Lithium iron phosphate battery and formation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium iron phosphate battery and a formation method thereof, the formation method comprises the following steps: S1, a first charging stage: charging a battery cell infiltrated by an electrolyte at a constant current of 0.08-0.12 C, the state of charge of the battery cell after the first charging stage is finished being 2-4% SOC; and S2, a second charging stage: charging the battery cell treated in the step S1 at a constant current of 0.14-0.20 C, wherein the state of charge of the battery cell is 33-36% SOC after the second charging stage is ended. According to the formation method provided by the invention, the formation time is relatively short while the formation of the SEI film with excellent performance is ensured, so that the production efficiency is improved, the cycle performance of the lithium ion battery is also improved, and the impedance of the SEI film is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium iron phosphate battery and a formation method thereof. Background Art

[0002] Lithium-ion battery production requires formation to achieve electrode wetting and fully activate the electrode materials. During the initial charge, as lithium ions embed into the negative electrode, the electrolyte components undergo a reduction reaction at the negative electrode to form a stable solid electrolyte interface film (SEI film), which prevents irreversible consumption of electrolyte and lithium ions during subsequent cycles. Therefore, formation is of extraordinary significance to battery performance, and the effect of formation directly affects the subsequent performance of lithium-ion batteries, including storage performance, cycle life, rate capability, and safety.

[0003] The existing formation process is relatively complex, using multi-stage charging operations, and the formation time is long, which reduces the production efficiency of lithium batteries. Excessive formation time may cause the electrolyte to continue to decompose, forming an overly thick or poorly structured SEI film. An overly thick or poorly structured SEI film will increase the resistance of lithium ions from the electrolyte through the SEI film into the negative electrode active material, resulting in an increase in the interfacial impedance of the battery. The poorly structured SEI film is more likely to rupture and repair during long-term cycling, continuously consuming active lithium and electrolyte, accelerating capacity decay, and shortening battery life.

[0004] Therefore, how to provide a SEI film with a short formation time and excellent performance is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a lithium iron phosphate battery and a formation method thereof. The formation method provided by the present invention has a shorter formation time while ensuring the formation of an SEI film with excellent performance, thereby improving production efficiency, while also improving the cycle performance of the lithium-ion battery and reducing the impedance of the SEI film.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a formation method for a lithium iron phosphate battery, the formation method comprising the following steps:

[0008] S1, the first charging stage: the battery cell soaked in electrolyte is charged at a constant current of 0.08C to 0.12C. After the first charging stage, the state of charge of the battery cell is 2% to 4% SOC;

[0009] S2, second charging stage: the battery cell treated in step S1 is charged at a constant current of 0.14C to 0.20C. After the second charging stage, the state of charge of the battery cell is 33% to 36% SOC.

[0010] The formation method provided by the present invention has a shorter formation time while ensuring the formation of an SEI film with excellent performance, thereby improving production efficiency, and also improving the cycle performance of the lithium ion battery and reducing the impedance of the SEI film.

[0011] Furthermore, after step S1 and before step S2, the formation method further comprises the following steps:

[0012] Standing: The standing temperature is 35-50°C, the pressure is 0.4-0.5MPa, and the standing time is 5-30min.

[0013] Furthermore, the negative electrode material of the battery cell includes graphite, and the positive electrode material includes lithium iron phosphate.

[0014] Furthermore, the electrolyte includes a lithium salt, an organic solvent and an additive, and the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, methylene disulfonate, tris(trimethylsilyl)phosphate, LiPO2F2, and lithium difluorooxalatoborate.

[0015] Furthermore, in step S1, the constant current charging time is 15 to 25 minutes.

[0016] Furthermore, in step S1 , the cutoff voltage is 2.5-2.8V.

[0017] Furthermore, in step S2, the constant current charging time is 115 to 125 minutes.

[0018] Furthermore, in step S2, the cutoff voltage is 3.3-3.4V;

[0019] And / or, after step S2, the formation method further comprises the following steps:

[0020] S3. Aging treatment: Aging at 40-50°C for 8-16 hours.

[0021] Furthermore, the battery cell is formed at a temperature of 35-50° C. and a pressure of 0.4-0.5 MPa;

[0022] And / or, the entire process of the chemical formation method is in a negative pressure environment; the pressure of the negative pressure is -70 to -90 kPa.

[0023] In a second aspect, the present invention provides a lithium iron phosphate battery, which is a lithium iron phosphate battery obtained by the formation method of the lithium iron phosphate battery described in the first aspect.

[0024] Compared with the prior art, the present invention has at least one of the following advantages:

[0025] (1) The formation method provided by the present invention has a shorter formation time while ensuring the formation of an SEI film with excellent performance, thereby improving production efficiency, while also improving the cycle performance of the lithium-ion battery and reducing the impedance of the SEI film.

[0026] (2) The present invention provides a highly efficient formation method, and the total formation charging time can be 2h18min. By optimizing the SOC state of the first stage of formation, a good SEI film can be formed at the negative electrode, reducing the film formation impedance, and avoiding the following two situations: ① The first charging stage is short, resulting in incomplete formation of the film; ② The first charging stage is too long, and the SEI film formation impedance is large.

[0027] (3) The formation method provided by the present invention can significantly extend the cycle life of the battery cell. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally based on conventional conditions. Unless otherwise specified, all raw materials can be purchased from the market or are commonly used materials in this industry.

[0029] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0030] In a first aspect, the present invention provides a formation method for a lithium iron phosphate battery, the formation method comprising the following steps:

[0031] S1. First charging stage: The battery cell soaked in electrolyte is charged at a constant current of 0.08C to 0.12C (for example, 0.08C, 0.09C, 0.1C, 0.11C or 0.12C). After the first charging stage, the state of charge of the battery cell is 2% to 4% SOC (for example, 2% SOC, 3% SOC or 4% SOC).

[0032] S2, second charging stage: the battery cell treated in step S1 is charged at a constant current of 0.14C to 0.20C (for example, 0.14C, 0.16C, 0.18C or 0.2C). After the second charging stage, the state of charge of the battery cell is 33% to 36% SOC (for example, 33% SOC, 34% SOC, 35% SOC or 36% SOC).

[0033] Here, cell state of charge SOC = charging current × charging time (min) / 60.

[0034] The formation method provided by the present invention has a shorter formation time while ensuring the formation of an SEI film with excellent performance, thereby improving production efficiency, and also improving the cycle performance of the lithium ion battery and reducing the impedance of the SEI film.

[0035] After the second charging stage of the present invention, the charge state of the battery cell is relatively high, the lithium embedding amount of the negative electrode is larger, and the surface potential of the negative electrode is lower, which will accelerate the decomposition of the lithium salt and form a more uniform and dense SEI film; it can also increase the initial capacity loss.

[0036] In step S1, if the current is too small, the formation time is long, affecting the production efficiency of the formation process; if the current is too large, there is a greater risk of uneven SEI film formation, and the formed SEI film is loose, porous or locally too thick, which cannot effectively passivate the negative electrode surface, increase the lithium ion transfer impedance resistance, aggravate the decomposition of the electrolyte, and accelerate the cycle attenuation.

[0037] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional embodiment, after step S1 and before step S2, the formation method further includes the following steps:

[0038] Standing: the standing temperature is 35-50°C (for example, 35°C, 40°C, 45°C or 50°C), the pressure is 0.4-0.5 MPa, and the standing time is 5-30 min (for example, 5 min, 10 min, 15 min, 20 min, 25 min or 30 min).

[0039] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional embodiment, the negative electrode material of the battery cell includes graphite, and the positive electrode material includes lithium iron phosphate.

[0040] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional embodiment, the electrolyte includes a lithium salt, an organic solvent and an additive, and the additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (1,3,2-Dioxathiolane-2,2-dioxide, DTD), methylene disulfonate, tris(trimethylsilyl) phosphate (TMSP), LiPO2F2, and lithium difluorooxalatoborate.

[0041] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional implementation, in step S1, the constant current charging time is 15 to 25 minutes (for example, it can be 15 minutes, 20 minutes or 25 minutes).

[0042] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional implementation, in step S1, the cut-off voltage is 2.5-2.8V, for example, it can be 2.5V, 2.6V, 2.7V or 2.8V.

[0043] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional implementation, in step S2, the constant current charging time is 115 to 125 minutes (for example, it can be 115 minutes, 120 minutes or 125 minutes).

[0044] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional implementation, in step S2, the cut-off voltage is 3.3-3.4V.

[0045] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional embodiment, after step S2, the formation method further includes the following steps:

[0046] S3. Aging treatment: aging at 40-50°C (for example, 40°C, 42°C, 44°C, 46°C, 48°C or 50°C) for 8-16 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours or 16 hours.

[0047] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional embodiment, the battery cell is formed at a temperature of 35-50°C (for example, 35°C, 40°C, 45°C or 50°C) and a pressure of 0.4-0.5 MPa.

[0048] Specifically, a hot pressing device is used to apply pressure to the battery cell, and the battery cell is kept warm by a clamping plate that applies pressure, and the temperature of the clamping plate is 35 to 50°C.

[0049] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional implementation manner, the entire process of the formation method is in a negative pressure environment; the pressure of the negative pressure is -70 to -90 kPa.

[0050] In the above-mentioned formation method of the lithium iron phosphate battery, as an optional implementation, the lithium iron phosphate battery includes a soft-pack lithium iron phosphate battery.

[0051] In a second aspect, the present invention provides a lithium iron phosphate battery, wherein the lithium iron phosphate battery is a lithium iron phosphate battery obtained by the formation method of the lithium iron phosphate battery described in the first aspect.

[0052] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0053] In the following examples and comparative examples:

[0054] The positive electrode material of the battery cell is lithium iron phosphate, the negative electrode material is graphite, and the components of the electrolyte include: in terms of mass percentage, 12.5wt% LiPF6 lithium salt; solvents EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DMC (dimethyl carbonate), with a mass ratio of 30:40:30; additives 1.8wt% VC (vinylene carbonate), 0.5wt% FEC (fluoroethylene carbonate), 1.2wt% DTD (vinyl sulfate), 0.5wt% MMDS (methylene methanedisulfonate), 0.5wt% TMSP (tris(trimethylsilyl) phosphate), 0.4wt% LiPO2F2, 0.2wt% LiDFOB (lithium difluorooxalatoborate), and the total additive content is 5.1wt%.

[0055] Example 1

[0056] This embodiment provides a formation method for a soft-pack lithium iron phosphate battery, comprising the following steps:

[0057] First charging stage: After ensuring that the battery cell is fully soaked, it is placed on the cabinet and charged in the first step. A soft-pack battery fixture is used to apply a pressure of 0.42MPa to the battery cell. Then, it is charged at a constant current of 0.1C at 45°C and a negative pressure of -90KPa. The charging time is 18min, the charging SOC is 3%, the cut-off voltage is 2.66V, and the film formation of the first stage formation additive is basically complete;

[0058] Standing: Standing at 45℃ and 0.42MPa pressure for 10min;

[0059] Second charging stage: Continue with the second step of charging, use the soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell, then charge at a constant current of 0.16C at 45°C and a negative pressure of -90KPa. The charging time is 120min, the charging SOC is 32%, the formation is completed, and the cut-off voltage is 3.32V;

[0060] Aging treatment: Aging at 45°C for 12h.

[0061] The total charging time of the formation method provided in this embodiment is only about 2 hours and 18 minutes, and the charging SOC is about 35%.

[0062] Example 2

[0063] This embodiment provides a formation method for a soft-pack lithium iron phosphate battery, comprising the following steps:

[0064] First charging stage: After ensuring that the battery cell is fully soaked, put it on the cabinet and perform the first charging step. Use a soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell. Then charge it at a constant current of 0.1C at 45°C and a negative pressure of -90KPa for 24 minutes. The charging SOC is 4% and the cut-off voltage is 2.75V.

[0065] Standing: Standing at 45℃ and 0.42MPa pressure for 10min;

[0066] Second charging stage: Continue with the second step of charging, use the soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell, then charge at a constant current of 0.16C at 45°C and a negative pressure of -90KPa. The charging time is 117min, the charging SOC is 31.2%, and the formation is completed with a cut-off voltage of 3.32V.

[0067] Aging treatment: Aging at 45°C for 12h.

[0068] Comparative Example 1

[0069] This comparative example provides a formation method for a soft-pack lithium iron phosphate battery, comprising the following steps:

[0070] For the same batch of cells as in Example 1, in the first charging stage: after ensuring that the cells are completely wetted, they are placed on the cabinet and charged in the first step. A pressure of 0.42 MPa is applied to the cells using a soft-pack battery fixture. Then, the cells are charged at a constant current of 0.1C at 45°C and a negative pressure of -90 kPa for 7 minutes. The charging SOC is 1.2% and the cut-off voltage is 2.30 V.

[0071] Standing: Standing at 45℃ and 0.42MPa pressure for 10min;

[0072] Second charging stage: Continue with the second step of charging, use the soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell, then charge at a constant current of 0.16C at 45°C and a negative pressure of -90KPa. The charging time is 127min, the charging SOC is 34%, the formation is completed, and the cut-off voltage is 3.32V;

[0073] Aging treatment: Aging at 45°C for 12h.

[0074] Comparative Example 2

[0075] This comparative example provides a formation method for a soft-pack lithium iron phosphate battery, comprising the following steps:

[0076] For the same batch of cells as in Example 1, in the first charging stage, after ensuring that the cells are completely wetted, they are placed on the cabinet and charged in the first step. A pressure of 0.42 MPa is applied to the cells using a soft-pack battery fixture. The cells are then charged at a constant current of 0.1C at 45°C and a negative pressure of -90 kPa for 30 minutes. The charging SOC is 5% and the cut-off voltage is 2.9 V.

[0077] Standing: Standing at 45℃ and 0.42MPa pressure for 10min;

[0078] Second charging stage: Continue with the second step of charging, use the soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell, then charge at a constant current of 0.16C at 45°C and a negative pressure of -90KPa. The charging time is 113min, the charging SOC is 30%, the formation is completed, and the cut-off voltage is 3.32V;

[0079] Aging treatment: Aging at 45°C for 12h.

[0080] Comparative Example 3

[0081] This comparative example provides a formation method for a soft-pack lithium iron phosphate battery, comprising the following steps:

[0082] For the same batch of cells as in Example 1, in the first charging stage, after ensuring that the cells are completely wetted, they are placed on the cabinet and charged in the first step. A pressure of 0.42 MPa is applied to the cells using a soft-pack battery fixture. The cells are then charged at a constant current of 0.02C at 45°C and a negative pressure of -90 kPa for 90 minutes. The charging SOC is 3% and the cut-off voltage is 2.67 V.

[0083] Standing: Standing at 45℃ and 0.42MPa pressure for 10min;

[0084] Second charging stage: Continue with the second step of charging, use the soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell, then charge with a constant current of 0.06C for 128min at 45°C and a negative pressure of -90KPa, let it rest for 2min, and continue to charge with a constant current of 0.12C for 96min. The charging SOC is 32%, the formation is completed, and the cut-off voltage is 3.32V;

[0085] Aging treatment: Aging at 45°C for 12h.

[0086] The total charging time of the two-stage formation method provided in this comparative example is 314 minutes, which is 176 minutes longer than that of Example 1. The formation method provided in this comparative example is relatively complex, adopts a multi-stage charging operation, and the formation time is long, which reduces the production efficiency of lithium batteries.

[0087] Comparative Example 4

[0088] This comparative example provides a formation method for a soft-pack lithium iron phosphate battery, comprising the following steps:

[0089] For the same batch of cells as in Example 1, in the first charging stage, after ensuring that the cells are completely wetted, they are placed on the cabinet and charged in the first step. A pressure of 0.42 MPa is applied to the cells using a soft-pack battery fixture. The cells are then charged at a constant current of 0.02C at 45°C and a negative pressure of -90 kPa for 90 minutes. The charging SOC is 3% and the cut-off voltage is 2.67 V.

[0090] Standing: Standing at 45℃ and 0.42MPa pressure for 10min;

[0091] Second charging stage: Continue with the second step of charging, use the soft pack battery fixture to apply a pressure of 0.42MPa to the battery cell, then charge with a constant current of 0.1C for 78min at 45°C and a negative pressure of -90KPa, let it rest for 2min, and continue to charge with a constant current of 0.16C for 71min. The charging SOC is 32%, the formation is completed, and the cut-off voltage is 3.32V;

[0092] Aging treatment: Aging at 45°C for 12h.

[0093] Performance Testing

[0094] The formed lithium iron phosphate batteries provided in the examples and comparative examples were divided into different capacities according to conventional methods, and then subjected to AC impedance, EIS impedance and cycle performance tests.

[0095] AC impedance and EIS impedance data test method: ① Under 25℃ environment, perform AC internal resistance test on the above-mentioned cells after capacity division. Apply a small AC signal at both ends of the battery, then measure the battery's AC response and measure the AC impedance at a frequency of 1kHz. ② Under 25℃ environment, perform EIS test on the above-mentioned cells in the first charging stage, the second charging stage and the 20% SOC after capacity division. Set the frequency range to 10 -2 ~10 5 Hz, voltage disturbance 5mV, tested with controlled voltage method. The 20% SOC cell after capacity division refers to the cell that is first charged to 3.65V at a constant current of 1C after capacity division, then switched to constant voltage charging until the charging current drops to 0.05C, and then discharged to 20% SOC at a constant current of 1C after standing for 30 minutes.

[0096] Cycling performance test method: The above-mentioned capacity-divided battery was tested at 45°C. (1) Charged at a constant current of 1C to 3.65V, then switched to constant voltage charging until the charging current dropped to 0.05C and stopped charging. The battery was allowed to stand for 30 minutes. (2) Discharged at a constant current of 1C to 2.5V and stopped discharging. The battery was allowed to stand for 30 minutes and the discharge capacity was recorded. (3) The battery was cycled 1180 times continuously according to (1) to (2). The ratio of the 1180 discharge capacity to the initial discharge capacity was used as the discharge capacity retention rate.

[0097] The AC impedance, EIS impedance, and cycle data are shown in Table 1.

[0098] Table 1

[0099]

[0100] From Table 1, we can see at least the following points:

[0101] (1) Comparing Examples 1 and 2 with Comparative Examples 3 and 4, it can be seen that the formation time of the formation methods provided by Examples 1 and 2 is shorter, which improves the production efficiency, and the impedance (R SEI ) is smaller (the impedance is smaller, the resistance of lithium ions passing through the SEI film is low, the battery cell rate performance is good, the polarization is smaller, and the energy efficiency is high), and the cycle performance of the lithium ion battery is better, indicating that the formation method provided by Examples 1 and 2 has a shorter formation time while ensuring the formation of an SEI film with excellent performance, thereby improving the production efficiency, and also improving the cycle performance of the lithium ion battery and reducing the impedance of the SEI film; the formation process of Comparative Examples 3 and 4 is more complicated, adopts a multi-stage charging operation, and the formation time is longer, which reduces the production efficiency of the lithium battery, and the impedance (RSEI) of the SEI film formed thereby is larger, and the cycle performance of the lithium ion battery provided thereby is poor. It can be seen that the SEI film formed in Comparative Examples 3 and 4 has a poor structure, is more likely to rupture and repair during long-term circulation, and continuously consumes active lithium and electrolyte, resulting in poor cycle performance.

[0102] (2) Comparing Examples 1 and 2 with Comparative Examples 1 and 2, it can be seen that after the first charging stage, when the state of charge of the cell is low or high, the impedance (R SEI ) is large, and the poor cycle performance of the lithium ion batteries provided by Comparative Examples 1 and 2 indicates that the structure of the SEI film formed therein is poor.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A formation method for a lithium iron phosphate battery, characterized in that: The formation method comprises the following steps: S1, the first charging stage: the battery cell soaked in electrolyte is charged at a constant current of 0.08C to 0.12C. After the first charging stage, the state of charge of the battery cell is 2% to 4% SOC; S2, second charging stage: the battery cell treated in step S1 is charged at a constant current of 0.14C to 0.20C. After the second charging stage, the state of charge of the battery cell is 33% to 36% SOC.

2. The formation method of a lithium iron phosphate battery according to claim 1, characterized in that: After step S1 and before step S2, the formation method further comprises the following steps: Standing: The standing temperature is 35-50°C, the pressure is 0.4-0.5MPa, and the standing time is 5-30min.

3. The formation method of a lithium iron phosphate battery according to claim 1, characterized in that: The negative electrode material of the battery cell includes graphite, and the positive electrode material includes lithium iron phosphate.

4. The formation method of a lithium iron phosphate battery according to claim 1, characterized in that: The electrolyte includes a lithium salt, an organic solvent and an additive, wherein the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, methylene disulfonate, tris(trimethylsilyl)phosphate, LiPO2F2 and lithium difluorooxalatoborate.

5. The formation method of lithium iron phosphate battery according to claim 1, characterized in that: In step S1 , the constant current charging time is 15 to 25 minutes.

6. The formation method of a lithium iron phosphate battery according to claim 1, characterized in that: In step S1 , the cutoff voltage is 2.5 to 2.8V.

7. The formation method of a lithium iron phosphate battery according to claim 1, characterized in that: In step S2, the constant current charging time is 115 to 125 minutes.

8. The formation method of a lithium iron phosphate battery according to claim 1, characterized in that: In step S2, the cutoff voltage is 3.3-3.4V; And / or, after step S2, the formation method further comprises the following steps: S3. Aging treatment: Aging at 40-50°C for 8-16 hours.

9. The formation method of a lithium iron phosphate battery according to any one of claims 1 to 8, characterized in that: The battery cell is formed at a temperature of 35-50° C. and a pressure of 0.4-0.5 MPa; And / or, the entire process of the chemical formation method is in a negative pressure environment; the pressure of the negative pressure is -70 to -90 kPa.

10. A lithium iron phosphate battery, characterized in that: The lithium iron phosphate battery is a lithium iron phosphate battery obtained by the lithium iron phosphate battery formation method according to any one of claims 1 to 9.

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