Formation method and application of lithium iron manganese phosphate soft package battery

Abstract

The application provides a formation method and application of a lithium manganese iron phosphate soft package battery, and relates to the field of lithium ion batteries. The formation method is performed under high-temperature and high-pressure conditions. The lithium manganese iron phosphate soft package battery after liquid injection aging is first placed for the first time, then the battery is charged at a constant current to 10-30% SOC, after the second time of placement, the battery is charged at a constant current to 20-40% SOC, after the third time of placement, the battery is charged at a constant current and constant voltage to 100% SOC. The formation method can make the lithium manganese iron phosphate soft package battery achieve a relatively optimal formation effect. Specifically, the first efficiency, normal-temperature capacity, high-temperature capacity and low-temperature capacity and other electrical properties of the battery are good, and the battery has no obvious bulging and inflation during the short-term electrical property test process, the battery disassembly interface is good, there is no obvious spot and lithium precipitation phenomenon, which is beneficial to the later cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a formation method and application of lithium manganese iron phosphate soft-pack batteries. Background Technology

[0002] Currently, most battery manufacturers use hot-pressing formation method for pouch cells. This method involves applying pressure and temperature to the battery during the formation process, and then charging the pouch cell with multiple small-rate currents in stages. The charging rate usually increases gradually, but remains within a relatively small range.

[0003] Application No. 202110378803.0 discloses a formation method for lithium batteries, which establishes a relationship between current, temperature, and charge during cell formation using formulas, making the formation method somewhat systematic. However, research has found that the formation and charging conditions are not universally applicable for pouch batteries with different material systems. Using the same process steps is not conducive to achieving optimal formation results for batteries with different material systems, leading to problems ranging from low formation efficiency to insufficient battery capacity, poor cycle performance, and poor high and low temperature performance. For example, when using the above-mentioned conventional formation process for lithium manganese iron phosphate pouch batteries, problems such as battery bulging and gas accumulation, poor electrode interface conditions, and insufficient capacity are frequently observed. Therefore, it is necessary to adopt specific formation processes for batteries with different material systems (such as lithium manganese iron phosphate pouch batteries) to achieve optimal formation results.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a formation method for lithium manganese iron phosphate pouch batteries, so as to improve the problems that often occur when using existing conventional formation processes, such as battery bulging and gas accumulation, poor electrode interface condition, and insufficient capacity utilization.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for forming a lithium manganese iron phosphate pouch cell, comprising the following steps:

[0008] (a) Allow the lithium iron phosphate soft-pack battery after liquid injection and aging to stand for the first time.

[0009] (b) Charge the lithium iron phosphate pouch battery with constant current I1 to 10-30% SOC after the first settling period, and then perform a second settling period.

[0010] (c) Charge the lithium iron phosphate pouch battery after the second settling period with a constant current of I2 to 20-40% SOC, and then set it for the third time.

[0011] (d) The lithium iron phosphate pouch battery after the third settling period is charged with constant current and constant voltage at current I3 to 100% SOC, and the formation is completed.

[0012] The resting and / or charging processes in steps (a), (b), (c), and (d) are all carried out under high temperature and high pressure conditions.

[0013] Furthermore, based on the above technical solution of the present invention, in step (a), the first settling time is 0.5-3h.

[0014] Furthermore, based on the above technical solution of the present invention, in step (b), the current I1 is 0.02-0.06C.

[0015] Furthermore, based on the above-mentioned technical solution of the present invention, in step (b), the second settling time is 5-30 minutes.

[0016] Furthermore, based on the above technical solution of the present invention, in step (c), the current I2 is 0.1-0.6C;

[0017] And / or, the third settling time shall not be less than 10 hours.

[0018] Furthermore, based on the above-mentioned technical solution of the present invention, in step (c), the third settling time is 10-20 hours.

[0019] Furthermore, based on the above technical solution of the present invention, in step (d), the current I3 is 0.1-0.6C.

[0020] Furthermore, based on the above technical solution of the present invention, in step (d), the lithium manganese iron phosphate soft pack battery is charged with constant current and constant voltage at a current I3 until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the soft pack battery reaches 100% SOC.

[0021] Furthermore, based on the above-mentioned technical solution of the present invention, steps (a), (b), (c) and (d) are all carried out in a heating and pressurizing formation device;

[0022] And / or, the temperature under high temperature and high pressure conditions is 25-60℃, and the pressure is 100-800kgf.

[0023] The present invention also provides the application of the above-mentioned formation method of lithium manganese iron phosphate soft-pack battery in the field of lithium-ion batteries.

[0024] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0025] (1) This invention provides a formation method for lithium manganese iron phosphate pouch batteries. The formation method is carried out under high temperature and high pressure conditions. First, the lithium manganese iron phosphate pouch batteries after liquid injection and aging are allowed to stand for the first time. Then, the batteries are charged with constant current to 10-30% SOC. After a second stand, the batteries are charged with constant current to 20-40% SOC. After a third stand, the batteries are charged with constant current and constant voltage to 100% SOC. This formation method can achieve better formation results for lithium manganese iron phosphate pouch batteries. Specifically, the batteries have good electrical performance such as initial efficiency, room temperature capacity, high temperature capacity and low temperature capacity. In the later short-term electrical performance test, the batteries do not have obvious bulging and gas swelling. The battery disassembly interface is good, with no obvious plaques and lithium plating. This is conducive to the later cycle performance and improves the problems of battery bulging and gas swelling, poor disassembly electrode interface state and insufficient capacity performance that often occur when using existing conventional formation processes.

[0026] (2) The present invention provides the application of the above-mentioned formation method of lithium manganese iron phosphate soft pack battery. Given the advantages of the above-mentioned formation method of lithium manganese iron phosphate soft pack battery, it has good application prospects in the field of lithium-ion batteries. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0028] Figure 1 The electrode interface diagram is shown after disassembly of a lithium iron phosphate pouch battery formed using the method of Embodiment 1 of the present invention.

[0029] Figure 2 The electrode interface diagram is shown after disassembly of a lithium manganese iron phosphate soft-pack battery formed using the method of Embodiment 2 of the present invention.

[0030] Figure 3 The electrode interface diagram is shown after disassembly of a lithium manganese iron phosphate soft-pack battery formed using the method of Embodiment 3 of the present invention.

[0031] Figure 4 The electrode interface diagram is shown after disassembly of the lithium manganese iron phosphate soft-pack battery formed using the formation method of Comparative Example 1 of this invention.

[0032] Figure 5 The electrode interface diagram is shown after disassembly of the lithium manganese iron phosphate soft-pack battery formed using the formation method of Comparative Example 2 of this invention.

[0033] Figure 6 The image shows the electrode interface of a lithium iron phosphate pouch battery after disassembly using the formation method of Comparative Example 3 of this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0035] The endpoints and any values ​​of the ranges disclosed in this invention 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0036] According to a first aspect of the present invention, a method for forming a lithium manganese iron phosphate pouch cell is provided, comprising the following steps:

[0037] (a) Allow the lithium iron phosphate soft-pack battery after liquid injection and aging to stand for the first time.

[0038] (b) Charge the lithium iron phosphate pouch battery with constant current I1 to 10-30% SOC after the first settling period, and then perform a second settling period.

[0039] (c) Charge the lithium iron phosphate pouch battery after the second settling period with a constant current of I2 to 20-40% SOC, and then set it for the third time.

[0040] (d) The lithium iron phosphate pouch battery after the third settling period is charged with constant current and constant voltage at current I3 to 100% SOC, and the formation is completed.

[0041] Among them, the settling process and / or charging process in steps (a), (b), (c) and (d) are all carried out under high temperature and high pressure conditions. Specifically, the first settling in step (a), the charging process and the second settling in step (b), the charging process and the third settling in step (c), and the charging process in step (d) are all carried out under high temperature and high pressure conditions.

[0042] Specifically, in step (a) of the present invention, the lithium manganese iron phosphate soft-pack battery after liquid injection and aging is subjected to a first static condition under high temperature and high pressure so that the battery as a whole is in a high temperature and high pressure state, the internal materials of the battery are in close contact with each other, and are in a state of high activity.

[0043] Steps (b) and (c) involve performing staged constant-current charging of the lithium manganese iron phosphate pouch battery under high temperature and high pressure conditions to bring the battery to a specific state of charge (SOC). Step (b) involves constant-current charging the battery to 10-30% SOC, including but not limited to 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, or 30% SOC, or any range between any two points. Step (c) involves constant-current charging the battery to 20-40% SOC, including but not limited to 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, or 40% SOC, or any range between any two points.

[0044] During the charging process in steps (b) and (c), a dense and stable SEI film gradually forms on the surface of the negative electrode. After the constant current charging of the battery in step (c) is completed, it must be left to stand for a relatively long time under high temperature and high pressure conditions; otherwise, the SEI film on the surface of the negative electrode will not form completely, resulting in a high risk of gas expansion in the battery later and a deterioration in cycle performance.

[0045] After the third settling period, step (d) is performed, which involves charging to 100% SOC under constant current and constant voltage conditions at high temperature and high pressure. At this point, the film formation reaction on the negative electrode surface is complete, the battery gas production reaches its maximum, and the formation reaction ends. If the battery's state of charge cannot reach 100% SOC, the side reactions at the electrolyte-negative electrode interface are still insufficient, and gas will still be generated during subsequent battery use.

[0046] This invention provides a formation method for lithium manganese iron phosphate (MFP) pouch batteries. This formation method is carried out under high temperature and high pressure conditions. First, the MFP pouch battery, after electrolyte injection and aging, undergoes a first settling period. Then, the battery is charged with constant current to 10-30% SOC. After a second settling period, the battery is charged with constant current to 20-40% SOC. After a third settling period, the battery is charged with constant current and constant voltage to 100% SOC. This formation method can achieve better formation results for MFP pouch batteries, specifically manifested in good initial efficiency, room temperature capacity, high temperature capacity, and low temperature capacity. Furthermore, during subsequent short-term electrical performance testing, the battery shows no obvious bulging or gas buildup, and the battery disassembly interface is good, with no obvious plaques or lithium plating. This is beneficial for subsequent cycle performance and improves upon the problems often encountered with existing conventional formation processes, such as battery bulging, poor electrode interface condition, and insufficient capacity utilization.

[0047] In this formation method, the settling and charging processes in each step are carried out under high temperature and high pressure conditions. As a preferred embodiment of the invention, the temperature under these conditions is 25-60°C, and the pressure is 100-800 kgf. Typical but non-limiting temperatures are 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C, and any range between any two points. Typical but non-limiting pressures are 100 kgf, 200 kgf, 300 kgf, 400 kgf, 500 kgf, 600 kgf, 600 kgf, or 800 kgf, and any range between any two points.

[0048] By further limiting the temperature and pressure during resting and charging, the battery can be charged and rested under more suitable conditions, while improving the formation effect.

[0049] In a preferred embodiment of the present invention, the high-temperature and high-pressure conditions in this formation method can be provided by a heating and pressurizing formation device. That is, the lithium manganese iron phosphate pouch battery after liquid injection and aging is first placed in the heating and pressurizing formation device, and then subjected to the first settling and subsequent steps (b)-(d).

[0050] In a preferred embodiment of the present invention, in step (a), the first settling time is 0.5-3 hours; typical but non-limiting times for the first settling time are 0.5 hours, 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours, or 3.0 hours, and any range between any two points. If the first settling time is too short, the internal temperature of the cell will not reach the set temperature value, resulting in low battery activity; if the first settling time is too long, it will lead to low formation reaction efficiency.

[0051] In a preferred embodiment of the present invention, in step (a), the temperature of the first settling is 25-60°C; the typical but non-limiting temperature of the first settling is 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C and any range between any two points.

[0052] In a preferred embodiment of the present invention, in step (a), the pressure for the first settling is 100-800 kgf; the typical but non-limiting pressure for the first settling is 300 kgf, 400 kgf, 500 kgf, 600 kgf, 700 kgf or 800 kgf and any range between any two points.

[0053] By further limiting the temperature, pressure, and time of the first settling period, the battery can be charged under more suitable conditions, thereby improving the formation effect and formation efficiency.

[0054] Steps (b), (c), and (d) involve performing staged constant current or constant current-constant voltage charging on the lithium manganese iron phosphate pouch battery using multiple low-rate currents, with the charging current gradually increasing in steps (b), (c), and (d).

[0055] As an optional embodiment of the present invention, currents I1, I2 and I3 are all 0.02-0.6C, and current I1 < current I2 ≤ current I3.

[0056] In a preferred embodiment of the present invention, the current I1 is 0.02-0.06C; and / or, the current I2 is 0.1-0.6C; and / or, the current I3 is 0.1-0.6C.

[0057] Typical but non-limiting currents I1 are 0.02C, 0.03C, 0.04C, 0.05C, or 0.06C, and any range between any two points; typical but non-limiting currents I2 are 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, or 0.6C, and any range between any two points; typical but non-limiting currents I3 are 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, or 0.6C, and any range between any two points.

[0058] During the constant current charging to a specific SOC in step (b), a second resting period is performed.

[0059] As an optional embodiment of the present invention, in step (b), the second settling time is 5-30 minutes. Typical but non-limiting settling times are 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, and any range between any two points.

[0060] By further limiting the second settling time, the polarization voltage can be reduced, allowing the voltage to reach equilibrium.

[0061] As an optional embodiment of the present invention, in step (b), the temperature of the second settling is 25-60°C; the typical but non-limiting temperature of the second settling is 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C and any range between any two points.

[0062] As an optional embodiment of the present invention, in step (b), the pressure of the second settling is 100-800 kgf; typical but non-limiting pressures are 100 kgf, 200 kgf, 300 kgf, 400 kgf, 500 kgf, 600 kgf, 700 kgf or 800 kgf and any range between any two points.

[0063] During step (c), when the constant current charging reaches a specific SOC, a third resting period is performed.

[0064] In one optional embodiment of the present invention, the third settling time is at least 10 hours, preferably 10-20 hours. If the third settling time is insufficient (less than 10 hours), the SEI film on the surface of the negative electrode will not form completely, resulting in a high risk of gas expansion in the battery later and poor cycle performance. If the third settling time is too long (more than 20 hours), the formation efficiency will be reduced, and the interface resistance may increase due to an excessively thick SEI film, leading to increased internal resistance of the battery and hindering battery performance.

[0065] In addition to limiting the time for the third settling period, the temperature and pressure for the third settling period have been further optimized.

[0066] As an optional embodiment of the present invention, in step (c), the temperature of the third settling is 25-60°C; the typical but non-limiting temperature of the third settling is 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C and any range between any two points.

[0067] As an optional embodiment of the present invention, in step (c), the pressure of the third settling is 100-800 kgf; typical but non-limiting pressures are 100 kgf, 200 kgf, 300 kgf, 400 kgf, 500 kgf, 600 kgf, 700 kgf or 800 kgf and any range between any two points.

[0068] As an optional embodiment of the present invention, in step (d), the lithium manganese iron phosphate soft-pack battery is charged with a constant current and constant voltage of I3 until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the soft-pack battery reaches 100% SOC.

[0069] By limiting the cutoff voltage and cutoff current, lithium manganese iron phosphate pouch batteries can be made to reach a fully charged state.

[0070] According to a second aspect of the present invention, the application of the above-described formation method for lithium manganese iron phosphate pouch cells is also provided.

[0071] Given the advantages of the above-mentioned formation method for lithium iron phosphate pouch batteries, it has found good applications in the field of lithium-ion batteries.

[0072] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. It should be noted that the cell system of the lithium manganese iron phosphate pouch battery in the following embodiments and comparative examples is lithium manganese iron phosphate-artificial graphite pouch cell.

[0073] Example 1

[0074] This embodiment provides a formation method for lithium manganese iron phosphate pouch batteries, including the following steps:

[0075] (a) Set the temperature of the heating and pressurizing formation chamber to 45°C and the pressure to 425 kgf;

[0076] Eight lithium iron phosphate pouch batteries (in total) were subjected to a first settling process in a heated and pressurized formation cabinet after being injected with electrolyte and aged. The temperature of the first settling process was 45°C, the pressure was 425 kgf, and the time was 1 hour.

[0077] (b) The lithium manganese iron phosphate soft-pack battery after the first settling was charged with a constant current of I1 0.05C for 6 hours until the battery reached 30% SOC, and then a second settling was performed; the temperature of the second settling was 45°C, the pressure was 425 kgf, and the time was 5 min.

[0078] (c) The lithium manganese iron phosphate pouch battery after the second settling is charged with a constant current of I2 0.2C for 0.5h until the battery reaches 40% SOC, and then a third settling is performed; the temperature of the third settling is 45℃, the pressure is 425kgf, and the time is 12h.

[0079] (d) The lithium manganese iron phosphate pouch battery after the third settling period is charged with constant current and constant voltage at a current of I3 0.2C until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the battery reaches 100% SOC and the formation is completed.

[0080] Example 2

[0081] This embodiment provides a formation method for lithium manganese iron phosphate pouch batteries, including the following steps:

[0082] (a) Set the temperature of the heating and pressurizing formation chamber to 45°C and the pressure to 425 kgf;

[0083] The lithium manganese iron phosphate pouch batteries (a total of 8) after liquid injection and aging were placed in a heated and pressurized formation cabinet for the first settling; the temperature of the first settling was 45℃, the pressure was 425kgf, and the time was 1h.

[0084] (b) The lithium manganese iron phosphate soft-pack battery after the first settling was charged with a constant current of I1 0.05C for 6 hours until the battery reached 30% SOC, and then a second settling was performed; the temperature of the second settling was 45°C, the pressure was 425 kgf, and the time was 5 min.

[0085] (c) The lithium manganese iron phosphate soft-pack battery after the second settling was charged with a constant current of I2 0.3C for 20 minutes until the battery reached 40% SOC, and then a third settling was performed; the temperature of the third settling was 45℃, the pressure was 425kgf, and the time was 12h.

[0086] (d) The lithium manganese iron phosphate pouch battery after the third settling period is charged with constant current and constant voltage at a current of I3 0.3C until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the battery reaches 100% SOC and the formation is completed.

[0087] Example 3

[0088] This embodiment provides a formation method for lithium manganese iron phosphate soft-pack batteries. Except for replacing the first settling time in step (a) with 5 minutes instead of 1 hour, the other steps are the same as in embodiment 1.

[0089] Example 4

[0090] This embodiment provides a formation method for lithium manganese iron phosphate soft-pack batteries. Except for replacing the first settling time in step (a) with 12 hours, the other steps are the same as in embodiment 1.

[0091] Example 5

[0092] This embodiment provides a formation method for lithium manganese iron phosphate soft-pack batteries. Except that the temperature of the heating and pressurizing formation cabinet is set from 45°C to 25°C, that is, the temperature of the resting process and / or charging process in steps (a), (b), (c) and (d) is 25°C, the other steps are the same as in embodiment 1.

[0093] Example 6

[0094] This embodiment provides a formation method for lithium manganese iron phosphate pouch batteries. Except that the temperature of the heating and pressurizing formation cabinet is changed from 45°C to 60°C, that is, the temperature of the resting process and / or charging process in steps (a), (b), (c) and (d) is 60°C, the other steps are the same as in embodiment 1.

[0095] Example 7

[0096] This embodiment provides a formation method for lithium manganese iron phosphate soft-pack batteries. Except that the temperature of the heating and pressurizing formation cabinet is set from 45°C to 15°C, that is, the temperature of the resting process and / or charging process in steps (a), (b), (c) and (d) is 15°C, the other steps are the same as in embodiment 1.

[0097] Example 8

[0098] This embodiment provides a formation method for lithium manganese iron phosphate pouch batteries. Except for replacing the third settling time in step (c) with 22 hours instead of 12 hours, the other steps are the same as in embodiment 1.

[0099] Example 9

[0100] This embodiment provides a formation method for lithium manganese iron phosphate pouch batteries, including the following steps:

[0101] (a) Set the temperature of the heating and pressurizing formation chamber to 45°C and the pressure to 600 kgf;

[0102] The lithium manganese iron phosphate pouch batteries (a total of 8) after liquid injection and aging were subjected to the first settling in a heated and pressurized formation cabinet; the temperature of the first settling was 45℃, the pressure was 600kgf, and the time was 0.5h.

[0103] (b) After the first settling, the lithium manganese iron phosphate soft-pack battery was charged with a constant current of I1 0.06C for 200 min until the battery reached 20% SOC, and then a second settling was performed; the temperature of the second settling was 45°C, the pressure was 600 kgf, and the time was 5 min.

[0104] (c) The lithium manganese iron phosphate soft-pack battery after the second settling is charged with a constant current of I2 0.4C for 15 minutes until the battery reaches 30% SOC, and then a third settling is performed; the temperature of the third settling is 45℃, the pressure is 600kgf, and the time is 12h.

[0105] (d) The lithium manganese iron phosphate pouch battery after the third settling period is charged with constant current and constant voltage at a current of I3 0.6C until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the battery reaches 100% SOC and the formation is completed.

[0106] Comparative Example 1

[0107] This comparative example provides a method for forming a lithium manganese iron phosphate pouch cell, including the following steps:

[0108] (a) Set the temperature of the heating and pressurizing formation chamber to 45°C and the pressure to 425 kgf;

[0109] The lithium manganese iron phosphate pouch batteries (a total of 8) after liquid injection and aging were placed in a heated and pressurized formation cabinet for the first settling; the temperature of the first settling was 45℃, the pressure was 425kgf, and the time was 1h.

[0110] (b) The lithium manganese iron phosphate soft-pack battery after the first settling was charged with a constant current of I1 0.05C for 6 hours until the battery reached 30% SOC, and then a second settling was performed; the temperature of the second settling was 45°C, the pressure was 425 kgf, and the time was 5 min.

[0111] (c) The lithium manganese iron phosphate pouch battery after the second settling period is charged with constant current and constant voltage at a current of I2 0.2C until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the battery reaches 100% SOC and the formation is completed.

[0112] Comparative Example 2

[0113] This comparative example provides a formation method for a lithium manganese iron phosphate pouch battery. Except for replacing the third settling time in step (c) with 8 hours instead of 12 hours, the other steps are the same as in Example 1.

[0114] Comparative Example 3

[0115] This comparative example provides a method for the formation of a lithium manganese iron phosphate pouch battery. Except for replacing the constant voltage charging to 100% SOC in step (d) with 90% SOC, the remaining steps are the same as in Example 1.

[0116] To further illustrate the technical effects of the above embodiments and comparative examples, the following experimental examples are provided.

[0117] Experimental Example 1

[0118] After the formation of each embodiment and comparative example, the lithium manganese iron phosphate pouch battery was directly subjected to a discharge test (i.e., capacity testing) on ​​a heated and pressurized formation cabinet (the temperature of the heated and pressurized formation cabinet was 45°C and the pressure was 425 kgf). The 0.33C discharge capacity was tested, and the battery's initial efficiency was calculated based on the test data.

[0119] The lithium manganese iron phosphate pouch batteries of the embodiments and comparative examples after capacity testing were divided into two groups. One group (6 batteries in total) was used for initial performance testing and bulging / gasification testing, while the other group (2 batteries in total) was disassembled to test the full electrode interface.

[0120] Initial performance testing: The initial thickness of the lithium manganese iron phosphate pouch batteries of the examples and comparative examples after capacity testing was measured and recorded as h0. Then, after the lithium manganese iron phosphate pouch batteries of the examples and comparative examples were fully charged, their 0.33C discharge capacity was tested at different temperatures of -20℃, 25℃ and 45℃ to analyze the initial performance of the batteries.

[0121] Bulging and Swelling Detection: The lithium manganese iron phosphate pouch batteries of the embodiments and comparative examples, after initial performance testing, were subjected to charge-discharge cycles at 25°C and a current of 1C for 1000 cycles. The battery thickness was measured and recorded as h1. The rate of change in battery thickness (h1-h0) / h0 (also known as the expansion rate) was used to determine whether the lithium manganese iron phosphate pouch battery exhibited bulging or swelling. Specifically, the criteria were: if the rate of change in battery thickness (h1-h0) / h0 was greater than or equal to 30%, the lithium manganese iron phosphate pouch battery was considered to have bulged or swelled; if the rate of change in battery thickness (h1-h0) / h0 was less than 30%, the lithium manganese iron phosphate pouch battery was considered not to have bulged or swelled.

[0122] Fully charged electrode interface inspection: After fully charging the lithium manganese iron phosphate pouch batteries of the examples and comparative examples, they were disassembled to observe the fully charged electrode interface. It should be noted that a good fully charged electrode interface means that after the battery is fully charged, there are no obvious black spots, purple spots, or lithium plating on the negative electrode after disassembly. Specific results are shown in Table 1. Figures 1-6 As shown.

[0123] Table 1

[0124]

[0125] The data above shows that the lithium manganese iron phosphate pouch battery formed using the method of this invention exhibits higher initial efficiency and discharge capacity during charge-discharge testing due to more thorough side reactions during the formation stage and better film formation on the negative electrode. The initial efficiency is between 88.5% and 90.3%, while batteries formed using other methods have an initial efficiency between 86% and 89%. The discharge capacity of the battery formed using the method of this invention, especially the high-temperature and low-temperature discharge capacities, is significantly higher than that of the battery formed using the comparative method. Furthermore, after 1000 charge-discharge cycles, the battery showed no significant bulging or gas buildup. In addition, disassembly of the battery formed using the method of this invention revealed a good disassembly interface with no obvious black spots, purple spots, or lithium plating. Therefore, the formation method of this invention can effectively improve the problems often encountered with existing conventional formation processes, such as battery bulging, poor electrode interface condition, and insufficient capacity utilization.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for forming a lithium manganese iron phosphate pouch battery, characterized in that, Includes the following steps: (a) Allow the lithium manganese iron phosphate soft-pack batteries that have been injected and aged to stand for the first time. The first standing time is 0.5-3 hours. (b) The lithium manganese iron phosphate pouch battery after the first settling is charged with a constant current I1 to 20-30% SOC, where I1 is 0.02-0.06C, and then subjected to a second settling. (c) Charge the lithium manganese iron phosphate soft-pack battery after the second settling period to 22-40% SOC with a constant current I2 of 0.1-0.6C, and then set it for a third time for no less than 10 hours. (d) The lithium manganese iron phosphate pouch battery after the third settling period is charged to 100% SOC with constant current and constant voltage at a current I3 of 0.1-0.6C, and the formation is completed. The settling process and / or charging process in steps (a), (b), (c) and (d) are all carried out under high temperature and high pressure conditions, where the temperature is 25-60℃ and the pressure is 100-800 kgf.

2. The formation method of lithium manganese iron phosphate soft-pack battery according to claim 1, characterized in that, In step (b), the second settling time is 5-30 minutes.

3. The formation method of lithium manganese iron phosphate soft-pack battery according to claim 1, characterized in that, In step (c), the third settling time is 10-20 hours.

4. The formation method of lithium manganese iron phosphate soft-pack battery according to claim 1, characterized in that, In step (d), the lithium manganese iron phosphate soft-pack battery is charged with a constant current I3 and constant voltage until the cutoff voltage is 4.2V and the cutoff current is 0.05C, so that the battery reaches 100% SOC.

5. The formation method of a lithium manganese iron phosphate pouch battery according to any one of claims 1-4, characterized in that, Steps (a), (b), (c) and (d) are all carried out in a heating and pressurizing formation apparatus.

6. The application of the formation method of lithium manganese iron phosphate soft-pack battery according to any one of claims 1-5 in the field of lithium-ion batteries.

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