Formation method for lithium-ion battery

Abstract

The present invention belongs to the technical field of lithium-ion battery processing, and, in particular, relates to a formation method for a lithium-ion battery. According to the present invention, a formation process of charging three times, discharging one time, and then performing fourth charging is used, and a third charging current > a first charging current > a second charging current; a combination of the two can increase the delithiation efficiency for a lithium-supplementing material in a formation stage, and oxygen in a lithium-supplementing agent is released in the formation stage. Gas production during deoxidation is carried out as much as possible in the formation stage; thus, the problems of later stage high-temperature cycling and gas production during high-temperature storage of a battery are solved, and the high-temperature cycling performance of the battery is improved. Furthermore, according to the present invention, the delithiation efficiency is controlled by means of regulating and controlling the pressure, current, temperature, and SOC during charging and discharging during formation, so that the lithium-supplementing agent on a positive electrode side undergoes complete delithiation on a delithiation platform. In general, the formation processing steps in the present invention affect one another and are associated with one another, and jointly solve the problem of gas production during delithiation of the lithium-supplementing material. Moreover, the high-temperature storage and high-temperature cycling performance are improved.

Description

A formation method for lithium ion battery Technical Field

[0001] The invention belongs to the technical field of lithium ion battery processing, and in particular relates to a formation method of a lithium ion battery. Background Art

[0002] At present, the positive electrode lithium replenishment is combined with oxides (silicon oxide, tin oxide) and amorphous carbon negative electrodes to improve the battery energy density. It mainly adds a high-capacity, low-initial-efficiency positive electrode lithium replenishment material to the positive electrode to compensate for the consumption of lithium ions. This method can effectively avoid safety risks and complex processes. However, the commonly used lithium replenishment materials for positive electrode lithium replenishment are metal oxides / nitrides, including Li3N, Li5FeO4, Li2O, Li6CoO4, etc., all of which will produce gas due to the decomposition of the lithium replenishment agent, thereby affecting the performance of the battery in the later stage.

[0003] Existing formation methods typically utilize high charging currents and cutoff voltages to ensure both production efficiency and stable battery performance with a dense solid electrolyte interface (SEI) membrane structure. However, these high charging currents and cutoff voltages prevent the initial release of positive electrode lithium-supplementing additives during the formation phase, leading to a decrease in subsequent cycling and storage gas production performance.

[0004] Summary of the Invention

[0005] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0006] The present invention aims to address at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a lithium-ion battery formation method. The formation process steps of the present invention interact and are interrelated, collectively improving the delithiation and gasification of the lithium-supplementing material, thereby enhancing high-temperature storage and high-temperature cycling performance.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a formation method for a lithium ion battery, wherein the positive electrode material of the lithium ion battery comprises an active material and a lithium supplement agent, and the formation method comprises the following steps:

[0009] S1. Fill the lithium-ion battery with liquid and then form it under a pressure of 1.1Mpa to 1.6Mpa;

[0010] S2, hot pressing the lithium-ion battery at 75° C. to 90° C.;

[0011] S3: Constant current charging at 0.03C to 0.1C to 30% to 40% state of charge (SOC);

[0012] S4, constant current charging at 0.01C ~ 0.045C to 60% ~ 80% SOC;

[0013] S5, constant current charging at 0.1C to 1.2C to 100% to 120% SOC;

[0014] S6, perform constant current discharge to 0% to 10% SOC;

[0015] S7, constant current and constant voltage charging at 0.1C to 1.5C to 70% to 90% SOC;

[0016] The current in step S5 is greater than the current in step S3 and greater than the current in step S4.

[0017] From a technical perspective, the present invention adopts a formation process of three charges, one discharge, and then a fourth charge, and regulates the magnitude of each charging current; further, the present invention also regulates factors such as pressure, current, temperature, and SOC during the formation charge and discharge process. The inventors found that these formation process steps influence and are interrelated with each other, and ultimately have a significant impact on the de-lithiation and gasification phenomenon of the lithium-supplementing material, as well as its high-temperature storage and high-temperature cycling performance. Specifically:

[0018] (1) In step S1 of the present invention, after the lithium-ion battery is filled with liquid, it is formed at a preset pressure of 1.1 MPa to 1.6 MPa. At this pressure, the formation interface is better, and the gas generated during the subsequent charge and discharge process can be discharged into the air bag in a timely manner, avoiding the side reaction of oxygen generated by the lithium supplement agent during lithium removal with the electrolyte. On the contrary, if the pressure is too high, the electrolyte will be squeezed out of the air bag, the wettability is insufficient, and the battery will have serious lithium deposition.

[0019] (2) In step S2 of the present invention, hot pressing at 75°C to 90°C is beneficial to shaping the battery and prevents the battery from becoming soft in subsequent steps.

[0020] (3) In steps S3 to S5 of the present invention, first, charging is performed with a small current in S3, and then the charging current is further reduced in S4, and then a large current is used for constant charging in S5 (i.e., the third charging current > the first charging current > the second charging current). The reason for this is that the small current formation is to form a dense SEI film on the negative electrode side, and at the same time, the lithium supplement agent has a better delithiation effect. Moreover, according to the characteristics of the lithium supplement material, the lithium supplement agent will release oxygen on both delithiation platforms, and the amount of oxygen released on the second platform is greater. Therefore, a smaller current is used (i.e., the second current density is less than the first current density) to allow the lithium supplement material to release oxygen and reduce storage gas production. In order to improve the delithiation efficiency, the third charging is performed with a larger current, but it must be lower than 1.2C. Otherwise, the polarization will be too large, the SEI film density will be low, and even the delithiation efficiency in subsequent discharge and recharging will be affected. In steps S3 to S5 of the present invention, the charging SOC has the advantage of increasing gradually. It should be noted that the formation SOC in each charging stage should be controlled within a certain range. If it is lower than the protection range, the lithium supplement will not be completely delithiated, the battery will produce gas and affect the battery capacity.

[0021] (4) In step S6 of the present invention, discharging to a SOC range of 0% to 10% can further remove lithium.

[0022] (5) In step S7 of the present invention, the charging temperature is raised to 70°C to 90°C in order to make the residual alkali on the surface of the lithium supplement agent and the lithium delithiation reaction of the lithium supplement agent more complete; below this range, the lithium delithiation effect of the material and the reaction of the residual alkali are insufficient.

[0023] In some embodiments of the present invention, in step S1, the pressure is 1.1Mpa~1.6Mpa, including but not limited to: 1.1Mpa~1.5Mpa, 1.1Mpa~1.4Mpa, 1.1Mpa~1.3Mpa, 1.1Mpa~1.2Mpa, 1.2Mpa~1.6Mpa, 1.2Mpa~1.5Mpa, 1.2Mpa~1.4Mpa, 1.2Mpa~1.3Mpa, 1.2Mpa.

[0024] In some embodiments of the present invention, in step S2, the hot pressing temperature is 75°C to 90°C, including but not limited to: 75°C to 85°C, 75°C to 80°C, 80°C to 90°C, 80°C to 85°C, 80°C.

[0025] In some embodiments of the present invention, in step S2, the hot pressing time is 5 min to 20 min, including but not limited to: 5 min to 15 min, 5 min to 10 min, 10 min to 20 min, 10 min to 15 min, 10 min.

[0026] In some embodiments of the present invention, in step S3, the current is 0.03C to 0.1C, including but not limited to: 0.05C to 0.1C, 0.04C to 0.06C, 0.08C to 0.1C, 0.05C, 0.1C.

[0027] In some embodiments of the present invention, in step S3, charging to 30% to 40% SOC includes but is not limited to: 35% to 40% SOC, 30% SOC, 35% SOC, and 40% SOC.

[0028] In some embodiments of the present invention, in step S3, the charging cutoff current is 0.01-0.03C, including but not limited to: 0.01-0.02C, 0.02-0.03C, and 0.02C.

[0029] In some embodiments of the present invention, in step S4, the current is 0.01C to 0.045C, including but not limited to: 0.02C to 0.045C, 0.01C to 0.03C, 0.04C to 0.045C, 0.02C, and 0.045C.

[0030] In some embodiments of the present invention, in step S4, charging to 60% to 80% SOC includes but is not limited to: 60% to 75% SOC, 60% to 70% SOC, 60% to 65% SOC, 65% to 80% SOC, 65% to 75% SOC, 65% to 70% SOC, 70% to 80% SOC, 70% to 75% SOC, 75% to 80% SOC, 60% SOC, 65% SOC, 70% SOC, 75% SOC, and 80% SOC.

[0031] In some embodiments of the present invention, in step S5, the current is 0.1C to 1.2C, including but not limited to: 0.1C to 1.0C, 0.2C to 0.8C, 0.4C to 0.6C, and 0.5C.

[0032] In some embodiments of the present invention, in step S5, charging to 100% to 120% SOC includes but is not limited to: 100% to 115% SOC, 100% to 110% SOC, 100% to 105% SOC, 105% to 120% SOC, 105% to 115% SOC, 105% to 110% SOC, 110% to 120% SOC, 110% to 115% SOC, 115% to 120% SOC, 100% SOC, 105% SOC, 110% SOC, 115% SOC, and 120% SOC.

[0033] In some embodiments of the present invention, in step S5, the charging cutoff current is 0.01-0.03C, including but not limited to: 0.01-0.02C, 0.02-0.03C, and 0.02C.

[0034] In some embodiments of the present invention, in step S5, the battery is left to stand for 5 to 20 minutes after charging, including but not limited to: 5 to 15 minutes, 5 to 10 minutes, 10 to 20 minutes, 10 to 15 minutes, and 10 minutes. The purpose of the standing time is to allow the battery to stabilize.

[0035] In some embodiments of the present invention, in step S6, constant current discharge is performed at a current of 0.3-1.8C to a SOC of 0%-10%. The current of 0.3-1.8C includes, but is not limited to, 0.3-1.5C, 0.3-1.0C, 1.0-1.8C, 1.2-1.8C, 1.5-1.8C, 0.5-1.8C, 0.3C, 0.5C, and 1.8C; the current of 0%-10% SOC includes, but is not limited to, 0%-5% SOC, 5%-10% SOC, 0% SOC, and 10% SOC.

[0036] In some embodiments of the present invention, steps S3, S4, S5, and S6 are performed at 45°C to 65°C, including but not limited to: 45°C to 60°C, 45°C to 55°C, 45°C to 50°C, 50°C to 65°C, 50°C to 60°C, 50°C to 55°C, and 50°C.

[0037] In some embodiments of the present invention, in step S7, the current is 0.1C to 1.5C, including but not limited to: 0.1C to 1.0C, 0.1C to 0.5C, 1.0C to 1.5C, 0.5C to 1.5C, 0.1C, 0.5C, 1.5C.

[0038] In some embodiments of the present invention, in step S7, charging to 70% to 90% SOC includes but is not limited to: 70% to 80% SOC, 80% to 90% SOC, 70% SOC, 80% SOC, and 90% SOC.

[0039] In some embodiments of the present invention, step S7 is performed at 70°C to 90°C, including but not limited to: 70°C to 80°C, 80°C to 90°C, 70°C, 80°C, 90°C.

[0040] In some embodiments of the present invention, in step S7, the battery is left to stand for 5 to 20 minutes after charging, including but not limited to 5 to 15 minutes, 5 to 10 minutes, 10 to 20 minutes, 10 to 15 minutes, and 10 minutes. The purpose of the standing time is to allow the battery to stabilize.

[0041] In some embodiments of the present invention, the outer surface of the active material is further provided with a coating layer.

[0042] In some embodiments of the present invention, the lithium replenisher is mixed with the positive electrode active material. Since the positive electrode active material has a coating layer on its surface, the lithium in the lithium replenisher is preferentially consumed during formation.

[0043] In some embodiments of the present invention, the coating layer has a thickness of 0.03 μm to 1 μm, preferably 0.05 μm to 0.1 μm. A thicker coating layer allows lithium in the lithium supplement to be preferentially removed during formation, consuming lithium ions in the SEI, increasing the reversible specific capacity of the positive electrode active material and improving battery performance.

[0044] In some embodiments of the present invention, the coating layer material may be selected from one or more of metal oxides, phosphates, silicates, solid electrolytes, etc., but is not limited thereto.

[0045] In some embodiments of the present invention, the current in step S4 and the thickness of the coating layer satisfy the following relationship:

[0046] Wherein, c represents the current in step S4, measured in C; d represents the thickness of the coating layer, measured in μm.

[0047] In the present invention, the coating thickness and the current in S4 need to satisfy a certain relationship, which can further improve the high-temperature cycle performance. This is because: the S4 charging stage is the stage where the positive electrode active material begins to delithiate. By regulating the current in the S4 stage and the coating thickness of the positive electrode active material to satisfy the above relationship, the lithium in the lithium supplement agent is preferentially removed during formation to be used for lithium ion consumption of SEI, the reversible gram capacity of the positive electrode active material is increased, and the battery performance is improved.

[0048] In some embodiments of the present invention, the lithium replenisher has a delithiation platform of ≥3V. Preferably, the lithium replenisher is selected from at least one of lithium-rich lithium ferrite (LFO) and lithium-rich lithium nickelate (LNO). The reason is that the present invention selects lithium-rich compounds as lithium replenishers, such as LFO, LNO, etc. LFO / LNO materials have a clear delithiation platform above 3.0V and a high gram capacity. When matching the formation steps and formation parameters of the present invention, delithiation is more complete, which can solve the gas production problem and improve high-temperature cycles. On the contrary, other lithium replenishers, such as Li3S, have a delithiation platform of 2.5V. When the formation steps of the present invention are used, delithiation is incomplete and the cycle performance is significantly reduced.

[0049] In some embodiments of the present invention, the positive electrode active material of the lithium-ion battery is selected from at least one of lithium cobalt oxide, lithium-rich manganese-based, ternary materials, lithium manganese oxide, and lithium iron phosphate. Preferably, the positive electrode active material of the lithium-ion battery is lithium cobalt oxide.

[0050] In some embodiments of the present invention, the negative electrode active material of the lithium-ion battery is selected from at least one of graphite, silicon-carbon, and silicon-oxygen. Preferably, the negative electrode active material of the lithium-ion battery is silicon-carbon. More preferably, the negative electrode active material of the lithium-ion battery is 5% silicon-carbon.

[0051] In some preferred embodiments of the present invention, the lithium-ion battery adopts a lithium cobalt oxide-silicon carbon system in order to improve the battery energy density.

[0052] The formation method of a lithium-ion battery according to an embodiment of the present invention has at least the following beneficial effects:

[0053] The formation process of the positive-electrode lithium-supplemented lithium-ion battery provided by the present invention specifically adopts a formation process of three charges, one discharge, and then a fourth charge, and the third charging current>the first charging current>the second charging current; the combination of the two can improve the delithiation efficiency of the lithium-supplementing material in the formation stage, and release the oxygen in the lithium-supplementing agent in the formation stage, deoxygenate and produce gas as much as possible in the formation stage, thereby improving the battery's late high-temperature cycle and high-temperature storage gas production problems, and improving the battery's high-temperature cycle performance. Further, by regulating the pressure, current, temperature, and SOC during the formation charge and discharge process, the delithiation efficiency is controlled, so that the lithium-supplementing agent on the positive electrode side is completely delithiated on the delithiation platform. The formation process steps of the present invention influence each other and are interrelated, and together improve the delithiation and gas production phenomenon of the lithium-supplementing material, and improve high-temperature storage and high-temperature cycle performance.

[0054] In addition, compared with the existing technology, the present invention adopts small current charging, which makes the lithium removal effect of the lithium supplement agent better, deoxygenates and produces gas as much as possible in the formation stage, thereby improving the battery's later cycle and storage gas production problems. DETAILED DESCRIPTION

[0055] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0056] Example

[0057] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0058] The structure of the lithium-ion battery cell in the specific embodiment of the present invention is prepared by the following method:

[0059] The positive electrode is a lithium-replenishing electrode, the negative electrode is a silicon-carbon electrode, and the separator is a JL 7μm oil-based membrane. A fully automated winding process is used to produce the bare cell. The bare cell is then sealed with a defined aluminum-plastic film outer wrapper. A defined amount of electrolyte is injected into the dried, partially encapsulated cell, and the packaging is complete. The resting, formation, shaping, and capacity grading processes continue to complete the preparation of the lithium-ion soft-pack battery.

[0060] Example 1

[0061] This embodiment provides a formation method for a lithium-ion battery. The positive electrode material of the lithium-ion battery includes an active material, lithium cobalt oxide, and a lithium supplement, LFO. The LFO and lithium cobalt oxide are mixed. The outer surface of the lithium cobalt oxide is provided with a coating layer, and the coating layer has a thickness of 0.06 μm.

[0062] The formation method of a lithium-ion battery comprises the following steps:

[0063] (1) Place the pre-sealed lithium-ion battery cell into the formation cabinet, adjust the temperature inside the cabinet, apply a pressure of 1.2 MPa to the surface of the battery cell, and start segmented charging of the battery cell;

[0064] (2) In the first stage, the battery is hot pressed at 80°C for 10 minutes;

[0065] (3) In the second stage, the formation cabinet is cooled to 50°C and a constant current and constant voltage charge is performed at 0.05C to 40% SOC, with a cut-off current of 0.02C.

[0066] (4) In the third stage, the battery cell is charged at a constant current of 0.02C to 80% SOC;

[0067] (5) In the fourth stage, the battery cell is charged at a constant current of 0.5C to a predetermined voltage of 105% SOC, with a cut-off current of 0.02C, and allowed to stand for 10 minutes;

[0068] (6) In the fifth stage, the battery cell is discharged at a constant current of 0.5C to reduce the voltage to 0% SOC;

[0069] (7) In the sixth stage, the temperature of the formation cabinet is raised to 80°C, and the battery is charged to 80% SOC at 0.5C constant current and constant voltage, and then left for 10 minutes.

[0070] Example 2

[0071] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of embodiment 1, except that step (3) is charging to 35% SOC.

[0072] Example 3

[0073] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of Example 1, except that step (6) is discharging to 10% SOC.

[0074] Example 4

[0075] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of embodiment 1, except that step (4) is charging to 70% SOC.

[0076] Example 5

[0077] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of embodiment 1, except that step (4) is charging to 60% SOC.

[0078] Example 6

[0079] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of embodiment 1, except that: step (3) is charging to 30% SOC.

[0080] Example 7

[0081] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of embodiment 1, except that step (5) is charging to 110% SOC.

[0082] Example 8

[0083] This embodiment provides a lithium ion battery formation method, which is carried out with reference to the embodiment 1, except that the current in step (3) is 0.1C.

[0084] Example 9

[0085] This embodiment provides a lithium ion battery formation method, which is carried out with reference to the embodiment 1, except that the current in step (6) is 1.8C.

[0086] Example 10

[0087] This embodiment provides a lithium ion battery formation method, which is carried out with reference to the embodiment 1, except that the temperature of step (7) is 70°C.

[0088] Example 11

[0089] This embodiment provides a lithium ion battery formation method, which is carried out with reference to the embodiment 1, except that the current in step (7) is 1.5C.

[0090] Example 12

[0091] This embodiment provides a formation method for a lithium-ion battery, which is carried out with reference to the method of Example 1, except that the lithium supplement is replaced by LNO.

[0092] Example 13

[0093] This embodiment provides a formation method for a lithium ion battery, which is carried out with reference to the process of Example 1, except that the current in step (4) is 0.045C and the thickness of the coating layer is 0.1 μm.

[0094] Comparative Example 1

[0095] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the pressure in step (1) is 1.0 MPa.

[0096] Comparative Example 2

[0097] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that step (7) is omitted.

[0098] Comparative Example 3

[0099] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that steps (6) and (7) are omitted.

[0100] Comparative Example 4

[0101] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the temperature in step (2) is 45°C.

[0102] Comparative Example 5

[0103] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that step (3) is charging to 20% SOC.

[0104] Comparative Example 6

[0105] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the current in step (3) is 0.15C.

[0106] Comparative Example 7

[0107] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that step (4) is charging to 50% SOC.

[0108] Comparative Example 8

[0109] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the current in step (4) is 0.05C, which does not satisfy the relationship:

[0110] Wherein, c represents the current in step S4, measured in C; d represents the thickness of the coating layer, measured in μm.

[0111] Comparative Example 9

[0112] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the temperature of step (7) is 60°C.

[0113] Comparative Example 10

[0114] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the current in step (7) is 2C.

[0115] Comparative Example 11

[0116] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that step (6) discharges the battery to 12%.

[0117] Comparative Example 12

[0118] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the lithium supplement agent is Li2S.

[0119] Comparative Example 13

[0120] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the current in step (5) is 1.3C.

[0121] Comparative Example 14

[0122] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that step (4) is omitted.

[0123] Comparative Example 15

[0124] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that step (7) is omitted and steps (4) to (6) are repeated 4 times.

[0125] Comparative Example 16

[0126] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 1, except that the thickness of the coating layer is 0.05 μm, which does not satisfy the relationship.

[0127] Comparative Example 17

[0128] This comparative example provides a lithium ion battery formation method, which is carried out with reference to Example 13, except that the thickness of the coating layer is 0.06 μm, which does not satisfy the relationship.

[0129] Test Case

[0130] Formation gas production test: The difference in displacement volume when the battery is immersed in water is used to measure the battery gas production, ΔV = V2-V1.

[0131] High-temperature storage test: The divided battery is charged to 4.48V at room temperature using a constant current and constant voltage of 0.5C (cut-off current is 0.02C), and the initial discharge capacity of the battery is measured. Then, after storing at 85°C for 6 hours, the battery is discharged to 3.0V at 0.5C to measure the battery's retention capacity and recovery capacity.

[0132] Cycle test: At room temperature 25±2℃ or high temperature 45℃±2℃, charge the divided battery to 4.48V with 0.5C constant current and constant voltage (cut-off current is 0.01C), and then discharge it to 3.0V with 0.5C constant current.

[0133] The test results are shown in Table 1 below.

[0134] Table 1

[0135] The test results of Examples 1 to 13 show that the use of the technical solution of the present invention to optimize the formation process allows the lithium supplement agent LFO to completely delithiate during the formation stage, which is beneficial to gas production during the formation process and can improve the high-temperature cycling performance and high-temperature storage performance of the battery. When the formation pressure, charging current, SOC, and temperature exceed the range, the lithium supplement material's delithiation effect is poor. During performance testing, the lithium supplement material releases oxygen, which reacts with the electrolyte, causing gas production in the battery and affecting storage and cycling performance. The formation process steps of the present invention influence and are interrelated. Exceeding the scope of this solution or missing a step will have a significant impact on gas production or high-temperature cycling.

[0136] Specifically:

[0137] It can be seen from Example 1 and Comparative Example 1 that the pressure range throughout the formation process needs to be above 1.1 MPa. If it is below 1.1 MPa, or if some steps are not above 1.1 MPa, especially during the three charging processes, the gas generated during the formation cannot be discharged into the air bag in time, affecting the formation interface and deteriorating the high-temperature cycle performance.

[0138] It can be seen from Examples 1 and 8 and Comparative Examples 6 / 8 / 13 that the three charging currents must satisfy the following conditions: the third charging current > the first charging current > the second charging current, and the three charging currents must satisfy the following conditions: the first charging current is 0.03C to 0.1C, the second charging current is 0.01C to 0.045C, and the third charging current is 0.1 to 1.2C. When the charging current is higher, the delithiation effect deteriorates, which also affects the delithiation efficiency during subsequent discharge and the fourth charge, as well as the residual alkali reaction on the surface of the lithium supplement agent.

[0139] It can be seen from Examples 1, 10, 11 and Comparative Examples 2 / 3 / 9 / 10 that the fourth charge after discharge is performed to allow the residual alkali on the surface of the lithium supplement agent and the lithium delithiation reaction of the lithium supplement agent to be more complete. If the fourth charge temperature or charging current is not within the range, the lithium delithiation effect of the material will be affected and the reaction of the residual alkali will be incomplete.

[0140] It can be seen from Example 1 and Comparative Example 13 that a larger current is used for the third charge, but it must be lower than 1.2C, otherwise the polarization will be large and the SEI film density will be low, affecting the subsequent discharge and the delithiation efficiency in the fourth charge.

[0141] It can be seen from Examples 1, 10, and 11 and Comparative Examples 9 / 10 that the temperature and current of the fourth charge affect the residual alkali on the surface of the lithium supplement and the lithium removal effect. When the fourth charge current or temperature is not within the range, the 85°C storage thermal thickness expansion coefficient and high-temperature cycling performance are significantly deteriorated.

[0142] It can be seen from Example 1 and Comparative Examples 2 / 3 / 14 that the formation pressure and the charge and discharge steps are interrelated and coordinated. If any step in the formation of this solution is removed, the formation gas production and high-temperature cycle will be significantly deteriorated.

[0143] Examples 1 / 12 and Comparative Example 12 show that the lithium-rich LFO / LNO materials exhibit a clear delithiation platform above 3.0V and high specific capacity. When used with the aforementioned formation process, delithiation is more complete, addressing gas production issues while also improving high-temperature cycling. The delithiation platform for Li3S is around 2.5V. Using this formation process, delithiation and oxygen release from the lithium supplement are incomplete, significantly reducing cycling performance.

[0144] It can be seen from Example 1 and Comparative Example 15 that if there is no fourth charging step of this scheme, the gas production and high-temperature storage performance will also decrease if the S4-S6 charge and discharge steps are continuously cycled, and the cycle performance is significantly reduced due to multiple charge and discharge. Comparative Example 15 takes a long time to form and has complicated steps. Repeated charge and discharge cannot completely solve the gas production and high-temperature cycle problems.

[0145] It can be seen from Examples 1 / 13 and Comparative Examples 8 / 16 / 17 that the coating thickness satisfies the relationship, and the high-temperature cycle performance is improved. This is because the S4 charging stage is the stage where lithium cobalt oxide begins to delithiate. By regulating the current in the S4 stage and the coating thickness of the positive electrode active material to satisfy the above relationship, the lithium in the lithium supplement agent is preferentially removed during formation to be used for lithium ion consumption of SEI, the reversible gram capacity of the positive electrode active material is increased, and the battery performance is improved.

[0146] In summary, Examples 1-13 and Comparative Examples 1-17, each featuring an LCO & LFO battery system with a silicon-carbon composite material, were compared and analyzed. Table 1 shows that the present invention's technical solution optimizes the formation process, allowing for complete delithiation of the LFO lithium supplement during the formation phase. This facilitates gassing during the formation process and improves the battery's high-temperature cycling and storage performance. However, when the formation pressure, charge current, SOC, and temperature exceed these limits, the lithium supplement material's delithiation performance is poor. During performance testing, the lithium supplement material releases oxygen, which reacts with the electrolyte, causing gassing and impacting storage and high-temperature cycling performance.

[0147] The above content describes the embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. In addition, the embodiments of the present invention and the features thereof can be combined with each other unless there is a conflict.

Claims

1. A formation method for a lithium-ion battery, characterized in that, The positive electrode material of the lithium-ion battery includes an active material and a lithium supplement agent, and the formation method includes the following steps: S1. After injecting electrolyte into the lithium-ion battery, perform formation under a pressure of 1.1 Mpa to 1.6 Mpa; S2. Perform hot pressing on the lithium-ion battery at 75 °C to 90 °C; S3. Perform constant current charging at a current of 0.03C to 0.1C until 30% to 40% SOC; S4. Perform constant current charging at a current of 0.01C to 0.045C until 60% to 80% SOC; S5. Perform constant current charging at a current of 0.1C to 1.2C until 100% to 120% SOC; S6. Perform constant current discharging until 0% to 10% SOC; S7. Perform constant current and constant voltage charging at 0.1C to 1.5C until 70% to 90% SOC, wherein, the current in step S5 > the current in step S3 > the current in step S4.

2. The formation method according to claim 1, wherein In step S2, the time of the hot pressing is 5 min to 20 min.

3. The forming method according to claim 1, characterized in that, In step S5, the cut-off current of the charging is 0.01C to 0.03C; Preferably, after charging, it is left standing for 5 min to 20 min.

4. The forming method according to claim 1, characterized in that In step S6, perform constant current discharging at a current of 0.3C to 1.8C.

5. The forming method according to claim 1, characterized in that, Steps S3, S4, S5, and S6 are carried out at 45 °C to 65 °C.

6. The formation method according to claim 1, characterized in that, Step S7 is carried out at 70 °C to 90 °C; Preferably, in step S7, after charging, it is left standing for 5 min to 20 min.

7. The formation method according to claim 1, characterized in that, A coating layer is further provided on the outer surface of the active material; Preferably, the thickness of the coating layer is 0.03 μm to 1 μm.

8. The formation method according to claim 7, characterized in that, The current in the step S4 and the thickness of the coating layer satisfy the following relational expression: Wherein, c represents the current in step S4, in C; d represents the thickness of the coating layer, in μm.

9. The formation method according to claim 1, characterized in that The de-lithiation platform of the lithium supplement agent ≥ 3V; Preferably, the lithium supplement agent is selected from at least one of lithium-rich lithium ferrite and lithium-rich lithium nickelate.

10. The formation method according to claim 1, characterized in that, The positive electrode active material of the lithium-ion battery is selected from at least one of lithium cobaltate, lithium-rich manganese-based, ternary materials, lithium manganate, and lithium iron phosphate; Preferably, the negative electrode active material of the lithium-ion battery is selected from at least one of graphite, silicon-carbon, and silicon-oxygen.

Images