Formation method of lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery formation method and a lithium ion battery, the formation method comprises the following steps: S1, allowing a soft package cell to stand in a vacuum environment; s2, applying a first pressure and heating, and then carrying out constant current charging to 20%-40% SOC at a small current of 0.02-0.05 C; s3, second pressure is applied, heating is conducted, then constant current charging is conducted to 50%-70% SOC with the large current of 0.1-0.2 C, and the second pressure is larger than the first pressure; s4, applying a third pressure and heating, and then performing constant-current discharge at the current of 0.2-0.5 C until the SOC is 30-50%; and S5, performing high-temperature aging on the soft package battery cell. According to the formation method provided by the invention, the cycle performance of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery is improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a formation method of a lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery and a lithium ion battery. Background Art

[0002] In the process of reducing carbon emissions and developing green energy, lithium-ion batteries play an extremely important role. However, conventional lithium-ion battery positive electrode materials have certain disadvantages when used alone. When lithium iron manganese phosphate materials are used alone as positive electrodes, although they have high safety performance and low price, they have low energy density, poor conductivity, poor rate performance, dual-platform voltage phenomenon, short driving range, etc. When ternary materials are used alone as positive electrodes, although they have high energy density, good driving range and good rate performance, they have disadvantages such as low safety and high price. Mixing lithium iron manganese phosphate with ternary materials can achieve the requirements of medium and low cost, high safety, long driving range and long cycle life. Therefore, more and more research is being conducted on lithium iron manganese phosphate-ternary material composite positive electrode lithium-ion batteries.

[0003] As the most important link in the post-process of lithium-ion battery production, formation is the process of charging the battery for the first time and activating the electrochemical reaction inside the battery. As the formation charging proceeds, lithium ions are deintercalated from the positive electrode material, transported through the electrolyte through the diaphragm to the negative electrode and embedded in the negative electrode material, thereby forming a potential difference between the positive and negative electrodes and converting electrical energy into chemical energy of the battery. When the formation voltage reaches a certain value, a redox reaction occurs at the solid-liquid interface between the negative electrode and the electrolyte to form a solid electrolyte interface film (SEI film). On the one hand, some lithium ions are consumed during the formation of the SEI film, reducing the initial coulombic efficiency of the battery; on the other hand, the SEI film can exist relatively stably in the electrolyte solvent, avoiding the excessive expansion of the negative electrode material caused by the co-embedding of the solvated lithium ions into the negative electrode, ensuring that the battery can work stably for a long time.

[0004] At present, the formation process of lithium iron phosphate system lithium ion batteries mostly adopts lithium iron phosphate formation process, including high temperature infiltration, small current stage charging (usually charging to 40% SOC), and high temperature aging steps. The traditional formation process has low utilization rate of electrolyte, insufficient formation reaction, and is more likely to produce gas during the later battery charge and discharge cycle, which makes the cycle performance of lithium ion batteries poor. At present, even for similar materials and process systems, the formation SOC values ​​used by various research institutions, including manufacturing companies, to make lithium ion batteries are not the same, and are basically selected based on past experience. There are few related research reports on the influence of formation charging SOC on battery performance of lithium iron phosphate-ternary material composite positive electrode lithium ion batteries. Therefore, it is of great significance to study a formation method for lithium iron phosphate-ternary material composite positive electrode lithium ion batteries to improve the cycle performance of the lithium ion battery. 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 formation method for a lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery and a lithium ion battery. The formation method provided by the present invention improves the cycle performance of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery by charging to 50% to 70% SOC in stages and then discharging to 30% to 50% SOC.

[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 manganese phosphate-ternary material composite positive electrode lithium ion battery, the formation method comprising the following steps:

[0008] S1. Vacuum infiltration: Place the pre-sealed soft-pack battery cell in a vacuum environment;

[0009] S2, first pressure hot pressing and low current charging: applying a first pressure to the vacuum-impregnated soft-pack battery cell and heating it, and then charging it at a low current constant current of 0.02 to 0.05C until it is charged to 20% to 40% SOC;

[0010] S3, second pressure hot pressing and high current charging: applying a second pressure and heating the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging, and then charging with a high current constant current of 0.1-0.2C until it is charged to 50%-70% SOC, wherein the second pressure is greater than the first pressure;

[0011] S4, third pressure hot pressing and discharge: applying a third pressure and heating the soft-pack battery cell that has been subjected to the second pressure hot pressing and high current charging, and then discharging at a constant current of 0.2-0.5C until the SOC is discharged to 30%-50%;

[0012] S5, high temperature aging: performing high temperature aging on the soft-pack battery cell that has been hot pressed at the third pressure and discharged.

[0013] The formation method provided by the present invention improves the cycle performance of the lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery by charging to 50% to 70% SOC in stages and then discharging to 30% to 50% SOC.

[0014] Furthermore, in step S1, the liquid-injected pre-sealed soft-pack battery cell is obtained by injecting electrolyte into the soft-pack battery cell and then sealing the airbag bag, the vacuum environment is an environment with a vacuum degree of ≤-95kPa, the standing temperature is 45 to 65°C, and the standing time is 8 to 12 hours.

[0015] Furthermore, in step S2, the first pressure is 0.1-0.3 MPa, and the heating temperature is 45-60°C.

[0016] Furthermore, in step S3, the second pressure is 0.3-0.5 MPa, and the heating temperature is 45-60°C.

[0017] Furthermore, in step S4, the third pressure is 0.5 MPa to 1.0 MPa, and the heating temperature is 45 to 60°C.

[0018] Furthermore, in step S5, the temperature of the high temperature aging is 45-60° C., and the time of the high temperature aging is 8-24 hours.

[0019] Furthermore, the negative electrode active material of the lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery includes at least one of graphite, silicon oxygen, silicon carbon, and hard carbon.

[0020] Furthermore, the ternary material includes at least one of NCM and NCA.

[0021] Furthermore, the mass ratio of the lithium manganese iron phosphate to the ternary material is (1-9):(9-1) and the sum of the mass ratios is 10.

[0022] In a second aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery is produced by the formation method described in the first aspect.

[0023] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0024] (1) The formation method provided by the present invention improves the cycle performance of the lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery by charging to 50% to 70% SOC in stages and then discharging to 30% to 50% SOC.

[0025] (2) The present invention can firstly accelerate the absorption of electrolyte by positive and negative electrodes and diaphragms through vacuum high-temperature infiltration, thereby reducing the time required for normal temperature or high-temperature infiltration; secondly, during the charging process of the lithium iron manganese phosphate-ternary material composite positive electrode soft-pack lithium ion battery, the first pressure and the second pressure are applied in sequence to shorten the distance between the positive electrode and the negative electrode under the first pressure, reduce the lithium ion transmission path, and at the same time ensure that the positive and negative electrode interfaces of the battery are flat and in uniform contact, which is conducive to the uniform distribution of electrons and makes it easier to form the negative electrode SEI film during low-current charging. Under the second pressure, the gas generated during the charging process can be discharged from the electrolyte, avoiding the gas generated during the formation process from hindering the contact between the electrolyte and the positive and negative electrodes, thereby generating a gas path at the electrode interface. In addition, as the pressure increases and the SOC increases, lithium ions can be better embedded in the negative electrode to form a more complete, dense and uniform SEI film. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art 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 ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0027] The endpoints and any values ​​of the ranges disclosed in the present 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0028] In a first aspect, the present invention provides a formation method for a lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery, the formation method comprising the following steps:

[0029] S1. Vacuum infiltration: Place the pre-sealed soft-pack battery cell in a vacuum environment;

[0030] S2, first pressure hot pressing and low current charging: applying a first pressure to the vacuum-impregnated soft-pack battery cell and heating it, and then charging it at a low current constant current of 0.02-0.05C (for example, 0.02C, 0.03C, 0.04C or 0.05C) until it is charged to 20%-40% SOC (for example, 20% SOC, 25% SOC, 30% SOC, 35% SOC or 40% SOC);

[0031] S3, second pressure hot pressing and high current charging: apply a second pressure and heat the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging, and then charge it with a high current constant current of 0.1-0.2C (0.1C, 0.15C or 0.2C) until it is charged to 50%-70% SOC (for example, 50% SOC, 55% SOC, 60% SOC, 65% SOC or 70% SOC), wherein the second pressure is greater than the first pressure;

[0032] S4, third pressure hot pressing and discharge: apply a third pressure and heat the soft-pack battery cell that has been subjected to the second pressure hot pressing and high current charging, and then discharge it at a constant current of 0.2 to 0.5C (for example, 0.2C, 0.3C, 0.4C or 0.5C) until it is discharged to 30% to 50% SOC;

[0033] S5, high temperature aging: performing high temperature aging on the soft-pack battery cell that has been hot pressed at the third pressure and discharged.

[0034] The formation method provided by the present invention improves the cycle performance of the lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery by charging to 50% to 70% SOC in stages and then discharging to 30% to 50% SOC.

[0035] In step S2, a small current of 0.02 to 0.05C is used to form a thick, uniform and dense passivation layer on the surface of the negative electrode, effectively stabilize the electrode / electrolyte interface, buffer the volume change of the negative electrode in the subsequent cycle, and avoid the continuous decomposition of the electrolyte caused by the exposure of the negative electrode active sites to the electrolyte, thereby improving the electrochemical performance of the negative electrode. If the current is too large, the SEI film formed is too loose, which is not conducive to the later electrochemical performance; if the current is too small, the SEI film formed is of good quality, but the formation time is long, the production efficiency is low, and long-term small current charging will lead to an increase in the impedance of the SEI film, thereby affecting the battery's rate and cycle performance.

[0036] In step S3, constant current charging is performed at 0.1-0.2C, so that the SEI film formed in the formation process contains more organic lithium salts and less inorganic lithium salts, which can wrap the negative electrode more evenly and protect the electrode material well.

[0037] In step S3, the battery is charged to 50% to 70% SOC, and the formation voltage reaches the charge and discharge platform of the lithium manganese iron phosphate-ternary material composite positive electrode material to make the film formation on the negative electrode more complete. Then, the battery is further formed to the rated voltage (full charge), and the SEI film impedance will gradually increase, resulting in deterioration of its electrochemical performance.

[0038] In the formation method of the above-mentioned lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery, as an optional implementation mode, in step S1, the soft-pack battery cell after the liquid injection pre-sealing is obtained by injecting electrolyte into the dry soft-pack battery cell and then sealing the airbag bag, the vacuum environment is an environment with a vacuum degree of ≤-95kPa, the standing temperature is 45 to 65°C (for example, it can be 45°C, 50°C, 55°C, 60°C or 65°C), and the standing time is 8 to 12h (for example, it can be 8h, 10h or 12h).

[0039] In the above-mentioned lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery formation method, as an optional implementation, in step S2, the first pressure is 0.1~0.3Mpa (for example, it can be 0.1Mpa, 0.2Mpa or 0.3Mpa), and the heating temperature is 45~60℃ (for example, it can be 45℃, 50℃, 55℃ or 60℃).

[0040] In the above-mentioned lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery formation method, as an optional implementation, in step S3, the second pressure is 0.3~0.5Mpa (for example, it can be 0.3Mpa, 0.4Mpa or 0.5Mpa), and the heating temperature is 45~60℃ (for example, it can be 45℃, 50℃, 55℃ or 60℃).

[0041] In the above-mentioned lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery formation method, as an optional implementation, in step S4, the third pressure is 0.5Mpa~1.0Mpa (for example, it can be 0.5Mpa, 0.7Mpa or 1Mpa), and the heating temperature is 45~60℃ (for example, it can be 45℃, 50℃, 55℃ or 60℃).

[0042] In the above-mentioned lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery formation method, as an optional implementation, in step S5, the high temperature aging temperature is 45-60°C (for example, it can be 45°C, 50°C, 55°C or 60°C), and the high temperature aging time is 8-24h (for example, it can be 8h, 12h, 14h, 16h, 18h, 20h, 22h or 24h).

[0043] In the formation method of the above-mentioned lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery, as an optional implementation, the negative electrode active material of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery includes at least one of graphite (fast charging type / high energy type), silicon oxygen, silicon carbon, and hard carbon.

[0044] In the above-mentioned formation method of lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery, as an optional implementation, the ternary material includes at least one of NCM and NCA.

[0045] In the formation method of the above-mentioned lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery, as an optional implementation, the mass ratio of the lithium manganese iron phosphate to the ternary material is (1-9): (9-1) and the sum of the mass ratios is 10, for example, it can be 1:9, 2:8, 4:6, 5:5, 7:3 or 9:1.

[0046] In a second aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery is produced by the formation method described in the first aspect.

[0047] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0048] The soft-packed cells used in the following examples and comparative examples are: the cell capacity is 3.5Ah, the positive electrode is NCM801010 and LMFP-64 (LiMn x Fe 1-x PO4, 0<X<1, 64 represents the molar ratio of manganese to iron is 6:4,), the mass ratio of NCM801010 and LMFP-64 is 3:7, the negative electrode is Gr (graphite), the separator is 9+3 (9um base film (PE) + 3um ceramic layer), electrolyte: solvent: EMC, DEC and EC in a volume ratio of 6:3:1, solute: 0.8mol / L LiPF6 and 0.3mol / L LiFSI and 2wt% VC, 1wt% DTD, 0.5wt% TMSP and 0.2wt% PS as solvent-based additives, the soft-pack battery cell after liquid injection and pre-sealing consists of a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, external positive and negative electrode tabs, and a battery cell outer packaging film.

[0049] Example 1

[0050] The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery provided in this embodiment comprises the following steps:

[0051] S1. Vacuum high-temperature infiltration: inject electrolyte into the dry soft-pack battery cell, and then seal the airbag bag to obtain the soft-pack battery cell after liquid injection and pre-sealing. Put the soft-pack battery cell after liquid injection and pre-sealing into a high-temperature box with a vacuum degree of -95kpa and 45°C and let it stand for 12 hours.

[0052] S2, first pressure hot pressing and low current charging: Apply a first pressure of 0.3 MPa to the soft-pack battery cell that has undergone vacuum high-temperature infiltration and heat it at 45°C, then charge it at a low current constant current of 0.05C for 360 minutes to 30% SOC.

[0053] S3, second pressure hot pressing and high current charging: apply a second pressure of 0.5 MPa to the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging and heat it to 45°C, then charge it with a high current constant current of 0.2C for 90 minutes, and charge it to 60% SOC at a constant current.

[0054] S4, third pressure hot pressing and discharge: apply a third pressure of 1.0 MPa and heat to 45°C to the soft-pack battery cell that has undergone the second pressure hot pressing and high-current charging, and then discharge at a constant current of 0.2C until it is discharged to 40% SOC.

[0055] S5. High temperature aging: The soft-packed cells that have been hot-pressed and discharged at the third pressure are subjected to high temperature aging at 45°C for 8 hours.

[0056] Example 2

[0057] The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery provided in this embodiment comprises the following steps:

[0058] S1. Vacuum high-temperature infiltration: inject electrolyte into the dry soft-pack battery cell, and then seal the airbag bag to obtain the soft-pack battery cell after liquid injection and pre-sealing. Put the soft-pack battery cell after liquid injection and pre-sealing into a high-temperature box with a vacuum degree of -95kpa and 50°C and let it stand for 10 hours.

[0059] S2, first pressure hot pressing and low current charging: Apply a first pressure of 0.3 MPa to the soft-pack battery cell that has undergone vacuum high-temperature infiltration and heat it to 60°C, then charge it with a low current constant current of 0.02C to 20% SOC.

[0060] S3, second pressure hot pressing and high current charging: apply a second pressure of 0.5 MPa and heat to 60°C to the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging, and then charge with a high current constant current of 0.1C to 50% SOC.

[0061] S4, third pressure hot pressing and discharge: apply a third pressure of 0.5 MPa and heat to 60° C. to the soft-pack battery cell that has undergone the second pressure hot pressing and high-current charging, and then discharge at a constant current of 0.5 C until it is discharged to 30% SOC.

[0062] S5. High temperature aging: The soft-packed cells that have been hot-pressed and discharged at the third pressure are subjected to high temperature aging at 45°C for 8 hours.

[0063] Example 3

[0064] The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery provided in this embodiment comprises the following steps:

[0065] S1. Vacuum high-temperature infiltration: inject electrolyte into the dry soft-pack battery cell, and then seal the airbag bag to obtain the soft-pack battery cell after liquid injection and pre-sealing. Put the soft-pack battery cell after liquid injection and pre-sealing into a high-temperature box with a vacuum degree of -95kpa and 60°C and let it stand for 8 hours.

[0066] S2, first pressure hot pressing and low current charging: Apply a first pressure of 0.3 MPa to the soft-pack battery cell that has undergone vacuum high-temperature infiltration and heat it at 45°C, then charge it at a low current constant current of 0.05C to 40% SOC.

[0067] S3, second pressure hot pressing and high current charging: apply a second pressure of 0.5 MPa to the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging and heat it to 45°C, then charge it with a high current constant current of 0.2C to 60% SOC.

[0068] S4, third pressure hot pressing and discharge: apply a third pressure of 1.0 MPa and heat at 45°C to the soft-pack battery cell that has undergone the second pressure hot pressing and high-current charging, and then discharge at a constant current of 0.2C until it is discharged to 50% SOC.

[0069] S5. High temperature aging: The soft-packed cells that have been hot-pressed and discharged at the third pressure are subjected to high temperature aging at 60°C for 10 hours.

[0070] Comparative Example 1

[0071] This comparative example provides a formation method for a lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery. Except for omitting step S4, the remaining steps are the same as those in Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a formation method for a lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery. Except for discharging to a cut-off voltage (0% SOC) in step S4, the remaining steps are the same as those in Example 1.

[0074] Comparative Example 3

[0075] The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery provided in this comparative example comprises the following steps:

[0076] S1. Vacuum high-temperature infiltration: inject electrolyte into the dry soft-pack battery cell, and then seal the airbag bag to obtain the soft-pack battery cell after liquid injection and pre-sealing. Put the soft-pack battery cell after liquid injection and pre-sealing into a high-temperature box with a vacuum degree of -95kpa and 45°C and let it stand for 12 hours.

[0077] S2, first pressure hot pressing and low current charging: Apply a first pressure of 0.3 MPa to the soft-pack battery cell that has undergone vacuum high-temperature infiltration and heat it at 45°C, then charge it at a low current constant current of 0.05C to 10% SOC.

[0078] S3, second pressure hot pressing and high current charging: apply a second pressure of 0.5 MPa to the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging and heat it to 45°C, then charge it with a high current constant current of 0.2C to 40% SOC.

[0079] S4. High temperature aging: The soft-packed cells that have undergone the second pressure hot pressing and high current charging are subjected to high temperature aging at 45°C for 8 hours.

[0080] Comparative Example 4

[0081] This comparative example provides a formation method for a lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery. Except for constant current charging to 80% SOC in step S3, the remaining steps are the same as those in Example 1.

[0082] Comparative Example 5

[0083] This comparative example provides a formation method for a lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery. Except for constant current charging to 100% SOC in step S3, the remaining steps are the same as those in Example 1.

[0084] Comparative Example 6

[0085] This comparative example provides a formation method for a lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery. Except for constant current charging to 100% SOC in step S3 and omitting step S4, the remaining steps are the same as those in Example 1.

[0086] Performance Testing

[0087] The performance test of the lithium ion battery formed by the formation method provided in the embodiment and the comparative example is carried out, and the specific process is as follows:

[0088] The test method for the first coulombic efficiency is as follows: the battery is first charged at a constant current of 0.2C to a rated voltage of 4.2V, then charged at a constant voltage with a cut-off current of 0.05C, and finally discharged at a constant current of 0.2C to 2.5V; the first coulombic efficiency = first discharge capacity / first charge capacity*100%.

[0089] Cycle performance test: The charge and discharge cycle performance tests were carried out at 25°C and 45°C respectively. The test conditions are as follows: voltage range: 2.5-4.2V, charging current 0.5C, discharging current 1C, 45°C capacity cycle retention rate = 600th cycle discharge capacity / 1st cycle discharge capacity, 25°C cycle 1000 times capacity cycle retention rate = 1000th cycle discharge capacity / 1st cycle discharge capacity.

[0090] The specific results of the above performance tests are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] From Table 1 we can at least see that:

[0095] (1) Comparing Example 1 with Comparative Example 1, when the formation method does not include a discharge step, the initial coulombic efficiency is reduced, the cycle performance is degraded, and after 600 cycles at high temperature, the battery is disassembled and a small amount of black spots are found on the interface, indicating that the negative electrode is not uniformly intercalated with lithium and lithium plating occurs.

[0096] (2) Comparing Example 1 with Comparative Example 2, when discharged to the cut-off voltage (0% SOC) in step S4, the high temperature cycle performance is significantly reduced. After 600 cycles at high temperature, the battery is disassembled and a small amount of black spots are found on the interface, indicating that the negative electrode is not uniformly embedded with lithium and lithium plating occurs.

[0097] (3) Comparing Examples 1-3 with Comparative Example 3, when the conventional formation method in the prior art is used and the battery is charged in stages to 40% SOC, the cycle performance of the battery is significantly reduced. After 600 cycles at high temperature, the battery is disassembled and a large number of black spots are found on the interface, indicating that the negative electrode is not evenly embedded with lithium and lithium plating occurs.

[0098] (4) Comparing Example 1 with Comparative Example 4, when constant current charging to 80% SOC is performed in step S3, the high temperature cycle performance is significantly reduced. After 600 cycles at high temperature, the battery is disassembled and a small amount of black spots are found on the interface, indicating that the negative electrode is not uniformly embedded with lithium and lithium plating occurs.

[0099] (5) Comparing Example 1 with Comparative Example 5, when constant current charging to 100% SOC is performed in step S3, the cycle performance decreases, especially the cycle performance at high temperature decreases significantly. After 600 cycles at high temperature, the battery is disassembled and a small amount of black spots are found on the interface, indicating that the negative electrode is not uniformly embedded with lithium and lithium plating occurs.

[0100] (6) Comparing Example 1 with Comparative Example 6, when constant current charging to 100% SOC is performed in step S3 and step S4 is omitted, the initial coulombic efficiency decreases significantly, and the cycle performance, especially the high-temperature cycle performance, decreases significantly. After 600 cycles at high temperature, the battery is disassembled and a small amount of black spots are found on the interface, indicating that the negative electrode is not evenly intercalated with lithium and lithium plating occurs.

[0101] In summary, the formation method provided in the present application can enable lithium-ion batteries to have excellent cycle performance, especially cycle performance at high temperatures. The better the high-temperature performance of the battery, the better it can meet the needs and applications of more scenarios, and it can also reflect the safety and stability of the battery under high temperature conditions.

[0102] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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 manganese iron phosphate-ternary material composite positive electrode lithium ion battery, characterized in that: The formation method comprises the following steps: S1. Vacuum infiltration: Place the pre-sealed soft-pack battery cell in a vacuum environment; S2, first pressure hot pressing and low current charging: applying a first pressure to the vacuum-impregnated soft-pack battery cell and heating it, and then charging it at a low current constant current of 0.02 to 0.05C until it is charged to 20% to 40% SOC; S3, second pressure hot pressing and high current charging: applying a second pressure and heating the soft-pack battery cell that has undergone the first pressure hot pressing and low current charging, and then charging with a high current constant current of 0.1-0.2C until it is charged to 50%-70% SOC, wherein the second pressure is greater than the first pressure; S4, third pressure hot pressing and discharge: applying a third pressure and heating the soft-pack battery cell that has been subjected to the second pressure hot pressing and high current charging, and then discharging at a constant current of 0.2-0.5C until the SOC is discharged to 30%-50%; S5, high temperature aging: performing high temperature aging on the soft-pack battery cell that has been hot pressed at the third pressure and discharged.

2. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: In step S1, the liquid-injected pre-sealed soft-pack battery cell is obtained by injecting electrolyte into the soft-pack battery cell and then sealing the airbag bag. The vacuum environment is an environment with a vacuum degree of ≤-95kPa, the standing temperature is 45-65°C, and the standing time is 8-12h.

3. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: In step S2, the first pressure is 0.1-0.3 MPa, and the heating temperature is 45-60°C.

4. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: In step S3, the second pressure is 0.3-0.5 MPa, and the heating temperature is 45-60°C.

5. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: In step S4, the third pressure is 0.5 MPa to 1.0 MPa, and the heating temperature is 45 to 60°C.

6. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: In step S5, the high temperature aging temperature is 45-60° C., and the high temperature aging time is 8-24 hours.

7. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: The negative electrode active material of the lithium manganese iron phosphate-ternary material composite positive electrode lithium ion battery includes at least one of graphite, silicon oxygen, silicon carbon, and hard carbon.

8. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: The ternary material includes at least one of NCM and NCA.

9. The formation method of the lithium iron manganese phosphate-ternary material composite positive electrode lithium ion battery according to claim 1, characterized in that: The mass ratio of the lithium manganese iron phosphate to the ternary material is (1-9):(9-1) and the sum of the mass ratios is 10.

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

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