Control system

Abstract

When an environmental temperature sensor for a secondary battery senses a high temperature exceeding the maximum temperature of an acceptable range, a problem arises wherein the supply of power from the secondary battery is stopped and an electronic device becomes unusable. It has been problematic that, when the environmental temperature sensor for a secondary battery senses a high temperature, an emergency call cannot be made by the electronic device. In the present invention, a microcontroller unit (MCU, also referred to as microcomputer) for high temperature operation is provided separately from a CPU used during normal operation. When an environmental temperature sensor for a secondary battery senses a high temperature, the CPU used during normal operation is caused to transition to a deep sleep mode, and an electronic device is controlled by the MCU for high temperature operation. It should be noted that, during normal operation of the CPU, the MCU for high temperature operation is in the deep sleep mode.

Description

Control System

[0001] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. Another embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof. Another embodiment of the present invention relates to a control device or a control system for an electronic device.

[0002] In this specification, the term "power storage device" refers to all elements and devices having a power storage function, including, for example, storage batteries (also called secondary batteries) such as lithium ion secondary batteries, lithium ion capacitors, nickel-metal hydride batteries, all-solid-state batteries, and electric double layer capacitors.

[0003] 2. Description of the Related Art Electronic devices that are carried by users or worn by users have been actively developed.

[0004] Electronic devices carried by users or worn by users are both called portable information terminals. Portable information terminals operate using primary or secondary batteries, which are examples of power storage devices, as their power source. Portable information terminals are expected to be used for long periods of time, and for this reason, large-capacity secondary batteries are used. However, if a large-capacity secondary battery is built into a portable information terminal, it will be large and heavy, which is a problem. Therefore, development is underway to develop small or thin, large-capacity secondary batteries that can be built into portable information terminals.

[0005] In particular, demand for high-power, high-energy-density lithium-ion secondary batteries has rapidly expanded in conjunction with the development of the semiconductor industry, and they are now indispensable in today's information society as a repeatedly rechargeable energy source, for use in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical equipment, and next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs).

[0006] While lithium-ion secondary batteries have a large capacity, there is a risk that the temperature inside the battery may rise if abnormal heat is generated due to an internal short circuit, overcharging, or the like.

[0007] Patent Document 1 discloses a charge control circuit that detects when the ambient temperature of the battery of an electric vehicle is outside of a normal operating range and controls the temperature to within an appropriate range.

[0008] WO2020 / 084386

[0009] If the secondary battery's environmental temperature sensor detects a high temperature that exceeds the maximum allowable range, the power supply to the secondary battery will be stopped, rendering the electronic device unusable. If the secondary battery's environmental temperature sensor detects a high temperature, there is a problem that the electronic device will not be able to make emergency calls.

[0010] Global warming is causing rising outside temperatures. In addition, as portable information terminals become increasingly integrated, heat generated by IC chips within the terminals is becoming a problem. Furthermore, while portable information terminals are becoming smaller, secondary batteries with higher capacities are being demanded. Therefore, high-capacity secondary batteries are being placed close to IC chips, and both become sources of heat when the terminals are in use.

[0011] A typical example of an IC chip is the central processing unit (CPU) core, which is responsible for the main control of a mobile information terminal. As mobile information terminals become more sophisticated, CPUs have become multi-core, and graphical processing unit (GPU) cores have become larger in size, leading to the use of many components that generate heat energy. Components that generate heat energy include not only CPUs but also power amplifiers.

[0012] Depending on the load on the CPU, a heavy load can cause the CPU and other components to heat up. If the sensor detects that the secondary battery's ambient temperature is outside the allowable range due to the heat generated, the control circuit may stop supplying power. During this time, the mobile information terminal may become unusable. Therefore, if the temperature exceeds the maximum allowable temperature set by the manufacturer, the mobile information terminal may be unable to make emergency calls even if the user's life is in imminent danger due to injury. As such, the miniaturization of mobile information terminals reduces the distance between the secondary battery's ambient temperature sensor and the CPU, which can lead to malfunctions. Furthermore, if a design were to prevent malfunctions by increasing the distance between the secondary battery and the CPU, the wiring length would increase, increasing wiring resistance and resulting in significant power loss.

[0013] Furthermore, in a portable information terminal, the secondary battery accounts for a large proportion of the total weight, and the placement of the secondary battery must be considered for balance, so it is placed in the center of the portable information terminal, making it difficult to place it in an extreme position, such as at the edge. Also, in order to withstand shocks such as being dropped, portable information terminals often place the CPU, which is vulnerable to shocks, in the center of the portable information terminal. Therefore, the placement of the secondary battery and the CPU is inevitably close to each other.

[0014] The heat generated by using a high-performance CPU for long periods of time under high load can be avoided by installing a heat sink or fan to dissipate the heat, but there are limitations. It is difficult to cool down a sudden heat generation all at once, and if the secondary battery's environmental temperature sensor detects it even for a moment, the power supply from the secondary battery will be stopped.

[0015] Therefore, an MCU (microcontroller unit, also called a microcomputer) for high temperature operation is provided in addition to the CPU for normal operation, and when the environmental temperature sensor of the secondary battery detects a high temperature, the CPU for normal operation is put into deep sleep mode and the electronic device is controlled by the MCU for high temperature operation. Note that when the CPU is in normal operation, the MCU for high temperature operation is in deep sleep mode.

[0016] The secondary battery's environmental temperature sensor detects a rise in ambient temperature or heat generated by the CPU, but this is not the temperature of the secondary battery itself, and the secondary battery itself can still be used. In addition, the allowable temperature range, specifically (5°C to 45°C or 5°C to 60°C), is set with a certain margin, so the secondary battery itself can still be used even immediately after a high temperature is detected exceeding 45°C or 60°C.

[0017] The MCU for high temperature operation receives power supply from the secondary battery, switches the display on the display unit to an image for high temperature operation, and then goes into sleep mode.

[0018] The electronic device has a display unit with a touch input unit that allows the user to perform touch input operations, and is controlled by the CPU when the CPU is in normal operation, and is controlled by the MCU for high-temperature operation when the MCU for high-temperature operation is in high-temperature operation.

[0019] After the display on the display unit is switched to an image for high temperature operation, the MCU, which is in a sleep mode, is activated by a touch input operation when the user wants to communicate urgently, enabling emergency contact.

[0020] Conventionally, when a high temperature is detected by the secondary battery's environmental temperature sensor, the power supply is immediately stopped, the electronic device is turned off, and emergency calls cannot be made.

[0021] By providing an MCU for high temperature operation, when a high temperature is detected, the CPU immediately transitions to deep sleep mode to stop heat generation, and the display switches to high temperature operation, allowing the user to make an emergency call by touch input operation.

[0022] For example, even if the outside temperature is high and an electronic device is left inside a closed car during the day and becomes hot due to sunlight, the present invention allows the user to pick up the electronic device and immediately perform touch input operations, and even make an emergency call.

[0023] In this specification, deep sleep mode refers to a mode in which the power consumption of the chip during operation is lower than that of a normal operation mode (normal mode, normal mode), standby mode, or sleep mode. Sleep mode refers to a mode in which the power consumption of the chip during operation is lower than that of the normal mode or standby mode. Normal mode refers to normal use in which some processing is being performed by touch input operation, and standby mode refers to a mode in which no touch input operation is being performed, the display screen is still or off, but some processing is being performed.

[0024] The configuration of the invention disclosed in this specification is a control system comprising a first control circuit, a second control circuit, a secondary battery, a temperature sensor, a display unit, and a communication circuit, and switching between the first control circuit and the second control circuit, wherein the second control circuit has a lower maximum power consumption and lower processing capability than the first control circuit, the temperature sensor is a sensor that measures the ambient temperature of the secondary battery, and when the measurement result of the temperature sensor is within an acceptable range, the first control circuit drives the display unit, and when the measurement result of the temperature sensor exceeds the upper limit temperature of the acceptable range, the first control circuit switches to a low power consumption mode, and the second control circuit drives the display unit.

[0025] In the above configuration, the display unit has a touch input operation unit, and if the measurement result of the temperature sensor is within an allowable range, the first control circuit drives the touch input operation unit, and if the measurement result of the temperature sensor exceeds the upper limit temperature of the allowable range, the first control circuit switches to a low power consumption mode, and the second control circuit drives the touch input operation unit.

[0026] The secondary battery is not particularly limited as long as it is capable of operating at high temperatures, and lithium ion secondary batteries, lithium ion capacitors, nickel-metal hydride batteries, all-solid-state secondary batteries, electric double layer capacitors, etc. can be used.

[0027] Even if the outside temperature rises or a control circuit such as a CPU generates heat and the environmental temperature sensor of the secondary battery detects a high temperature due to the heat, it is possible to make an emergency call by touch input operation on the electronic device.

[0028] While the CPU of the electronic device is in the deep sleep mode, power can be saved by control from the MCU, and the capacity consumption of the secondary battery can be reduced.

[0029] FIG. 1 is an example of a flow diagram illustrating one embodiment of the present invention. FIG. 2 is an example of a block diagram illustrating one embodiment of the present invention. FIG. 3 is an example of a block diagram illustrating one embodiment of the present invention. FIG. 4 is an example of a block diagram illustrating one embodiment of the present invention. FIG. 5 is a perspective view illustrating an example of a signal processing board illustrating one embodiment of the present invention. FIGS. 6A, 6B, 6C, and 6D each illustrate an example of an electronic device including a control system according to one embodiment of the present invention. FIGS. 7A to 7D are cross-sectional views illustrating examples of a positive electrode of a secondary battery. FIG. 8A is an exploded perspective view of a coin-type secondary battery, FIG. 8B is a perspective view of the coin-type secondary battery, and FIG. 8C is a cross-sectional perspective view thereof. FIG. 9A illustrates an example of a cylindrical secondary battery. FIG. 9B illustrates an example of a cylindrical secondary battery. FIG. 9C illustrates an example of a plurality of cylindrical secondary batteries. FIG. 9D illustrates an example of a power storage system including a plurality of cylindrical secondary batteries. FIGS. 10A and 10B illustrate an example of a secondary battery, and FIG. 10C illustrates the internal structure of the secondary battery. FIGS. 11A to 11C illustrate examples of a secondary battery. FIGS. 12A and 12B are diagrams showing the appearance of a secondary battery. FIGS. 13A to 13C are diagrams illustrating a method for producing a secondary battery. FIG. 14A is a diagram showing the appearance of a battery pack, FIG. 14B is a diagram showing an example of the configuration of a battery pack, and FIG. 14C is a diagram showing an example of the configuration of a battery pack. FIGS. 15A and 15B are diagrams illustrating an example of a secondary battery. FIGS. 16A to 16C are diagrams illustrating an example of a secondary battery. FIGS. 17A and 17B are diagrams illustrating an example of a secondary battery. FIG. 18A is a cross-sectional view of a positive electrode active material, and FIG. 18B is a diagram illustrating the distribution of added elements in the positive electrode active material. FIGS. 19A and 19B are diagrams illustrating the results of DSC analysis. FIG. 20 is an example of a TEM image in which the crystal orientations are roughly consistent. FIG. 21A is an example of an STEM image in which the crystal orientations are roughly consistent. FIG. 21B is an FFT pattern of the region of the rock salt-type crystal RS, and FIG. 21C is an FFT pattern of the region of the layered rock salt-type crystal LRS. Fig. 22 is a diagram illustrating the crystal structure of a positive electrode active material. Fig. 23 is a diagram illustrating the crystal structure of a conventional positive electrode active material. Fig. 24 is a diagram illustrating an XRD pattern calculated from the crystal structure. Fig. 25 is a diagram illustrating an XRD pattern calculated from the crystal structure.26A and 26B are diagrams showing XRD patterns calculated from the crystal structure. Fig. 27 is a cross-sectional view of a positive electrode active material. Fig. 28 is a diagram explaining a method for manufacturing a positive electrode active material. Figs. 29A to 29C are diagrams explaining a method for manufacturing a positive electrode active material.

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0031] Embodiment 1 FIG. 1 is an example of a flow diagram illustrating one embodiment of the present invention.

[0032] The normal mode (within the allowable temperature range) of the electronic device is started, and the operation state of the first control circuit of the electronic device, typically the CPU, is monitored, and the monitor determines the state of the CPU. This stage is referred to as step 1 (S1).

[0033] A block diagram of step 1 (S1) is shown in Figure 2. Figure 2 shows a block diagram in normal mode in which the CPU is active. The electronic device has at least a display unit 204 with a touch input operation unit, an application processor 201, a power supply monitoring IC 206, a charging IC 207, a secondary battery 205, an environmental temperature sensor 212 for the secondary battery, an antenna 211, a transmitting / receiving circuit 210, a baseband processor 209, and a communication control circuit 208. The secondary battery supplies power to each IC, and the power paths are shown by solid lines in Figure 2. The paths shown by dotted lines in Figure 2 indicate power paths through which minimum power is supplied, indicating that the MCU 202 is in deep sleep mode.

[0034] 1 refers to an application processor 201, and multiple types of CPUs are used in electronic devices. The CPU uses data or programs stored in semiconductor memory such as ROM (Read Only Memory) or RAM (Random Access Memory). The electronic device also has a baseband processor 209 for communication.

[0035] In this embodiment, the CPU state is illustrated as being selectable from four types: normal mode, standby mode, sleep mode, and deep sleep mode, but at least normal mode and deep sleep mode are selectable. Because standby mode and sleep mode are modes for low power consumption, more types of modes may be selectable.

[0036] If the CPU is in the normal mode, a normal image is displayed on the display unit, and if the CPU is in the standby mode or sleep mode, a standby image or black display is displayed on the display unit.

[0037] Depending on whether the CPU is in deep sleep mode or not, the MCU 202 becomes active and the process proceeds to step 2 (S2).

[0038] In this embodiment, the CPU switches to deep sleep mode when the secondary battery's environmental temperature sensor 212 detects a high temperature. For example, if the secondary battery's environmental temperature sensor 212 detects a maximum allowable temperature of 45°C or higher, or 60°C or higher, the CPU switches to deep sleep mode. During normal operation, the CPU itself typically generates heat of about 50°C, and the temperature rises further as the load increases. For example, it is known that the temperature rises significantly when an image capture application using a camera is executed due to the heavy load.

[0039] 2 is a block diagram and is shown as being located at a distance, but when actually implemented in an electronic device, the secondary battery's environmental temperature sensor 212 and the CPU are located close to each other and are affected by heat generation. The smaller the electronic device, the closer they are located and the more susceptible they are to heat generation. The allowable range of the secondary battery's environmental temperature sensor 212 is often set by the manufacturer depending on the type of secondary battery used. For example, for lithium-ion secondary batteries that use electrolyte, the allowable range is 5°C to 45°C.

[0040] When the CPU enters deep sleep mode due to rising outside temperature or heat generated by the CPU, control of the communication circuit is switched to the MCU 202. That is, control of the communication circuit is switched to MCU 202. This stage is step 3 (S3). The MCU 202 may completely turn off only the receiving circuit of the communication circuit, allowing only transmission. The MCU 202 can be called a second control circuit. The communication circuit collectively refers to the antenna 211, transmitting / receiving circuit 210, baseband processor 209, and communication control circuit 208, which are surrounded by a chain line in FIG. 2.

[0041] Then, since the CPU enters deep sleep mode, control of the display unit (touch input unit) is switched to the MCU 202. That is, control of the display unit 204 is switched to the MCU 202. This stage is step 4 (S4). The MCU 202 consumes less power than the CPU and consumes only a small amount of capacity from the secondary battery. For example, the MCU 202 can be operated in a discharged state of 0.1C or 0.05C.

[0042] It is determined whether the control of the display unit is being switched to the MCU or not, and if the control of the display unit has been switched to the MCU, the process proceeds to step 5 (S5).

[0043] In step 5 (S5), an emergency call image is displayed on the display unit 204 using image data stored in the ROM 203 included in the MCU 202. At this time, if a touch input is made on the display of the emergency call image, an emergency call can be made because the communication circuit is also controlled by the MCU 202. A block diagram at this stage is shown in FIG. 3. The power paths are indicated by solid lines in FIG. 3. The paths indicated by dotted lines in FIG. 3 indicate power paths through which the minimum amount of power is supplied, indicating that the CPU is in deep sleep mode. FIG. 3 also shows that the image data stored in the ROM 203 is input to the display unit 204 and displayed.

[0044] Here, an example has been shown in which image data in the ROM 203 included in the MCU 202 is used, but this is not particularly limited, and an emergency notification image may be implemented as a separate IC.

[0045] After the emergency call image is displayed, the MCU 202 is switched to sleep mode. By switching the MCU 202 to sleep mode, power saving is achieved. Even when the MCU 202 is in sleep mode, control of the touch input unit continues. This stage is step 6 (S6). Step 6 (S6) can also be called a standby state for an emergency call.

[0046] To further reduce power consumption, the display unit 204 is turned off and the touch input unit is switched to a standby state. The touch input unit performs sensing only at regular time intervals. This stage is step 7 (S7). Step 7 (S7) can also be called the standby state for emergency calls. The block diagram at this stage is shown in FIG. 4. In FIG. 4, the MCU 202 is in sleep mode and the display unit 204 is turned off (however, the touch input unit is active), so this can be said to be the mode that achieves the greatest power consumption savings.

[0047] Since the device is in standby mode for an emergency call, when the user performs a touch input operation for an emergency call, the MCU is switched to active mode. This is step 8 (S8). Since the MCU 202 is active again, the corresponding block diagram is the same as that in FIG. 3.

[0048] Then, the active MCU 202 can control the communication circuit to make an emergency call. This stage is step 9 (S9).

[0049] By following the above flow, it is possible to minimize the output of the secondary battery at high temperatures while maintaining the ability to make emergency calls, thereby reducing the deterioration of the secondary battery. If a large amount of power is supplied from the secondary battery at high temperatures, the deterioration of the secondary battery tends to progress easily in the case of lithium-ion secondary batteries that use an electrolyte.

[0050] In the case of lithium-ion secondary batteries that use an electrolyte, depending on the material of the electrolyte, high temperatures can cause it to evaporate, generating a large amount of gas and causing it to expand. It is therefore preferable to provide a pressure sensor to detect this expansion.

[0051] Since expansion is dangerous, it is preferable to immediately turn off the power when a pressure sensor detects deformation of the secondary battery. In this case, the power is turned off without switching control of the electronic device from the CPU to the MCU.

[0052] Furthermore, the flow chart shown in Fig. 1 is merely an example for the purpose of explanation, and does not imply that the steps of various aspects must be performed in the order shown in Fig. 1. The steps may be performed in any order that would be understood by one skilled in the art, and some steps may be performed in parallel. For example, steps 3 and 4 may be performed simultaneously or in reverse order. Furthermore, steps 6 and 7 may be performed simultaneously or in reverse order.

[0053] Next, the configuration of the control system will be described. Figures 2, 3, and 4 can also be considered block diagrams outlining the control system. Therefore, the electronic device can also be called a control system that controls the operation modes of the three figures, or an emergency notification system.

[0054] The electronic device disclosed in this embodiment is designed to switch from a first control circuit (application processor) to a second control circuit (MCU) at high temperatures, and to operate in a way that fully maximizes power savings across the entire system, making it useful because it allows the user to make emergency calls even at high temperatures.

[0055] Second Embodiment In this embodiment, an example in which a chip of a first control circuit (application processor) and a chip of a second control circuit (MCU) are mounted on the same signal processing board substrate 651 is shown in FIG.

[0056] The signal processing board 620 shown in Fig. 5 is an example of a board mounted with components equivalent to the first control circuit (application processor) or the second control circuit (MCU) of the electronic device shown in Fig. 2, Fig. 3, and Fig. 4. The signal processing board substrate 651 can also be said to be a wiring board or circuit board containing a ceramic material called a green sheet.

[0057] The semiconductor device 658 has a plurality of terminals, and the terminals can be soldered, for example, by reflow soldering, to wiring provided on the signal processing board substrate 651, thereby electrically connecting the semiconductor device 658 to the wiring on the signal processing board substrate 651. Examples of the semiconductor device 658 include an FPGA (Field Programmable Gate Array), a GPU, and a CPU. The semiconductor device 658 has better driving performance than the MCU 656, but consumes more power.

[0058] In this embodiment, when the electronic device is in use, the semiconductor device 658 controls the display unit and the like during normal operation, and when the temperature is high, the semiconductor device 658 enters deep sleep mode and the MCU 656 controls the display unit and the like. When the environmental temperature sensor of the secondary battery detects a high temperature, it is determined that the temperature is high, and the semiconductor device 658 enters deep sleep mode. The smaller the electronic device, the closer the distance between the secondary battery and the signal processing board 620. The semiconductor device 658 generates heat when driven, and the environmental temperature sensor of the secondary battery may detect a high temperature. When the temperature is high, an image for emergency notification is displayed on the display unit using data pre-stored in the memory 657. The image for emergency notification does not have to be displayed in color; it may be displayed in monochrome, which consumes less power.

[0059] The MCU 656 has terminals (not shown) for inputting and outputting signals, and is electrically connected to the power supply monitoring IC and the secondary battery via the connection terminal 653. At high temperatures, the MCU 656 functions as a charge / discharge control circuit for the secondary battery, a protection circuit for the secondary battery, and a power supply circuit that supplies power or signals from the secondary battery to other elements.

[0060] The connection terminal 652 has a shape that allows the connector of the FPC 659 to be inserted, and the connection terminal 652 functions as an interface for connecting to another board or a display module. The FPC 659 is connected to the display module and can display an image on the display unit of the display module. The display module also has a touch input operation unit on the display unit, allowing the user to perform touch input operations, and the signal is also input to the semiconductor device 658 or the MCU 656 via the FPC 659.

[0061] The connection terminals 653, 654, and 655 can be, for example, interfaces for supplying power to the signal processing board 620, inputting signals, etc. They can also be, for example, interfaces for outputting signals calculated by the signal processing board 620. Examples of standards for the connection terminals 654 and 655 include USB (Universal Serial Bus), SATA (Serial ATA), and SCSI (Small Computer System Interface). When a video signal is output from the connection terminals 654 and 655, examples of the respective standards include HDMI (registered trademark).

[0062] By mounting a control system according to one embodiment of the present invention on a board or the like of the various electronic devices, the electronic devices can be made to operate at high speed or consume less power even at high temperatures.Furthermore, electronic devices that can make emergency calls even at high temperatures can be realized.

[0063] In this embodiment, an example is shown in which a chip for a first control circuit (application processor) and a chip for a second control circuit (MCU) are mounted on the same signal processing board substrate 651, but this is not particularly limited, and they may be mounted on separate board substrates.

[0064] This embodiment mode can be freely combined with other embodiment modes.

[0065] (Embodiment 3) An example of an electronic device including a control system according to one embodiment of the present invention will be described. Note that FIGS. 6A to 6C illustrate how two types of semiconductor devices 4700a and 4700b implementing the control system are included in each electronic device. The control system according to one embodiment of the present invention can issue an emergency call even when the ambient temperature of the secondary battery 5512 is high. Therefore, the control system according to one embodiment of the present invention can be suitably used in the following electronic devices. In particular, the control system can be suitably used in electronic devices that require durability.

[0066] 6A is a mobile phone (smartphone), which is a type of portable information terminal. The information terminal 5500 includes at least a housing 5510, a display unit 5511, a secondary battery 5512, and a communication circuit. As input interfaces, the display unit 5511 is provided with a touch panel, and the housing 5510 is provided with buttons.

[0067] The information terminal 5500 also includes semiconductor devices 4700a and 4700b, including the semiconductor device 4700a that operates normally and the semiconductor device 4700b that operates when the environmental temperature of the secondary battery 5512 is high. The semiconductor device 4700b is an IC chip (MCU) that is smaller than the semiconductor device 4700a, and when the semiconductor device 4700b operates, the semiconductor device 4700a enters a deep sleep mode.

[0068] Furthermore, when the temperature is high, an image for emergency notification is displayed on the display portion 5511, and an emergency notification is made by touch input. After that, even when the display portion 5511 is in an off state, an emergency notification can be made by touch input.

[0069] 6B illustrates an information terminal 5900, which is an example of a wearable terminal. The information terminal 5900 includes at least a housing 5901, a display unit 5902, operation switches 5903 and 5904, a band 5905, a secondary battery 5512, and a communication circuit. The display unit 5902 is provided with a touch panel as an input interface.

[0070] The information terminal 5900 has semiconductor devices 4700a and 4700b, including the semiconductor device 4700a that operates normally and the semiconductor device 4700b that operates when the environmental temperature of the secondary battery 5512 is high. The semiconductor device 4700b is an IC chip (MCU) that is smaller than the semiconductor device 4700a, and when the semiconductor device 4700b is operating, the semiconductor device 4700a enters a deep sleep mode.

[0071] At high temperatures, an image for emergency notification is displayed on the display portion 5902, and an emergency notification is made by touching the display portion 5902. After that, even when the display portion 5902 is turned off, an emergency notification can be made by touching the display portion 5902.

[0072] 6A and 6B, a smartphone and a wearable terminal are used as examples of electronic devices, but information terminals other than smartphones and wearable terminals can also be used. Examples of information terminals other than smartphones and wearable terminals include personal digital assistants (PDAs), notebook information terminals, and workstations.

[0073] 6C illustrates a portable game machine 5200, which is an example of a game machine. The portable game machine 5200 includes at least a housing 5201, a display unit 5202, buttons 5203, a secondary battery 5512, and a communication circuit. The display unit 5202 is provided with a touch panel as an input interface.

[0074] The portable game console 5200 has semiconductor devices 4700a and 4700b, including the semiconductor device 4700a that operates normally and the semiconductor device 4700b that operates when the environmental temperature of the secondary battery 5512 is high. The semiconductor device 4700b is an IC chip (MCU) that is smaller than the semiconductor device 4700a, and when the semiconductor device 4700b is operating, the semiconductor device 4700a enters a deep sleep mode.

[0075] The portable game console 5200 has semiconductor devices 4700a and 4700b overlapping the secondary battery 5512, and heat generated by the semiconductor device 4700a may cause the temperature of an environmental temperature sensor of the secondary battery 5512 to rise, resulting in the stop of power supply from the secondary battery 5512. In this embodiment, after high temperature is detected, the semiconductor device 4700b, which is smaller in size than the semiconductor device 4700a, is driven.

[0076] Furthermore, when the temperature is high, an image for emergency notification is displayed on the display portion 5202, and an emergency notification is made by touch input. After that, even when the display portion 5202 is in an off state, an emergency notification can be made by touch input.

[0077] Furthermore, the images of the above-mentioned game machine can be output by a display device such as a television device, a display for a personal computer, a game display, or a head-mounted display.

[0078] Although a portable game machine is illustrated in FIG. 6C as an example of a game machine, the electronic device of one embodiment of the present invention is not limited to this.

[0079] [Mobile Body] The control system described in the above embodiment can be applied to the interior of a mobile body such as an automobile.

[0080] FIG. 6D illustrates an automobile 5700 as an example of a moving object.

[0081] An instrument panel that provides various information by displaying a speedometer, tachometer, mileage, fuel gauge, gear status, air conditioning settings, etc. is provided near the driver's seat of the automobile 5700. A display device that displays such information may also be provided near the driver's seat. By using a secondary battery 5512 under the seat of the automobile 5700, the vehicle balance of the automobile 5700 can be stabilized.

[0082] The automobile 5700 has semiconductor devices 4700a and 4700b, including the semiconductor device 4700a that operates normally and the semiconductor device 4700b that operates when the environmental temperature of the secondary battery 5512 is high. The semiconductor device 4700b is an IC chip (MCU) that is smaller than the semiconductor device 4700a, and when the semiconductor device 4700b operates, the semiconductor device 4700a enters a deep sleep mode.

[0083] An automobile 5700 has semiconductor devices 4700a and 4700b inside the vehicle, and an environmental temperature sensor of a secondary battery 5512 may become hot due to heat from direct sunlight for a long time, which may cause the power supply from the secondary battery 5512 to be stopped. In this embodiment, after a high temperature is detected, a semiconductor device 4700b, which is smaller in scale than the semiconductor device 4700a, is driven.

[0084] Furthermore, when the temperature is high, an image for emergency calls is displayed on the display device around the driver's seat, and an emergency call is made by touch input. After that, even when the display device around the driver's seat is turned off, an emergency call can be made by touch input.

[0085] Although an automobile is described above as an example of a moving body, the moving body is not limited to vehicles such as an automobile. For example, moving bodies can also include trains, monorails, ships, and flying bodies (helicopters, airplanes).

[0086] This embodiment mode can be freely combined with other embodiment modes.

[0087] (Embodiment 4) In this embodiment, a lithium-ion secondary battery will be described. The secondary battery has at least an outer casing, a current collector, an active material (positive electrode active material or negative electrode active material), a conductive additive, and a binder. It also has an electrolyte solution in which lithium salt or the like is dissolved. In the case of a secondary battery using an electrolyte solution, a positive electrode, a negative electrode, and a separator are provided between the positive electrode and the negative electrode.

[0088] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material, and may further contain a binder, a conductive additive, and the like.

[0089] There is no particular limitation on the material of the positive electrode active material used in the positive electrode active material layer. ｘ O ｙ (x>0 and y>0, more specifically, for example, y=2 and 0.8<x<1.2), but is not limited to lithium composite oxides represented by LiNi ｘ Co １−ｘ O ２ NiCo-based compounds represented by (0<x<1), LiM ｘ O ｙ As examples of lithium composite oxides represented by the formula: LiNi ｘ Mn １−ｘ O ２ It can also be used as a positive electrode active material for NiMn-based materials represented by (0<x<1). ｘ Co ｙ Mn ｚ O ２The present invention can also be applied to NiCoMn-based materials (also referred to as NCM) represented by the formula (x>0, y>0, 0.8<x+y+z<1.2). Specifically, for example, it is preferable to satisfy 0.1x<y<8x and 0.1x<z<8x. As an example, it is preferable that x, y, and z satisfy x:y:z=1:1:1 or a value in the vicinity thereof. As another example, it is preferable that x, y, and z satisfy x:y:z=5:2:3 or a value in the vicinity thereof. As another example, it is preferable that x, y, and z satisfy x:y:z=8:1:1 or a value in the vicinity thereof. As another example, it is preferable that x, y, and z satisfy x:y:z=6:2:2 or a value in the vicinity thereof. As another example, it is preferable that x, y, and z satisfy x:y:z=1:4:1 or a value in the vicinity thereof. Furthermore, lithium iron phosphate (LiFePO ) is used as the positive electrode active material. ４ ) may also be used.

[0090] In this specification, the positive electrode active material refers to a compound containing a transition metal and oxygen, capable of inserting and extracting lithium. Carbonates, hydroxyl groups, and the like adsorbed after the preparation of the positive electrode active material are not included in the positive electrode active material. Lithium salts, organic solvents, binders, conductive materials, and compounds derived from these that are attached after the preparation of the positive electrode active material are also not included in the positive electrode active material.

[0091] FIG. 7A shows an example of a schematic cross-sectional view of a positive electrode.

[0092] The current collector 550 is a metal foil, and the positive electrode is formed by applying a slurry onto the metal foil and drying it. After drying, the metal foil may be further pressed. The positive electrode is formed by forming an active material layer on the current collector 550.

[0093] The slurry is a material liquid used to form an active material layer on the current collector 550, and refers to a material containing at least an active material, a binder, and a solvent, and preferably further mixed with a conductive additive. The slurry is also called an electrode slurry or an active material slurry, and is sometimes called a positive electrode slurry when forming a positive electrode active material layer, and a negative electrode slurry when forming a negative electrode active material layer.

[0094] The conductive additive, also called a conductivity-imparting agent or conductive material, is made of a carbon material. By attaching the conductive additive between multiple active materials, the active materials are electrically connected to each other, thereby increasing their conductivity. Note that "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also encompasses cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive additive covering part of the surface of the active material, the conductive additive fitting into the surface irregularities of the active material, and electrical connection even when not in contact with each other.

[0095] A typical carbon material used as a conductive additive is carbon black (furnace black, acetylene black, graphite, etc.).

[0096] 7A illustrates acetylene black 553 as a conductive additive. Also, FIG. 7A illustrates an example in which a second active material 562 having a particle size smaller than that of the active material 561 is mixed. By mixing particles of different sizes, a high-density positive electrode active material layer can be obtained, and the charge / discharge capacity of the secondary battery can be increased.

[0097] A binder (resin) is mixed to bond the current collector 550, such as a metal foil, and the active material to form the positive electrode of the secondary battery. The binder is also called a binding agent. The binder is a polymer material, and if a large amount of binder is added, the proportion of active material in the positive electrode decreases, resulting in a smaller discharge capacity of the secondary battery. Therefore, the amount of binder mixed is kept to a minimum. In Figure 7A, the areas not filled with the active material 561, second active material 562, and acetylene black 553 represent voids or binder.

[0098] 7A shows an example in which the active material 561 is spherical, but the shape is not particularly limited and various shapes are possible. The cross-sectional shape of the active material 561 may be elliptical, rectangular, trapezoidal, conical, quadrangular with rounded corners, or asymmetrical.

[0099] 7B shows an example in which the active material 561 has various shapes. FIG. 7B shows an example different from FIG. 7A.

[0100] In addition, in the positive electrode in FIG. 7B, graphene 554 is used as a carbon material used as a conductive additive.

[0101] Graphene is a carbon material that has amazing electrical, mechanical, and chemical properties and is expected to be applied in various fields, such as field-effect transistors and solar cells.

[0102] In FIG. 7B, a positive electrode active material layer including an active material 561 , graphene 554 , and acetylene black 553 is formed over a current collector 550 .

[0103] In the step of mixing the graphene 554 and the acetylene black 553 to obtain electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of the graphene.

[0104] Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, the dispersion stability of acetylene black 553 is excellent and agglomerations are less likely to occur during slurry preparation. Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, a higher electrode density can be achieved than a positive electrode using only acetylene black 553 as a conductive additive. Increasing the electrode density can increase the capacity per unit weight. Specifically, the density of the positive electrode active material layer measured gravimetrically can be increased to more than 3.5 g / cc.

[0105] Furthermore, although the electrode density is lower than that of a positive electrode using only graphene as a conductive additive, by mixing the first carbon material (graphene) and the second carbon material (acetylene black) within the above range, rapid charging is possible.

[0106] These features are effective for use as a secondary battery for vehicles.

[0107] Increasing the number of secondary batteries and increasing the vehicle's weight reduces the driving range because the energy required to move increases. By using high-density secondary batteries, the driving range can be maintained with almost no change in the total weight of the vehicle equipped with the same weight of secondary batteries.

[0108] Furthermore, as vehicle secondary batteries reach high capacity, they require more power for charging, so it is desirable to complete charging in a short time.Furthermore, charging is performed under high-rate charging conditions during so-called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the power is charged, so good rate characteristics are required for vehicle secondary batteries.

[0109] 7B, the regions that are not filled with the active material 561, the graphene 554, and the acetylene black 553 indicate voids or binders. The voids are necessary for the electrolyte to penetrate, but if there are too many voids, the electrode density decreases, and if there are too few voids, the electrolyte cannot penetrate, and if these voids remain even after the secondary battery is fabricated, the energy density decreases.

[0110] 7C illustrates an example of a positive electrode in which carbon nanotubes 555 are used instead of graphene. Fig. 7C shows an example different from Fig. 7B. The use of carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and improve dispersibility.

[0111] In FIG. 7C, the regions not filled with the active material 561, the carbon nanotubes 555, and the acetylene black 553 indicate voids or binders.

[0112] Another example of a positive electrode is shown in Fig. 7D. Fig. 7C shows an example in which carbon nanotubes 555 are used in addition to graphene 554. Using both graphene 554 and carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and further improve dispersibility.

[0113] In FIG. 7D, the regions not filled with the active material 561, the carbon nanotubes 555, the graphene 554, and the acetylene black 553 indicate voids or binders.

[0114] A secondary battery can be produced by using any one of the positive electrodes shown in FIGS. 7A to 7D , placing a separator on the positive electrode, and placing the laminate obtained by placing the negative electrode on the separator in a container (such as an exterior body or a metal can) and filling the container with an electrolyte.

[0115] Although the above configuration shows an example of a secondary battery using an electrolytic solution, the present invention is not particularly limited.

[0116] For example, semi-solid or all-solid state batteries can be fabricated.

[0117] In this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of the electrolyte layer, positive electrode, and negative electrode. Here, semi-solid does not mean that the ratio of solid material is 50%. Semi-solid means that while having solid properties such as small volume change, it also has some liquid-like properties such as flexibility. As long as these properties are met, the battery may be made of a single material or multiple materials. For example, a porous solid material may be impregnated with a liquid material.

[0118] In this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between a positive electrode and a negative electrode. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries. Polymer electrolyte secondary batteries may also be called semi-solid batteries.

[0119] When a semi-solid battery is fabricated, it becomes a secondary battery with a large charge / discharge capacity, a high charge / discharge voltage, or a high safety or reliability.

[0120] Alternatively, a mixture of positive electrode active materials may be used. Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, LiFePO ４ , LiFeO ２ , LiNiO ２ , LiMn ２ O ４ , V ２ O ５ , Cr ２ O ５ , MnO ２ The following compounds are exemplified:

[0121] Other positive electrode active materials include LiMn ２ O ４Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0122] In addition, as another positive electrode active material, the composition formula Li ａ Mn ｂ M ｃ O ｄ A lithium-manganese composite oxide that can be expressed by the formula (1) can be used. Here, element M is preferably a metal element selected from among lithium and manganese, or silicon or phosphorus, and more preferably nickel. Furthermore, when measuring the entire lithium-manganese composite oxide particle, it is preferable that 0<a / (b+c)<2, c>0, and 0.26≦(b+c) / d<0.5 are satisfied during discharge. The composition of metals, silicon, phosphorus, etc. in the entire lithium-manganese composite oxide particle can be measured, for example, using an inductively coupled plasma mass spectrometer (ICP-MS). The oxygen composition in the entire lithium-manganese composite oxide particle can be measured, for example, using energy dispersive X-ray spectroscopy (EDX). Furthermore, the composition can be determined by using valence evaluation of fused gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.

[0123] <Binder> As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Furthermore, as the binder, fluororubber can be used.

[0124] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0125] Alternatively, it is preferable to use, as the binder, materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

[0126] The binder may be used in combination with two or more of the above.

[0127] For example, a material with a particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with a particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with a particularly excellent viscosity adjusting effect. Furthermore, as a water-soluble polymer with a particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose derivatives such as regenerated cellulose, or starch may be used.

[0128] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials or other components when preparing electrode slurries. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0129] Water-soluble polymers stabilize viscosity by dissolving in water, and can stably disperse active materials or other materials combined as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups, such as hydroxyl or carboxyl groups, and the functional groups are expected to allow interactions between polymers, resulting in widespread coverage of the active material surface.

[0130] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and have the effect of suppressing decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0131] <Positive Electrode Current Collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable that the current collector have a thickness of 5 μm to 30 μm.

[0132] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer has a negative electrode active material, and may further have a conductive additive and a binder.

[0133] <Negative Electrode Active Material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0134] As the negative electrode active material, an element capable of undergoing a charge-discharge reaction by alloying / de-alloying with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. These elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Alternatively, a compound containing these elements may be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials.

[0135] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0136] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0137] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is therefore preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0138] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), the graphite exhibits a potential as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋This allows lithium-ion secondary batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety than metallic lithium.

[0139] Titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten oxide (WO ２ ), molybdenum oxide (MoO ２ ) and other oxides can be used.

[0140] In addition, as the negative electrode active material, a composite nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N ３ has a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0141] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, can be used as the positive electrode active material. ２ O ５ , Cr ３ O ８ It is preferable that the composite nitride of lithium and a transition metal can be used as the negative electrode active material, even when a material containing lithium ions is used as the positive electrode active material, by first removing the lithium ions contained in the positive electrode active material.

[0142] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0143] As the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0144] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0145] [Separator] A separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include those made of cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0146] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0147] Coating with ceramic materials improves oxidation resistance, so Li ｘ CoO ２ This suppresses separator deterioration during repeated charging and discharging so that x in the formula is 0.24 or less, thereby improving the reliability of the secondary battery. Furthermore, coating with a fluorine-based material facilitates adhesion between the separator and electrodes, improving output characteristics. Coating with a polyamide-based material, especially aramid, improves heat resistance, thereby improving the safety of the secondary battery.

[0148] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0149] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0150] [Electrolyte] The electrolyte contains a solvent and an electrolyte. The solvent for the electrolyte is preferably an aprotic organic solvent, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone, or any combination and ratio of two or more of these.

[0151] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the electricity storage device from exploding or catching fire even if the internal temperature of the electricity storage device rises due to an internal short circuit or overcharging. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0152] The electrolyte to be dissolved in the solvent is, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (Li(C) ２ O ４ ) ２ , LiBOB), or two or more of these can be used in any combination and ratio.

[0153] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0154] The electrolyte may contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % of the total solvent.

[0155] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0156] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0157] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0158] In addition, instead of an electrolytic solution, a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0159] By applying the positive electrode slurry or electrode to an all-solid-state battery, it is possible to obtain an all-solid-state battery that is highly safe and has good characteristics.

[0160] [Exterior Body] The exterior body of the secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0161] This embodiment can be used in combination with other embodiments.

[0162] Embodiment Mode 5 In this embodiment mode, examples of various shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0163] [Coin-Type Secondary Battery] An example of a coin-type secondary battery will be described. Fig. 8A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 8B is an external view, and Fig. 8C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0164] 8A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 8A and 8B are not completely corresponding views.

[0165] In Fig. 8A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed by a negative electrode can 302 and a positive electrode can 301. Note that a gasket for sealing is not shown in Fig. 11A. The spacer 322 and the washer 312 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0166] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0167] To prevent short-circuiting between the positive electrode and the negative electrode, a separator 310 and a ring-shaped insulator 313 are arranged so as to cover the side and top surfaces of the positive electrode 304. The separator 310 has a larger planar area than the positive electrode 304.

[0168] FIG. 8B is a perspective view of the completed coin-type secondary battery.

[0169] In the coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The negative electrode 307 is not limited to a laminated structure, and may be formed of lithium metal foil or a lithium-aluminum alloy foil.

[0170] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0171] The positive electrode can 301 and the negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, or the like. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0172] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in FIG. 8C , the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, thereby producing a coin-shaped secondary battery 300.

[0173] By using the secondary battery, it is possible to obtain a coin-type secondary battery 300 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that when a secondary battery is formed between the negative electrode 307 and the positive electrode 304, the separator 310 may not be necessary.

[0174] [Cylindrical Secondary Battery] An example of a cylindrical secondary battery will be described with reference to Fig. 9A. As shown in Fig. 9A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0175] 9B is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in FIG. 9B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0176] A battery element is provided inside a hollow cylindrical battery can 602, which includes a strip-shaped positive electrode 604 and a negative electrode 606 wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal, such as nickel, aluminum, or titanium, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery can 602 with nickel, aluminum, or the like to prevent corrosion by the electrolyte. Inside the battery can 602, the wound battery element, which includes the positive electrode, negative electrode, and separator, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, which contains the battery element. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0177] Since the positive and negative electrodes used in a cylindrical storage battery are wound up, it is preferable to form active materials on both sides of the current collector.

[0178] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature increases, and the increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element is made of barium titanate (BaTiO ３ )-based semiconductor ceramics, etc. can be used.

[0179] 9C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the secondary batteries are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected via wiring 623 to a signal processing board 620 on which the two types of control circuits shown in Embodiment 2 are mounted. Furthermore, the negative electrodes of the secondary batteries are electrically connected via wiring 626 to the control circuits mounted on the signal processing board 620.

[0180] 9D shows an example of a power storage system 615. The power storage system 615 has multiple secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The multiple secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or in parallel and then further connected in series. By configuring the power storage system 615 to have multiple secondary batteries 616, it is possible to extract a large amount of power.

[0181] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0182] 9D , in a power storage system 615, multiple types of control circuits mounted on a signal processing board substrate 651 are electrically connected via a connection terminal 653, wiring 621, and wiring 622. The wiring 621 is electrically connected to the positive electrodes of multiple secondary batteries 600 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of multiple secondary batteries 600 via a conductive plate 614.

[0183] The two types of control circuits mounted on the signal processing board 620 can be the circuits or ICs described in Embodiment 2. In addition, in Figures 9C and 9D, the same reference numerals are used for the same parts as in Figure 5.

[0184] [Another Example of Secondary Battery Structure] An example of the structure of a secondary battery will be described with reference to FIGS. 10 and 11. FIG.

[0185] The secondary battery 913 shown in FIG. 10A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 10A , the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0186] 10B, the housing 930 shown in Fig. 10A may be formed using a plurality of materials. For example, the secondary battery 913 shown in Fig. 10B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0187] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0188] 10C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that a plurality of layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0189] 11A may be a secondary battery 913 having a wound body 950a. The wound body 950a shown in Fig. 11A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0190] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0191] 11B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0192] 11C , the wound body 950 a and the electrolyte are covered by the housing 930 to form the secondary battery 913. It is preferable to provide the housing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0193] 11B, the secondary battery 913 may have multiple wound bodies 950a. By using multiple wound bodies 950a, the secondary battery 913 can have a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in FIGS. 11A and 11B, the descriptions of the secondary battery 913 shown in FIGS. 10A to 10C can be referred to.

[0194] 12A and 12B show examples of external views of a laminated secondary battery, which includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0195] 13A shows an external view of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The area or shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 13A .

[0196] <Method of Manufacturing Laminated Secondary Battery> Here, an example of a method of manufacturing the laminated secondary battery whose external view is shown in FIG. 12A will be described with reference to FIGS. 13B and 13C.

[0197] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 13B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0198] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are arranged on the outer casing 509 .

[0199] Next, as shown in Fig. 13C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding or the like may be used for joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that the electrolyte solution 508 can be introduced later.

[0200] Next, the electrolyte solution 508 (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution 508 is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0201] [Example of Battery Pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be described with reference to FIG.

[0202] Fig. 14A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (also called a thick flat plate shape). Fig. 14B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is affixed to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0203] The inside of the secondary battery 513 may have a structure including a wound body or a laminated body.

[0204] 14B , the secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to the terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one 551 of the positive and negative leads of the secondary battery 513, and the other 552 of the positive and negative leads.

[0205] Alternatively, as shown in FIG. 14C, the device may have a circuit system 590 a provided on a circuit board 540 and a circuit system 590 b electrically connected to the circuit board 540 via a terminal 514 .

[0206] The antenna 517 is not limited to a coil shape and may be, for example, a wire shape or a plate shape. Furthermore, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may also be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields but also by electric fields.

[0207] The secondary battery pack 531 includes a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field generated by the secondary battery 513. The layer 519 can be formed using, for example, a magnetic material.

[0208] This embodiment mode can be freely combined with other embodiment modes.

[0209] Embodiment 6 In this embodiment, an example of manufacturing an all-solid-state battery will be described.

[0210] As shown in FIG. 15A , a secondary battery 400 of one embodiment of the present invention includes a positive electrode 410 , a solid electrolyte layer 420 , and a negative electrode 430 .

[0211] The positive electrode 410 includes a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 includes a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material layer 414 may also include a conductive additive and a binder.

[0212] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0213] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not include the solid electrolyte 421, as shown in FIG. 15B . Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0214] The solid electrolyte 421 of the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a halide-based solid electrolyte.

[0215] The sulfide-based solid electrolytes include thiolithium-based (Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ etc.), sulfide glass (70Li ２ S・30P ２ S ５ , 30Li ２ S・26B ２ S ３ ・44LiI, 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４ SiO ４ , 50Li ２ S・50GeS ２ etc.), sulfide crystallized glass (Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0216] The oxide-based solid electrolyte includes a material having a perovskite crystal structure (La２／３−ｘ Li ３ｘ TiO ３ etc.), materials having a NASICON type crystal structure (Li １−Ｙ Al Ｙ Ti ２−Ｙ (P.O. ４ ) ３ etc.), materials having a garnet-type crystal structure (Li ７ La ３ Zr ２ O １２ etc.), materials having a LISICON type crystal structure (Li １４ ZnGe ４ O １６ etc.), LLZO (Li ７ La ３ Zr ２ O １２ ), oxide glass (Li ３ P.O. ４ -Li ４ SiO ４ , 50Li ４ SiO ４ ・50Li ３ BO ３ etc.), oxide crystallized glass (Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0217] Halide-based solid electrolytes include LiAlCl ４ , Li ３ InBr ６ , LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as the solid electrolyte.

[0218] Also, different solid electrolytes may be mixed and used.

[0219] Among them, Li having a NASICON type crystal structure １＋ｘAl ｘ Ti ２−ｘ (P.O. ４ ) ３ (0<x<1) (hereinafter, LATP) is preferable because it contains aluminum and titanium, elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, and therefore a synergistic effect can be expected in improving cycle characteristics. In addition, productivity can be expected to be improved by reducing the number of steps. Note that in this specification and the like, the NASICON-type crystal structure refers to a structure having a NASICON-type crystal structure, which is a structure having a NASICON-type crystal structure, and which is ... ２ (XO ４ ) ３ (M: transition metal, X: S, P, As, Mo, W, etc.), ６ Octahedron and XO ４ It refers to a structure in which tetrahedrons are arranged three-dimensionally with their vertices shared.

[0220] [Exterior Body and Shape of Secondary Battery] Various materials and shapes can be used for the exterior body of the secondary battery 400 of one embodiment of the present invention, but it is preferable that the exterior body has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0221] For example, FIG. 16 shows an example of a cell for evaluating materials for an all-solid-state battery.

[0222] 16A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw or wing nut 764 that fixes them together, and electrode plate 753 is pressed to fix the evaluation material by rotating a holding screw 763. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is also provided between upper member 762 and holding screw 763 to provide a tight seal.

[0223] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. An enlarged perspective view of the evaluation material and its surroundings is shown in Figure 16B.

[0224] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 16C. Note that the same reference numerals are used for the same parts in Figs. 16A to 16C.

[0225] The electrode plate 751 and the lower member 761, which are electrically connected to the positive electrode 750a, can be said to correspond to a positive electrode terminal. The electrode plate 753 and the upper member 762, which are electrically connected to the negative electrode 750c, can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0226] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0227] Fig. 17A is a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 16. The secondary battery in Fig. 17A has external electrodes 771 and 772 and is sealed in an exterior body having a plurality of package members.

[0228] An example of a cross section taken along the dashed line in Figure 17A is shown in Figure 17B. A stack including a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed within a package member 770a having a flat plate with an electrode layer 773a, a frame-shaped package member 770b, and a flat plate with an electrode layer 773b. The package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramics.

[0229] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0230] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0231] Embodiment 7 In this embodiment, a positive electrode active material 100 used to realize a lithium ion secondary battery that can withstand charge and discharge at a relatively high temperature, for example, 45° C. or higher, preferably 60° C., and a method for manufacturing the same will be described below.

[0232] In this embodiment, a positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIGS.

[0233] Fig. 18A is a cross-section of a positive electrode active material 100 of one embodiment of the present invention. Fig. 18B is a schematic diagram of an element concentration distribution when measurement is performed from the surface toward the inside in a cross-section analysis including the surface and a surface layer portion of the positive electrode active material 100. Measurement from the surface toward the inside is also referred to as measurement in the depth direction, and the X1-X2 and Y1-Y2 arrows in Fig. 18A are examples of the depth direction.

[0234] As shown in Fig. 18A, the positive electrode active material 100 has a surface layer 100a and an inner portion 100b. In Fig. 18A, the boundary between the surface layer 100a and the inner portion 100b is indicated by a dashed line. (001) in the figure indicates LiMO ２ This shows the (001) plane of LiMO. ２ belongs to the space group R-3m.

[0235] In this specification, the surface layer 100a of the positive electrode active material 100 refers to, for example, a region extending from the surface toward the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm perpendicular or approximately perpendicular from the surface toward the interior. Note that "approximately perpendicular" refers to an angle of 80° to 100°. Surfaces resulting from cracks and / or fissures may also be referred to as the surface. The surface layer 100a is synonymous with the near-surface, near-surface region, or shell.

[0236] The region of the positive electrode active material deeper than the surface layer 100a is referred to as the inner portion 100b, which is synonymous with the inner region or core.

[0237] Furthermore, when the positive electrode active material 100 has a layered rock-salt crystal structure of space group R-3m, the surface layer portion 100a has an edge region and a basal region. Here, the edge region has a surface exposed in a direction intersecting with the (001) plane (also referred to as a surface other than the (001) orientation), and the edge region is a region extending from the surface to the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm perpendicular or substantially perpendicular from the surface to the interior. Note that, "intersect" here means that the angle between the perpendicular to the first plane (the (001) plane) and the normal to the second plane (the surface of the positive electrode active material 100) is 10 degrees or more and 90 degrees or less, more preferably 30 degrees or more and 90 degrees or less, and even more preferably 50 degrees or more and 90 degrees or less.

[0238] The basal region has a surface parallel to the (001) plane (also referred to as a (001)-oriented surface), and the region extending from the surface to the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm perpendicular or approximately perpendicular from the surface to the interior is referred to as the basal region. Note that "parallel" here means that the angle formed between the perpendicular to the first surface (the (001) plane) and the normal to the second surface (the surface of the positive electrode active material 100) is 0 degrees or more and less than 10 degrees, preferably 0 degrees or more and 5 degrees or less, and more preferably 0 degrees or more and 2.5 degrees or less.

[0239] The surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer 100a and the interior 100b. Therefore, the positive electrode active material 100 does not include metal oxides such as aluminum oxide that do not have lithium sites that can contribute to charge and discharge, carbonates that are chemically adsorbed after the preparation of the positive electrode active material, hydroxyl groups, etc. The attached metal oxide refers to, for example, a metal oxide whose crystal structure does not match that of the interior 100b.

[0240] Furthermore, the positive electrode active material 100 does not include electrolytes, organic solvents, binders, conductive materials, or compounds derived from these materials that are attached to the positive electrode active material 100 .

[0241] Although not shown, the positive electrode active material 100 may have a crystal grain boundary. The crystal grain boundary refers to, for example, a portion where particles of the positive electrode active material 100 adhere to each other, a portion where the crystal orientation changes within the positive electrode active material 100, i.e., a portion where the repetition of bright and dark lines in an STEM image or the like becomes discontinuous, a portion containing many crystal defects, a portion where the crystal structure is disordered, etc. Furthermore, the crystal defect refers to a defect that can be observed in a cross-sectional TEM (transmission electron microscope) image, a cross-sectional STEM image, etc., i.e., a structure in which other atoms have entered between the lattices, a cavity, etc. The crystal grain boundary can be considered a type of planar defect. Furthermore, the vicinity of the crystal grain boundary refers to a region within 10 nm from the crystal grain boundary.

[0242] <Containing Elements> The positive electrode active material 100 contains lithium, a transition metal M, oxygen, and an additive element. The transition metal M is at least one selected from cobalt, nickel, and manganese. Alternatively, the positive electrode active material 100 may be a composite oxide of lithium and the transition metal M (LiMO). ２ However, the positive electrode active material 100 of one embodiment of the present invention may have a distribution or a crystal structure of the additive element described later. Therefore, the composition is not strictly limited to Li:M:O=1:1:2 (atomic ratio).

[0243] The positive electrode active material of a lithium-ion secondary battery must contain a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted and removed. The positive electrode active material 100 of one embodiment of the present invention preferably uses cobalt as the transition metal M responsible for the oxidation and reduction reaction. It is preferable that the positive electrode active material 100 contains 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more of cobalt, among the transition metals M contained in the positive electrode active material 100, because of many advantages such as relatively easy synthesis, ease of handling, and excellent cycle characteristics.

[0244] Furthermore, when cobalt is 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more of the transition metal M in the positive electrode active material 100, lithium nickel oxide (LiNiO ２Compared to composite oxides in which nickel accounts for the majority of the transition metal, such as lithium nickel oxide (LiNiO), the stability when a large amount of lithium is released upon charging is superior. This is thought to be because cobalt is less susceptible to distortion due to the Jahn-Teller effect than nickel. The strength of the Jahn-Teller effect in transition metal compounds varies depending on the number of electrons in the d orbital of the transition metal. Layered rock-salt composite oxides in which octahedral-coordinated low-spin nickel(III) accounts for the majority of the transition metal M, such as lithium nickel oxide, are significantly affected by the Jahn-Teller effect, making the octahedral layers of nickel and oxygen more susceptible to distortion. This increases the risk of crystal structure collapse during charge-discharge cycles. Furthermore, nickel ions are larger than cobalt ions and are closer in size to lithium ions. Therefore, layered rock-salt composite oxides in which nickel accounts for the majority of the transition metal M, such as lithium nickel oxide, have the problem of prone to cation mixing between nickel and lithium.

[0245] The additive elements contained in the positive electrode active material 100 are preferably one or more selected from magnesium, titanium, nickel, aluminum, fluorine, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron.

[0246] That is, the positive electrode active material 100 may include lithium cobalt oxide to which magnesium and titanium are added, lithium cobalt oxide to which magnesium, titanium, and fluorine are added, lithium cobalt oxide to which magnesium, nickel, aluminum, and titanium are added, lithium cobalt oxide to which magnesium, nickel, aluminum, titanium, and fluorine are added, and the like.

[0247] The additive element is preferably dissolved in the positive electrode active material 100. Therefore, for example, when performing a line analysis using STEM-EDX, the depth at which the amount of the additive element detected increases is preferably located deeper than the depth at which the amount of the transition metal M detected increases, i.e., closer to the interior of the positive electrode active material 100.

[0248] In this specification and the like, the depth at which the amount of a certain element detected increases in STEM-EDX line analysis refers to the depth at which measurement values ​​that can be determined not to be noise in terms of intensity, spatial resolution, etc. are continuously obtained.

[0249] These added elements further stabilize the crystal structure of the positive electrode active material 100, as will be described later.

[0250] The additive elements do not necessarily have to include all of fluorine, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron.

[0251] For example, if the cathode active material 100 is substantially free of manganese, the advantages of relatively easy synthesis and handling, and excellent cycle characteristics, are further enhanced. The weight of manganese contained in the cathode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0252] The positive electrode active material 100 has the above-described additive element in the surface layer portion 100a. It is more preferable that the positive electrode active material 100 has a plurality of additive elements. It is also preferable that the surface layer portion 100a has a higher concentration of one or more selected from the additive elements than the inner portion 100b. Alternatively, it is preferable that the surface layer portion 100a has a higher detected amount of one or more selected from the additive elements than the inner portion 100b. It is also preferable that the one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient.

[0253] It is also preferable that the distribution of the positive electrode active material 100 differs depending on the added element. For example, it is more preferable that the depth of the peak of the detected amount in the surface layer 100a from the surface or from a reference point in EDX-ray analysis described below differs depending on the added element. The peak of the detected amount here refers to the maximum value of the detected amount at a depth of 50 nm or less from the surface in the surface layer 100a. The detected amount refers to, for example, the count in EDX-ray analysis.

[0254] [Titanium] The presence of titanium as an additive element in the surface layer portion 100 a can promote the insertion and desorption of lithium ions into and from the positive electrode active material 100 .

[0255] Although titanium exists stably in the octahedral sites coordinated with 6 oxygen atoms in the oxide, titanium oxide and lithium titanate cannot form a stable layered rock salt type crystal structure. For example, TiO ２ The rutile crystal structure is the most stable, and Li ４ Ti ５ O １２ has a spinel-type crystal structure. Therefore, when a small amount of titanium is dissolved in the surface layer 100a having a layered rock salt type or rock salt type crystal structure, defects occur in part of the crystal structure of the surface layer 100a.

[0256] Lithium cobalt oxide is in a discharged state (i.e., Li ｘ CoO ２ When x is 1 in the formula (1), the band gap is large and the resistance is high. Therefore, by introducing titanium defects into a part of the surface layer 100a, the band gap can be narrowed and the resistance can be reduced to a desirable degree.

[0257] Cobalt is also present in the oxide. ３＋ is the most stable, while titanium is Ti ４＋ Therefore, the charge on the lithium ion around titanium is relatively lower than that around cobalt. ４＋ Defects may be induced in the cation sites near the titanium, and such defects reduce the diffusion resistance of cations, especially lithium ions. Therefore, the diffusion resistance of lithium ions is reduced around the titanium. Note that part of the cobalt around the titanium is Co ２＋ It may be the case.

[0258] Therefore, the presence of titanium in the surface layer portion 100a can reduce the diffusion resistance of lithium ions at the interface between the electrolyte and the positive electrode active material 100. Furthermore, it is believed that the titanium present in the surface layer portion 100a does not significantly reduce the electrical resistance (e.g., volume resistivity) of the positive electrode active material 100. A relatively high electrical resistance of the positive electrode active material 100 is preferable because it contributes to safety in the event of a short circuit in the secondary battery.

[0259] If the amount of titanium is too small, the effect of promoting the insertion and desorption of lithium ions described above is not fully exhibited. On the other hand, if the amount of titanium is too large, it may form a different phase from other added elements such as magnesium (for example, MgTiO with an ilmenite-type crystal structure). ３ Furthermore, magnesium may be lost in the formation of a different phase, which may reduce the magnesium concentration in the surface layer 100a, whose crystal structure is roughly the same as that of the interior 100b. ＋ For the positive electrode active material 100 of one embodiment of the present invention, which is intended for high-voltage charging exceeding 100 V, magnesium present at a high concentration in the surface layer portion 100a is essential for suppressing phase change. Therefore, the loss of magnesium due to heterophase formation is a significant disadvantage. Furthermore, if there are too many titanium defects, there is a concern that oxygen may be more likely to be desorbed from the surface. Therefore, titanium, together with magnesium, fluorine, and the like, is preferably present at a lower concentration than magnesium in the surface and near-surface regions of the surface layer portion 100a.

[0260] Specifically, the Ti / Co ratio of the entire positive electrode active material is preferably 0.0001 (atomic ratio) or more, more preferably 0.001 (atomic ratio) or more, and is preferably less than 0.0075 (atomic ratio), more preferably 0.004 (atomic ratio) or less, and even more preferably 0.003 (atomic ratio) or less.

[0261] Furthermore, in EDX analysis of the surface layer portion 100a, when the denominator is the sum of carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, gallium, and molybdenum, the maximum titanium concentration is preferably 0.3 at% or more and 3 at% or less, and more preferably 0.5 at% or more and 2 at% or less.

[0262] The titanium source is not particularly limited, but may be, for example, TiO ２ Titanium oxide such as Li ２ TiO ３ , LiTiO ２ , Li ４ Ti ５ O １２Lithium titanate such as the above can be used.

[0263] Furthermore, the element that can be added to promote the insertion and desorption of lithium ions is not limited to titanium. Other elements may also be added. When using elements other than titanium, it is preferable that the element stably exists at the hexacoordinated octahedral oxygen site in the oxide, but that the oxide of lithium and the element does not form a stable layered rock-salt type crystal structure. Furthermore, elements that are stable at a higher oxidation number than cobalt are preferable. For example, niobium, manganese, tungsten, chromium, molybdenum, rhenium, tantalum, etc. can be used.

[0264] [Distribution] To achieve the above-described effect, it is preferable that the concentration of at least magnesium, nickel, and titanium among the additive elements is higher in the surface layer 100a than in the interior 100b, as shown in FIG. 18B. Alternatively, it is preferable that the detected amount in the surface layer 100a is greater than that in the interior 100b. Furthermore, it is preferable that the detected amount peak in the surface layer 100a be closer to the surface. For example, it is preferable that the detected amount peak be located on the surface or within 3 nm from the reference point. It is also preferable that the distributions of magnesium and nickel overlap. The detected amount peaks of magnesium and nickel may be at the same depth, or the magnesium peak may be closer to the surface, or the nickel peak may be closer to the surface. The difference in depth between the detected amount peak of nickel and the detected amount peak of magnesium is preferably within 3 nm, and more preferably within 1 nm. Furthermore, it is preferable that the half-width of the detected amount is narrow. In this specification, the half-width refers to the full width at half maximum.

[0265] Similarly, it is preferable that the distributions of magnesium and titanium overlap. The peaks of the detected amounts of magnesium and titanium may be at the same depth, or the magnesium peak may be closer to the surface, or the titanium peak may be closer to the surface. The difference in depth between the peak of the detected amount of titanium and the peak of the detected amount of magnesium is preferably within 3 nm, and more preferably within 1 nm. It is also preferable that the half-width of the detected amount is narrow.

[0266] In other words, it is preferable that the distributions of magnesium, nickel, and titanium overlap. The difference in depth between the peaks of the detected amount of titanium, nickel, and magnesium is preferably within 3 nm, and more preferably within 1 nm. It is also preferable that the half-width of the detected amount is narrow.

[0267] The above-mentioned region where the distributions of magnesium and nickel overlap, the region where the distributions of magnesium and titanium overlap, or the region where the distributions of magnesium, nickel, and titanium overlap is preferably located in the edge region of the surface layer portion 100a where lithium ions are inserted and desorbed. In other words, the distribution of the additional element shown in the schematic diagram of Figure 18B is preferably observed in the direction of the X1-X2 arrow in Figure 18A. On the other hand, the above-mentioned overlapping region is not necessarily required in the basal region of the surface layer portion 100a.

[0268] Furthermore, the amount of nickel detected in the inner portion 100b is very small compared to the surface portion 100a, or may not be detected, or may be 1 atomic % or less.

[0269] Although not shown, it is preferable that the detectable amount of fluorine in the surface layer portion 100a is greater than the detectable amount inside, similar to magnesium or nickel. It is also preferable that the detectable amount peak in the surface layer portion 100a is closer to the surface. For example, it is preferable that the detectable amount peak is on the surface or within 3 nm from the reference point. Similarly, it is preferable that the detectable amount of titanium, silicon, phosphorus, boron, and / or calcium is greater than the detectable amount inside the surface layer portion 100a. It is also preferable that the detectable amount peak is on the surface or within 3 nm from the reference point.

[0270] Furthermore, it is preferable that at least aluminum, among the additive elements, has a peak of detection amount further inward than magnesium and titanium. As shown in FIG. 18B, the distributions of magnesium and aluminum may overlap, but there may be almost no overlapping region. The peak of detection amount of aluminum may be present in the surface layer portion 100a, or may be deeper than the surface layer portion 100a. For example, it is preferable that the peak be present on the surface, or in a region of 5 nm to 30 nm from the reference point toward the interior.

[0271] The distribution of aluminum as described above can further stabilize the layered rock-salt crystal structure of the positive electrode active material 100. For example, it is expected that the change from the layered rock-salt crystal structure to a spinel crystal structure in the surface layer 100a of the positive electrode active material 100 can be suppressed. The spinel crystal structure generated in the layered rock-salt crystal structure may move or expand due to the transfer of charge of the transition metal M. Furthermore, defects such as grain boundaries in the positive electrode active material 100 can serve as diffusion paths for lithium ions in the c-axis direction. Additional elements such as aluminum may be present near the defects. In other words, the presence of aluminum may facilitate the diffusion of lithium ions.

[0272] The reason why aluminum is distributed deeper than magnesium and titanium is thought to be because aluminum has a faster diffusion rate than magnesium. On the other hand, the reason why the amount of aluminum detected in the region closest to the surface is low is presumably because aluminum exists more stably in regions where magnesium and other elements are not present in solid solution at high concentrations than in regions where they are not.

[0273] More specifically, in the region of the layered rock salt type of space group R-3m or the cubic rock salt type where magnesium is dissolved at a high concentration, layered rock salt type LiAlO ２ Compared to the case of cobalt, the distance between the cation and oxygen is long, making it difficult for aluminum to exist stably. ＋ is Mg ２＋ The valence change due to substitution to Co ３＋ From Co ２＋However, since Al can only be trivalent, it is thought that it is difficult for it to exist stably near magnesium in rock salt or layered rock salt structures.

[0274] However, the added element does not necessarily have to have the same concentration gradient or distribution throughout the entire surface layer portion 100 a of the positive electrode active material 100 .

[0275] The (001)-oriented surface of the positive electrode active material 100 may have a different distribution of additive elements than the other surfaces. For example, the (001)-oriented surface and its surface layer 100a may have a lower detectable amount of one or more additive elements compared to surfaces other than the (001)-oriented surface. Specifically, the detectable amount of one or more of magnesium, nickel, and titanium may be low. Alternatively, the (001)-oriented surface and its surface layer 100a may have no detectable amount of one or more additive elements or a detectable amount of 1 atomic % or less. Specifically, the detectable amount of nickel may be no detectable amount or 1 atomic % or less. In particular, with analytical methods that detect characteristic X-rays such as EDX, the Kβ of cobalt and the Kα of nickel are close in energy, making it difficult to detect trace amounts of nickel in materials where cobalt is the primary element. Alternatively, the (001)-oriented surface and its surface layer 100a may have a peak detectable amount of one or more additive elements shallower from the surface compared to surfaces other than the (001)-oriented surface. Specifically, the peaks of the detected amounts of magnesium and aluminum may be shallower than those of other surfaces.

[0276] In the layered rock salt type crystal structure of R-3m, cations are arranged parallel to the (001) plane. ２ The structure is composed of alternately stacked layers and lithium layers parallel to the (001) plane, and the diffusion path of lithium ions is also parallel to the (001) plane.

[0277] MO ２ Since the layer is relatively stable, it is more stable if the surface of the positive electrode active material 100 has a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.

[0278] On the other hand, the diffusion path of lithium ions is exposed on the surface other than the (001) orientation. Therefore, the surface and the surface layer 100a other than the (001) orientation are important regions for maintaining the diffusion path of lithium ions, and at the same time, they are regions from which lithium ions are first desorbed and are therefore prone to instability. Therefore, reinforcing the surface and the surface layer 100a other than the (001) orientation is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.

[0279] Therefore, in the positive electrode active material 100 according to another embodiment of the present invention, it is important that the distribution of the additive elements in the surface and the surface layer 100a other than the (001) orientation is, for example, as shown in FIG. 18B . Of the additive elements, nickel is particularly preferably detected in the surface and the surface layer 100a other than the (001) orientation. On the other hand, the concentration of the additive element in the (001)-oriented surface and the surface layer 100a may be low or absent, as described above.

[0280] For example, the magnesium distribution in the (001)-oriented surface and its surface layer 100a preferably has a half-width of 10 nm to 200 nm, more preferably 50 nm to 150 nm, and even more preferably 80 nm to 120 nm. Also, the magnesium distribution in the non-(001)-oriented surface and its surface layer 100a preferably has a half-width of more than 200 nm to 500 nm, more preferably more than 200 nm to 300 nm, and even more preferably 230 nm to 270 nm.

[0281] Furthermore, the nickel distribution in the surface that is not (001) oriented and in the surface layer 100a thereof preferably has a half-width of 30 nm or more and 150 nm or less, more preferably 50 nm or more and 130 nm or less, and even more preferably 70 nm or more and 110 nm or less.

[0282] High-purity LiMO, which will be described in a later embodiment ２In the manufacturing method in which the additive element is mixed and heated after the (001) orientation, the additive element spreads mainly through the diffusion path of lithium ions, and therefore the distribution of the additive element in the surface other than the (001) orientation and in the surface layer 100a thereof can be easily controlled to a preferred range.

[0283] [Magnesium] Magnesium is divalent, and magnesium ions are more stable at the lithium site than at the cobalt site in the layered rock salt crystal structure, so they are more likely to enter the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer 100a makes it easier to maintain the layered rock salt crystal structure. This is because magnesium present at the lithium site is easily absorbed by the MO ２ It is presumed that this is because it functions as a pillar supporting the layers. ｘ CoO ２ When x in the formula (1) is, for example, 0.24 or less, the desorption of oxygen from around the magnesium can be suppressed. Furthermore, the presence of magnesium is expected to increase the density of the positive electrode active material 100. Furthermore, a high magnesium concentration in the surface layer portion 100a is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0284] At an appropriate concentration, magnesium does not adversely affect the lithium intercalation and deintercalation processes during charging and discharging, providing the above benefits. However, excessive magnesium may adversely affect lithium intercalation and deintercalation. Furthermore, its effect on stabilizing the crystal structure may be reduced. This is thought to be due to magnesium occupying both the lithium and cobalt sites. Furthermore, unnecessary magnesium compounds (e.g., oxides and fluorides) that do not substitute for either the lithium or cobalt sites may segregate on the surface of the positive electrode active material and become resistance components in secondary batteries. Furthermore, as the magnesium concentration in the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be due to excessive magnesium occupancy at the lithium sites, reducing the amount of lithium contributing to charging and discharging.

[0285] Therefore, it is preferable that the amount of magnesium contained in the entire positive electrode active material 100 is appropriate. For example, the number of magnesium atoms is preferably 0.002 to 0.06 times the number of cobalt atoms, more preferably 0.005 to 0.03 times, and even more preferably about 0.01 times. The amount of magnesium contained in the entire positive electrode active material 100 referred to here may be a value obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.

[0286] [Nickel] Nickel is LiMO ２ In the layered rock salt crystal structure of the present invention, nickel can exist on either the cobalt site or the lithium site. When present on the cobalt site, its redox potential is lower than that of cobalt, making it easier to release lithium and electrons during charging. This can be expected to result in faster charge and discharge speeds. Therefore, even at the same charge voltage, a greater charge and discharge capacity can be obtained when the transition metal M is nickel than when it is cobalt.

[0287] Furthermore, when nickel exists at the lithium site, the layer structure consisting of octahedra of cobalt and oxygen can be prevented from shifting. Also, the change in volume caused by charging and discharging is prevented. Also, the elastic modulus increases, that is, the material becomes hard. This is because nickel existing at the lithium site also acts as a catalyst for MO ２ This is presumably because they function as pillars supporting the layers together, which is preferable because it is expected that the crystal structure will be more stable especially in a charged state at high temperatures, for example, 45° C. or higher.

[0288] In addition, the distance between the cations and anions of nickel oxide (NiO) is closer to that of LiCoO than that of rock salt MgO and rock salt CoO. ２ The average distance between the cations and anions is close to that of LiCoO ２ The orientation is likely to match.

[0289] In addition, the order of ionization tendency is lowest for magnesium, aluminum, cobalt, and nickel (Mg>Al>Co>Ni). Therefore, nickel is thought to be less likely to dissolve into the electrolyte than the other elements listed above during charging. Therefore, it is thought to be highly effective in stabilizing the crystalline structure of the surface layer in the charged state.

[0290] Furthermore, nickel is Ni ２＋ , Ni ３＋ , Ni ４＋ Of which Ni ２＋ is the most stable, and nickel has a higher trivalent ionization energy than cobalt. Therefore, it is known that nickel and oxygen alone do not form a spinel-type crystal structure. Therefore, nickel is thought to have the effect of suppressing the phase change from the layered rock salt type to the spinel-type crystal structure.

[0291] On the other hand, excessive nickel is undesirable because it increases the influence of strain due to the Jahn-Teller effect, and excessive nickel may also adversely affect lithium insertion and extraction.

[0292] Therefore, it is preferable that the entire positive electrode active material 100 contains an appropriate amount of nickel. For example, the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% but not more than 7.5% of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Alternatively, more than 0% but not more than 4% is preferable. Alternatively, more than 0% but not more than 2% is preferable. Alternatively, 0.05% to 7.5% is preferable. Alternatively, 0.05% to 2% is preferable. Alternatively, 0.1% to 7.5% is preferable. Alternatively, 0.1% to 4% is preferable. The amount of nickel shown here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0293] [Aluminum] Aluminum can also be present at the cobalt site in a layered rock salt crystal structure. Because aluminum is a trivalent typical element and its valence does not change, lithium around the aluminum is less likely to move during charging and discharging. Therefore, the aluminum and its surrounding lithium function as pillars, suppressing changes in the crystal structure. Therefore, as described below, even if the positive electrode active material 100 experiences a force that causes it to expand and contract in the c-axis direction due to the insertion and desorption of lithium ions, i.e., even if a force that causes it to expand and contract in the c-axis direction due to changes in the charge depth or charge rate occurs, deterioration of the positive electrode active material 100 can be suppressed.

[0294] Aluminum also has the effect of suppressing the elution of surrounding cobalt and improving continuous charge durability. Furthermore, since the Al—O bond is stronger than the Co—O bond, it can suppress the desorption of oxygen from the aluminum's surroundings. These effects improve thermal stability. Therefore, the presence of aluminum as an additive element can improve safety when the positive electrode active material 100 is used in a secondary battery. Furthermore, the positive electrode active material 100 can be made to have a crystal structure that is resistant to collapse even after repeated charge and discharge.

[0295] On the other hand, an excess of aluminum may adversely affect the intercalation and deintercalation of lithium.

[0296] Therefore, it is preferable that the amount of aluminum contained in the entire positive electrode active material 100 is appropriate. For example, the number of aluminum atoms contained in the entire positive electrode active material 100 is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferable. Alternatively, 0.1% to 4% is preferable. The amount contained in the entire positive electrode active material 100 referred to here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.

[0297] [Fluorine] Fluorine is a monovalent anion, and when a portion of the oxygen in the surface layer portion 100a is replaced by fluorine, the lithium desorption energy decreases. This is because the redox potential of cobalt ions accompanying lithium desorption differs depending on the presence or absence of fluorine. That is, in the absence of fluorine, cobalt ions change from trivalent to tetravalent upon lithium desorption. On the other hand, when fluorine is present, cobalt ions change from divalent to trivalent upon lithium desorption. The redox potential of cobalt ions differs between the two. Therefore, when a portion of the oxygen in the surface layer portion 100a of the positive electrode active material 100 is replaced by fluorine, it can be said that desorption and insertion of lithium ions near the fluorine easily occurs. Therefore, when the positive electrode active material 100 is used in a secondary battery, the charge / discharge characteristics, large current characteristics, etc. can be improved. Furthermore, the presence of fluorine in the surface layer portion 100a, which has a surface that contacts the electrolyte, or the adhesion of fluoride to the surface, can suppress excessive reaction between the positive electrode active material 100 and the electrolyte. Furthermore, corrosion resistance to hydrofluoric acid can be effectively improved.

[0298] Furthermore, when the melting point of a fluoride such as lithium fluoride is lower than the melting point of the other additive element source, it can function as a flux (also called a fluxing agent) that lowers the melting point of the other additive element source. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, it is preferable to set the heating temperature to 742°C or higher in the heating step after mixing the additive element.

[0299] Here, differential scanning calorimetry (DSC measurement) for fluorides and mixtures will be described with reference to Figures 19A and 19B. In both cases, the horizontal axis represents the temperature of the sample, and the vertical axis represents the difference in heat flow with respect to the reference. The DSC measurement device and conditions are not particularly limited, but in this embodiment, measurements were performed using the following device and conditions. DSC device: EVO2 DSC8271 manufactured by Rigaku Corporation Heating rate: 20°C / min The obtained measurement results were subjected to background correction using the analysis software Thermo Plus EVO, and the initial melting temperature T ｉｍ , melting peak temperature Tｐｍ and the melting end temperature T ｅｍ The heat flow was calculated as the heat flow per sample weight.

[0300] FIG. 19A shows a fluoride mixture of lithium fluoride and magnesium fluoride, LiF:MgF ２ 19B shows the DSC measurement results of the mixture to which lithium cobalt oxide (C-10N manufactured by Nippon Chemical Industry Co., Ltd.) was added. ２ :LiF:MgF ２ The components were mixed so that the molar ratio was 100:0.33:1.

[0301] As shown in FIG. 19A, the initial melting temperature T ｉｍ is 731 ° C, the melting peak temperature T ｐｍ is 739°C, and the melting end temperature T ｅｍ The T of the mixture of lithium cobalt oxide, lithium fluoride, and magnesium fluoride was 746°C. ｉｍ is 779°C, T ｐｍ is 815℃, T ｅｍ The temperature was 826°C.

[0302] Therefore, the heating temperature after mixing the additive element is preferably 731°C or higher, and more preferably 826°C or higher. Alternatively, a temperature of 800°C or higher, which is between these two, is also acceptable. A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is high; however, if the temperature is too high, there is a risk of decomposition of lithium cobalt oxide. Therefore, the upper limit of the heating temperature is set to be lower than 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 a small amount. Therefore, a temperature of 1000°C or lower is more preferable.

[0303] [Other additive elements] When phosphorus is contained in the surface layer portion 100a, Li ｘ CoO ２ When the value of x in the graph is kept small, short circuits can be prevented, which is preferable. For example, it is preferable that the graphite oxide is present in the surface layer portion 100a as a compound containing phosphorus and oxygen.

[0304] When the positive electrode active material 100 contains phosphorus, the phosphorus reacts with hydrogen fluoride generated by decomposition of the electrolytic solution or electrolyte, which may reduce the concentration of hydrogen fluoride in the electrolyte, which is preferable.

[0305] The electrolyte is LiPF ６ In the case where the electrolyte contains PVDF, there is a risk of hydrogen fluoride being generated by hydrolysis. Furthermore, hydrogen fluoride may also be generated by a reaction between polyvinylidene fluoride (PVDF), which is used as a component of the positive electrode, and an alkali. By reducing the hydrogen fluoride concentration in the electrolyte, corrosion of the current collector and / or peeling of the coating 104 may be suppressed. Furthermore, there is a risk of suppressing a decrease in adhesion due to gelation and / or insolubilization of PVDF.

[0306] When the positive electrode active material 100 contains phosphorus together with magnesium, Li ｘ CoO ２ This is preferable because stability is extremely high when x is small in the positive electrode active material 100. When the positive electrode active material 100 contains phosphorus, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. Alternatively, 1% to 10% is preferable. Alternatively, 1% to 8% is preferable. Alternatively, 2% to 20% is preferable. Alternatively, 2% to 8% is preferable. Alternatively, 3% to 20% is preferable. Alternatively, 3% to 10% is preferable. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and more preferably 0.7% to 4%. Alternatively, 0.1% to 5% is preferable. Alternatively, 0.1% to 4% is preferable. Alternatively, 0.5% to 10% is preferable. Alternatively, 0.5% to 4% is preferable. Alternatively, 0.7% to 10% is preferable. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by performing elemental analysis of the entire cathode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on values ​​of the composition of raw materials in the process of producing the cathode active material 100.

[0307] Furthermore, when the positive electrode active material 100 has cracks, the progression of the cracks can be suppressed by the presence of phosphorus, more specifically, a compound containing phosphorus and oxygen, inside the positive electrode active material with the cracks on the surface, for example, in the embedded portion.

[0308] [Synergistic Effect of Multiple Added Elements] Furthermore, when the surface layer portion 100a contains both magnesium and nickel, there is a possibility that divalent nickel can exist more stably near divalent magnesium. ｘ MO ２ Even when the value of x in the formula is small, the elution of magnesium can be suppressed, which can contribute to the stabilization of the surface layer portion 100a.

[0309] For the same reason, when adding an additive element to lithium cobalt oxide in the manufacturing process, it is preferable to add magnesium in a step before adding nickel. Alternatively, it is preferable to add magnesium and nickel in the same step. Magnesium has a large ionic radius and tends to remain in the surface layer of lithium cobalt oxide regardless of the step in which it is added, whereas nickel can diffuse widely into the interior of lithium cobalt oxide in the absence of magnesium. Therefore, if nickel is added before magnesium, there is a concern that nickel will diffuse into the interior of the lithium cobalt oxide and not remain in the surface layer in the desired amount.

[0310] Furthermore, when the surface layer 100a contains magnesium, nickel, and titanium, the presence of nickel results in the formation of MgTiO with an ilmenite-type crystal structure. ３ The formation of heterophases such as MgTiO is suppressed. The ilmenite crystal structure has hexagonal close-packed anions, which differs from the rock salt and layered rock salt crystal structures, which have cubic close-packed anions, and therefore requires a certain amount of activation energy for the phase transition. NiO(II) is a compound with low chemical activity, so MgTiO ３ It has the effect of suppressing the production of

[0311] For the above reasons, when adding an additional element to lithium cobalt oxide in the manufacturing process, if titanium is added in a process later than magnesium and nickel, the effect of nickel in suppressing the formation of heterophases is particularly strong.

[0312] Furthermore, having additive elements with different distributions in combination is preferable because it can stabilize the crystal structure in a wider region. For example, if the positive electrode active material 100 has both magnesium and nickel distributed in a region closer to the surface of the surface layer 100a and aluminum distributed in a deeper region, it can stabilize the crystal structure in a wider region than if it had only one of these elements. In this way, when the positive electrode active material 100 has additive elements with different distributions in combination, aluminum is not essential to the surface because surface stabilization can be sufficiently achieved by magnesium, nickel, etc. Rather, it is preferable for aluminum to be widely distributed in a deeper region. For example, it is preferable for aluminum to be continuously detected in a region from 1 nm to 25 nm in the depth direction from the surface. A wide distribution in a region from 0 nm to 100 nm from the surface, preferably a region from 0.5 nm to 50 nm from the surface, is preferable because it can stabilize the crystal structure in a wider region.

[0313] When a plurality of additive elements are contained as described above, the effects of the respective additive elements are synergistic and can contribute to further stabilization of the surface layer portion 100 a. In particular, when magnesium, nickel, and aluminum are contained, the effect of providing a stable composition and crystal structure is high and is therefore preferable.

[0314] However, if the surface layer 100a is occupied only by a compound of the additive element and oxygen, it is not preferable because it makes it difficult to insert and extract lithium. For example, it is not preferable for the surface layer 100a to be occupied only by MgO or a structure in which MgO and MO(II) are solid-solved. Therefore, the surface layer 100a must contain at least a transition metal M such as cobalt, and also contain lithium in the discharged state, so that it has a path for the insertion and extraction of lithium.

[0315] In order to ensure sufficient paths for lithium insertion and desorption, the surface layer portion 100a preferably has a higher cobalt concentration than magnesium. For example, when measured from the surface of the positive electrode active material 100 by XPS, the ratio Mg / Co of the number of magnesium atoms Mg to the number of cobalt atoms Co is preferably 0.62 or less. The surface layer portion 100a preferably has a higher cobalt concentration than nickel. The surface layer portion 100a preferably has a higher cobalt concentration than aluminum. The surface layer portion 100a preferably has a higher cobalt concentration than fluorine.

[0316] Furthermore, since an excessive amount of nickel may inhibit the diffusion of lithium, it is preferable that the concentration of magnesium is higher than that of nickel in the surface layer portion 100 a. For example, when measured from the surface of the positive electrode active material 100 by XPS, the number of nickel atoms is preferably 1 / 6 or less of the number of magnesium atoms.

[0317] Furthermore, while it is preferable that some of the added elements, particularly magnesium, nickel, and aluminum, have a higher concentration in the surface layer 100a than in the interior 100b, they are also preferably present randomly and dilutely in the interior 100b. When magnesium and aluminum are present at appropriate concentrations at the lithium sites in the interior 100b, it has the effect of making it easier to maintain the layered rock-salt crystal structure, as described above. Furthermore, when nickel is present at an appropriate concentration in the interior 100b, it can suppress the shift in the layered structure consisting of cobalt and oxygen octahedra, as described above. Furthermore, when magnesium and nickel are present together, a synergistic effect of suppressing magnesium elution can be expected, as described above.

[0318] It is preferable that the crystal structure continuously changes from the interior 100b toward the surface due to the concentration gradient of the added element as described above, or that the crystal orientation of the surface layer 100a and the interior 100b roughly coincide.

[0319] For example, it is preferable that the crystal structure continuously change from the interior 100b of the layered rock salt type toward the surface and surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type. Alternatively, it is preferable that the crystal orientation of the surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type, and the interior 100b of the layered rock salt type are roughly the same.

[0320] In this specification, the layered rock-salt crystal structure belonging to the space group R-3m, which is possessed by a composite oxide containing lithium and a transition metal such as cobalt, refers to a crystal structure having a rock-salt ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as vacancies of cations or anions may also be present. Furthermore, strictly speaking, the layered rock-salt crystal structure may have a structure in which the lattice of the rock-salt crystal is distorted.

[0321] The rock salt crystal structure refers to a cubic crystal structure, such as a crystal structure belonging to the space group Fm-3m, in which cations and anions are arranged alternately, and may contain cation or anion defects.

[0322] The fact that it has both the characteristics of the layered rock salt type and the rock salt type crystal structure can be determined by electron diffraction, TEM images, cross-sectional STEM images, and the like.

[0323] In the rock salt type, there is no distinction in the cation sites, but in the layered rock salt type, there are two types of cation sites in the crystal structure, one of which is mostly occupied by lithium and the other by a transition metal. The layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged is the same for both the rock salt type and the layered rock salt type. Among the bright spots in the electron diffraction pattern corresponding to the crystal planes that form this two-dimensional plane, when the central spot (transmitted spot) is set as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in the ideal rock salt type, and, for example, the (003) plane in the layered rock salt type. For example, rock salt type MgO and layered rock salt type LiCoO ２ When comparing the electron diffraction patterns of LiCoO ２The distance between the bright spots on the (003) plane of LiCoO is observed to be about half the distance between the bright spots on the (111) plane of MgO. ２ In the case of a material with these two phases, the electron diffraction pattern shows a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. Bright spots common to both the rock salt type and the layered rock salt type have strong brightness, while bright spots occurring only in the layered rock salt type have weak brightness.

[0324] Furthermore, when a layered rock-salt crystal structure is observed from a direction perpendicular to the c-axis in cross-sectional STEM images, layers observed with high brightness and layers observed with low brightness are observed alternately. This characteristic is not observed in the rock-salt structure, as there is no distinction in the cation sites. In the case of a crystal structure that has the characteristics of both the rock-salt and layered rock-salt structures, when observed from a specific crystal orientation, layers observed with high brightness and layers observed with low brightness are observed alternately in cross-sectional STEM images, and furthermore, metals with atomic numbers higher than that of lithium are present in some of the low-brightness layers, i.e., the lithium layers.

[0325] Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in the O3'-type and monoclinic O1(15) crystals described below also have a cubic close-packed structure. Therefore, when a layered rock salt crystal and a rock salt crystal come into contact, there are crystal faces where the cubic close-packed structure formed by the anions is aligned.

[0326] Alternatively, it can be explained as follows: Anions on the {111} plane of a cubic crystal structure have a triangular lattice. Layered rock salt has a space group R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally expressed as a compound hexagonal lattice, and the (0001) plane of the layered rock salt has a hexagonal lattice. The triangular lattice on the cubic {111} plane has the same atomic arrangement as the hexagonal lattice on the (0001) plane of the layered rock salt. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structures.

[0327] However, the space group of the layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group Fm-3m (space group of general rock salt crystals) of the rock salt crystals, and therefore the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt crystals and O3'-type crystals and the rock salt crystals. In this specification, when the orientations of the cubic close-packed structures formed by anions in the layered rock salt crystals, O3'-type and rock salt crystals are aligned, it may be said that the crystal orientations are approximately the same. In addition, having a three-dimensional structural similarity such that the crystal orientations are approximately the same, or having the same crystallographic orientation, is called topotaxis.

[0328] The fact that the crystal orientations of the two regions roughly coincide can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron beam diffraction patterns, and the like. The determination can also be made based on the FFT pattern of a TEM image, the FFT pattern of a STEM image, etc. Furthermore, XRD (X-ray diffraction), neutron diffraction, etc. can also be used as materials for the determination.

[0329] 20 shows an example of a TEM image in which the orientations of the layered rock salt crystals LRS and the rock salt crystals RS are roughly the same. Images reflecting the crystal structure can be obtained in TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc.

[0330] For example, in high-resolution TEM images, contrast originating from crystal planes can be observed. When an electron beam is incident perpendicularly to the c-axis of a layered rock-salt type composite hexagonal lattice, for example, due to the diffraction and interference of the electron beam, the contrast originating from the (0003) plane is observed as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, a repetition of bright and dark lines is observed in the TEM image, and the bright lines (for example, the L shown in FIG. 20) ＲＳ and L ＬＲＳ When the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal planes are roughly aligned, i.e., the crystal orientations are roughly aligned. Similarly, when the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are roughly aligned.

[0331] Furthermore, in HAADF-STEM images, contrast proportional to atomic number is obtained, with elements with higher atomic numbers appearing brighter. For example, in the case of layered rock-salt lithium cobaltate belonging to the space group R-3m, cobalt (atomic number 27) has the highest atomic number, so the electron beam is strongly scattered at the cobalt atoms, and the arrangement of the cobalt atoms is observed as a bright line or an arrangement of highly bright dots. Therefore, when lithium cobaltate with a layered rock-salt crystal structure is observed perpendicular to the c-axis, the arrangement of the cobalt atoms perpendicular to the c-axis is observed as a bright line or an arrangement of highly bright dots, while the arrangements of lithium and oxygen atoms are observed as dark lines or low-brightness regions. The same is true when lithium cobaltate contains fluorine (atomic number 9) and magnesium (atomic number 12) as additive elements.

[0332] Therefore, in an HAADF-STEM image, when repetitions of bright and dark lines are observed in two regions with different crystal structures and the angle between the bright lines is 5 degrees or less or 2.5 degrees or less, it can be determined that the atomic arrangements are roughly consistent, i.e., the crystal orientations are roughly consistent. Similarly, when the angle between the dark lines is 5 degrees or less or 2.5 degrees or less, it can also be determined that the crystal orientations are roughly consistent.

[0333] In ABF-STEM, elements with smaller atomic numbers are observed brighter, but like HAADF-STEM, contrast according to the atomic number is obtained, so the crystal orientation can be determined in the same way as with HAADF-STEM images.

[0334] Figure 21A shows an example of an STEM image in which the orientations of the layered rock salt crystal LRS and the rock salt crystal RS roughly coincide. Figure 21B shows the FFT pattern of the region of the rock salt crystal RS, and Figure 21C shows the FFT pattern of the region of the layered rock salt crystal LRS. The left side of Figures 21B and 21C shows the composition, JCPDS card number, and d value and angle calculated from the data on the JCPDS card. The right side shows the measured values. The spot marked with O is the zeroth-order diffraction.

[0335] The spot marked A in Figure 21B is derived from the 11-1 reflection of the cubic crystal. The spot marked A in Figure 21C is derived from the 0003 reflection of the layered rock salt type. From Figures 21B and 21C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 21B is roughly parallel to the line passing through AO in Figure 21C. Here, "roughly coincident" and "roughly parallel" mean that the angle is 5 degrees or less, or 2.5 degrees or less.

[0336] In this way, in the FFT pattern and the electron beam diffraction pattern, when the orientations of the layered rock salt type crystal and the rock salt type crystal are roughly the same, the <0003> orientation of the layered rock salt type and the <11-1> orientation of the rock salt type may roughly coincide. In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. A reciprocal lattice point being spot-like and not continuous with other reciprocal lattice points means high crystallinity.

[0337] Furthermore, as described above, when the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt crystal are approximately the same, depending on the incident orientation of the electron beam, spots not originating from the 0003 reflection of the layered rock salt crystal may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt crystal. For example, the spot marked B in FIG. 21C originates from the 1014 reflection of the layered rock salt crystal. This spot may be observed at an angle of 52° to 56° (i.e., ∠AOB is 52° to 56°) from the orientation of the reciprocal lattice point (A in FIG. 21C) originating from the 0003 reflection of the layered rock salt crystal, and at a point where d is 0.19 nm to 0.21 nm. Note that this index is merely an example and does not necessarily have to be identical. For example, reciprocal lattice points equivalent to 0003 and 1014 may also be used.

[0338] Similarly, spots not originating from the 11-1 reflection of the cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of the cubic crystal is observed. For example, the spot marked B in FIG. 21B is originating from the 200 reflection of the cubic crystal. This is because a diffraction spot may be observed at an angle of 54° or more and 56° or less (i.e., ∠AOB is 54° or more and 56° or less) from the orientation of the reflection (A in FIG. 21B) originating from the 11-1 reflection of the cubic crystal. Note that this index is merely an example and does not necessarily have to match this. For example, reciprocal lattice points equivalent to the 11-1 and 200 reflections of the cubic crystal may also be used.

[0339] It is known that layered rock salt type positive electrode active materials, such as lithium cobalt oxide, tend to have the (0003) plane and its equivalents, as well as the (10-14) plane and its equivalents, as crystal planes. Therefore, for example, when observing the (0003) plane using a TEM or the like, first select positive electrode active material particles in which a crystal plane expected to be the (0003) plane is observed using a SEM or the like, and then thin-section the positive electrode active material particles using a FIB (Focused Ion Beam) or the like so that the (0003) plane can be observed in a TEM or the like with an electron beam incident in the [12-10] direction. When determining whether the crystal orientation is consistent, it is preferable to thin-section the layered rock salt type (0003) plane so that it is easy to observe.

[0340] <Crystal structure> <Liｘ MO ２ When x is 1 in the positive electrode active material 100 of one embodiment of the present invention is in a discharged state, that is, Li ｘ MO ２ When x = 1 in the formula, the composite oxide has a layered rock-salt type crystal structure belonging to the space group R-3m. Layered rock-salt type composite oxides have high discharge capacity, have two-dimensional lithium ion diffusion paths, and are suitable for lithium ion insertion / extraction reactions, making them excellent as positive electrode active materials for secondary batteries. Therefore, it is particularly preferable that the inner portion 100b, which occupies the majority of the volume of the positive electrode active material 100, has a layered rock-salt type crystal structure. Figure 22 shows the layered rock-salt type crystal structure, labeled R-3m O3. R-3m O3 has lattice constants a = 2.81610, b = 2.81610, c = 14.05360, α = 90.0000, β = 90.0000, γ = 120.0000, and the coordinates of lithium, cobalt, and oxygen in the unit cell are Li(0,0,0), Co(0,0,0.5), and O(0,0,0.23951).

[0341] On the other hand, the surface layer portion 100a of the cathode active material 100 according to one embodiment of the present invention preferably has a function of reinforcing the inner portion 100b so that the layered structure of the transition metal M and oxygen octahedra is not destroyed even when lithium is removed from the cathode active material 100 upon charging. Alternatively, the surface layer portion 100a preferably functions as a barrier film for the cathode active material 100. Alternatively, the surface layer portion 100a, which is the outer periphery of the cathode active material 100, preferably reinforces the cathode active material 100. Here, "reinforcement" refers to suppressing structural changes in the surface layer portion 100a and inner portion 100b of the cathode active material 100, such as oxygen desorption and / or shifting of the layered structure of the transition metal M and oxygen octahedra. And / or suppressing oxidative decomposition of the electrolyte on the surface of the cathode active material 100.

[0342] Therefore, the surface layer portion 100a preferably has a different crystal structure from the interior portion 100b. Furthermore, the surface layer portion 100a preferably has a composition and crystal structure that are more stable at room temperature (25°C) than the interior portion 100b. For example, at least a portion of the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention preferably has a rock salt crystal structure. Alternatively, the surface layer portion 100a preferably has both a layered rock salt crystal structure and a rock salt crystal structure. Alternatively, the surface layer portion 100a preferably has characteristics of both a layered rock salt crystal structure and a rock salt crystal structure.

[0343] The surface layer 100a is the region from which lithium ions are first released during charging, and is a region where the lithium concentration is likely to be lower than that of the interior 100b. In addition, it can be said that the atoms on the surface of the particles of the positive electrode active material 100 in the surface layer 100a are in a state where some of the bonds are broken. Therefore, the surface layer 100a is likely to become unstable, and is a region where deterioration of the crystal structure is likely to begin. For example, if the crystal structure of the layered structure consisting of transition metal M and oxygen octahedra in the surface layer 100a is displaced, this effect will be transmitted to the interior 100b, causing the layered crystal structure in the interior 100b to also be displaced, which is thought to lead to deterioration of the crystal structure of the entire positive electrode active material 100. On the other hand, if the surface layer 100a can be sufficiently stabilized, Li ｘ MO ２ Even when x is small, for example, 0.24 or less, the layered structure of the inner portion 100b made of the transition metal M and oxygen octahedra can be made less likely to break. Furthermore, displacement of the layer made of the transition metal M and oxygen octahedra in the inner portion 100b can be suppressed.

[0344] Furthermore, the interior 100b of the positive electrode active material 100 preferably has a low density of defects, including dislocations. Furthermore, the positive electrode active material 100 preferably has a large crystallite size as measured by XRD. In other words, the interior 100b preferably has high crystallinity. Furthermore, the surface of the positive electrode active material 100 preferably has a smooth surface. These characteristics are important factors supporting the reliability of the positive electrode active material 100 when used in a secondary battery. If the reliability of the positive electrode active material is high, the upper limit of the charging voltage of the secondary battery can be increased, resulting in a secondary battery with a high charge / discharge capacity.

[0345] Dislocations in the interior 100b can be observed, for example, by a TEM. If the density of defects, including dislocations, is sufficiently low, they may not be observed within a specific 1 μm square of the observation sample. Note that dislocations are a type of crystal defect and are different from vacancy defects.

[0346] The larger the crystallite size, the greater the amount of Li ｘ CoO ２ When x is small, the O3' type crystal structure is easily maintained, and contraction of the c-axis length is easily suppressed.

[0347] It is believed that the fewer defects, including dislocations, observed by TEM, the larger the crystallite size measured by XRD.

[0348] When calculating the crystallite size, the XRD diffraction pattern is preferably obtained from the positive electrode active material alone. However, it may also be obtained from the positive electrode, which includes the positive electrode active material, a current collector, a binder, a conductive material, and the like. However, in the positive electrode state, the positive electrode active material may be oriented due to the influence of pressure during the manufacturing process. Strong orientation may prevent accurate calculation of the crystallite size. Therefore, it is more preferable to obtain the pattern by removing the positive electrode active material layer from the positive electrode, removing some of the binder, etc., from the positive electrode active material layer using a solvent, etc., and then loading the sample into a sample holder. Another method is to apply grease to a silicon anti-reflective plate and then attach the powder sample.

[0349] The crystallite size can be calculated using, for example, a Bruker D8 ADVANCE, with X-rays using CuKα1, 2θ between 15° and 90° increments of 0.005, and a LYNXEYEXE-T detector, and the diffraction pattern obtained using ICSD Coll. Code. 172909 as the literature value for lithium cobaltate. Analysis can be performed using DIFFRAC. TOPAS ver. 6 crystal structure analysis software, with the following settings, for example: Emission Profile: CuKa5. lam Background: Chebychev polynomial, 5th Instrument Primary radius: 280mm Secondary radius: 280mm Linear PSD 2Th angular range: 2.9 FDS angle: 0.3 Full Axial Convolution Filament length: 12mm Sample length: 15mm Receiving Slit length: 12mm Primary Sollers: 2.5 Secondary Sollers: 2.5 Corrections Specimen displacement: Refine LP Factor: 0

[0350] It is preferable to use the value of LVol-IB, which is the crystallite size corrected by the integral width standard calculated by the above method, as the crystallite size. Note that if the calculated preferred orientation is less than 0.8, the orientation of the sample may be too strong and it may not be suitable for determining the crystallite size.

[0351] <Li ｘ MO ２ The positive electrode active material 100 of one embodiment of the present invention has the above-described distribution of the additive element and / or the crystal structure in a discharged state, and therefore, ｘ MO ２ The crystal structure when x is small is different from that of conventional positive electrode active materials. Here, "small x" means 0.1<x≦0.24.

[0352] Using Figures 22 to 26, Li ｘ MO ２ The change in the crystal structure accompanying the change in x in the positive electrode active material 100 will be described by comparing a conventional positive electrode active material with the positive electrode active material 100 of one embodiment of the present invention.

[0353] The change in the crystal structure of a conventional positive electrode active material is shown in FIG. 23. The conventional positive electrode active material shown in FIG. 23 is lithium cobalt oxide (LiCoO ２ )

[0354] Figure 23 shows the R-3m O3 and Li ｘ CoO ２ The crystal structure of lithium cobalt oxide with x=1 in Fig. 1 shows that lithium occupies octahedral sites and CoO ２ There are three layers. Therefore, this crystal structure is sometimes called an O3 type crystal structure. ２ The layer is defined as a structure in which octahedral structures in which oxygen is six-coordinated to cobalt are connected in a plane with edge sharing. This is sometimes called a layer consisting of cobalt and oxygen octahedra.

[0355] It is also known that conventional lithium cobalt oxide has a crystal structure that has high lithium symmetry when x is about 0.5 and belongs to the monoclinic space group P2 / m. This structure has CoO ２ There is one layer, so it is sometimes called O1 type or monoclinic O1 type.

[0356] When x = 0, the positive electrode active material has a crystal structure of the trigonal space group P-3m1, and also contains CoO ２ There is one layer. Therefore, this crystal structure is sometimes called O1 type or trigonal O1 type. In addition, when the trigonal crystal is converted into a composite hexagonal lattice, it is sometimes called hexagonal O1 type.

[0357] Furthermore, when x is about 0.12, conventional lithium cobalt oxide has a crystal structure of the space group R-3m. This structure is similar to CoO, such as trigonal O1 type. ２ and LiCoO such as R-3m O ２It can also be said that the structure of and the structure of are stacked alternately. Therefore, this crystal structure is sometimes called an H1-3 crystal structure. Note that, since the actual insertion and desorption of lithium does not necessarily occur uniformly within the positive electrode active material and the lithium concentration may become uneven, the H1-3 crystal structure is experimentally observed from about x = 0.25. In fact, the number of cobalt atoms per unit cell in the H1-3 crystal structure is twice that of other structures. However, in Figure 23 and other parts of this specification, to facilitate comparison with other crystal structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0358] As an example of the H1-3 type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co (0,0,0.42150±0.00016), O1 (0,0,0.27671±0.00045), and O2 (0,0,0.11535±0.00045). O1 and O2 are each oxygen atoms. Which unit cell should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, it is sufficient to adopt a unit cell that results in a small GOF (goodness of fit) value.

[0359] Li ｘ CoO ２ When charging and discharging are repeated so that x in the formula is 0.24 or less, conventional lithium cobalt oxide undergoes repeated changes in crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0360] However, these two crystal structures are different from CoO ２ As shown by the dotted lines and arrows in FIG. 23, in the H1-3 type crystal structure, CoO ２ The layer is significantly different from the R-3m O3 in the discharged state. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0361] Furthermore, the difference in volume between these two crystal structures is large, so that, when compared per equal number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the discharged R-3mO3 crystal structure exceeds 3.5%, typically 3.9% or more.

[0362] In addition, the H1-3 type crystal structure has CoO like the trigonal O1 type. ２ A structure with continuous layers is likely to be unstable.

[0363] Therefore, when charging and discharging are repeated so that x is 0.24 or less, the crystal structure of conventional lithium cobalt oxide collapses. This collapse of the crystal structure causes a deterioration in cycle characteristics. This is because the collapse of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0364] On the other hand, in the positive electrode active material 100 of one embodiment of the present invention shown in FIG. ｘ MO ２ The change in the crystal structure between the discharge state where x is 1 and the state where x is 0.24 or less is smaller than that of conventional positive electrode active materials. ２ The layer misalignment can be reduced. Furthermore, the change in volume per cobalt atom can be reduced. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to lose its crystal structure even when repeatedly charged and discharged so that x is 0.24 or less, and excellent cycle characteristics can be achieved. Furthermore, the positive electrode active material 100 of one embodiment of the present invention is less likely to lose its crystal structure even when repeatedly charged and discharged so that x is 0.24 or less. ｘ MO ２ When x is 0.24 or less, the positive electrode active material 100 can have a more stable crystal structure than conventional positive electrode active materials. ｘ MO ２ When the value of x in the formula (1) is kept at 0.24 or less, short circuits are unlikely to occur. In such a case, the safety of the secondary battery is further improved, which is preferable.

[0365] Li ｘ MO ２The crystal structure of the inner portion 100b of the positive electrode active material 100 when x is 1, approximately 0.2, and approximately 0.15 is shown in FIG. 22. The inner portion 100b occupies the majority of the volume of the positive electrode active material 100 and is the portion that contributes greatly to charge and discharge. ２ The most problematic areas are layer misalignment and volume changes.

[0366] When x=1, the positive electrode active material 100 has the same crystal structure of R-3m O3 as conventional lithium cobalt oxide.

[0367] However, the positive electrode active material 100 has a different crystal structure from that of conventional lithium cobalt oxide when x is 0.24 or less, for example, about 0.2 or 0.15, which results in an H1-3 type crystal structure.

[0368] The positive electrode active material 100 according to one embodiment of the present invention when x is about 0.2 has a crystal structure belonging to the trigonal space group R-3m. ２ The symmetry of the layers is the same as that of O3. Therefore, this crystal structure is called an O3'-type crystal structure. This crystal structure is shown in Figure 22 with the notation R-3m O3'.

[0369] In the O3'-type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed in the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25. Furthermore, the lattice constant of the unit cell is preferably 2.797≦a≦2.837 (Å), more preferably 2.807≦a≦2.827 (Å), typically a=2.817 (Å). The c-axis is preferably 13.681≦c≦13.881 (Å), more preferably 13.751≦c≦13.811 (Å), typically c=13.781 (Å).

[0370] The positive electrode active material 100 of one embodiment of the present invention when x is about 0.15 may have a crystal structure belonging to the monoclinic space group P2 / m. ２ There is one layer. In addition, the amount of lithium present in the positive electrode active material 100 is about 15 atomic % in the discharged state. Therefore, this crystal structure is called a monoclinic O1(15) type crystal structure. This crystal structure is shown in Figure 22 with the P2 / m monoclinic O1(15) symbol.

[0371] The monoclinic O1(15) type crystal structure has the coordinates of cobalt and oxygen in the unit cell as follows: Co1(0.5,0,0.5), Co2(0,0.5,0.5), O1(X Ｏ１ , 0, Z Ｏ１ ), 0.23≦X Ｏ１ ≦0.24, 0.61≦Z Ｏ１ ≦0.65, O2(X Ｏ２ , 0.5, Z Ｏ２ ), 0.75≦X Ｏ２ ≦0.78, 0.68≦Z Ｏ２ The lattice constants of the unit cell are a = 4.880 ± 0.05 Å, b = 2.817 ± 0.05 Å, c = 4.839 ± 0.05 Å, α = 90°, β = 109.6 ± 0.1°, and γ = 90°.

[0372] This crystal structure can also show the lattice constant in the space group R-3m if some error is allowed. In this case, the coordinates of cobalt and oxygen in the unit cell are Co(0,0,0.5), O(0,0,Z Ｏ ), 0.21≦Z Ｏ The lattice constants of the unit cell are a = 2.817 ± 0.02 Å and c = 13.68 ± 0.1 Å.

[0373] In both the O3' and monoclinic O1(15) crystal structures, ions of cobalt, nickel, magnesium, etc. occupy hexacoordinated oxygen sites, although lighter elements such as lithium and magnesium may occupy tetracoordinated oxygen sites.

[0374] As shown by the dotted line in FIG. 22, the CoO ２ There is almost no layer misalignment.

[0375] The difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1.8%.

[0376] The difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the monoclinic O1(15) type crystal structure is 3.3% or less, more specifically 3.0% or less, typically 2.5%.

[0377] Table 1 shows the difference in volume per cobalt atom between discharged R-3m O3, O3', monoclinic O1(15), H1-3 type, and trigonal O1. The lattice constants of the crystal structures of discharged R-3m O3 and trigonal O1 used in the calculations in Table 1 can be found in CSD Coll. Code. 172909 and 88721. The lattice constants of O3' and monoclinic O1(15) can be calculated from experimental XRD data.

[0378]

[0379] As described above, in the positive electrode active material 100 according to one embodiment of the present invention, Li ｘ MO ２ When x is small, i.e., when a large amount of lithium is released, the change in crystal structure is suppressed compared to conventional positive electrode active materials. Furthermore, the change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the positive electrode active material 100 is resistant to collapse of its crystal structure even when repeatedly charged and discharged so that x is 0.24 or less. Therefore, the decrease in charge / discharge capacity during charge / discharge cycles is suppressed. Furthermore, because more lithium can be stably utilized than in conventional positive electrode active materials, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be fabricated.

[0380] The positive electrode active material 100 is Li ｘ MO ２ It has been confirmed that when x is 0.15 or more and 0.24 or less, the O3' type crystal structure may be present, and it is presumed that even when x is more than 0.24 and 0.27 or less, the O3' type crystal structure is present. ｘ MO ２ It has been confirmed that when x is greater than 0.1 and less than 0.2, typically when x is 0.15 or more and less than 0.17, the crystal structure may be monoclinic O1(15) type. However, the crystal structure is Li ｘMO ２ The range of x is not necessarily limited to the above range, since it is affected not only by the x in the formula but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc.

[0381] Therefore, the positive electrode active material 100 is Li ｘ MO ２ When x is greater than 0.1 and equal to or less than 0.24, the positive electrode active material 100 may have only the O3' type, only the monoclinic O1(15) type, or both crystal structures. Furthermore, not all of the particles in the interior 100b of the positive electrode active material 100 have the O3' type and / or the monoclinic O1(15) type crystal structure. Other crystal structures may be included, or some may be amorphous.

[0382] Also Li ｘ MO ２ To make the value of x small, it is generally necessary to charge at a high charging voltage. ｘ MO ２ The state where x is small can be rephrased as a state where the battery is charged at a high charging voltage. For example, when CC / CV charging is performed at a voltage of 4.6 V or higher relative to the potential of lithium metal in an environment of 25°C, a H1-3 crystal structure appears in conventional positive electrode active materials. Therefore, a charging voltage of 4.6 V or higher relative to the potential of lithium metal can be said to be a high charging voltage. Unless otherwise specified, in this specification, charging voltages are expressed relative to the potential of lithium metal.

[0383] Therefore, in other words, the positive electrode active material 100 of one embodiment 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, a voltage of 4.6 V or higher at 25°C.

[0384] Even with the positive electrode active material 100, an H1-3 crystal structure may be finally observed when the charge voltage is further increased. As described above, the crystal structure is affected by the number of charge / discharge cycles, the charge / discharge current, the temperature, the electrolyte, and the like. Therefore, when the charge voltage is lower, for example, even when the charge voltage is 4.5 V or more and less than 4.6 V at 25° C., the positive electrode active material 100 of one embodiment of the present invention may be able to adopt an O3′ crystal structure. Similarly, when charged at a voltage of 4.65 V or more and 4.7 V or less at 25° C., the positive electrode active material 100 may be able to adopt a monoclinic O1(15) crystal structure.

[0385] In addition, when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery is lower than the above by the potential of the graphite. The potential of graphite is 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, the same crystal structure is maintained at a voltage obtained by subtracting the potential of graphite from the above voltage.

[0386] In addition, in O3' and monoclinic O1(15) in FIG. 22, lithium is shown to exist at all lithium sites with equal probability, but this is not limited to this. It may exist unevenly at some lithium sites, for example, in monoclinic O1(Li ０．５ CoO ２ The distribution of lithium can be analyzed by, for example, neutron diffraction.

[0387] The O3' and monoclinic O1(15) crystal structures have random lithium between layers, but CdCl ２ It can be said that this crystal structure is similar to that of the CdCl type. ２ A similar crystal structure to the Li-type is lithium nickel oxide. ０．０６ NiO ２ The crystal structure is similar to that when charged to 1000V, but pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt usually have a CdCl ２ It is known that it does not have a typical crystal structure.

[0388] <Grain Boundaries> In addition to the above distribution, at least a portion of the additive element contained in the positive electrode active material 100 of one embodiment of the present invention is preferably unevenly distributed in and near the grain boundaries.

[0389] In this specification and the like, uneven distribution refers to the concentration of an element in a certain region being different from that in other regions, and is synonymous with segregation, precipitation, non-uniformity, bias, or the mixture of areas with high concentration and areas with low concentration.

[0390] For example, it is preferable that the magnesium concentration at and near the grain boundaries of the positive electrode active material 100 is higher than that in other regions of the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundaries is higher than that in other regions of the interior 100b. It is also preferable that the nickel concentration at and near the grain boundaries is higher than that in other regions of the interior 100b. It is also preferable that the aluminum concentration at and near the grain boundaries is higher than that in other regions of the interior 100b.

[0391] Grain boundaries are a type of planar defect. Therefore, like particle surfaces, they are prone to instability and are prone to initiating changes in the crystal structure. Therefore, if the concentration of added elements at and near the grain boundaries is high, changes in the crystal structure can be more effectively suppressed.

[0392] Furthermore, when the magnesium concentration and fluorine concentration are high at and near the grain boundaries, even if cracks occur along the grain boundaries of the positive electrode active material 100 of one embodiment of the present invention, the magnesium concentration and fluorine concentration are high near the surface where the cracks occur. Therefore, even after the cracks occur, the corrosion resistance to hydrofluoric acid of the positive electrode active material can be improved. Furthermore, even after the cracks occur, the side reaction between the electrolyte and the positive electrode active material can be suppressed.

[0393] <Particle diameter> If the particle diameter of the positive electrode active material 100 of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium, excessive roughness of the surface of the active material layer when applied to a current collector, etc. On the other hand, if the particle diameter is too small, problems such as excessive reaction with the electrolyte solution may occur.

[0394] The particle diameter of the positive electrode active material 100 can be measured, for example, by a laser diffraction particle size distribution analyzer. The particle diameter (D50) of the positive electrode active material 100 measured by the laser diffraction particle size distribution analyzer is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Alternatively, 1 μm or more and 40 μm or less is preferable. Alternatively, 1 μm or more and 30 μm or less is preferable. Alternatively, 2 μm or more and 100 μm or less is preferable. Alternatively, 2 μm or more and 30 μm or less is preferable. Alternatively, 5 μm or more and 100 μm or less is preferable. Alternatively, 5 μm or more and 40 μm or less is preferable.

[0395] D50 is the particle size at which the integrated amount in the cumulative curve of the particle size distribution measurement results accounts for 50%. Similarly, D10 is the particle size at which the integrated amount in the cumulative curve of the particle size distribution measurement results accounts for 10%. D90 is the particle size at which the integrated amount in the cumulative curve of the particle size distribution measurement results accounts for 90%.

[0396] Furthermore, when particles having different particle sizes are mixed and used in the positive electrode, the electrode density can be increased, which is preferable because it allows for a secondary battery with a high energy density. The positive electrode active material 100 having a relatively small particle size is expected to have high charge / discharge rate characteristics. The positive electrode active material 100 having a relatively large particle size is expected to have high charge / discharge cycle characteristics and maintain a high discharge capacity.

[0397] <Analysis method> A certain positive electrode active material is ｘ MO ２ When x in the formula (I) is small, it can be determined whether the positive electrode active material 100 of one embodiment of the present invention has an O3′-type and / or monoclinic O1(15)-type crystal structure by Li ｘ MO ２ This can be determined by analyzing a positive electrode having a positive electrode active material with a small x using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like.

[0398] In particular, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, it can obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling the secondary battery as it is, etc. Among XRD methods, powder XRD can obtain diffraction peaks that reflect the crystalline structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100.

[0399] When analyzing the crystallite size by powder XRD, it is preferable to measure the size while excluding the influence of the orientation of the positive electrode active material particles due to pressure, etc. For example, it is preferable to take out the positive electrode active material from the positive electrode obtained by disassembling a secondary battery, prepare a powder sample, and then measure the size.

[0400] As described above, the positive electrode active material 100 according to one embodiment of the present invention is ｘ MO ２ The characteristic of this material is that there is little change in the crystal structure when x is 1 and when it is 0.24 or less. Materials in which the crystal structure that undergoes large changes when charged at high voltage accounts for 50% or more of the crystal structure are not preferable because they cannot withstand repeated high-voltage charging and discharging.

[0401] It should also be noted that simply adding an additive element may not result in an O3' or monoclinic O1(15) crystal structure. For example, even if lithium cobalt oxide containing magnesium and fluorine or lithium cobalt oxide containing magnesium and aluminum has something in common, depending on the concentration and distribution of the additive element, Li ｘ MO ２ In some cases, x is 0.24 or less and the O3' type and / or monoclinic O1(15) type crystal structure accounts for 60% or more, and in other cases, the H1-3 type crystal structure accounts for 50% or more.

[0402] Furthermore, even in the positive electrode active material 100 of one embodiment of the present invention, an H1-3 type or trigonal O1 type crystal structure may be generated when x is too small, such as 0.1 or less, or under conditions where the charge voltage exceeds 4.9 V. Therefore, to determine whether or not the positive electrode active material 100 of one embodiment of the present invention is the positive electrode active material 100, analysis of the crystal structure, such as XRD, and information such as the charge capacity or the charge voltage are required.

[0403] However, when a positive electrode active material with a small x is exposed to the air, its crystal structure may change. For example, the crystal structure may change from O3'-type or monoclinic O1(15)-type to H1-3-type. Therefore, it is preferable to handle all samples used for crystal structure analysis in an inert atmosphere such as an argon atmosphere.

[0404] Furthermore, whether or not the distribution of the additive elements contained in a certain positive electrode active material is in the state described above can be determined by analysis using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0405] The crystal structure of the surface layer 100 a and the grain boundaries can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100 .

[0406] <Charging Method> To determine whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention, for example, a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using the composite oxide as a positive electrode and lithium metal as a counter electrode can be fabricated as a test battery and charged. The coin cell includes an electrolyte, a separator, a positive electrode can, and a negative electrode can.

[0407] More specifically, the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive material, and a binder.

[0408] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery differs from the potential of the positive electrode. Unless otherwise specified, voltages and potentials in this specification refer to the potential of the positive electrode.

[0409] The electrolyte contained in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF ６ ) is used, and the electrolyte may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7 with 2 wt % vinylene carbonate (VC).

[0410] The separator may be a 25 μm thick porous polypropylene film.

[0411] The positive electrode can and the negative electrode can may be made of stainless steel (SUS).

[0412] Note that the above coin cell (test battery) may be fabricated using the positive electrode removed by disassembling a battery (for example, a battery in an initial state mounted on a commercially available product), and charging may be performed to determine whether or not the coin cell is the positive electrode active material 100 of one embodiment of the present invention described below.

[0413] The coin cell prepared under the above conditions is charged at a desired voltage (e.g., 4.5 V, 4.55 V, 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V). The charging method is not particularly limited as long as charging is performed at the desired voltage for a sufficient period of time. For example, when charging by CCCV, the CC charging current can be set to 20 mA / g or more and 100 mA / g or less. CV charging can be terminated at 2 mA / g or more and 10 mA / g or less. To observe the phase change of the positive electrode active material, it is desirable to charge at such a small current value. On the other hand, if the current does not reach 2 mA / g or more and 10 mA / g or less even after long-term CV charging, it is considered that the current is being consumed not for charging the positive electrode active material but for decomposing the electrolyte. Therefore, CV charging may be terminated after a sufficient time has elapsed since the start of the charging. In this case, a sufficient time can be, for example, 1.5 hours or more and 3 hours or less. The temperature is set to 25°C or 45°C. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere and the positive electrode is removed to obtain a positive electrode active material with a desired charge capacity. When various analyses are performed thereafter, it is preferable to seal the cell in an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing the cell in a sealed container under an argon atmosphere. Furthermore, it is preferable to quickly remove the positive electrode and subject it to analysis after charging is complete. Specifically, it is preferable to do so within one hour after charging is complete, and more preferably within 30 minutes.

[0414] When analyzing the crystal structure in the charged state after multiple charge / discharge cycles, the conditions for the multiple charge / discharge cycles may be different from the above-mentioned conditions for charge / discharge. For example, charging may be performed by constant current charging at a current value of 20 mA / g or more and 100 mA / g or less up to a given voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V), followed by constant voltage charging until the current value reaches 2 mA / g or more and 10 mA / g or less, and then constant current discharging at 2.5 V and 20 mA / g or more and 100 mA / g or less.

[0415] Furthermore, when analyzing the crystal structure in the discharged state after multiple charge / discharge cycles, constant current discharge can be performed at 2.5 V with a current value of 20 mA / g or more and 100 mA / g or less.

[0416] <<XRD>> The apparatus and conditions for XRD measurement are not particularly limited. For example, the measurement can be performed using the following apparatus and conditions. XRD apparatus: D8 ADVANCE manufactured by Bruker AXS X-ray source: CuKα １ Line output: 40 kV, 40 mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0417] If the measurement sample is a powder, it can be set by placing it in a glass sample holder, or by sprinkling the sample on a greased silicone anti-reflective plate, etc. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.

[0418] CuKα calculated from the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure model １ Ideal powder XRD patterns based on the line are shown in Figures 24, 25, 26A, and 26B. ｘ MO ２ LiCoO where x=1 ２ Also shown are ideal XRD patterns calculated from the crystal structure of O3 and trigonal O1 with x = 0. Figures 26A and 26B show the XRD patterns of the O3'-type crystal structure, the monoclinic O1(15)-type crystal structure, and the H1-3-type crystal structure, with Figure 26A showing an enlarged view of the region where 2θ is in the range of 18° to 21°, and Figure 26B showing an enlarged view of the region where 2θ is in the range of 42° to 46°. ２ (O3) and CoO ２The pattern of (O1) was created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database). The 2θ range was 15° to 75°, step size = 0.01, and wavelength λ = 1.540562 × 10 −１０ m and λ2 were not set, and the monochromator was single. The pattern of the H1-3 type crystal structure was similarly created from the crystal structure information. The crystal structure patterns of the O3' type and monoclinic O1(15) type crystal structures were estimated from the XRD pattern of the positive electrode active material, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and XRD patterns were created in the same way as the others.

[0419] As shown in Figures 24, 26A and 26B, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.25 ± 0.12° (19.13° or more and less than 19.37°) and 2θ = 45.47 ± 0.10° (45.37° or more and less than 45.57°).

[0420] In addition, in the monoclinic O1(15) type crystal structure, diffraction peaks appear at 2θ=19.47±0.10° (19.37° or more and 19.57° or less) and 2θ=45.62±0.05° (45.57° or more and 45.67° or less).

[0421] However, as shown in Figures 25, 26A and 26B, no peaks appear at these positions in the H1-3 type crystal structure and trigonal O1. ｘ CoO ２ The appearance of peaks at 19.13° or more and less than 19.37° and / or 19.37° or more and less than 19.57°, and at 45.37° or more and less than 45.57° and / or 45.57° or more and less than 45.67° when x is small can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0422] This can also be said to be because, in the positive electrode active material 100 of one embodiment of the present invention, the positions at which XRD diffraction peaks appear are close between the crystal structures where x = 1 and where x ≦ 0.24. More specifically, among the main diffraction peaks of the crystal structures where x = 1 and where x ≦ 0.24, the difference in 2θ between peaks that appear at 2θ of 42° to 46° is 0.7° or less, more preferably 0.5° or less.

[0423] The positive electrode active material 100 according to one embodiment of the present invention is Li ｘ CoO ２ When x in the formula is small, the particles may have an O3'-type and / or monoclinic O1(15)-type crystal structure, but not all of the particles may have an O3'-type and / or monoclinic O1(15)-type crystal structure. Other crystal structures may be included, or some may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type and / or monoclinic O1(15)-type crystal structure is preferably 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3'-type and / or monoclinic O1(15)-type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, the positive electrode active material can have sufficiently excellent cycle characteristics.

[0424] Similarly, when Rietveld analysis is performed, the H1-3 type and O1 type crystal structures are preferably 50% or less, more preferably 34% or less, and even more preferably substantially not observed.

[0425] Furthermore, even after 100 or more charge / discharge cycles from the start of measurement, when Rietveld analysis is performed, the O3' type and / or monoclinic O1(15) type crystal structure is preferably 35% or more, more preferably 40% or more, and even more preferably 43% or more.

[0426] Furthermore, the sharpness of the diffraction peaks in the XRD pattern indicates the degree of crystallinity. Therefore, it is preferable that each diffraction peak after charging is sharp, i.e., the half-width is narrow. For example, a narrow full width at half maximum is preferable. Even for peaks arising from the same crystalline phase, the half-width varies depending on the XRD measurement conditions and the value of 2θ. Under the above-mentioned measurement conditions, for peaks observed between 2θ = 43° and 46°, the full width at half maximum is preferably, for example, 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily meet this requirement. If some peaks meet this requirement, it can be said that the crystallinity of that crystalline phase is high. Such high crystallinity contributes to sufficient stabilization of the crystal structure after charging.

[0427] The crystallite size of the O3'-type and monoclinic O1(15) crystal structures of the positive electrode active material 100 is approximately equal to that of LiCoO in a discharged state. ２ Therefore, even under the same XRD measurement conditions as the positive electrode before and after charging and discharging, the ｘ CoO ２ When x in the formula is small, the peaks of the crystal structure of the O3' type and / or monoclinic O1(15) can be clearly observed. ２ In this case, even if some of the crystal structure resembles the O3' type and / or monoclinic O1(15) crystal structure, the crystallite size will be small and the peaks will be broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0428] As described above, the positive electrode active material 100 of one embodiment of the present invention preferably has a small influence of the Jahn-Teller effect. As long as the influence of the Jahn-Teller effect is small, the positive electrode active material 100 may contain a transition metal such as nickel or manganese as an additive element in addition to cobalt.

[0429] For example, when the nickel concentration is 5% or 7.5%, the a-axis / c-axis tends to change significantly, and when the nickel concentration is 7.5%, the distortion of the a-axis increases. This distortion may be due to Jahn-Teller distortion of trivalent nickel. Therefore, it is preferable that the nickel content of the transition metal M contained in the positive electrode active material 100 is less than 7.5 atomic %.

[0430] Furthermore, when the manganese concentration is 5% or more, the behavior of the change in lattice constant is different and it is suggested that it does not follow Vegard's law. Therefore, of the transition metals M contained in the positive electrode active material 100, manganese is preferably 4 atomic % or less.

[0431] The above ranges of nickel concentration and manganese concentration do not necessarily apply to the surface layer 100a, that is, the concentrations in the surface layer 100a may be higher than the above ranges.

[0432] As a result of considering a preferable range of the lattice constant from the above, it was found that in the positive electrode active material of one embodiment of the present invention, the layered rock-salt crystal structure of the positive electrode active material 100 in a state where no charge and discharge are performed or in a discharged state, which can be estimated from the XRD pattern, has an a-axis lattice constant of 2.814 × 10 −１０ m is greater than 2.817 x 10 −１０ m and the lattice constant of the c-axis is 14.05 × 10 −１０ m or larger, 14.07 x 10 −１０ It has been found that the value is preferably smaller than m. The state in which no charge and discharge are performed may be, for example, the state of powder before the positive electrode of the secondary battery is produced.

[0433] Alternatively, in the layered rock-salt crystal structure of the positive electrode active material 100 in a state where no charge or discharge is performed or in a discharged state, it is preferable that the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is greater than 0.20000 and smaller than 0.20049.

[0434] Alternatively, when XRD analysis is performed on the layered rock salt type crystal structure of the positive electrode active material 100 in a state where no charge or discharge is performed or in a discharged state, a first peak may be observed at 2θ of not less than 18.50° and not more than 19.30°, and a second peak may be observed at 2θ of not less than 38.00° and not more than 38.80°.

[0435] <XPS> In X-ray photoelectron spectroscopy (XPS), in the case of inorganic oxides, when monochromatic aluminum Kα rays are used as the X-ray source, it is possible to analyze a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less), so the concentration of each element can be quantitatively analyzed in a region about half the depth of the surface layer 100a. Furthermore, narrow scan analysis can be used to analyze the bonding state of the elements. The quantitative accuracy of XPS is often about ±1 atomic %, with a lower limit of about 1 atomic %, depending on the element.

[0436] In the cathode active material 100 according to one embodiment of the present invention, the concentration of one or more selected additive elements is preferably higher in the surface layer portion 100a than in the interior portion 100b. This is equivalent to saying that the concentration of one or more selected additive elements in the surface layer portion 100a is preferably higher than the average concentration throughout the cathode active material 100. Therefore, for example, it can be said that the concentration of one or more selected additive elements in the surface layer portion 100a measured by XPS or the like is preferably higher than the average concentration of the additive elements throughout the cathode active material 100 measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry). For example, the magnesium concentration in at least a portion of the surface layer portion 100a measured by XPS or the like is preferably higher than the average magnesium concentration throughout the cathode active material 100. Furthermore, the titanium concentration in at least a portion of the surface layer portion 100a is preferably higher than the average titanium concentration throughout the cathode active material 100. It is also preferable that the nickel concentration in at least a portion of the surface layer portion 100a is higher than the average nickel concentration in the entire positive electrode active material 100. It is also preferable that the aluminum concentration in at least a portion of the surface layer portion 100a is higher than the average aluminum concentration in the entire positive electrode active material 100. It is also preferable that the fluorine concentration in at least a portion of the surface layer portion 100a is higher than the average fluorine concentration in the entire positive electrode active material 100.

[0437] Note that the surface and surface layer 100a of the positive electrode active material 100 according to one embodiment of the present invention do not contain carbonates, hydroxyl groups, and the like that are chemically adsorbed after the preparation of the positive electrode active material 100. Furthermore, the surface of the positive electrode active material 100 also does not contain the electrolyte, binder, conductive material, or compounds derived therefrom that are attached to the surface of the positive electrode active material 100. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, and the like that can be detected by surface analysis such as XPS. For example, XPS can separate the types of bonds by analysis, and corrections may be made to exclude C—F bonds derived from the binder.

[0438] Furthermore, before subjecting the sample to various analyses, the sample of the positive electrode active material and the positive electrode active material layer may be washed to remove the electrolyte, binder, conductive material, or compounds derived therefrom that adhere to the surface of the positive electrode active material. In this case, lithium may dissolve in the solvent used for washing, but even in this case, the added element is unlikely to dissolve, and therefore the atomic ratio of the added element is not affected.

[0439] The concentration of the added element may also be compared in terms of its ratio to cobalt. Using the ratio to cobalt is preferable because it allows comparisons to be made while reducing the influence of carbonates and other substances chemisorbed after the preparation of the positive electrode active material. For example, the ratio of the number of magnesium atoms to cobalt atoms (Mg / Co) determined by XPS analysis is preferably 0.4 to 1.5. Meanwhile, the ratio of Mg / Co determined by ICP-MS analysis is preferably 0.001 to 0.06.

[0440] Similarly, in order to ensure sufficient lithium insertion / extraction paths, the positive electrode active material 100 preferably has a higher concentration of lithium and cobalt in the surface layer portion 100a than the concentrations of the respective additive elements. This means that the concentrations of lithium and cobalt in the surface layer portion 100a are preferably higher than the concentrations of one or more additive elements selected from the additive elements contained in the surface layer portion 100a as measured by XPS or the like. For example, the concentration of cobalt in at least a portion of the surface layer portion 100a as measured by XPS or the like is preferably higher than the concentration of magnesium in at least a portion of the surface layer portion 100a as measured by XPS or the like. Similarly, the concentration of lithium is preferably higher than the concentration of magnesium. Furthermore, the concentration of cobalt is preferably higher than the concentration of nickel. Similarly, the concentration of lithium is preferably higher than the concentration of nickel. Furthermore, the concentration of cobalt is preferably higher than the concentration of aluminum. Similarly, the concentration of lithium is preferably higher than the concentration of aluminum. Furthermore, the concentration of cobalt is preferably higher than the concentration of fluorine. Similarly, the concentration of lithium is preferably higher than the concentration of fluorine.

[0441] Furthermore, it is more preferable that aluminum be widely distributed in a deep region, for example, the surface or a region at a depth of 5 nm to 50 nm from the reference point. Therefore, although aluminum is detected in an analysis of the entire cathode active material 100 using ICP-MS, GD-MS, or the like, it is more preferable that the concentration of aluminum is not detected by XPS or the like, or is 1 atomic % or less.

[0442] Furthermore, when XPS analysis was performed on the positive electrode active material 100 of one embodiment of the present invention, the number of magnesium atoms was preferably 0.4 to 1.2 times, more preferably 0.65 to 1.0 times, relative to the number of cobalt atoms. The number of nickel atoms was preferably 0.15 to 0.15 times, more preferably 0.03 to 0.13 times, relative to the number of cobalt atoms. The number of aluminum atoms was preferably 0.12 to 0.09 times, more preferably 0.09 times, relative to the number of cobalt atoms. The number of fluorine atoms was preferably 0.3 to 0.9 times, more preferably 0.1 to 1.1 times, relative to the number of cobalt atoms. The above ranges indicate that these additive elements are not attached to a narrow area on the surface of the positive electrode active material 100 but are widely distributed at preferred concentrations in the surface layer 100a of the positive electrode active material 100.

[0443] When performing XPS analysis, for example, monochromated aluminum Kα rays can be used as X-rays. The take-off angle can be set to, for example, 45°. Measurement can be performed, for example, using the following equipment and conditions. Measurement equipment: PHI Quantera II X-rays: monochromated Al Kα (1486.6 eV) Detection area: 100 μmφ Detection depth: approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: wide scan, narrow scan for each detected element

[0444] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is analyzed by XPS, the peak representing the bond energy between fluorine and another element is preferably greater than or equal to 682 eV and less than 685 eV, and more preferably about 684.3 eV, which is different from both the bond energy of lithium fluoride (685 eV) and the bond energy of magnesium fluoride (686 eV).

[0445] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is analyzed by XPS, the peak representing the bond energy between magnesium and another element is preferably greater than or equal to 1302 eV and less than 1304 eV, and more preferably about 1303 eV, which is a value different from the bond energy of magnesium fluoride, 1305 eV, and is close to the bond energy of magnesium oxide.

[0446] <EDX> Preferably, one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. More preferably, the depth from the surface of the concentration peak varies depending on the additive element in the positive electrode active material 100. The concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 using a focused ion beam (FIB) or the like and analyzing the cross section using energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0447] Among EDX measurements, EDX area analysis is performed by scanning an area and evaluating the area two-dimensionally. EDX area analysis is performed by linear scanning and evaluating the distribution of atomic concentrations within the positive electrode active material. Linear analysis is also used to refer to data extracted from a linear area of ​​EDX area analysis. Point analysis is used to measure an area without scanning.

[0448] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentration of the added element in the surface layer 100a, the interior 100b, and near the grain boundaries of the positive electrode active material 100. Furthermore, EDX ray analysis can analyze the concentration distribution and maximum value of the added element. Furthermore, analysis that thins the sample, such as STEM-EDX, is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.

[0449] Since the positive electrode active material 100 is a compound containing a transition metal and oxygen capable of lithium insertion / extraction, the interface between a region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced upon lithium insertion / extraction and oxygen is present and a region where it is not present is defined as the surface of the positive electrode active material. When the positive electrode active material is subjected to analysis, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. The protective film may be a single-layer or multilayer film of carbon, metal, oxide, resin, etc.

[0450] In STEM-EDX-ray analysis or the like, in principle or due to measurement errors, the graph of the detected amount of characteristic X-rays of the element does not change sharply, and it may be difficult to precisely determine the surface. Therefore, when referring to the depth direction in STEM-EDX-ray analysis or the like, the detected amount of characteristic X-rays of the transition metal M is the average value M of the detected amount of characteristic X-rays of the internal transition metal M. ＡＶＥ and the average M of the detected amount of characteristic X-rays of the transition metal M in the background. ＢＧ The point where the detected amount of oxygen characteristic X-rays is 50% of the sum of the detected amount of oxygen characteristic X-rays and the average value O ＡＶＥ and the average value O of the detected amount of characteristic X-rays of oxygen in the background ＢＧ The reference point is the point where the detected amount of the characteristic X-rays of the transition metal M is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal transition metal M and the average value of the detected amount of the characteristic X-rays of the background transition metal M. If the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal oxygen and the average value of the detected amount of the characteristic X-rays of the background oxygen is different from the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal oxygen and the average value of the detected amount of the characteristic X-rays of the background oxygen, this is considered to be due to the influence of metal oxides, carbonates, etc. containing oxygen attached to the surface, and therefore, the detected amount of the characteristic X-rays of the transition metal M is different from the point where ... oxygen is different from the sum of the average value of the detected amount of the characteristic X-rays of the internal transition metal M. ＡＶＥ and the average M of the detected amount of characteristic X-rays of the transition metal M in the background. ＢＧ In the case of a positive electrode active material containing a plurality of transition metals M, the M of the element with the largest amount of characteristic X-rays detected inside can be used as the reference point. ＡＶＥ and M ＢＧ The reference point can be determined using the following formula:

[0451] The average value M of the detected amount of characteristic X-rays of the transition metal M in the background ＢＧ can be obtained by averaging, for example, a range of 2 nm or more, preferably 3 nm or more, from the outside of the positive electrode active material, avoiding the vicinity where the detected amount of characteristic X-rays of the transition metal M starts to increase. ＡＶＥcan be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, at a depth of 30 nm or more, preferably more than 50 nm, from the region where the detected amount of characteristic X-rays of the transition metal M and oxygen becomes saturated and stable, for example, the region where the detected amount of characteristic X-rays of the transition metal M starts to increase. ＢＧ and the average value O of the detected amount of characteristic X-rays of oxygen inside ＡＶＥ can also be found in the same way.

[0452] Furthermore, the surface of the positive electrode active material 100 in a cross-sectional STEM image or the like is the boundary between an area where an image derived from the crystalline structure of the positive electrode active material is observed and an area where an image is not observed, and is the outermost area of ​​an area where atomic columns derived from the atomic nuclei of metal elements having atomic numbers larger than that of lithium among the metal elements constituting the positive electrode active material are confirmed.

[0453] In addition, a peak in STEM-EDX-ray analysis refers to a convex maximum value that appears in a graph of the characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element. Note that noise in STEM-EDX-ray analysis may be a measured value with a half-width less than the spatial resolution (R), for example, R / 2 or less.

[0454] The influence of noise can be reduced by scanning the same location multiple times under the same conditions. For example, the integrated value measured over six scans can be used as the detection value for each element. The number of scans is not limited to six, and more scans can be performed, and the average can be used as the detection value for each element.

[0455] The STEM-EDX analysis can be performed, for example, as follows: First, a protective film is vapor-deposited on the surface of the positive electrode active material. For example, carbon can be vapor-deposited using an ion sputtering device (MC1000 manufactured by Hitachi High-Technologies).

[0456] Next, the positive electrode active material is sliced ​​to prepare a STEM cross-section sample. For example, the slice processing can be performed using an FIB-SEM device (Hitachi High-Tech XVision 200TBS). Pickup is performed using an MPS (microprobing system), and the finishing conditions can be, for example, an acceleration voltage of 10 kV.

[0457] STEM-EDX ray analysis can be performed using, for example, a STEM device (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W (two-pronged) EDX detector. During EDX ray analysis, the emission current of the STEM device is set to 6 μA or more and 10 μA or less, and a portion of the thinned sample with minimal depth and unevenness is measured. The magnification is, for example, approximately 150,000 times. The conditions for EDX ray analysis can be drift correction, a line width of 42 nm, a pitch of 0.2 nm, and six or more frames.

[0458] When EDX area analysis or EDX point analysis is performed on positive electrode active material 100 of one embodiment of the present invention, the concentration of each additional element, particularly additional element X, in surface layer portion 100a is preferably higher than that in inner portion 100b.

[0459] For example, when EDX area analysis or EDX point analysis is performed on a cathode active material 100 containing magnesium as an additive element, the magnesium concentration in the surface layer 100a is preferably higher than the magnesium concentration in the interior 100b. Furthermore, when EDX analysis is performed, the magnesium concentration peak in the surface layer 100a is preferably present on the surface of the cathode active material 100 or at a depth of 3 nm from the reference point toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. Furthermore, the magnesium concentration preferably decays to 60% or less of the peak at a depth of 1 nm from the peak top. Furthermore, it is preferable that the magnesium concentration decays to 30% or less of the peak at a depth of 2 nm from the peak top. Note that the "peak top" of concentration here refers to the maximum value or the position where the maximum value appears in the convex shape that appears in the concentration distribution graph for each element.

[0460] Furthermore, when EDX-ray analysis is performed, the maximum value of the magnesium concentration (detected amount of magnesium / (sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, titanium, and nickel) in the surface layer portion 100a is preferably 0.5 Atomic% or more and 10 Atomic% or less, and more preferably 1 Atomic% or more and 5 Atomic% or less.

[0461] Furthermore, when EDX-ray analysis is performed, the maximum value of the titanium concentration (detected amount of titanium / (sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, titanium, and nickel) in the surface layer portion 100a is preferably 0.2 Atomic% or more and 5 Atomic% or less, and more preferably 0.5 Atomic% or more and 2 Atomic% or less.

[0462] Furthermore, when EDX-ray analysis is performed, the maximum value of the nickel concentration (detected amount of nickel / (sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, titanium, and nickel) in the surface layer portion 100a is preferably 0.2 Atomic% or more and 5 Atomic% or less, and more preferably 0.5 Atomic% or more and 3 Atomic% or less.

[0463] In addition, in the positive electrode active material 100 containing magnesium and fluorine as additive elements, the distribution of fluorine preferably has a region overlapping with the distribution of magnesium. For example, the difference in the depth direction between the peak of the fluorine concentration and the peak of the magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.

[0464] Furthermore, when EDX-ray analysis is performed, the fluorine concentration peak of the surface layer portion 100a preferably exists on the surface of the positive electrode active material 100 or at a depth of 3 nm from the reference point toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. Furthermore, if the fluorine concentration peak exists slightly closer to the surface than the magnesium concentration peak, resistance to hydrofluoric acid is increased, which is more preferable. For example, the fluorine concentration peak is more preferably 0.5 nm or more closer to the surface than the magnesium concentration peak, and even more preferably 1.5 nm or more closer to the surface.

[0465] In the cathode active material 100 containing nickel as an additive element, the nickel concentration peak in the surface layer 100a preferably exists at a depth of 3 nm from the surface or reference point toward the center of the cathode active material 100, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. In the cathode active material 100 containing magnesium and nickel, the nickel distribution preferably has an overlapping region with the magnesium distribution. For example, the difference in depth between the nickel concentration peak and the magnesium concentration peak is preferably within 3 nm, more preferably within 1 nm.

[0466] In the cathode active material 100 containing titanium as an additive element, the titanium concentration peak in the surface layer 100a preferably exists at a depth of 3 nm from the surface or reference point toward the center of the cathode active material 100, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. In the cathode active material 100 containing magnesium and titanium, the titanium distribution preferably has an overlapping region with the magnesium distribution. For example, the difference in depth between the titanium concentration peak and the magnesium concentration peak is preferably within 3 nm, more preferably within 1 nm.

[0467] Furthermore, when the positive electrode active material 100 contains aluminum as an additive element, it is preferable that the peak of the magnesium, nickel, or fluorine concentration is closer to the surface than the peak of the aluminum concentration in the surface layer portion 100 a when EDX-ray analysis is performed. For example, the peak of the aluminum concentration is preferably present on the surface of the positive electrode active material 100 or at a depth of 0.5 nm to 50 nm from the reference point toward the center, and more preferably at a depth of 5 nm to 50 nm.

[0468] When the positive electrode active material 100 contains magnesium, titanium, nickel, and aluminum as described above, a battery using the positive electrode active material 100 can achieve both "high cycle characteristics" that can suppress deterioration in discharge capacity due to repeated high-voltage charging (for example, charging with an upper limit of 4.6 V) and discharging, and "high low-temperature characteristics" that can obtain a large discharge capacity at low temperatures (for example, 0°C, -20°C, -40°C).

[0469] Furthermore, when EDX-ray analysis, area analysis, or point analysis is performed on the positive electrode active material 100, the ratio of the number of atoms of magnesium (Mg) to cobalt (Co) (Mg / Co) at the peak of the magnesium concentration is preferably 0.05 or more and 0.6 or less, more preferably 0.1 or more and 0.4 or less. The ratio of the number of atoms of aluminum (Al) to cobalt (Co) (Al / Co) at the peak of the aluminum concentration is preferably 0.05 or more and 0.6 or less, more preferably 0.1 or more and 0.45 or less. The ratio of the number of atoms of nickel (Ni) to cobalt (Co) (Ni / Co) at the peak of the nickel concentration is preferably 0 or more and 0.2 or less, more preferably 0.01 or more and 0.1 or less. The ratio of the number of atoms of fluorine (F) to cobalt (Co) (F / Co) at the peak of the fluorine concentration is preferably 0 or more and 1.6 or less, more preferably 0.1 or more and 1.4 or less.

[0470] Furthermore, when the positive electrode active material 100 is subjected to linear or area analysis, the ratio of the number of atoms of the additive element to cobalt (Co) in the vicinity of the grain boundaries (A / Co) is preferably 0.020 or more and 0.50 or less. It is even more preferably 0.025 or more and 0.30 or less. It is even more preferably 0.030 or more and 0.20 or less. It is also preferably 0.020 or more and 0.30 or less. It is also preferably 0.020 or more and 0.20 or less. It is also preferably 0.025 or more and 0.50 or less. It is also preferably 0.025 or more and 0.20 or less. It is also preferably 0.030 or more and 0.50 or less. It is also preferably 0.030 or more and 0.30 or less.

[0471] For example, when the additive element is magnesium, when linear or area analysis is performed on the positive electrode active material 100, the ratio of the number of magnesium atoms to the number of cobalt atoms (Mg / Co) near the grain boundaries is preferably 0.020 or more and 0.50 or less. It is even more preferably 0.025 or more and 0.30 or less. It is even more preferably 0.030 or more and 0.20 or less. It is also preferably 0.020 or more and 0.30 or less. It is also preferably 0.020 or more and 0.20 or less. It is also preferably 0.025 or more and 0.50 or less. It is also preferably 0.025 or more and 0.20 or less. It is also preferably 0.030 or more and 0.50 or less. It is also preferably 0.030 or more and 0.30 or less. Furthermore, when the ratio is within the above range at multiple locations, for example, three or more locations, on the positive electrode active material 100, it can be said that this indicates that the additive element is not attached to a narrow area on the surface of the positive electrode active material 100, but is widely distributed at a preferred concentration in the surface layer portion 100a of the positive electrode active material 100.

[0472] <EPMA> EPMA (Electron Probe Microanalysis) can also quantify elements. Area analysis can analyze the distribution of each element.

[0473] When EPMA surface analysis is performed on a cross section of the positive electrode active material 100 according to one embodiment of the present invention, it is preferable that one or more selected from the additive elements have a concentration gradient, similar to the EDX analysis results. It is also more preferable that the depth from the surface of the concentration peak differs depending on the additive element. The preferred range of the concentration peak for each additive element is also the same as in the case of EDX.

[0474] However, EPMA analyzes a region from the surface to a depth of about 1 μm. Therefore, the quantitative values ​​of each element may differ from the measurement results obtained using other analytical methods. For example, when the surface of the positive electrode active material 100 is analyzed using EPMA, the concentration of each added element present in the surface layer 100 a may be lower than the result obtained using XPS.

[0475] <Raman Spectroscopy> As described above, in the positive electrode active material 100 according to one embodiment of the present invention, at least a portion of the surface layer 100a preferably has a rock salt crystal structure. Therefore, when the positive electrode active material 100 and a positive electrode including the positive electrode active material 100 are analyzed by Raman spectroscopy, it is preferable to observe not only the layered rock salt crystal structure but also cubic crystal structures such as rock salt crystal structure. In the STEM image and the electron microbeam diffraction pattern described below, unless cobalt is substituted at lithium positions with a certain frequency in the depth direction during observation, or cobalt is present at the oxygen tetracoordination positions, they cannot be detected as bright spots in the STEM image and the electron microbeam diffraction pattern. On the other hand, because Raman spectroscopy is an analysis that captures the vibrational modes of bonds such as Co—O, peaks of the wavenumbers of the corresponding vibrational modes may be observed even when the amount of the corresponding Co—O bond is small. Furthermore, Raman spectroscopy can be performed on a surface layer having an area of ​​several μm ２ Since it is possible to measure a range of about 1 μm in depth, it is possible to capture with high sensitivity the state that exists only on the particle surface.

[0476] For example, when the laser wavelength is 532 nm, layered rock salt LiCoO ２ So, 470 cm −１ ~490cm −１ , 580 cm −１ ~600cm −１ Peak at (vibration mode: E ｇ , A １ｇ ) is observed. On the other hand, cubic CoO ｘ (0<x<1) (rock salt type Co １−ｙ O (0<y<1) or spinel type Co ３ O ４ ) is 665 cm −１ ~685cm −１ Peak at (Vibration mode: A １ｇ ) is observed.

[0477] Therefore, 470 cm −１ ~490cm −１ The integrated intensity of I1, 580 cm −１ ~600cm −１ The integrated intensity of I2, 665 cm −１ ~685cm −１When the integrated intensity of the above is I3, the value of I3 / I2 is preferably 1% or more and 10% or less, and more preferably 3% or more and 9% or less.

[0478] If a cubic crystal structure such as a rock salt type is observed within the above range, it can be said that the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure within a preferred range.

[0479] <<Electron Diffraction Pattern>> As with Raman spectroscopy, it is preferable that the characteristics of the rock salt-type crystal structure are observed in the electron diffraction pattern as well as the layered rock salt crystal structure. However, in the STEM image and the electron diffraction pattern, taking into account the above-mentioned difference in sensitivity, it is preferable that the characteristics of the rock salt-type crystal structure are not too strong in the surface layer portion 100a, particularly in the outermost surface (for example, 1 nm deep from the surface). This is because, rather than the outermost surface being covered with a rock salt-type crystal structure, it is preferable that the lithium layer has a layered rock salt-type crystal structure and an additive element such as magnesium is present in the lithium layer, which can ensure a lithium diffusion path and have a stronger function of stabilizing the crystal structure.

[0480] Therefore, for example, when a micro-electron beam diffraction pattern is obtained from a region having a depth of 1 nm or less from the surface and a micro-electron beam diffraction pattern from a region having a depth of 3 nm to 10 nm, it is preferable that the difference in lattice constant calculated from these patterns is small.

[0481] For example, the difference in lattice constant calculated from a measurement point at a depth of 1 nm or less from the surface and a measurement point at a depth of 3 nm to 10 nm is preferably 0.1 Å or less for the a-axis and 1.0 Å or less for the c-axis. It is more preferably 0.05 Å or less for the a-axis and 0.6 Å or less for the c-axis. It is even more preferably 0.04 Å or less for the a-axis and 0.3 Å or less for the c-axis.

[0482] <Surface Roughness and Specific Surface Area> The positive electrode active material 100 of one embodiment of the present invention preferably has a smooth surface with little unevenness. A smooth surface with little unevenness indicates that the effect of the flux described below is sufficiently exerted, and the surface of the additive element source and the lithium cobalt oxide are melted. Therefore, this is one factor indicating that the distribution of the additive element in the surface layer portion 100 a is good.

[0483] Whether the surface is smooth and has few irregularities can be determined from, for example, a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of ​​the positive electrode active material 100, or the like.

[0484] For example, the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 as follows.

[0485] First, the cathode active material 100 is processed using an FIB or the like to expose a cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken. The SEM image is subjected to noise processing using image processing software. For example, Gaussian blurring (σ = 2) is performed, followed by binarization. Interface extraction is then performed using image processing software. The interface line between the protective film or the like and the cathode active material 100 is selected using an automatic selection tool or the like, and the data is extracted into a spreadsheet or the like. Using the functions of the spreadsheet or the like, correction is performed from a regression curve (quadratic regression), and parameters for calculating roughness are obtained from the data after slope correction, and the root mean square surface roughness (RMS) is calculated by calculating the standard deviation. This surface roughness is the surface roughness at least within 400 nm of the outer periphery of the particle of the cathode active material.

[0486] On the particle surfaces of the positive electrode active material 100 of this embodiment, the root mean square (RMS) surface roughness, which is an index of roughness, is preferably less than 3 nm, more preferably less than 1 nm, and even more preferably less than 0.5 nm.

[0487] The image processing software used for noise processing, boundary extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. The spreadsheet software is also not particularly limited, but for example, Microsoft Office Excel can be used.

[0488] For example, the actual specific surface area S measured by the gas adsorption method using the constant volume method Ｒ and the ideal specific surface area S ｉ The smoothness of the surface of the positive electrode active material 100 can also be quantified from the ratio of

[0489] Ideal specific surface area S ｉ is calculated assuming that all particles have the same diameter as D50, the same weight, and an ideal spherical shape.

[0490] The median diameter D50 can be measured by a particle size distribution analyzer using a laser diffraction / scattering method, etc. The specific surface area can be measured by a specific surface area measuring device using a gas adsorption method based on a constant volume method, for example.

[0491] The positive electrode active material 100 according to one embodiment of the present invention has an ideal specific surface area S calculated from the median diameter D50. ｉ and the actual specific surface area S Ｒ The ratio S Ｒ / S ｉ is preferably 2.1 or less.

[0492] Alternatively, the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 by the following method.

[0493] First, a surface SEM image of the positive electrode active material 100 is obtained. At this time, a conductive coating may be applied as a pretreatment for observation. The observation surface is preferably perpendicular to the electron beam. When comparing multiple samples, the measurement conditions and observation area are the same.

[0494] Next, image processing software (for example, "ImageJ") is used to convert the SEM image into, for example, an 8-bit image (called a grayscale image). The grayscale image contains luminance (brightness information). For example, in an 8-bit grayscale image, luminance can be expressed in 2 to the power of 8 = 256 gradations. Dark areas have lower gradations, and bright areas have higher gradations. The luminance change can be quantified in relation to the number of gradations. This numerical value is called the grayscale value. By obtaining the grayscale value, it is possible to evaluate the unevenness of the positive electrode active material as a numerical value.

[0495] Furthermore, it is possible to display the brightness change of the target area as a histogram. A histogram is a three-dimensional representation of the gradation distribution in the target area, and is also called a brightness histogram. Obtaining a brightness histogram makes it possible to visually evaluate the unevenness of the positive electrode active material in an easy-to-understand manner.

[0496] When evaluating the positive electrode active material 100 of one embodiment of the present invention, the difference between the maximum and minimum grayscale values ​​is preferably 120 or less, more preferably 115 or less, and even more preferably 70 to 115. The standard deviation of the grayscale values ​​is preferably 11 or less, more preferably 8 or less, and even more preferably 4 to 8.

[0497] <Particle Size Distribution Analysis Using Cross-Sectional SEM Image of Positive Electrode> The particle size distribution of the positive electrode active material 100 can also be calculated from a cross-sectional SEM image of the positive electrode active material 100 by the following method.

[0498] First, an analysis region is cut out from the acquired cross-sectional SEM image. A range having a sufficient area for image analysis can be cut out, for example, a range of 50 μm or more × 100 μm or more, but this is not limited thereto. Depending on factors such as the size of the positive electrode active material, a smaller or larger area may be cut out.

[0499] The cross-sectional SEM image may be cut out using a function of image processing software, for example, ImageJ, which may be used as the image processing software, and cut out using its crop function.

[0500] Next, the cut-out first image is binarized using image processing software, and particle analysis is performed.

[0501] ImageJ, for example, can be used as the image processing software. The binarization process will be described below. A first image displayed on a 256-value grayscale is used as a frequency graph excluding black (value 0) and white (value 255), and the low-value side (HWHM_L) and high-value side (HWHM_H) are determined as the half-width at half maximum (HWHM) of the maximum peak in the frequency graph. Next, a minimum value a in a range twice the width of HWHM_L on the low-value side from the value corresponding to the peak top (maximum frequency) of the maximum peak, and a maximum value b in a range twice the width of HWHM_H on the high-value side are determined.

[0502] Next, binarization is performed so that values ​​less than a are white, values ​​greater than a and less than b are black, and values ​​greater than b are white. Specifically, the threshold function of ImageJ is used to perform binarization as Threshold (a, b). After that, random bright spots thought to be caused by the conductive material are removed using the Gray Morphology (radius = 3, operator = open, type = circle) and Gray Morphology (radius = 1, operator = close, type = circle) conditions, and a second image can be obtained.

[0503] Next, using the second image, the particle size (projected area) was determined to be 0.5 μm using the Analyze Particles function of ImageJ. ２ 700 μm or more ２ The following particles are detected, and the area S of each particle is obtained. Next, the diameter r of each particle is calculated based on the area S of each particle (Equation 1).

[0504]

[0505] In this way, the particle size distribution of each particle can be calculated from the cross-sectional SEM image. Performing the above analysis is called performing particle size distribution analysis using a cross-sectional SEM image of the positive electrode.

[0506] A coating portion may be attached to at least a portion of the surface of the positive electrode active material 100. Fig. 27 shows an example of a positive electrode active material 100 to which a coating portion 104 is attached.

[0507] The coating portion 104 is preferably formed by the accumulation of decomposition products of the electrolyte and the organic electrolytic solution during charging and discharging. ｘ CoO ２ When repeated charging is performed such that x in the formula is 0.24 or less, the presence of a coating portion derived from the electrolyte on the surface of the positive electrode active material 100 is expected to improve charge-discharge cycle characteristics. This is due to reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing cobalt elution. The coating portion 104 preferably contains, for example, carbon, oxygen, and fluorine. Furthermore, when LiBOB and / or SUN (suberonitrile) are used as the electrolyte, a high-quality coating portion is easily obtained. Therefore, a coating portion 104 containing one or more elements selected from boron, nitrogen, sulfur, and fluorine may be a high-quality coating portion and is therefore preferred. Furthermore, the coating portion 104 does not have to cover the entire positive electrode active material 100. For example, it is sufficient for the coating portion 104 to cover 50% or more of the surface of the positive electrode active material 100, with 70% or more being more preferable and 90% or more being even more preferable.

[0508] <<Powder Resistivity Measurement>> The positive electrode active material 100 according to one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in a charged state can suppress a decrease in charge / discharge capacity due to repeated charge / discharge. The positive electrode active material 100 having the above-described excellent properties is characterized in that, in the above-described <<XRD>>, Li ｘ CoO ２ It has been explained that when x in the formula is small, the cathode active material 100 has an O3'-type and / or monoclinic O1(15)-type crystal structure. Furthermore, in the above section <<EDX>>, a preferred distribution of the added elements when STEM-EDX analysis is performed on the cathode active material 100 has been explained. Furthermore, the cathode active material 100 according to one embodiment of the present invention is also characterized by the volume resistivity of the powder.

[0509] A feature of the positive electrode active material 100 according to one embodiment of the present invention is that the volume resistivity of the powder of the positive electrode active material 100 is 1.0×10 ８ Ω・cm or more 1.0×10 １０ It is preferable that the resistance is Ω cm or less, and 5.0 × 10 ８ Ω・cm or more 1.5×10 ９ It is more preferable that the resistivity is Ω·cm or less.

[0510] The positive electrode active material 100 having the above volume resistivity has a stable crystal structure even at high voltages. Therefore, the volume resistivity of the powder of the positive electrode active material 100 being within the above range can be used as an indicator that the surface layer portion 100 a, which is important for the stability of the crystal structure of the positive electrode active material in a charged state, has been successfully formed.

[0511] A method for measuring the volume resistivity of the powder of the positive electrode active material 100 according to one embodiment of the present invention will be described.

[0512] The volume resistivity of a powder is preferably measured using an instrument with a resistance measurement terminal and a mechanism for applying pressure to the powder to be measured. The resistance measurement terminal preferably has four terminals (also referred to as four-point probes). For example, the MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. can be used as a measurement device having a resistance measurement terminal and a mechanism for applying pressure to the powder (sample) to be measured. The resistance measurement device can be the Loresta-GP low resistance meter or the Hiresta-GP high resistance meter. The Loresta-GP can be used to measure low resistance samples, and the Hiresta-GP can be used to measure high resistance samples. The measurement environment is preferably a stable environment such as a dry room. A dry room environment, for example, with a temperature of 25°C and a dew point of -40°C or lower, is preferable. When performing measurements in a humid environment, the electrical resistance may decrease due to the influence of moisture in the air, potentially preventing the actual physical property values ​​from being obtained.

[0513] Measurement of the volume resistivity of powder using the measuring device shown above will be described. First, a powder sample is set in the measuring unit. The measuring unit is structured so that the powder sample and a terminal for resistance measurement are in contact with each other and can apply pressure to the powder sample. The measuring unit also has a structure for measuring the volume of the powder sample. Specifically, the measuring unit has a cylindrical space in which the powder sample is set. The structure for measuring the volume of the powder sample described above can measure the volume occupied by the powder at that time by measuring the height of the powder set in the space.

[0514] In measuring the volume resistivity of a powder, the electrical resistance of the powder and the volume of the powder are measured while pressure is applied to the powder. The pressure applied to the powder can be measured under a variety of conditions. For example, the electrical resistance and volume of the powder can be measured under pressure conditions of 16 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa. The volume resistivity of the powder can be calculated from the measured electrical resistance and volume of the powder.

[0515] When the above-described measurement is performed, the volume resistivity of the powder of the positive electrode active material 100 according to one embodiment of the present invention is 1.0×10 when measured under a pressure of 64 MPa. ８ Ω・cm or more 1.0×10 １０ When the capacitance is 5.0×10 Ω cm or less, favorable cycle characteristics are exhibited in a charge-discharge cycle test under high charge voltage conditions. ８ Ω・cm or more 1.5×10 ９ When the electrical resistance is Ω·cm or less, more preferable cycle characteristics are exhibited in a charge / discharge cycle test under high voltage conditions.

[0516] Unless otherwise specified in the present specification, the volume resistivity measured as above is the volume resistivity of the powder.

[0517] Furthermore, even when the positive electrode active material 100 of one embodiment of the present invention is used as a positive electrode active material for an all-solid-state battery, the powder preferably has low volume resistivity and can be used in the configuration of the all-solid-state battery described in Embodiment 6.

[0518] An example of a method for manufacturing the positive electrode active material 100 of one embodiment of the present invention will be described below with reference to FIGS.

[0519] In order to prepare the positive electrode active material 100 having the distribution, composition, and / or crystalline structure of the additive elements as described above, the method of adding the additive elements is important. At the same time, it is also important that the crystallinity of the inner portion 100b is good.

[0520] Therefore, in the process of producing the positive electrode active material 100, it is preferable to first synthesize lithium cobalt oxide, and then mix in the additive element source and perform a heat treatment.

[0521] In the method of synthesizing lithium cobalt oxide containing an additive element by mixing an additive element source simultaneously with a cobalt source and a lithium source, it is difficult to increase the concentration of the additive element in the surface layer portion 100a. Furthermore, if the additive element source is simply mixed without heating after synthesizing lithium cobalt oxide, the additive element will simply adhere to the lithium cobalt oxide without dissolving in the lithium cobalt oxide. Without sufficient heating, it is also difficult to achieve a good distribution of the additive element. Therefore, it is preferable to mix the additive element source after synthesizing lithium cobalt oxide and then perform a heat treatment. This heat treatment after mixing the additive element source is sometimes called annealing.

[0522] However, if the annealing temperature is too high, cation mixing occurs, increasing the possibility that an added element, such as magnesium, enters the cobalt site. ｘ CoO ２ When the value of x in the matrix is ​​small, the layered rock salt crystal structure of R-3m cannot be maintained. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to divalent and the evaporation of lithium.

[0523] Therefore, it is preferable to mix a material that functions as a flux with the additive element source. Any material with a lower melting point than lithium cobalt oxide can function as a flux. For example, fluorine compounds such as lithium fluoride are suitable. Adding a flux lowers the melting points of the additive element source and lithium cobalt oxide. Lowering the melting point makes it easier to distribute the additive elements well at a temperature where cation mixing is unlikely to occur.

[0524] <<Method for Manufacturing Positive Electrode Active Material>> A method for manufacturing the positive electrode active material 100 will be described with reference to FIGS. 28 to 29C.

[0525] <Step S11> In step S11 shown in FIG. 28, a lithium source (Li source) and a cobalt source (Co source) are prepared as starting materials for lithium and transition metal, respectively.

[0526] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, and it is preferable to use a material with a purity of, for example, 99.99% or higher.

[0527] As the cobalt source, it is preferable to use a compound containing cobalt, for example, cobalt oxide such as tricobalt tetroxide, cobalt hydroxide, or the like.

[0528] The cobalt source preferably has a high purity, for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity and / or reliability of the secondary battery can be increased.

[0529] In addition, the cobalt source preferably has high crystallinity, for example, single crystal grains. The crystallinity of the cobalt source can be evaluated using a TEM (transmission electron microscope) image, a STEM (scanning transmission electron microscope) image, a HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) image, an ABF-STEM (annular bright-field scanning transmission electron microscope) image, or by X-ray diffraction (XRD), electron diffraction, neutron diffraction, or the like. Note that the above-mentioned methods for evaluating crystallinity can be applied not only to the evaluation of cobalt sources but also to the evaluation of the crystallinity of other sources.

[0530] <Step S12> Next, in step S12 shown in FIG. 28 , the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed by either a dry or wet method. The wet method is preferred because it allows for smaller fragments. When using the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react 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 the cobalt source with dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then pulverize and mix them. Using dehydrated acetone with the above purity can reduce potential impurities.

[0531] A ball mill, a bead mill, or the like can be used as a means for pulverizing and mixing. When using a ball mill, aluminum oxide balls or zirconium oxide balls are preferably used as pulverizing media. Zirconium oxide balls are preferred because they emit less impurities. Furthermore, when using a ball mill, a bead mill, or the like, the peripheral speed should be set 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).

[0532] <Step S13> Next, in step S13 shown in FIG. 28 , the mixed material is heated. Heating is preferably performed at a temperature of 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower, and even more preferably at approximately 950°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, lithium may evaporate from the lithium source and / or cobalt may be excessively reduced, resulting in defects. For example, cobalt may change from trivalent to divalent, inducing oxygen defects.

[0533] If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time is preferably from 1 hour to 100 hours, and more preferably from 2 hours to 20 hours.

[0534] The temperature rise rate depends on the heating temperature reached, but is preferably 80° C. / h to 250° C. / h. For example, when heating at 1000° C. for 10 hours, the temperature rise rate should be 200° C. / h.

[0535] 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 less, more preferably an atmosphere with a dew point of -80°C or less. In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. In addition, in order to suppress impurities that may be mixed into the material, the CH ４ , CO, CO ２ , and H ２ The impurity concentrations of the above should be 5 ppb (parts per billion) or less.

[0536] An oxygen-containing atmosphere is preferred as the heating atmosphere. For example, dry air can be continuously introduced 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 allowing oxygen to flow through the reaction chamber is called flow.

[0537] When the heating atmosphere is an atmosphere containing oxygen, a method of not allowing oxygen to flow may be used. For example, a method of reducing the pressure of the reaction chamber and then filling it with oxygen (which may also be called purging) may be used to prevent the oxygen from entering or leaving the reaction chamber. For example, the reaction chamber may be reduced in pressure to -970 hPa and then filled with oxygen to 50 hPa.

[0538] After heating, the material may be cooled naturally, but it is preferable that the time required for the temperature to drop from the specified temperature to room temperature is within a range of 10 to 50 hours. However, cooling to room temperature is not necessarily required, as long as the material is cooled to a temperature acceptable for the next step.

[0539] The heating in this step may be carried out using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln can be carried out while stirring, whether in a continuous or batch system.

[0540] The container for accommodating the object to be heated during heating is preferably an aluminum oxide crucible or an aluminum oxide setter (also called a sheath). An aluminum oxide crucible is a material that is almost free of impurities. In this embodiment, a setter made of aluminum oxide with a purity of 99.9% is used. It is preferable to heat the crucible or setter with a lid, as this prevents the material from volatilizing. Mullite-cordierite may also be used as the material for the crucible and setter.

[0541] Furthermore, it is preferable to use a crucible that has been used multiple times rather than a new one. In this specification, a new crucible refers to one that has undergone two or fewer heating processes with materials containing lithium, transition metal M, and / or additive elements. A multiple-use crucible refers to one that has undergone three or more heating processes with materials containing lithium, transition metal M, and / or additive elements. This is because using a new crucible may result in some of the materials, including lithium fluoride, being absorbed, diffused, migrated, and / or adhered to the sheath during heating. If some of the materials are lost as a result of this, there is a growing concern that the distribution of elements, particularly in the surface layer of the positive electrode active material, may not fall within the desired range. On the other hand, this risk is less likely with a multiple-use crucible.

[0542] After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. It is preferable to use an aluminum oxide mortar. Aluminum oxide mortars are made of a material that does not easily release impurities. Specifically, an aluminum oxide mortar with a purity of 90% or more, preferably 99% or more, is used. Heating conditions equivalent to those of step S13 can also be applied to heating steps other than step S13, which will be described later.

[0543] <Step S14> By the above steps, lithium cobalt oxide (LiCoO ２ ) can be synthesized.

[0544] Although the example of producing the composite oxide by the solid phase method in steps S11 to S14 has been shown, the composite oxide may also be produced by a coprecipitation method or a hydrothermal method.

[0545] Note that pre-synthesized lithium cobalt oxide may be used in step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on pre-synthesized lithium cobalt oxide, lithium cobalt oxide with a smooth surface can be obtained.

[0546] <Step S20> Next, as shown in step S20, it is preferable to add an additive element to the lithium cobalt oxide. In the method for producing a positive electrode active material described in this embodiment, the additive element is added in multiple steps, so in the flow shown in Figure 28, the additive element added first will be referred to as A1, the additive element added second time will be referred to as A2, and the additive element added third time will be referred to as A3. The step of adding additive element A1 will be described with reference to Figure 29A.

[0547] 29A, an additive element source (Al source) to be added to lithium cobalt oxide is prepared. A lithium source may be prepared together with the Al source.

[0548] The additive element A1 can be any of the additive elements described in the previous embodiment. Specifically, one or more elements selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. Also, one or two elements selected from bromine and beryllium can be used.

[0549] When magnesium is selected as the additive element, the source of the additive element can be called a magnesium source. As the magnesium source, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used. Furthermore, a plurality of the above-mentioned magnesium sources may be used.

[0550] When fluorine is selected as the additive element, the source of the additive element can be called a fluorine source. Examples of the fluorine source include lithium fluoride (LiF) and magnesium fluoride (MgF ２ ), aluminum fluoride (AlF ３ ), titanium fluoride (TiF ４ ), cobalt fluoride (CoF ２ , CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF ２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF ２ ), cerium fluoride (CeF ３ , CeF ４ ), lanthanum fluoride (LaF ３ ), or sodium aluminum hexafluoride (Na ３ AlF ６ Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.

[0551] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as a lithium source. Another lithium source that can be used in step S21 is lithium carbonate.

[0552] The fluorine source may also be gaseous, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O ４ F ２ , O ５ F ２ , O ６ F ２ , O ２ F), nitrogen trifluoride (NF ３ ) or the like may be used and mixed in the atmosphere during the heating step described below. Also, a plurality of the above-mentioned fluorine sources may be used.

[0553] 28 and 29C, magnesium and fluorine are used as the additive element A1. Lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF ２ Lithium fluoride and magnesium fluoride are prepared as LiF:MgF ２ The effect of lowering the melting point is greatest when the molar ratio is about 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be excessive and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is set to LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x: 1 (x = 0.33 or its vicinity) is more preferable. In this specification, "or its vicinity" refers to a value that is greater than 0.9 times and smaller than 1.1 times the value.

[0554] 29A, the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under pulverization and mixing conditions selected from those described in step S12.

[0555] 29A, the pulverized and mixed materials are collected to obtain the Al source. The Al source shown in step S23 contains multiple starting materials and can be called a mixture.

[0556] The particle size of the mixture is preferably D50 (median diameter) of 600 nm to 10 μm, more preferably 1 μm to 5 μm. Even when a single material is used as the additive element source, the D50 (median diameter) is preferably 600 nm to 10 μm, more preferably 1 μm to 5 μm.

[0557] Such a finely powdered mixture (including the case where only one type of additive element is included) can be easily adhered to the surfaces of the lithium cobalt oxide particles when mixed with the lithium cobalt oxide in a later step. If the mixture is evenly adhered to the surfaces of the lithium cobalt oxide particles, it is preferable because the additive element can be easily distributed or diffused uniformly in the surface layer portion 100a of the composite oxide after heating.

[0558] 28 , lithium cobalt oxide and an Al source are mixed together. The ratio of the number of cobalt atoms Co in the lithium cobalt oxide to the number of magnesium atoms Mg in the Al source is preferably Co:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0559] The mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the shape of the lithium cobalt oxide particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter mixing time than those in step S12. It can also be said that dry mixing provides milder conditions than wet mixing. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconium oxide balls as the medium.

[0560] In this embodiment, dry mixing is performed in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour in a dry room with a dew point of −100° C. or higher and −10° C. or lower.

[0561] <Step S32> Next, in step S32 of Fig. 28, the mixed materials are collected to obtain a mixture 901. When collecting the materials, they may be crushed and then sieved, if necessary.

[0562] <Step S33> Next, in step S33 shown in Fig. 28, the mixture 901 is heated. This can be performed by selecting from the heating conditions described in step S13. The heating time is preferably 2 hours or more. At this time, the pressure inside the furnace may exceed atmospheric pressure in order to increase the oxygen partial pressure in the heating atmosphere. This is because if the oxygen partial pressure in the heating atmosphere is insufficient, cobalt and the like may be reduced, and lithium cobalt oxide and the like may no longer be able to maintain a layered rock salt type crystal structure.

[0563] Here, a supplementary note about the heating temperature will be provided. The lower limit of the heating temperature in step S33 must be equal to or higher than the temperature at which the reaction between the lithium cobalt oxide and the additive element source proceeds. The temperature at which the reaction proceeds may be any temperature at which interdiffusion of elements contained in the lithium cobalt oxide and the additive element source occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example for explanation, and the melting temperature T ｍ 0.757 times (Tammann temperature T ｄ ) solid-phase diffusion occurs. Therefore, the heating temperature in step S33 should be 650° C. or higher.

[0564] Of course, the reaction is more likely to proceed if the temperature is equal to or higher than the melting point of one or more of the materials contained in the mixture 901. For example, LiF and MgF are used as the additive element source. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.

[0565] Also, LiCoO ２ :LiF:MgF ２ The mixture 903 obtained by mixing the components so that the molar ratio was 100:0.33:1 showed an initial melting temperature T ｉｍ is 779 ° C, the melting peak temperature T ｐｍ is 815°C, and the melting end temperature T ｅｍ Therefore, the lower limit of the heating temperature is more preferably 826°C or higher.

[0566] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0567] The upper limit of the heating temperature is set to 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 only slightly. Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source, etc., within an appropriate range. If the temperature is too high, fluoride will decrease due to evaporation. For example, the vapor pressure of lithium fluoride rises sharply from 900°C. Therefore, a temperature of 1000°C or less is more preferable, 950°C or less is even more preferable, 900°C or less is even more preferable, and 850°C or less is even more preferable. If the evaporation of lithium fluoride is suppressed, the surface layer 100a can be made to have high concentrations of fluorine and lithium. If the surface layer 100a contains a sufficient amount of lithium, a heterophase (MgTiO ３ Another advantage is that it makes it harder for problems like these to occur.

[0568] In light of these, the heating temperature in step S33 is preferably 650°C or higher and 1130°C or lower, more preferably 650°C or higher and 1000°C or lower, even more preferably 650°C or higher and 950°C or lower, and even more preferably 650°C or higher and 900°C or lower. Also, it is preferably 742°C or higher and 1130°C or lower, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower. Also, it is preferably 826°C or higher and 1100°C or lower, or 826°C or higher and 1130°C or lower, more preferably 826°C or higher and 1000°C or lower, even more preferably 826°C or higher and 950°C or lower, and even more preferably 826°C or higher and 900°C or lower. The heating temperature in step S33 is preferably higher than that in step S13.

[0569] Furthermore, when the mixture 901 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0570] In the manufacturing method described in this embodiment, some materials, for example, LiF as a fluorine source, may function as a flux, which allows the heating temperature to be lowered below the decomposition temperature of lithium cobalt oxide, for example, to 742° C. or higher and 950° C. or lower, and allows additive elements such as magnesium to be distributed in the surface layer, thereby enabling the manufacture of a positive electrode active material with excellent characteristics.

[0571] However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF may volatilize or sublime when heated, and if it volatilizes, the amount of LiF in the mixture 903 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, etc., LiCoO ２ There is a possibility that Li on the surface reacts with F in the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0572] Therefore, it is preferable to heat the mixture 901 in an atmosphere containing LiF, that is, to heat the mixture 901 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the volatilization of LiF in the mixture 901.

[0573] The heating in this step is preferably performed so as not to cause adhesion between particles of the mixture 901. If the particles of the mixture 901 adhere to each other during heating, the contact area with oxygen in the atmosphere decreases and the route along which the additive elements (e.g., fluorine) diffuse is blocked, which may result in poor distribution of the additive elements (e.g., magnesium and fluorine) in the surface layer portion.

[0574] Furthermore, it is believed that uniform distribution of the additive element (e.g., fluorine) in the surface layer portion results in a smooth cathode active material with few irregularities. Therefore, in order to maintain or further smooth the surface after the heating in step S15 in this process, it is preferable that the particles of mixture 901 do not adhere to each other.

[0575] Furthermore, when heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and then not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen may cause the fluorine source to evaporate, which is undesirable in terms of maintaining surface smoothness.

[0576] When heating is performed using a roller hearth kiln, the mixture 901 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 901 .

[0577] Regarding the heating time, the heating time varies depending on conditions such as the heating temperature, the size and composition of the lithium cobalt oxide in step S14, etc. When the lithium cobalt oxide is small, a lower temperature or a shorter heating time may be preferable than when the lithium cobalt oxide is large.

[0578] 28, when the median diameter (D50) of the lithium cobalt oxide is about 12 μm, the heating temperature is preferably, for example, 650° C. or more and 950° C. or less. The heating time is preferably, for example, 3 hours or more and 60 hours or less, more preferably 10 hours or more and 30 hours or less, and even more preferably about 20 hours. The temperature-lowering time after heating is preferably, for example, 10 hours or more and 50 hours or less.

[0579] On the other hand, when the median diameter (D50) of the lithium cobalt oxide in step S14 is about 7 μm, the heating temperature is preferably, for example, 650° C. or higher and 950° C. or lower. The heating time is preferably, for example, 1 hour or higher and 10 hours or lower, and more preferably about 5 hours. The temperature-lowering time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.

[0580] <Step S34> Next, in step S34 shown in FIG. 28, the heated material is recovered and crushed as necessary to obtain a composite oxide 902.

[0581] <Step S40> Next, in step S40 shown in FIG. 28 , an additive element source (A2 source) is prepared. The additive element described in step S21 can be used as the additive element A2. In the method for producing a positive electrode active material described in FIGS. 28 to 29C , nickel and aluminum are used as the additive element A2. Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source. As shown in steps S41 to S43 of FIG. 29B , the nickel source and the aluminum source can be crushed to obtain the A2 source. The crushing conditions can be determined by taking into account the conditions in step S22.

[0582] 28, the composite oxide 902 and the A2 source are mixed. The mixing conditions can be determined by referring to the description of step S31.

[0583] <Step S52> Next, in step S52 shown in Fig. 28, the mixed materials are recovered to obtain a mixture 903. When recovering the materials, they may be crushed and then sieved, if necessary.

[0584] 28, the mixture 903 is heated. The heating conditions can be determined by referring to the description of step S33.

[0585] <Step S54> Next, in step S54 shown in FIG. 28, the heated material is recovered and crushed as necessary to obtain a composite oxide 904.

[0586] <Step S60> Next, in step S60 shown in FIG. 28 , an additive element source (A3 source) is prepared. The additive element described in step S21 can be used as the additive element A3. In the method for producing a positive electrode active material described in FIGS. 28 to 29C , titanium is used as the additive element A3. Lithium titanate, titanium oxide, titanium hydroxide, etc. can be used as the titanium source. As shown in steps S61 to S63 of FIG. 29C , the titanium source can be pulverized to obtain the A3 source. The pulverization conditions can be determined by taking into account the conditions in step S22.

[0587] <Step S71> In step S71 shown in Fig. 28, the composite oxide 904 and the A3 source are mixed. The mixing conditions can be determined by referring to the description of step S31.

[0588] <Step S72> Next, in step S72 shown in Fig. 28, the mixed materials are recovered to obtain a mixture 905. When recovering the materials, they may be crushed and then sieved, if necessary.

[0589] 28, the mixture 905 is heated. The heating conditions can be determined by referring to the description of step S33.

[0590] <Step S74> Next, in step S74 shown in Fig. 28 , the heated material is recovered and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. Through the above steps, the positive electrode active material 100 of one embodiment of the present invention can be produced. The positive electrode active material of one embodiment of the present invention has a smooth surface.

[0591] Positive electrode active material 100 with a smooth surface may be more resistant to physical destruction due to pressure, etc. than positive electrode active material that does not have a smooth surface. For example, positive electrode active material 100 is less likely to be destroyed in a test involving pressure, such as a nail penetration test, and as a result, safety may be improved.

[0592] [Initial Heating] In the above-described production method, it may be more preferable to perform heating after synthesizing lithium cobalt oxide and before mixing the additive element. This heating is called initial heating.

[0593] The initial heating causes lithium to be released from a part of the surface layer 100a of the lithium cobalt oxide, resulting in a more favorable distribution of the additive elements.

[0594] More specifically, it is believed that initial heating facilitates different distributions depending on the additive element through the following mechanism. First, lithium is released from a portion of the surface layer 100a by initial heating. Next, this lithium-deficient surface layer 100a is mixed with an additive element source, such as a nickel source, an aluminum source, or a magnesium source, and the mixture is heated. Of the additive elements, magnesium is a divalent typical element, and nickel is a transition metal, but it easily becomes a divalent ion. Therefore, Mg is released from a portion of the surface layer 100a. ２＋ and Ni ２＋ and Co reduced by lithium deficiency. ２＋ However, since this phase is formed only in a part of the surface layer portion 100a, it may not be clearly observed in an electron microscope image such as an STEM or an electron beam diffraction pattern.

[0595] Among the additive elements, nickel is likely to dissolve and diffuse into the interior 100b when the surface layer 100a is a layered rock-salt lithium cobaltate, but when part of the surface layer 100a is a rock-salt lithium cobaltate, nickel tends to remain in the surface layer 100a. Therefore, initial heating can make it easier for divalent additive elements such as nickel to remain in the surface layer 100a. The effect of this initial heating is particularly significant on the surface other than the (001)-oriented surface of the positive electrode active material 100 and on the surface layer 100a.

[0596] Furthermore, in these rock salt types, the bond distance between the metal Me and oxygen (Me-O distance) tends to be longer than in the layered rock salt type.

[0597] For example, rock salt type Ni ０．５ Mg ０．５ The Me-O distance in rock salt MgO is 2.09 Å, and the Me-O distance in rock salt MgO is 2.11 Å. Even if a spinel phase is formed in a part of the surface layer 100a, the spinel phase is not formed in the spinel NiAl ２ O ４ The Me-O distance is 2.0125 Å, and the spinel type MgAl ２ O ４ The Me-O distance is 2.02 Å. In both cases, the Me-O distance exceeds 2 Å. Note that 1 Å = 10 −１０ m.

[0598] On the other hand, in the layered rock salt type, the bond distance between metals other than lithium and oxygen is shorter than the above. For example, layered rock salt type LiAlO ２ The Al-O distance in the layered rock salt LiCoO is 1.905 Å (the Li-O distance is 2.11 Å). ２ The Co—O distance in this case is 1.9224 Å (the Li—O distance is 2.0916 Å).

[0599] According to Shannon's ionic radii, the ionic radius of hexacoordinated aluminum is 0.535 Å, the ionic radius of hexacoordinated oxygen is 1.4 Å, and the sum of these is 1.935 Å.

[0600] From the above, it is believed that aluminum exists more stably in non-lithium sites in the layered rock-salt structure than in the rock-salt structure, and therefore aluminum is more likely to be distributed in the deeper region having the layered rock-salt structure and / or the interior 100b than in the region close to the surface having the rock-salt structure in the surface layer portion 100a.

[0601] Furthermore, the initial heating is expected to have the effect of increasing the crystallinity of the layered rock salt type crystal structure in the inner portion 100b.

[0602] However, initial heating is not necessarily required. In other heating steps, such as annealing, the atmosphere, temperature, time, etc. can be controlled to prevent Li ｘ CoO ２When x in the formula is small, a positive electrode active material 100 having an O3' type can sometimes be produced.

[0603] 100: positive electrode active material, 100a: surface layer, 100b: interior, 104: coating, 201: application processor, 202: MCU, 203: ROM, 204: display, 205: secondary battery, 206: power supply monitoring IC, 207: charging IC, 208: communication control circuit, 209: baseband processor, 210: transmitting / receiving circuit, 211: antenna, 212: environmental temperature sensor, 300: secondary battery, 301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode Active material layer, 310: separator, 312: washer, 313: ring-shaped insulator, 322: spacer, 400: secondary battery, 410: positive electrode, 411: positive electrode active material, 413: positive electrode current collector, 414: positive electrode active material layer, 420: solid electrolyte layer, 421: solid electrolyte, 430: negative electrode, 431: negative electrode active material, 433: negative electrode current collector, 434: negative electrode active material layer, 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolyte, 509: outer casing, 510: positive electrode ring lead electrode, 511: negative electrode lead electrode, 513: secondary battery, 514: terminal, 515: seal, 517: antenna, 519: layer, 529: label, 531: secondary battery pack, 540: circuit board, 550: current collector, 552: other side, 553: acetylene black, 554: graphene, 555: carbon nanotubes, 561: active material, 562: second active material, 590a: circuit system, 590b: circuit system, 590: control circuit, 600: secondary battery, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 613: safety valve mechanism, 614: conductive plate, 615: power storage system, 616: secondary battery, 620: signal processing board, 621: wiring, 622: wiring, 623: wiring, 624: conductor, 625: insulator, 626: wiring, 627: wiring, 628: conductive plate, 651: signal processing board substrate, 652: connection terminal, 653: connection terminal, 654: connection terminal, 655: connection terminal, 656: MCU, 657: memory, 658: semiconductor device, 659: FPC, 750a: positive electrode, 750b: solid electrolyte layer,750c: negative electrode, 751: electrode plate, 752: insulating tube, 753: electrode plate, 761: lower member, 762: upper member, 763: retaining screw, 764: wing nut, 765: O-ring, 766: insulator, 770a: packaging member, 770b: packaging member, 770c: packaging member, 771: external electrode, 772: external electrode, 773a: electrode layer, 773b: electrode layer, 901: mixture, 902: composite oxide, 903: mixture, 904: composite oxide, 905: mixture, 911a: terminal, 911b: terminal, 913: secondary battery, 930a: housing, 930b: housing , 930: housing, 931a: negative electrode active material layer, 931: negative electrode, 932a: positive electrode active material layer, 932: positive electrode, 933: separator, 950a: wound body, 950: wound body, 951: terminal, 952: terminal, 4700a: semiconductor device, 4700b: semiconductor device, 5200: portable game console, 5201: housing, 5202: display unit, 5203: button, 5500: information terminal, 5510: housing, 5511: display unit, 5512: secondary battery, 5700: automobile, 5900: information terminal, 5901: housing, 5902: display unit, 5903: operation switch, 5904: operation switch, 5905: band,

Claims

A control system including a first control circuit, a second control circuit, a secondary battery, a temperature sensor, a display unit, and a communication circuit, and switching between the first control circuit and the second control circuit, the second control circuit has a lower maximum power consumption and a lower processing capability than the first control circuit; the temperature sensor is a sensor for measuring an environmental temperature of the secondary battery, If the measurement result of the temperature sensor is within a tolerance range, the first control circuit drives the display unit; When the measurement result of the temperature sensor exceeds an upper limit temperature of the allowable range, the first control circuit transitions to a low power consumption mode, and the second control circuit drives the display unit.

2. The display device according to claim 1, wherein the display unit has a touch input operation unit, If the measurement result of the temperature sensor is within the allowable range, the first control circuit drives the touch input operation unit, When the measurement result of the temperature sensor exceeds an upper limit temperature of the allowable range, the first control circuit transitions to a low power consumption mode, and the second control circuit drives the touch input operation unit.

2. The control system according to claim 1, wherein the allowable range is between 5°C and 45°C.

2. The control system according to claim 1, wherein the secondary battery is a lithium ion secondary battery. 　 The control system according to claim 1 , wherein the secondary battery is an all-solid-state secondary battery.

Images