A method for forming positive electrode lithium supplementing battery

Abstract

The application relates to a formation method of a positive electrode lithium supplementing battery cell, which comprises the following steps: S1, constant current charging under a negative pressure environment until SEI film formation is completed; S2, constant current charging under a normal pressure environment to a platform voltage; S3, constant power charging under a negative pressure environment to an upper limit of a first delithiation stage voltage of a lithium supplementing agent; S4, discharging under a normal pressure environment to the platform voltage with the first power; S5, constant power charging under a negative pressure environment to an upper limit of a second delithiation stage voltage of the lithium supplementing agent; S6, discharging under a normal pressure environment to the upper limit of the first delithiation stage voltage of the lithium supplementing agent with the second power; and S7, constant power charging under a negative pressure environment to the upper limit of the second delithiation stage voltage of the lithium supplementing agent with the second power. The formation method of the positive electrode lithium supplementing battery cell guarantees complete delithiation of the lithium supplementing agent, reduces liquid loss, and has high formation efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for forming a positive electrode lithium-ion battery cell. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles, higher requirements have been placed on the performance of lithium-ion batteries, among which improving battery energy density is the most urgent. Under the existing lithium-ion battery system, energy density can be improved by optimizing the battery structure; on the other hand, significant improvements in battery energy density can be achieved through the iteration of positive and negative electrode materials. Furthermore, lithium replenishment technology is also an important means of improving battery energy density. During the first charge of a lithium-ion battery, the organic electrolyte will reduce and decompose on the surface of the negative electrode, such as graphite, forming a solid electrolyte interphase (SEI) film. This permanently consumes a large amount of lithium from the positive electrode, resulting in a low coulombic efficiency (ICE) in the first cycle, reducing the capacity and energy density of the lithium-ion battery. In addition, processes such as the deactivation of negative electrode material particles due to detachment and irreversible deposition of lithium metal also consume the active lithium of the positive electrode, reducing the battery's capacity and energy density.

[0003] Lithification technology includes negative electrode lithium replenishment and positive electrode lithium replenishment. Negative electrode lithium replenishment technology has been researched and developed earlier, encompassing various methods such as physical mixing lithium replenishment based on metallic lithium, vacuum winding lithium plating, self-discharge lithiation, chemical lithium replenishment, and electrochemical lithiation. Currently, negative electrode lithium replenishment is still limited by several major challenges in battery manufacturing processes: the incompatibility of metallic lithium with the production environment, conventional solvents, binders, air, and heat treatment processes makes the path to negative electrode lithium replenishment fraught with difficulties. Positive electrode lithium replenishment typically employs an electrochemical method, adding lithium replenishing materials to the positive electrode of a lithium-ion battery. During battery charging, these materials decompose and release active lithium, compensating for the irreversible loss of active lithium caused by the growth of the SEI (Sediment Injection) in the negative electrode. Positive electrode lithium replenishment materials possess advantages such as relatively stable chemical properties, ease of synthesis, low cost, and high lithium replenishment capacity. Furthermore, the positive electrode lithium replenishment process is well-compatible with existing lithium-ion battery manufacturing processes.

[0004] Lithium-added positive electrode cells typically use at least one of LFO and LNO as a lithium replenishing agent in the positive electrode. Lithium replenishment is achieved by delithiating the lithium replenishing agent during the formation process. Existing lithium-added positive electrode cells have the following problems during formation: First, the commonly used constant current charging method cannot completely delithiate the lithium, and the delithiation products of the lithium replenishing agent have poor conductivity and voltage hysteresis, resulting in a relatively large overpotential. Furthermore, the residual lithium replenishing agent that has not been delithiated will continue to undergo delithiation reactions during cell cycling, releasing oxygen and causing gas production, which degrades cell performance. Second, the lithium replenishing agent material undergoes a chemical reaction that releases gases such as O2. To remove these gases, a high vacuum of -80 kPa or higher is generally used throughout the process, but this also leads to the simultaneous absorption of electrolyte, resulting in high liquid loss. Third, while reducing the current rate and using a small current for formation can be achieved, small current charging is time-consuming, increasing costs. Simultaneously, due to the long charging time and the extended negative pressure pumping process, liquid loss is also high. How to provide a formation method for positive electrode lithium-filled cells that ensures complete delithiation of the lithium replenishing agent, reduces liquid loss, and has high formation efficiency is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] Therefore, the present invention provides a formation method for a positive electrode lithium-filled battery cell that ensures complete delithiation of the lithium replenishing agent, reduces liquid loss, and has high formation efficiency.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for forming a positive electrode lithium-ion battery cell, comprising the following steps:

[0007] S1, under negative pressure environment, the positive electrode lithium battery cell is charged with constant current with the first current I1 until the SEI film is formed.

[0008] S2, under normal pressure, the positive electrode lithium battery cell is charged to the platform voltage V1 by the second current I2;

[0009] S3, under negative pressure environment, the positive electrode lithium-ion cell is charged at constant power with the first power P1 to the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent.

[0010] S4. Under normal pressure, the positive electrode lithium battery cell is discharged at constant power to the platform voltage V1 using the first power P1.

[0011] S5, under negative pressure environment, the positive electrode lithium-ion cell is charged at constant power to the upper limit of the second delithiation stage voltage V3 of the lithium replenishing agent with the second power P2.

[0012] S6, under normal pressure, the positive electrode lithium-ion cell is discharged at constant power to the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent using the second power P2.

[0013] S7, under negative pressure, the positive electrode lithium-ion cell is charged at constant power using the second power P2 to the upper limit of the second delithiation stage voltage V3 of the lithium replenishing agent.

[0014] Furthermore, in step S1, the first current I1 is 0.05 to 0.2C.

[0015] Furthermore, in step S2, the second current I2 is 0.5 to 1C.

[0016] Furthermore, in steps S3 and S4, the first power P1 is 0.5 to 1 times the rated power of the battery cell.

[0017] Furthermore, in steps S5, S6, and S7, the second power P2 is 0.2 to 0.5 times the rated power of the battery cell.

[0018] Furthermore, the negative pressure in step S1 is F1, which is -40 to -80 kPa, and the negative pressure in steps S3, S5 and S7 is F2, which is -60 to -100 kPa.

[0019] Further, in step S1, the positive electrode lithium battery cell is charged at a constant current to a first charge level Q1.

[0020] Furthermore, in step S1, the first charge Q1 is 20-40%.

[0021] Furthermore, in steps S2 and S4, the platform voltage V1 is 3.2 to 3.9V; in steps S3 and S6, the upper limit voltage V2 of the first delithiation stage of the lithium replenishing agent is 3.9 to 4.0V; and in steps S5 and S7, the upper limit voltage V3 of the second delithiation stage of the lithium replenishing agent is 4.1 to 4.3V.

[0022] Furthermore, steps S1 to S7 are all carried out at room temperature of 20–35°C.

[0023] The technical solution of the present invention has the following advantages compared with the prior art:

[0024] (1) The formation method of the positive electrode lithium-ion battery cell disclosed in this invention firstly adopts a segmented formation process, in which the lithium-ion agent is charged with different parameters at each reaction stage and the process is repeated twice to fully activate the lithium-ion agent material and ensure complete delithiation of the lithium-ion agent; secondly, the delithiation process adopts constant power charging instead of constant current charging, which can alleviate the polarization of the lithium-ion agent material and avoid the problem of excessively fast delithiation reaction and excessive gas production that cannot be eliminated due to high current constant current charging. It also avoids the problem of long time consumption caused by low current constant current charging; thirdly, a negative pressure environment is used only in the lithium-ion agent charging and delithiation process, while the rest of the process is kept at normal pressure, which can reduce the amount of liquid loss during the formation process.

[0025] (2) In the positive electrode lithium battery cell formation method disclosed in this invention, in step S1, the first current I1 is set between 0.05 and 0.2C, which can ensure the film formation temperature and the time consumption will not be too long.

[0026] (3) In the positive electrode lithium battery cell formation method disclosed in this invention, in step S2, the second current I2 is set between 0.5 and 1C, which can shorten the time of this step and prevent excessive polarization, thus facilitating charging.

[0027] (4) In the positive electrode lithium-ion cell formation method disclosed in this invention, in steps S3 and S4, the first power P1 is set to 0.5 to 1 times the rated power of the cell, the gas generation is slow, and the reaction is complete.

[0028] (5) In the positive electrode lithium replenishment cell formation method disclosed in this invention, in steps S5, S6 and S7, the second power P2 is set to 0.2 to 0.5 times the rated power of the cell, which is beneficial to complete delithiation, and the delithiation time will not be too long and the liquid loss will not be too high.

[0029] (6) The positive electrode lithium-ion battery cell formation method disclosed in this invention sets the negative pressure F1 in step S1 to -40 to -80 kPa, and the negative pressure F2 in steps S3, S5 and S7 to -60 to -100 kPa, which can absorb the generated gas as much as possible and will not absorb the electrolyte.

[0030] (7) The positive electrode lithium-ion battery cell formation method disclosed in this invention, in step S1, the positive electrode lithium-ion battery cell is charged at a constant current to a first charge Q1, and the SEI film formation is determined according to the SOC, which has a wider range of applications.

[0031] (8) In the formation method of positive electrode lithium battery cell disclosed in this invention, in step S1, the first charge Q1 is set to 20-40%, the SEI film can be completed and the formation time will not be too long.

[0032] (9) In the formation method of the positive electrode lithium replenishment cell disclosed in this invention, in step S3, according to the material system, the upper limit of the first delithiation stage voltage V2 of the lithium replenishment agent is set to 3.9 to 4.0, and the upper limit of the second delithiation stage voltage V3 of the lithium replenishment agent is set to 4.1 to 4.3V, which is suitable for the corresponding cell.

[0033] (10) The positive electrode lithium-ion battery cell formation method disclosed in this invention is more suitable because steps S1 to S7 are all carried out at room temperature. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0035] The present invention discloses a method for forming a positive electrode lithium-ion battery cell, comprising the following steps:

[0036] S1, under negative pressure environment, the positive electrode lithium battery cell is charged with constant current with the first current I1 until the SEI film is formed.

[0037] S2, under normal pressure, the positive electrode lithium battery cell is charged to the platform voltage V1 by the second current I2;

[0038] S3, under negative pressure environment, the positive electrode lithium-ion cell is charged at constant power with the first power P1 to the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent.

[0039] S4. Under normal pressure, the positive electrode lithium battery cell is discharged at constant power to the platform voltage V1 using the first power P1.

[0040] S5, under negative pressure environment, the positive electrode lithium-ion cell is charged at constant power to the upper limit of the second delithiation stage voltage V3 of the lithium replenishing agent with the second power P2.

[0041] S6, under normal pressure, the positive electrode lithium-ion cell is discharged at constant power to the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent using the second power P2.

[0042] S7, under negative pressure, the positive electrode lithium-ion cell is charged at constant power using the second power P2 to the upper limit of the second delithiation stage voltage V3 of the lithium replenishing agent.

[0043] During the initial charge and discharge of a liquid lithium-ion battery, the electrode material and electrolyte react at the solid-liquid interface to form a passivation layer covering the electrode material surface. This passivation layer is an interface layer with characteristics of a solid electrolyte; this passivation film is called the solid electrolyte interphase (SEI) film. The formation process of the SEI film is an electrochemical reaction process. When the voltage reaches a certain value, a series of physicochemical changes occur on the surface of the negative electrode. In actual production, the film is mainly formed during the battery formation step.

[0044] Generally, the nominal voltage is the center voltage of the plateau voltage. Near this voltage, the voltage change is very slow during charging and discharging. The rated voltage, the upper limit of the voltage for the first delithiation stage, and the upper limit of the voltage for the second delithiation stage are different for different materials, and are set according to the material of the battery cell.

[0045] In step S1 above, constant current charging ensures stable current density, consistent chemical reaction rate of the material, constant film formation rate, and high quality of SEI film.

[0046] In step S2 above, the second current is greater than the first current, resulting in faster constant current charging.

[0047] In steps S3 to S7, during the constant power charging process, the voltage gradually increases and the current gradually decreases, similar to stepped charging. This ensures the lowest degree of polarization at the fastest charging speed, allowing the lithium replenishment agent to undergo a more complete delithiation reaction during this stage.

[0048] Gas is generated in steps S1, S3, S5, and S7 above, therefore they are set to be carried out under negative pressure, that is, charging and evacuation are performed simultaneously. Gas is not generated in steps S2, S4, and S6 above, therefore they are set to be carried out under normal pressure, that is, evacuation is not required during steps S2, S4, and S6.

[0049] The function of step S4 is the same as that of step S3. Since the lithium replenishment reaction has an initial voltage, usually around the plateau voltage V1, and this process is to discharge to the S2 state, the discharge to the plateau voltage V1 is chosen.

[0050] Step S5 above has the same function as step S3, charging to the upper limit of the second delithiation stage voltage of the lithium replenishing agent. V3 is the upper limit of the second-stage delithiation reaction voltage of the lithium replenishing agent. If it is higher, the battery will be overcharged; if it is lower, the lithium replenishing agent will not be able to completely delithigate.

[0051] In step S6 above, this process discharges the battery cell to state S3 so that step S5 can be repeated, allowing the second reaction stage of the lithium replenishment agent to proceed once more. Discharging below V2 is unnecessary and would increase the formation time. Discharging above V2 would result in incomplete delithiation. Therefore, discharging to V2 is chosen. Discharging to V1 is unnecessary because the first stage has already been repeated twice, ensuring a complete reaction. This shortens the time for step S7, reduces the time spent pumping gas under negative pressure, and minimizes liquid loss.

[0052] Step S7 above allows the second-stage delithiation reaction of the lithium replenishing agent to be repeated to ensure complete delithiation.

[0053] The above technical solution achieves the following: First, a segmented formation process is employed, with the lithium replenisher charged at each reaction stage using different parameters and repeated twice to fully activate the lithium replenisher material, ensuring complete delithiation. Second, the delithiation process uses constant power charging instead of constant current charging, which alleviates the polarization of the lithium replenisher material. This avoids the problems of excessively rapid delithiation reaction and excessive gas production that can be difficult to eliminate, which are caused by high-current constant current charging. It also avoids the long processing time caused by low-current constant current charging. Third, a negative pressure environment is used only during the lithium replenisher charging and delithiation process, while the rest of the process is kept at atmospheric pressure, which reduces liquid loss during the formation process.

[0054] In some preferred embodiments, in step S1, the first current I1 is 0.05 to 0.2C.

[0055] In step S1 above, if the first current is too large, the current density is high, the chemical reaction rate is high, the film formation is too fast, and the film formation is unstable. If the first current is too small, the rate of change is too low, the film formation is too thick, the internal resistance is high, and the time consumption is also long. Therefore, setting the first current I1 between 0.05 and 0.2C can ensure the film formation temperature and prevent the time consumption from being too long. Specifically, the first current can be set to 0.05C, 0.1C, 0.15C, or 0.2C, etc.

[0056] In some preferred embodiments, in step S2, the second current I2 is 0.5 to 1C.

[0057] In step S2 above, a larger second current results in a higher multiplier, shortening the step time. However, if the second current is too large, the polarization will be too great, hindering charging. Therefore, setting the second current I2 to 0.5–1C shortens the step time without causing excessive polarization, thus facilitating charging. Specifically, the second current can be set to 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, or 1C, etc.

[0058] In some preferred embodiments, in steps S3 and S4, the first power P1 is 0.5 to 1 times the rated power of the battery cell.

[0059] In steps S3 and S4 above, if the first power is too high, the gas production rate is fast but the reaction is incomplete; if the first power is too low, the reaction time is long. The longer the reaction time, the longer the negative pressure pumping time, and the greater the electrolyte loss. Therefore, the first power P1 is set to 0.5 to 1 times the rated power of the battery cell, resulting in slow gas production and a complete reaction. Specifically, the first power can be 0.5, 0.6, 0.7, 0.8, 0.9, or 1 times the rated power of the battery cell.

[0060] In some preferred embodiments, in steps S5, S6, and S7, the second power P2 is 0.2 to 0.5 times the rated power of the battery cell.

[0061] In steps S5, S6, and S7 above, the lithium removal reaction product of the lithium replenishing agent is a substance with poor conductivity. Therefore, as the lithium removal reaction proceeds and approaches the upper voltage limit, its conductivity decreases. Excessive second power will lead to incomplete lithium removal, while insufficient second power will result in a prolonged lithium removal process. The longer the negative pressure application time, the higher the liquid loss. Therefore, setting the second power P2 to 0.2 to 0.5 times the rated power of the cell is beneficial for complete lithium removal without excessively long removal time or excessive liquid loss. Specifically, the second power can be 0.2, 0.3, 0.4, or 0.5 times the rated power of the cell.

[0062] In some preferred embodiments, the negative pressure in step S1 is F1, where F1 is -40 to -80 kPa, and the negative pressure in steps S3, S5, and S7 is F2, where F2 is -60 to -100 kPa.

[0063] Since the gas production in steps S3, S5, and S7 is greater, the negative pressure F1 in step S1 is set to -40 to -80 kPa, and the negative pressure F2 in steps S3, S5, and S7 is set to -60 to -100 kPa. This maximizes the removal of the generated gas without drawing away the electrolyte. Specifically, F1 can be set to -40 kPa, -45 kPa, -50 kPa, -55 kPa, -60 kPa, -65 kPa, -70 kPa, -75 kPa, or -80 kPa. F2 can be set to -60 kPa, -65 kPa, -70 kPa, -75 kPa, -80 kPa, -85 kPa, -90 kPa, -95 kPa, or -100 kPa.

[0064] In some preferred embodiments, in step S1, the positive electrode lithium battery cell is charged at a constant current to a first charge level Q1.

[0065] Generally, SEI film formation is completed when the battery is charged to below 2.9–3.1V, although this varies depending on the cell material system. 3.2V corresponds to a cell SOC of approximately 30%, but lithium iron phosphate (LFP) cells are at a voltage plateau at 3.2V. Therefore, judging the completion of SEI film formation based on voltage is not applicable to LFP cells. Thus, in step S1, the positive electrode of the lithium-ion battery is charged at a constant current to the first charge level Q1. Judging the completion of SEI film formation based on SOC is more widely applicable.

[0066] In some preferred embodiments, in step S1, the first charge Q1 is 20-40%.

[0067] Generally, if the upper limit of SOC is too high, the formation time will be too long; if it is too low, SEI film formation will not be completed. At 40% SOC, the voltage begins to enter a voltage plateau. Therefore, in step S1, the first charge Q1 is set to 20-40% to ensure SEI film formation is completed without excessively long formation time. Specifically, the first charge Q1 can be set to 20%, 25%, 30%, 35%, or 40%, etc.

[0068] In some preferred embodiments, in steps S2 and S4, the platform voltage V1 is 3.2 to 3.9V; in steps S3 and S6, the upper limit voltage V2 of the first delithiation stage of the lithium replenishing agent is 3.9 to 4.0V; and in steps S5 and S7, the upper limit voltage V3 of the second delithiation stage of the lithium replenishing agent is 4.1 to 4.3V.

[0069] The rated voltage of the positive electrode material varies depending on the material system. For example, lithium iron phosphate is 3.2V, and ternary lithium is 3.6-3.7V. Therefore, in step S1, based on the material system, the rated voltage V1 of the battery cell is set to 3.2-3.9V. Lithium replenishing agents such as LFO and LNO typically undergo a two-stage delithiation reaction. Therefore, in step S3, based on the material system, the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent is set to 3.9-4.0V, and the upper limit of the second delithiation stage voltage V3 is set to 4.1-4.3V, adapting to the corresponding battery cell. Specifically, the aforementioned platform voltage may be 3.6V or 3.7V, etc., and the aforementioned rated voltage of the battery cell may be 3.2V, 3.3V, 3.4V, 3.5V, 3.6V, 3.7V, 3.8V, or 3.9V, etc.

[0070] In some preferred embodiments, steps S1 to S7 are all performed at room temperature (20–35°C).

[0071] If the formation process is carried out at a high temperature, the electrolyte will be more easily vaporized and removed due to the high temperature. Furthermore, the lithium removal reaction of the lithium replenishment agent is itself an exothermic reaction, which will lead to even higher temperatures. Therefore, steps S1 to S7 are more suitable to be carried out at room temperature. Specifically, room temperature environments include 20℃, 22℃, 24℃, 25℃, 28℃, 30℃, 32℃, 34℃, or 35℃.

[0072] Example 1

[0073] In this embodiment, the positive electrode material of the battery cell is lithium iron phosphate, with 2% lithium supplementer LFO added to the positive electrode. The rated capacity is 100Ah and the rated power is 320W. The formation is carried out according to the following steps:

[0074] Step 1: Charge the battery cell with a constant current of 0.05C to 20% SOC, and convert the environment to negative pressure, with negative pressure F1 being -40kPa;

[0075] Step S2: Charge the battery cell to 3.2V with a constant current of 0.5C; bring the environment to normal pressure.

[0076] Step S3: Charge the battery cell at 0.5 times the rated power of the cell to the upper limit of the first delithiation stage voltage of the lithium replenishing agent, 4.0V, with the formation environment being negative pressure and the negative pressure being -60kPa;

[0077] Step S4: Discharge the battery cell to 3.2V at 0.5 times the rated power of the battery cell, and convert the environment to normal pressure.

[0078] Step S5: Charge the battery cell at 0.2 times the rated power of the cell to the upper limit of the second delithiation stage voltage of the lithium replenishing agent, 4.2V, with the formation environment being negative pressure and the negative pressure being -60kPa;

[0079] Step S6: Discharge the battery cell to 4.0V at 0.2 times the rated power of the battery cell, and convert the environment to normal pressure.

[0080] Step S7: Charge the battery cell at 0.2 times the rated power of the cell to the upper limit of the second delithiation stage voltage of the lithium replenishing agent, 4.2V, with the formation environment being negative pressure and the negative pressure being -60kPa.

[0081] The entire transformation process takes place at room temperature, specifically at 25°C.

[0082] Example 2

[0083] The rest is the same as in Example 1, except that the current in step S1 is 0.2C and the charging capacity is 40% SOC. Step 1: Charge the battery cell with a constant current of 0.2C to 40% SOC, and set the formation environment to negative pressure, with negative pressure F1 being -40kPa.

[0084] Example 3

[0085] The rest is the same as in Example 1, except that the current in step S2 is 1C. Step S2: Charge the battery cell with a constant current of 1C to a voltage of 3.2V; the formation environment is at normal pressure.

[0086] Example 4

[0087] The rest is the same as in Example 1, except that the power in step S3 is 1 times the rated power of the cell, and the negative pressure is -80kPa. Step S3: Charge the cell at a constant power of 1 times the rated power of the cell to the upper limit of the first delithiation stage voltage of the lithium replenishing agent, 4.0V, and the formation environment is under negative pressure, with a negative pressure of -80kPa.

[0088] Example 5

[0089] The rest is the same as in Example 1, except that the power in step S5 is 0.5 times the rated power of the cell, and the negative pressure is -80kPa. Step S5: Charge the cell at a constant power of 0.5 times the rated power of the cell to the upper limit of the second delithiation stage voltage of the lithium replenishing agent, 4.2V, and the formation environment is under negative pressure, with a negative pressure of -80kPa.

[0090] Example 6

[0091] The rest is the same as in Example 1, except that the current in step S1 is 0.5C and the charging capacity is 20% SOC. Step 1: Charge the battery cell with a constant current of 0.5C to 20% SOC, and set the formation environment to negative pressure, with negative pressure F1 being -40kPa.

[0092] Example 7

[0093] The rest is the same as in Example 1, except that the current in step S1 is 0.2C and the charging capacity is 10% SOC. Step 1: Charge the battery cell with a constant current of 0.2C to 10% SOC, and set the formation environment to negative pressure, with negative pressure F1 being -40kPa.

[0094] Example 8

[0095] The rest is the same as in Example 1, except that the power in step S3 is 0.1 times the rated power of the cell. Step S3: Charge the cell at a constant power of 0.1 times the rated power of the cell to the upper limit of the first delithiation stage voltage of the lithium replenishing agent, 4.0V, with the formation environment being negative pressure and the negative pressure being -60kPa.

[0096] Example 9

[0097] The rest is the same as in Example 1, except that the power in step S3 is 0.5 times the rated power of the cell, and the negative pressure is -40kPa. Step S3: Charge the cell at a constant power of 0.5 times the rated power of the cell to the upper limit of the first delithiation stage voltage of the lithium replenishing agent, 4.0V, and the formation environment is under negative pressure, with a negative pressure of -40kPa.

[0098] After formation, the battery cells undergo the following related tests:

[0099] Formation time: The total time from the start to the end of cell formation.

[0100] Liquid loss during formation: Weigh the cell before formation and weigh the cell after formation. The difference in weight is the liquid loss during formation.

[0101] Formation charging capacity: Calculate the charging capacity for each step of the formation process.

[0102] Capacity retention rate after 1000 cycles: The capacity retention rate is calculated after 1000 cycles by performing a cycle test on the formed cells.

[0103] The results of relevant tests on the battery cells of Examples 1 to 9 are shown in the table below.

[0104]

[0105]

[0106] As can be seen from the table above, different embodiments show significant differences in formation time, formation liquid loss, formation charging capacity, and retention rate.

[0107] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for forming a positive electrode lithium-ion battery cell, characterized in that, Includes the following steps: S1, under negative pressure environment, the positive electrode lithium battery cell is charged with constant current with the first current I1 until the SEI film is formed. S2, under normal pressure, the positive electrode lithium battery cell is charged to the platform voltage V1 by the second current I2; S3, under negative pressure environment, the positive electrode lithium-ion cell is charged at constant power with the first power P1 to the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent. S4. Under normal pressure, the positive electrode lithium battery cell is discharged at constant power to the platform voltage V1 using the first power P1. S5, under negative pressure environment, the positive electrode lithium-ion cell is charged at constant power to the upper limit of the second delithiation stage voltage V3 of the lithium replenishing agent with the second power P2. S6, under normal pressure, the positive electrode lithium-ion cell is discharged at constant power to the upper limit of the first delithiation stage voltage V2 of the lithium replenishing agent using the second power P2. S7, Under negative pressure, the positive electrode lithium-ion cell is charged at constant power to the upper limit of the second delithiation stage voltage V3 of the lithium replenishing agent using the second power P2; In step S1, the first current I1 is 0.05~0.2C; In step S2, the second current I2 is 0.5~1C; In steps S3 and S4, the first power P1 is 0.5 to 1 times the rated power of the battery cell; In steps S5, S6, and S7, the second power P2 is 0.2 to 0.5 times the rated power of the battery cell; In steps S2 and S4, the platform voltage V1 is 3.2~3.9V; in steps S3 and S6, the upper limit voltage V2 of the first delithiation stage of the lithium replenishing agent is 3.9~4.0V; and in steps S5 and S7, the upper limit voltage V3 of the second delithiation stage of the lithium replenishing agent is 4.1~4.3V.

2. The formation method of the positive electrode lithium-ion battery cell according to claim 1, characterized in that, The negative pressure in step S1 is F1, which is -40 to -80 kPa. The negative pressure in steps S3, S5 and S7 is F2, which is -60 to -100 kPa.

3. The method for forming a positive electrode lithium-ion battery cell according to claim 1, characterized in that, In step S1, the positive electrode lithium battery cell is charged at a constant current to the first charge level Q1.

4. The method for forming a positive electrode lithium-ion battery cell according to claim 3, characterized in that, In step S1, the first charge Q1 is 20~40% SOC.

5. The method for forming a positive electrode lithium-ion battery cell according to claim 1, characterized in that, Steps S1 to S7 are all carried out at room temperature (20-35°C).

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