JP2019145247A - Regeneration process of solid secondary battery - Google Patents

Abstract

To fully recover the capacity of a solid secondary battery containing silicon particles in a negative electrode active material.SOLUTION: A control device recovers the capacity of a solid secondary battery by performing a high restraint process on a solid secondary battery containing silicon particles in a negative electrode active material. In the high restraint process, the control device performs a charge/discharge process in which charging is performed until the voltage reaches 3.0 V, and then discharging is performed until the voltage is decreased to 1.5 V in a state in which the solid secondary battery is restrained at a pressure A of 5 MPa or more and 40 MPa or less. (Step S42), and pressurizes the solid secondary battery with a pressure B that is 5 MPa or more and 40 MPa or less and higher than the pressure A at a constant voltage (1.5 V) after the charge/discharge process (Step S44).SELECTED DRAWING: Figure 8

Description

  The present disclosure relates to a method for regenerating a solid secondary battery including silicon particles in a negative electrode active material.

  Japanese Patent Laying-Open No. 2011-108558 (Patent Document 1) discloses a method for regenerating a lithium solid state secondary battery in which graphite is used as a negative electrode active material. This regeneration method recovers the capacity of the lithium solid state secondary battery by charging and discharging while applying a pressure of 60 MPa to the lithium solid state secondary battery.

JP 2011-108558 A JP 2012-248414 A JP 2017-59534 A

  Factors that cause the capacity of the solid secondary battery to deteriorate include mechanical deterioration due to energization (charging / discharging) in addition to chemical deterioration over time. Since the mechanical deterioration is caused by a reversible physical change due to expansion and contraction of the electrode active material, it can be removed by charging and discharging while applying pressure as in Patent Document 1.

  However, some solid secondary batteries use silicon particles (Si) as the negative electrode active material instead of the graphite disclosed in Patent Document 1. The negative electrode active material containing silicon particles has characteristics that the degree of expansion due to charging and the degree of shrinkage due to discharge are larger than those of the negative electrode active material containing graphite. Therefore, in a solid secondary battery that includes silicon particles in the negative electrode active material, if the battery is overcharged in the process of recovering its capacity, the silicon particles will expand greatly due to high voltage and new cracks will occur in the negative electrode active material. Therefore, there is a concern that the capacity recovery effect cannot be obtained sufficiently. In addition, excessive discharge in the process of recovering the capacity can reduce the pressure applied to the solid secondary battery by reducing the voltage and causing the silicon particles Si to contract greatly, so that mechanical deterioration can be removed sufficiently. There is a concern that it will not be possible. Therefore, it is desired to develop a capacity recovery method suitable for a solid secondary battery containing silicon particles Si in the negative electrode active material.

  This indication is made in order to solve the above-mentioned subject, and the object is to fully recover the capacity of the solid secondary battery which contains silicon particles in the anode active material.

  A regeneration method according to the present disclosure regenerates a solid secondary battery including a positive electrode active material layer, a negative electrode active material layer containing silicon particles, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. Is the method. In this regeneration method, the solid state secondary battery is charged until the voltage of the solid state secondary battery reaches the first voltage, and then the solid state secondary battery is decreased until the voltage of the solid state secondary battery decreases to a second voltage lower than the first voltage. The step of performing charge / discharge treatment for discharging the secondary battery in a state where a first pressure of 5 MPa or more and 40 MPa or less is applied to the solid secondary battery, and after performing the charge / discharge treatment, the voltage of the solid secondary battery is the second voltage. Applying a second pressure not lower than the first pressure and not lower than the first pressure to the solid state secondary battery.

  According to the present disclosure, the capacity of a solid secondary battery including silicon particles in the negative electrode active material can be sufficiently recovered.

It is a figure which shows typically an example of the whole structure of a solid secondary battery and a capacity | capacitance recovery apparatus. It is a figure which shows typically the internal structure of a solid secondary battery. It is a figure which shows the capacity deterioration pattern of a solid secondary battery illustratively. It is a flowchart which shows an example of the process sequence at the time of a control apparatus performing reusability determination. It is a figure which shows the result of the verification experiment of restraint pressure. It is a figure which shows the result of the verification experiment of charging / discharging conditions. It is a figure which shows the result of the verification experiment of restraint timing. It is a flowchart which shows the detailed procedure of the high restraint process which a control apparatus performs.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a diagram schematically showing an example of the entire configuration of a solid secondary battery 200 and a capacity recovery device 1 used in the regeneration method according to the present embodiment. The regeneration method according to the present embodiment recovers the capacity of the solid secondary battery 200 by charging and discharging the solid secondary battery 200 having a deteriorated capacity while being pressurized using the capacity recovery device 1. is there.

  The solid secondary battery 200 is a solid secondary battery (for example, a lithium solid secondary battery) containing silicon particles in the negative electrode active material. Since the solid secondary battery 200 can be repeatedly charged and discharged, it is useful, for example, as an in-vehicle battery.

  The solid secondary battery 200 includes a positive electrode terminal 201 and a negative electrode terminal 202. The internal structure of the solid secondary battery 200 will be described in detail later.

  The capacity recovery device 1 is configured to pressurize and charge / discharge the solid secondary battery 200. The capacity recovery device 1 includes a charger / discharger 10, measurement terminals T1 and T2, lead wires L1 and L2, a pressurizer 20, and a control device 100.

  The measurement terminals T1 and T2 are configured to be connectable to the positive electrode terminal 201 and the negative electrode terminal 202 of the solid secondary battery 200, respectively. The measurement terminals T1, T2 are connected to the charger / discharger 10 by lead wires L1, L2. For example, when the measurement terminals T1 and T2 are connected to the positive electrode terminal 201 and the negative electrode terminal 202 of the solid secondary battery 200 by an operator's manual operation, the charger / discharger 10 can charge and discharge the solid secondary battery 200. It becomes a state. In this state, the charger / discharger 10 operates in response to a control signal from the control device 100 to charge and discharge the solid secondary battery 200.

  The pressurizer 20 includes pressurizing jigs 21 and 22 for sandwiching the solid secondary battery 200 and pressurizing the solid secondary battery 200. The pressurizer 20 can adjust the pressure applied to the solid secondary battery 200 by adjusting the positions of the pressurizing jigs 21 and 22 in accordance with a control signal from the control device 100.

  Further, the capacity recovery device 1 is provided with a voltage sensor 11 and a current sensor 12. The voltage sensor 11 measures the voltage between the lead wires L1 and L2 (the voltage between the positive terminal 201 and the negative terminal 202 of the solid secondary battery 200), and transmits the measurement result to the control device 100. The current sensor 12 measures the current flowing through the lead wire L1 (current flowing between the solid secondary battery 200 and the charger / discharger 10) and transmits the measurement result to the control device 100. Note that, when the solid state secondary battery 200 includes a monitoring unit in which a voltage sensor, a current sensor, and the like are embedded, information from the monitoring unit may be transmitted to the control device 100.

  The control device 100 includes a CPU (Central Processing Unit) and a memory (not shown), and controls the charger / discharger 10 and the pressurizer 20 based on information stored in the memory and information from the sensors 11 and 12.

  FIG. 2 is a diagram schematically showing the internal structure of the solid secondary battery 200. The solid secondary battery 200 includes a positive electrode active material layer 210, a negative electrode active material layer 220, a solid electrolyte layer 230, a positive electrode current collector 240, and a negative electrode current collector 250.

The positive electrode active material layer 210 is a layer containing a positive electrode active material. For example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) can be used as the positive electrode active material.

  The negative electrode active material layer 220 is a layer containing a negative electrode active material. In the present embodiment, silicon particles Si having a larger capacity than graphite is used as the negative electrode active material.

  The solid electrolyte layer 230 is a layer containing a solid electrolyte material that is formed between the positive electrode active material layer 210 and the negative electrode active material layer 220. As the solid electrolyte material, an inorganic solid electrolyte material such as a sulfide solid electrolyte material can be used.

  The positive electrode current collector 240 collects current from the positive electrode active material layer 210. The positive electrode current collector 240 is connected to the positive electrode terminal 201. The negative electrode current collector 250 collects current from the negative electrode active material layer 220. The negative electrode current collector 250 is connected to the negative electrode terminal 202.

<Determining whether or not solid secondary batteries can be reused>
From the viewpoint of effectively using resources, it is desirable to recover the used solid secondary battery 200 from the market and reuse it. However, some of the solid secondary batteries 200 collected from the market have deteriorated in capacity so that they cannot be reused.

  Therefore, the control apparatus 100 calculates the capacity deterioration amount of the solid secondary battery 200 by measuring the state of the used solid secondary battery 200 collected from the market, and the calculated capacity deterioration amount is less than the reuse threshold. The process of determining whether or not the solid secondary battery 200 can be reused (hereinafter also referred to as “reusability determination”) is performed.

  FIG. 3 is a diagram exemplarily showing a capacity deterioration pattern of the solid secondary battery 200. The vertical axis in FIG. 3 indicates the capacity deterioration amount of the solid secondary battery 200. Factors that cause the capacity of the solid secondary battery 200 to deteriorate include chemical deterioration due to aging and mechanical deterioration due to energization (charging / discharging). The total of the chemical deterioration and the mechanical deterioration is the total capacity deterioration amount of the solid secondary battery 200.

  FIG. 3 shows patterns 1 to 4 as capacity deterioration patterns. Pattern 1 is a pattern in which both the chemical deterioration amount and the mechanical deterioration amount are small, and the entire capacity deterioration amount is less than the reuse threshold. Pattern 2 is a pattern in which the amount of chemical deterioration is less than the reuse threshold but the amount of overall capacity deterioration exceeds the reuse threshold because the amount of mechanical deterioration is large. Pattern 3 is a pattern in which the amount of chemical deterioration is small but the amount of chemical deterioration alone exceeds the reuse threshold. Pattern 4 is a pattern in which both the amount of chemical deterioration and the amount of mechanical deterioration are large, and the amount of chemical deterioration alone exceeds the reuse threshold.

  Of the total capacity deterioration amount, the chemical deterioration is caused by an irreversible chemical reaction inside the solid secondary battery 200, and thus it is difficult to remove. On the other hand, the mechanical deterioration is caused by a reversible physical change caused by the expansion and contraction of the negative electrode active material layer 220. Therefore, a process of charging and discharging the solid secondary battery 200 while applying pressure (hereinafter also referred to as “high restraint process”). It can be removed by applying.

  Therefore, the control device 100 performs the above-described high constraint process on the solid secondary battery 200 whose capacity degradation amount exceeds the reuse threshold value, and whether or not the capacity degradation amount after the high constraint process is less than the reuse threshold value. Determine whether. Thereby, among the patterns 2 to 4 in which the capacity deterioration amount exceeds the reuse threshold at the beginning of collection (before the high restraint process), the pattern 2 whose chemical deterioration amount is smaller than the reuse threshold is entirely changed by the high restraint process. The amount of capacity degradation of the battery falls below the reuse threshold, and it is determined that reuse is possible. Thereby, the solid secondary battery 200 with little chemical deterioration can be reused to the maximum extent.

  FIG. 4 is a flowchart illustrating an example of a processing procedure when the control device 100 determines whether or not reuse is possible.

  The control device 100 measures the state of the solid secondary battery 200 that is a determination target for reuse, and calculates the capacity deterioration amount of the solid secondary battery 200 (total capacity deterioration amount including chemical deterioration and mechanical deterioration). (Step S10). Note that since a known technique can be used as the capacity deterioration amount calculation method itself, detailed description thereof will not be given here.

  Next, the control device 100 determines whether or not the capacity deterioration amount is less than the reuse threshold (step S20). When the capacity deterioration amount is less than the reuse threshold value (YES in step S20), control device 100 determines that solid secondary battery 200 is reusable (step S30).

  When the capacity deterioration amount exceeds the reuse threshold value (NO in step S20), control device 100 performs high restraint processing on solid secondary battery 200 (step S40). Thereby, the mechanical deterioration of the solid secondary battery 200 is removed. Details of the high constraint process will be described later.

  After completion of the high restraint process, control device 100 performs the same process as step S10, and again calculates the capacity deterioration amount of solid secondary battery 200 (step S50). And the control apparatus 100 determines whether the capacity | capacitance degradation amount after a high restraint process is less than a reuse threshold value (step S60).

  If the capacity deterioration amount after the high constraint process is less than the reuse threshold (YES in step S60), control device 100 determines that solid secondary battery 200 is reusable (step S30).

  When the capacity deterioration amount after the high constraint processing exceeds the reuse threshold (NO in step S60), control device 100 determines that solid secondary battery 200 is not reusable (step S70). Note that the solid secondary battery 200 determined to be non-reusable is discarded without being reused.

  As described above, the control device 100 performs the high restraint process on the solid secondary battery 200 whose capacity deterioration amount exceeds the reuse threshold. As a result, the amount of mechanical deterioration decreases, and thus the amount of capacity deterioration after the high restraint processing can decrease below the reuse threshold (that is, the capacity can be restored). Therefore, the solid secondary battery 200 with little chemical deterioration can be reused to the maximum.

<< High restraint processing >>
Hereinafter, details of the high constraint process will be described. As already described, the solid secondary battery 200 according to the present embodiment uses silicon particles Si as the negative electrode active material. The negative electrode active material containing silicon particles Si has characteristics that the degree of expansion due to charging and the degree of shrinkage due to discharge are larger than those of the negative electrode active material containing graphite.

  Therefore, in the solid secondary battery 200 according to the present embodiment, if the battery is excessively charged in the charging process during the high restraint process, the silicon particles Si expand greatly and new cracks occur in the negative electrode active material. However, there is a concern that a sufficient capacity recovery effect cannot be obtained. In addition, if the discharge is excessively performed during the high restraint process, the pressure applied to the solid secondary battery 200 is reduced due to the low voltage and the silicon particles Si contracting greatly, thereby sufficiently removing mechanical deterioration. There is concern that it will not be possible. Therefore, it is desired to perform a high restraint process suitable for the solid secondary battery 200 including silicon particles Si in the negative electrode active material.

  In view of the above problems, the inventors of the present application conducted experiments for verifying appropriate restraint pressure, charge / discharge conditions, and restraint timing of the solid secondary battery 200 in the high restraint process. In addition, all the verification experiments were performed under durability conditions of 25 ° C., 2C, and 200 cycles.

(1) Verification of Restraint Pressure The inventors of the present application conducted a charge / discharge treatment for charging until the voltage of the solid secondary battery 200 reaches 3.0V and then discharging until the voltage decreases to 1.5V. It carried out in the state restrained (pressurized) with the restraint pressures 1-5, respectively, and measured the subsequent capacity maintenance rate.

-Restraint pressure 1: 1 MPa
-Restraint pressure 2: 5 MPa
-Restraint pressure 3: 20 MPa
-Restraint pressure 4: 40 MPa
-Restraint pressure 5: 60 MPa
FIG. 5 shows the result of the constraint pressure verification experiment, that is, the relationship between each constraint pressure and the capacity retention rate. In addition, it means that the capacity | capacitance is recovering, so that a capacity | capacitance maintenance factor is large. From the results shown in FIG. 5, it can be understood that a value of 5 MPa to 40 MPa is effective for capacity recovery as the restraint pressure.

(2) Verification of charge / discharge conditions The inventors of the present invention performed charge / discharge under the following plurality of charge / discharge conditions 1 to 4 in a state where the constraint pressure was set to a constant value of 20 MPa, and then measured the capacity retention rate.

・ Charging / discharging condition 1: Untreated (no charging / discharging)
・ Charging / discharging condition 2: Charging voltage 3.0V-Discharging voltage 1.5V
・ Charging / discharging condition 3: Charging voltage 3.0V-Discharging voltage 2.0V
-Charging / discharging condition 4: Charging voltage 4.2V-discharging voltage 2.0V
FIG. 6 shows the result of the verification experiment of the charge / discharge conditions, that is, the relationship between each charge / discharge condition and the capacity retention rate. From the results shown in FIG. 6, the charge / discharge conditions are a charge voltage of 3.0 V and a discharge voltage of 1.5 V (charging until the voltage reaches 3.0 V, and then the voltage drops to 1.5 V) It can be understood that discharging is effective for capacity recovery.

(3) Verification of restraint timing The inventors of the present application restrained the solid secondary battery 200 at a restraint pressure of 20 MPa at the following plurality of restraint timings 1 to 3, and measured the capacity retention rate thereafter.

-Restraint timing 1: Unprocessed (not restrained)
Constraint timing 2: Constraint when battery voltage is 3.0V (high voltage) Constraint timing 3: Constraint when battery voltage is 1.5V (low voltage) FIG. That is, the relationship between each constraint timing and the capacity maintenance rate is shown. From the results shown in FIG. 7, it can be understood that, as the restraint timing, restraint when the battery voltage is 1.5 V (low voltage) is effective for capacity recovery.

<<< Flow of high restraint processing >>>
Based on the above verification results, the inventors of the present application decided to perform the high restraint processing of the solid secondary battery 200 in the procedure shown in FIG.

  FIG. 8 is a flowchart showing a detailed procedure of the high constraint process (the process of step S40 of FIG. 4) executed by the control device 100.

  In step S42, the control device 100 charges the solid secondary battery 200 with the pressure A (first pressure) until the voltage of the solid secondary battery 200 reaches the charging voltage V1 (first voltage). Then, the charger / discharger 10 and the pressurizer 20 are controlled so as to perform a charging / discharging process of discharging until the voltage decreases to the discharge voltage V2 (V2 <V1) (first step).

  Here, the charging voltage V1 and the discharging voltage V2 are set to 3.0 V and 1.5 V, respectively, based on the verification result of the above-described charging / discharging conditions (see FIG. 6). Further, the pressure A is set to a value of 5 MPa or more and 40 MPa or less based on the verification result of the restraint pressure (see FIG. 5).

  In this way, when the voltage becomes 3.0 V (high voltage), by constraining with the pressure A of 5 MPa or more and 40 MPa or less, even if the silicon particle Si expands greatly at the time of high voltage, a new crack is generated in the negative electrode active material. Is appropriately suppressed. As a result, a greater capacity recovery effect is likely to be obtained.

  In step S42, the method of applying the pressure A to the solid secondary battery 200 is as follows: (i) The initial positions of the pressure jigs 21 and 22 are set so that the pressure A is applied to the solid secondary battery 200 before the start of charging. The initial position may be adjusted and maintained during charging and discharging. (Ii) The pressure applied to the solid secondary battery 200 during charging and discharging is measured and measured. The position of the pressurizing jigs 21 and 22 may be feedback controlled so that the pressure becomes the pressure A.

  After the process of step S42, that is, in a state where the voltage of the solid secondary battery 200 is reduced to 1.5 V (low voltage) due to discharge, the control device 100 pressurizes the solid secondary battery 200 with the pressure B in step S44. Thus, the pressurizer 20 is controlled (second step).

  Here, the pressure B is set to a value of 5 MPa or more and 40 MPa or less based on the verification result of the constraint pressure (see FIG. 5). And the restraint timing by the pressure B is set at the time of a constant voltage (at the time of 1.5V) based on the verification result (refer FIG. 7) of the above-mentioned restraint timing. Therefore, a larger capacity recovery effect can be obtained as compared with the case where no pressure is applied at the pressure B at the constant voltage after the charge / discharge treatment.

  Further, in the present embodiment, the pressure B is set to a value larger than the pressure A. During the discharge in step S42 (first step), the voltage decreases and the silicon particles Si contract significantly. Therefore, for example, when the positions of the pressurizing jigs 21 and 22 are maintained at the initial positions during charging and discharging, the pressure applied to the solid secondary battery 200 due to the shrinkage of the silicon particles Si during discharging is before the charging starts. The pressure A of the solid secondary battery 200 may be insufficient and the binding force of the solid secondary battery 200 may be insufficient. In view of this point, the restraint force of the solid secondary battery 200 is insufficient due to the shrinkage of the silicon particles Si by restraining the solid secondary battery 200 with the pressure B higher than the pressure A in step S44 (second step). Is appropriately suppressed. As a result, a greater capacity recovery effect is likely to be obtained.

  As described above, the control device 100 according to the present embodiment performs the high restraint process of the solid secondary battery 200 including the silicon particles Si in the negative electrode active material according to the following procedure.

  (First Step) The solid secondary battery 200 is restrained by a pressure A of 5 MPa or more and 40 MPa or less, in which charging and discharging are performed until the voltage reaches 3.0 V and then discharged until the voltage drops to 1.5 V. Do in state.

  (Second Step) The solid secondary battery 200 is pressurized with a pressure B that is 5 MPa or more and 40 MPa or less and higher than the pressure A at a constant voltage (1.5 V) after the charge / discharge treatment.

  Thus, after charging / discharging while pressurizing the solid secondary battery 200 with the pressure A in the first step, the solid secondary battery 200 is further pressurized with the pressure B larger than the pressure A in the second step. The pressure applied to the solid secondary battery 200 is appropriately suppressed from being reduced by the shrinkage of the silicon particles Si. Therefore, the capacity of the solid secondary battery 200 can be sufficiently recovered.

<Modification 1>
In the above-described embodiment, the example in which the pressure B applied to the solid secondary battery 200 in the second step is set to a value larger than the pressure A applied to the solid secondary battery 200 in the first step has been described.

  However, the pressure B applied to the solid secondary battery 200 in the second step may be the same value as the pressure A applied to the solid secondary battery 200 in the first step. That is, after discharging in the first step, pressurization with the same pressure A as in the first step may be continued. By doing in this way, even if the pressurization with the pressure A is not continued after the discharge in the first step, a larger capacity recovery effect can be expected.

<Modification 2>
In the above-described embodiment, the example in which the pressure B is applied to the solid secondary battery 200 in the state where the battery voltage is lowered to 1.5 V (low voltage) in the second step has been described.

  However, in the second step, the pressure B may be applied to the solid secondary battery 200 after the battery voltage is lowered to a voltage lower than a predetermined value by 1.5V. Even if it does in this way, the larger capacity | capacitance recovery effect can be anticipated rather than the case where the pressurization by the pressure B is not continued after the discharge in a 1st step.

<Modification 3>
In the above-described embodiment, an example has been described in which the charging voltage V1 and the discharging voltage V2 in the charging / discharging process of the first step are set to 3.0 V and 1.5 V, respectively.

  However, the charge voltage V1 and the discharge voltage V2 in the charge / discharge process of the first step are not necessarily limited to 3.0V and 1.5V, respectively. For example, in view of the charge / discharge condition 3 (charge voltage 3.0V-discharge voltage 2.0V) being the second best in the verification result (see FIG. 6) of the charge / discharge condition described above, the charge voltage V1 is set to 3. The discharge voltage V2 may be set to 2.0V while maintaining 0V. Even in this case, since the pressure B is applied after the discharge in the first step, a larger capacity recovery effect can be expected than in the case where the pressure B is not applied after the discharge in the first step.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Capacity recovery apparatus, 10 charger / discharger, 11 voltage sensor, 12 current sensor, 20 pressurizer, 21,22 pressurizing jig, 100 control apparatus, 200 solid state secondary battery, 201 positive electrode terminal, 202 negative electrode terminal, 210 positive electrode Active material layer, 220 negative electrode active material layer, 230 solid electrolyte layer, 240 positive electrode current collector, 250 negative electrode current collector, T1, T2 measuring terminal.

Claims (1)

A method for regenerating a solid secondary battery comprising a positive electrode active material layer, a negative electrode active material layer containing silicon particles, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer,
The solid state secondary battery is charged until the voltage of the solid state secondary battery reaches a first voltage, and then the solid state secondary battery is reduced until the voltage of the solid state secondary battery drops to a second voltage lower than the first voltage. Performing a charge / discharge treatment for discharging the secondary battery in a state where the solid secondary battery is pressurized at a first pressure of 5 MPa or more and 40 MPa or less;
After performing the charge / discharge treatment, the solid secondary battery at a second pressure of 5 MPa to 40 MPa and a pressure equal to or higher than the first pressure in a state where the voltage of the solid secondary battery is equal to or lower than the second voltage. Pressurizing the solid secondary battery.

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