WO2024040510A1

WO2024040510A1 - Preparation method for secondary battery, secondary battery and electric device

Info

Publication number: WO2024040510A1
Application number: PCT/CN2022/114788
Authority: WO
Inventors: 张海明; 杨成龙; 刘醒醒
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-08-25
Filing date: 2022-08-25
Publication date: 2024-02-29

Abstract

The present application provides a preparation method for a secondary battery, a secondary battery and an electric device. The preparation method for a secondary battery comprises the following steps: performing constant current-constant voltage charging pre-formation treatment n times on an assembled battery pre-finished product, wherein each constant current-constant voltage charging comprises first constant-current charging and constant-voltage charging reaching the current pre-formation voltage which are performed sequentially, n is an integer greater than or equal to 1, the current of each first constant-current charging is the same or different, an electrolyte in the battery pre-finished product comprises an additive and a solvent, and the reduction potential of the additive is less than or equal to the reduction potential of the solvent; and performing formation treatment of second constant current charging to a formation target voltage on the battery pre-finished product subjected to the pre-formation treatment.

Description

Preparation method of secondary battery, secondary battery and electrical device

Technical field

The present application relates to the field of secondary batteries, and specifically to a preparation method of secondary batteries, secondary batteries and electrical devices.

Background technique

Secondary batteries such as lithium-ion batteries are widely used because of their excellent electrical properties such as high energy density and good cycle performance. During the preparation process of secondary batteries, a solid electrolyte interface film can be formed on the electrode plate through chemical formation. The existence of the solid electrolyte interface film can protect the electrode to a certain extent and maintain the cycle performance of the battery. However, traditional formation methods are not very effective in improving the cycle stability of secondary batteries, and the cycle stability of batteries needs to be further improved.

Contents of the invention

Based on the above problems, the present application provides a secondary battery preparation method, a secondary battery and a power device, which can effectively improve the cycle stability of the secondary battery.

In order to achieve the above purpose, the first aspect of the present application provides a method for preparing a secondary battery, which includes the following steps: performing n times of constant current-constant voltage charging preformation treatment on the assembled battery preform, each time -Constant voltage charging includes the first constant current charging and the constant voltage charging that reaches the current preformation voltage in sequence, n is an integer ≥1, the electrolyte in the battery preform includes additives and solvents, and the additives The reduction potential ≤ the reduction potential of the solvent;

The preformed battery product after the preformation treatment is charged with a second constant current to a formation target voltage.

In the secondary battery preparation method of the present application, through the selection of electrolyte additives and solvents, as well as the pre-formation treatment of n times of constant current-constant voltage charging and the formation treatment of constant current charging to the formation target voltage, the solid electrolyte interface membrane can be The components are adjusted to improve the uniformity of the ionic conductivity of the solid electrolyte interface membrane and improve the cycle stability of the secondary battery.

In some embodiments, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone.

In some embodiments, the volume percentage of the additive is 2% to 10% based on the volume percentage of the electrolyte;

Optionally, the volume percentage of the additive is 4% to 6% based on the volume percentage of the electrolyte.

In some embodiments, the solvent includes at least one of ethylene carbonate and ethyl methyl carbonate.

In some embodiments, in the preformation treatment, the constant voltage charging time is 0.5h to 2h;

Optionally, in the preformation treatment, the constant voltage charging time is 0.8h to 1.2h.

In some embodiments, the voltage of the battery preform after n preformation treatments is ≤ the reduction potential of the solvent + 0.3V.

In some embodiments, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.3V;

Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.1V.

In some of the embodiments, in the first preformation process, the voltage of constant voltage charging is 2.1V~2.7V;

Optionally, in the first preformation process, the voltage of constant voltage charging is 2.3V~2.5V.

In some of these embodiments, n is 2.

In some of the embodiments, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.3V; in the second preformation treatment, the voltage of constant voltage charging and The absolute value of the difference in reduction potentials of the solvents is ≤0.3V;

Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.1V; in the second preformation treatment, the voltage of constant voltage charging and the reduction potential of the solvent The absolute value of the difference in reduction potentials is ≤0.1V.

In some of the embodiments, in the first preformation process, the voltage of constant voltage charging is 2.1V~2.7V; in the second preformation process, the voltage of constant voltage charging is 2.5V~3.1V;

Optionally, in the first preformation process, the voltage of constant voltage charging is 2.3V~2.5V; in the second preformation process, the voltage of constant voltage charging is 2.7V~2.9V.

In some embodiments, in each constant current-constant voltage charging, the current of the first constant current charging is equal, and the current of the first constant current charging is equal to the current of the second constant current charging.

In some embodiments, the first constant current charging current is 0.1C to 0.5C;

Optionally, the current of the first constant current charging is 0.2C~0.4C.

In some embodiments, the current of the second constant current charging is 0.1C to 0.5C;

Optionally, the current of the second constant current charging is 0.2C˜0.4C.

In a second aspect, this application also provides a secondary battery prepared by the above preparation method.

In a third aspect, the present application also provides an electrical device, including the above-mentioned secondary battery.

Description of drawings

In order to explain the technical solution of the present application more clearly, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on the drawings without exerting creative efforts.

FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .

FIG. 3 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

Figure 4 is a morphological view of the negative electrode plate of the secondary battery in Example 1 of the present application after the battery capacity retention rate test.

Figure 5 is a morphology diagram of the negative electrode plate of the secondary battery in Example 2 of the present application after the battery capacity retention rate test.

Figure 6 is a morphology diagram of the negative electrode plate of the secondary battery in Example 3 of the present application after the battery capacity retention rate test.

Figure 7 is a morphological view of the negative electrode plate of the secondary battery in Comparative Example 2 of the present application after the battery capacity retention rate test.

Explanation of reference symbols:

5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device.

To better describe and illustrate embodiments and/or examples of those inventions disclosed herein, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the drawings should not be construed as limiting the scope of any of the disclosed inventions, the embodiments and/or examples presently described, and the best modes currently understood of these inventions.

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the accompanying drawings. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough understanding of the disclosure of the present application will be provided.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing specific embodiments only and is not intended to limit the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2~4 and 2~5. In this application, unless otherwise stated, the numerical range “a˜b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between "0~5" have been listed in this article, and "0~5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprising" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).

Unless otherwise stated, terms used in this application have their commonly understood meanings as generally understood by those skilled in the art. Unless otherwise stated, the values of each parameter mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

The present application provides a method for preparing a secondary battery, a secondary battery prepared by the method, and an electrical device. This kind of secondary battery is suitable for various electrical devices that use batteries, such as mobile phones, portable devices, laptops, battery cars, electric toys, power tools, electric cars, ships and spacecraft. For example, spacecraft include aircraft, rockets , space shuttles and spacecrafts, etc.

Wherein, the secondary battery preparation method includes the following steps: performing n times of constant current-constant voltage charging preformation processing on the assembled battery pre-product, and each constant current-constant voltage charging includes sequentially performing the first constant current charging and reaching For the current constant voltage charging of the preformation voltage, n is an integer ≥ 1. The electrolyte in the battery preform includes additives and solvents, and the reduction potential of the additive ≤ the reduction potential of the solvent; the preformed battery after preformation treatment is The second constant current charging is a formation process until the target voltage is reached.

In some embodiments, the current of each first constant current charge is the same or different.

It can be understood that the reduction potential represents the corresponding potential value when a substance undergoes a reduction reaction, and the unit is V. The acquisition method can be expressed as follows: During the formation process of the assembled battery pre-product, the electric quantity-voltage curve can be obtained. The voltage corresponding to the first peak in the electric quantity-voltage curve is taken as the reduction potential of the additive. The electric quantity-voltage curve is taken as the reduction potential of the additive. The voltage corresponding to the second peak is the reduction potential of the solvent. It can be understood that existing additives and solvents have corresponding reduction potentials. When selecting additives and solvents in this application, you can choose from existing additives and solvents so that the reduction potential of the selected additives and solvents satisfies The reduction potential of the additive ≤ the reduction potential of the solvent.

It can be understood that the sequential first constant current charging and the constant voltage charging that reaches the current preformed voltage mean that in each constant current-constant voltage charging, the constant current charging charges the battery preform to a certain voltage. This voltage is the current preformation voltage, and then the battery preform is charged at a constant voltage with the current preformation voltage.

It can be understood that the assembled battery pre-product may be a battery pre-product including a battery case, a battery core and an electrolyte. Among them, the battery core and the electrolyte are installed in the battery case. It can also be understood that the assembled battery pre-finished product refers to the battery after being packaged but not formed.

During the preparation process of secondary batteries, a solid electrolyte interface film can be formed on the electrode plate through chemical formation. The existence of the solid electrolyte interface film can protect the electrode to a certain extent and maintain the cycle performance of the battery. However, traditional formation methods are not very effective in improving the cycle stability of secondary batteries, and the cycle stability of batteries needs to be further improved. In the secondary battery preparation method of the present application, through the selection of electrolyte additives and solvents, as well as the pre-formation treatment of n times of constant current-constant voltage charging and the formation treatment of constant current charging to the formation target voltage, the solid electrolyte interface can be modified The membrane components are regulated to improve the uniformity of the ionic conductivity of the solid electrolyte interface membrane, reduce the risk of lithium evolution, and improve the cycle stability of the secondary battery.

In one embodiment, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone. Through the selection of additives, combined with pre-formation treatment and formation treatment, the composition of the solid electrolyte interface membrane can be controlled. For example, the organic and inorganic components of the solid electrolyte interface membrane can be controlled to facilitate the production of high ionic conductivity and good toughness. solid electrolyte interface membrane. Among them, the reduction potential of fluoroethylene carbonate is 2.3V~2.4V, the reduction potential of vinylene carbonate is 2.3V~2.4V, and the reduction potential of 1,3-propane sultone is 2.3V~2.4V.

Optionally, the volume percentage of the additive is 2% to 10% based on the volume percentage of the electrolyte. The amount of additives used in the range of 2% to 10% can stabilize the solid electrolyte interface film, maintain the stability of the cycle process, and inhibit the occurrence of lithium evolution problems. When the amount of additives is too small, it is difficult to form a dense solid electrolyte interface film, which may reduce the capacity retention rate of the battery. When the amount of additives is too large, the excess additives will decompose during the cycle and increase gas production, which may lead to lithium precipitation at the interface, which will adversely affect the cycle performance of the battery. Alternatively, the volume percentage of the additive may be, but is not limited to, 3%, 4%, 5%, 7%, 8% or 9%. Further optionally, the volume fraction of the additive is 4% to 6%.

In one embodiment, the solvent includes at least one of ethylene carbonate and ethyl methyl carbonate. Optionally, the reduction potential of the solvent is 2.8V~3.0V.

In one embodiment, in the preformation process, each constant voltage charging time is 0.5h to 2h. When the time of each constant voltage charging is too short, the proportion of inorganic components in the solid electrolyte interface film is small, and the ion transmission at the interface is slow, which is prone to the problem of lithium precipitation on the electrode surface. When each constant voltage charging time is too long, the solid electrolyte interface film has a large proportion of inorganic components and the interface has poor toughness. Volume expansion may occur during the cycle, causing structural damage to the interface film and worsening the cycle of the electrode. life. Optionally, the time of each constant voltage charging is 0.6h, 0.8h, 1h, 1.5h or 1.8h. Further optionally, the time of each constant voltage charging is 0.8h~1.2h. Alternatively, the constant voltage charging times should be equal for each time.

In one embodiment, the voltage of the battery preform after n preformation treatments is ≤ the reduction potential of the solvent + 0.3V. The voltage of the battery preform after n times of preformation treatment is too high, which may increase the organic component content of the solid electrolyte interface membrane, restricting the improvement of ion conductivity, and thus restricting the improvement of battery cycle stability. It can be understood that the voltage of the battery preform after n times of preformation treatment ≤ the formation target voltage.

In one embodiment, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.3V. At this time, the voltage of constant voltage charging is close to the reduction potential voltage of the additive, which is beneficial to controlling the inorganic components of the solid electrolyte interface film and improving the uniformity of the ionic conductivity of the solid electrolyte interface film. Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.2V. Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.1V. Optionally, in the first preformation treatment, the voltage of constant voltage charging is equal to the reduction potential of the additive.

Specifically, in the first preformation process, the voltage of constant voltage charging is 2.1V~2.7V. Optionally, in the first preformation process, the voltage of constant voltage charging is 2.2V~2.6V. Optionally, in the first preformation process, the voltage of constant voltage charging is 2.3V~2.5V. Further optionally, in the first preformation process, the voltage of constant voltage charging is 2.4V.

In one embodiment, n is 2. At this time, in the secondary battery preparation method, the assembled battery preform is subjected to a preformation process of constant current-constant voltage charging twice. In this way, a solid electrolyte interface film including a layered structure of inorganic components and organic components can be formed. Compared with the traditional mosaic structure, the stacked inorganic components and organic components can obtain a more uniform interface and improve the uniformity of ion transmission speed at the interface, which is conducive to further improving the ionic conductivity of the solid electrolyte interface membrane. Uniformity. At the same time, as the uniformity of the ionic conductivity of the solid electrolyte interface film is further improved, the problem of lithium evolution is better avoided, which in turn can reduce the impact of lithium evolution on battery performance and improve the cycle performance of the battery.

In addition, generally, inorganic components have higher ionic conductivity but poorer toughness, while organic components have better toughness but lower ionic conductivity. In the traditional mosaic structure, inorganic components and organic components are arranged at intervals. In this structure, it is often difficult to effectively balance high ionic conductivity and good toughness. In this embodiment, by forming a stack of organic components and inorganic components, the advantages of high ionic conductivity of the inorganic layer and good toughness of the organic layer can be fully utilized, so that the solid electrolyte interface film has both high ionic conductivity and good toughness. Good toughness. On the basis of maintaining high ionic conductivity, the solid electrolyte interface film is not prone to damage. This allows the electrode material to maintain a complete structure during the cycle and improves the cycle stability of the electrode material.

In addition, in the traditional mosaic structure, inorganic components and organic components are arranged at intervals, and usually the high temperature resistance of organic components is often lower than that of inorganic components, that is, organic components have poor stability at high temperatures. sex. At this time, in the traditional solid electrolyte interface film, once the high temperature generated during the cycle decomposes the organic components, the interface film will be damaged on the solid electrolyte interface film. Therefore, the solid electrolyte interface membrane with a traditional mosaic structure has a greater risk of damage during cycling. In this embodiment, through the preformation treatment of two times of constant current-constant voltage charging, a solid electrolyte interface film in which organic components and inorganic components are stacked can be constructed in situ. In the solid electrolyte interface film of the present application, through inorganic With the stacked arrangement of the organic layer and the organic layer, even if the organic layer is decomposed by high temperature, the inorganic layer can still play part of the role of the interface film to maintain the relative integrity of the solid electrolyte interface film. Therefore, in this application, the high-temperature stability of the solid electrolyte interface film can be improved by stacking the inorganic layer and the organic layer, thereby improving the stability of the battery.

Furthermore, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.3V; in the second preformation treatment, the difference between the voltage of constant voltage charging and the reduction potential of the solvent The absolute value is ≤0.3V. At this time, by controlling the voltage of the constant voltage charging in the first preformation treatment and the second preformation treatment, the inorganic components in the formed solid electrolyte interface film can be closer to the electrode plate than the organic components. . At this time, the inorganic component is located between the organic component and the electrode piece, so that the tougher organic layer can be used to create a more stable solid electrolyte interface film and maintain the stability of the solid electrolyte interface film and the electrode piece structure. . At the same time, when the high temperature generated during the cycle causes the organic components to decompose, the inorganic components can play a certain isolation role to prevent the decomposition products from adversely affecting the electrode materials. Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤ 0.2V; in the second preformation treatment, the difference between the voltage of constant voltage charging and the reduction potential of the solvent is ≤ 0.2V. The absolute value of the difference is ≤0.2V. Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤ 0.1V; in the second preformation treatment, the difference between the voltage of constant voltage charging and the reduction potential of the solvent is ≤ 0.1V. The absolute value of the difference is ≤0.1V. Optionally, in the first preformation treatment, the voltage of constant voltage charging is equal to the reduction potential of the additive; in the second preformation treatment, the voltage of constant voltage charging is equal to the reduction potential of the solvent.

Specifically, in the first preformation process, the voltage of constant voltage charging is 2.1V~2.7V; in the second preformation process, the voltage of constant voltage charging is 2.5V~3.1V. Optionally, in the first preformation process, the voltage of constant voltage charging is 2.2V~2.6V; in the second preformation process, the voltage of constant voltage charging is 2.6V~3V. Optionally, in the first preformation process, the voltage of constant voltage charging is 2.3V~2.5V; in the second preformation process, the voltage of constant voltage charging is 2.7V~2.9V. Further optionally, in the first preformation process, the voltage of constant voltage charging is 2.4V; in the second preformation process, the voltage of constant voltage charging is 2.8V.

In one embodiment, in the solid electrolyte interface film in which organic components and inorganic components are stacked and arranged through two preformation treatments of constant current-constant voltage charging, the inorganic components include lithium oxide, lithium fluoride, sulfide, At least one of lithium and lithium carbonate. The organic component includes lithium alkoxide.

In one embodiment, in each constant current-constant voltage charging, the current of the first constant current charging is equal, and the current of the first constant current charging is equal to the current of the second constant current charging.

In one embodiment, the current of the first constant current charging ranges from 0.1C to 0.5C. Optionally, the current of the first constant current charging is 0.2C~0.4C. Optionally, the current of the first constant current charging is 0.3C.

In one embodiment, the current of the second constant current charging ranges from 0.1C to 0.5C. Optionally, the current of the second constant current charging is 0.2C~0.4C. Optionally, the current of the second constant current charging is 0.3C.

Another embodiment of the present application provides a secondary battery. The secondary battery is prepared by the above preparation method.

The secondary battery and electric device of the present application will be described below with appropriate reference to the drawings.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

Positive electrode piece

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. Composite current collectors can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

As an example, the cathode active material may include cathode active materials for batteries known in the art. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon. The weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100% by weight, based on the total weight of the positive electrode film layer count.

In some embodiments, the positive electrode film layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 to 20% by weight, based on the total weight of the positive electrode film layer.

In some embodiments, the positive electrode film layer optionally further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 to 20% by weight, based on the total weight of the positive electrode film layer.

In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone), forming a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40 to 80 wt%, the viscosity at room temperature is adjusted to 5000 to 25000 mPa·s, and the positive electrode slurry is coated on the surface of the positive electrode current collector , dried and cold-pressed by a cold rolling mill to form a positive electrode piece; the unit area density of the positive electrode powder coating is 150-350 mg/m ² , and the compacted density of the positive electrode piece is 3.0-3.6g/cm ³ , optionally 3.3 -3.5g/cm ³ . The calculation formula of the compacted density is: compacted density = coating surface density / (thickness of the pole piece after extrusion - thickness of the current collector).

It can be understood that the positive electrode piece in the embodiment of the present application can be made by using the above-mentioned positive electrode piece as the main body of the positive electrode piece, and forming a solid electrolyte interface film on the surface of the main body of the positive electrode piece.

Negative pole piece

The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative active material may be a negative active material known in the art for batteries. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination. The weight ratio of the negative electrode active material in the negative electrode film layer is 70 to 100% by weight, based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight, based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20% by weight, based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like. The weight ratio of the other additives in the negative electrode film layer is 0 to 15% by weight, based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30 to 70 wt%, and the viscosity at room temperature is adjusted to 2000 to 10000 mPa·s; the obtained negative electrode slurry is coated on the negative electrode current collector, After the drying process and cold pressing, such as against rollers, the negative electrode piece is obtained. The negative electrode powder coating unit area density is 75-220 mg/m ² , and the negative electrode plate compacted density is 1.2-2.0 g/m ³ .

It can be understood that the negative electrode piece in the embodiment of the present application can be made by using the above-mentioned negative electrode piece as the main body of the negative electrode piece, and forming a solid electrolyte interface film on the surface of the main body of the negative electrode piece.

electrolyte

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), bisfluorosulfonyl Lithium amine (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium difluoromethane borate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is usually 0.5 to 5 mol/L.

In some embodiments, the solvent may be selected from fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) ), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate Ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) , one or more of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) kind.

In some embodiments, the electrolyte optionally further includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

Isolation film

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like. This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 1 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 2 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In addition, the present application also provides an electrical device, which includes the secondary battery provided by the present application. The secondary battery may be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the power-consuming device, a secondary battery can be selected according to its usage requirements.

Figure 3 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Example

In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, this application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Example 1:

Preparation of the main body of the positive electrode plate:

Mix the nickel cobalt manganese (NCM) ternary material, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) in a weight ratio of 97.34:28.86:2.7:1.1 and mix evenly. , to obtain the positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the main body of the positive electrode piece.

Preparation of the main body of the negative electrode plate:

Dissolve the active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2 , mix evenly and prepare negative electrode slurry; apply the negative electrode slurry one or more times evenly on the negative electrode current collector copper foil, and then dry, cold press, and cut to obtain the main body of the negative electrode sheet.

Preparation of electrolyte:

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) evenly according to the volume ratio of 3/7, and add 1 mol /L LiPF6 lithium salt is dispersed evenly, then add additives and dissolve in the organic solvent, stir evenly, and obtain electrolyte. Among them, the additive is fluoroethylene carbonate, and the volume percentage of the additive in the electrolyte is 2%. The reduction potential of organic solvents is 2.8V.

Isolation film: Polypropylene film is used as the isolation film.

Preparation of secondary batteries:

Stack the main body of the positive electrode piece, the isolation film, and the main body of the negative electrode piece in order so that the isolation film acts as an isolation between the main bodies of the positive and negative electrode pieces, then wind it to obtain a bare cell, and weld the tabs to the bare cell , put the bare battery core into an aluminum case, bake it at 80°C to remove water, then inject electrolyte and seal it to obtain an uncharged battery. The uncharged battery is then left to stand and hot and cold pressed to obtain a pre-finished battery product. The pre-finished battery product is then subjected to processes such as formation, shaping, and capacity testing to obtain a secondary battery product. Among them, the formation includes the following steps: charging with a 0.3C constant current to 2.4V, then charging with a 2.4V constant voltage for 1 hour, and then charging with a 0.3C constant current to the formation target voltage of 3.4V.

Example 2

Compared with Embodiment 1, the difference in Embodiment 2 is that the formation includes the following steps: charging to 2.4V with a constant current of 0.3C, then charging with a constant voltage of 2.4V for 1 hour, and then charging to 2.8V with a constant current of 0.3C. Then charge at 2.8V constant voltage for 1 hour, and then charge at 0.3C constant current until the target voltage is 3.4V.

Example 3

Compared with Embodiment 1, the difference in Embodiment 2 is that the formation includes the following steps: charging to 2.8V with a constant current of 0.3C, then charging with a constant voltage of 2.8V for 1 hour, and then charging with a constant current of 0.3C to the formation target voltage. 3.4V.

Examples 4 to 6

Compared with Examples 1 to 3 respectively, the difference between Examples 4 to 6 is that the volume percentage of the additive in the electrolyte is 5%.

Examples 7 to 9

Compared with Examples 1 to 3 respectively, the difference between Examples 7 to 9 is that the volume percentage of the additive in the electrolyte is 10%.

Examples 10 to 12

Compared with Examples 1 to 3 respectively, the difference between Examples 10 to 12 is that the additive is vinylene carbonate.

Examples 13-15

Compared with Examples 10 to 12 respectively, the difference between Examples 13 to 15 is that the volume percentage of the additive in the electrolyte is 5%.

Examples 16-18

Compared with Examples 10 to 12 respectively, the difference between Examples 16 to 18 is that the volume percentage of the additive in the electrolyte is 10%.

Examples 19-21

Compared with Examples 1 to 3 respectively, the difference between Examples 19 to 21 is that the additive is 1,3-propane sultone.

Examples 22 to 24

Compared with Examples 19 to 21 respectively, the difference between Examples 22 to 24 is that the volume percentage of the additive in the electrolyte is 5%.

Examples 25 to 27

Compared with Examples 19 to 21 respectively, the difference between Examples 25 to 27 is that the volume percentage of the additive in the electrolyte is 10%.

Comparative example 1

Compared with Example 1, the difference of Comparative Example 1 is that the electrolyte does not contain additives. The formation includes the following steps: charging with a constant current of 0.3C to the formation target voltage of 3.4V.

Comparative example 2

Compared with Example 1, the difference of Comparative Example 2 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

Comparative example 3

Compared with Example 4, the difference of Comparative Example 3 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

Comparative example 4

Compared with Example 7, the difference of Comparative Example 4 is that the formation includes the following steps: charging with a constant current of 0.3C to the formation target voltage of 3.4V.

Comparative example 5

Compared with Example 10, the difference of Comparative Example 5 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

Comparative example 6

Compared with Example 13, the difference of Comparative Example 6 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

Comparative example 7

Compared with Example 16, the difference of Comparative Example 7 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

Comparative example 8

Compared with Embodiment 19, the difference of Comparative Example 8 is that the formation includes the following steps: using 0.3C constant current charging to the formation target voltage of 3.4V.

Comparative example 9

Compared with Example 22, the difference of Comparative Example 9 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

Comparative example 10

Compared with Example 25, the difference of Comparative Example 10 is that the formation includes the following steps: charging with a 0.3C constant current to the formation target voltage of 3.4V.

The types of additives, the volume percentage of the additives in the electrolyte, and the voltage and time of constant voltage charging in the examples and comparative examples are shown in Table 1.

Table 1

Note: "2.4V 1h + 2.8V 1h" in Table 1 means first 2.4V constant voltage charging for 1h, then 2.8V constant voltage charging for 1h, "2.4V1h" means only 2.4V constant voltage charging for 1h, other similar descriptions in the table has a similar meaning. Test part:

Secondary battery capacity retention test: At 25°C, the lithium-ion batteries prepared in the Examples and Comparative Examples were discharged to 0.01V at a constant current of 0.1C, and then discharged to 1.0V at a constant current of 0.1C. The resulting capacity was recorded as Initial capacity C ₀ . Repeat the above steps for the same battery, and record the discharge capacity C _n of the battery after the nth cycle. Then, the battery capacity retention rate after each cycle P _n =C _n /C ₀ *100%. After 200 cycles, record C ₂₀₀ and calculate P ₂₀₀ =C ₂₀₀ /C ₀ *100%. The capacity retention rate results are shown in Table 1.

The morphology of the negative electrode piece in the battery after cycling was tested. The morphology of the negative electrode piece in Examples 1 to 3 is shown in Figures 4 to 6. The morphology of the negative electrode piece in Comparative Example 2 is shown in Figure 7. shown.

It can be seen from Figures 4 to 7 that the surface of the negative electrode piece in Examples 1 to 3 is smoother than that in Comparative Example 2.

It can be seen from Table 1 that the secondary battery in the embodiment has better cycle performance. And under the same additive, the volume percentage of the additive is 5%. The formation includes the following steps: charge with 0.3C constant current to 2.4V, then charge with 2.4V constant voltage for 1 hour, then charge with 0.3C constant current to 2.8V, and then Charging at 2.8V constant voltage for 1 hour, and then charging at 0.3C constant current until the target voltage is 3.4V, the battery has better cycle stability.

The technical features of the above-described embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, All should be considered to be within the scope of this manual.

The above-mentioned embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be understood as limiting the scope of the invention patent. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the scope of protection of this patent application shall be determined by the appended claims.

Claims

A method for preparing a secondary battery, characterized in that it includes the following steps:

The assembled battery preform is subjected to n constant current-constant voltage charging preformation processes. Each constant current-constant voltage charge includes the first constant current charge and the constant voltage charge that reaches the current preformation voltage, n is an integer ≥ 1, the electrolyte in the battery preform includes additives and solvents, and the reduction potential of the additive ≤ the reduction potential of the solvent;

The preformed battery product after the preformation treatment is charged with a second constant current to a formation target voltage.
The method for preparing a secondary battery according to claim 1, wherein the additive includes at least one of fluoroethylene carbonate, vinylene carbonate and 1,3-propane sultone.
The method for preparing a secondary battery according to any one of claims 1 to 2, wherein the volume percentage of the additive is 2% to 10% based on the volume percentage of the electrolyte;

Optionally, the volume percentage of the additive is 4% to 6% based on the volume percentage of the electrolyte.
The method for preparing a secondary battery according to any one of claims 1 to 3, wherein the solvent includes at least one of ethylene carbonate and ethyl methyl carbonate.
The method for preparing a secondary battery according to any one of claims 1 to 4, wherein in the preformation treatment, the time for each constant voltage charging is 0.5h to 2h;

Optionally, in the preformation treatment, the constant voltage charging time is 0.8h to 1.2h.
The method for preparing a secondary battery according to any one of claims 1 to 5, wherein the voltage of the battery preform after n preformation treatments is ≤ the reduction potential of the solvent + 0.3V.
The method for preparing a secondary battery according to any one of claims 1 to 6, wherein in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive ≤ 0.3V;

Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.1V.
The method for preparing a secondary battery according to any one of claims 1 to 7, wherein in the first preformation treatment, the voltage of constant voltage charging is 2.1V to 2.7V;

Optionally, in the first preformation process, the voltage of constant voltage charging is 2.3V~2.5V.
The method for manufacturing a secondary battery according to any one of claims 1 to 8, wherein n is 2.
The method for preparing a secondary battery according to claim 9, wherein in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.3V; In the preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the solvent is ≤0.3V;

Optionally, in the first preformation treatment, the absolute value of the difference between the voltage of constant voltage charging and the reduction potential of the additive is ≤0.1V; in the second preformation treatment, the voltage of constant voltage charging and the reduction potential of the solvent The absolute value of the difference in reduction potential is ≤0.1V.
The method for preparing a secondary battery according to claim 9, characterized in that in the first preformation treatment, the voltage of constant voltage charging is 2.1V~2.7V; in the second preformation treatment, the voltage of constant voltage charging is The voltage is 2.5V~3.1V;

Optionally, in the first preformation process, the voltage of constant voltage charging is 2.3V~2.5V; in the second preformation process, the voltage of constant voltage charging is 2.7V~2.9V.
The method for preparing a secondary battery according to any one of claims 1 to 11, wherein in each constant current-constant voltage charging, the currents of the first constant current charging are equal, and the first constant current charging The charging current is equal to the second constant current charging current.
The method for preparing a secondary battery according to any one of claims 1 to 12, wherein the current of the first constant current charging is 0.1C to 0.5C;

Optionally, the current of the first constant current charging is 0.2C~0.4C.
The method for preparing a secondary battery according to any one of claims 1 to 13, wherein the current of the second constant current charging is 0.1C to 0.5C;

Optionally, the current of the second constant current charging is 0.2C˜0.4C.
A secondary battery, characterized in that it is prepared by the preparation method described in claims 1 to 14.
An electrical device, characterized by comprising the secondary battery according to claim 15.