Lithium secondary battery and electric device comprising same

Abstract

Disclosed are a lithium secondary battery and an electric device. The lithium secondary battery comprises a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material comprises secondary particles formed by the aggregation of primary particles; at least part of the surfaces of the secondary particles are provided with a carbonaceous material; and the thickness of the carbonaceous material is h nm, and the average diameter of the primary particles is d μm, both satisfying: 0.002≤h / d≤0.01. The electrolyte comprises a first additive, wherein the first additive comprises a compound as represented by at least one of formula (II-1), formula (II-2) and formula (II-3): Formula (II-1), Formula (II-2) and Formula (II-3).

Description

Lithium secondary batteries and electrical equipment containing them

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202510205856.0, filed on February 24, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of battery technology, and in particular to a lithium secondary battery and an electrical device containing the same. Background Technology

[0004] Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Lithium-ion rechargeable batteries consume active lithium during the initial charge and cycling processes, causing capacity decay and reducing initial efficiency and lifespan. Summary of the Invention

[0005] The first aspect of this application provides a lithium secondary battery, which includes a positive electrode and an electrolyte.

[0006] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes a compound represented by formula (I): Li m A x Fe 1-y B y P 1-z D z O 4-n E n Formula I,

[0007] Wherein, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; D includes one or more elements selected from B, S, Si, and N; E includes one or more elements selected from S, F, Cl, and Br; 0.5≤m≤1.15, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, and 0≤n≤0.5;

[0008] The positive electrode active material includes secondary particles formed by the aggregation of primary particles. At least a portion of the surface of the secondary particles has a carbonaceous material with a thickness of h nm. The average diameter of the primary particles is d μm, and satisfies 0.002 ≤ h / d ≤ 0.01.

[0009] The electrolyte includes a first additive, which includes at least one compound represented by formula (Π-1), formula (Π-2), or formula (Π-3):

[0010] Among them, R 1 R 2 R 3 R 4 Each group independently comprises any one of the following: groups, hydrogen atoms, halogen atoms, C1-C6 alkyl groups, C1-C6 haloalkyl groups, C1-C6 alkoxy groups, C1-C6 haloalkoxy groups, C2-C6 alkenyl groups, C2-C6 ester groups, cyano groups, and sulfonic acid groups, wherein n1 and n2 are each independently any integer from 0 to 2.

[0011] R 5 and R 6 Each group independently comprises any one of the following: a group, a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, wherein n3 is any integer from 0 to 2.

[0012] This application achieves a lithium replenishment effect by maintaining the ratio of carbonaceous material thickness to the average diameter of primary particles within the aforementioned range. As charging and discharging proceed, the specific capacity of the positive electrode active material gradually increases, thus reducing capacity decay in the lithium-ion secondary battery. Simultaneously, by adding a first additive to the electrolyte, the film formation efficiency of the electrolyte interphase (SEI) film on the negative electrode surface is improved, reducing lithium-ion consumption during formation. This compensates for the reduced initial efficiency caused by the carbonaceous material on the surface of the positive electrode active material, thereby improving the initial efficiency of the lithium-ion secondary battery. Furthermore, it enhances the stability and electron blocking ability of the SEI film, reducing the continuous decomposition of the electrolyte at the negative electrode and extending the lifespan of the lithium-ion secondary battery.

[0013] According to some embodiments of this application, 0.0025 ≤ h / d ≤ 0.005. Therefore, as charging and discharging proceed, the specific capacity of the positive electrode active material can be gradually increased, achieving a lithium replenishment effect and thus reducing the capacity decay of the lithium secondary battery.

[0014] According to some embodiments of this application, 0.0028 ≤ h / d ≤ 0.0033. Therefore, as charging and discharging proceed, the specific capacity of the positive electrode active material can be gradually increased, achieving a lithium replenishment effect and thus reducing the capacity decay of the lithium secondary battery.

[0015] According to some embodiments of this application, the lithium secondary battery satisfies one or more of the following conditions: 1nm≤h≤5nm; 0.2μm≤d≤0.6μm.

[0016] According to some embodiments of this application, the lithium secondary battery satisfies one or more of the following conditions: 2nm≤h≤4nm; 0.2μm≤d≤0.4μm.

[0017] According to some embodiments of this application, the lithium secondary battery satisfies one or more of the following conditions: 2nm≤h≤3nm; 0.3μm≤d≤0.4μm.

[0018] Therefore, by making the value of h within the above range, carbonaceous materials can be used to overlay the positive electrode active material particles, hiding part of the initial capacity of the positive electrode active material and acting as a capacity release agent during charging and discharging; by making the value of d within the above range, the positive electrode active material has good ion transport performance, improving the rate performance of lithium secondary batteries.

[0019] According to some embodiments of this application, based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material is 1%-2%.

[0020] According to some embodiments of this application, based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material is 1%-1.8%.

[0021] According to some embodiments of this application, based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material is 1.1%-1.6%.

[0022] Therefore, by adjusting the mass ratio of the carbonaceous material, both the capacity release effect of the positive electrode active material and the energy density of the lithium secondary battery can be taken into account.

[0023] According to some embodiments of this application, the lithium secondary battery satisfies at least one of the following conditions: 0.95≤m≤1.05; 0.001≤x≤0.005; 0.001≤y≤0.1; 0.001≤z≤0.1; 0.001≤n≤0.1. This improves the kinetic performance of the positive electrode active material.

[0024] According to some embodiments of this application, R 1 and R 2Not simultaneously hydrogen atoms and R 3 and R 4 Instead of being hydrogen atoms, substituents can be introduced to form an elastic SEI film at the negative electrode. This improves the SEI film's tolerance to negative electrode volume changes during cycling, reduces the risk of SEI film rupture, and increases the cycle life of lithium secondary batteries.

[0025] According to some embodiments of this application, R 1 and R 2 Both are hydrogen atoms and R 3 and R 4 One is a hydrogen atom and the other is a group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, and R is present in the group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2). 5 and R 6 They are not both hydrogen atoms. Therefore, the mechanical strength and stability of the SEI film are improved, further enhancing the cycle performance of the lithium-ion secondary battery.

[0026] According to some embodiments of this application, R 3 and R 4 Both are hydrogen atoms and R 1 and R 2 One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, and R in the group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2) 5 and R 6 They are not both hydrogen atoms. Therefore, the mechanical strength and stability of the SEI film are improved, further enhancing the cycle performance of the lithium-ion secondary battery.

[0027] According to some embodiments of this application, in the first additive, n1=n2=n3=0, where R 1 R 2 R 3 R 4 Each group independently comprises one of the following: a group, a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, R. 5 and R6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group.

[0028] This improves the compactness of the SEI film and increases the SEI film formation rate.

[0029] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1); a hydrogen atom; a halogen atom; a C1-C3 alkyl group; a C1-C3 haloalkyl group; a C1-C3 alkoxy group; a C1-C3 haloalkoxy group; a C2-C3 alkenyl group; a C1-C3 ester group; a cyano group; or a sulfonic acid group. This improves the density of the SEI film and increases the SEI film formation rate.

[0030] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following: a group, a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group, as shown in formula (Ⅲ-1-1) or (Ⅲ-2-1). This improves the density of the SEI film and increases the SEI film formation rate.

[0031] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following groups, hydrogen atoms, F atoms, Cl atoms, Br atoms, methyl groups, ethyl groups, propyl groups, and isopropyl groups, representing the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1). This improves the compactness of the SEI film and increases its formation rate.

[0032] According to some embodiments of this application, the first additive includes one or more of the following compounds:

[0033] This improves the stability of the SEI film, reduces the deposition of transition metals and the excessive decomposition of the electrolyte, and enhances the cycle performance of lithium secondary batteries.

[0034] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is W1, and satisfies: 0.001% ≤ W1 ≤ 5%.

[0035] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is W1, and satisfies: 0.1% ≤ W1 ≤ 2%.

[0036] Therefore, by keeping the mass percentage of the first additive within the above range, the stability and electron blocking ability of the SEI film are improved, while the kinetic performance of the lithium secondary battery is also enhanced.

[0037] According to some embodiments of this application, the electrolyte further includes a second additive, the second additive comprising one or both of the compounds represented by formula (IV) or formula (V):

[0038] R 7 R 8 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 It is a C1-C6 alkylene group, a C1-C6 haloalkylene group, a C2-C6 alkenyl group, or a C2-C6 ynylene group, R 14 R 15 R 16 Each of these can be independently represented by a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group; * indicates a linking site.

[0039] Among them, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, and *R. 13 -OR 14 , * = CR15 R 16 Any one of them, R 13 It is a C1-C6 alkylene group, a C1-C6 haloalkylene group, a C2-C6 alkenyl group, or a C2-C6 ynylene group, R 14 R 15 R 16 Each of these can be independently represented by a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group. * indicates a linking site, and R... 9 R 10 R 11 R 12 They are not both hydrogen atoms. Therefore, the second additive can participate in the formation of the SEI film, improve the density and elasticity of the SEI film, and alleviate the damage to the SEI caused by the expansion and contraction of the negative electrode.

[0040] According to some embodiments of this application, R 7 R 8 Each of the following independently includes any one of hydrogen atom, halogen atom, C1-C4 alkyl group, C1-C4 haloalkyl group, C1-C4 alkoxy group, C2-C4 alkenyl group, and C2-C4 alkynyl group.

[0041] According to some embodiments of this application, R 7 R 8 Each component independently comprises any one of the following: hydrogen atom, halogen atom, C1-C4 alkyl group, C1-C4 haloalkyl group, or C2-C4 alkenyl group. This reduces film-forming impedance and improves the kinetic performance of lithium-ion batteries.

[0042] According to some embodiments of this application, R 7 R 8 Each component independently comprises any one of the following: hydrogen atom, halogen atom, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, halomethyl, haloethyl, halopropyl, vinyl, and propylene. This reduces film-forming impedance and improves the kinetic performance of lithium-ion secondary batteries.

[0043] According to some embodiments of this application, the R 7 R 8 Each component independently comprises any one of the following: hydrogen atom, halogen atom, methyl, ethyl, n-propyl, isobutyl, halomethyl, haloethyl, or vinyl. This reduces film-forming impedance and improves the kinetic performance of lithium-ion batteries.

[0044] According to some embodiments of this application, the halogen atom is an F atom or a Cl atom. This reduces film-forming resistance and improves the kinetic performance of the lithium secondary battery.

[0045] According to some embodiments of this application, the second additive satisfying formula (Ⅳ) includes one or more of the following compounds: This reduces film-forming resistance.

[0046] According to some embodiments of this application, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C1-C4 alkoxy group, a C2-C4 alkenyl group, a C2-C4 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 R is any one of C1-C4 alkylene, C1-C4 haloalkylene, C2-C4 alkenylene, and C2-C4 ynylene. 14 R 15 R 16 Each of the following can be independently composed of a hydrogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group. This reduces the film-forming resistance.

[0047] According to some embodiments of this application, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, a C2-C4 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 R is any one of C1-C4 alkylene, C2-C4 alkenylene, and C2-C4 ynylene. 14 R 15 R 16 Each of the following can be independently composed of a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group. This reduces the film-forming resistance.

[0048] According to some embodiments of this application, R 9 R 10 R 11 R 12Each of the following independently includes a hydrogen atom, a halogen atom, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a halomethyl group, a haloethyl group, a halopropyl group, a vinyl group, an acrylonitrile group, an ethynyl group, a propynyl group, and a methylene group (OR). 14 *Ethylene-OR 14 、*=CR 15 R 16 Any one of them, R 14 R is any one of hydrogen atom, methyl, ethyl, vinyl, or ethynyl. 15 R 16 Each atom can be independently composed of hydrogen or fluorine atoms. This reduces the film-forming impedance.

[0049] According to some embodiments of this application, the halogen atom is an F atom or a Cl atom. This reduces film-forming resistance.

[0050] According to some embodiments of this application, the second additive satisfying formula (V) includes one or more of the following compounds: This reduces film-forming resistance.

[0051] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is W2, and satisfies: 0.01% ≤ W2 ≤ 10%.

[0052] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is W2, and satisfies: 1% ≤ W2 ≤ 5%.

[0053] Therefore, by keeping the mass ratio of the second additive within the above range, the elasticity and density of the SEI film are improved while the film-forming resistance is reduced.

[0054] According to some embodiments of this application, 0.01 ≤ W1 / W2 ≤ 10.

[0055] According to some embodiments of this application, 0.05 ≤ W1 / W2 ≤ 5.

[0056] Therefore, by keeping the ratio of W1 to W2 within the above range, an SEI film with both excellent electron blocking ability and elasticity can be obtained.

[0057] The second aspect of this application provides an electrical device, including the lithium secondary battery provided in the first aspect of this application.

[0058] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0059] Figure 1 is a SEM image of a cross-section of a positive electrode sheet prepared according to an embodiment of this application.

[0060] Figure 2 is a schematic diagram of a battery according to one embodiment of this application.

[0061] Figure 3 is an exploded view of the battery according to one embodiment of this application, as shown in Figure 2.

[0062] Figure 4 is a schematic diagram of a battery module according to one embodiment of this application.

[0063] Figure 5 is a schematic diagram of a battery pack according to one embodiment of this application.

[0064] Figure 6 is an exploded view of the battery pack of one embodiment of this application shown in Figure 5.

[0065] Figure 7 is a schematic diagram of an electrical device in which a battery is used as a power source according to an embodiment of this application.

[0066] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Lithium secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0067] The embodiments of the technical solution of this application are described in detail below. These embodiments are only used to more clearly illustrate the technical solution of this application, and are therefore merely examples and should not be used to limit the scope of protection of this application.

[0068] 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.

[0069] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0070] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0071] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0072] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0073] Lithium iron phosphate cathode active materials have poor conductivity. To improve the migration speed of lithium ions, carbonaceous materials can be formed on the surface of lithium iron phosphate cathode active materials to improve their conductivity.

[0074] This application proposes a lithium secondary battery. By ensuring the ratio of the carbonaceous material thickness to the average diameter of the primary particles is within the aforementioned range, the integrity of the carbonaceous material on the surface of the lithium iron phosphate cathode active material is enhanced, reducing electrolyte wetting and increasing the polarization of the lithium iron phosphate cathode active material. This reduces the diffusion rate of lithium ions in the cathode active material, resulting in a decrease in the number of lithium ions that can participate in the reaction during the initial charge and discharge phases, thus "hiding" part of the initial specific capacity of the cathode active material. As charge and discharge progress, the cathode active material cracks, exposing new surfaces and increasing electrolyte wetting. This allows the specific capacity of the cathode active material to gradually increase, achieving a lithium replenishment effect and reducing the capacity decay of the lithium secondary battery. After the formation of carbonaceous material on the surface of the lithium iron phosphate cathode active material, the increased polarization reduces the lithium intercalation specific capacity, causing some active lithium to exist in the form of LiC6. LiC6 is highly reactive, accelerating the decomposition of the electrolyte solvent and SEI film, increasing side reactions, and ultimately losing active lithium, thus deteriorating the lifespan of the lithium secondary battery. This application adds a first additive to the electrolyte. The first additive has a high film-forming potential and will preferentially form a film on the negative electrode. The resulting SEI film has better stability and stronger electron blocking ability, thereby reducing the decomposition of solvent and SEI and improving the life of lithium secondary batteries.

[0075] The lithium secondary battery proposed in this application can be used in electrical devices that use lithium secondary batteries as a power source or in various energy storage systems that use lithium secondary batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0076] The first aspect of this application provides a lithium secondary battery, which includes a positive electrode and an electrolyte.

[0077] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes a compound represented by formula (I): Li m A x Fe 1-y B y P 1-z D z O 4-n E n Formula I,

[0078] Wherein, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; D includes one or more elements selected from B, S, Si, and N; E includes one or more elements selected from S, F, Cl, and Br; 0.5≤m≤1.15, 0≤x≤1, 0≤y≤0.5, 0≤z≤0.5, and 0≤n≤0.5;

[0079] The positive electrode active material includes secondary particles formed by the aggregation of primary particles. Referring to Figure 1, at least a portion of the surface of the secondary particles has a carbonaceous material with a thickness of h nm. The average diameter of the primary particles is d μm, and satisfies 0.002 ≤ h / d ≤ 0.01.

[0080] The electrolyte includes a first additive, which includes at least one compound represented by formula (Π-1), formula (Π-2), or formula (Π-3):

[0081] Among them, R 1 R 2 R 3 R 4Each group independently comprises any one of the following: groups, hydrogen atoms, halogen atoms, C1-C6 alkyl groups, C1-C6 haloalkyl groups, C1-C6 alkoxy groups, C1-C6 haloalkoxy groups, C2-C6 alkenyl groups, C2-C6 ester groups, cyano groups, and sulfonic acid groups, wherein n1 and n2 are each independently any integer from 0 to 2.

[0082] R 5 and R 6 Each group independently includes any one of the following: groups, hydrogen atoms, halogen atoms, C1-C6 alkyl groups, C1-C6 haloalkyl groups, C1-C6 alkoxy groups, C1-C6 haloalkoxy groups, C2-C6 alkenyl groups, C2-C6 ester groups, cyano groups, and sulfonic acid groups, where n3 is any integer from 0 to 2.

[0083] This application achieves a lithium replenishment effect by maintaining the ratio of carbonaceous material thickness to the average diameter of primary particles within the aforementioned range. As charging and discharging proceed, the specific capacity of the positive electrode active material gradually increases, thus reducing capacity decay in the lithium-ion secondary battery. Simultaneously, by adding a first additive to the electrolyte, the film formation efficiency of the electrolyte interphase (SEI) film on the negative electrode surface is improved, reducing lithium-ion consumption during formation. This compensates for the reduced initial efficiency caused by the carbonaceous material on the surface of the positive electrode active material, thereby improving the initial efficiency of the lithium-ion secondary battery. Furthermore, it enhances the stability and electron blocking ability of the SEI film, reducing the continuous decomposition of the electrolyte at the negative electrode and extending the lifespan of the lithium-ion secondary battery.

[0084] In this application, the thickness of the carbonaceous material can be measured using conventional methods in the art, such as FIB (Focused Ion Beam). The specific method may include the following steps: randomly selecting a single particle from the powder of the positive electrode active material to be tested, cutting a thin slice of about 100 nm thickness from the middle position or near the middle position of the selected particle, and then performing TEM testing on the thin slice to obtain the original TEM image. The original image obtained from the TEM test is opened in DigitalMicrograph software, and the coating material on the surface of the positive electrode active material is identified through the lattice spacing and angle information. The thickness of the coating material is measured at 3 to 5 positions, excluding values ​​of 0, and the average value is taken.

[0085] In this application, the average diameter of primary particles is measured statistically using a combination of scanning electron microscopy (SEM) and image analysis software. The specific procedure is as follows: A positive electrode sheet is obtained. The surface of the positive electrode active material layer is imaged using a Zeiss Sigma 300 SEM at 10,000x (10k) magnification in backscatter mode. Avizo software is used to identify the primary particles on the surface of the positive electrode active material layer. Based on the identified primary particles, the optimal circumscribed quadrilateral of each primary particle is fitted, resulting in two diagonals. The longer diagonal is the major axis r1, and the shorter diagonal is the minor axis r2. The particle diameter is then determined.

[0086] As an example, h / d can be 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc., or a range of any of the above values.

[0087] According to some specific embodiments of this application, 0.0025 ≤ h / d ≤ 0.005.

[0088] According to some specific embodiments of this application, 0.0028 ≤ h / d ≤ 0.0033.

[0089] Therefore, as charging and discharging proceed, the specific capacity of the positive electrode active material can be gradually improved, achieving the effect of lithium replenishment, thereby reducing the capacity decay of the lithium secondary battery.

[0090] According to some embodiments of this application, 1nm≤h≤5nm, for example, can be 1nm, 2nm, 3nm, 4nm, 5nm, etc., or can be any range of the above values. Therefore, carbonaceous material can be used to gradually coat the positive electrode active material particles, hiding part of the initial capacity of the positive electrode active material and acting as a capacity-releasing agent during charge and discharge.

[0091] According to some specific embodiments of this application, 2nm≤h≤4nm.

[0092] According to some specific embodiments of this application, 2nm≤h≤3nm.

[0093] According to some embodiments of this application, 0.2μm ≤ d ≤ 0.6μm. For example, it can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, etc., or a range of any of the above values. Therefore, by ensuring that the value of d is within the above range, the positive electrode active material possesses good ion transport performance, improving the rate performance of the lithium secondary battery. In addition, it can also improve the processing performance of the positive electrode slurry and the positive electrode sheet; for example, it can reduce problems such as excessive viscosity of the positive electrode slurry and cracking of the positive electrode active material layer.

[0094] According to some embodiments of this application, 0.2μm≤d≤0.4μm.

[0095] According to some embodiments of this application, 0.3μm≤d≤0.4μm.

[0096] According to some embodiments of this application, based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material can be 1%-2%. For example, it can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc., or a range of any of the above values. Therefore, by keeping the carbonaceous material content within the above range, on the one hand, the integrity of the carbonaceous material's coating on the positive electrode active material can be improved, enhancing the kinetic performance of the positive electrode active material and increasing the energy density of the battery; on the other hand, during the sintering process of the positive electrode active material, the influence of the carbonaceous material on particle growth can be reduced, forming secondary particles with larger particle sizes, thus balancing the capacity release effect of the positive electrode active material with the energy density of the lithium secondary battery.

[0097] According to some embodiments of this application, based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material can be 1%-1.8%.

[0098] According to some embodiments of this application, based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material can be 1.1%-1.6%.

[0099] In this application, the method for testing the mass percentage of carbonaceous materials is as follows: a C / S content analyzer (model: Dekai HCS-140) is used. Based on the determination of total carbon and sulfur content in steel, the carbon content in the powder is tested using the high-frequency induction furnace combustion infrared absorption method (conventional method) GBT 20123-2006. The sample is burned in oxygen, converting carbon and sulfur into CO2 and SO2, which are then converted into corresponding signals by a detector after entering the absorption cell. This signal is sampled by a computer, linearly corrected, and converted into a value proportional to the CO2 and SO2 concentrations. The values ​​from the entire analysis process are then accumulated. After the analysis, this accumulated value is divided by the weight value in the computer, multiplied by a correction factor, and the blank is subtracted to obtain the percentage of carbon and sulfur in the sample, thus yielding the mass percentage of carbonaceous materials.

[0100] As an example, m can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.15, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.95 ≤ m ≤ 1.05.

[0101] It should be noted that for positive electrode sheets, lithium secondary batteries, or electrical devices, lithium ions are consumed during the formation and cycling processes of lithium secondary batteries. Therefore, the measured lithium element content m in the positive electrode active material may be less than 1. Conversely, if lithium replenishment agents are used on both the positive and negative electrode sheets, the measured lithium element content m in the positive electrode active material may be greater than 1 after the formation and cycling processes of the lithium secondary battery.

[0102] As an example, x can be 0, 0.001, 0.005, 0.01, 0.05, 0.1, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.001 ≤ x ≤ 0.005.

[0103] As an example, y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.001 ≤ y ≤ 0.1.

[0104] As an example, z can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.001 ≤ z ≤ 0.1.

[0105] As an example, n can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.001 ≤ n ≤ 0.1.

[0106] 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.).

[0107] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0108] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0110] Lithium-ion rechargeable batteries also include a negative electrode, during which active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. A separator is placed between the positive and negative electrodes, primarily to prevent short circuits while allowing ions to pass through.

[0111] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0112] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0113] 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.).

[0114] 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 titanates. 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. When the battery is a lithium-ion battery, lithium titanate is used; when the battery is a sodium-ion battery, sodium titanate is used. 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.

[0115] In some embodiments, the negative electrode active material layer may optionally 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).

[0116] In some embodiments, the negative electrode active 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.

[0117] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0118] 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.

[0119] According to some embodiments of this application, R in the first additive 1 and R 2 Not simultaneously hydrogen atoms and R 3 and R 4 Instead of being hydrogen atoms, substituents can be introduced to form an elastic SEI film at the negative electrode. This improves the SEI film's tolerance to negative electrode volume changes during cycling, reduces the risk of SEI film rupture, and increases the cycle life of lithium secondary batteries.

[0120] According to some embodiments of this application, R 1 and R2 Both are hydrogen atoms and R 3 and R 4 One is a hydrogen atom and the other is a group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, and R is present in the group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2). 5 and R 6 It also contains hydrogen atoms. This improves the mechanical strength and stability of the SEI film, further enhancing the cycle performance of the lithium-ion battery.

[0121] According to some embodiments of this application, R 3 and R 4 Both are hydrogen atoms and R 1 and R 2 One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, and R in the group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2) 5 and R 6 It is also a hydrogen atom.

[0122] By making R 1 R 2 R 3 R 4 The presence of substituents, such as alkyl substituents, in the groups can form a flexible, long-chain elastic SEI film on the negative electrode surface. During battery cycling, when the negative electrode active material undergoes volume expansion and contraction, this improves the SEI film's resilience and reduces the risk of SEI film rupture. When cyclic sulfate compounds and cyclic carbonate compounds contain substituents such as F and N, an SEI film rich in inorganic components such as LiF and Li3N can be formed on the negative electrode surface, improving the mechanical strength of the SEI film, thereby enhancing its stability and further improving the cycle performance of the lithium secondary battery.

[0123] According to some embodiments of this application, in the first additive, n1=n2=n3=0, R 1 R 2 R 3 R 4Each group independently comprises one of the following: a group, a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, R. 5 and R 6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group.

[0124] Therefore, the first additives of the above types are all five-membered rings, which have greater ring strain than six-membered rings, making it easier to form a film on the negative electrode surface, thus improving film formation efficiency. They form a dense SEI film on the negative electrode, improving the blocking effect on electrons, reducing transition metal deposition and electrolyte decomposition, and improving the cycle life of lithium secondary batteries.

[0125] It should be noted that the curved line segments in formulas (Ⅲ-1) and (Ⅲ-2) represent chemical bonds connected to formulas (Π-1), (Π-2), and (Π-3).

[0126] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1); a hydrogen atom; a halogen atom; a C1-C3 alkyl group; a C1-C3 haloalkyl group; a C1-C3 alkoxy group; a C1-C3 haloalkoxy group; a C2-C3 alkenyl group; a C1-C3 ester group; a cyano group; or a sulfonic acid group. This improves the density of the SEI film and increases the SEI film formation rate.

[0127] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1), a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group. This improves the density of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle life of the lithium secondary battery.

[0128] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following groups, hydrogen atoms, F atoms, Cl atoms, Br atoms, methyl groups, ethyl groups, propyl groups, and isopropyl groups, representing the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1). This improves the compactness of the SEI film and increases its formation rate.

[0129] According to some embodiments of this application, the first additive includes one or more of the following compounds: This improves the stability of the SEI film, reduces the deposition of transition metals and the excessive decomposition of the electrolyte, and enhances the cycle performance of lithium secondary batteries.

[0130] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is W1, and satisfies: 0.001% ≤ W1 ≤ 5%, for example, it can be 0.001%, 0.01%, 0.1%, 1%, 3%, 5%, etc., or a range of any of the above values. Thus, while forming a stable SEI film, the viscosity of the electrolyte is reduced, and the ionic conductivity of the electrolyte is increased.

[0131] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is W1, and satisfies: 0.1% ≤ W1 ≤ 2%.

[0132] Therefore, by keeping the mass percentage of the first additive within the above range, the stability and electron blocking ability of the SEI film are improved, while the kinetic performance of the lithium secondary battery is also enhanced.

[0133] In this application, the content of the first additive can be calculated by nuclear magnetic resonance H-spectroscopy.

[0134] According to some embodiments of this application, the electrolyte further includes a second additive, the second additive comprising one or both of the compounds represented by formula (IV) or formula (V):

[0135] R 7 R 8 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, and *R. 13 -OR14 , * = CR 15 R 16 Any one of them, R 13 It is a C1-C6 alkylene group, a C1-C6 haloalkylene group, a C2-C6 alkenyl group, or a C2-C6 ynylene group, R 14 R 15 R 16 Each of these can be independently represented by a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group; * indicates a linking site.

[0136] Among them, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 It is a C1-C6 alkylene group, a C1-C6 haloalkylene group, a C2-C6 alkenyl group, or a C2-C6 ynylene group, R 14 R 15 R 16 Each of these can be independently represented by a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group. * indicates a linking site, and R... 9 R 10 R 11 R 12 They are not both hydrogen atoms. Therefore, the second additive can participate in the formation of the SEI film, improve the density and elasticity of the SEI film, and alleviate the damage to the SEI caused by the expansion and contraction of the negative electrode.

[0137] According to some embodiments of this application, R 7 R 8 Each of the following components independently comprises any one of hydrogen atoms, halogen atoms, C1-C4 alkyl groups, C1-C4 haloalkyl groups, C1-C4 alkoxy groups, C2-C4 alkenyl groups, and C2-C4 alkynyl groups. This reduces film-forming resistance.

[0138] According to some embodiments of this application, R 7 R 8Each component independently comprises any one of the following: hydrogen atom, halogen atom, C1-C4 alkyl group, C1-C4 haloalkyl group, or C2-C4 alkenyl group. This reduces film-forming resistance.

[0139] According to some embodiments of this application, R 7 R 8 Each of these components independently includes any one of the following: hydrogen atom, halogen atom, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, halomethyl, haloethyl, halopropyl, vinyl, and propylene. This reduces film-forming resistance.

[0140] According to some embodiments of this application, the R 7 R 8 Each component independently includes any one of the following: hydrogen atom, halogen atom, methyl, ethyl, n-propyl, isobutyl, halomethyl, haloethyl, or vinyl. This reduces film-forming resistance.

[0141] According to some embodiments of this application, the halogen atom is an F atom or a Cl atom. This reduces film-forming resistance.

[0142] According to some embodiments of this application, the second additive satisfying formula (Ⅳ) includes one or more of the following compounds: This reduces film-forming resistance.

[0143] According to some embodiments of this application, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C1-C4 alkoxy group, a C2-C4 alkenyl group, a C2-C4 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 R is any one of C1-C4 alkylene, C1-C4 haloalkylene, C2-C4 alkenylene, and C2-C4 ynylene. 14 R 15 R 16 Each of the following can be independently composed of a hydrogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group. This reduces the film-forming resistance.

[0144] According to some embodiments of this application, R 9 R 10 R 11 R 12Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, a C2-C4 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 R is any one of C1-C4 alkylene, C2-C4 alkenylene, and C2-C4 ynylene. 14 R 15 R 16 Each of the following can be independently composed of a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group. This reduces the film-forming resistance.

[0145] According to some embodiments of this application, R 9 R 10 R 11 R 12 Each of the following independently includes a hydrogen atom, a halogen atom, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a halomethyl group, a haloethyl group, a halopropyl group, a vinyl group, an acrylonitrile group, an ethynyl group, a propynyl group, and a methylene group (OR). 14 *Ethylene-OR 14 、*=CR 15 R 16 Any one of them, R 14 R is any one of hydrogen atom, methyl, ethyl, vinyl, or ethynyl. 15 R 16 Each atom can be independently composed of hydrogen or fluorine atoms. This reduces the film-forming impedance.

[0146] According to some embodiments of this application, the halogen atom is an F atom or a Cl atom. This reduces film-forming resistance.

[0147] According to some embodiments of this application, the second additive satisfying formula (V) includes one or more of the following compounds: This reduces film-forming resistance.

[0148] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is W2, and satisfies: 0.01% ≤ W2 ≤ 10%. For example, it can be 0.01%, 0.05%, 0.1%, 1%, 3%, 5%, 7%, 9%, 10%, etc., or it can be a range of any of the above values.

[0149] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is W2, and satisfies: 1% ≤ W2 ≤ 5%.

[0150] Therefore, by keeping the mass ratio of the second additive within the above range, the elasticity and density of the SEI film are improved while the film-forming resistance is reduced.

[0151] In this application, the content of the second additive can be calculated by nuclear magnetic resonance H-spectroscopy.

[0152] According to some embodiments of this application, 0.01 ≤ W1 / W2 ≤ 10. For example, it can be 0.01, 0.1, 1, 3, 5, 7, 9, 10, etc., or it can be a range of any of the above values.

[0153] According to some embodiments of this application, 0.05 ≤ W1 / W2 ≤ 5.

[0154] Therefore, by keeping the ratio of W1 to W2 within the above range, an SEI film with both excellent electron blocking ability and elasticity can be obtained.

[0155] In some embodiments, the electrolyte further includes an electrolyte salt and a solvent. The electrolyte salt may include 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.

[0156] 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.

[0157] The lithium secondary battery also includes a separator. This application does not have any particular restrictions on the type of separator, and any well-known porous structure separator with good chemical and mechanical stability can be selected.

[0158] 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.

[0159] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0160] In some embodiments, the lithium secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0161] In some implementations, the outer packaging of the lithium secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the lithium 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.

[0162] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 shows a square-structured lithium secondary battery 5 as an example.

[0163] In some embodiments, referring to FIG3, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0164] In some implementations, lithium secondary batteries can be assembled into battery modules, and the number of batteries contained in a 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.

[0165] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple lithium secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple lithium secondary batteries 5 can be fixed in place by fasteners.

[0166] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of lithium secondary batteries 5 are received.

[0167] 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.

[0168] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0169] This application also proposes a method for preparing a positive electrode active material, the method comprising:

[0170] A lithium phosphate precursor is provided, and the lithium phosphate precursor is mixed with a carbon source and then ground.

[0171] The ground material is heated to a first temperature T1 at a first rate V1 under a protective atmosphere and held at the first temperature T1 for a first time t1. Then, it is heated to a second temperature T2 at a second rate V2 and held at the second temperature T2 for a second time t2 to obtain a positive electrode active material, wherein the positive electrode active material comprises a compound represented by formula (I): Li m A x Fe 1-y B y P 1-z D z O 4-n E n Formula I,

[0172] Wherein, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; D includes one or more elements selected from B, S, Si, and N; E includes one or more elements selected from S, F, Cl, and Br; 0.5≤m≤1.15, 0≤x≤0.1, 0≤y≤0.5, 0≤z≤0.5, and 0≤n≤0.5;

[0173] The positive electrode active material includes secondary particles formed by the aggregation of primary particles. At least a portion of the surface of the secondary particles has a carbonaceous material with a thickness of h nm. The average diameter of the primary particles is d μm, and satisfies 0.002 ≤ h / d ≤ 0.01.

[0174] According to some embodiments of this application, T1≥400℃, V1≤4℃ / min, t1≥1h.

[0175] As an example, T1 can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, etc., or it can be a range of any of the above values.

[0176] As an example, V1 can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, etc., or it can be a range of any of the above values.

[0177] As an example, t1 can be 1h, 3h, 5h, 7h, 9h, etc., or it can be a range of any of the above values.

[0178] According to some embodiments of this application, 400℃≤T1≤600℃.

[0179] According to some other specific embodiments of this application, 450℃≤T1≤550℃.

[0180] According to some embodiments of this application, 1℃ / min≤V1≤4℃ / min.

[0181] According to some embodiments of this application, 1h≤t1≤7h.

[0182] According to some other specific embodiments of this application, 3h≤t1≤5h.

[0183] According to some embodiments of this application, T2≥720℃, 1℃ / min≤V2≤10℃ / min, 5h≤t2≤20h.

[0184] As an example, T2 can be 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, etc., or it can be a range of any of the above values.

[0185] As an example, V2 can be 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min, 9℃ / min, 10℃ / min, etc., or it can be a range of any of the above values.

[0186] As an example, t2 can be 5h, 7h, 10h, 13h, 16h, 19h, 20h, etc., or it can be a range of any of the above values.

[0187] According to some embodiments of this application, 720℃≤T2≤850℃.

[0188] According to some other specific embodiments of this application, 750℃≤T2≤810℃.

[0189] According to some embodiments of this application, 5℃ / min≤V2≤9℃ / min.

[0190] According to some embodiments of this application, 8h≤t2≤15h.

[0191] According to some embodiments of this application, the carbon source includes a first carbon source and a second carbon source, wherein the first carbon source comprises a water-soluble polymer. As an example, the water-soluble polymer includes one or more of polyethylene glycol, polyaniline, and their respective derivatives. The second carbon source includes one or more of glucose, sucrose, lactose, and maltose.

[0192] According to some embodiments of this application, the mass percentage of the first carbon source is greater than or equal to 50% based on the total mass of the carbon source. As an example, the mass percentage of the first carbon source can be 50%-70%, for example, it can be 50%, 55%, 60%, 65%, 70%, etc., or it can be a range of any of the above values.

[0193] According to some embodiments of this application, the mass percentage of the second carbon source is less than or equal to 50% based on the total mass of the carbon source. As an example, the mass percentage of the second carbon source can be 30%-50%, for example, it can be 30%, 35%, 40%, 45%, 50%, etc., or it can be a range of any of the above values.

[0194] The second aspect of this application provides an electrical device, including the lithium secondary battery provided in the first aspect of this application.

[0195] The electrical equipment includes at least one of the batteries, battery modules, or battery packs provided in this application. The battery, battery module, or battery pack can be used as a power source for the electrical equipment or as an energy storage unit for the electrical equipment. The electrical equipment may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems, etc.

[0196] As for the aforementioned electrical equipment, lithium secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0197] Figure 7 shows an example of an electrical device. This 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 this device, a battery pack or battery module can be used.

[0198] Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0199] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0200] Example 1

[0201] 1. Preparation of positive electrode sheet

[0202] Preparation of positive electrode active materials

[0203] FePO4, Li2CO3, glucose and polyethylene glycol were mixed evenly, a small amount of water was added, and the mixture was ground and then spray-dried. The spray-dried powder was placed in a sintering furnace and heated from 25°C to 500°C at a rate of 2°C / min under a nitrogen atmosphere and held at that temperature for 3 hours. Then the temperature was increased to 840°C at a rate of 5°C / min and held at that temperature for 10 hours. After the process was completed, the powder was cooled and crushed by airflow to obtain the positive electrode active material, namely carbon-coated LiFePO4.

[0204] The carbon source is a mixture of glucose and polyethylene glycol (50% by weight of glucose and 50% by weight of polyethylene glycol based on the total mass of the carbon source). The amount of carbon source added is such that the residual carbon content (i.e., the weight content m of the carbonaceous material) is 1.15%, based on the total weight of the prepared positive electrode active material.

[0205] The above-mentioned positive electrode active material was mixed evenly with carbon black SP and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system at a weight ratio of 92:2.5:5.5. The mixture was then coated onto aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0206] 2. Preparation of negative electrode sheet

[0207] The negative electrode active materials graphite, acetylene black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed evenly in deionized water at a weight ratio of 95:2:2:1, coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0208] 3. Separating membrane

[0209] Polyethylene porous polymer membrane.

[0210] 4. Preparation of electrolyte

[0211] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. A first additive, Π-1-20, is added to the solvent at a mass ratio of 0.5%.

[0212] 5. Preparation of lithium secondary batteries

[0213] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain the electrode assembly. The electrode assembly is placed in the battery casing, dried, and then injected with electrolyte. After formation and settling processes, a lithium secondary battery is obtained.

[0214] The preparation methods of lithium secondary batteries in Examples 2-26 and Comparative Examples 1-3 are the same as those in the Examples, with the differences detailed in Table 1.

[0215] Table 1

[0216] Performance testing

[0217] 1. First-time coulombic efficiency of lithium secondary batteries

[0218] Under constant temperature of 25℃, after standing for 5 minutes, charge at 0.1C to 3.8V, then charge at 3.8V at constant voltage until the current is ≤0.05C, and stand for 5 minutes. The initial charging capacity at this time is recorded as C0. Then discharge at 0.1C to 2.0V. The discharge capacity at this time is D0. The initial coulombic efficiency is D0 / C0×100%.

[0219] 2. Range of sustained release

[0220] Slow-release amplitude = maximum capacity retention after 200 cycles - 100%.

[0221] 3.45℃ Cyclic Capacity Retention

[0222] 1) Let the battery stand at 45℃ for 120 minutes;

[0223] 2) Discharge the battery to 2.5V at 0.5P;

[0224] 3) Let the battery stand at 45℃ for 30 minutes;

[0225] 4) Charge the battery to 3.8V at a constant power of 0.5P;

[0226] 5) Let stand at 45℃ for 1 minute;

[0227] 6) Charge to 3.8V with 0.05P constant power;

[0228] 7) Let the battery stand at 45℃ for 30 minutes;

[0229] 8) Discharge the battery to 2.5V at 0.5P;

[0230] 9) Let the battery stand at 45℃ for 5 minutes;

[0231] 10) Steps 4) to 8) above constitute one charge-discharge cycle of the battery.

[0232] The capacity retention rate after the 200th cycle = (discharge capacity after the 200th cycle / initial discharge capacity of the cycle) × 100%.

[0233] 4. Maximum capacity retention

[0234] Record the number of cycles in the first 200 cycles where the capacity retention rate is continuously above 100%. If the number of cycles continuously above 100% is ≥10, the cycle is considered to have experienced cyclic ramping, and the maximum capacity retention rate when the capacity retention rate is above 100% is recorded. If the number of cycles continuously above 100% is <10, the cycle is considered not to have experienced cyclic ramping, and is recorded as "-".

[0235] The test results of the lithium secondary batteries in Examples 1-26 and Comparative Examples 1-3 are shown in Table 2.

[0236] Table 2

[0237] As can be seen from the comparison between Examples 1-26 and Comparative Examples 1-3, this application, by limiting the h / d ratio and adding a first additive to the electrolyte, can improve the initial coulombic efficiency of the lithium secondary battery and increase the cycle capacity retention rate. As the battery is charged and discharged, the specific capacity of the positive electrode active material gradually increases, achieving a lithium replenishment effect and thus reducing the capacity decay of the lithium secondary battery. In other words, by limiting the h / d ratio and adding a first additive to the electrolyte, a synergistic effect can be achieved, resulting in a lithium secondary battery with high initial coulombic efficiency and good cycle life.

[0238] As can be seen from Examples 1-8 and Comparative Examples 2 and 3, by setting different second temperatures T2 during the preparation of positive electrode active materials, positive electrode active materials with different average diameters can be obtained. By controlling the mass ratio of carbonaceous materials, the thickness of carbonaceous materials can be controlled, thereby adjusting the h / d ratio. When used in combination with the first additive in the electrolyte, lithium secondary batteries with high initial coulombic efficiency and good cycle performance can be obtained.

[0239] As can be seen from Examples 9-14, the content of the first additive in the electrolyte can be adjusted to optimize the cycle performance and efficiency of the battery, resulting in a lithium secondary battery with high initial coulombic efficiency and good cycle performance.

[0240] As can be seen from Examples 15-18, different types of first additives can be combined with positive electrode active materials to obtain lithium secondary batteries with high initial coulombic efficiency and good cycle performance.

[0241] As can be seen from Examples 19-26, adding different types and amounts of second additives to the electrolyte can further improve the battery's hand efficiency and cycle capacity retention rate. This indicates that the addition of the second additive can further improve the density and elasticity of the SEI film and alleviate the damage to the SEI film caused by the expansion and contraction of the negative electrode sheet.

[0242] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium secondary battery, wherein, Includes the positive electrode and the electrolyte; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer including a positive active material, the positive active material including a compound represented by formula (I): Li m A x Fe 1-y B y P 1-z D z O 4-n E n Formula Ι Wherein, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; D includes one or more elements selected from B, S, Si, and N; E includes one or more elements selected from S, F, Cl, and Br; 0.5≤m≤1.15, 0≤x≤0.1, 0≤y≤0.5, 0≤z≤0.5, and 0≤n≤0.5; The positive electrode active material includes secondary particles formed by the aggregation of primary particles. At least a portion of the surface of the secondary particles has a carbonaceous material with a thickness of h nm. The average diameter of the primary particles is d μm, and satisfies 0.002 ≤ h / d ≤ 0.

01. The electrolyte includes a first additive, which includes at least one compound represented by formula (Π-1), formula (Π-2), or formula (Π-3): Among them, R 1 R 2 R 3 R 4 Each group independently comprises any one of the following: groups, hydrogen atoms, halogen atoms, C1-C6 alkyl groups, C1-C6 haloalkyl groups, C1-C6 alkoxy groups, C1-C6 haloalkoxy groups, C2-C6 alkenyl groups, C2-C6 ester groups, cyano groups, and sulfonic acid groups, wherein n1 and n2 are each independently any integer from 0 to 2. R 5 and R 6 Each group independently comprises any one of the following: a group, a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, wherein n3 is any integer from 0 to 2.

2. The lithium secondary battery according to claim 1, wherein, 0.0025≤h / d≤0.

005.

3. The lithium secondary battery according to claim 1 or 2, wherein, 0.0028≤h / d≤0.0033.

4. The lithium secondary battery according to any one of claims 1-3, wherein, It must satisfy one or more of the following conditions: 1nm≤h≤5nm; 0.2μm≤d≤0.6μm.

5. The lithium secondary battery according to any one of claims 1-4, wherein, It must satisfy one or more of the following conditions: 2nm≤h≤4nm; 0.2μm≤d≤0.4μm.

6. The lithium secondary battery according to any one of claims 1-5, wherein, It must satisfy one or more of the following conditions: 2nm≤h≤3nm; 0.3μm≤d≤0.4μm.

7. The lithium secondary battery according to any one of claims 1-6, wherein, Based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material is 1%-2%.

8. The lithium secondary battery according to any one of claims 1-7, wherein, Based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material is 1%-1.8%.

9. The lithium secondary battery according to any one of claims 1-8, wherein, Based on the total mass of the positive electrode active material and the carbonaceous material, the mass percentage of the carbonaceous material is 1.1%-1.6%.

10. The lithium secondary battery according to any one of claims 1-9, wherein, At least one of the following conditions must be met: 0.95≤m≤1.05; 0.001≤x≤0.005; 0.001≤y≤0.1; 0.001≤z≤0.1; 0.001≤n≤0.

1.

11. The lithium secondary battery according to any one of claims 1-10, wherein, R 1 and R 2 Not simultaneously hydrogen atoms and R 3 and R 4 They are not both hydrogen atoms.

12. The lithium secondary battery according to any one of claims 1-10, wherein, R 1 and R 2 Both are hydrogen atoms and R 3 and R 4 One is a hydrogen atom and the other is a group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, and R is present in the group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2). 5 and R 6 It is also a hydrogen atom.

13. The lithium secondary battery according to any one of claims 1-10, wherein, R 3 and R 4 Both are hydrogen atoms and R 1 and R 2 One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, and R in the group having the structure shown in formula (Ⅲ-1) or (Ⅲ-2) 5 and R 6 It is also a hydrogen atom.

14. The lithium secondary battery according to any one of claims 1-10, wherein, In the first additive, n1 = n2 = n3 = 0. Among them, R 1 R 2 R 3 R 4 Each group independently comprises one of the following: a group, a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, R. 5 and R 6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group.

15. The lithium secondary battery according to claim 14, wherein, R 1 R 2 R 3 R 4 R 5 and R 6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1) (or a group with the structure shown in formula (Ⅲ-2-1)); a hydrogen atom; a halogen atom; a C1-C3 alkyl group; a C1-C3 haloalkyl group; a C1-C3 alkoxy group; a C1-C3 haloalkoxy group; a C2-C3 alkenyl group; a C1-C3 ester group; a cyano group; or a sulfonic acid group.

16. The lithium secondary battery according to claim 14 or 15, wherein, R 1 R 2 R 3 R 4 R 5 and R 6 Each independently comprises a group, a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group, representing the structure shown in formula (Ⅲ-1-1) or (Ⅲ-2-1).

17. The lithium secondary battery according to any one of claims 14-16, wherein, R 1 R 2 R 3 R 4 R 5 and R 6 Each of the following groups, hydrogen atoms, F atoms, Cl atoms, Br atoms, methyl, ethyl, propyl, and isopropyl groups, independently includes the structure shown in formula (Ⅲ-1-1) or formula (Ⅲ-2-1).

18. The lithium secondary battery according to any one of claims 1-10, wherein, The first additive includes one or more of the following compounds:

19. The lithium secondary battery according to any one of claims 1-18, wherein, Based on the total mass of the electrolyte, the mass percentage of the first additive is W1, and satisfies: 0.001% ≤ W1 ≤ 5%.

20. The lithium secondary battery according to any one of claims 1-19, wherein, Based on the total mass of the electrolyte, the mass percentage of the first additive is W1, and satisfies: 0.1% ≤ W1 ≤ 2%.

21. The lithium secondary battery according to any one of claims 1-20, wherein, The electrolyte further includes a second additive, which comprises one or two compounds of formula (IV) or formula (V): R 7 R 8 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 It is a C1-C6 alkylene group, a C1-C6 haloalkylene group, a C2-C6 alkenyl group, or a C2-C6 ynylene group, R 14 R 15 R 16 Each of these can be independently represented by a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group; * indicates a linking site. Among them, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 It is a C1-C6 alkylene group, a C1-C6 haloalkylene group, a C2-C6 alkenyl group, or a C2-C6 ynylene group, R 14 R 15 R 16 Each of these can be independently represented by a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group. * indicates a linking site, and R... 9 R 10 R 11 R 12 They are not both hydrogen atoms.

22. The lithium secondary battery according to claim 21, wherein, R 7 R 8 Each of the following independently includes any one of hydrogen atom, halogen atom, C1-C4 alkyl group, C1-C4 haloalkyl group, C1-C4 alkoxy group, C2-C4 alkenyl group, and C2-C4 alkynyl group.

23. The lithium secondary battery according to claim 21 or 22, wherein, R 7 R 8 Each of the following is independently included: hydrogen atom, halogen atom, C1-C4 alkyl group, C1-C4 haloalkyl group, and C2-C4 alkenyl group.

24. The lithium secondary battery according to any one of claims 21-23, wherein, R 7 R 8 Each of the following can be independently selected: hydrogen atom, halogen atom, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, halomethyl, haloethyl, halopropyl, vinyl, and propylene.

25. The lithium secondary battery according to any one of claims 21-24, wherein, The R 7 R 8 Each of the following can be independently selected: hydrogen atom, halogen atom, methyl, ethyl, n-propyl, isobutyl, halomethyl, haloethyl, and vinyl.

26. The lithium secondary battery according to any one of claims 21-25, wherein, The halogen atom is an F atom or a Cl atom.

27. The lithium secondary battery according to any one of claims 21-26, wherein, The second additive satisfying formula (Ⅳ) includes one or more of the following compounds:

28. The lithium secondary battery according to any one of claims 21-27, wherein, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C1-C4 alkoxy group, a C2-C4 alkenyl group, a C2-C4 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 R is any one of C1-C4 alkylene, C1-C4 haloalkylene, C2-C4 alkenylene, and C2-C4 ynylene. 14 R 15 R 16 Each of the following can be independently a hydrogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group.

29. The lithium secondary battery according to any one of claims 21-28, wherein, R 9 R 10 R 11 R 12 Each of the following independently comprises a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C1-C4 haloalkyl group, a C2-C4 alkenyl group, a C2-C4 alkynyl group, and *R. 13 -OR 14 , * = CR 15 R 16 Any one of them, R 13 R is any one of C1-C4 alkylene, C2-C4 alkenylene, and C2-C4 ynylene. 14 R 15 R 16 Each of the following can be independently a hydrogen atom, a halogen atom, a C1-C4 alkyl group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group.

30. The lithium secondary battery according to any one of claims 21-29, wherein, R 9 R 10 R 11 R 12 Each of the following independently includes a hydrogen atom, a halogen atom, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a halomethyl group, a haloethyl group, a halopropyl group, a vinyl group, an acrylonitrile group, an ethynyl group, a propynyl group, and a methylene group (OR). 14 *Ethylene-OR 14 、*=CR 15 R 16 Any one of them, R 14 R is any one of hydrogen atom, methyl, ethyl, vinyl, or ethynyl. 15 R 16 They can be independently identified as hydrogen atoms or F atoms.

31. The lithium secondary battery according to any one of claims 21-30, wherein, The halogen atom is an F atom or a Cl atom.

32. The lithium secondary battery according to any one of claims 21-31, wherein, The second additive satisfying formula (V) includes one or more of the following compounds:

33. The lithium secondary battery according to any one of claims 21-32, wherein, Based on the total mass of the electrolyte, the mass percentage of the second additive is W2, and satisfies: 0.01% ≤ W2 ≤ 10%.

34. The lithium secondary battery according to any one of claims 21-33, wherein, Based on the total mass of the electrolyte, the mass percentage of the second additive is W2, and satisfies: 1% ≤ W2 ≤ 5%.

35. The lithium secondary battery according to any one of claims 21-34, wherein, 0.01≤W1 / W2≤10.

36. The lithium secondary battery according to any one of claims 21-35, wherein, 0.05≤W1 / W2≤5.

37. An electrical appliance, wherein, The lithium secondary battery includes any one of claims 1-36.

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