Lithium-ion battery

Abstract

The present application provides a battery, specifically a lithium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte. Carboxylic ester containing a branched chain structure is used as a main solvent of the electrolyte, better meeting the requirement of high-voltage battery systems, well improving the high-temperature and high-voltage stability of batteries, and improving the low-temperature cycle performance of batteries.

Description

A lithium ion battery TECHNICAL FIELD

[0001] The present application relates to a lithium ion battery, in particular to a lithium ion battery. BACKGROUND

[0002] With the rapid development of electric vehicles and energy storage power stations, developing high energy density lithium ion batteries (LIBs) has become a top priority in the new energy field. One of the most effective strategies to improve the energy density of lithium ion batteries is to increase the output voltage of the battery, which mainly depends on the positive electrode material. The high-voltage lithium ion battery positive electrode materials currently studied mainly include four categories (>4V vs. Li / Li+), including lithium-rich layered oxides, nickel-rich layered oxides, spinel oxides, and high-voltage polyanion compounds. However, it still faces severe challenges to maintain high capacity, excellent rate performance and long service life while increasing the output voltage of these positive electrode materials.

[0003] The electrochemical window of the traditional carbonate-based electrolyte (EC) is less than 4.3V, which cannot match the electrochemical window of the high-voltage positive electrode. Currently, several failure mechanisms of EC-based electrolytes have been proposed. It should be noted that these reaction mechanisms play a synergistic role in the decomposition of EC-based electrolytes. The design of oxidation-resistant electrolytes mainly focuses on the selection of oxidation-resistant solvents and film-forming additives. In addition, high-salt electrolytes also have the potential to match high-voltage positive electrodes.

[0004] SUMMARY

[0005] To solve the claimed technical problems, the present application provides a lithium ion battery, comprising a positive electrode, a negative electrode, an electrolyte, the positive electrode comprising a positive electrode active material, the charge cut-off voltage of the positive electrode active material being higher than 4.5V, the electrolyte comprising a solvent, the solvent comprising one or more compounds A satisfying the following structural formula:

[0006] wherein R1 is a saturated hydrocarbon group or a fluorocarbon group and the number of hydrogen atoms in the main chain thereof is ≤1;

[0007] R2 is selected from a hydrocarbon group or a fluorocarbon group having a carbon atom number of 1-8.

[0008] Preferably, the number of carbon atoms in the main chain of R1 is 1-5.

[0009] Preferably, the number of carbon atoms in the main chain of R2 is 1-3.

[0010] Preferably, R2 is a methyl group or an ethyl group.

[0011] Preferably, R1 and R2 are independently selected from a hydrocarbon group or a fluorocarbon group having a carbon atom number of 1-3.

[0012] Preferably, the R2 backbone carbon atoms do not contain hydrogen atoms or fluorine atoms.

[0013] Preferably, the R1 backbone carbon atoms do not contain hydrogen atoms or fluorine atoms.

[0014] Preferably, in the compound A, at least one H atom in R1 is replaced by F.

[0015] Preferably, in the compound A, at least one H atom in R2 is replaced by F.

[0016] Preferably, the number of hydrogen atoms in the R2 backbone is less than 1.

[0017] Preferably, the mass of the compound A is 70-100% of the total mass of the solvent.

[0018] Preferably, the mass of the compound A is 80-100% of the total mass of the solvent.

[0019] Preferably, the solvent further comprises a cyclic carbonate, and the mass of the cyclic carbonate is 0-20% of the total mass of the solvent.

[0020] Preferably, the mass of the cyclic carbonate is 0-10% of the total mass of the solvent.

[0021] Preferably, the mass of the cyclic carbonate is 5% of the total mass of the solvent.

[0022] Preferably, the solvent further comprises a chain carbonate, and the mass of the chain carbonate is 0-20% of the total mass of the solvent.

[0023] Preferably, the mass of the chain carbonate is 0-10% of the total mass of the solvent.

[0024] Preferably, the sum of the mass of the cyclic carbonate and the mass of the chain carbonate is 0-5% of the total mass of the solvent, and the mass of the cyclic carbonate and the mass of the chain carbonate are not both zero.

[0025] Preferably, the positive active material is a mixture, and at least one of the positive active materials has a charge cut-off voltage higher than 4.5V.

[0026] Preferably, the positive active material is a mixture of multiple positive active materials with charge cut-off voltages greater than 4.5V.

[0027] Preferably, the positive active material is a pure substance.

[0028] Preferably, the positive active material has a charge cut-off voltage higher than 4.5V.

[0029] Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.6V.

[0030] Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.7V.

[0031] Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.8V.

[0032] Preferably, the lithium ion battery further comprises a separator or an electrolyte membrane.

[0033] The lithium ion battery of the present application can simultaneously take into account good cycle performance, safety performance and kinetic performance, and can maintain stable performance under the use of high-voltage positive electrode material. DETAILED DESCRIPTION

[0034] The present embodiment relates to a lithium ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode active material, the charging cut-off voltage of the positive electrode active material is higher than 4.5V, and the electrolyte comprises a solvent, the solvent comprising one or more compounds A satisfying the following structural formula I:

[0035] wherein, R1 is a saturated hydrocarbon group or a fluorocarbon group, and the number of hydrogen atoms in the main chain thereof is ≤1;

[0036] R2 is selected from a hydrocarbon group or a fluorocarbon group having 1-8 carbon atoms.

[0037] As an embodiment, the number of carbon atoms in the main chain of R1 is 1-5.

[0038] As an embodiment, the number of carbon atoms in the main chain of R1 is 1-3.

[0039] As an embodiment, the number of carbon atoms in the main chain of R2 is 1-3.

[0040] As an embodiment, R2 is a methyl group or an ethyl group.

[0041] As an embodiment, R1 and R2 are independently selected from a hydrocarbon group having 1-3 carbon atoms.

[0042] As an embodiment, the number of carbon atoms in the main chain of R2 does not contain hydrogen atoms or fluorine atoms.

[0043] As an embodiment, in the compound A, at least one H atom of R1 and R2 is substituted by F.

[0044] As an embodiment, in the compound A, at least one H atom of R1 is substituted by F.

[0045] As an embodiment, at least one H atom in R2 is replaced by F in the compound A.

[0046] As an embodiment, the number of methyl groups in R2 is more than 2, and each methyl group has at least one H replaced by F.

[0047] As an embodiment, the number of hydrogen atoms in the main chain of R2 is less than or equal to 1.

[0048] It can be understood that, no matter R1 or R2, the meaning of the main chain is that when R1 or R2 contains a special functional group, the carbon chain containing the special functional group is the main chain; if it does not contain a special functional group, the longest carbon chain is the main chain, and it should be noted that the hydrogen itself is not counted in the length of the main chain.

[0049] For example, R1C(O)OCH(CH3)C(CH3)3, wherein R2 is CH(CH3)C(CH3)3, and -CH-C- is the main chain, the number of carbon atoms in the main chain is 2, wherein -CH-C- is counted as the number of carbon atoms in the main chain, and the terminal methyl group (CH3) is not counted as the number of carbon atoms in the main chain; therefore, the H in the terminal methyl group is not counted as the number of hydrogen atoms in the main chain. The number of hydrogen atoms in the main chain of -CH-C- is 1.

[0050] It can be understood that F substitution is a known technology, and fluorine-substituted ester compounds have relatively better certain performance, and any fluorine-substituted modification of ester compounds based on actual use needs without departing from the inventive concept of the present application should be considered as the protection scope of the present application.

[0051] It can be understood that high-voltage positive electrode material refers to a positive electrode active material having a relatively high working voltage, and generally, a positive electrode material having a charge cut-off voltage of 4.5 V or higher is referred to as a high-voltage material. At present, the traditional carbonate-based electrolyte cannot be well adapted to the high-voltage system, and improving the oxidation resistance of the electrolyte is the main means, and the present application does not have special requirements for the positive electrode material, and any known high-voltage positive electrode material can be used in the present application without departing from the inventive concept of the present application.

[0052] Preferably, the positive electrode active material is a mixture, and at least one of the positive electrode active materials has a charge cut-off voltage higher than 4.5 V.

[0053] Preferably, the positive electrode active material is a mixture of a plurality of positive electrode active materials having a charge cut-off voltage greater than 4.5 V.

[0054] Preferably, the positive electrode active material is a pure substance.

[0055] Preferably, the positive electrode active material has a charge cut-off voltage higher than 4.5 V.

[0056] Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.6 V;

[0057] Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.7 V;

[0058] Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.8 V.

[0059] It can be understood that the pure material refers to only containing one positive electrode active material, and the existence of impurities and non-positive electrode active material additives in the single positive electrode active material system should not be understood as the positive electrode active material system being a mixture.

[0060] Preferably, the positive electrode active material with a charging cut-off voltage greater than 4.5 V accounts for more than 50 wt% of all positive electrode active materials in the positive electrode active material layer.

[0061] Preferably, the positive electrode active material with a charging cut-off voltage greater than 4.5 V accounts for more than 60 wt% of all positive electrode active materials in the positive electrode active material layer.

[0062] Preferably, the positive electrode active material with a charging cut-off voltage greater than 4.5 V accounts for more than 70 wt% of all positive electrode active materials in the positive electrode active material layer.

[0063] Preferably, the positive electrode active material with a charging cut-off voltage greater than 4.5 V accounts for more than 80 wt% of all positive electrode active materials in the positive electrode active material layer.

[0064] Preferably, the positive electrode active material with a charging cut-off voltage greater than 4.5 V accounts for more than 90 wt% of all positive electrode active materials in the positive electrode active material layer.

[0065] Preferably, the positive electrode active material with a charging cut-off voltage greater than 4.5 V accounts for more than 95 wt% of all positive electrode active materials in the positive electrode active material layer.

[0066] It can be understood that when a multi-layer electrode is used, as long as one layer in the entire positive electrode active material layer meets the above proportion requirement, it should be considered to belong to the protection scope of the present application. The above positive electrode active material layer should be understood as the active material layer containing the positive electrode active material with a charging cut-off voltage greater than 4.5 V, rather than the entire positive electrode active material layer.

[0067] Only as an illustrative example, but not as a limitation of the protection scope, the positive electrode active material working at a potential of 4.5 V or higher with respect to lithium is preferably a lithium-containing composite oxide. The lithium-containing composite oxide includes spinel-type lithium-manganese composite oxide, olivine-type lithium-containing manganese composite oxide, and inverse spinel-type lithium-containing manganese composite oxide. Specifically, for example, Li a (M x Mn2-x )O4 represents a compound, wherein 0.4 < x < 2, and 0 < a < 1.2; and M is at least one selected from the group consisting of Ni, Co, Fe, Cr, and Cu. Among them, from the viewpoint of safety, spinel-type lithium manganese composite oxides are preferable.

[0068] In addition, as the lithium manganese composite oxide containing Mn, for example, a spinel-type manganese oxide can be used.

[0069] Preferably, a lithium manganese composite oxide represented by the following formula is preferably used. Li a (M x Mn 2-x-y Y y )(O 4-w Z w ) wherein 0.4 < x < 1.2, 0 < y, x + y < 2, 0 < a < 1.2, and 0 < w < 1; M is at least one selected from Co, Ni, Fe, Cr, and Cu; Y is at least one selected from Li, B, Na, Mg, Al, Ti, Si, K, and Ca; and Z is at least one selected from F and Cl.

[0070] Preferably, from the viewpoint of obtaining sufficient capacity and achieving longer life, among these lithium manganese composite oxides, a spinel-type compound represented by the following formula is more preferably used. LiNi x Mn 2-x-y A y O4 wherein, 0.4 < x < 0.6 and 0 < y < 0.3, and A represents at least one metal selected from Li, B, Na, Mg, Al, Ti, and Si. Preferably, 0 < y < 0.2.

[0071] Preferably, examples of other high-voltage positive electrode active materials include olivine-type compounds represented by the following formula.

[0072] Li x MPO4F y wherein 0 < x < 2 and 0 < y < 1, and M is at least one selected from Co and Ni.

[0073] Preferably, examples of positive electrode active materials for which the charge cut-off voltage reaches 4.8 V include compounds represented by the following formula.

[0074] Li x [Li a M b Mn 1-a-b ]O2 wherein 0 < x < 1, 0.05 < a < 0.3, and 0.1 < b < 0.4, and M is at least one selected from Ni, Co, Fe, and Cr.

[0075] It can be understood that when the positive active material is a mixture of high-voltage positive active material and positive active material with a charge cut-off voltage lower than 4.5V, the kind of positive active material with a charge cut-off voltage lower than 4.5V is not particularly limited in the present application, and any kind of positive active material that can be inhibited can be used in the present application without departing from the inventive concept of the present application. By way of example only and not by way of limitation, the positive active material with a charge cut-off voltage lower than 4.5V is one of a layered oxide positive material, a spinel positive and a polyanion positive. For example, the layered oxide positive (e.g., rock salt layered oxide) comprises one or more lithium-based positive active materials selected from the group consisting of LiCoO2(LCO), LiNi 1-x-y Co x Al y O2(0≤x≤1 and 0≤y≤1) and Li 1+x MO2(M is one of Ni, Co and Al and 0≤x≤1); the spinel positive comprises one or more lithium-based positive active materials selected from the group consisting of LiMn2O4(LMO) and LiNi x Mn 1.5 O4. The olivine-type cathode comprises one or more lithium-based positive active materials LiMPO4(wherein M is at least one of Fe, Ni, Co); it can be understood that the above-mentioned materials are only illustrative examples and not by way of limitation.

[0076] In one embodiment, one or more lithium-based positive active materials can optionally be coated (e.g., by LiNbO3and / or Al2O3) and / or can be doped (e.g., by magnesium (Mg)) and / or can be coated with two positive active materials to form a core-shell structure, such as coating a high voltage positive material with a low voltage positive material, it being understood that modifications to the positive material or positive active material layer are within the scope of the present application. Further, in certain embodiments, one or more lithium-based positive active materials can optionally be mixed with one or more conductive agents that provide an electronic conduction path and / or at least one polymeric binder that improves the structural integrity of the positive electrode. For example, the positive active material layer can include greater than or equal to about 30 wt% to less than or equal to about 99 wt% of one or more lithium-based positive active materials; greater than or equal to about 0 wt% to less than or equal to about 30 wt% of a conductive agent; and greater than or equal to about 0 wt% to less than or equal to about 20 wt% of a binder, and in certain aspects, optionally greater than or equal to about 1 wt% to less than or equal to about 20 wt% of a binder. In the lithium-based positive active materials, the present application does not limit the proportion of high voltage positive materials, and adjustments to the amount of high voltage positive materials should be considered within the scope of the present application without departing from the inventive concept; as a preferred technical solution, the positive active material with a charge cut-off voltage greater than 4.5 V accounts for more than 50 wt% of all positive active materials; further preferably, the positive active material with a charge cut-off voltage greater than 4.5 V accounts for more than 70 wt% of all positive active materials; particularly preferably, the positive active material with a charge cut-off voltage greater than 4.5 V accounts for more than 90 wt% of all positive active materials.

[0077] The positive active material can optionally be mixed with a binder such as polytetrafluoroethylene (PTFE), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, or combinations thereof. The conductive agent can include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials can include, for example, particles of carbon black, graphite, acetylene black (e.g., KETCHEN™ black or DENKA™ black), carbon fibers and nanotubes, graphene, and the like. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like.

[0078] Surprisingly, the electrolyte system described herein is particularly suitable for high voltage battery systems, while also being resistant to reduction at the negative electrode, and having good overall performance.

[0079] It is known that for most ester solvents, branched chains cause electrolyte viscosity to be too high, thereby affecting battery performance. Surprisingly, the electrolyte system of the present application has good viscosity performance and maintains a good low-temperature capacity retention rate even under low-temperature conditions.

[0080] For compound A, an increase in the number of methyl groups increases electrolyte viscosity, which adversely affects the battery. Surprisingly, under a high-voltage system, the branched structure improves the oxidation resistance of the electrolyte, thereby exhibiting particular advantages.

[0081] As an embodiment, the mass of the compound A accounts for 70-100% of the total mass of the solvent.

[0082] As a preferred embodiment, the mass of the compound A accounts for 80-100% of the total mass of the solvent.

[0083] Surprisingly, a high mass fraction of the compound has good oxidation resistance to a high-voltage positive electrode system and excellent stability to the negative electrode as well.

[0084] The electrolyte solvent can include other compounds that do not meet the structural formula I.

[0085] It can be understood that the electrolyte can include one compound A that meets the structural formula, or can include, or can be composed of two or more compounds A that meet the relevant structural formula.

[0086] As an embodiment, the solvent includes two or more compounds that meet the structural formula;

[0087] As an embodiment, the solvent includes two or more compounds that meet the structural formula and at least one of the compounds has a main chain with 0 hydrogen atoms.

[0088] As an embodiment, the solvent includes two or more compounds that meet the structural formula and all of the compounds have a main chain with 0 hydrogen atoms.

[0089] As an embodiment, the solvent includes two or more compounds that meet the structural formula and all of the compounds have a main chain with 0 hydrogen atoms.

[0090] It is understood that the use of compounds satisfying the structural formula or mixtures of two or more such compounds as the main solvent can significantly improve the performance of the battery, but the scope of protection of the present application does not exclude the use of other technical solutions of ester compounds not satisfying the structural formula I, for example, the use of two compounds satisfying the structural formula, and the volume of the two compounds accounts for 70% of the total mass of the electrolyte solvent, at the same time, the electrolyte solvent also includes a carboxylic acid ester compound B with more than one hydrogen atom in the R1 main chain, and the mass of the compound B accounts for 5% of the total mass of the electrolyte. This technical solution should still be considered as falling within the scope of protection of the present application. It is understood that as long as the compound A satisfying the volume ratio of the present application is used in the electrolyte solvent of the high-voltage lithium ion battery system, it should be considered to fall within the scope of protection of the present application, and not all carboxylic acid ester compounds must use the compound satisfying the structural formula I.

[0091] As an embodiment, the solvent further comprises a cyclic carbonate, and the mass of the cyclic carbonate accounts for 0-20% of the total mass of the solvent.

[0092] As a preferred embodiment, the mass of the cyclic carbonate accounts for 0-10% of the total volume of the mass.

[0093] As a more preferred embodiment, the mass of the cyclic carbonate accounts for 5% of the total mass of the solvent.

[0094] As an embodiment, the solvent further comprises a chain carbonate, and the mass of the chain carbonate accounts for 0-20% of the total mass of the solvent.

[0095] As a preferred embodiment, the mass of the chain carbonate accounts for 0-10% of the total mass of the solvent.

[0096] As a most preferred embodiment, the sum of the mass of the cyclic carbonate and the mass of the chain carbonate accounts for 0-5% of the total mass of the solvent, and the mass of the cyclic carbonate and the mass of the chain carbonate are not zero.

[0097] As a particularly preferred embodiment, the electrolyte comprises a fluorinated carbonate.

[0098] Preferably, the fluorinated carbonate is fluoroethylene carbonate.

[0099] It is understood that the electrolyte also includes a lithium salt, and the application does not have a particular requirement for the type of lithium salt. Any known type of lithium salt can be used in the application without departing from the inventive concept of the application, and only exemplary examples are provided herein without limiting the scope of protection. Suitable lithium salts generally have inert anions. A non-limiting list of lithium salts that are soluble in organic solvents or mixtures of organic solvents to form non-aqueous liquid electrolyte solutions includes: lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)borate (LiBF2(C2O4)) (LiODFB), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalato)borate (LiB(C2O4)2) (LiBOB), lithium tetrafluoro(oxalato)phosphate (LiPF4(C2O4)) (LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiFSI), and combinations thereof. In certain variations, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) (LiFSI), lithium fluoroalkylphosphonate (LiFAP), lithium phosphate (Li3PO4), and combinations thereof.

[0100] In certain embodiments, the electrolyte can include one or more lithium salts at a concentration greater than or equal to 1 M to less than or equal to about 2 M. In certain variations, for example, when the electrolyte has a lithium concentration greater than about 2 M or has an ionic liquid, the electrolyte can include one or more diluents, such as hydrofluoroethers (HFE). Related embodiments are still considered within the scope of the application,

[0101] Meanwhile, the cyclic carbonate and the chain carbonate in the above are not particularly limited, and known cyclic carbonates and chain carbonates can be used in the application without departing from the inventive concept of the application, and only exemplary examples are provided herein without limiting the scope of protection. The cyclic carbonate can be one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC); and the linear carbonate can be one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0102] It is understood that the solvent can also include other solvents besides carbonates, carboxylate compounds of the formula, such as at least one of sulfites, sulfonates, sulfones, ethers, organosilicon compounds, organoboron compounds, nitriles, ionic liquids, and phosphine nitrile compounds, without departing from the inventive concept of the present application, and the use of other solvents in the solvent should still be considered within the scope of the present application.

[0103] As an embodiment, the electrolyte further includes an additive, and the additive of the present application includes, but is not limited to, at least one of a film-forming additive, an overcharge-preventing additive, a flame-retardant additive, a conductive additive, and a wetting additive. It is understood that the above-mentioned additives are only illustrative examples, and the use of related additives based on the needs of different functions should still be considered within the scope of the present application without departing from the inventive concept of the present application.

[0104] The lithium ion battery further includes a separator or a solid-state electrolyte membrane or a combination of both. The separator can be a microporous polymeric separator, such as a polyolefin, including polyolefins made from homopolymers (derived from a single monomer component) or heteropolymers (derived from more than one monomer component), which can be linear or branched. In some aspects, the polyolefin can be polyethylene (PE), polypropylene (PP), or a blend of PE and PP, or a multi-layer structured porous membrane of PE and / or PP.

[0105] When the separator is a microporous polymeric separator, it can be a single layer or a multi-layer laminate. For example, in one embodiment, a single layer of polyolefin can form the entire microporous polymeric separator. As another embodiment, similar or different layers can be assembled to form the separator.

[0106] In addition, the separator can be mixed with a ceramic material, or its surface can be coated with a ceramic material. For example, the ceramic coating can include aluminum oxide (AI2O3), silicon dioxide (SiO2), or a combination thereof.

[0107] The solid-state electrolyte membrane can also serve as a separator to isolate the positive electrode and the negative electrode to prevent short circuiting of the battery. The present application does not have a particular requirement for the material system or structure of the solid-state electrolyte membrane, and any known solid-state electrolyte material can be used in the present application without departing from the inventive concept of the present application, including oxide solid-state electrolytes, sulfide solid-state electrolytes, halide solid-state electrolytes, boride solid-state electrolytes, polymer solid-state electrolytes, or a combination thereof.

[0108] The negative electrode is not particularly required in the present application, and known negative electrode materials or systems can be used in the present application without departing from the inventive concept of the present application. Generally, the negative electrode is formed of a lithium host material that can be used as a lithium-ion battery negative electrode active material. The negative electrode active material is disposed in one or more layers, and in certain embodiments, the negative electrode can also include an electrolyte, such as a plurality of electrolyte particles.

[0109] The negative electrode can include a lithium-based negative electrode active material that includes, for example, lithium metal and / or lithium alloys. In certain embodiments, the negative electrode is a silicon-based negative electrode active material that includes silicon, such as silicon alloys, silicon oxides, or combinations thereof, which in certain cases can also be mixed with graphite. In other embodiments, the negative electrode can include a carbon-based negative electrode active material that includes one or more of graphite, graphene, carbon nanotubes (CNTs), and combinations thereof. In still further embodiments, the negative electrode includes one or more lithium-accepting negative electrode active materials, such as lithium titanium oxide (Li4Ti5O12), one or more transition metals (e.g., tin (Sn)), one or more metal oxides (e.g., vanadium oxide (V2O5), tin oxide (SnO), titanium dioxide (TiO2)), titanium niobium oxide (TiNbO5), one or more metal alloys (e.g., copper-tin alloy (Cu6Sn5)), and one or more metal sulfides (e.g., iron sulfide (FeS)). 12 x y z wherein 0≤x≤2, 0≤y≤24, and 0≤z≤64), metal alloys (such as copper-tin alloy (Cu6Sn5)), and one or more metal sulfides (such as iron sulfide (FeS)).

[0110] Optionally, the negative electrode active material in the negative electrode can be mixed with one or more conductive agents that provide an electron conduction path and / or at least one polymeric binder material that improves the structural integrity of the negative electrode. For example, the binder can be, optionally, poly(tetrafluoroethylene) (PTFE), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), poly(vinylidene fluoride) (PVDF), nitrile butadiene rubber (NBR), styrene ethylene butylene styrene copolymer (SEBS), styrene butadiene styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, or combinations thereof. The conductive agent can include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials can include, for example, particles of carbon black, graphite, superP, acetylene black, carbon fibers and nanotubes, graphene, and the like. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), and the like.

[0111] ​​​The negative electrode can include greater than or equal to about 50 wt% to less than or equal to about 97 wt% of a negative electrode active material, optionally greater than or equal to about 0 wt% to less than or equal to about 60 wt% of a solid-state electrolyte, optionally greater than or equal to about 0 wt% to less than or equal to about 15 wt% of an electrically conductive material, and optionally greater than or equal to about 0 wt% to less than or equal to about 10 wt% of a binder.

[0112] Embodiments:

[0113] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and should not be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0114] The electrolyte was prepared as follows: The electrolyte was prepared in a glove box (water content ≤0.01 ppm, oxygen content ≤0.01 ppm). Compound A, compound B (if present) were mixed according to the corresponding mass fraction to obtain a mixed organic solvent. Then the mixed organic solvent, fully dried LiPF6, lithium difluorophosphate (LiPO2F2) and 1,3-propanesultone (PS), and boronic acid tris(2,2,2-trifluoroethyl) ester were mixed according to a mass ratio of 85:13:0.5:1:0.5 to prepare the electrolyte, and the total weight of the electrolyte was 100 wt%.

[0115] Battery preparation:

[0116] Battery preparation: 1.5 wt% of binder PVDF, 2 wt% of conductive agent Super-P, 96.5 wt% of lithium nickel manganese oxide LNMO positive electrode material, and an appropriate amount of dispersant N-methyl pyrrolidone were prepared into a slurry with a solid content of 65 wt%, and after homogenization, coating, rolling, and cutting, a positive electrode sheet was prepared.

[0117] 97.5 wt% of graphite negative electrode material, 1.5 wt% of conductive agent Super-P, 0.5 wt% of sodium carboxymethyl cellulose (CMC), and 0.5 wt% of binder SBR were mixed with an appropriate amount of water, and after homogenization, coating, rolling, and cutting, a negative electrode sheet was prepared.

[0118] The electrolyte provided by the examples and comparative examples was assembled into a lithium ion battery with the above positive electrode sheet and the above negative electrode sheet, and the ratio of the capacity of the negative electrode to the capacity of the positive electrode (N / P ratio) was designed to be 1.12, and the capacity was 1 Ah.

[0119] Performance test method:

[0120] Normal temperature cycle performance test: the charge and discharge potential range is 3.5V-4.9V, the charge process is constant current 1C to 4.9V, 4.9V constant voltage charging to the cutoff current ≤0.05C, standing for 5 minutes, 1C discharging to 3.5V, standing for 5 minutes; so cycle charge and discharge, test the cycle performance at room temperature (25℃), record the cycle capacity retention rate after 30 cycles.

[0121] Low temperature conductivity retention rate = the ratio of conductivity at-20℃ to that at 25℃. Conductivity is directly tested by Mettler Toledo S7 conductivity meter, and the electrolyte is placed in a specific temperature oven for 2h before testing.

[0122] The electrolyte system of the specific examples and comparative examples is shown in the following table:

[0123] From the examples, it is known that the traditional cognition believes that linear carboxylic acid ester has good performance, but in the high voltage system, the linear carboxylic acid ester cannot meet the requirements of solvent capacity retention rate and low temperature conductivity performance. Surprisingly, the carboxylic acid ester containing branched structure exhibits good adaptability to the high voltage system, especially when compound A is used as the main solvent (mass content is more than 70%), the performance advantage is more obvious, and the possible reason is that the branched structure of carboxylic acid ester helps to improve the oxidation resistance of the electrolyte. It can be seen that the present application overcomes the cognition of carboxylic acid ester solvent system in the prior art, and develops a solvent that can adapt to the high voltage battery system.

[0124] Those skilled in the art can easily understand that the above description is only an example of the present application and does not limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that: The positive electrode includes a positive electrode active material, the charge cutoff voltage of the positive electrode active material is higher than 4.5V, and the electrolyte includes a solvent, and the solvent includes one or more compounds A that satisfy the following structural formula: Wherein, R1 is a saturated hydrocarbon group or a fluorocarbon group and the number of hydrogen atoms in its main chain is ≤1; R2 is selected from a hydrocarbon group or a fluorocarbon group having 1 to 8 carbon atoms.

2. The lithium-ion battery according to claim 1, wherein The number of carbon atoms in the main chain of R1 is 1-5; preferably, the number of carbon atoms in the main chain of R1 is 1-3.

3. The lithium-ion battery according to claim 1, wherein The main chain carbon number of R2 is 1-3.

4. The lithium-ion battery according to claim 1, wherein The R2 is methyl or ethyl.

5. The lithium ion battery according to claim 2 or 3, wherein: The R1 and R2 are independently selected from hydrocarbon groups or fluorocarbon groups having 1 to 3 carbon atoms.

6. The lithium-ion battery according to claim 1, wherein The R2 main chain carbon atoms do not contain hydrogen atoms or fluorine atoms; Preferably, the R1 main chain carbon atoms do not contain hydrogen atoms or fluorine atoms.

7. The lithium-ion battery according to claim 1, wherein In the compound A, at least one H atom in R1 is replaced by F.

8. The lithium-ion battery according to claim 7, wherein In the compound A, at least one H atom in R2 is replaced by F.

9. The lithium ion battery according to claim 7 or 8, wherein The number of hydrogen atoms in the main chain of R2 is less than 1.

10. The lithium-ion battery according to claim 1, wherein The mass of the compound A accounts for 70-100% of the total mass of the solvent; Preferably, the mass of the compound A accounts for 80-100% of the total mass of the solvent.

11. The lithium-ion battery according to claim 1, wherein The positive electrode active material is a mixture; Preferably, the charge cut-off voltage of at least one positive electrode active material is higher than 4.5V; Preferably, the positive electrode active material is a mixture of multiple materials with a charge cut-off voltage greater than 4.5V.

12. The lithium-ion battery according to claim 1, wherein The positive electrode active material is a pure substance.

13. The lithium-ion battery according to claim 1, wherein The lithium-ion battery further includes a separator or an electrolyte membrane.

14. The lithium-ion battery according to claim 1, wherein The charging cut-off voltage of the positive electrode active material is higher than 4.6V; Preferably, the charging cut-off voltage of the positive electrode active material is higher than 4.7V; Preferably, the charge cut-off voltage of the positive electrode active material is higher than 4.8V.

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