Electrochemical and Electronic Devices

Abstract

The present invention provides an electrochemical device and an electronic device. The electrochemical device includes a negative electrode and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode current collector contains elemental chromium, and the content of the elemental chromium is 0.001% to 0.5% relative to the mass of the negative electrode current collector. The electrolyte includes a compound derived from oxalic acid, and the content of the compound derived from oxalic acid is 0.01% to 5% relative to the mass of the electrolyte. The compound derived from oxalic acid includes at least one of a compound represented by formula I, a compound represented by formula II, a compound represented by formula III, a compound represented by formula IV, and a compound represented by formula V. The electrochemical device has significantly reduced self-discharge.

Description

[Technical Field]

[0001] This invention claims priority from a Chinese patent application filed with the China Patent Office on March 7, 2023, bearing international application number PCT / CN2023 / 080022 and entitled "Electrochemical Device and Electronic Device," the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the field of energy storage, and in particular to electrochemical and electronic devices. [Background technology]

[0003] Electrochemical devices (e.g., lithium-ion batteries) have advantages such as high energy density, stable operating voltage, low self-discharge rate, long cycle life, no memory effect, and environmental friendliness, and are therefore widely used in fields and industries such as home appliances (including electronic products such as mobile phones, laptops, and cameras), electric vehicles, power tools, drones, intelligent robots, and large-scale energy storage. However, with the rapid advancement of information and communication technology and various changes in market needs, the requirements and challenges for power sources of electronic products are becoming increasingly higher, such as thinner, lighter, more diverse shapes, higher volumetric energy density and mass energy density, higher safety, and higher output.

[0004] Because the cathode active material, anode active material, and electrolyte solution contained in electrochemical devices are sensitive to moisture, battery preparation must be carried out in a low-humidity environment as much as possible, which significantly affects the control of the battery preparation process, battery characteristics, production costs, etc.

[0005] In light of this, there is a need to provide an electrochemical device that can accommodate the effects of humidity in the battery manufacturing environment. Summary of the Invention

[0006] SUMMARY OF THE INVENTION The present invention seeks to solve, at least in part, at least one problem in the related art by providing electrochemical and electronic devices.

[0007] According to one aspect of the present invention, there is provided an electrochemical device comprising a negative electrode and an electrolyte, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode current collector contains elemental chromium, and the content of the elemental chromium is 0.001% to 0.5% with respect to the mass of the negative electrode current collector; The electrolyte solution contains a compound based on oxalic acid, and the content of the compound based on oxalic acid is 0.01% to 5% by mass of the electrolyte solution; and The compound of oxalic acid includes at least one of a compound represented by formula I, a compound represented by formula II, a compound represented by formula III, a compound represented by formula IV, and a compound represented by formula V, [ka] where: A + are each independently, Li + , Na + , K. + or Cs + is selected from R 11 , R 12 , R 21 , R 22 , R 31 , R 32 , R 33 and R 34 are each independently a halogen, unsubstituted or halogen-substituted C 1-4 Alkyl, unsubstituted or halogen-substituted C 2-4 Alkenyl or unsubstituted or halogen-substituted C 2-4 alkynyl, R 41 and R 42 are each independently H, Li, Na, K, Cs, NH4, unsubstituted or halogen-substituted C 1-4Alkyl, unsubstituted or fluorine-substituted C 2-4 Alkenyl, or unsubstituted or fluorine-substituted C 2-4 alkynyl, and R 41 and R 42 may optionally be bonded to each other to form a ring together with the atoms to which they are attached.

[0008] According to an embodiment of the present invention, the compound represented by Formula I includes at least one of lithium bis(oxalato)borate (LiBOB), sodium bis(oxalato)borate (NaBOB), cesium bis(oxalato)borate (CsBOB), and potassium bis(oxalato)borate (KBOB).

[0009] The compound represented by formula II is [ka] It includes at least one of the following.

[0010] The compound represented by formula III is [ka] It includes at least one of the following.

[0011] The compound of formula IV is [ka] It includes at least one of the following.

[0012] The compound represented by formula V includes H2C2O4, Li2C2O4, Na2C2O4, K2C2O4, Cs2C2O4, NH4C2O4, CH3C2O4Li, [ka] It includes at least one of the following.

[0013] According to an embodiment of the present invention, the content of the oxalic acid compound is 0.01% to 3% by mass of the electrolyte solution.

[0014] According to an embodiment of the present invention, the content of the oxalic acid compound is 0.01% to 1% by mass of the electrolyte solution.

[0015] According to an embodiment of the present invention, the content of the chromium element is 0.001% to 0.1% based on the mass of the negative electrode current collector.

[0016] According to an embodiment of the present invention, the content of the chromium element is 0.001% to 0.05% based on the mass of the negative electrode current collector.

[0017] According to an embodiment of the present invention, the negative electrode current collector is a copper foil.

[0018] According to an embodiment of the present invention, the electrolyte solution further comprises a cyclic ester and a chain ester; the cyclic ester includes at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and fluoroethylene carbonate (FEC); The chain ester includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), and propyl propionate (PP); and When the content of the cyclic ester is S1% and the content of the chain ester is S2% relative to the mass of the electrolyte solution, S1 / S2 is in the range of 0.20 to 1.00.

[0019] According to an embodiment of the present invention, S1 is in the range of 15-50.

[0020] According to an embodiment of the present invention, the electrolyte further comprises an additive, The additive is at least one selected from the group consisting of 1,3-propane sultone (PS), ethylene sulfate (DTD), lithium difluorophosphate (LiPO2F2), and vinylene carbonate (VC); and The content of the additive is 0.01% by weight to 5% by weight relative to the mass of the electrolyte solution.

[0021] According to another aspect of the present invention, there is provided an electronic device comprising an electrochemical device according to the present invention.

[0022] The present invention provides an electrochemical device and an electronic device that use an electrolyte containing an oxalic acid compound on a negative electrode current collector containing elemental chromium. On the one hand, the oxalic acid compound reacts with water in the electrolyte, consuming excess water and preventing the production of hydrofluoric acid, thereby preventing the destruction of the protective oxide layer made of chromium. On the other hand, the oxalate ions produced by hydrolysis of the oxalic acid compound combine with the eluted chromium ions to form a compound that is insoluble in the electrolyte and deposits on the surface of the negative electrode current collector, forming a protective layer. This prevents the metal ions from being eluted from the negative electrode current collector and subsequently reduced to form elemental metals at the negative electrode. The combined effect of these factors allows the electrochemical device of the present invention to have significantly reduced self-discharge.

[0023] Other aspects and advantages of the present invention are set forth in part in the description that follows, and in part are illustrated by, or may be learned through the practice of, embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and examples. It is clear that the described examples are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present invention are included in the protection scope of the present invention.

[0025] Examples of the present invention are described in detail below, but should not be construed as limiting the present invention.

[0026] In the detailed description and claims, a list of items connected by the term "at least one of" can refer to any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means A only, B only, or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means A only, B only, C only, A and B (excluding C), A and C (excluding B), B and C (excluding A), or all of A, B, and C. Item A can include one or more elements. Item B can include one or more elements. Item C can include one or more elements.

[0027] The term "alkyl" refers to a linear saturated hydrocarbon structure having 1 to 20 carbon atoms. It also refers to a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When an alkyl having a specific number of carbon atoms is specified, all geometric isomers having that number of carbon atoms are intended to be included. Thus, for example, "butyl" is meant to include n-butyl, sec-butyl, iso-butyl, tert-butyl, and cyclobutyl. "Propyl" includes n-propyl, iso-propyl, and cyclopropyl. Examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, iso-pentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, iso-hexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, and norbornyl.

[0028] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that is straight-chained or branched and has at least one, and typically one, two, or three carbon-carbon double bonds. Unless otherwise defined, the alkenyl typically contains from 2 to 20 carbon atoms and includes, for example, -C 2-4 Alkenyl, -C 2-6 Alkenyl and -C 2-10 Representative alkenyls include (for example) vinyl, n-propenyl, iso-propenyl, n-but-2-enyl, but-3-enyl, and n-hex-3-enyl.

[0029] The term "alkynyl" refers to a monovalent unsaturated hydrocarbon group that is straight-chained or branched and has at least one, and typically one, two, or three, carbon-carbon triple bonds. Unless otherwise defined, the alkynyl typically contains from 2 to 20 carbon atoms and includes, for example, -C 2-4 Alkynyl, -C 3-6 Alkynyl and -C 3-10 Representative alkynyl groups include (for example) ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, and n-hex-3-ynyl.

[0030] The term "halogen" may be F, Cl, Br or I.

[0031] Positive and negative electrode active materials and electrolytes in electrochemical devices (e.g., lithium-ion batteries) are sensitive to moisture. For example, in a relatively humid environment, negative electrode current collectors (e.g., copper foil) are prone to corrosion, which has many adverse effects on electrochemical devices. Although the use of chromium-containing copper current collectors can somewhat slow the oxidation of copper current collectors in air and the corrosion of copper current collectors by electrolytes, the protective oxide layer made of chromium is still destroyed by hydrofluoric acid in the electrolyte, causing copper to dissolve, resulting in increased self-discharge of the electrochemical device.

[0032] To solve the above problems, the present invention provides an electrochemical device that uses an electrolyte containing an oxalic acid compound and an anode current collector containing elemental chromium. On the one hand, the oxalic acid compound reacts with water in the electrolyte, consuming excess water and preventing the production of hydrofluoric acid, thereby preventing the destruction of the protective oxide layer made of chromium. On the other hand, the oxalate ions generated by the hydrolysis of the oxalic acid compound combine with the eluted chromium ions to form a compound that is insoluble in the electrolyte and deposits on the surface of the anode current collector, forming a protective layer. This prevents the metal ions from being eluted from the anode current collector and subsequently reduced to form elemental metals at the anode. The combined effect of these factors allows the electrochemical device of the present invention to have significantly reduced self-discharge.

[0033] electrolyte The electrolyte in the electrochemical device of the present invention contains a compound derived from oxalic acid, and the content of the compound derived from oxalic acid is 0.01% to 5% by mass of the electrolyte, and the compound derived from oxalic acid includes at least one of a compound represented by formula I, a compound represented by formula II, a compound represented by formula III, a compound represented by formula IV, and a compound represented by formula V. [ka] where: A + are each independently, Li + , Na + , K. + or Cs + is selected from R 11 , R 12 , R 21 , R 22 , R 31 , R 32 , R 33 and R 34 are each independently a halogen, unsubstituted or halogen-substituted C 1-4 Alkyl, unsubstituted or halogen-substituted C 2-4 Alkenyl, or unsubstituted or halogen-substituted C 2-4alkynyl, R 41 and R 42 are each independently H, Li, Na, K, Cs, NH4, unsubstituted or halogen-substituted C 1-4 Alkyl, unsubstituted or fluorine-substituted C 2-4 Alkenyl, or unsubstituted or fluorine-substituted C 2-4 alkynyl, and R 41 and R 42 may optionally be bonded to each other to form a ring together with the atoms to which they are attached.

[0034] In some embodiments, the compound according to Formula I includes at least one of lithium bis(oxalato)borate (LiBOB), sodium bis(oxalato)borate (NaBOB), cesium bis(oxalato)borate (CsBOB), and potassium bis(oxalato)borate (KBOB).

[0035] In some embodiments, the compound of formula II is [ka] It includes at least one of the following.

[0036] In some embodiments, the compound of formula III is [ka] It includes at least one of the following.

[0037] In some embodiments, the compound of formula IV is [ka] It includes at least one of the following.

[0038] In some embodiments, the compound of formula V is H2C2O4, Li2C2O4, Na2C2O4, K2C2O4, Cs2C2O4, NH4C2O4, CH3C2O4Li, [ka] It includes at least one of the following.

[0039] In some embodiments, the content of the oxalic acid compound is 0.01% to 3% by weight of the electrolyte. In some embodiments, the content of the oxalic acid compound is 0.01% to 1% by weight of the electrolyte. In some embodiments, the content of the oxalic acid compound is 0.1% to 0.5% by weight of the electrolyte. In some embodiments, the content of the oxalic acid compound is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5% by weight of the electrolyte, or a range consisting of any two of the foregoing values. Having the oxalic acid compound in the electrolyte within the above ranges contributes to further reducing self-discharge of the electrochemical device.

[0040] In some embodiments, the electrolytic solution further comprises a cyclic ester and a chain ester, the cyclic ester comprising at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and fluoroethylene carbonate (FEC), and the chain ester comprising at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), and propyl propionate (PP), and when the content of the cyclic ester is S1% and the content of the chain ester is S2%, relative to the mass of the electrolytic solution, S1 / S2 is in the range of 0.2 to 1.

[0041] In some embodiments, S1 / S2 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, or is within a range consisting of any two of the foregoing values.

[0042] In some embodiments, S1 is in the range of 15 to 50. In some embodiments, S1 is 15, 30, 40, or 50, or a range consisting of any two of the foregoing values.

[0043] In some embodiments, S2 is in the range of 15 to 75. In some embodiments, S2 is 15, 25, 35, 45, 55, 65, or 75, or a range consisting of any two of the foregoing numbers.

[0044] When the electrolyte contains the above-mentioned amounts of cyclic esters and chain esters, the mixed solvent and electrolyte salt (e.g., LiPF6) form an appropriate coordination relationship and exist in the form of ionic clusters. This weakens the redox reaction activity of the solvent alone, helping to reduce chemical self-discharge due to side reactions and maintaining a stable self-discharge evaluation parameter K value. At the same time, sufficient dissociation of the electrolyte salt and a relatively low viscosity of the entire electrolyte are ensured, improving the electrical conductivity of the electrolyte and thereby improving the low-temperature discharge characteristics of the battery.

[0045] In some embodiments, the electrolyte further contains an additive, the additive being at least one selected from the group consisting of 1,3-propane sultone (PS), ethylene sulfate (DTD), lithium difluorophosphate (LiPO2F2), and vinylene carbonate (VC), and the content of the additive is 0.01 wt % to 5 wt % based on the mass of the electrolyte.

[0046] In some embodiments, the additive is present in an amount of 0.05% to 3% by weight based on the weight of the electrolyte. In some embodiments, the additive is present in an amount of 0.1% to 1% by weight based on the weight of the electrolyte. In some embodiments, the additive is present in an amount of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5% by weight based on the weight of the electrolyte, or in a range consisting of any two of the foregoing values.

[0047] The addition of the additive can further reduce the self-discharge of the electrochemical device and significantly improve the problem of gas generation during storage due to the low oxidation potential of the oxalic acid compound. This is because the additive forms a protective layer on the surface of the electrode and reduces the occurrence of side reactions, thereby reducing chemical self-discharge. At the same time, the additive can reduce the gas generation due to the oxidative decomposition of the oxalic acid compound at the positive electrode, improving the high-temperature storage characteristics of the electrochemical device.

[0048] The electrolyte used in the present invention includes LiPF6, and in some embodiments, the concentration of LiPF6 is in the range of 0.8 mol / L to 3 mol / L, 0.8 mol / L to 2.5 mol / L, 0.8 mol / L to 2 mol / L, or 1 mol / L to 2 mol / L. In some embodiments, the concentration of the lithium salt is about 1 mol / L, about 1.15 mol / L, about 1.2 mol / L, about 1.5 mol / L, about 2 mol / L, or about 2.5 mol / L.

[0049] Solvents in the electrolyte solution used in the embodiments of the present invention include, but are not limited to, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0050] In some embodiments, the cyclic carbonate includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate. In some embodiments, the cyclic carbonate has 3 to 6 carbon atoms.

[0051] In some embodiments, the linear carbonate includes, but is not limited to, linear carbonates such as methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate, and fluorine-substituted linear carbonates such as bis(fluoromethyl)carbonate, bis(difluoromethyl)carbonate, bis(trifluoromethyl)carbonate, bis(2-fluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, bis(2,2,2-trifluoroethyl)carbonate, 2-fluoroethylmethylcarbonate, 2,2-difluoroethylmethylcarbonate, and 2,2,2-trifluoroethylmethylcarbonate.

[0052] In some embodiments, the cyclic carboxylic acid ester includes, but is not limited to, γ-valerolactone. In some embodiments, some of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0053] In some embodiments, the chain carboxylic acid ester includes, but is not limited to, methyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl pentanoate, ethyl pentanoate, methyl pivalate, and ethyl pivalate. In some embodiments, some of the hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, the fluorine-substituted chain carboxylic acid ester includes, but is not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0054] In some embodiments, cyclic ethers include, but are not limited to, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

[0055] In some embodiments, linear ethers include, but are not limited to, dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane.

[0056] In some embodiments, phosphorus-containing organic solvents include, but are not limited to, trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(2,2,3,3,3-pentafluoropropyl)phosphate.

[0057] In some embodiments, the sulfur-containing organic solvent includes, but is not limited to, sulfolane, 2-methyl sulfolane, 3-methyl sulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some of the hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

[0058] In some embodiments, aromatic fluorine-containing solvents include, but are not limited to, fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0059] In some embodiments, the solvent used in the electrolyte solution of the present invention includes one or more of the above. In some embodiments, the solvent used in the electrolyte solution of the present invention includes a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester, a chain carboxylic acid ester, and a combination thereof. In some embodiments, the solvent used in the electrolyte solution of the present invention includes an organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and a combination thereof. In some embodiments, the solvent used in the electrolyte solution of the present invention includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, or a combination thereof.

[0060] negative electrode The negative electrode in the electrochemical device of the present invention includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode current collector contains elemental chromium, and the content of the elemental chromium is 0.001% to 0.5% relative to the mass of the negative electrode current collector. In some embodiments, the content of the elemental chromium is 0.001% to 0.1% relative to the mass of the negative electrode current collector. In some embodiments, the content of the elemental chromium is 0.001% to 0.05% relative to the mass of the negative electrode current collector. In some embodiments, the content of the elemental chromium is 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or is within a range consisting of any two of the foregoing values ​​relative to the mass of the negative electrode current collector.

[0061] In some embodiments, the negative electrode current collector is a copper foil. Copper foil containing chromium may be expressed as Cu(Cr). Cu(Cr) is an alloy containing copper as a main component and a small amount of Cr. Cr may be a protective film formed on the surface of the current collector or a crystalline phase embedded in Cu. Cu(Cr) may contain components other than Cu and Cr, or may essentially contain only Cu and Cr.

[0062] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the specific type of the negative electrode active material is not particularly limited and can be selected as needed. Specifically, the negative electrode active material can be natural graphite, artificial graphite, mesocarbon microbeads (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or lithiated TiO2-Li4Ti5O with a spinel structure. 12 , Li metal, and Li-Al alloy. The silicon-carbon composite refers to a silicon-carbon negative electrode active material containing at least about 5 wt. % silicon, based on the weight of the silicon-carbon negative electrode active material.

[0063] In some embodiments, the negative electrode active material layer further comprises a negative electrode binder, which comprises one or more of styrene butadiene rubber, fluorine-based rubber, and ethylene propylene diene.

[0064] In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent. In some embodiments, the negative electrode conductive agent includes one or more of a conductive metal material and a conductive polymer. In some embodiments, the negative electrode conductive agent includes one or more of a carbon material. In some embodiments, the carbon material includes, but is not limited to, graphite, carbon black, acetylene black, and ketjen black.

[0065] In some embodiments, the negative electrode current collector has a negative electrode active material layer on one surface thereof. In some embodiments, the negative electrode current collector has a negative electrode active material layer on two surfaces thereof. In some embodiments, at least one surface of the negative electrode current collector includes a region where no negative electrode active material layer is provided, i.e., a blank region.

[0066] positive electrode The positive electrode includes a positive electrode current collector and a positive electrode active material provided on the positive electrode current collector. The specific type of the positive electrode active material is not particularly limited and can be selected as needed.

[0067] In some embodiments, the active cathode material comprises a cathode material capable of absorbing and releasing lithium (Li). Examples of cathode materials capable of absorbing / releasing lithium (Li) may include lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials.

[0068] Specifically, the chemical formula of lithium cobalt oxide can be expressed as Chemical Formula 1. Li x Coa M1 b O 2-c chemical formula 1

[0069] M1 represents at least one element selected from the group consisting of nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr), silicon (Si), fluorine (F), and sulfur (S), and the values ​​of x, a, b, and c satisfy 0.8≦x≦1.2, 0.8≦a≦1, 0≦b≦0.2, and −0.1≦c≦0.2, respectively.

[0070] The chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate can be expressed as Chemical Formula 2. Li y Ni d M2 e O 2-f chemical formula 2

[0071] M2 represents at least one element selected from the group consisting of cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr), silicon (Si), fluorine (F), and sulfur (S), and the values ​​of y, d, e, and f satisfy 0.8≦y≦1.2, 0.3≦d≦0.98, 0.02≦e≦0.7, and −0.1≦f≦0.2, respectively.

[0072] The chemical formula of lithium manganese oxide can be expressed as Chemical Formula 3. Li z Mn 2-g M3 g O 4-h chemical formula 3

[0073] M3 represents at least one element selected from the group consisting of cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), niobium (Nb), tantalum (Ta), and tungsten (W), and the values ​​of z, g, and h satisfy 0.8≦z≦1.2, 0≦g<1.0, and −0.2≦h≦0.2, respectively.

[0074] In some embodiments, the positive electrode active material layer may have a coating layer on its surface, or may be mixed with another compound that forms a coating layer. The coating layer may include at least one compound of a coating element selected from the group consisting of oxides of the coating element, hydroxides of the coating element, hydroxyoxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compound used in the coating layer may be amorphous or crystalline. The coating element contained in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or a mixture thereof. The coating layer may be formed by any method that does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method known to those skilled in the art, such as spray coating or impregnation.

[0075] In some embodiments, the positive electrode active material layer further comprises a binder and, optionally, a positive electrode conductive material.

[0076] The binder can enhance the bonding between the positive electrode active material particles and further enhance the bonding between the positive electrode active material and the current collector. Non-limiting examples of the binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic acid (ester)-modified styrene-butadiene rubber, epoxy resin, nylon, etc.

[0077] The positive electrode active material layer contains a positive electrode conductive material, thereby imparting electrical conductivity to the electrode. The positive electrode conductive material can include any conductive material as long as it does not cause a chemical change. Non-limiting examples of positive electrode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders such as copper, nickel, aluminum, and silver, metal fibers, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0078] The positive electrode current collector used in the electrochemical device according to the present invention may be made of aluminum (Al), but is not limited to this.

[0079] Separator In some embodiments, the electrochemical device of the present invention includes a separator between the positive electrode and the negative electrode to prevent electrical short circuits due to contact between the two pole pieces and to allow lithium ions to pass through.

[0080] The material and shape of the separator used in the electrochemical device of the present invention are not particularly limited and may be any of those disclosed in the prior art. In some embodiments, the separator comprises a polymer (e.g., synthetic resin) or an inorganic material (e.g., ceramics) made of a material stable to the electrolyte solution of the present invention. In some embodiments, the separator comprises a porous film made of the polymer or inorganic material. In some embodiments, the separator comprises a laminate film in which two or more porous films are laminated. In some embodiments, the polymer includes, but is not limited to, polytetrafluoroethylene, polypropylene, and polyethylene.

[0081] In some embodiments, the separator includes the porous film (substrate layer) and a polymer compound layer provided on one or two surfaces of the substrate layer, thereby increasing the separator's adhesion to the positive and negative electrodes and preventing miswinding during winding of the electrode pieces. This prevents decomposition of the electrolyte and prevents leakage of the electrolyte impregnated in the substrate layer. By using such a separator, the electrical resistance of the electrochemical device does not increase significantly even after repeated charge and discharge, and expansion of the electrochemical device can be suppressed.

[0082] In some embodiments, the polymer layer includes, but is not limited to, polyvinylidene fluoride, which has excellent physical strength and electrochemical stability. The polymer layer can be formed by preparing a solution containing the polymer material, applying the solution to the substrate layer, or by immersing the substrate layer in the solution and then drying it.

[0083] application The electrochemical device of the present invention includes any device in which an electrochemical reaction occurs, and examples thereof include any type of primary or secondary battery. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0084] The use of the electrochemical device of the present invention is not particularly limited, and it can be used for any application known in the prior art. In one embodiment, the electrochemical device of the present invention can be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, mobile phones, portable fax machines, portable copiers, portable printers, headphone stereos, video recorders, LCD televisions, portable vacuum cleaners, portable CD players, minidiscs, walkie-talkies, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorbikes, power-assisted bicycles, bicycles, lighting equipment, toys, game consoles, watches, power tools, flashes, cameras, large household storage batteries, and lithium-ion capacitors.

[0085] The following will take lithium ion batteries as an example to describe the preparation of lithium ion batteries with reference to specific examples. Those skilled in the art should understand that the preparation methods described in the present invention are merely exemplary, and any other suitable preparation methods are within the scope of the present invention. Example

[0086] In the following, examples and comparative examples of the lithium ion battery according to the present invention will be described, and characteristics will be evaluated.

[0087] 1. Preparation of lithium-ion batteries 1. Preparation of the negative electrode The negative electrode current collector Cu(Cr) used in the examples and comparative examples is a copper foil that substantially contains chromium, but the Cu(Cr) actually used as the current collector is not limited to one containing only Cu and Cr. The Cr content in Cu(Cr) can be controlled by any conventional method in the art, for example, by adjusting the temperature, current density, and concentration of the chromium plating solution during chromium plating.

[0088] The negative electrode active material (artificial graphite), conductive agent (Super P), sodium carboxymethylcellulose (CMC), and binder (styrene butadiene rubber (SBR)) were mixed in a weight ratio of 96.4:1.5:0.5:1.6, deionized water was added, and the mixture was stirred uniformly to obtain a negative electrode slurry with a solids content of 54 wt%. This negative electrode slurry was uniformly coated on both surfaces of 8 μm thick Cu(Cr) foil to form a negative electrode material layer. After drying at 85°C, the negative electrode was cold pressed, die-cut, slit, wound, and dried under vacuum at 120°C for 12 hours to obtain a negative electrode. The thickness of the negative electrode material layer on one side was 52 μm.

[0089] 2. Preparation of the positive electrode The positive electrode active material, LiCoO2, conductive carbon black (Super-P), and polyvinylidene fluoride were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:1.4:1.6 and stirred uniformly to obtain a positive electrode slurry with a solids content of 72% by weight. This positive electrode slurry was uniformly coated on two surfaces of 10 μm thick aluminum foil to form a positive electrode material layer. After drying at 85°C, the foil was cold pressed, die-cut, slit, and tab-welded. The cathode was then dried under vacuum at 85°C for 4 hours to obtain a positive electrode. The thickness of the positive electrode material layer on one side was 35.6 μm.

[0090] 3. Preparation of electrolyte The electrolyte solutions of Comparative Examples 1-1 to 1-4, Examples 1-1 to 1-20, and Examples 3-1 to 3-10 were prepared as follows.

[0091] In a dry argon atmosphere, 20% EC, 25% PC, 20% DEC, and 20% EMC were mixed in the mass proportions based on the total mass of the electrolyte, dissolved, and thoroughly stirred. After that, additives were added according to the required content and type listed in the table, and continued stirring. Finally, the lithium salt LiPF6 was added in the corresponding percentage so that the content of each component in the electrolyte totaled 100%, and then mixed uniformly to obtain the electrolyte.

[0092] The electrolyte solutions of Examples 2-1 to 2-11 were prepared as follows.

[0093] In a dry argon atmosphere, the solvents were mixed in the percentages shown in the table relative to the total mass of the electrolyte solution, and then 0.10% of the additive II-1 in Examples 1-6 was added. Finally, the lithium salt LiPF6 was added in the corresponding percentage so that the total content of each component in the electrolyte solution was 100%, and the mixture was mixed uniformly to obtain the electrolyte solution.

[0094] The abbreviations for each component used in the electrolyte and their corresponding compound names are shown in the table below.

[0095] [Table 1]

[0096] 4. Preparation of separator A 7-μm-thick polyethylene (PE) film was used, and two surfaces were coated with PVDF slurry and dried. One surface was then coated with a slurry of inorganic particles (the mass ratio of plate-like boehmi to Al2O3 was 70:30), and dried. The total thickness of the polyethylene film and coating layer was 12 μm, resulting in a separator. The single layer formed with the PVDF slurry was 1.25 μm thick, and the layer formed with the inorganic particle slurry was 2.5 μm thick.

[0097] 5. Preparation of Lithium-ion Battery The resulting positive electrode, separator, and negative electrode were wound in this order and placed in an outer foil package, with the inlet left open. The electrolyte was poured through the inlet, packaged, and subjected to a formation process (constant current charging at 0.02 C to 3.3 V, and then constant current charging at 0.1 C to 3.8 V) and a capacity process to produce a lithium-ion battery (approximately 9.1 mm thick, 49 mm wide, and 74 mm long). The inorganic particle slurry layer faced the positive electrode.

[0098] 2.Measurement method 1. Method for measuring the chromium content in negative electrode current collector The Cr content in Cu(Cr) was obtained by inductively coupled plasma (ICP) test.

[0099] 2. How to measure self-discharge of lithium-ion batteries The lithium-ion battery was placed in a 25°C incubator and allowed to stand for 30 minutes to allow the battery to reach a constant temperature. The lithium-ion battery was then charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage of 0.025C at 4.2V, allowed to stand for 5 minutes, discharged at a constant current of 0.5C to 3.0V, allowed to stand for 5 minutes, and then charged at a constant current of 0.5C for 60 minutes. The open-circuit voltage (OCV1) of the lithium-ion battery was recorded, and the battery was then allowed to stand for 48±0.5 hours at 25°C. The open-circuit voltage (OCV2) of the lithium-ion battery was measured. The self-discharge evaluation parameter K (mV / h) of the lithium-ion battery was calculated using the following formula:

[0100] K = 1000 × (OCV1 - OCV2) / 48.

[0101] 3. Measurement method for high-temperature storage characteristics of lithium-ion batteries The lithium-ion battery was placed in a 25°C incubator and allowed to stand for 30 minutes to allow the battery to reach a constant temperature. The lithium-ion battery was then charged at a constant current of 0.5C to 4.2V, and then at 4.2V, it was charged at a constant voltage of 0.025C, and the initial thickness (H0) of the lithium-ion battery was measured. The lithium-ion battery was then stored in an 80°C high-temperature oven for 24 hours, after which the thickness (H1) of the lithium-ion battery was recorded. The storage thickness expansion rate of the lithium-ion battery was calculated using the following formula:

[0102] Storage thickness expansion rate = (H1-H0) / H0 x 100%.

[0103] 4. Measurement method for low-temperature discharge characteristics of lithium-ion batteries The lithium-ion battery was placed in a temperature-controlled thermostat and set to 25°C. After 60 minutes of standing, it was charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage until the current reached 0.025C at 4.2V. After 10 minutes of standing, it was discharged at a constant current of 0.5C to 3.0V. The discharge capacity at this time was recorded as D0. At 25°C, the battery was further charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage until the current reached 0.025C at 4.2V. The temperature was adjusted to -10°C, and after 60 minutes of standing, it was discharged at a constant current of 0.5C to 3.0V, obtaining a discharge capacity D1. The low-temperature discharge capacity retention rate (D) of the lithium-ion battery was calculated using the following formula:

[0104] D = D1 / D0 × 100%.

[0105] 3. Measurement results Table 1 shows the effects of the chromium content in the negative electrode current collector, and the oxalic acid compounds and their contents in the electrolyte on the self-discharge of a lithium-ion battery.

[0106] [Table 2]

[0107] In Comparative Example 1-1, the electrolyte does not contain an oxalic acid compound, and the negative electrode current collector does not contain Cr. In Comparative Example 1-2, the negative electrode current collector contains a certain amount of Cr, but the electrolyte does not contain an oxalic acid compound. In Comparative Example 1-3, the electrolyte contains a certain amount of oxalic acid compound, but the negative electrode current collector does not contain Cr. In Comparative Example 1-4, the electrolyte does not contain an oxalic acid compound, and the negative electrode current collector contains excess Cr. The lithium-ion batteries of these comparative examples have relatively high self-discharge rates, making it difficult to meet usage needs.

[0108] As shown in Examples 1-1 to 1-20, when the electrolyte contains 0.01% to 5% of an oxalic acid compound and the negative electrode current collector contains 0.001% to 0.5% of chromium element, the self-discharge of the lithium ion battery can be significantly reduced.

[0109] Since the cost of the oxalic acid compound is higher than that of other compounds in the electrolyte, taking into consideration the self-discharge characteristics and cost of the lithium-ion battery, when the content of the oxalic acid compound in the electrolyte is within the range of 0.01% to 3%, the self-discharge improvement effect of the lithium-ion battery is better and the cost is reasonable. When the content of the oxalic acid compound in the electrolyte is within the range of 0.01% to 1%, the self-discharge improvement effect of the lithium-ion battery is particularly significant and the cost is more reasonable.

[0110] Since a higher chromium content increases the cost of the negative electrode current collector, taking into consideration the self-discharge characteristics and cost of the lithium-ion battery, a chromium content of 0.001% to 0.1% in the negative electrode current collector provides a more effective improvement in the self-discharge characteristics of the lithium-ion battery and is more cost-effective.A chromium content of 0.001% to 0.05% in the negative electrode current collector provides a particularly significant improvement in the self-discharge characteristics of the lithium-ion battery and is more cost-effective.

[0111] Table 2 shows the effects of the cyclic ester and chain ester in the electrolyte and their contents on the self-discharge and low-temperature discharge characteristics of the lithium ion battery. Examples 2-1 to 2-11 were set in the same manner as Example 1-6, except for the parameters listed in Table 2.

[0112] [Table 3]

[0113] As a result, it was found that when the electrolyte further contains a cyclic ester and a chain ester, and the ratio S1 / S2 of the cyclic ester content (S1%) to the chain ester content (S2%) is within the range of 0.2 to 1, the lithium-ion battery can maintain a relatively low self-discharge rate and have a low-temperature discharge capacity retention rate of at least 80%. This is because within this range, the mixed solvent and the electrolyte salt (e.g., LiPF6) form an appropriate coordination relationship and exist in the form of ion clusters, which weakens the redox reaction activity of the solvent alone, helps reduce chemical self-discharge due to side reactions, maintains a stable K value, and simultaneously ensures sufficient dissociation of the electrolyte salt and a relatively low viscosity of the entire electrolyte, improving the electrical conductivity of the electrolyte and thereby improving the low-temperature discharge characteristics of the battery.

[0114] Table 3 shows the effects of additives in the electrolyte on the self-discharge and high-temperature storage characteristics of lithium-ion batteries. Examples 3-1 to 3-10 were set in the same manner as Example 1-6, except for the parameters listed in Table 3.

[0115] [Table 4]

[0116] The results showed that adding 0.01% to 5% by weight of an additive (at least one of PS, DTD, LiPO2F2, and VC) to the electrolyte further reduced self-discharge and significantly reduced the high-temperature storage thickness expansion rate of the lithium-ion battery. This is mainly because the operating voltage range of the lithium battery exceeds the electrochemical stability window of the solvent in the electrolyte, causing continuous side reactions on the electrode surface and resulting in chemical self-discharge. However, adding a certain amount of additive to the electrolyte forms a protective layer on the electrode surface, further mitigating the side reactions of the solvent on the electrode surface, resulting in improved K value and gas generation.

[0117] Throughout the specification, references to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some of the examples" mean that at least one embodiment or example of the invention includes the particular feature, structure, material, or characteristic described in that embodiment or example. Thus, various references throughout the specification, such as "in some embodiments," "in embodiments," "in one embodiment," "in another example," "in one example," "in a particular example," or "an example," do not necessarily refer to the same embodiment or example of the invention. Furthermore, particular features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

[0118] Although illustrative embodiments have been disclosed and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present invention, and that modifications, substitutions, and amendments to the embodiments may be made without departing from the spirit, principle, and scope of the present invention.

[0119] The above description is merely a preferred embodiment of the present invention and does not limit the present invention. Any amendments, equivalent replacements, and improvements made within the technical spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. 1. An electrochemical device comprising a negative electrode and an electrolyte, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode current collector contains chromium element, and the content of the chromium element is 0.001% to 0.5% with respect to the mass of the negative electrode current collector; The electrolyte solution contains a compound based on oxalic acid, and the content of the compound based on oxalic acid is 0.01% to 5% by mass of the electrolyte solution; and The compound based on oxalic acid includes at least one of a compound represented by formula I, a compound represented by formula II, a compound represented by formula III, a compound represented by formula IV, and a compound represented by formula V, 【Chemistry 1】 where: A ＋ are each independently Li ＋ , Na ＋ , K. ＋ or Cs ＋ is selected from R １１ , R １２ , R ２１ , R ２２ , R ３１ , R ３２ , R ３３ and R ３４ are each independently a halogen, unsubstituted or halogen-substituted C １－４ Alkyl, unsubstituted or halogen-substituted C ２－４ Alkenyl or unsubstituted or halogen-substituted C ２－４ alkynyl, R ４１ and R ４２ are each independently H, Li, Na, K, Cs, or NH ４ , unsubstituted or halogen-substituted C １－４ Alkyl, unsubstituted or fluorine-substituted C ２－４ Alkenyl or unsubstituted or fluorine-substituted C ２－４ alkynyl, and R ４１ and R ４２ are electrochemical devices which may optionally be bonded to each other to form a ring together with the atoms to which they are bonded.

2. the compound represented by formula I comprises at least one of lithium bis(oxalato)borate, sodium bis(oxalato)borate, cesium bis(oxalato)borate, and potassium bis(oxalato)borate; The compound of formula II is 【Chemistry 2】 and The compound of formula III is 【Transformation 3】 and The compound of formula IV is 【Chemistry 4】 and The compound represented by formula V is H ２ C ２ O ４ , Li ２ C ２ O ４ , Na ２ C ２ O ４ , K. ２ C ２ O ４ , Cs ２ C ２ O ４ , N.H. ４ C ２ O ４ , C.H. ３ C ２ O ４ Li, 【Transformation 5】 and The electrochemical device according to claim 1 , wherein at least one of the following conditions is satisfied:

3. 2. The electrochemical device according to claim 1, wherein the content of the compound based on oxalic acid is 0.01% to 3% by mass of the electrolyte solution.

4. 2. The electrochemical device according to claim 1, wherein the content of the compound based on oxalic acid is 0.01% to 1% by mass of the electrolyte solution.

5. 2. The electrochemical device according to claim 1, wherein the content of the chromium element is 0.001% to 0.1% with respect to the mass of the negative electrode current collector.

6. 2. The electrochemical device according to claim 1, wherein the content of the chromium element is 0.001% to 0.05% with respect to the mass of the negative electrode current collector.

7. 10. The electrochemical device of claim 1, wherein the negative electrode current collector is a copper foil.

8. The electrolyte solution further contains a cyclic ester and a chain ester, the cyclic ester includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, and fluoroethylene carbonate; The chain ester includes at least one of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, and propyl propionate; and 2. The electrochemical device according to claim 1, wherein, when the content of the cyclic ester is S1% and the content of the chain ester is S2% relative to the mass of the electrolyte solution, S1 / S2 is in the range of 0.20 to 1.

00.

9. 9. The electrochemical device of claim 8, wherein S1 is in the range of 15 to 50.

10. The electrolyte solution further comprises an additive, the additive is at least one selected from the group consisting of 1,3-propane sultone, ethylene sulfate, lithium difluorophosphate, and vinylene carbonate; 2. The electrochemical device according to claim 1, wherein the content of the additive is 0.01% by weight to 5% by weight relative to the mass of the electrolyte solution.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

Images