Low-temperature-resistant lithium ion battery pack for energy storage power station

Abstract

The application discloses a low-temperature-resistant lithium ion battery pack for energy storage power stations, which comprises a plurality of series-connected lithium iron phosphate batteries, wherein the lithium iron phosphate battery comprises a positive electrode containing positive active material, a negative electrode containing negative active material, a diaphragm for separating the positive electrode and the negative electrode, and an electrolyte; the positive active material is lithium iron phosphate, and the negative active material is FeS2-expansion graphite composite material. The FeS2-expansion graphite composite material is used as the negative active material in the lithium iron phosphate battery, so that the deintercalation lithium performance of the negative electrode material at low temperature is improved, the low-temperature charging capacity of the battery is improved, and the lithium ion battery pack meets the low-temperature working requirement.

Description

Technical Field

[0001] This invention relates to the field of energy storage battery technology, and in particular to a low-temperature resistant lithium-ion battery pack for energy storage power stations. Background Technology

[0002] The increasingly prominent environmental and resource issues have spurred the rapid development of new energy sources, such as wind and solar power. Currently, the development of these renewable energy sources faces bottlenecks such as poor power quality and difficulties in grid connection. Meanwhile, users have increasingly higher requirements for power quality, and traditional power systems can no longer adequately meet these needs. This has led to the emergence of new grid technologies such as robust smart grids and microgrids. Energy storage technology is considered a key technology for solving the grid connection problems of new energy power generation and building smart grids, and the application of energy storage power stations is becoming increasingly widespread.

[0003] Currently, lithium-ion batteries are widely used in energy storage power stations due to their excellent rate performance and cycle life. Among them, lithium iron phosphate batteries are particularly suitable for energy storage applications due to their high safety, long lifespan, and fewer resource constraints. However, lithium iron phosphate batteries have poor low-temperature charge-discharge performance, which limits their application in high-altitude and cold regions. Summary of the Invention

[0004] This invention aims to overcome the problem of poor low-temperature charge and discharge performance of lithium iron phosphate energy storage batteries in the prior art, which limits their application in energy storage power stations in cold regions. It provides a low-temperature resistant lithium-ion battery pack for energy storage power stations, which uses FeS2-expanded graphite composite material as the negative electrode active material in the lithium iron phosphate battery. This can improve the lithium insertion / extraction performance of the negative electrode material at low temperatures, improve the low-temperature charging capability of the battery, and enable the lithium-ion battery pack to meet the requirements for low-temperature operation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A low-temperature resistant lithium-ion battery pack for an energy storage power station includes several lithium iron phosphate batteries connected in series. Each lithium iron phosphate battery includes a positive electrode containing a positive active material, a negative electrode containing a negative active material, a separator separating the positive and negative electrodes, and an electrolyte. The positive active material is lithium iron phosphate, and the negative active material is FeS2-expanded graphite composite material. The preparation method of the FeS2-expanded graphite composite material includes the following steps:

[0007] (1) Natural flake graphite is mixed with concentrated sulfuric acid and hydrogen peroxide and reacted. The resulting product is washed and dried to obtain intercalated graphite.

[0008] (2) The intercalated graphite is pre-expanded at 800-900℃ for 20-30s to obtain pre-expanded graphite;

[0009] (3) Add pre-expanded graphite to ferrous sulfate solution and stir for 30-40 min. Then add sulfuric acid solution and hydrogen peroxide dropwise and continue stirring for 30-40 min. Then add sodium hydroxide solution dropwise and stir for 30-40 min. After aging for 1-3 h, wash and dry the product to obtain hydroxyl iron oxide intercalated graphite.

[0010] (4) Mix iron hydroxyl oxide intercalated graphite and sulfur powder, and react them at 450-550°C for 2-4 hours in an inert atmosphere to obtain the FeS2-expanded graphite composite material.

[0011] This invention connects lithium iron phosphate batteries in series to form a lithium-ion battery pack, and uses FeS2-expanded graphite composite material as the negative electrode active material in the lithium iron phosphate battery. In the preparation process of the FeS2-expanded graphite composite material in this invention, firstly, in step (1), concentrated sulfuric acid is used as an intercalating agent and hydrogen peroxide is used as an oxidizing agent to intercalate natural graphite; then, in step (2), the intercalated graphite is pre-expanded to increase the interlayer spacing of the graphite; then, in step (3), ferrous sulfate is loaded into the expanded interlayer of the graphite, and ferric hydroxide is formed in the interlayer of the graphite through oxidation and hydrolysis; finally, in step (4), the ferric hydroxide in the interlayer of the graphite is converted into FeS2 through the reaction of sulfur powder and ferric hydroxide, thus obtaining the FeS2-expanded graphite composite material.

[0012] This invention adds FeS2 to a graphite anode material. While the addition of FeS2 improves the low-temperature performance of the battery, it is prone to volume expansion during charge and discharge, which reduces the battery's cycle stability. Therefore, this invention first modifies natural graphite through intercalation and pre-expansion to increase the interlayer spacing of the graphite material. Then, FeS2 is embedded into the interlayer space of the pre-expanded graphite material. Firstly, the increased interlayer spacing of the graphite through intercalation and pre-expansion of natural graphite facilitates lithium-ion insertion at low temperatures, thereby further improving the battery's charging performance at low temperatures. Secondly, fixing FeS2 into the interlayer space of the expanded graphite restricts its volume expansion through the layered structure of the graphite, improving the battery's cycle stability. Therefore, using the FeS2-expanded graphite composite material of this invention as the anode active material in a lithium iron phosphate battery can improve the lithium insertion / extraction performance of the anode material at low temperatures while ensuring good cycle stability, enabling the lithium-ion battery pack to meet the requirements for low-temperature operation.

[0013] Preferably, the hydrogen peroxide concentration in step (1) is 28-30%, and the ratio of the amount of natural flake graphite, concentrated sulfuric acid and hydrogen peroxide added is 4-6g:13-15mL:1mL.

[0014] Preferably, in step (3), the mass ratio of pre-expanded graphite to ferrous sulfate in the ferrous sulfate solution is 1:7 to 9; the molar ratio of H2SO4 to ferrous sulfate in the added sulfuric acid solution is 0.2 to 0.3:1; and the molar ratio of H2O2 to ferrous sulfate in the added hydrogen peroxide is 1 to 1.5:1.

[0015] Preferably, the pH of the system after adding sodium hydroxide solution in step (3) is 6-7, and the stirring reaction temperature after adding sodium hydroxide solution is 30-40℃.

[0016] Preferably, in step (4), the mass ratio of iron hydroxyl oxide intercalated graphite to sulfur powder is 1:2 to 3.

[0017] Preferably, the electrolyte comprises an organic solvent, a lithium salt, and a low-temperature additive. The electrolyte plays a role in transferring lithium ions. At low temperatures, the electrolyte's viscosity tends to increase, affecting its ionic conductivity and wettability with the positive and negative electrode active materials, thus degrading the battery's low-temperature performance. This invention adds a low-temperature additive to the electrolyte, which lowers the electrolyte's melting point and improves its stability at low temperatures, thereby further enhancing the battery's low-temperature resistance.

[0018] Preferably, the organic solvent includes ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl formate in a mass ratio of 2–3:2–3:2–3:1. This invention screens organic solvents in the electrolyte according to the positive and negative electrode active materials used. The organic solvent ratio described in this invention ensures good compatibility between the electrolyte and the positive and negative electrode active materials, while also exhibiting low viscosity, thus improving the low-temperature cycle life of the battery.

[0019] Preferably, the low-temperature additive comprises vinyl sulfite and γ-butyrolactone in a mass ratio of 1:1 to 3. The addition of vinyl sulfite and γ-butyrolactone as low-temperature additives to the electrolyte in this invention can improve the stability of the SEI film, increase the solubility of lithium salts, lower the low-temperature eutectic point, and improve the low-temperature discharge performance and cycle performance of the battery.

[0020] Preferably, the mass concentration of the low-temperature additive in the electrolyte is 3-5%.

[0021] Preferably, the concentration of lithium salt in the electrolyte is 1 to 1.2 mol / L.

[0022] Therefore, the present invention has the following beneficial effects:

[0023] (1) Using FeS2-expanded graphite composite material as the negative electrode active material in lithium iron phosphate battery can improve the lithium insertion / extraction performance of negative electrode material at low temperature while ensuring good cycle stability of battery, so that lithium-ion battery pack meets the low temperature operation requirements.

[0024] (2) Based on the properties of the positive and negative electrode active materials, the organic solvent system in the electrolyte is screened, and low-temperature additives are added to the electrolyte to reduce the melting point of the electrolyte, increase the solubility of lithium salt, reduce the low-temperature eutectic point, improve the stability of the SEI film, and improve the low-temperature performance of the battery. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0027] Example 1:

[0028] A low-temperature resistant lithium-ion battery pack for energy storage power stations includes 10 lithium iron phosphate batteries connected in series. Each single lithium iron phosphate battery is a square aluminum-cased battery that includes a positive electrode containing positive electrode active material, a negative electrode containing negative electrode active material, a polyethylene separator for separating the positive and negative electrodes, and an electrolyte.

[0029] The preparation method of lithium iron phosphate batteries is as follows:

[0030] S1: Preparation of electrolyte: The electrolyte components include organic solvent, LiPF6, and low-temperature additive; the organic solvent is a mixture of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl formate in a mass ratio of 3:3:2:1; the concentration of LiPF6 in the electrolyte is 1.1 mol / L, the mass concentration of the low-temperature additive is 4%, and the low-temperature additive is ethylene sulfite and γ-butyrolactone in a mass ratio of 1:1;

[0031] S2: Preparation of positive electrode: The positive electrode slurry is coated on aluminum foil, dried and rolled to obtain the positive electrode; the positive electrode slurry includes lithium iron phosphate, carbon nanotube, and PVDF in a mass ratio of 97:3:4, and NMP is used as the solvent;

[0032] S3: Preparation of negative electrode: The negative electrode slurry is coated on copper foil, dried, and rolled to obtain the negative electrode; the negative electrode slurry includes negative electrode active material, conductive carbon nanotube, thickener CMC, binder styrene-butadiene rubber in a mass ratio of 95:3:3:3, and water as solvent;

[0033] The negative electrode active material is a FeS2-expanded graphite composite material, and its preparation method includes the following steps:

[0034] (1) Natural flake graphite was mixed with concentrated sulfuric acid and 30wt% hydrogen peroxide. The ratio of the amount of natural flake graphite, concentrated sulfuric acid and hydrogen peroxide added was 5g:14mL:1mL. After stirring evenly, the mixture was reacted at 40℃ for 60min. The resulting product was washed and dried to obtain intercalated graphite.

[0035] (2) The intercalated graphite was pre-expanded at 850℃ for 25s to obtain pre-expanded graphite;

[0036] (3) Add pre-expanded graphite to ferrous sulfate solution, with a mass ratio of pre-expanded graphite to ferrous sulfate in ferrous sulfate solution of 1:8; stir the reaction for 35 min, then add sulfuric acid solution and 30 wt% hydrogen peroxide dropwise, with a molar ratio of H2SO4 to ferrous sulfate in the added sulfuric acid solution of 0.25:1; and a molar ratio of H2O2 to ferrous sulfate in the added hydrogen peroxide solution of 1.2:1; continue stirring the reaction for 35 min; then add sodium hydroxide solution dropwise to make the pH of the system 6.3, stir the reaction at 35℃ for 35 min, and then age for 2 h. Wash and dry the obtained product to obtain hydroxyl iron oxide intercalated graphite.

[0037] (4) Hydroxy iron oxide intercalated graphite and sulfur powder are mixed at a mass ratio of 1:2.5 and reacted at 500°C for 3 hours in an argon atmosphere to obtain the FeS2-expanded graphite composite material.

[0038] S4: Stacking, assembly, and electrolyte injection: Stack the diaphragm, positive electrode, and negative electrode to form a battery cell, and weld the tabs; then install the battery cell into an aluminum shell and inject electrolyte.

[0039] S5: Formation and aging: The battery is charged with constant current to a voltage of 2.8V and a charging current of 0.1C, followed by constant voltage charging with a cutoff current of 0.05C; then aged at 45°C for 24 hours to obtain the lithium iron phosphate battery.

[0040] Example 2:

[0041] A low-temperature resistant lithium-ion battery pack for energy storage power stations includes 10 lithium iron phosphate batteries connected in series. Each single lithium iron phosphate battery is a square aluminum-cased battery that includes a positive electrode containing positive electrode active material, a negative electrode containing negative electrode active material, a polyethylene separator for separating the positive and negative electrodes, and an electrolyte.

[0042] The preparation method of lithium iron phosphate batteries is as follows:

[0043] S1: Preparation of electrolyte: The electrolyte components include organic solvent, LiPF6, and low-temperature additive; the organic solvent is a mixture of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl formate in a mass ratio of 2:3:3:1; the concentration of LiPF6 in the electrolyte is 1 mol / L, the mass concentration of the low-temperature additive is 3%, and the low-temperature additive is ethylene sulfite and γ-butyrolactone in a mass ratio of 1:2;

[0044] S2: Preparation of positive electrode: The positive electrode slurry is coated on aluminum foil, dried and rolled to obtain the positive electrode; the positive electrode slurry includes lithium iron phosphate, carbon nanotube, and PVDF in a mass ratio of 97:3:4, and NMP is used as the solvent;

[0045] S3: Preparation of negative electrode: The negative electrode slurry is coated on copper foil, dried, and rolled to obtain the negative electrode; the negative electrode slurry includes negative electrode active material, conductive carbon nanotube, thickener CMC, binder styrene-butadiene rubber in a mass ratio of 95:3:3:3, and water as solvent;

[0046] The negative electrode active material is a FeS2-expanded graphite composite material, and its preparation method includes the following steps:

[0047] (1) Natural flake graphite was mixed with concentrated sulfuric acid and 30wt% hydrogen peroxide. The ratio of the amount of natural flake graphite, concentrated sulfuric acid and hydrogen peroxide added was 4g:13mL:1mL. After stirring evenly, the mixture was reacted at 50℃ for 40min. The resulting product was washed and dried to obtain intercalated graphite.

[0048] (2) The intercalated graphite was pre-expanded at 800℃ for 30s to obtain pre-expanded graphite;

[0049] (3) Add pre-expanded graphite to ferrous sulfate solution, with a mass ratio of pre-expanded graphite to ferrous sulfate in ferrous sulfate solution of 1:7; stir the reaction for 30 min, then add sulfuric acid solution and 30 wt% hydrogen peroxide dropwise, with a molar ratio of H2SO4 to ferrous sulfate in the added sulfuric acid solution of 0.2:1; and a molar ratio of H2O2 to ferrous sulfate in the added hydrogen peroxide solution of 1.5:1; continue stirring the reaction for 30 min; then add sodium hydroxide solution dropwise to make the pH of the system 6.0, stir the reaction at 30℃ for 40 min, and then age for 1 h. Wash and dry the obtained product to obtain hydroxyl iron oxide intercalated graphite.

[0050] (4) Hydroxy iron oxide intercalated graphite and sulfur powder were mixed at a mass ratio of 1:2 and reacted at 450°C for 4 hours in an argon atmosphere to obtain the FeS2-expanded graphite composite material.

[0051] S4: Stacking, assembly, and electrolyte injection: Stack the diaphragm, positive electrode, and negative electrode to form a battery cell, and weld the tabs; then install the battery cell into an aluminum shell and inject electrolyte.

[0052] S5: Formation and aging: The battery is charged with constant current to a voltage of 3.0V and a charging current of 0.1C, followed by constant voltage charging with a cutoff current of 0.05C; then aged at 45°C for 24 hours to obtain the lithium iron phosphate battery.

[0053] Example 3:

[0054] A low-temperature resistant lithium-ion battery pack for energy storage power stations includes 10 lithium iron phosphate batteries connected in series. Each single lithium iron phosphate battery is a square aluminum-cased battery that includes a positive electrode containing positive electrode active material, a negative electrode containing negative electrode active material, a polyethylene separator for separating the positive and negative electrodes, and an electrolyte.

[0055] The preparation method of lithium iron phosphate batteries is as follows:

[0056] S1: Preparation of electrolyte: The electrolyte components include organic solvent, LiPF6, and low-temperature additive; the organic solvent is a mixture of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl formate in a mass ratio of 3:2:3:1; the concentration of LiPF6 in the electrolyte is 1.2 mol / L, the mass concentration of the low-temperature additive is 5%, and the low-temperature additive is ethylene sulfite and γ-butyrolactone in a mass ratio of 1:3;

[0057] S2: Preparation of positive electrode: The positive electrode slurry is coated on aluminum foil, dried and rolled to obtain the positive electrode; the positive electrode slurry includes lithium iron phosphate, carbon nanotube, and PVDF in a mass ratio of 97:3:4, and NMP is used as the solvent;

[0058] S3: Preparation of negative electrode: The negative electrode slurry is coated on copper foil, dried, and rolled to obtain the negative electrode; the negative electrode slurry includes negative electrode active material, conductive carbon nanotube, thickener CMC, binder styrene-butadiene rubber in a mass ratio of 95:3:3:3, and water as solvent;

[0059] The negative electrode active material is a FeS2-expanded graphite composite material, and its preparation method includes the following steps:

[0060] (1) Natural flake graphite was mixed with concentrated sulfuric acid and 30wt% hydrogen peroxide. The ratio of the amount of natural flake graphite, concentrated sulfuric acid and hydrogen peroxide added was 6g:15mL:1mL. After stirring evenly, the mixture was reacted at 40℃ for 60min. The resulting product was washed and dried to obtain intercalated graphite.

[0061] (2) The intercalated graphite was pre-expanded at 900℃ for 20s to obtain pre-expanded graphite;

[0062] (3) Add pre-expanded graphite to ferrous sulfate solution, with a mass ratio of pre-expanded graphite to ferrous sulfate in ferrous sulfate solution of 1:9; stir the reaction for 40 min, then add sulfuric acid solution and 30 wt% hydrogen peroxide dropwise, with a molar ratio of H2SO4 to ferrous sulfate in the added sulfuric acid solution of 0.3:1; and a molar ratio of H2O2 to ferrous sulfate in the added hydrogen peroxide solution of 1:1; continue stirring the reaction for 40 min; then add sodium hydroxide solution dropwise to make the pH of the system 6.9, stir the reaction at 40℃ for 30 min, and then age for 2 h. Wash and dry the obtained product to obtain hydroxyl iron oxide intercalated graphite.

[0063] (4) Hydroxy iron oxide intercalated graphite and sulfur powder were mixed at a mass ratio of 1:3 and reacted at 550°C for 2 hours in an argon atmosphere to obtain the FeS2-expanded graphite composite material.

[0064] S4: Stacking, assembly, and electrolyte injection: Stack the diaphragm, positive electrode, and negative electrode to form a battery cell, and weld the tabs; then install the battery cell into an aluminum shell and inject electrolyte.

[0065] S5: Formation and aging: The battery is charged with constant current to a voltage of 3.3V and a charging current of 0.1C, followed by constant voltage charging with a cutoff current of 0.05C; then aged at 45°C for 24 hours to obtain the lithium iron phosphate battery.

[0066] Example 4:

[0067] In the lithium iron phosphate battery of Example 4, the organic solvent of the electrolyte is a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate in a mass ratio of 3:3:2; the rest are the same as in Example 1.

[0068] Example 5:

[0069] In the lithium iron phosphate battery of Example 5, the low-temperature additive in the electrolyte is γ-butyrolactone; the rest are the same as in Example 1.

[0070] Example 6:

[0071] In the lithium iron phosphate battery of Example 6, the low-temperature additive in the electrolyte is vinyl sulfite; the rest are the same as in Example 1.

[0072] Comparative Example 1 (No FeS2 added to the negative electrode active material):

[0073] In Comparative Example 1, the negative electrode active material of the lithium iron phosphate battery is expanded graphite, and its preparation method is as follows:

[0074] (1) Natural flake graphite was mixed with concentrated sulfuric acid and 30wt% hydrogen peroxide. The ratio of the amount of natural flake graphite, concentrated sulfuric acid and hydrogen peroxide added was 6g:15mL:1mL. After stirring evenly, the mixture was reacted at 40℃ for 60min. The resulting product was washed and dried to obtain intercalated graphite.

[0075] (2) The intercalated graphite was expanded at 900℃ for 20s to obtain expanded graphite;

[0076] Everything else is the same as in Example 1.

[0077] Comparative Example 2 (without pre-intercalation of natural graphite):

[0078] In Comparative Example 2, the negative electrode active material of the lithium iron phosphate battery is a FeS2-graphite composite material, and its preparation method includes the following steps:

[0079] (1) Natural flake graphite was expanded at 900℃ for 20s to obtain pre-expanded graphite;

[0080] (2) Pre-expanded graphite was added to ferrous sulfate solution, with a mass ratio of 1:8 between the pre-expanded graphite and ferrous sulfate in the solution; the mixture was stirred for 35 min, and then sulfuric acid solution and 30 wt% hydrogen peroxide were added dropwise. The molar ratio of H2SO4 to ferrous sulfate in the added sulfuric acid solution was 0.25:1; the molar ratio of H2O2 to ferrous sulfate in the added hydrogen peroxide was 1.2:1; the mixture was stirred for another 35 min; sodium hydroxide solution was added dropwise to make the pH of the system 6.3; the mixture was stirred at 35 °C for 35 min and then aged for 2 h. The resulting product was washed and dried to obtain hydroxyl iron oxide-graphite composite material.

[0081] (3) The hydroxyl iron oxide-graphite composite material and sulfur powder were mixed at a mass ratio of 1:2.5 and reacted at 500°C for 3 hours in an argon atmosphere to obtain the FeS2-graphite composite material.

[0082] Everything else is the same as in Example 1.

[0083] The lithium iron phosphate batteries in the above embodiments and comparative examples were subjected to charge-discharge cycle tests at different temperatures to determine their rate output characteristics and charge-discharge cycle stability. The results are shown in Table 1. The charge-discharge voltage range was 1.5–2.8V, and the constant current charging rate was 0.5C.

[0084] Table 1: Performance of lithium iron phosphate batteries based on test results.

[0085]

[0086] As shown in Table 1, the lithium iron phosphate batteries prepared using the materials of this invention in Examples 1-3 exhibit good cycle stability, with a capacity retention rate of over 85% after 5000 cycles at room temperature. Simultaneously, the batteries also demonstrate good low-temperature performance, maintaining a capacity retention rate of over 75% after 5000 cycles at -20°C and over 70% at -40°C. In Examples 4-6, changes to the composition of the organic solvent or the low-temperature additives in the electrolyte resulted in a decrease in low-temperature cycle stability compared to Example 1, with a capacity retention rate of less than 70% after 5000 cycles at -40°C.

[0087] In Comparative Example 1, expanded graphite was used as the negative electrode active material. Since the expanded graphite was not combined with FeS2, the battery's cycle performance and low-temperature performance were significantly reduced. This indicates that fixing FeS2 within the expanded graphite layers is beneficial for improving the battery's cycle stability and low-temperature performance. In Comparative Example 2, the negative electrode active material was not pre-intercalated with natural graphite during preparation. FeS2 could not enter the interlayer of the graphite material, and the layered structure of graphite could not limit the volume expansion of FeS2, resulting in a significant decrease in the battery's cycle stability compared to Example 1.

Claims

1. A low-temperature resistant lithium-ion battery pack for an energy storage power station, characterized in that, The invention comprises several lithium iron phosphate batteries connected in series. Each lithium iron phosphate battery includes a positive electrode containing a positive active material, a negative electrode containing a negative active material, a separator for separating the positive and negative electrodes, and an electrolyte. The positive active material is lithium iron phosphate, and the negative active material is FeS2-expanded graphite composite material. The preparation method of the FeS2-expanded graphite composite material includes the following steps: (1) Natural flake graphite is mixed with concentrated sulfuric acid and hydrogen peroxide and reacted. The resulting product is washed and dried to obtain intercalated graphite. (2) Pre-expand intercalated graphite at 800~900℃ for 20~30s to obtain pre-expanded graphite; (3) Add pre-expanded graphite to ferrous sulfate solution and stir for 30-40 min. Then add sulfuric acid solution and hydrogen peroxide dropwise and continue stirring for 30-40 min. Then add sodium hydroxide solution dropwise and stir for 30-40 min. After aging for 1-3 h, wash and dry the product to obtain hydroxyl iron oxide intercalated graphite. (4) Mix iron hydroxyl oxide intercalated graphite and sulfur powder, and react them at 450~550℃ for 2~4h in an inert atmosphere to obtain the FeS2-expanded graphite composite material.

2. The low-temperature resistant lithium-ion battery pack for energy storage power stations according to claim 1, characterized in that, The hydrogen peroxide concentration in step (1) is 28-30%, and the ratio of the amount of natural flake graphite, concentrated sulfuric acid and hydrogen peroxide added is 4-6g:13-15mL:1mL.

3. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 1, characterized in that, In step (3), the mass ratio of pre-expanded graphite to ferrous sulfate in the ferrous sulfate solution is 1:7~9; the molar ratio of H2SO4 to ferrous sulfate in the added sulfuric acid solution is 0.2~0.3:1; and the molar ratio of H2O2 to ferrous sulfate in the added hydrogen peroxide is 1~1.5:

1.

4. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 1 or 3, characterized in that, In step (3), the pH of the system after adding sodium hydroxide solution is 6-7, and the stirring reaction temperature after adding sodium hydroxide solution is 30-40℃.

5. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 1, characterized in that, In step (4), the mass ratio of iron hydroxyl oxide intercalated graphite to sulfur powder is 1:2~3.

6. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 1, characterized in that, The electrolyte comprises organic solvents, lithium salts, and low-temperature additives.

7. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 6, characterized in that, The organic solvents include ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl formate in a mass ratio of 2~3:2~3:2~3:

1.

8. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 6, characterized in that, The low-temperature additives include vinyl sulfite and γ-butyrolactone in a mass ratio of 1:1 to 3.

9. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 8, characterized in that, The electrolyte contains a low-temperature additive at a mass concentration of 3-5%.

10. A low-temperature resistant lithium-ion battery pack for an energy storage power station according to claim 6, characterized in that, The concentration of lithium salt in the electrolyte is 1~1.2 mol / L.

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