A lithium-ion battery

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery with excellent high-temperature cycle performance. The lithium-ion battery includes a positive electrode containing a positive electrode material layer, a negative electrode containing a negative electrode material layer, and a non-aqueous electrolyte; the negative electrode material layer contains Co element; the non-aqueous electrolyte includes lithium salt, organic solvent, and additives; the additives include a first additive and a wetting-improving additive; the wetting-improving additive includes compounds shown in structural formula 1 and / or compounds shown in structural formula 2; the lithium-ion battery satisfies the following conditions: 0.2≤(X+Z)×M / 10Y≤10, 0.1≤X≤3, 0.5≤Y≤5, 10≤Z≤200, 0.8≤M≤1.8. The lithium-ion battery of this invention can improve the wetting of the electrolyte on the electrode, increase the electrolyte retention, form a good SEI film on the negative electrode, significantly improve the high-temperature cycle performance of the battery, and extend the battery's service life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a lithium-ion battery with improved high-temperature cycle performance. Background Technology

[0002] Lithium-ion batteries have achieved significant development in the field of portable electronic products due to their high operating voltage, high safety, long lifespan, and lack of memory effect. Consumer electronics, as the starting point for lithium-ion battery development, has seen widespread application in the market after more than 30 years of development. Cobalt-containing cathodes, the most commonly used cathodes in consumer batteries, have seen their cycle life increased from the initial 400 cycles to the current 700 cycles to meet the increasingly demanding lifespan requirements of mobile devices. However, when matched with high voltage, the cycle life often suffers a significant reduction. This is due to the damage to the SEI film in the later stages of cycling, coupled with the large-scale side reactions triggered by electrolyte drying, leading to rapid performance degradation. Therefore, developing a lithium-ion battery that can significantly improve high-temperature cycle performance is of great significance. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a lithium-ion battery with excellent high-temperature cycle performance.

[0004] The present invention adopts the following technical solution:

[0005] A lithium-ion battery includes a positive electrode comprising a positive electrode material layer, a negative electrode comprising a negative electrode material layer, and a non-aqueous electrolyte.

[0006] The negative electrode material layer contains Co element;

[0007] The non-aqueous electrolyte includes lithium salts, organic solvents, and additives;

[0008] The additives include a first additive and a wetting-improving additive;

[0009] The first additive includes at least one of the following compounds:

[0010]

[0011] The wetting improver includes the compound shown in structural formula 1 and / or the compound shown in structural formula 2:

[0012]

[0013] In structural formula 1, R 11 ~R 16 Each is independently selected from H, F, C1-C5 hydrocarbon groups or C1-C5 fluorinated hydrocarbon groups, and R 11 ~R 16At least one of them contains a fluorine atom;

[0014] In structural formula 2, 1≤a≤5, 1≤b≤5, x≥1;

[0015] The lithium-ion battery meets the following conditions:

[0016] 0.2≤(X+Z)×M / 10Y≤10, 0.1≤X≤3, 0.5≤Y≤5, 10≤Z≤200, 0.8≤M≤1.8;

[0017] Where X is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0018] Y represents the mass percentage of wetting improver additives in the non-aqueous electrolyte, in %;

[0019] Z represents the Co content in the negative electrode material layer, expressed in ppm.

[0020] M is the ratio of the total mass of the non-aqueous electrolyte to the battery's discharge capacity, expressed in g / Ah.

[0021] The lithium-ion battery of this invention uses a first additive with a specific structure and a wetting-improving additive as additives in the non-aqueous electrolyte. During the first charge and cycle of the battery, although the first additive can form a porous and stable SEI film on the surface of the negative electrode, improving the dynamic performance of the battery, the inventors have found that the degree of influence of the formed SEI film on the battery performance is closely related to several factors, including the content Z of Co element in the negative electrode, the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery, the mass percentage X of the first additive in the non-aqueous electrolyte, and the mass percentage Y of the wetting-improving additive in the non-aqueous electrolyte. Through extensive research, the inventors have found that when the above parameters satisfy the following formulas: 0.2≤(X+Z)×M / 10Y≤10, 0.1≤X≤3, 0.5≤Y≤5, 10≤Z≤200, 0.8≤M≤1.8, the high-temperature cycle performance of the battery can be significantly improved and the battery life can be extended. The reason for this is likely that: the wetting improver, being a fluorine-substituent, reduces the surface tension of the electrolyte on the electrode surface, improves the wetting of the electrolyte in the positive and negative electrodes, and increases the amount of electrolyte retained per unit battery capacity (i.e., the ratio of the total mass of non-aqueous electrolyte to the battery's discharge capacity). Simultaneously, the first additive forms a cross-linked SEI film of organic salt, inorganic salt, and inorganic metal with the Co element in the negative electrode. This type of SEI film is dense, tough, and thermally stable, significantly improving the battery's high-temperature cycle performance and extending its lifespan. The ratio of the total mass of non-aqueous electrolyte to the battery's discharge capacity largely determines the number of first additive molecules retained in the battery, while the Co content in the negative electrode material layer significantly affects the number of molecules required for the first additive to form the SEI film. When these relationships are satisfied, the number of first additive molecules in the battery is just enough to form a complete SEI film without excess. Therefore, this battery exhibits excellent high-temperature cycle performance and extends its lifespan.

[0022] Preferably, the lithium-ion battery satisfies 0.5≤(X+Z)×M / 10Y≤5.

[0023] The first additive can participate in the formation of a dense and uniform interfacial film at both the positive and negative electrodes, improving the film's stability and thus enhancing the battery's high-temperature performance. If the X value is too high, the battery impedance will be too large, leading to a significant increase in battery charging and discharging polarization and heat generation, causing a series of negative effects such as impedance growth and ultimately degrading the battery's various electrochemical performance characteristics; if the X value is too low, it will be difficult to improve the battery's high-temperature performance. Specifically, in some embodiments of the present invention, the mass percentage X% of the first additive in the non-aqueous electrolyte is 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.7%, 2.8%, 3%, or any combination of these values; preferably, the mass percentage X of the first additive in the non-aqueous electrolyte is 0.5% to 2%.

[0024] Co deposition in negative electrode materials is often considered to have negative effects. However, through extensive research, the inventors discovered that a small amount of Co participating in the formation of the SEI film on the negative electrode can improve film quality and enhance cycle stability. Through synergistic action with the first additive, a cross-linked SEI film of organic salt, inorganic salt, and inorganic metals is rapidly formed on the negative electrode, improving the battery's cycle performance. If the Z-value is too large, excessive Co deposition on the negative electrode leads to film thickening and decreased toughness, degrading battery cycle performance. If the Z-value is too small, it does not effectively synergize with the first additive, resulting in limited improvement in film quality. Specifically, in some embodiments of the present invention, the content Z of Co element in the negative electrode material layer is 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 110ppm, 120ppm, 130ppm, 140ppm, 150ppm, 160ppm, 170ppm, 180ppm, 190ppm, 200ppm, or any combination of these values; preferably, the content Z of Co element in the negative electrode material layer is 20 to 100ppm.

[0025] Improving wetting additives are substances containing F-substituents that can reduce the surface tension of the electrolyte on the electrode surface, improve the wetting of the electrolyte in the positive and negative electrodes, and increase the amount of electrolyte retained per unit battery capacity. By using improving wetting additives, the wetting of the electrolyte on the negative electrode surface is improved, which can better assist the first additive and Co element in the rapid film formation on the negative electrode. At the same time, since the electrolyte is gradually consumed with the increase of the number of cycles, if the electrolyte is depleted, the battery cycle life will drop rapidly. Improving wetting additives increase the ratio of the total mass of the electrolyte to the discharge capacity of the lithium-ion battery, increasing the amount of electrolyte that can be consumed in the battery, and further delaying the battery cycle life drop. When the Y value is too large, it will produce a series of negative effects, such as a significant increase in film impedance; when the Y value is too small, the improvement of the electrolyte wetting effect is limited. Specifically, in some embodiments of the present invention, the mass percentage Y% of the wetting improver in the non-aqueous electrolyte is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.7%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, or any combination of these values; preferably, the mass percentage Y% of the wetting improver in the non-aqueous electrolyte is 2-4%.

[0026] The ratio of the total mass of the non-aqueous electrolyte to the battery's discharge capacity reflects the amount of electrolyte retained per unit battery capacity. Since the electrolyte is continuously consumed with each battery cycle, controlling this ratio can delay battery degradation and improve cycle performance. Specifically, in some embodiments of the present invention, the ratio M of the total mass of the non-aqueous electrolyte to the battery's discharge capacity is 0.8 g / Ah, 0.9 g / Ah, 1 g / Ah, 1.1 g / Ah, 1.2 g / Ah, 1.3 g / Ah, 1.4 g / Ah, 1.5 g / Ah, 1.6 g / Ah, 1.7 g / Ah, 1.8 g / Ah, or any combination of these values; preferably, the ratio M is 0.9–1.4 g / Ah.

[0027] Specifically, in some embodiments of the present invention, the total mass of the non-aqueous electrolyte in the lithium-ion battery = the mass of the battery after capacity grading - the mass of the battery before electrolyte injection, or the total mass of the non-aqueous electrolyte in the lithium-ion battery = the total amount of liquid squeezed out after the capacity-graded cells are centrifuged at 8000 r / min for 20 minutes; the discharge capacity of the battery is the discharge capacity of the battery after being fully charged at 0.2C at 25°C and then discharged at a constant current of 0.2C to 3.0V.

[0028] Specifically, in some embodiments of the present invention, the lithium-ion battery satisfies: 2≤X+Y≤6, 0.5≤X / Y≤3. Through the synergistic effect of the first additive and the wetting-improving additive, the wetting-improving additive can improve the wetting of the electrolyte on the negative electrode surface, and can better assist the first additive and Co element in rapid film formation on the negative electrode, significantly improving the high-temperature cycle performance of the battery.

[0029] Specifically, in some embodiments of the present invention, the compound represented by structural formula 1 includes one or more of the following compounds:

[0030]

[0031] Specifically, in some embodiments of the present invention, the compound represented by structural formula 2 includes one or more of the following compounds:

[0032]

[0033] Compounds 2-4.

[0034] Specifically, in some embodiments of the present invention, the method for testing the Co element content in the negative electrode material layer is as follows:

[0035] The battery was discharged to 3.0V at 0.5C, disassembled, and the negative electrode was removed. Nitrification was performed at room temperature using a nitric acid:pure water solution of 2:1. The amount of nitric acid solution used corresponded to the cell capacity as 35mL / 1Ah; that is, 35mL of nitric acid solution was used for nitration of the negative electrode of a 1Ah rated capacity cell, and 70mL of nitric acid solution was used for nitration of the negative electrode of a 2Ah rated capacity cell. The nitration process lasted at least 24 hours. Then, a sample solution of m1g was diluted with pure water to m2g (e.g., 1g of sample solution could be diluted with pure water to 25g). Finally, the blank solution and the diluted sample solution were tested using an inductively coupled plasma atomic emission spectrometer (ICP) with a standard curve method. The concentration of the blank solution was measured as C1μg / mL, and the concentration of the sample solution was measured as C2μg / mL. The Co element content Z was calculated as: Z = (C2 - C1) × m2 / m1.

[0036] Specifically, in some embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO₂F₂, LiBF₄, LiBOB, LiSbF₆, LiAsF₆, LiCF₃SO₃, LiDFOB, LiDFOP, LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, LiN(SO₂C₂F₅)₂, LiCl, LiBr, LiI, LiClO₄, and LiB₂. 10 Cl10 At least one of the following: LiAlCl4, lithium chloroborane, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, and lithium tetraphenylborate.

[0037] Specifically, in some embodiments of the present invention, the organic solvent includes at least one of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, or ether solvents.

[0038] In some preferred embodiments, the cyclic carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, and butene carbonate.

[0039] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0040] In some preferred embodiments, the carboxylic acid ester solvent includes at least one of ethyl acetate, ethyl propionate, propyl propionate, ethyl difluoroacetate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0041] Specifically, in some embodiments of the present invention, the additive further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and nitrile compounds.

[0042] In some preferred embodiments, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0043] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0044] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 3 below:

[0045]

[0046] In the structural formula 3 shown, R 21 R 22 R 23 R 24 R 25 R 26Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group;

[0047] In some preferred embodiments, the compound represented by structural formula 3 includes at least one of the compounds represented by compounds 3-1 to 3-6 below:

[0048]

[0049] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds shown in structural formula 4:

[0050]

[0051] In structural formula 4, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; more preferably, the compound represented by structural formula 4 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargylpropyl phosphate, diargylpropylmethyl phosphate, diargylpropylethyl phosphate, diargylpropylpropyl phosphate, diargylpropyltrifluoromethyl phosphate, diargylpropyl-2,2,2-trifluoroethyl phosphate, diargylpropyl-3,3,3-trifluoropropyl phosphate, diargylpropylhexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0052] In some preferred embodiments, the nitrile compound includes at least one selected from succinic anhydride, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebacate.

[0053] In some embodiments, the content of the auxiliary additive is 0.01% to 10% based on 100% of the total mass of the non-aqueous electrolyte. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any one optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, or 5%.

[0054] Specifically, in some embodiments of the present invention, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes LiNi x Co y Mn z L (1-x-y-z) O2, LiCo x’ L (1-x’) O2, LiNi x” L’ y’ Mn (2-x”-y’) O4, Li z’ MPO4, where L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, or Fe, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < x + y + z ≤ 1, 0 < x’ ≤ 1, 0.3 ≤ x” ≤ 0.6, 0.01 ≤ y’ ≤ 0.2, L’ is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 0.5 ≤ z’ ≤ 1, M is at least one of Fe, Mn, Co. Preferably, the positive electrode active material is selected from LiNi x Co y Mn z L (1-x-y-z) O2, LiCo x’ L (1-x’) O2, LiNi x” Co y’ Mn (2-x”-y’) O4, LiCoPO4, where L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, or Fe, 0 ≤ x ≤ 1, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 < x + y + z ≤ 1, 0 < x’ ≤ 1, 0.3 ≤ x” ≤ 0.6, 0.01 ≤ y’ ≤ 0.2. More preferably, the positive electrode active material is selected from LiCoO2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.5 Co 0.2Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 One or more of O2 and LiCoPO4.

[0055] Specifically, in some embodiments of the present invention, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent.

[0056] The positive electrode binder includes one or more of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0057] The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0058] Specifically, in some embodiments of the present invention, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector. The positive electrode current collector includes a metallic material capable of conducting electrons; preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0059] The negative electrode includes a negative electrode material layer containing a negative electrode active material. Specifically, in some embodiments of the present invention, the negative electrode material is any one or more of silicon-based materials, carbon materials, or metallic lithium. The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon materials, and silicon alloy materials; preferably, the silicon material is nano-silicon material; preferably, the silicon oxide material is SiOx material, wherein 0≤x<2; preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiOy and carbon materials, wherein 0≤y<2; preferably, the silicon alloy material is Mg2Si alloy material and / or Fe2Si alloy material. The carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; preferably, the carbon material is artificial graphite. More preferably, the negative electrode active material includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, mesophase microcarbon spheres, silicon, silicon oxide compounds, silicon-carbon composites, or metallic lithium.

[0060] In some embodiments, the porosity ε% of the negative electrode material layer satisfies 20≤ε≤40, for example 20≤ε≤30, 20≤ε≤40, 25≤ε≤35, 20≤ε≤25, 30≤ε≤40, etc. Therefore, the porosity of the negative electrode material layer in this application is controlled within the above range. On the one hand, a negative electrode material layer with this porosity can increase the contact area between the negative electrode active material and the electrolyte, which is beneficial for lithium-ion transport, thereby improving battery performance. On the other hand, a negative electrode material layer with this porosity can slow down the continuous growth of uneven interfacial film, thereby mitigating the increase in impedance during cycling.

[0061] In some preferred embodiments, the porosity ε% of the negative electrode material layer and the mass percentage X of the first additive in the non-aqueous electrolyte satisfy 0.01≤X / ε≤0.1, which can ensure that the first additive forms a uniform film on the negative electrode surface, thereby reducing the increase in impedance during cycling.

[0062] Specifically, in some embodiments of the present invention, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector may be the same as that of the negative electrode current collector, and will not be described in detail here.

[0063] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0064] Specifically, in some embodiments of the present invention, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0065] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0066] The lithium-ion battery of the present invention uses a first additive with a specific structure and a wetting-improving additive as additives in the non-aqueous electrolyte. The relationship between the mass percentage X of the first additive in the non-aqueous electrolyte, the mass percentage Y of the wetting-improving additive, the content Z of Co element in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery satisfies the following conditions: 0.2≤(X+Z)×M / 10Y≤10, 0.1≤X≤3, 0.5≤Y≤5, 10≤Z≤200, 0.8≤M≤1.8. This improves the wetting of the electrolyte on the electrode, increases the electrolyte retention, forms a good SEI film on the negative electrode, significantly improves the high-temperature cycle performance of the battery, and extends the battery's service life. Detailed Implementation

[0067] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0068] Example 1

[0069] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0070] 1) Preparation of the positive electrode:

[0071] The positive electrode active material, lithium nickel cobalt manganese oxide (LiNiO), was mixed in a mass ratio of 93:4:3. 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed and dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil to form a positive electrode material layer. After drying, calendering, and vacuum drying, aluminum leads are welded on using an ultrasonic welder to obtain the positive electrode sheet.

[0072] 2) Preparation of the negative electrode:

[0073] Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1.0:2.5:2.5 to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil to form a negative electrode material layer. After drying, calendering, and vacuum drying, the porosity of the negative electrode material layer was controlled to 28% by calendering. Nickel leads were then welded on using an ultrasonic welding machine to obtain the negative electrode sheet.

[0074] 3) Preparation of non-aqueous electrolytes:

[0075] Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a mass ratio of EC:PC:DEC:PP:EP = 10:15:20:40:15. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. Additive compound 1 and compound 1-1 were then added. Based on the total weight of the non-aqueous electrolyte being 100%, the content of compound 1 was 2%, and the content of compound 1-1 was 5%.

[0076] 4) Cell fabrication:

[0077] A three-layer separator with a thickness of 20 μm is placed between the positive electrode and the negative electrode. Then, the sandwich structure composed of the positive electrode, the negative electrode and the separator is wound up. The wound body is then flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the battery cell to be injected with electrolyte.

[0078] 5) Electrolyte injection and formation of battery cells

[0079] In a glove box with the dew point controlled below -40°C, the electrolyte prepared above was injected into the battery cell, vacuum sealed, and left to stand for 24 hours. Then, the first charge was carried out at 80°C for hot-pressing formation according to the following steps: 0.1C constant current charging for 4 minutes, pressure 12.51 kg / cc; 0.3C constant current charging for 15 minutes, pressure 12.51 kg / cc; 1C constant current charging for 45 minutes, pressure 12.51 kg / cc; secondary vacuum sealing, and then further constant current charging at 0.2C to 4.5V, left to stand at room temperature for 24 hours, and then constant current discharging at 0.2C to 3.0V.

[0080] The Co content in the negative electrode material layer and the ratio of the total mass of the lithium-ion battery electrolyte to the discharge capacity were tested according to the aforementioned method in this embodiment. Specifically, the Co content in the negative electrode material layer was 50 ppm, and the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery was 1.3 g / Ah.

[0081] Examples 2-49 and Comparative Examples 1-28

[0082] This embodiment and comparative example are used to illustrate the lithium-ion battery disclosed in this invention. They include most of the operating steps in the above embodiment 1, but differ in the composition and content of additives in the non-aqueous electrolyte, the Co element content in the negative electrode material layer, and the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery, as shown in Table 1.

[0083] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to performance testing according to the following methods:

[0084] 1. High-temperature cycling performance test

[0085] The lithium-ion batteries prepared in each embodiment and comparative example were placed in an oven at a constant temperature of 45°C and charged at a constant current of 1C to 4.5V. Then they were charged at a constant voltage until the current dropped to 0.02C. Finally, they were discharged at a constant current of 1C to 3.0V. This cycle was repeated, and the discharge capacity, internal resistance, and thickness were recorded for the 1st and 500th cycles.

[0086] Calculate using the following formula:

[0087] Capacity retention rate (%) = Discharge capacity at the 500th discharge / Discharge capacity at the 1st discharge × 100%;

[0088] Internal resistance growth rate (%) = (internal resistance of the 500th iteration - internal resistance of the 1st iteration) / internal resistance of the 1st iteration × 100%;

[0089] Thickness growth rate (%) = (thickness of the 500th time - thickness of the 1st time) / thickness of the 1st time × 100%.

[0090] Test Results

[0091] Table 1 shows the test results of Examples 1-18 and Comparative Examples 1-28; the differences between Examples 2-18 and Comparative Examples 1-28 and Example 1 are the relevant parameters in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] As can be seen from the test results of Examples 1-18 and Comparative Examples 1-28, the lithium-ion battery of the present invention, using a first additive and a wetting-improving additive as non-aqueous electrolyte additives, and limiting the relationship between the mass percentage X of the first additive in the non-aqueous electrolyte, the mass percentage Y of the wetting-improving additive, the content Z of Co element in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery, satisfies the following conditions: 0.2≤(X+Z)×M / 10Y≤10, 0.1≤X≤3, 0.5≤Y≤5, 10≤Z≤200, 0.8≤M≤1.8. This can improve the wetting of the electrolyte on the electrode, increase the electrolyte retention, form a good SEI film on the negative electrode, significantly improve the high-temperature cycle performance of the battery, and extend the battery's service life.

[0096] As can be seen from the test results of Example 1 and Comparative Examples 1-28, when any one of the following parameters—the mass percentage X of the first additive in the non-aqueous electrolyte, the mass percentage Y of the wetting improvement additive, the Co content Z in the negative electrode material layer, or the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery—is outside the specified range, or when the value of (X+Z)×M / 10Y is too large or too small, it is impossible to guarantee that the lithium-ion battery has good high-temperature cycling performance. This indicates that the mass percentage X of the first additive in the non-aqueous electrolyte, the mass percentage Y of the wetting improvement additive, the Co content Z in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery are strongly correlated with improving the high-temperature cycling performance of lithium-ion batteries.

[0097] Table 2 shows the test results of Examples 1 and Examples 19-25; the difference between Examples 19-25 and Example 1 lies in the relevant parameters in Table 2.

[0098] Table 2

[0099]

[0100]

[0101] As can be seen from the test results in Table 2, when the mass percentage of the first additive X, the mass percentage of the wetting improvement additive Y, the content of Co element Z in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery meet the relevant requirements, the improvement effect on the high-temperature cycle performance of lithium-ion batteries is even better when the mass percentage of the first additive X and the mass percentage of the wetting improvement additive Y further meet 2≤X+Y≤6 and 0.5≤X / Y≤3.

[0102] Table 3 shows the test results of Examples 1 and Examples 26-34; the difference between Examples 26-34 and Example 1 lies in the relevant parameters in Table 3.

[0103] Table 3

[0104]

[0105] As can be seen from the test results in Table 3, when the mass percentage X of the first additive in the non-aqueous electrolyte, the mass percentage Y of the wetting improvement additive, the content Z of Co element in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery meet the relevant requirements, the addition of different types of first additives or wetting improvement additives can optimize the high-temperature cycle performance of lithium-ion batteries. This indicates that the battery system of the present invention has universality for different types of first additives and wetting improvement additives.

[0106] Table 4 shows the test results of Examples 1 and Examples 35-38; the difference between Examples 35-38 and Example 1 lies in the relevant parameters in Table 4.

[0107] Table 4

[0108]

[0109] As can be seen from the test results in Table 4, when the mass percentage X of the first additive in the non-aqueous electrolyte, the mass percentage Y of the wetting improvement additive, the Co content Z in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery meet the relevant requirements, the high-temperature cycle performance of lithium-ion batteries can be optimized for different types of cobalt-containing positive electrode active materials. This indicates that the battery system of the present invention has universality for different cobalt-containing positive electrodes.

[0110] Table 5 shows the test results of Examples 1 and Examples 39-49; the difference between Examples 39-49 and Example 1 lies in the relevant parameters in Table 5.

[0111] Table 5

[0112]

[0113] As can be seen from the test results in Table 5, when the mass percentage of the first additive X in the non-aqueous electrolyte, the mass percentage of the wetting-improving additive Y, the Co content Z in the negative electrode material layer, and the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery meet the relevant requirements, and further when the porosity ε of the negative electrode material layer and the relationship X / ε between the content of the first additive and the porosity satisfy 20≤ε≤40 and 0.01≤X / ε≤0.1, the high-temperature performance of the lithium-ion battery can be further improved and the impedance growth can be suppressed.

[0114] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that, This includes a positive electrode containing a positive electrode material layer, a negative electrode containing a negative electrode material layer, and a non-aqueous electrolyte; The negative electrode material layer contains Co element; The non-aqueous electrolyte includes lithium salts, organic solvents, and additives; The additives include a first additive and a wetting-improving additive; The first additive includes at least one of the following compounds: The wetting improver includes the compound shown in structural formula 1 and / or the compound shown in structural formula 2: In structural formula 1, R 11 ~R 16 Each is independently selected from H, F, C1-C5 hydrocarbon groups or C1-C5 fluorinated hydrocarbon groups, and R 11 ~R 16 At least one of them contains a fluorine atom; In structural formula 2, 1≤a≤5, 1≤b≤5, x≥1; The lithium-ion battery meets the following conditions: 0.2≤(X+Z)×M / 10Y≤10, 0.1≤X≤3, 0.5≤Y≤5, 10≤Z≤200, 0.8≤M≤1.8; Where X is the mass percentage of the first additive in the non-aqueous electrolyte, in %; Y represents the mass percentage of wetting improver additives in the non-aqueous electrolyte, in %; Z represents the Co content in the negative electrode material layer, expressed in ppm. M is the ratio of the total mass of the non-aqueous electrolyte to the battery's discharge capacity, expressed in g / Ah.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery satisfies 0.5≤(X+Z)×M / 10Y≤5.

3. The lithium-ion battery according to claim 1, characterized in that, The mass percentage (X%) of the first additive in the non-aqueous electrolyte is 0.5% to 2%; and / or, The mass percentage (Y%) of the wetting improver additive in the non-aqueous electrolyte is 2-4%; and / or, The Co content Z in the negative electrode material layer is 20–100 ppm; and / or, The ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery is 0.9 to 1.4 g / Ah.

4. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery satisfies: 2≤X+Y≤6, 0.5≤X / Y≤3.

5. The lithium-ion battery according to claim 1, characterized in that, The compound represented by structural formula 1 includes one or more of the following compounds:

6. The lithium-ion battery according to claim 1, characterized in that, The compound represented by structural formula 2 includes one or more of the following compounds:

7. The lithium-ion battery according to claim 1, characterized in that, The additive further includes auxiliary additives, which include at least one selected from cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and nitrile compounds; and / or, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additives is 0.01% to 10%; and / or, The cyclic sulfate compounds include at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sulfonyl lactone compounds include at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone; and / or, The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 3: In the structural formula 3 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, C1-C5 group; and / or, The phosphate ester compounds include at least one of the compounds shown in structural formula 4 below: In structural formula 4, R 31 R 32 R 33 Each independent group is selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; and / or, The nitrile compounds include at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitol.

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes LiNi x Co y Mn z L (1-x-y-z) O2, LiCo x’ L (1-x’) O2, LiNi x” L’ y’ Mn (2-x”-y’) O4, Li z’ MPO4, where L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, or Fe, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < x + y + z ≤ 1, 0 < x’ ≤ 1, 0.3 ≤ x” ≤ 0.6, 0.01 ≤ y’ ≤ 0.2, L’ is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 0.5 ≤ z’ ≤ 1, and M is at least one of Fe, Mn, Co.

9. The lithium-ion battery according to claim 1, characterized in that, The negative electrode material layer includes a negative electrode active material, which includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, mesophase micro carbon spheres, silicon, silicon oxide, silicon-carbon composite, or metallic lithium.

10. The lithium-ion battery according to claim 1, characterized in that, The porosity ε% of the negative electrode material layer satisfies: 20≤ε≤40.

Images