A positive electrode slurry, a positive electrode material, and a secondary battery and a method for manufacturing the same

Abstract

This application relates to the field of battery materials, specifically to a positive electrode slurry, a positive electrode material, a secondary battery, and a method for preparing the same. The positive electrode slurry includes a positive electrode active material, a first additive having the structure shown in Formula I, and a first initiator. By adding the first additive and the first initiator shown in Formula I to the positive electrode slurry, not only is the problem of film-forming components reacting and forming a film at the negative electrode avoided, but also, under the action of the first initiator, the compound undergoes a polymerization reaction during the coating and drying process of the positive electrode slurry, forming a dense protective film on the surface of the positive electrode sheet. This significantly improves the structural stability of the battery and greatly alleviates the performance instability problem of high-nickel positive electrode lithium-ion batteries under high voltage conditions, reducing phenomena such as gas generation and cycle failure. Furthermore, the battery has low internal resistance, enabling it to achieve both good cycle performance and rate performance.

Description

Technical Field

[0001] This application relates to the field of battery materials, specifically to a positive electrode slurry, a positive electrode material, a secondary battery, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long lifespan, and excellent charge-discharge performance, have become the primary power source for mobile electronic devices and electric vehicles. Among them, high-nickel cathode lithium-ion batteries have attracted widespread attention due to their higher voltage platform and higher specific capacity. However, high-nickel cathode lithium-ion batteries exhibit poor stability at high voltages, easily experiencing problems such as gas generation or cycle failures, which severely limits their application range and lifespan. Existing technological solutions include adding cathode film-forming additives to the electrolyte. These additives form a protective film on the surface of the cathode material, preventing direct contact between the electrolyte and the cathode material, thereby reducing side reactions. Additionally, antioxidant additives are needed to prevent decomposition reactions of the electrolyte under high voltages. While adding cathode film-forming additives to the electrolyte can improve the cycle performance of high-nickel cathode lithium-ion batteries, some additives react and form a film at the negative electrode, leading to increased internal resistance of the cell and affecting the battery's rate performance. Summary of the Invention

[0003] This application provides a positive electrode slurry, a positive electrode material, and a secondary battery, as well as a method for preparing the same, aiming to solve to some extent the problem of existing secondary batteries where the addition of positive electrode film-forming additives to the electrolyte leads to the reaction with the negative electrode to form a film, resulting in increased internal resistance and poor rate performance.

[0004] In a first aspect, this application provides a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material, a first additive having the structure shown in Formula I, and a first initiator;

[0005]

[0006] R1 is selected from substituted or unsubstituted C2-C6 alkenyl or substituted or unsubstituted C2-C6 alkynyl; "substituted" means that the hydrogen atom on the group is replaced by one or more of halogens and C1-C3 alkyl groups; optionally, R1 is selected from C2-C6 alkenyl; more preferably, R1 is selected from vinyl.

[0007] R2, R3, and R4 are independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C2-C6 alkenyl groups, or substituted or unsubstituted C5-C15 aryl groups; "substituted" means that the hydrogen atom on the group is replaced by one or more of halogens and C1-C3 alkyl groups; optionally, R2, R3, and R4 are independently selected from C1-C3 alkyl groups, C2-C6 alkenyl groups, or phenyl groups; more preferably, R2, R3, and R4 are independently selected from methyl, vinyl, or phenyl groups.

[0008] Furthermore, the first additive is selected from one or more of tetravinylsilane, vinyltrimethylsilane, and hexadiene diphenylsilane.

[0009] Furthermore, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the first additive is 1%-5%, optionally 1.5%-3.5%.

[0010] Furthermore, the first initiator includes an azo initiator; and / or, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the first initiator is 0.02%-0.1%.

[0011] Furthermore, the positive electrode slurry also includes a third additive, which comprises a phosphate ester additive containing two OH groups; optionally, the third additive has the structural formula shown in Formula II:

[0012]

[0013] R5 is selected from C2-C6 alkenyl groups or Where n is an integer from 1 to 4;

[0014] Alternatively, the third additive may include one or more of vinyl phosphate and polyethylene glycol monomethacrylate phosphate.

[0015] Furthermore, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the third additive is 1%-5%, optionally 1.5%-3.5%.

[0016] Furthermore, the positive electrode active material has the following chemical formula: LiNi x Co y Mn z O2, 0.8≤x<1, 0<y<0.2, 0<z<0.2 and x+y+z=1; and / or, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the positive electrode active material is 88%-99%; and / or, the positive electrode slurry further includes at least one of a conductive agent and a binder.

[0017] Secondly, this application provides a method for preparing any of the above-mentioned positive electrode slurries, comprising mixing the components of the positive electrode slurry with a solvent to obtain the slurry.

[0018] Thirdly, this application provides a positive electrode material, which is prepared by drying any of the positive electrode slurries described above or the positive electrode slurries prepared by the preparation methods described above.

[0019] Furthermore, the drying temperature is ≥90℃, and the drying time is 2-3 minutes.

[0020] Fourthly, this application provides a positive electrode sheet, including a current collector and a positive electrode material layer disposed on at least one side of the current collector, wherein the positive electrode material layer includes the aforementioned positive electrode material.

[0021] Fifthly, this application also provides a secondary battery, including the aforementioned positive electrode, as well as a negative electrode and an electrolyte.

[0022] Furthermore, it also includes an electrolyte containing a second initiator, and the positive electrode slurry for preparing the positive electrode sheet also includes a second additive, which includes phosphate esters or phosphite esters.

[0023] Alternatively, the second additive has the structural formula shown in Formula III or Formula IV:

[0024]

[0025] R6-R8 are independently selected from C1-C6 alkyl groups and halogen-substituted C1-C6 alkyl groups;

[0026]

[0027] Among them, R9-R 11 Alkyl groups independently selected from C1-C6 and halogen-substituted C1-C6 alkyl groups.

[0028] Furthermore, the phosphate ester additive includes one or more of tris(hexafluoroisopropyl) phosphate, triethyl phosphite, and tris(2,2,2-trifluoroethyl) phosphite; and / or, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the second additive is 2%-8%, optionally 3%-6%.

[0029] Furthermore, based on the total mass of the electrolyte, the mass percentage of the second initiator is 0.05-0.2%; and / or, the second initiator includes a peroxide initiator.

[0030] Sixthly, this application also provides a method for preparing a secondary battery, including allowing the packaged battery to stand; optionally, the standing temperature is 50℃~70℃ and the standing time is 6~24h.

[0031] Furthermore, before encapsulating the battery, the positive electrode, separator, and negative electrode are assembled, and then an electrolyte is injected.

[0032] In a seventh aspect, this application also provides an electrical device, including the aforementioned secondary battery or the secondary battery prepared as described above.

[0033] The technical solution of this application has the following advantages:

[0034] 1. The positive electrode slurry provided in this application comprises a positive electrode active material, a first additive having the structure shown in Formula I, and a first initiator. By adding the first additive and the first initiator shown in Formula I to the positive electrode slurry, not only is the problem of film-forming components forming a film during the negative electrode reaction avoided, but also, under the action of the first initiator, the compound undergoes a polymerization reaction during the coating and drying process of the positive electrode slurry, forming a dense protective film on the surface of the positive electrode sheet. This significantly improves the structural stability of the battery, greatly alleviates the performance instability problem of high-nickel positive electrode lithium-ion batteries under high voltage conditions, and reduces phenomena such as gas generation and cycle failure. Furthermore, the battery has a low internal resistance, enabling the battery to achieve both good cycle performance and rate performance.

[0035] 2. The cathode slurry provided in this application can achieve higher cycle stability by using one or more of tetravinylsilane, vinyltrimethylsilane, and hexadiene diphenylsilane as the first additive.

[0036] 3. The cathode slurry provided in this application, based on the total mass of dry matter in the cathode slurry, has a mass percentage content of the first additive of 1%-5%, particularly 1.5%-3.5%. This enables the battery to improve cycle stability while maintaining high-rate performance.

[0037] 4. The positive electrode slurry provided in this application further includes a third additive, which includes a phosphate ester additive containing two OH groups. This additive can react with the residual alkali on the surface of the high-nickel positive electrode, solving the problem of homogenization and gelation of the slurry caused by high residual alkali in the high-nickel positive electrode, resulting in loss of slurry fluidity. Moreover, the use of the third additive can form a protective film on the surface of the positive electrode. In particular, one or more of vinyl phosphate, diethyl propylene phosphate, and polyethylene glycol monomethacrylate phosphate, when used in combination with the first additive, can further improve the rate performance of the battery.

[0038] 5. The positive electrode material and positive electrode sheet provided in this application can be manufactured using conventional methods in the field, and the operation is simple and reliable.

[0039] 6. The secondary battery provided in this application contains a second initiator in the electrolyte, and the positive electrode slurry for preparing the positive electrode sheet further includes a second additive, which includes phosphate esters or phosphite esters. The second additive itself has strong antioxidant capacity and polymerizes with the second initiator in the electrolyte during the normal standing process after conventional battery assembly, forming a secondary film on the surface of the positive electrode material, thereby further enhancing the protection of the positive electrode active material and improving the cycle performance of the battery.

[0040] Furthermore, the above method ensures that the second additive and the first additive do not share the same initiator. The second initiator is a peroxide initiator, and the first initiator is an azo initiator. The first initiator initiates the polymerization reaction during the conventional drying process after the positive electrode slurry is coated, while the second initiator initiates the polymerization reaction during the conventional settling process after battery encapsulation. The two do not affect each other, thus solving the problem of incomplete or excessive reactions caused by different reaction conditions required by different additives.

[0041] Based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the second additive is 2%-8%, especially 3%-6%. The settling temperature is 50℃~70℃, and the settling time is 6~24h;

[0042] By controlling the amount of the second additive or the temperature and time of standing, the thickness and uniformity of the film can be precisely controlled, thereby improving the performance and stability of the battery.

[0043] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Detailed Implementation

[0044] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0046] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0047] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0048] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0050] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0052] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0053] High-nickel cathode lithium-ion batteries exhibit poor stability at high voltages, prone to gas generation or cycle failures, severely limiting their application range and lifespan. Existing technological solutions include adding cathode film-forming additives to the electrolyte. These additives form a protective film on the cathode material surface. While this improves the cycle performance of high-nickel cathode lithium-ion batteries, some additives react and form a film at the negative electrode, increasing the cell's internal resistance and thus affecting its rate performance.

[0054] In a first aspect, this application provides a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material, a first additive having the structure shown in Formula I, and a first initiator;

[0055]

[0056] R1 is selected from substituted or unsubstituted C2-C6 alkenyl or substituted or unsubstituted C2-C6 alkynyl; "substituted" means that the hydrogen atom on the group is replaced by one or more of halogens and C1-C3 alkyl groups; optionally, R1 is selected from C2-C6 alkenyl; more preferably, R1 is selected from vinyl.

[0057] R2, R3, and R4 are independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C2-C6 alkenyl groups, or substituted or unsubstituted C5-C15 aryl groups; "substituted" means that the hydrogen atom on the group is replaced by one or more of halogens and C1-C3 alkyl groups; optionally, R2, R3, and R4 are independently selected from C1-C3 alkyl groups, C2-C6 alkenyl groups, or phenyl groups; more preferably, R2, R3, and R4 are independently selected from methyl, vinyl, or phenyl groups.

[0058] By incorporating the first additive and first initiator shown in Formula I into the positive electrode slurry, the problem of film formation during the negative electrode reaction is avoided. Furthermore, under the action of the first initiator, this compound undergoes a polymerization reaction during the coating and drying process of the positive electrode slurry, forming a dense protective film on the surface of the positive electrode sheet. This significantly improves the structural stability of the battery and greatly alleviates the performance instability of high-nickel positive electrode lithium-ion batteries under high-voltage conditions, reducing phenomena such as gas generation and cycle failure. Moreover, the battery has low internal resistance, enabling it to achieve both good cycle performance and rate performance.

[0059] To achieve higher cycling stability, in one alternative embodiment, the first additive is selected from one or more of tetravinylsilane, vinyltrimethylsilane, and hexadiene diphenylsilane.

[0060] In one alternative embodiment, the mass percentage of the first additive is 1%-5% based on the total mass of dry matter in the cathode slurry. Limiting the mass percentage of the first additive within this range allows for better improvement in cycle stability while maintaining high-rate performance. For example, the mass percentage of the first additive may be 1%, 2%, 3%, or 5% based on the total mass of dry matter in the cathode slurry.

[0061] In one optional embodiment, the first initiator comprises an azo initiator. The type of azo initiator is not limited, and it is a conventional azo initiator in the art. For example, the azo initiator is selected from one or more of azobisisobutyronitrile and azobisisoheptanenitrile.

[0062] Based on the total mass of dry matter in the cathode slurry, the mass percentage of the first initiator is 0.02%-0.1%. For example, based on the total mass of dry matter in the cathode slurry, the mass percentage of the first initiator is 0.02%, 0.03%, 0.05%, 0.08%, or 0.1%.

[0063] In an optional embodiment, the positive electrode slurry further includes a third additive, which is a phosphate ester additive containing two OH groups. The phosphate ester additive containing two OH groups can react with residual alkali on the surface of the high-nickel positive electrode, solving the problem of slurry gelation and loss of fluidity caused by high residual alkali in the high-nickel positive electrode. Furthermore, the use of the third additive can form a protective film on the positive electrode surface. In particular, the use of one or more of vinyl phosphate, diethyl propylene phosphate, and polyethylene glycol monomethacrylate phosphate in combination with the first additive can further improve the rate performance of the battery.

[0064] In one alternative embodiment, the mass percentage of the third additive is 1%-5% based on the total mass of dry matter in the positive electrode slurry. Limiting the mass percentage of the third additive within this range allows for better improvement in cycle stability while maintaining high-rate performance. For example, the mass percentage of the third additive may be 1%, 2%, 3%, or 5% based on the total mass of dry matter in the positive electrode slurry.

[0065] In one optional embodiment, the positive electrode active material has the following chemical formula: LiNi x Co y Mn z O2, 0.8 ≤ x < 1, 0 < y < 0.2, 0 < z < 0.2 and x + y + z = 1. For example, the chemical formula of the positive electrode active material is as follows: LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0066] In one alternative embodiment, the mass percentage of the positive electrode active material is 88%-99% based on the total mass of dry matter in the positive electrode slurry. For example, the mass percentage of the positive electrode active material is 88%, 90%, 92%, 95%, 98%, or 99% based on the total mass of dry matter in the positive electrode slurry.

[0067] In one optional embodiment, the positive electrode slurry further includes at least one of a conductive agent and a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. 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.

[0068] Secondly, this application provides a method for preparing any of the above-described positive electrode slurries, comprising mixing the components of the positive electrode slurry with a solvent. For example, positive electrode active materials, conductive agents, binders, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry.

[0069] Thirdly, this application provides a positive electrode material, which is prepared by drying any of the positive electrode slurries described above or the positive electrode slurries prepared by the preparation methods described above.

[0070] In one alternative embodiment, the drying temperature is ≥90°C (e.g., 90-100°C), and the drying time is 2-3 minutes. For example, the drying temperature can be 90°C, 95°C, or 100°C. The drying time is 2 minutes, 2.5 minutes, or 3 minutes.

[0071] Fourthly, this application provides a positive electrode sheet, including a current collector and a positive electrode material layer disposed on at least one side of the current collector, wherein the positive electrode material layer includes the aforementioned positive electrode material.

[0072] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In some embodiments, the positive electrode sheet can be prepared by: coating the positive electrode slurry onto the positive electrode current collector with the above-mentioned components for preparing the positive electrode sheet, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0074] Fifthly, this application also provides a secondary battery, including the aforementioned positive electrode plate.

[0075] In an optional embodiment, the battery further includes an electrolyte containing a second initiator, and the positive electrode slurry for preparing the positive electrode sheet further includes a second additive, which includes phosphate esters or phosphites. Phosphate ester additives have strong antioxidant capabilities and polymerize with the second initiator in the electrolyte during the normal settling process after conventional battery assembly, forming a secondary film on the surface of the positive electrode material. This further enhances the protection of the positive electrode active material and improves the battery's cycle performance.

[0076] In an alternative embodiment, the second additive has the structural formula shown in Formula III or Formula IV:

[0077]

[0078] R6-R8 are independently selected from C1-C6 alkyl groups and halogen-substituted C1-C6 alkyl groups;

[0079]

[0080] Among them, R9-R 11 Alkyl groups independently selected from C1-C6 and halogen-substituted C1-C6 alkyl groups.

[0081] In one optional embodiment, the phosphate ester additive includes one or more of tris(hexafluoroisopropyl) phosphate, triethyl phosphite, and tris(2,2,2-trifluoroethyl) phosphite.

[0082] In one alternative implementation, the mass percentage of the second additive is 2%-8% based on the total mass of dry matter in the cathode slurry. For example, the mass percentage of the second additive is 2%, 3%, 5%, or 8% based on the total mass of dry matter in the cathode slurry.

[0083] In one alternative embodiment, the mass percentage of the second initiator is 0.05-0.2% based on the total mass of the electrolyte. For example, the mass percentage of the second initiator is 0.05%, 0.08%, 0.1%, or 0.2% based on the total mass of the electrolyte.

[0084] In one optional embodiment, the second initiator comprises a peroxide initiator. The second additive and the first additive do not share an initiator; the second initiator is a peroxide initiator, and the first initiator is an azo initiator. The first initiator initiates the polymerization reaction during the conventional drying process after the positive electrode slurry is coated, and the second initiator initiates the polymerization reaction during the conventional settling process after battery encapsulation. The two initiators do not affect each other, solving the problem of incomplete or excessive reactions caused by different reaction conditions required by different additives. For example, the peroxide initiator is selected from one or more of benzoyl peroxide, benzoyl tert-butyl peroxide, and methyl ethyl ketone peroxide.

[0085] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0086] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The concentration of the electrolyte salt in the electrolyte solution is 1-2 mol / L.

[0087] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0088] In one alternative embodiment, the secondary battery further includes a negative electrode.

[0089] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer including a negative electrode active material.

[0090] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0091] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode 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, and lithium titanate, etc. 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, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0093] In some embodiments, the negative electrode material layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0094] In some embodiments, the negative electrode material layer may optionally include 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.

[0095] In some embodiments, the negative electrode material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0096] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0097] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0098] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0099] Sixthly, this application also provides a method for preparing a secondary battery, including allowing the packaged battery to stand still.

[0100] In one alternative embodiment, the settling temperature is 50°C to 70°C, and the settling time is 6 to 24 hours. For example, the settling temperature is 50°C, 60°C, or 70°C, and the settling time is 6 hours, 10 hours, 18 hours, or 24 hours.

[0101] In one alternative implementation, the process of packaging the battery includes assembling the positive electrode, separator, and negative electrode, followed by injecting an electrolyte.

[0102] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0103] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0104] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0106] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0107] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0108] In a seventh aspect, this application also provides an electrical device, including the aforementioned secondary battery or the secondary battery prepared as described above.

[0109] In some embodiments, the aforementioned electrical device may also include a battery module or battery pack assembled from the aforementioned secondary batteries. The secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0110] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. An example electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0111] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0112] In this document, the term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain and branched structures. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, isobutyl, sec-butyl, tert-butyl), and pentyl (e.g., n-pentyl, isopentyl, neopentyl). In various embodiments, C1-C6 alkyl groups, i.e., alkyl groups, may contain 1 to 6 carbon atoms.

[0113] The term "alkenyl" refers to an unsaturated hydrocarbon group containing carbon-carbon double bonds, including both straight-chain and branched structures, and the number of carbon-carbon double bonds can be one or more. Examples of alkenyl groups include, but are not limited to, vinyl, propenyl, allyl, and butadienyl. In various embodiments, C2-C6 alkenyl groups, i.e., alkenyl groups, can contain 2 to 6 carbon atoms.

[0114] The term "aryl" refers to a carbocyclic system with aromatic properties, whose structure can be monocyclic, polycyclic, or fused-ring. Examples of aryl groups include, but are not limited to, phenyl. In various embodiments, C5-C15 aryl groups, i.e., aryl groups, can contain 5 to 15 carbon atoms.

[0115] The term "halogen" refers to fluorine, chlorine, bromine, and iodine.

[0116] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0117] Example 1

[0118] This embodiment provides a positive electrode slurry, the preparation method of which is as follows: The positive electrode active material NCM811 (LiNi) is... 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black (SP), conductive carbon nanotubes (CNT), binder polyvinylidene fluoride (PVDF), first additive tetravinylsilane (A1), and first initiator azobisisobutyronitrile (AIBN) are dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 95.85:1:0.5:1.1:1.5:0.05 and stirred evenly to form a positive electrode slurry.

[0119] This embodiment also provides a positive electrode sheet, which is prepared as follows: the above-mentioned positive electrode slurry is uniformly coated on the surface of the positive electrode current collector, and dried at 90°C for 2 minutes to form an active material layer. After conventional processing such as cold pressing, slitting, welding, and adhesive bonding, the manufacturing of the positive electrode sheet is completed.

[0120] This embodiment also provides a lithium-ion battery, including the above-mentioned positive electrode sheet, an electrolyte, and a negative electrode sheet. The electrolyte is prepared as follows: 1.0M lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent of EC (ethylene carbonate), EMC (diethyl carbonate), and DMC (dimethyl carbonate) in a volume ratio of 1:1:1 to form an electrolyte solution. The negative electrode sheet is prepared as follows: graphite (a negative electrode active material), silicon, acetylene black (a conductive agent), styrene-butadiene rubber (SBR) (a binder), and sodium carboxymethyl cellulose (CMC) (a thickener) are dissolved in an appropriate amount of deionized water in a mass ratio of 90:6:1.2:1.5:1.3 and stirred evenly to form a negative electrode slurry. Subsequently, the slurry is uniformly coated on both sides of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet meeting the winding requirements is obtained.

[0121] The manufacturing process of lithium-ion batteries is as follows: A porous PE polymer film is used as the separator. The positive electrode, separator, and negative electrode are stacked sequentially, ensuring the separator is positioned between the positive and negative electrodes for isolation. Subsequently, the stacked electrodes and separator are wound into an electrode assembly and placed in a pre-formed aluminum-plastic film for top and side sealing. Finally, the prepared electrolyte is injected into the baked and dried battery cell. After vacuum sealing, settling (6 hours at 60°C), formation, and shaping, the lithium-ion battery is complete.

[0122] Example 2

[0123] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that the mass percentage of the first additive is adjusted from 1.5% to 2% based on the total mass of dry matter in the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the first additive A1 and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 95.35:1:0.5:1.1:2:0.05 and stirred evenly to form a positive electrode slurry.

[0124] Example 3

[0125] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that the mass percentage of the first additive is adjusted from 1.5% to 3.5% based on the total mass of dry matter in the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the first additive A1 and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 93.85:1:0.5:1.1:3.5:0.05 and stirred evenly to form a positive electrode slurry.

[0126] Example 4

[0127] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that the mass percentage of the first additive is adjusted from 1.5% to 1% based on the total mass of dry matter in the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the first additive A1 and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 96.35:1:0.5:1.1:1:0.05 and stirred evenly to form a positive electrode slurry.

[0128] Example 5

[0129] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that the mass percentage of the first additive is adjusted from 1.5% to 5% based on the total mass of dry matter in the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the first additive A1 and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 92.35:1:0.5:1.1:5:0.05 and stirred evenly to form a positive electrode slurry.

[0130] Example 6

[0131] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 1, except that vinyltrimethylsilane (denoted as A2) of the same mass is used instead of vinylsilane.

[0132] Example 7

[0133] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 1, except that the same mass of hexadiene diphenylsilane (denoted as A3) is used instead of vinylsilane.

[0134] Example 8

[0135] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a third additive with a mass percentage of 1.5%. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, first additive A1, third additive B1, and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.35:1:0.5:1.1:1.5:1.5:0.05 and stirred evenly to form a positive electrode slurry.

[0136] Example 9

[0137] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a third additive with a mass percentage of 2%. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the first additive A1, the third additive B1, and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 93.85:1:0.5:1.1:1.5:2:0.05 and stirred evenly to form a positive electrode slurry.

[0138] Example 10

[0139] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a third additive with a mass percentage of 3.5%. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, first additive A1, third additive B1, and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 92.35:1:0.5:1.1:1.5:3.5:0.05 and stirred evenly to form a positive electrode slurry.

[0140] Example 11

[0141] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a third additive with a mass percentage of 1%. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the first additive A1, the third additive B1, and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.85:1:0.5:1.1:1.5:1:0.05 and stirred evenly to form a positive electrode slurry.

[0142] Example 12

[0143] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1, except that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a third additive with a mass percentage of 5%. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, first additive A1, third additive B1, and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 90.85:1:0.5:1.1:1.5:5:0.05 and stirred evenly to form a positive electrode slurry.

[0144] Example 13

[0145] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 8, except that the same mass of diethyl propylene phosphate (denoted as B2) is used instead of vinyl phosphate.

[0146] Example 14

[0147] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1. The only difference is that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a second additive with a mass percentage of 3%, and based on the total mass of the electrolyte, the electrolyte also includes a second initiator with a mass percentage of 0.1%.

[0148] Specifically, the preparation method of the positive electrode slurry is as follows: The positive electrode active material NCM811, SP, CNT, PVDF, first additive A1, second additive tris(hexafluoroisopropyl) phosphate (denoted as C1) and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 92.85:1:0.5:1.1:1.5:3:0.05 and stirred evenly to form the positive electrode slurry.

[0149] The electrolyte is prepared as follows: 1.0 M lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent of EC (ethylene carbonate), EMC (diethyl carbonate), and DMC (dimethyl carbonate) in a volume ratio of 1:1:1 to form the electrolyte base. Benzoyl peroxide, the second initiator, is weighed according to the above-mentioned mass percentage and added to the electrolyte base; the mixture is then homogeneous to obtain the electrolyte.

[0150] Example 15

[0151] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 14, except that the mass percentage of the second additive is adjusted from 3% to 8% based on the total mass of dry matter in the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, first additive A1, second additive C1, and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 87.85:1:0.5:1.1:1.5:8:0.05 and stirred evenly to form a positive electrode slurry.

[0152] Example 16

[0153] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 14, except that triethyl phosphite (denoted as C2) of the same mass is used instead of tris(hexafluoroisopropyl) phosphate.

[0154] Example 17

[0155] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Embodiment 1. The only difference is that, based on the total mass of dry matter in the positive electrode slurry, the positive electrode slurry also includes a second additive with a mass percentage of 3% and a third additive with a mass percentage of 1.5%, and based on the total mass of the electrolyte, the electrolyte also includes a second initiator with a mass percentage of 0.1%.

[0156] Specifically, the preparation method of the positive electrode slurry is as follows: The positive electrode active materials NCM811, SP, CNT, PVDF, first additive A1, second additive C1, third additive B1 and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 91.35:1:0.5:1.1:1.5:3:1.5:0.05 and stirred evenly to form the positive electrode slurry.

[0157] The electrolyte is prepared as follows: 1.0 M lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent of EC (ethylene carbonate), EMC (diethyl carbonate), and DMC (dimethyl carbonate) in a volume ratio of 1:1:1 to form the electrolyte base. Benzoyl peroxide, the second initiator, is weighed according to the above-mentioned mass percentage and added to the electrolyte base; the mixture is then homogeneous to obtain the electrolyte.

[0158] Example 18

[0159] This embodiment provides a positive electrode slurry, the preparation method of which is as follows: The positive electrode active material NCM955 (LiNi) is... 0.9 Co 0.05 Mn 0.05 O2), SP, CNT, PVDF, first additive A1, second additive C1, third additive B1 and AIBN are dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 88.32:1:0.5:1.1:2:5:2:0.08 and stirred evenly to form a positive electrode slurry.

[0160] This embodiment also provides a positive electrode sheet, which is prepared as follows: the above-mentioned positive electrode slurry is uniformly coated on the surface of the positive electrode current collector, and dried at 100°C for 3 minutes to form an active material layer. After conventional processing such as cold pressing, slitting, welding, and adhesive bonding, the manufacturing of the positive electrode sheet is completed.

[0161] This embodiment also provides a lithium-ion battery, including the above-mentioned positive electrode, as well as an electrolyte and a negative electrode.

[0162] The electrolyte includes a second initiator at a mass percentage of 0.1%, based on the total mass of the electrolyte. The electrolyte is prepared as follows: 1.2M lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent of EC (ethylene carbonate), EMC (diethyl carbonate), and DMC (dimethyl carbonate) in a volume ratio of 1:1:1 to form the base electrolyte. The second initiator, benzoyl peroxide, is weighed according to the above mass percentage and added to the base electrolyte; the mixture is then homogeneous to obtain the electrolyte.

[0163] The negative electrode sheet is prepared as follows: The negative electrode active material graphite, silicon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in an appropriate amount of deionized water at a mass ratio of 90:6:1.2:1.5:1.3, and stirred evenly to form a negative electrode slurry. Subsequently, the slurry is uniformly coated on both sides of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet meeting the winding requirements is obtained.

[0164] The manufacturing process of lithium-ion batteries is as follows: A porous PE polymer film is used as the separator. The positive electrode, separator, and negative electrode are stacked sequentially, ensuring the separator is positioned between the positive and negative electrodes for isolation. Subsequently, the stacked electrodes and separator are wound into an electrode assembly and placed in a pre-formed aluminum-plastic film for top and side sealing. Finally, the prepared electrolyte is injected into the baked and dried battery cell. Following conventional processes such as vacuum sealing, settling (at 70°C for 16 hours), formation, and shaping, the lithium-ion battery manufacturing is completed.

[0165] Comparative Example 1

[0166] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 1, except that the first additive and the first initiator are not added to the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, and PVDF are fully dissolved in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97.4:1:0.5:1.1 and stirred evenly to form a positive electrode slurry.

[0167] Comparative Example 2

[0168] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 1, except that the first initiator is not added to the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, and the first additive A1 are fully dissolved in N-methylpyrrolidone (NMP) solvent at a mass ratio of 95.9:1:0.5:1.1:1.5 and stirred evenly to form the positive electrode slurry.

[0169] Comparative Example 3

[0170] This embodiment provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery, which is basically the same as that in Example 14, except that the first additive and the first initiator are not added to the positive electrode slurry. The preparation method of the positive electrode slurry is as follows: the positive electrode active materials NCM811, SP, CNT, PVDF, the second additive tris(hexafluoroisopropyl) phosphate (denoted as C1), and AIBN are fully dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 94.4:1:0.5:1.1:3 and stirred evenly to form a positive electrode slurry.

[0171] Test case

[0172] (1) Cyclic performance test

[0173] In an environment of 25℃, the first charge and discharge cycle was performed. The battery was charged at a constant current of 1C until the full charge voltage of 4.48V was reached. Then, it was charged at the maximum voltage until the current reached 0.02C. Finally, it was discharged at a constant current of 0.5C until the final voltage reached 2.75V. The discharge capacity of the first cycle was recorded. This process was repeated for 400 charge and discharge cycles, and the discharge capacity of the 400th cycle was recorded. The capacity retention rate (%) of the lithium-ion battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0174] (2) Gas production performance test at 70℃:

[0175] The test method is as follows: The lithium-ion battery is charged to 4.48V at a constant current and voltage of 1C in a constant temperature chamber at 25±2℃, with a cutoff current of 0.05C. The cell volume before storage is measured using the water displacement method. The fully charged cells / batteries are then left open-circuit at (70±2)℃ for 30 days. After 30 days of storage, they are left open-circuit at room temperature for 2 hours. The cell volume after storage is measured using the water displacement method to obtain the lithium-ion battery volume expansion, and the ampere-hour gas production is calculated.

[0176] (3) Ratio Performance Testing Method

[0177] The lithium-ion battery was charged to 4.48V at a constant current and constant voltage of 0.5C in a constant temperature chamber at 25±2℃. Then, it was charged at a constant voltage at the maximum voltage until the current was 0.05C. Then, it was discharged at a constant current of 0.5C / 1C / 2C / 3C until the final voltage was 2.75V. The capacity at each discharge rate was recorded. Using the 0.5C discharge capacity as the reference, the capacity retention rate at the 3C rate was obtained by dividing the 3C discharge capacity by the 0.5C discharge capacity and multiplying by 100%.

[0178] Table 1 Electrical performance of lithium-ion secondary batteries

[0179]

[0180]

[0181] As shown in Table 1, based on the above examples and comparative examples, the examples containing compound I have both good cycle performance and rate performance. With the addition of one or more of the second additive and the third salt additive, the density of the protective film is further enhanced, the cycle stability is improved, and the battery has better cycle stability or rate performance.

[0182] 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 application.

Claims

1. A positive electrode slurry, characterized in that, The positive electrode slurry includes a positive electrode active material, a first additive having the structure shown in Formula I, and a first initiator; R1 is selected from substituted or unsubstituted C2-C6 alkenyl or substituted or unsubstituted C2-C6 alkynyl; "substituted" means that the hydrogen atom on the group is replaced by one or more of halogens and C1-C3 alkyl groups; optionally, R1 is selected from C2-C6 alkenyl; more preferably, R1 is selected from vinyl. R2, R3, and R4 are independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C2-C6 alkenyl groups, or substituted or unsubstituted C5-C15 aryl groups; "substituted" means that the hydrogen atom on the group is replaced by one or more of halogens and C1-C3 alkyl groups; optionally, R2, R3, and R4 are independently selected from C1-C3 alkyl groups, C2-C6 alkenyl groups, or phenyl groups; more preferably, R2, R3, and R4 are independently selected from methyl, vinyl, or phenyl groups.

2. The positive electrode slurry according to claim 1, characterized in that, The first additive is selected from one or more of tetravinylsilane, vinyltrimethylsilane, and hexadiene diphenylsilane.

3. The positive electrode slurry according to claim 1 or 2, characterized in that, Based on the total mass of dry matter in the cathode slurry, the mass percentage of the first additive is 1%-5%, optionally 1.5%-3.5%.

4. The positive electrode slurry according to any one of claims 1-3, characterized in that, The first initiator includes an azo initiator; and / or, based on the total mass of dry matter in the cathode slurry, the mass percentage of the first initiator is 0.02%-0.1%.

5. The positive electrode slurry according to any one of claims 1-4, characterized in that, The positive electrode slurry also includes a third additive, which comprises a phosphate ester additive containing two OH groups. Optionally, the third additive has the structural formula shown in Formula II. R5 is selected from C2-C6 alkenyl groups or Where n is an integer from 1 to 4; Alternatively, the third additive may include one or more of vinyl phosphate and polyethylene glycol monomethacrylate phosphate.

6. The positive electrode slurry according to claim 5, characterized in that, Based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the third additive is 1%-5%, optionally 1.5%-3.5%.

7. The positive electrode slurry according to any one of claims 1-6, characterized in that, The positive electrode active material has the following chemical formula: LiNi x Co y Mn z O2, 0.8≤x<1, 0<y<0.2, 0<z<0.2 and x+y+z=1; and / or, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the positive electrode active material is 88%-99%.

8. A method for preparing the positive electrode slurry according to any one of claims 1-7, characterized in that, This includes preparing the positive electrode slurry by mixing the components of the slurry with a solvent.

9. A positive electrode material, characterized in that, The positive electrode material is prepared by drying the positive electrode slurry obtained by any one of claims 1 to 7 or the preparation method described in claim 8. Optionally, the drying temperature is ≥90℃ and the drying time is 2-3 minutes.

10. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode material layer disposed on at least one side of the current collector, the positive electrode material layer comprising the positive electrode material of claim 9.

11. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 10; Optionally, it also includes an electrolyte containing a second initiator, and the positive electrode slurry for preparing the positive electrode sheet further includes a second additive, which includes phosphate esters or phosphite esters. Alternatively, the second additive has the structural formula shown in Formula III or Formula IV: R6-R8 are independently selected from C1-C6 alkyl groups and halogen-substituted C1-C6 alkyl groups; Among them, R9-R 11 Alkyl groups independently selected from C1-C6 and halogen-substituted C1-C6 alkyl groups.

12. The secondary battery according to claim 11, characterized in that, The phosphate ester additive includes one or more of tris(hexafluoroisopropyl) phosphate, triethyl phosphite, and tris(2,2,2-trifluoroethyl) phosphite; and / or, based on the total mass of dry matter in the positive electrode slurry, the mass percentage of the second additive is 2%-8%, optionally 3%-6%.

13. The secondary battery according to claim 11, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the second initiator is 0.05-0.2%; and / or, the second initiator includes a peroxide initiator.

14. A method for preparing a secondary battery, characterized in that, This includes allowing the packaged battery to stand still; optionally, the standing temperature is 50℃~70℃, and the standing time is 6~24h.

15. An electrical appliance, characterized in that, This includes the secondary battery described in any one of claims 11-13 or the secondary battery prepared by the method described in claim 14.

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