Electrolyte and electrochemical device and electronic device using same

Abstract

The invention relates to an electrolyte, and an electrochemical device and an electronic device using the same. Specifically, the electrolyte comprises fluorine-containing cyclic carbonate as shown in a formula I, a first compound and a second compound, the first compound comprises at least one of a compound as shown in a formula II and a compound as shown in a formula III, and the second compound comprises at least one of a compound as shown in a formula IV and a compound as shown in a formula V. The electrolyte can significantly improve the low-temperature discharge performance and the high-rate discharge performance of the electrochemical device using the electrolyte.

Description

Electrolyte and electrochemical device and electronic device using the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 28, 2023, with application number 202311279437.9 and invention name “An electrolyte and an electrochemical device and an electronic device using the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage technology, and in particular to an electrolyte and an electrochemical device and an electronic device using the same. Background Art

[0003] Lithium-ion batteries are widely used in portable electronics, electric vehicles, aerospace, energy storage, and other fields due to their high energy density, excellent cycle performance, safety, environmental friendliness, and lack of memory effect. To meet the demands of society, the search for electrochemical devices with higher energy and power densities has become a pressing issue, driving the development of cathode active materials towards higher voltages. As voltage increases, electrolyte reactions at the cathode interface intensify, causing rapid performance degradation, particularly at low-temperature and high-rate discharge.

[0004] Therefore, it is necessary to provide an electrolyte that can improve the low-temperature discharge performance and high-rate discharge performance of electrochemical devices.

[0005] Summary of the Invention

[0006] The present invention provides an electrolyte solution to at least partially solve at least one problem existing in the related art. The present invention also provides an electrochemical device and an electronic device using the electrolyte solution.

[0007] In one embodiment, the present application provides an electrolyte, wherein the electrolyte comprises:

[0008] (1) Fluorine-containing cyclic carbonate represented by formula I:

[0009] where R 41 、R 42 、R 43 and R 44 Each is independently F, or substituted or unsubstituted C1-C3 alkyl; when substituted, the substituents are each independently halogen; wherein R 41 、R 42 、R 43 and R 44 At least one of contains F;

[0010] (2) a first compound, the first compound comprising at least one of a compound of formula II and a compound of formula III:

[0011] where R 11 、R 12 、R 21 and R 22 Each independently is C1-C 10 alkyl; and

[0012] (3) a second compound, the second compound comprising at least one of a compound of Formula IV and a compound of Formula V:

[0013] in:

[0014] R 13 and R 14 are each independently substituted or unsubstituted C1-C 10 Alkyl, where R 13 and R 14 At least one of is replaced;

[0015] R 23 and R 24 are each independently substituted or unsubstituted C1-C 10 Alkyl, where R 23 and R 24 At least one of is replaced;

[0016] When substituted, each substituent is independently halogen,

[0017] Based on the mass of the electrolyte, the mass percentage of the first compound is A%, the mass percentage of the fluorinated cyclic carbonate is B%, and the mass percentage of the second compound is C%, wherein A, B and C satisfy: 30≤(A+B+C)≤90 and 20≤C≤61.

[0018] In some embodiments, 50≤(A+B+C)≤87.5.

[0019] In some embodiments, 4≤B≤15.

[0020] In some embodiments, 2.8≤(A+C) / B≤12.

[0021] In some embodiments, the electrolyte further comprises a fluoroether compound represented by Formula VI:

[0022] where R 31 and R 32 Each is independently selected from substituted or unsubstituted C1-C8 alkyl or -R'-OR";

[0023] R' is selected from substituted or unsubstituted C1-C8 alkylene;

[0024] R" is selected from substituted or unsubstituted C1-C8 alkyl;

[0025] When substituted, each substituent is independently halogen;

[0026] The substituent is halogen; R 31 and R 32 At least one of contains F; and

[0027] Based on the mass of the electrolyte, the mass percentage of the fluoroether compound is D%, and D satisfies: 5≤D≤30.

[0028] In some embodiments, A, B, C, and D satisfy: 50≤(A+B+C+D)≤87.5.

[0029] In some embodiments, A, B, C, and D satisfy: 60≤(A+B+C+D)≤80.

[0030] In some embodiments, the compound of formula II comprises at least one of the following: methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate; and / or

[0031] The compound of formula III comprises at least one of the following compounds: dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0032] In some embodiments, the fluorine-containing cyclic carbonate includes at least one of the following compounds:

[0033] In some embodiments, the compound of Formula IV comprises at least one of the following compounds:

[0034] and / or

[0035] The compound of formula V comprises at least one of the following compounds:

[0036] In some embodiments, the fluoroether compound comprises at least one of the following compounds:

[0037] In some embodiments, the electrolyte further includes a first lithium salt, the first lithium salt including at least one of lithium hexafluorophosphate (LiPF6) or lithium bis(fluorosulfonyl)imide (LiFSI); based on the mass of the electrolyte, the mass percentage of the first lithium salt is E%, where 2.5≤(A+B+C) / E≤8.5.

[0038] In some embodiments, the electrolyte further includes a second lithium salt, the second lithium salt including at least one of the following: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), or lithium difluorophosphate (LiPO2F2); wherein the mass percentage of the second lithium salt is 0.1% to 5% based on the mass of the electrolyte.

[0039] In some embodiments, the electrolyte further includes a third compound, the third compound including at least one of the following compounds: vinylene carbonate, 1,3-propane sultone, succinonitrile, adiponitrile, or 1,3,6-hexanetrinitrile.

[0040] In some embodiments, the mass percentage of the third compound is 0.5% to 6% based on the mass of the electrolyte.

[0041] In another embodiment, the present application provides an electrochemical device comprising: a positive electrode, a negative electrode, a separator, and an electrolyte according to an embodiment of the present application.

[0042] In another embodiment, the present application provides an electronic device comprising the electrochemical device according to the embodiment of the present application.

[0043] The electrochemical device provided according to the embodiment of the present application has improved low-temperature discharge performance and high-rate discharge performance. The reason may be that the first compound, the second compound and the fluorinated cyclic carbonate shown in Formula I have a lower binding energy with lithium ions, and lithium ions are more easily separated from the solvent at low temperatures and high rates, thereby improving the discharge performance of the electrochemical device. When the mass percentage A% of the first compound, the mass percentage B% of the fluorinated cyclic carbonate shown in Formula I and the mass percentage C% of the second compound meet 30≤(A+B+C)≤90 and 20≤C≤61, the low-temperature discharge performance and high-rate discharge performance of the electrochemical device can be significantly improved. When the electrolyte further contains a fluoroether compound, a lithium salt additive and / or a third compound, the low-temperature discharge performance and high-rate discharge performance of the electrochemical device can be further improved.

[0044] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The following briefly describes the drawings necessary to describe the embodiments of the present application or the prior art to facilitate the description of the embodiments of the present application. Obviously, the drawings described below only represent some of the embodiments of the present application. Those skilled in the art can, without requiring creative effort, derive drawings for other embodiments based on the structures illustrated in these drawings.

[0046] FIG1 shows a schematic structural diagram of a lithium-ion battery of the present application. DETAILED DESCRIPTION

[0047] 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 present application.

[0048] Amounts, ratios, and other numerical values ​​are presented herein in a range format. It should be understood that such range format is used for convenience and brevity and should be interpreted flexibly to include not only the values ​​explicitly specified as range limits, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0049] In the detailed description and claims, a list of items linked by the terms "one of," "one of," "a kind of," or other similar terms may 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 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.

[0050] In the detailed description and claims, a list of items connected by the terms "at least one of," "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" 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" 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 contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0051] As used herein, the term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having 1 to 20 carbon atoms. "Alkyl" is also intended to be a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When specifying an alkyl group with a specific carbon number, it is intended to encompass all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples 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.

[0052] As used herein, the term "halogen" may be F, Cl, Br, or I.

[0053] 1. Electrolyte

[0054] The present application provides an electrolyte, wherein the electrolyte comprises:

[0055] (1) Fluorine-containing cyclic carbonate represented by formula I:

[0056] where R 41 、R 42 、R 43 and R 44 Each is independently F, or substituted or unsubstituted C1-C3 alkyl; when substituted, the substituents are each independently halogen; wherein R 41 、R 42 、R 43 and R 44 At least one of contains F;

[0057] (2) a first compound, the first compound comprising at least one of a compound of formula II and a compound of formula III:

[0058] where R 11 、R 12 、R 21 and R 22 Each independently is C1-C 10 alkyl; and

[0059] (3) a second compound, the second compound comprising at least one of a compound of Formula IV and a compound of Formula V:

[0060] in:

[0061] R 13 and R 14are each independently a substituted or unsubstituted C1-C10 alkyl group, wherein at least one of R13 and R14 is substituted;

[0062] R 23 and R 24 are each independently substituted or unsubstituted C1-C 10 Alkyl, where R 23 and R 24 At least one of is replaced;

[0063] When substituted, each substituent is independently halogen,

[0064] Based on the mass of the electrolyte, the mass percentage of the first compound is A%, the mass percentage of the fluorinated cyclic carbonate is B%, and the mass percentage of the second compound is C%, wherein A, B and C satisfy: 30≤(A+B+C)≤90 and 20≤C≤61.

[0065] In some embodiments, C is 20, 25, 30, 32, 35, 40, 45, 50, 52, 55, 60, 61, or a range consisting of any two of these values.

[0066] The inventors have found that using a combination of a fluorinated cyclic carbonate, a first compound, and a second compound as shown in Formula I in an electrolyte and controlling the total content of the three can significantly improve the low-temperature discharge performance and high-rate discharge performance of an electrochemical device. Without being bound by any theory, this may be because the three compounds have a low binding energy with lithium ions, making it easier for lithium ions to separate from the solvent at low temperatures and high rates, thereby improving the discharge performance of the electrochemical device. When the sum of the mass percentage A% of the first compound, the mass percentage B% of the fluorinated cyclic carbonate shown in Formula I, and the mass percentage C% of the second compound (A% + B% + C%) is less than 30%, the three compounds cannot play a leading role in the solvation structure of lithium ions, the energy barrier for the escape of lithium ions is still very high, and there is no significant improvement in performance; when A% + B% + C% is greater than 90%, the corresponding lithium salt concentration is low, and sufficient lithium ions cannot be provided during low-temperature and high-rate discharge, polarization increases, and the performance of the electrochemical device deteriorates. When the second compound is replaced by a halogen, its ability to dissociate lithium salts is reduced. When its content is too high, it cannot fully dissociate lithium salts, increasing polarization and deteriorating the performance of the electrochemical device. If the content of the second compound is too low, the improvement is not significant. When the content of the first compound, the second compound, and the fluorinated cyclic carbonate in the electrolyte meets the above requirements, the low-temperature discharge performance and high-rate discharge performance of the electrochemical device can be significantly improved.

[0067] In some embodiments, R 41 、R 42 、R 43 and R44 Each is independently F or methyl, ethyl or propyl optionally substituted with F.

[0068] In some embodiments, R 11 、R 12 、R 21 and R 22 Each is independently a C1-C9 alkyl group, a C1-C8 alkyl group, a C1-C7 alkyl group, a C1-C6 alkyl group, a C1-C5 alkyl group, a C1-C4 alkyl group, a C1-C3 alkyl group or a C1-C2 alkyl group.

[0069] In some embodiments, R 13 、R 14 、R 23 and R 24 are each independently substituted or unsubstituted C1-C 10 Alkyl, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C7 alkyl, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1-C3 alkyl or substituted or unsubstituted C1-C2 alkyl, wherein R 13 and R 14 At least one of is replaced.

[0070] In some embodiments, 50≤(A+B+C)≤87.5. In some embodiments, the value of A+B+C is 30, 40, 45, 48, 50, 55, 60, 65, 68, 70, 72, 72.5, 75, 78, 80, 83, 85, 87.5, 90, or a range consisting of any two of these values.

[0071] In some embodiments, A is 5 to 50. In some embodiments, A is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range consisting of any two of these values.

[0072] In some embodiments, B is 3 to 20. In some embodiments, 4 ≤ B ≤ 15. In some embodiments, B is 3, 4, 5, 8, 10, 12.5, 15, 20, or a range consisting of any two of these values.

[0073] In some embodiments, A, B, and C satisfy: 2.8≤(A+C) / B≤12.

[0074] In some embodiments, the value of (A+C) / B is 2.8, 3, 5, 5.3, 6, 7, 7.5, 7.8, 8.8, 9, 9.4, 9.9, 10, 10.3, 12, or a range consisting of any two of these values.

[0075] When the contents of the first compound, the second compound and the fluorine-containing cyclic carbonate in the electrolyte meet the above requirements, the low-temperature discharge performance and high-rate discharge performance of the electrochemical device can be further improved.

[0076] In some embodiments, the electrolyte further comprises a fluoroether compound represented by Formula VI:

[0077] where R 31 and R 32 Each is independently selected from substituted or unsubstituted C1-C8 alkyl or -R'-OR";

[0078] R' is selected from substituted or unsubstituted C1-C8 alkylene;

[0079] R" is selected from substituted or unsubstituted C1-C8 alkyl;

[0080] When substituted, each substituent is independently halogen;

[0081] The substituent is halogen; R 31 and R 32 At least one of them contains F.

[0082] In some embodiments, R 31 、R 32 , R' and R" are each independently selected from unsubstituted or halogen-substituted C1-C8 alkyl, C1-C7 alkyl, C1-C6 alkyl, C1-C5 alkyl, C1-C4 alkyl, C1-C3 alkyl or C1-C2 alkyl.

[0083] In some embodiments, R' is selected from unsubstituted or halogen-substituted C1-C8 alkylene, C1-C7 alkylene, C1-C6 alkylene, C1-C5 alkylene, C1-C4 alkylene, C1-C3 alkylene, or C1-C2 alkylene.

[0084] In some embodiments, the weight percentage of the fluoroether compound based on the weight of the electrolyte is D%, where D satisfies 5≤D≤50. In some embodiments, 5≤D≤30. In some embodiments, D is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range consisting of any two of these values.

[0085] Fluoroethers can further lower the freezing point of the electrolyte, allowing it to maintain good fluidity at low temperatures and improving low-temperature discharge performance. However, their ability to dissociate lithium salts is weak. Too low a fluoroether content results in insignificant improvement, while too high a content prevents sufficient dissociation of lithium salts, increasing polarization and failing to improve performance. When the fluoroether content meets these requirements, it can significantly improve both the low-temperature and high-rate discharge performance of lithium-ion batteries.

[0086] In some embodiments, A, B, C, and D satisfy the following: 50 ≤ (A + B + C + D) ≤ 87.5. In some embodiments, A, B, C, and D satisfy the following: 60 ≤ (A + B + C + D) ≤ 80. In some embodiments, the value of A + B + C + D is 50, 55, 60, 65, 70, 75, 80, 85, 87.5, or a range consisting of any two of these values. When A + B + C + D is within the above ranges, the low-temperature discharge performance and high-rate discharge performance of the electrochemical device can be further improved.

[0087] In some embodiments, the compound of Formula II comprises at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

[0088] In some embodiments, the compound of Formula III comprises at least one of the following: dimethyl carbonate, diethyl carbonate (DEC), or ethyl methyl carbonate (EMC).

[0089] In some embodiments, the fluorine-containing cyclic carbonate includes at least one of the following compounds:

[0090] In some embodiments, the compound of Formula IV comprises at least one of the following compounds:

[0091] In some embodiments, the compound of Formula V comprises at least one of the following compounds:

[0092] In some embodiments, the fluoroether compound comprises at least one of the following compounds:

[0093] In some embodiments, the electrolyte further comprises a first lithium salt, wherein the first lithium salt comprises at least one of lithium hexafluorophosphate (LiPF 6 ) or lithium bis(fluorosulfonyl)imide (LiFSI).

[0094] In some embodiments, based on the mass of the electrolyte, the mass percentage of the first lithium salt is E%, where 2.5≤(A+B+C) / E≤8.5. In some embodiments, the value of (A+B+C) / E is 2.5, 3, 4, 5, 6, 7, 8, 8.5 or a range consisting of any two of these values. When the value of (A+B+C) / E is too low, the content of the first compound, the second compound and the fluorine-containing cyclic carbonate is insufficient, and the rate performance is not significantly improved. When the value of (A+B+C) / E is too high, the lithium salt concentration is insufficient, the polarization may be large, and the rate performance cannot be further improved. When the value of (A+B+C) / E meets the above requirements, the low-temperature discharge performance and high-rate discharge performance of the lithium-ion battery can be significantly improved.

[0095] In some embodiments, E is 10 to 25. In some embodiments, E is 10, 12, 12.5, 15, 20, 22, 23, 25, or a range consisting of any two of these values.

[0096] In some embodiments, the electrolyte further comprises a second lithium salt, the second lithium salt comprising at least one of the following: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), or lithium difluorophosphate (LiPO2F2). In some embodiments, the weight percentage of the second lithium salt is 0.1% to 5% based on the weight of the electrolyte. In some embodiments, the weight percentage of the second lithium salt is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values.

[0097] The second lithium salt forms a low-impedance and stable interfacial layer, further reducing interfacial impedance and improving the low-temperature and rate performance of the electrochemical device. However, if the second lithium salt content is too high, the reaction continues to consume lithium ions, resulting in a thicker interfacial layer and increased impedance, which can deteriorate the rate performance of the electrochemical device. If the second lithium salt content is too low, the improvement is minimal.

[0098] In some embodiments, the electrolyte further includes a third compound including at least one of vinylene carbonate (VC), 1,3-propane sultone (PS), succinonitrile (SN), adiponitrile (ADN), and 1,3,6-hexanetrionitrile (HTCN).

[0099] In some embodiments, the weight percentage of the third compound is 0.5%-6% based on the weight of the electrolyte. In some embodiments, the weight percentage of the third compound is 0.5%, 1%, 2%, 2.5%, 3%, 4%, 5%, 6%, or a range consisting of any two of these values.

[0100] The third compound can preferentially form a stable interfacial layer, reducing the reaction between the first compound, the fluorinated cyclic carbonate, and the second compound at the interface, thereby improving the rate performance of the electrochemical device. Excessive levels of the third compound increase interfacial impedance, thereby deteriorating the rate performance of the electrochemical device. When the third compound content is too low, the rate performance improvement is minimal.

[0101] In some embodiments, the electrolyte further includes a fourth compound, the fourth compound including at least one of ethylene carbonate (EC) or propylene carbonate (PC). The mass percentage of the fourth compound based on the mass of the electrolyte is less than or equal to 70%. In some embodiments, the mass percentage of the fourth compound is 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or a range consisting of any two of these values.

[0102] 2. Negative electrode

[0103] The material, composition and manufacturing method of the negative electrode used in the electrochemical device of the present application may include any technology disclosed in the prior art. In some embodiments, the negative electrode is the negative electrode described in US patent application US9812739B, which is incorporated into the present application by reference in its entirety.

[0104] In some embodiments, the negative electrode includes a current collector and a negative electrode active material layer located on the current collector. 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, platelet-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0105] In some embodiments, the negative electrode active material layer includes a negative electrode active material. 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 (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy or any combination thereof.

[0106] When the negative electrode includes a silicon-carbon compound, based on the total weight of the negative electrode active material, silicon:carbon=1:10-10:1, and the median particle size Dv50 of the silicon-carbon compound is 0.1μm-100μm. When the negative electrode includes an alloy material, the negative electrode active material layer can be formed using a method such as evaporation, sputtering, and plating. When the negative electrode includes lithium metal, the negative electrode active material layer is formed, for example, using a conductive skeleton having a spherical twisted shape and metal particles dispersed in the conductive skeleton. In some embodiments, the spherical twisted conductive skeleton may have a porosity of 5%-85%. In some embodiments, a protective layer may also be provided on the lithium metal negative electrode active material layer.

[0107] 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.

[0108] In some embodiments, the conductive material includes, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, or 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, and silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0109] In some embodiments, the current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and any combination thereof.

[0110] The negative electrode can be prepared by methods 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 then coating the active material composition on a current collector. In some embodiments, the solvent may include water, etc., but is not limited thereto.

[0111] 3. Positive electrode

[0112] The materials 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.

[0113] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector. 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.

[0114] In some embodiments, the positive electrode active material is selected from lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese (NCM) ternary material, lithium ferrous phosphate (LiFePO4), lithium manganese oxide (LiMn2O4), sodium nickel oxide (NaNiO2), sodium metal oxide, such as sodium manganese oxide (NaMnO2), sodium iron oxide (NaFeO2), sodium cobalt oxide (NaCoO2), polyanion NaMx[(XO)y]z, Prussian blue (Fe4[Fe(CN)6]3) or any combination thereof.

[0115] 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 the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compound used for the coating may be amorphous or crystalline.

[0116] In some embodiments, the coating element contained in the coating may include Mg, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, 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.

[0117] The positive electrode active material layer also includes a binder and, optionally, a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0118] 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.

[0119] 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, and silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0120] In some embodiments, the current collector may be aluminum, but is not limited thereto.

[0121] The positive electrode can be prepared by methods 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 then coating the active material composition on a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone.

[0122] In some embodiments, the positive electrode is made by forming a positive electrode material using a positive electrode active material layer including lithium transition metal compound powder and a binder on a current collector.

[0123] In some embodiments, the positive electrode active material layer can generally be made by dry mixing the positive electrode active material and the binder (conductive material and thickener used as needed) to form a sheet, pressing the obtained sheet to the positive electrode current collector, or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry on the positive electrode current collector and drying. In some embodiments, the material of the positive electrode active material layer includes any material known in the art.

[0124] 4. Diaphragm

[0125] In some embodiments, the electrochemical device of the present application includes a separator between the positive electrode and the negative electrode to prevent short circuits. The material and shape of the separator used in the electrochemical device of the present application are not particularly limited and may be any known prior art technology. In some embodiments, the separator comprises a polymer or inorganic material formed from a material that is stable to the electrolyte of the present application.

[0126] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or 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, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0127] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The thickness ratio of the substrate layer to the surface treatment layer is 1:1 to 20:1, the thickness of the substrate layer is 4μm to 14μm, and the thickness of the surface treatment layer is 1μm to 5μm.

[0128] The inorganic layer includes inorganic particles and a binder, wherein 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, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0129] 5. Electrochemical device

[0130] The present application provides an electrochemical device, which includes the positive electrode, the negative electrode, the separator and the electrolyte according to the present application.

[0131] In some embodiments, the electrochemical device comprises a bare cell and an outer packaging bag, wherein the bare cell comprises a first tab and a second tab. Figure 1 shows a schematic structural diagram of a lithium-ion battery of the present application, which comprises an outer packaging bag 1, a bare cell 2, a first tab 3 and a second tab 4. In some embodiments, the electrochemical device of the present application includes, but is not limited to, all types of primary batteries, secondary batteries or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: 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 is a sodium ion battery.

[0132] 6. Electronic devices

[0133] The present application provides an electronic device, which includes the electrochemical device according to the present application.

[0134] In some embodiments, the electronic device includes, but is not limited to: a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0135] The preparation of lithium-ion batteries is described below using lithium-ion batteries as an example and in combination with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0136] Example

[0137] The following describes the performance evaluation of the lithium-ion battery according to the embodiments and comparative examples of the present application.

[0138] 1. Preparation of lithium-ion batteries

[0139] Positive electrode preparation: The positive electrode active material, LiCoO2, conductive carbon black (Super P), and binder, polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97:1.4:1.6. The mixture was added to N-methylpyrrolidone (NMP) and thoroughly stirred to form a uniform positive electrode slurry with a solids content of 72 wt%. The slurry was evenly coated onto the positive electrode current collector aluminum foil. The positive electrode was then dried, cold-pressed, and slit.

[0140] Negative electrode preparation: Artificial graphite (the negative electrode active material), conductive carbon black (Super P), sodium carboxymethyl cellulose (a thickener), and styrene-butadiene rubber (SBR) (a binder) were mixed in a weight ratio of 96.4:1.5:0.5:1.6. Deionized water was added and stirred thoroughly to obtain a negative electrode slurry with a solids content of 54 wt%. This slurry was then coated onto a copper foil negative electrode current collector. The negative electrode was then dried, cold-pressed, and slit.

[0141] Preparation of the diaphragm: A 9μm thick polyethylene (PE) porous membrane is selected as the diaphragm substrate, and a 2μm thick heat-resistant layer is coated on one surface of the diaphragm substrate (wherein, in the heat-resistant layer slurry, based on the total mass of alumina and binder PVDF, the mass percentage of alumina is 95%, and the mass percentage of PVDF is 5%), and then polyvinylidene fluoride (PVDF) slurry is coated on both sides, and the final diaphragm is obtained after drying.

[0142] Preparation of the electrolyte: Under a dry argon environment, the components (the fourth compound, the fluorinated cyclic carbonate represented by Formula I, the first compound, the second compound, and the fluoroether compound represented by Formula VI) are mixed in corresponding proportions and mixed evenly to obtain a mixed solvent. The fully dried lithium salt is dissolved in the mixed solvent, and then other corresponding additives are added (mixed evenly to obtain an electrolyte. The content of each component in the electrolyte is shown in the following tables. The content of each component is the mass percentage calculated based on the mass of the electrolyte, and the sum of the contents of each component is 100%.

[0143] Preparation of a lithium-ion battery: The positive electrode, separator, and negative electrode are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes are then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film package. After dehydration at 80°C, the electrolyte is injected and the battery is packaged. The battery undergoes several steps, including resting, formation, degassing, trimming, shaping, and capacity testing, to produce a lithium-ion battery.

[0144] 2. Lithium-ion battery performance test method

[0145] (1) Test method for low-temperature discharge capacity retention

[0146] Place the battery in a 25°C constant temperature box, charge it to 4.53V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.53V, and then discharge it to 3.4V at a constant current of 0.2C. Record the discharge capacity at this time, which is recorded as the initial discharge capacity D1; then charge it to 4.53V at a constant current of 0.5C, and charge it to 0.05C at a constant voltage at 4.53V; then take out the battery, transfer it to a -20°C constant temperature box, keep it for 1 hour, and then discharge it to 3.4V at a constant current of 0.2C. Record the discharge capacity at this time, which is recorded as the low-temperature discharge capacity D2. Calculate the low-temperature discharge capacity retention rate of lithium-ion batteries at -20°C and 3.4V using the following formula:

[0147] Low-temperature discharge capacity retention rate=low-temperature discharge capacity D2 / initial discharge capacity D1×100%.

[0148] (2) Test method for high-rate discharge capacity retention

[0149] Place the battery in a 25°C constant temperature box, charge it to 4.53V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.53V, and then discharge it to 3.0V at a constant current of 0.2C. Record the discharge capacity at this time, which is recorded as the initial discharge capacity W1; then charge it to 4.53V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.53V, and then discharge it to 3.0V at a constant current of 4C. Record the discharge capacity at this time, which is recorded as the initial discharge capacity W2. Calculate the discharge capacity retention rate of the lithium-ion battery at a 2C rate using the following formula:

[0150] High-rate discharge capacity retention rate=high-rate discharge capacity W2 / initial discharge capacity W1×100%.

[0151] 3. Lithium-ion battery performance test results

[0152] The following tables show the relevant parameters of the electrolyte and lithium-ion battery of each embodiment and comparative example, wherein the mass percentage content A% of the first compound is the sum of the content A1% of the compound of formula II and the content A2% of the compound of formula III, the mass percentage content of the fluorinated cyclic carbonate shown in formula I is B%, and the mass percentage content C% of the second compound is the sum of the content C1% of the compound of formula IV and the content C2% of the compound of formula V, based on the mass of the electrolyte.

[0153] It can be seen from Table 1-1 and Table 1-2 that the electrolyte in Examples 1-1 to 1-22 contains a first compound, a second compound and a fluorinated cyclic carbonate represented by Formula I, and the mass percentage A% of the first compound, the mass percentage B% of the fluorinated cyclic carbonate represented by Formula I and the mass percentage C% of the second compound satisfy 30≤(A+B+C)≤90 and 20≤C≤61. Therefore, the lithium-ion batteries in Examples 1-1 to 1-22 have significantly improved low-temperature discharge performance and high-rate discharge performance.

[0154] Compared with Examples 1-1 to 1-22, the low-temperature discharge performance and high-rate discharge performance of the electrolyte in Comparative Example 1 are significantly deteriorated due to the absence of the second compound.

[0155] Compared with Examples 1-1 to 1-22, the electrolyte in Comparative Example 2 has significantly deteriorated low-temperature discharge performance and high-rate discharge performance due to the absence of the fluorine-containing cyclic carbonate represented by Formula I.

[0156] Compared with Examples 1-1 to 1-22, the low-temperature discharge performance and high-rate discharge performance of the electrolyte in Comparative Example 3 are significantly deteriorated because the electrolyte does not contain the first compound.

[0157] Compared with Examples 1-1 to 1-22, the A+B+C value of the electrolyte in Comparative Example 4 is less than 30, and its low-temperature discharge performance and high-rate discharge performance are significantly deteriorated.

[0158] Compared with Examples 1-1 to 1-22, the A+B+C value of the electrolyte in Comparative Example 5 is greater than 90, and its low-temperature discharge performance and high-rate discharge performance are significantly deteriorated.

[0159] The above embodiments and comparative examples demonstrate that when the electrolyte comprises a first compound, a second compound, and a fluorinated cyclic carbonate represented by Formula I, and the sum of the contents of the three is in the range of 30%-90% and the mass percentage of the second compound is C% in the range of 20-60, the low-temperature discharge performance and high-rate discharge performance of the lithium-ion battery are significantly improved.

[0160] The lithium-ion batteries of Examples 2-1 to 2-5 in Tables 2-1 and 2-2 have the same composition conditions as those of Example 1-4, except for the parameters shown in Tables 2-1 and 2-2. The lithium-ion batteries of Examples 2-6 to 2-9 in Tables 2-1 and 2-2 have the same composition conditions as those of Example 1-9, except for the parameters shown in Tables 2-1 and 2-2.

[0161] Table 2-1 “ / ” indicates that the substance and parameter do not exist.

[0162] Table 2-2 “ / ” indicates that the substance and parameter do not exist.

[0163] From the comparison of Examples 2-1 to 2-5 with Example 1-4 and the comparison of Examples 2-6 to 2-9 with Example 1-9, it can be seen that when the electrolyte contains the first compound, the second compound and the fluorinated cyclic carbonate represented by Formula I, and the mass percentage A% of the first compound, the mass percentage B% of the fluorinated cyclic carbonate represented by Formula I and the mass percentage C% of the second compound satisfy 30≤(A+B+C)≤90 and 20≤C≤61, a fluoroether compound with a mass percentage of 5%-30% is added to the electrolyte, and the low temperature discharge performance and high rate discharge performance of the lithium ion battery are further improved.

[0164] In Table 3, the lithium-ion batteries in Examples 3-1 to 3-9 are the same as those in Examples 1-4 except for the parameters shown in Table 3.

[0165] From the comparison of Examples 3-1 and 3-9 with Examples 1-4, it can be seen that when the electrolyte contains the first compound, the second compound and the fluorinated cyclic carbonate represented by Formula I, and the mass percentage A% of the first compound, the mass percentage B% of the fluorinated cyclic carbonate represented by Formula I and the mass percentage C% of the second compound satisfy 30≤(A+B+C)≤90 and 20≤C≤61, when the mass percentage E% of the first lithium salt added to the electrolyte satisfies 2.5≤(A+B+C) / E≤8.5, the low-temperature discharge performance and high-rate discharge performance of the lithium-ion battery are further improved.

[0166] In addition, from the comparison of Examples 3-2 and 3-3 with Examples 1-4 and 3-1, it can be seen that the addition of LiFSI to the electrolyte containing a specific content of the first compound, the second compound, the fluorinated cyclic carbonate represented by Formula I, and LiPF6 can significantly improve the low-temperature discharge performance and high-rate discharge performance of the lithium-ion battery.

[0167] Moreover, from the comparison of Examples 3-5 to 3-9 with Examples 1-4, 3-1, and 3-2, it can be seen that the addition of a second lithium salt (at least one of LiTFSI, LiBF4, LiBOB, LiPO2F2, or LiPO2F2) to the electrolyte containing a specific content of the first compound, the second compound, the fluorinated cyclic carbonate represented by Formula I, and the first lithium salt can significantly improve the low-temperature discharge performance and high-rate discharge performance of the lithium-ion battery.

[0168] In Table 4, the lithium-ion batteries in Examples 4-1 to 4-6 have the same composition conditions as in Examples 1-4 except for the parameters shown in Table 4.

[0169] From the comparison of Examples 4-1 to 4-6 with Examples 1-4, it can be seen that when the electrolyte contains a first compound, a second compound and a fluorinated cyclic carbonate represented by Formula I, and the mass percentage A% of the first compound, the mass percentage B% of the fluorinated cyclic carbonate represented by Formula I and the mass percentage C% of the second compound satisfy 30≤(A+B+C)≤90 and 20≤C≤61, a third compound having a mass percentage of 0.5%-6% is added to the electrolyte, and the low-temperature discharge performance and high-rate discharge performance of the lithium-ion battery are further improved.

[0170] References throughout this specification to "some embodiments," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "a portion of an example" mean that at least one embodiment or example in this application includes the particular features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "an example," are not necessarily references to the same embodiment or example in this application. In addition, the particular features, structures, materials, or characteristics described herein may be combined in any suitable manner in one or more embodiments or examples.

[0171] Although illustrative embodiments have been shown 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 electrolyte, wherein the electrolyte comprises: (1) Fluorine-containing cyclic carbonate represented by formula I: Where R 41 , R 42 , R 43 and R 44 Each is independently F, or substituted or unsubstituted C1-C3 alkyl; when substituted, the substituents are each independently halogen; wherein R 41 , R 42 , R 43 and R 44 At least one of includes F; (2) a first compound, wherein the first compound comprises at least one of a compound of formula II and a compound of formula III: Where R 11 , R 12 , R 21 and R 22 Each independently is C1-C 10 Alkyl; and (3) a second compound, the second compound comprising at least one of a compound of formula IV and a compound of formula V: in: R 13 and R 14 are each independently substituted or unsubstituted C1-C 10 Alkyl, where R 13 and R 14 At least one of is replaced; R 23 and R 24 are each independently substituted or unsubstituted C1-C 10 Alkyl, where R 23 and R 24 At least one of is replaced; When substituted, each substituent is independently halogen, Based on the mass of the electrolyte, the mass percentage of the first compound is A%, the mass percentage of the fluorine-containing cyclic carbonate is B%, and the mass percentage of the second compound is C%, wherein A, B and C satisfy: 30≤(A+B+C)≤90 and 20≤C≤61.

2. The electrolyte according to claim 1, wherein 50≤(A+B+C)≤87.

5.

3. The electrolyte according to claim 1, wherein 4≤B≤15. The electrolyte according to claim 1 , wherein 2.8≤(A+C) / B≤12.

5. The electrolyte according to any one of claims 1 to 4, wherein the electrolyte further comprises a fluoroether compound shown in formula VI: Where R 31 and R 32 Each is independently selected from substituted or unsubstituted C1-C8 alkyl or -R'-OR"; R' is selected from substituted or unsubstituted C1-C8 alkylene; R" is selected from substituted or unsubstituted C1-C8 alkyl; When substituted, each substituent is independently halogen; R 31 and R 32 At least one of includes F; and Based on the mass of the electrolyte, the mass percentage of the fluoroether compound is D%, and D satisfies: 5≤D≤30.

6. The electrolyte according to claim 5, wherein A, B, C and D satisfy: 50≤(A+B+C+D)≤87.

5.

7. The electrolyte according to claim 5, wherein A, B, C and D satisfy: 60≤(A+B+C+D)≤80.

8. The electrolyte according to any one of claims 1 to 7, wherein The compound of formula II comprises at least one of the following compounds: methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate; and / or The compound of formula III comprises at least one of the following compounds: dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

9. The electrolyte according to any one of claims 1 to 8, wherein the fluorine-containing cyclic carbonate comprises at least one of the following compounds:

10. The electrolyte according to any one of claims 1 to 9, wherein the compound of formula IV comprises at least one of the following compounds: and / or The compound of formula V comprises at least one of the following compounds:

11. The electrolyte according to claim 5, wherein the fluoroether compound comprises at least one of the following compounds:

12. The electrolyte according to any one of claims 1 to 11, wherein the electrolyte further comprises a first lithium salt, the first lithium salt comprising at least one of lithium hexafluorophosphate LiPF6 or lithium bis(fluorosulfonyl)imide LiFSI; Based on the mass of the electrolyte, the mass percentage of the first lithium salt is E%, wherein 2.5≤(A+B+C) / E≤8.

5.

13. The electrolyte according to claim 12, wherein the electrolyte further comprises a second lithium salt, the second lithium salt comprising at least one of the following: lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium tetrafluoroborate LiBF4, lithium difluorooxalatoborate LiDFOB, lithium dioxalatoborate LiBOB or lithium difluorophosphate LiPO2F2; Wherein, based on the mass of the electrolyte, the mass percentage of the second lithium salt is 0.1% to 5%.

14. The electrolyte according to any one of claims 1 to 13, wherein the electrolyte further comprises a third compound, the third compound comprising at least one of the following compounds: vinylene carbonate, 1,3-propane sultone, succinonitrile, adiponitrile or 1,3,6-hexanetrinitrile; Wherein, based on the mass of the electrolyte, the mass percentage of the third compound is 0.5% to 6%.

15. An electrochemical device comprising: A positive electrode, a negative electrode, a separator and an electrolyte according to any one of claims 1 to 14.

16. An electronic device comprising the electrochemical device according to claim 15.

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