All-solid-state lithium secondary battery system

Abstract

To provide means for suppressing decrease in energy density owing to progress of overcharge in an all-solid type lithium secondary battery having a cathode containing a cathode active material including sulfur and a solid electrolyte.SOLUTION: An all-solid type lithium secondary battery system comprises an all-solid type lithium secondary battery including a cathode containing a cathode active material including sulfur and a solid electrolyte. In the all-solid type lithium secondary battery, a cathode active material layer contains a lithium-containing compound having a given redox potential. The system performs the judgement about whether a reaction current corresponding to a desorbing reaction of a lithium ion from the lithium-containing compound is generated when performing a process of charging the battery. If having determined that the reaction current has been generated, the system stops the charging process.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an all-solid-state lithium secondary battery system. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. In the automobile industry, there are high hopes for a reduction in carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and there has been active development of non-aqueous electrolyte secondary batteries, such as motor drive secondary batteries, which hold the key to putting these into practical use.

[0003] Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium secondary batteries used in mobile phones, notebook computers, etc. Therefore, lithium secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being rapidly developed.

[0004] Currently, lithium secondary batteries in widespread use use flammable organic electrolytes as electrolytes, and these liquid-based lithium secondary batteries require stricter safety measures against leakage, short circuits, overcharging, etc. than other batteries.

[0005] In recent years, research and development of all-solid-state lithium secondary batteries using oxide-based or sulfide-based solid electrolytes has been actively conducted. A solid electrolyte is a material that is mainly composed of an ion conductor capable of ion conduction in a solid state. Therefore, in principle, all-solid-state lithium secondary batteries do not have various problems caused by flammable organic electrolytes, as in conventional liquid-based lithium secondary batteries. In addition, in general, the use of high-potential, large-capacity positive electrode materials and large-capacity negative electrode materials can significantly improve the output density and energy density of the battery. For example, elemental sulfur (S8) has an extremely large theoretical capacity of about 1670 mAh / g, and has the advantages of being low cost and abundant in resources.

[0006] In general, from the viewpoint of preventing deterioration of a secondary battery, it is preferable to prevent the occurrence of so-called "overcharging," in which a secondary battery is further charged from a fully charged state. As a technique for improving stability against such overcharging, Patent Document 1 discloses a technique in which an electrolyte used in a liquid-based lithium-sulfur battery contains an electrolyte salt in at least two aprotic solvents, and the electrolyte is configured to have a eutectic concentration or a concentration within ±30% of the eutectic concentration. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2014-17256 A Summary of the Invention [Problem to be solved by the invention]

[0008] The above-mentioned "overcharge" state may also occur in an all-solid-state lithium secondary battery in which the electrolyte layer contains a solid electrolyte. However, the technology disclosed in Patent Document 1 is intended for liquid-based lithium-sulfur batteries that use an electrolyte solution, and therefore cannot be directly applied to all-solid-state lithium secondary batteries. In addition, according to the study by the present inventors, it has been found that when overcharge occurs in an all-solid-state lithium secondary battery in which the positive electrode active material layer contains a solid electrolyte, oxidative decomposition of the solid electrolyte contained in the positive electrode active material layer occurs, the reaction interface where the positive electrode active material and the solid electrolyte coexist is reduced, and the energy density of the battery is reduced.

[0009] Therefore, an object of the present invention is to provide a means capable of suppressing a decrease in energy density caused by the progress of overcharging in an all-solid-state lithium secondary battery that includes a sulfur-containing positive electrode active material and a solid electrolyte in the positive electrode. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems. As a result, they have found that the above problems can be solved by including a lithium-containing compound having a predetermined oxidation-reduction potential in a positive electrode active material layer in an all-solid-state lithium secondary battery including a sulfur-containing positive electrode active material and a solid electrolyte in a positive electrode, determining whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound occurs during a charging process of the battery, and stopping the charging process when it is determined that the reaction current occurs, thereby completing the present invention.

[0011] A lithium secondary battery system according to one embodiment of the present invention includes an all-solid-state lithium secondary battery including a power generating element having a positive electrode including a positive electrode active material layer containing a sulfur-containing positive electrode active material, a solid electrolyte, and a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li], a negative electrode including a negative electrode active material layer containing a lithium-containing negative electrode active material, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. The system is characterized in that it further includes a control unit that determines whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound has occurred during a charging process of the all-solid-state lithium secondary battery, and controls to stop the charging process when it is determined that the reaction current has occurred. Effect of the Invention

[0012] According to the present invention, in an all-solid-state lithium secondary battery including a positive electrode active material containing sulfur and a solid electrolyte in the positive electrode, a decrease in energy density caused by the progress of overcharging can be suppressed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram illustrating the configuration of an all-solid-state lithium secondary battery system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cyclic voltammogram during charging of a lithium secondary battery containing lithium sulfide (Li2S) as a positive electrode active material. [Diagram 3] FIG. 3 is a flowchart showing the procedure of the charging process in the secondary battery system 1. [Figure 4] FIG. 4 is a perspective view showing the appearance of an all-solid-state lithium secondary battery according to one embodiment of the present invention. [Diagram 5] FIG. 5 is a cross-sectional view taken along line 5-5 shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the above-mentioned embodiment of the present invention will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the claims, and is not limited to only the following embodiment. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. Hereinafter, the present invention will be described by taking as an example a non-bipolar (internal parallel connection) all-solid-state lithium secondary battery, which is one form of secondary battery. As described above, the solid electrolyte constituting the all-solid-state lithium secondary battery is a material mainly composed of an ion conductor capable of ion conduction in a solid. For this reason, the all-solid-state lithium secondary battery has the advantage that, in principle, various problems caused by a flammable organic electrolyte do not occur as in conventional liquid-based lithium secondary batteries. In addition, in general, there is also the advantage that the output density and energy density of the battery can be significantly improved by using a high-potential, large-capacity positive electrode material and a large-capacity negative electrode material.

[0015] [Secondary battery system] FIG. 1 is a block diagram illustrating the configuration of an all-solid-state lithium secondary battery system according to one embodiment of the present invention.

[0016] This all-solid-state lithium secondary battery system (hereinafter also referred to as "secondary battery system 1") includes an all-solid-state lithium secondary battery (hereinafter also referred to as "secondary battery 2"). It also includes a voltage sensor 3 that measures the cell voltage (terminal voltage) of the secondary battery 2, a voltage and current adjustment unit 4 that adjusts the input and output of power to and from the secondary battery 2, a current sensor 5 that measures the charge and discharge current of the secondary battery 2, and a control unit 6 that controls the charge and discharge of the secondary battery 2. The voltage and current adjustment unit 4 is connected to an external power source 7 and receives power during charging, while supplying power to an external load (not shown) via the voltage and current adjustment unit 4 during discharging (details will be described later).

[0017] The details of each part will be explained below.

[0018] The secondary battery 2 includes a power generating element having a positive electrode (hereinafter also simply referred to as a "sulfur-containing positive electrode") including a positive electrode active material layer containing a sulfur-containing positive electrode active material, a solid electrolyte, and a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li], a negative electrode including a negative electrode active material layer containing a lithium-containing negative electrode active material, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer. Details of the all-solid-state lithium secondary battery will be described later, but FIG. 2 shows a cyclic voltammogram during charging of a lithium secondary battery containing lithium sulfide (Li2S) as a positive electrode active material. According to the cyclic voltammogram shown in FIG. 2, it can be seen that the range of the potential (sulfur reaction potential) at which a reaction current flows as a result of the lithium ion desorption reaction (Li2S→S+2Li) from lithium sulfide (Li2S) proceeding when charging the sulfur-containing positive electrode is about 1.5 to 3.1 [V vs. Li+ / Li].

[0019] When the potential of the sulfur-containing positive electrode exceeds the above-mentioned reaction potential of sulfur (occurrence of overcharging) and reaches approximately 4.0 [V], a reaction occurs in which the solid electrolyte contained in the positive electrode active material layer is oxidized and decomposed. For example, if the solid electrolyte contains phosphorus sulfide, PS4 3- Ion is oxidized and PS4 4-In solid electrolytes where such oxidative decomposition reactions have occurred, the lithium ion conductivity during charging and discharging is significantly reduced. As a result, the reaction interface where the positive electrode active material and the solid electrolyte (and even the conductive additive) coexist is reduced, and the energy density of the lithium secondary battery is significantly reduced.

[0020] In contrast, in the all-solid-state lithium secondary battery system according to the present embodiment, the positive electrode active material layer constituting the positive electrode contains a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li]. This makes it possible to detect the occurrence of overcharging as described above before the potential of the sulfur-containing positive electrode reaches a potential at which oxidative decomposition of the solid electrolyte proceeds. For example, in the embodiment shown in FIG. 2, lithium iron phosphate (LiFePO4) having an oxidation-reduction potential of about 3.5 [V vs. Li+ / Li] is contained in the positive electrode active material layer as the lithium-containing compound. Here, consider a case where overcharging occurs during charging of an all-solid-state lithium secondary battery including a sulfur-containing positive electrode having such a configuration. When the potential of the sulfur-containing positive electrode rises beyond the reaction potential of sulfur due to the occurrence of overcharging and the potential of the positive electrode reaches the oxidation-reduction potential of lithium iron phosphate, a desorption reaction of lithium ions from the lithium-containing compound (lithium iron phosphate) proceeds. In the lithium secondary battery system according to the present embodiment, when the generation of a reaction current corresponding to the desorption reaction of lithium ions from such a lithium-containing compound is detected, control is performed to stop the charging process. This makes it possible to prevent the progress of the oxidative decomposition reaction of the solid electrolyte contained in the positive electrode active material layer, and to suppress the reduction of the reaction interface where the positive electrode active material and the solid electrolyte (and further the conductive additive) coexist, thereby making it possible to prevent a decrease in the energy density of the all-solid-state lithium secondary battery.

[0021] The voltage sensor 3 may be, for example, a voltmeter, and measures the cell voltage (terminal voltage) of the secondary battery 2, which is defined as the potential difference between the positive and negative electrodes of the secondary battery 2. The cell voltage V is calculated as the potential difference between the equilibrium potential of the positive electrode and the equilibrium potential of the negative electrode. There are no particular limitations on the location where the voltage sensor 3 is attached, and it may be any location within the circuit connected to the secondary battery 2 where the cell voltage between the positive and negative electrodes can be measured.

[0022] When charging the secondary battery 2, the voltage / current adjustment unit 4 adjusts the voltage and current of the power from the external power source 7 based on a command from the control unit 6, and supplies the power to the secondary battery 2. When discharging the secondary battery 2, the voltage / current adjustment unit 4 releases the electricity discharged from the secondary battery 2 to an external load (not shown).

[0023] Here, the external power source 7 is a power source for electric vehicles, also known as a power grid, used for charging electric vehicles and the like, and outputs direct current. Such power sources for electric vehicles convert commercial power (alternating current) into the direct current required for charging the secondary battery 2 and provide it. The external power source 7 is also provided with a power regeneration function, and when the secondary battery 2 is discharged, the direct current can be converted into alternating current and regenerated to the commercial power source. Note that a well-known power source with a power regeneration function can be used as a device constituting such an external power source 7, and therefore a detailed description thereof will be omitted here (power sources with a power regeneration function are described, for example, in Japanese Patent Application Laid-Open No. 7-222369 and Japanese Patent Application Laid-Open No. 10-080067).

[0024] When the external power source 7 is not connected to an external power source device such as a commercial power source, for example, when charging the secondary battery 2 using another externally installed secondary battery as a power source, it is preferable to store the power discharged from the secondary battery 2 in the other secondary battery, thereby reducing energy waste.

[0025] The current sensor 5 is, for example, an ammeter. The current sensor 5 measures the current value of the power supplied from the voltage / current adjustment unit 4 to the secondary battery 2 when the secondary battery 2 is being charged, and measures the current value of the power supplied from the secondary battery 2 to the voltage / current adjustment unit 4 when the secondary battery 2 is being discharged. There are no particular limitations on the installation position of the current sensor 5, and it may be any position as long as it is disposed in a circuit that supplies power from the voltage / current adjustment unit 4 to the secondary battery 2 and allows the measurement of the current value during charging and discharging.

[0026] The control unit 6 is a so-called computer including, for example, a CPU 61 and a storage unit 62. The control unit 6 controls the conditions of the charging process when charging the secondary battery 2 according to a procedure described later. In an electric vehicle, for example, an ECU (Electronic Control Unit) may be used as such a control unit 6.

[0027] Here, the storage unit 62 is equipped with a non-volatile memory in addition to the RAM used as a working area by the CPU 61. The non-volatile memory stores a program for controlling the conditions of the charging and discharging process of the secondary battery 2 in this embodiment.

[0028] The storage unit 62 also stores a map showing the relationship between the integrated value of the charging current I of the secondary battery 2 and the state of charge (SOC) of the secondary battery 2. The storage unit 62 also stores a lower limit threshold value (SOC1) of SOC and an upper limit threshold value (SOC2) of SOC that define the range of SOC in which the control according to this embodiment is executed. That is, the control according to this embodiment is executed when the SOC of the secondary battery 2 is equal to or greater than SOC1 and less than SOC2. The lower limit threshold value (SOC1) of SOC may be any SOC when the charging process has progressed to a certain extent, and is set in consideration of the cell voltage at which overcharging may occur. The SOC1 is, for example, 90%. The upper limit threshold value (SOC2) of SOC is an SOC that may be considered to have reached almost full charge. The SOC2 is, for example, 100%. When these threshold values ​​are set, the control according to this embodiment is executed when the SOC is equal to or greater than 90% and less than 100%. The storage unit 62 stores an upper threshold value (ΔV1) of the increase amount ΔV of the cell voltage per unit time as an index of the occurrence of a reaction current corresponding to the desorption reaction of lithium ions from the lithium-containing compound in the control according to this embodiment. In the control according to this embodiment, when the increase amount ΔV of the cell voltage per unit time becomes equal to or less than ΔV1, it is determined that the reaction current has occurred, and control is performed to stop the charging process.

[0029] [Charging process] The procedure of the charging process in the secondary battery system 1 configured as above will be described.

[0030] This charging process is performed when the secondary battery system 1 is connected to an external power source 7 and is in a state in which charging power can be supplied to the secondary battery 2. In addition, the charging process in this embodiment is controlled by a constant current (CC) charging method that is performed until the voltage of the secondary battery 2 reaches a predetermined voltage. However, the form of the charging process is not limited to this, and a constant current / constant voltage (CC-CV) charging method may also be used in which charging is performed by the constant current (CC) charging method and then switched to constant voltage (CV) charging after the voltage of the secondary battery 2 reaches the predetermined voltage.

[0031] The charging process in this embodiment is performed while judging whether or not a reaction current corresponding to a desorption reaction of lithium ions from a lithium-containing compound contained in a positive electrode active material layer is generated. Specifically, based on the value of the cell voltage of the secondary battery 2 measured at predetermined time intervals by the voltage sensor 3, it is determined that the reaction current is generated when the increase (ΔV) per unit time of the cell voltage is equal to or less than a predetermined threshold value (ΔV1), using as an index whether or not the increase (ΔV) per unit time of the cell voltage is equal to or less than the threshold value (ΔV1). Then, when it is determined that the reaction current is generated, the charging process in this embodiment is stopped. Unless otherwise specified, the control of this charging process is performed by the control unit 6. Hereinafter, the procedure of this charging process will be described with reference to FIG. 3. FIG. 3 is a flowchart showing the procedure of the charging process in the secondary battery system 1.

[0032] First, the control unit 6 starts control for performing charging processing of the secondary battery 2 (step S101). Specifically, power is introduced from the external power source 7 to the voltage / current adjustment unit 4 to start charging processing (in this embodiment, constant current (CC) charging is started).

[0033] Next, the control unit 6 acquires the charging current I from the current sensor 5 and the battery voltage V from the voltage sensor 3 (step S102). In this embodiment, the control unit 6 calculates the state of charge (SOC) value of the secondary battery 2 based on the integrated value of the charging current I acquired from the current sensor 5 (step S103). After that, the control unit 6 determines whether the SOC value of the secondary battery 2 calculated in step S103 is equal to or greater than a lower limit threshold value (SOC1) of the SOC range for executing the control according to this embodiment, which is preset and stored in the storage unit (step S104). Here, if it is determined that the SOC value is not equal to or greater than SOC1 (S104: NO), the control unit 6 repeats the control from step S102. On the other hand, if it is determined that the SOC value is equal to or greater than SOC1 (S104: YES), the control unit 6 determines whether or not the SOC value of the secondary battery 2 calculated in step S103 is equal to or greater than the upper limit threshold value (SOC2) of the SOC range for executing the control according to this embodiment, which is preset and stored in the storage unit (step S105). If it is determined that the SOC value is equal to or greater than SOC2 (S105: YES), the control unit 6 stops the charging process of the secondary battery 2 (step S106) and ends this control. On the other hand, if it is determined that the SOC value is not equal to or greater than SOC2 (S105: NO), the control unit 6 calculates the increase amount ΔV per unit time for the cell voltage V acquired in step S102 (step S107). Specifically, the control unit 6 calculates the cell voltage increase amount ΔV per second = (V2 - V1) / (t2 - t1) from the cell voltage V1 acquired at a certain time t1 and the cell voltage V2 acquired at a time t2 after a certain time (for example, 10 seconds) has elapsed from the time t1. Next, the control unit 6 determines whether the cell voltage increase amount ΔV per unit time calculated in this manner is equal to or less than the upper limit threshold value (ΔV1) of the cell voltage increase amount ΔV per unit time that is preset and stored in the storage unit (step S108). If it is determined that the value of ΔV is not equal to or less than ΔV1 (S108: NO), the control unit 6 repeats the control from step S102. On the other hand, if it is determined that the value of ΔV is equal to or less than ΔV1 (S108: YES), the control unit 6 stops the charging process of the secondary battery 2 (step S106) and ends this control.

[0034] By carrying out the above-mentioned control, it becomes possible to detect the occurrence of overcharging, using as an indicator the occurrence of a reaction current corresponding to the desorption reaction of lithium ions from the lithium-containing compound, before the potential of the sulfur-containing positive electrode reaches a potential at which the oxidative decomposition of the solid electrolyte proceeds. Then, by carrying out control to stop the charging process when the occurrence of overcharging is detected, it is possible to prevent the progress of the oxidative decomposition reaction of the solid electrolyte contained in the positive electrode active material layer, and to suppress the reduction of the reaction interface where the positive electrode active material and the solid electrolyte (and further the conductive assistant) coexist. As a result, it becomes possible to prevent a decrease in the energy density of the all-solid-state lithium secondary battery.

[0035] Although the control according to the present invention has been described in detail above, the embodiment described with reference to the drawings is merely an example, and the present invention may be practiced by appropriately modifying it within the scope of the technical idea of ​​the invention described in the claims. For example, in the above-mentioned embodiment, the determination of whether or not a reaction current corresponding to a desorption reaction of lithium ions from a lithium-containing compound has occurred is performed based on the value of the increase amount ΔV of the cell voltage per unit time. Specifically, in determining whether or not a reaction current corresponding to a desorption reaction of lithium ions from a lithium-containing compound has occurred, the control unit 6 calculates ΔV, and determines whether or not the reaction current has occurred based on whether or not the calculated value is equal to or less than a predetermined threshold value ΔV1. However, the method of determining whether or not the reaction current has occurred is not limited to this form. For example, when the increase rate of ΔV can be continuously measured as a differential coefficient, the occurrence or absence of the reaction current may be determined based on whether or not the increase rate of ΔV measured in this way is equal to or less than a predetermined value.

[0036] In the above-described embodiment, the determination as to whether or not control based on the value of ΔV needs to be performed is performed based on the value of the state of charge (SOC) of the secondary battery 2. Specifically, when determining whether or not control based on the value of ΔV needs to be performed, the control unit 6 calculates the SOC of the secondary battery 2 based on the integrated value of the charging current I, and determines whether or not control based on the value of ΔV needs to be performed based on whether or not the SOC is within a range of SOC1 or more and less than SOC2. In this way, by performing the above determination based on the value of the state of charge (SOC) of the secondary battery 2, there is an advantage that the influence of overvoltage can be eliminated and precise control is possible. However, the method of determining whether or not control based on the value of ΔV needs to be performed is not limited to this form. For example, there is a method of performing the above determination based on the value of the cell voltage V defined as the potential difference between the positive electrode and the negative electrode of the secondary battery 2. According to such a method, since it is possible to use the value of the cell voltage V detected by the voltage sensor 3, there is an advantage that control can be performed by a simple method.

[0037] According to another aspect of the present invention, there is provided a method for controlling the above-mentioned all-solid-state lithium secondary battery, which includes determining whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound is generated when a charging process of the all-solid-state lithium secondary battery is performed, and stopping the charging process when it is determined that the reaction current is generated.

[0038] According to yet another embodiment of the present invention, there is provided a control device for an all-solid-state lithium secondary battery that controls the above-mentioned all-solid-state lithium secondary battery. The control device for an all-solid-state lithium secondary battery that controls the all-solid-state lithium secondary battery includes a control unit (corresponding to the above-mentioned control unit 6) that determines whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound is generated when a charging process of the all-solid-state lithium secondary battery is performed, and controls to stop the charging process when it is determined that the reaction current is generated.

[0039] Hereinafter, components of the all-solid-state lithium secondary battery according to the above-described embodiment will be described.

[0040] FIG. 4 is a perspective view showing the appearance of an all-solid-state lithium secondary battery according to one embodiment of the present invention. FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. 4. The laminated structure allows the battery to be compact and have a high capacity. In this specification, the flat laminated non-bipolar all-solid-state lithium secondary battery (hereinafter also simply referred to as a "laminated battery") shown in FIG. 4 and FIG. 5 will be described in detail as an example. However, in terms of the internal electrical connection form (electrode structure) of the all-solid-state lithium secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0041] 4, the stacked battery 10a has a flat rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 for extracting electric power extending from both sides. The power generating element 21 is wrapped in a battery exterior material (laminate film 29) of the stacked battery 10a, and the periphery is heat-sealed, with the power generating element 21 being sealed with the negative electrode current collector 25 and the positive electrode current collector 27 extending to the outside.

[0042] There is also no particular limitation on the removal of the current collectors (25, 27) shown in Fig. 4. The negative current collector 25 and the positive current collector 27 may be pulled out from the same side, or the negative current collector 25 and the positive current collector 27 may each be divided into a plurality of pieces and removed from each side, and so on, and are not limited to what is shown in Fig. 4. In addition, in a wound type lithium ion battery, the terminals may be formed using, for example, a cylindrical can (metal can) instead of tabs.

[0043] 5, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a structure in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode collector 11". The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode collector 11'. Specifically, the positive electrode, solid electrolyte layer, and negative electrode are stacked in this order such that one positive electrode active material layer 15 and an adjacent negative electrode active material layer 13 face each other with a solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10a shown in FIG. 1 has a structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

[0044] Negative current collector 11′ and positive current collector 11″ are respectively attached with negative current collector plate (tab) 25 and positive current collector plate (tab) 27 that are electrically connected to the respective electrodes (positive and negative electrodes), and have a structure in which they are sandwiched between ends of laminate film 29, which is a battery exterior material, and are led out of laminate film 29. Positive current collector 27 and negative current collector 25 may be attached to positive current collector 11″ and negative current collector 11′ of each electrode by ultrasonic welding, resistance welding, or the like, respectively, via positive electrode leads and negative electrode leads (not shown) as necessary.

[0045] Hereinafter, the main components of the all-solid-state lithium secondary battery according to this embodiment will be described.

[0046] [Current collector] The current collector has a function of mediating the movement of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0047] The current collector may have a single layer structure made of a single material, or may have a laminate structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a resin having conductivity. In addition, from the viewpoint of blocking the movement of lithium ions between the single cell layers, a metal layer may be provided on a part of the current collector. Furthermore, if the negative electrode active material layer and the positive electrode active material layer described later are conductive by themselves and can perform a current collecting function, it is not necessary to use a current collector as a member separate from these electrode active material layers. In such a form, the negative electrode active material layer described later constitutes the negative electrode as it is, and the positive electrode active material layer described later constitutes the positive electrode as it is.

[0048] [Negative electrode (negative electrode active material layer)] In the secondary battery according to this embodiment, the negative electrode active material layer 13 includes a negative electrode active material containing lithium. Such a negative electrode active material absorbs lithium ions desorbed from the positive electrode during charging, and releases lithium ions during discharging. The type of the negative electrode active material containing lithium is not particularly limited, and may include metallic lithium and lithium-containing alloys. Examples of the lithium-containing alloy include alloys of Li and at least one of In, Al, Si, and Sn. In some cases, two or more types of negative electrode active materials may be used in combination.

[0049] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99 mass %, and more preferably within the range of 50 to 90 mass %, for example.

[0050] The negative electrode active material layer preferably further contains a solid electrolyte. By containing the solid electrolyte in the negative electrode active material layer, the ionic conductivity of the negative electrode active material layer can be improved. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, and from the viewpoint of excellent ionic conductivity, the sulfide solid electrolyte is preferable.

[0051] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In). The description "Li2S-P2S5" means a sulfide solid electrolyte obtained by using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0052] The sulfide solid electrolyte may have, for example, a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of sulfide solid electrolytes having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS solid electrolytes called LPS (for example, Li7P3S 11 ) As the sulfide solid electrolyte, for example, Li (4-x) Ge (1-x) P xAn LGPS or the like represented by S4 (where 0 < x < 1) may be used. Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing P element, and more preferably the sulfide solid electrolyte is a material mainly composed of Li2S-P2S5. Furthermore, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). In a preferred embodiment, the sulfide solid electrolyte contains Li6PS5X (where X is Cl, Br or I, preferably Cl).

[0053] Also, when the sulfide solid electrolyte is of the Li2S-P2S5 system, the ratio of Li2S and P2S5 is preferably in the range of Li2S:P2S5 = 50:50 to 100:0 in terms of molar ratio, and more preferably Li2S:P2S5 = 70:30 to 80:20.

[0054] Also, the sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on a raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by performing heat treatment on the sulfide glass at a temperature above the crystallization temperature. Also, the ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is, for example, 1×10 -5 S / cm or more, preferably 1×10 -4 S / cm or more. The value of the ionic conductivity of the solid electrolyte can be measured by an alternating current impedance method.

[0055] Examples of the oxide solid electrolyte include compounds having a NASICON-type structure. As an example of a compound having a NASICON-type structure, a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≦ x ≦ 2) (LAGP), a compound represented by the general formula Li 1+x Al x Ti 2-x(PO4)3 (0≦x≦2) (LATP) and the like. Another example of an oxide solid electrolyte is LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0056] The shape of the solid electrolyte may be, for example, a particulate shape such as a spherical shape or an oval spherical shape, or a thin film shape. When the solid electrolyte is particulate, its average particle diameter (D 50 ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. 50 ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

[0057] The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60 mass %, and more preferably in the range of 10 to 50 mass %.

[0058] The negative electrode active material layer may further contain at least one of a conductive assistant and a binder, in addition to the above-mentioned negative electrode active material and solid electrolyte.

[0059] The thickness of the negative electrode active material layer differs depending on the intended configuration of the secondary battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0060] [Solid electrolyte layer] In the secondary battery according to this embodiment, the solid electrolyte layer is interposed between the above-mentioned positive electrode active material layer and negative electrode active material layer, and is a layer that essentially contains a solid electrolyte.

[0061] There is no particular restriction on the specific form of the solid electrolyte contained in the solid electrolyte layer, and the solid electrolytes exemplified in the section on the negative electrode active material layer and their preferred forms can be similarly adopted. In some cases, a solid electrolyte other than the above-mentioned solid electrolyte may be used in combination. However, the content ratio of the sulfide solid electrolyte in the total amount of the solid electrolyte (100 mass%) is preferably 50 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, even more preferably 90 mass% or more, particularly preferably 95 mass% or more, and most preferably 100 mass%.

[0062] The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte.

[0063] The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium ion secondary battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. On the other hand, there is no particular restriction on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more.

[0064] [Cathode active material layer] In the secondary battery according to this embodiment, the positive electrode active material layer includes a positive electrode active material containing sulfur. The type of the positive electrode active material containing sulfur is not particularly limited, but may include, in addition to elemental sulfur (S), particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and may be any material capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur. Examples of the organic sulfur compound include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbonate sulfide, and the like, which are typified by compounds described in the pamphlet of International Publication No. 2010 / 044437. Among these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubeanic acid are preferred, and sulfur-modified polyacrylonitrile is particularly preferred. As the disulfide compound, a compound having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group is more preferred. Here, the sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms, which is obtained by mixing sulfur powder with polyacrylonitrile and heating the mixture under an inert gas or under reduced pressure. Its estimated structure is, for example, as shown in Chem. Mater. 2011, 23, 5024-5028, in which polyacrylonitrile is ring-closed to form a polycyclic ring, and at least a part of S is bonded to C. The compound described in this document has a peak at 1330 cm in the Raman spectrum. -1 and 1560cm -1 There is a strong peak signal near 307 cm -1 , 379cm -1 , 472cm -1 , 929cm -1There is a peak around 1000 nm. On the other hand, inorganic sulfur compounds are preferred because of their excellent stability, and specific examples thereof include sulfur element (S), Li2S, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, MoS2, and MoS3. Among them, S, Li2S, S-carbon composite, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferred, sulfur element (S), Li2S, TiS2, and FeS2 are more preferred, and sulfur element (S) or Li2S is particularly preferred from the viewpoint of high capacity. As the sulfur element (S), α-sulfur, β-sulfur, or γ-sulfur having an S8 structure can be used. These sulfur elements (S) absorb lithium ions during discharge and exist in the positive electrode active material layer in the form of lithium (poly)sulfides.

[0065] In some cases, two or more kinds of positive electrode active materials may be used in combination. Of course, other positive electrode active materials than those mentioned above may be used. However, the content ratio of the positive electrode active material containing sulfur in the total amount of the positive electrode active material (100% by mass) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0066] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably within the range of 35 to 99 mass %, and more preferably within the range of 40 to 90 mass %, for example.

[0067] The positive electrode active material layer essentially contains a solid electrolyte, and the solid electrolyte preferably contains a sulfide solid electrolyte. The specific and preferred forms of the solid electrolyte, such as the sulfide solid electrolyte, may be the same as those described in the negative electrode active material layer. Furthermore, the positive electrode active material layer may further contain a conductive assistant and / or a binder.

[0068] In the all-solid-state lithium secondary battery according to the present embodiment, the positive electrode active material layer essentially contains a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li]. There is no particular limitation on such a lithium-containing compound, and it may be any compound that contains lithium and has the above-mentioned oxidation-reduction potential. An example of the lithium-containing compound is a lithium-containing transition metal oxide or a lithium-containing polyanion compound. These materials are preferable because they can exist stably in the positive electrode active material layer and contribute to the detection of the occurrence of overcharging without adversely affecting the charge / discharge reaction by the positive electrode active material. Examples of the lithium-containing transition metal oxide include lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), lithium cobalt nickel manganese oxide (Li(Co,Ni,Mn)O2), lithium nickel oxide (LiNiO2), lithium titanium oxide (Li4Ti5O 12 ) and the like. Examples of the lithium-containing polyanion compound include lithium iron phosphate (LiFePO4) and lithium iron silicate (Li2FeSiO4). Among these, lithium manganese oxide, lithium cobalt nickel manganese oxide, lithium iron phosphate, and lithium iron silicate are preferred, lithium iron phosphate and lithium iron silicate are more preferred, and lithium iron phosphate is particularly preferred.

[0069] The content of the specified lithium-containing compound in the positive electrode active material layer is not particularly limited, but is preferably, for example, within a range of 0.01 to 20 mass% relative to 100 mass% of the total of components other than the specified lithium-containing compound, and from the viewpoint of suppressing a decrease in energy density due to a decrease in the content of the sulfur-containing positive electrode active material, is more preferably within a range of 0.01 to 2 mass% relative to 100 mass% of the total of components other than the specified lithium-containing compound.

[0070] [Positive and negative current collectors] The material constituting the current collector plates (25, 27) is not particularly limited, and any known highly conductive material conventionally used as a current collector plate for a secondary battery may be used. As the material constituting the current collector plates, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material or different materials.

[0071] [Positive and negative leads] Although not shown in the figures, the current collectors (11", 11') and the current collecting plates (27, 25) may be electrically connected via positive and negative electrode leads. As the constituent materials of the positive and negative electrode leads, materials used in known lithium ion secondary batteries may be similarly used. Note that the parts removed from the exterior are preferably covered with a heat-resistant insulating heat-shrink tube or the like to prevent them from coming into contact with peripheral devices or wiring, causing electric leakage and affecting products (e.g., automobile parts, particularly electronic devices, etc.).

[0072] [Battery exterior materials] As the battery exterior material, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element as shown in Figures 4 and 5 can be used.

[0073] Although one embodiment of the all-solid-state lithium secondary battery has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be appropriately modified based on the recitations of the claims.

[0074] For example, in the all-solid-state lithium secondary battery according to the present embodiment, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limit to the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolytic solution) does not occur.

[0075] [Battery pack] A battery pack is a device that consists of multiple batteries connected together. More specifically, it is a device that uses at least two batteries and is configured in series or parallel or both. By connecting them in series or parallel, it is possible to freely adjust the capacity and voltage.

[0076] A small, removable assembled battery can be formed by connecting a plurality of batteries in series or in parallel. Then, a large capacity, high output assembled battery (battery module, battery pack, etc.) suitable for a vehicle driving power source or an auxiliary power source that requires a high volumetric energy density and a high volumetric output density can be formed by further connecting a plurality of such small, removable assembled batteries in series or in parallel. How many batteries are connected to form an assembled battery, and how many stages of small assembled batteries are stacked to form a large capacity assembled battery can be determined according to the battery capacity and output of the vehicle (electric vehicle) in which the battery is to be installed.

[0077] [vehicle] The battery or a battery pack formed by combining a plurality of batteries can be mounted on a vehicle. In the present invention, a battery with excellent long-term reliability and long life can be configured, and thus, by mounting such a battery, a plug-in hybrid electric vehicle with a long EV driving distance or an electric vehicle with a long driving distance per charge can be configured. For example, if the battery or a battery pack formed by combining a plurality of batteries is used in a hybrid vehicle, a fuel cell vehicle, or an electric vehicle (all of which include four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, and buses, and light vehicles, etc.), as well as two-wheeled vehicles (motorcycles) and three-wheeled vehicles), the vehicle will have a long life and high reliability. However, the application is not limited to automobiles, and the battery pack can be applied to, for example, various power sources for other vehicles, such as moving bodies such as trains, and can also be used as a mounted power source for an uninterruptible power supply device or the like. EXAMPLES

[0078] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. In the following, the tools and devices used in the glove box were thoroughly dried in advance.

[0079] <Example of all-solid-state lithium secondary battery production> <Comparative Example 1> (Preparation of Positive Electrode Mixture) First, sulfur element (S) as a positive electrode active material, porous carbon as a conductive assistant (Kansai Ceramic Chemicals Co., Ltd., activated carbon, MSC-30), and sulfide solid electrolyte (Ampcera, Li6PS5Cl) were weighed out to a mass ratio of 50:10:40, and placed in a zirconia ball mill pot with an internal volume of 150 mL in a glove box so that the total amount was 0.5 g. Next, zirconia balls were placed in the pot, the pot was closed and sealed, and the mixture was ground and mixed at 280 ppm for 12 hours using a planetary ball mill device, and then mixed at 160 ppm for 1 hour, to obtain a sulfur composite as a positive electrode mixture.

[0080] (Preparation of test cell) 100 mg of the same sulfide solid electrolyte as above was weighed out and placed in a McCol tube with a φ10 mm stainless steel pin inserted. After the upper pin was inserted, the tube was pressed at a pressure of 100 MPa using a hydraulic press to produce a solid electrolyte layer.

[0081] Next, 7 mg of the positive electrode mixture prepared above was weighed out, the upper pin was removed, and the positive electrode mixture was added onto the solid electrolyte layer prepared above. After inserting the upper pin again, the positive electrode active material layer was pressed onto the solid electrolyte layer at a pressure of 300 MPa using a hydraulic press.

[0082] Meanwhile, indium foil and lithium foil were attached together and placed on the surface of the solid electrolyte layer opposite the positive electrode active material layer, with the indium foil facing the solid electrolyte layer. The upper pin was then inserted again, and the In-Li foil was pressed to the solid electrolyte layer at a pressure of 100 MPa using a hydraulic press.

[0083] The power generating element thus obtained was restrained at a pressure of 100 MPa using a restraining member to produce a test cell for this comparative example.

[0084] <Example 1> A test cell of this example was prepared in the same manner as in Comparative Example 1 described above, except that in preparing the positive electrode mixture, 0.01 mass% of lithium iron phosphate (LiFePO4) was added relative to 100 mass% in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0085] <Example 2> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 0.05 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0086] <Example 3> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 0.1 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0087] <Example 4> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 0.2 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0088] <Example 5> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 0.5 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0089] <Example 6> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 1 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0090] <Example 7> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 2 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0091] <Example 8> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 5 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0092] <Example 9> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 10 mass % relative to 100 mass % in total of the sulfur element (S), the porous carbon, and the sulfide solid electrolyte.

[0093] <Example 10> A test cell of this example was produced in the same manner as in Example 1 described above, except that the amount of lithium iron phosphate added was changed to 15 mass % relative to 100 mass % in total of the elemental sulfur (S), porous carbon, and sulfide solid electrolyte.

[0094] <Evaluation example of all-solid-state lithium secondary battery> The test cells prepared above were evaluated by the following method. The test cells were evaluated using a battery charge / discharge device (HJ1020mSD8, manufactured by Hokuto Denko Corporation) with a recording range of 1 point / 10 mV and 1 point / 1 sec.

[0095] (Check battery capacity) The battery was charged in constant current / constant voltage (CCCV) mode and discharged in constant current (CC) mode to confirm the battery capacity and calculate the energy density. At this time, the voltage range was 1.1 to 2.5 V, the current rate during charging and discharging was 0.05 C, and the cutoff current during charging was 0.01 C. The energy density calculated in this manner is shown in Table 1 below as a relative value when the value of Comparative Example 1 is set to 100%.

[0096] (Overcharge test) The charging process was performed with a charging rate set to 0.05C and a cutoff voltage of 3.6V. During this process, the cell voltage was recorded every second. When the voltage increase rate for 10 seconds in the cell voltage range exceeding the reaction potential of sulfur became 1mV / second or less (i.e., 10mV in 10 seconds), it was determined that the desorption reaction of lithium ions from the lithium iron phosphate had progressed, and the charging process was stopped. Table 1 below shows whether or not such a reaction of lithium iron phosphate was detected. Cases where detection was possible are indicated with "◯", and cases where detection was not possible are indicated with "×".

[0097] [Table 1]

[0098] From the results shown in Table 1, it is found that by adding lithium iron phosphate, which is a lithium-containing compound, to the positive electrode active material layer, it is possible to detect the cell voltage in the overcharge region, and it is possible to stop the charging process before overcharge progresses. In contrast, in Comparative Example 1, in which lithium iron phosphate is not added to the positive electrode active material layer, such overcharge could not be detected. Therefore, if overcharge continues in the test cell of Comparative Example 1, the oxidative decomposition reaction of the solid electrolyte contained in the positive electrode active material layer will progress, and the energy density of the all-solid-state lithium secondary battery will decrease. Note that, since the energy density of the battery decreases when the composition ratio of elemental sulfur, which is the positive electrode active material, decreases, it is preferable to add the lithium-containing compound (lithium iron phosphate) in a smaller amount, and it is also found that, in particular, if the amount added to the positive electrode mixture is 2 mass% or less, the relative value of the energy density can be maintained at 95% or more. [Explanation of symbols]

[0099] 1 All-solid-state lithium secondary battery system, 2 All-solid-state lithium secondary battery, 3 voltage sensors, 4 Voltage and current adjustment section, 5 current sensors, 6 control section, 7 external power supply, 10a Stacked battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 cell layer, 21 Power generation elements, 25 negative current collector plate, 27 Positive current collector, 29 Laminating film, 61 CPU, 62 memory unit.

Claims

1. A positive electrode including a positive electrode active material layer containing a sulfur-containing positive electrode active material, a sulfide solid electrolyte or an oxide solid electrolyte, and a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li]; a negative electrode including a negative electrode active material layer containing a negative electrode active material including lithium; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer, the solid electrolyte layer including a sulfide solid electrolyte or an oxide solid electrolyte; An all-solid-state lithium secondary battery having a power generating element having the a control unit that determines whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound has occurred when a charging process of the all-solid-state lithium secondary battery is performed, and performs control to stop the charging process when it is determined that the reaction current has occurred; An all-solid-state lithium secondary battery system comprising:

2. 2. The all-solid-state lithium secondary battery system according to claim 1, wherein the lithium-containing compound is a lithium-containing transition metal oxide or a lithium-containing polyanion compound.

3. 3. The all-solid-state lithium secondary battery system according to claim 2, wherein the lithium-containing compound is lithium manganese oxide, lithium cobalt nickel manganese oxide, lithium iron phosphate or lithium iron silicate.

4. The content of the lithium-containing compound in the positive electrode active material layer is within a range of 0.01 to 20 mass% relative to 100 mass% of the total of components other than the lithium-containing compound. The all-solid-state lithium secondary battery system according to any one of claims 1 to 3.

5. The all-solid-state lithium secondary battery system according to any one of claims 1 to 4, wherein the control unit makes the determination based on a value of a cell voltage of the all-solid-state lithium secondary battery defined as a potential difference between the positive electrode and the negative electrode.

6. 6. The all-solid-state lithium secondary battery system according to claim 5, wherein the control unit determines whether or not a rate of increase or an amount of increase per unit time of the cell voltage is equal to or less than a predetermined threshold value, and determines that the reaction current has been generated when the rate of increase or the amount of increase is equal to or less than the threshold value.

7. A positive electrode including a positive electrode active material layer containing a sulfur-containing positive electrode active material, a sulfide solid electrolyte or an oxide solid electrolyte, and a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li]; a negative electrode including a negative electrode active material layer containing a lithium-containing negative electrode active material; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer, the solid electrolyte layer including a sulfide solid electrolyte or an oxide solid electrolyte; A method for controlling an all-solid-state lithium secondary battery having a power generating element having determining whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound is generated when a charging process of the all-solid-state lithium secondary battery is performed; Stopping the charging process when it is determined that the reaction current is generated; A method for controlling an all-solid-state lithium secondary battery, comprising:

8. A positive electrode including a positive electrode active material layer containing a sulfur-containing positive electrode active material, a sulfide solid electrolyte or an oxide solid electrolyte, and a lithium-containing compound having an oxidation-reduction potential of 3.1 to 4.3 [V vs. Li+ / Li]; a negative electrode including a negative electrode active material layer containing a negative electrode active material including lithium; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer, the solid electrolyte layer including a sulfide solid electrolyte or an oxide solid electrolyte; A control device for an all-solid-state lithium secondary battery including a power generating element having a control unit that determines whether or not a reaction current corresponding to a desorption reaction of lithium ions from the lithium-containing compound has occurred when a charging process of the all-solid-state lithium secondary battery is performed, and performs control to stop the charging process when it is determined that the reaction current has occurred.

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