Secondary battery management system

Abstract

Provided is a secondary battery management system for obtaining a secondary battery that can be used even in a low temperature. This secondary battery management system has: a secondary battery that is charged and discharges at a temperature of -50 degrees to 0 degrees, inclusive; a first circuit having a function of measuring the voltage of the secondary battery; a second circuit having a function of measuring the current of the secondary battery; and a control circuit to which voltage information from the first circuit or current information from the second circuit is input. The control circuit starts charging the secondary battery, calculates data indicating battery characteristics on the basis of values input from the first circuit or the second circuit, detects a maximal value for the data, and stops the charging when detecting the maximal value.

Description

Technical Field

[0001] One aspect of the present invention relates to a secondary battery management system.

[0002] Note that one aspect of the present invention is not limited to the above technical field. The technical fields of one aspect of the present invention disclosed in this specification and the like include semiconductor devices, light-emitting devices, power storage devices, storage devices, electronic devices, lighting devices, input devices, or input / output devices, and also include manufacturing methods thereof.

Background Art

[0003] Unlike primary batteries, secondary batteries can be repeatedly used by charging, and are also called storage batteries or batteries. Charging means sending electricity into the secondary battery, and discharging means taking electricity out of the secondary battery. A secondary battery that uses lithium ions as carrier ions is called a lithium ion secondary battery or a lithium ion battery. Lithium ion secondary batteries can be made to have a higher capacity and be smaller in size, and are mounted in electronic devices and the like.

[0004] The voltage during charging of a secondary battery has an upper limit determined in consideration of safety, and in this specification and the like, this is referred to as the upper limit voltage. The upper limit voltage may also be referred to as the maximum charging voltage, the cut-off voltage, the specified voltage, or the full charge voltage. The upper limit voltage of a secondary battery using lithium cobalt oxide for the positive electrode and graphite for the negative electrode is about 4.2V. Since increasing the upper limit voltage increases the capacity of the secondary battery, research and development are being conducted on methods for increasing the upper limit voltage.

[0005] As a method for increasing the upper limit voltage, Patent Document 1 describes the charging power limit. The charging power limit in Patent Document 1 is determined from the predicted terminal voltage and total resistance of the secondary battery using an equivalent circuit model of the secondary battery. Further, Patent Document 1 also describes transmitting the temperature measured by the temperature measurement unit to the control unit, and determining the open circuit voltage (V OCV ) from the state of charge (SOC) and temperature of the secondary battery in the voltage source.

Prior Art Documents

[0006] [Patent Document 1] Special Publication No. 2020-524875 [Overview of the project] [Problems that the invention aims to solve]

[0007] In the aforementioned Patent Document 1, the crystal structure of the active material, such as the positive electrode active material, was not considered in determining the charging power limit. Therefore, predictions using the simple equivalent circuit model in Patent Document 1 sometimes failed to significantly increase the charging power limit.

[0008] Furthermore, Patent Document 1 mentioned above makes no mention of low temperatures such as -40°C. The battery characteristics at such low temperatures differ significantly from those at so-called room temperature (around 25°C), with discharge capacity being lower at lower temperatures than at room temperature. In other words, increasing the upper voltage limit was particularly desirable at low temperatures.

[0009] Therefore, one aspect of the present invention aims to provide a secondary battery management system that can increase the upper voltage limit to its maximum and can charge and discharge even at low temperatures.

[0010] Furthermore, the description of these problems does not preclude the existence of other problems. These problems are considered independent of each other, and one aspect of the present invention only needs to solve one of these problems; it is not necessary to solve all of them. Moreover, it is possible to extract other problems from the description, drawings, and claims of this specification, etc. [Means for solving the problem]

[0011] In view of the above issues, according to one aspect of the present invention, a secondary battery management system is provided that maximizes the upper voltage limit by deriving an optimal voltage that takes into account the crystal structure of the positive electrode active material, and that can be charged and discharged even at low temperatures. In this specification, low temperature is defined as -50°C or higher and 0°C or lower, room temperature is defined as higher than 0°C and 35°C or lower, and high temperature is defined as higher than 35°C and 65°C or lower. Temperatures lower than 0°C are sometimes referred to as below freezing point.

[0012] One aspect of the present invention is a secondary battery management system comprising: a secondary battery that charges and discharges at -50°C or higher and 0°C or lower; a first circuit having a function to measure the voltage of the secondary battery; a second circuit having a function to measure the current of the secondary battery; and a control circuit that receives voltage information from the first circuit or current information from the second circuit. The control circuit initiates charging of the secondary battery, calculates data indicating battery characteristics based on the values ​​input from the first circuit or the second circuit, detects a maximum value for the data, and stops charging when a maximum value is detected.

[0013] One aspect of the present invention is a secondary battery management system comprising: a secondary battery that charges and discharges at temperatures between -50°C and 0°C; a first circuit having a function to measure the voltage of the secondary battery; a second circuit having a function to measure the current of the secondary battery; a control circuit that receives voltage information from the first circuit or current information from the second circuit; and a temperature sensor electrically connected to the control circuit. The control circuit measures the temperature of the secondary battery using the temperature sensor, initiates charging of the secondary battery, calculates data indicating battery characteristics according to temperature based on the values ​​input from the first circuit or the second circuit, detects a maximum value for the data, and stops charging when a maximum value is detected.

[0014] One aspect of the present invention is a secondary battery management system comprising: a secondary battery that charges and discharges at temperatures between -50°C and 0°C; a first circuit having a function to measure the voltage of the secondary battery; a second circuit having a function to measure the current of the secondary battery; and a control circuit that receives voltage information from the first circuit or current information from the second circuit. The control circuit records the temperature of the secondary battery in a memory circuit, starts charging the secondary battery, calculates a dt / dV value that indicates the battery characteristics according to the temperature based on the value input from the first circuit or the second circuit, detects a maximum value in dt / dV, and stops charging when a maximum value is detected.

[0015] In one embodiment of the present invention, it is preferable that the control circuit performs an averaging process on dt / dV and divides the difference between the second value and the first value of dt / dV in the comparison range by the first value.

[0016] In one aspect of the present invention, charging is preferably performed with a constant current.

[0017] In one embodiment of the present invention, the secondary battery has a positive electrode, the positive electrode has lithium cobalt oxide, and the crystal structure identified by X-ray diffraction is preferably a crystal structure represented by the space group R-3m.

[0018] In one embodiment of the present invention, lithium cobalt oxide preferably has magnesium in its surface layer.

[0019] In one embodiment of the present invention, the secondary battery has a negative electrode, and it is preferable that the negative electrode is made of lithium metal or graphite. [Effects of the Invention]

[0020] According to one aspect of the present invention, a secondary battery management system capable of raising the upper voltage limit to its maximum is provided. According to one aspect of the present invention, a secondary battery management system capable of charging and discharging even at low temperatures is provided.

[0021] Furthermore, the description of these effects does not preclude the existence of other effects. These effects are considered independent of each other, and one aspect of the present invention only needs to achieve one of these effects; it is not necessary to achieve all of them. Moreover, it is possible to extract other effects from the description, drawings, and claims of this specification, etc. [Brief explanation of the drawing]

[0022] Figures 1A to 1C are block diagrams showing an example of a secondary battery management system. Figures 2A and 2B are block diagrams showing an example of a secondary battery management system. Figure 3 is a flowchart illustrating the charging method of the secondary battery management system. Figure 4 is a flowchart illustrating the charging method of the secondary battery management system. Figure 5 is a block diagram showing an example of a secondary battery management system. Figure 6 is a block diagram showing an example of a secondary battery management system. Figures 7A and 7B are block diagrams showing an example of a secondary battery management system. Figure 8 is a flowchart illustrating the differential processing. Figure 9 illustrates the crystal structure of the positive electrode active material. Figures 10A to 10C illustrate an example of a method for preparing a positive electrode active material. Figure 11 illustrates an example of a method for preparing a positive electrode active material. Figure 12 illustrates an example of a method for preparing a positive electrode active material. Figures 13A to 13C illustrate an example of a method for preparing a positive electrode active material. Figure 14 illustrates an example of a laminated secondary battery. Figures 15A to 15C illustrate an example of a method for manufacturing a laminate-type secondary battery. Figures 16A and 16B illustrate an example of a bendable secondary battery. Figures 17A and 17B illustrate a part of a bendable secondary battery. Figure 18 is a block diagram showing an example of a vehicle with a motor. Figures 19A to 19E show examples of transport vehicles. Figures 20A and 20B illustrate a house that utilizes a secondary battery. Figures 21A to 21E show examples of electronic devices. Figures 22A to 22C illustrate an example of an electronic device. Figures 23A to 23D illustrate an example of electronic equipment, etc. Figure 24 is a graph showing the results of the example. Figure 25 is a graph showing the results of the example. [Modes for carrying out the invention]

[0023] The embodiments will be described below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the embodiments can be implemented in many different ways, and their form and details can be modified in various ways without departing from the spirit and scope. Accordingly, the present invention shall not be construed as being limited to the contents of the following embodiments.

[0024] In this specification, the ordinal numbers "1st," "2nd," and "3rd" are used to avoid confusion of constituent elements. Therefore, they do not limit the number of constituent elements, nor do they limit the order of the constituent elements.

[0025] In this specification, elements that are identical in appearance or have similar functions, are made of the same material, or are formed simultaneously may be denoted by the same reference numeral in the drawings, and the use of the same reference numeral may omit repeated explanations.

[0026] Furthermore, in top views (also called "plan views") and perspective views, some components may be omitted to make the drawings easier to understand.

[0027] In this specification, "electrically connected" includes both direct connections and connections made via "something that has some electrical function." Here, "something that has some electrical function" is not particularly limited as long as it enables the exchange of electrical signals between the connected objects. Therefore, even when it is expressed as "electrically connected," there may be no physical connection in the actual circuit.

[0028] In this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar above the number, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a bar above it. Furthermore, individual orientations indicating directions within a crystal are indicated by [ ], collective orientations indicating all equivalent directions are indicated by < >, individual planes indicating crystal planes are indicated by ( ), and collective planes having equivalent symmetry are indicated by {}.

[0029] In this specification, segregation refers to the phenomenon in which a certain element (e.g., B) is spatially non-uniformly distributed in a solid composed of multiple elements (e.g., A, B, C).

[0030] In this specification, the surface layer of particles such as active material refers to the region within 10 nm, 50 nm, or 5 nm from the surface inward, perpendicular or nearly perpendicular to the surface. The surface layer is synonymous with the near-surface region or shell. Perpendicular or nearly perpendicular specifically refers to the range of 80° to 100° from the surface. Surfaces created by cracks or fissures may also be considered the surface. Furthermore, the region deeper than the surface layer of the positive electrode active material is called the bulk. The bulk is synonymous with the interior or core.

[0031] In this specification, when lithium is used as a carrier ion, the layered rock salt type crystal structure of a composite oxide containing lithium and a transition metal has a rock salt type ionic arrangement in which cations and anions are arranged alternately, and the transition metal and lithium are regularly arranged to form a plane, thus enabling two-dimensional diffusion of lithium. The composite oxide may have defects such as vacancies of cations or anions. Furthermore, the layered rock salt type crystal structure may have a distorted lattice structure of the rock salt type crystal structure. In this specification, a rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately. The rock salt type crystal structure may have vacancies of cations or anions.

[0032] In this specification, the O3'-type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure that belongs to the space group R-3m and is not a spinel-type crystal structure, but in which ions such as cobalt and magnesium occupy the oxygen 6-coordinate positions, and the arrangement of cations has a symmetry similar to that of a spinel-type crystal structure. In the O3'-type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate positions.

[0033] Furthermore, the O3' type crystal structure can be described as a crystal structure similar to the CdCl2 type crystal structure, although it has Li randomly placed between layers. Known lithium cobalt oxides, or layered rock salt type cathode active materials containing a large amount of cobalt, are generally known not to adopt a crystal structure similar to the CdCl2 type.

[0034] In both the layered rock salt crystal structure and the rock salt crystal structure, the anions adopt a cubic close-packed structure (face-centered cubic lattice structure). When the layered rock salt crystal structure and the rock salt crystal structure are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of the layered rock salt crystal structure is R-3m, and the space groups of the rock salt crystal structure are Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry), and are different from each other, so the Miller indices of the crystal planes when the orientations are aligned are different from each other. In this specification, etc., when the orientation of the cubic close-packed structure composed of anions is aligned in the layered rock salt crystal structure and the rock salt crystal structure, it is sometimes said that the crystal orientations are identical or approximately identical. Since the O3'-type crystal structure is also presumed to have anions in a cubic close-packed structure, by replacing the above layered rock salt-type crystal structure with the O3'-type crystal structure, we can understand the crystal planes that align with the orientation of the rock salt-type crystal structure.

[0035] Furthermore, the space group of a crystal structure is identified by X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. XRD and the like should be measured at room temperature or above. Therefore, in this specification, "belonging to a certain space group," "being part of a certain space group," or "being a certain space group" can be rephrased as "being identified to a certain space group."

[0036] In this specification, a structure in which anions are stacked in three layers, such as ABCABC, with each layer offset from the others, is referred to as a cubic close-packed structure. Therefore, the anions do not necessarily have to be strictly cubic in shape. At the same time, since real crystals have defects, the analytical results do not necessarily conform to theory. For example, in FFT (Fast Fourier Transform) patterns such as electron diffraction patterns or TEM images, spots may appear at positions slightly different from the theoretical positions. For example, if the deviation between the theoretical position and orientation is 5 degrees or less, or 2.5 degrees or less, it can be said that the structure is a cubic close-packed structure.

[0037] A secondary battery has, for example, a positive electrode and a negative electrode. The positive electrode is composed of a positive electrode active material. The positive electrode active material is a substance that performs reactions that contribute to the charge and discharge capacity, and specifically it is a compound containing a transition metal and oxygen that allows for the insertion and removal of lithium, or a composite oxide containing a transition metal. The positive electrode active material may also be referred to as a composite oxide, positive electrode material, positive electrode material, or positive electrode material for lithium-ion batteries.

[0038] When a secondary battery is used at a low temperature, its characteristics, such as the discharge curve, differ from those at room temperature. For example, when a secondary battery is used at a low temperature, its discharge capacity tends to be smaller than at room temperature. In other words, to obtain the same discharge capacity, a higher voltage than that at room temperature may be used at low temperatures. Therefore, one aspect of the present invention, a secondary battery management system, can adjust the optimal charge and discharge conditions according to the operating temperature of the secondary battery.

[0039] In a secondary battery management system according to one aspect of the present invention, the temperature of the secondary battery includes the temperature inside the secondary battery and the temperature outside the secondary battery. Furthermore, the temperature outside the secondary battery includes the temperature of the secondary battery's casing, the temperature of the housing in which the casing is enclosed, and the ambient temperature in which the secondary battery is placed. In this specification, the ambient temperature may be referred to as the operating temperature of the secondary battery. In a secondary battery management system, the temperature can be distinguished as described above by the position of the temperature sensor, but a secondary battery management system can be provided using any of the temperatures.

[0040] In this specification, the temperature used in charge-discharge cycle tests refers to the temperature of the constant-temperature chamber in which the lithium-ion secondary battery is placed. It is advisable to allow sufficient time (e.g., 1 hour or more) for the temperature of the lithium-ion secondary battery to be measured (e.g., the test battery) placed in the constant-temperature chamber to equalize with the temperature of the constant-temperature chamber before starting the measurement. The temperature of the constant-temperature chamber corresponds to the temperature of the secondary battery management system described above.

[0041] Furthermore, when a secondary battery is charged at low temperatures, the energy barrier for detaching lithium ions from the positive electrode active material tends to increase. In other words, the lower the charging temperature, the greater the overvoltage required to detach lithium ions from the positive electrode active material, and there is a risk that the positive electrode active material will be exposed to a high voltage (a high potential relative to the lithium potential). In other words, when charging at low temperatures, if the positive electrode active material is not exposed to a high voltage, there is a risk that the charging capacity will be reduced. For this reason, the inventors considered it preferable to use a positive electrode active material that can withstand high voltage as the positive electrode active material for a lithium-ion battery that has excellent charging and discharging characteristics even at low temperatures.

[0042] Furthermore, when the positive electrode active material is exposed to high voltage, its crystal structure begins to break down, which can prevent carrier ions from entering or leaving the material. Therefore, the inventors considered it important to maximize the upper voltage limit while maintaining the crystal structure, and thus devised the above secondary battery management system.

[0043] The theoretical capacity of a positive electrode active material refers to the amount of electric charge that would be generated if all of the insertable and removeable lithium in the positive electrode active material were to be removed. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0044] Furthermore, the amount of lithium remaining in the positive electrode active material relative to its theoretical capacity is indicated by x in the composition formula, for example, Li x x in CoO2, or Li x Indicated by x in MO2, where M represents the transition metal that undergoes oxidation-reduction with lithium insertion and deinsertion. Li x CoO2 contains Li as appropriate. x This can be interpreted as MO2. In the case of the positive electrode active material in a secondary battery, x can be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2 mAh / g, Li 0.2 It can be expressed as CoO2 or x=0.2. x A small x in CoO2 means, for example, 0.1 <x≦0.24をいう。

[0045] When lithium cobalt oxide approximately satisfies the stoichiometric ratio, it is LiCoO2 and the lithium occupancy rate x=1 at the lithium site. Similarly, a secondary battery that has finished discharging is also LiCoO2, and it can be said that x=1. Discharge completion here refers to the state where, for example, with a current of 100mA / g, the voltage falls below 2.5V (counter electrode lithium). In lithium-ion secondary batteries, when the lithium occupancy rate at the lithium site becomes x=1 and no more lithium can be added, the voltage drops sharply. At this point, discharge can be said to have finished. Generally, in lithium-ion secondary batteries using LiCoO2, the discharge voltage drops sharply before reaching 2.5V, so discharge is considered to have finished under the above conditions.

[0046] If LiCoO2 is used as the positive electrode active material, Li x When charging is performed at a voltage such that x, represented by CoO2, is 0.2 or greater, the crystal structure changes from an O3 structure to an H1-3 structure. When discharging occurs after charging that causes a change to an H1-3 structure, it may not revert to the original crystal structure, the O3 structure. In this specification, the state in which the H1-3 structure is present and does not revert to the O3 structure is called an irreversible crystal structure. The range in which the above crystal structure does not collapse can be said to be the range in which LiCoO2 does not have an irreversible crystal structure.

[0047] In the above-mentioned secondary battery management system, it is desirable to obtain information about the secondary battery non-destructively in order to understand the crystal structure of the positive electrode active material, etc., and therefore, data indicating the battery characteristics is used. As an example of such data, there is a value that shows the change in voltage (sometimes written as terminal voltage) over time. When the change in voltage over time is plotted on a graph, a curve is formed, and a peak can be identified. By determining the position or intensity of the peak, information about the secondary battery can be obtained non-destructively. The above-mentioned peak is a maximum value, and there may be two or more such peaks.

[0048] Another piece of data used is, for example, the value of dQ / dV (denoted as dQ / dV), which is the ratio of the change in the electric charge (referred to as charge amount) Q of the secondary battery to the change in voltage V (referred to as dV) of the secondary battery. When dQ / dV is plotted on a graph, it forms a curve, and is sometimes referred to as a dQ / dV curve. A peak can be observed in the dQ / dV curve, and information about the secondary battery can be obtained non-destructively by determining the peak position or peak intensity. The above-mentioned peak is a maximum value, and there may be two or more such peaks.

[0049] Since the above changes can be expressed as functions of time, the change in voltage V, dV, is sometimes written as dV(t), and the change in electric charge Q, dQ, is sometimes written as dQ(t).

[0050] This type of battery characteristic data can be acquired at regular intervals using a secondary battery management system. In other words, by using this battery characteristic data, it is possible to obtain the latest information on the secondary battery, including the operating temperature.

[0051] As mentioned above, the data indicating battery characteristics differs depending on the temperature of the secondary battery. Therefore, a secondary battery management system, which is one aspect of the present invention, can select the optimal data from the above data to be used when determining the upper limit voltage. For example, the secondary battery management system can determine the temperature of the secondary battery and select data indicating battery characteristics according to that temperature.

[0052] Furthermore, a secondary battery management system, according to one aspect of the present invention, detects a maximum value in data indicating battery characteristics.

[0053] In one aspect of the present invention, a secondary battery management system may perform noise reduction processing or noise reduction processing when detecting a maximum value.

[0054] In one aspect of the present invention, a secondary battery management system can, when detecting a maximum value, pre-determine the voltage of a secondary battery that has an irreversible crystal structure, and set the target for detection to a predetermined voltage range.

[0055] In one aspect of the present invention, a secondary battery management system can, when detecting a maximum value, pre-determine the amount of electricity in a secondary battery that will result in an irreversible crystal structure, and set the target for detection to a predetermined range of electricity amounts.

[0056] In one aspect of the present invention, a secondary battery management system can, when detecting a maximum value, pre-determine the charging time at which the irreversible crystal structure described above occurs, and set the target for detection to a predetermined charging time range.

[0057] One embodiment of the present invention is a secondary battery management system that can stop charging after detecting the above-mentioned maximum value. The maximum value is a value within the range in which the crystal structure does not collapse, and it is preferable that the upper limit voltage be maximized within the range in which the crystal structure does not collapse by stopping charging based on this maximum value.

[0058] The data showing the battery characteristics described above reflects the temperature of the secondary battery. Therefore, by using a secondary battery management system according to one aspect of the present invention, it is possible to determine the optimal upper voltage limit according to the temperature, and this secondary battery management system is particularly suitable for determining the upper voltage limit of secondary batteries used at low temperatures.

[0059] While we have described secondary batteries for use at low temperatures, a secondary battery management system according to one aspect of the present invention can also be used at high temperatures. Of course, a secondary battery management system according to one aspect of the present invention can also be used at room temperature.

[0060] Furthermore, in a secondary battery management system according to one aspect of the present invention, it is preferable that charging is performed with a constant current from the start of charging until it is stopped. This is because, even if it takes time to stop charging in the secondary battery management system, the upper limit voltage will not change abruptly during the constant current charging period.

[0061] (Embodiment 1) Based on the above description, this embodiment will explain a secondary battery management system according to one aspect of the present invention.

[0062] <Example 1 of a secondary battery management system> Figure 1A shows an example of a secondary battery management system 100 according to one aspect of the present invention. The secondary battery management system 100 can operate at low temperatures, room temperatures, and high temperatures. Specifically, the secondary battery management system 100 has a secondary battery 121 that charges and discharges at temperatures between -50°C and 0°C.

[0063] Furthermore, the secondary battery management system 100 has a charging circuit 101. The charging circuit 101 is electrically connected to the secondary battery 121. Specifically, the charging circuit 101 is electrically connected to the positive electrode and the negative electrode of the secondary battery 121. The secondary battery 121 may have a positive electrode terminal such as a positive electrode lead or a positive electrode tab as the positive electrode. The secondary battery 121 may have a negative electrode terminal such as a negative electrode lead or a negative electrode tab as the negative electrode. In this case, the charging circuit 101 is electrically connected to the positive electrode terminal and the negative electrode terminal.

[0064] The charging circuit 101 shown in Figure 1A includes at least a voltage measurement circuit 151, a current measurement circuit 152, and a control circuit 153. The charging circuit 101 shown in Figure 1B differs from that in Figure 1A in that it further includes a temperature sensor 156.

[0065] <Voltage Measurement Circuit> As shown in Figures 1A and 1B, the voltage measurement circuit 151 is electrically connected to the positive and negative terminals of the secondary battery 121, respectively. The voltage measurement circuit 151 may also be electrically connected to the positive terminal and the negative terminal.

[0066] The voltage measurement circuit 151 has the function of measuring the voltage of the secondary battery 121 (referred to as terminal voltage), and for example, it has the function of measuring the terminal voltage (referred to as charging voltage) when the secondary battery 121 is being charged. In addition to the charging voltage, the voltage measurement circuit 151 may also have the function of measuring the terminal voltage (referred to as discharge voltage) when the secondary battery 121 is being discharged. To distinguish between the charging voltage and the discharge voltage, for example, a positive sign may be attached to the charging voltage and a negative sign to the discharge voltage. Of course, a negative sign may also be attached to the charging voltage and a positive sign to the discharge voltage.

[0067] The voltage measurement circuit 151 measures each voltage at regular intervals, which can be 80 msec to 10 sec, preferably 90 msec to 1 sec. Shortening the interval allows for a high-precision assessment of the secondary battery's state. For example, the interval can be shortened only when the secondary battery's voltage fluctuates significantly.

[0068] The voltage measurement circuit 151 can measure the charging voltage or discharging voltage of the secondary battery 121. For example, if the secondary battery is placed at a low temperature, the voltage measurement circuit 151 can measure the charging voltage or discharging voltage at that temperature. The voltage measurement circuit 151 can provide the measured voltage value to the control circuit 153. If the measured voltage value is an analog value, the analog value may be converted to digital and provided to the control circuit 153. That is, the voltage measurement circuit 151 may have a circuit for converting analog values ​​to digital, and this circuit can use an analog-to-digital converter (ADC). The ADC configuration can be a ΔΣ modulation type, a parallel comparison type (also written as flash type), or a pipeline type. The ΔΣ modulation type is suitable for voltage measurement circuits because it has high resolution.

[0069] <Example 1 of measuring voltage Vb1> Using Figure 2A, we will explain an example of measuring the voltage Vb1 between the positive and negative electrodes of a secondary battery. In Figure 2A, only the voltage measurement circuit 151 is shown in the charging circuit 101, and the rest is omitted. As shown in Figure 2A, the above voltage measurement circuit 151 can directly measure the voltage Vb1 between the positive and negative electrodes of a secondary battery.

[0070] <Example 2 of measuring voltage Vb1> As shown in Figure 2B, the voltage measurement circuit 151 can also measure the voltage Vb1 divided by resistance. In Figure 2B, only the voltage measurement circuit 151 is shown in the charging circuit 101, and the others are omitted. In Figure 2B, the voltage Vb1 is divided into voltage Vb2 and voltage Vb3 by resistors 122 and 123, and the voltage measurement circuit 151 can measure, for example, voltage Vb3. To enable the measurement of voltage Vb3, the voltage measurement circuit 151 is electrically connected to the negative terminal of the secondary battery 121 and between resistors 122 and 123.

[0071] If the voltage measurement circuit 151 measures the voltage obtained by dividing the voltage between the positive and negative electrodes of the secondary battery 121 by resistance, the voltage measurement circuit 151 or the control circuit 153 may estimate the voltage Vb1 between the positive and negative electrodes of the secondary battery 121 from the voltage obtained by resistance division.

[0072] <Current measurement circuit> The current measurement circuit 152 is electrically connected to the positive terminal of the secondary battery 121, as shown in Figures 1A and 1B. The current measurement circuit 152 may also be electrically connected to the positive terminal.

[0073] The current measurement circuit 152 has the function of measuring the current flowing through the positive and negative electrodes of the secondary battery 121, and preferably has the function of measuring the current when the secondary battery 121 is charging (referred to as the charging current). In addition to the charging current, the current measurement circuit 152 may also have the function of measuring the current when the secondary battery 121 is discharging (referred to as the discharge current).

[0074] Figure 1C shows a specific example of the current measurement circuit 152. The current measurement circuit 152 preferably includes a resistive element 152a and a circuit 152b, and circuit 152b is preferably electrically connected to the control circuit 153. A shunt resistor may be used for the resistive element 152a. The resistance value of the shunt resistor should be between 10mΩ and 300mΩ, preferably between 50mΩ and 120mΩ. Circuit 152b may include an operational amplifier. This is preferable because the voltage drop across the shunt resistor can be amplified by the operational amplifier.

[0075] The current measurement circuit 152 can measure the charging current or discharging current of the secondary battery 121 according to its temperature. For example, if the secondary battery 121 is placed at a low temperature, the current measurement circuit 152 can measure the charging current or discharging current at that temperature. The current measurement circuit 152 can supply the measured current value to the control circuit 153. The measured current value is an analog value, but the analog value may also be converted to digital and supplied to the control circuit 153, and the above-mentioned analog-to-digital converter (ADC) can be used.

[0076] <Control circuit> The control circuit 153 has the function of starting and stopping the charging of the secondary battery based on the voltage and current information. In addition to these, the control circuit 153 has calculation functions, detection functions, or determination functions.

[0077] As the control circuit 153 having the functions described above, a central processing unit (CPU) or a Microcontroller Unit (MCU) can be used.

[0078] If the secondary battery 121 is placed in a low temperature environment, the control circuit 153 can operate even at low temperatures.

[0079] Furthermore, in the secondary battery management system 100, a heater may be installed so as to be in contact with the control circuit 153 or in the vicinity of the control circuit 153. The heater ensures that the control circuit 153 operates reliably even when placed in a low-temperature environment.

[0080] <Memory circuit> The control circuit 153 may have a memory circuit 154, as shown in Figures 1A and 1B, in addition to the CPU or MCU. The control circuit 153 can record values ​​input from the voltage measurement circuit 151 or current measurement circuit 152, etc., in the memory circuit 154.

[0081] <Temperature sensor> The secondary battery management system 100 may have a temperature sensor 156 as shown in Figure 1B. The temperature sensor 156 can measure the temperature of the secondary battery. The temperature sensor 156 only needs to be able to measure temperatures in a range from low to high. The temperature that the temperature sensor 156 can measure depends on its position. If the temperature sensor is placed inside the secondary battery, the internal temperature of the secondary battery can be measured. If the temperature sensor is placed in contact with the casing of the secondary battery, the temperature of the casing of the secondary battery can be measured. If the temperature sensor is placed between the casing of the secondary battery and the housing, and in contact with the housing, the temperature of the housing can be measured. If the temperature sensor is placed next to the secondary battery, the ambient temperature of the secondary battery can be measured.

[0082] For the temperature sensor in contact with the outer casing or the temperature sensor in contact with the housing, for example, a temperature sensor equipped with a T-type thermocouple function can be used. The control circuit 153 can record the value input from the temperature sensor 156 in the memory circuit 154.

[0083] The temperature information obtained from the temperature sensor 156 is used in the secondary battery management system 100 to determine the upper limit voltage. In particular, when the secondary battery is used continuously at different temperatures, such as from low to high temperature, or from low temperature to room temperature, this information is useful in determining the upper limit voltage in the secondary battery management system 100.

[0084] Furthermore, even in secondary battery management systems that do not have temperature sensors, it is possible to determine the upper voltage limit if data indicating the battery characteristics can be obtained.

[0085] <External power supply> The power for each circuit in the charging circuit may be shared from the secondary battery 121, but it may also be supplied from a secondary battery or power supply device separate from the secondary battery 121. For example, the secondary battery management system 100 can be electrically connected to an external power source, and power from the external power source may be used as the power for each circuit in the charging circuit.

[0086] <Calculation and detection functions> The calculation function of the control circuit 153 can calculate data indicating battery characteristics from the measured values ​​of voltage, current, and time. Furthermore, the detection function of the control circuit 153 can detect maximum values ​​from this data. The detection function determines a value to be a maximum value when a decrease from the maximum value is observed.

[0087] <Example 1 of detecting a local maximum> The control circuit 153 can, for example, use a calculation function to calculate the time change of the voltage of the secondary battery 121. This function allows the secondary battery management system 100 to obtain a numerical value or graph relating to the voltage change (ΔV) over time. The graph may show one or more maximum values. These maximum values ​​are due to changes in the crystal structure, indicating that the crystal structure of the active material begins to differ at the maximum value boundary.

[0088] The control circuit 153 can, for example, use a calculation function to differentiate the obtained time by voltage. This function allows the secondary battery management system 100 to obtain numerical values ​​or graphs related to dt / dV. One or more maximum values ​​can be observed in the graph. These maximum values ​​are due to changes in the crystal structure, indicating that the crystal structure of the active material begins to differ, or change, at the boundary of these maximum values. This change is sometimes referred to as a phase change.

[0089] The secondary battery management system 100 can detect changes in the crystal structure of the positive electrode active material, etc., using dt / dV. Changes in crystal structure can be reversible or irreversible, but irreversible changes will cause the active material, etc. to deteriorate. Therefore, the control circuit 153 has a function to detect a maximum value corresponding to the start of an irreversible change and to determine the voltage of the secondary battery when it reaches that maximum value as the upper limit voltage.

[0090] In data showing battery characteristics, multiple maximum values ​​are observed when reversible changes in crystal structure are included. On the other hand, the secondary battery management system 100 wants to detect one of the maximum values ​​corresponding to the start of irreversible changes in crystal structure. Therefore, the secondary battery management system 100 should ignore the maximum values ​​related to reversible changes in crystal structure. As a method of ignoring them, it is good to pre-determine a range corresponding to irreversible changes in crystal structure. If it is known that irreversible changes in crystal structure occur near the upper limit voltage, the lower limit of this range should be set to -10%, preferably -8%, of the upper limit voltage. The upper limit of this range is the upper limit voltage.

[0091] In the above, the range was defined based on the charging voltage, but the lower limit of the range can also be defined based on the time corresponding to the charging voltage. Furthermore, the lower limit of the range can also be defined based on the amount of electricity corresponding to the charging voltage.

[0092] The charging voltage at which irreversible changes in crystal structure occur can be determined in advance by performing one or more charge-discharge cycles on the secondary battery. The lower limit of this range can be set to -8%, preferably -5%, of the charging voltage at which irreversible changes in crystal structure occur.

[0093] We just need to find the maximum value within the above range.

[0094] <Averaging process> If a clear local maximum cannot be identified, the control circuit 153 can, for example, use a calculation function to average the dt / dV values. This averaging process can yield an average of 10 points, sometimes referred to as a moving average. The number of points used to obtain the average is not limited to 10. This averaging process makes it easier to detect local maximums. This averaging process is sometimes referred to as a smoothing process.

[0095] <Rate of Change> If a clear local maximum cannot be identified, the control circuit 153 can obtain the rate of change using, for example, a calculation function. The rate of change can be calculated from the value after averaging. For example, a comparison range of 100 points can be set for the average value of the 10 points, and the rate of change for each of those 100 points can be calculated. The rate of change can be obtained by performing a difference calculation from the value of the 1st point (first value) to the value of the 100th point (second value), and then dividing the difference value by the value of the 1st point. Note that the comparison range for calculating the rate of change is not limited to 100 points. Once the rate of change is determined, it becomes easier to detect local maximums.

[0096] <Calculation and detection functions> The control circuit 153 can, for example, use a calculation function to calculate the amount of electricity in the secondary battery using the voltage of the secondary battery 121 provided by the voltage measurement circuit 151 or the current of the secondary battery 121 provided by the current measurement circuit 152. Through this function, the secondary battery management system 100 can obtain numerical values ​​or graphs relating voltage (V) to capacity (C).

[0097] <dq dv> The control circuit 153 can, for example, use a calculation function to differentiate the obtained electric quantity by voltage. This function allows the secondary battery management system 100 to obtain numerical values ​​or graphs related to dQ / dV. In the graph showing dQ / dV, the horizontal axis represents voltage V(t), and the vertical axis represents dQ(t) / dV(t).

[0098] <Example 2 of detecting a local maximum> A graph showing dQ / dV will reveal one or more maximum values. These maximum values ​​are due to changes in the crystal structure, indicating that the crystal structure of the active material begins to differ, or change, at the boundary of the maximum value. This change is sometimes referred to as a phase change.

[0099] The secondary battery management system 100 can detect changes in the crystal structure of the positive electrode active material, etc., using dQ / dV. Changes in crystal structure can be reversible or irreversible, but irreversible changes will cause the active material, etc. to deteriorate. Therefore, the control circuit 153 has a function to detect a maximum value corresponding to the start of an irreversible change and to determine the voltage of the secondary battery when it reaches that maximum value as the upper limit voltage.

[0100] In data showing battery characteristics, multiple maximum values ​​are observed when reversible changes in crystal structure are included. On the other hand, the secondary battery management system 100 wants to detect one of the maximum values ​​corresponding to the start of irreversible changes in crystal structure. Therefore, the secondary battery management system 100 should ignore the maximum values ​​related to reversible changes in crystal structure. As a method of ignoring them, it is good to pre-determine a range corresponding to irreversible changes in crystal structure. If it is known that irreversible changes in crystal structure occur near the upper limit voltage, the lower limit of this range should be set to -10%, preferably -8%, of the upper limit voltage. The upper limit of this range is the upper limit voltage.

[0101] In the above, the range was defined based on the charging voltage, but the lower limit of the range can also be defined based on the time corresponding to the charging voltage. Furthermore, the lower limit of the range can also be defined based on the amount of electricity corresponding to the charging voltage.

[0102] The charging voltage at which an irreversible change in the crystal structure occurs may be grasped in advance by performing charging and discharging on the secondary battery for one or more cycles. The lower limit of the range can be set to -8%, preferably -5%, of the charging voltage at which an irreversible change in the crystal structure occurs.

[0103] The maximum value may be detected within the above range.

[0104] <d 2 Q / dV 2 > At low temperatures, the diffusion of carrier ions in the secondary battery, for example, the diffusion of lithium ions in the positive electrode active material and the diffusion of lithium ions in the negative electrode active material, is slow, and a phase change occurs partially. Therefore, the change amount of dQ / dV may be small. At this time, a clear maximum value cannot be confirmed in dQ / dV. In such a case, the control circuit 153 may calculate 2 Q / dV 2 . In the value of d 2 Q / dV 2 , when it exceeds zero, it corresponds to the above maximum value.

[0105] In the data indicating the battery characteristics, when including the reversible change in the crystal structure, multiple maximum values are confirmed. Therefore, there are multiple occurrences when it exceeds the above zero. On the other hand, in the secondary battery management system 100, it is desired to detect the occurrence when it exceeds zero corresponding to one of the maximum values corresponding to the start of the irreversible change in the crystal structure. Therefore, in the secondary battery management system 100, it is advisable to ignore the maximum values related to the reversible crystal structure. As a method of ignoring, a range corresponding to the irreversible change in the crystal structure may be determined in advance. When it is known that the irreversible change in the crystal structure occurs near the upper limit voltage, the lower limit of the range is set to -10%, preferably -8%, of the upper limit voltage. The upper limit of the range is the upper limit voltage.

[0106] In the above, the range was defined based on the charging voltage, but the lower limit of the range can also be defined based on the time corresponding to the charging voltage. Furthermore, the lower limit of the range can also be defined based on the amount of electricity corresponding to the charging voltage.

[0107] The charging voltage at which irreversible changes in crystal structure occur can be determined in advance by performing one or more charge-discharge cycles on the secondary battery. The lower limit of this range can be set to -8%, preferably -5%, of the charging voltage at which irreversible changes in crystal structure occur.

[0108] You only need to detect when the value exceeds zero within the above range.

[0109] Depending on the temperature of the secondary battery, either detection example 1 or detection example 2 of the maximum value can be selected.

[0110] <Crystal structure of layered rock salt> It is preferable to use an active material having a layered rock salt crystal structure for the positive electrode, and the secondary battery management system 100 should be able to detect changes in the layered rock salt crystal structure from data indicating battery characteristics. For example, in a positive electrode active material having a layered rock salt crystal structure, the metals that become carrier ions are arranged in layers, and as the carrier ions desorb during charging, changes in the crystal structure occur, such as layer displacement and reduction of interlayer distance. Since some of these changes in crystal structure are reversible and others are irreversible, the control circuit 153 should detect a maximum value corresponding to the irreversible state as described above.

[0111] <Judgment function> The control circuit 153 has a determination function that can determine the time it takes to reach the state corresponding to the maximum value. The determination function can also determine the voltage or amount of electricity of the secondary battery when the state corresponding to the maximum value is reached.

[0112] <Charging stopped> The control circuit 153 has a function to stop charging based on the detected maximum value. Furthermore, the control circuit 153 can stop charging using time-related information associated with the maximum value. The control circuit 153 can also stop charging using information related to the amount of electricity associated with the maximum value.

[0113] If the secondary battery management system 100 requires a significant amount of time to stop charging, the control circuit 153 can stop charging after a predetermined period of time has elapsed.

[0114] In this way, the secondary battery management system 100 can determine the upper limit voltage using data indicating the battery characteristics obtained from the secondary battery in use. This is particularly preferable when using the secondary battery at low temperatures, as it allows the upper limit voltage to be determined according to the data indicating the battery characteristics. By determining the upper limit voltage in this way, it is possible to realize a secondary battery with high energy density.

[0115] <Charging conditions> In some cases, constant current-constant voltage (CC-CV) charging is used to charge secondary batteries. CC-CV charging involves performing constant current charging, and after the upper limit of the charging voltage is reached during constant current charging, constant voltage charging is performed.

[0116] It is preferable that the charging conditions from the start of charging to the stop of charging be constant current charging. For example, even if it takes time from the time the upper limit voltage is determined until charging stops, the upper limit voltage will not change abruptly during the constant current charging period.

[0117] <Coulomb counter> Preferably, the charging circuit 101 also functions as a Coulomb counter. For example, as a Coulomb counter, the charging circuit 101 can calculate the total amount of electricity in the secondary battery 121 using the current measurement circuit 152 and the control circuit 153. The charging capacity and discharging capacity of the secondary battery can be calculated from the calculated amount of electricity.

[0118] <soc> Furthermore, the control circuit 153 may have a function to analyze the state of charge (SOC) using the calculated charging capacity and discharge capacity. The state of charge is one of the indicators that represent the charge rate, with a fully charged state being SOC=100% and a completely discharged state being SOC=0%. The control circuit 153 can determine the upper limit voltage based on the state of charge.

[0119] <Secondary battery> Details of the secondary battery 121 will be described later.

[0120] <Example of charging method 1> Next, an example of a charging method using the secondary battery management system 100 according to one embodiment of the present invention will be explained using the flowchart shown in Figure 3.

[0121] First, in step S50, the process is started.

[0122] If the secondary battery management system 100 has a temperature sensor or the like, in step S50a, it is advisable to measure the temperature of the secondary battery, for example, the operating temperature, and record it in the memory circuit 154 or the like. Since the value of the overvoltage differs depending on the temperature, it is also possible to record the temperature and the overvoltage in association. Alternatively, it is also possible to record the temperature and the detection conditions for the maximum value in association. The secondary battery management system 100 can also use these associated values ​​as information regarding temperature.

[0123] Next, in step S51, constant current charging of the secondary battery is started. This constant current charging is continued until charging is stopped.

[0124] Next, in step S52, the voltage measurement circuit 151 starts measuring the voltage of the secondary battery. The control circuit 153 measures time using a clock signal or the like. Alternatively, the current measurement circuit 152 may start measuring the current of the secondary battery.

[0125] Next, in step S53, the voltage measured by the voltage measurement circuit 151 is recorded in the memory circuit 154. The current measured by the current measurement circuit 152 is recorded in the memory circuit 154. If the voltage and current are analog values, the analog values ​​may be converted to digital before being recorded in the memory circuit 154, and the above-mentioned analog-to-digital converter (ADC) can be used.

[0126] For example, the time elapsed from the start of charging, i.e., the time elapsed from step S50, can be used as the time associated with the voltage.

[0127] Next, in step S54, the control circuit 153 calculates the voltage derivative waveform (dt / dV) over time using the measured voltage, current, and time data set. The graph of dt / dV has time t on the horizontal axis and the voltage derivative over time dt / dV on the vertical axis, and is a curve.

[0128] Next, in step S55, the process proceeds to step S56 only if the measured voltage is V2 or greater. If the voltage is less than V2, the process returns to step S52, as indicated by "No" in the figure, and the measurements are continued. Here, the voltage V2 is 10% lower (-10%) than the upper limit voltage mentioned above, preferably 8% lower (-8%), and is 4.5V, preferably 4.6V, when the upper limit voltage is 5V.

[0129] Alternatively, the determination in step S55 may be made based on the charge depth of the secondary battery.

[0130] Next, in step S56, the control circuit 153 analyzes dt / dV and detects a local maximum. If a local maximum cannot be detected, the control circuit 153 may perform an averaging process. If a local maximum cannot be detected after the averaging process, the control circuit 153 may perform a rate of change acquisition.

[0131] If no maximum value is detected, return to step S52 and continue with each measurement.

[0132] The control circuit 153 preferably repeatedly performs the steps from step S53 to step S56 to accumulate at least voltage and time data sets. That is, if the steps from step S53 to step S56 are repeated n times (where n is an integer of 2 or more), data indicating the battery characteristics can be calculated using the n measured values.

[0133] Next, in step S57, after a maximum value is detected in the data indicating the battery characteristics, charging is stopped.

[0134] Furthermore, although step S57 states that charging is stopped after a maximum value is detected, charging may also be stopped after a predetermined time has elapsed after a maximum value is detected. This is because, in the secondary battery using lithium cobalt oxide described later, the irreversible change to the crystal structure will not be completed within a predetermined time after a maximum value is detected. In other words, after a maximum value is detected, the change in crystal structure remains within the realm of reversible change until a predetermined time has elapsed.

[0135] The information of the maximum value detected in step S56 may be used as the upper limit voltage for the next charging cycle. For example, consider the case where steps S51 to S56 are repeated s times, where s is an integer greater than or equal to 2. In such a case, the times t1 and t2 determined based on the maximum value may be used as the upper limit voltage for the next charging cycle, and charging may be stopped.

[0136] Next, in step S199, the process is terminated.

[0137] In addition, an example was described in which constant current charging is performed continuously from the start of charging in step S51 until charging is stopped in step S57. In this case, the current value is set to a constant value from the start of charging until charging is stopped.

[0138] Furthermore, the current value may be changed in stages from the start of charging until it is stopped. For example, if steps S52 to S56 are repeated multiple times, the second current value may be set to be lower than the first current value. Alternatively, the second current value may be set to be higher than the first current value.

[0139] The secondary battery management system 100 detects a maximum value from the charging characteristics of the secondary battery and, in step S57, can change the charging conditions of the secondary battery according to the detected maximum value. The charging characteristics change depending on the ambient temperature during charging and discharging of the secondary battery, the degradation of the secondary battery due to the charge-discharge cycle, etc. The secondary battery management system 100 can suppress the degradation 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 these changes in charging characteristics.

[0140] Furthermore, the secondary battery management system 100 can detect a maximum value from the charging characteristics and change the charging conditions according to the detected maximum value, thereby enabling charging to the maximum extent possible while suppressing the degradation of the secondary battery.

[0141] <Example of charging method 2> Next, an example of a charging method using the secondary battery management system 100 according to one embodiment of the present invention will be explained using the flowchart shown in Figure 4.

[0142] First, in step S100, the process is started.

[0143] If the secondary battery management system 100 has a temperature sensor or the like, in step S50a, it is advisable to measure the temperature of the secondary battery, for example, the operating temperature, and record it in the memory circuit 154 or the like.

[0144] Next, in step S101, constant current charging of the secondary battery is started. This constant current charging is continued until charging is stopped.

[0145] 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 control circuit 153 measures time using a clock signal or the like.

[0146] Next, in step S103, the voltage measured by the voltage measurement circuit 151 is recorded in the memory circuit 154. The current measured by the current measurement circuit 152 is recorded in the memory circuit 154. If the voltage and current are analog values, the analog values ​​may be converted to digital before being recorded in the memory circuit 154, and the above-mentioned analog-to-digital converter (ADC) can be used.

[0147] For example, the time elapsed from the start of charging, i.e., the time elapsed from step S100, can be used as the time associated with the voltage and current.

[0148] Next, in step S104, the control circuit 153 calculates the voltage derivative waveform (dQ / dV) of the electric charge of the secondary battery using the measured voltage, current, and time data set. The graph of dQ / dV has the voltage V on the horizontal axis and the voltage derivative dQ / dV over time on the vertical axis, and is a curve.

[0149] Next, in step S105, the process proceeds to step S56 only if the measured voltage is V2 or greater. If the voltage is less than V2, the process returns to step S52, as indicated by "No" in the diagram, and the measurements are continued. Here, the voltage V2 is 10% lower (-10%) than the upper limit voltage mentioned above, preferably 8% lower (-8%), and is 4.5V, preferably 4.6V, when the upper limit voltage is 5V.

[0150] Alternatively, the determination in step S105 may be made based on the charge depth of the secondary battery.

[0151] Next, in step S106, the control circuit 153 analyzes dQ / dV and detects the maximum value. If the maximum value cannot be detected, the control circuit 153 performs d 2 Q / dV 2 It is best to perform the calculation d. 2 Q / dV 2 When the value of exceeds zero, it corresponds to the above-mentioned local maximum.

[0152] If no maximum value is detected, return to step S102 and continue each measurement.

[0153] The control circuit 153 preferably repeatedly performs the steps from step S103 to step S106 to accumulate at least a set of voltage, current, and time data. That is, if the steps from step S103 to step S106 are repeated n times, data indicating the battery characteristics can be calculated using the n measured values.

[0154] Next, in step S107, after a maximum value is detected in the data indicating the battery characteristics, charging is stopped.

[0155] Furthermore, although step S107 states that charging is stopped after a maximum value is detected, charging may also be stopped after a predetermined time has elapsed after a maximum value is detected. This is because, in the secondary battery using lithium cobalt oxide described later, the irreversible change to the crystal structure will not be completed within a predetermined time after a maximum value is detected. In other words, after a maximum value is detected, the change in crystal structure remains within the realm of reversible change until a predetermined time has elapsed.

[0156] The information of the maximum value detected in step S106 may be used as the upper limit voltage for the next charging cycle. For example, consider the case where steps S101 to S106 are repeated s times, where s is an integer greater than or equal to 2. In such a case, the times t1 and t2 determined based on the maximum value may be used as the upper limit voltage for the next charging cycle, and charging may be stopped.

[0157] Next, in step S199, the process is terminated.

[0158] In addition, an example was described in which constant current charging is performed continuously from the start of charging in step S101 until charging is stopped in step S107. In this case, the current value is set to a constant value from the start of charging until charging is stopped.

[0159] Furthermore, the current value may be changed in stages from the start of charging until it is stopped. For example, if steps S102 to S106 are repeated multiple times, the second current value may be set to be lower than the first current value. Alternatively, the second current value may be set to be higher than the first current value.

[0160] The secondary battery management system 100 detects a maximum value from the charging characteristics of the secondary battery and, in step S107, can change the charging conditions of the secondary battery according to the detected maximum value. The charging characteristics change depending on the ambient temperature during charging and discharging of the secondary battery, the degradation of the secondary battery due to the charge-discharge cycle, etc. The secondary battery management system 100 can suppress the degradation 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 these changes in charging characteristics.

[0161] Furthermore, the secondary battery management system 100 can detect a maximum value from the charging characteristics and change the charging conditions according to the detected maximum value, thereby enabling charging to the maximum extent possible while suppressing the degradation of the secondary battery.

[0162] <Temperature-restricted charging control> The charging circuit 101 preferably controls charging using temperature.

[0163] The control circuit 153 preferably changes the charging conditions according to the ambient temperature of the secondary battery measured by the temperature sensor 156. The ambient temperature should preferably be low.

[0164] Preferably, the memory circuit 154 of the control circuit 153 has a table that links the ambient temperature of the secondary battery with the charging conditions.

[0165] Furthermore, it is preferable that the memory circuit 154 of the control circuit 153 stores the charging characteristics linked to the ambient temperature of the secondary battery. These charging characteristics may be past measurements of the secondary battery 121, measurements of other secondary batteries with similar characteristics, or waveforms obtained by calculation. In addition, in the flow shown in Figures 3 to 4, these measurements may be used to estimate the maximum value. For example, machine learning can be used for estimation.

[0166] The control circuit 153 may use the charging characteristics of the secondary battery stored in the memory circuit 154 to analyze the extreme values ​​(which include local maximums and local minimums) in the differential waveforms of voltage and electric quantity. Here, the charging characteristics can be, for example, a capacity-voltage curve, a voltage-dQ / dV curve, a ΔV-t curve, impedance characteristics, etc.

[0167] <Example 2 of a secondary battery management system> Figure 5 shows an example of the secondary battery management system 100A. The secondary battery management system 100A can operate even at low temperatures.

[0168] The charging circuit 101 shown in Figure 5 has the configuration shown in Figure 1B, plus detection circuits, etc. An example of the detection circuits, etc., is shown which includes a detection circuit 185 that has the function of detecting overcharging and over-discharging, a detection circuit 186 that has the function of detecting charging overcurrent and discharging overcurrent, a short circuit detection circuit SD, a micro-short circuit detection circuit MSD, transistors 140 and 150.

[0169] The charging circuit 101 shown in Figure 5 has functions to suppress overcharging, over-discharging, overcurrent during charging, overcurrent during discharging, short circuits, micro-short circuits, etc., and can function as a protection circuit for secondary batteries. Here, a micro-short refers to a minute short circuit inside a secondary battery, and it refers to a phenomenon in which a small short circuit current flows in a minute short circuit, rather than a short circuit between the positive and negative electrodes of the secondary battery that makes charging impossible. Even if it is for a relatively short time and in a small area, a large voltage change may occur.

[0170] For example, transistors called power MOSFETs can be used as transistors 140 and 150.

[0171] The control circuit 153 has the function of interrupting the current flowing to the secondary battery 121 by applying signals to the gates of transistors 140 and 150, respectively.

[0172] The detection circuit 185 monitors the voltage of the secondary battery and, if it detects overcharging or over-discharging, can provide a signal to the control circuit 153 indicating the detection. The control circuit receives this signal and can provide a signal to at least one of the gates of transistor 140 and transistor 150 to interrupt the current flowing to the secondary battery.

[0173] The detection circuit 186 monitors the current of the secondary battery and, if it detects an overcurrent during charging or discharging, can provide a signal to the control circuit 153 indicating the detection. The control circuit receives this signal and can provide a signal to at least one of the gates of transistor 140 and transistor 150 to interrupt the current flowing to the secondary battery.

[0174] The overcharge detected by the detection circuit 185 may be detected using the extreme value of the time-varying waveform of the charging voltage, or the extreme value of the voltage derivative waveform of the charged amount, as described above. Alternatively, the overcharge detected by the detection circuit 185 may be detected by comparing it 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 corresponding to the ambient temperature of the secondary battery is stored, for example, in the memory circuit 154 of the control circuit 153.

[0175] The secondary battery management system 100B shown in Figure 6 has m secondary batteries 121 connected in series (where m is an integer of 2 or more).

[0176] The charging circuit 101 of the secondary battery management system 100B is the same as in Figure 1A, Figure 1B, or Figure 5. However, in the secondary battery management system 100B, the voltage measurement circuit measures the voltage of each secondary battery 121, so Figure 6 shows m voltage measurement circuits 151(m) corresponding to the number of secondary batteries 121(m). It is also possible to measure the voltage of each secondary battery 121 sequentially, and the number of voltage measurement circuits in the charging circuit 101 can be reduced to less than the number of secondary batteries, for example, to one voltage measurement circuit.

[0177] In the secondary battery management system 100B, the detection circuit 185 of the charging circuit 101 may detect overcharging in the voltage between terminal 124, which is electrically connected to the positive electrode of secondary battery 121(1), and terminal 125, which is electrically connected to the negative electrode of secondary battery 121(m). Alternatively, for example, the detection circuit 186 and the short-circuit detection circuit SD of the charging circuit 101 may detect overcharging or a short circuit based on the current between terminal 124 and terminal 125.

[0178] The secondary battery management system 100B may also independently control each of the m secondary batteries 121 using a charging circuit 101 connected to each of them. In this case, for the secondary battery 121 that completes charging first, after charging is complete, the current flows through a path connected in parallel to the secondary battery 121, such as a transistor, resistor, or diode connected in parallel to the secondary battery 121. Therefore, it is preferable that the charging circuit 101 has the secondary battery 121 as a current path and a switch to switch between the paths.

[0179] Furthermore, the secondary battery management system 100B may control the charging of m secondary batteries 121 using the total voltage of the m secondary batteries (for example, the voltage between the positive electrode of secondary battery 121(1) and the negative electrode of secondary battery 121(m) in Figure 6). In such cases, a voltage value m times greater can be used as the voltage used for charging control.

[0180] <Example 3 of a secondary battery management system> Figure 7 shows an example of the secondary battery management system 200. The secondary battery management system 200 can operate even at low temperatures.

[0181] The charging circuit 101 shown in Figure 7A differs from the configuration shown in Figure 1A in that it includes a differencer 161. The differencer 161 has the function of outputting a time difference, and can output the time difference when, for example, there is a difference between the terminal voltage at time t1 and the terminal voltage at time t2. Furthermore, in addition to the above function, the differencer 161 also has the function of converting from analog values ​​to digital values, a so-called AD converter function. Since such a differencer 161 has a voltage measurement function, the voltage measurement circuit 151 shown in Examples 1 and 2 can be omitted in Example 3, and the other configurations are the same as in Examples 1 and 2.

[0182] Figure 7B shows the differencer 161 and the control circuit 153. The differencer 161 includes a sample-and-hold circuit 300, a comparator 301, a DA converter 302, a successive approximation register 303, a second control circuit 304, and a clock generation circuit 305. The differencer 161 may have an AD converter, and the AD converter can be configured as any one of the following: double integration type, successive approximation type, ΔΣ modulation type, parallel approximation type (also referred to as flash type), or pipeline type. The number of bits for the successive approximation type can be 10 bits or more and 18 bits or less, and the conversion speed is preferably several tens of kHz or more and several MHz or less. The number of bits for the double integration type can be 8 bits or more and 20 bits or less, and the conversion speed is preferably several Hz or more and several kHz or less.

[0183] The differencer 161 can hold the acquired voltage (analog value) in the sample-and-hold circuit 300. It is preferable to hold the value in the sample-and-hold circuit 300 while converting the analog value to a digital value. The transistor in the sample-and-hold circuit 300 can be an OS transistor. An OS transistor is a transistor in which an oxide semiconductor layer is applied to the active layer.

[0184] The off-current value of an OS transistor is, for example, 1 aA (1 × 10⁻¹⁶) per 1 μm of channel width at room temperature. -18 A) Below, 1zA(1×10 -21 A) Less than or equal to, or 1yA(1×10 -24 A) It can be less than or equal to the following. Note that the off-current value of a Si transistor per 1 μm of channel width at room temperature is 1 fA (1 × 10⁻¹⁰). -15 A) More than 1pA (1×10 -12 A) The following applies. Therefore, the off-current of the OS transistor is about 10 orders of magnitude lower than that of the Si transistor. Transistors with such low off-currents are suitable for the sample-and-hold circuit 300.

[0185] The value output from the sample-and-hold circuit 300 is input to the comparator 301 and compared with the data output from the successive approximation register 303. The successive approximation register 303 outputs digital data in which the analog value of the voltage is divided into at least two parts, each of which is assigned to a bit. This digital data is converted from digital data to analog data via the DA converter 302 before being input to the comparator 301. The comparator 301 compares the data from the sample-and-hold circuit 300 with the data from the successive approximation register 303. If the data match, 0 is output; if the data do not match, 1 is output. The value of 0 or 1 is output to the second control circuit 304, and if they match, the voltage (digital) is output from the successive approximation register 303. In this way, the voltage converted to a digital value can be obtained.

[0186] Data A, Data B, and Data C are output from the second control circuit 304 to the control circuit 153. Data A is, for example, a sign (+ or -) indicating whether it is charging or discharging. Data B is, for example, count data related to time. Data C is an error flag. An example of an error that would trigger the flag is when, if the voltage difference is assigned as 1 bit, it is determined to be 2 bits or more.

[0187] The differencer 161 should ideally be able to output the time between time t1 and time t2. It can count based on the clock signal or other input to the differencer 161 and output data corresponding to the above time.

[0188] The differencer 161 may be capable of outputting a positive or negative sign. This sign allows for distinguishing between the charging voltage and the discharging voltage. If this distinction is not necessary, there is no need to output a sign.

[0189] Figure 8 shows a flowchart related to differential processing.

[0190] First, in step S11, the differential processing is started.

[0191] Next, in step S12, the analog voltage value acquired at any time T0 can be converted to a digital value (D0). The voltage value also includes information about the time it was acquired. For example, the successive approximation AD converter described above can be used for the conversion to a digital value. This digital value (D0) is then used as the reference for the difference processing.

[0192] Next, in step S13, the analog voltage value acquired T1 seconds after an arbitrary time is converted to a digital value (D1). The voltage value also includes information about the time it was acquired. Depending on the specifications of the management system, the interval after T seconds is 50ms to 1s, preferably 100ms to 150ms, and the acquisition of the analog voltage should be performed periodically at the above intervals.

[0193] Next, in step S14, a subtraction operation is performed between the reference digital value (D0) and the digital value after T seconds (D1), and the difference operation is executed.

[0194] Next, in step S15, it is determined whether the result of the subtraction process is not 0. If it is not 0 (corresponding to "No" in the diagram), the process proceeds. If it is 0 (corresponding to "Yes" in the diagram), the process returns to step S13, a new voltage value is obtained, converted to a digital value, and then the difference processing with the reference voltage digital value (D0) is repeated.

[0195] If the result is not 0, proceed to step S16, calculate the time difference (ΔT = T1 - T0), and output it.

[0196] Subsequently, the differential processing is completed as shown in step S17.

[0197] Based on the time difference (ΔT), graphs related to battery characteristics such as voltage differential waveforms are calculated, and the charging process is carried out until it stops, as shown in Figure 3, etc.

[0198] This embodiment can be appropriately combined with descriptions of other embodiments.

[0199] (Embodiment 2) This embodiment describes an example of a secondary battery according to one aspect of the present invention. Preferably, the secondary battery according to one aspect of the present invention includes a positive electrode, a negative electrode, and an electrolyte.

[0200] <Positive electrode> A positive electrode according to one aspect of the present invention has a positive electrode active material.

[0201] [Cathode active material] The positive electrode active material comprises lithium, a transition metal M, oxygen, and an additive element A. Alternatively, the positive electrode active material may be a composite oxide (LiMO2) containing lithium and a transition metal M, to which the additive element A is added. However, the composition of the composite oxide is not strictly limited to Li:M:O=1:1:2. Furthermore, a positive electrode active material to which the additive element A is added may also be referred to as a composite oxide.

[0202] In one embodiment of the present invention, the positive electrode active material preferably uses cobalt as the transition metal M responsible for the redox reaction. In addition to cobalt, at least one or more selected from nickel and manganese may be used. It is preferable that the cobalt content of the transition metal M in the positive electrode active material is 75 atomic% or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, as this offers many advantages, such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics.

[0203] Furthermore, if the cobalt content of the transition metal M in the positive electrode active material is 75 atomic percent or more, preferably 90 atomic percent or more, and more preferably 95 atomic percent or more, then compared to composite oxides such as lithium nickelate (LiNiO2) in which nickel accounts for the majority of the transition metal M, Li x Stability is better when x is small in CoO2.

[0204] Using nickel as the transition metal M in the positive electrode active material in an amount of 33 atomic percent or more, preferably 60 atomic percent or more, and more preferably 80 atomic percent or more, may result in lower raw material costs compared to cases with a high cobalt content, and may also increase the charge / discharge capacity per unit weight, which is preferable.

[0205] The additive element A in the positive electrode active material is preferably one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium. Furthermore, the sum of transition metals among the additive element A is preferably less than 25 atomic%, more preferably less than 10 atomic%, and even more preferably less than 5 atomic%.

[0206] In other words, the positive electrode active material can include lithium cobalt oxide with magnesium and fluorine added, lithium cobalt oxide with magnesium, fluorine and titanium added, lithium cobalt oxide with magnesium, fluorine and aluminum added, lithium cobalt oxide with magnesium, fluorine and nickel added, lithium cobalt oxide with magnesium, fluorine, nickel and aluminum added, and so on.

[0207] These added elements A can further stabilize the crystal structure of the positive electrode active material.

[0208] It is not necessary to include all the elements listed in additive element A; for example, a cathode active material that is substantially free of manganese can be used. A cathode active material that is substantially free of manganese has the advantages mentioned above, such as being relatively easy to synthesize, easy to handle, and having excellent cycle properties. In a cathode active material that is substantially free of manganese, the weight of manganese is preferably 600 ppm or less, more preferably 100 ppm or less. The weight of manganese can be analyzed, for example, using GD-MS.

[0209] <Crystal structure> In this specification, the extent to which insertable and detachable lithium remains in the positive electrode active material is expressed by x in the composition formula, for example, Li x x in CoO2, or Li x Indicated by x in MO2. Li in this specification. x CoO2 contains Li as appropriate. x This can be interpreted as MO2. In the case of the positive electrode active material in a secondary battery, x can be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2 mAh / g, Li 0.2 It can be expressed as CoO2 or x=0.2. x A small x in CoO2 means, for example, 0.1 <x≦0.24をいう。

[0210] When properly synthesized lithium cobalt oxide, before being used as the positive electrode, approximately satisfies the stoichiometric ratio, it is LiCoO2 and the Li occupancy rate of the lithium sites is x=1. Similarly, a secondary battery that has finished discharging is also LiCoO2, and it can be said that x=1. Here, "finished discharging" refers to a state where, for example, with a current of 100mA / g, the voltage is 2.5V (counter electrode lithium) or less.

[0211] ≪Li x When x in CoO2 is 1 >> A positive electrode active material according to one aspect of the present invention is Li, as shown in Figure 9. x In CoO2, when x=1, it is preferable to have a layered rock salt type crystal structure that belongs to the space group R-3m. x In CoO2, when x=1, it is in a discharge state. The above layered rock salt type composite oxide has a high discharge capacity, possesses a two-dimensional lithium ion diffusion pathway, is suitable for lithium ion insertion / desorption reactions, and is excellent as a positive electrode active material for secondary batteries. For this reason, it is particularly preferable that the interior, which occupies most of the volume of the positive electrode active material, has a layered rock salt type crystalline structure.

[0212] The surface layer is a region containing additive element A and can function as a barrier film for the positive electrode active material. The surface layer refers to, for example, a region within 50 nm from the surface of the positive electrode active material toward the interior, more preferably within 35 nm from the surface toward the interior, even more preferably within 20 nm from the surface toward the interior, and most preferably within 10 nm from the surface toward the interior.

[0213] The surface layer is the region where lithium ions first desorb during charging, and it is a region where the lithium concentration tends to be lower than in the interior. Therefore, the surface layer is prone to instability, and it is a region where degradation of the crystal structure is likely to begin. On the other hand, if the surface layer can be made sufficiently stable, Li x Even when x in CoO2 is small, for example, when x is 0.24 or less, the layered structure consisting of internal transition metal M and oxygen octahedra can be made less prone to breaking. Furthermore, the displacement of the layers consisting of internal transition metal M and oxygen octahedra can be suppressed.

[0214] To ensure a stable composition and crystal structure in the surface layer, it is preferable that the surface layer contains additive element A, and more preferably that it contains multiple additive element A. Furthermore, it is preferable that the surface layer has a higher concentration of one or more selected additive element A than the interior. It is also preferable that the positive electrode active material has a concentration gradient of one or more selected additive element A. Moreover, it is more preferable that the distribution of the positive electrode active material differs depending on the additive element A. For example, it is more preferable that the depth of the concentration peak from the surface differs depending on the additive element A. Here, "concentration peak" refers to the maximum value of the concentration.

[0215] For example, magnesium, one of the additive elements A, is divalent, and magnesium is more likely to exist at lithium sites than at transition metal M sites in the layered rock salt crystal structure. The presence of magnesium at an appropriate concentration at the surface lithium sites makes it easier to maintain the layered rock salt crystal structure. This is presumed to be because the magnesium present at the lithium sites functions as pillars that support the CoO2 layers. Furthermore, the presence of magnesium allows Li x When the x value in CoO2 is, for example, 0.24 or less, the desorption of oxygen around magnesium can be suppressed. Furthermore, the presence of magnesium is expected to increase the density of the positive electrode active material. Additionally, a high magnesium concentration in the surface layer is expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0216] It is preferable that the total amount of magnesium in the positive electrode active material is appropriate. For example, in one embodiment of the present invention, the ratio of magnesium to the transition metal M (sum of multiple transition metals if present) (Mg / M) is preferably 0.25% to 5%, more preferably 0.5% to 2%, and even more preferably about 1% when M is cobalt. The amount of magnesium in the total positive electrode active material referred to here may be the value obtained by elemental analysis of the entire positive electrode active material using, for example, GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0217] Furthermore, nickel, one of the additive elements A, can be present at both the transition metal M site and the lithium site. When present at the transition metal M site, its oxidation-reduction potential is lower compared to cobalt, which leads to an increase in discharge capacity and is therefore preferable.

[0218] Furthermore, when nickel is present at the lithium site, the displacement of the layered structure consisting of the transition metal M and oxygen octahedra can be suppressed. Volume changes associated with charging and discharging are also suppressed. Additionally, the elastic modulus increases, meaning it becomes harder. This is presumed to be because the nickel present at the lithium site also functions as a pillar supporting the CoO2 layers. Therefore, it is desirable that the crystal structure becomes more stable, especially in the charged state at high temperatures, such as 45°C or above.

[0219] It is preferable that the total nickel content of the positive electrode active material is appropriate. For example, the number of nickel atoms in the positive electrode active material 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, it is preferable that it is more than 0% and 4% or less. Alternatively, it is preferable that it is more than 0% and 2% or less. Alternatively, it is preferable that it is more than 0% and 7.5% or less. Alternatively, it is preferable that it is more than 0.05% to 2%. Alternatively, it is preferable that it is more than 0.1% to 7.5%. Alternatively, it is preferable that it is more than 0.1% to 4%. The amount of nickel shown here may be the value obtained by elemental analysis of the entire positive electrode active material using, for example, GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition during the process of manufacturing the positive electrode active material.

[0220] Furthermore, aluminum, one of the additive elements A, can be present at the transition metal M sites in the layered rock salt crystal structure. Since aluminum is a trivalent typical element and its valency does not change, lithium around the aluminum does not easily move during charging and discharging. Therefore, aluminum and the surrounding lithium can function as pillars, suppressing changes in the crystal structure. In addition, aluminum suppresses the dissolution of the surrounding transition metal M, improving continuous charging endurance. Moreover, since the Al-O bond is stronger than the Co-O bond, it can suppress the desorption of oxygen around the aluminum. These effects improve thermal stability. Therefore, having aluminum as additive element A can improve the safety when the positive electrode active material of the present invention is used in a secondary battery. Furthermore, it is possible to create a positive electrode active material whose crystal structure is less likely to collapse even after repeated charging and discharging.

[0221] It is preferable that the total amount of aluminum in the positive electrode active material is appropriate. For example, the total number of aluminum atoms in the positive electrode active material is preferably 0.05% to 4% of the total number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferred, or 0.1% to 4% is preferred. The total amount of aluminum in the positive electrode active material referred to here may be, for example, the value obtained by elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0222] Furthermore, fluorine, one of the additive elements A, is a monovalent anion, and if some of the oxygen in the surface layer is replaced by fluorine, the lithium desorption energy decreases. This is because the change in the valence of cobalt ions accompanying lithium desorption is from trivalent to tetravalent when fluorine is absent, and from divalent to trivalent when fluorine is present, resulting in different oxidation-reduction potentials. Therefore, if some of the oxygen in the surface layer of the positive electrode active material is replaced by fluorine, the desorption and insertion of lithium ions near the fluorine can occur more smoothly. As a result, when the positive electrode active material of the present invention is used in a secondary battery, the charge-discharge characteristics, current characteristics, etc. can be improved. In addition, the presence of fluorine in the surface layer, which is the part that comes into contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid. Furthermore, as will be described in later embodiments, if the melting point of fluorides, including lithium fluoride, is lower than the melting point of other additive element A sources, it can function as a flux (also called a fluxing agent) that lowers the melting point of other additive element A sources.

[0223] Furthermore, titanium oxide, one of the additive element A, is known to be superhydrophilic. Therefore, by using a positive electrode active material with titanium oxide on its surface, it may be possible to improve wettability with highly polar solvents. When used in a secondary battery, this may improve contact at the interface between the positive electrode active material and the highly polar electrolyte, potentially suppressing an increase in internal resistance.

[0224] Furthermore, if phosphorus, one of the additive elements A, is present in the surface layer, Li x Maintaining a small x value in CoO2 can suppress short circuits, which is preferable. For example, it is preferable for the compound containing phosphorus and oxygen to exist in the surface layer.

[0225] When the positive electrode active material contains phosphorus, it is preferable because the phosphorus reacts with hydrogen fluoride generated by the decomposition of the electrolyte or electrolyte solution, potentially lowering the concentration of hydrogen fluoride in the electrolyte.

[0226] If the electrolyte contains LiPF6, hydrolysis may generate hydrogen fluoride. Furthermore, the reaction between polyvinylidene fluoride (PVDF), used as a component of the positive electrode, and alkali may also generate hydrogen fluoride. Reducing the hydrogen fluoride concentration in the electrolyte may suppress corrosion of the current collector and / or peeling of the coating. It may also suppress the decrease in adhesion due to gelation and / or insolubilization of PVDF.

[0227] However, it is undesirable if the surface layer is occupied solely by compounds of additive element A and oxygen, as this makes lithium insertion and removal difficult. For example, it is undesirable for the surface layer to be occupied solely by structures of MgO, MgO and NiO(II) in solid solution, and / or MgO and CoO(II) in solid solution. Therefore, the surface layer must contain at least cobalt, and in the discharge state, lithium as well, and have pathways for lithium insertion and removal.

[0228] To ensure sufficient pathways for lithium insertion and removal, it is preferable that the surface layer has a higher cobalt concentration than magnesium. For example, the ratio of magnesium atoms (Mg) to cobalt atoms (Co), Mg / Co, is preferably 0.62 or less. It is also preferable that the surface layer has a higher cobalt concentration than nickel. Furthermore, it is preferable that the surface layer has a higher cobalt concentration than aluminum. Furthermore, it is preferable that the surface layer has a higher cobalt concentration than fluorine.

[0229] ≪Li x When x is small during CoO2≫ Using Figure 9, Li x This section explains the change in crystal structure associated with changes in x in CoO2.

[0230] A positive electrode active material according to one aspect of the present invention has, in the discharge state, the distribution and / or crystal structure of the additive element A as described above, and as a result, Li x The crystal structure of CoO2 when x is small differs from that of conventional cathode active materials. Here, x is small when it is 0.1 <x≦0.24をいうこととする。

[0231] In the positive electrode active material of one embodiment of the present invention shown in Figure 9, Li x The change in crystal structure between the discharge state where x is 1 and the state where x is 0.24 or less in CoO2 is less than that of conventional positive electrode active materials. More specifically, the displacement of the CoO2 layer between the state where x is 1 and the state where x is 0.24 or less can be reduced. Furthermore, the change in volume when compared per cobalt atom can be reduced. Therefore, the positive electrode active material of one aspect of the present invention is less prone to crystal structure collapse even when repeated charging and discharging where x is 0.24 or less, and can achieve excellent cycle characteristics. In addition, the positive electrode active material of one aspect of the present invention is Li x When x in CoO2 is 0.24 or less, it can adopt a more stable crystal structure than conventional positive electrode active materials. Therefore, the positive electrode active material in one aspect of the present invention is Li x When the value of x in CoO2 remains below 0.24, short circuits are less likely to occur. In such cases, the safety of the secondary battery is further improved, which is preferable.

[0232] Li x Figure 9 shows the crystal structure of the interior of the positive electrode active material when x in CoO2 is approximately 1 and 0.2. The interior occupies the majority of the volume of the positive electrode active material and contributes greatly to charging and discharging, so it is the part where shifting and volume changes of the CoO2 layer are most problematic.

[0233] When x=1, the positive electrode active material has the same R-3m O3 crystal structure as conventional lithium cobalt oxide.

[0234] However, when x is 0.24 or less, for example around 0.2 and 0.12, which is the value at which conventional lithium cobalt oxide has an H1-3 type crystal structure, the positive electrode active material has a crystal structure different from that.

[0235] When x = approximately 0.2, the positive electrode active material of one embodiment of the present invention has a crystal structure that belongs to the trigonal space group R-3m. This is because the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure will be called the O3' type crystal structure. Figure 9 shows this crystal structure labeled R-3m O3'.

[0236] In the O3' type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co(0,0,0.5), O(0,0,x), and within the range of 0.20≦x≦0.25. The lattice constant of the unit cell is preferably 0.2797≦a≦0.2837(nm) for the a axis, more preferably 0.2807≦a≦0.2827(nm), and typically a=0.2817(nm). For the c axis, it is preferably 1.3681≦c≦1.3881(nm), more preferably 1.3751≦c≦1.3811(nm), and typically c=1.3781(nm).

[0237] The above-mentioned positive electrode active material, represented by an O3'-type crystal structure, may exhibit diffraction intensity maxima at 2θ = 19.35 ± 0.10° and 2θ = 45.55 ± 0.20° when analyzed at 25°C using powder X-ray analysis with CuKα1 rays during charging.

[0238] In the O3' type crystal structure, ions such as cobalt, nickel, and magnesium occupy the six-coordinate positions of oxygen. Lighter elements such as lithium may occupy the four-coordinate positions of oxygen.

[0239] As shown by the dotted line in Figure 9, there is almost no displacement of the CoO2 layer between the R-3m(O3) in the discharged state and the O3'-type crystal structure.

[0240] Also, the volume difference per cobalt atom between R-3m(O3) in the discharged state and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0241] Thus, in the positive electrode active material of one embodiment of the present invention, when x in Li x CoO2 is small, that is, when a large amount of lithium has desorbed, the change in the crystal structure is suppressed more than that of the conventional positive electrode active material. Also, the volume change when compared per the same number of cobalt atoms is suppressed. Therefore, even when charge and discharge are repeated such that x becomes 0.24 or less, the crystal structure of the positive electrode active material is difficult to collapse. Therefore, the decrease in the charge-discharge capacity in the charge-discharge cycle of the positive electrode active material is suppressed. Also, since more lithium can be stably utilized than in the conventional positive electrode active material, the positive electrode active material has a large discharge capacity per unit weight and per unit volume. Therefore, by using the positive electrode active material, a secondary battery with a high discharge capacity per unit weight and per unit volume can be manufactured.

[0242] Note that the positive electrode active material may have an O3'-type crystal structure when x in Li x CoO2 is 0.15 or more and 0.24 or less, and it is presumed that it also has an O3'-type crystal structure even when x exceeds 0.24 and is 0.27 or less. However, since the crystal structure is affected not only by x in Li x CoO2 but also by the number of charge-discharge cycles, charge-discharge current, temperature, electrolyte, etc., it is not necessarily limited to the above range of x.

[0243] Therefore, when x in Li x CoO2 exceeds 0.1 and is 0.24 or less, not all of the inside of the positive electrode active material needs to have an O3'-type crystal structure. It may contain other crystal structures or a part may be amorphous.

[0244] Also, to make x in Li x CoO2 small, generally, it is necessary to charge at a high charging voltage. Therefore, Li x The state where x in CoO2 is small can be rephrased as the state charged at a high charging voltage. For example, when charging at a voltage of 4.6 V or higher with respect to the potential of lithium metal in an environment of 25°C by CC / CV charging, the H1-3 type crystal structure appears in the conventional positive electrode active material. Therefore, a charging voltage of 4.6 V or higher with respect to the potential of lithium metal can be referred to as a high charging voltage. Also, in this specification etc., unless otherwise specified, the charging voltage is expressed with respect to the potential of lithium metal.

[0245] Therefore, it can be rephrased that the positive electrode active material of one aspect of the present invention is preferable because it can maintain a crystal structure having the symmetry of R-3m O3 even when charged at a high charging voltage, for example, at a voltage of 4.6 V or higher at 25°C. Also, it can be rephrased that it is preferable because it can take an O3'-type crystal structure when charged at an even higher charging voltage, for example, at a voltage of 4.65 V or higher and 4.7 V or lower at 25°C.

[0246] When the charging voltage of the positive electrode active material is further increased, the H1-3 type crystal may be observed in some cases. Also, as described above, since the crystal structure is affected by the number of charge-discharge cycles, charge-discharge current, electrolyte, etc., when the charging voltage is lower, for example, even when the charging voltage is 4.5 V or higher and less than 4.6 V at 25°C, the positive electrode active material of one aspect of the present invention may take an O3'-type crystal structure in some cases.

[0247] In addition, in a secondary battery, for example, when using graphite as the negative electrode active material, the voltage of the secondary battery decreases by the potential of graphite compared to the above. The potential of graphite is about 0.05 V to 0.2 V with respect to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, it has the same crystal structure at the voltage obtained by subtracting the potential of graphite from the above voltage.

[0248] [Method for producing positive electrode active material] In order to produce a positive electrode active material having the distribution, composition, and / or crystal structure of the additive element A as described in the previous embodiment, the method of adding the additive element A is important. At the same time, it is also important that the internal crystallinity is good.

[0249] Therefore, in the process of preparing the positive electrode active material, it is preferable to first synthesize a composite oxide having lithium and a transition metal, and then mix in the additive element A source and perform a heat treatment.

[0250] In a method of synthesizing a composite oxide containing additive element A, lithium, and transition metal M by mixing a transition metal M source and a lithium source simultaneously with an additive element A source, it is difficult to increase the concentration of additive element A in the surface layer. Furthermore, if the additive element A source is only mixed after synthesizing the composite oxide containing lithium and transition metal M without heating, the additive element A will only adhere to the composite oxide without solid solution. Without sufficient heating, it is also difficult to properly distribute the additive element A. Therefore, it is preferable to synthesize the composite oxide, then mix in the additive element A source, and then perform a heat treatment. This heat treatment after mixing in the additive element A source is sometimes called annealing.

[0251] However, if the annealing temperature is too high, cation mixing occurs, increasing the likelihood that the added element A, for example, magnesium, will enter the transition metal M site. Magnesium present at the transition metal M site is Li x When x in CoO2 is small, it does not maintain the layered rock salt crystal structure of R-3m. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to divalent cobalt and the sublimation or evaporation of lithium.

[0252] Therefore, it is preferable to mix a material that functions as a flux with the source of additive element A. Any material that has a lower melting point than the composite oxide having lithium and transition metal M can be considered to function as a flux. Suitable materials that function as a flux include fluorine compounds, such as lithium fluoride. Adding a flux causes a melting point depression in both the source of additive element A and the composite oxide having lithium and transition metal M. By lowering the melting point, it becomes easier to distribute the additive element A well at a temperature where cation mixing is less likely to occur.

[0253] Furthermore, it is even more preferable to heat the composite oxide containing lithium and transition metal M before mixing in the added element A. This heating is sometimes referred to as initial heating.

[0254] Initial heating causes lithium to desorb from a portion of the surface layer of the composite oxide containing lithium and transition metal M, which further improves the distribution of additive element A.

[0255] More specifically, the following mechanism suggests that initial heating makes it easier to differentiate the distribution of added element A. First, lithium is desorbed from a portion of the surface layer by initial heating. Next, a composite oxide containing lithium and a transition metal M, which has a lithium-deficient surface layer, is mixed with a source of added element A, including nickel, aluminum, and magnesium, and heated. Of the added element A, magnesium is a divalent typical element, and nickel is a transition metal but is prone to becoming a divalent ion. Therefore, Mg is released into a portion of the surface layer. 2+ and Ni 2+ And, due to lithium deficiency, Co 2+ A rock salt-type phase is formed, which has the following characteristics.

[0256] Of the additive element A, nickel readily dissolves and diffuses into the interior when the surface layer is a composite oxide containing layered rock salt-type lithium and transition metal M, but tends to remain on the surface when part of the surface layer is rock salt-type.

[0257] Furthermore, in these rock salt types, the bond distance between metallic Me and oxygen (Me-O distance) tends to be longer than in layered rock salt types.

[0258] For example, rock salt mold mayonnaise 0.5 Mg 0.5 The Me-O distance in O is 0.209 nm, and in rock salt-type MgO it is 0.211 nm. Furthermore, even if a spinel-type phase is formed in part of the surface layer, the Me-O distance in spinel-type NiAl2O4 is 0.20125 nm, and in spinel-type MgAl2O4 it is 0.202 nm. In both cases, the Me-O distance exceeds 0.2 nm.

[0259] On the other hand, in the layered rock salt type, the bond distance between the metal other than lithium and oxygen is shorter than that described above. For example, the Al-O distance in layered rock salt type LiAlO2 is 0.1905 nm (the Li-O distance is 0.211 nm). Also, the Co-O distance in layered rock salt type LiCoO2 is 0.19224 nm (the Li-O distance is 0.20916 nm).

[0260] According to the Shannon ionic radius (Shannon, R. D. Acta Crystallogr. 1976, A32, 751.), the ionic radius of aluminum in 6-fold coordination is 0.0535 nm, and the ionic radius of oxygen in 6-fold coordination is 0.14 nm, and the sum of these is 0.1935 nm.

[0261] From the above, it is considered that aluminum exists more stably in the sites other than lithium in the layered rock salt type than in the rock salt type. Therefore, aluminum is more likely to be distributed in the deeper region having the layered rock salt type and / or inside, rather than in the region closer to the surface having the rock salt type phase among the surface layer portions.

[0262] Also, an effect of enhancing the crystallinity of the internal layered rock salt type crystal structure can be expected by the initial heating.<0>

[0263] However, the initial heating does not necessarily have to be performed. By controlling the atmosphere, temperature, time, etc. in other heating processes, for example, annealing, a positive electrode active material having the O3' type may be produced when x in Li x CoO2 is small.

[0264] <Example 1 of the method for producing a positive electrode active material> Using FIGS. 10A to 10C, an example of a method for producing a positive electrode active material (Example 1 of the method for producing a positive electrode active material) that can be used as one aspect of the present invention will be described. The production method described here is an example of the production method of the positive electrode active material 10 having the features described above in this embodiment.

[0265] <Step S11> In step S11 shown in Figure 10A, lithium sources (Li sources) and cobalt sources (Co sources) are prepared as the starting materials, lithium and transition metals, respectively.

[0266] As a lithium source, it is preferable to use a lithium-containing compound, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. The lithium source should preferably have high purity; for example, a material with a purity of 99.99% or higher is preferable.

[0267] As the cobalt source, it is preferable to use a compound containing cobalt, such as cobalt oxide or cobalt hydroxide. The cobalt source should preferably have high purity; for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher is used. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased and / or the reliability of the secondary battery is improved.

[0268] In addition, the cobalt source preferably has high crystallinity, for example, it is preferable to have single crystal grains. The crystallinity of the cobalt source can be evaluated by TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or by X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. The above methods for evaluating crystallinity can be applied not only to cobalt sources but also to the evaluation of other materials.

[0269] <Step S12> Next, as shown in step S12 in Figure 10A, the lithium source and cobalt source are crushed and mixed to prepare a mixed material. Crushing and mixing can be done dry or wet. Wet crushing is preferred because it allows for finer crushing. If wet crushing is used, a solvent is prepared. As a solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used, but it is preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and cobalt source with dehydrated acetone with a purity of 99.5% or higher, with a water content of 10 ppm or less, and then crush and mix them. By using dehydrated acetone of the above purity, the amount of impurities that may be mixed in can be reduced.

[0270] For mixing and other processes, a ball mill or bead mill can be used. When using a ball mill, it is preferable to use aluminum oxide balls or zirconium oxide balls as the grinding media. Zirconium oxide balls are preferable because they produce less impurity. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0271] <Step S13> Next, as step S13 shown in Figure 10A, the mixed material is heated. The heating is preferably carried out at 800°C to 1100°C, more preferably at 900°C to 1000°C, and even more preferably at 950°C to 1000°C. If the temperature is too low, the decomposition and melting of the lithium source and cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to the evaporation of lithium from the lithium source and / or the excessive reduction of cobalt. For example, cobalt may change from trivalent to divalent, inducing oxygen defects, etc.

[0272] If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. Therefore, the heating time should be between 1 hour and 100 hours, and preferably between 2 hours and 20 hours.

[0273] The heating rate depends on the target temperature, but a rate between 80°C / h and 250°C / h is generally recommended. For example, when heating to 1000°C for 10 hours, a heating rate of 200°C / h is appropriate.

[0274] Heating is preferably carried out in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of -50°C or lower, more preferably an atmosphere with a dew point of -80°C or lower. In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. In order to suppress impurities that may be mixed into the material, the concentrations of impurities such as CH4, CO, CO2, and H2 in the heating atmosphere should be kept below 5 ppb (parts perbillion).

[0275] An oxygen-containing atmosphere is preferred as the heating atmosphere. For example, one method is to continuously introduce dry air into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method of continuously introducing oxygen into the reaction chamber and having oxygen flow through the chamber is called flow.

[0276] When the heating atmosphere is an oxygen-containing atmosphere, a method that does not involve flowing oxygen is also acceptable. For example, the reaction chamber can be depressurized and then filled with oxygen, preventing the oxygen from entering or leaving the reaction chamber; this method is called purging. For example, the reaction chamber can be depressurized to -970 hPa and then filled with oxygen up to 50 hPa.

[0277] After heating, natural cooling is acceptable, but it is preferable that the cooling time from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary; it is sufficient if it cools to a temperature acceptable for the next step.

[0278] Heating in this process may be carried out using a rotary kiln or a roller hearth kiln. When using a rotary kiln, heating can be performed while stirring, whether in a continuous or batch system.

[0279] For heating, a crucible made of aluminum oxide is preferred. Aluminum oxide crucibles are less likely to release impurities. In this embodiment, a crucible made of aluminum oxide with a purity of 99.9% is used. Furthermore, it is preferable to heat the crucible with a lid on it, as this prevents the material from volatilizing.

[0280] After heating is complete, the material may be crushed and sieved as needed. When collecting the heated material, it may be transferred from the crucible to a mortar before collection. It is preferable to use an aluminum oxide or zirconium oxide mortar. Aluminum oxide mortars are less likely to release impurities. Specifically, an aluminum oxide mortar with a purity of 90% or higher, preferably 99% or higher, should be used. In addition, heating conditions equivalent to those in step S13 can be applied to the heating processes described later, other than step S13.

[0281] <Step S14> Through the above process, lithium cobalt oxide (LiCoO2) shown in step S14 in Figure 10A can be synthesized.

[0282] Although examples of producing composite oxides by a solid-phase method have been shown as in steps S11 to S14, composite oxides may also be produced by a coprecipitation method. Alternatively, composite oxides may be produced by a hydrothermal method.

[0283] <Step S20> Next, as shown in step S20, it is preferable to add element A as source A to lithium cobalt oxide. Next, the details of step S20, in which element A is prepared as source A, will be explained using Figures 10B and 10C.

[0284] <Step S21> Step S20, shown in Figure 10B, comprises steps S21 to S23. Step S21 involves preparing additive element A. As additive element A, the additive elements described in the previous embodiment, for example, additive element X and additive element Y, can be used. Specifically, one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. Alternatively, one or more selected from bromine and beryllium can also be used. Figure 10B illustrates the case where a magnesium source and a fluorine source are prepared. In addition to additive element A, a lithium source may be prepared separately in step S21.

[0285] When magnesium is selected as additive element A, the additive element source can be called a magnesium source. Magnesium sources can include magnesium fluoride, magnesium oxide, magnesium hydroxide, or magnesium carbonate. Multiple magnesium sources may be used.

[0286] When fluorine is selected as additive element A, the additive element source can be called a fluorine source. Examples of such fluorine sources include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF3, CeF4), lanthanum fluoride (LaF3), or sodium aluminum hexafluoride (Na3AlF6). Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating process described later.

[0287] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Another lithium source used in step S21 is lithium carbonate.

[0288] Furthermore, the fluorine source may be a gas, and may be fluorine (F2), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O5F2, O6F2, O2F), etc., which may be mixed into the atmosphere during the heating process described later. Multiple fluorine sources may be used.

[0289] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The effect of lowering the melting point is greatest when lithium fluoride and magnesium fluoride are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be in excess and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is preferably LiF:MgF2 = x:1 (0≦x≦1.9), more preferably LiF:MgF2 = x:1 (0.1≦x≦0.5), and even more preferably LiF:MgF2 = x:1 (x=0.33). In this specification, unless otherwise specified, "nearby" means a value greater than 0.9 times and less than 1.1 times the value.

[0290] <Step S22> Next, in step S22 shown in Figure 10B, the magnesium source and the fluorine source are crushed and mixed. This step can be performed by selecting from the crushing and mixing conditions described in step S12.

[0291] Here, a heating step may be performed after step S22 if necessary. The heating step can be performed by selecting from the heating conditions described in step S13. The heating time is preferably 2 hours or more, and the heating temperature is preferably 800°C to 1100°C.

[0292] <Step S23> Next, in step S23 shown in Figure 10B, the material that has been crushed and mixed above is recovered to obtain the additive element A source (A source). The additive element A source shown in step S23 has multiple starting materials and can also be called a mixture.

[0293] The particle size of the above mixture is preferably such that the D50 (median diameter) is 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. Even when one material is used as the source of additive element A, the D50 (median diameter) is preferably such that it is 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

[0294] Such finely powdered mixtures (including those containing only one additive element) are more likely to adhere uniformly to the surface of lithium cobalt oxide when mixed with it in a later step. Uniform adhesion of the mixture to the surface of lithium cobalt oxide is preferable because it facilitates the uniform distribution or diffusion of the additive element to the surface layer of the composite oxide after heating.

[0295] <Step S21> A process different from that shown in Figure 10B will be explained using Figure 10C. Step S20 shown in Figure 10C includes steps S21 to S23.

[0296] In step S21 shown in Figure 10C, four types of additive element sources are prepared to be added to lithium cobalt oxide. That is, Figure 10C shows different types of additive element sources than Figure 10B. In addition to the additive element sources, a lithium source may also be prepared separately.

[0297] Four types of additive element sources are prepared: a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source). The magnesium and fluorine sources can be selected from the compounds described in Figure 10B. Nickel sources such as nickel oxide and nickel hydroxide can be used. Aluminum sources such as aluminum oxide and aluminum hydroxide can be used.

[0298] <Steps S22 and S23> Next, steps S22 and S23 shown in Figure 10C are the same as the steps described in Figure 10B.

[0299] <Step S31> Next, in step S31 shown in Figure 10A, lithium cobalt oxide is mixed with the additive element source (source A). The ratio of the number of cobalt atoms Co in lithium cobalt oxide to the number of magnesium atoms Mg in the additive element X is preferably Co:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0300] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the shape of the lithium cobalt oxide. For example, it is preferable to use conditions with a lower rotation speed or shorter duration than the mixing in step S12. Also, dry mixing is generally milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconium oxide balls as the media.

[0301] In this embodiment, the mixing is performed dry using a ball mill with zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour. The mixing is carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0302] <Step S32> Next, in step S32 of Figure 10A, the materials mixed above are recovered to obtain mixture 903. During recovery, if necessary, the materials may be crushed and then sieved.

[0303] The method is not limited to those shown in Figures 10A to 10C. The added elements may be added at other times, or in multiple steps. Furthermore, the timing may be varied depending on the element.

[0304] For example, the additive elements may be added to the lithium source and cobalt source at step S11, that is, at the stage of the starting materials for the composite oxide. Then, lithium cobaltate containing the additive elements can be obtained in step S13. In this case, it is not necessary to separate the processes of steps S11 to S14 from the processes of steps S21 to S23. This can be said to be a simple and highly productive method.

[0305] Alternatively, lithium cobaltate containing some of the additive elements may be used. For example, if lithium cobaltate with magnesium and fluorine added is used, steps S11 to S14 and some steps in S20 can be omitted. This can be considered a simple and highly productive method.

[0306] Alternatively, after heating in step S15 with lithium cobalt oxide to which magnesium and fluorine have been added beforehand, a magnesium source and a fluorine source, or a magnesium source, a fluorine source, a nickel source, and an aluminum source may be added as in step S20.

[0307] <Step S33> Next, in step S33 shown in Figure 10A, the mixture 903 is heated. This can be performed by selecting from the heating conditions described in step S13. A heating time of 2 hours or more is preferable. The lower limit of the heating temperature in step S33 must be above the temperature at which the reaction between lithium cobalt oxide and the additive element source proceeds. The temperature at which the reaction proceeds is any temperature at which interdiffusion of the elements in lithium cobalt oxide and the additive element source occurs, and may be lower than the melting temperature of these materials. Using oxides as an example, the melting temperature T m 0.757 times (Tammann temperature T) d Solid-phase diffusion occurs from this point. Therefore, the heating temperature in step S33 should be 500°C or higher.

[0308] Furthermore, the reaction proceeds more easily if the heating temperature is above the melting point of one or more of the materials selected from the mixture 903. For example, when LiF and MgF2 are used as additive element sources, the eutectic point of LiF and MgF2 is around 742°C, so it is preferable to set the lower limit of the heating temperature in step S33 to 742°C or higher.

[0309] Furthermore, when mixture 903 is obtained by mixing LiCoO2:LiF:MgF2 in a molar ratio of 100:0.33:1, a maximum endothermic temperature (sometimes called an endothermic maximum) is observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, a lower limit of the heating temperature of 830°C or higher is more preferable.

[0310] A higher heating temperature is preferable because it facilitates the reaction, shortens the heating time, and increases productivity.

[0311] The upper limit of the heating temperature should be below the decomposition temperature of lithium cobalt oxide (1130°C). At temperatures near the decomposition temperature, there is a concern that lithium cobalt oxide may decompose, albeit in small amounts. Therefore, it is preferable that the temperature be 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower.

[0312] Based on these considerations, the heating temperature in step S33 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Furthermore, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 800°C to 1100°C, 830°C to 1130°C are preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C. The heating temperature in step S33 should be lower than that in step S13.

[0313] Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride, which may be caused by a fluorine source, to an appropriate range.

[0314] In the manufacturing method described in this embodiment, some materials, such as LiF (a fluorine source), may function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of lithium cobalt oxide, for example, between 742°C and 950°C, enabling the distribution of additive elements, including magnesium, to the surface layer and producing a positive electrode active material with good properties.

[0315] However, since LiF is less dense than oxygen in its gaseous state, it may volatilize upon heating, and if it volatilizes, the amount of LiF in mixture 903 will decrease. This weakens its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li on the surface of LiCoO2 may react with F from the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress volatilization is required.

[0316] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 while the partial pressure of LiF in the heating furnace is high. Such heating can suppress the volatilization of LiF in the mixture 903.

[0317] Furthermore, it is preferable to heat the mixture 903 in a way that prevents it from sticking together. If the mixture 903 sticks together during heating, the contact area with oxygen in the atmosphere decreases, and the diffusion pathway of the added elements (e.g., fluorine) is obstructed, which may worsen the distribution of added elements (e.g., magnesium and fluorine) to the surface layer.

[0318] Furthermore, it is believed that if the additive elements (e.g., fluorine) are uniformly distributed on the surface, a smooth positive electrode active material with few irregularities can be obtained. Therefore, in order to maintain or further improve the smooth surface after heating in step S15 of this process, it is preferable that the mixture 903 does not adhere to each other.

[0319] Furthermore, when heating with a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere inside the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to purge the atmosphere initially and then not allow the atmosphere to flow after introducing the oxygen atmosphere into the kiln. If oxygen flows, the fluorine source may evaporate, which is undesirable for maintaining surface smoothness.

[0320] When heating by roller hearth kiln, for example, the mixture 903 can be heated in an atmosphere containing LiF by placing a lid on the container containing the mixture 903.

[0321] In step S14 of Figure 10A, if the median diameter (D50) of lithium cobalt oxide is approximately 12 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0322] Furthermore, if the median diameter (D50) of the lithium cobalt oxide in step S14 is about 5 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 1 hour to 10 hours, and more preferably about 2 hours. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0323] <Step S34> Next, in step S34 shown in Figure 10A, the heated material is recovered and crushed as necessary to obtain the positive electrode active material 10. At this time, it is preferable to further sift the recovered positive electrode active material 10. Through the above steps, a positive electrode active material 10 having the characteristics described in this embodiment can be produced.

[0324] <Example 2 of a method for preparing positive electrode active material> Using Figure 11, another example of a method for producing a positive electrode active material that can be used as one aspect of the present invention (Example 2 of the method for producing a positive electrode active material) will be explained.

[0325] In Figure 11, steps S11 to S14 are performed in the same manner as in Figure 10A to prepare lithium cobalt oxide.

[0326] <Step S15> Next, as shown in step S15 in Figure 11, the lithium cobalt oxide is heated. Because this is the first heating of the lithium cobalt oxide, the heating in step S15 is sometimes called initial heating. Alternatively, because it is heated before step S20 shown below, it may be called preheating or pretreatment.

[0327] As described above, initial heating causes lithium to desorb from a portion of the surface layer of lithium cobalt oxide. It is also expected to enhance the internal crystallinity. Furthermore, the lithium source and / or cobalt source prepared in step S11, etc., may contain impurities. Initial heating makes it possible to reduce impurities from the lithium cobalt oxide completed in step 14. The effect of enhancing internal crystallinity refers to, for example, the effect of mitigating distortions and displacements caused by differences in shrinkage in the lithium cobalt oxide prepared in step S13.

[0328] Furthermore, the initial heating process has the effect of smoothing the surface of lithium cobalt oxide. A smooth surface means that there are few irregularities, the composite oxide is generally rounded, and the corners are also rounded. Alternatively, a surface with few foreign substances attached is also referred to as smooth. Foreign substances are thought to be a cause of irregularities, so it is preferable not to allow them to adhere to the surface.

[0329] Furthermore, it is not necessary to separately prepare a lithium compound source, an additive element source, or a material that functions as a flux for this initial heating.

[0330] If the heating time in this process is too short, sufficient results will not be obtained, but if it is too long, productivity will decrease. For example, it can be selected from the heating conditions described in step S13. Note that the heating temperature in step S15 should be lower than the temperature in step S13 in order to maintain the crystal structure of the composite oxide. Also, the heating time in step S15 should be shorter than the time in step S13 in order to maintain the crystal structure of the composite oxide. For example, heating at a temperature of 700°C to 1000°C for 2 to 20 hours is recommended.

[0331] In lithium cobalt oxide, heating in step S13 can create a temperature difference between the surface and the interior. This temperature difference can induce a difference in shrinkage. It is thought that the difference in shrinkage occurs because the fluidity of the surface and the interior differs due to the temperature difference. The energy associated with the difference in shrinkage creates a difference in internal stress in the lithium cobalt oxide. This difference in internal stress is also called strain, and the energy associated with it is sometimes called strain energy. The internal stress is removed by the initial heating in step S15, or in other words, the strain energy is considered to be homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in lithium cobalt oxide is relieved. Consequently, the surface of the lithium cobalt oxide may become smoother. This is also referred to as the surface being improved. In other words, it is thought that after step S15, the difference in shrinkage that occurred in the lithium cobalt oxide is relieved, and the surface of the composite oxide becomes smoother.

[0332] Furthermore, the difference in shrinkage can cause microscopic displacements in the lithium cobalt oxide, such as crystal displacements. To reduce these displacements, it is advisable to perform step S15. After step S15, it is possible to homogenize the displacement of the composite oxide (alleviate crystal displacements in the composite oxide, or align the crystal grains). As a result, the surface of the composite oxide may become smoother.

[0333] Using lithium cobalt oxide, which has a smooth surface, as the positive electrode active material reduces degradation during charging and discharging in a secondary battery and prevents cracking of the positive electrode active material.

[0334] Alternatively, pre-synthesized lithium cobaltate may be used as step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on pre-synthesized lithium cobaltate, lithium cobaltate with a smooth surface can be obtained.

[0335] Subsequently, in Figure 11, steps S20 to S33 are carried out in the same manner as in Figure 10A to obtain the positive electrode active material 10 in step S34. For details of step S20 in Figure 11, please refer to Figures 10B and 10C. Through the above steps, a positive electrode active material 10 having the characteristics described in this embodiment can be produced.

[0336] <Example 3 of a method for preparing positive electrode active material> Using Figures 12 and 13, another example of a method for producing a positive electrode active material that can be used as one embodiment of the present invention (Example 3 of the method for producing a positive electrode active material) will be described. In Example 3 of the method for producing a positive electrode active material, the number of times the additive elements are added and the mixing method differ from Examples 1 and 2 of the method for producing a positive electrode active material described above, but the descriptions of Examples 1 and 2 of the method for producing a positive electrode active material can be applied to other aspects.

[0337] In Figure 12, steps S11 to S15 are performed in the same manner as in Figure 10A to prepare lithium cobalt oxide that has undergone initial heating.

[0338] <Step S20a> Next, as shown in step S20a, element A is added to the lithium cobalt oxide that has undergone initial heating. Step S20a will be explained with reference to Figure 13A.

[0339] <Step S21> In step S21 shown in Figure 13A, a first additive element source (A1 source) is prepared. The A1 source can be selected from the additive elements A described in step S21 shown in Figure 10B. For example, as additive element A1, one or more can be selected from magnesium, fluorine, and calcium. Figure 13A illustrates the case where a magnesium source (Mg source) and a fluorine source (F source) are used as additive element A1.

[0340] Steps S21 to S23 shown in Figure 13A can be prepared under the same conditions as steps S21 to S23 shown in Figure 10B. As a result, an additive element source (A1 source) can be obtained in step S23.

[0341] Furthermore, steps S31 to S33 shown in Figure 12 can be manufactured under the same conditions as steps S31 to S33 shown in Figure 10A.

[0342] <Step S34a> Next, the material heated in step S33 is recovered to produce lithium cobalt oxide containing additive element A1. Here, to distinguish it from the composite oxide (first composite oxide) in step S14, it is also called the second composite oxide.

[0343] <Step S40> In step S40, shown in Figure 12, a second source of added elements is added. Step S40 will be explained with reference to Figures 13B and 13C.

[0344] <Step S41> In step S41, shown in Figure 13B, a second additive element source (A2 source) is prepared. The A2 source can be selected from the additive elements A described in step S21, shown in Figure 10B. For example, one or more of nickel, titanium, boron, zirconium, and aluminum can be suitably used as additive element A2. Figure 13B illustrates the case where nickel and aluminum are used as additive element A2.

[0345] Steps S41 to S43 shown in Figure 13B can be prepared under the same conditions as steps S21 to S23 shown in Figure 10B. As a result, an additive element source (A2 source) can be obtained in step S43.

[0346] Steps S41 to S43 shown in Figure 13C are a modified version of those in Figure 13B. In step S41 shown in Figure 13C, a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are each ground independently. As a result, in step S43, multiple second additive element sources (A2 sources) are prepared. The steps in Figure 13C differ from those in Figure 13B in that the additive elements are ground independently in step S42a.

[0347] <Steps S51 to S53> Next, steps S51 to S53 shown in Figure 12 can be carried out under the same conditions as steps S31 to S33 shown in Figure 10A. The conditions for step S53, which relates to the heating process, can be at a lower temperature and for a shorter time than in step S33.

[0348] <Step S54> Next, in step S54 shown in Figure 12, the heated material is recovered and crushed as necessary to obtain the positive electrode active material 10. Through the above steps, a positive electrode active material 10 having the characteristics described in this embodiment can be produced.

[0349] As shown in Figures 12 and 13, in manufacturing method 2, the additive elements to lithium cobalt oxide are introduced separately as a first additive element A1 and a second additive element A2. By introducing them separately, the depth profile of each additive element can be changed. For example, it is possible to profile the first additive element so that its concentration is higher in the surface layer than in the interior, and the second additive element so that its concentration is higher in the interior than in the surface layer.

[0350] <Negative electrode> A negative electrode according to one aspect of the present invention has a negative electrode active material.

[0351] It is preferable to use materials as the negative electrode active material that can react with carrier ions in a secondary battery, materials that can insert and remove carrier ions, materials that can react with metals that become carrier ions in an alloying reaction, and materials that can dissolve and precipitate metals that become carrier ions.

[0352] As the negative electrode active material, carbon materials such as graphite, easily graphitizable carbon, poorly graphitizable carbon, carbon nanotubes, carbon black, and graphene can be used.

[0353] Furthermore, as the negative electrode active material, a material having one or more elements selected from silicon, lithium, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used.

[0354] Furthermore, silicon may be made to have lower resistance by adding impurity elements such as phosphorus, arsenic, boron, aluminum, and gallium.

[0355] For example, a material containing silicon is SiO x A material represented by (where x is preferably less than 2, and more preferably between 0.5 and 1.6) can be used.

[0356] As a material containing silicon, for example, a form having multiple crystal grains within a single particle can be used. For example, a form having one or more silicon crystal grains within a single particle can be used. Furthermore, the single particle may have silicon oxide surrounding the silicon crystal grain. Furthermore, the silicon oxide may be amorphous.

[0357] Furthermore, as silicon-containing compounds, for example, Li2SiO3 and Li4SiO4 can be used. Li2SiO3 and Li4SiO4 may be crystalline or amorphous, respectively.

[0358] The analysis of silicon-containing compounds can be performed using NMR, XRD, Raman spectroscopy, etc.

[0359] A lithium foil can be prepared as the negative electrode containing lithium. The lithium foil can be manufactured by sputtering, CVD, or vapor deposition, and is sometimes called a lithium layer or lithium metal.

[0360] Furthermore, examples of materials that can be used as negative electrode active materials include oxides having one or more elements selected from titanium, niobium, tungsten, and molybdenum.

[0361] Multiple metals, materials, compounds, etc., as described above can be used in combination as the negative electrode active material.

[0362] The negative electrode active material in one aspect of the present invention may have fluorine in its surface layer. Having a halogen in the surface layer of the negative electrode active material can suppress a decrease in charge-discharge efficiency. Furthermore, it is believed that the reaction with the electrolyte on the surface of the active material is suppressed. In addition, the negative electrode active material in one aspect of the present invention may have at least a portion of its surface covered by a halogen-containing region. This region may, for example, be in the form of a film. Fluorine is particularly preferred as the halogen.

[0363] Furthermore, as another form of negative electrode, there may be a negative electrode that does not have negative electrode active material at the end of battery manufacturing. As an example of a negative electrode without negative electrode active material, there may be a negative electrode that has only a negative electrode current collector at the end of battery manufacturing, in which lithium ions that detach from the positive electrode active material during battery charging deposit as lithium metal on the negative electrode current collector, forming a negative electrode active material layer. Batteries using such a negative electrode are sometimes called negative electrode-free (anode-free) batteries or negative electrode-less (anode-less) batteries.

[0364] When using a negative electrode without a negative electrode active material, a film may be provided on the negative electrode current collector to homogenize the deposition of lithium. As a film to homogenize the deposition of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As a solid electrolyte, sulfide particle-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes can be used. Among these, polymer-based solid electrolytes are suitable as a film to homogenize the deposition of lithium because it is relatively easy to form a uniform film on the negative electrode current collector. Alternatively, as a film to homogenize the deposition of lithium, for example, a metal film that forms an alloy with lithium can be used. As a metal film that forms an alloy with lithium, for example, a magnesium metal film can be used. Since lithium and magnesium form a solid solution over a wide composition range, it is suitable as a film to homogenize the deposition of lithium.

[0365] Furthermore, when using a negative electrode without negative electrode active material, a negative electrode current collector with irregularities can be used. When using a negative electrode current collector with irregularities, the recesses in the negative electrode current collector become cavities where lithium can easily be deposited, thus suppressing the formation of dendrite-like shapes when lithium is deposited.

[0366] <Electrolytes> The electrolyte preferably has a solvent and a metal salt serving as carrier ions. When the carrier ions are lithium ions, the metal salt is referred to as a lithium salt. As the solvent of the electrolyte, an aprotic organic solvent is preferable. For example, 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, sultone, etc., one kind, or two or more of these can be used in any combination and ratio.

[0367] As the solvent of the electrolyte, it can include ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). When the total content of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 100 vol%, those with a volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate of x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) can be used. More specifically, an organic solvent containing EC, EMC, and DMC in a volume ratio of EC:EMC:DMC = 30:35:35 can be used.

[0368] EC is a cyclic carbonate and has a high relative dielectric constant, thus having the effect of promoting the dissociation of lithium salts. On the other hand, since EC has a high viscosity and a high freezing point (melting point) of 38 °C, it is difficult to use EC alone as an organic solvent in a low-temperature environment. Therefore, as one aspect of the present invention, the organic solvent specifically described may contain not only EC but also EMC and DMC. EMC is a chain carbonate, which has the effect of lowering the viscosity of the electrolyte and has a freezing point of -54 °C. Also, DMC is a chain carbonate, which has the effect of lowering the viscosity of the electrolyte and has a freezing point of -43 °C. An electrolyte prepared using an organic solvent obtained by mixing EC, EMC, and DMC having such physical properties with the total content of these three organic solvents being 100 vol% and the volume ratio being x:y:100 - x - y (where 5 ≤ x ≤ 35 and 0 < y < 65) preferably has a freezing point of -40 °C or lower.

[0369] In addition, by using one or more ionic liquids (room-temperature molten salts) that are flame-retardant and hardly volatile as the solvent of the electrolyte, even if the internal temperature of the secondary battery rises due to an internal short circuit or overcharging of the secondary battery, rupture or ignition of the secondary battery can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions.

[0370] Also, examples of the salt dissolved in the above solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), and LiN(C2F5SO2)2 can be used individually or in any combination and ratio of two or more of these salts.

[0371] For secondary batteries, it is preferable to use a highly purified electrolyte with a low content of granular debris or elements other than the constituent elements of the electrolyte (hereinafter also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0372] Furthermore, additives such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the added material should be, for example, 0.1 wt% to 5 wt% relative to the total solvent. VC or LiBOB are particularly preferred because they readily form a good film.

[0373] A solution containing a solvent and a salt that acts as a carrier ion is sometimes called an electrolyte.

[0374] A polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may also be used.

[0375] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0376] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide-based gels, polypropylene oxide-based gels, fluorine-based polymer gels, and the like can be used.

[0377] 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, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The resulting polymer may also have a porous structure.

[0378] Furthermore, a solid electrolyte containing inorganic materials can be used as the electrolyte. For example, sulfide-based solid electrolytes, oxide-based solid electrolytes, halide-based solid electrolytes, etc., can be used. In addition, a solid electrolyte containing polymer materials such as PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of separators and spacers becomes unnecessary. Moreover, since the entire battery can be solidified, the risk of leakage is eliminated, and safety is dramatically improved.

[0379] Sulfide-based solid electrolytes include thiolysicone-based (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 Li 3.25 P 0.95 It contains S4, etc. Sulfide-based solid electrolytes have advantages such as the availability of materials with high conductivity, the ability to be synthesized at low temperatures, and their relatively soft nature which helps maintain conductive paths even after charging and discharging.

[0380] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (La 2 / 3-x Li 3x Materials having a NASICON-type crystal structure (Li 1-X Al X Ti 2-X (PO4)3 etc.) Materials having a garnet-type crystal structure (Li7La3Zr2O 12 Materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glass (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc. are included. Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0381] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, and LiI. Furthermore, composite materials in which these halide-based solid electrolytes are packed into the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0382] Alternatively, different solid electrolytes may be mixed and used.

[0383] In particular, Li has a NASICON-type crystal structure. 1+x Al x Ti 2-x (PO4)3(0[x[1])(hereinafter referred to as LATP) contains aluminum and titanium, which are elements that may be present in the positive electrode active material used in one embodiment of the present invention, and is therefore preferable because a synergistic effect on improving cycle characteristics can be expected. Furthermore, an improvement in productivity can be expected by reducing the number of processes. In this specification, the NASICON type crystal structure refers to a compound represented as M2(AO4)3 (M: transition metal, A: S, P, As, Mo, W, etc.) that has a structure in which MO6 octahedra and AO4 tetrahedra share vertices and are arranged three-dimensionally.

[0384] <Voltage of secondary battery> When a secondary battery has a compound represented by the chemical formula LiCoO2 as the positive electrode active material and 70% by weight or more of graphite as the negative electrode active material, the charging voltage of the secondary battery is preferably higher than 4.2V, and more preferably higher than 4.3V. Furthermore, the charging voltage of the secondary battery is, for example, 4.8V or less, or 4.7V or less, or 4.65V or less.

[0385] When a secondary battery has a compound represented by the chemical formula LiMO2 as the positive electrode active material, in which M is 40 mol% or more nickel, and graphite as the negative electrode active material, the charging voltage of the secondary battery is preferably higher than 4.1V, and more preferably higher than 4.2V. Furthermore, the charging voltage of the secondary battery is, for example, 4.8V or less, or 4.7V or less, or 4.65V or less.

[0386] <Capacity of secondary batteries> When charging is performed using a charging circuit according to one embodiment of the present invention, the charging capacity is preferably, for example, 200 mAh / g or more per unit weight of positive electrode active material, more preferably 210 mAh / g or more, and even more preferably 215 mAh / g or more (at 45°C and a charging rate of 0.5C).

[0387] This embodiment can be appropriately combined with descriptions of other embodiments.

[0388] (Embodiment 3) This embodiment describes an example of a secondary battery configuration to which a secondary battery management system according to one aspect of the present invention can be applied.

[0389] <Laminated rechargeable battery> Figure 14 shows an example of the external view of a laminate-type secondary battery 121. Figure 14 shows a positive electrode layer 106, a negative electrode layer 107, a separator 103, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0390] <Method for manufacturing laminated rechargeable batteries> An example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 14, will be explained using Figures 15A to 15C.

[0391] Figure 15A shows the external view of the positive electrode layer 106 and the negative electrode layer 107. The positive electrode layer 106 has a configuration in which a positive electrode active material layer is formed on the positive electrode current collector. The positive electrode layer 106 also has a region in which the positive electrode current collector is partially exposed (hereinafter referred to as the tab region), and a positive electrode tab 501 is provided in this region. The negative electrode layer 107 has a configuration in which a negative electrode active material layer is formed on the negative electrode current collector. The negative electrode layer 107 also has a region in which the negative electrode current collector is partially exposed, i.e., the tab region, and a negative electrode tab 504 is provided in this region.

[0392] As shown in Figure 15B, the negative electrode layer 107, separator 103, and positive electrode layer 106 are stacked. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. Next, the tab regions of the positive electrode layer 106 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode layer 107 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0393] Next, as shown in Figure 15C, the laminate shown in Figure 15B is placed on the outer casing 509, and the outer casing 509 is folded at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is bonded together. The area used for bonding is referred to as the bonded area. For bonding, for example, heat compression bonding may be used.

[0394] Next, the electrolyte can be injected into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 121 can be manufactured.

[0395] This embodiment can be used in combination with other embodiments.

[0396] (Embodiment 4) This embodiment describes an example of the configuration of a secondary battery as described in the previous embodiment.

[0397] For example, the laminated secondary battery 121 described above can be bent. In other words, the secondary battery 121 is flexible.

[0398] Figure 16A shows a bent secondary battery 121. Figure 16A shows a secondary battery 121 having a positive electrode layer 106, a separator 103, and a negative electrode layer 107, bent toward the positive electrode layer 106. Of course, the secondary battery 121 can also have a bent shape toward the negative electrode layer 107. Note that a bent shape includes a shape in which one cross-section of the secondary battery 121 has an arc-shaped portion.

[0399] Although the casing is not shown in Figure 16A, the secondary battery 121 also has a casing. The casing described in the above embodiment can conform to a curved shape.

[0400] Next, we will describe the bent state in detail. As shown in Figure 16A, in the secondary battery 121, the radius of curvature 1802 of the layer closer to the center of curvature 1800, for example, the positive electrode layer 106, is smaller than the radius of curvature 1804 of the layer further away from the center of curvature 1800, for example, the negative electrode layer 107. To make it easier to bend, it is preferable to make the thickness of the layer with a smaller radius of curvature, for example, the positive electrode layer 106, smaller than that of the negative electrode layer 107.

[0401] As shown in Figure 16B, when the secondary battery 121 is bent as in Figure 16A, compressive stress is applied to the surface of the positive electrode layer 106 and tensile stress is applied to the surface of the negative electrode layer 107, as indicated by the arrows. To alleviate the compressive stress, the layer with a smaller radius of curvature, such as the positive electrode layer 106, may be made thicker than the negative electrode layer 107.

[0402] As one way to alleviate the compressive and tensile stresses mentioned above, a configuration in which recesses and protrusions are provided on the exterior body will be explained using Figures 17A and 17B.

[0403] The recesses and protrusions are formed on the surface of the exterior body 1805, creating a pattern-like appearance. As can be seen in one cross-section of the exterior body 1805, when protrusions are provided on the exterior body, recesses are also formed simultaneously, and when recesses are provided on the exterior body, protrusions are also formed simultaneously. In other words, it is not necessary to provide both recesses and protrusions on the exterior body; providing one will simultaneously provide the other.

[0404] The outer casing 1805 can alleviate the compressive and tensile stresses mentioned above. In other words, the secondary battery 121 can be deformed within a range where the radius of curvature of the outer casing on the side closer to the center of curvature is 30 mm or more, preferably 10 mm or more.

[0405] The ends of the outer casing 1805 shown in Figures 17A and 17B have adhesive regions 1807. The adhesive region 1807 is the area where the outer casing 1805 is bonded by heat compression or the like. In the adhesive region 1807, an adhesive layer 1803 is preferably located between the outer casing 1805.

[0406] In the bonding region 1807, it is preferable that the recesses or protrusions provided on the upper and lower parts of the outer casing 1805 overlap. To ensure that the recesses or protrusions overlap, recesses or protrusions may be formed on the outer casing 1805 again when bonding the outer casing. This configuration can increase the bonding strength.

[0407] Figure 17A shows the secondary battery 121, where the end portion of the outer casing 1805, region 1808 (which is not the adhesive region 1807), has a space 1810.

[0408] In Figure 17B, the end portion of the outer casing 1805, region 1808 which is not the adhesive region 1807, represents the secondary battery 121 containing the electrolyte 108. Due to the high adhesive strength of the outer casing 1805, the electrolyte 108 will not leak out of the outer casing 1805. Note that in Figure 17B, region 1808 may have a space if it is not filled with the electrolyte 108.

[0409] The shape of the curved secondary battery 121 is not limited to a simple arc shape in cross-sectional view, but may also be a shape in which a part is an arc.

[0410] This embodiment can be used in combination with other embodiments.

[0411] (Embodiment 5) In this embodiment, an example of the application of a secondary battery management system according to one aspect of the present invention will be explained with reference to Figures 18 to 23.

[0412] In the following application examples, the secondary battery management system preferably has a charging circuit according to one aspect of the present invention. The charging circuit according to one aspect of the present invention preferably has the components of the charging circuit described in the earlier embodiment. Furthermore, the charging circuit according to one aspect of the present invention may have a circuit that has the function of converting the voltage, current, etc. of the supplied power. Examples of circuits that have the function of converting the voltage, current, etc. of power include a regulator, a step-down circuit, a step-up circuit, a circuit that has the function of converting AC power to DC power, a modulation circuit, a demodulation circuit, an amplification circuit, and the like.

[0413] [vehicle] First, we will show an example of applying a secondary battery management system according to one aspect of the present invention to an electric vehicle (EV).

[0414] Figure 18 shows a block diagram of a vehicle with a motor. The electric vehicle is equipped with a first battery 1301a, 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the 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 require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a, 1301b.

[0415] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0416] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and this is provided in the first battery 1301a.

[0417] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V (high-voltage) onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0418] Furthermore, the second battery 1311 supplies power to 14V (low-voltage) in-vehicle components (audio 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0419] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to their cost advantages.

[0420] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor.

[0421] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and used to charge the second battery 1311 from the motor controller 1303 or the battery controller 1302. Alternatively, it can be used to charge the first battery 1301a from the battery controller 1302 via the control circuit unit 1321, or to charge the first battery 1301b from the battery controller 1302 via the control circuit unit 1321. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0422] 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 the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0423] A charging circuit according to one embodiment of the present invention can be used as the battery controller 1302. A circuit having a function for converting power voltage, current, etc., may be provided between the motor 1304 and the battery controller 1302. By using a charging circuit according to one embodiment of the present invention as the battery controller 1302, the charging capacity of the first batteries 1301a and 1301b can be increased while also improving the reliability of the first batteries 1301a and 1301b. Because the charging capacity of the first batteries 1301a and 1301b can be increased, the driving range of the electric vehicle can be extended. Furthermore, because the degradation of the first batteries 1301a and 1301b can be suppressed, the frequency of battery replacement in the electric vehicle can be reduced. Additionally, because the reliability of the first batteries 1301a and 1301b can be improved, the safety of the electric vehicle can be enhanced.

[0424] Next, an example of implementing a secondary battery management system according to one aspect of the present invention in a vehicle, typically a transport vehicle, will be described.

[0425] By installing a secondary battery management system according to one aspect of the present invention in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Furthermore, secondary batteries can also be installed in agricultural machinery such as electric tractors, motorized bicycles including electric assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing or rotary-wing aircraft, rockets, satellites, space probes or planetary probes, and other transport vehicles. By using the secondary battery manufacturing method according to one aspect of the present invention, large secondary batteries can be produced. Therefore, the secondary battery according to one aspect of the present invention is suitably used in transport vehicles.

[0426] Figures 19A to 19E show a transport vehicle using a secondary battery management system according to one embodiment of the present invention. The automobile 2001 shown in Figure 19A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on a vehicle, the secondary battery is installed in one or more locations. The automobile 2001 shown in Figure 19A has a secondary battery management system according to one embodiment of the present invention. The secondary battery management system includes a charging circuit according to one embodiment of the present invention and a first battery 1301a shown in Figure 18. The secondary battery management system may also have a plurality of secondary batteries connected in series as a battery pack. This battery pack is electrically connected to the charging circuit according to one embodiment of the present invention.

[0427] Furthermore, the secondary battery management system of the vehicle 2001 can receive power from an external power supply facility via a plug-in system or a contactless power supply system. For power supply, a connector standard and power supply method such as CHAdeMO® or Combo can be used. Power may be supplied from a charging station installed in a commercial facility, or from a household power supply.

[0428] In a charging circuit according to one aspect of the present invention, if it is determined that charging should be stopped, a signal to the charging station to stop charging can be sent via the control circuit of the charging circuit according to one aspect of the present invention. Alternatively, the charging circuit according to one aspect of the present invention may be applied to a charging station. For example, the charging station may have at least some of the components of the charging circuit according to one aspect of the present invention, such as the control circuit of the charging circuit according to one aspect of the present invention.

[0429] Furthermore, it is preferable that the automobile 2001 has a function to convert AC power to 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 secondary battery management system.

[0430] Although not shown in the diagram, a power receiving device can be mounted on the vehicle, allowing it to receive power wirelessly from a ground-based power transmission device. In this wireless power supply system, by incorporating the power transmission device into the road or exterior wall, power can be received not only when the vehicle is stopped but also while it is in motion. Furthermore, this wireless power supply system can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to receive power when it is stopped or in motion. For such wireless power supply, electromagnetic induction or magnetic resonance methods can be used.

[0431] Figure 19B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a voltage of 3.5V to 4.7V. The secondary battery management system 2201 includes a charging circuit according to one aspect of the present invention and a secondary battery module. Except for differences in the number of secondary batteries constituting the secondary battery module, it has the same functions as Figure 19A, so a detailed explanation is omitted.

[0432] Figure 19C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The transport vehicle 2003 has a secondary battery management system 2202. The secondary battery management system 2202 includes a charging circuit according to one embodiment of the present invention and a secondary battery module. The secondary battery module has a maximum voltage of 600V, for example, by connecting 100 or more secondary batteries with voltages of 3.5V to 4.7V in series. Except for differences in the number of secondary batteries constituting the secondary battery module, it has the same functions as Figure 19A, so the explanation is omitted.

[0433] Figure 19D shows an aircraft 2004 having a fuel-burning engine as an example. The aircraft 2004 shown in Figure 19D has wheels for takeoff and landing, and can therefore be considered part of a transport vehicle. It has a secondary battery management system 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging circuit according to one aspect of the present invention.

[0434] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery management system 2203 has the same functions as Figure 19A, except for differences in the number of secondary batteries that make up the secondary battery module, so the explanation is omitted.

[0435] Figure 19E shows a transport vehicle 2005 for transporting cargo as an example. The transport vehicle 2005 has a secondary battery management system 2204. The secondary battery management system 2204 has a charging circuit and a secondary battery module according to one aspect of the present invention. The transport vehicle 2005 has an electrically controlled motor and performs various tasks by receiving power from the secondary battery constituting the secondary battery module of the secondary battery management system 2204. Furthermore, the transport vehicle 2005 is not limited to being driven and operated by a human; unmanned operation is also possible via CAN communication or the like. Figure 19E illustrates a forklift, but is not particularly limited, and a secondary battery management system according to one aspect of the present invention can be installed on industrial machinery that can be operated via CAN communication or the like, such as automated transport machines, work robots, or small construction machinery.

[0436] [Buildings] Next, an example of implementing a secondary battery management system according to one aspect of the present invention in a building will be described using Figures 20A and 20B.

[0437] The house shown in Figure 20A has a secondary battery management system 2612 and solar panels 2610. The secondary battery management system 2612 has, for example, a battery pack consisting of multiple secondary batteries. The secondary battery management system 2612 is electrically connected to the solar panels 2610 via wiring 2611, etc.

[0438] The secondary battery management system 2612 has a charging circuit according to one aspect of the present invention. Power obtained from the solar panel 2610 can be used to charge the secondary battery management system 2612 via the charging circuit.

[0439] Furthermore, the secondary battery management system 2612 and the ground-mounted charging device 2604 may be electrically connected. In the charging circuit of the secondary battery management system 2612, if it is determined that charging should be stopped, a signal to stop charging can be sent to the charging device 2604 via the control circuit of the charging circuit. Alternatively, a charging circuit according to one aspect of the present invention may be applied to the charging device 2604. For example, the charging device 2604 may have at least some of the components of the charging circuit according to one aspect of the present invention, for example, the control circuit of the charging circuit according to one aspect of the present invention.

[0440] The power stored in the secondary battery management system 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The secondary battery management system 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the secondary battery management system 2612 may be installed on the floor.

[0441] The power stored in the secondary battery management 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 other reasons, the secondary battery management system 2612 can be used as an uninterruptible power supply, making it possible to use electronic devices.

[0442] Figure 20B shows an example of a secondary battery management system according to one aspect of the present invention. As shown in Figure 20B, a secondary battery management system 791 having a large secondary battery and a charging circuit according to one aspect of the present invention is installed in the underfloor space 796 of the building 799.

[0443] The secondary battery management system 791 includes a control unit 790, which is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control unit), the display unit 706, and the router 709.

[0444] Power is supplied from the commercial power supply 701 to the distribution panel 703 via the service drop connection section 710. Power is also supplied to the distribution panel 703 from the secondary battery management system 791 and the commercial power supply 701, and the distribution panel 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0445] The general load 707 is, for example, an electronic device such as a television or a personal computer, and the energy storage load 708 is, for example, an electronic device such as a microwave oven, refrigerator, or air conditioner.

[0446] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during a day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the secondary battery management system 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during the day. The planning unit 713 has the function of planning the charging and discharging of the secondary battery management system 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0447] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked on electronic devices such as televisions or personal computers via the router 709. Furthermore, it can be checked on mobile electronic devices such as smartphones or tablets via the router 709. Additionally, the amount of electricity demand predicted by the forecasting unit 712 for each time period (or hourly) can be checked on the display unit 706, electronic devices, and mobile electronic devices.

[0448] [Electronic equipment] A secondary battery according to one aspect of the present invention can be used, for example, in either or both electronic devices and lighting devices. Examples of electronic devices include mobile phones, smartphones, or notebook computers, portable game consoles, portable music players, digital cameras, and digital video cameras.

[0449] Figure 21A shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 built into the 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 has a secondary battery management system. The secondary battery management system includes a secondary battery 7407 and a charging circuit 7408 electrically connected to the secondary battery 7407. The charging circuit 7408 can receive power from an external power source via the external connection port 7404. For example, power is supplied to the external connection port 7404 from an AC adapter. The AC adapter has the function of converting AC power to DC power and supplying it to the external connection port 7404. Alternatively, the mobile phone 7400 may have the function of converting AC power to DC power via a conversion circuit such as an AC-DC converter. Furthermore, the charging circuit 7408 may have a circuit that converts AC power to DC power.

[0450] Furthermore, power may be supplied to the mobile phone 7400 from an external power source via wireless power transfer. The Qi standard or similar may be used as the wireless power transfer standard. The signal transmitted to the mobile phone 7400 via wireless power transfer is provided to the charging circuit 7408, for example, via a demodulation circuit or the like. Alternatively, the charging circuit 7408 may have circuits for wireless communication, such as a modulation circuit, a demodulation circuit, etc.

[0451] By having a charging circuit according to one embodiment of the present invention as the charging circuit 7408 of the mobile phone 7400, the safety of the mobile phone 7400 can be enhanced. Furthermore, since the discharge energy density of the secondary battery can be increased, the volume and weight of the secondary battery can be reduced, making the mobile phone 7400 smaller and lighter. In addition, since the lifespan of the secondary battery can be extended, the mobile phone 7400 can be used for a long time without replacing the secondary battery.

[0452] Furthermore, since the charging circuit according to one aspect of the present invention combines the functions of a charging control circuit and a protection circuit, it is possible to reduce the area or number of chips in the mobile phone 7400. Therefore, the mobile phone 7400 can be made smaller and lighter, and its reliability can be improved.

[0453] Figure 21B shows the mobile phone 7400 in a curved state. When the mobile phone 7400 is deformed by an external force and the entire device is curved, the secondary battery 7407 located inside it is also curved.

[0454] Figure 21C shows an example of a bangle-type display device. The portable display device 7100 comprises a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery management system. The secondary battery management system includes a secondary battery 7104 and a charging circuit 7105 electrically connected to the secondary battery 7104. When the secondary battery 7104 in the secondary battery management system is worn on the user's arm in a bent state, the housing deforms, causing a change in the curvature of part or all of the secondary battery 7104. The degree of curvature at any point in the curve is expressed as the radius of the corresponding circle, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or secondary battery changes within the range of radius of curvature of 40 mm to 150 mm. High reliability can be maintained as long as the radius of curvature on the main surface of the secondary battery is within the range of 40 mm to 150 mm.

[0455] Figure 21D shows an example of a wristwatch-type personal information terminal. The personal information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

[0456] The 7200 personal digital assistant (PDCA) can run various applications such as mobile phone calls, email, document viewing and creation, music playback, internet communication, and computer games.

[0457] The display unit 7202 has a curved display surface, allowing it to display information along the curved surface. The display unit 7202 also features a touch sensor, allowing it to be operated by touching the screen with a finger or stylus. For example, touching the icon 7207 displayed on the display unit 7202 can launch an application.

[0458] The operation button 7205 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 7205 can be freely configured by the operating system built into the personal digital assistant 7200.

[0459] Furthermore, the 7200 portable information terminal is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless-enabled headset to enable hands-free calling.

[0460] Furthermore, the portable information terminal 7200 is equipped with an input / output terminal 7206, allowing it to directly exchange data with other information terminals via a connector. It can also be charged via the input / output terminal 7206. Note that charging may also be performed wirelessly without using the input / output terminal 7206.

[0461] The display unit 7202 of the portable information terminal 7200 has a secondary battery management system. Furthermore, the secondary battery 7104 and charging circuit 7105 shown in Figure 21C can be incorporated inside the housing 7201 in a curved state, or inside the band 7203 in a bendable state.

[0462] The portable information terminal 7200 preferably has sensors. Preferably, the sensors include, for example, a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0463] Figure 21E shows an example of an armband-type display device. The display device 7300 includes a display unit 7304 and a secondary battery management system. The secondary battery 7104 and charging circuit 7105 shown in Figure 21C can be incorporated into the display device 7300. The display device 7300 can also be equipped with a touch sensor on the display unit 7304 and can function as a portable information terminal.

[0464] The display unit 7304 has a curved display surface, allowing it to display information along the curved surface. Furthermore, the display device 7300 can change its display status via standardized short-range wireless communication.

[0465] Furthermore, the display device 7300 is equipped with input / output terminals, allowing it to directly exchange data with other information terminals via connectors. It can also be charged via the input / output terminals. Note that charging may also be performed wirelessly without using the input / output terminals.

[0466] Figure 22A shows an example of a wearable device. The wearable device uses a secondary battery management system as its power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when the user uses the device in their daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging with an exposed connector.

[0467] For example, a secondary battery management system according to one aspect of the present invention can be mounted on a spectacle-type device 9000 as shown in Figure 22A. The spectacle-type device 9000 has a frame 9000a and a display unit 9000b. By mounting the secondary battery management system on the temple portion of the curved frame 9000a, a lightweight spectacle-type device 9000 with good weight balance and long continuous use time can be achieved. By incorporating a secondary battery management system according to one aspect of the present invention, the energy density of the secondary battery management system can be increased, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0468] Furthermore, a secondary battery management system according to one aspect of the present invention can be mounted on the headset-type device 9001. The headset-type device 9001 has at least a microphone section 9001a, a flexible pipe 9001b, and an earphone section 9001c. The secondary battery management system can be provided in the flexible pipe 9001b or in the earphone section 9001c. By incorporating a secondary battery management system according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0469] Furthermore, a secondary battery management system according to one aspect of the present invention can be mounted on a device 9002 that can be directly attached to the body. The secondary battery management system 9002b can be provided within the thin housing 9002a of the device 9002. By incorporating the secondary battery management system according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0470] Furthermore, a secondary battery management system according to one aspect of the present invention can be mounted on a device 9003 that can be attached to clothing. The secondary battery management system 9003b can be provided within the thin housing 9003a of the device 9003. By incorporating a secondary battery management system according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0471] Furthermore, a secondary battery management system according to one aspect of the present invention can be mounted on the belt-type device 9006. The belt-type device 9006 has a belt section 9006a and a wireless power supply / receiving section 9006b, and the secondary battery management system can be mounted inside the belt section 9006a. By incorporating a secondary battery management system according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0472] Furthermore, a secondary battery management system according to one aspect of the present invention can be mounted on the wristwatch-type device 9005. The wristwatch-type device 9005 has a display unit 9005a and a strap unit 9005b, and the secondary battery management system can be provided on either the display unit 9005a or the strap unit 9005b. By incorporating a secondary battery management system according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0473] The display unit 9005a can display not only the time, but also various other information such as incoming emails and phone calls.

[0474] Furthermore, since the wristwatch-type device 9005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, and manage their health.

[0475] Figure 22B shows a perspective view of the wristwatch-type device 9005 after it has been removed from the arm.

[0476] A side view is also shown in Figure 22C. Figure 22C shows how a secondary battery management system 913 according to one embodiment of the present invention is built into the interior. The secondary battery management system 913 is located in a position that overlaps with the display unit 9005a, and is small and lightweight.

[0477] Figure 23A shows an example of a cleaning robot. The cleaning robot 9300 has a display unit 9302 located on the top surface of the housing 9301, multiple cameras 9303 located on the sides, a brush 9304, operation buttons 9305, a secondary battery management system 9306, and various sensors. Although not shown, the cleaning robot 9300 is equipped with wheels, a suction port, etc. The cleaning robot 9300 is self-propelled, can detect dirt 9310, and can suck up the dirt from a suction port located on the bottom surface.

[0478] For example, the cleaning robot 9300 can analyze images captured by the camera 9303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that could become entangled in the brush 9304, such as wiring, the rotation of the brush 9304 can be stopped. The cleaning robot 9300 is equipped with a secondary battery management system 9306 according to one aspect of the present invention and a semiconductor device or electronic component. By using the secondary battery management system 9306 according to one aspect of the present invention in the cleaning robot 9300, the cleaning robot 9300 can be made into a highly reliable electronic device with a long operating time.

[0479] Figure 23B shows an example of a robot. The robot 9400 shown in Figure 23B is equipped with a secondary battery management system 9409, an illuminance sensor 9401, a microphone 9402, an upper camera 9403, a speaker 9404, a display unit 9405, a lower camera 9406 and an obstacle sensor 9407, a movement mechanism 9408, a computing device, and the like.

[0480] Microphone 9402 has the function of detecting the user's voice and ambient sounds. Speaker 9404 has the function of emitting sound. Robot 9400 can communicate with the user using microphone 9402 and speaker 9404.

[0481] The display unit 9405 has the function of displaying various types of information. The robot 9400 can display the user's desired information on the display unit 9405. The display unit 9405 may be equipped with a touch panel. The display unit 9405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 9400, charging and data transfer can be made possible.

[0482] The upper camera 9403 and lower camera 9406 have the function of imaging the area around 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 its surrounding environment and move safely using the upper camera 9403, lower camera 9406 and obstacle sensor 9407.

[0483] The robot 9400 is equipped with a secondary battery management system 9409 according to one aspect of the present invention and a semiconductor device or electronic components. By using the secondary battery management system according to one aspect of the present invention in the robot 9400, the robot 9400 can be made into an electronic device with a long operating time and high reliability.

[0484] Figure 23C shows an example of an aircraft. The aircraft 9500 shown in Figure 23C has a propeller 9501, a camera 9502, and a secondary battery management system 9503, and is capable of autonomous flight.

[0485] For example, image data captured by camera 9502 is stored in electronic component 9504. Electronic component 9504 can analyze the image data and detect the presence or absence of obstacles during movement. Furthermore, electronic component 9504 can estimate the remaining battery level from the change in the storage capacity of the secondary battery management system 9503. The aircraft 9500 is equipped with a secondary battery management system 9503 according to one aspect of the present invention. By using the secondary battery management system according to one aspect of the present invention in the aircraft 9500, the aircraft 9500 can be made into an electronic device with a long operating time and high reliability.

[0486] Figure 23D shows an example of satellite 6800. Satellite 6800 consists of a body 6801, a solar panel 6802, an antenna 6803, and a secondary battery 6805. The solar panel is sometimes called a solar cell module.

[0487] When sunlight shines on the solar panel 6802, the power necessary for the satellite 6800 to operate is generated. However, in situations where, for example, the solar panel is not exposed to sunlight, or the amount of sunlight shining on the solar panel is low, the amount of power generated will decrease. Therefore, there is a possibility that the power necessary for the satellite 6800 to operate may not be generated. To operate the satellite 6800 even under conditions where the amount of power generated is low, it is advisable to equip the satellite 6800 with a secondary battery 6805.

[0488] It is preferable to include a secondary battery management system according to one aspect of the present invention as a system for managing the secondary battery 6805 of the artificial satellite 6800. When managing the secondary battery 6805 of the artificial satellite 6800, power to each circuit of the charging circuit may be supplied from a secondary battery or power supply device separate from the secondary battery 6805.

[0489] The secondary battery 6805 in satellite 6800 may reach a temperature roughly equivalent to that of outer space if no heaters or other components are present. To measure the temperature of the secondary battery 6805, it is sufficient to measure the temperature of the battery's casing or the enclosure in which it is sealed. Even if this temperature is roughly equivalent to that of outer space, the secondary battery management system can determine an upper voltage limit.

[0490] The satellite 6800 can generate a signal. This signal is transmitted via antenna 6803 and can be received, for example, by a receiver on the ground or another satellite. By receiving the signal transmitted by satellite 6800, the position of the receiver that received the signal can be measured, for example. Thus, satellite 6800 can constitute, for example, a satellite positioning system.

[0491] Alternatively, the satellite 6800 can be configured to include sensors. For example, by configuring it to include a visible light sensor, the satellite 6800 can have the function of detecting sunlight reflected off objects on the ground. Alternatively, by configuring it to include a thermal infrared sensor, the satellite 6800 can have the function of detecting thermal infrared radiation emitted from the Earth's surface. Thus, the satellite 6800 can function, for example, as an Earth observation satellite.

[0492] This embodiment can be implemented in appropriate combination with other embodiments. [Examples]

[0493] In this embodiment, battery characteristic data for a secondary battery using graphite as the negative electrode is shown. The secondary battery management system 100 can detect the maximum value in this battery characteristic data.

[0494] <Fabrication of positive electrode active material> The positive electrode active material was prepared.

[0495] As the lithium cobalt oxide (LiCoO2) in step S14 shown in Figure 12, commercially available lithium cobalt oxide without any particular additives (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.) was prepared.

[0496] Lithium cobalt oxide was heated at 850°C for 2 hours in an oxygen atmosphere according to step S15 shown in Figure 12. The oxygen atmosphere was designed to prevent oxygen from entering or leaving the reaction chamber.

[0497] According to step S20a shown in Figure 12, source A1 was prepared as the additive element source. Source A1 consisted of lithium fluoride and magnesium fluoride, weighed in a ratio of lithium fluoride:magnesium fluoride = 1:3 (molar ratio). These were mixed to obtain the mixture that constitutes source A1. This mixture may be called the magnesium source or the fluorine source.

[0498] Next, the magnesium source was weighed so that the amount of magnesium in the magnesium source was 1 at% of the cobalt in the lithium cobalt oxide. Then, according to step S31 shown in Figure 12, the heated lithium cobalt oxide and the magnesium source were mixed to obtain the mixture 903 shown in step S32 in Figure 12. This mixture 903 is denoted as mixture A.

[0499] Next, following step S33 shown in Figure 12, mixture A was heated at 900°C for 20 hours in an oxygen atmosphere. The oxygen atmosphere was designed to prevent oxygen from entering or leaving the reaction chamber. The composite oxide obtained in step S34a, shown in Figure 12, was then described as composite oxide A.

[0500] Next, according to step S40 shown in Figure 12, source A2 was prepared as the additive element source. Source A2 consisted of nickel hydroxide as the nickel source and aluminum hydroxide as the aluminum source. The nickel in the nickel hydroxide was weighed so that it was 0.5 at% of the cobalt in composite oxide A, and the aluminum in the aluminum hydroxide was weighed so that it was 0.5 at% of the cobalt in composite oxide A. These were then mixed with composite oxide A to obtain mixture 904 as shown in step S52 in Figure 12. This mixture 904 is referred to as mixture B.

[0501] Next, following step S53 shown in Figure 12, mixture B was heated at 850°C for 10 hours in an oxygen atmosphere to obtain the positive electrode active material 10 shown in step S54 in Figure 12. This positive electrode active material 10 is denoted as sample Sa1.

[0502] <Fabrication of the positive electrode> Sample Sa1, acetylene black (AB), polyvinylidene fluoride (PVDF), and NMP were mixed to prepare a slurry. The ratio of Sample Sa1, AB, and PVDF was set to Sample Sa1:AB:PVDF = 95:3:2 (weight ratio).

[0503] The prepared slurry was applied to one side of an aluminum foil serving as a current collector. Then, heating was performed at 80 °C to volatilize the solvent. Pressing was performed after heating to obtain a positive electrode.

[0504] <Fabrication of Negative Electrode> Graphite, VGCF (registered trademark)-H (manufactured by Showa Denko K.K., fiber diameter 150 nm, specific surface area 13 m 2 / g), carboxymethyl cellulose sodium salt (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed to prepare a slurry. The ratio of graphite, VGCF, CMC-Na, and SBR was set to graphite:VGCF:CMC-Na:SBR = 96:1:1:2 (weight ratio).

[0505] The prepared slurry was applied to one side of a copper foil serving as a current collector. Then, heating was performed at 50 °C to obtain a negative electrode.

[0506] <Fabrication of Secondary Battery> A secondary battery was fabricated using the positive electrode and negative electrode fabricated above. The electrolyte contained ethylene carbonate (EC) and diethyl carbonate (DEC) as organic solvents. When the total content of EC and DEC was 100 vol%, the volume ratio of EC and DEC was EC:DEC = 30:70 (volume ratio). Lithium hexafluorophosphate (LiPF6) dissolved to a concentration of 1 mol / L in this organic solvent was used as the electrolyte. Polypropylene was used as the separator. A film serving as the exterior, which was 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.

[0507] A secondary battery was fabricated through the above steps.

[0508] < / soc> < / dq> A charge-discharge cycle test was conducted on a secondary battery manufactured at a temperature of -20°C. Specifically, the casing of the secondary battery was sandwiched between metal plates, a temperature sensor was attached to the metal plates, and the device was placed in a constant temperature chamber. The chamber temperature was set to -20°C, and the charge-discharge cycle test was started after the temperature sensor indicated -20°C. For charging, only constant current charging at 0.1C (1C = 40mA / h) was performed; constant voltage charging was not performed. The upper limit voltage for constant current charging was set to 5V, and for discharging, constant current discharge at 0.1C was performed, with the lower limit voltage for constant current charging set to 2V. A rest period of 5 to 15 minutes may be provided between charging and discharging; in this charge-discharge cycle test, a 10-minute rest period was provided. The ambient temperature during the rest period was also -20°C.

[0509] Figure 24 shows a graph relating to the voltage change of the secondary battery over time. The secondary battery management system 100 can obtain the above graph using the control circuit etc. shown in the above embodiment.

[0510] If a local maximum is observed in the graph shown in Figure 24, the control circuit can detect this local maximum.

[0511] In this embodiment, since no clear maximum value was observed in the graph shown in Figure 24, the control circuit performs the following process. Specifically, the rate of change was calculated as shown in Figure 25. Considering the upper limit voltage in constant current charging in this embodiment, voltages below 4.5V can be ignored. Also, it can be seen from Figure 24 that a voltage of 4.5V corresponds to a time of 29,000 seconds. Therefore, Figure 25 shows the rate of change for times greater than 29,000 seconds. In the graph shown in Figure 25, a maximum value was observed at the point indicated by the arrow. When this maximum value is detected, the control circuit can stop charging. [Explanation of symbols]

[0512] 10: Positive electrode active material, 100A: Secondary battery management system, 100B: Secondary battery management system, 100: Secondary battery management system, 101: Charging circuit, 103: Separator, 106: Positive electrode layer, 107: Negative electrode layer, 108: Electrolyte, 121: Secondary battery, 122: Resistor element, 123: Resistor element, 124: Terminal, 125: Terminal, 140: Transistor, 150: Transistor, 151: Voltage measurement circuit, 152: Current measurement circuit, 153: Control circuit, 154: Memory circuit, 156: Temperature sensor, 161: Differential, 185: Detection circuit, 186: Detection circuit, 200: Secondary battery management System, 300: Hold circuit, 301: Comparator, 302: DA converter, 303: Comparison register, 304: Second control circuit, 305: Clock generation circuit, 501: Positive tab, 504: Negative tab, 509: Enclosure, 510: Positive lead electrode, 511: Negative lead electrode, 701: Commercial power supply, 703: Distribution board, 705: Energy storage controller, 706: Display unit, 707: General load, 708: Energy storage system load, 709: Router, 710: Service drop connection section, 711: Measurement section, 712: Prediction section, 713: Planning section, 790: Control device, 791: Secondary battery management system, 79 6: Underfloor space, 799: Building, 903: Mixture, 904: Mixture, 913: Secondary battery management system, 1301a: First battery, 1301b: First battery, 1302: Battery controller, 1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DC-DC circuit, 1307: Electric power steering, 1308: Heater, 1309: Defogger, 1310: DC-DC circuit, 1311: Second battery, 1312: Inverter, 1313: Audio, 1314: Power windows, 1315: Lights, 1316: Tires, 131 7: Rear motor, 1321: Control circuit unit, 1800: Center of curvature, 1803: Adhesive layer, 1805: Outer body, 1807: Adhesive area, 1808: Area, 1810: Space, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2005: Transport vehicle, 2201: Secondary battery management system, 2202: Secondary battery management system, 2203: Secondary battery management system, 2204: Secondary battery management system, 2603: Vehicle, 2604: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Secondary battery management system, 6800: Artificial satellite,6801: Aircraft, 6802: Solar panel, 6803: Antenna, 6805: Rechargeable battery, 7100: Portable display device, 7101: Housing, 7102: Display unit, 7103: Operation buttons, 7104: Rechargeable battery, 7105: Charging circuit, 7200: Portable information terminal, 7201: Housing, 7202: Display unit, 7203: Band, 7204: Buckle, 7205: Operation buttons, 7206: Input / output terminal, 7207: Icon, 7300: Display device, 7304 : Display unit, 7400: Mobile phone, 7401: Housing, 7402: Display unit, 7403: Operation buttons, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Rechargeable battery, 7408: Charging circuit, 9000a: Frame, 9000b: Display unit, 9000: Glasses-type device, 9001a: Microphone unit, 9001b: Flexible pipe, 9001c: Earphone unit, 9001: Headset-type device, 9002a: Housing 9002b: Secondary battery management system, 9002: Device, 9003a: Housing, 9003b: Secondary battery management system, 9003: Device, 9005a: Display unit, 9005b: Belt unit, 9005: Wristwatch-type device, 9006a: Belt unit, 9006b: Wireless power supply / receiving unit, 9006: Belt-type device, 9300: Cleaning robot, 9301: Housing, 9302: Display unit, 9303: Camera, 9304: Brush, 9305: Operation Button, 9306: Secondary battery management system, 9310: Trash, 9400: Robot, 9401: Illuminance sensor, 9402: Microphone, 9403: Upper camera, 9404: Speaker, 9405: Display unit, 9406: Lower camera, 9407: Obstacle sensor, 9408: Movement mechanism, 9409: Secondary battery management system, 9500: Aircraft, 9501: Propeller, 9502: Camera, 9503: Secondary battery management system, 9504: Electronic component,

Claims

1. A secondary battery that charges and discharges at temperatures between -50°C and 0°C, A first circuit having the function of measuring the voltage of the secondary battery, A second circuit having the function of measuring the current of the secondary battery, The system includes a control circuit that receives voltage information from the first circuit or current information from the second circuit, The control circuit records the temperature of the secondary battery in a memory circuit. The control circuit initiates charging of the secondary battery. The control circuit calculates a dt / dV value that indicates the battery characteristics according to the temperature, based on the value input from the first circuit or the second circuit. The control circuit detects the maximum value in dt / dV, The control circuit stops the charging when it detects the maximum value. Secondary battery management system.

2. In claim 1, The control circuit can perform an averaging process on the dt / dV and divide the difference between the second value and the first value of the dt / dV in the comparison range by the first value. Secondary battery management system.

3. In claim 1 or claim 2, The secondary battery has a temperature sensor that measures the temperature of the secondary battery. Secondary battery management system.

4. In claim 1 or claim 2, The aforementioned charging is performed with a constant current. Secondary battery management system.

5. In claim 1 or claim 2, The aforementioned secondary battery has a positive electrode, The positive electrode contains lithium cobalt oxide, and the crystal structure of the lithium cobalt oxide, as identified by X-ray diffraction, has a space group R-3m. Secondary battery management system.

6. In claim 5, The lithium cobalt oxide has magnesium in its surface layer. Secondary battery management system.

7. In claim 1 or claim 2, The aforementioned secondary battery has a negative electrode, The negative electrode has lithium metal or graphite. Secondary battery management system.

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