A sodium-ion battery positive electrode slurry, a positive electrode sheet, a battery, and a preparation method

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium ion battery positive electrode slurry, a positive electrode sheet, a battery and a preparation method. The sodium ion battery positive electrode slurry provided by the application uses iron phosphate as a positive electrode active material, cooperates with a sodium supplement agent, supplements consumed sodium ions in the formation of a solid-state electrolyte film in the step of a first formation process, and supplements failed sodium ions that are embedded in a negative electrode and cannot be removed in a subsequent cycle process, thereby significantly improving the energy density and the first coulomb efficiency of the sodium ion battery. After the addition of sodium ferrite, a strong alkaline solution is generated, which leads to an increase in the alkalinity of the positive electrode slurry, a high viscosity of the slurry and a serious agglomeration phenomenon, which has a great influence on the processing performance of the positive electrode sheet in the later stage. Therefore, an organic acid is added to neutralize the alkalinity, so as to avoid the above problems. Meanwhile, a large amount of gas is generated in the sodium supplement process, and the inventors completely remove the gas generated in the sodium supplement process through specific formation and aging processes and ensure that there is no risk of gas generation in the subsequent cycle process.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium-ion battery positive electrode slurry, positive electrode sheet, battery, and preparation method. Background Technology

[0002] With societal development, the application of lithium-ion batteries has become increasingly widespread, leading to the massive consumption of lithium resources and a shortage. Therefore, the search for new battery materials is imperative, and sodium-ion batteries have emerged as a result.

[0003] Sodium-ion batteries work on a similar principle to lithium-ion batteries, utilizing the movement of sodium ions between the positive and negative electrodes. Compared to lithium-ion batteries, sodium-ion batteries have advantages in terms of resource abundance and cost, and currently use olivine-type sodium iron phosphate as the positive electrode material. However, during the first charge, sodium ions released from the positive electrode react at the negative electrode, forming an SEI film or undergoing other side reactions, resulting in the loss of active sodium ions. Consequently, during discharge, an equal number of sodium ions cannot be released from the negative electrode back to the positive electrode, leading to a low initial coulombic efficiency. Furthermore, poor compatibility with the negative electrode material results in a lower energy density for sodium iron phosphate batteries.

[0004] To address the aforementioned issues, existing technologies disclose a method for replenishing sodium at the positive electrode of a sodium-ion battery. This method involves adding a metallic element and sodium salt to the positive electrode material of the sodium-ion battery, and controlling the voltage range during the first charging process of battery formation to ensure complete reaction between the metallic element and sodium salt, releasing sodium ions to compensate for sodium ion losses caused by the formation of the SEI film or other side reactions at the negative electrode of the sodium-ion battery during battery formation. This reduces the loss of active sodium ions in the positive electrode material and improves the first coulombic efficiency of the sodium-ion battery.

[0005] However, while the theoretical sodium replenishment capacity of this method is 425 mAh / g, the actual sodium replenishment capacity is only around 200 mAh / g, indicating low efficiency. Adding a small amount of sodium replenishing agent is insufficient to compensate for the loss of sodium ions in the active material, while adding too much will lead to excessive metal compounds remaining in the battery, resulting in excessive internal resistance, poor rate performance, and safety hazards such as cycle failure. Furthermore, this method uses different metals as reactants, introducing metal ions other than those in the cathode material, which may lead to other side reactions later on. Other sodium replenishing agents exist in existing technologies, but they all have some insurmountable problems in practical applications. For example, the alum in sodium vanadium phosphate is highly toxic, making its application unlikely; Prussian blue has a high moisture content, and its preparation process is complex. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the above-mentioned defects in the sodium replenishment method of sodium-ion battery in the prior art, thereby providing a sodium-ion battery positive electrode slurry, positive electrode sheet, battery, and preparation method.

[0007] Therefore, the present invention provides the following technical solution:

[0008] This invention provides a sodium-ion battery positive electrode slurry, comprising the following components by mass percentage:

[0009] Positive electrode active material content: 96-97%;

[0010] Conductive agent 1.5-2%;

[0011] Adhesive 1.5-2%;

[0012] Organic acids 0.1-0.5%;

[0013] The positive electrode active material includes sodium iron phosphate and sodium ferrite in a mass ratio of (86.5-95.5):(1-10).

[0014] Optionally, the organic acid is at least one of oxalic acid and acetic acid;

[0015] And / or, the conductive agent is at least one of carbon black, graphene, carbon nanotubes, Ketjen black, and conductive graphite;

[0016] And / or, the adhesive is polyvinylidene fluoride.

[0017] The present invention also provides a positive electrode sheet for a sodium-ion battery, comprising a current collector and the aforementioned positive electrode slurry coated on one or both sides of the current collector.

[0018] The present invention also provides a method for preparing the above-mentioned sodium-ion battery positive electrode sheet, comprising the following steps:

[0019] S1, mix binder, conductive agent and sodium iron phosphate, add solvent, stir, add sodium ferrite in batches during stirring, add organic acid to obtain positive electrode slurry;

[0020] S2, the positive electrode slurry is coated on one or both sides of the current collector and dried to obtain the positive electrode sheet of the sodium-ion battery.

[0021] Optionally, in step S1, the sodium ferrite is added in three portions:

[0022] Stir at a rate of 1500-2000 rad / min for 60-90 min, and add some sodium ferrite;

[0023] Stir at a rate of 1500-2000 rad / min for 60-90 min, then add some sodium ferrite;

[0024] Stir at a rate of 1500-2000 rad / min for 60-90 min, add the remaining sodium ferrite, and stir at a rate of 1500-2000 rad / min for 60-90 min.

[0025] Optionally, the same mass of sodium ferrite is added each time.

[0026] Optionally, the solvent is N-methylpyrrolidone;

[0027] And / or, the amount of solvent used is such that the solid content of the positive electrode slurry is 45-55% and the viscosity is 4000-6000 CP.

[0028] The present invention also provides a sodium-ion battery, comprising the sodium-ion battery positive electrode sheet described above or the sodium-ion battery positive electrode sheet prepared by the above preparation method.

[0029] Optionally, it also includes a negative electrode, a separator, and an electrolyte.

[0030] The present invention also provides a method for preparing the above-mentioned sodium-ion battery, comprising the following steps:

[0031] S1, stack the positive electrode, separator, and negative electrode in sequence to obtain the battery cell;

[0032] S2, encapsulation, electrolyte injection, formation, aging, to obtain sodium-ion batteries.

[0033] Optionally, the transformation is a step-by-step transformation, specifically including:

[0034] (1) Charge the battery cell to 30-60% capacity in segments at 0.02C-0.2C; optionally, the segmented constant current charging is to first charge at 0.02C-0.05C for 1-5 hours, and then charge at 0.05-0.2C for 1-5 hours.

[0035] (2) Charge to 3.7V with constant current and constant voltage at 0.1C-0.3C, and cut off current at 0.01C-0.05C;

[0036] (3) Charge the battery to 3.8-4.0V at a constant current and constant voltage of 0.1C-0.3C, with a cutoff current of 0.01C-0.05C; optionally, this step can be performed by charging with negative pressure pumping.

[0037] And / or, the aging step is performed by standing at 40-50°C for 12-24 hours, venting the gas, and encapsulating to obtain the final battery.

[0038] The composition and preparation method of the negative electrode sheet in this invention is a well-known method in the art and can be used for the composition and preparation of negative electrode sheets for sodium-ion batteries.

[0039] Typically, and not specifically, the negative electrode slurry for sodium-ion batteries, by mass percentage, comprises the following components:

[0040] 95%-96% of the negative electrode active material;

[0041] Negative electrode conductive agent 0.5%-1%;

[0042] Negative electrode binder 3-4%.

[0043] The negative electrode active material can be hard carbon; the negative electrode conductive agent can be carbon black; the negative electrode binder can be a mixture of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA) in any proportion, for example, PAA:SBR:CMC = 1:1:1.

[0044] In this invention, the diaphragm can be a polypropylene membrane; the electrolyte of the electrolyte is NaPF6 with a concentration of 1 mol / L, and the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in any proportion, for example, EC:DEC:DMC = 1:1:1 in the solvent.

[0045] The technical solution of this invention has the following advantages:

[0046] The sodium-ion battery cathode slurry provided by this invention, after comprehensive comparison with current sodium replenishment methods, finds that directly mixing sodium salt sodium ferrite into the cathode is the simplest method. Compared with other sodium replenishment agents in the prior art, it has a higher sodium replenishment efficiency. By adjusting the amount of sodium ferrite added, the initial efficiency and energy density of the battery cell can also be improved.

[0047] The sodium-ion battery cathode slurry provided by this invention uses sodium iron phosphate as the cathode active material. The reason for choosing sodium iron phosphate as the cathode material is that its stable olivine structure is similar to that of lithium iron phosphate, which has very good safety performance and cycle performance. Moreover, its charge and discharge voltage range is 1.6V-3.7V, which perfectly matches the specific capacity utilization voltage of the selected sodium supplementer, sodium ferrite, i.e., the sodium ion desorption voltage. This ensures that the sodium iron phosphate battery is fully charged during the formation stage and also ensures the capacity utilization of the sodium supplementer. Furthermore, the addition of sodium ferrite does not introduce other metal ions besides iron ions into the sodium iron phosphate battery system. In addition, the cathode slurry is simple to homogenize and easy to operate. In conjunction with a sodium replenisher, it replenishes the sodium ions consumed in forming the solid electrolyte membrane during the initial formation process, as well as the sodium ions that are trapped in the negative electrode and cannot be removed during subsequent cycles, significantly improving the energy density and initial coulombic efficiency of sodium-ion batteries. However, the addition of sodium ferrite replenisher generates a strongly alkaline solution, which increases the alkalinity of the positive electrode slurry, resulting in excessively high slurry viscosity and severe agglomeration, greatly affecting the subsequent electrode processing performance. Therefore, organic acids are added to neutralize the alkalinity and avoid the above problems.

[0048] The method for preparing the positive electrode of a sodium-ion battery provided by this invention involves adding sodium ferrite as a sodium supplement through segmented stirring. By controlling the timing, amount, stirring rate, and stirring time of the segmented addition, the method improves the particle agglomeration phenomenon in the slurry after the addition of sodium ferrite, avoids the appearance of bumps on the positive electrode, and solves the problems of cell consistency and internal resistance that may occur in the later stage due to electrode wetting. This method helps to further improve the electrochemical performance of sodium-ion batteries.

[0049] The sodium-ion battery preparation method provided by this invention effectively controls the gas production of sodium ferrite by limiting the formation steps. All generated oxygen is eliminated during the formation and aging process, preventing cell expansion failure caused by re-gas production during subsequent cycles. This is because the specific capacity utilization voltage of sodium ferrite (the sodium ion extraction voltage) is 3.8V-4.1V; the full charge voltage of the current sodium battery cathode material, sodium nickel cobalt manganese oxide, is 4.3V, far exceeding the capacity utilization voltage of sodium ferrite. Under high voltage conditions, the oxygen generated by the sodium ferrite will react with the electrolyte, causing a series of cell failure problems in the later stages. This invention completely decomposes this oxygen during the formation process, avoiding the negative impact of increased gas production as the amount of sodium ferrite increases. Detailed Implementation

[0050] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0051] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0052] Example 1

[0053] A sodium-ion battery, the specific composition and preparation method of which are as follows:

[0054] (1) Weigh 1.5g of sodium ferrite supplement and divide it into three equal portions;

[0055] (2) Add 1.5g of binder polyvinylidene fluoride (Furoxin FL2032), 1.5g of conductive agent carbon black and 95g of sodium iron phosphate to a mixing tank and stir at a rate of 400 rad / min for 60 min. After stirring evenly, add 100g of solvent NMP and stir at a rate of 1500 rad / min for 60 min. After stirring evenly, add the first portion of sodium supplement and stir at a rate of 1500 rad / min for 60 min. Add the second portion of sodium supplement and stir at a rate of 1500 rad / min for 60 min. Add the third portion of sodium supplement and stir at a rate of 1500 rad / min for 60 min.

[0056] (3) Add 0.5g of oxalic acid, mix well to obtain positive electrode slurry, and the viscosity is tested to be 4000CP;

[0057] (4) The positive electrode slurry was prepared at 17 mg / cm³ 3 The areal density is uniformly coated on one side of the positive electrode current collector, and then heated and dried. After the heating and drying are completed, the areal density is then uniformly coated on the other side of the positive electrode current collector at 17 mg / cm³. 3 The areal density is uniformly coated with positive electrode slurry and then heated and dried to obtain a positive electrode sheet containing a positive electrode active material layer;

[0058] (5) The negative electrode sheet includes 95g of hard carbon as the negative electrode active material, 1g of carbon black as the negative electrode conductive agent, and 4g of negative electrode binder. The negative electrode binder is a mixture of carboxymethyl cellulose (Changguang MAC300), styrene-butadiene rubber (Huachuang 403b), and polyacrylic acid (Alderich-LA133) in a mass ratio of 1:1:1.

[0059] (6) The preparation method of the negative electrode sheet is as follows: the negative electrode slurry is prepared at 8 mg / cm³. 3 The areal density is uniformly coated on one side of the negative electrode current collector, and then heated and dried. After the heating and drying are completed, the areal density is then uniformly coated on the other side of the negative electrode current collector at 8 mg / cm². 3The areal density is uniformly coated with negative electrode slurry and then heated and dried to obtain a negative electrode sheet containing a negative electrode active material layer.

[0060] (7) The diaphragm used in this embodiment is a polypropylene membrane (Enjie 0161); the electrolyte of the electrolyte is NaPF6 with a concentration of 1 mol / L, and the solvent contains ethylene carbonate EC: diethyl carbonate DEC: dimethyl carbonate DMC = 1:1:1.

[0061] (8) The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. The stacked electrodes are then used to obtain a bare cell. The cells are then bonded to positive and negative electrodes, pre-packaged with aluminum-plastic film, dried, and injected with electrolyte. The cells are then sealed, formed, aged, vented, and finally sealed to obtain a soft-pack sodium-ion battery. The specific operations of the formation and aging are as follows: The first step is the pre-formation process of sodium iron phosphate, i.e., 0.02C constant current charging for 5 hours followed by 0.1C charging for 5 hours, charging to 60% capacity of the cell; the second step is the full charge step of sodium iron phosphate formation, i.e., 0.2C constant current and constant voltage charging to 3.7V, with a cutoff current of 0.01C; the third step is the sodium ferrite decomposition and gas generation process, i.e., 0.1C constant current and constant voltage charging to 3.8V, with a cutoff current of 0.01C. This process uses a vacuum device to evacuate the entire battery under negative pressure, ensuring that the soft-pack battery does not swell due to gas production and that the electrolyte is not extracted. The fourth step is the high-temperature aging stage, in which the battery cells after being degassed are placed at a high temperature of 45°C for 12 hours, and finally the gas is vented and the battery is sealed.

[0062] Example 2

[0063] A sodium-ion battery, compared with Example 1, differs in that: the amount of sodium iron phosphate is 93.5g, the amount of sodium ferrite is 3g, and the aging stage is standing at 45°C for 15 hours.

[0064] Example 3

[0065] A sodium-ion battery, compared with Example 1, differs in that: the amount of sodium iron phosphate is 90.5g, the amount of sodium ferrite is 5g, and the aging stage is standing at 45°C for 20 hours.

[0066] Example 4

[0067] A sodium-ion battery, compared with Example 1, differs in that: the amount of sodium iron phosphate is 86.5g, the amount of sodium ferrite is 10g, the amount of positive electrode conductive agent is 1.5g, the amount of positive electrode binder is 1.5g, the amount of oxalic acid is 0.5g, and the aging stage is standing at 45°C for 24 hours.

[0068] Example 5

[0069] A sodium-ion battery, compared with Example 1, differs in that: the amount of sodium iron phosphate is 95.5g, the amount of sodium ferrite is 1g, the amount of positive electrode conductive agent is 1.5g, the amount of positive electrode binder is 1.5g, and the amount of oxalic acid is 0.5g.

[0070] Comparative Example 1

[0071] A sodium-ion battery, compared with Example 1, differs in that: the operation of step (2) is as follows:

[0072] Add 1.5g of binder polyvinylidene fluoride, 1.5g of conductive agent carbon black, and 95g of sodium iron phosphate to a mixing tank and stir at a rate of 400 rad / min for 60 min. After stirring evenly, add 100g of solvent NMP and stir at a rate of 1500 rad / min for 60 min. After stirring evenly, add sodium supplement and stir at a rate of 1500 rad / min for 60 min.

[0073] Comparative Example 2

[0074] A sodium-ion battery, which differs from Example 1 in that it does not contain oxalic acid.

[0075] Comparative Example 3

[0076] A sodium-ion battery, compared with Example 1, differs in that sodium oxide is used instead of sodium ferrite as the sodium replenishing agent.

[0077] Comparative Example 4

[0078] A sodium-ion battery, compared with Example 1, differs in that sodium sulfide is used instead of sodium ferrite as the sodium replenishing agent.

[0079] Comparative Example 5

[0080] A sodium-ion battery, which differs from Example 1 in that it does not contain a sodium supplement.

[0081] Comparative Example 6

[0082] A sodium-ion battery, compared with Example 1, differs in that: in the formation process, during the sodium replenishment capacity utilization stage, the charging cut-off voltage changes from 3.8V to 3.7V.

[0083] Comparative Example 7

[0084] A sodium-ion battery, compared with Example 1, differs in that: in the formation process, during the sodium replenishment capacity utilization stage, the charging cut-off voltage changes from 3.8V to 4.2V.

[0085] Test case

[0086] The sodium-ion batteries provided in the examples and comparative examples were subjected to electrical performance tests. The specific test methods are as follows:

[0087] Initial Coulombic Efficiency: At room temperature, after the cell is fully charged following formation, the initial Coulombic efficiency of the cell = initial discharge capacity / initial charge capacity. Wherein, initial discharge capacity: The first discharge capacity is obtained by discharging the battery at a constant current of 0.5C to a cutoff voltage of 1.5V after the formation and aging stage, when the battery is left at room temperature for 30 minutes; initial charge capacity: The total charge capacity during the battery formation stage in each embodiment, i.e., the total charge capacity from the pre-formation stage (charged at 0.02C-0.05C for 1-5 hours, then charged at 0.05-0.2C for 1-5 hours), plus the charge capacity from the full charge stage (charged at a constant current and voltage of 0.1C-0.3C to 3.7V, with a cutoff current of 0.01C-0.05C), plus the charge capacity from the sodium supplementation stage (charged at a constant current and voltage of 0.1C-0.3C to 3.8-4.0V, with a cutoff current of 0.01C-0.05C).

[0088] Energy density: At room temperature, first charge the battery at a constant current of 0.5C until the battery voltage reaches 3.7V, then charge it at a constant voltage of 3.7V until the charging current reaches 0.05C and charging is stopped. Let the battery rest for 30 minutes, then discharge it at a current of 1C with a discharge cutoff voltage of 1.5V to obtain the room temperature discharge capacity. Then weigh the battery. Energy density = discharge capacity / battery mass.

[0089] The specific test results are shown in the table below:

[0090] Table 1

[0091]

[0092]

[0093] The data in the table above shows that, based on the comparison of data from Examples 1-5, as the amount of sodium supplement added increases, the aging time required for the battery cell increases (because the more sodium supplement added, the more potential gas is generated, so more high-temperature aging time is needed to allow all the gas to be discharged), the initial efficiency of the battery cell increases, and the energy density of the battery cell gradually increases; based on the data from Comparative Example 1, adding sodium supplement all at once will cause severe agglomeration of the positive electrode slurry particles, making normal coating impossible; the comparison between Comparative Example 5 and Example 1 shows that the initial efficiency of the battery cell without sodium supplement is significantly lower than that of the battery cell with sodium supplement; the comparison between Comparative Example 2 and Example 1 shows that not adding oxalic acid to the positive electrode slurry will lead to excessive viscosity of the positive electrode slurry. The high efficiency of the slurry caused it to solidify and prevent proper coating. Compared with Example 1, Comparative Examples 3 and 4, which used sodium sulfide and sodium oxide as sodium replenishing agents, showed lower lithium replenishment efficiency, and the initial efficiency and energy density were not as good as those brought by sodium ferrite as a sodium replenishing agent. The comparison between Comparative Example 6 and Example 1 showed that when the sodium replenishing agent's operating voltage in the formation process decreased from 3.8V to 3.7V, the sodium replenishing agent did not play a role, and there was no performance improvement compared to Comparative Example 5 without sodium replenishing agent. The comparison between Comparative Example 7 and Example 1 showed that when the sodium replenishing agent's operating voltage in the formation process increased from 3.8V to 4.2V, the initial efficiency and energy density of the cell did not improve, and the higher voltage would bring more electrolyte side reactions.

[0094] 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 sodium-ion battery positive electrode slurry, characterized in that, The components, expressed as a percentage by mass, include the following components: Positive electrode active material 96-97%; Conductive agent 1.5-2%; Adhesive 1.5-2%; Organic acids 0.1-0.5%; The positive electrode active material includes sodium iron phosphate and sodium ferrite in a mass ratio of (86.5-95.5):(1-10).

2. The sodium-ion battery positive electrode slurry according to claim 1, characterized in that, The organic acid is at least one of oxalic acid and acetic acid; And / or, the conductive agent is at least one of carbon black, graphene, carbon nanotubes, Ketjen black, and conductive graphite; And / or, the adhesive is polyvinylidene fluoride.

3. A positive electrode sheet for a sodium-ion battery, characterized in that, Includes a current collector and a positive electrode slurry as described in claim 1 or 2 coated on one or both sides of the current collector.

4. A method for preparing the positive electrode sheet of a sodium-ion battery according to claim 3, characterized in that, Includes the following steps: S1, mix binder, conductive agent and sodium iron phosphate, add solvent, stir, add sodium ferrite in batches during stirring, add organic acid to obtain positive electrode slurry; S2, the positive electrode slurry is coated on one or both sides of the current collector and dried to obtain the positive electrode sheet of the sodium-ion battery.

5. The method for preparing the positive electrode of a sodium-ion battery according to claim 4, characterized in that, In step S1, the sodium ferrite is added in three portions: Stir at a rate of 1500-2000 rad / min for 60-90 min, and add some sodium ferrite; Stir at a rate of 1500-2000 rad / min for 60-90 min, then add some sodium ferrite; Stir at a rate of 1500-2000 rad / min for 60-90 min, add the remaining sodium ferrite, and stir at a rate of 1500-2000 rad / min for 60-90 min. Optionally, the same mass of sodium ferrite is added each time.

6. The method for preparing the positive electrode of a sodium-ion battery according to claim 4 or 5, characterized in that, The solvent is N-methylpyrrolidone; And / or, the amount of solvent used is such that the solid content of the positive electrode slurry is 45-55% and the viscosity is 4000-6000 CP.

7. A sodium-ion battery, characterized in that, This includes the sodium-ion battery positive electrode sheet as described in claim 3 or the sodium-ion battery positive electrode sheet prepared by the preparation method described in any one of claims 4-6.

8. The sodium-ion battery according to claim 7, characterized in that, It also includes the negative electrode plate, the separator, and the electrolyte.

9. A method for preparing a sodium-ion battery according to claim 7 or 8, characterized in that, Includes the following steps: S1, stack the positive electrode, separator, and negative electrode in sequence to obtain the battery cell; S2, encapsulation, electrolyte injection, formation, aging, to obtain sodium-ion batteries.

10. The method for preparing a sodium-ion battery according to claim 9, characterized in that, The transformation is a step-by-step transformation, specifically including: (1) Charge the battery cell to 30-60% capacity in segments at 0.02C-0.2C; optionally, the segmented constant current charging is to first charge at 0.02C-0.05C for 1-5 hours, and then charge at 0.05-0.2C for 1-5 hours. (2) Charge to 3.7V with constant current and constant voltage at 0.1C-0.3C, and cut off current at 0.01C-0.05C; (3) Charge the battery to 3.8-4.0V at a constant current and constant voltage of 0.1C-0.3C, with a cutoff current of 0.01C-0.05C; optionally, this step can be performed by charging with negative pressure pumping. And / or, the aging step is performed by standing at 40-50°C for 12-24 hours, venting the gas, and sealing to obtain the final battery.

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