

[0653] Next, at the time when the moving average of dt / dV became smaller than 0.8 times the maximum value of dt / dV, the process proceeded to step S006, and charging was stopped.

[0654] Next, in step S099, charging was stopped.

[0655] The charging condition described above is referred to as charging condition Ch-1.

[0656] <Cycle Characteristics> Cycle characteristics were evaluated using the above-described charging conditions (charging conditions Ch-1) and constant current charging conditions with an upper limit voltage of 4.6 V (hereinafter referred to as charging conditions Ch-2). Under each charging condition, the charging current was 20 mA. The discharging conditions were constant current discharge, with a lower limit voltage of 3.0 V and a discharge current of 20 mA. The number n of secondary batteries evaluated under charging condition Ch-1 was set to 2 (two secondary batteries were evaluated under each charging condition), and these are shown as Ch-1(1) and Ch-1(2), respectively, in the graph. The number n of secondary batteries evaluated under charging condition Ch-1 was set to 1.

[0657] The results of the cycle characteristics are shown in Figure 52. The horizontal axis represents the number of charge / discharge cycles, and the vertical axis represents the discharge capacity. The results in Figure 52 show that the secondary battery charged under charging condition Ch-1 using a charger of one embodiment of the present invention exhibited a suppressed decrease in discharge capacity with cycling, and significantly improved cycle characteristics. Furthermore, the secondary battery charged under charging condition Ch-1 exhibited a decrease in discharge capacity after 300 cycles, but the decrease in capacity was gradual.

[0658] Figure 53 shows the relationship between the end-of-charge voltage of a secondary battery and the number of charge / discharge cycles. The horizontal axis shows the number of charge / discharge cycles, and the vertical axis shows the end-of-charge voltage. The results in Figure 53 suggest that the end-of-charge voltage was kept low for the secondary battery charged under charge condition Ch-1, which improved the cycle characteristics.

[0659] 53 , under charging condition Ch-1, the end-of-charge voltage was high in the early stages of the cycle and tended to gradually decrease. When such a change in the end-of-charge voltage is observed, it is possible that the internal resistance of the secondary battery is unstable. When charging is performed using a charger according to one embodiment of the present invention, sufficient charging can be performed even in such an unstable state. Furthermore, because charging can be performed without increasing the end-of-charge voltage more than necessary, both high capacity and a long lifespan of the secondary battery can be achieved.

[0660] When charging using a charger according to one embodiment of the present invention, even if variations occur in the internal resistance of a plurality of secon...

Claims

1. A method for charging a secondary battery using a charger having a control circuit, a voltage measurement circuit, and a current measurement circuit, the control circuit has a function of controlling the start and stop of charging of the secondary battery and a function of controlling a charging current of the secondary battery; the control circuit has a function of calculating a voltage differential of an amount of electricity of the secondary battery and a function of detecting a maximum of the voltage differential of the amount of electricity; the voltage measurement circuit has a function of measuring a charging voltage of the secondary battery, the current measurement circuit has a function of measuring a charging current of the secondary battery, At time t1, charging of the secondary battery is started with a constant current; Calculate the quantity of electricity Q(t) using the current I(t) at time t, a first curve is analyzed, the horizontal axis of which is voltage V(t) and the vertical axis of which is voltage differential of quantity of electricity Q(t) [dQ(t) / dV(t)], to detect a time tp at which the first curve has a first maximum; The charging is stopped at a time t2 that is a predetermined time after the time tp, The method for charging a secondary battery, wherein the voltage V(tp) at time tp is 4.25 V or more and less than 4.8 V.

2. In claim 1, The secondary battery has a positive electrode, The positive electrode comprises lithium and cobalt, A method for charging a secondary battery, wherein when the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation at the time tp, the positive electrode has diffraction peaks at 2θ of 19.25° or more and 19.45° or less and at 2θ of 45.35° or more and 45.75 or less.

3. In claim 1 or 2, The charger includes a memory circuit, The memory circuit stores data according to an environmental temperature, The method for charging a secondary battery includes detecting the time tp using the data.

4. In claim 1 or 2, The charger includes a memory circuit, The memory circuit stores data corresponding to the positive electrode active material of the secondary battery, The method for charging a secondary battery includes detecting the time tp using the data.