Formation method of a square aluminum shell lithium iron phosphate battery

Abstract

The present invention relates to the field of lithium iron phosphate batteries, specifically to a formation method for a square aluminum shell lithium iron phosphate battery. Before formation, the battery is aged by statically standing at a high temperature of 45 - 50°C. During formation, a negative pressure method at a high temperature (40 - 80°C) is adopted, which can effectively shorten the formation time and improve production efficiency. At the same time, it can ensure that the positive and negative electrode interfaces of the battery are flat and in uniform contact, which is beneficial to the uniform distribution of electrons. The pole piece and the separator of the lithium battery prepared by the formation method of the present invention are in good fit, without bubbles, the formation interface is good, the internal resistance is small, the SEI film is formed densely, the electrolyte will not be lost, and the performance is excellent.

Description

[0001] The present invention relates to the field of lithium iron phosphate batteries, and in particular to a formation method for a square aluminum shell lithium iron phosphate battery. Background Art

[0002] The properties of the SEI film greatly affect the performance of lithium-ion batteries. During the formation process, the amount of SEI film formed represents the amount of lithium consumed in the lithium-ion battery, directly determining the capacity of the lithium-ion battery. Therefore, during the formation of the SEI film, the less lithium consumed, the better, that is, the smaller the irreversible capacity loss. During the cycling process of lithium-ion batteries, if the electron isolation property of the SEI film is poor, electrons will come into contact with the electrolyte, and the reduction reaction will proceed further, consuming the lithium content in the battery. The SEI film is continuously formed, resulting in poor cycle life of the lithium-ion battery. When the SEI film is incompletely formed or decomposed, the lithium embedded in the negative electrode will react with the electrolyte and the binder to generate heat, and the reaction heat increases with the increase of the lithium intercalation amount, greatly affecting the safety of the battery. The SEI film has a direct or indirect impact on battery performance. Forming an SEI film that meets the requirements is extremely helpful for improving battery performance.

[0003] The formation temperature affects the reaction rate of the chemical reaction for forming the SEI film and the corresponding reaction products on the one hand; when the temperature rises, some components of the SEI film will decompose, causing the SEI film to rupture and further consuming the lithium stock to form a new SEI film. During the formation of the SEI film, EC directly generates ROCO2Li through a reduction reaction, and then ROCO2Li is converted into Li2CO3 while generating gas. The higher the temperature, the more intense this process is, the more gas is generated, and thus the more defect points are formed on the SEI film, and the thicker the formed SEI film. This provides more paths for the co-intercalation of lithium ions and solvated solvent molecules. Therefore, the passivation of the SEI film on graphite is further deepened, and the irreversible capacity loss of the battery increases.

[0004] CN202120716582.9 provides a vacuum liquid injection device for lithium battery processing, including a box body. Inside the box body, an injection assembly and a tray are sequentially arranged from top to bottom. The outer diameter of the liquid injection pipe is smaller than the aperture of the liquid injection hole. The piston rod pressure adjustment cavity is divided into a first pressure cavity and a second pressure cavity. The first pressure cavity is communicated with the liquid storage cavity, and the second pressure cavity is communicated with the adsorption cavity of the elastic adsorbent through a connecting pipe. Thus, during the liquid supply process, the gas in the original lithium battery liquid storage cavity is discharged into the second pressure cavity. When the liquid injection is completed, the pressure in the second pressure cavity is reduced by moving the piston, thereby removing the bubbles in the electrolyte in the lithium battery liquid injection cavity.

[0005] The liquid injection of lithium-ion batteries is mostly carried out under the condition of surface atmospheric pressure. When injecting liquid into lithium-ion batteries using a liquid injection tube, although the liquid can enter the interior of the lithium-ion batteries, due to the factors of the internal structure of the lithium-ion batteries, there are still air bubbles inside the lithium-ion batteries, resulting in incomplete liquid injection, affecting the quality of the batteries, and also affecting the completion of the formation process. Summary of the Invention

[0006] Aiming at the deficiencies existing in the above-mentioned prior art, the purpose of the present invention is to disclose a formation method for a square aluminum shell lithium iron phosphate battery. The battery pole pieces and diaphragms obtained by the formation method of the lithium battery of the present invention are well adhered, without air bubbles, have a good formation interface, small internal resistance, a dense SEI film is formed, the electrolyte will not be lost, and the performance is excellent.

[0007] The above invention purpose is achieved through the following technical solutions:

[0008] A formation method for a square aluminum shell lithium iron phosphate battery includes the following steps:

[0009] S1: High-temperature standing after liquid injection;

[0010] S2: Shelving: Install the lithium iron phosphate power battery on the needle bed formation cabinet, fix it with battery adhesive nails, shelve for 5 - 10 minutes, turn on the vacuum, control the ambient temperature, and evacuate the gas inside the battery under negative pressure to make the battery core closer;

[0011] S3: Constant current charging: After shelving, charge the battery at a current of 0.01 - 0.05C for 90 - 120 minutes until the charged state is activated; turn on the vacuum, control the ambient temperature; ensure that the SEI film fully reacts to generate a stable SEI film, make all the generated gases react out, reduce the polarization phenomenon, and then evacuate it through the vacuum. Increase the ionic conductivity and the fluidity of the active material through high temperature;

[0012] S4: Secondary shelving: After constant current charging is completed, shelve the battery for 5 - 10 minutes, turn on the vacuum, control the ambient temperature;

[0013] S5: Secondary charging: After secondary shelving is completed, charge the battery at a current of 0.1 - 0.2C for 120 - 150 minutes until the high-voltage state; evacuate the vacuum, control the ambient temperature; take the battery out of the cabinet, and fix and seal the liquid injection hole with battery adhesive nails;

[0014] S6: Supplementary injection of electrolyte: Pull out the battery adhesive nails, inject liquid. The negative pressure formation will take away all the generated gases, and at the same time will evacuate part of the electrolyte. Supplementary injection of liquid to ensure the amount of electrolyte, and laser weld to seal the liquid injection hole to make the battery life longer;

[0015] S7: Secondary high-temperature standing and aging;

[0016] S8: Constant current discharge: Assemble the lithium iron phosphate power battery on the pin bed formation cabinet and let it stand for 5 - 10 min. Control the ambient temperature at 40 - 80°C. After standing, discharge the battery at a constant current with a current of 0.2 - 0.5C until the voltage reaches 3.0 - 3.3V.

[0017] Further, in S1 and S7, the high-temperature standing temperature is 45 - 50°C, and the standing time is 24 - 72 hours.

[0018] Further, in S2, S3, S4, and S5, the opening vacuum degree is -0.05 to -0.095 MPa, and the ambient temperature is controlled at 40 - 80°C.

[0019] Further, in S3 and S5, the upper limit of the charging voltage is 3.65V or 3.85V.

[0020] Further, in S6, the liquid injection volume is 8 - 11% of the total liquid injection volume.

[0021] Further, in S8, the depth of constant current discharge is 25 - 40%.

[0022] Further, an antifoaming agent for liquid injection is added to the electrolyte, and the addition amount is 0.01 - 0.05% of the mass percentage content of the electrolyte.

[0023] Further, the preparation method of the antifoaming agent for liquid injection is as follows:

[0024] According to the mass parts, slowly add 14 - 22 parts of ethylene glycol bis(3-mercaptopropionate), 0.1 - 1.5 parts of 1-vinyl-3-butylimidazolium bromide, 4 - 11 parts of glycidyl ether acrylate, and 2.2 - 3.6 parts of catalyst into 100 - 200 parts of acetonitrile. Heat up and stir for reaction, and remove acetonitrile by vacuum distillation to obtain an antifoaming agent for liquid injection.

[0025] Further, the catalyst is sodium methoxide.

[0026] Further, the reaction temperature is 70 - 80°C, and the reaction time is 100 - 300 min.

[0027] Beneficial technical effects:

[0028] (1) The formation process of the present invention includes standing, constant current charging, secondary standing, and constant current discharge. Constant current charging ensures that the SEI film reacts fully, allows all gases to react out, reduces the polarization phenomenon, and then removes them by vacuum pumping. High temperature is used to increase the ionic conductivity and the mobility of active substances. Constant current discharge ages the battery at 25 - 40% SOC, ensuring that side reactions during battery aging are reduced, the positive and negative electrodes fully absorb the electrolyte, and the battery capacity meets the requirements.

[0029] (2) Before formation, the present invention adopts static aging at a high temperature of 50-70 °C, and the formation adopts a negative pressure method at a high temperature (50-60 °C); high-temperature, high-pressure and high-current formation can effectively shorten the formation time, improve production efficiency, apply a certain pressure to the battery, which is beneficial to shortening the diffusion distance of lithium ions, and at the same time can ensure that the positive and negative electrode interfaces of the battery are flat and in uniform contact, which is beneficial to the uniform distribution of electrons; during the formation process, applying a high temperature can reduce the viscosity of the electrolyte, accelerate the diffusion of ions, and ensure that electrons and ions quickly combine under a high current.

[0030] (3) The addition of the defoaming agent for liquid injection can prevent the generation of bubbles during the liquid injection process. The pole piece and the separator of the lithium battery prepared by the lithium battery formation method of the present invention are well bonded, without bubbles, the formation interface is good, the internal resistance is small, the SEI film is formed densely, the electrolyte will not be lost, and the performance is excellent. Detailed implementation mode

[0031] Defoaming agent 1 for liquid injection

[0032] 14 g of ethylene glycol bis(3-mercaptopropionate), 0.1 g of 1-vinyl-3-butylimidazolium bromide, 4 g of glycidyl ether acrylate, and 2.2 g of sodium methoxide were slowly added to 100 g of acetonitrile. After heating to 70 °C and stirring for 100 min, acetonitrile was removed by vacuum distillation; Defoaming agent 1 for liquid injection was obtained.

[0033] Defoaming agent 2 for liquid injection

[0034] 22 g of ethylene glycol bis(3-mercaptopropionate), 1.5 g of 1-vinyl-3-butylimidazolium bromide, 11 g of glycidyl ether acrylate, and 3.6 g of sodium methoxide were slowly added to 200 g of acetonitrile. After heating to 80 °C and stirring for 300 min, acetonitrile was removed by vacuum distillation; A defoaming agent 2 for liquid injection was obtained.

[0035] Example 1

[0036] A formation method for a square aluminum shell lithium iron phosphate battery, comprising the following steps:

[0037] S1: High-temperature static after liquid injection: temperature 45 °C, time 72 hours, the defoaming agent 1 for liquid injection was added to the electrolyte, and the addition amount was 0.01% of the mass percentage content of the electrolyte;

[0038] S2: Shelving: The lithium iron phosphate power battery was installed on a needle bed formation cabinet, fixed with battery adhesive nails, shelved for 5 min, the vacuum was -0.05 MPa, the ambient temperature was controlled at 40 °C, and the internal gas of the battery was pumped out under negative pressure to make the battery core closer;

[0039] S3: Constant current charging: After the rest is completed, charge the battery at a current of 0.01C for 90 minutes until the charged state is activated, with a voltage upper limit of 3.65V; turn on the vacuum to -0.05MPa, and control the ambient temperature at 40°C; ensure that the SEI film reacts fully to form a stable SEI film, allowing all the generated gases to react and reducing the polarization phenomenon, and then evacuate them through the vacuum. Increase the ionic conductivity and the mobility of the active material by increasing the temperature.

[0040] S4: Second rest: After the constant current charging is completed, rest the battery for 5 minutes, turn on the vacuum to -0.05MPa, and control the ambient temperature at 40°C;

[0041] S5: Second charging: After the second rest is completed, charge the battery at a current of 0.1C for 120 minutes until the high-voltage state is reached, with a voltage upper limit of 3.65V; evacuate the air to a vacuum degree of -0.05MPa, and control the ambient temperature at 40°C; take it out of the cabinet and use battery glue nails to fix and seal the injection holes;

[0042] S6: Supplementary injection of electrolyte: Pull out the battery glue nails, inject the liquid, and the injection volume is 8% of the total injection volume. The negative pressure formation will take away all the generated gases and also evacuate part of the electrolyte. Supplementary injection is carried out to ensure the amount of electrolyte, and then laser weld to seal the injection holes to make the battery life longer;

[0043] S7: Second high-temperature static aging: Temperature 45°C, time 72 hours;

[0044] S8: Constant current discharge: Assemble the lithium iron phosphate power battery on the pin bed formation cabinet and rest for 5 minutes, control the ambient temperature at 80°C. After the rest is completed, discharge the battery at a current of 0.2C until the voltage reaches 3.0V, and the constant current discharge depth is 25%.

[0045] Example 2

[0046] A formation method for a square aluminum shell lithium iron phosphate battery, comprising the following steps:

[0047] S1: High-temperature static after injection: Temperature 45°C, time 48 hours. Add defoaming agent 1 for injection to the electrolyte, and the addition amount is 0.03% of the mass percentage content of the electrolyte;

[0048] S2: Rest: Install the lithium iron phosphate power battery on the pin bed formation cabinet, fix it with battery glue nails, rest for 5 minutes, turn on the vacuum to -0.06MPa, control the ambient temperature at 50°C, and evacuate the gas inside the battery under negative pressure to make the battery core more compact;

[0049] S3: Constant current charging: After the standby is completed, the battery is charged with a constant current of 0.02C for 120 minutes until the charged state is activated, with a voltage upper limit of 3.65V; the vacuum is turned on to -0.06MPa, and the ambient temperature is controlled at 50°C; ensure that the SEI film reacts fully to generate a stable SEI film, allow all the generated gases to react, reduce the polarization phenomenon, and then evacuate them through vacuum, and increase the ionic conductivity and the mobility of the active material by high temperature.

[0050] S4: Second standby: After the constant current charging is completed, the battery is standby for 5 minutes, the vacuum is turned on to -0.06MPa, and the ambient temperature is controlled at 50°C;

[0051] S5: Second charging: After the second standby is completed, the battery is charged with a constant current of 0.1C for 150 minutes until the high-voltage state, with a voltage upper limit of 3.65V; evacuate to a vacuum degree of -0.06MPa, and the ambient temperature is controlled at 50°C; take it out of the cabinet and use battery glue nails to fix and seal the injection holes;

[0052] S6: Supplementary injection of electrolyte: Pull out the battery glue nails, inject liquid, and the injection volume is 9% of the total injection volume. The negative pressure formation will take away all the generated gases and at the same time take away part of the electrolyte. Supplementary injection is carried out to ensure the amount of electrolyte, and the injection holes are sealed by laser welding to make the battery life longer;

[0053] S7: Second high-temperature standing and aging: The temperature is 45°C and the time is 48 hours;

[0054] S8: Constant current discharging: Assemble the lithium iron phosphate power battery on the needle bed formation cabinet and standby for 5 minutes. The ambient temperature is controlled at 40°C. After the standby is completed, the battery is discharged with a constant current of 0.2C. The constant current discharging is carried out until 3.2V, and the constant current discharging depth is 30%.

[0055] Example 3

[0056] A formation method for a square aluminum shell lithium iron phosphate battery, comprising the following steps:

[0057] S1: High-temperature standing after liquid injection: The temperature is 45°C and the time is 24 hours. Defoaming agent 1 for liquid injection is added to the electrolyte, and the addition amount is 0.05% of the mass percentage content of the electrolyte;

[0058] S2: Standby: Assemble the lithium iron phosphate power battery on the needle bed formation cabinet, fix it with battery glue nails, standby for 10 minutes, turn on the vacuum to -0.07MPa, and control the ambient temperature at 60°C. Evacuate the gas inside the battery under negative pressure to make the battery core closer;

[0059] S3: Constant current charging: After the standby is completed, the battery is charged at a current of 0.03C to the activated charged state with a voltage upper limit of 3.65V; the vacuum is turned on to -0.07MPa, and the ambient temperature is controlled at 60°C; ensure that the SEI film reacts fully to form a stable SEI film, allowing all the generated gases to react and reducing the polarization phenomenon, and then evacuating them through the vacuum. Increase the ionic conductivity and the mobility of the active material by raising the temperature.

[0060] S4: Second standby: After the constant current charging is completed, the battery is standby for 5 minutes, the vacuum is turned on to -0.07MPa, and the ambient temperature is controlled at 60°C;

[0061] S5: Second charging: After the second standby is completed, the battery is charged at a current of 0.1C to the high voltage state with a voltage upper limit of 3.65V; evacuate to a vacuum degree of -0.07MPa, and the ambient temperature is controlled at 60°C; take it out of the cabinet and use battery glue nails to fix and seal the injection hole;

[0062] S6: Supplementary injection of electrolyte: Pull out the battery glue nails and perform injection. The injection volume is 9% of the total injection volume. The negative pressure formation will take away all the generated gases and at the same time will evacuate part of the electrolyte. Supplementary injection is carried out to ensure the amount of electrolyte, and the injection hole is sealed by laser welding to make the battery life longer;

[0063] S7: Second high-temperature static aging: Temperature 45°C, time 24 hours;

[0064] S8: Constant current discharge: Assemble the lithium iron phosphate power battery on the pin bed formation cabinet and standby for 5 minutes. The ambient temperature is controlled at 60°C. After the standby is completed, the battery is discharged at a current of 0.2C. The constant current discharge is carried out until 3.2V, and the constant current discharge depth is 35%.

[0065] Example 4

[0066] A formation method for a square aluminum shell lithium iron phosphate battery, comprising the following steps:

[0067] S1: High-temperature static after injection: Temperature 50°C, time 24 hours. Add defoaming agent 2 for injection to the electrolyte, and the addition amount is 0.01% of the mass percentage content of the electrolyte;

[0068] S2: Standby: Install the lithium iron phosphate power battery on the pin bed formation cabinet, fix it with battery glue nails, standby for 10 minutes, turn on the vacuum to -0.07MPa, and control the ambient temperature at 60°C. Evacuate the gas inside the battery under negative pressure to make the battery core tighter;

[0069] S3: Constant current charging: After the rest is completed, the battery is charged at a current of 0.04C until it reaches the activated charged state, with a voltage upper limit of 3.65V; the vacuum is turned on to -0.07MPa, and the ambient temperature is controlled at 60°C; ensure that the SEI film reacts fully to form a stable SEI film, allowing all the generated gases to react and reducing the polarization phenomenon, and then evacuating them through the vacuum. Increase the ionic conductivity and the mobility of the active material by raising the temperature.

[0070] S4: Second rest: After the constant current charging is completed, the battery is rested for 10 minutes, the vacuum is turned on to -0.07MPa, and the ambient temperature is controlled at 60°C.

[0071] S5: Second charging: After the second rest is completed, the battery is charged at a current of 0.2C until it reaches the high voltage state, with a voltage upper limit of 3.65V; the vacuum is pumped to -0.07MPa, and the ambient temperature is controlled at 60°C; the battery is taken out of the cabinet and the injection hole is fixed and sealed with a battery glue nail.

[0072] S6: Supplementary electrolyte injection: Pull out the battery glue nail, inject the electrolyte, and the injection volume is 9% of the total injection volume. The negative pressure formation will take away all the generated gases and also pump away some of the electrolyte. Supplementary injection is carried out to ensure the amount of electrolyte, and the injection hole is laser welded and sealed to make the battery have a longer lifespan.

[0073] S7: Second high-temperature static aging: The temperature is 50°C and the time is 24 hours.

[0074] S8: Constant current discharge: Assemble the lithium iron phosphate power battery on the needle bed formation cabinet and rest for 10 minutes, with the ambient temperature controlled at 60°C. After the rest is completed, discharge the battery at a current of 0.3C. The constant current discharge is carried out until 3.3V, and the constant current discharge depth is 30%.

[0075] Example 5

[0076] A formation method for a square aluminum shell lithium iron phosphate battery, comprising the following steps:

[0077] S1: High-temperature static after injection: The temperature is 50°C and the time is 48 hours. Antifoaming agent 2 for injection is added to the electrolyte, and the addition amount is 0.03% of the mass percentage content of the electrolyte.

[0078] S2: Rest: Install the lithium iron phosphate power battery on the needle bed formation cabinet, fix it with a battery glue nail, rest for 10 minutes, turn on the vacuum to -0.08MPa, control the ambient temperature at 70°C, and evacuate the gas inside the battery under negative pressure to make the battery core tighter.

[0079] S3: Constant current charging: After the standby is completed, the battery is charged at a current of 0.04C until it reaches the activated charged state, with a voltage upper limit of 3.65V; the vacuum is turned on to -0.08MPa, and the ambient temperature is controlled at 70°C; ensure that the SEI film reacts fully to form a stable SEI film, allowing all the generated gases to react and reducing the polarization phenomenon, and then evacuating them through vacuum, and increasing the ionic conductivity and the mobility of the active material by high temperature.

[0080] S4: Second standby: After the constant current charging is completed, the battery is put on standby for 10 min, the vacuum is turned on to -0.08MPa, and the ambient temperature is controlled at 70°C;

[0081] S5: Second charging: After the second standby is completed, the battery is charged at a current of 0.2C until it reaches the high voltage state, with a voltage upper limit of 3.65V; the vacuum is pumped to -0.08MPa, and the ambient temperature is controlled at 70°C; take it out of the cabinet and use battery glue nails to fix and seal the injection hole;

[0082] S6: Supplementary injection of electrolyte: Pull out the battery glue nails and perform injection. The injection volume is 10% of the total injection volume. The negative pressure formation will take away all the generated gases and also pump away part of the electrolyte. Supplementary injection is carried out to ensure the amount of electrolyte, and the injection hole is sealed by laser welding to make the battery life longer;

[0083] S7: Second high-temperature static aging: The temperature is 50°C and the time is 48 hours;

[0084] S8: Constant current discharge: Assemble the lithium iron phosphate power battery on the pin bed formation cabinet and put it on standby for 10 min. The ambient temperature is controlled at 70°C. After the standby is completed, discharge the battery at a current of 0.4C. The constant current discharge is carried out until 3.3V, and the constant current discharge depth is 35%.

[0085] Example 6

[0086] A formation method for a square aluminum shell lithium iron phosphate battery, comprising the following steps:

[0087] S1: High-temperature static after injection: The temperature is 50°C and the time is 72 hours. Defoaming agent 2 for injection is added to the electrolyte, and the addition amount is 0.05% of the mass percentage content of the electrolyte;

[0088] S2: Standby: Assemble the lithium iron phosphate power battery on the pin bed formation cabinet, fix it with battery glue nails, standby for 5 - 10 min, turn on the vacuum to -0.095MPa, control the ambient temperature at 80°C, and evacuate the gas inside the battery under negative pressure to make the battery core tighter;

[0089] S3: Constant current charging: After the rest is completed, the battery is charged at a current of 0.05C until it reaches the activated charged state, with a voltage upper limit of 3.85V; vacuum is turned on to -0.095MPa, and the ambient temperature is controlled at 80°C; ensure that the SEI film reacts fully to form a stable SEI film, so that all the generated gases react out, reduce the polarization phenomenon, and then evacuate through vacuum. Increase the ionic conductivity and the mobility of the active material by high temperature.

[0090] S4: Second rest: After the constant current charging is completed, the battery is rested for 10 min, vacuum is turned on to -0.095MPa, and the ambient temperature is controlled at 80°C;

[0091] S5: Second charging: After the second rest is completed, the battery is charged at a current of 0.2C until it reaches the high voltage state, with a voltage upper limit of 3.85V; evacuate to a vacuum degree of -0.095MPa, and the ambient temperature is controlled at 80°C; take it out of the cabinet and use battery glue nails to fix and seal the injection holes;

[0092] S6: Supplementary injection of electrolyte: Pull out the battery glue nails and perform injection. The injection volume is 11% of the total injection volume. The negative pressure formation will take away all the generated gases and will also evacuate part of the electrolyte. Supplementary injection is carried out to ensure the amount of electrolyte, and the injection holes are laser welded and sealed to make the battery life longer;

[0093] S7: Second high-temperature static aging: Temperature is 50°C, time is 72 hours;

[0094] S8: Constant current discharge: Assemble the lithium iron phosphate power battery on the pin bed formation cabinet and rest for 10 min. The ambient temperature is controlled at 80°C. After the rest is completed, discharge the battery at a current of 0.5C. The constant current discharge is carried out until 3.3V, and the constant current discharge depth is 40%.

Claims

1. A formation method for a square aluminum-shell lithium iron phosphate battery, characterized in that, It includes the following steps: S1: High-temperature static placement after liquid injection; S2: Shelving: Mount the battery on the needle bed formation cabinet, fix it with battery adhesive nails, shelve for 5 - 10 min, turn on the vacuum, control the ambient temperature, and evacuate the gas inside the battery under negative pressure; S3: Constant current charging: After shelving, charge the battery at a current of 0.01 - 0.05C for 90 - 120 min until the charged state is activated, with the voltage upper limit being 3.65V or 3.85V; Turn on the vacuum and control the ambient temperature; fully react to form the SEI film, and then evacuate through vacuum pumping; S4: Secondary shelving: After constant current charging is completed, shelve the battery for 5 - 10 min, turn on the vacuum, and control the ambient temperature; S5: Secondary charging: After secondary shelving is completed, charge the battery at a current of 0.1 - 0.2C for 120 - 150 min until the high-voltage state is reached, with the voltage upper limit being 3.65V or 3.85V; evacuate the air, control the ambient temperature; take the battery off the cabinet, and fix and seal the liquid injection hole with battery adhesive nails; S6: Supplementary electrolyte injection: Pull out the battery adhesive nails, perform supplementary liquid injection, and then laser-weld and seal the liquid injection hole; S7: Secondary high-temperature static aging; S8: Constant current discharge: Mount the battery on the needle bed formation cabinet and shelve for 5 - 10 min, control the ambient temperature at 40 - 80°C. After shelving, discharge the battery at a current of 0.2 - 0.5C until the voltage drops to 3.0 - 3.3V; In S1 and S7, the high-temperature static placement temperature is 45 - 50°C, and the static placement time is 24 - 72 hours; In S2 to S5, the vacuum degree for turning on the vacuum is -0.05~-0.095MPa, and the ambient temperature is 40 - 80°C; The electrolyte also contains an antifoaming agent for liquid injection, and the addition amount is 0.01 - 0.05% of the mass percentage of the electrolyte; The preparation method of the antifoaming agent is as follows: By mass fraction, slowly add 14 - 22 parts of ethylene glycol bis(3-mercaptopropionate), 0.1 - 1.5 parts of 1-vinyl-3-butylimidazolium bromide, 4 - 11 parts of glycidyl ether acrylate, and 2.2 - 3.6 parts of catalyst into 100 - 200 parts of acetonitrile, heat up and stir for reaction, and remove acetonitrile by vacuum distillation.

2. The formation method of a square aluminum shell lithium iron phosphate battery according to claim 1, wherein: In S6, the liquid injection amount is 8 - 11% of the total liquid injection amount.

3. The formation method of a square aluminum shell lithium iron phosphate battery according to claim 1, characterized in that: In S8, the depth of constant current discharge is 25 - 40%.

4. The formation method of a square aluminum shell lithium iron phosphate battery according to claim 1, characterized in that: The catalyst is sodium methoxide.

5. The formation method of a square aluminum shell lithium iron phosphate battery according to claim 1, characterized in that: When preparing the antifoaming agent, the reaction temperature for heating up and stirring for reaction is 70 - 80°C, and the reaction time is 100 - 300 min.