A method for failure analysis of lithium-sulfur soft-pack batteries

Abstract

The present invention belongs to the technical field of lithium-sulfur batteries and relates to a method for failure analysis of lithium-sulfur soft-pack batteries. The present invention adopts a method combining in-situ and ex-situ to calibrate and quantify the reversible capacity loss and irreversible capacity loss parts of lithium-sulfur soft-pack batteries, wherein the reversible capacity loss is polarization loss, interface loss and electrolyte loss; the irreversible capacity loss is negative electrode deposition, diaphragm blockage and others. According to the method for failure analysis of lithium-sulfur soft-pack batteries provided by the present invention, the results caused by various factors can be obtained more intuitively. Based on the decomposed results, targeted improvements can be made to the failure of lithium-sulfur soft-pack batteries, which provides beneficial help for improving the cycle performance and capacity of lithium-sulfur soft-pack batteries, and provides technical accumulation for the reaction mechanism and practical application process of lithium-sulfur soft-pack batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and relates to a method for analyzing the failure of lithium-sulfur soft-pack batteries. Background Art

[0002] As one of the next-generation high-energy-density energy storage batteries, lithium-sulfur batteries have attracted much attention from scientific researchers, and their theoretical energy density reaches 2600 wh / kg. However, there are still many problems in the development of current lithium-sulfur batteries, mainly concentrated in the complex reaction by-products of the sulfur cathode, which are easily soluble in the electrolyte and shuttle to the negative electrode for deposition, seriously affecting the capacity performance and causing the failure of lithium-sulfur batteries.

[0003] Regarding the problem of polysulfide shuttle, researchers mostly adopt the method of positively suppressing polysulfide shuttle, such as pore-forming sulfur fixation, chemical bond molecular adsorption of polysulfide displacement, active group catalysis of polysulfide kinetic conversion, etc., and the actual effects are shown by excellent capacity performance and cycle performance. However, in terms of reaction principle, the conversion of polysulfide by-products is an inevitable step for the sulfur cathode to participate in multi-electron reactions. Even if the above-mentioned various measures are adopted, the capacity loss caused by the dissolution of polysulfide in ether-based electrolytes is inevitable. Therefore, the reverse analysis after the battery fails due to polysulfide dissolution and shuttle is imperative.

[0004] The charge and discharge reactions of lithium-sulfur batteries are relatively complex, and there are many intermediate by-products during the charge and discharge process of the sulfur cathode. Among them, polysulfide Li2S 8~4 will dissolve in the electrolyte and shuttle to the separator and negative electrode along the concentration gradient; Li2S 2~1 is an insoluble substance and is easily deposited on the surface of the lithium negative electrode, resulting in capacity loss during the charge and discharge process. High-energy-density lithium-sulfur soft-pack batteries need to improve the utilization rate of the active substance sulfur to achieve a high loading amount. However, at the same time, the problem of polysulfide dissolution and shuttle will be more serious. The capacity attenuation caused by the shuttle problem and its additional effects (such as increased internal resistance, electrode expansion, etc.) have always restricted the practical application process of lithium-sulfur batteries. Therefore, it is necessary to focus on analyzing the capacity loss caused by polysulfide.

[0005] There are many important analysis methods for electrochemical failure analysis, which have good applications in lithium-ion batteries. For example, CN109581240A uses the AC impedance method to in-situ analyze the resistance change, and then evaluate the battery life and safety; CN113466721A has developed a failure identification method for lithium-ion batteries, setting a failure threshold to judge whether a lithium-ion battery fails, and so on. However, there are few failure analyses for lithium-sulfur soft-pack batteries at present. Especially, there is almost no in-depth research on the failure analysis of polysulfide in lithium-sulfur soft-pack batteries. The contribution of polysulfide to the capacity loss and the change of internal resistance in lithium-sulfur soft-pack batteries are not clear and not quantified, and the understanding of polysulfide is insufficient. Summary of the Invention

[0006] There is little failure analysis on existing lithium-sulfur soft-pack batteries. In particular, there is almost no in-depth research on the failure analysis of polysulfides in lithium-sulfur soft-pack batteries. The contribution of polysulfides to the capacity loss of lithium-sulfur soft-pack batteries is unclear, not quantified, and there is insufficient understanding of polysulfides. To address these technical problems, the present invention proposes a method for analyzing the failure of lithium-sulfur soft-pack batteries, which analyzes and quantifies the factors causing the capacity loss of lithium-sulfur soft-pack batteries. Based on the analysis results, targeted improvements can be made to enhance the cycle performance and capacity utilization of the batteries, providing technical accumulation for the reaction mechanism and practical application process of lithium-sulfur soft-pack batteries.

[0007] To achieve the above object, the technical solution of the present invention is implemented as follows:

[0008] A method for analyzing the failure of lithium-sulfur soft-pack batteries first decomposes the capacity loss of the battery into two parts: reversible capacity loss and irreversible capacity loss. Reversible capacity loss refers to the part of the capacity that can be restored by a certain method, and irreversible capacity loss refers to the part of the capacity that cannot be restored by any method. The analysis steps for different types of capacity loss are as follows:

[0009] (1) Reversible capacity loss analysis steps

[0010] a. In-situ rate depolarization: Re-calibrate the capacity of the battery and record the discharge capacity C1, and record the in-situ depolarization discharge capacity C2 at a small current rate.

[0011] b. In-situ interface depolarization: Increase the clamping pressure and test the clamping pressure and the discharge capacity C3 at the small current rate in step a.

[0012] c. In-situ infiltration depolarization: Refill the soft-pack battery and restore the capacity. After standing, test the discharge capacity C4 at the clamping pressure and small current rate in step b.

[0013] Among them, the polarization capacity loss Q1 = C2 - C1; the capacity loss affected by interface contact Q2 = C3 - C2; the capacity loss affected by electrolyte infiltration / liquid shortage Q3 = C4 - C3;

[0014] (2) Irreversible capacity loss analysis steps

[0015] d. Charge the lithium-sulfur soft-pack battery to full capacity at a small current rate, then disassemble the battery in a low dew point environment, take out the positive and negative electrode plates and the separator, and clean them with DOL.

[0016] e. Punch the failed positive electrode plate into small-sized electrode plates, corresponding to fresh separators and lithium sheets, reassemble the battery, and test the capacity performance C 正-新鲜 、C 正-失效 and convert them to capacities C5 and C6 according to the weight of the active material.

[0017] f. After the lithium sheet fails, sample it and punch it into small-sized lithium sheets. Take 3 to 5 lithium sheets, dissolve them in a solvent, and add them to the transition metal solution to react to form a sulfide precipitate. Then wash, evaporate to dryness, and weigh the precipitate, calculate the sulfur loss, and finally convert it to the capacity loss Q of the polysulfide-deposited negative electrode according to the area and the specific capacity of sulfur. 负 ;

[0018] g. After the separator fails, sample it and punch it into small-sized separators. Take 3 to 5 separators, soak them in a solvent for cleaning, then add the cleaning solution containing the separator to the transition metal solution to react to form a sulfide precipitate. Then wash, evaporate to dryness, and weigh the precipitate, calculate the sulfur loss, and finally convert it to the capacity loss Q of the polysulfide-deposited separator according to the area and the specific capacity of sulfur. 膜 ;

[0019] Among them, the capacity loss Q caused by the dissolution and shuttling of polysulfide 正 = C5 - C6; the capacity loss Q caused by the electrolyte and others 其它 = Q 正 - Q 负 - Q 膜 .

[0020] Furthermore, the test voltage range for re-fixing the volume in step a is 1.5 - 3.0V.

[0021] Furthermore, the rate for re-fixing the volume in step a is 0.1 - 1C, and the small current rate is 0.001 - 0.01C.

[0022] Furthermore, the clamping pressure in step b is 0.1 - 0.5MPa, and the small current rate is 0.001 - 0.01C.

[0023] Furthermore, the liquid supplement amount in step c is 0.5 - 1 times the mass of the battery active material, the clamping pressure is 0.1 - 0.5MPa, and the small current rate is 0.001 - 0.01C.

[0024] Furthermore, the small current rate of the lithium-sulfur soft-pack battery in step d is 0.1C, the full charge state voltage is 3.0V, and the temperature of the low dew point environment is lower than -40°C.

[0025] Furthermore, the area of the small-sized electrode sheet in step e is 0.001 - 0.01 times that of the failed positive electrode sheet or a 12-15 circular electrode sheet, and the small current rate is 0.001 - 0.01C.

[0026] Furthermore, the area of the small-sized lithium sheet in step f is 0.001 - 0.01 times that of the failed lithium sheet or a 12-16Round lithium wafer, with a small current rate of 0.001 - 0.01C; the solvent is ethanol, and the transition metal solution is a solution in which ions of Cu 2+ 、Fe 2+ 、Fe 3+ easily form sulfide precipitates in the reaction of the solution.

[0027] Furthermore, in step g, the area of the small-sized separator is 0.001 - 0.01 times that of the separator after failure or R 12-16 Round separator sheet, with a small current rate of 0.001 - 0.01C.

[0028] Furthermore, in step g, the solvent is ethanol, and the transition metal solution is a solution in which ions of Cu 2+ 、Fe 2+ 、Fe 3+ easily form sulfide precipitates in the reaction of the solution.

[0029] The failure analysis method of the lithium-sulfur soft-pack battery provided by the present invention is different from that of the lithium-ion battery. The differences are as follows: First, the reaction principles of the lithium-ion battery and the lithium-sulfur soft-pack battery are different. In the lithium-ion battery, lithium ions are mainly intercalated and deintercalated in the positive and negative electrode materials, while in the lithium-sulfur soft-pack battery, lithium ions react with sulfur. Second, from the perspective of the method of capacity decomposition, the capacity quantification of the lithium-ion battery mainly starts from the reaction mass of lithium, while the lithium-sulfur soft-pack battery starts from the reaction mass of sulfur. Third, their failure mechanisms are also different. The capacity failure of the lithium-ion battery mainly includes the collapse of the material structure, lithium deposition on the negative electrode, electrolyte loss, and polarization caused by swelling. The lithium-sulfur soft-pack battery mainly includes the swelling and pulverization of the lithium negative electrode, the shuttling and deposition of polysulfides (on the separator and the surface of the negative electrode), and the polarization part caused by electrolyte consumption.

[0030] The present invention has the following beneficial effects:

[0031] 1. The present invention studies the factors causing the failure of the lithium-sulfur soft-pack battery, obtains the main factors causing the failure of the lithium-sulfur soft-pack battery, and quantifies and summarizes the proportion of each factor in the capacity loss of the lithium-sulfur soft-pack battery, enabling a more intuitive analysis of the results caused by each factor.

[0032] 2. The method for analyzing the failure of the lithium-sulfur soft-pack battery provided by the present invention is simple to operate, and at the same time, it can be used to improve the failure of the lithium-sulfur soft-pack battery specifically, providing ideas for the cycle performance and capacity utilization of the battery.

[0033] 3. The present invention provides methodological support for the analysis of the failure mechanism of the lithium-sulfur soft-pack battery and provides technical support for the development and practical application process of the lithium-sulfur soft-pack battery. Description of the Drawings

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0035] Figure 1 It is a pie chart for decomposing the capacity loss of the lithium-sulfur soft-pack battery in Example 1. Detailed implementation manners

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] Example 1

[0038] This example is a method for analyzing the failure of a lithium-sulfur soft-pack battery, and the steps are as follows:

[0039] The battery used in the example is a lithium-sulfur soft-pack battery, and the electrolyte is a special electrolyte for lithium-sulfur. The positive electrode material is a carbon-sulfur composite material with a size of 74*104mm, the negative electrode is a lithium sheet with a size of 76*106mm, and the capacity is about 5Ah. After 10 normal-temperature cycles, it is found that there is a sign of capacity attenuation, so the failure analysis of this battery is carried out.

[0040] 1. Reversible capacity loss analysis

[0041] In-situ depolarization: The battery is re-calibrated at 0.1C (the voltage range is 1.5 - 3.0V, the same range as below), the discharge capacity C1 is 2.44Ah, and the in-situ depolarization discharge capacity C2 at a small current of 0.01C is 3.24Ah;

[0042] Improve interface contact: Increase the clamping pressure to 0.1MPa, and the discharge capacity C3 measured at this pressure and the above small current rate is 3.49Ah;

[0043] Improve infiltration: Recharge the soft-pack battery (the recharge amount is 0.5 times the mass of the battery active material) to recover the capacity. After standing, the discharge capacity C4 is measured at the above pressure and current rate, which is 3.95Ah;

[0044] Calculate the capacity loss of each part, where the polarization capacity loss Q1 = C2 - C1 = 0.8 Ah; the capacity loss affected by interface contact Q2 = C3 - C2 = 0.25 Ah; the capacity loss affected by electrolyte infiltration / liquid shortage Q3 = C4 - C3 = 0.46 Ah;

[0045] 2. Analysis of irreversible capacity loss

[0046] Charge the 5 Ah lithium-sulfur soft-pack battery at 0.01 C to 3.0 V (fully charged state), then disassemble it in a low dew point environment (< -40 °C), take out the positive and negative electrode plates and the separator, and wash them 2 - 3 times with DOL and dry them;

[0047] Punch the positive electrode plate before and after failure into small-sized electrode plates (the area is 0.01 times that of the large battery electrode plate), corresponding to the fresh separator and lithium sheet, reassemble the battery, and test the discharge capacity C at a small current of 0.01 C 正-新鲜 、C 正-失效 Convert the capacity according to the weight of the active material to C5 = 4.8 Ah and C6 = 3.68 Ah;

[0048] Take samples of the lithium sheet after failure and punch them into small-sized lithium sheets. Take 3 lithium sheets and dissolve them in ethanol, then add this solution to the Cu(NO3)2 solution to react to form CuS precipitate. Then wash, evaporate to dryness, and weigh the precipitate to calculate the sulfur loss. Finally, convert the capacity loss Q of the polysulfide-deposited negative electrode according to the area and the specific capacity of sulfur 负 is 0.55 Ah;

[0049] Take samples of the separator after failure and punch them into small-sized separators. Take 3 separators and soak them in ethanol for thorough cleaning, then add this solution to the Cu(NO3)2 solution to react to form CuS precipitate. Then wash, evaporate to dryness, and weigh the precipitate to calculate the sulfur loss. Finally, convert the capacity loss Q of the polysulfide-deposited separator according to the area and the specific capacity of sulfur 膜 is 0.31 Ah;

[0050] Among them, the capacity loss Q caused by polysulfide dissolution and shuttling 正 = C5 - C6 = 1.12 Ah; the capacity loss Q caused by polysulfide deposition on the lithium negative electrode 负 = 0.55 Ah; the capacity loss Q caused by polysulfide adhesion to the separator 膜 = 0.31 Ah, and the capacity loss Q caused by the electrolyte and others 其它 = Q 正 - Q 负 - Q 膜 = 0.26 Ah.

[0051] The capacity loss of this 5 Ah lithium-sulfur soft-pack battery is decomposed as follows:

[0052]

[0053] After the normal temperature cycle fails, the capacity is decomposed. Among them, the reversible capacity loss is mainly about 53% in terms of polarization. Through interface optimization and liquid addition, part of the capacity can be restored. By disassembling the battery to decompose the capacity, the irreversible capacity loss is all caused by the shuttle of polysulfides at the positive electrode, and the irreversible capacity caused by the deposition of polysulfides at the negative electrode accounts for about half.

[0054] Example 2

[0055] This example is a method for analyzing the failure of a lithium-sulfur soft-pack battery, and the steps are as follows:

[0056] The battery used in the example is a lithium-sulfur soft-pack battery, and the injected electrolyte is the special lithium-sulfur electrolyte with the same formula as in Example 1. The positive electrode material is a carbon-sulfur composite material with a size of 74*144 mm, the negative electrode is a lithium sheet with a size of 76*146 mm, and the capacity is about 9.5 Ah. Different rate tests have been carried out at present, and it is found that there is a phenomenon of capacity loss. Therefore, a failure analysis of this battery is carried out.

[0057] 1. Reversible capacity loss analysis

[0058] In-situ depolarization: The battery is re-sized at 0.1 C (voltage range 1.5 - 3.0 V, the same range below), the discharge capacity C1 is 5. to 14 Ah, and the in-situ depolarization discharge capacity C2 at a small current of 0.01 C is 8.07 Ah;

[0059] Improve interface contact: Increase the clamping pressure to 0.1 MPa, and the capacity C3 at this pressure and the above small current rate is 8.49 Ah; <s

[0060] Improve infiltration: Add liquid to the soft-pack battery (the liquid addition amount is 0.5 times the mass of the battery active material) to restore the capacity. After standing, the capacity C4 is measured at the above pressure and current rate to be 8.95 Ah;

[0061] Calculate the capacity loss of each part. Among them, the polarization capacity loss Q1 = C2 - C1 = 2.93 Ah; the capacity loss affected by interface contact Q2 = C3 - C2 = 0.42 Ah; the capacity loss affected by electrolyte infiltration Q3 = C4 - C3 = 0.46 Ah.

[0062] 2. Irreversible capacity loss analysis

[0063] Charge the lithium-sulfur soft-pack battery to 3.0 V (fully charged state) at 0.01 C, then disassemble the soft-pack battery in a low dew point environment (< -40 °C), take out the positive and negative electrode plates and the separator, and wash them 2 - 3 times with DOL and dry them;

[0064] The positive electrode sheets before and after failure are punched into small-sized electrode sheets (with an area 0.01 times that of the large battery electrode sheet), corresponding to fresh separators and lithium sheets, and the battery is reassembled to test the capacity at a small current of 0.01C 正-新鲜 and C 正-失效 According to the conversion of the active material weight, the capacities C5 and C6 are 8.05 Ah and 9.24 Ah respectively;

[0065] The lithium sheets after failure are sampled and punched into small-sized lithium sheets. Three lithium sheets are dissolved in ethanol, and then the solution is added to the Fe(NO3)2 solution to react to form FeS precipitate. Then the precipitate is washed, dried, and weighed to calculate the sulfur loss. Finally, the capacity loss Q of the polysulfide-deposited negative electrode is calculated according to the area and the specific capacity of sulfur 负 is 0.68 Ah;

[0066] The separators after failure are sampled and punched into small-sized separators. Three separators are soaked in ethanol for thorough cleaning, and then the solution is added to the Fe(NO3)2 solution to react to form FeS precipitate. Then the precipitate is washed, dried, and weighed to calculate the sulfur loss. Finally, the capacity loss Q of the polysulfide-deposited separator is calculated according to the area and the specific capacity of sulfur 膜 is 0.31 Ah;

[0067] Among them, the capacity loss Q caused by the dissolution and shuttling of polysulfides 正 =C 正-新鲜 -C 正-失效 =1.19 Ah; the capacity loss Q caused by the deposition of polysulfides on the lithium negative electrode 负 is 0.68 Ah; the capacity loss Q caused by the adhesion of polysulfides to the separator 膜 is 0.31 Ah, and the capacity loss Q caused by the electrolyte and others 其它 =Q 正 -Q 负 -Q 膜 =0.2 Ah.

[0068] The capacity loss of the 9.5 Ah soft-pack lithium-sulfur battery is decomposed as follows:

[0069] Table 2 Decomposition of the capacity loss of the 9.5 Ah soft-pack lithium-sulfur battery

[0070]

[0071] After multiple rate tests, the capacity of the failed battery is decomposed. Among them, the reversible capacity loss is mainly in polarization, accounting for about 76%. Through interface optimization and electrolyte replenishment, most of the capacity can be restored. By disassembling the battery to decompose the capacity, the irreversible capacity loss part, the deposition of polysulfides on the negative electrode, dominates, accounting for about 57%.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for failure analysis of a lithium-sulfur soft-pack battery, characterized in that: First, the capacity loss of the battery is decomposed into two parts: reversible capacity loss and irreversible capacity loss. Reversible capacity loss refers to the part of the capacity that can be restored by a certain method, and irreversible capacity loss refers to the part of the capacity that cannot be restored by any method. The analysis steps for different types of capacity loss are as follows: (1)Analysis steps for reversible capacity loss a. In-situ rate depolarization: Re-calibrate the capacity of the battery, record the discharge capacity C1, and record the in-situ depolarization discharge capacity C2 at a small current rate; b. In-situ interface depolarization: Increase the clamping pressure and test the clamping pressure and the discharge capacity C3 at the small current rate in step a; c. In-situ infiltration depolarization: Refill the liquid of the soft-pack battery and recover the capacity. After standing, test the discharge capacity C4 at the clamping pressure and small current rate in step b; Among them, the polarization capacity loss Q1 = C2 - C1; the capacity loss affected by interface contact Q2 = C3 - C2; the capacity loss affected by electrolyte infiltration / liquid shortage Q3 = C4 - C3; (2)Analysis steps for irreversible capacity loss d. Charge the lithium-sulfur soft-pack battery to full capacity at a small current rate, then disassemble the battery in a low dew point environment, take out the positive and negative electrode plates and the separator, and clean them with DOL; e. Punch the positive electrode sheets before and after failure into small-sized electrode sheets, corresponding to fresh separators and lithium sheets, reassemble the battery, and test the capacity performance C at a small current rate 正-新鲜 , C 正-失效 , and convert them into capacities C5 and C6 according to the weight of the active material f. After the lithium sheet fails, sample it and punch it into small-sized lithium sheets. Take 3 to 5 lithium sheets, dissolve them in a solvent, add them to a transition metal solution to react and form a sulfide precipitate. Then wash, evaporate to dryness, and weigh the precipitate, calculate the sulfur loss, and finally convert it into the capacity loss Q of the polysulfide-deposited negative electrode according to the area and the specific capacity of sulfur 负 ; g. After the diaphragm fails, sample it and cut it into small-sized diaphragms. Take 3 - 5 diaphragms, soak them in a solvent for cleaning, then add the cleaning solution containing the diaphragms to a transition metal solution to react and form a sulfide precipitate. Then wash, evaporate to dryness, and weigh the precipitate, calculate the sulfur loss, and finally convert it to the capacity loss Q of the polysulfide-deposited diaphragm according to the area and the specific capacity of sulfur 膜 ; where the capacity loss Q caused by the dissolution and shuttling of polysulfides 正 = C5 - C6; the capacity loss Q caused by the electrolyte and others 其它 = Q 正 - Q 负 - Q 膜 .

2. The method for failure analysis of the lithium-sulfur soft-pack battery according to claim 1, wherein: The test voltage range for re-calibrating the capacity in step a is 1.5 - 3.0V.

3. The method for analyzing the failure of the lithium-sulfur soft-pack battery according to claim 2, characterized in that: The rate for re-calibrating the capacity in step a is 0.1 - 1C, and the small current rate is 0.001 - 0.01C.

4. The method for failure analysis of the lithium-sulfur soft-pack battery according to claim 3, wherein: The clamping pressure in step b is 0.1 - 0.5MPa, and the small current rate is 0.001 - 0.01C.

5. The method for analyzing the failure of the lithium-sulfur soft-pack battery according to claim 4, characterized in that: The liquid refill volume in step c is 0.5 - 1 times the mass of the battery active material, the clamping pressure is 0.1 - 0.5MPa, and the small current rate is 0.001 - 0.01C.

6. The method for analyzing the failure of the lithium-sulfur soft-pack battery according to claim 5, wherein: The small current rate of the lithium-sulfur soft-pack battery in step d is 0.1C, the full charge state voltage is 3.0V, and the temperature of the low dew point environment is lower than -40°C.

7. The method for failure analysis of the lithium-sulfur soft-pack battery according to claim 6, wherein: In step e, the area of the small-sized electrode is 0.001-0.01 times that of the positive electrode after failure or R 12-15 For circular electrodes, the small current rate is 0.001-0.01C.

8. The method for failure analysis of the lithium-sulfur soft-pack battery according to claim 7, wherein: In step f, the area of the small-sized lithium sheet is 0.001-0.01 times that of the lithium sheet after failure or R 12-16 Round lithium sheet, small current rate is 0.001-0.01C; the solvent is ethanol, and the transition metal solution is a solution containing Cu 2+ , Fe 2+ , Fe 3+ A solution in which the reaction of ions is likely to form a sulfide precipitate.

9. The method for failure analysis of the lithium-sulfur soft-pack battery according to claim 8, wherein: In step g, the area of the small-sized diaphragm is 0.001 - 0.01 times that of the diaphragm after failure or R 12-16 Circular diaphragm, small current rate is 0.001 - 0.01C.

10. The method for failure analysis of the lithium-sulfur soft-pack battery according to any one of claims 1-9, characterized in that: In step g, the solvent is ethanol and the transition metal solution is a solution containing Cu 2+ , Fe 2+ , Fe 3+ ions, in which sulfide precipitates are likely to form during the reaction.

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