Method for improving wide temperature characteristics of lithium iron phosphate battery

Abstract

This invention discloses a method for improving the wide-temperature characteristics of lithium iron phosphate batteries. Specifically, electrolyte 1 is injected into a lithium iron phosphate cell, and after being left to stand at 40-50°C for 12-36 hours, negative pressure pre-formation is performed. Electrolyte 2 is then injected into the pre-formed lithium iron phosphate cell, and after sealing, it is left to stand at 0-10°C for 12-36 hours before secondary formation to obtain the lithium iron phosphate battery. In electrolyte 1, propylene carbonate, when added as a co-solvent, can more effectively inhibit the crystallization of ethylene carbonate, improving the low-temperature performance of the lithium battery. The gas generated in the reaction is discharged under negative pressure and then injected into electrolyte 2. Ethylene sulfate has two highly negative S=O bonds, which can react with Li... + A strong bond, low-temperature storage and low-temperature formation can promote electrolyte wetting of the battery cell and ensure that ethylene sulfate does not degrade. Two-stage electrolyte injection based on the characteristics of different additives can effectively improve the high and low temperature performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for improving the wide-temperature characteristics of lithium iron phosphate batteries. Background Technology

[0002] As the application scope of lithium iron phosphate (LFP) batteries continues to expand, the requirements for their wide temperature range applications are also increasing. This means LFP batteries must be able to discharge at low temperatures and withstand high-temperature storage. Under low-temperature conditions, conventional electrolyte lithium-ion batteries experience increased viscosity, decreased conductivity, and increased electrode interface resistance, resulting in low charge / discharge capacity, lithium plating at the negative electrode, and decreased safety performance. At high temperatures, lithium salts and solvents decompose, causing battery gas production, which affects both electrical and safety performance. Special lithium salts, solvents, and additives can improve the high and low temperature performance of lithium-ion batteries, but solvents and additives suitable for specific effective low temperatures can negatively impact high-temperature performance; therefore, high-temperature and low-temperature performance are incompatible. Summary of the Invention

[0003] To address the incompatibility between high-temperature and low-temperature performance in existing lithium iron phosphate batteries, this invention provides a method to improve the wide-temperature characteristics of lithium iron phosphate batteries by enhancing the synergistic effect of electrolyte additives in both low-temperature and high-temperature applications, thereby improving the high and low temperature performance of lithium iron phosphate batteries.

[0004] This invention is achieved through the following technical solution: A method for improving the wide-temperature characteristics of lithium iron phosphate batteries includes the following steps: (1) Inject electrolyte 1 into the lithium iron phosphate cell, and then perform negative pressure pre-forming after standing at 40~50℃ for 12~36h; (2) Electrolyte 2 is injected into the lithium iron phosphate cell after negative pressure pre-formation. After sealing, it is placed at 0~10℃ for 12~36h and then subjected to secondary formation to obtain lithium iron phosphate battery.

[0005] The electrolyte 1 comprises lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium difluorooxalate borate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, and ethylene carbonate. The electrolyte 2 comprises lithium hexafluorophosphate, lithium difluorosulfonyl imide, dimethyl carbonate, methyl ethyl carbonate, vinylene carbonate, and vinyl sulfate.

[0006] Further, the electrolyte 1 comprises the following components in parts by weight: 7-9 parts lithium hexafluorophosphate, 6-8 parts lithium difluorosulfonylimide salt, 0.5-2 parts lithium difluorooxalate borate, 20-40 parts dimethyl carbonate, 20-30 parts methyl ethyl carbonate, 2-6 parts propylene carbonate, and 20-30 parts ethylene carbonate.

[0007] Furthermore, the electrolyte 2 comprises the following components in parts by weight: 4-6 parts lithium hexafluorophosphate, 4-6 parts lithium difluorosulfonyl imide, 40-60 parts dimethyl carbonate, 30-50 parts methyl ethyl carbonate, 2-4 parts vinylene carbonate, and 1-2 parts vinyl sulfate.

[0008] Furthermore, the pre-formation conditions in steps (1) and (2) are negative pressure -40KPa to -70KPa and temperature 60℃ to 80℃; the secondary formation conditions in step (2) are negative pressure -40KPa to -70KPa and temperature 10℃ to 20℃.

[0009] Furthermore, the lithium iron phosphate battery cell mentioned in step (1) is a baked lithium iron phosphate battery cell.

[0010] This invention first injects electrolyte 1 into a lithium iron phosphate battery cell. Ethylene carbonate (EC) in electrolyte 1 plays a crucial role in stabilizing the SEI formation of the negative electrode. However, ethylene carbonate has a high melting point and is prone to solidification. When ethylene carbonate crystallizes, it reduces the conductivity of the remaining liquid phase and may even clog electrode pores, leading to a decrease in capacity. Propylene carbonate (PC), when added as a co-solvent, can more effectively inhibit ethylene carbonate (EC) crystallization and improve the low-temperature performance of the lithium battery. After injecting electrolyte 1, the battery cell is placed at high temperature to allow for more thorough wetting of the electrolyte 1 within the battery. Then, negative pressure pre-formation is performed. The gas generated by the reaction of the propylene carbonate (PC)-based electrolyte in the battery is discharged under negative pressure, and then electrolyte 2 is injected. Ethylene sulfate (DTD) in electrolyte 2 has two highly negative S=O bonds and can react with Li... + The strong bond between propylene carbonate (PC) and vinyl sulfate (DTD) allows for excellent synergy, resulting in improved battery performance. After electrolyte injection, a low-temperature resting period is performed. Because DTD has an unstable structure and is prone to decomposition and failure at high temperatures, this low-temperature resting and low-temperature formation process promotes electrolyte wetting of the cell while preventing DTD deterioration. Two injection processes, tailored to the characteristics of different additives, effectively improve the battery's high and low temperature performance.

[0011] Beneficial effects The present invention provides a method for improving the wide-temperature characteristics of lithium iron phosphate batteries. By setting different electrolyte compositions and resting temperatures, and by employing a process of double electrolyte injection, negative pressure pre-formation, and secondary formation, the synergistic effect of low-temperature and high-temperature electrolyte additives is enhanced, thereby improving the high-temperature and low-temperature performance of lithium iron phosphate batteries. Attached Figure Description

[0012] Figure 1 The discharge curve of the 54173200-200Ah-3.2V lithium iron phosphate battery at a low temperature of -20℃ and a current of 100A. Figure 2 The discharge curve of a 54173200-200Ah-3.2V lithium iron phosphate battery stored at 85℃ for 28 days. Detailed Implementation

[0013] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0014] Example 1 Electrolyte composition: Electrolyte 1: Electrolyte 1 is composed of the following components in parts by weight: 8 parts lithium hexafluorophosphate (LiPF6), 7 parts lithium difluorosulfonyl imide (LiFSI), 1 part lithium difluorooxalate borate (LiODFB), 30 parts dimethyl carbonate (DMC), 25 parts methyl ethyl carbonate (EMC), 5 parts propylene carbonate (PC), and 24 parts ethylene carbonate (EC). Electrolyte 2: Electrolyte 2 is composed of the following components in parts by weight: 5% lithium hexafluorophosphate (LiPF6), 5 parts lithium difluorosulfonyl imide (LiFSI), 50 parts dimethyl carbonate (DMC), 35 parts methyl ethyl carbonate (EMC), 3.5 parts vinylene carbonate (VC), and 1.5 parts vinyl sulfate (DTD). Methods to improve the wide-temperature characteristics of lithium iron phosphate batteries: (1) Inject 600g of electrolyte 1 into the baked 54173200-200Ah-3.2V lithium iron phosphate cell, and after standing at 45℃ for 12h, perform negative pressure pre-formation. The formation conditions are negative pressure -60Kpa, temperature 80℃, charging current 20A, and constant current charging time 6h. (2) 200g of electrolyte 2 was injected into the lithium iron phosphate cell after negative pressure pre-formation. After sealing, it was placed at 10℃ for 12h and then subjected to secondary negative pressure formation. The formation conditions were negative pressure -60Kpa, temperature 15℃, charging current 10A, constant current charging time 8h, to obtain lithium iron phosphate battery.

[0015] The capacity retention of the prepared lithium iron phosphate battery was tested at low temperature (-20℃) and high temperature (85℃). The discharge curve of the 54173200-200Ah-3.2V battery at low temperature (-20℃) and 100A current is shown below. Figure 1 As shown, the current-discharge curve of the 54173200-200Ah-3.2V battery after 28 days of high-temperature storage at 85℃ is as follows. Figure 2 As shown, by Figure 1 and Figure 2It can be seen that the 54173200-200Ah-3.2V battery can achieve a discharge rate of 88% at a low temperature of -20℃ and a capacity retention rate of 89% after 28 days of high storage at 85℃.

[0016] Comparative Example 1 A traditional process for preparing lithium iron phosphate batteries involves injecting 600g of electrolyte into a baked 54173200-200Ah-3.2V lithium iron phosphate cell. The electrolyte consists of the following components by weight: 17 parts lithium hexafluorophosphate (LiPF6), 2 parts vinylene carbonate (VC), and 1 part ethylene sulfate (DTD); 30 parts dimethyl carbonate (DMC), 25 parts methyl ethyl carbonate (EMC), 5 parts propylene carbonate (PC), and 20% ethylene carbonate (EC). After resting at 45°C for 12 hours, a negative pressure pre-formation is performed under the following conditions: negative pressure -60 kPa, temperature 80°C, constant current charging at 20A for 6 hours, followed by constant current charging at 10A for 8 hours, to obtain the lithium iron phosphate battery.

[0017] The capacity retention of the prepared lithium iron phosphate battery was tested at low temperature (-20℃) and high temperature (85℃). The discharge curve of the 54173200-200Ah-3.2V battery at low temperature (-20℃) and 100A current is shown below. Figure 1 As shown, the current-discharge curve of the 54173200-200Ah-3.2V battery after 28 days of high-temperature storage at 85℃ is as follows. Figure 2 As shown, by Figure 1 and Figure 2 It can be seen that the 54173200-200Ah-3.2V battery can achieve a discharge rate of 67% at a low temperature of -20℃ and a capacity retention rate of 82% after 28 days of storage at 85℃.

[0018] Example 1 shows that the 54173200-200Ah-3.2V battery manufactured at low temperature (-20℃) with a 100A current discharge rate and a capacity retention rate after 28 days of storage at 85℃ are significantly higher than those of Comparative Example 1.

Claims

1. A method for improving the wide-temperature characteristics of lithium iron phosphate batteries, characterized in that, Includes the following steps: (1) Inject electrolyte 1 into the lithium iron phosphate cell, and then perform negative pressure pre-forming after standing at 40~50℃ for 12~36h; (2) Electrolyte 2 is injected into the lithium iron phosphate cell after negative pressure pre-formation. After sealing, it is placed at 0~10℃ for 12~36h and then subjected to secondary formation to obtain lithium iron phosphate battery. The pre-formation conditions in steps (1) and (2) are negative pressure -40KPa to -70KPa and temperature 60℃ to 80℃; the secondary formation conditions in step (2) are negative pressure -40KPa to -70KPa and temperature 10℃ to 20℃. The electrolyte 1 comprises lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium difluorooxalate borate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, and ethylene carbonate. The electrolyte 2 comprises lithium hexafluorophosphate, lithium difluorosulfonyl imide, dimethyl carbonate, methyl ethyl carbonate, vinylene carbonate, and vinyl sulfate.

2. The method for improving the wide-temperature characteristics of lithium iron phosphate batteries according to claim 1, characterized in that, The electrolyte 1 comprises the following components in parts by weight: 7-9 parts lithium hexafluorophosphate, 6-8 parts lithium difluorosulfonylimide salt, 0.5-2 parts lithium difluorooxalate borate, 20-40 parts dimethyl carbonate, 20-30 parts methyl ethyl carbonate, 2-6 parts propylene carbonate, and 20-30 parts ethylene carbonate.

3. The method for improving the wide-temperature characteristics of lithium iron phosphate batteries according to claim 1, characterized in that, The electrolyte 2 comprises the following components in parts by weight: 4-6 parts lithium hexafluorophosphate, 4-6 parts lithium difluorosulfonyl imide, 40-60 parts dimethyl carbonate, 30-50 parts methyl ethyl carbonate, 2-4 parts vinylene carbonate, and 1-2 parts vinyl sulfate.

4. The method for improving the wide-temperature characteristics of lithium iron phosphate batteries according to claim 1, characterized in that, The lithium iron phosphate battery cell mentioned in step (1) is a baked lithium iron phosphate battery cell.

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