Lithium battery formation process

Abstract

The invention specifically discloses a lithium battery formation process. A lithium battery formation process comprises the following steps: an iron platform charging stage: setting a charging current as a first charging current, an environment pressure as a first charging pressure and a charging temperature as a first charging temperature, and charging a battery under the conditions, so that the state of charge of the battery is increased from 0% SOC to Q1; in the transition charging stage, the charging current is set to be second charging current, the environment pressure is set to be second charging pressure, the charging temperature is set to be second charging temperature, and the battery is charged under the conditions, so that the state of charge of the battery is increased to Q2 from Q1; and a manganese platform charging stage: setting the charging current as a third charging current, the environment pressure as a third charging pressure and the charging temperature as a third charging temperature, and charging the battery under the conditions, so that the state of charge of the battery is increased to 100% SOC from Q2. The method has the advantages that the stability of the SEI membrane and the CEI membrane is improved, and the cycle performance of the lithium battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium battery formation process. Background Art

[0002] The formation process is the most critical step in the manufacturing process of lithium-ion batteries. The formation process refers to the process of charging the lithium-ion battery for the first time after filling and leaving it to stand, 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 negative electrode's continued reaction with the electrolyte during the subsequent charging and discharging of the lithium battery, reducing the continuous consumption of the electrolyte. On the other hand, during the first charging of the lithium battery, the positive electrode material at the positive electrode will also react chemically with the electrolyte to generate an electrochemical interface film (CEI film) that can also isolate the electrolyte from the subsequent reaction of the positive electrode material. Therefore, the formation process will affect the electrical performance of lithium-ion batteries by affecting the formation of SEI and CEI films in lithium batteries.

[0004] As an upgraded product of lithium iron phosphate material, lithium manganese iron phosphate cathode material has a higher voltage platform during the charge and discharge process due to the addition of Mn element, which can greatly improve the energy density of lithium batteries. However, Mn in lithium manganese iron phosphate will also reduce its conductivity (the conductivity of lithium manganese iron phosphate is lower than that of lithium iron phosphate); in addition, the valence state of Mn is unstable, and it is also very easy to generate non-stoichiometric phases during the synthesis of lithium manganese iron phosphate cathode materials, such as Li(Mn a Fe(1-a) 2 (PO4) 3 In addition, the sudden increase of the double platform area of ​​Mn and Fe in the lithium manganese iron phosphate material will aggravate the lattice distortion during the lithium ion insertion and extraction process, thereby aggravating the side reaction between the positive electrode material and the electrolyte, especially affecting the quality of the CEI film generated by the formation, which is not conducive to the improvement of the cycle performance of the lithium battery. Summary of the invention

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

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

[0007] A lithium battery formation process, the lithium battery formation process comprising an iron platform charging stage, a transition charging stage and a manganese platform charging stage performed in sequence;

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

[0009] The transition charging stage: setting the charging current to the second charging current, setting the ambient pressure to the second charging pressure, setting the charging temperature to the second charging temperature, charging the lithium battery under the above conditions so that the state of charge of the lithium battery increases from Q1 to Q2, Q2 = the second charging current C1 × the charging time t2 of the transition charging stage;

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

[0011] The second charging current is less than the third charging current and less than the first charging current;

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

[0013] The first charging pressure is less than the second charging pressure, and the third charging pressure is less than the second charging pressure;

[0014] The positive electrode active material of the lithium battery includes lithium iron manganese phosphate, and the structural formula of the lithium iron manganese phosphate is LiFe a Mn (1-a) PO 4 , 0<a<1;

[0015] The Q1=(a / 2+X)×100%SOC, the Q2=(Q1+Y)×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 invention, a three-stage charging operation is adopted, and the cut-off charge state of each stage in the three-stage charging operation is adjusted for lithium iron manganese phosphate materials with different iron and manganese content, and the shelf temperature of the corresponding charging stage and the control of the charging current in each charging stage are coordinated to form a more stable SEI film and CEI film, thereby improving the stability of the lithium battery; and the pole pieces can be in close contact with each other, thereby properly balancing the polarization degree of each part of the pole piece, which helps to improve the formation efficiency; thereby reducing gas production during the cycle. Secondly, it can avoid lattice distortion caused by lithium ion deintercalation and deintercalation, avoid side reactions between the positive electrode and the electrolyte, and significantly improve the stability of the CEI film.

[0018] Specifically, the first charging current is relatively large, which can activate the battery cell and provide a basis for the film-forming reaction in the formation process. At this stage, the reaction of the positive electrode material is mainly Fe 2+ Oxidized to Fe 3+ The second charging current is the smallest. During this charging process, the positive electrode material reacts with Fe 2+ Oxidized to Fe 3+ Gradually towards Mn 2+ Oxidized to Mn 3+ In this stage, a smaller current is required to avoid the distortion of the crystal structure caused by large current. In addition, a small current can form a more stable CEI film, avoiding the damage of the CEI film caused by lithium ion deintercalation during the lithium battery cycle. This is not only beneficial to improve the cycle performance of the lithium battery, but also the high stability of the CEI film will effectively protect the positive and negative electrode materials, avoid the side reactions between the positive and negative electrode materials and the electrolyte, and reduce the gas production during the lithium battery cycle. The third charging current is higher than the second charging current. At this time, the reaction is completely Mn 2+ To Mn 3+ Oxidation of Mn 2+ To Mn 3+ The oxidation sensitivity of Fe is higher than that of Fe 2+ To Fe 3+ oxidation, so a large current is required which is smaller than the first charging current.

[0019] The Fe / Mn ratio in the LMFP material is used to determine the cut-off charge state Q1 in the iron platform charging stage and the cut-off charge state Q2 in the transition charging stage. The appropriate charging current is selected according to the stability of the oxidation reaction in different charging stages, which can improve the formation efficiency and formation effect. By controlling the formation temperature and 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 membrane and CEI membrane can maintain a dynamic balance between generation and decomposition, which helps to further improve the stability of the SEI membrane and CEI membrane, 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° C., 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, the lithium battery is subjected to a first resting operation, 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 minutes.

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

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

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

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

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

[0028] Preferably, the third charging temperature is 40-50° C., 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 cut-off voltage of the manganese platform during the charging stage is 4.2-4.3V, and the charging cut-off current is 0.03-0.08C.

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

[0032] By placing the battery on hold before the manganese platform charging stage, the battery cell temperature is adapted to the third charging temperature, so that the lithium battery can adapt to the charging conditions of the next process (constant current and constant voltage charging).

[0033] Preferably, the lithium battery is aged after the manganese platform charging stage.

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

[0035] By performing the above-mentioned high-temperature aging operation, on the one hand, it can promote the full infiltration of the electrolyte into the electrodes in the lithium battery, and on the other hand, it can stabilize the electrochemical properties of the lithium battery, help form a stable electrolyte interface film, and help improve the cycle performance of the lithium battery.

[0036] Preferably, a fourth rest operation is further included between the manganese platform charging stage and the aging operation, the temperature in the fourth rest operation is 40-50° C., the ambient pressure is 0.4-0.6 MPa, and the rest time is 5-20 min. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the entire stage of lithium battery formation. DETAILED DESCRIPTION

[0038] The embodiments clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0040] Unless otherwise indicated, all numerical values ​​expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that can vary depending upon the desired properties desired to be obtained.

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

[0042] As used herein, “including” and “comprising” encompasses the case where only the stated elements are present as well as the case where there are other elements other than the stated elements.

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

[0044] Unless otherwise indicated, "a", "an", "an" and "the" used in this specification are intended to include "at least one" or "one or more". For example, "a component" means one or more components, so more than one component may be considered and may be employed or used in the implementation of the embodiment.

[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 lithium iron manganese phosphate is LiFe a Mn (1-a) PO 4 , a=0.4; X=0.1, Y=0.1;

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

[0048] S1 (first rest operation), placing the lithium battery after injection in a fixture for the first rest, setting the temperature to 45°C, the fixture pressure to 0.3MPa, and resting for 5 minutes;

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

[0050] S3 (second resting operation), placing the lithium battery obtained in S2 for the second time, setting the temperature to 60° C. and the clamp pressure to 0.8 MPa, and resting for 5 minutes;

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

[0052] S5 (third resting operation), placing the lithium battery obtained in S4 for the third time, setting the temperature to 45° C. and the clamp pressure to 0.6 MPa, and resting for 5 minutes;

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

[0054] S7 (aging operation), the lithium battery obtained in the above S6 is placed for the fourth time, the temperature is adjusted to 45°C, the clamp pressure is 0.6MPa, after being placed for 5 minutes, it is aged at 45°C for 48 hours, and then degassed and sealed.

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

[0056] Example 2

[0057] The positive electrode material of the lithium battery in this embodiment is lithium iron manganese phosphate, and the chemical formula of lithium iron manganese phosphate is LiFe a Mn (1-a) PO 4 , a=0.5; X=0.05, Y=1;

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

[0059] S1 (first rest operation), placing the lithium battery after injection in a fixture for the first rest, setting the temperature to 40°C, the fixture pressure to 0.4MPa, and resting for 10min;

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

[0061] S3 (second rest operation), placing the lithium battery obtained in S2 for the second time, setting the temperature to 55° C. and the clamp pressure to 0.7 MPa, and resting for 10 minutes;

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

[0063] S5 (third resting operation), placing the lithium battery obtained in S4 for the third time, setting the temperature to 40° C. and the clamp pressure to 0.5 MPa, and resting for 10 minutes;

[0064] S6 (manganese platform charging stage), charging the lithium battery to a state of charge of Q3 (100% SOC) at a third charging temperature (40°C) and a third charging pressure (0.5MPa) with a third charging current C3 (0.08C), and controlling the charging operation cut-off voltage to 4.2V and the charging cut-off current to 0.05C;

[0065] S7 (aging operation), the lithium battery obtained in the above S6 is placed for the fourth time, the temperature is adjusted to 40°C, the clamp pressure is 0.5MPa, after being placed for 10 minutes, it is aged at 40°C for 72 hours, and then degassed and sealed.

[0066] Example 3

[0067] The positive electrode material of the lithium battery in this embodiment is lithium iron manganese phosphate, and the chemical formula of lithium iron manganese phosphate is LiFe a Mn (1-a) PO 4 , a=0.6; X=0.1, Y=0.05;

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

[0069] S1 (first rest operation), placing the lithium battery after injection in a fixture for the first rest, setting the temperature to 50°C, the fixture pressure to 0.1MPa, and resting for 15min;

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

[0071] S3 (second rest operation), placing the lithium battery obtained in S2 for the second time, setting the temperature to 65° C. and the clamp pressure to 0.9 MPa, and resting for 15 minutes;

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

[0073] S5 (third rest operation), placing the lithium battery obtained in S4 for the third time, setting the temperature to 50° C. and the clamp pressure to 0.4 MPa, and placing for 15 minutes;

[0074] S6 (manganese platform charging stage), charging the lithium battery to a state of charge of Q3 (100% SOC) at a third charging temperature (50°C) and a third charging pressure (0.4MPa) with a third charging current C3 (0.12C), and controlling the charging operation cut-off voltage to 4.2V and the charging cut-off current to 0.03C;

[0075] S7 (aging operation), the lithium battery obtained in the above S6 is placed for the fourth time, the temperature is adjusted to 50°C, the clamp pressure is 0.4MPa, after being placed for 15min, it is aged at 50°C for 45h, and then degassed and sealed.

[0076] Example 4

[0077] The positive electrode material of the lithium battery in this embodiment is lithium iron manganese phosphate, and the chemical formula of lithium iron manganese phosphate is LiFe a Mn (1-a) PO 4 , a=0.7; X=0.15, Y=0.08;

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

[0079] S1 (first rest operation), placing the lithium battery after injection in a fixture for the first rest, setting the temperature to 50°C and the fixture pressure to 0.2MPa, and resting for 20min;

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

[0081] S3 (second resting operation), placing the lithium battery obtained in S2 for the second time, setting the temperature to 60° C. and the clamp pressure to 0.7 MPa, and resting for 20 minutes;

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

[0083] S5 (third rest operation), placing the lithium battery obtained in S4 for the third time, setting the temperature to 50° C. and the clamp pressure to 0.5 MPa, and resting for 20 minutes;

[0084] S6 (manganese platform charging stage), charging the lithium battery to a state of charge of Q3 (100% SOC) at a third charging temperature (50°C) and a third charging pressure (0.5MPa) with a third charging current C3 (0.1C), and controlling the charging operation cut-off voltage to 4.25V and the charging cut-off current to 0.03C;

[0085] S7 (aging operation), the lithium battery obtained in the above S6 is placed for the fourth time, the temperature is adjusted to 50°C, the clamp pressure is 0.5MPa, after being placed for 20min, it is aged at 45°C for 56h, and then degassed and sealed.

[0086] Example 5

[0087] The positive electrode material of the lithium battery in this embodiment is lithium iron manganese phosphate, and the chemical formula of lithium iron manganese phosphate is LiFe a Mn (1-a) PO 4 , a=0.4; X=0.1, Y=0.1;

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

[0089] S1 (first rest operation), placing the lithium battery after injection in a fixture for the first rest, setting the temperature to 45°C, the fixture pressure to 0.3MPa, and resting for 5 minutes;

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

[0091] S3 (second resting operation), placing the lithium battery obtained in S2 for the second time, setting the temperature to 60° C. and the clamp pressure to 0.8 MPa, and resting for 5 minutes;

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

[0093] S5 (third resting operation), placing the lithium battery obtained in S4 for the third time, setting the temperature to 45° C. and the clamp pressure to 0.6 MPa, and resting for 5 minutes;

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

[0095] S7 (aging operation), the lithium battery obtained in the above S6 is placed for the fourth time, the temperature is adjusted to 45°C, the clamp pressure is 0.6MPa, after being placed for 5 minutes, it is aged at 45°C for 48 hours, and then degassed and sealed.

[0096] Example 6

[0097] The difference between this 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 in Example 1.

[0099] Comparative Example 1

[0100] The difference between this comparative example 1 and embodiment 1 is that the corresponding charging currents in the three charging operations of the iron platform charging stage, the transition charging stage and the manganese platform charging stage are different;

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

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

[0103] Comparative Example 2

[0104] The difference between this comparative example 1 and the embodiment 1 is that the corresponding clamp pressures are 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) in the iron platform charging stage is 0.5 MPa, the second charging pressure (clamp pressure) in the transition charging stage is 0.6 MPa, and the third charging pressure (clamp pressure) in the manganese platform charging stage is 0.3 MPa;

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

[0107] Comparative Example 3

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

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

[0110] Comparative Example 4

[0111] The difference between this comparative example 1 and embodiment 1 is that during the three charging operations in the iron platform charging stage, the transition charging stage and the manganese platform charging stage and during all the shelving processes, all charging temperatures remain the same, which is 45°C;

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

[0113] Comparative Example 5

[0114] The difference between this comparative example 1 and the embodiment 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 in Example 1.

[0116] Comparative Example 6

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

[0118] Test Method

[0119] 1. Lithium battery cycle performance test

[0120] The lithium-ion batteries in the above embodiments and comparative examples were tested for cycle performance, and the aged lithium batteries were tested for charge and discharge. The specific test steps are as follows: ① At room temperature, constant current and constant voltage charging was performed with a current of 0.5C, a cut-off voltage of 4.2V, a cut-off current of 0.05C, and a standstill of 10 minutes, and then constant current discharge was performed with a current of 0.5C, and after discharging to 2.5V, the battery was left for 10 minutes; the above steps were performed 3 times; ② 1C cycle test: Then, a current of 1C was used for charge and discharge, and the current and voltage cut-off conditions were the same as above. The first discharge capacity at 1C was recorded as Q1, and after the battery cycled for 1000 cycles, the discharge capacity was recorded as Q2; ③ Calculate the 1000-cycle capacity retention rate = Q2 / Q1×100%. The results are recorded in Table 1.

[0121] 2. Gas production test of lithium battery after cycling

[0122] The lithium-ion batteries in the above embodiments and comparative examples were tested for cycle gas production, and the specific steps are as follows: Use the drainage method to calculate the gas production of the battery after cycling: ① Use tape to stick the aged battery cell ears, above the portable tape, and place the battery cell in a beaker (with scale) filled with 100 mL of pure water, record the liquid level rise h1, and then take out the battery cell; ② After the battery has been cycled for 1000 weeks, the lithium battery after the cycle is operated in the same way as above, and the liquid level rise h2 is recorded; ③ Cycle gas production = h2-h1; The results are recorded in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] Combining 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 to be the minimum, the second charging temperature and the second charging pressure (clamp pressure) to be the highest during the three-stage charging process, it is possible to achieve low-current charging in the transition stage of the lithium iron manganese phosphate material, forming a more stable and dense SEI and CEI film; and, it is possible to improve the close contact between the pole pieces at the critical stage of generating the SEI film and the CEI film, which can not only balance the polarization degree of each area on the electrode surface, but also improve the formation efficiency, thereby helping to reduce the gas production. At this time, the cycle performance of the lithium battery in Comparative Examples 1-4 is reduced compared to the cycle performance of the lithium battery in Example 1, and the gas production of the lithium battery in Comparative Examples 1-4 is increased by 116.7%, 245.8%, 104.2%, and 337.5% respectively compared to the gas production of the lithium battery in Example 1.

[0127] In combination with 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 meet the formula limit, it is helpful to improve the formation efficiency and formation effect, thereby improving the cycle capacity retention rate of the lithium battery and reducing the gas production; It can be seen from Table 1 that in Comparative Example 5, when Q3 takes 95% SOC, the cycle capacity retention rate of the lithium battery decreases significantly, and its gas production increases by 408.3% compared with the gas production of the lithium battery in Example 1.

[0128] In combination with Example 1, Comparative Example 6 and Table 1, it can be seen that by controlling the state of charge Q3 of the lithium battery after the manganese platform charging stage to 100% SOC, on the one hand, the gas in the formation process can be completely generated, and gas production can continue during charging after the shelving operation; on the other hand, a more stable electrolyte interface film can be formed, which is helpful to improve the cycle performance of the lithium battery; It can be seen from Table 1 that in Comparative Example 6, when Q3 takes 95% SOC, the cycle capacity retention rate of the lithium battery decreases significantly, and its gas production increases by 537.5% compared with the gas production of the lithium battery in Example 1.

[0129] In combination with 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 are controlled to satisfy the second charging current < the third charging current < the first charging current, the charging current in each stage is not controlled within a suitable range, resulting in a decrease in the cycle capacity retention rate and an increase in gas production of the lithium battery in Example 5 compared to the lithium battery in Example 1.

[0130] Combining Example 1, Example 6 and Table 1, it can be seen that by controlling the cut-off voltage in the transition charging stage to meet the limited range of 4.2-4.3V, it is helpful to improve the cycle performance of the lithium battery and reduce the gas production.

[0131] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A lithium battery formation process, characterized in that: The lithium battery formation process includes an iron platform charging stage, a transition charging stage and a manganese platform charging stage which are performed in sequence; The iron platform charging stage: setting the charging current to a first charging current, setting the ambient pressure to a first charging pressure, setting the charging temperature to a first charging temperature, and charging the lithium battery under the above conditions so that the state of charge of the lithium battery increases from 0% SOC to Q1; The transition charging stage: setting the charging current to the second charging current, setting the ambient pressure to the second charging pressure, setting the charging temperature to the second charging temperature, and charging the lithium battery under the above conditions so that the state of charge of the lithium battery increases from Q1 to Q2; The manganese platform charging stage: setting the charging current to a third charging current, setting the ambient pressure to a third charging pressure, setting the charging temperature to a third charging temperature, and charging the lithium battery under the above conditions so that the state of charge of the lithium battery increases from Q2 to 100% SOC; The second charging current is less than the third charging current and less than the first charging current; The first charging temperature = the third charging temperature < the second charging temperature; The first charging pressure is less than the second charging pressure, and the third charging pressure is less than the second charging pressure; The positive electrode active material of the lithium battery includes lithium iron manganese phosphate, and the 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, the Q2=(Q1+Y)×100%SOC, 0.05≤X≤0.15, 0.05≤Y≤0.

1.

2. The lithium battery formation process according to claim 1, characterized in that: The first charging temperature is 40-50° C., and the first charging pressure is 0.1-0.4 MPa.

3. The lithium battery formation process according to claim 2, characterized in that: The first charging current is 0.15-0.35C.

4. The lithium battery formation process according to claim 1, characterized in that: The second charging temperature is 55-65° C., and the second charging pressure is 0.7-0.9 MPa.

5. The lithium battery formation process according to claim 4, characterized in that: The second charging current is 0.02-0.06C.

6. The lithium battery formation process according to claim 1, characterized in that: The third charging temperature is 40-50° C., and the third charging pressure is 0.4-0.6 MPa.

7. The lithium battery formation process according to claim 6, characterized in that: The third charging current is 0.08-0.12C.

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

9. The lithium battery formation process according to claim 1, characterized in that: After the manganese platform charging stage is completed, the lithium battery is aged.

10. The lithium battery formation process according to claim 9, characterized in that: The aging temperature in the aging operation is 40-50°C, and the aging time is 48-72h.

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