CN116454381A - High-voltage lithium ion battery - Google Patents

Abstract

In order to overcome the problems of low gas production at high temperature and short cycle life of the existing high-voltage lithium ion battery, the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the nonaqueous electrolyte comprises a nonaqueous organic solvent, an additive and lithium salt, the additive comprises fluorinated cyclic carbonate, a phosphate compound containing unsaturated hydrocarbon groups, a boron-containing lithium salt type additive and a second additive, and the second additive comprises at least one of a tri-nitrile compound and cyclic carboxylic anhydride; the high-voltage lithium ion battery meets the following conditions: 1-26 [ (p+q) x E ]/b-0.05-1, 0.2-1.5,0.01-1.5,2.6-3.3; the charge cut-off voltage of the high-voltage lithium ion battery is more than or equal to 4.6V. The lithium ion battery provided by the invention has a great improvement effect on the cycle life of the high-voltage lithium ion battery through controlling the additive and the liquid retention coefficient, and simultaneously effectively inhibits the gas production of the high-voltage lithium ion battery at a high temperature.

Description

High-voltage lithium ion battery

Technical Field

The invention belongs to the technical field of energy storage devices, and particularly relates to a high-voltage lithium ion battery.

Background

Compared with lead-acid batteries, nickel-hydrogen batteries and nickel-cadmium batteries, the lithium ion batteries have the advantages of higher energy density, long cycle life and the like, and are widely applied to various fields.

Spinel-structured lithium nickel manganese oxide (LiNi _0.5 Mn _1.5 O ₄ ) Has three-dimensional diffusion channel with theoretical discharge specific capacity up to 147mAh g ^-1 The voltage platform is as high as 4.7V, has higher energy density and power density compared with the battery system (lithium iron phosphate system and ternary system) commonly used in the market at present, has the advantage of low cost because the lithium iron phosphate system does not contain cobalt, is suitable for power batteries and large-scale energy storage application, and is one of the most promising and attractive positive electrode materials in the future development of lithium ion batteries.

However, the main obstacle to commercialization is the stability of the positive electrode electrolyte interface (CEI). The current commercial electrolytes still rely on early developed organic systems, based primarily on various carbonate solvents and LiPF ₆ The upper limit of the steady operation voltage is generally limited to around 4.5v vs. li+/Li. The electrolyte is continuously decomposed at high voltage, and trace hydrogen fluoride erodes the lithium nickel manganese oxide anode, so that the performance and the service life of the battery are seriously deteriorated.

For electric vehicle applications, it is desirable that the battery have low internal resistance, long storage life and cycle life. The lower internal resistance is beneficial to the automobile to have better acceleration performance and power performance, and the automobile can recover energy to a greater extent and improve fuel efficiency when being applied to the hybrid electric vehicle. The long storage life and cycle life are intended to allow the battery to have long-term reliability, maintaining good performance over the normal life of the automobile. The interaction of the electrolyte with the anode and cathode has a large impact on these properties. Therefore, in order to meet the performance requirements of electric vehicles on batteries, it is necessary to provide an electrolyte with good comprehensive performance and a high-voltage lithium ion battery.

Disclosure of Invention

Aiming at the problems of insufficient high-temperature gas production and cycle life of the existing high-voltage lithium ion battery, the invention provides the high-voltage lithium ion battery.

The technical scheme adopted by the invention for solving the technical problems is as follows:

the invention provides a high-voltage lithium ion battery, which comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the nonaqueous electrolyte comprises a nonaqueous organic solvent, an additive and lithium salt, the additive comprises fluorinated cyclic carbonate, a phosphate compound containing unsaturated hydrocarbon groups, a boron-containing lithium salt type additive and a second additive, and the second additive comprises at least one of a tri-nitrile compound and cyclic carboxylic anhydride;

the high-voltage lithium ion battery meets the following conditions:

1-26 [ (p+q) x E ]/b-0.05-1, 0.2-1.5,0.01-1.5,2.6-3.3;

wherein b is the mass percentage content of fluorinated cyclic carbonate in the nonaqueous electrolyte, and the unit is;

p is the sum of the mass percent of the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive in the nonaqueous electrolyte, and the unit is;

q is the mass percentage content of the second additive in the nonaqueous electrolyte, and the unit is;

E is the liquid retention coefficient of nonaqueous electrolyte in the lithium ion battery, and the unit is g/Ah;

the charge cut-off voltage of the high-voltage lithium ion battery is more than or equal to 4.6V.

Optionally, the high-voltage lithium ion battery meets the following conditions:

1.5≤[(p+q)×E]/b≤16。

optionally, the high-voltage lithium ion battery meets the following conditions: b is more than or equal to 0.1 and less than 1, p is more than or equal to 0.2 and less than or equal to 1.1,0.01, q is more than or equal to 1.2,2.6 and E is more than or equal to 3.1.

Optionally, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate, 4-difluoroethylene carbonate, 4, 5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4, 5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4-difluoro-5-methylethylene carbonate, 4- (fluoromethyl) -ethylene carbonate, 4- (difluoromethyl) -ethylene carbonate, 4- (trifluoromethyl) -ethylene carbonate, 4- (fluoromethyl) -4-fluoroethylene carbonate, 4- (fluoromethyl) -5-fluoroethylene carbonate, 4-fluoro-4, 5-dimethylethylene carbonate, 4, 5-difluoro-4, 5-dimethylethylene carbonate, and 4, 4-difluoro-5, 5-dimethylethylene carbonate.

Alternatively, the unsaturated hydrocarbon group-containing phosphate compound is selected from the group consisting of compounds represented by structural formula 1:

in the structural formula 1, R ₁ 、R ₂ 、R ₃ Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halogenated hydrocarbon groups, -Si (C) _m H _2m+1 ) ₃ M is a natural number of 1 to 3, and R ₁ 、R ₂ 、R ₃ At least one of them is an unsaturated hydrocarbon group.

Optionally, the compound represented by the structural formula 1 includes at least one of tripropylethyl phosphate, dipropylethyl ethyl phosphate, dipropylethyl propyl phosphate, dipropylethyl trifluoromethyl phosphate, dipropylethyl-2, 2-trifluoroethyl phosphate, dipropylethyl-3, 3-trifluoropropyl phosphate, dipropylethyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2, 2-trifluoroethyl phosphate, diallyl-3, 3-trifluoropropyl phosphate and diallyl hexafluoroisopropyl phosphate.

Optionally, the mass percentage of the phosphate ester compound containing unsaturated hydrocarbon groups in the nonaqueous electrolyte is 0.05-0.8%.

Optionally, the boron-containing lithium salt type additive comprises at least one of lithium bisoxalato borate and lithium difluorooxalato borate.

Optionally, the mass percentage of the boron-containing lithium salt type additive in the nonaqueous electrolyte is 0.1-1%.

Optionally, the dinitrile compound comprises at least one of 1,2, 4-butane dinitrile, 1,3, 5-benzene dinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-dinitrile, 2-bromobenzene-1, 3, 5-dinitrile, 1,3, 6-hexane dinitrile, 1,2, 3-propane dinitrile or 1,3, 5-pentane dinitrile.

Optionally, the mass percentage of the tri-nitrile compound in the non-aqueous electrolyte is 0.1-1.5%.

Optionally, the cyclic carboxylic anhydride includes at least one of phthalic anhydride, citraconic anhydride, maleic anhydride, 2, 3-dimethylmaleic anhydride, 1-cyclohexyldiacetic anhydride, glutaric anhydride, and succinic anhydride.

Optionally, the mass percentage of the cyclic carboxylic anhydride in the non-aqueous electrolyte is 0.01-1%.

Optionally, the nonaqueous organic solvent comprises cyclic carbonate and chain carbonate, wherein the mass percentage of the cyclic carbonate in the nonaqueous electrolyte is a%, a is more than or equal to 1 and less than or equal to 30, b/a is more than or equal to 0 and less than or equal to 1, and b is more than or equal to 1 and less than or equal to 10;

optionally, the positive electrode includes a positive electrode material layer including a positive electrode active material including at least one of compounds represented by formula (a) or formula (B):

LiNi _x M _2-x A _y O _r B _p (A)

nLi ₂ MnO ₃ ·(1-n)LiMO ₂ (B)

In the formula (A), x is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 2-x is more than or equal to 2, y is more than or equal to 0 and less than or equal to 0.05,1, r is more than or equal to 0 and less than or equal to 4, p is more than or equal to 0 and less than or equal to 4, M is selected from at least one of Mn or Al, A is selected from at least one of Zr, zn, cu, cr, fe, V, ti, sr, sb, sn, Y, W, al, nb, and B is selected from at least one of F, cl and Br;

In the formula (B), 0< n <1, and M is selected from at least one of Ni, co, mn or Al.

According to the lithium ion battery provided by the invention, the fluorinated cyclic carbonate, the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive are added into the nonaqueous electrolyte as the fixing additive, and at least one of the tri-nitrile compound and the cyclic carboxylic anhydride is adopted as the second additive, wherein the fluorinated cyclic carbonate, the phosphate compound containing unsaturated hydrocarbon groups, the boron-containing lithium salt type additive and the second additive jointly influence the formation of an interface film on the positive electrode surface and the negative electrode surface of the battery, and functional interaction exists among different additives, and the inventor has summarized that through a large amount of researches: when the mass percent b of the fluorinated cyclic carbonate, the sum p of the mass percent of the unsaturated hydrocarbon group-containing phosphate compound and the boron-containing lithium salt type additive, the mass percent q of the second additive (the tri-nitrile compound and/or the cyclic carboxylic anhydride) and the retention coefficient E in the nonaqueous electrolytic solution satisfy the conditions: when [ (p+q) ×E ]/b is less than or equal to 1 and less than or equal to 26, and 0.05 is less than or equal to 1, p is less than or equal to 0.2 and less than or equal to 1.5,0.01 and less than or equal to 1.5,2.6 and less than or equal to 3.3, the electrolyte membrane has a great improvement effect on the cycle life of the high-voltage lithium ion battery, and simultaneously effectively inhibits the gas production of the high-voltage lithium ion battery at high temperature, presumably because the electrolyte membrane can provide electrochemical stability of the nonaqueous electrolyte solution by adjusting the relative proportion of the fluorinated cyclic carbonate, the unsaturated hydrocarbon-containing phosphate compound, the boron-containing lithium salt type additive and the second additive, reduce the risk of decomposing gas production of the nonaqueous electrolyte solution under high voltage, effectively inhibit the dissolution of transition metal ions in the positive active material, ensure the structural stability of the positive active material, and simultaneously, the electrolyte coefficient E in the lithium ion battery can also play a regulating effect on the interaction between different additives, and is mainly used for controlling the infiltration effect of the nonaqueous electrolyte solution on the positive and negative material, and further plays a role in regulating and controlling the final phase of forming a compact interfacial membrane.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects solved by the invention more clear, the invention is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

The embodiment of the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the nonaqueous electrolyte comprises a nonaqueous organic solvent, an additive and lithium salt, the additive comprises fluoroethylene carbonate, a phosphate compound containing unsaturated hydrocarbon groups, a boron-containing lithium salt additive and a second additive, and the second additive comprises at least one of a tri-nitrile compound and cyclic carboxylic anhydride;

the high-voltage lithium ion battery meets the following conditions:

1-26 [ (p+q) x E ]/b-0.05-1, 0.2-1.5,0.01-1.5,2.6-3.3;

wherein b is the mass percentage content of fluorinated cyclic carbonate in the nonaqueous electrolyte, and the unit is;

p is the sum of the mass percent of the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive in the nonaqueous electrolyte, and the unit is;

q is the mass percentage content of the second additive in the nonaqueous electrolyte, and the unit is;

e is the liquid retention coefficient of electrolyte in the lithium ion battery, and the unit is g/Ah;

the charge cut-off voltage of the high-voltage lithium ion battery is more than or equal to 4.6V.

The fluorinated cyclic carbonate, the phosphate compound containing unsaturated hydrocarbon groups, the boron-containing lithium salt type additive, the tri-nitrile compound and/or the cyclic carboxylic anhydride together influence the formation of the battery positive/negative electrode surface interface film, and functional interactions exist among different additives, so that the inventor has summarized through a large amount of researches: when the mass percent b of the fluorinated cyclic carbonate, the sum p of the mass percent of the unsaturated hydrocarbon group-containing phosphate compound and the boron-containing lithium salt type additive, the mass percent q of the second additive (the tri-nitrile compound and/or the cyclic carboxylic anhydride) and the retention coefficient E in the nonaqueous electrolytic solution satisfy the conditions: when [ (p+q) ×E ]/b is less than or equal to 1 and less than or equal to 26, and 0.05 is less than or equal to 1, p is less than or equal to 0.2 and less than or equal to 1.5,0.01, q is less than or equal to 1.5,2.6 and less than or equal to 3.3, the electrolyte membrane has a great improvement effect on the cycle life of a lithium ion battery with high voltage, and simultaneously effectively inhibits the gas production of the lithium ion battery at high temperature and high voltage (more than or equal to 4.6V), and presumably because the relative proportion of fluoroethylene carbonate, an unsaturated hydrocarbon-containing phosphate compound, a boron-containing lithium salt type additive and a second additive is regulated, the electrolyte membrane can provide electrochemical stability of the nonaqueous electrolyte per se, reduces the risk of gas production by decomposition of the nonaqueous electrolyte under high voltage, can effectively inhibit the dissolution of transition metal ions in an anode active material, ensures the structural stability of the anode active material, and simultaneously, the electrolyte coefficient E in the lithium ion battery can play a regulating effect on the interaction between different additives, is mainly embodied in that the electrolyte membrane is used for controlling positive and negative infiltration liquid, has a good stability on the cathode active material, and further has a stable effect on the phase V of the battery in the phase of forming a compact and stable working phase in 6 at 4. Stable boundary membrane.

In a preferred embodiment, the high voltage lithium ion battery has a charge cutoff voltage of 4.7 to 5.0V.

In a preferred embodiment, the high voltage lithium ion battery meets the following conditions:

1.5≤[(p+q)×E]/b≤16。

when the mass percentage content b of the fluorinated cyclic carbonate, the sum p of the mass percentage contents of the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive in the nonaqueous electrolyte, the mass percentage content q of the second additive and the liquid retention coefficient E further meet the conditions, the lithium ion battery is beneficial to further improving the performance of the lithium ion battery under high working voltage, effectively inhibits the decomposition and gas production of the electrolyte under high voltage, ensures the stability of the structure of the positive electrode active material, has better lithium ion conductivity and improves the cycle performance and the storage performance of the battery.

In a specific embodiment, the mass percentage b of the fluorinated cyclic carbonate in the nonaqueous electrolytic solution may be 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%; the mass percentage p of the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive in the nonaqueous electrolyte solution can be 0.2%, 0.3%, 0.4%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45% or 1.5%; the mass percentage q of the second additive in the nonaqueous electrolyte solution can be 0.01%, 0.05%, 0.1%, 0.12%, 0.15%, 0.3%, 0.5%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4% or 1.5%; the electrolyte retention coefficient E of the electrolyte in the high-voltage lithium ion battery can be 2.6g/Ah, 2.7g/Ah, 2.8g/Ah, 2.9g/Ah, 3.0g/Ah, 3.1g/Ah, 3.2g/Ah or 3.3g/Ah.

In a preferred embodiment, the high voltage lithium ion battery meets the following conditions: b is more than or equal to 0.1 and less than 1, p is more than or equal to 0.2 and less than or equal to 1.1,0.01, q is more than or equal to 1.2,2.6 and E is more than or equal to 3.1.

The retention coefficient e=electrolyte mass (g) of the nonaqueous electrolyte in the lithium ion battery/rated capacity (Ah) of the lithium ion battery after formation.

In some embodiments, the retention factor E of the nonaqueous electrolyte in the lithium ion battery may be 2.6g/Ah, 2.8g/Ah, 2.85g/Ah, 2.9g/Ah, 2.95g/Ah, 2.98g/Ah, 3.0g/Ah, 3.05g/Ah, 3.1g/Ah, 3.15g/Ah, 3.2g/Ah, or 3.3g/Ah.

In a preferred embodiment, the retention coefficient E of the nonaqueous electrolyte in the lithium ion battery is 2.6.ltoreq.E.ltoreq.3.1 g/Ah.

The electrolyte retention coefficient E of the nonaqueous electrolyte in the lithium ion battery influences the relative quality of the positive electrode material layer and the nonaqueous electrolyte in the lithium ion battery, the electrolyte retention coefficient E of the nonaqueous electrolyte and the content of each additive determine the addition amount of each additive in the lithium ion battery, when the electrolyte retention coefficient E of the nonaqueous electrolyte is in the range, positive and negative electrode active materials, diaphragms and the like in the battery can be fully infiltrated by the nonaqueous electrolyte, and enough additives are provided to form a stable passivation film on the surfaces of the positive and negative electrodes, so that the full play of the battery capacity is ensured, and the battery capacity and the circulation and storage performance are improved.

In some embodiments, the mass percentage of the phosphate ester compound containing unsaturated hydrocarbon groups in the nonaqueous electrolytic solution is 0.05-0.8%;

the mass percentage of the boron-containing lithium salt type additive in the nonaqueous electrolyte is 0.1-1%;

the mass percentage of the dinitrile compound in the non-aqueous electrolyte is 0.1-1.5%;

the mass percentage of the cyclic carboxylic anhydride in the non-aqueous electrolyte is 0.01-1%.

In a preferred embodiment, the mass percentage of the phosphate compound containing an unsaturated hydrocarbon group in the nonaqueous electrolytic solution is 0.1 to 0.4%;

the mass percentage of the boron-containing lithium salt type additive in the nonaqueous electrolyte is 0.3-0.8%;

the mass percentage of the dinitrile compound in the non-aqueous electrolyte is 0.3-1.2%;

the mass percentage of the cyclic carboxylic anhydride in the non-aqueous electrolyte is 0.01-0.6%.

In the non-aqueous electrolyte provided by the invention, the fluorinated cyclic carbonate has higher oxidation stability, and can effectively inhibit continuous oxidation of the electrolyte on the surface of the positive electrode, so that gas production and impedance accumulation are reduced; the fluorine-containing substituent makes the molecule more resistant to decomposition by increasing oxidation potential due to its electron withdrawing effect, and the fluorinated cyclic carbonate can form a good interfacial film on the negative electrode to realize long-term circulation.

In the nonaqueous electrolyte provided by the invention, the film forming property of the phosphate compound containing unsaturated hydrocarbon groups on the positive and negative electrode surfaces and the unsaturated hydrocarbon groups carried by the phosphate compound have certain unsaturation degree, so that the phosphate compound has the capability of respectively carrying out oxidative decomposition and reduction on the positive and negative electrode surfaces, and the conventional saturated phosphate compound has relatively stable property, mainly plays the role of a flame retardant and does not participate in film forming. The unsaturated hydrocarbon group-containing phosphate compound has a high HOMO and a low LUMO, so that it can dominate the chemical composition of the anode and cathode surface interface film before the participation of the electrolyte solvent. The addition of the phosphate compound containing unsaturated hydrocarbon groups can effectively reduce gas generation, relieve impedance increase and effectively inhibit the formation of negative-side lithium dendrites; can obviously improve the high-temperature (45-60 ℃) cycle and storage performance of the lithium ion battery.

In some embodiments, the unsaturated hydrocarbon group-containing phosphate compound is selected from the group consisting of compounds represented by structural formula 1:

in the structural formula 1, R ₁ 、R ₂ 、R ₃ Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halogenated hydrocarbon groups, -Si (C) _m H _2m+1 ) ₃ M is a natural number of 1 to 3, and R ₁ 、R ₂ 、R ₃ At least one of them is an unsaturated hydrocarbon group.

In particular, the method comprises the steps of, the compound shown in the structural formula 1 comprises at least one of tripolyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2, 2-trifluoroethyl phosphate, dipropargyl-3, 3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2, 2-trifluoroethyl phosphate, diallyl-3, 3-trifluoropropyl phosphate and diallyl hexafluoroisopropyl phosphate.

In some embodiments, the mass percentage of the phosphate ester compound containing an unsaturated hydrocarbon group in the nonaqueous electrolytic solution is 0.05 to 0.8%.

In specific embodiments, the mass percentage of the unsaturated hydrocarbon group-containing phosphate compound in the nonaqueous electrolytic solution may be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%.

In some preferred embodiments, the mass percentage of the phosphate ester compound containing an unsaturated hydrocarbon group in the nonaqueous electrolytic solution is 0.1 to 0.4%.

In the nonaqueous electrolyte provided by the invention, the boron-containing lithium salt type additive is decomposed and ring-opened on the positive electrode side, and then polymerized to form a small amount of inorganic salt type protective film, so that the decomposition of the electrolyte under high pressure is inhibited to damage the electrode structure, and simultaneously, the B atoms exposed outside due to ring opening can attract hexafluorophosphate and fluoride ions to be combined with the electrolyte to inhibit the decomposition of the electrolyte. In addition, trace Hydrogen Fluoride (HF) in the dioxaboronate consumable system, and small amounts of lithium difluorooxalato borate and lithium tetrafluoroborate generated in the circulation process are beneficial to the comprehensive performance of the battery.

In some embodiments, the boron-containing lithium salt type additive includes at least one of lithium bis (oxalato) borate (LiBOB) and lithium difluoro (oxalato) borate (LiODFB).

In some embodiments, the non-aqueous electrolyte contains 0.1-1% by mass of the boron-containing lithium salt type additive.

In specific embodiments, the mass percentage of the boron-containing lithium salt type additive in the nonaqueous electrolyte may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95% or 1%.

In some preferred embodiments, the mass percentage of the boron-containing lithium salt type additive in the nonaqueous electrolyte is 0.3-0.8%

In the nonaqueous electrolyte provided by the invention, the tri-nitrile compound contains carbon-nitrogen triple bonds, and has high bond energy and is not easy to oxidize. Therefore, the tri-nitrile compound has strong oxidation resistance under high voltage (more than or equal to 4.6V) and good stability at the positive electrode side; in addition, the tri-nitrile compound can coordinate with metal ions with high valence state on the surface of the electrode, mask active ions on the surface of the positive electrode, and reduce the decomposition effect of the electrode on the electrolyte. In summary, the following is said: the tri-nitrile compound enhances the resistance of the electrolyte to the oxidation of the positive electrode, inhibits the decomposition of the electrolyte under high voltage, reduces the gas expansion of the battery under high voltage and high temperature, and improves the cycle stability and the high-temperature storage performance.

In some embodiments, the dinitrile compound comprises at least one of 1,2, 4-butane dinitrile, 1,3, 5-benzene dinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-dinitrile, 2-bromobenzene-1, 3, 5-dinitrile, 1,3, 6-hexane dinitrile, 1,2, 3-propane dinitrile or 1,3, 5-pentane dinitrile.

In some embodiments, the mass percentage of the tri-nitrile compound in the non-aqueous electrolyte is 0.1-1.5%.

In specific embodiments, the percentage by mass of the tri-nitrile compound in the non-aqueous electrolyte is 0.1%, 0.12%, 0.15%, 0.3%, 0.5%, 0.8%, 0.9%, 1.0%, 1.2%, 1.3%, 1.4% or 1.5%

In some preferred embodiments, the mass percentage of the tri-nitrile compound in the non-aqueous electrolyte is 0.3-1.2%.

In the nonaqueous electrolyte provided by the invention, the annular carboxylic anhydride can be subjected to preferential oxidation or reduction decomposition on the surface of the electrode in the charging process to form a good interface film, so that the electrolyte is prevented from directly contacting with the interface between the positive electrode and the negative electrode, and the corrosion of the electrolyte to the electrode and the dissolution of transition metal ions are inhibited; the cyclic carboxylic anhydride is acidic and can undergo a neutralization reaction with the basic positive electrode material, thereby inhibiting the decomposition of the carbonate by the alkali of the metal oxide. The annular carboxylic anhydride has better protection effect on the anode or the cathode, can improve the cycle life and coulombic efficiency of the lithium ion battery, and can inhibit the impedance from increasing.

In some embodiments, the cyclic carboxylic anhydride includes at least one of phthalic anhydride, citraconic anhydride, maleic anhydride, 2, 3-dimethylmaleic anhydride, 1-cyclohexyldiacetic anhydride, glutaric anhydride, and succinic anhydride.

In some embodiments, the mass percent of cyclic carboxylic anhydride in the nonaqueous electrolyte is 0.01-1%.

In specific embodiments, the mass percentage of cyclic carboxylic anhydride in the nonaqueous electrolyte is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.9% or 1%.

In some preferred embodiments, the mass percentage of the cyclic carboxylic anhydride in the nonaqueous electrolyte is 0.01-0.6%.

In some embodiments, the second additive comprises a tri-nitrile compound, and the mass percentage q of the second additive in the non-aqueous electrolyte is 0.3-1.2%; or,

the second additive comprises cyclic carboxylic anhydride, and the mass percentage content q of the second additive in the nonaqueous electrolyte is 0.01-1%; or,

the second additive comprises a tri-nitrile compound and cyclic carboxylic anhydride, and the mass percentage q of the second additive in the nonaqueous electrolyte is 0.3-1.5%.

In some embodiments, the non-aqueous organic solvent comprises at least one of a carbonate solvent, an ether solvent, a nitrile solvent, a carboxylate solvent, and a sulfone solvent.

In a preferred embodiment, the nonaqueous organic solvent comprises cyclic carbonate and chain carbonate, and the mass percentage of the cyclic carbonate in the nonaqueous electrolyte is a%, wherein a is more than or equal to 1 and less than or equal to 30, b/a is more than or equal to 0 and less than or equal to 1, and b is more than or equal to 1 and less than or equal to 10.

In some embodiments, the cyclic carbonate may specifically be, but is not limited to, at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), gamma-butyrolactone (GBL), butylene Carbonate (BC); the chain carbonate may be, but not limited to, at least one of dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC).

The content of the chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, and more preferably 25% by volume or more, based on the total amount of the solvent of the nonaqueous electrolytic solution. In addition, the volume ratio is usually 90% or less, preferably 85% or less, and more preferably 80% or less. By setting the content of the chain carbonate in the above range, the viscosity of the nonaqueous electrolytic solution can be easily set to an appropriate range, and the decrease in the ionic conductivity can be suppressed, thereby contributing to the improvement in the output characteristics of the nonaqueous electrolyte battery. When two or more kinds of chain carbonates are used in combination, the total amount of the chain carbonates may be set to satisfy the above range.

In some embodiments, it may also be preferable to use a chain carbonate having a fluorine atom (hereinafter simply referred to as "fluorinated chain carbonate"). The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, preferably 4 or less. In the case where the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms may be bonded to the same carbon or may be bonded to different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, and fluorinated diethyl carbonate derivatives.

In some embodiments, the ether solvent includes cyclic or chain ethers, preferably chain ethers of 3 to 10 carbon atoms and cyclic ethers of 3 to 6 carbon atoms, which may be specifically but not limited to 1, 3-Dioxolane (DOL), 1, 4-Dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH) ₃ -THF), 2-trifluoromethyl tetrahydrofuran (2-CF) ₃ -THF) at least one of; the chain ether may be, but not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether. Since the chain ether has high solvation ability with lithium ions and can improve ion dissociation properties, dimethoxymethane, diethoxymethane and ethoxymethoxymethane, which have low viscosity and can impart high ion conductivity, are particularly preferable. The ether compound may be used alone, or two or more of them may be used in any combination and ratio. The amount of the ether compound to be added is not particularly limited, and is arbitrary within a range that does not significantly impair the effect of the highly compacted lithium ion battery of the present invention, and is usually 1% or more, preferably 2% or more, more preferably 3% or more in terms of the volume ratio of the nonaqueous solvent of 100%, and is usually 30% or less, preferably 25% or less, more preferably 20% or less in terms of the volume ratio. When two or more ether compounds are used in combination, the total amount of the ether compounds may be set to satisfy the above range. When the amount of the ether compound is within the above preferred range, the effect of improving the ionic conductivity due to the increase in the dissociation degree of lithium ions and the decrease in the viscosity of the chain ether can be easily ensured. In addition, when the negative electrode active material is a carbon-based material, co-intercalation phenomenon due to the chain ether and lithium ions together can be suppressed, and thus input/output can be made possible The discharge characteristics and the charge/discharge rate characteristics are in appropriate ranges.

In some embodiments, the carboxylate solvent comprises a cyclic carboxylate and/or a chain carbonate. Examples of the cyclic carboxylic acid ester include: at least one of gamma-butyrolactone, gamma-valerolactone and delta-valerolactone. Examples of the chain carbonate include, for example: at least one of Methyl Acetate (MA), ethyl Acetate (EA), propyl acetate (EP), butyl acetate, propyl Propionate (PP) and butyl propionate.

In some embodiments, the sulfone-based solvent includes cyclic sulfones and chain sulfones, preferably compounds having generally 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms in the case of cyclic sulfones, and generally 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms in the case of chain sulfones. The amount of the sulfone-based solvent to be added is not particularly limited, and is arbitrary within a range that does not significantly impair the effect of the lithium ion battery of the present invention, and is usually 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume, and is usually 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume, based on the total amount of the solvent of the nonaqueous electrolyte. When two or more sulfone solvents are used in combination, the total amount of sulfone solvents may be set to satisfy the above range. When the amount of the sulfone-based solvent added is within the above range, a nonaqueous electrolytic solution excellent in high-temperature storage stability tends to be obtained.

In some embodiments, the nonaqueous organic solvent includes cyclic carbonate and chain carbonate, the mass percent of cyclic carbonate in the nonaqueous electrolyte is a%, wherein a is 1-30, and b/a is 0-1, b is 1-10.

In some embodiments, the lithium salt is selected from LiPF ₆ 、LiPO ₂ F ₂ 、LiBF ₄ 、LiSbF ₆ 、LiAsF ₆ 、LiN(SO ₂ CF ₃ ) ₂ 、LiN(SO ₂ C ₂ F ₅ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ 、LiN(SO ₂ F) ₂ 、LiClO ₄ 、LiAlCl ₄ 、LiCF ₃ SO ₃ 、Li ₂ B ₁₀ Cl ₁₀ 、LiSO ₂ F. At least one of LiTOP (lithium trioxalate phosphate), liDODFP (lithium difluorodioxalate phosphate), liOTFP (lithium tetrafluorooxalate phosphate), and a lower aliphatic carboxylic acid lithium salt.

In some embodiments, the concentration of the lithium salt in the nonaqueous electrolytic solution is 0.1mol/L to 8mol/L. In a preferred embodiment, the concentration of the lithium salt in the nonaqueous electrolytic solution is 0.5mol/L to 2.5mol/L. Specifically, in the nonaqueous electrolytic solution, the concentration of the lithium salt may be 0.5mol/L, 1mol/L, 1.5mol/L, 2mol/L, 2.5mol/L.

In some embodiments, the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound;

preferably, the content of the additive is 0.01 to 30% based on 100% of the total mass of the nonaqueous electrolytic solution.

In some embodiments, the cyclic sulfate compound is selected from the group consisting of vinyl sulfate, propylene sulfate, vinyl methyl sulfate, At least one of (a) and (b);

the sultone compound is at least one selected from 1, 3-propane sultone, 1, 4-butane sultone and 1, 3-propylene sultone;

the cyclic carbonate compound is at least one selected from ethylene carbonate, methylene ethylene carbonate, trifluoromethyl ethylene carbonate, difluoro ethylene carbonate or a compound shown in a structural formula 2:

in the structural formula 2, R ₂₁ 、R ₂₂ 、R ₂₃ 、R ₂₄ 、R ₂₅ 、R ₂₆ Each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group.

In other embodiments, the additive may further comprise other additives that improve battery performance: for example, additives that enhance the safety performance of the battery, specifically flame retardant additives such as fluorophosphate and cyclophosphazene, or overcharge-preventing additives such as t-amyl benzene and t-butyl benzene.

In general, the content of any one of the optional substances in the additive is 10% or less, preferably 0.1 to 5%, more preferably 0.1 to 2% in the nonaqueous electrolytic solution unless otherwise specified. Specifically, the content of any optional substance in the additive may 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%, 8.5%, 9%, 9.5%, 10%.

In some embodiments, the positive electrode includes a positive electrode material layer including a positive electrode active material including at least one of a compound represented by formula (a) or formula (B):

LiNi _x M _2-x A _y O _r B _p (A)

nLi ₂ MnO ₃ ·(1-n)LiMO ₂ (B)

In the formula (A), x is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 2-x is more than or equal to 2, y is more than or equal to 0 and less than or equal to 0.05,1, r is more than or equal to 0 and less than or equal to 4, p is more than or equal to 0 and less than or equal to 4, M is selected from at least one of Mn or Al, A is selected from at least one of Zr, zn, cu, cr, fe, V, ti, sr, sb, sn, Y, W, al, nb, and B is selected from at least one of F, cl and Br;

in the formula (B), 0< n <1, and M is selected from at least one of Ni, co, mn or Al.

Preferably, the positive electrode active material is selected from LiNi _0.5 Mn _1.5 O ₄ 、LiNi _0.45 Mn _1.55 O ₄ 、LiNi _0.55 Mn ₁₄₅ O ₄ Or LiNi _0.6 Mn _1.4 O ₄ 、Li _1.2 Ni _0.2 Mn _0.6 O ₂ 、Li ₂ MnO ₃ 、0.5Li ₂ MnO ₃ ·0.5LiNiO ₂ Or 0.3Li ₂ MnO ₃ ·0.7LiNiO ₂ 。

In a more preferred embodiment, the surface of the positive electrode active material is provided with an oxide coating layer, and the oxide coating layer includes a coating element selected from at least one of Al, ba, zn, ti, mg, zr, W, Y, si, sn, B, co, P.

In some embodiments, the positive current collector is selected from a metal material that is electron conductive, preferably, the positive current collector includes at least one of Al, ni, tin, copper, stainless steel, and in more preferred embodiments, the positive current collector is selected from aluminum foil.

In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent.

The positive electrode binder includes thermoplastic resins such as polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, polypropylene, and the like; an acrylic resin; sodium hydroxymethyl cellulose; and at least one of styrene butadiene rubber.

The positive electrode conductive agent comprises at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

In some embodiments, the anode material layer includes an anode active material including at least one of a carbon-based anode, a silicon-based anode, a tin-based anode, and a lithium anode. Wherein the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, and the like; the silicon-based anode may include a silicon material, an oxide of silicon, a silicon-carbon composite material, a silicon alloy material, or the like; the tin-based negative electrode may include tin, tin carbon, tin oxygen, and tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium silicon alloy, a lithium sodium alloy, a lithium potassium alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.

In some embodiments, the negative electrode material layer further comprises 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 selectable ranges of the negative electrode binder and the negative electrode conductive agent are the same as those of the positive electrode binder and the positive electrode conductive agent, respectively, and are not described in detail herein.

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

The negative electrode current collector is selected from a metal material capable of conducting electrons, preferably, the negative electrode current collector comprises at least one of Al, ni, tin, copper, stainless steel, and in a more preferred embodiment, the negative electrode current collector is selected from copper foil.

In some embodiments, the high voltage lithium ion battery further comprises a separator positioned between the positive electrode and the negative electrode.

The membrane can be a conventional membrane, such as a ceramic membrane, a polymer membrane, a non-woven fabric, and an inorganic-organic composite membrane, and the polymer membrane is at least one selected from polyolefin, polyamide, polysulfone, polyphosphazene, polyethersulfone, polyetheretherketone, polyetheramide, and polyacrylonitrile, including but not limited to a membrane such as single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP, and three-layer PP/PE/PP.

In a preferred embodiment, the separator comprises a substrate separator and a surface coating, wherein the surface coating is inorganic particles or organic gel or a mixture of the inorganic particles and the organic gel, and is coated on at least one side surface of the substrate separator.

The invention is further illustrated by the following examples.

TABLE 1

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Example 1

The present embodiment describes the present invention by taking a lithium ion battery as an example, and the present invention comprises the following operation steps:

1) Preparation of nonaqueous electrolyte:

mixing Ethylene Carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) according to the mass ratio of EC: DEC: EMC=1:1:1, and then adding lithium hexafluorophosphate (LiPF) ₆ ) To a molar concentration of 1mol/L, additives were added in the mass percentages indicated in Table 1.

2) Preparation of a positive plate:

mixed positive electrode active material LiNi _0.5 Mn _1.5 O ₄ Conductive carbon black Super-P and a positive electrode binder, and then dispersing them in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. And (3) taking the aluminum foil as a positive electrode current collector, uniformly coating the slurry on two sides of the aluminum foil, drying, calendaring and vacuum drying to obtain a positive electrode material layer, and welding an aluminum outgoing line by using an ultrasonic welding machine to obtain the positive electrode plate.

3) Preparing a negative plate:

the negative electrode active material artificial graphite, conductive carbon black Super-P, binder Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry. Coating the slurry on two sides of a copper foil, drying, calendaring and vacuum drying, and welding a nickel outgoing line by an ultrasonic welding machine to obtain the negative plate.

4) Preparation of the battery cell:

and placing a three-layer diaphragm with the thickness of 20 mu m between the positive plate and the negative plate, winding a sandwich structure formed by the positive plate, the negative plate and the diaphragm, flattening the winding body, putting into an aluminum foil packaging bag, and baking for 48 hours at the temperature of 85 ℃ in vacuum to obtain the battery cell to be injected with the liquid.

5) And (3) filling and forming the battery cell:

and (3) injecting the prepared electrolyte into a cell in a glove box with the dew point controlled below-40 ℃, recording the injection amount of the electrolyte, and standing for 24 hours after vacuum packaging.

Then the first charge is conventionally formed by the following steps: charging for 2-3 h at constant current of 0.05C, charging for 2-3 h at constant current of 0.1C, charging for 1-2 h at constant current of 0.2C, vacuum sealing, charging to 4.7V at constant current of 0.2C, charging to 0.02C at constant voltage, standing for 5min, discharging to 3.4V at constant current of 0.2C, calculating the retention coefficient of the battery cell according to discharge capacity, and recording in Table 1 to obtain LiNi _0.5 Mn _1.5 O ₄ Artificial graphite lithium ion battery.

Examples 2 to 25

Examples 2 to 25 are for illustrating the lithium ion battery and the method for preparing the same disclosed in the present invention, and include most of the operation steps in example 1, which are different in that:

Additives and amounts thereof and retention coefficients shown in examples 2 to 25 in Table 1 were used.

Comparative examples 1 to 23

Comparative examples 1 to 23 are for comparative illustration of the lithium ion battery and the method for preparing the same disclosed in the present invention, including most of the operation steps in example 1, which are different in that:

additives and amounts thereof as shown in comparative examples 1 to 23 and liquid retention coefficients in Table 1 were used.

Performance testing

The lithium ion battery prepared by the method is subjected to the following performance test:

1. battery cycle performance test:

the lithium ion batteries prepared in examples and comparative examples were charged at a rate of 0.5C and discharged at a rate of 1C at 25C, the capacity of the battery at the first cycle of discharge was recorded, a full charge discharge cycle test was performed in a range of 4.7V at the upper limit of the charge-discharge cut-off voltage and 3.4V at the lower limit of the cut-off voltage, the discharge capacity of the battery at the 600 th cycle was recorded after 600 cycles, and the capacity retention rate was calculated according to the following formula:

capacity retention (%) at 600 cycles at 25 ℃ =discharge capacity at 600 cycles/battery capacity at first cycle discharge ×100%.

2. High temperature storage performance test for battery

And (3) charging the conventionally formed battery to 4.7V at 25 ℃ with a constant current and constant voltage of 0.5C until the current reaches 0.05C, then discharging to 3.4V with a constant current and constant voltage of 1C, continuously charging to 4.7V with a constant current and constant voltage of 0.5C until the current reaches 0.05C, recording the initial volume of the battery, then standing for 30 days at 45 ℃, and testing the stored volume of the battery. The calculation formula is as follows:

Gas production= (volume after battery storage-initial volume of battery)/battery rated capacity.

(1) The test results obtained in examples 1 to 19 and comparative examples 1 to 23 are filled in Table 2.

TABLE 2

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From the test results of examples 1 to 19 and comparative examples 1 to 23, it is understood that fluoroethylene carbonate, an unsaturated hydrocarbon group-containing phosphate ester compound, a boron-containing lithium salt type additive, a second additive (a tri-nitrile compound and/or a cyclic carboxylic anhydride) have a clear correlation in terms of the formation of an interface film on the positive and negative electrode surfaces, and that when the mass percentage b of the fluorocyclic carbonate in the nonaqueous electrolytic solution, the sum p of the mass percentages of the unsaturated hydrocarbon group-containing phosphate ester compound and the boron-containing lithium salt type additive, the mass percentage q of the second additive (the tri-nitrile compound and/or the cyclic carboxylic anhydride) and the retention coefficient E satisfy the following formula: when [ (p+q) x E ]/b is more than or equal to 1 and less than or equal to 26, b is more than or equal to 0.05 and less than or equal to 1, p is more than or equal to 0.2 and less than or equal to 1.5,0.01, q is more than or equal to 1.5,2.6 and E is more than or equal to 3.3, the obtained lithium ion battery has better high-voltage resistance, and can effectively inhibit gas production of high-temperature storage and improve the cycle life under the condition of high working voltage. It is supposed that fluoroethylene carbonate, a phosphate compound containing unsaturated hydrocarbon groups, a boron-containing lithium salt additive and a second additive are jointly involved in the formation of an interfacial film on the surface of the positive electrode and the negative electrode, and the interfacial film formed by adjusting the mutual proportion of the additives can effectively inhibit the dissolution of transition metal ions in the positive electrode active material, on the other hand, the electrolyte retention coefficient E of the electrolyte in the lithium ion battery influences the infiltration effect of the electrolyte on the positive electrode material and the negative electrode material, plays an indirect regulation role on the film forming quality of the interfacial film, and is beneficial to obtaining a compact and stable interfacial film on the surface of the positive electrode and the negative electrode through the definition of the relationship, thereby effectively inhibiting the interfacial reaction of the electrolyte on the surface of the positive electrode and the negative electrode under the conditions of high pressure and high temperature, reducing the gas production of the battery and prolonging the cycle life of the battery.

As is clear from the test results of examples 1 to 16, when the mass percentage content b of the fluorinated cyclic carbonate, the sum p of the mass percentages of the unsaturated hydrocarbon group-containing phosphate compound and the boron-containing lithium salt type additive, the mass percentage content q of the second additive (the tri-nitrile compound and/or the cyclic carboxylic anhydride) and the retention coefficient E in the nonaqueous electrolytic solution further satisfy the condition of 1.5 [ (p+q) ×E ]/b.ltoreq.16, and 0.1.ltoreq.b < 1, 0.2.ltoreq.p.ltoreq. 1.1,0.01.ltoreq.q.ltoreq. 1.2,2.6.E.ltoreq.3.1, the obtained lithium ion battery has the best overall performance.

From the test results of comparative examples 2 to 6 and comparative examples 10 to 11, it is apparent that when only one of the unsaturated hydrocarbon group-containing phosphate compound and the boron-containing lithium salt type additive is added to the nonaqueous electrolyte, the resulting lithium ion battery has problems of serious gas generation at high temperature and cycle skip, indicating that the performance improvement effect on the positive and negative electrode interface film is exhibited if and only if the unsaturated hydrocarbon group-containing phosphate compound and the boron-containing lithium salt type additive are simultaneously present, the addition of the unsaturated hydrocarbon group-containing phosphate compound alone or the boron-containing lithium salt type additive alone cannot satisfy the application of the high-voltage lithium ion battery at high temperature. In particular, as can be seen from comparative example 7, when the unsaturated hydrocarbon group-containing phosphate compound is replaced with a saturated phosphate compound, it does not exert a similar effect of elevation to the unsaturated hydrocarbon group-containing phosphate compound, indicating that the unsaturated hydrocarbon group carried in the phosphate compound plays a decisive role in its synergistic effect with the boron-containing lithium salt type additive. As can be seen from comparative examples 8 and 9, when the tri-nitrile compound is replaced with a nitrile compound such as acetonitrile or succinonitrile, the performance improvement effect on the lithium ion battery is inferior to that of the tri-nitrile compound, indicating that the number of nitrile groups in the tri-nitrile compound is related to the performance exertion thereof in the battery system of the present invention.

From the test results of comparative examples 20 to 23, it was revealed that when the b value, q value, p value and E value do not satisfy the limits of 1.ltoreq [ (p+q). Times.E ]/b.ltoreq.26, deterioration of the high temperature performance and cycle performance of the battery resulted, indicating that the sum p of the mass percentages of the fluorinated cyclic carbonate b, the unsaturated hydrocarbon group-containing phosphate compound and the boron-containing lithium salt type additive in the nonaqueous electrolyte, the mass percentage q of the second additive (the tri-nitrile compound and/or the cyclic carboxylic anhydride) and the retention coefficient E had an effect of mutual influence, and only when the four reached a better equilibrium state, a more remarkable improvement effect was achieved on the high temperature performance and cycle performance of the high-voltage lithium ion battery. From the test results of comparative examples 10 to 17, it is understood that when one of the b value, q value, p value and E value exceeds the limit range, even if the relation is satisfied: the requirements of [ (p+q) x E ]/b is less than or equal to 26, and the gas production and the circulation performance of the lithium ion battery at normal temperature under the high-temperature storage condition are also poor, which indicates that the mass percent b of the fluorinated cyclic carbonate, the sum p of the mass percent of the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive in the nonaqueous electrolyte, the mass percent q of the second additive (the tri-nitrile compound and/or the cyclic carboxylic anhydride) and the excessively high or excessively low liquid retention coefficient E can influence the formation quality of the anode and cathode surface interface film, and further the requirements of the high-voltage lithium ion battery cannot be met.

(2) The test results obtained in examples 14 and 20 to 25 are shown in Table 3.

TABLE 3 Table 3

Group of	45 ℃ cycle storage 30 days gas production (mL/Ah)	600 cycles (0.5/1C) of capacity retention (%)
			Example 14	0.82	96.3
Example 20	0.81	95.2
			Example 21	0.81	95.2
Example 22	0.73	95.9
			Example 23	0.74	95.3
Example 24	0.72	94.2
			Example 25	0.69	95.8

From the test results of examples 14, 20 to 25, when different fluorinated cyclic carbonates, different unsaturated hydrocarbon group-containing phosphate compounds, different boron-containing lithium salt type additives, different tri-nitrile compounds and different cyclic carboxylic anhydrides were used, and the mass percentage b of the fluorinated cyclic carbonates, the sum p of the mass percentages of the unsaturated hydrocarbon group-containing phosphate compounds and the boron-containing lithium salt type additives, the mass percentage q of the second additives (tri-nitrile compounds and cyclic carboxylic anhydrides) and the liquid retention coefficient E in the nonaqueous electrolytic solution satisfied the following relationship: when [ (p+q) ×E ]/b is less than or equal to 1 and less than or equal to 26, and b is less than or equal to 0.05 and less than or equal to 1, p is less than or equal to 0.2 and less than or equal to 1.5,0.01, q is less than or equal to 1.5,2.6 and E is less than or equal to 3.3, the obtained lithium ion battery has better performance at high pressure and high temperature, which shows that the battery system provided by the invention has universality for different fluorinated cyclic carbonates, different phosphate compounds containing unsaturated hydrocarbon groups, different boron-containing lithium salt type additives, different dinitrile compounds and different cyclic carboxylic acid anhydrides.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims (10)

1. A high voltage lithium ion battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, the nonaqueous electrolyte comprising a nonaqueous organic solvent, an additive comprising a fluorinated cyclic carbonate, a phosphate compound containing an unsaturated hydrocarbon group, a boron-containing lithium salt additive, and a second additive comprising at least one of a tri-nitrile compound and a cyclic carboxylic anhydride;

the high-voltage lithium ion battery meets the following conditions:

1-26 [ (p+q) x E ]/b-0.05-1, 0.2-1.5,0.01-1.5,2.6-3.3;

wherein b is the mass percentage content of fluorinated cyclic carbonate in the nonaqueous electrolyte, and the unit is;

p is the sum of the mass percent of the phosphate compound containing unsaturated hydrocarbon groups and the boron-containing lithium salt type additive in the nonaqueous electrolyte, and the unit is;

q is the mass percentage content of the second additive in the nonaqueous electrolyte, and the unit is;

E is the liquid retention coefficient of nonaqueous electrolyte in the lithium ion battery, and the unit is g/Ah;

the charge cut-off voltage of the high-voltage lithium ion battery is more than or equal to 4.6V.

2. The high voltage lithium ion battery of claim 1, wherein the high voltage lithium ion battery meets the following conditions:

1.5≤[(p+q)×E]/b≤16。

3. the high voltage lithium ion battery of claim 1, wherein the high voltage lithium ion battery meets the following conditions: b is more than or equal to 0.1 and less than 1, p is more than or equal to 0.2 and less than or equal to 1.1,0.01, q is more than or equal to 1.2,2.6 and E is more than or equal to 3.1.

4. The high voltage lithium ion battery of claim 1, wherein the fluorinated cyclic carbonate comprises at least one of fluoroethylene carbonate, 4-difluoroethylene carbonate, 4, 5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4, 5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4-difluoro-5-methylethylene carbonate, 4- (fluoromethyl) -ethylene carbonate, 4- (difluoromethyl) -ethylene carbonate, 4- (trifluoromethyl) -ethylene carbonate, 4- (fluoromethyl) -4-fluoroethylene carbonate, 4- (fluoromethyl) -5-fluoroethylene carbonate, 4-fluoro-4, 5-dimethylethylene carbonate, 4, 5-difluoro-4, 5-dimethylethylene carbonate, and 4, 4-difluoro-5, 5-dimethylethylene carbonate.

5. The high voltage lithium ion battery of claim 1, wherein the unsaturated hydrocarbon group-containing phosphate compound is selected from the group consisting of compounds represented by structural formula 1:

in the structural formula 1, R ₁ 、R ₂ 、R ₃ Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halogenated hydrocarbon groups, -Si (C) _m H _2m+1 ) ₃ M is a natural number of 1 to 3, and R ₁ 、R ₂ 、R ₃ At least one of them is an unsaturated hydrocarbon group;

preferably, the method comprises the steps of, the compound shown in the structural formula 1 comprises at least one of tripolyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2, 2-trifluoroethyl phosphate, dipropargyl-3, 3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2, 2-trifluoroethyl phosphate, diallyl-3, 3-trifluoropropyl phosphate and diallyl hexafluoroisopropyl phosphate;

preferably, the mass percentage of the unsaturated hydrocarbon group-containing phosphate compound in the nonaqueous electrolytic solution is 0.05 to 0.8%.

6. The high voltage lithium ion battery of claim 1, wherein the boron-containing lithium salt additive comprises at least one of lithium bis (oxalato) borate and lithium difluoro (oxalato) borate;

preferably, the mass percentage of the boron-containing lithium salt type additive in the nonaqueous electrolyte is 0.1-1%.

7. The high voltage lithium ion battery of claim 1, wherein the tri-nitrile compound comprises at least one of 1,2, 4-butane tri-nitrile, 1,3, 5-benzene tri-nitrile, 2,4, 6-trifluorobenzene-1, 3, 5-tri-nitrile, 2-bromobenzene-1, 3, 5-tri-nitrile, 1,3, 6-hexane tri-nitrile, 1,2, 3-propane tri-nitrile, or 1,3, 5-pentane tri-nitrile;

preferably, the mass percentage of the tri-nitrile compound in the non-aqueous electrolyte is 0.1-1.5%.

8. The high voltage lithium ion battery of claim 1, wherein the cyclic carboxylic anhydride comprises at least one of phthalic anhydride, citraconic anhydride, maleic anhydride, 2, 3-dimethylmaleic anhydride, 1-cyclohexyldiacetic anhydride, glutaric anhydride, and succinic anhydride;

preferably, the mass percentage of the cyclic carboxylic anhydride in the nonaqueous electrolyte is 0.01-1%.

9. The high-voltage lithium ion battery according to claim 1, wherein the second additive comprises a tri-nitrile compound, and the mass percentage q of the second additive in the nonaqueous electrolyte is 0.3-1.2%; or,

The second additive comprises cyclic carboxylic anhydride, and the mass percentage content q of the second additive in the nonaqueous electrolyte is 0.01-1%; or,

the second additive comprises a tri-nitrile compound and cyclic carboxylic anhydride, and the mass percentage q of the second additive in the nonaqueous electrolyte is 0.3-1.5%.

10. The high voltage lithium ion battery of claim 1, wherein the positive electrode comprises a positive electrode material layer comprising a positive electrode active material comprising at least one of a compound represented by formula (a) or formula (B):

LiNi _x M _2-x A _y O _r B _p (A)

nLi ₂ MnO ₃ ·(1-n)LiMO ₂ (B)

In the formula (A), x is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 2-x is more than or equal to 2, y is more than or equal to 0 and less than or equal to 0.05,1, r is more than or equal to 0 and less than or equal to 4, p is more than or equal to 0 and less than or equal to 4, M is selected from at least one of Mn or Al, A is selected from at least one of Zr, zn, cu, cr, fe, V, ti, sr, sb, sn, Y, W, al, nb, and B is selected from at least one of F, cl and Br;

in the formula (B), 0< n <1, and M is selected from at least one of Ni, co, mn or Al.