CN118645691A - Secondary batteries and electrical devices - Google Patents

Abstract

The present application provides a secondary battery and an electrical device, wherein the electrolyte of the secondary battery comprises a first additive of a structure shown in Formula I and a second additive comprising at least one of an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, and an alkali metal salt of difluorooxalate boric acid; wherein the mass content W2 of the second additive in the electrolyte is 0.01%≤W2%≤5%; and the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02≤W2/W1≤10. The secondary battery has a good cathode and anode interface film, thereby having excellent cycle performance and storage performance.

Description

Secondary batteries and electrical devices

Technical Field

The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device.

Background Art

Secondary batteries have attracted much attention due to their high specific energy, long cycle life, low self-discharge and good safety performance. The application of secondary batteries has penetrated into all aspects of daily life, such as cameras, laptops, electric vehicles, etc., and the requirements for battery power performance, cycle and storage life are also increasing.

During the cycle, the electrolyte and active ions react with each other at the anode and cathode interface, resulting in electrolyte decomposition or active ion precipitation, which reduces the cycle life and storage life of the secondary battery. Therefore, it is necessary to develop a secondary battery with good cycle life and storage life.

Summary of the invention

The secondary battery of the first aspect provided by the present application has both good cycle life and storage life.

The secondary battery provided in the first aspect comprises an electrolyte, wherein the electrolyte comprises:

The first additive has a structure shown in Formula I,

R1 is selected from substituted or unsubstituted C3-C6 alkynyl, R2 is selected from substituted or unsubstituted C1-C6 alkyl;

The second additive comprises at least one of an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, and an alkali metal salt of difluorooxalatoboric acid;

Wherein, the mass content W2 of the second additive in the electrolyte is 0.01%≤W2%≤5%;

The ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02≤W2/W1≤10.

In a secondary battery, the first additive can effectively form a film at the anode of the secondary battery and participate in the formation of a solid electrolyte interface (SEI), which can effectively inhibit the decomposition of the electrolyte on the anode side; the second additive can preferentially undergo a reduction reaction on the anode side of the secondary battery, participate in the formation of a LiF-rich SEI, and inhibit the reduction reaction of the first additive on the anode side and inhibit the increase of the anode interface impedance. The second additive can also participate in the cathode interface film formation, protect the cathode and inhibit the dissolution of transition metals or doping elements in the positive electrode active material. The first additive and the second additive can be used in combination to form a good interface film at the anode and cathode, reduce side reactions in the electrolyte of the secondary battery, and improve the cycle performance and storage performance of the secondary battery.

In any embodiment, R ₁ is an acetylenic ethyl group, and R ₂ is a methyl group or an ethyl group. The acetylenic ethyl group in the first additive helps to react at the anode, produce organic substances, and better participate in the formation of the anode interface film.

In any embodiment, the mass content W2 of the second additive in the electrolyte is 0.05%≤W2%≤5%, thereby further forming a good interface film at the cathode and anode, reducing side reactions on the anode side of the secondary battery and inhibiting the increase of the anode interface impedance.

In any embodiment, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2/W1≤9.5, which can effectively inhibit the deterioration of the anode interface impedance caused by the first additive, thereby improving the cycle performance and storage performance of the secondary battery.

In any embodiment, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤6.5%, and can be optionally 0.01%≤W1%≤0.1%, so that the first additive can form a good interface film on the anode side and reduce the increase in the impedance of the anode interface film.

In any embodiment, the alkali metal salt includes any one or a combination of lithium, sodium, potassium, rubidium, and cesium salts, and may be lithium salts.

In any embodiment, the secondary battery includes a positive electrode active material, the positive electrode active material includes a doping element, and the doping element includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al. The doping element helps to improve the structural stability of the positive electrode active material during the cycle process.

In any embodiment, the mass content W3 of the doping element in the positive electrode active material is 0.01%≤W3%≤1%, and can be optionally 0.04%≤W3%≤1%, thereby improving the structural stability of the positive electrode active material in the secondary battery and inhibiting the structural phase change of the positive electrode active material caused by the extraction and insertion of active lithium ions during the charge and discharge process.

In any embodiment, the secondary battery satisfies: 0.1≤W1/W3≤13; and/or 0.1≤W2/W3≤35. Controlling the ratio of W1/W3 helps to control the increase of the anode interface impedance and improve the structural stability of the positive electrode active material during the cycle. Controlling the ratio of W2/W3 helps to inhibit the dissolution of doped element ions in the positive electrode active material, improve the structural stability of the positive electrode active material during the cycle, and reduce the influence of the anode interface film on the active ion transport performance.

In any embodiment, the positive electrode active material includes lithium nickel cobalt manganese oxide with a molecular formula of Li[Ni _x Co _y Mn _z M _1-xyz ]O ₂ , wherein M includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al, and 0≤x<1, 0≤y≤1, 0≤z≤1, and x+y+z≤1.

In any embodiment, the electrolyte salt in the electrolyte includes _LiPF6 and lithium bis(fluorosulfonyl)imide, and the concentration C1 of the _LiPF6 and the concentration C2 of the lithium bis(fluorosulfonyl)imide satisfy: 0.8M≤C1+C2≤1.5M, 0.1M≤C2≤1M. The electrolyte salt has good chemical stability and ionic conductivity. The combined use of the two can improve the conductivity of the electrolyte and reduce the risk of corrosion of the aluminum foil.

In any embodiment, the electrolyte includes a cyclic carbonate and/or a linear carboxylate solvent, the cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate and propylene carbonate; the linear carboxylate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate and propyl propionate. The solvent helps to reduce the viscosity of the electrolyte and improve the transport performance of active ions, thereby improving the cycle performance of the secondary battery.

A second aspect of the present application provides an electric device, comprising a secondary battery selected from the first aspect of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

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 the embodiment of the present application shown in FIG. 1 .

FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.

FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

Description of reference numerals:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate.

DETAILED DESCRIPTION

Below, the embodiments of the positive electrode active material and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack and electrical device of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination 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" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

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

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

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[Secondary battery]

Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

The electrolyte includes solvents, electrolyte salts and additives. It is a carrier for transporting active ions and plays a vital role in the fast charging performance, specific capacity, cycle efficiency and safety performance of secondary batteries.

During the first charge and discharge process of a secondary battery, the electrode material and the electrolyte react at the solid-liquid interface to form a passivation layer (also called an interface film) covering the surface of the electrode material. The passivation layer formed on the anode side is called the "solid electrolyte interface", referred to as the SEI film, and the passivation layer formed on the cathode side is called the "cathode electrolyte interphase", referred to as the CEI film. During the cycle, the solvent in the electrolyte reacts with the electrode and the electrolyte interface to produce gas, which affects the stability of the electrode interface and the impedance of the interface film, thereby reducing the cycle performance and storage performance of the secondary battery.

Based on this, the present application provides a secondary battery including an additive, which helps the secondary battery form a good SEI film and/or CEI film, can reduce the gas production of the electrolyte, and improve the stability of the electrode interface and the impedance of the interface film.

The secondary battery provided in the present application includes an electrolyte, and the electrolyte includes:

The first additive has a structure shown in Formula I,

_R1 is selected from substituted or unsubstituted C3-C6 alkynyl groups, and _R2 is selected from substituted or unsubstituted C1-C6 alkyl groups;

The second additive includes an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, and an alkali metal salt of difluorooxalatoboric acid, wherein the mass content W2 of the second additive in the electrolyte is 0.01%≤W2%≤5%;

The ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02≤W2/W1≤10.

Herein, "C1-C6 alkyl" refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturation in the group, having from one to six carbon atoms, and attached to the rest of the molecule by a single bond. In some embodiments, the C1-C6 alkyl includes any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and n-pentyl, and optionally, the C1-C6 alkyl is selected from methyl and ethyl.

Herein, "C3-C6 alkynyl" refers to an alkyl group having 3 to 6 carbon atoms and containing at least one alkynyl group. The C3-C6 alkynyl includes any one of CH≡C-CH ₂ -(alkynylethyl), CH≡C-CH ₂ -CH ₂ -, and CH≡CC≡C-CH ₂ -. Optionally, the C3-C6 alkynyl is selected from alkynylethyl.

As used herein, the term "substituted" refers to substitution with a substituent, wherein the substituent is independently selected from: a halogen atom, a C1-C6 alkyl group, a C3-C6 group, such as a fluoro group.

In a secondary battery, the unsaturated alkenyl group in the first additive can undergo a reduction reaction at the anode of the secondary battery, producing loose organic matter to participate in the formation of the SEI film, but it is not conducive to reducing the interfacial impedance of the SEI film. The second additive can be preferentially deposited at the anode of the secondary battery, preferentially undergo a reduction reaction during formation, and participate in the formation of a dense SEI film rich in LiF, which helps to reduce the reduction reaction of the first additive at the anode and inhibit the increase of the anode interface impedance; at the same time, the second additive can also participate in the cathode interface film formation, protect the cathode and inhibit the dissolution of transition metals or doping elements in the positive electrode active material. The combined use of the first additive and the second additive helps to obtain a SEI film with both rigidity and toughness, inhibit the increase of the anode interface impedance and the reduction and decomposition of the electrolyte at the anode, and improve the cycle performance and storage performance of the secondary battery.

In some embodiments, _R1 is an acetylenic ethyl group, and _R2 is a methyl group or an ethyl group. In some embodiments, _R1 is an acetylenic ethyl group, and _R2 is a methyl group. In some embodiments, _R1 is an acetylenic ethyl group, and _R2 is an ethyl group. The unsaturated group contained in the first additive can react at the anode and better participate in the formation of the SEI film; and the _R2 group has good chemical stability and structural toughness, which helps to improve the electronic insulation of the SEI film and the flexibility of the interface film.

In some embodiments, the mass content W2 of the second additive in the electrolyte is 0.05%≤W2%≤5%. In some embodiments, the mass content W2 of the second additive in the electrolyte is 0.05%≤W2%≤5.0%, 0.1%≤W2%≤2.5%, 0.05%≤W2%≤3.0%, 0.2%≤W2%≤2.5%, 0.1%≤W2%≤5.0%, 0.3%≤W2%≤2.5%, 0.75%≤W2%≤5.0%. In some embodiments, the mass content W2 of the second additive in the electrolyte is 0.07%, 0.15%, 0.25%, 0.5%, 0.75%, 1.85%, 2.95% or a range between any two of the above values. Controlling the mass content of the second additive in the electrolyte can form a good interface film at the anode and cathode, and help inhibit the reduction reaction of the first additive at the anode side of the secondary battery and inhibit the increase of the anode interface impedance.

In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2/W1≤10. In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2/W1≤9.5. In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1≤W2/W1≤7.5, 2≤W2/W1≤10, 3≤W2/W1≤10, 1≤W2/W1≤9, 1≤W2/W1≤8, 3.5≤W2/W1≤7. In some embodiments, the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 1.3, 1.8, 2.4, 3.7, 4, 5, 6, 7.5, 8.7, 9.2, 9.8 or a range between any two of the above values. When the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is too small, the first additive may deteriorate the anode interface impedance of the secondary battery, which is not conducive to the cycle performance of the secondary battery. When the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is too high, the second additive may deteriorate the conductivity of the electrolyte, which is not conducive to the migration of active ions and affects the cycle performance of the secondary battery. Controlling the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte can take into account the anode interface impedance of the secondary battery and the conductivity of the electrolyte, and improve the cycle performance and storage performance of the secondary battery.

In some embodiments, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤6.5%. In some embodiments, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤0.1%, 0.05%≤W1%≤5%, 0.01%≤W1%≤4%, 0.01%≤W1%≤3%, 0.01%≤W1%≤1%. In some embodiments, the mass content W1 of the first additive in the electrolyte is 0.03%, 0.08%, 0.1%, 0.5%, 0.8%, 1.2%, 2.3%, 3.4%, 4.1%, 4.9%, 5.5%, 6.3% or a range between any two of the above values. Adjusting the mass content of the first additive in the electrolyte helps it form a good interface film on the anode side, reduces the side reactions on the anode side, and does not increase the interface impedance of the anode too much.

In some embodiments, in the secondary battery, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤1%, the mass content W2 of the second additive in the electrolyte is 0.1%≤W2%≤5%, and the ratio of W2 to W1 is 1≤W2/W1≤10, which can further improve the cycle performance and storage performance of the secondary battery.

In some embodiments, the alkali metal salt includes any one or a combination of lithium, sodium, potassium, rubidium, and cesium salts, and may be lithium salts.

In some embodiments, the second additive includes lithium difluorophosphate and/or lithium tetrafluoroborate. In some embodiments, the second additive includes lithium difluorophosphate. In some embodiments, the second additive includes lithium tetrafluoroborate. The additive is widely available, cost-controlled, and helps to form a cathode and cathode interface film of good quality.

In some embodiments, the secondary battery includes a positive electrode active material, and the positive electrode active material may be a positive electrode active material for a battery known in the art.

As an example, the positive electrode active material may also include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, 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 for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (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 (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co 0.2 Mn _0.2 O ₂ (also referred to as NCM ₆₂₂ ), LiNi 0.8 Co _0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), and LiNi _0.8 Co _0.2 Mn _0.2 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 modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode active material includes a doping element. In some embodiments, the doping element includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al, and the doping element helps to improve the structural stability of the positive electrode active material during the cycle. In some embodiments, the doping element includes Zr.

In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide with a molecular formula of Li[Ni _x Co _y Mn _z M _1-xyz ]O ₂ , wherein the doping element M includes one or more of B, Zr, Ti, Li, Cr, Cu, Zn, Mg, and Al, and 0≤x<1, 0≤y≤1, 0≤z≤1, and x+y+z≤1.

In some embodiments, 0<x<1, 0≤y≤0.3, 0≤z≤0.01, x+y+z≤1.

In some embodiments, lithium nickel cobalt manganese oxide with the molecular formula Li[Ni _x Co _y Mn _z M _1-xyz ]O ₂ can be prepared using methods known in the art, for example, by referring to the methods or part of the methods in CN117334860A, CN117334852A, and CN115986105A.

In some embodiments, the mass content W3 of the doping element in the positive electrode active material is 0.01%≤W3%≤1%. In some embodiments, the secondary battery includes a positive electrode active material containing a doping element, and the mass content W3 of the doping element in the positive electrode active material is 0.04%≤W3%≤1%, 0.1%≤W3%≤1%, 0.05%≤W3%≤0.9%, 0.05%≤W3%≤0.8%, 0.05%≤W3%≤0.7%, 0.2%≤W3%≤1%, 0.01%≤W3%≤0.5%. The secondary battery includes a positive electrode active material containing a doping element, and the mass content W3 of the doping element in the positive electrode active material is 0.03%, 0.08%, 0.15%, 0.25%, 0.38%, 0.41%, 0.52%, 0.64%, 0.72%, 0.83%, 0.94% or a range between the above two values. The doping element can improve the crystalline stability of the positive electrode active material, and adjusting the content of the doping element in the positive electrode active material can inhibit the structural phase change of the positive electrode active material caused by the deintercalation of active ions during the charge and discharge process, and improve the structural stability of the positive electrode active material during the cycle process; and reduce the influence of the doping element on the energy density of the secondary battery, thereby improving the cycle performance and storage performance of the secondary battery.

The mass content W3 of the doping element in the positive electrode active material can be determined using methods known in the art. As an example, it can be determined by inductively coupled plasma (ICP) spectroscopy analysis, for example, it can be determined using an inductively coupled plasma emission spectrometer, or it can refer to standards YS/T1006.2-2014, GB/T23367.2-2009 or YS/T1028.5-2015.

In some embodiments, in the secondary battery, the mass content W1 of the first additive in the electrolyte is 0.01%≤W1%≤1%, the mass content W2 of the second additive in the electrolyte is 0.05%≤W2%≤5%, and the mass content W3 of the doping element in the positive electrode active material is 0.02%≤W3%≤1%, which can take into account both the cycle performance and storage performance of the secondary battery.

In some embodiments, the secondary battery satisfies: 0.1≤W1/W3≤13. In some embodiments, the ratio of the mass content W1 of the first additive in the electrolyte to the mass content W3 of the doping element in the positive electrode active material is 0.5-13, 0.8-13, 1-13, 2-13, 3-13, 0.1-10, 0.1-7, 0.1-6.7, 0.1-5, 0.1-3. In some embodiments, the ratio of the mass content W1 of the first additive in the electrolyte to the mass content W3 of the doping element in the positive electrode active material is 0.3, 0.7, 1.3, 2.7, 3.8, 4.3, 5.7, 6.3, 7.8, 8.8, 9.4, 10, 11.4, 12.1, 13 or a range between the above two values. Adjusting the ratio of W1/W3 helps to control the increase of anode interface impedance and improve the structural stability of the positive electrode active material during the cycle process, which helps to improve the cycle performance and storage performance of the secondary battery.

In some embodiments, the secondary battery satisfies: 0.1≤W2/W3≤35. In some embodiments, the ratio of W2/W3 is 1-35, 0.5-35, 1-30, 2-25, 3-20, 0.1-33, 0.3-27, 0.7-30. In some embodiments, the ratio of W2/W3 is 0.15, 0.55, 0.96, 1.7, 3.5, 5.3, 8.7, 10.2, 13.4, 15, 17.6, 18.9, 21.5, 23.1, 24.8, 28.9, 34.5 or a range between any two of the above values. Adjusting the ratio of W2/W3 helps to inhibit the dissolution of doped element ions in the positive electrode active material, improve the structural stability of the positive electrode active material during the cycle, and reduce the influence of the anode interface film on the active ion transport performance.

[Positive electrode]

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, wherein the positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film 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, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Negative electrode]

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, wherein the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite to each other in its 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, a copper foil may 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 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. 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, 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, the present application is not limited to these materials, and other traditional 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.

In some embodiments, the negative electrode film layer may further include a binder. The binder 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).

In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[Electrolyte]

The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

In some embodiments, the electrolyte salt in the electrolyte includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The electrolyte salt has good chemical stability, provides active ions for the electrolyte, and helps to improve the rate performance and cycle performance of the secondary battery.

In some embodiments, the concentration C1 of lithium hexafluorophosphate (LiPF ₆ ) and the concentration C2 of lithium bis(fluorosulfonyl)imide (LiFSI) satisfy: 0.8M≤C1+C2≤1.5M, 0.1M≤C2≤1M. The high degree of dissociation of LiFSI in the electrolyte can significantly improve the conductivity of the electrolyte and the lithium ion transfer rate, but LiFSI has the risk of corroding the aluminum foil; while LiPF ₆ can form a dense passivation layer on the surface of the aluminum foil to inhibit the corrosion of the aluminum foil. The combined use of the two can improve the conductivity of the electrolyte and reduce the risk of corrosion of the aluminum foil.

In some embodiments, the solvent of the electrolyte includes a cyclic carbonate and/or a linear carboxylate solvent, wherein the cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate and propylene carbonate; and the linear carboxylate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate and propyl propionate. The solvent helps to reduce the viscosity of the electrolyte and improve the transport performance of active ions, thereby improving the cycle performance of the secondary battery.

[Isolation film]

In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

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 membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the 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 package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG1 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to FIG. 2 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in 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 some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

FIG3 is a battery module 4 as an example. Referring to FIG3 , in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

FIG4 and FIG5 are battery packs 1 as an example. Referring to FIG4 and FIG5, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical 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, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

Fig. 6 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

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

Example

Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

1. Test Method

1. Cycle performance test of secondary batteries

At an ambient temperature of 25°C, the battery cell is charged to 4.25V at 1C, then charged to 0.05C at a constant voltage, left to stand for 10 minutes, and discharged to 2.8V at 1C. The discharge capacity is recorded as C0. 300 cycles are performed according to the above charge and discharge process. The discharge capacity of the 300th cycle is C1, and the cycle capacity retention rate of the battery cell = C1/C0×100%.

2. Storage performance test of secondary batteries

The cell was charged to 4.25V at 1C, charged to 0.05C at constant voltage, left to stand for 5 minutes, and discharged to 2.8V at 1C, and the discharge capacity was recorded as D0. The cell was stored at 60°C for 60 days, the cell was taken out and returned to 25°C, then released to 2.8V at 1C, left to stand for 2 hours, charged to 4.25V at 1C, then charged to 0.05C at constant voltage, left to stand for 2 hours, then discharged to 2.8V at 1C, and the discharge capacity was recorded as D1. Discharge capacity retention rate = D1/D0×100%.

3. Determination of doping element content in positive electrode active materials

The results were determined by inductively coupled plasma optical emission spectrometry according to the reference standard YS/T1006.2-2014.

2. Preparation of secondary batteries

Example 1

1) Preparation of electrolyte

In a glove box filled with argon (water content <10 ppm, oxygen content <1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain a non-aqueous organic solvent, and dried lithium salt _LiPF6 and lithium bis(fluorosulfonyl)imide were dissolved in the mixed organic solvent so that the concentrations of lithium salt _LiPF6 and lithium bis(fluorosulfonyl)imide in the prepared electrolyte were 0.8 mol/L and 0.2 mol/L, respectively. A first additive (structural formula: _R1 is acetylenic ethyl, _R2 is methyl), and the second additive lithium tetrafluoroborate with a mass content W2 of 0.05%.

2) Preparation of positive electrode

The positive electrode active material Li[Ni _0.8 Co _0.1 Mn _0.098 Zr _0.002 ]O ₂ , the conductive agent Super P, and the binder polyvinylidene fluoride were mixed at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added and stirred evenly to obtain a positive electrode slurry with a solid content of 50wt%. The positive electrode slurry was coated on the current collector aluminum foil, and the positive electrode sheet was obtained after drying, cold pressing, and slitting.

3) Preparation of negative electrode sheet

The negative electrode active material graphite, the conductive agent Super P, the thickener sodium carboxymethyl cellulose, and the adhesive styrene butadiene rubber are mixed evenly in deionized water at a mass ratio of 80:15:3:2 to prepare a negative electrode slurry with a solid content of 30wt%. The negative electrode slurry is coated on the current collector copper foil, and the negative electrode sheet is prepared by drying, pressing, trimming, cutting, and stripping.

4) Preparation of secondary batteries

A polyethylene film (PE) with a thickness of 16 μm was used as a separator. The prepared positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrodes, and the electrode assembly was wound, and the pole ears were welded. The electrode assembly was placed in an outer package, and the prepared electrolyte was injected into the dried battery cell, and the battery was packaged, left to stand, formed, shaped, and tested for capacity, etc., to obtain the lithium-ion battery of Example 1.

Examples 2 to 19 and Comparative Examples 1 to 2

The secondary batteries of Examples 2 to 18 and Comparative Examples 1 to 2 were prepared in a similar manner to the secondary battery of Example 1, but the dosage of the additives and the mass content of the doping element in the positive electrode active material were adjusted, as shown in Table 1.

The secondary battery preparation method of Example 19 is similar to that of Example 1, except that: the substituent _R1 of the first additive is ethyl, _R2 is ethyl, and the mass content is 0.10%; the second additive is lithium difluorophosphate, and the mass content is 0.10%, see Table 1 for details.

Table 1

serial number W1 W2 Positive electrode active material W3 Example 1 0.05% 0.05% Li[Ni _0.8 Co _0.1 Mn _0.098 Zr _0.002 ]O ₂ 0.20% Example 2 0.10% 0.05% Li[Ni _0.8 Co _0.1 Mn _0.0967 Zr _0.0033 ]O ₂ 0.33% Example 3 0.10% 0.50% Li[Ni _0.8 Co _0.1 Mn _0.0996 Zr _0.0004 ]O ₂ 0.04% Example 4 0.10% 0.75% Li[Ni _0.8 Co _0.1 Mn _0.0995 Zr _0.0005 ]O ₂ 0.05% Example 5 0.01% 0.10% Li[Ni _0.8 Co _0.1 Mn _0.0999 Zr _0.0001 ]O ₂ 0.01% Example 6 0.50% 0.01% Li[Ni _0.8 Co _0.1 Mn _0.099 Zr _0.001 ]O ₂ 0.10% Example 7 0.50% 1.00% Li[Ni _0.8 Co _0.1 Mn _0.097 Zr _0.003 ]O ₂ 0.30% Example 8 0.50% 3.00% Li[Ni _0.8 Co _0.1 Mn _0.095 Zr _0.005 ]O ₂ 0.50% Example 9 0.50% 5.00% Li[Ni _0.8 Co _0.1 Mn _0.09 Zr _0.01 ]O ₂ 1.00% Example 10 0.50% 2.50% Li[Ni _0.8 Co _0.1 Mn _0.095 Zr _0.005 ]O ₂ 0.50% Embodiment 11 1.00% 2.50% Li[Ni _0.8 Co _0.1 Mn _0.095 Zr _0.005 ]O ₂ 0.50% Example 12 3.00% 2.50% Li[Ni _0.8 Co _0.1 Mn _0.095 Zr _0.005 ]O ₂ 0.50% Example 13 5.00% 2.50% Li[Ni _0.8 Co _0.1 Mn _0.095 Zr _0.005 ]O ₂ 0.50% Embodiment 14 6.50% 2.50% Li[Ni _0.8 Co _0.1 Mn _0.095 Zr _0.005 ]O ₂ 0.50% Embodiment 15 0.10% 0.50% Li[Ni _0.8 Co _0.1 Mn _0.09 Zr _0.01 ]O ₂ 1.00% Example 16 0.10% 0.50% Li[Ni _0.8 Co _0.1 Mn _0.098 Zr _0.002 ]O ₂ 0.20% Embodiment 17 0.10% 0.50% Li[Ni _0.8 Co _0.1 Mn _0.0998 Zr _0.0002 ]O ₂ 0.02% Embodiment 18 0.10% 0.50% Li[Ni _0.8 Co _0.1 Mn _0.09985 Zr _0.00015 ]O ₂ 0.015% Embodiment 19 0.10% 0.10% Li[Ni _0.8 Co _0.1 Mn _0.0998 Zr _0.0002 ]O ₂ 0.02% Comparative Example 1 0.01% 0.11% Li[Ni _0.8 Co _0.1 Mn _0.0998 Zr _0.0002 ]O ₂ 0.02% Comparative Example 2 1.00% 6.00% Li[Ni _0.8 Co _0.1 Mn _0.096 Zr _0.004 ]O ₂ 0.40%

The secondary batteries prepared in Examples 1 to 19 and Comparative Examples 1 to 2 were tested using the above method, and the test results are shown in Table 2 below:

Table 2

serial number W2/W1 W1/W3 W2/W3 Cycle performance Storage performance Example 1 1.0 0.3 0.3 96.50% 94.20% Example 2 0.5 0.3 0.2 96.20% 94.00% Example 3 5.0 2.5 12.5 98.90% 97.40% Example 4 7.5 2.0 15.0 98.70% 97.20% Example 5 10.0 1.0 10.0 98.60% 96.90% Example 6 0.02 5.00 0.1 92.30% 91.10% Example 7 2.0 1.67 3.3 97.10% 96.10% Example 8 6.0 1.00 6.0 96.80% 95.70% Example 9 10.0 0.50 5.0 96.40% 97.00% Example 10 5.0 1.00 5.0 96.70% 97.40% Embodiment 11 2.5 2.00 5.0 96.60% 97.50% Example 12 0.8 6.00 5.0 91.20% 90.40% Example 13 0.5 10.00 5.0 90.80% 89.70% Embodiment 14 0.4 13.00 5.0 90.10% 89.40% Embodiment 15 5.0 0.10 0.5 96.00% 93.80% Example 16 5.0 0.50 2.5 96.60% 95.10% Embodiment 17 5.0 5.00 25.0 96.30% 94.90% Embodiment 18 5.0 6.67 33.3 90.10% 89.50% Embodiment 19 1.0 5 5.0 95.40% 93.50% Comparative Example 1 11.0 0.5 5.5 86.00% 85.70% Comparative Example 2 6.0 2.5 15.0 87.40% 87.20%

It can be seen from Examples 1 to 19 and Comparative Examples 1 to 2 that when the mass content of the second additive is between 0.01% and 5%, and the ratio of the mass content W2 of the second additive to the mass content W1 of the first additive is between 0.02 and 10, the secondary battery can form a good interface film at both the anode and cathode, so that the secondary battery has both good cycle performance and storage performance.

It can be seen from Examples 1 to 5 that the ratio of W2 to W1 in the range of 1 to 10 can further improve the deterioration of the anode interface impedance of the secondary battery, thereby further improving the cycle performance and storage performance of the secondary battery.

From Examples 6 to 10, it can be seen that when the mass content W2 of the second additive is in the range of 0.01% to 5.00%, the second additive can participate in the interface film formation at the cathode and anode, and inhibit the deterioration of the anode interface impedance and the structural stability of the positive electrode active material, thereby improving the cycle performance and storage performance of the secondary battery. When the mass content W2 of the second additive is in the range of 1.00% to 5.00%, the cycle performance and storage performance of the secondary battery can be further improved.

It can be seen from Examples 10 to 14 that when the mass content of the first additive is in the range of 0.5% to 6.5%, the secondary battery has good cycle performance and storage performance. At the same time, it is shown that when the mass content of the first additive increases, the first additive increases the deterioration effect on the anode interface impedance, resulting in a decrease in the improvement effect of the first additive on the cycle performance and storage performance of the secondary battery; the mass content of the first additive in the range of 0.50% to 1.0% can significantly improve the cycle performance and storage performance of the secondary battery.

It can be seen from Examples 6 and 15 to 18 that when the mass content of the doping element in the positive electrode active material is in the range of 0.01% to 1.00%, the structural stability of the positive electrode active material is improved, and the secondary battery has good cycle performance and storage performance. When the mass content of the doping element in the positive electrode active material is in the range of 0.02% to 1.00%, the cycle performance and storage performance of the secondary battery can be further improved.

It can be seen from Example 19 that when _R2 in the first additive containing an acetylenic group is selected from an ethyl group and the second additive is lithium difluorophosphate, the prepared secondary battery also has excellent cycle performance and storage performance.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (13)

1. A secondary battery comprising an electrolyte, the electrolyte comprising:

A first additive having a structure of formula I,

R ₁ is selected from substituted or unsubstituted C3-C6 alkynylalkyl, R ₂ is selected from substituted or unsubstituted C1-C6 alkyl;

A second additive comprising at least one of an alkali metal salt of difluorophosphoric acid, an alkali metal salt of tetrafluoroboric acid, an alkali metal salt of fluorosulfonic acid, an alkali metal salt of difluorooxalic acid boric acid;

Wherein the mass content W2 of the second additive in the electrolyte is more than or equal to 0.01% and less than or equal to 2% and less than or equal to 5%;

the ratio of the mass content W2 of the second additive in the electrolyte to the mass content W1 of the first additive in the electrolyte is 0.02-10W 2/W1.

2. The secondary battery according to claim 1, wherein R ₁ is an alkynylethyl group and R ₂ is a methyl group or an ethyl group.

3. The secondary battery according to claim 1 or 2, wherein the mass content W2 of the second additive in the electrolyte is 0.05% to 2% to 5%.

4. The secondary battery according to any one of claims 1 to 3, wherein a ratio of a mass content W2 of the second additive in the electrolyte to a mass content W1 of the first additive in the electrolyte is 1.ltoreq.w2/w1.ltoreq.9.5.

5. The secondary battery according to any one of claims 1 to 4, wherein the mass content W1 of the first additive in the electrolyte is 0.01% to 6.5% W1%, optionally 0.01% to W1% to 1%.

6. The secondary battery according to any one of claims 1 to 5, wherein the alkali metal salt comprises any one or a combination of lithium, sodium, potassium, rubidium, cesium salts, optionally lithium salts.

7. The secondary battery according to any one of claims 1 to 6, wherein the secondary battery comprises a positive electrode active material including a doping element including one or more of B, zr, ti, li, cr, cu, zn, mg, al.

8. The secondary battery according to claim 7, wherein the mass content W3 of the doping element in the positive electrode active material is 0.01% to 1% W3%, optionally 0.04% to 1% W3%.

9. The secondary battery according to claim 7 or 8, wherein the secondary battery satisfies:

w1 is more than or equal to 0.1% W3 is less than or equal to 13; and/or 0.1.ltoreq.W2/W3.ltoreq.35.

10. The secondary battery according to claim 7 or 8, wherein the positive electrode active material comprises a lithium nickel cobalt manganese oxide of the formula Li [ Ni _xCo_yMn_zM_1-x-y-z]O₂ ], wherein M comprises one or more of B, zr, ti, li, cr, cu, zn, mg, al, 0.ltoreq.x <1,

0≤y≤1，0≤z≤1，x+y+z≤1。

11. The secondary battery according to any one of claims 1 to 10, wherein the electrolyte salt in the electrolyte solution includes LiPF ₆ and lithium difluorosulfonimide, and the concentration C1 of LiPF ₆ and the concentration C2 of lithium difluorosulfonimide satisfy: C1+C2 is more than or equal to 0.8M 1.5M,0.1M C2 is less than or equal to 1M.

12. The secondary battery according to any one of claims 1 to 11, wherein the electrolyte solution comprises a cyclic carbonate and/or linear carboxylate solvent,

The cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate;

The linear carboxylic acid ester includes at least one of dimethyl carbonate, methylethyl carbonate, diethyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

13. An electric device comprising the secondary battery according to any one of claims 1 to 12.