A lithium ion battery

Abstract

In order to overcome the problem that manganese dissolution affects battery performance in existing lithium ion batteries containing manganese positive electrodes, the present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and a diaphragm, wherein the diaphragm is located between the positive electrode and the negative electrode, the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a lithium manganese-based positive electrode active material, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the additive comprises a compound shown in structural formula 1: the lithium ion battery satisfies the following conditions: 0.1≤q*m / p≤20 and 20≤q≤60, 0.01≤m≤2, 1.5≤p≤5; the lithium ion battery provided by the present invention can significantly reduce Mn 2+ The ion exchange effect with the lithium in the negative electrode inhibits the damage of manganese to the negative electrode and improves the stability of the negative electrode, thereby improving the safety performance of the lithium-ion battery while ensuring the high energy density and cycle performance of the lithium-ion battery.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage electronic components, and in particular relates to a lithium ion battery. Background Art

[0002] Lithium-ion batteries (LIBs) have dominated the portable electronic devices and electric vehicle markets due to their advantages such as high operating voltage, low self-discharge, long cycle life, no memory effect, environmental friendliness and good safety performance. Lithium-ion batteries are usually composed of four main materials: positive electrode, negative electrode, separator and electrolyte, and each part directly affects the performance of lithium-ion batteries.

[0003] By using positive electrode active materials containing manganese, the safety performance of lithium-ion batteries can be improved. However, since manganese in the positive electrode is prone to disproportionation reaction, the generated manganese ions dissolve in the electrolyte and migrate to the negative electrode, undergo ion exchange with the lithium in the negative electrode, occupy the lithium insertion position of the negative electrode, and are not easy to be removed, resulting in a decrease in the negative electrode's lithium storage capacity. In addition, the lithium ions removed by ion exchange will no longer be able to participate in the deintercalation between the positive and negative electrodes, thereby causing capacity loss and deteriorating the cycle performance and storage performance of the lithium-ion battery. The impact is more serious at high temperatures (above 40°C).

[0004] Therefore, how to inhibit the dissolution of manganese in the positive electrode material and prevent the dissolved manganese from entering the negative electrode is particularly important for improving the cycle performance and storage performance of manganese-containing lithium-ion batteries. Summary of the invention

[0005] Aiming at the problem that manganese dissolution in existing manganese-containing lithium ion batteries affects battery performance, the present invention provides a lithium ion battery.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0007] The present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator, wherein the separator is located between the positive electrode and the negative electrode, the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a lithium manganese-based positive electrode active material, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, and the additive comprises a compound shown in structural formula 1:

[0008]

[0009] Structural formula 1

[0010] Where n is 0 or 1, and X is selected from or , R1, R2 are each independently selected from H, C1-C5 hydrocarbon group, , or , and X, R1 and R2 contain at least one sulfur atom;

[0011] The lithium-ion battery meets the following conditions:

[0012] 0.1≤q*m / p≤20

[0013] And 20≤q≤60, 0.01≤m≤2, 1.5≤p≤5;

[0014] Wherein, q is the porosity of the diaphragm, unit is %;

[0015] m is the weight percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in units of %;

[0016] p is the capacitance per unit area of ​​the positive electrode material layer, in mAh / cm 2 .

[0017] Optionally, the lithium-ion battery meets the following conditions:

[0018] 1≤q*m / p≤10.

[0019] Optionally, the porosity q of the diaphragm is 30%~50%.

[0020] Optionally, the weight percentage m of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.1% to 1%.

[0021] Optionally, the capacitance per unit area of ​​the positive electrode material layer is 2-4 mAh / cm 2 .

[0022] Optionally, the compound represented by structural formula 1 is selected from one or more of the following compounds:

[0023]

[0024]

[0025] Optionally, the lithium manganese-based positive electrode active material includes one or more compounds represented by formula (A), formula (B) and formula (C):

[0026] Li 1+x Mn a Ni b M 1-a-b O 2-y A y Formula (A)

[0027] Li 1+z Mn c N 2-c O 4-d B dFormula (B)

[0028] LiMn q Fe 1-q PO4 Formula (C)

[0029] Among them, in Formula (A), -0.1 ≤ x ≤ 0.2, 0 < a < 1, 0 ≤ b < 1, 0 < a + b < 1, 0 ≤ y < 0.2, M is one or more of Co, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce; A includes one or more of S, N, F, Cl, Br, and I;

[0030] In Formula (B), -0.1 ≤ z ≤ 0.2, 0 < c ≤ 2, 0 ≤ d < 1, N includes one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr, and Ce; B includes one or more of S, N, F, Cl, Br, and P;

[0031] In Formula (C), 0 < q < 1.

[0032] Optionally, at least one side surface of the separator is coated with a surface coating, and the surface coating includes one or more of inorganic particles and organic gels.

[0033] Optionally, the content of manganese element in the separator per unit area is 50 ppm / m 2 ~2000 ppm / m 2 .

[0034] Optionally, the additive further includes at least one of cyclic carbonate compounds, unsaturated phosphate compounds, borate compounds, and nitrile compounds;

[0035] Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the content of the additive is 0.01% - 30%;

[0036] Preferably, the cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene vinylene carbonate, fluorinated ethylene carbonate, or the compound shown in Structural Formula 2,

[0037]

[0038] Structural Formula 2

[0039] In the Structural Formula 2, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group;

[0040] The unsaturated phosphate compound is selected from at least one of the compounds shown in Structural Formula 3:

[0041] Structural formula 3

[0042] In the structural formula 3, 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 R 31 , R 32 , R 33 At least one of them is an unsaturated hydrocarbon group;

[0043] The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0044] The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0045] According to the lithium-ion battery provided by the present invention, a lithium-manganese-based positive electrode active material is used in the positive electrode material layer. The lithium-manganese-based positive electrode active material has good structural stability, can withstand more severe impact force, and reduce the thermal runaway problem caused by material structure damage. In addition, the oxidation effect of the electrolyte on the surface of the lithium-manganese-based positive electrode active material is lower, which can reduce the side reaction of the electrolyte on the surface of the positive electrode active material, inhibit gas production, and reduce heat production, thereby effectively improving the safety performance of the lithium-ion battery; in order to avoid the problem of manganese ion dissolution, the diaphragm selection is screened, and at the same time, in non The compound represented by structural formula 1 is added to the aqueous electrolyte. The inventors have found through extensive research that when the porosity q of the diaphragm, the weight percentage content m of the compound represented by structural formula 1 in the non-aqueous electrolyte and the capacitance p per unit area of ​​the positive electrode material layer meet the condition 0.1≤q*m / p≤20, the synergistic effect between the diaphragm, the compound represented by structural formula 1 in the non-aqueous electrolyte and the lithium manganese-based positive electrode active material and the capacitance of the positive electrode material layer can be fully exerted, so that a dense interface film with more optimized structure and composition and more stable can be generated at the positive electrode interface, thereby inhibiting the Mn 2+ The flow channel between the positive and negative electrodes significantly reduces the Mn 2+ The ion exchange effect with the lithium in the negative electrode inhibits the damage of manganese to the negative electrode and improves the stability of the negative electrode, thereby improving the safety performance of the lithium-ion battery while ensuring the high energy density and cycle performance of the lithium-ion battery. DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] An embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator, wherein the separator is located between the positive electrode and the negative electrode, the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a lithium manganese-based positive electrode active material, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, and the additive comprises a compound shown in structural formula 1:

[0048]

[0049] Structural formula 1

[0050] Where n is 0 or 1, and X is selected from or , R1, R2 are each independently selected from H, C1-C5 hydrocarbon group, , or , and X, R1 and R2 contain at least one sulfur atom;

[0051] The lithium-ion battery meets the following conditions:

[0052] 0.1≤q*m / p≤20

[0053] And 20≤q≤60, 0.01≤m≤2, 1.5≤p≤5;

[0054] Wherein, q is the porosity of the diaphragm, unit is %;

[0055] m is the weight percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in units of %;

[0056] p is the capacitance per unit area of ​​the positive electrode material layer, in mAh / cm 2 .

[0057] The lithium-ion battery adopts a lithium-manganese-based positive electrode active material in the positive electrode material layer. The lithium-manganese-based positive electrode active material has good structural stability, can withstand relatively severe impact force, and reduces the thermal runaway problem caused by material structure damage. In addition, the oxidation effect of the electrolyte on the surface of the lithium-manganese-based positive electrode active material is lower, which can reduce the side reaction of the electrolyte on the surface of the positive electrode active material, inhibit gas production, and reduce heat production, thereby effectively improving the safety performance of the lithium-ion battery; in order to avoid the problem of manganese ion dissolution, the diaphragm selection is screened, and the compound shown in structural formula 1 is added to the non-aqueous electrolyte. The inventor has found through a large number of studies that when the porosity q of the diaphragm, the weight percentage content m of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the capacitance p per unit area of ​​the positive electrode material layer meet the condition 0.1≤q*m / p≤20, the synergistic effect between the diaphragm, the compound shown in structural formula 1 in the non-aqueous electrolyte, the lithium-manganese-based positive electrode active material, and the capacitance of the positive electrode material layer can be fully utilized, so that a dense interface film with a more optimized structure and composition and a more stable structure can be generated at the positive electrode interface, and Mn 2+ The flow channel between the positive and negative electrodes significantly reduces the Mn 2+ The ion exchange effect with the lithium in the negative electrode inhibits the damage of manganese to the negative electrode and improves the stability of the negative electrode, thereby improving the safety performance of the lithium-ion battery while ensuring the high energy density and cycle performance of the lithium-ion battery.

[0058] In the description of the present invention, the C1-C5 hydrocarbon group includes but is not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, vinyl, propenyl, allyl, 2-butenyl, 1-butenyl, ethynyl, propynyl, propargyl, 2-butynyl or 1-butynyl.

[0059] In some embodiments, when n is 0, the compound represented by structural formula 1 is:

[0060] ;

[0061] Among them, X is selected from or , R1, R2 are each independently selected from H, C1-C5 hydrocarbon group, , or , and X, R1 and R2 contain at least one sulfur atom.

[0062] In some embodiments, when n is 1, the compound represented by structural formula 1 is:

[0063] or ;

[0064] Among them, X is selected from or , R1, R2 are each independently selected from H, C1-C5 hydrocarbon group, , or , and X, R1 and R2 contain at least one sulfur atom.

[0065] In a preferred embodiment, the lithium-ion battery meets the following conditions:

[0066] 1≤q*m / p≤10.

[0067] By correlating the porosity q of the diaphragm, the weight percentage m of the compound represented by structural formula 1 in the non-aqueous electrolyte and the capacitance p per unit area of ​​the positive electrode material layer, it is possible to comprehensively consider the effects of the diaphragm, non-aqueous electrolyte and positive electrode on the dissolution of manganese ions in the battery and the embedding of manganese ions in the negative electrode to a certain extent, thereby obtaining a lithium-ion battery with high energy density and excellent high-temperature cycle performance.

[0068] In a specific embodiment, the porosity q of the diaphragm may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%.

[0069] In a preferred embodiment, the porosity q of the diaphragm is 30% to 50%.

[0070] The diaphragm serves as a barrier material between the positive electrode and the negative electrode, which can avoid direct contact and short circuit between the positive electrode and the negative electrode but allow lithium ions to pass through. At the same time, the micropores on the diaphragm are also the flow channels for manganese ions to enter the negative electrode. By controlling the porosity q of the diaphragm to be within the above range, it is beneficial to suppress the mobility of manganese ions between the positive electrode and the negative electrode; if the porosity of the diaphragm is too small, it will affect the efficiency of lithium ions shuttling between the positive and negative electrodes, reduce the kinetic performance of the lithium-ion battery and increase the battery impedance; if the porosity of the diaphragm is too large, the diaphragm cannot effectively prevent the manganese ions dissolved in the positive electrode active material from entering the negative electrode active material, which will significantly increase the ion exchange between manganese ions and lithium in the negative electrode, and cannot effectively suppress the damage of manganese elements to the negative electrode. In severe cases, the positive and negative electrodes will be in direct contact or easily pierced by lithium dendrites, causing a short circuit.

[0071] The porosity q of the diaphragm can be tested and obtained by the following method:

[0072] The porosity is the ratio of the volume of the pores to the volume of the membrane. d ) After soaking in n-butanol for a certain period of time (such as 2 hours), take it out, gently absorb the liquid on its surface with filter paper, and then weigh it (W w ), the mass W of n-butanol absorbed in the membrane can be obtained b =W w -W dThe pore volume of the membrane can be calculated from the mass of n-butanol (W b ) and the density of n-butanol (ρ b ) is divided by the dry film volume (V p ) is the porosity of the diaphragm q% = (W w -W d ) / (ρ b ·V p ).

[0073] In a specific embodiment, the weight percentage m of the compound represented by structural formula 1 in the non-aqueous electrolyte can be 0.01%, 0.03%, 0.05%, 0.1%, 0.12%, 0.15%, 0.3%, 0.5%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.7%, 1.9% or 2%.

[0074] In a preferred embodiment, the weight percentage m of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.1% to 1%.

[0075] The compound shown in the structural formula 1 decomposes on the surface of the positive electrode material layer and participates in the formation of a passivation film on the surface of the positive electrode material layer. The passivation film has a certain inhibitory effect on the dissolution of manganese ions. If the content of the compound shown in the structural formula 1 in the non-aqueous electrolyte is too little, it will affect the quality of the passivation film on the surface of the lithium manganese-based positive electrode active material, and it is difficult to effectively inhibit the dissolution of manganese ions. If the content of the compound shown in the structural formula 1 in the non-aqueous electrolyte is too much, it will cause a strong film-forming reaction on the surface of the lithium manganese-based positive electrode active material, causing the interface film to be too thick, resulting in an increase in interface impedance and affecting battery performance.

[0076] In a specific embodiment, the capacitance p per unit area of ​​the positive electrode material layer may be 1.5 mAh / cm 2 、1.8mAh / cm 2 , 2 mAh / cm 2 , 2.2 mAh / cm 2 、2.5 mAh / cm 2 、2.8 mAh / cm 2 、3.0 mAh / cm 2 、3.2 mAh / cm 2 , 3.5 mAh / cm 2 , 3.8 mAh / cm 2 , 4.0 mAh / cm 2 , 4.2 mAh / cm 2 , 4.5 mAh / cm 2 , 4.8 mAh / cm 2 or 5.0mAh / cm2 .

[0077] In a preferred embodiment, the capacitance per unit area of ​​the positive electrode material layer is 2-4 mAh / cm 2 .

[0078] In a more preferred embodiment, the capacitance p per unit area of ​​the positive electrode material layer is 2.5-4 mAh / cm 2 .

[0079] The capacity per unit area of ​​the positive electrode material layer indicates the total amount of active ions that can be released per unit area of ​​the positive electrode material layer when the battery is fully discharged. When the battery design capacity is the same and the discharge rate is the same, if the capacity per unit area of ​​the positive electrode material layer is larger, it means that more active ions are instantly detached from the surface unit area of ​​the positive electrode material layer. There is a certain correlation between the manganese element in the lithium-manganese-based positive electrode active material and the capacity per unit area of ​​the positive electrode material layer. The lower the manganese content in the lithium-manganese-based positive electrode active material, the worse the battery cycle performance; however, the larger the capacity per unit area of ​​the positive electrode material layer, the smaller the area of ​​lithium-manganese-based positive electrode active material can release more active ions from the positive electrode, and the higher the energy density of the battery; conversely, the smaller the battery energy density is, which is not conducive to commercial application.

[0080] The capacitance p per unit area of ​​the positive electrode material layer can be obtained by testing in the following manner:

[0081] Step 1): Average discharge capacity test of the positive electrode material layer.

[0082] Take the positive electrode and use the punching die to obtain a small disc of the positive electrode material layer. Use the metal lithium sheet as the counter electrode, the Celgard membrane as the isolation membrane, and the solution of EC+EMC+DEC (ethylene carbonate, ethyl methyl carbonate, diethyl carbonate with a volume ratio of 1:1:1) dissolved with LiPF6 (1 mol / L) as the electrolyte. Assemble 5 identical CR2430 button batteries in an argon-protected glove box. After the battery is assembled, let it stand for 12 hours, and perform constant current charging at a charging current of 0.1C until the voltage reaches the upper cut-off voltage (such as 4.5V). Finally, perform constant current discharge at a discharge current of 0.1C until the voltage reaches the lower cut-off voltage (such as 3.0V), and record the discharge capacity of the first cycle. The average discharge capacity of the 5 button batteries is the average discharge capacity of the positive electrode active layer.

[0083] Step 2): Take the average discharge capacity of the positive electrode material layer measured by the "average discharge capacity test method of the positive electrode material layer" in step 1. Use a caliper to measure the diameter d of the small positive electrode disc of the button battery, and then use the formula π*(0.5*d) 2 Calculate the area of ​​the small disc of the positive electrode of the button battery.

[0084] Step 3): According to the capacity per unit area of ​​the positive electrode material layer p = average discharge capacity of the positive electrode material layer (mAh) / area of ​​the positive electrode small disc (cm 2 ), and calculate the capacitance p per unit area of ​​the positive electrode material layer.

[0085] It should be noted that the above analysis is only based on the impact of each parameter on the performance of lithium-ion batteries when it exists alone. However, in actual application, in terms of inhibiting the dissolution of manganese ions in the positive electrode and protecting the negative electrode, the above parameters are interrelated and inseparable. For example, by controlling the capacitance per unit area of ​​the positive electrode material layer to control the content of manganese ions in the positive electrode material layer, and by optimizing the porosity of the diaphragm, while ensuring the smooth passage of lithium ions, the diffusion rate of manganese ions in the diaphragm is reduced, reducing the ion exchange effect of manganese ions passing through the diaphragm with lithium in the negative electrode, inhibiting the damage of manganese to the negative electrode, and improving the stability of the negative electrode; at the same time, the non-aqueous electrolyte contains the compound shown in structural formula 1, which can form a dense passivation film at the interface of the positive electrode material layer, stabilize the positive electrode structure, reduce the dissolution of manganese ions, and thus reduce the oxidative decomposition of the electrolyte on the positive electrode interface. The three cooperate with each other through the relationship 0.1≤q*m / p≤20 to achieve a better mutual promotion effect.

[0086] In some embodiments, the compound represented by structural formula 1 is selected from one or more of the following compounds:

[0087]

[0088]

[0089] It should be noted that the above are only preferred compounds of the present invention and do not represent limitations on the present invention.

[0090] A person skilled in the art who knows the structure of the compound shown in Structural Formula 1 can know the preparation method of the above compound according to the common knowledge in the field of chemical synthesis. For example, Compound 11 can be prepared by the following method:

[0091] Sorbitol, dimethyl carbonate, methanol, alkaline substance catalyst potassium hydroxide and organic solvent such as DMF are placed in a reaction container, and reacted under heating conditions for several hours. Then, a certain amount of oxalic acid is added to adjust the pH to neutral. After filtering and recrystallization, intermediate product 1 can be obtained. Then, intermediate product 1, carbonate, dichlorothionyl, etc. are subjected to esterification reaction under high temperature conditions to obtain intermediate product 2. Then, intermediate product 2 is oxidized with an oxidant such as sodium periodate to obtain compound 11.

[0092] In some embodiments, the lithium manganese-based positive electrode active material includes one or more compounds represented by formula (A), formula (B) and formula (C):

[0093] Li 1+x Mn a Ni b M 1-a-b O 2-y A y Formula (A)

[0094] Li 1+z Mn c N 2-c O 4-d B d Formula (B)

[0095] LiMn q Fe 1-q PO4 Formula (C)

[0096] Among them, in Formula (A), -0.1 ≤ x ≤ 0.2, 0 < a < 1, 0 ≤ b < 1, 0 < a + b < 1, 0 ≤ y < 0.2, M is one or more of Co, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce; A includes one or more of S, N, F, Cl, Br, and I;

[0097] In Formula (B), -0.1 ≤ z ≤ 0.2, 0 < c ≤ 2, 0 ≤ d < 1, N includes one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr, and Ce; B includes one or more of S, N, F, Cl, Br, and P;

[0098] In Formula (C), 0 < q < 1.

[0099] In a preferred embodiment, in Formula (A), 0.5 ≤ b < 1. Further, in Formula (A), 0.5 ≤ b < 1, M is one or both of Co and Al, and A is one or both of S and F.

[0100] In a preferred embodiment, in Formula (B), 1 ≤ c ≤ 2. Further, in Formula (B), 1 ≤ c ≤ 2, N is one or both of Ni and Al, and A is one or both of F and P.

[0101] In a preferred embodiment, in Formula (C), 0.3 ≤ q ≤ 0.8.

[0102] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the lithium manganese-based positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0103] Based on the total mass of the positive electrode material layer being 100%, the mass percentage content of the positive electrode binder is 1 - 2%, and the mass percentage content of the positive electrode conductive agent is 0.5 - 2%.

[0104] The positive electrode binder includes 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, thermoplastic resins such as polyethylene and polypropylene; acrylic resin; sodium hydroxymethyl cellulose; polyvinyl butyral; ethylene-vinyl acetate copolymer; polyvinyl alcohol; and one or more of styrene butadiene rubber.

[0105] The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

[0106] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is formed on a surface of the positive electrode current collector.

[0107] The positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0108] In some embodiments, the separator may be a polymer separator, non-woven fabric, etc., 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 separators.

[0109] In some embodiments, at least one surface of the separator is coated with a surface coating, wherein the surface coating comprises one or more of inorganic particles and organic gel.

[0110] By providing a surface coating, the mechanical strength and anti-puncture capability of the diaphragm can be effectively improved, thereby improving the safety performance of the lithium-ion battery.

[0111] In some embodiments, the content of manganese in the membrane per unit area is 50 ppm / m 2 ~2000 ppm / m 2 .

[0112] In some embodiments, the non-aqueous organic solvent includes one or more of an ether solvent, a nitrile solvent, a carbonate solvent, and a carboxylate solvent.

[0113] In some embodiments, the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether with 3 to 10 carbon atoms and a cyclic ether with 3 to 6 carbon atoms. The cyclic ether may be, but is not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether may be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since the chain ether has a high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone or in any combination and ratio. The content of ether compounds is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. In the non-aqueous solvent volume ratio of 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of ether compounds is made to meet the above range. When the content of ether compounds is within the above-mentioned preferred range, it is easy to ensure the improvement of ionic conductivity brought about by the increase in the dissociation degree of lithium ions of chain ethers and the decrease in viscosity. In addition, when the negative electrode active material is a carbon material, the phenomenon of co-embedding of chain ethers and lithium ions can be suppressed, so that the input-output characteristics and the charge-discharge rate characteristics can reach an appropriate range.

[0114] In some embodiments, the nitrile solvent may specifically be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.

[0115] In some embodiments, the carbonate solvent includes a cyclic carbonate or a chain carbonate, and the cyclic carbonate may be, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate may be, but is not limited to, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the lithium ion battery of the present invention, but when one is used alone, the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the conductivity can be reduced due to the reduction in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the large current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery reach a good range. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolyte can be improved, thus contribute to the stability during high temperature storage. The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolyte, it is usually more than 15% by volume, preferably more than 20% by volume, and more preferably more than 25% by volume. In addition, usually the volume ratio is less than 90%, preferably less than 85% by volume, and more preferably less than 80% by volume. By making the content of linear carbonate in the above-mentioned scope, it is easy to make the viscosity of nonaqueous electrolyte reach appropriate range, suppress the reduction of ionic conductivity, and then contribute to make the output characteristics of nonaqueous electrolyte battery reach good scope. When two or more linear carbonates are used in combination, the total amount of linear carbonate is made to meet the above-mentioned scope.

[0116] In certain embodiments, it is also possible to preferably use chain carbonates with fluorine atoms (hereinafter referred to as "fluorinated chain carbonates"). The number of fluorine atoms possessed by the fluorinated chain carbonate is not particularly limited as long as it is more than 1, but is generally less than 6, preferably less than 4. When the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms can be bonded to the same carbon or to different carbons. As the fluorinated chain carbonate, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc. can be listed.

[0117] Carboxylate solvents include cyclic carboxylate and / or chain carbonate. Examples of cyclic carboxylate include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonate include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0118] In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone. Preferably, in the case of a cyclic sulfone, it is usually a compound with 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and in the case of a chain sulfone, it is usually a compound with 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. The content of the sulfone solvent is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the lithium ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, the volume ratio is usually 0.3% or more, preferably 0.5% or more, and more preferably 1% or more. In addition, the volume ratio is usually 40% or less, preferably 35% or less, and more preferably 30% or less. In the case of using two or more sulfone solvents in combination, the total amount of the sulfone solvent is sufficient to meet the above range. When the content of the sulfone solvent is within the above range, an electrolyte with excellent high temperature storage stability tends to be obtained.

[0119] In a preferred embodiment, the solvent is a mixture of cyclic carbonate and linear carbonate.

[0120] In some embodiments, the lithium salt includes one or more of LiPF6, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, and lower aliphatic carboxylic acid lithium salts.

[0121] In a preferred embodiment, the lithium salt includes LiPF6 and an auxiliary lithium salt, and the auxiliary lithium salt includes one or more of LiPO2F2, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, and lower aliphatic carboxylic acid lithium salts.

[0122] When the above conditions are met, adding LiPF6 as the main lithium salt and the above auxiliary lithium salts to the non-aqueous electrolyte can further improve the thermal shock resistance of the battery. It is speculated that this is because a small amount of the compound represented by formula II contained in the positive electrode is dissolved in the non-aqueous electrolyte, and the combination with the above lithium salt has the effect of improving the stability of the non-aqueous electrolyte and avoiding the decomposition and gas production of the non-aqueous electrolyte.

[0123] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L-8 mol / L. In a preferred embodiment, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.5 mol / L-4 mol / L. Specifically, the concentration of the lithium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L.

[0124] In some embodiments, in the non-aqueous electrolyte, the mass percentage of LiPF6 is 5%~20%, and the mass percentage of the auxiliary lithium salt is 0.05%~5%.

[0125] In some embodiments, the additive further comprises at least one of a cyclic carbonate compound, an unsaturated phosphate compound, a borate compound, and a nitrile compound;

[0126] Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the content of the additive is 0.01% to 30%;

[0127] Preferably, the cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate or the compound shown in formula 2.

[0128]

[0129] Structural formula 2

[0130] In the structural formula 2, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

[0131] The unsaturated phosphate compound is selected from at least one of the compounds shown in Structural Formula 3:

[0132] Structural formula 3

[0133] In the structural formula 3, 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 R 31 , R 32 , R 33At least one of them is an unsaturated hydrocarbon group;

[0134] In a preferred embodiment, the unsaturated phosphate compound may be at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl 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;

[0135] The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0136] The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0137] In other embodiments, the additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety performance, such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0138] It should be noted that, unless otherwise specified, in general, the content of any one of the optional substances in the additives in the non-aqueous electrolyte is less than 10%, preferably, the content is 0.1-5%, and more preferably, the content is 0.1%~2%. Specifically, the content of any one of the optional substances in the additives can be 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%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%.

[0139] In some embodiments, when the additive is selected from fluoroethylene carbonate, the content of the fluoroethylene carbonate is 0.05% to 30% based on the total mass of the non-aqueous electrolyte as 100%.

[0140] In some embodiments, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material is selected from at least one of a silicon-based negative electrode, a carbon-based negative electrode, a lithium-based negative electrode, and a tin-based negative electrode.

[0141] The silicon-based negative electrode includes one or more of silicon materials, silicon oxides, silicon-carbon composite materials and silicon alloy materials; the carbon-based negative electrode includes one or more of graphite, hard carbon, soft carbon, graphene and mesophase carbon microspheres; the lithium-based negative electrode includes one or more of metal lithium or lithium alloys. The lithium alloy can be at least one of lithium silicon alloy, lithium sodium alloy, lithium potassium alloy, lithium aluminum alloy, lithium tin alloy and lithium indium alloy. The tin-based negative electrode includes one or more of tin, tin carbon, tin oxide and tin metal compounds.

[0142] In some embodiments, 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.

[0143] The selectable ranges of the negative electrode binder and the negative electrode conductor are the same as those of the positive electrode binder and the positive electrode conductor, respectively, and will not be described in detail here.

[0144] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer is formed on a surface of the negative electrode current collector.

[0145] The negative electrode current collector is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0146] The present invention is further described below by way of examples.

[0147] The compounds represented by structural formula 1 used in the following examples are specifically shown in Table 1 below.

[0148] Table 1

[0149]

[0150] Table 2 Parameter design of the embodiments and comparative examples

[0151]

[0152]

[0153] Example 1

[0154] This embodiment is used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and includes the following steps:

[0155] 1) Preparation of positive electrode

[0156] Step 1: Add PVDF as a binder to NMP solvent and stir well to obtain PVDF glue.

[0157] Step 2: Add the conductive agent (super P+CNT) into the PVDF glue and stir thoroughly.

[0158] Step 3: Continue to add the positive electrode active materials shown in Table 2, stir thoroughly and evenly, and finally obtain the required positive electrode slurry.

[0159] Step 4: The prepared positive electrode slurry is evenly coated on the positive electrode collector (such as aluminum foil), and the positive electrode sheet is obtained by drying, rolling, die-cutting or striping. The capacitance of the positive electrode sheet is shown in Table 2.

[0160] 2) Preparation of negative electrode

[0161] Step 1: Weigh each material according to the negative electrode sheet ratio of graphite (Shanghai Shanshan, FSN-1): conductive carbon (super P): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 96.3:1.0:1.2:1.5 (mass ratio).

[0162] Step 2: First, add CMC into pure water at a solid content of 1.5%, stir well (for example, stirring time 120 minutes) to prepare a transparent CMC glue solution.

[0163] Step 3: Add conductive carbon (super P) to the CMC glue solution and stir well (for example, stirring time 90 minutes) to prepare a conductive glue.

[0164] Step 4: Continue to add graphite and stir thoroughly to finally obtain the required negative electrode slurry.

[0165] Step 5: Evenly coat the prepared negative electrode slurry on the copper foil, and obtain the negative electrode sheet by drying, rolling, die-cutting or striping.

[0166] 3) Preparation of non-aqueous electrolyte

[0167] Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:DEC:EMC=1:1:1, additives were added in mass percentages as shown in Table 2, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L.

[0168] 4) Lithium-ion battery preparation

[0169] The prepared positive electrode sheet, the negative electrode sheet and a separator with a porosity as shown in Table 2 were assembled into a laminated soft-pack battery cell.

[0170] 5) Battery filling and formation

[0171] In a glove box with a dew point controlled below -40°C, the prepared electrolyte was injected into the battery cell, vacuum-sealed, and left to stand for 24 hours. Then, the conventional formation of the first charge was carried out according to the following steps: 0.05C constant current charging for 180 minutes, 0.1C constant current charging for 120 minutes, 0.2C constant current charging for 120 minutes, secondary vacuum sealing, and then further full charging at 0.2C current (100% SOC), after being left at room temperature for 24 hours, full discharge at 0.2C current (0% SOC).

[0172] Embodiments 2 to 29

[0173] Examples 2 to 29 are used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that:

[0174] The positive electrode active material, positive electrode capacity, electrolyte additive components and separator shown in Table 2 were used.

[0175] Comparative Examples 1 to 24

[0176] Comparative Examples 1 to 24 are used to compare and illustrate the battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that:

[0177] The positive electrode active material, positive electrode capacity, electrolyte additive components and separator shown in Table 2 were used.

[0178] Performance Testing

[0179] The lithium-ion battery prepared above was subjected to the following performance tests:

[0180] High temperature cycle performance test:

[0181] At 45°C, the lithium ion batteries prepared in the examples and comparative examples were charged at a 1C rate and discharged at a 1C rate, and full charge and discharge cycle tests were performed within the charge and discharge cut-off voltage range until the capacity of the lithium ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0182] Manganese content test on the diaphragm:

[0183] The lithium-ion battery whose capacity has decayed to 80% of the initial capacity is fully discharged at a rate of 0.1C, and then the battery is disassembled to remove the diaphragm, and the removed diaphragm is immersed in an acid solution (such as a nitric acid aqueous solution) for a predetermined time (such as about 30 minutes). Thus, the manganese element on the diaphragm is dissolved (eluted) in the acid solution, and the solution is detected by an inductively coupled plasma optical emission spectrometer (ICP-OES), thereby obtaining the manganese element content (ppm) of the diaphragm.

[0184] (1) The test results obtained in Examples 1 to 20 and Comparative Examples 1, 6 to 24 are entered in Table 3.

[0185] Table 3

[0186]

[0187]

[0188] From the test results of Examples 1 to 20 and Comparative Examples 1, 6 to 24, it can be seen that the Mn content of the lithium manganese-based positive electrode active material is increased. 2+ Dissolution and Mn 2+ In the inhibition of the flow between the positive and negative electrodes, there is a correlation between the porosity q of the diaphragm, the weight percentage m of the compound shown in the structural formula 1 in the non-aqueous electrolyte and the capacitance p per unit area of ​​the positive electrode material layer. When the porosity q of the diaphragm, the weight percentage m of the compound shown in the structural formula 1 in the non-aqueous electrolyte and the capacitance p per unit area of ​​the positive electrode material layer satisfy the condition 0.1≤q*m / p≤20, the obtained lithium ion battery has a higher initial battery capacity and excellent high temperature cycle performance. At the same time, the content of manganese ions on the diaphragm after the cycle is significantly reduced, indicating that the adjustment and coordination of the above parameters is conducive to the formation of a more stable interface film at the positive electrode interface, which has a more obvious inhibition on the dissolution of manganese ions, and reduces the decomposition of the electrolyte on the positive electrode interface. At the same time, the setting of the diaphragm porosity has a certain inhibitory effect on the shuttling of manganese ions without affecting the shuttling of lithium ions, thereby improving its cycle life and high temperature stability while ensuring the energy density of the lithium ion battery.

[0189] In particular, it can be seen from the test results of Examples 1 to 20 that when the lithium ion battery meets the condition 1≤q*m / p≤10, the lithium ion battery has the best comprehensive electrochemical performance.

[0190] From the test results of Comparative Examples 14, 19 and 22, it can be seen that even if the q value, m value and p value all meet the parameter range limits, if the q*m / p value is too small, the manganese ion content on the diaphragm will increase after the cycle, and the high temperature cycle life of the lithium ion battery will be shortened; and from the test results of Comparative Examples 17, 23 and 24, it can be seen that an excessively large q*m / p value is also not conducive to inhibiting the shuttle of manganese ions between the positive and negative electrodes, resulting in a decrease in the battery cycle performance; It indicates that the porosity q of the diaphragm, the weight percentage m of the compound represented by the structural formula 1 in the non-aqueous electrolyte and The capacitance p per unit area of ​​the positive electrode material layer influences each other in inhibiting the shuttling of manganese ions between the positive and negative electrodes. When and only when the three reach a better equilibrium state, can the dissolution of manganese ions at the positive electrode and the embedding of manganese ions in the negative electrode be better inhibited; at the same time, from the test results of Comparative Examples 13, 15, 18, 20 and 21, it can be seen that when one of the q value, m value and p value exceeds its parameter limit range, even if the q value, m value and p value meet the condition 0.1≤q*m / p≤20, the obtained lithium ion battery still does not have good high temperature cycle performance.

[0191] From the test results of Examples 12 to 20 and Comparative Examples 5 to 12, it can be seen that as the manganese content in the lithium manganese-based positive electrode active material increases to a higher level, the dissolution of manganese ions is intensified, resulting in a decrease in the stability of the lithium manganese-based positive electrode active material. At this time, the interfacial film formed by the compound shown in Structural Formula 1 is crucial to improving the stability of the lithium manganese-based positive electrode active material, but an excessively high content of the compound shown in Structural Formula 1 will also lead to a decrease in the initial capacity of the battery and a decrease in the number of cycles. It is necessary to adjust the porosity of the diaphragm and the capacitance per unit area of ​​the positive electrode material to achieve a better overall performance of the battery.

[0192] (2) The test results obtained in Examples 1, 21-24 and Comparative Examples 2-5 are entered in Table 4.

[0193] Table 4

[0194]

[0195] From the test results of Example 1 and Examples 21 to 24, it can be seen that in the battery system provided by the present invention, when the additives VC (vinylene carbonate), PS (1,3-propane sultone), LiPO2F2 (lithium difluorophosphate) or FEC (fluoroethylene carbonate) are added, the cycle performance of the battery can be further improved, and the dissolution of manganese ions can be reduced. It is speculated that the compound shown in Structural Formula 1 and the above-mentioned additives jointly participate in the formation of the surface interface film of the lithium-manganese-based positive electrode active material, thereby obtaining an interface film with better stability and performance, thereby effectively reducing the reaction of the electrolyte on the electrode surface and improving the electrochemical performance of the battery. More preferably, among the above-mentioned additives, it can be seen that the use of FEC in the electrolyte in combination with the compound shown in Structural Formula 1 has the most obvious improvement in the cycle performance of the battery.

[0196] From the test results of Example 1 and Comparative Examples 2 to 5, it can be seen that when VC (vinylene carbonate), PS (1,3-propane sultone), LiPO2F2 (lithium difluorophosphate) or FEC (fluoroethylene carbonate) is used to replace the compound shown in Structural Formula 1 in the electrolyte, the degree of improvement of the battery is far less than that of adding the compound shown in Structural Formula 1 to the electrolyte. It is speculated that under the lithium manganese-based positive electrode active material system, the compound shown in Structural Formula 1 is more conducive to the film-forming reaction on the surface of the material, and the formed interface film is more solid and stable, so that the protection effect of the positive electrode material is better, resulting in a greater degree of improvement in the cycle of the lithium manganese-based battery system. In Comparative Example 5, although PS and the compound shown in Structural Formula 1 are both cyclic sulfur additives, their improvement is far less than that of the compound shown in Structural Formula 1. It is speculated that the lithium manganese-based positive electrode active material system is selective for such cyclic sulfur additives.

[0197] (3) The test results obtained in Examples 1 and 25 to 29 are entered in Table 5.

[0198] Table 5

[0199]

[0200] It can be seen from the test results of Example 1 and Examples 25 to 19 that when different compounds represented by structural formula 1 are used as additives to non-aqueous electrolytes, the relationship of 0.1≤q*m / p≤20 is also satisfied, indicating that the cyclic sulfate groups contained in the compounds represented by different structural formulas 1 play a decisive role in the formation of the passivation film on the surface of the positive and negative electrodes, and the passivation film rich in S elements produced by its decomposition can effectively inhibit the dissolution of Mn ions and form a good protective effect on the positive electrode material layer. The relationship provided by the present invention is universal for compounds represented by different structural formulas 1, and has an improving effect on the high temperature cycle performance of lithium-ion batteries.

[0201] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: It includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. The separator is located between the positive electrode and the negative electrode. The positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a lithium manganese-based positive electrode active material. The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes a compound represented by Structural Formula 1: Structural Formula 1 Where n is 0 or 1, and X is selected from or , R1, R2 are each independently selected from H, C1-C5 hydrocarbon group, , or , and X, R1 and R2 contain at least one sulfur atom; The lithium-ion battery satisfies the following conditions: 0.1 ≤ q*m / p ≤ 20 and 20 ≤ q ≤ 60, 0.01 ≤ m ≤ 2, 1.5 ≤ p ≤ 5; wherein, q is the porosity of the separator, in %; m is the weight percentage content of the compound represented by Structural Formula 1 in the non-aqueous electrolyte, in %; p is the capacitance per unit area of ​​the positive electrode material layer, in mAh / cm 2 .

2. The lithium-ion battery according to claim 1, characterized in that The lithium-ion battery satisfies the following conditions: 1 ≤ q*m / p ≤ 10.

3. The lithium-ion battery according to claim 1, characterized in that The porosity q of the separator is 30% - 50%.

4. The lithium-ion battery according to claim 1, characterized in that: The weight percentage content m of the compound represented by Structural Formula 1 in the non-aqueous electrolyte is 0.1% - 1%.

5. The lithium-ion battery according to claim 1, characterized in that: The capacitance per unit area of ​​the positive electrode material layer is 2-4 mAh / cm 2 .

6. The lithium-ion battery according to claim 1, characterized in that The compound represented by Structural Formula 1 is selected from one or more of the following compounds: 。 7. The lithium-ion battery according to claim 1, characterized in that: The lithium manganese-based positive electrode active material includes one or more of the compounds represented by Formula (A), Formula (B), and Formula (C): Li 1+x Mn a Ni b M 1-a-b O 2-y A y Formula (A) Li 1+z Mn c N 2-c O 4-d B d Formula (B) LiMn q Fe 1-q PO4 formula (C) wherein, in Formula (A), -0.1 ≤ x ≤ 0.2, 0 < a < 1, 0 ≤ b < 1, 0 < a + b < 1, 0 ≤ y < 0.2, M is one or more of Co, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce, and A includes one or more of S, N, F, Cl, Br, and I; in Formula (B), -0.1 ≤ z ≤ 0.2, 0 < c ≤ 2, 0 ≤ d < 1, N is one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr, and Ce, and B includes one or more of S, N, F, Cl, Br, and P; in Formula (C), 0 < q < 1.

8. The lithium-ion battery according to claim 1, characterized in that At least one surface of the separator is coated with a surface coating, and the surface coating includes one or more of inorganic particles and organic gels.

9. The lithium-ion battery according to claim 1, characterized in that: The content of manganese in the membrane per unit area is 50 ppm / m 2 ~2000 ppm / m 2 .

10. The lithium ion battery according to claim 1, characterized in that: The additive further includes at least one of cyclic carbonate compounds, unsaturated phosphate compounds, borate compounds, and nitrile compounds.

11. The lithium ion battery according to claim 10, characterized in that: Based on the total mass of the non-aqueous electrolyte being 100%, the content of the additive is 0.01% - 30%.

12. The lithium ion battery according to claim 10, characterized in that: The cyclic carbonate compounds are selected from at least one of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, or the compound represented by Structural Formula 2, Structural Formula 2 In the structural formula 2, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group; The unsaturated phosphate compounds are selected from at least one of the compounds represented by Structural Formula 3: Structural Formula 3 In the structural formula 3, 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 R 31 , R 32 , R 33 At least one of them is an unsaturated hydrocarbon group; The borate compounds are selected from at least one of tris(trimethylsilyl) borate and tris(triethylsilyl) borate; The nitrile compounds are selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

Images