A lithium battery formation process

Abstract

The application discloses a lithium battery formation process. The lithium battery formation process comprises the following steps: an iron platform charging stage: setting a charging current as a first charging current, an environmental pressure as a first charging pressure, a charging temperature as a first charging temperature, and charging the battery under the above conditions so that the state of charge of the battery is increased from 0% SOC to Q1; a transition charging stage: setting a charging current as a second charging current, an environmental pressure as a second charging pressure, a charging temperature as a second charging temperature, and charging the battery under the above conditions so that the state of charge of the battery is increased from Q1 to Q2; a manganese platform charging stage: setting a charging current as a third charging current, an environmental pressure as a third charging pressure, a charging temperature as a third charging temperature, and charging the battery under the above conditions so that the state of charge of the battery is increased from Q2 to 100% SOC. The application has the advantages of improving the stability of SEI film and CEI film and improving the cycle performance of the lithium battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a lithium battery formation process. BACKGROUND

[0002] Formation is the most critical process in the production process of lithium ion batteries. The formation process refers to the first charging of the lithium ion battery after standing after liquid injection, so as to form a stable solid electrolyte interface film (SEI film) on the surface of the negative electrode.

[0003] A good SEI film can slow down the continued reaction of the negative electrode with the electrolyte in the subsequent charging and discharging process of the lithium battery, and reduce the continuous consumption of the electrolyte. On the other hand, during the first charging of the lithium battery, the positive material at the positive electrode will also react with the electrolyte, generating an electrochemical interface film (CEI film) that can also isolate the electrolyte from the subsequent reaction of the positive material. Therefore, the formation process will affect the formation of the SEI film and the CEI film in the lithium battery, and thus affect the electrical performance of the lithium ion battery.

[0004] As an upgraded product of lithium iron phosphate material, lithium manganese iron phosphate positive material has a higher voltage platform in the charging and discharging process due to the addition of Mn element, which can greatly improve the energy density of the lithium battery. However, Mn in lithium manganese iron phosphate also reduces its conductivity (the conductivity of lithium manganese iron phosphate is less than that of lithium iron phosphate); in addition, the valence state of Mn is unstable, and non-stoichiometric phases such as Li(Mn a Fe(1-a))2(PO4)3, etc. In addition, the sudden increase of the Mn and Fe double platform region in the lithium manganese iron phosphate material will exacerbate the lattice distortion during the lithium ion deintercalation process, and thus exacerbate the side reaction between the positive material and the electrolyte, especially affecting the quality of the CEI film formed during formation, which is not conducive to improving the cycle performance of the lithium battery. SUMMARY

[0005] In order to improve the stability of the SEI film and the CEI film generated after the formation of the lithium manganese iron phosphate battery and improve the cycle performance of the lithium battery, the present application provides a lithium battery formation process.

[0006] The present application provides a lithium battery formation process, which adopts the following technical scheme:

[0007] A lithium battery formation process, the lithium battery formation process includes sequentially performed iron platform charging stage, transition charging stage and manganese platform charging stage;

[0008] The iron platform charging stage: setting the charging current as a first charging current, setting the environmental pressure as a first charging pressure, setting the charging temperature as a first charging temperature, charging the lithium battery under the above conditions to increase the state of charge of the lithium battery from 0% SOC to Q1, Q1 = first charging current C1 x charging time t1 of the iron platform charging stage;

[0009] The transition charging stage: setting the charging current as a second charging current, setting the environmental pressure as a second charging pressure, setting the charging temperature as a second charging temperature, charging the lithium battery under the above conditions to increase the state of charge of the lithium battery from Q1 to Q2, Q2 = second charging current C1 x charging time t2 of the transition charging stage;

[0010] The manganese platform charging stage: setting the charging current as a third charging current, setting the environmental pressure as a third charging pressure, setting the charging temperature as a third charging temperature, charging the lithium battery under the above conditions to increase the state of charge of the lithium battery from Q2 to 100% SOC;

[0011] The second charging current < the third charging current < the first charging current;

[0012] The first charging temperature = the third charging temperature < the second charging temperature;

[0013] The first charging pressure < the second charging pressure, and the third charging pressure < the second charging pressure;

[0014] The positive active material of the lithium battery comprises lithium iron manganese phosphate, and the structural formula of the lithium iron manganese phosphate is LiFe a Mn (1-a) PO4, 0 < a < 1;

[0015] The Q1 = (a / 2 + X) x 100% SOC, the Q2 = (Q1 + Y) x 100% SOC, 0.05 ≤ X ≤ 0.15, 0.05 ≤ Y ≤ 0.1.

[0016] Preferably, the environmental pressure refers to the clamp pressure of the lithium battery.

[0017] In the present application, three-stage charging operation is adopted, and the cut-off state of charge of each stage in the three-stage charging operation is adjusted for different iron element and manganese element content of the lithium iron manganese phosphate material, and the corresponding charging stage is combined with the storage temperature and the control of the charging current in each charging stage, which can form more stable SEI film and CEI film, improve the stability of the lithium battery; and the positive plate can be in close contact with each other, so as to balance the polarization degree of each part of the positive plate, which helps to improve the formation efficiency; thereby reducing the gas production in the cycle process. Secondly, it can avoid the lattice distortion generated in the lithium ion deintercalation process, avoid the side reaction between the positive electrode and the electrolyte, and significantly improve the stability of the CEI film.

[0018] Specifically, the first charging current is large enough to activate the battery cell and provide a basis for the film forming reaction in the formation process. The reaction of the positive electrode material in this stage is mainly Fe 2+ oxidized to Fe 3+ . The second charging current is the smallest, and in this charging process, the reaction of the positive electrode material is gradually from Fe 2+ oxidized to Fe 3+ to Mn 2+ oxidized to Mn 3+ . In this stage, a small current is required to avoid the distortion of the crystal structure caused by large current, and small current can form a more stable CEI film to avoid the damage of the CEI film caused by the deintercalation of lithium ions in the lithium battery cycle process. This not only helps to improve the cycle performance of the lithium battery, but also the high stability of the CEI film can effectively protect the positive and negative electrode materials, avoid the side reaction between the positive and negative electrode materials and the electrolyte, and reduce the gas production in the lithium battery cycle process. The third charging current is higher than the second charging current. At this time, the reaction is completely the oxidation of Mn 2+ to Mn 3+ . A slightly larger current can be used. The oxidation of Mn 2+ to Mn 3+ is more sensitive to the environment than the oxidation of Fe 2+ to Fe 3+ , so a large current is required and the first charging current is smaller.

[0019] The cut-off state of charge Q1 of the iron platform charging stage and the cut-off state of charge Q2 of the transition charging stage are determined by the Fe / Mn ratio in the LMFP material, and the appropriate charging current is selected according to the oxidation reaction stability in different charging stages, which can improve the formation efficiency and effect. By controlling the formation temperature, the pressure of the lithium battery clamp in the three charging stages, the appropriate temperature setting can improve the mobility of lithium ions in the electrolyte, and the SEI film and the CEI film can maintain a dynamic balance between generation and decomposition, which helps to further improve the stability of the SEI film and the CEI film, improve the cycle performance of the lithium battery, and reduce the gas production of the lithium battery.

[0020] Preferably, the first charging temperature is 40-50℃, and the first charging pressure is 0.1-0.4 MPa.

[0021] Preferably, the first charging current is 0.15-0.35C.

[0022] Preferably, before the iron platform charging stage, a first resting operation is performed on the lithium battery, and the temperature and ambient pressure settings during the first resting operation are consistent with the first charging temperature and the first charging pressure of the iron platform charging stage; in the first resting operation, the resting time is 5-20 min.

[0023] By resting before the iron platform charging stage, the cell temperature is adapted to facilitate the first charging temperature.

[0024] Preferably, the second charging temperature is 55-65℃, and the second charging pressure is 0.7-0.9 MPa.

[0025] Preferably, the second charging current is 0.02-0.06C.

[0026] Preferably, between the iron platform charging stage and the transition charging stage, a second resting operation is further included, and the temperature and ambient pressure settings during the second resting operation are consistent with the second charging temperature and the second charging pressure of the transition charging stage; in the second resting operation, the resting time is 5-20 min.

[0027] By resting before the manganese platform charging stage, the cell temperature is adapted to facilitate the second charging temperature.

[0028] Preferably, the third charging temperature is 40-50℃, and the third charging pressure is 0.4-0.6 MPa.

[0029] Preferably, the third charging current is 0.08-0.12C.

[0030] Preferably, the charging cutoff voltage of the manganese platform charging stage is 4.2-4.3V, and the charging cutoff current is 0.03-0.08C.

[0031] Preferably, between the transition charging stage and the manganese platform charging stage, a third resting operation is further included, and the temperature and ambient pressure settings during the third resting operation are consistent with the third charging temperature and the third charging pressure of the transition charging stage; in the third resting operation, the resting time is 5-20 min.

[0032] By the resting before the manganese platform charging stage, the temperature of the battery cell is adapted to the third charging temperature, and the lithium battery is adapted to the charging condition of the next process (constant current and constant voltage charging).

[0033] Preferably, the lithium battery is subjected to an aging operation after the manganese platform charging stage.

[0034] Preferably, the aging temperature is 40-50℃, and the aging time is 48-72h.

[0035] By the above high-temperature aging operation, on the one hand, the electrolyte can be fully infiltrated into the electrode of the lithium battery, and on the other hand, the electrochemical performance of the lithium battery can be stabilized, which is helpful to form a stable electrolyte interface film and improve the cycle performance of the lithium battery.

[0036] Preferably, the manganese platform charging stage and the aging operation further comprise a fourth resting operation, the temperature in the fourth resting operation is 40-50℃, the environmental pressure is 0.4-0.6Mpa, and the resting time is 5-20min. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The figure is a schematic diagram of the whole formation stage of the lithium battery. DETAILED DESCRIPTION

[0038] The embodiments described are only a part of the embodiments of the present application, and are not all the embodiments.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0040] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as approximations as the exact properties are not necessarily critical in light of the underlying technical nature of the application.

[0041] As used herein, "and / or" means one or all of the listed items.

[0042] As used herein, "comprises" and "comprising" are open-ended language that is intended to encompass both the recited elements and additional ones without excluding other elements.

[0043] All percentages in the present application are weight percentages, unless otherwise specified.

[0044] As used in the present specification, "a", "an", "one", and "the" are intended to include "at least one" or "one or more" unless specified otherwise. For example, "a component" means one or more components, and thus, possibly more than one component is considered in the implementation of the described embodiments.

[0045] Example 1

[0046] The positive electrode material of the lithium battery in this embodiment is lithium iron manganese phosphate, and the chemical formula of the lithium iron manganese phosphate is LiFe a Mn (1-a) PO4, a = 0.4; X = 0.1, Y = 0.1;

[0047] A lithium battery formation process, comprising the following steps:

[0048] S1 (first resting operation), the lithium battery after liquid injection is placed in a clamp for the first time to rest, the temperature is set to 45°C, the clamp pressure is 0.3 MPa, and the resting time is 5 min;

[0049] S2 (iron platform charging stage), the lithium battery is charged to a state of charge Q1 (30% SOC) at a first charging temperature (45°C) and a first charging pressure (0.3 MPa) with a first charging current (0.2C);

[0050] S3 (second resting operation), the lithium battery obtained in S2 is subjected to the second resting operation, the temperature is set to 60°C, the clamp pressure is 0.8 MPa, and the resting time is 5 min;

[0051] S4 (transition charging stage), the lithium battery is charged to a state of charge Q2 (40% SOC) at a second charging temperature (60°C) and a second charging pressure (0.8 MPa) with a second charging current C2 (0.05C);

[0052] S5 (third resting operation), the lithium battery obtained in S4 is subjected to the third resting operation, the temperature is set to 45°C, the clamp pressure is 0.6 MPa, and the resting time is 5 min;

[0053] S6 (manganese platform charging stage), the lithium battery is charged to a state of charge Q3 (100% SOC) at a third charging temperature (45°C) and a third charging pressure (0.6 MPa) with a third charging current C3 (0.1C), and the charging cutoff voltage is controlled to be 4.2V, and the charging cutoff current is 0.05C;

[0054] S7 (aging operation), the lithium battery obtained in S6 is subjected to the fourth resting operation, the temperature is adjusted to 45°C, the clamp pressure is 0.6 MPa, and the resting time is 5 min, then the lithium battery is aged at 45°C for 48h, and then degassing and sealing are performed.

[0055] The full-stage schematic diagram of lithium battery formation in this embodiment is shown in Figure 1 .

[0056] Embodiment 2

[0057] The positive electrode material of the lithium battery in this embodiment is lithium manganese iron phosphate, and the chemical formula of the lithium manganese iron phosphate is LiFe a Mn (1-a) PO4, a = 0.5; X = 0.05, Y = 1;

[0058] A lithium battery formation process, comprising the following steps:

[0059] S1 (first resting operation), the lithium battery after liquid injection is placed in a clamp for the first time resting, the temperature is set to 40℃, the clamp pressure is 0.4MPa, and the resting is 10min;

[0060] S2 (iron platform charging stage), the temperature and clamp pressure are kept consistent with the above S1, the lithium battery is charged to the state of charge Q1 (30% SOC) at the first charging temperature (40℃) and the first charging pressure (0.4MPa) with the first charging current (0.3C);

[0061] S3 (second resting operation), the lithium battery obtained by the above S2 is subjected to the second resting, the temperature is set to 55℃, the clamp pressure is 0.7MPa, and the resting is 10min;

[0062] S4 (transition charging stage), the lithium battery is charged to the state of charge Q2 (40% SOC) at the second charging temperature (55℃) and the second charging pressure (0.7MPa) with the second charging current C2 (0.03C);

[0063] S5 (third resting operation), the lithium battery obtained by the above S4 is subjected to the third resting, the temperature is set to 40℃, the clamp pressure is 0.5MPa, and the resting is 10min;

[0064] S6 (manganese platform charging stage), the lithium battery is charged to the state of charge Q3 (100% SOC) at the third charging temperature (40℃) and the third charging pressure (0.5MPa) with the third charging current C3 (0.08C), and the charging operation cutoff voltage is controlled to be 4.2V, and the charging cutoff current is 0.05C;

[0065] S7 (aging operation), the lithium battery obtained by the above S6 is subjected to the fourth resting, the temperature is adjusted to 40℃, the clamp pressure is 0.5MPa, and the resting is 10min, then the aging is performed at the temperature of 40℃ for 72h, and then the degassing and sealing are performed.

[0066] Embodiment 3

[0067] The positive electrode material of the lithium battery in the embodiment is lithium iron manganese phosphate, and the chemical formula of the lithium iron manganese phosphate is LiFe a Mn (1-a) PO4, a = 0.6; X = 0.1, Y = 0.05;

[0068] A lithium battery formation process, comprising the following steps:

[0069] S1 (first resting operation), the lithium battery after injection is placed in a clamp for the first time, the temperature is set to 50 DEG C, the clamp pressure is 0.1 MPa, and the resting is 15 min;

[0070] S2 (iron platform charging stage), the temperature and clamp pressure are consistent with the above S1, the first charging temperature (50 DEG C) and the first charging pressure (0.1 MPa) are used to charge the above lithium battery to the state of charge Q1 (40% SOC) at the first charging current (0.3C);

[0071] S3 (second resting operation), the lithium battery obtained by the above S2 is subjected to the second resting, the temperature is set to 65 DEG C, the clamp pressure is 0.9 MPa, and the resting is 15 min;

[0072] S4 (transition charging stage), the lithium battery is charged to the state of charge Q2 (45% SOC) at the second charging temperature (65 DEG C) and the second charging pressure (0.9 MPa) by the second charging current C2 (0.06C);

[0073] S5 (third resting operation), the lithium battery obtained by the above S4 is subjected to the third resting, the temperature is set to 50 DEG C, the clamp pressure is 0.4 MPa, and the resting is 15 min;

[0074] S6 (manganese platform charging stage), the lithium battery is charged to the state of charge Q3 (100% SOC) at the third charging temperature (50 DEG C) and the third charging pressure (0.4 MPa) by the third charging current C3 (0.12C), and the charging operation cutoff voltage is controlled to be 4.2V, and the charging cutoff current is 0.03C;

[0075] S7 (aging operation), the lithium battery obtained by the above S6 is subjected to the fourth resting, the temperature is adjusted to 50 DEG C, the clamp pressure is 0.4 MPa, and the resting is 15 min, then the aging is performed at 50 DEG C for 45h, and the degassing sealing can be performed.

[0076] Example 4

[0077] The positive electrode material of the lithium battery in the embodiment is lithium iron manganese phosphate, and the chemical formula of the lithium iron manganese phosphate is LiFe a Mn (1-a)PO4, a = 0.7; X = 0.15, Y = 0.08;

[0078] A lithium battery formation process, comprising the following steps:

[0079] S1 (first resting operation), the lithium battery after injection is placed in the clamp for the first time to rest, the temperature is set to 50℃, the clamp pressure is 0.2MPa, and the resting time is 20min;

[0080] S2 (iron platform charging stage), the temperature and clamp pressure are consistent with the above S1, the first charging temperature (50℃) and the first charging pressure (0.2MPa) are used to charge the above lithium battery to the state of charge Q1 (50% SOC) at the first charging current (0.25C);

[0081] S3 (second resting operation), the lithium battery obtained by the above S2 is subjected to the second resting operation, the temperature is set to 60℃, the clamp pressure is 0.7MPa, and the resting time is 20min;

[0082] S4 (transition charging stage), the lithium battery is charged to the state of charge Q2 (58% SOC) at the second charging temperature (60℃) and the second charging pressure (0.7MPa) by the second charging current C2 (0.04C);

[0083] S5 (third resting operation), the lithium battery obtained by the above S4 is subjected to the third resting operation, the temperature is set to 50℃, the clamp pressure is 0.5MPa, and the resting time is 20min;

[0084] S6 (manganese platform charging stage), the lithium battery is charged to the state of charge Q3 (100% SOC) at the third charging temperature (50℃) and the third charging pressure (0.5MPa) by the third charging current C3 (0.1C), and the charging operation cutoff voltage is controlled to be 4.25V, and the charging cutoff current is 0.03C;

[0085] S7 (aging operation), the lithium battery obtained by the above S6 is subjected to the fourth resting operation, the temperature is adjusted to 50℃, the clamp pressure is 0.5MPa, and the resting time is 20min, then the aging is performed at the temperature of 45℃ for 56h, and then the degassing and sealing are performed.

[0086] Example 5

[0087] In this embodiment, the positive electrode material of the lithium battery is lithium manganese iron phosphate, and the chemical formula of the lithium manganese iron phosphate is LiFe a Mn (1-a) PO4, a = 0.7; X = 0.15, Y = 0.08;

[0088] A lithium battery formation process, comprising the following steps:

[0089] S1 (first resting operation), the lithium battery after injection is placed in the clamp for the first time to rest, the temperature is set to 45℃, the clamp pressure is 0.3MPa, and the resting time is 5min;

[0090] S2 (iron platform charging stage), the lithium battery is charged to the state of charge Q1 (30% SOC) at the first charging temperature (45℃) and the first charging pressure (0.3MPa) with the first charging current (0.4C);

[0091] S3 (second resting operation), the lithium battery obtained in S2 is subjected to the second resting operation, the temperature is set to 60℃, the clamp pressure is 0.8MPa, and the resting time is 5min;

[0092] S4 (transition charging stage), the lithium battery is charged to the state of charge Q2 (40% SOC) at the second charging temperature (60℃) and the second charging pressure (0.8MPa) with the second charging current C2 (0.1C);

[0093] S5 (third resting operation), the lithium battery obtained in S4 is subjected to the third resting operation, the temperature is set to 45℃, the clamp pressure is 0.6MPa, and the resting time is 5min;

[0094] S6 (manganese platform charging stage), the lithium battery is charged to the state of charge Q3 (100% SOC) at the third charging temperature (45℃) and the third charging pressure (0.6MPa) with the third charging current C3 (0.2C), and the charging cut-off voltage is controlled to be 4.2V and the charging cut-off current is 0.05C;

[0095] S7 (aging operation), the lithium battery obtained in S6 is subjected to the fourth resting operation, the temperature is adjusted to 45℃, the clamp pressure is 0.6MPa, and the resting time is 5min, then the lithium battery is aged at 45℃ for 48h, and then the degassing and sealing are performed.

[0096] Example 6

[0097] The difference between the present comparative example 1 and example 1 is that the charging cut-off voltage of the lithium battery in the transition charging stage is 4.15V;

[0098] The other steps and parameter settings are consistent with those of example 1.

[0099] Comparative example 1

[0100] The difference between the present comparative example 1 and example 1 is that the charging current in the three charging operations of the iron platform charging stage, the transition charging stage and the manganese platform charging stage is different;

[0101] Specifically, the first charging current of the iron platform charging stage is 0.05C, the second charging current of the transition charging stage is 0.1C, and the third charging current of the manganese platform charging stage is 0.2C;

[0102] The other steps and parameter settings are consistent with those of Example 1.

[0103] Comparative Example 2

[0104] The difference between the present comparative example 1 and Example 1 is that the corresponding clamp pressure is different in the three charging operations of the iron platform charging stage, the transition charging stage and the manganese platform charging stage;

[0105] Specifically, the first charging pressure (clamp pressure) of the iron platform charging stage is 0.5MPa, the second charging pressure (clamp pressure) of the transition charging stage is 0.6MPa, and the third charging pressure (clamp pressure) of the manganese platform charging stage is 0.3MPa;

[0106] The other steps and parameter settings are consistent with those of Example 1.

[0107] Comparative Example 3

[0108] The difference between the present comparative example 1 and Example 1 is that the clamp pressure is 0.3MPa in the three charging operations of the iron platform charging stage, the transition charging stage and the manganese platform charging stage and all the resting processes;

[0109] The other steps and parameter settings are consistent with those of Example 1.

[0110] Comparative Example 4

[0111] The difference between the present comparative example 1 and Example 1 is that all the charging temperatures are kept consistent at 45℃ in the three charging operations of the iron platform charging stage, the transition charging stage and the manganese platform charging stage and all the resting processes;

[0112] The other steps and parameter settings are consistent with those of Example 1.

[0113] Comparative Example 5

[0114] The difference between the present comparative example 1 and Example 1 is that the state of charge of the lithium battery after charging in the iron platform charging stage is 45%, the state of charge of the lithium battery after charging in the transition charging stage is 50%, and the state of charge of the lithium battery after charging in the manganese charging stage is 85%; wherein, a=0.6; X=0.15, Y=0.15;

[0115] The other steps and parameter settings are consistent with those of Example 1.

[0116] Comparative Example 6

[0117] The difference between the present comparative example 1 and the example 1 is that the state of charge of the lithium battery after the end of the manganese platform charging stage is 95%; other steps and parameter settings are consistent with the example 1.

[0118] Test method

[0119] I. Cycle performance test of lithium battery

[0120] The lithium ion batteries in the above examples and comparative examples were subjected to cycle performance test, and the aged lithium battery was subjected to charge-discharge test. The specific test steps are as follows: ① under normal temperature conditions, constant current and constant voltage charging was carried out at a current of 0.5C, the cut-off voltage was 4.2V, the cut-off current was 0.05C, and the standing time was 10 min, then constant current discharging was carried out at a current of 0.5C, and the discharging was stopped when the voltage reached 2.5V, and the standing time was 10 min; the above steps were carried out for 3 times; ② 1C cycle test: then charge-discharge was carried out at a current of 1C, the current and voltage cut-off conditions were the same as above, the first discharge capacity at 1C was recorded as Q1, and after 1000 cycles of the battery, the discharge capacity was recorded as Q2; ③ the capacity retention rate after 1000 cycles was calculated as Q2 / Q1x100%. The results are recorded in Table 1.

[0121] II. Gas production test of lithium battery after cycling

[0122] The lithium ion batteries in the above examples and comparative examples were subjected to cycle gas production test, and the specific steps are as follows: the drainage method was used to calculate the gas production after battery cycling: ① the aged cell tab was adhered with adhesive tape, the cell was placed in a beaker (with scale) containing 100 mL of pure water, the liquid level rising height h1 was recorded, and then the cell was taken out; ② after 1000 cycles of the battery, the lithium battery after cycling was operated in the same way as above, and the liquid level rising height h2 was recorded; ③ the cycle gas production was h2-h1; the results are recorded in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] With reference to Examples 1-4, Comparative Examples 1-4 and Table 1, it can be seen that by controlling the second charging current of the transition platform charging stage in the three-stage charging process to be the smallest, and the second charging temperature and the second charging pressure (jig pressure) to be the highest, small current charging can be achieved in the transition stage of the lithium manganese iron phosphate material, forming a more stable and dense SEI and CEI film; and in the critical stage of generating the SEI film and the CEI film, the close contact between the electrode sheets can be improved, which not only balances the polarization degree of each region of the electrode surface, improves the formation efficiency, and thus helps to reduce the gas production. At this time, the cycle performance of the lithium battery in Comparative Example 1-4 is lower than that of the lithium battery in Example 1, and the gas production of the lithium battery in Comparative Example 1-4 is increased by 116.7%, 245.8%, 104.2% and 337.5% respectively compared with the gas production of the lithium battery in Example 1.

[0127] With reference to Example 1, Comparative Example 5 and Table 1, it can be seen that by controlling the values of Q1 and Q2 in the charging stage to satisfy the formula, the formation efficiency and effect can be improved, thereby improving the cycle capacity retention rate of the lithium battery and reducing the gas production; as can be seen from Table 1, when Q3 is 95% SOC in Comparative Example 5, the cycle capacity retention rate of the lithium battery is significantly reduced, and the gas production is increased by 408.3% compared with the gas production of the lithium battery in Example 1.

[0128] With reference to Example 1, Comparative Example 6 and Table 1, it can be seen that by controlling the state of charge Q3 of the lithium battery to be 100% SOC after the end of the manganese platform charging stage, on the one hand, the gas generation during the formation process can be completed, and the charging after the standby operation can continue to produce gas; on the other hand, a more stable electrolyte interface film can be formed, which helps to improve the cycle performance of the lithium battery; as can be seen from Table 1, when Q3 is 95% SOC in Comparative Example 6, the cycle capacity retention rate of the lithium battery is significantly reduced, and the gas production is increased by 537.5% compared with the gas production of the lithium battery in Example 1.

[0129] With reference to Example 1, Example 5 and Table 1, it can be seen that although the sizes of the first charging current, the second charging current and the third charging current in Example 5 satisfy the condition that the second charging current < the third charging current < the first charging current, the charging currents in each stage are not controlled within a suitable range, resulting in a decrease in the cycle capacity retention rate of the lithium battery in Example 5 compared with the lithium battery in Example 1, and an increase in the gas production.

[0130] With reference to Example 1, Example 6 and Table 1, it can be seen that by controlling the cut-off voltage of the transition charging stage to satisfy the range of 4.2-4.3V, the cycle performance of the lithium battery can be improved, and the gas production can be reduced.

[0131] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application is described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A lithium battery formation process, characterized by, The lithium battery formation process comprises an iron platform charging stage, a transition charging stage and a manganese platform charging stage in sequence; The iron platform charging stage: setting the charging current as a first charging current, setting the environmental pressure as a first charging pressure, setting the charging temperature as a first charging temperature, and charging the lithium battery under the above conditions to increase the state of charge of the lithium battery from 0% SOC to Q1; The transition charging stage: setting the charging current as a second charging current, setting the environmental pressure as a second charging pressure, setting the charging temperature as a second charging temperature, and charging the lithium battery under the above conditions to increase the state of charge of the lithium battery from Q1 to Q2; The manganese platform charging stage: setting the charging current as a third charging current, setting the environmental pressure as a third charging pressure, setting the charging temperature as a third charging temperature, and charging the lithium battery under the above conditions to increase the state of charge of the lithium battery from Q2 to 100% SOC; The second charging current < the third charging current < the first charging current; The first charging temperature = the third charging temperature < the second charging temperature; The first charging pressure < the second charging pressure, and the third charging pressure < the second charging pressure; The positive active material of the lithium battery comprises lithium iron manganese phosphate, and a structural formula of the lithium iron manganese phosphate is LiFe a Mn (1-a) PO4, 0 < a < 1; The Q1 = (a / 2+X)×100% SOC, and the Q2 = (Q1+Y)×100% SOC, 0.05≤X≤0.15, 0.05≤Y≤0.1; The first charging pressure is 0.1-0.4 MPa, the second charging pressure is 0.7-0.9 MPa, and the third charging pressure is 0.4-0.6 MPa.

2. The lithium battery formation process of claim 1, wherein, The first charging temperature is 40-50℃.

3. The lithium battery formation process of claim 2, wherein, The first charging current is 0.15-0.35C.

4. The lithium battery formation process of claim 1, wherein, The second charging temperature is 55-65℃.

5. The lithium battery formation process of claim 4, wherein, The second charging current is 0.02-0.06C.

6. The lithium battery formation process of claim 1, wherein, The third charging temperature is 40-50℃.

7. The lithium battery formation process of claim 6, wherein, The third charging current is 0.08-0.12C.

8. The lithium battery formation process according to any one of claims 1, 4-5, wherein, The charging cut-off voltage of the manganese platform charging stage is 4.2-4.3V, and the charging cut-off current is 0.03-0.08C.

9. The lithium battery formation process of claim 1, wherein, The lithium battery is subjected to an aging operation after the manganese platform charging stage.

10. The lithium battery formation process of claim 9, wherein, The aging temperature in the aging operation is 40-50℃, and the aging time is 48-72h.

Images