Lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery with excellent high-temperature cycle performance. The lithium ion battery comprises 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 comprises a lithium salt, an organic solvent and an additive; the additives comprise a first additive and an infiltration improving additive; the infiltration improving additive comprises a compound as shown in a structural formula 1 and / or a compound as shown in a 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 provided by the invention can improve the infiltration of the electrolyte in the pole piece, improve the retention of the electrolyte, form a good SEI film on the negative electrode, significantly improve the high-temperature cycle performance of the battery and prolong the service life of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery with improved high-temperature cycle performance. Background Art

[0002] Due to its characteristics such as high working voltage, high safety, long life, and no memory effect, lithium-ion batteries have achieved great development in the field of portable electronic products. As the starting point for the development of lithium-ion batteries, consumer electronics has experienced more than 30 years of development and has been widely used in the market. Among them, cobalt-containing cathodes are the most commonly used cathodes for consumer batteries. To meet people's increasingly high requirements for the service life of mobile devices, the cycle life of batteries has been increased from the initial 400 cycles to the current 700 cycles. However, after matching with high voltage, the cycle life often decreases significantly. This is because the SEI film is damaged in the later stage of cycling, and after the electrolyte dries up, a large area of side reactions is triggered, resulting in a rapid decline in battery performance. Therefore, developing a lithium-ion battery that can significantly improve high-temperature cycle performance is of great significance. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a lithium-ion battery with excellent high-temperature cycle performance.

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

[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 a lithium salt, an organic solvent, and an additive;

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

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

[0010]

[0011] The wetting-improving additive 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 are each independently selected from H, F, a C1-C5 hydrocarbon group, or a C1-C5 fluorinated hydrocarbon group, and R 11 ~R 16At least one of them contains fluorine atoms;

[0014] In Structural Formula 2, 1 ≤ a ≤ 5, 1 ≤ b ≤ 5, x ≥ 1;

[0015] The lithium-ion battery satisfies 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] Among them, X is the mass percentage content of the first additive in the non-aqueous electrolyte, with the unit of %;

[0018] Y is the mass percentage content of the wetting-improving additive in the non-aqueous electrolyte, with the unit of %;

[0019] Z is the content of Co element in the negative electrode material layer, with the unit of ppm;

[0020] M is the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery, with the unit of g / Ah.

[0021] The lithium-ion battery of the present invention uses a first additive with a specific structure and a wetting-improving additive as non-aqueous electrolyte additives. During the first charge and cycling process of the battery, although the first additive can form a porous and stable SEI film on the negative electrode surface to improve the kinetic performance of the battery, the inventors 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 content X of the first additive in the non-aqueous electrolyte, and the mass percentage content Y of the wetting-improving additive in the non-aqueous electrolyte. Through a large number of studies, the inventors found that when the above parameters satisfy the following formula: 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 cycling performance of the battery can be significantly improved and the service life of the battery can be extended. It is speculated that because: the wetting-improving additive is a substance with fluorine substituents, which can reduce the surface tension of the electrolyte on the electrode surface, improve the wetting of the electrolyte in the positive and negative electrode plates, improve the retention of the electrolyte in the unit battery capacity (i.e., the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery), and at the same time, the first additive forms a cross-linked SEI film of organic salt + inorganic salt + inorganic metal with the Co element in the negative electrode. Such an SEI film is dense, has good toughness, and good thermal stability, which can significantly improve the high-temperature cycling performance of the battery and extend the service life of the battery; the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery largely determines the number of molecules of the first additive retained in the battery, while the content of the Co element in the negative electrode material layer largely affects the number of molecules required for the first additive to form the SEI film. When the relationship between them satisfies the above relationship, the number of molecules of the first additive in the battery can just form a complete SEI film without excess. Therefore, the battery has excellent high-temperature cycling performance and extends the service life of the battery.

[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 interface film on both the positive and negative electrodes, improving the stability of the film, and thus enhancing the high-temperature performance of the battery. If the value of X is too high, the battery impedance will be too large, and the charge-discharge polarization and heat generation of the battery will increase significantly, causing a series of negative effects such as impedance growth and ultimately deteriorating the electrochemical performance of the battery; if the value of X is too low, it is difficult to improve the high-temperature performance of the battery. Specifically, in some embodiments of the present invention, the mass percentage content 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 the range composed of any two of these values; preferably, the mass percentage content X of the first additive in the non-aqueous electrolyte is 0.5-2%.

[0024] The deposition of Co element in the negative electrode material is often considered to have a negative impact. However, through a large number of studies, the inventors found that a small amount of Co element participating in the formation of the negative electrode SEI film can improve the film formation quality and enhance the cycle stability; through synergistic action with the first additive, a cross-linked SEI film of organic salt + inorganic salt + inorganic metal is formed on the negative electrode quickly, improving the cycle performance of the battery. If the value of Z is too large, too much Co element is deposited on the negative electrode, resulting in the thickening of the negative electrode film and poor toughness, deteriorating the cycle performance of the battery; if the value of Z is too small, the synergistic effect with the first additive is not good, and the improvement effect on the film quality is limited. 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 the range composed of any two of these values; preferably, the content Z of Co element in the negative electrode material layer is 20-100ppm.

[0025] The wetting improvement additive is a substance containing F substituents, which can reduce the surface tension of the electrolyte on the electrode surface, improve the wetting of the electrolyte in the positive and negative electrode sheets, and improve the retention of the electrolyte in the unit battery capacity. By using the wetting improvement additive, the wetting of the electrolyte on the negative electrode surface is improved, which can better assist the first additive and Co element to form a film quickly on the negative electrode. At the same time, as the electrolyte is gradually consumed with the increase of the number of cycles, if the electrolyte is consumed and exhausted, the battery cycle will drop rapidly. The wetting improvement additive increases the ratio of the total mass of the lithium-ion battery electrolyte to the discharge capacity, and the consumable electrolyte in the battery increases, further delaying the battery cycle drop. When the value of Y is too large, a series of negative effects will occur, such as a significant increase in film impedance; when the value of Y is too small, the improvement effect on the wetting of the electrolyte is limited. Specifically, in some embodiments of the present invention, the mass percentage Y% of the wetting improvement additive 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 the range composed of any two of these values; preferably, the mass percentage Y% of the wetting improvement additive in the non-aqueous electrolyte is 2-4%.

[0026] The ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery reflects the retention of the electrolyte in the unit battery capacity. Since the electrolyte is continuously consumed with the increase of the number of cycles, by controlling the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery, the battery cycle drop is delayed and the battery cycle performance is improved. Specifically, in some embodiments of the present invention, the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery 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 the range composed of any two of these values; preferably, the ratio M of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery 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 grading - the mass of the battery before injecting the liquid, or the total mass of the non-aqueous electrolyte in the lithium-ion battery = the total amount of the liquid extruded after the graded battery core is centrifuged at a speed of 8000 r / min for 20 minutes; the discharge capacity of the battery is the discharge capacity when the battery is charged at a current of 0.2C and then discharged at a constant current of 0.2C to 3.0V at 25°C.

[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 surface of the negative electrode, and can better assist the first additive and Co element to form a film quickly on the negative electrode, significantly improving the high-temperature cycling performance of the battery.

[0029] Specifically, in some embodiments of the present invention, the compound shown in Structural Formula 1 includes one or more of the following compounds:

[0030]

[0031] Specifically, in some embodiments of the present invention, the compound shown in Structural Formula 2 includes one or more of the following compounds:

[0032]

[0033] Compound 2-4.

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

[0035] Discharge the battery at 0.5C to 3.0V, disassemble it, take out the negative electrode sheet, and perform nitrolysis at room temperature using a nitric acid aqueous solution with nitric acid: pure water = 2:1. The corresponding relationship between the amount of nitric acid aqueous solution used and the cell capacity is 35 mL / 1 Ah, that is, a 1 Ah rated capacity cell uses 35 mL of nitric acid aqueous solution for nitrolysis of the negative electrode sheet, and a 2 Ah rated capacity cell uses 70 mL of nitric acid aqueous solution for nitrolysis of the negative electrode sheet. The digestion treatment duration is at least 24 h or more; then take the sample solution m 1 g and dilute it with pure water to m 2 g (for example, 1 g of the sample solution can be taken and diluted to 25 g with pure water); finally, use an inductively coupled plasma spectrometer (ICP) to test the blank solution and the diluted sample solution using the standard curve method. The concentration of the blank solution is measured as C 1 μg / mL, and the concentration of the sample solution is measured as C 2 μg / mL. The calculation result of the content Z of Co element is: Z = (C 2 - C 1 ) × m 2 / m 1 .

[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), LiPO 2 F 2 、LiBF4 , LiBOB, LiSbF 6 , LiAsF 6 , LiCF 3 SO 3 , LiDFOB, LiDFOP, LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiN(SO 2 C 2 F 5 ) 2 , LiCl, LiBr, LiI, LiClO 4 , LiB 10 Cl 10 , LiAlCl 4 , at least one of lithium chloroborane, lithium lower aliphatic carboxylate having 4 or less 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 ester solvents, or ether solvents.

[0038] In some preferred embodiments, the cyclic carbonate solvents include at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, and butylene carbonate.

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

[0040] In some preferred embodiments, the carboxylic ester solvents include 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 an auxiliary additive, and the auxiliary additive includes at least one of cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, phosphate compounds, and nitrile compounds.

[0042] In some preferred embodiments, the cyclic sulfate compounds include at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate.

[0043] In some preferred embodiments, the sultone compounds include at least one of 1,3 - propane sultone, 1,4 - butane sultone, and allyl - 1,3 - sultone.

[0044] In some preferred embodiments, the cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in the following Structural Formula 3:

[0045]

[0046] In Structural Formula 3 shown, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 each independently selected from a hydrogen atom, a halogen atom, and a C1 - C5 group;

[0047] In some preferred embodiments, the compound shown in Structural Formula 3 includes at least one of the compounds shown in Compounds 3 - 1 to 3 - 6 below:

[0048]

[0049] In some preferred embodiments, the phosphate compounds include at least one of the compounds shown in the following Structural Formula 4:

[0050]

[0051] In Structural Formula 4, R 31 , R 32 , R 33 each independently selected from a C1 - C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 ) 3, where m is a natural number from 1 to 3; more preferably, the compound shown in Structural Formula 4 includes at least one of tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tripropargyl phosphate, dipropargylmethyl phosphate, dipropargylethyl phosphate, dipropargylpropyl phosphate, dipropargyl(trifluoromethyl) phosphate, dipropargyl(2,2,2-trifluoroethyl) phosphate, dipropargyl(3,3,3-trifluoropropyl) phosphate, dipropargyl(hexafluoroisopropyl) phosphate, triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyl(trifluoromethyl) phosphate, diallyl(2,2,2-trifluoroethyl) phosphate, diallyl(3,3,3-trifluoropropyl) phosphate, diallyl(hexafluoroisopropyl) phosphate.

[0052] In some preferred embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

[0053] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% - 10%. Preferably, the content is 0.1% - 5%; more preferably, the content is 0.1% - 2%. Specifically, the content of any 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%, 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) O 2 、LiCo x’ L (1-x’) O 2 、LiNi x” L’ y’ Mn (2-x”-y’) O 4 、Li z’ MPO 4at least one of them, 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) O 2 、LiCo x’ L (1-x’) O 2 、LiNi x” Co y’ Mn (2-x”-y’) O 4 、LiCoPO 4 at least one of them, 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 LiCoO 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.7 Co 0.1 Mn 0.2 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.9 Co 0.05 Mn 0.05 O 2 、LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O 2 、LiNi 0.5 Co 0.2Al 0.3 O 2 、LiCoPO 4 One or more of the above.

[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 thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - 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 fibers, 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 metal 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 materials are selected from one or more of silicon materials, silicon oxide materials, silicon - carbon materials, and silicon alloy materials; preferably, the silicon material is a nanosilicon material; preferably, the silicon oxide material is a SiOx material, where 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, where 0 ≤ y < 2; preferably, the silicon alloy material is Mg 2 Si alloy material and / or Fe 2 Si alloy material. The carbon materials are 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 oxides, silicon - carbon composites, or metallic lithium.

[0060] In some embodiments, the porosity ε% of the negative electrode material layer satisfies 20 ≤ ε ≤ 40, such as 20 ≤ ε ≤ 30, 20 ≤ ε ≤ 40, 25 ≤ ε ≤ 35, 20 ≤ ε ≤ 25, 30 ≤ ε ≤ 40, etc. Thus, by controlling the porosity of the negative electrode material layer of the present application within the above range, on the one hand, the negative electrode material layer with such porosity can increase the contact area between the negative electrode active material and the electrolyte, which is beneficial to the transmission of lithium ions, thereby improving the battery performance; on the other hand, the negative electrode material layer with such porosity can slow down the continuous growth of the uneven interface film, thereby slowing down the increase in impedance during the cycling process.

[0061] In some preferred embodiments, the porosity ε% of the negative electrode material layer and the mass percentage content 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 surface of the negative electrode, thereby reducing the increase in impedance during the cycling process.

[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, which will not be elaborated 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 may be the same as the positive electrode binder and the positive electrode conductive agent respectively, which will not be elaborated here.

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

[0065] The separator can be a conventional existing separator, which can be a ceramic separator, a polymer separator, a non-woven fabric, an inorganic-organic composite separator, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and three-layer PP / PE / PP separators.

[0066] For the lithium-ion battery of the present invention, a first additive with a specific structure and a wetting-improving additive are used as non-aqueous electrolyte additives, and the relationships among the mass percentage content X of the first additive, the mass percentage content 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 in the non-aqueous electrolyte satisfy 0.2 ≤ (X + Z) × M / 10Y ≤ 10, 0.1 ≤ X ≤ 3, 0.5 ≤ Y ≤ 5, 10 ≤ Z ≤ 200, and 0.8 ≤ M ≤ 1.8. In this case, the wetting of the electrolyte on the electrode sheet can be improved, the electrolyte retention can be increased, a good SEI film can be formed on the negative electrode, the high-temperature cycling performance of the battery can be significantly improved, and the service life of the battery can be extended. Detailed implementation manners

[0067] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts belong to the protection scope of the present invention.

[0068] Embodiment 1

[0069] In this embodiment, the preparation method of the lithium-ion battery includes the following steps:

[0070] 1) Preparation of the positive electrode sheet:

[0071] Mix the positive electrode active material lithium nickel cobalt manganese oxide LiNi 0.5 Co 0.2 Mn 0.3 O 2 , conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 93:4:3, and then disperse them in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. Coat the slurry evenly on both sides of the aluminum foil to form a positive electrode material layer, and after drying, rolling, and vacuum drying, weld an aluminum lead wire with an ultrasonic welder to obtain the positive electrode sheet.

[0072] 2) Preparation of the negative electrode sheet:

[0073] Mix the negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) in a mass ratio of 94:1.0:2.5:2.5, and then disperse them in deionized water to obtain a negative electrode slurry. Coat the slurry on both sides of the copper foil to form a negative electrode material layer, and after drying, rolling, and vacuum drying, control the porosity of the negative electrode material layer to be 28% by rolling, and weld a nickel lead wire with an ultrasonic welder to obtain the negative electrode sheet.

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

[0075] Mix ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP) and ethyl propionate (EP) in a mass ratio of EC:PC:DEC:PP:EP = 10:15:20:40:15, and then add lithium hexafluorophosphate (LiPF 6 ) to a molar concentration of 1 mol / L, and then add additive compound 1 and compound 1-1. Based on the total weight of the non-aqueous electrolyte being 100%, the content of compound 1 is 2% and the content of compound 1-1 is 5%.

[0076] 4) Preparation of battery cells:

[0077] Place a three-layer separator with a thickness of 20 μm between the positive electrode sheet and the negative electrode sheet, then wind the sandwich structure composed of the positive electrode sheet, the negative electrode sheet and the separator, and then flatten the wound body and put it into an aluminum foil packaging bag, and bake it in vacuum at 75 °C for 48 h to obtain a battery cell to be filled with electrolyte.

[0078] 5) Filling electrolyte and formation of battery cells

[0079] In a glove box with the dew point controlled below -40 °C, inject the electrolyte prepared above into the battery cell, perform vacuum packaging, and let it stand for 24 h. Then perform hot pressing formation at 80 °C for the first charge according to the following steps: constant current charging at 0.1C for 4 min, pressure 12.51 kg / cc; constant current charging at 0.3C for 15 min, pressure 12.51 kg / cc; constant current charging at 1C for 45 min, pressure 12.51 kg / cc; perform secondary vacuum sealing, and then further charge at a constant current of 0.2C until 4.5V, let it stand at room temperature for 24 hr, and then discharge at a constant current of 0.2C until 3.0V.

[0080] Test the content of Co element in the negative electrode material layer and the ratio of the total mass of the lithium ion battery electrolyte to the discharge capacity in this example according to the foregoing method. Specifically, the content of Co element in the negative electrode material layer is 50 ppm, and the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery is 1.3 g / Ah.

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

[0082] This example and the comparative examples are used to comparatively illustrate the lithium ion battery disclosed in the present invention, including most of the operation steps in the above Example 1. The differences are: the composition and content of additives in the non-aqueous electrolyte, the content of Co element 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 specifically.

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

[0084] 1. High-temperature cycle performance test

[0085] The lithium-ion batteries prepared in each example and comparative example were placed in an oven at a constant temperature of 45 °C, charged at a constant current of 1C to 4.5V, then charged at a constant voltage until the current dropped to 0.02C, and then discharged at a constant current of 1C to 3.0V. Such cycles were carried out, and the discharge capacity, internal resistance, and thickness at the 1st and 500th times were recorded.

[0086] Calculated according to the following formula:

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

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

[0089] Thickness growth rate (%) = (Thickness at the 500th time - Thickness at the 1st time) / Thickness at 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 lie in the relevant parameters in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] From the test results of Examples 1-18 and Comparative Examples 1-28, it can be seen that for the lithium-ion batteries of the present invention, using the first additive and the wetting-improving additive as non-aqueous electrolyte additives, and defining the relationship between the mass percentage content X of the first additive, the mass percentage content 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 0.2 ≤ (X + Z) × M / 10Y ≤ 10, 0.1 ≤ X ≤ 3, 0.5 ≤ Y ≤ 5, 10 ≤ Z ≤ 200, 0.8 ≤ M ≤ 1.8, it can improve the wetting of the electrolyte on the electrode sheet, increase the electrolyte retention amount, form a good SEI film on the negative electrode, significantly improve the high-temperature cycle performance of the battery, and extend the service life of the battery.

[0096] As can be seen from the test results of Example 1 and Comparative Examples 1-28, when any one of the parameters of the mass percentage content X of the first additive in the non-aqueous electrolyte, the mass percentage content 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 does not meet the range, or the value of (X + Z)×M / 10Y is too large or too small, it is impossible to ensure that the lithium-ion battery has good high-temperature cycling. This shows that the mass percentage content X of the first additive in the non-aqueous electrolyte, the mass percentage content 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 are strongly correlated in improving the high-temperature cycling performance of the lithium-ion battery.

[0097] Table 2 shows the test results of Example 1 and Examples 19-25; the differences between Examples 19-25 and Example 1 lie 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 content X of the first additive in the non-aqueous electrolyte, the mass percentage content 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 meet the relevant requirements, and when the mass percentage content X of the first additive and the mass percentage content Y of the wetting-improving additive further satisfy 2 ≤ X + Y ≤ 6 and 0.5 ≤ X / Y ≤ 3, the improvement effect on the high-temperature cycling performance of the lithium-ion battery is better.

[0102] Table 3 shows the test results of Example 1 and Examples 26-34; the differences between Examples 26-34 and Example 1 lie 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 content X of the first additive in the non-aqueous electrolyte, the mass percentage content 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 meet the relevant requirements, adding different types of the first additive or wetting-improving additive can optimize the high-temperature cycling performance of the lithium-ion battery, indicating that the battery system of the present invention has universality for different types of the first additive and wetting-improving additive.

[0106] Table 4 shows the test results of Example 1 and Examples 35-38; the differences between Examples 35-38 and Example 1 lie 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 content X of the first additive in the non-aqueous electrolyte, the mass percentage content 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 meet the relevant requirements, for different types of cobalt-containing positive electrode active materials, the high-temperature cycling performance of the lithium-ion battery can be optimized, indicating that the battery system of the present invention has universality for different cobalt-containing positive electrodes.

[0110] Table 5 shows the test results of Example 1 and Examples 39-49; the differences between Examples 39-49 and Example 1 lie 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 content X of the first additive in the non-aqueous electrolyte, the mass percentage content 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 meet the relevant requirements, and further when the porosity ε of the negative electrode material layer and the relationship X / ε between the first additive content 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 inhibited.

[0114] The above further describes the present invention with the aid of specific embodiments. However, it should be understood that this specific description should not be construed as a limitation on the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A lithium ion battery, characterized in that: comprising a positive electrode including a positive electrode material layer, a negative electrode including a negative electrode material layer, and a non-aqueous electrolyte; The negative electrode material layer contains Co element; The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive; The additives include a first additive and an additive for improving wetting; The first additive comprises at least one of the following compounds: The wettability improving additive comprises a compound shown in Structural Formula 1 and / or a compound shown in Structural Formula 2: In structural formula 1, R 11 ~R 16 Each is independently selected from H, F, a C1-C5 hydrocarbon group or a C1-C5 fluorinated hydrocarbon group, 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; Wherein, X is the mass percentage of the first additive in the non-aqueous electrolyte, in %; Y is the mass percentage of the wetting-improving additive in the non-aqueous electrolyte, in %; Z is the content of Co element in the negative electrode material layer, in ppm; M is the ratio of the total mass of the non-aqueous electrolyte to the discharge capacity of the battery, 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 0.5-2%; and / or, The mass percentage Y% of the wettability improving additive in the non-aqueous electrolyte is 2-4%; and / or, The content Z of the Co element in the negative electrode material layer is 20 to 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 the 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 the 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 an auxiliary additive, and the auxiliary additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound and a nitrile compound; and / or, Based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% to 10%; and / or, The cyclic sulfate ester compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and propenyl-1,3-sultone; and / or, The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound shown in the following 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 a hydrogen atom, a halogen atom, a C1-C5 group; and / or, The phosphate compound includes at least one of the compounds shown in the following structural formula 4: In the structural formula 4, R 31 , R 32 , R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3; and / or, The nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile.

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, and the negative electrode active material includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, mesophase micro carbon beads, silicon, silicon-oxygen compounds, silicon-carbon composites 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.

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