JP2012256430A - Solid secondary battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid secondary battery system capable of recovering deterioration of output characteristics.SOLUTION: The solid secondary battery system includes a solid secondary battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, and a switch provided outside of the solid secondary battery and for starting an overdischarge treatment.

Description

  The present invention relates to a solid secondary battery system that can recover a decrease in output characteristics.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, among various batteries, lithium secondary batteries are attracting attention from the viewpoint of high energy density.

  Since lithium secondary batteries currently on the market use an electrolyte containing a flammable organic solvent, they are equipped with a safety device that prevents the temperature rise during short-circuiting and in terms of structure and materials for short-circuit prevention. Improvement is needed. In contrast, a lithium solid state secondary battery in which the electrolyte is changed to a solid electrolyte layer to solidify the battery does not use a flammable organic solvent in the battery. It is considered to be excellent in productivity.

  In addition, secondary batteries can be repeatedly charged and discharged, but it is known that battery performance deteriorates due to overdischarge. Therefore, a normal secondary battery is provided with means for measuring the voltage of the battery at the time of discharging and terminating the discharge at a predetermined voltage. On the other hand, Patent Document 1 discloses a battery module that does not include overdischarge protection means for preventing overdischarge of a lithium secondary battery (referred to as discharging to a rated voltage or lower; the same applies hereinafter). No. 2 discloses an electric device that is not provided with overdischarge protection means for preventing overdischarge of a lithium secondary battery.

JP 2010-225581 A JP 2010-225582 A

  The solid secondary battery has a problem that the internal resistance increases and the output characteristics deteriorate due to repeated charge and discharge. Further, when the solid secondary battery is stored at a high temperature (for example, about 60 ° C.), there is a problem that the internal resistance increases and the output characteristics deteriorate. Furthermore, it is usually difficult to recover the output characteristics once lowered. The present invention has been made in view of the above problems, and a main object of the present invention is to provide a solid secondary battery system capable of recovering a decrease in output characteristics.

  In order to recover the output characteristics that have once declined as a result of extensive research conducted by the present inventors in order to achieve the above-mentioned object, it is surprisingly effective to carry out overdischarge positively (intentionally). The knowledge that it is. The present invention has been made based on such knowledge.

  In the present invention, the solid secondary battery system includes a positive electrode active material layer, a negative electrode active material layer, and a solid state battery having a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. A secondary battery, and a switch provided outside the solid secondary battery and for starting an overdischarge process of the solid secondary battery.

  The solid secondary battery system includes a solid secondary battery and a switch. The solid secondary battery includes a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. The switch is provided outside the solid secondary battery and is a switch for starting the overdischarge process. Therefore, the switch may be an interface for the user to instruct execution of overdischarge, and the shape and the like are not limited. The “overdischarge treatment” is a treatment for overdischarging the solid secondary battery, and specifically, a treatment for discharging the solid secondary battery until it becomes a predetermined voltage or lower such as a rated lower limit voltage, or / And the process which maintains the voltage of the solid secondary battery after discharge is pointed out. Therefore, the external discharge of the solid secondary battery is also included in the overdischarge process. “External short circuit” refers to short-circuiting the positive electrode active material layer and the negative electrode active material layer of the solid secondary battery through an external circuit. Note that the overdischarge treatment may be one in which the voltage is discharged to 0 V, or one in which the battery is reversed (the voltage becomes negative).

  Thus, the solid secondary battery system includes a switch operated by the user, and can start the overdischarge process based on the user's operation. Thereby, the solid secondary battery system can make the solid secondary battery be in an overdischarged state based on an arbitrary timing of the user, and can realize recovery of a decrease in output of the solid secondary battery and extension of the life.

  The aspect of the solid secondary battery system may further include an overdischarge processing unit that starts an overdischarge process of the solid secondary battery based on an input from the switch. Thereby, the solid secondary battery system can perform the overdischarge process of the solid secondary battery based on the user's arbitrary timing, and can realize the recovery of the output decrease of the solid secondary battery and the extension of the lifetime.

  In another aspect of the solid secondary battery system, the overdischarge processing unit includes a discharge unit that discharges the solid secondary battery until a remaining capacity of the solid secondary battery becomes 0, and the solid secondary battery And an external short-circuit unit that performs an external short-circuit of the solid secondary battery when the remaining capacity of the battery becomes zero. Here, “remaining capacity” refers to the remaining amount of charge. By having such a configuration, the solid secondary battery system can prevent the solid secondary battery from being damaged, overheated, ignited, electric shock, etc. due to a short circuit when the switch is operated. It is possible to recover the decrease in output by causing an overdischarge state.

  In another aspect of the solid secondary battery system, the discharge unit includes a discharge load whose load value is variable. With this configuration, the solid secondary battery system can maintain a low current by suppressing an excessive increase in current when discharging until the remaining capacity of the solid secondary battery becomes zero. Can be increased.

  The solid secondary battery system of the present invention has an effect that it is possible to recover a decrease in output characteristics due to charging / discharging based on a user's arbitrary timing.

It is a schematic diagram which shows an example of the solid secondary battery system of this embodiment. It is a schematic sectional drawing which shows an example of the solid secondary battery in this embodiment. It is a flowchart which shows the process sequence which a control part performs. It is a schematic diagram which shows the structure of the solid secondary battery system which concerns on a modification. It is a schematic diagram which shows the structure of the solid secondary battery system which concerns on a modification, and the structure of a charging / discharging apparatus. It is a result of the resistivity with respect to the solid secondary battery obtained in Example 1. It is a result of the resistivity with respect to the solid secondary battery obtained in Example 2.

  Hereinafter, preferred embodiments of the solid secondary battery system according to the present invention will be described in detail.

[Solid rechargeable battery system]
First, the solid secondary battery system of this embodiment will be described. FIG. 1 is a schematic diagram illustrating an example of the solid secondary battery system of the present embodiment. A solid secondary battery system 20 shown in FIG. 1 includes a solid secondary battery 10, an overdischarge start switch 11, a switch unit 12, a load 15 such as a motor or electrical equipment, a discharge load 16, and an ammeter. 17, a voltmeter 18, and a control unit 19.

  The solid secondary battery 10 includes a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. Here, the configuration of the solid secondary battery 10 will be specifically described with reference to FIG. FIG. 2 is a schematic cross-sectional view showing an example of the solid secondary battery in the present embodiment. 2 includes a positive electrode active material layer 1, a negative electrode active material layer 2, a solid electrolyte layer 3 formed between the positive electrode active material layer 1 and the negative electrode active material layer 2, a positive electrode It has a positive electrode current collector 4 for collecting current of the active material layer 1 and a negative electrode current collector 5 for collecting current of the negative electrode active material layer 2.

  Returning to FIG. 1 again, other components of the solid secondary battery system 20 will be described. The overdischarge start switch 11 is an interface that can be operated by the user, and when the solid secondary battery 10 is brought into an overdischarged state, the user performs an operation such as pressing. Therefore, the overdischarge start switch 11 is exposed to the outside so that the user can operate it. When a certain operation such as pressing the overdischarge start switch 11 is performed, a predetermined input signal is supplied from the overdischarge start switch 11 to the control unit 19. Thereby, the control part 19 starts control, such as switching of the switch part 12 for making the solid secondary battery 10 into an overdischarge state.

  The switch unit 12 includes a common terminal 120, a first selection terminal 121, a second selection terminal 122, and a third selection terminal 123. The switch unit 12 connects the common terminal 120 to any one of the first selection terminal 121 to the third selection terminal 123 based on the control signal S <b> 12 transmitted from the control unit 19. As will be described later, when the common terminal 120 of the switch unit 12 is connected to the second selection terminal 122, the discharge load from the solid secondary battery 10 is set so that the amount of charge remaining in the solid secondary battery 10 becomes zero. 16 is discharged. When the common terminal 120 is connected to the third selection terminal 123, a closed circuit including the solid secondary battery 10 is formed, and an external short circuit of the solid secondary battery 10 is performed.

  The discharge load 16 consumes the power remaining in the solid secondary battery 10 when the common terminal 120 of the switch unit 12 is connected to the second selection terminal 122. The discharge load 16 has a variable load value. For the discharge load 16, the load value is set so that the current flowing from the solid secondary battery 10 becomes a predetermined value or less than a predetermined value from the viewpoint of safety. The predetermined value is determined in advance based on experiments or the like, for example, to a value that can sufficiently ensure safety. Note that the value of the load of the discharge load 16 may be determined based on, for example, a control signal supplied from the control unit 19, and the discharge load 16 autonomously controls so that the current becomes a predetermined value or less. It may be determined by.

  The ammeter 17 detects the current flowing from the solid secondary battery 10 when the common terminal 120 of the switch unit 12 is connected to the second selection terminal 122. Here, the internal resistance of the ammeter 17 is sufficiently small to be negligible compared to the discharge load 16. The ammeter 17 transmits a detection signal S17 corresponding to the detected current value to the control unit 19 at a predetermined or indefinite period. The voltmeter 18 detects a voltage corresponding to the electromotive force of the solid secondary battery 10 when the common terminal 120 of the switch unit 12 is connected to the second selection terminal 122. Here, the internal resistance of the voltmeter 18 is sufficiently large to be negligible compared to the discharge load 16. The voltmeter 18 supplies a detection signal S18 corresponding to the detected voltage value to the control unit 19 at a predetermined or indefinite period.

  The control unit 19 is, for example, an ECU (Electronic Control Unit), and controls the entire solid secondary battery system 20. Specifically, the control unit 19 transmits a control signal S12 to the switch unit 12 based on the detection signal S17 supplied from the ammeter 17 and the detection signal S18 supplied from the voltmeter 18, and is shared by the switch unit 12. The terminal 120 is switched.

  In FIG. 1, the overdischarge start switch 11 is an example of the “switch” in the present invention, and the circuit including the control unit 19, the switch unit 12, the load 15, the discharge load 16, etc. It is an example of a “discharge processing part”.

  Here, the process executed by the control unit 19 will be described in more detail with reference to FIG. FIG. 3 is a flowchart showing a processing procedure according to this embodiment. The control unit 19 repeatedly executes the processing flow shown in FIG. 3 according to a predetermined cycle, for example.

  First, the control unit 19 determines whether or not the overdischarge start switch 11 has been operated (step S101). For example, the control unit 19 determines whether a predetermined input signal is detected from the overdischarge start switch 11. When the overdischarge start switch 11 is not operated (step S101; No), that is, in the normal time when the solid secondary battery 10 does not need to be overdischarged, the control unit 19 is common to the switch unit 12. The terminal 120 is connected to the first selection terminal 121 (step S102). As a result, power is supplied from the solid secondary battery 10 to the load 15, and power is consumed at the load 15.

  On the other hand, when the control unit 19 determines that the overdischarge start switch 11 has been operated (step S101; Yes), the control unit 19 connects the common terminal 120 of the switch unit 12 to the second selection terminal 122 (step S103). Thereby, electric power is supplied from the solid secondary battery 10 to the discharging load 16, and the electric power is consumed by the discharging load 16. And the control part 19 determines whether the remaining capacity of the solid secondary battery 10 became "0" (step S104). Specifically, the control unit 19 monitors the voltage value corresponding to the control signal S18 supplied from the voltmeter 18 and the current value corresponding to the control signal S17 supplied from the ammeter 17, and the solid secondary battery 10 It is determined whether or not the remaining capacity of the disk becomes “0”. Preferably, the control unit 19 appropriately changes the load value of the discharge load 16 so that the current value does not exceed a predetermined value from the viewpoint of safety. When the remaining capacity of the solid secondary battery 10 is not “0” (step S104; No), the control unit 19 continues to monitor whether the remaining capacity of the solid secondary battery 10 is “0”. To do.

  Next, when it is determined that the remaining capacity of the solid secondary battery 10 has become “0” (step S104; Yes), the control unit 19 connects the common terminal 120 to the third selection terminal 123 (step S105). Thereby, the control part 19 externally short-circuits the solid secondary battery 10, and maintains the solid secondary battery 10 in the state of 0V. By doing in this way, the solid secondary battery system 20 can make the solid secondary battery 10 an overdischarge state, and can recover an output fall.

  Hereinafter, a supplementary explanation will be given on the effects of the solid secondary battery system 20 according to the present embodiment.

  The solid secondary battery system 20 can cause the solid secondary battery 10 to be in an overdischarged state. Thereby, internal resistance can be reduced and output characteristics can be recovered. Therefore, the lifetime of the solid secondary battery 10 can be extended. Conventionally, since it is known that battery performance deteriorates due to overdischarge, an ordinary solid secondary battery is provided with overdischarge protection means for preventing overdischarge. On the other hand, in the present invention, the internal resistance can be reduced and the output characteristics can be recovered by positively bringing the cycle-degraded solid secondary battery into an overdischarged state.

  In addition, the solid secondary battery system 20 includes an overdischarge start switch 11 that can be operated by the user, and starts an overdischarge process that causes the solid secondary battery 10 to be in an overdischarge state at any timing of the user. Thereby, users, such as a user of a solid rechargeable battery system 20, a person in charge of maintenance, can recover the output fall of solid rechargeable battery 10 based on arbitrary timing.

  In addition, when the control unit 19 puts the solid secondary battery 10 into an overdischarged state, the common terminal 120 is connected to the second selection terminal 122 and the remaining capacity of the solid secondary battery 10 is consumed by the discharge load 16. Later, the common terminal 120 is connected to the third selection terminal 123 to perform an external short circuit. This is because, when it is determined that overdischarge should be performed, if the common terminal 120 is immediately connected to the third selection terminal 123 and an external short circuit is performed, a large current is generated from the solid secondary battery 10. This is because there is a risk of damage to the battery. Therefore, in this embodiment, the control part 19 can suppress reliably the failure | damage of the battery by heavy current generation, etc.

  In addition, the mechanism which can reduce internal resistance by overdischarge is estimated as follows. That is, in the solid secondary battery 10, since the battery reaction occurs at the solid / solid interface, a new film (SEI: Solid Electrolyte Interface) is generated at the interface, and the resistance of the film is large, resulting in an increase in internal resistance. Occurs. On the other hand, in this invention, it is thought that this film | membrane can be removed and internal resistance can be reduced by making the solid secondary battery 10 into an overdischarge state. Further, this film may be generated at an arbitrary solid / solid interface in the solid secondary battery 10, but it is considered that this film is often generated particularly at the interface between the active material and the solid electrolyte material. The reason is that the active material undergoes an active reaction of occluding and releasing metal ions on the surface thereof, and the solid electrolyte material usually has a large area in contact with the active material. In particular, it is considered that a coating tends to be formed when the active material and the solid electrolyte material are combinations derived from different types of compounds. For example, it is considered that the oxide active material (derived from the oxide) and the sulfide solid electrolyte material (derived from the sulfide) are relatively likely to react and easily form a film.

[Modification]
Next, modifications 1 to 4 of the above-described embodiment suitable for the present invention will be described. The following modifications may be applied to the above-described embodiment in any combination.

(1) Modification 1
In the description of FIGS. 2 and 3, when the overdischarge start switch 11 is pressed, the control unit 19 switches the switch unit 12 based on the detection value of the ammeter 17 and the like. However, the configuration to which the present invention is applicable is not limited to this.

  Instead of this, the state of the switch unit 12 may be directly switched by a user such as a vehicle user or a person in charge of maintenance by the solid secondary battery system 20. In this case, the user operates the switch unit 12 to connect the common terminal 120 to the second selection terminal 122 when the solid secondary battery 10 is to be overdischarged. Thereafter, when the user monitors the voltmeter 18 and / or the ammeter 17 and determines that the remaining capacity of the solid secondary battery 10 has become “0”, the user connects the common terminal 120 to the third selection terminal 123. The switch unit 12 may be operated as described above. Also by this, the solid secondary battery system 20 can put the solid secondary battery 10 into an overdischarged state at any timing of the user. In the first modification, the switch unit 12 is an example of the “switch” in the present invention.

(2) Modification 2
The solid secondary battery system 20 shown in FIG. 1 includes a discharge load 16 for discharging the remaining capacity of the solid secondary battery 10. However, the configuration to which the present invention is applicable is not limited to this. This will be described with reference to FIG.

  FIG. 4 shows a configuration of a solid secondary battery system 20A according to the second modification. As shown in FIG. 4, the solid secondary battery system 20 </ b> A includes a secondary battery 50 for charging and a secondary battery charging device 51 for charging the secondary battery 50. In this case, when the overdischarge start switch 11 is operated, the control unit 19 electrically connects the solid secondary battery 10 and the secondary battery charging device 51 by connecting the common terminal 120 to the second selection terminal 122. Connect. Thereby, the secondary battery charging device 51 supplies power from the solid secondary battery 10 to the secondary battery 50. When the control unit 19 determines that the remaining capacity of the solid secondary battery 10 has become “0”, the control unit 19 connects the common terminal 120 to the third selection terminal 123 to externally short the solid secondary battery 10. Also according to this, the present invention can be suitably implemented. The secondary battery charging device 51 is an example of the “overdischarge processing unit” in the present invention.

(3) Modification 3
Although the solid secondary battery system 20 shown in FIG. 1 performed the overdischarge process by itself, the structure which can apply this invention is not limited to this. This will be described with reference to FIG.

  FIG. 5 shows a configuration of a solid state secondary battery system 20B according to Modification 3. As shown in FIG. 5, the solid secondary battery system 20 </ b> B includes the solid secondary battery 10, a load 15, a common terminal 120, a first selection terminal 121, and a connection terminal 125. The charging / discharging device 62 is, for example, a charger installed in a charging stand or the like, and can be connected to the AC power supply 61 and to the second selection terminal 122 that can be connected to the common terminal 120 and to the connection terminal 125. And a connection terminal 126. The charging / discharging device 62 is equipped with a program for performing an overdischarge process. When the second selection terminal 122 and the common terminal 120 are connected and the connection terminals 125 and 126 are connected, The overdischarge process of the solid secondary battery 10 is performed. Specifically, the discharge / charge device 62 preferably performs a process of discharging the solid secondary battery 10 to a predetermined voltage and a process of maintaining the voltage by constant voltage discharge (CV discharge) or the like.

  Here, the common terminal 120 of the switch unit 12B is connected to either the first selection terminal 121 or the second selection terminal 122 in accordance with a user operation on the switch unit 12B. Therefore, the solid secondary battery system 20B can recover the output decrease by causing the solid secondary battery 10 to be in an overdischarged state based on any timing of the user.

(4) Modification 4
Although the solid secondary battery system 20 includes the ammeter 17 and the voltmeter 18, it may have only one of them instead. Even in this case, the solid secondary battery system 20 can determine whether or not the remaining capacity of the solid secondary battery 10 has become “0” based on the one detected value.

[Details about solid secondary batteries]
Next, the solid secondary battery in the present invention will be described in detail. The solid secondary battery in the present invention has at least a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, and usually further includes a positive electrode current collector and a negative electrode current collector.

(1) Positive electrode active material layer The positive electrode active material layer in the present invention is a layer containing at least a positive electrode active material, and further contains at least one of a solid electrolyte material, a conductive material, and a binder as necessary. You may do it. The type of the positive electrode active material is appropriately selected according to the type of the solid secondary battery, and examples thereof include an oxide active material and a sulfide active material. For example, as a positive electrode active material used for a lithium solid state secondary battery, for example, a layered positive electrode such as LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiVO ₂ , LiCrO _2, etc. Active materials, spinel type positive electrode active materials such as LiMn ₂ O ₄ , Li (Ni _0.25 Mn _0.75 ) ₂ O ₄ , LiCoMnO ₄ , Li ₂ NiMn ₃ O ₈ , LiCoPO ₄ , LiMnPO ₄ , LiFePO _4, etc. Examples thereof include an olivine type positive electrode active material and a NASICON type positive electrode active material such as Li ₃ V ₂ P ₃ O ₁₂ .

Examples of the shape of the positive electrode active material include particles and thin films. The average particle diameter (D ₅₀ ) of the positive electrode active material is, for example, preferably in the range of 1 nm to 100 μm, and more preferably in the range of 10 nm to 30 μm. Further, the content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably in the range of 40 wt% to 99 wt%, for example.

  The positive electrode active material layer may contain a solid electrolyte material. By adding the solid electrolyte material, the ion conductivity of the positive electrode active material layer can be improved. The solid electrolyte material will be described in “(3) Solid electrolyte layer” described later. Although content of the solid electrolyte material in a positive electrode active material layer is not specifically limited, For example, it is preferable to exist in the range of 10 weight%-90 weight%.

  The positive electrode active material layer may contain a conductive material. By adding a conductive material, the electron conductivity of the positive electrode active material layer can be improved. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. The positive electrode active material layer preferably contains a binder. This is because a positive electrode active material layer having excellent flexibility can be obtained. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. The thickness of the positive electrode active material layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 1 μm to 100 μm.

(2) Negative electrode active material layer The negative electrode active material layer in the present invention is a layer containing at least a negative electrode active material, and further contains at least one of a solid electrolyte material, a conductive material and a binder as necessary. You may do it. The type of the negative electrode active material is not particularly limited as long as it can occlude and release metal ions. Examples of the negative electrode active material include a carbon active material, an oxide active material, and a metal active material. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of the oxide active material include Nb ₂ O ₅ , Li ₄ Ti ₅ O ₁₂ , and SiO. Examples of the metal active material include In, Al, Si, and Sn.

Examples of the shape of the negative electrode active material include particles and thin films. The average particle diameter (D ₅₀ ) of the negative electrode active material is, for example, preferably in the range of 1 nm to 100 μm, and more preferably in the range of 10 nm to 30 μm. Moreover, the content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 wt% to 99 wt%, for example.

  The negative electrode active material layer may contain a solid electrolyte material. By adding a solid electrolyte material, the ion conductivity of the negative electrode active material layer can be improved. The solid electrolyte material will be described in “(3) Solid electrolyte layer” described later. Although content of the solid electrolyte material in a negative electrode active material layer is not specifically limited, For example, it is preferable to exist in the range of 10 weight%-90 weight%. Note that the conductive material and the binder used for the negative electrode active material layer are the same as the contents described in the above “(1) Positive electrode active material layer”, and thus description thereof is omitted here. Moreover, the thickness of the negative electrode active material layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 1 μm to 100 μm.

(3) Solid electrolyte layer The solid electrolyte layer in the present invention is a layer containing at least a solid electrolyte material. Examples of the solid electrolyte material include inorganic solid electrolyte materials such as a sulfide solid electrolyte material, an oxide solid electrolyte material, a nitride solid electrolyte material, and a halide solid electrolyte material. The sulfide solid electrolyte material is preferable in terms of high ion conductivity compared to the oxide solid electrolyte material, and the oxide solid electrolyte material is preferable in terms of high chemical stability compared to the sulfide solid electrolyte material. . The halide solid electrolyte material refers to an inorganic solid electrolyte material containing halogen.

  The sulfide solid electrolyte material usually contains a metal element (M) that becomes conductive ions and sulfur (S). As said M, Li, Na, K, Mg, Ca etc. can be mentioned, for example, Li is especially preferable. In particular, the sulfide solid electrolyte material preferably contains Li, A (A is at least one selected from the group consisting of P, Si, Ge, Al, and B) and S. The sulfide solid electrolyte material may contain a halogen such as Cl, Br, or I. By containing halogen, ion conductivity can be improved. The sulfide solid electrolyte material may contain O. By containing O, chemical stability can be improved.

Examples of the sulfide solid electrolyte material having Li ion conductivity include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₅ —LiI, Li ₂ S—P ₂ S ₅ —Li ₂ O, Li _{2 S-P 2 S 5 -Li} 2 O-LiI, Li 2 S-SiS 2, Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 _{S-SiS 2 -B 2 S 3} -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z m S n ( provided that , M, and n are positive numbers. Z is any of Ge, Zn, and Ga.), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ —Li _x MO _y (where, x, y is the number of positive .M is, P, Si, e, B, Al, Ga, either an In.) and the like. The description of “Li ₂ S—P ₂ S ₅ ” means a sulfide solid electrolyte material using a raw material composition containing Li ₂ S and P ₂ S _5, and the same applies to other descriptions. is there.

Also, the sulfide solid electrolyte material is preferably substantially free of Li 2 _S. This is because a sulfide solid electrolyte material having high chemical stability can be obtained. Li ₂ S reacts with water to generate hydrogen sulfide. For example, when the proportion of Li ₂ S contained in the raw material composition is large, Li ₂ S tends to remain. “Substantially free of Li ₂ S” can be confirmed by X-ray diffraction. Specifically, when it does not have a Li ₂ S peak (2θ = 27.0 °, 31.2 °, 44.8 °, 53.1 °), it is determined that it does not substantially contain Li ₂ S. can do.

Moreover, it is preferable that sulfide solid electrolyte material does not contain bridge | crosslinking sulfur substantially. This is because a sulfide solid electrolyte material having high chemical stability can be obtained. “Bridged sulfur” refers to bridged sulfur in a compound obtained by reacting Li ₂ S with the sulfide of A described above. For example, Li ₂ S and _P 2 _{S 5} is bridging sulfur reactions to become _{S 3} PS-PS 3 structure corresponds. Such bridging sulfur easily reacts with water and easily generates hydrogen sulfide. Furthermore, “substantially free of bridging sulfur” can be confirmed by measurement of a Raman spectrum. For example, in the case of a Li ₂ S—P ₂ S ₅ based sulfide solid electrolyte material, the peak of the S ₃ P—S—PS ₃ structure usually appears at 402 cm ⁻¹ . Therefore, it is preferable that this peak is not detected. Moreover, the peak of PS ₄ ³⁻ structure usually appears at 417 cm ⁻¹ . In the present invention, the intensity _{I 402} at 402 cm ^-1 is preferably smaller than the intensity _{I 417} at 417 cm ^-1. More specifically, the strength I ₄₀₂ is preferably 70% or less, more preferably 50% or less, and even more preferably 35% or less with respect to the strength I ₄₁₇ .

Also, the sulfide solid electrolyte material, if it is made by using the raw material composition containing Li ₂ S and _P 2 _{S 5,} the proportion of Li ₂ S to the total of Li ₂ S and _P 2 _{S 5} is For example, it is preferably in the range of 70 mol% to 80 mol%, more preferably in the range of 72 mol% to 78 mol%, and still more preferably in the range of 74 mol% to 76 mol%. This is because a sulfide solid electrolyte material having an ortho composition or a composition in the vicinity thereof can be obtained, and a sulfide solid electrolyte material having high chemical stability can be obtained. Here, ortho generally refers to one having the highest degree of hydration among oxo acids obtained by hydrating the same oxide. In the present invention, the crystal composition in which Li ₂ S is added most in the sulfide is called the ortho composition. In the Li ₂ S—P ₂ S ₅ system, Li ₃ PS ₄ corresponds to the ortho composition. In the case of a Li ₂ S—P ₂ S ₅ -based sulfide solid electrolyte material, the ratio of Li ₂ S and P ₂ S ₅ to obtain the ortho composition is Li ₂ S: P ₂ S ₅ = 75: 25 on a molar basis. It is. Instead of _P 2 _{S 5} in the raw material composition, even when using the _Al 2 _{S 3,} or _B 2 _{S 3,} a preferred range is the same. In the Li ₂ S—Al ₂ S ₃ system, Li ₃ AlS ₃ corresponds to the ortho composition, and in the Li ₂ S—B ₂ S ₃ system, Li ₃ BS ₃ corresponds to the ortho composition.

Also, the sulfide solid electrolyte material, if it is made by using the raw material composition containing Li ₂ S and SiS _2, the ratio of Li ₂ S to the total of Li ₂ S and SiS _2, for example 60 mol% ~ It is preferably within the range of 72 mol%, more preferably within the range of 62 mol% to 70 mol%, and even more preferably within the range of 64 mol% to 68 mol%. This is because a sulfide solid electrolyte material having an ortho composition or a composition in the vicinity thereof can be obtained, and a sulfide solid electrolyte material having high chemical stability can be obtained. In the Li ₂ S—SiS ₂ system, Li ₄ SiS ₄ corresponds to the ortho composition. In the case of the Li ₂ S—SiS ₂ -based sulfide solid electrolyte material, the ratio of Li ₂ S and SiS ₂ to obtain the ortho composition is Li ₂ S: SiS ₂ = 66.6: 33.3 on a molar basis. . Instead of SiS ₂ in the raw material composition, even when using a GeS _2, the preferred range is the same. In the Li ₂ S—GeS ₂ system, Li ₄ GeS ₄ corresponds to the ortho composition.

Moreover, when the sulfide solid electrolyte material is formed using a raw material composition containing LiX (X = Cl, Br, I), the ratio of LiX is, for example, in the range of 1 mol% to 60 mol%. It is preferably within a range of 5 mol% to 50 mol%, more preferably within a range of 10 mol% to 40 mol%. Also, the sulfide solid electrolyte material, if it is made by using the raw material composition containing Li ₂ O, the ratio of Li ₂ O is, for example, is preferably in the range of 1 mol% 25 mol%, More preferably, it is in the range of 3 mol% to 15 mol%.

The sulfide solid electrolyte material may be sulfide glass, 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 (ball mill or the like) on the raw material composition. Crystallized sulfide glass can be obtained, for example, by subjecting sulfide glass to a heat treatment at a temperature equal to or higher than the crystallization temperature. When the sulfide solid electrolyte material is a Li ion conductor, the Li ion conductivity at room temperature is preferably, for example, 1 × 10 ⁻⁵ S / cm or more, and preferably 1 × 10 ⁻⁴ S / cm or more. More preferably.

On the other hand, examples of the oxide solid electrolyte material having Li ion conductivity include a compound 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 (PO ₄ ) ₃ (0 ≦ x ≦ 2) can be given. Among them, the oxide solid electrolyte material _is preferably _{Li 1.5 Al 0.5 Ge 1.5 (PO} 4) _3. Another example of the compound having a NASICON structure is a compound represented by the general formula Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2). Among them, the oxide solid electrolyte material _is preferably _{Li 1.5 Al 0.5 Ti 1.5 (PO} 4) _3. Other examples of the oxide solid electrolyte material include LiLaTiO (for example, Li _0.34 La _0.51 TiO ₃ ), LiPON (for example, Li _2.9 PO _3.3 N _0.46 ), LiLaZrO ( for _example, mention may be made of _{Li 7 La 3 Zr 2 O 12} ) or the like.

Examples of the shape of the solid electrolyte material include particles and thin films. The average particle diameter (D ₅₀ ) of the solid electrolyte material is, for example, preferably in the range of 1 nm to 100 μm, and more preferably in the range of 10 nm to 30 μm. The content of the solid electrolyte material in the solid electrolyte layer is, for example, preferably 60% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more. The solid electrolyte layer may contain a binder or may be composed only of a solid electrolyte material. The thickness of the solid electrolyte layer varies greatly depending on the configuration of the battery. For example, the thickness is preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 1 μm to 100 μm.

(4) Other members The solid secondary battery in the present invention further includes a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Also good. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Examples of the material for the negative electrode current collector include SUS, copper, nickel, and carbon. Moreover, the battery case of a general solid secondary battery can be used for the battery case used for this invention. Examples of the battery case include a SUS battery case.

(5) Solid secondary battery Examples of the solid secondary battery in the present invention include a lithium solid secondary battery, a sodium solid secondary battery, a potassium solid secondary battery, a magnesium solid secondary battery, and a calcium solid secondary battery. Among them, a lithium solid state secondary battery is preferable. Moreover, since the solid secondary battery in this invention can be charged / discharged repeatedly, it is useful, for example as a vehicle-mounted battery. Examples of the shape of the solid secondary battery include a coin type, a laminate type, a cylindrical type, and a square type. Moreover, the manufacturing method of a solid secondary battery will not be specifically limited if it is a method which can obtain the solid secondary battery mentioned above, The method similar to the manufacturing method of a general solid secondary battery is used. be able to. For example, a press method, a coating method, a vapor deposition method, a spray, etc. can be mentioned.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Example 1]
(Synthesis of sulfide solid electrolyte materials)
As starting materials, lithium sulfide (Li ₂ S, manufactured by Nippon Chemical Industry Co., Ltd.) and diphosphorus pentasulfide (P ₂ S ₅ , manufactured by Aldrich) were used. Next, in a glove box under an Ar atmosphere (dew point −70 ° C.), Li ₂ S and P ₂ S ₅ have a molar ratio of 75Li ₂ S · 25P ₂ S ₅ (Li ₃ PS ₄ , ortho composition). Weighed as follows. 2 g of this mixture was mixed for 5 minutes in an agate mortar. Then, 2 g of the obtained mixture was put into a planetary ball mill container (45 cc, made of ZrO ₂ ), 4 g of dehydrated heptane (moisture content of 30 ppm or less) was added, and 53 g of ZrO ₂ balls (φ = 5 mm) were added. The container was completely sealed (Ar atmosphere). This container was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed for 40 hours at a base plate rotation speed of 500 rpm. Then, the obtained sample was dried so as to remove heptane on a hot plate to obtain a sulfide solid electrolyte material (75Li ₂ S · 25P ₂ S ₅ glass).

(Preparation of solid secondary battery)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (positive electrode active material, manufactured by Nichia Corporation) 12.03 mg, VGCF (vapor-grown carbon fiber, conductive material, manufactured by Showa Denko KK) 51 mg, 5.03 mg of the above-mentioned sulfide solid electrolyte material was weighed, and these were mixed to obtain a positive electrode mixture. Further, 9.06 mg of graphite (negative electrode active material, manufactured by Mitsubishi Chemical Corporation) and 8.24 mg of the above sulfide solid electrolyte material were weighed and mixed to obtain a negative electrode mixture.

Next, 18 mg of the above-mentioned sulfide solid electrolyte material was added to a 1 cm ² mold and pressed at a pressure of 1 ton / cm ² to form a solid electrolyte layer. 17.57 mg of the positive electrode mixture was added to one surface side of the obtained solid electrolyte layer, and pressed at a pressure of 1 ton / cm ² to form a positive electrode active material layer. Next, 17.3 mg of the negative electrode mixture was added to the other surface side of the solid electrolyte layer, and pressed at a pressure of 4 ton / cm ² to obtain a power generation element. SUS304 (positive electrode current collector, negative electrode current collector) was disposed on both surfaces of the obtained power generation element to obtain a solid secondary battery.

(Measurement of initial resistance)
The obtained solid secondary battery was CC (constant current) charged up to 4.2 V at 0.3 mA, and then CC discharged to 2.5 V at 0.3 mA. Next, the voltage was adjusted by charging to 3.6 V, and impedance analysis was performed with an impedance analyzer (manufactured by Solartron) to obtain resistance (initial).

(Storage test and overdischarge treatment)
After the initial resistance measurement, the battery was charged with CV (constant voltage) to 4.2 V and stored at 60 ° C. for 30 days. After storage, resistance (after 30 days) was determined by the same method as above. Next, CC discharge was performed to 0 V at 1.5 mA, and CV discharge was performed at 0 V for 10 hours. Then, it confirmed that the open circuit voltage was 0.5 V or less, and hold | maintained at 25 degreeC for 24 hours. After holding, the resistance (after 30 days, overdischarge treatment) was determined by the same method as described above.

(Resistivity)
Based on the resistance (initial), the resistivity of the resistance (after 30 days) and the resistance (after 30 days, overdischarge treatment) were calculated. The result is shown in FIG. As shown in FIG. 6, the resistance (after 30 days) increased with respect to the resistance (initial), but the resistance (after 30 days, overdischarge treatment) recovered to almost the same as the resistance (initial). That is, it was confirmed that by performing the overdischarge treatment, the internal resistance is reduced and the output characteristics are improved.

[Example 2]
(Preparation of solid secondary battery)
A solid secondary battery was prepared in the same manner as in Example 1 except that Al foil (manufactured by Nippon Foil Co., Ltd.) was used as the positive electrode current collector and Cu foil (manufactured by Nippon Foil Co., Ltd.) was used as the negative electrode current collector. Obtained.

(Measurement of initial resistance)
The resistance (initial) was determined in the same manner as in Example 1.

(Cycle test and overdischarge treatment)
After the initial resistance measurement, CC charge / discharge (2.5 V-4.2 V) was performed at 60 ° C. and 6 mA for 300 cycles and 500 cycles. After this charge / discharge, resistance (after 300 cycles) and resistance (after 500 cycles) were determined by the same method as described above. Next, CC discharge was performed to 0 V at 1.5 mA, and CV discharge was performed at 0 V for 10 hours. Then, it confirmed that the open circuit voltage was 0.5 V or less, and hold | maintained at 25 degreeC for 24 hours. After holding, the resistance (after 500 cycles, overdischarge treatment) was determined by the same method as described above.

(Resistivity)
Based on the resistance (initial), the resistivity of the resistance (after 300 cycles), the resistance (after 500 cycles), and the resistance (after 500 cycles, overdischarge treatment) were calculated. The result is shown in FIG. As shown in FIG. 7, the resistance (after 300 cycles) and the resistance (after 500 cycles) were larger than the resistance (initial), but the resistance (after 500 cycles, overdischarge treatment) was the resistance (300 cycles). It recovered until it became lower than (after). That is, it was confirmed that by performing the overdischarge treatment, the internal resistance is reduced and the output characteristics are improved.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material layer 2 ... Negative electrode active material layer 3 ... Solid electrolyte layer 4 ... Positive electrode collector 5 ... Negative electrode collector 10 ... Solid secondary battery 11 ... Overdischarge start switch 12, 12B ... Switch part 15 ... Load DESCRIPTION OF SYMBOLS 16 ... Discharge load 17 ... Ammeter 18 ... Voltmeter 19 ... Control part 20, 20A, 20B ... Solid secondary battery system

Claims (4)

A solid secondary battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer;
A switch provided outside the solid state secondary battery for starting an overdischarge process of the solid state secondary battery;
A solid-state secondary battery system comprising:   The solid secondary battery system according to claim 1, further comprising an overdischarge processing unit that starts an overdischarge process of the solid secondary battery based on an input from the switch. The overdischarge processing unit
A discharge unit for discharging the solid secondary battery until the remaining capacity of the solid secondary battery becomes 0;
An external short-circuit portion for performing an external short circuit of the solid secondary battery when the remaining capacity of the solid secondary battery becomes 0;
A solid secondary battery system according to claim 2.   The solid secondary battery system according to claim 3, wherein the discharge unit includes a discharge load whose load value is variable.

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