Battery and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to a battery and electric equipment. The battery comprises a positive electrode, a negative electrode and electrolyte, wherein the positive electrode comprises a nickel-cobalt-manganese ternary material; the negative electrode comprises a silicon-based material and a carbon-based material; wherein the electrolyte comprises a first additive and a second additive, and high-quality interfacial films can be formed on the surfaces of the positive electrode and the negative electrode of the battery, so that the battery has relatively good low-temperature cycle performance and high-temperature cycle performance and relatively low initial DCIR.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a battery, a battery pack, and an electrical device. Background Technology

[0002] Lithium-ion batteries, as high-energy-density energy storage devices, are widely used in consumer electronics (such as smartphones and laptops), electric vehicles (EVs / HEVs), and energy storage systems (such as grid energy storage and home energy storage). With the continuous increase in requirements for the driving range of electronic products, the driving range of electric vehicles, and the energy density of energy storage systems, the anode materials for lithium-ion batteries are evolving from traditional graphite to high-capacity materials (such as silicon-based materials). However, the volume expansion effect of silicon-based anodes and the interface stability issues of nickel-containing cathodes have become key technical bottlenecks restricting battery performance (especially low-temperature and high-temperature cycling performance). Summary of the Invention

[0003] The battery provided by this invention can form a high-quality interface film on both the positive and negative electrode surfaces, and has both good low-temperature cycling performance, high-temperature cycling performance and low initial DCIR (internal resistance of the battery).

[0004] The electrical equipment provided by this invention has a longer lifespan under both high and low temperature conditions.

[0005] The battery provided by the present invention includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material, which includes a nickel-cobalt-manganese ternary material. The negative electrode includes a negative electrode active material, which includes silicon-based materials and carbon-based materials.

[0006] The electrolyte includes a first additive and a second additive, wherein the first additive has the structure shown in Formula I:

[0007] Formula I;

[0008] R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1-12 substituted or unsubstituted carbon atoms, alkenyl groups with 2-12 substituted or unsubstituted carbon atoms, alkynyl groups with 2-12 substituted or unsubstituted carbon atoms, and aryl groups with 6-12 substituted or unsubstituted carbon atoms. When substituted, the substituent is selected from at least one of halogen atoms, cyano, alkyl groups with 1-6 carbon atoms, alkenyl groups with 2-6 carbon atoms, and alkynyl groups with 2-6 carbon atoms.

[0009] The second additive comprises n sulfur-containing heterocycles, where n ≥ 2.

[0010] Based on the total mass of the electrolyte, the mass content of the first additive in the battery described above is 0.1%-4%; and / or the mass content of the second additive is 0.1%-4%.

[0011] In the battery described above, the first additive includes at least one of the following compounds:

[0012]

[0013] .

[0014] The second additive includes at least one of erythritol sulfate, pentaerythritol bicyclic sulfate, and mannitol carbonate sulfate.

[0015] The electrolyte of the battery described above further includes a third additive, which includes at least one of 1,3-propanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, and vinyl sulfate.

[0016] And / or, the electrolyte further includes a fourth additive, which includes nitrile compounds.

[0017] Based on the total mass of the electrolyte, the mass percentage of the third additive in the battery described above is 0.1%-4%.

[0018] The battery described above, wherein the nitrile compound includes at least one of a first nitrile compound and a second nitrile compound, wherein the first nitrile compound includes a P=O bond; preferably, the first nitrile compound includes at least one of the following C1-C9 compounds:

[0019] ;

[0020] In the battery described above, the second nitrile compound includes at least one of ethylene glycol bis(propionitrile) ether, 1,2,4-butanetrionitrile, adiponitrile, succinic anhydride, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4-tetra(2-cyanoethoxy)butane, tetra(2-cyanoethoxymethyl)methane, and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane.

[0021] Based on the total mass of the electrolyte, the mass percentage of the first nitrile compound in the battery described above is 0.1%-3%, and / or the mass percentage of the second nitrile compound is 0.5%-6%.

[0022] The electrolyte in the battery described above further includes 2,2-difluoroethyl acetate, and the mass percentage of 2,2-difluoroethyl acetate is 5%-60% based on the total mass of the electrolyte.

[0023] The electrolyte of the battery described above further includes lithium salt additives, which include boron-containing lithium salts. Preferably, the boron-containing lithium salts include at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium dioxalate borate. Preferably, the mass percentage of the boron-containing lithium salts is 0.01%-2% based on the total mass of the electrolyte.

[0024] Based on the total mass of the electrolyte, the mass percentage of ethylene carbonate in the electrolyte is ≤5% of the battery described above.

[0025] Based on the battery described above, the general structural formula of the nickel-cobalt-manganese ternary material is: Li a Ni x Co y Mn z K b O2, formula (1); where 0.85≤a≤1.2, 0.6≤x≤1, 0<y≤0.4, 0<z≤0.4, 0≤b≤0.1; K is selected from at least one of Al, Ti, V, Cr, Y, W, Zr, Mg, Nb, Mo, Sr, B and Fe;

[0026] And / or, the nickel-cobalt-manganese ternary material comprises single-crystal particles, wherein the particle size Dv50 of the single-crystal particles is 1μm-6μm.

[0027] And / or, the nickel-cobalt-manganese ternary material comprises polycrystalline particles, wherein the particle size Dv50 of the polycrystalline particles is 4μm-15μm.

[0028] The positive electrode active material of the battery described above further includes lithium cobalt oxide; preferably, the molar ratio of cobalt to nickel in the positive electrode active material is 1:(1-6.2).

[0029] In the battery described above, the silicon-based material includes at least one of silicon-carbon composite materials, silicon-oxygen materials, elemental silicon, and silicon alloys; the carbon-based material includes at least one of graphite, hard carbon, and soft carbon; and the negative electrode satisfies at least one of the following conditions:

[0030] 1) Based on the total mass of the negative electrode active layer, the mass percentage of silicon is 2.5%-40%;

[0031] 2) The particle size Dv50 of the silicon-based material is 1μm-15μm;

[0032] 3) The negative electrode also includes at least one of carbon nanotubes and carbon fibers.

[0033] The present invention also provides an electrical device, including the battery or battery pack described above.

[0034] The battery provided by the present invention uses a nickel-containing positive electrode and a silicon-doped negative electrode as the positive and negative electrodes, and adds specific first and second additives to the electrolyte, so that high-quality interface films can be formed on both the surface of the nickel-containing positive electrode and the surface of the silicon-doped negative electrode. Therefore, the battery has both good high and low temperature cycle performance and low initial DCIR. Detailed Implementation

[0035] To enable those skilled in the art to better understand the solutions of this invention, the following provides a further detailed description of this application. The specific embodiments listed below are merely descriptions of the principles and features of this invention; the examples are only for explaining the invention and are not intended to limit its scope. Based on the embodiments of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the scope of protection of this invention.

[0036] To meet the ever-increasing demand for energy density, lithium-ion battery anode materials are evolving from traditional graphite to high-capacity materials such as silicon-based materials. Specifically, silicon-based materials theoretically have a much higher specific capacity (4200 mAh / g) than graphite (372 mAh / g), but they suffer from high volume expansion. Current technologies mitigate this volume expansion by embedding silicon particles into a porous carbon matrix. However, increasing the silicon content still leads to drastic volume changes in the anode during charging and discharging, resulting in excessive electrolyte consumption, thickening of the SEI (solid electrolyte interphase), and increased ion transport resistance, ultimately causing deterioration in the battery's low-temperature performance.

[0037] High-nickel ternary materials (such as NCM811) have become core cathode materials for high-energy-density batteries due to their high specific capacity (>200 mAh / g). However, the Ni content on their surface... 4+ The strong oxidizing properties of nickel readily catalyze the decomposition of the electrolyte, leading to instability at the cathode interface (CEI film) and accelerating capacity decay. Furthermore, high-nickel cathodes are prone to lattice distortion and oxygen loss during high-temperature cycling, further deteriorating battery performance.

[0038] Therefore, the volume expansion effect of silicon-based anodes and the interface stability problem of nickel-containing cathodes (especially high-nickel cathodes) have become key technical bottlenecks restricting battery performance (especially low-temperature cycling performance and high-temperature cycling performance).

[0039] Based on this, the present invention provides a battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode active material, which is a nickel-cobalt-manganese ternary material. The negative electrode comprises a negative electrode active material, which is a silicon-based material and a carbon-based material. The electrolyte comprises a first additive and a second additive. The first additive has a structure shown in Formula I.

[0040] Formula I;

[0041] R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1-12 substituted or unsubstituted carbon atoms, alkenyl groups with 2-12 substituted or unsubstituted carbon atoms, alkynyl groups with 2-12 substituted or unsubstituted carbon atoms, and aryl groups with 6-12 substituted or unsubstituted carbon atoms (such as phenyl, naphthyl, etc.). When substituted, the substituent is selected from at least one of halogen atoms, cyano, alkyl groups with 1-6 carbon atoms, alkenyl groups with 2-6 carbon atoms, and alkynyl groups with 2-6 carbon atoms.

[0042] The second additive includes n sulfur-containing heterocycles, where n ≥ 2. The sulfur-containing heterocycles are multi-rings containing sulfur atoms. The sulfur atoms can be connected to carbon atoms, and the sulfur atoms can also be connected to other heteroatoms by double or single bonds. Other heteroatoms can include oxygen atoms.

[0043] The battery provided by this invention uses a nickel-containing transition metal oxide as the active material of the positive electrode and silicon-doped negative electrodes as both, exhibiting high energy density. The first additive can form a boron-containing SEI film on the silicon-doped surface. The strong electron-withdrawing inductive effect of the boron centers weakens the binding energy between lithium ions and solvent molecules, accelerating the migration rate of lithium ions in the SEI film, thereby improving the battery's low-temperature discharge performance. Simultaneously, the second additive has a lower highest occupied molecular orbital (HOMO) energy, enabling it to preferentially undergo oxidation reactions before solvent molecules, generating a three-dimensional network-structured CEI film layer to protect the positive electrode interface. Furthermore, it can preferentially undergo film-forming reactions on the nickel-containing positive electrode surface before the first additive, forming a stable CEI film composition, inhibiting contact between nickel and the first additive, and thus inhibiting the oxidative decomposition of the first additive by nickel ions. This prevents side reactions of the first additive on the positive electrode surface, thereby improving the battery's high-temperature and safety performance.

[0044] Appropriate addition amounts of the first and second additives are beneficial for better ensuring membrane performance, thereby improving the high and low temperature cycle performance of the battery. Studies have shown that when the mass content of the first additive is 0.1%-4% and the mass content of the second additive is 0.1%-4% based on the total mass of the electrolyte, the formed SEI and CEI membranes are both of better quality, and the high and low temperature cycle performance of the battery is also better.

[0045] In some embodiments, the first additive is selected from at least one of the following compounds: .

[0046] In some embodiments, the second additive includes at least one of erythritol sulfate (BDTD), pentaerythritol bicyclic sulfate (TDT), and mannitol carbonate sulfate (BDD).

[0047] In some embodiments, the electrolyte also includes a third additive, which includes at least one of 1,3-propanesulfonyl lactone (PS), propylene-1,3-sulfonyl lactone (PST), and vinyl sulfate (DTD). This type of additive can fill defects in the CEI film formed by the second additive, forming a denser CEI film and optimizing interfacial impedance. Furthermore, the third additive can form inorganic substances such as lithium sulfate and lithium sulfide. Films rich in these inorganic substances have higher mechanical strength and chemical inertness, resisting the penetration of electrolyte decomposition products. This inhibits the continuous growth and thickening of the three-dimensional network CEI film formed by the second additive, further reducing electrode / electrolyte interfacial impedance, improving battery cycle stability, and extending service life.

[0048] In some implementations, the third additive comprises 0.1%-4% of the total mass of the electrolyte. Specifically, the mass percentage of the third additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, or any value between any two of the above. In this case, the battery exhibits better high and low temperature cycle performance while maintaining a lower initial resistance.

[0049] In some embodiments, the electrolyte also includes a fourth additive, which includes nitrile compounds. Nitrile compounds can make the formed positive electrode interphase (CEI) film more stable, thereby further improving the high-temperature cycle performance of the battery.

[0050] For example, the nitrile compound may be selected from at least one of a first nitrile compound and a second nitrile compound. Specifically, the first nitrile compound includes a P=O bond. The second nitrile compound includes at least one of ethylene glycol bis(propionitrile) ether, 1,2,4-butanetrionitrile, adiponitrile, succinic anhydride, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4-tetra(2-cyanoethoxy)butane, tetra(2-cyanoethoxymethyl)methane, and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane.

[0051] For example, the first nitrile compound may be selected from at least one of the following C1-C9 compounds: .

[0052] In some embodiments, the electrolyte includes both a first nitrile compound and a second nitrile compound. The first nitrile compound can form a cyano-containing CEI film, further improving the film's stability, and P=O can coordinate with lithium ions, also improving the ion transport efficiency at the cathode interface. However, the first nitrile compound degrades impedance, while the second nitrile compound, while exerting a complexing effect, does not significantly degrade impedance. By using both the first and second nitrile compounds together, high-temperature cycling performance can be significantly improved.

[0053] In some implementations, when the mass percentage of the first nitrile compound is 0.1%-3% and / or the mass percentage of the second nitrile compound is 0.5%-6% based on the total mass of the electrolyte, a better balance between high and low temperature cycling performance and initial DCIR can be achieved.

[0054] Specifically, the mass percentage of the first nitrile compound can be 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, or any value between any two of the above. The mass percentage of the second nitrile compound can be 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, or any value between any two of the above.

[0055] In some embodiments, the electrolyte also includes 2,2-difluoroethyl acetate (DFEA). DFEA has a low viscosity and dielectric constant, and can preferentially distribute on the outer layer of the solvated structure, prompting the first additive to enter the inner layer of the solvated structure and quickly form a stable interface film, thereby further improving the low-temperature cycling stability of the battery and further reducing the initial DCIR.

[0056] When the mass percentage of 2,2-difluoroethyl acetate (DFEA) is 5%-60% based on the total mass of the electrolyte, it can play a better role in forming a more stable SEI film, thereby improving the charge-discharge performance and low-temperature cycle stability of the battery.

[0057] Specifically, the mass percentage of 2,2-difluoroethyl acetate (DFEA) can be 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, or any value between any two of the above. When the 2,2-difluoroethyl acetate content is between 15% and 60%, the battery exhibits better low-temperature cycling performance and simultaneously reduces the initial DCIR.

[0058] It is understood that the electrolyte also includes a solvent, which can be an organic solvent. For example, the solvent can be selected from at least one of propyl propionate (PP), ethylene carbonate (EC), propylene carbonate (PC), butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, and methyl ethyl carbonate (EMC).

[0059] In a preferred embodiment, the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP), wherein the mass ratio of ethylene carbonate, propylene carbonate, and propyl propionate is (10-30):(5-15):(60-80). Within this preferred range, the battery exhibits better high and low temperature performance and lower impedance.

[0060] In this invention, the electrolyte also includes a lithium salt. For example, the lithium salt may be selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0061] In some embodiments, the electrolyte also includes lithium salt additives, including boron-containing lithium salts. Boron-containing lithium salts include one or more of lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiODFB), and lithium bis(oxalate borate) (LiBOB).

[0062] This type of lithium salt can generate a thin and boron-rich SEI reinforcement layer on the basis of the boron-containing SEI film formed by the first additive, thereby enhancing the mechanical strength of the SEI film and further improving the high-temperature cycle performance and safety of lithium-ion batteries.

[0063] In this invention, the mass percentage of boron-containing lithium salt is 0.01%-2% based on the total mass of the electrolyte. Specifically, the mass percentage of boron-containing lithium salt can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, or any value between any two of the above.

[0064] When the mass percentage of boron-containing lithium salt exceeds this range, it leads to an increase in impedance; when the mass percentage of boron-containing lithium salt is below this range, the effect of further improving high-temperature stability is not good.

[0065] In some embodiments, the general structural formula of the nickel-cobalt-manganese ternary material is: Li a Ni x Co y Mn z K b O2, Equation (1);

[0066] Wherein, 0.85≤a≤1.2, 0.6≤x≤1, 0<y≤0.4, 0<z≤0.4, 0≤b≤0.1; K is selected from at least one of Al, Ti, V, Cr, Y, W, Zr, Mg, Nb, Mo, Sr, B and Fe.

[0067] By using this high-nickel cathode active material, nickel can achieve multiple electron transfers during charging and discharging through valence state transitions from +2 to +3 to +4, which is beneficial to improving the energy density of the battery.

[0068] When nickel-cobalt-manganese ternary materials use single-crystal particles, the particle size Dv50 of the single-crystal particles is usually controlled between 1μm and 6μm. When nickel-cobalt-manganese ternary materials use polycrystalline particles, the particle size Dv50 of the polycrystalline particles is usually controlled between 4μm and 15μm.

[0069] The preferred nickel-cobalt-manganese ternary material is a single-crystal particle. The small particle size of the single-crystal particle can shorten the lithium-ion diffusion path and enhance the fast charge and discharge capability. In addition, the single crystal can eliminate grain boundaries. The surface structure of the single-crystal ternary material is uniform and there are few grain boundary defects, which provides a smoother deposition substrate for the CEI film formed by the second additive, prevents the CEI from being too thick and increasing the impedance, and reduces the side reactions at the cathode interface, further improving the thermal safety performance of the cathode.

[0070] In some embodiments, the positive electrode active material also includes lithium cobalt oxide, the general structural formula of which is: Li c Co d M k O2, wherein 0.85≤c≤1.1, 0.8≤d≤1, 0≤k<0.1, and M is at least one of Al, Y, Na, Mg, Ti, Ni, Sr, Sc, B, W, Si, Zr, Sn, Tb, Nb, Sb, Se, Ce, and Te.

[0071] When the positive electrode active material also includes the above-mentioned active materials, it is beneficial to improve the battery's operating voltage and volumetric energy density.

[0072] In some embodiments, the molar ratio of cobalt to nickel in the positive electrode active material is 1:(1-6.2).

[0073] When the molar ratio of cobalt to nickel is within this range, the energy density of the battery can be improved, and the dependence on cobalt resources can be reduced.

[0074] Silicon-based materials include at least one of silicon-carbon composite materials, silicon-oxygen materials, elemental silicon, and silicon alloys; carbon-based materials include at least one of graphite, hard carbon, and soft carbon.

[0075] In some implementations, the negative electrode satisfies at least one of the following conditions:

[0076] 1) Based on the total mass of the negative electrode active layer, the mass percentage of silicon is 2.5%-40%;

[0077] 2) The particle size Dv50 of silicon-based materials is 5μm-15μm;

[0078] 3) The negative electrode also includes at least one of carbon nanotubes and carbon fibers.

[0079] In some embodiments, the silicon-carbon material includes a porous carbon matrix and silicon material deposited in the porous carbon matrix.

[0080] By controlling the silicon content within the range of 2.5%-40%, a better balance can be struck between energy density and volume expansion. When the silicon content exceeds this range, the volume expansion is significant, leading to reduced cycle stability. Conversely, when the silicon content is below this range, the improvement in energy density is not substantial.

[0081] When the Dv50 of silicon-based materials is 1μm-15μm, it is beneficial to improve rate performance, build a more stable conductive network, alleviate silicon volume expansion, and increase compaction density.

[0082] In detail, the particle size (volume-based cumulative distribution particle size) of silicon-based materials can be measured using laser particle size analysis methods, such as the Malvern particle size analyzer. The testing procedure is as follows: disperse the silicon-based material in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content 0.02~0.03wt%) to form a mixture, sonicate the mixture for 2 minutes, and then place it in the Malvern particle size analyzer for testing.

[0083] In this invention, the silicon content in the silicon-carbon composite material is generally 35-70%. It can be tested using thermogravimetric analysis (TGA), for example, using a Shimadzu DTG-60 TGA analyzer. The test conditions are: sample volume 5 mg, air atmosphere, heating rate 10 °C / min from room temperature to 900 °C and held at that temperature for 40 min, allowing the non-silicon components in the sample to volatilize while the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content; dividing this ash value by the molar mass of silicon dioxide and then multiplying it by the molar mass of silicon gives the percentage of silicon in the sample.

[0084] When the negative electrode also includes carbon nanotubes and / or carbon fibers, it is beneficial to construct a more efficient conductive network, improve the mechanical strength and conductivity of the negative electrode active layer, thereby enhancing cycle performance and rate performance.

[0085] When the amount of carbon nanotubes or carbon fibers added is 0.1%-1.5% of the total mass of the negative electrode active material, it is beneficial to better balance cycle performance and rate performance. Specifically, the amount of carbon nanotubes or carbon fibers added can be 0.1%, 0.5%, 1%, 1.5% of the total mass of the negative electrode active material, or any value between any two of the above.

[0086] In this invention, the carbon fiber can be selected from at least one of pitch-based carbon fiber, viscose-based carbon fiber, carbon nanofiber, graphene fiber, polyacrylonitrile-based carbon fiber, and vapor-grown carbon fiber.

[0087] Understandably, the aforementioned battery also includes a separator and outer packaging.

[0088] In this invention, the membrane material can be one of the following: polypropylene membrane (PP), polyethylene membrane (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun membrane (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven membrane, and membrane with ceramic coating.

[0089] In the preparation of lithium-ion batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0090] The present invention also provides an electrical device including the battery described above. For the same reason, this electrical device is highly safe and has excellent performance. This electrical device can be a conventional electrical device in the art, including consumer electronics (mobile communication devices, laptops, tablets, wearable devices, etc.), drones, power tools, energy storage devices, electric bicycles, electric vehicles, etc.

[0091] The technical solution of this application will be further explained below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, all reagents used are commercially available or obtained through public channels.

[0092] The silicon-carbon composite materials involved in the following embodiments and comparative examples were prepared by the following method: First, porous carbon was used as a precursor and activated at high temperature under nitrogen protection to form a porous framework. Then, silane was introduced into a negative pressure environment, and its high-temperature self-ignition and decomposition characteristics were used to deposit nano-silicon particles in the voids of the carbon framework. Next, acetylene gas was switched, and a carbon coating layer was formed on the surface and in the pores of the silicon particles through high-temperature decomposition. Finally, a structurally stable silicon-carbon composite material was obtained through processes such as mixing, demagnetization, and sieving.

[0093] Examples 1-46, Comparative Examples 1-2

[0094] This embodiment provides a battery and its preparation method, specifically including the following steps:

[0095] (1) Preparation of positive electrode

[0096] The positive electrode active material (specifically LiNi) 0.8 Co 0.1 Mn 0.1O2), polyvinylidene fluoride (PVDF-500) binder, and Super P conductive carbon material were mixed in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:2:3 and stirred to form a uniform positive electrode slurry. Subsequently, the positive electrode slurry was coated onto a 10 μm thick aluminum foil and vacuum dried at 120°C for 6 hours to form the positive electrode active layer. After rolling and slitting, the positive electrode sheet was obtained.

[0097] (2) Preparation of negative electrode sheet

[0098] The negative electrode active material (specifically, a mixture of silicon-carbon composite material with a Dv50 of 9.4 μm, graphite, and carbon nanotubes in a mass ratio of 20:79:1), conductive carbon material Super P, binder carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 97.5:1:0.3:1.2) was mixed in water and stirred to form a uniform negative electrode slurry. Subsequently, the negative electrode slurry was coated onto the surface of a 10 μm thick copper foil and vacuum dried at 120°C for 6 hours to form the negative electrode active layer. After rolling and slitting, the negative electrode sheet was obtained. The silicon element accounted for 10% of the total mass of the negative electrode active layer.

[0099] (3) Electrolyte preparation

[0100] In an argon-filled glove box (moisture < 1 ppm, oxygen < 1 ppm), lithium salt (specifically lithium hexafluorophosphate), fluoroethylene carbonate, first additive, second additive, third additive, first nitrile compound, second nitrile compound, DFEA, and lithium salt additive were added to a mixed solvent (prepared by EC:PC:PP in a volume ratio of 20:10:70), wherein the mass content of lithium hexafluorophosphate was 12.5% ​​and the mass content of fluoroethylene carbonate was 8%. The mixture was thoroughly mixed to obtain the electrolyte. The specific raw materials and amounts are shown in Table 2 below.

[0101] (4) Preparation of the diaphragm

[0102] A composite layer of polyvinylidene fluoride and boehmite is coated onto a polyethylene substrate.

[0103] (5) Preparation of lithium-ion batteries

[0104] The prepared positive electrode, separator, and negative electrode are wound together to form a bare cell. The bare cell is then placed in an aluminum-plastic film package, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, room temperature standing, and high temperature formation, the target lithium battery is obtained.

[0105] The preparation methods of each embodiment are the same, and the differences are shown in Tables 1 and 2 below. Table 1 shows the combination of positive and negative active materials involved in each embodiment and comparative example. Dv50 in Table 1 is the index of silicon-based silicon-carbon composite material particles. Table 2 shows the differences in electrolyte. The contents in Table 2 are based on the total mass of the electrolyte and the mass percentage of each raw material.

[0106] Table 1

[0107]

[0108] Table 2

[0109]

[0110]

[0111]

[0112] The following performance tests were performed on the batteries in Examples 1-46 and Comparative Examples 1-2, and the test results are shown in Table 3.

[0113] 1) Low-temperature cycling performance test

[0114] The battery was charged at a constant current of 1C to 4.2V at room temperature (10℃), and then charged at a constant voltage of 4.2V to the cutoff current of 0.05C. The battery was then discharged at 1C to 2.75V. This charge-discharge cycle was repeated for 200 cycles. The discharge capacity of the 200th cycle was recorded and divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate.

[0115] 2) High-temperature cycling performance test

[0116] The battery was charged at a constant current of 1C to 4.2V at a high temperature of 45℃, and then charged at a constant voltage of 4.2V to the cutoff current of 0.05C. The battery was then discharged at 1C to 2.75V. This charge-discharge cycle was repeated for 200 cycles. The discharge capacity of the 200th cycle was recorded and divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate.

[0117] 3) Initial DCIR test

[0118] After capacity grading, the battery is charged to 4.2V at 1C at room temperature, left to stand for 5 minutes, then discharged at 1C for 30 minutes, left to stand for 1 hour, and then discharged at 2C for 10 seconds. Calculate the DCIR (internal resistance of the battery) at 50% SOC.

[0119] Table 3

[0120]

[0121]

[0122] The results above show that the high and low temperature cycling performance of Examples 1-46 is better than that of Comparative Examples 1 and 2, and the initial DCIR is lower than that of Comparative Examples 1 and 2. This indicates that the addition of the first additive and the second additive is beneficial to improving the high and low temperature cycling performance and reducing the initial DCIR.

[0123] A comparison of Examples 1-5, 30, and 31 shows that when the mass content of the first additive is 0.1%-4% and the mass content of the second additive is 0.1%-4%, the high and low temperature cycling performance and the initial DCIR can be better balanced.

[0124] A comparison of Examples 1, 6, 7, 32, and 33 shows that when a third additive is present and its mass percentage is 0.1-4%, the initial DCIR is reduced while further improving the high and low temperature cycling performance.

[0125] As can be seen from Examples 1, 8-11, 24-29, and 34-37, the battery exhibits better high-temperature cycling performance when both a first nitrile compound and a second nitrile compound are present. When the mass percentage of the first nitrile compound is 0.1-1.5% and the mass percentage of the second nitrile compound is 0.5-3%, it can better balance high and low temperature cycling performance and initial DCIR.

[0126] As can be seen from Examples 1, 12, 13, and 38, when DFEC is present and the mass percentage of the DFEC is 5-60%, the low-temperature cycling performance is better and the initial DCIR is reduced.

[0127] As can be seen from Examples 1, 14, 15, 40, and 41, when boron-containing lithium salt is present and the mass percentage of boron-containing lithium salt is 0.01-2%, the high-temperature cycling performance is better and the initial DCIR is reduced.

[0128] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material, which is a nickel-cobalt-manganese ternary material. The negative electrode includes a negative electrode active material, which is a silicon-based material and a carbon-based material. The electrolyte includes a first additive and a second additive, wherein the first additive has the structure shown in Formula I: Equation I; R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1-12 substituted or unsubstituted carbon atoms, alkenyl groups with 2-12 substituted or unsubstituted carbon atoms, alkynyl groups with 2-12 substituted or unsubstituted carbon atoms, and aryl groups with 6-12 substituted or unsubstituted carbon atoms. When substituted, the substituent is selected from at least one of halogen atoms, cyano, alkyl groups with 1-6 carbon atoms, alkenyl groups with 2-6 carbon atoms, and alkynyl groups with 2-6 carbon atoms. The second additive comprises n sulfur-containing heterocycles, where n ≥ 2.

2. The battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass content of the first additive is 0.1%-4%; And / or, the mass content of the second additive is 0.1%-4%; And / or, the first additive comprises at least one of the following compounds: ； And / or, the second additive includes at least one of erythritol sulfate, pentaerythritol bicyclic sulfate, and mannitol carbonate sulfate.

3. The battery according to claim 1 or 2, characterized in that, The electrolyte also includes a third additive, which includes at least one of 1,3-propanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, and vinyl sulfate. And / or, the electrolyte further includes a fourth additive, which includes nitrile compounds.

4. The battery according to claim 3, characterized in that, Based on the total mass of the electrolyte, the third additive accounts for 0.1%-4% of the total mass. And / or, the nitrile compound includes at least one of a first nitrile compound and a second nitrile compound, wherein the first nitrile compound includes a P=O bond; preferably, the first nitrile compound includes at least one of the following C1-C9 compounds: ； Preferably, the second nitrile compound includes at least one selected from ethylene glycol bis(propionitrile) ether, 1,2,4-butanetrionitrile, adiponitrile, succinic anhydride, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4-tetra(2-cyanoethoxy)butane, tetra(2-cyanoethoxymethyl)methane, and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane; Preferably, based on the total mass of the electrolyte, the mass percentage of the first nitrile compound is 0.1%-3%, and / or the mass percentage of the second nitrile compound is 0.5%-6%.

5. The battery according to any one of claims 1-4, characterized in that, The electrolyte also includes 2,2-difluoroethyl acetate, and the mass percentage of 2,2-difluoroethyl acetate is 5%-60% based on the total mass of the electrolyte.

6. The battery according to claim 5, characterized in that, The electrolyte also includes lithium salt additives, which include boron-containing lithium salts. Preferably, the boron-containing lithium salts include at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(oxalate borate). Preferably, the mass percentage of the boron-containing lithium salts is 0.01%-2% based on the total mass of the electrolyte.

7. The battery according to any one of claims 1-6, characterized in that, The general structural formula of the nickel-cobalt-manganese ternary material is: Li a Ni x Co y Mn z K b O2, formula (1); where 0.85≤a≤1.2, 0.6≤x≤1, 0<y≤0.4, 0<z≤0.4, 0≤b≤0.1; K is selected from at least one of Al, Ti, V, Cr, Y, W, Zr, Mg, Nb, Mo, Sr, B and Fe; And / or, the nickel-cobalt-manganese ternary material comprises single-crystal particles, wherein the particle size Dv50 of the single-crystal particles is 1μm-6μm. And / or, the nickel-cobalt-manganese ternary material comprises polycrystalline particles, wherein the particle size Dv50 of the polycrystalline particles is 4μm-15μm.

8. The battery according to any one of claims 1-7, wherein the positive electrode active material further comprises lithium cobalt oxide; Preferably, in the positive electrode active material, the molar ratio of cobalt to nickel is 1:(1-6.2).

9. The battery according to any one of claims 1-8, characterized in that, The silicon-based material includes at least one of silicon-carbon composite materials, silicon-oxygen materials, elemental silicon, and silicon alloys; the carbon-based material includes at least one of graphite, hard carbon, and soft carbon; and the negative electrode satisfies at least one of the following conditions: 1) Based on the total mass of the negative electrode active layer, the mass percentage of silicon is 2.5%-40%; 2) The particle size Dv50 of the silicon-based material is 1μm-15μm; 3) The negative electrode also includes at least one of carbon nanotubes and carbon fibers.

10. An electrical device comprising the battery as described in any one of claims 1-9.

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