Electrochemical device and electronic device including the same

Abstract

The present application relates to an electrochemical device and an electronic device including the same. The electrochemical device includes an electrolyte, a positive electrode and a negative electrode, wherein the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the electrolyte includes fluoroethylene carbonate, the mass of the fluoroethylene carbonate corresponding to 1g of the negative electrode active material is Ag, and the specific surface area of ​​the negative electrode active material is Bm. 2 / g, and the value range of A is 0.01 to 0.1. The present application aims to maintain the cycle performance of the electrochemical device while improving its fast charging performance.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrochemical device and an electronic device comprising the electrochemical device. Background Art

[0002] Electrochemical devices (e.g., lithium-ion batteries) have the advantages of high energy density, long cycle life, and no memory effect, and are widely used in wearable devices, smart phones, drones, and even electric vehicles. With the expansion of lithium-ion battery applications and the development of information technology, higher performance requirements are placed on lithium-ion batteries - fast charging and discharging, and excellent cycle performance.

[0003] Existing research on fast charging and discharging technology often focuses on improving materials (graphite or optimizing electrolytes) and the impedance of lithium-ion batteries, but lacks in-depth research on the entire system. As a result, it is impossible to significantly increase the charging speed. While pursuing fast charging and discharging performance, it is necessary to reduce other aspects of performance, such as cycle performance. Summary of the invention

[0004] Starting from the electrochemical device system, this application not only considers the impedance that affects the fast charge and discharge performance, but also considers the relationship between the electrolyte solvent and the electrolyte film-forming additive, and takes into account the factors such as the negative electrode active material and the separator that affect the fast charge and discharge performance, and optimizes the relationship between the characteristics of the negative electrode active material itself and the content of the electrolyte film-forming additive, thereby optimizing the entire electrochemical device system. This application aims to maintain the cycle performance of the electrochemical device while improving its fast charging performance.

[0005] In some embodiments, the present application provides an electrochemical device comprising an electrolyte, a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the electrolyte comprises fluoroethylene carbonate, wherein the electrochemical device satisfies the relationship:

[0006] 0.5 <R ct / R cp <1.5, and R ct and R cp All are less than 35 milliohms,

[0007] Where R ct It represents the charge transfer impedance at 50% state of charge at 25 degrees Celsius, R cp represents the concentration polarization impedance at 50% state of charge at 25 degrees Celsius; and

[0008] 0.005≤A / B≤0.1,

[0009] Wherein, the mass of the fluoroethylene carbonate corresponding to 1g of the negative electrode active material is Ag, and the specific surface area of ​​the negative electrode active material is Bm. 2 / g.

[0010] In some embodiments, the value range of A is 0.01 to 0.1, and the value range of B is 1.0 to 2.0.

[0011] In some embodiments, the electrolyte comprises a compound of formula I:

[0012]

[0013] Among them, R 11 Selected from hydrogen, hydroxyl, C 1-20 Alkyl, C 1-20 Alkoxy, C 2-20 Alkenyl, C 6-30 Aryl, or C 6-30 aryloxy;

[0014] R 12 Selected from hydrogen, C 1-20 Alkyl, C 2-20 Alkenyl, or C 6-30 Aryl;

[0015] Wherein, the mass of the compound of formula I corresponding to 1g of the negative electrode active material is X g, and the value range of X is 0.035 to 0.39.

[0016] In some embodiments, X and A satisfy the following relationship:

[0017] 0.67≤X / A≤20.

[0018] In some embodiments, the compound of formula I comprises at least one of the following compounds: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, or n-pentyl valerate.

[0019] In some embodiments, X and the porosity P of the negative electrode active material layer satisfy the following relationship: 0.1≤X / P≤3, wherein the value range of P is 0.13 to 0.35.

[0020] In some embodiments, the electrolyte further comprises vinylene carbonate, wherein the mass of the vinylene carbonate corresponding to 1 g of the negative electrode active material is C g, and B and C satisfy the following relationship: 0.001≤C / B≤0.03.

[0021] In some embodiments, the compound of formula I comprises ethyl propionate, the mass of ethyl propionate corresponding to 1 g of the negative electrode active material is D g, and C and D satisfy the following relationship: 1≤D / C≤240.

[0022] In some embodiments, the electrolyte further comprises at least one of a compound of formula II or a compound of formula III:

[0023]

[0024] Among them, R 21 and R 22 Each is independently selected from unsubstituted or fluorine-substituted C 1-5 Alkyl, and R 21 and R 22 At least one of them contains fluorine;

[0025] R 31 and R 32 Each is independently selected from unsubstituted or fluorine-substituted C 1-20 Alkyl, and R 31 and R 32 At least one of them contains fluorine, and Y is selected from -O- or

[0026] In some embodiments, the mass of the compound of formula II corresponding to 1 g of the negative electrode active material is 0.015 g to 0.15 g. In some embodiments, the mass of the compound of formula III corresponding to 1 g of the negative electrode active material is 0.015 g to 0.065 g.

[0027] In some embodiments, the compound of formula II comprises at least one of the following compounds: methyl difluoroacetate, ethyl difluoroacetate, propyl difluoroacetate, methyl difluoropropionate, ethyl difluoropropionate, propyl difluoropropionate, methyl fluoroacetate, ethyl fluoroacetate, propyl fluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, or propyl trifluoroacetate;

[0028] The compound of formula III comprises at least one of the following compounds: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, or perfluoro(2-methyl-3-pentanone).

[0029] Another aspect of the present application provides an electronic device, which includes the electrochemical device as described above.

[0030] The present application aims to maintain the cycling performance of the electrochemical device while improving its fast charging performance. Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description or through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Demonstrated R during lithium-ion battery transfer ct and R cp

[0032] Figure 2 A schematic diagram of primary particles and secondary particles of a negative electrode active material in an embodiment is given.

[0033] Figure 3A For R ct The analog equivalent circuit of .

[0034] Figure 3B This is an EIS test diagram of a lithium-ion battery in one embodiment. DETAILED DESCRIPTION

[0035] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the scope of protection claimed in the present application. Unless otherwise clearly indicated, the following terms used herein have the meanings indicated below.

[0036] As used herein, the term "about" is used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. In addition, amounts, ratios, and other numerical values ​​are sometimes presented in this article in a range format. It should be understood that such a range format is for convenience and simplicity, and should be flexibly understood to include not only numerical values ​​explicitly designated as range limits, but also all individual numerical values ​​or subranges encompassed within the range, as if each numerical value and subrange were explicitly designated.

[0037] In the detailed description and claims, a list of items connected by the term "one of" can mean any of the listed items. For example, if items A and B are listed, the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, the phrase "one of A, B, and C" means only A; only B; or only C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0038] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" or "at least one of A or B" means only A; only B; 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" or "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0039] In the detailed description and claims, the number after the capital letter "C" is used to represent the carbon number, such as "C1-C 10 ”, “C3-C 10 ”, etc., the number after “C”, such as “1”, “3” or “10”, indicates the number of carbon atoms in the specific functional group. That is, the functional group may include 1-10 carbon atoms and 3-10 carbon atoms, respectively. For example, “C1-C4 alkyl” or “C 1-4 "Alkyl" refers to an alkyl group having 1 to 4 carbon atoms, for example, CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, CH3CH2CH(CH3)- or (CH3)3C-.

[0040] The term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having 1 to 20, 1 to 18, 1 to 16, 1 to 14, 1 to 12, 1 to 10, 1 to 8, 1 to 6, 1 to 4, or 3 to 5 carbon atoms. "Alkyl" is also intended to be a branched or cyclic hydrocarbon structure having 3 to 20, 3 to 18, 3 to 16, 3 to 14, 3 to 12, 3 to 10, 3 to 8, 3 to 6, or 3 to 5 carbon atoms. When an alkyl having a specific carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl, and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc. In addition, the alkyl group may be optionally substituted.

[0041] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group which may be straight or branched and has at least one, and typically 1, 2 or 3, carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains 2 to 20, 2 to 18, 2 to 16, 2 to 14, 2 to 12, 2 to 10, 2 to 8, 2 to 6 or 2 to 4 carbon atoms and includes, for example, -C 2-4 Alkenyl, -C 2-6 Alkenyl and -C 2-10 Representative alkenyl groups include, for example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, etc. In addition, the alkenyl group may be optionally substituted.

[0042] The term "aryl" encompasses monocyclic and polycyclic systems. Polycyclics may have two or more rings in which two carbons are common to two adjacent rings (the rings are "fused"), wherein at least one of the rings is aromatic, for example, the other rings may be cycloalkyl, cycloalkenyl, aryl, heterocycle and / or heteroaryl. For example, aryl may be aryl of 6-30 carbon atoms, aryl of 6-24 carbon atoms, aryl of 6-20 carbon atoms, aryl of 6-16 carbon atoms, aryl of 6-12 carbon atoms, or aryl of 6-10 carbon atoms. Representative aryl groups include, for example, phenyl, methylphenyl, propylphenyl, isopropylphenyl, benzyl, and naphthalene-1-yl, naphthalene-2-yl, etc. In addition, aryl may be optionally substituted.

[0043] The term "aryloxy" refers to an "-O-aryl" group wherein aryl is as defined herein.

[0044] The term "alkoxy" refers to an "-O-alkyl" group wherein alkyl is as defined herein.

[0045] When the above substituents are substituted, unless otherwise stated, they are substituted with one or more halogens.

[0046] As used herein, the term "halogen" encompasses fluorine (F), chlorine (Cl), bromine (Br) and iodine (I), preferably F or Cl.

[0047] Electrochemical Devices

[0048] The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, and its specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. 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. In some embodiments, the electrochemical device of the present application is an electrochemical device having a positive electrode with a positive electrode active material capable of occluding and releasing metal ions and a negative electrode with a negative electrode active material capable of occluding and releasing metal ions.

[0049] In some embodiments, the present application provides an electrochemical device comprising an electrolyte, a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the electrolyte comprises fluoroethylene carbonate, wherein the electrochemical device satisfies the relationship:

[0050] 0.5 <R ct / R cp <1.5, and R ct and R cp All are less than 35 milliohms,

[0051] Where R ct It represents the charge transfer impedance at 50% state of charge at 25 degrees Celsius, R cp represents the concentration polarization impedance at 50% state of charge at 25 degrees Celsius; and

[0052] 0.005≤A / B≤0.1

[0053] Wherein, the mass of the fluoroethylene carbonate corresponding to 1g of the negative electrode active material is Ag, and the specific surface area of ​​the negative electrode active material is Bm. 2 / g.

[0054] The inventors have found that when R ct / R cp Range 0.5 <R ct / R cp <1.5, while satisfying R ct and Rcp When both are less than 35 milliohms (mΩ), it is conducive to the rapid passage of lithium ions through the solid electrolyte interface membrane (SEI) into the negative electrode active material layer. At the same time, the diffusion of lithium ions in the negative electrode active material layer is also faster, which can achieve ultra-high rate charging of lithium-ion batteries.

[0055] When R cp Much larger than R ct When the electrolyte diffuses in the negative electrode active material layer, the concentration polarization becomes the limiting factor for high-rate charging of lithium-ion batteries. ct It is already very small. Since the electrolyte cannot diffuse to the surface of the negative electrode active material, lithium-ion batteries cannot achieve high-rate charging.

[0056] When R ct Much larger than R cp When R cp It is already very small. Although lithium ions can quickly reach the surface of the negative electrode active material, they cannot quickly complete the embedding of the negative electrode active material, resulting in the deposition of lithium ions on the surface of the negative electrode active material layer. Lithium deposition occurs under high-rate charging. The low-temperature performance of lithium-ion batteries is limited and cannot have excellent fast charging performance.

[0057] When R ct and R cp At the same time, when it is greater than 35 milliohms, the lithium ion diffusion and charge transfer processes are restricted, and fast charging performance cannot be achieved.

[0058] When the mass of fluoroethylene carbonate and the specific surface area of ​​the negative electrode active material satisfy the above relationship, the diffusion of the electrolyte and the transmission of lithium ions can be further guaranteed, thereby realizing the rapid charge and discharge of the lithium-ion battery.

[0059] Figure 1 R during lithium-ion battery transmission ct and R cp Decomposed.

[0060] In some embodiments, the R ct With the R cp The ratio R ct / R cp The range of R is 0.7 to 1.2. In some embodiments, R ct / R cp The value of is about 0.55, about 0.6, about 0.65, about 0.7, about 0.75, about 0.8, about 0.85, about 0.9, about 0.95, about 1.0, about 1.05, about 1.1, about 1.15, about 1.2, about 1.25, about 1.3, about 1.35, about 1.4, or about 1.45. In some embodiments, R ct / Rcp The value of is about 0.54, about 0.71, about 0.92, about 1.03, about 1.15, about 1.23, about 1.37 or about 1.47.

[0061] In some embodiments, the ratio of A to B, A / B, ranges from 0.005 to 0.07. In some embodiments, the value of A / B is about 0.005, about 0.006, about 0.007, about 0.008, about 0.009, about 0.01, about 0.012, about 0.014, about 0.016, about 0.018, about 0.02, about 0.022, about 0.024, about 0.026, about 0.028, about 0.03, about 0.032, about 0.034, about 0.036, about 0.038, about 0.04, about 0.042, about 0.044, about 0.046, about about 0.048, about 0.05, about 0.052, about 0.054, about 0.056, about 0.058, about 0.06, about 0.062, about 0.064, about 0.066, about 0.068, about 0.07, about 0.072, about 0.074, about 0.076, about 0.078, about 0.08, about 0.082, about 0.084, about 0.086, about 0.088, about 0.09, about 0.092, about 0.094, about 0.096, about 0.098 or about 0.1. In some embodiments, the value of A / B is about 0.005, about 0.0053, about 0.0122, about 0.04, about 0.0636, about 0.0889, about 0.0917, or about 0.1.

[0062] In some embodiments, the value range of A is 0.01 to 0.1, and the value range of B is 1.0 to 2.0.

[0063] In some embodiments, the value of A ranges from 0.02 to 0.1. In some embodiments, the value of A is about 0.01, about 0.015, about 0.02, about 0.025, about 0.03, about 0.035, about 0.04, about 0.045, about 0.05, about 0.055, about 0.06, about 0.065, about 0.07, about 0.075, about 0.08, about 0.085, about 0.09, about 0.095 or about 0.1. In some embodiments, the value of A is about 0.01, about 0.0195, about 0.02, about 0.052, about 0.07, about 0.08, about 0.09 or about 0.1.

[0064] In some embodiments, the value of B ranges from 1.1 to 1.6. In some embodiments, the value of B is about 1.0, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9 or about 2.0. In some embodiments, the electrolyte comprises a compound of formula I:

[0065]

[0066] Among them, R 11 Selected from hydrogen, hydroxyl, C 1-20 Alkyl, C 1-20 Alkoxy, C 2-20 Alkenyl, C 6-30 Aryl, or C 6-30 aryloxy;

[0067] R 12 Selected from hydrogen, C 1-20 Alkyl, C 2-20 Alkenyl, or C 6-30 Aryl.

[0068] The inventors have found that when the electrochemical device further contains the compound of formula 1, the diffusion performance of the electrolyte can be further improved, and the rapid charge and discharge performance of the electrochemical device can be further improved.

[0069] Wherein, the mass of the compound of formula I corresponding to 1g of the negative electrode active material is X g, and the value range of X is 0.035 to 0.39.

[0070] In some embodiments, R 11 Selected from: hydrogen, hydroxyl, C 1-16 Alkyl, C 1-12 Alkyl, C 1-10 Alkyl, C 1-8 Alkyl, C 1-6 Alkyl or C 1-4 Alkyl, C 1-16 Alkoxy, C 1-12 Alkoxy, C 1-10 Alkoxy, C 1-8 Alkoxy, C 1-6 Alkoxy or C 1-4 Alkoxy, C 2-16 Alkenyl, C 2-12 Alkenyl, C 2-8 Alkenyl, C 2-6 Alkenyl or C 2-4 Alkenyl, C 6-24 Aryl, C 6-20 Aryl, C 6-16 Aryl, C 6-12 Aryl or C 6-10 Aryl, or C6-24 Aryloxy, C 6-20 Aryloxy, C 6-16 Aryloxy, C 6-12 Aryloxy or C 6-10 Aryloxy.

[0071] In some embodiments, R 11 Selected from: hydrogen, hydroxy, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl or isopentyl.

[0072] In some embodiments, R 12 Selected from: hydrogen, C 1-16 Alkyl, C 1-12 Alkyl, C 1-10 Alkyl, C 1-8 Alkyl, C 1-6 Alkyl or C 1-4 Alkyl, C 2-16 Alkenyl, C 2-12 Alkenyl, C 2-8 Alkenyl, C 2-6 Alkenyl or C 2-4 Alkenyl, or C 6-24 Aryl, C 6-20 Aryl, C 6-16 Aryl, C 6-12 Aryl or C 6-10 Aryl.

[0073] In some embodiments, R 12 Selected from: hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl or isopentyl.

[0074] In some embodiments, the value of X ranges from 0.05 to 0.3 or 0.09 to 0.25; in some embodiments, the value of X is about 0.04, about 0.045, about 0.05, about 0.055, about 0.06, about 0.065, about 0.07, about 0.075, about 0.08, about 0.085, about 0.09, about 0.095, about 0.1, about 0.12, about 0.14, about 0.16, about 0.18, about 0.2, about 0.22, about 0.24, about 0.26, about 0.28, about 0.3, about 0.32, about 0.34, about 0.36, or about 0.38. In some embodiments, the value of X ranges from about 0.035, about 0.093, about 0.25, about 0.32, or about 0.39.

[0075] In some embodiments, X and A satisfy the following relationship: 0.67≤X / A≤20. When the X / A ratio is in the range of 0.67 to 20, the viscosity of the electrolyte is low, a stable SEI film is formed on the surface of the negative electrode, and the electrolyte has excellent fast charging performance and good cycle performance.

[0076] In some embodiments, the ratio of X to A, X / A, ranges from 1 to 20 or from 5 to 20. In some embodiments, the value of X / A is about 0.7, about 0.8, about 0.9, about 1, about 1.5, about 2, about 2.5, about 3, about 3.5, about 4, about 4.5, about 5, about 5.5, about 6, about 6.5, about 7, about 7.5, about 8, about 8.5, about 9, about 9.5, about 10, about 10.5, about 11, about 11.5, about 12, about 12.5, about 13, about 13.5, about 14, about 14.5, about 15, about 15.5, about 16, about 16.5, about 17, about 17.5, about 18, about 18.5, about 19, about 19.5, or about 20. In some embodiments, the value of X / A is about 0.67, about 1.79, about 4.77, about 12.82, about 16.41, or about 20.

[0077] In some embodiments, the compound of formula I comprises at least one of the following compounds: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, or n-pentyl valerate.

[0078] In some embodiments, the compound of formula I is selected from at least one of ethyl acetate or ethyl propionate.

[0079] In some embodiments, the X and the porosity P of the negative electrode active material layer satisfy the following relationship: 0.1≤X / P≤3, wherein the value range of P is 0.13 to 0.35.

[0080] In some embodiments, the ratio X / P of X to P ranges from 0.3 to 3; in some embodiments, the range of X / P is about 0.3, about 0.5, about 0.7, about 0.9, about 1.1, about 1.3, about 1.5, about 1.7, about 1.9, about 2.1, about 2.3, about 2.5, about 2.7, about 2.9 or about 3.0. In some embodiments, the range of X / P is about 0.1, about 0.3, about 1.0, about 1.78, or about 3.

[0081] In some embodiments, the value of P is about 0.13, about 0.15, about 0.17, about 0.19, about 0.21, about 0.23, about 0.25, about 0.27, about 0.29, about 0.31, about 0.33 or about 0.35. In some embodiments, the value of P is about 0.13, about 0.18, about 0.25, about 0.31 or about 0.35.

[0082] In some embodiments, the electrolyte further comprises vinylene carbonate, wherein the mass of the vinylene carbonate corresponding to 1 g of the negative electrode active material is C g, and B and C satisfy the following relationship: 0.001≤C / B≤0.03.

[0083] In some embodiments, the ratio of C to B, C / B, ranges from 0.001 to 0.02. In some embodiments, the value of C / B is about 0.001, about 0.0015, about 0.002, about 0.0025, about 0.003, about 0.0035, about 0.004, about 0.0045, about 0.005, about 0.0055, about 0.006, about 0.0065, about 0.007, about 0.0075, about 0.008, about 0.0085, about 0.009, about 0.0095, about 0.01, about 0.015, about 0.02, about 0.025 or about 0.03. In some embodiments, the value of C / B is about 0.001, about 0.00125, about 0.01875, about 0.0025 or about 0.003. When the C / B ratio is within the above range, the decomposition amount and decomposition rate of vinylene carbonate on the surface of the negative electrode active material in the electrochemical device are within an appropriate range, and excessive high-impedance LiF will not be formed, so that the fast charging performance and cycle performance of the electrochemical device are further improved.

[0084] In some embodiments, the compound of formula I comprises ethyl propionate, the mass of ethyl propionate corresponding to 1 g of the negative electrode active material is D g, and C and D satisfy the following relationship: 1≤D / C≤240.

[0085] In some embodiments, the ratio D / C of D to C ranges from 1 to 200, 1 to 100, 1 to 50, or 1 to 20. In some embodiments, the value of D / C is about 2, about 4, about 6, about 8, about 10, about 12, about 14, about 16, about 18, about 20, about 30, about 40, about 50, about 60, about 70, about 80, about 90, about 100, about 110, about 120, about 130, about 140, about 150, about 160, about 170, about 180, or about 190. In some embodiments, the value of D / C is about 1, about 1.5, about 2, about 2.5, about 3, about 3.5, or about 4.5. When the ratio of D / C is within the above range, the fast charging performance of the electrochemical device can be further improved.

[0086] In some embodiments, the electrolyte further comprises at least one of a compound of formula II or a compound of formula III:

[0087]

[0088] Among them, R 21and R 22 Each is independently selected from unsubstituted or fluorine-substituted C 1-5 Alkyl, and R 21 and R 22 At least one of them contains fluorine;

[0089] R 31 and R 32 Each is independently selected from unsubstituted or fluorine-substituted C 1-20 Alkyl, and R 31 and R 32 At least one of them contains fluorine, and Y is selected from -O- or

[0090] In some embodiments, R 21 and R 22 Each is independently selected from unsubstituted or substituted with one or more fluorine-substituted C 1-3 Alkyl, and R 21 and R 22 At least one of contains fluorine. In some embodiments, R 21 and R 22 Each is independently selected from the following groups substituted with one or more fluorine groups: methyl, ethyl, propyl. 21 and R 22 Each is independently selected from -CH3, -CH2F, -CHF2, -CF3, -CH2CH3, -CH2CH2F, -CH2CHF2, -CH2CF3, -CHFCH3, -CF2CH3, -CHFCH2F, or -CH2CH2CH3.

[0091] In some embodiments, R 31 and R 32 Each is independently selected from the following groups which are unsubstituted or substituted with fluorine: C 1-16 Alkyl, C 1-12 Alkyl, C 1-8 Alkyl, C 1-6 Alkyl or C 1-4 Alkyl, and R 31 and R 32 At least one of contains fluorine. In some embodiments, R 31 and R 32 Each is independently selected from the following groups substituted with one or more fluorine groups: methyl, ethyl, propyl. 31 and R 32 Each is independently selected from -CH2F, -CHF2, -CH2CH2F, -CH2CHF2, -CH2CF3, -CHFCH3, -CF2CH3, -CHFCH2F, -CF2CHF2, -CF3, -CF2CF3, -CF2CF2CF3 or -CF(CF3)2.

[0092] In some embodiments, the mass of the compound of formula II corresponding to 1 g of the negative electrode active material is 0.015 g to 0.15 g.

[0093] In some embodiments, the mass of the compound of formula II corresponding to 1 g of the negative electrode active material is 0.02 g to 0.1 g. In some embodiments, the mass of the compound of formula II corresponding to 1 g of the negative electrode active material is about 0.015 g, about 0.02 g, about 0.025 g, about 0.03 g, about 0.035 g, about 0.04 g, 0.045 g, about 0.05 g, about 0.055 g, about 0.06 g, about 0.065 g, about 0.07 g, 0.075 g, about 0.08 g, about 0.085 g, about 0.09 g, about 0.095 g, about 0.1 g, about 0.11 g, about 0.12 g, about 0.13 g, about 0.14 g or about 0.15 g. In some embodiments, the mass of the compound of formula II corresponding to 1 g of the negative electrode active material is about 0.015 g, about 0.037 g, about 0.076 g, about 0.098 g, about 0.13 g or about 0.15 g.

[0094] In some embodiments, the mass of the compound of formula III corresponding to 1 g of the negative electrode active material is 0.015 g to 0.065 g.

[0095] In some embodiments, the mass of the compound of formula III corresponding to 1g of the negative electrode active material is 0.02g to 0.6g. In some embodiments, the mass of the compound of formula II corresponding to 1g of the negative electrode active material is about 0.02g, about 0.04g, about 0.06g, about 0.08g, about 0.1g, 0.15g, about 0.2g, 0.25g, about 0.3g, 0.35g, about 0.4g, 0.45g, about 0.5g, 0.55g, about 0.6g, or 0.65g. In some embodiments, the mass of the compound of formula III corresponding to 1g of the negative electrode active material is about 0.015g, about 0.022g, about 0.0036g, about 0.053g, or about 0.065g.

[0096] In some embodiments, the compound of formula II comprises at least one of the following compounds: methyl difluoroacetate, ethyl difluoroacetate, propyl difluoroacetate, methyl difluoropropionate, ethyl difluoropropionate, propyl difluoropropionate, methyl fluoroacetate, ethyl fluoroacetate, propyl fluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, or propyl trifluoroacetate; in some embodiments, the compound of formula II comprises ethyl difluoroacetate.

[0097] In some embodiments, the compound of formula III comprises at least one of the following compounds: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, or perfluoro(2-methyl-3-pentanone). In some embodiments, the compound of formula III comprises 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0098] In some embodiments, the electrolyte further includes a lithium salt and an organic solvent.

[0099] In some embodiments, the lithium salt is selected from one or more of an inorganic lithium salt and an organic lithium salt. In some embodiments, the lithium salt contains at least one of a fluorine element, a boron element or a phosphorus element. In some embodiments, the lithium salt comprises: lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI), bis(oxalyl)boric acid (abbreviated as LiBOB), difluoro(oxalyl)boric acid (abbreviated as LiDFOB), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), or at least one of lithium trifluoromethanesulfonate (LiCF3SO3).

[0100] In some embodiments, the concentration of the lithium salt is 0.5 mol / L to 1.5 mol / L. In some embodiments, the concentration of the lithium salt is 0.8 mol / L to 1.2 mol / L.

[0101] In some embodiments, the organic solvent comprises a carbonate solvent, the carbonate solvent comprises a cyclic carbonate and a chain carbonate, the cyclic carbonate is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (BL) or butylene carbonate; the chain carbonate is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and propylene carbonate. The amount of the cyclic carbonate is greater than that of the chain carbonate, and the solvent system preferably does not contain a chain carbonate.

[0102] In some embodiments, in order to further improve the fast charging performance of lithium-ion batteries, the electrolyte described in the present application has certain characteristics: at 25°C, the electrolyte conductivity is ≥7mS / cm, at 0°C, the electrolyte conductivity is ≥4mS / cm; at 25°C, the electrolyte viscosity is ≤6mPa·s, at 0°C, the electrolyte viscosity is ≤9mPa·s; the surface tension of the electrolyte at 25°C is ≤40mN / m.

[0103] When the electrolyte has higher conductivity, lower viscosity and lower surface tension, the transmission speed of lithium ions is faster, which is conducive to achieving the fast charging performance of lithium-ion batteries; when the electrolyte has lower conductivity, higher viscosity and higher surface tension, the transmission of lithium ions is hindered, which is not conducive to improving the fast charging and discharging performance.

[0104] negative electrode

[0105] In the electrochemical device described in the present application, the negative electrode includes a current collector and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer includes a negative electrode active material, and the specific types of the negative electrode active material are not subject to specific restrictions and can be selected according to needs.

[0106] The negative electrode can be prepared by a preparation method known in the art. For example, the negative electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector.

[0107] The negative electrode active material includes a material that reversibly intercalates / deintercalates lithium ions. In some embodiments, the material that reversibly intercalates / deintercalates lithium ions includes a carbon material. In some embodiments, the carbon material can be any carbon-based negative electrode active material commonly used in lithium-ion rechargeable batteries. In some embodiments, the carbon material includes, but is not limited to: crystalline carbon, amorphous carbon, or a mixture thereof. Crystalline carbon can be amorphous, flaky, flake-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0108] In some embodiments, the negative electrode active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase microcarbon beads (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon or silicon-oxygen containing materials, silicon-carbon composites or any combination thereof.

[0109] In some embodiments, the negative electrode active material is composed of a combination of single particles and secondary particles. Figure 2 A schematic diagram of primary and secondary particles of negative electrode active materials is given.

[0110] In some embodiments, the raw materials of the negative electrode active material include raw material A and raw material B, the single particle Dv50 of raw material A is 3 microns to 10 microns, the single particle Dv50 of raw material B is 2 microns to 10 microns, and the Dv50 of secondary particles prepared by granulation is 5 microns to 20 microns; wherein the addition ratio of raw material A to raw material B is 1:9 to 5:5.

[0111] In some embodiments, the OI value (C004 / C110—the ratio of the peak area of ​​the 004 peak of the negative electrode active material to the peak area of ​​the 110 peak) of the negative electrode active material ranges from 8 to 15, which greatly shortens the transmission distance of lithium ions in the negative electrode active material and reduces the R cp , which increases the transmission rate of lithium ions and improves the performance of fast charging.

[0112] In some embodiments, the negative electrode active material may further include the following orientations:

[0113] The distribution ratio of the layer structure of orientation 1 is 6% to 25%, the distribution ratio of the layer structure of orientation 2 is 27% to 65%, and the distribution ratio of the layer structure of orientation 3 is 5% to 10%. With the plane direction parallel to the current collector, the particles with an inclination angle of 0 to 20 degrees with the current collector are oriented 1, the particles with an inclination angle of 20 to 70 degrees with the current collector are oriented 2, and the particles with an inclination angle of 70 to 90 degrees with the current collector are oriented 3.

[0114] In some embodiments, the specific surface area (BET) of the negative electrode active material is 1.0 m 2 / g to 2.0m 2 / g.

[0115] In some embodiments, the negative electrode active material layer may include a binder and optionally a conductive material. The binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0116] In some embodiments, the conductive material includes, but is not limited to: a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0117] In the electrochemical device described herein, the current collector of the negative electrode can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof. In some embodiments, the current collector comprises copper foil.

[0118] positive electrode

[0119] The material of the positive electrode used in the electrochemical device of the present application can be prepared using materials, structures and manufacturing methods known in the art. In some embodiments, the positive electrode of the present application can be prepared using the technology described in US9812739B, which is incorporated into the present application by reference in its entirety.

[0120] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material includes a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel.

[0121] In some embodiments, the positive electrode active material is selected from one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0122] In some embodiments, the positive electrode active material may have a coating on its surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound for the coating may be amorphous or crystalline.

[0123] In some embodiments, the coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or any combination thereof. The coating may be applied by any method as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method may include any coating method known in the art, such as spraying, dipping, etc.

[0124] The positive electrode active material layer also includes a binder, and optionally a conductive material. The binder improves the bonding of the positive electrode active material particles to each other and also improves the bonding of the positive electrode active material to the current collector.

[0125] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0126] In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0127] In some embodiments, the current collector may be aluminum, but is not limited thereto.

[0128] The positive electrode can be prepared by a preparation method known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent may include N-methylpyrrolidone, etc., but is not limited thereto.

[0129] In some embodiments, the positive electrode is made by forming a positive electrode material using a positive electrode active material layer including a lithium transition metal compound powder and a binder on a current collector.

[0130] In some embodiments, the positive electrode active material layer can be generally prepared by dry mixing the positive electrode material and the binder (conductive material and thickener used as needed) to form a sheet, pressing the obtained sheet to the positive electrode collector, or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry on the positive electrode collector and drying. In some embodiments, the material in the positive electrode active material layer includes any material known in the art.

[0131] Isolation film

[0132] In some embodiments, the electrochemical device of the present application is provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0133] For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be selected. The substrate layer may be one or more layers. When the substrate layer is multi-layered, the composition of the polymers of different substrate layers may be the same or different, and the weight average molecular weight may be different; when the substrate layer is multi-layered, the closed-cell temperatures of the polymers of different substrate layers are different.

[0134] In some embodiments, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0135] In some embodiments, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from one or more combinations of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or more combinations of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0136] application

[0137] The electrochemical device of the embodiment of the present application has improved cycle performance and high temperature stability under over-discharge conditions, and is suitable for use in various electronic devices.

[0138] The use of the electrochemical device of the present application is not particularly limited, and can be used for various known uses, such as laptop computers, pen-input computers, mobile computers, electronic book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0139] Example

[0140] Hereinafter, the present application will be described in more detail with reference to Examples and Comparative Examples, but the present application is not limited to these Examples unless departing from the gist of the present application.

[0141] 1. Preparation of lithium-ion batteries

[0142] (1) Preparation of negative electrode

[0143] The negative electrode active material includes a first particle and a second particle, wherein the first particle is a secondary particle, and the secondary particle contains no less than 2 primary particles. The Dv50 of the primary particles in the secondary particles is 2 microns to 10 microns, and the Dv50 of the secondary particles is 5 microns to 20 microns. The second particle is a primary particle, and the Dv50 of the second particle is 3 microns to 10 microns.

[0144] By controlling the graphitization temperature during preparation and the ratio of the first particle to the second particle, negative electrode active materials with different specific surface areas and porosities are obtained, and the graphitization temperature ranges from 2500 to 3200 degrees Celsius. The specific surface area (B) and porosity (P) of the examples are shown in the table below.

[0145] Artificial graphite, a negative electrode active material with an OI value (C004 / C110) of 8 to 15, a binder of styrene-butadiene rubber (abbreviated as SBR), and a thickener of sodium carboxymethyl cellulose (abbreviated as CMC) are fully stirred and mixed in a proper amount of deionized water solvent in a weight ratio of 97.4:1.2:1.4 to form a uniform negative electrode slurry; the slurry is coated on a negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode.

[0146] (2) Preparation of positive electrode

[0147] The positive electrode active material lithium cobalt oxide (molecular formula LiCoO2), the conductive agent acetylene black, and the binder polyvinylidene fluoride (abbreviated as PVDF) are fully stirred and mixed in a proper amount of N-methylpyrrolidone (abbreviated as NMP) solvent in a weight ratio of 96:2:2 to form a uniform positive electrode slurry; the slurry is coated on the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode.

[0148] (3) Preparation of electrolyte

[0149] Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) are mixed uniformly in a mass ratio of 3:3:4 to obtain a non-aqueous solvent, and then the fully dried lithium salt LiPF6 is dissolved in the above non-aqueous solvent, and a specific type and amount of additives are added (the type and amount of the added substances are shown in the following table, and the content of each additive in the electrolyte is calculated based on the mass (unit: gram) of the additive required for 1 gram of negative electrode active material. The concentration of LiPF6 in the electrolyte is about 1 mol / L.

[0150] (4) Preparation of isolation membrane

[0151] A polyethylene separator film with a thickness of about 9 microns is selected.

[0152] (5) Preparation of lithium-ion batteries

[0153] The positive electrode, the separator, and the negative electrode are stacked in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging aluminum-plastic film, and the prepared electrolyte is injected into the dried battery. After vacuum packaging, standing, formation, shaping and other processes, the preparation of the lithium-ion battery is completed.

[0154] 2. Lithium-ion battery performance test

[0155] (1) Electrochemical impedance spectroscopy (EIS-R ct test)

[0156] Preparation of three-electrode lithium-ion battery: stack the positive electrode, separator and negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role; weld a thin copper wire on the side of the separator close to the negative electrode, and cover the copper wire with another small piece of separator so that it does not contact the negative electrode; then wind to obtain the electrode assembly, place the electrode assembly in an outer packaging aluminum-plastic film, inject the prepared electrolyte into the dried battery, and complete the preparation of the three-electrode lithium-ion battery after vacuum packaging, standing, forming, shaping and other processes.

[0157] Place the prepared three-electrode lithium-ion battery in the electrochemical workstation and connect it in the order of working electrode and reference electrode. Apply a sine wave AC signal with an amplitude of 5mV and a frequency of 500KHz-30mHz to the electrochemical system to obtain the corresponding electrical signal feedback within the frequency domain. Figure 3A The model shown in the figure simulates the EIS curve of lithium-ion batteries (such as Figure 3B The right intersection of the first semicircle arc and the X-axis is the charge transfer impedance value, i.e., R ct , R described in this application ct It is the value at 50% SOC (state of charge) and the unit is milliohm.

[0158] (2) DC resistance test (DCR-R cp test)

[0159] Charge the lithium-ion battery to 4.4V at a constant current of 1.5C, and then charge it to 0.05C at a constant voltage. Let it stand for 30 minutes; discharge it for 10 seconds at a current of 0.1C (take a point once every 0.1 seconds and record the corresponding voltage value U1), and discharge it for 360 seconds at a current of 1C (take a point once every 0.1 seconds and record the corresponding voltage value U2). Repeat the charge and discharge steps 5 times. "1C" is the current value that completely discharges the battery capacity within 1 hour.

[0160] The DC resistance (DCR) is calculated by the following formula: R = (U2-U1) / (1C-0.1C). The obtained DCR is the concentration polarization resistance of the present application, which is the value at 50% SOC (state of charge), that is, R in the embodiment. cp , the unit is milliohm.

[0161] (3) Lithium deposition test

[0162] The lithium-ion battery was charged to 4.4V at 1.5C at 25°C, charged to 0.05C at 4.4V, and then discharged to 3.0V at 1.0C constant current for 30 cycles. The battery was disassembled to observe the degree of lithium deposition. No lithium deposition or lithium deposition area <2% is called no lithium deposition; lithium deposition area between 2% and 20% is called slight lithium deposition; lithium deposition area >20% is called severe lithium deposition.

[0163] (4) Temperature rise test

[0164] At a temperature of 25°C, the lithium-ion battery is charged to 4.4V at a constant current of 0.5C, then charged to 0.05C at a constant voltage, and allowed to stand for 60 minutes; then the lithium-ion battery is discharged to 3V at a constant current of 0.5C, and allowed to stand for 60 minutes; the lithium-ion battery is charged to 4.4V at a constant current of 8C, and then charged to 0.05C at a constant voltage, and the highest temperature during the 8C current charging process is obtained. The test temperature of 25°C is subtracted from the highest temperature to obtain the temperature rise value (referred to as temperature rise) during 8C charging, in degrees Celsius.

[0165] (5) 45℃ cycle test

[0166] The battery was placed in a 45°C constant temperature box, charged to 4.4V at a constant current of 1.5C, charged to 0.05C at a constant voltage at 4.4V, and then discharged to 3.0V at a constant current of 1.0C. This was a charge and discharge cycle process. The charge and discharge cycle test was performed 800 times in the above manner to monitor the capacity retention rate.

[0167] Capacity retention rate = remaining discharge capacity / initial discharge capacity x 100%.

[0168] (6) Conductivity test

[0169] The DDS-307 lightning magnetic conductivity meter standard test method was used for testing.

[0170] (7) Viscosity test

[0171] The DV2T viscometer standard test method was used for testing.

[0172] (8) Surface tension test

[0173] The BZY202-surface tension meter standard method was used.

[0174] A. The lithium ion batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were prepared according to the above method. The test results are shown in Table 1.

[0175] Table 1

[0176]

[0177] It can be seen from Table 1 that Examples 1 to 8 all meet the requirement (1) "0.5 <R ct / R cp <1.5 and R ct and R cp "All less than 35 milliohms" and requirement (2) "0.005≤A / B≤0.1"; while Comparative Examples 1 to 3 do not meet the above requirements (1) and (2). Therefore, in the three tests of cycle, temperature rise and lithium deposition, compared with Comparative Examples 1 to 3, Examples 1 to 8 obviously achieved better technical effects; among them, the comprehensive improvement effects of Examples 2 to 5 in the above three tests were particularly significant.

[0178] B. The lithium ion batteries of Examples 9 to 15 were prepared according to the above method. The test results are shown in Table 2.

[0179] Table 2

[0180]

[0181] As can be seen from Table 2, in Examples 9 to 14, an appropriate amount of compound of formula I (e.g., ethyl acetate) X g is further added to the electrolyte containing fluoroethylene carbonate (FEC), so that the requirement (1) "0.5 <R ct / R cp <1.5 and R ct and R cp While meeting requirement (2) "0.005≤A / B≤0.1", requirement (3) "0.67≤X / A≤20" is further met. Therefore, in the three tests of cycle, temperature rise and lithium deposition, compared with embodiments 2 to 4 and 15 that meet requirements (1) and (2) but not requirement (3), embodiments 9 to 14 obviously achieve better technical effects; among them, the comprehensive improvement effects of embodiments 10 to 13 in the above three tests are particularly significant.

[0182] C. The lithium ion batteries of Examples 16 to 21 were prepared according to the above method. The test results are shown in Table 3.

[0183] Table 3

[0184]

[0185] It can be seen from Table 3 that Examples 16 to 20 meet the requirement (1) "0.5 <R ct / R cp <1.5 and R ct and R cpOn the basis of requirement (2) "0.005≤A / B≤0.1", and requirement (3) "0.67≤X / A≤20", requirement (4) "0.1≤X / P≤3, wherein the value range of P is 0.13 to 0.35" is further satisfied; therefore, in the three tests of cycle, temperature rise and lithium deposition, compared with embodiments 9 to 13 and embodiment 21 which meet requirements (1) to (3) but do not meet requirement (4), embodiments 16 to 20 obviously achieve better technical effects.

[0186] D. The lithium ion batteries of Examples 22 to 27 were prepared according to the above method. The test results are shown in Table 4.

[0187] Table 4

[0188]

[0189] As can be seen from Table 4, in Examples 22 to 26, vinylene carbonate (VC) is further added to the electrolyte containing fluoroethylene carbonate (FEC) and the compound of formula I (e.g., ethyl acetate), so that the electrolyte can meet the requirement (1) "0.5 <R ct / R cp <1.5 and R ct and R cp On the basis of requirement (2) "0.005≤A / B≤0.1" and requirement (3) "0.67≤X / A≤20", requirement (5) "0.001≤C / B≤0.03" is further satisfied; therefore, in the three tests of cycle, temperature rise and lithium deposition, compared with embodiment 10 and embodiment 27 which meet requirements (1) to (3) but do not meet requirement (5), embodiments 22 to 26 obviously achieve better technical effects.

[0190] E. The lithium ion batteries of Examples 28 to 34 were prepared according to the above method, wherein the mass ratio of ethyl acetate to propyl propionate in Example 34 was 1:1. The test results are shown in Table 5.

[0191] Table 5

[0192]

[0193] As can be seen from Table 5, the electrolytes of Examples 28 to 34 contain ethyl propionate in addition to fluoroethylene carbonate (FEC), ethyl acetate, and vinylene carbonate (VC), so that the electrolytes of Examples 28 to 34 meet the requirement (1) "0.5 <R ct / R cp <1.5 and R ct and R cpOn the basis of requirement (2) "0.005≤A / B≤0.1", requirement (3) "0.67≤X / A≤20" and requirement (5) "0.001≤C / B≤0.03", requirement (6) "1≤D / C≤240" is further satisfied; therefore, in the three tests of cycle, temperature rise and lithium deposition, compared with embodiment 23 which satisfies requirements (1) to (3) and requirement (5) but does not satisfy requirement (6), embodiments 28 to 34 obviously achieve better technical effects.

[0194] F. The lithium ion batteries of Examples 35 to 45 were prepared according to the above method. The test results are shown in Table 6.

[0195] Table 6

[0196]

[0197] Note: “ / ” represents not included

[0198] As can be seen from Table 6, in Examples 35 to 40, an appropriate amount of a compound of Formula II (e.g., ethyl difluoroacetate) is further added to the electrolyte containing fluoroethylene carbonate (FEC) and a compound of Formula I (e.g., ethyl acetate); in the cycle and temperature rise tests, compared with Example 10 to which no compound of Formula II is added, Examples 35 to 40 achieve better technical effects.

[0199] In Examples 41 to 45, an appropriate amount of a compound of Formula III (e.g., 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether) is further added to the electrolyte containing fluoroethylene carbonate (FEC) and a compound of Formula I (e.g., ethyl acetate); in the cycle and temperature rise tests, compared with Example 10 in which no compound of Formula III is added, Examples 41 to 45 achieve better technical effects.

[0200] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

[0201] References to "some embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics herein may be combined in one or more embodiments or examples in any suitable manner.

[0202] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising an electrolyte, a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, the electrolyte comprises fluoroethylene carbonate, and 0.005≤A / B≤0.1, in, The mass of the fluoroethylene carbonate corresponding to 1g of the negative electrode active material is Ag, and the specific surface area of ​​the negative electrode active material is Bm 2 / g, and the value range of A is 0.01 to 0.

1.

2. The electrochemical device according to claim 1, wherein the electrochemical device satisfies the relationship: 0.5 <R ct / R cp <1.5, and R ct and R cp All are less than 35 milliohms, Where R ct It represents the charge transfer impedance at 50% state of charge at 25 degrees Celsius, R cp It represents the concentration polarization impedance at 50% state of charge at 25 degrees Celsius.

3. The electrochemical device according to claim 1, wherein the value of B ranges from 1.0 to 2.

0.

4. The electrochemical device according to claim 1, wherein the electrolyte comprises a compound of formula I: in, R 11 Selected from hydrogen, hydroxyl, C 1-20 Alkyl, C 1-20 Alkoxy, C 2-20 Alkenyl, C 6-30 Aryl or C 6-30 aryloxy; R 12 Selected from hydrogen, C 1-20 Alkyl, C 2-20 Alkenyl or C 6-30 Aryl; Wherein, the mass of the compound of formula I corresponding to 1g of the negative electrode active material is X g, and the value range of X is 0.035 to 0.

39.

5. The electrochemical device according to claim 4, wherein the X and the A satisfy the following relationship: 0.67≤X / A≤20.

6. The electrochemical device of claim 4, wherein the compound of formula I comprises at least one of the following compounds: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, propyl isobutyrate, n-pentyl n-butyrate, n-pentyl isobutyrate, n-butyl n-butyrate, isobutyl isobutyrate, or n-pentyl n-valerate. 7 . The electrochemical device according to claim 4 , wherein the X and the porosity P of the negative electrode active material layer satisfy the following relationship: 0.1≤X / P≤3, wherein the value range of P is 0.13 to 0.

35.

8. The electrochemical device according to claim 4, wherein the electrolyte further comprises vinylene carbonate, wherein the mass of the vinylene carbonate corresponding to 1 g of the negative electrode active material is C g, and B and C satisfy the following relationship: 0.001≤C / B≤0.

03.

9. The electrochemical device according to claim 8, wherein the compound of formula I comprises ethyl propionate, the mass of ethyl propionate corresponding to 1 g of the negative electrode active material is D g, and C and D satisfy the following relationship: 1≤D / C≤240.

10. The electrochemical device according to any one of claims 1 to 4, wherein the electrolyte comprises at least one of the compound of formula II or the compound of formula III: in, R 21 and R 22 Each is independently selected from unsubstituted or fluorine-substituted C 1-5 Alkyl, and R 21 and R 22 At least one of them contains fluorine; R 31 and R 32 Each is independently selected from unsubstituted or fluorine-substituted C 1-20 Alkyl, and R 31 and R 32 At least one of them contains fluorine, and Y is selected from -O- or 11 . The electrochemical device according to claim 10 , wherein the mass of the compound of formula II corresponding to 1 g of the negative electrode active material is 0.015 g to 0.15 g. 12 . The electrochemical device according to claim 10 , wherein the mass of the compound of formula III corresponding to 1 g of the negative electrode active material is 0.015 g to 0.065 g.

13. The electrochemical device according to claim 10, wherein The compound of formula II comprises at least one of the following compounds: methyl difluoroacetate, ethyl difluoroacetate, propyl difluoroacetate, methyl difluoropropionate, ethyl difluoropropionate, propyl difluoropropionate, methyl fluoroacetate, ethyl fluoroacetate, propyl fluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate or propyl trifluoroacetate; The compound of formula III comprises at least one of the following compounds: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether or perfluoro(2-methyl-3-pentanone).

14. An electronic device comprising the electrochemical device according to any one of claims 1 to 13.

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