Method for detecting changes in electrolyte state, method for estimating lithium salt concentration, and method for manufacturing a system or module including a recycled battery.

Abstract

To provide a method for detecting changes in the state of the electrolyte contained in a lithium-ion battery without damaging the lithium-ion battery. [Solution] A method for detecting changes in the state of the electrolyte contained in a lithium-ion battery, which detects changes in the state of the electrolyte contained in the lithium-ion battery based on the amount of change dZ of the ZF curve obtained by plotting the actual axial resistance Z, which is obtained by the AC impedance method of the lithium-ion battery, against the voltage frequency F, and the resulting change in the state of the electrolyte contained in the lithium-ion battery.

Description

[Technical Field]

[0001] This disclosure relates to a method for detecting changes in the state of an electrolyte, and further to a method for estimating lithium salt concentration and a method for manufacturing a system or module including a recycled battery using the same. [Background technology]

[0002] Japanese Patent Publication No. 2023-175531 (Patent Document 1) discloses a method for diagnosing the degradation of a secondary battery using the AC impedance method. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-175531 [Overview of the project] [Problems that the invention aims to solve]

[0004] For example, batteries used in vehicles may be removed from scrapped vehicles, re-stacked, and reused as stationary batteries. When batteries with different internal conditions are combined, cells that have deteriorated may deteriorate rapidly. Even batteries with the same characteristics may have different internal conditions. In particular, if batteries with low salt concentration are mixed in, it may lead to a rapid decrease in capacity due to insufficient salt concentration after durability testing, and a malfunction may occur in the stack even if other cells are still usable. However, conventional chemical analysis methods used to evaluate the salt concentration of batteries are destructive analyses, making it difficult to know the salt concentration inside the battery without destroying it. Furthermore, the deterioration diagnosis method disclosed in Patent Document 1 cannot estimate the salt concentration.

[0005] The object of this disclosure is to provide an electrolyte state change detection method that can detect changes in the state of the electrolyte contained in a lithium-ion battery without damaging the lithium-ion battery. Another object of this disclosure is to provide a lithium salt concentration estimation method that estimates the lithium salt concentration in the electrolyte contained in a lithium-ion battery without damaging the lithium-ion battery, and a method for manufacturing a system or module including a recycled battery using the same. [Means for solving the problem]

[0006] [1] The real axial resistance Z obtained by the AC impedance method of lithium-ion batteries is the voltage frequency F or its logarithm, Log 10 A method for detecting changes in the state of the electrolyte contained in a lithium-ion battery, which detects changes in the state of the electrolyte contained in the lithium-ion battery based on the amount of change dZ of Z at an arbitrary F, obtained by differentiating a curve plotted against F. [2] The method for detecting changes in the state of an electrolyte, wherein part or all of the solvent in the electrolyte precipitates at a temperature of -50°C or higher, as described in [1]. [3] The method for detecting changes in the state of an electrolyte, according to [1] or [2], wherein the solvent in the electrolyte has a freezing point of 0°C or higher. [4] A method for estimating the concentration of lithium salt in the electrolyte contained in a lithium-ion battery, The real-axis resistance Z obtained by the AC impedance method of a lithium-ion battery is the voltage frequency F or its logarithm, Log 10 Based on the change in Z dZ at any given F, obtained by differentiating the curve plotted against F, the temperature T corresponding to the change in the solvent state in the electrolyte is determined. A The first step in determining the value, The temperature T A The lithium salt concentration C in the electrolyte when this occurs A The second step is to determine, A method for estimating lithium salt concentration, including the method described above. [5] The lithium salt concentration estimation method according to [4], wherein part or all of the solvent in the electrolyte precipitates as crystals at a temperature of -50°C or higher. [6] The method for estimating the lithium salt concentration according to [4] or [5], wherein the solvent in the electrolytic solution includes a solvent having a freezing point of 0 °C or higher. [7] A method for manufacturing a system or module including a reused battery, including an inspection step of estimating the concentration of the lithium salt in the electrolytic solution contained in the battery taken out by disassembling the system or module by the method for estimating the lithium salt concentration according to any one of [4] to [6]; a method for manufacturing a system or module including a reused battery. [8] The method for manufacturing a system or module including a reused battery according to [7], including a stacking step of restacking the reused battery into the system or module. [Advantages of the Invention]

[0007] According to the present disclosure, it is possible to provide a method for detecting a change in the state of an electrolytic solution that can detect a change in the state of the electrolytic solution contained in a lithium-ion battery without destroying the lithium-ion battery. Further, according to the present disclosure, it is possible to provide a method for estimating the lithium salt concentration in the electrolytic solution contained in a lithium-ion battery without destroying the lithium-ion battery, and a method for manufacturing a system or module including a reused battery using the same. [Brief Description of the Drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a flowchart of a method for manufacturing a system or module including a reused battery. [Figure 2] FIG. 2 is a diagram showing a ReZ-log10F curve obtained by plotting the real-axis resistance Z obtained by the AC impedance method for Test Nos. 1 to 6 against the logarithm value of the voltage frequency F, Log10F. [Figure 3] FIG. 3 is a diagram showing a curve obtained by plotting the change amount dZ obtained by differentiating the ReZ-log10F curve against the logarithm value of the voltage frequency F, Log10F. [Figure 4] FIG. 4 is a diagram showing the relationship between the salt concentration in the electrolytic solution and the temperature at which the solvent in the electrolytic solution precipitates. [Modes for carrying out the invention]

[0009] <Method for detecting changes in electrolyte state> The electrolyte state change detection method of this disclosure involves using the real axial resistance Z (also called ReZ), obtained by the AC impedance method of a lithium-ion battery (hereinafter also referred to as battery), as the voltage frequency F or its logarithm, Log 10 This method detects changes in the state of the electrolyte contained in a battery based on the change in Z (dZ) at any given F, which is obtained by differentiating the curve plotted against F.

[0010] The battery may be a battery that can be used for any purpose. For example, the battery may be a battery used as the main power source or power assist power source in an electric vehicle.

[0011] A battery contains an electrolyte. The DC resistance and reaction resistance of a battery can change due to changes in the state of the electrolyte. The phenomenon in which changes in the state of the electrolyte near the active material manifest as resistance due to changes in the state of the substances in the electrolyte can be confirmed by the change in the real axis of the AC impedance method. According to this disclosure, changes in the state of substances in the electrolyte can be detected by confirming the change in the real axis of the AC impedance method.

[0012] The actual axial resistance Z of a battery may have different frequency dependence depending on, for example, the type and concentration of components constituting the electrolyte. The actual axial resistance Z of the battery, determined by the AC impedance method for each concentration of lithium salt in the electrolyte at a certain temperature, is used in relation to the voltage frequency F or its logarithm, Log 10 In the curve plotted against F, the frequency dependence of the battery's axial resistance Z can change depending on the concentration of lithium salt in the electrolyte. From this, it can be inferred that if the state of the electrolyte in the battery changes, a change in resistance will occur due to a deterioration in the mobility of lithium ions in the electrolyte and a change in the electrolyte structure near the active material. The axial resistance Z is plotted against the voltage frequency F or its logarithm, Log. 10The change in Z, dZ, at any F, determined by differentiating the curve plotted against F, is plotted against the voltage frequency F or its logarithmic value, Log 10 When plotted against F, behavior thought to correspond to a change in the state of the electrolyte was confirmed. For each concentration of lithium salt in the electrolyte at a certain temperature, the voltage frequency F or its logarithmic value, Log 10 In the curve of the change in Z, dZ, with respect to F, it was found that when the concentration of the lithium salt is low, the solvent precipitates and the change in dZ in the low-frequency region tends to be large. Based on the change in dZ, it was found that a change in the state of the electrolyte contained in the battery can be detected.

[0013] In the case of a change in the state of a deteriorated battery (deteriorated cell), by comparing the change in dZ at the temperature T determined for the deteriorated cells, if the change in dZ is different, it can be determined that the states of the deteriorated cells are different from each other. The voltage frequency F may be any frequency at which the change in dZ due to the change in state can appear. For example, it may be 1×10 -2 ~1×10 5 Hz, or it may be 1 to 10 Hz, or it may be 3 Hz. In this way, a change in the state of the electrolyte can be detected without destroying the deteriorated battery.

[0014] Examples of changes in the state of the electrolyte include, for example, freezing of the electrolyte and precipitation of components constituting the electrolyte. The precipitation of components constituting the electrolyte can be the precipitation of some or all of the solvent in the electrolyte. For example, in a deteriorated battery, the concentration of the lithium salt decreases, and compared to a non-deteriorated battery, the freezing point of the electrolyte is less likely to drop, and there is a tendency for some or all of the solvent to precipitate more easily at a temperature higher than the freezing point. Therefore, by comparing the change in the real-axis resistance Z, dZ, at the voltage frequency F or its logarithmic value, Log 10 F, obtained from the curve plotted against F, if they are different from each other, it can be determined that precipitation of some or all of the solvent in the electrolyte has occurred. 10 When plotted against F, behavior thought to correspond to a change in the state of the electrolyte was confirmed. For each concentration of lithium salt in the electrolyte at a certain temperature, the voltage frequency F or its logarithmic value, Log

[0015] The electrolyte contains a lithium salt and a solvent. The solvent may contain one or more solvents. The solvent may contain solvents that precipitate at temperatures above -50°C. Some or all of the solvent may be solvents that precipitate at temperatures above -50°C. If the solvent contains two or more solvents, the precipitation of part of the solvent may be the precipitation of at least one of the two or more solvents.

[0016] The solvent can be aprotic. The solvent may contain any components. For example, the solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL). If a change in state is observed, it is temperature-independent, but an electrolyte in a more practical temperature range (below -50°C) is desirable. This is more easily achieved by using solvent species with a freezing point above 0°C, such as DMC or EC.

[0017] The lithium salt may include at least one selected from the group consisting of, for example, LiPF6, LiBF4, and LiN(FSO2)2. The molar concentration of the lithium salt in the electrolyte may be, for example, 0.5 mol / L to 2.0 mol / L. The supporting electrolyte may have a molar concentration of, for example, 0.8 mol / L to 1.2 mol / L.

[0018] <Method for estimating lithium salt concentration> The lithium salt concentration estimation method disclosed herein involves using the real axial resistance Z obtained by the AC impedance method of the battery as the voltage frequency F or its logarithm, Log 10 Based on the change in Z dZ at any given F, obtained by differentiating the curve plotted against F, the temperature T corresponding to the change in the solvent state in the electrolyte is determined. A The first step is to determine the temperature T A The lithium salt concentration C in the electrolyte when this occursA This method estimates the concentration of lithium salt in the electrolyte contained in a battery, and includes a second step of determining the voltage frequency F or its logarithm. The battery, electrolyte, lithium salt, solvent, and the real axial resistance Z obtained by the AC impedance method of the battery are used. 10 The change in Z, dZ, at any given F, obtained by differentiating the curve plotted against F, is explained in the above-described method for detecting changes in electrolyte state.

[0019] Changes in the solvent state within the electrolyte can be due to the precipitation of some or all of the solvent. The lithium salt concentration can be estimated by detecting the change in resistance using the AC impedance method, based on the known relationship between the salt concentration and the precipitation temperature. For example, due to molar freezing point depression, the solvent type most likely to precipitate precipitates at low temperatures depending on the lithium salt concentration, solvent type, and solvent ratio. This precipitation of the solvent is thought to cause a change in resistance due to deterioration of lithium ion mobility in the electrolyte and changes in the electrolyte structure near the active material. From a curve plotting the change in lithium salt concentration dZ at different temperatures, it was found that the difference in the change in dZ tends to increase with decreasing lithium salt concentration. It was found that, given the known relationship between the electrolyte salt concentration and the precipitation temperature, the lithium salt concentration inside the battery can be estimated by determining the change in dZ using the AC impedance method.

[0020] In the first step, the real axial resistance Z obtained by the AC impedance method of the battery is used to determine the voltage frequency F or its logarithm, Log 10 Based on the change in Z dZ at any given F, obtained by differentiating the curve plotted against F, the temperature T corresponding to the change in the solvent state in the electrolyte is determined. A We will determine the following. Specifically, from the curve above, we will determine the temperature T3 at which a change in the state of the electrolyte contained in the undegraded battery occurs and the amount of change dZ3 at that temperature T3. Next, for the degraded battery, we will determine the real axis resistance Z obtained by the AC impedance method and the voltage frequency F or its logarithm, Log 10The change in Z, dZ, at any given F is found by differentiating the curve plotted against F, and the temperature at which the change in Z becomes dZ3 is defined as temperature T. A It can be calculated as follows. The voltage frequency F3 can be any frequency at which the change amount dZ due to the change in state can appear, for example, 1 × 10⁻⁶ -2 ~1 × 10 5 It may be Hz, or 1 to 10 Hz, or 3 Hz.

[0021] In the second step, temperature T A The lithium salt concentration C in the electrolyte when this occurs A We will determine the temperature T at which the solvent precipitates in the electrolyte, based on the relationship between the lithium salt concentration in the electrolyte and the temperature at which the solvent precipitates in the electrolyte. A The lithium salt concentration in the electrolyte is given by the lithium salt concentration C. A This can be estimated as follows. The relationship between the lithium salt concentration in the electrolyte and the temperature at which the solvent in the electrolyte precipitates is determined according to the method described in the Examples section below. In this way, the lithium salt concentration in the electrolyte can be estimated without damaging the degraded battery.

[0022] The lithium salt concentration estimation method can be used in a manufacturing method for a system or module containing recycled batteries (hereinafter also referred to as the first manufacturing method). In the first manufacturing method, for example, it can be used in an inspection step in which the lithium salt concentration in the electrolyte contained in batteries extracted by disassembling a system or module recovered from the market is estimated using the lithium salt concentration estimation method described above. Batteries with low salt concentrations may rapidly lose their capacity as the salt concentration decreases due to degradation, and if even one battery in a system / module loses its capacity, the entire system / module may become unusable. In addition, salt concentrations may differ even with the same capacity and resistance characteristics due to differences in the progression of degradation caused by charge / discharge methods, storage temperatures, etc. By using this method for inspection, batteries with uniform salt concentrations can be selected, and unexpected shutdowns of systems / modules using recycled batteries can be prevented.

[0023] The first manufacturing method includes an inspection step in which the concentration of lithium salt in the electrolyte contained in a degraded battery extracted by disassembling a system or module is estimated using the lithium salt concentration estimation method described above. The first manufacturing method will be explained with reference to Figure 3. In the first manufacturing method, the system or module obtained in step S1 is first discharged (step S2), the battery stack is disassembled, and batteries to be used as recycled batteries are extracted (step S3). Systems or modules can be obtained by recovering them from the market. After performing cell thickness inspection, visual inspection, and internal inspection using X-rays on the extracted batteries (step S4), the batteries are laid out on an inspection pallet (step S5), and capacity inspection (step S6), resistance inspection (step S7), and IMP inspection (step S8) can be performed. By using the lithium salt concentration estimation method described above in the IMP inspection (step S8), the concentration of lithium salt in the electrolyte can be estimated without destroying the batteries. After removing the batteries from the inspection pallet (step S9), performing cell thickness inspection and visual inspection of the batteries (step S10), stacking them into a new system / module (step S11), adjusting the state of charge (SOC) of the stack (step S12), and performing an SOC inspection of the batteries within the stack (step S13). If the SOC inspection of the batteries within the stack fails (NG), the module can be discharged (step S14), a usable battery can be selected (step S15), and stacked into a new system / module (step S11). In this way, a system or module containing recycled batteries can be manufactured. [Examples]

[0024] [Fabrication of the negative electrode plate] Graphite was prepared as the negative electrode active material. A mixture with a mass ratio of graphite, SBR, and CMC (graphite:SBR:CMC) of 100:1:1 wt% was mixed with water to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to the copper foil of the negative electrode current collector, dried, and then compressed to a predetermined thickness to produce a negative electrode plate.

[0025] [Fabrication of the positive electrode plate] A cathode slurry was prepared by mixing a composite material with a mass ratio of LiNiCoMnO2, AB, and pVdF (LiNiCoMnO2:AB:pVdF) of 100:1:1 wt% with NMP. The cathode slurry was applied to the aluminum foil of the cathode current collector, dried, and then compressed to a predetermined thickness to produce a cathode plate.

[0026] [Electrolyte preparation] Using LiPF6 as the lithium salt and EC, EMC, and DMC as solvents, electrolytes No. 1 to 8 were prepared with the LiPF6 concentration and solvent volume ratio (EC / EMC / DMC) shown in Table 1.

[0027] [Table 1]

[0028] [Fabrication of non-aqueous electrolyte secondary batteries] A positive electrode plate was cut out, the composite material was peeled off from a portion, and an Al lead was welded to the exposed metal portion. A negative electrode plate was cut out, the composite material was peeled off from a portion, and a Ni lead was welded to the exposed metal portion. The positive electrode plate was sandwiched between three layers of polypropylene / polyethylene / polypropylene separators, and the positive and negative electrodes were combined so that the positive and negative electrode leads did not overlap through the separator and the positive electrode composite material layer was completely opposed to the negative electrode composite material layer to create an electrode body. The electrode body was inserted into an aluminum laminate film extracorpore, a predetermined amount of electrolyte was injected, and the laminate film was sealed to create a non-aqueous electrolyte secondary battery (unfilled). Electrolytes No. 1 to 8 were injected, left for 3 hours, then charged to 2.5V at a current of 0.05C in a 25°C environment, left for 1 hour, and then activated to create a battery.

[0029] <Example 1> [Visual inspection of electrolyte deposition test] Electrolytes No. 3, 6, and 8 were each sealed in transparent glass containers under an inert atmosphere, and the lids were closed to seal them. The temperature was then lowered to -31°C in a constant temperature bath with a window, and after 12 hours, precipitation was visually confirmed. The results are shown in Table 1.

[0030] [Battery AC IMP test] Batteries prepared by injecting electrolytes No. 3, 6, and 8, respectively, were charged to 3.65V with a constant current of 0.5C, and then low-voltage charged to 0.05C. These batteries were then placed in an impedance analyzer, and after lowering the temperature of the constant-temperature bath to the temperatures shown in Table 2 and leaving it for 5 hours, the current response was measured when a voltage with an amplitude of 10mV was applied at frequencies from 10kHz to 0.1Hz. At this time, A=Log 10 The voltage frequency F was specified and measured so that A, when set to F, would have 66 evenly distributed points between its maximum and minimum values.

[0031] [Analysis of AC IMP test results] The real-axis resistance Z and imaginary-axis resistance ImZ were calculated from the phase difference information of the current response with respect to the scanning potential. Additionally, the logarithm of the frequency F was calculated as Log 10 The derivative value dZ was defined as the relationship between F and the actual axis resistance Z when the relationship was plotted. In Example 1, the state change was observed at a frequency of 3 Hz for ease of observation, but the frequency is independent if a resistance change corresponding to the state change is observed. The results are shown in Table 2.

[0032] [Table 2]

[0033] The melting (freezing) points of DMC and EC in the electrolyte are high, at 4°C and 38°C, respectively. Although there is a molar freezing point depression effect in the electrolyte, it was confirmed that 1.0M LiPF6EC / EMC / DMC (volume ratio 3:3:4) solidifies at around -40°C (Tests No. 1-3). In the battery, it was hypothesized that solidification would worsen the mobility of Li ions in the electrolyte and cause a change in resistance due to changes in the electrolyte structure near the active material. Therefore, this was confirmed by the AC impedance method, and it was found that at low temperatures, the logarithm of the voltage frequency F, Log 10 ReZ-Log for F 10The change in the F curve's value dZ exhibited behavior that is thought to correspond to the solidification of the electrolyte. In this example, a value of 3Hz was used, as this value clearly shows the change in state, but any frequency at which a change in resistance corresponding to the change in state is observed would suffice. Furthermore, a similar trend can be observed when the frequency F is used directly without using logarithmic values, and the fluctuation of the ReZ-F curve is defined as dZ. Figure 2 shows the logarithmic values ​​of the voltage frequency F for tests No. 1 to 6. 10 ReZ-Log for F 10 This shows the F curve. 10 In the F-curve, the real axis resistance Z is the logarithm of the voltage frequency F. 10 The change in Z, dZ, obtained by differentiating with respect to F, is the logarithm of the voltage frequency F, which is Log 10 Figure 3 shows the curve plotted against F. Here, if the dZ value in Test No. 1 is set to 100, it can be inferred that when dZ exceeds approximately 120, the electrolyte components are crystallizing within the battery.

[0034] In tests in which only the electrolyte was frozen at various temperatures, the crystal deposition observed visually matched the behavior of the dZ of the AC impedance cell in a battery using the same electrolyte at the same temperature. This confirmed that it is possible to confirm changes in crystal deposition within the cell using dZ.

[0035] <Example 2> In Example 1's [AC IMP test of battery] and [analysis of AC IMP test results], the temperature of the constant temperature bath was set to -25°C to -45°C in 1°C increments (each temperature was maintained for 5 hours), and the AC IMP test and analysis of the IMP results were performed. Furthermore, during the analysis, when the dZ of Test No. 1 in Example 1 was set to 100, the temperature -dZ of two points before and after the dZ value of 120, which was detected as the amount of change where a change in state occurs based on the results of Example 1, was approximated as a linear transition. The temperature T on this linear transition where the amount of change dZ is 120 was then determined. A We calculated the value. The results are shown in Table 2.

[0036] [Table 3]

[0037] Table 3 shows the relationship between LiPF6 concentration and temperature T A A graph plotting these factors is shown in Figure 4. From the relationship between the salt concentration in the electrolyte and the temperature at which the solvent in the electrolyte precipitates, as shown in Figure 4, we can see the temperature at which a change in the state of a degraded battery with an unknown internal state, such as one recovered from the market, occurs. A By determining the concentration of LiPF6 in the electrolyte (C) without disassembling the degraded battery, the concentration of LiPF6 in the electrolyte can be determined. A ) becomes possible to estimate. Note that in Figure 4, when the salt concentration is 0.7 M, the temperature T that exceeds the threshold of dZ is A A change was observed in the relationship between the concentration of DMC and LiPF6. This is presumed to be due to a change in the substance precipitated from DMC to EC. EC normally has a solvated structure with lithium salts, and solvated EC is not involved in precipitation, so it is thought that the amount of free EC is involved in precipitation. As the lithium salt concentration decreases, solvated EC decreases and free EC increases, so the molar freezing point depression of EC decreases, and it is thought that precipitation by solidification of EC becomes more dominant than that of DMC. This behavior was also confirmed by the method disclosed herein.

[0038] This disclosure allows us to confirm, through changes in the real axis of the AC impedance method, the phenomenon in which changes in the state of the electrolyte near the active material, due to changes in the state of substances in the electrolyte, including solidification and precipitation of the electrolyte, manifest as resistance. Furthermore, according to this disclosure, it is possible to estimate the lithium salt concentration in the electrolyte contained in a lithium-ion battery.

Claims

1. The real axial resistance Z obtained by the AC impedance method of the lithium-ion battery is used with the voltage frequency F or its logarithm, Log １０ A method for detecting changes in the state of the electrolyte contained in a lithium-ion battery, which detects changes in the state of the electrolyte contained in the lithium-ion battery based on the amount of change dZ of Z at an arbitrary F, obtained by differentiating a curve plotted against F.

2. The method for detecting changes in the state of an electrolyte according to claim 1, wherein part or all of the solvent in the electrolyte precipitates at a temperature of -50°C or higher.

3. The method for detecting changes in the state of an electrolyte according to claim 1, wherein the solvent in the electrolyte contains a solvent having a freezing point of 0°C or higher.

4. A method for estimating the concentration of lithium salt in the electrolyte contained in a lithium-ion battery, The real axial resistance Z obtained by the AC impedance method of the lithium-ion battery is used with the voltage frequency F or its logarithm, Log １０ Based on the change in Z dZ at any given F, obtained by differentiating the curve plotted against F, the temperature T corresponding to the change in the solvent state in the electrolyte is determined. Ａ The first step in determining the value, The temperature T Ａ The lithium salt concentration C in the electrolyte when this occurs Ａ The second step is to determine, A method for estimating lithium salt concentration, including the method described above.

5. The lithium salt concentration estimation method according to claim 4, wherein part or all of the solvent in the electrolyte precipitates as crystals at a temperature of -50°C or higher.

6. The lithium salt concentration estimation method according to claim 4, wherein the solvent in the electrolyte solution includes a solvent having a freezing point of 0°C or higher.

7. A method for manufacturing a system or module including a recycled battery, A method for manufacturing a system or module including a recycled battery, comprising an inspection step of estimating the concentration of lithium salt in the electrolyte contained in a battery removed by disassembling the system or module, using the lithium salt concentration estimation method described in claim 4.

8. A method for manufacturing a system or module including a reusable battery according to claim 7, comprising a stacking step of re-stacking the reusable battery into the system or module.

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