Electrochemical device and electronic device comprising the same

Abstract

The present application relates to an electrochemical device and an electronic device comprising the same. The electrochemical device comprises a positive electrode and an electrolyte, the electrolyte comprising ethylene carbonate (EC), propylene carbonate (PC) and succinonitrile (SN), the positive electrode comprising a positive electrode active material, the positive electrode active material comprising a metal element A, wherein the metal element A is at least one of the following elements: Mg, Zr or Al; wherein the mass content of the SN is a%, the mass content of the EC is b%, the mass content of the PC is c% based on the mass of the electrolyte, wherein k = b / c, 1.25 ≤ k ≤ 6 and a / k ≥ 0.2; and wherein the mass content of the metal element A is x% based on the mass of the positive electrode active material, wherein 0.01 ≤ x ≤ 1. The above electrochemical device exhibits excellent high-temperature cycle performance and high-temperature interval cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, and more particularly, to an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] Due to the advantages of high energy density and relatively simple reaction mechanism, high working voltage, long service life, green environmental protection, etc., rechargeable electrochemical devices are considered to be one of the most attractive energy storage systems. Nowadays, electrochemical devices such as lithium ion batteries have been widely applied in various fields such as wearable devices, smart phones, unmanned aerial vehicles, notebook computers, etc.

[0003] With the continuous expansion of the application field of electrochemical devices, the market has higher and higher requirements for the cycle performance of electrochemical devices such as lithium ion batteries, especially the high-temperature cycle performance and high-temperature interval cycle performance. For example, notebook computers are commonly used tools for people to work, and in the process of use, they are usually in a charging state, and the charging and use process is often accompanied by the occurrence of heat; in the above process, the notebook computer is first charged to a full charge state, then kept in the full charge state for several hours, and finally cut off the charger to be in a discharging state; the above process not only requires the electrochemical device of the notebook computer to have high-temperature cycle performance (i.e. to undergo "charging-discharging" multiple cycles at high temperature), but also puts forward higher requirements for high-temperature interval cycle performance (i.e. to undergo "charging-keeping for several hours in a full charge state-discharging" multiple cycles at high temperature). In view of this, the present application is committed to obtaining an electrochemical device with excellent high-temperature cycle performance and high-temperature interval cycle performance to meet the above needs of people. SUMMARY

[0004] At least to solve the above problems, the present application adjusts the composition of the electrolyte, the composition of the positive active material, and the adaptation between the electrolyte and the positive electrode, so as to improve the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device.

[0005] According to one aspect of the present application, the present application provides an electrochemical device, comprising a positive electrode and an electrolyte, the electrolyte comprising ethylene carbonate (EC), propylene carbonate (PC) and succinonitrile (SN), the positive electrode comprising a positive active material, the positive active material comprising a metal element A, wherein the metal element A comprises at least one of the following elements: Mg, Zr or Al; wherein the mass content of the SN is a%, the mass content of the EC is b%, and the mass content of the PC is c% based on the mass of the electrolyte, wherein k = b / c, 1.25 ≤ k ≤ 6 and a / k ≥ 0.2; and wherein the mass content of the metal element A is x% based on the mass of the positive active material, wherein 0.01 ≤ x ≤ 1.

[0006] According to embodiments of the present application, x / k≤0.4.

[0007] According to embodiments of the present application, 0.001≤x / a≤1.

[0008] According to embodiments of the present application, the positive electrode active material comprises lithium cobaltate.

[0009] According to embodiments of the present application, the positive electrode active material comprises lithium nickel cobalt manganese oxide.

[0010] According to embodiments of the present application, the positive electrode active material comprises lithium cobaltate and lithium nickel cobalt manganese oxide, the mass ratio of the lithium cobaltate and the lithium nickel cobalt manganese oxide is g, 1≤g≤9, based on the mass of the positive electrode active material.

[0011] According to embodiments of the present application, the positive electrode active material comprises lithium cobaltate, the median particle size Dv50 of the lithium cobaltate is m pm, wherein 8≤m≤20.

[0012] According to embodiments of the present application, the median particle size Dv50 of the positive electrode active material is y pm, wherein 2≤y≤25.

[0013] According to embodiments of the present application, 10≤y / x≤900.

[0014] According to embodiments of the present application, 1≤y / a≤36.

[0015] According to embodiments of the present application, the electrolyte further comprises lithium difluorophosphate, wherein the mass content of the LiPO2F2 is d%, 0.01≤d≤0.5, based on the mass of the electrolyte.

[0016] According to embodiments of the present application, 0.05≤d / x≤25.

[0017] According to embodiments of the present application, 0.001≤d / k≤0.4.

[0018] According to another aspect of the present application, the present application also provides an electronic device comprising the electrochemical device according to the above embodiments of the present application. DETAILED DESCRIPTION

[0019] Embodiments of the present application will be described in detail below. Embodiments of the present application should not be interpreted as limiting the present application.

[0020] As used in the present application, the terms “comprise”, “contain” and “include” are used in their open, non-limiting sense.

[0021] Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be taken as a shorthand for stating each separate value, sub- range, and combination of values and sub-ranges within the range. No numerical limitation is intended or should be inferred.

[0022] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "one or more of" can mean any combination of those items. For example, if items A and B are listed, the phrase "at least one of A or B" means A alone, B alone, or A and B together. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, or C" means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together. 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.

[0023] Electrolyte as an important component of electrochemical device, used to transport lithium ions between the positive and negative electrode to achieve lithium ions in the positive and negative electrode material constantly embedded and exfoliation, so as to play the function of charge and discharge. Therefore, electrolyte is essential for electrochemical device to obtain excellent high temperature performance.

[0024] One of the main features of the electrolyte described in the present application is that the electrolyte contains ethylene carbonate (EC), propylene carbonate (PC) and succinonitrile (SN) at the same time, wherein the mass content of the succinonitrile is a%, the mass content of the ethylene carbonate is b%, and the mass content of the propylene carbonate is c%, based on the mass of the electrolyte, wherein k = b / c, 1.25 ≤ k ≤ 6 and a / k ≥ 0.2.

[0025] The electrolyte is proposed based on the finding that adding a certain amount of ethylene carbonate to the electrolyte can improve the high-pressure resistance and high-temperature stability of the electrolyte itself. However, when the content of ethylene carbonate in the electrolyte is too high, it will cause serious gas production, which is not conducive to the high-temperature interval cycle performance. Propylene carbonate has excellent high-temperature stability, and its addition can make up for the defects of ethylene carbonate. Therefore, the addition of ethylene carbonate and propylene carbonate in the electrolyte can improve the high-temperature stability of the electrolyte itself, thereby improving the high-temperature interval cycle performance and high-temperature cycle performance of the electrochemical device. In addition, the addition of nitrile compounds in the electrolyte can effectively stabilize the transition metal (such as metal cobalt in lithium cobaltate) in the positive active material, reduce the dissolution of the transition metal, and stabilize the structure of the positive active material, thereby further improving the cycle stability and high-temperature performance of the electrochemical device. Among them, compared with other nitrile compounds, the effect of adding succinonitrile (SN) in the electrolyte is particularly prominent, because the cyanide group in the succinonitrile structure can coordinate with the metal ions in the positive active material, reduce the side reaction between the positive active material and the electrolyte, and reduce the gas production inside the electrochemical device; and the cyanide group can react with water or hydrogen fluoride in the electrolyte, improve the cycle stability of the electrolyte, and further improve the high-temperature cycle performance of the electrochemical device.

[0026] However, the present application finds that although propylene carbonate has excellent high-temperature stability, it is easy to reduce and decompose on the surface of the graphite negative electrode at the lithium intercalation potential, thereby destroying the graphite structure, affecting the deintercalation of active ions, and further affecting the cycle stability of the electrochemical device; and although succinonitrile can effectively stabilize the transition metal in the positive active material, when the addition amount is large, it will cause the impedance of the electrochemical device to rise and cause large polarization. Based on this, the present application adjusts the mass content and ratio of ethylene carbonate, propylene carbonate and succinonitrile in the electrolyte to meet 1.25≤k≤6 and a / k≥0.2 to promote the synergistic effect of the above three, so as to further improve the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. In some embodiments, k can be, but is not limited to, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 or within the range consisting of any two of the above. In some embodiments, a / k can be, but is not limited to, 0.2, 0.5, 1, 1.5, 2 or within the range consisting of any two of the above.

[0027] The positive electrode, as an important component of the electrochemical device, also has a crucial influence on the performance of the electrochemical device. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material. The positive electrode active material comprises a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive electrode active material layer can be one layer or multiple layers, and each layer in the multiple layers of the positive electrode active material layer can comprise the same or different positive electrode active materials. In addition, the positive electrode active material layer also comprises a binder and / or a conductive agent.

[0028] One main feature of the positive electrode described in the present application is that the positive electrode active material is doped with a metal element A, wherein the metal element A comprises at least one of the following elements: Mg, Zr or Al, and the mass content of the metal element A is x% based on the mass of the positive electrode active material, wherein 0.01≤x≤1.

[0029] The reason why the above-mentioned positive electrode is proposed in the present application is that the present application finds that, compared with other metal elements, doping at least one of Mg, Zr or Al in the positive electrode active material can better stabilize the structure of the positive electrode active material. For example, when the positive electrode active material contains an active metal cobalt element (Co), the element A will occupy the interstitial space of the crystal lattice, and the A-O bond formed after the positive electrode is delithiated is stronger than the Co-O bond, thereby relieving oxygen evolution and preventing the dissolution of Co, so as to achieve the purpose of stabilizing the structure of the positive electrode active material. In addition, by controlling the mass content of the metal element A in the positive electrode active material to be within the range of 0.01% to 1%, the deintercalation of active ions such as lithium ions in the positive electrode active material can also be promoted, the polarization is reduced, and the improvement of the high-temperature cycle performance and the high-temperature interval cycle performance is further promoted. In some embodiments, x can be, but is not limited to, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or within the range composed of any two of the above.

[0030] In addition, the combination of the electrolyte and the positive electrode having the above-mentioned features can further improve the high-temperature cycle performance and the high-temperature interval cycle performance of the electrochemical device, which can be due to the good matching relationship between the above-mentioned electrolyte and the positive electrode, which can promote the performance of each other.

[0031] Further, by adjusting the matching between some components in the electrolyte and the positive electrode active material, the high-temperature cycle performance and the high-temperature interval cycle performance of the electrochemical device can be further improved.

[0032] In some embodiments, further improvement of the high-temperature performance can be achieved by adjusting the relationship between the content x% of the doped element A in the positive electrode active material and the ratio k of ethylene carbonate and propylene carbonate in the electrolyte. This is because propylene carbonate has excellent high-temperature stability, but is prone to decomposition at the negative electrode, which can damage the structure of the negative electrode. Ethylene carbonate can decompose on the surface of the negative electrode to form a stable SEI film, which can weaken the damage to the negative electrode caused by the decomposition of propylene carbonate at the negative electrode interface. The combination of the two can improve the high-pressure resistance and high-temperature stability of the electrolyte itself, and the doped element A can stabilize the structure of the positive electrode active material. By adjusting the relationship between the content of the doped element A and the ratio k of ethylene carbonate and propylene carbonate, the high-pressure resistance and high-temperature stability of the electrolyte can be improved while the positive electrode structure stability is improved, further improving the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. In some embodiments, x / k≤0.4. In some embodiments, x / k≤0.3, x / k≤0.2, or x / k≤0.1.

[0033] In some embodiments, further improvement of the high-temperature performance can be achieved by adjusting the relationship between the content x% of the doped element A in the positive electrode active material and the content a% of butanedinitrile in the electrolyte. This is because the cyano group in the structure of butanedinitrile can form a coordination complex with metal ions in the positive electrode active material, stabilizing the structure of the positive electrode active material. Adjusting the content relationship of the two can better stabilize the structure of the positive electrode active material, while the electrolyte has lower impedance. In some embodiments, 0.001≤x / a≤1. In some embodiments, x / a can be, but is not limited to, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within a range consisting of any two of the above.

[0034] When the positive electrode active material particles are primary particles, the median particle size Dv50 of the positive electrode active material refers to the primary particle size of the positive electrode active material particles. When the primary particles of the positive electrode active material particles agglomerate to form secondary particles, the median particle size Dv50 of the positive electrode active material refers to the secondary particle size of the positive electrode active material particles.

[0035] In some embodiments, the median particle size Dv50 of the positive electrode active material is y pm, where 2≤y≤25. In some embodiments, the median particle size Dv50 of the positive electrode active material can be, but is not limited to, 2 pm, 3 pm, 5 pm, 8 pm, 10 pm, 13 pm, 15 pm, 18 pm, 20 pm, 23 pm, 25 pm, or within a range consisting of any two of the aforementioned values. When the median particle size Dv50 of the positive electrode active material is within the aforementioned range, not only can good contact between the positive electrode active material particles be ensured, but the contact area between the positive electrode active material and the electrolyte can also be ensured to be within an appropriate range, thereby reducing the occurrence of side reactions, avoiding excessive consumption of electrolyte during electrochemical cycling, and also reducing the risk of cracking of the positive electrode active material particles due to cold pressing during electrode preparation.

[0036] In some embodiments, the positive electrode active material comprises one or more of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium iron phosphate, lithium titanate, and lithium-containing manganese-based materials.

[0037] In some embodiments, the chemical formula of the lithium cobaltate can be, but is not limited to, LiCoO2.

[0038] In some embodiments, the chemical formula of the lithium nickel cobalt manganese oxide can be, but is not limited to, LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0039] In some embodiments, the positive electrode active material comprises at least one of lithium cobaltate or lithium nickel cobalt manganese oxide, and when the positive electrode active material comprises both lithium cobaltate and lithium nickel cobalt manganese oxide, the mass ratio of the lithium cobaltate to the lithium nickel cobalt manganese oxide is g, where 1≤g≤9, based on the mass of the positive electrode active material. In some embodiments, g can be, but is not limited to, 1, 2, 3, 4, 5, 6, 7, 8, or 9, or within a range consisting of any two of the aforementioned values.

[0040] In some embodiments, the positive electrode active material comprises lithium cobaltate, and the median particle size Dv50 of the lithium cobaltate is m pm, where 8≤m≤20. By controlling the median particle size of the lithium cobaltate to be within the aforementioned range, not only can the wettability of the electrolyte to the positive electrode active material be improved, but the rate of insertion and extraction of metal ions such as lithium ions in the positive electrode active material can also be improved, thereby further improving the electrochemical performance of the electrochemical device.

[0041] In some embodiments, the positive active material has a median particle size Dv50 (y pm) and the content of metal element A in the positive active material x %, and 10≤y / x≤900 is satisfied. When y / x is within the above range, the structural stability of the positive active material and its thermal stability at high temperature can be improved simultaneously, thereby further improving the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. In some embodiments, 20≤y / x≤800, 20≤y / x≤600, or 50≤y / x≤500.

[0042] In some embodiments, the positive active material has a median particle size Dv50 (y pm) and the content of malononitrile in the electrolyte a %, and 1≤y / a≤36 is satisfied. When y / a is within the above range, the complexation between malononitrile and transition metal in the positive active material can be further promoted, and the dissolution of transition metal can be reduced, thereby improving the structural stability of the positive active material and its thermal stability at high temperature, thereby further improving the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. In some embodiments, 2≤y / a≤30, 5≤y / a≤20, or 5≤y / a≤15.

[0043] In some embodiments, the electrolyte further comprises lithium difluorophosphate (LiPO2F2), and the addition of lithium difluorophosphate can form a structurally stable SEI film on the surface of the negative electrode through decomposition and reduction, thereby further improving the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. This is specifically manifested in that the addition of lithium difluorophosphate can increase the LiF component in the SEI film, thereby enhancing the stability of the SEI film and further reducing the occurrence of side reactions.

[0044] In some embodiments, the content of LiPO2F2 is d % based on the mass of the electrolyte, and 0.01≤d≤0.5 is satisfied. When the content of LiPO2F2 is within the above range, LiPO2F2 can be sufficiently dissolved in the electrolyte, significantly improving the high-temperature performance of the electrochemical device, and also ensuring the formation of an SEI film with moderate impedance and reducing polarization. In some embodiments, d can be, but is not limited to, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, or within a range between any two of the above values.

[0045] In some embodiments, the mass content d% of the LiPO2F2 and the content x% of the metal element A in the positive electrode active material satisfy 0.05≤d / x≤25. When d / x is within the above range, the LiPO2F2 has better solubility in the electrolyte, and a SEI film with lower impedance is formed at the negative electrode, while the metal element in the positive electrode active material can better stabilize the structure of the positive electrode active material, promote the deintercalation of active ions such as lithium ions in the positive electrode active material, and realize the synchronous improvement of the cycle stability of the positive electrode and the negative electrode, thereby further improving the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. In some embodiments, d / x can be, but is not limited to, 0.05, 0.1, 0.5, 1, 3, 5, 7, 9, 12, 15, 20, 25, or within a range between any two of the above values.

[0046] In some embodiments, the mass content d% of the LiPO2F2 and the ratio k of ethylene carbonate and propylene carbonate in the electrolyte satisfy 0.001≤d / k≤0.4. When d / k is within the above range, the electrolyte has lower impedance and better high-temperature resistance, and a SEI film with lower impedance can also be formed at the negative electrode interface, which can further improve the high-temperature cycle performance and high-temperature interval cycle performance of the electrochemical device. In some embodiments, d / k can be, but is not limited to, 0.001, 0.05, 0.1, 0.2, 0.3, 0.4, or within a range between any two of the above values.

[0047] The surface of the positive electrode active material described above can be attached with a substance different from its composition. Examples of the surface-attached substance can include, but are not limited to, at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide; at least one of lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, and other sulfates; at least one of lithium carbonate, calcium carbonate, magnesium carbonate; carbon, and the like. By attaching a substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte at the surface of the positive electrode active material can be inhibited, and the service life of the electrochemical device can be improved.

[0048] In this application, the positive electrode active material having a substance different from its composition attached to the surface of the positive electrode active material is also referred to as a "positive electrode active material".

[0049] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, blocky, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar, and the like. In some embodiments, the positive electrode active material particles include primary particles, secondary particles, or a combination thereof. In some embodiments, the primary particles can be agglomerated to form secondary particles.

[0050] In some embodiments, the binder in the positive electrode active material layer includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, polyvinylidene fluoride, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyfluorovinyl, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon.

[0051] In some embodiments, the conductive agent in the positive electrode active material layer includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymers include polyphenylene derivatives.

[0052] The present application does not have a particular limitation on the type of positive electrode current collector, which can be any material known to be suitable for use as a positive electrode current collector. Examples of the positive electrode current collector can include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and the like; and carbon materials such as carbon cloth, carbon paper, and the like. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum. In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector can include a conductive aid. Examples of the conductive aid can include, but are not limited to, carbon and noble metals such as gold, platinum, silver, and the like.

[0053] The positive electrode can be manufactured by forming a positive electrode active material layer containing a positive electrode active material, a binder, or a conductive agent on a current collector. The manufacturing of the positive electrode using the positive electrode active material can be performed by a conventional method, i.e., dry-mixing the positive electrode active material and the binder, and a conductive agent and a thickening agent, etc. as necessary, to make a sheet, and press-bonding the resulting sheet to the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to make a slurry, and coating the slurry onto the positive electrode current collector and drying, thereby forming a positive electrode active material layer on the current collector, whereby the positive electrode can be obtained. In some embodiments, the liquid medium can include N-methylpyrrolidone, etc., but is not limited thereto.

[0054] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art as a solvent for an electrolyte.

[0055] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of a cyclic carbonate, a chain carbonate, a cyclic carboxylate, a chain carboxylate, a cyclic ether, a chain ether, or an aromatic fluorine-containing solvent.

[0056] In some embodiments, examples of the cyclic carbonate can include, but are not limited to, butylene carbonate.

[0057] In some embodiments, examples of the chain carbonate can include, but are not limited to, one or more of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, or di-n-propyl carbonate.

[0058] In some embodiments, examples of the cyclic carboxylic acid ester can include, but are not limited to, one or more of the following: one or more of γ-butyrolactone and γ-valerolactone. In some embodiments, a portion of the hydrogen atoms of the cyclic carboxylic acid ester can be substituted with fluorine.

[0059] In some embodiments, examples of the chain carboxylic acid ester can include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate, etc. In some embodiments, a portion of the hydrogen atoms of the chain carboxylic acid ester can be substituted with fluorine. In some embodiments, examples of the fluorine-substituted chain carboxylic acid ester can include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate, etc.

[0060] In some embodiments, examples of the cyclic ether can include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl 1,3-dioxolane, 4-methyl 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

[0061] In some embodiments, examples of the chain ether can include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane, etc.

[0062] In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0063] In some embodiments, the electrolyte is not particularly limited and can be arbitrarily used as the electrolyte known per se. Examples of the electrolyte can include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiC104, LiAlF4, LiSbF6, LiWF7, and the like; lithium tungstate such as LiWOF5; lithium carboxylate such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li, and the like; lithium sulfonate such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li, and the like; lithium imide such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane bis-sulfonimide lithium, cyclic 1,3-perfluoropropane bis-sulfonimide lithium, LiN(CF3SO2)(C4F9SO2), and the like; methylated lithium salt such as LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, and the like; lithium (malonato)borate such as lithium bis(malonato)borate, lithium difluoro(malonato)borate, and the like; lithium (malonato)phosphate such as lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate, and the like; and fluorine-containing organic lithium salt such as LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, and the like; lithium oxalate borate such as lithium difluoro oxalate borate, lithium bis(oxalato)borate, and the like; lithium oxalato phosphate such as lithium tetrafluoro oxalato phosphate, lithium difluorobis(oxalato)phosphate, lithium tris(oxalato)phosphate, and the like.

[0064] In some embodiments, the electrolyte includes at least one of LiPF6, LiBF4, LiSbF6, FS03Li, CF3S03Li, LiN(FS02)2, LiN(FS02)(CF3S02), LiN(CF3S02)2. In the present application, the content of the electrolyte is not particularly limited as long as the effect of the present application is not impaired. In some embodiments, the mass content of the electrolyte is 10% to 15% based on the mass of the electrolyte. When the mass content of the electrolyte is within the above range, the viscosity of the electrolyte can be in an appropriate range, and thus good electrical conductivity can be easily ensured.

[0065] In the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer can be one layer or multiple layers, and each layer of the multiple layers of the negative electrode active material layer can contain the same or different negative electrode active material. The negative electrode active material is any material capable of reversibly intercalating and deintercalating active ions such as lithium ions. Examples of the negative electrode active material can include, but are not limited to, lithium metal, structured lithium metal, natural graphite, artificial graphite, meso-carbon microbe (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, Sn02, spinel-structured lithiated Ti02-Li4Ti50 12 or Li-Al alloy.

[0066] In the present application, the kind of the negative electrode current collector is not particularly limited, and a known current collector can be arbitrarily used. Examples of the negative electrode current collector include, but are not limited to, an aluminum foil, a copper foil, a nickel foil, a stainless steel foil, or a nickel-plated steel foil. In some embodiments, the negative electrode current collector is a copper foil.

[0067] The negative electrode active material layer can further include a negative electrode binder, a conductive agent, or a thickening agent. The negative electrode binder can improve the binding between the negative electrode active material particles and the binding between the negative electrode active material and the current collector. The kind of the negative electrode binder is not particularly limited as long as it is a material stable to the electrolyte or a solvent used at the time of electrode production. In some embodiments, the negative electrode binder includes, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, an epoxy resin, or nylon.

[0068] In some embodiments, the electrically conductive agent includes, but is not limited to, at least one of a carbon-based material, a metal-based material, and an electrically conductive polymer. In some embodiments, the carbon-based material includes at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; in some embodiments, the metal-based material includes at least one of metal powder, metal fiber, copper, nickel, aluminum, silver; in some embodiments, the electrically conductive polymer includes polyphenylene derivative. In some embodiments, the thickening agent includes sodium carboxymethyl cellulose.

[0069] The negative electrode can be prepared by a method known in the art. For example, a slurry of a negative active material layer including a negative active material, a binder, or an electrically conductive agent is coated on a negative electrode current collector, and the slurry is coated on both sides of the negative electrode current collector to form a negative active material layer, whereby the negative electrode can be obtained. In some embodiments, the solvent can include water or the like, but is not limited thereto.

[0070] 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 are not particularly limited in the present application, and can be any of the techniques disclosed in the prior art as long as the effects of the present application are not affected.

[0071] For example, the separator can include a base material layer and a surface treatment layer. The base material layer includes a porous sheet or a nonwoven fabric-like substance having excellent liquid retention, etc. Examples of the material of the resin or glass fiber separator can include, but are not limited to, polyolefin, aramid, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned materials of the separator can be used alone or in any combination. The base material layer can also be a material in which the above-mentioned materials are layered, and examples thereof include, but are not limited to, a three-layer separator in which polypropylene, polyethylene, and polypropylene are layered in this order.

[0072] The surface treatment layer is provided on at least one surface of the base material layer, and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. Examples of the material of the inorganic substance can include, but are not limited to, oxides such as alumina, silica, nitrides such as aluminum nitride, silicon nitride, and sulfates such as barium sulfate, calcium sulfate, etc. The form of the inorganic substance can include, but is not limited to, a granular or fibrous form. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0073] The electrochemical device assembly includes an electrode group, a current collecting structure, a case, and a protection element.

[0074] The electrode group can be any one of a stacked structure in which the above-described positive electrode and negative electrode are stacked with the above-described separator film interposed therebetween, and a structure in which the above-described positive electrode and negative electrode are wound with the above-described separator film interposed therebetween.

[0075] The current collecting structure is a structure for reducing the resistance of the wiring portion and the joining portion. When the electrode group is the above-described stacked structure, a structure in which the metal core portions of the respective electrode layers are bundled and welded to the terminal is suitably used. When the electrode group is the above-described wound structure, the internal resistance can be reduced by providing two or more lead structures to the positive electrode and the negative electrode, respectively, and bundling them on the terminal.

[0076] The material of the case is not particularly limited as long as it is a stable material with respect to the electrolytic solution used. The case can use, but is not limited to, a nickel-plated steel plate, stainless steel, aluminum or aluminum alloy, magnesium alloy, or the like, or a laminated film of resin and aluminum foil. In some embodiments, the outer case is a metal or a laminated film of aluminum or an aluminum alloy. The shape of the case is also arbitrary, and can be any one of, for example, a cylindrical shape, a square shape, a laminated type, a button type, and the like.

[0077] The protection element can use a positive temperature coefficient in which the resistance increases when abnormal heat release or excessive current flow occurs, a temperature fuse, a thermistor, a current cutoff valve, or the like. The above-described protection element can select an element that does not work in a condition of normal use of high current, or can be designed in a form in which abnormal heat release or thermal runaway does not occur even if the protection element is not present.

[0078] The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, including, but not limited to, a lithium-ion battery. In some embodiments, the electrochemical device of the present application has a positive electrode of the positive electrode active material capable of occluding and releasing active ions and a negative electrode of the negative electrode active material capable of occluding and releasing active ions in any one of the above-described embodiments, and an electrolyte in any one of the above-described embodiments.

[0079] The present application also provides an electronic device including the electrochemical device according to the present application.

[0080] The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium-ion capacitor, and the like.

[0081] The following uses a lithium-ion battery as an example and specific embodiments to further illustrate this application. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0082] I. Preparation of Lithium-ion Batteries

[0083] 1. Preparation of the negative electrode

[0084] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97.4:1.2:1.4 to form a uniform anode slurry. This slurry is then coated onto copper foil (anode current collector), dried, and cold-pressed to obtain the anode.

[0085] 2. Preparation of the positive electrode

[0086] Lithium cobalt oxide or lithium nickel cobalt manganese oxide doped with Mg, Zr or Al elements, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2 to form a uniform positive electrode slurry. This slurry is then coated onto the positive electrode current collector aluminum foil, dried, and cold-pressed to obtain the positive electrode.

[0087] 3. Preparation of electrolyte

[0088] In an argon-atmospheric glove box with a water content of <10 ppm, a certain mass of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed uniformly. Then, thoroughly dried lithium salt LiPF6 was dissolved in the above non-aqueous solvent to form a basic electrolyte. A certain mass of additives (e.g., nitrile compound additives SN and LiPO2F2) was added to the obtained basic electrolyte, and after uniform mixing, the electrolyte was obtained. The mass content of LiPF6 was 12.5% ​​based on the mass of the electrolyte. The mass contents of EC, PC, SN, and LiPO2F2 are listed in the example table, and the remainder represents the mass content of DEC in the electrolyte.

[0089] 4. Preparation of the separating membrane

[0090] Polyethylene (PE) porous polymer film is used as the separator.

[0091] 5. Preparation of lithium-ion batteries

[0092] The positive electrode, the separator and the negative electrode are stacked in order with the separator between the positive electrode and the negative electrode to play a role of isolation, and then the battery cell is obtained by winding; the battery cell is placed in an outer packaging foil, the electrolyte prepared above is injected into the dried battery cell, and the preparation of the lithium ion battery is completed through vacuum packaging, standing, formation, shaping and other processes.

[0093] The lithium ion batteries of the examples and the comparative examples are prepared according to the above preparation method, and the lithium ion batteries, the positive electrode active material and the electrolyte are tested as follows.

[0094] II. Test method

[0095] 1. High-temperature cycle test

[0096] The battery is placed in a 45℃ constant temperature box, charged to 4.4V at a constant current of 1.5C, charged to 0.05C at a constant voltage of 4.4V, and then discharged to 3.0V at a constant current of 1.0C. This is one charge-discharge cycle process, and the first discharge capacity is recorded as C1. The above process is repeated for 500 times, and the discharge capacity after the 500th cycle is recorded as C500. The cycle capacity retention rate of the lithium ion battery at 45℃ is calculated by the following formula: 500

[0097] Cycle capacity retention rate = (C500 / C1) x 100%. 500

[0098] 2. High-temperature interval cycle test

[0099] The battery is placed in a 45℃ constant temperature box, charged to 4.4V at a constant current of 0.5C, charged to 0.05C at a constant voltage of 4.4V, and then discharged to 3.0V at a constant current of 0.5C. This is one charge-discharge cycle process, and the first discharge capacity and the thickness of the battery in the full charge state in the first cycle are recorded as A1 and T1, respectively. The above process is repeated for 23 times. Subsequently, the battery is charged to 4.35V at a constant current of 0.5C, charged to 0.05C at a constant voltage of 4.35V, and then discharged to 3.0V at a constant current of 0.5C. This is one charge-discharge cycle process, and the above process is repeated for 113 times. The discharge capacity after the last cycle and the thickness of the battery in the full charge state in the last cycle are recorded as A500 and T500, respectively. The interval cycle capacity retention rate and the thickness growth rate of the lithium ion battery at 45℃ are calculated by the following formula: 136 136

[0100] Interval cycle capacity retention rate = (A500 / A1) x 100%; 136

[0101] Thickness growth rate = (T500 / T1) x 100%. 136 ​​​​​ / T1) x 100%.

[0102] 3. Median particle size Dv50 test of positive electrode active material particles

[0103] The particle size of the positive electrode active material particles is measured using a Malvern particle size tester. The positive electrode material is dispersed into a dispersant ethanol, after ultrasonic treatment for 30 minutes, the sample is added into the Malvern particle size tester, and the test is started. The particle size distribution of the positive electrode material in volume basis, from small particle size, to the particle size at which the volume accumulation is 50%, is the Dv50 of the positive electrode material.

[0104] 4. Mg, Zr or Al element content test of positive electrode active material

[0105] After disassembling the lithium ion battery after discharging, two positions (denoted as position 1 and position 2) of the positive electrode active material layer are randomly selected for the following tests:

[0106] 1) The positive electrode active material in the positive electrode active material layer at position 1 is obtained for inductively coupled plasma (ICP) test to obtain the content of Mg, Zr or Al elements in the positive electrode active material;

[0107] 2) The positive electrode active material layer at position 2 is subjected to surface energy spectrum (EDS) test, the test area is magnified by 3000 times, and the EDS test is performed on the whole area to obtain the content of Mg, Zr or Al elements in the positive electrode active material;

[0108] The highest value of the above two test results is taken as the content of Mg, Zr or Al elements in the positive electrode active material.

[0109] 5. Test of content of each component in electrolyte

[0110] After disassembling and centrifuging the lithium ion battery after discharging, the liquid obtained after centrifugation is subjected to gas chromatography-mass spectrometry (GC-MS) and ion chromatography (IC) test to detect each component in the electrolyte and test the content thereof.

[0111] III. Test results

[0112] Table 1 shows the influence of the positive electrode active material and the electrolyte on the high-temperature cycle performance and the high-temperature interval cycle performance of the lithium ion battery. In Table 1, the median particle size Dv50 of the positive electrode active material in the examples is 15 μm; the positive electrode active material in Examples 1-2 to 1-7 is lithium cobalt oxide (LiCoO2) and lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2The positive electrode active material in the other examples and comparative examples 1-1 to 1-10 is lithium cobalt oxide (LiCoO2).

[0113] As can be seen from the data in Table 1, compared with the comparative example, the electrolyte in the examples contains EC, PC and SN, and its content satisfies 1.25≤k≤6 and a / k≥0.2. In addition, the positive electrode active materials in the examples are all doped with Mg, Zr or Al elements, and their content satisfies 0.01≤x≤1. Therefore, the electrochemical device in the examples has a high capacity retention rate in both the 45°C cycling process and the interval cycling process, and also has a low thickness growth rate in the 45°C interval cycling process.

[0114] Furthermore, a comparison of Comparative Examples 1-6 and 1-7 with Example 1-1 shows that adding SN to the electrolyte can achieve better high-temperature performance. Meanwhile, a comparison of Comparative Examples 1-8 and 1-9 with the Example shows that when the contents of EC, PC, and SN in the electrolyte simultaneously satisfy 1.25 ≤ k ≤ 6 and a / k ≥ 0.2, better high-temperature performance can be achieved.

[0115] A comparison of Comparative Examples 1-10 with Example 1 shows that doping the positive electrode active material with Mg yields better high-temperature performance compared to doping with other metal elements (e.g., Zn). Furthermore, as shown in Examples 1-24 and 1-25, doping the positive electrode active material with Al or Zr also results in electrochemical devices with excellent high-temperature performance.

[0116] Furthermore, a comparison of Examples 1-30 to 1-31 with Examples 1-11 shows that when the electrochemical device further satisfies 0.001 ≤ x / a ≤ 1, its high-temperature cycling performance and high-temperature interval cycling performance can be further improved. A comparison of Examples 1-32 with Examples 1-22, 1-26, and 1-27 shows that when the electrochemical device further satisfies x / k ≤ 0.4, its high-temperature cycling performance and high-temperature interval cycling performance can be further improved.

[0117]

[0118]

[0119]

[0120] Tables 2 and 3 show the effect of the median particle size Dv50 of the positive electrode active material on the high-temperature cycle performance and high-temperature interval cycle performance of lithium-ion batteries. The examples in Tables 2 and 3 are all improvements based on Examples 1-10, and the only difference between them and Examples 1-10 is the parameters listed in Tables 2 and 3.

[0121] Table 2

[0122]

[0123] As shown in Table 2 above, when the electrochemical device further satisfies 2≤y≤25 and 10≤y / x≤900, the high-temperature cycle performance and the high-temperature interval cycle performance of the electrochemical device can be further improved.

[0124] Table 3

[0125]

[0126] As shown in Table 3 above, when the electrochemical device further satisfies 1≤y / a≤36, the high-temperature cycle performance and the high-temperature interval cycle performance of the electrochemical device can be further improved.

[0127] Examples 4-1 to 4-7 in Table 4 and Table 5 are improvements made on the basis of Example 1-10, Example 4-8 and Example 4-9 in Table 4 are improvements made on the basis of Example 1-22, and Example 5-1 and Example 5-2 in Table 5 are improvements made on the basis of Example 1-1, and the improvements are specifically adding a certain amount of LiPO2F2 to the electrolyte.

[0128] Table 4

[0129]

[0130] As can be seen by comparing Examples 4-1 to 4-7 with Example 1-10, after further adding LiPO2F2 to the electrolyte, the high-temperature cycle performance and the high-temperature interval cycle performance of the corresponding electrochemical device are both improved. In addition, as can be seen from Table 4, when the content d% of LiPO2F2 satisfies 0.01≤d≤0.5 and 0.05≤d / x≤25, the improvement effect on the electrochemical device is more obvious.

[0131] Table 5

[0132]

[0133] As can be seen from the data in Table 5, when the electrochemical device further satisfies 0.001≤d / k≤0.4, the high-temperature cycle performance and the high-temperature interval cycle performance of the electrochemical device can be further improved.

[0134] References throughout this specification to "an embodiment", "particular embodiments", "one embodiment", "another embodiment", "certain embodiments", "some embodiments", "one example" or "an example" mean that a particular feature, structure, material or characteristic is included in at least one embodiment or example of the present application. Thus, the appearances of the phrases such as "in some embodiments", "in an embodiment", "in one embodiment", "in another embodiment", "in one example", "in a particular example" or "in some examples" in various places throughout this specification are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0135] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device comprising a positive electrode and an electrolyte, the electrolyte comprising vinyl carbonate, propylene carbonate, and butanedinitrile, the positive electrode comprising a positive electrode active material, the positive electrode active material comprising a metal element A, wherein the metal element A comprises at least one of the following elements: Mg, Zr, or Al; wherein a mass content of the butanedinitrile is a%, a mass content of the vinyl carbonate is b%, and a mass content of the propylene carbonate is c% based on a mass of the electrolyte, wherein k = b / c, 1.25 < k < 6, and a / k > 0.31; and wherein a mass content of the metal element A is x% based on a mass of the positive electrode active material, wherein 0.02 < x < 1.

2. The electrochemical device according to claim 1, wherein x / k < 0.

4.

3. The electrochemical device according to claim 1, wherein 0.01 < x / a < 1.

4. The electrochemical device according to any one of claims 1 to 3, the positive electrode active material comprising lithium cobaltate.

5. The electrochemical device according to any one of claims 1 to 3, the positive electrode active material comprising lithium nickel cobalt manganese oxide.

6. The electrochemical device according to any one of claims 1 to 3, the positive electrode active material comprising lithium cobaltate and lithium nickel cobalt manganese oxide, a mass ratio of the lithium cobaltate and the lithium nickel cobalt manganese oxide being g based on a mass of the positive electrode active material, wherein 1 < g < 9.

7. The electrochemical device according to any one of claims 1 to 3, a median particle diameter Dv50 of the positive electrode active material being y pm, wherein 2 < y < 25.

8. The electrochemical device according to claim 7, wherein 10 < y / x < 900.

9. The electrochemical device according to claim 7, wherein 1 < y / a < 36.

10. The electrochemical device according to any one of claims 1 to 3, the electrolyte further comprising lithium difluorophosphate, wherein a mass content of the LiPO2F2 is d% based on a mass of the electrolyte, wherein 0.01 < d < 0.

5.

11. The electrochemical device according to claim 10, wherein 0.05 < d / x < 25.

12. The electrochemical device according to claim 10, wherein 0.006 < d / k < 0.

4.

13. An electronic device comprising the electrochemical device according to any one of claims 1 to 12.

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