Electrolyte and electrochemical device and electronic equipment

Abstract

The application relates to an electrolyte, an electrochemical device and an electronic device. The electrolyte comprises a first additive and a second additive, the first additive comprises a nitrogen-containing heterocyclic anhydride compound, the second additive comprises a borate compound, and 105 <= (Ya+Yb) / (M*N) <= 2000 between the first additive and the second additive and a positive and negative electrode material layer, wherein the mass percentage of the first additive in the electrolyte is Ya%, the mass percentage of the second additive in the electrolyte is Yb%, the mass of the positive electrode material layer per unit area on the positive electrode sheet is M g / cm 2 , and the mass of the negative electrode material layer per unit area on the negative electrode sheet is Ng / cm 2 . The scheme provided by the application can realize the expansion of the amount of the first additive by the cooperation of the second additive and the first additive and the matching of the content of the additive and the surface density of the positive electrode material layer and the negative electrode material layer, and further improve the high-temperature cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte, an electrochemical device and an electronic device. BACKGROUND

[0002] Lithium ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, electric vehicles and other fields due to their high specific energy, no memory effect, long cycle life and other advantages. The rapid development of electronic information technology and consumer products has put forward higher requirements for high voltage and high energy density of lithium ion batteries. In lithium ion batteries, high-voltage cathode materials are widely used in portable electronic devices such as mobile phones and notebook computers, as well as electric vehicles and large-scale energy storage devices due to their high energy density, environmental friendliness, long cycle life and other advantages.

[0003] However, as the limiting voltage of the cathode material continues to increase (especially 4.3V+), gas will be produced due to oxidation of the electrolyte on the positive electrode side at high voltage, or transition metals will be dissolved on the negative electrode side to destroy the SEI film, resulting in serious deterioration of the high-temperature performance of the battery and inability to guarantee long cycle life.

[0004] In related technologies, in order to improve the high-temperature performance of lithium ion batteries at high energy density, different types of high-temperature additives such as sulfonate, acid anhydride, carbonate and the like are usually introduced into the electrolyte, but too much addition of these additives will result in too large film-forming impedance, which will deteriorate the high-temperature cycle performance of the battery, thereby limiting the application of high-temperature additives.

[0005] Therefore, how to expand the application of high-temperature additives and further improve the high-temperature cycle performance of the battery is a problem to be solved. SUMMARY

[0006] To solve or partially solve the problems in the related art, the present application provides an electrolyte, an electrochemical device and an electronic device, which can expand the amount of the first additive by using the second additive and the first additive in combination and adapting the content of the additive to the surface density of the cathode material layer and the anode material layer, thereby further improving the high-temperature cycle performance of the battery.

[0007] The first aspect of the present application provides an electrolyte, comprising a first additive and a second additive, the first additive comprising a nitrogen-containing heterocyclic acid anhydride compound, and the second additive comprising a borate compound, the first additive and the second additive satisfying the following relationship with the positive and negative electrode material layers:

[0008] 105≤(Ya+Yb) / (M*N)≤2000

[0009] The first additive accounts for Ya% of the electrolyte, the second additive accounts for Yb% of the electrolyte, the mass of the positive electrode material layer per unit area on the positive electrode sheet is M g / cm 2 , and the mass of the negative electrode material layer per unit area on the negative electrode sheet is N g / cm 2 .

[0010] As an optional embodiment, the following relationship is satisfied between the first additive, the second additive, and the positive and negative electrode material layers:

[0011] 200≤(Ya+Yb) / (M*N)≤1000.

[0012] As an optional embodiment, the nitrogen-containing heterocyclic anhydride compound has the following structure:

[0013]

[0014] In formula 1, X1 is one of C and N atoms, X2 is an N atom, R1 and R2 are each independently selected from one of a benzene ring, a cyano group, a halogen atom, a hydrogen atom, a C1-C10 alkyl group, a C1-C10 unsaturated alkyl group, a C1-C10 halogenated alkyl group, and a C1-C10 halogenated unsaturated alkyl group; preferably, R1 and R2 are each independently selected from one of a benzene ring, a cyano group, a halogen atom, a hydrogen atom, a C1-C3 alkyl group, a C1-C3 unsaturated alkyl group, a C1-C3 fluorinated alkyl group, and a C1-C10 fluorinated unsaturated alkyl group.

[0015] As an optional embodiment, the first additive comprises at least one nitrogen-containing heterocyclic anhydride compound as follows:

[0016]

[0017]

[0018] As an optional embodiment, the borate compound has the following structure:

[0019]

[0020] In formula 2, R3, R4, and R5 are each independently selected from one of a C1-C10 alkyl group, a C1-C10 unsaturated alkyl group, a C1-C10 perhalogenated or partially halogenated alkyl group, and a C1-C10 perhalogenated or partially halogenated unsaturated alkyl group; preferably, R3, R4, and R5 are each independently selected from one of a C1-C5 perfluorinated or partially fluorinated alkyl group, and a C1-C5 perfluorinated or partially fluorinated unsaturated alkyl group.

[0021] As an optional embodiment, the second additive comprises at least one borate compound as follows:

[0022]

[0023]

[0024]

[0025] As an optional embodiment, 0.01≤Ya≤10; and / or, 0.01≤Yb≤5; and / or, 0.035≤M≤0.15; and / or, 0.025≤N≤0.12.

[0026] As an optional embodiment, 1≤Ya≤8; and / or, 0.5≤Yb≤3.

[0027] The second aspect of the present application provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte as described above.

[0028] As an optional embodiment, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active paste layer located on at least one side of the positive electrode current collector, and the positive electrode active paste layer comprises a positive electrode active material.

[0029] Preferably, the positive electrode active material is selected from one or more of lithium cobalt oxide LiCoO2, lithium nickel manganese cobalt ternary material, lithium iron phosphate LiFePO4, and lithium manganate LiMn2O4.

[0030] Further preferably, the positive electrode active material is selected from lithium nickel manganese cobalt ternary material.

[0031] The third aspect of the present application provides an electronic device, comprising the electrochemical device as described above.

[0032] The technical solution provided by the present application can include the following beneficial effects:

[0033] The inventors have found that the amount of the first additive and the second additive is related to the area density of the positive material layer and the negative material layer in the positive electrode and the negative electrode. The greater the area density of the positive material layer and the negative material layer in the positive electrode and the negative electrode, the greater the amount of the first additive and the second additive required. However, if the amount of the first additive and the second additive is too small and does not match the area density of the positive material layer and the negative material layer in the positive electrode and the negative electrode, the first additive and the second additive cannot effectively protect the positive electrode and the negative electrode. Conversely, if the amount of the first additive and the second additive is too large, the impedance of the system will increase, and the cycle performance will deteriorate. Therefore, the amount of the first additive and the second additive needs to be balanced with the area density of the positive material layer and the negative material layer, so that the amount of the first additive and the second additive matches the area density of the positive material layer and the negative material layer, to effectively protect the positive electrode and the negative electrode and improve the high-temperature cycle performance of the battery.

[0034] The inventors have found that when the amount of the first additive and the second additive and the area density of the positive material layer and the negative material layer satisfy 105≤(Ya+Yb) / (M*N)≤2000, the amount of the first additive and the second additive can be balanced with the area density of the positive material layer and the negative material layer, so that the amount of the first additive and the second additive matches the area density of the positive material layer and the negative material layer, to effectively protect the positive electrode and the negative electrode and improve the high-temperature cycle performance of the battery.

[0035] It should be understood that the general description above and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0036] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout the figures, and in which:

[0037] Figure 1 is an EIS test result graph of the battery according to an embodiment of the present application. DETAILED DESCRIPTION

[0038] Embodiments of the present application will be described in more detail by making reference to the drawings in which embodiments of the present application are shown. It is to be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0039] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or," as used herein, refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0040] It should be understood that although the terms "first," "second," "third," etc. can be used in this application to describe various information, the information should not be limited to these terms. These terms are only used to distinguish one type of information from another type of information. For example, the first information can also be referred to as the second information without departing from the scope of the application, and similarly, the second information can also be referred to as the first information. Therefore, the features defined with "first," "second" can explicitly or implicitly include one or more of the features. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0041] In the related art, in order to improve the high-temperature performance of lithium ion batteries at high energy density, different types of high-temperature additives such as sulfonate, acid anhydride, carbonate, etc. are usually introduced into the electrolyte, but too much addition of these additives will cause too large a film impedance, which will deteriorate the high-temperature cycle performance of the battery, thereby limiting the application of high-temperature additives.

[0042] To solve the above problems, the embodiments of the present application provide an electrolyte, which can realize the expansion of the amount of the first additive by the cooperation of the second additive and the first additive, and the content of the additive is adapted to the surface density of the positive electrode material layer and the negative electrode material layer, thereby further improving the effect of the high-temperature cycle performance of the battery.

[0043] The embodiments of the present application provide an electrolyte, which comprises a first additive and a second additive, the first additive comprises a nitrogen-containing heterocyclic acid anhydride compound, and the second additive comprises a borate compound, and the first additive and the second additive satisfy the following relationship with the positive and negative electrode material layers:

[0044] 105≤(Ya+Yb) / (M*N)≤2000

[0045] Wherein, the mass percentage of the first additive in the electrolyte is Ya%, the mass percentage of the second additive in the electrolyte is Yb%, the mass of the positive electrode material layer per unit area on the positive electrode sheet is M g / cm 2 , and the mass of the negative electrode material layer per unit area on the negative electrode sheet is N g / cm 2 .

[0046] In the embodiments of the present application, the mass per unit area of the positive electrode material layer on the positive electrode sheet refers to the areal density of the positive electrode material layer as M g / cm 2 , and the mass per unit area of the negative electrode material layer on the negative electrode sheet refers to the areal density of the negative electrode material layer as N g / cm 2 .

[0047] In the embodiments of the present application, the first additive includes a nitrogen-containing heterocyclic anhydride compound, which has an anhydride group and a nitrogen-containing heterocyclic structure. The anhydride group is prone to hydrolysis reaction with water because the carbonyl group in the anhydride group has strong electrophilicity and is easily attacked by the nucleophilic water. The lone pair of electrons on the oxygen atom of the water attacks the carbonyl carbon of the anhydride to form a tetrahedral intermediate, and then bond breaking and recombination occur to generate carboxylic acid and acid derivatives, thereby achieving the purpose of water removal. The nitrogen-containing heterocyclic structure is a Lewis base, and the N atom contained therein is an electron-deficient group. After ring opening, the N atom can combine with trace HF in the electrolyte, thereby reducing the content of HF in the system and preventing excessive HF from damaging the electrode material.

[0048] Meanwhile, the first additive can also participate in the film formation of the positive and negative electrodes, stabilize the positive and negative electrode interface, effectively reduce the damage to the positive electrode CEI and the negative electrode SEI, and improve the high-temperature performance of the battery. This is because the lone pair of electrons of the N atom in the nitrogen-containing heterocyclic structure in the first additive produces electrostatic adsorption with the negative charge on the electrode surface, laying a foundation for the subsequent film formation process. Secondly, in the process of the first formation, the carbon-nitrogen double bond of the nitrogen-containing heterocyclic structure is prone to reduction reaction on the negative electrode surface to form an SEI film, and the positive electrode surface can also polymerize and oxidize to participate in the generation of a CEI film. In addition, the anhydride group in the first additive will be reduced to form an SEI film at the negative electrode when the negative electrode is at a low potential, and will be oxidized to form a CEI film at the positive electrode. However, too much first additive will result in too large a film formation impedance, which will deteriorate the high-temperature cycle performance of the battery.

[0049] The second additive includes a borate compound, which is beneficial to form an SEI protective layer containing a B-O group compound on the surface of the negative electrode, and the SEI layer containing the B-O group compound can effectively alleviate the influence of Ni on the oxidation of the electrolyte to produce gas in the lithium nickel-manganese-cobalt ternary material. In addition, the borate compound can also form a uniform and thin CEI layer on the positive electrode side, and the CEI protective layer containing the B-O group compound can effectively reduce the dissolution of transition metal ions in other positive active materials such as lithium cobaltate LiCoO2, lithium ferrous phosphate LiFePO4, and lithium manganate LiMn2O4. The use of the second additive and the first additive can improve the stability of the battery during the cycle process, and can also prevent the first additive from generating excessive impedance, thereby further widening the dosage range of the first additive and further improving the high-temperature cycle performance of the battery.

[0050] The inventors of the present application have found that the dosage of the first additive and the second additive is related to the surface density of the positive electrode material layer and the negative electrode material layer in the positive electrode and the negative electrode. The greater the surface density of the positive electrode material layer and the negative electrode material layer in the positive electrode and the negative electrode, the more the first additive and the second additive are needed. However, if the dosage of the first additive and the second additive is too small, it is not suitable for the surface density of the positive electrode material layer and the negative electrode material layer in the positive electrode and the negative electrode, and thus cannot effectively protect the positive electrode material and the negative electrode material. On the contrary, if the dosage of the first additive and the second additive is too large, it will increase the impedance in the system and deteriorate the cycle performance. Therefore, it is necessary to balance the dosage of the first additive and the second additive and the surface density of the positive electrode material layer and the negative electrode material layer, so that the dosage of the first additive and the second additive is suitable for the surface density of the positive electrode material layer and the negative electrode material layer, so as to effectively protect the positive electrode and the negative electrode and improve the high-temperature cycle performance of the battery.

[0051] It is found that when the dosage of the first additive and the second additive and the surface density of the positive electrode material layer and the negative electrode material layer satisfy 105≤(Ya+Yb) / (M*N)≤2000, the dosage of the first additive and the second additive can be balanced with the surface density of the positive electrode material layer and the negative electrode material layer, so that the dosage of the first additive and the second additive is suitable for the surface density of the positive electrode material layer and the negative electrode material layer, so as to effectively protect the positive electrode and the negative electrode and improve the high-temperature cycle performance of the battery.

[0052] As an optional embodiment, the first additive and the second additive satisfy the following relationship with the positive electrode material layer and the negative electrode material layer:

[0053] 200≤(Ya+Yb) / (M*N)≤1000.

[0054] Further research finds that when the amount of the first additive and the second additive and the surface density of the positive electrode material layer and the negative electrode material layer satisfy 200≤(Ya+Yb) / (M*N)≤1000, the amount of the first additive and the second additive and the surface density of the positive electrode material layer and the negative electrode material layer can be more effectively balanced, so that the amount of the first additive and the second additive and the surface density of the positive electrode material layer and the negative electrode material layer are more suitable, so as to more effectively protect the positive and negative electrodes, and further improve the high-temperature cycle performance of the battery.

[0055] As an optional embodiment, the structure of the nitrogen-containing heterocyclic anhydride compound is as follows:

[0056]

[0057]

[0058] In formula 1, X1 is one of C and N atoms, X2 is N atom, and R1 and R2 are each independently selected from one of a benzene ring, a cyano group, a halogen atom, a hydrogen atom, a C1-C10 alkyl group, a C1-C10 unsaturated alkyl group, a C1-C10 halogenated alkyl group, and a C1-C10 halogenated unsaturated alkyl group.

[0059] Preferably, X1 is one of C and N atoms, X2 is N atom, and R1 and R2 are each independently selected from one of a benzene ring, a cyano group, a halogen atom, a hydrogen atom, a C1-C3 alkyl group, a C1-C3 unsaturated alkyl group, a C1-C3 fluorinated alkyl group, and a C1-C10 fluorinated unsaturated alkyl group.

[0060] As a preferred embodiment, the first additive comprises at least one nitrogen-containing heterocyclic anhydride compound as follows:

[0061]

[0062]

[0063] In the embodiments of the present application, the fluorinated alkyl substituent group contained in compound 1-2 can form an SEI film containing LiF, improve the stability of the SEI film and reduce the impedance of the film formation; the benzene ring substituent group contained in compound 1-3 can improve the oxidation resistance of the electrolyte and improve the overcharge performance of the battery; the cyano substituent group contained in compound 1-5 can remove acid and water, further stabilize the positive electrode material and improve the stability of the positive electrode side; the alkyl substituent group contained in compound 1-4, compound 1-7 and compound 1-8 can improve the solubility of the additive, reduce the viscosity of the additive and improve the ion mobility.

[0064] As an optional embodiment, the structure of the borate compound is as follows:

[0065]

[0066] In formula 2, R3, R4, R5 are each independently selected from one of C1-C10 alkyl, C1-C10 unsaturated alkyl, C1-C10 perhalogenated or partially halogenated alkyl, C1-C10 perhalogenated or partially halogenated unsaturated alkyl.

[0067] Preferably, R3, R4, R5 are each independently selected from one of C1-C5 perfluorinated or partially fluorinated alkyl, C1-C5 perfluorinated or partially fluorinated unsaturated alkyl.

[0068] The second additive of the embodiments of the present application includes a borate compound containing a fluorine atom, which is beneficial to form a SEI protective layer containing a B-F-based compound and a LiF compound on the surface of the negative electrode, and the SEI layer containing the two compounds can further effectively inhibit decomposition of the electrolyte. In addition, the borate compound can also form a uniform and thin CEI layer on the positive electrode side, forming a CEI protective layer containing a B-F-based compound, which can further effectively reduce the dissolution of transition metal ions.

[0069] As a preferred embodiment, the second additive contains at least one borate compound as follows:

[0070]

[0071]

[0072]

[0073] The borate compound selected by the second additive of the embodiments of the present application contains a perfluorinated alkyl group or a partially fluorinated alkyl group, which is beneficial to form a SEI protective layer containing a B-F-based compound and a LiF compound on the surface of the negative electrode, and the SEI layer containing the two compounds can further effectively inhibit decomposition of the electrolyte. In addition, the borate compound can also form a uniform and thin CEI layer on the positive electrode side, forming a CEI protective layer containing a B-F-based compound, which can further effectively reduce the dissolution of transition metal ions.

[0074] As an optional embodiment, 0.01≤Ya≤10.

[0075] In the embodiments of the present application, Ya can be 0.01, 0.3, 0.5, 1, 2, 5, 8, 10 or any value within the above range, which is not limited in the present application.

[0076] Further, 1≤Ya≤8.

[0077] In the embodiments of the present application, Ya can be 1, 2, 5, 8 or any value within the above range, which is not limited in the present application.

[0078] As an optional embodiment, 0.01≤Yb≤5.

[0079] In the embodiments of the present application, Yb can be 0.01, 0.3, 0.5, 1, 2, 3, 5 or any value within the above range, and the present application does not limit the comparison.

[0080] Further, 0.5≤Yb≤3.

[0081] In the embodiments of the present application, Yb can be 0.5, 1, 2, 3 or any value within the above range, and the present application does not limit the comparison.

[0082] As an optional embodiment, 0.035≤M≤0.15.

[0083] In the embodiments of the present application, M can be 0.035, 0.11, 0.15 or any value within the above range, and the present application does not limit the comparison.

[0084] As an optional embodiment, 0.025≤N≤0.12.

[0085] In the embodiments of the present application, N can be 0.025, 0.07, 0.11, 0.12 or any value within the above range, and the present application does not limit the comparison.

[0086] Ya and Yb below the above range cannot effectively protect the positive and negative electrodes of the battery, and Ya and Yb higher than the above range will deteriorate the battery performance. The range of M and N is limited according to business requirements or experience value, and lower than the above range will reduce the energy density of the battery cell, and higher than the above range will increase the energy density of the battery cell, but the dynamics performance of the battery cell will be relatively poor.

[0087] Corresponding to the foregoing application function implementation method embodiments, the present application also provides an electrochemical device, an electronic device and corresponding embodiments.

[0088] The embodiments of the present application provide an electrochemical device, which comprises a positive electrode sheet, a negative electrode sheet, a separator, and the foregoing electrolyte.

[0089] The electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, and the additive comprises a first additive and a second additive.

[0090] Preferably, the additive further comprises a fluorocarbon acid ester.

[0091] In the embodiments of the present application, the lithium salt is selected from at least one of an organic lithium salt or an inorganic lithium salt.

[0092] Preferably, the lithium salt is selected from at least one of a compound containing a fluorine element and a lithium element.

[0093] Preferably, the lithium salt is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluorosulfonate, lithium difluoro(trifluoromethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, lithium bisfluorimide sulfonate.

[0094] Preferably, the concentration of the lithium salt is 0.5M-1.5M. If the concentration of the lithium salt is too low, the conductivity of the electrolyte is low, which affects the rate and cycle performance of the entire battery system; if the concentration of the lithium salt is too high, the viscosity of the electrolyte is too large, which also affects the rate of the entire battery system.

[0095] Further preferably, the concentration of the lithium salt is 0.8M-1.3M.

[0096] In the embodiments of the present application, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0097] In the embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active paste layer on the positive electrode current collector, and the positive electrode active paste layer includes a positive electrode active material; the negative electrode includes a negative electrode current collector and a negative electrode active paste layer on the negative electrode current collector, and the negative electrode active paste layer includes a negative electrode active material.

[0098] The negative electrode current collector in the embodiments of the present application is not particularly limited as long as it can achieve the purpose of the present application, and for example, can be a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, etc.

[0099] In the embodiments of the present application, the type of the positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes aluminum, stainless steel, nickel plating, titanium, tantalum, and other metal materials, as well as carbon cloth, carbon paper, and other carbon materials. Preferably, the positive electrode current collector is a metal material.

[0100] Preferably, the positive electrode active material is selected from one or more of lithium cobalt oxide LiCoO2, lithium nickel manganese cobalt ternary material, lithium iron phosphate LiFePO4, and lithium manganate LiMn2O4.

[0101] Further preferably, the positive electrode active material is selected from lithium nickel manganese cobalt ternary material.

[0102] When the positive active material is selected as lithium nickel manganese cobalt ternary material, compared with lithium cobaltate LiCoO2, lithium iron phosphate LiFePO4, and lithium manganate LiMn2O4, the improvement of high-temperature cycle performance of the battery is more effective. This is because for the nickel cobalt lithium manganate ternary material, the higher the content of Ni, the stronger the oxidation of the electrolyte. The synergistic effect of the first additive and the second additive in the embodiment of the present application can effectively inhibit the oxidation of the electrolyte by Ni in the ternary material, so the first additive and the second additive have better adaptability with the nickel cobalt lithium manganate ternary material, and the performance improvement effect of the battery is more obvious.

[0103] Preferably, the negative active material is selected from graphite and / or silicon, such as natural graphite, artificial graphite, mesophase carbon microbeads (MCMB for short), 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 can be used as negative active material.

[0104] In one embodiment, the positive active material layer further comprises a conductive agent, a binder, and a solvent.

[0105] In one embodiment, the conductive agent comprises at least one of natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, and other carbon materials.

[0106] In one embodiment, the binder comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0107] In the embodiment of the present application, the material and shape of the separator are not particularly limited, as long as they do not significantly impair the effects of the present application.

[0108] In one embodiment, the separator comprises a substance in a porous sheet or non-woven fabric form with excellent liquid retention. The material of the resin or glass fiber separator includes, but is not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, and the like.

[0109] In some embodiments, the electrochemical device can comprise an outer package that can be used to package the above-mentioned electrode assembly and electrolyte.

[0110] In some embodiments, the outer package of the electrochemical device can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the electrochemical device can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0111] The shape of the electrochemical device is not particularly limited in the present application, which can be cylindrical, square or any other shape.

[0112] The present application also provides an electronic device comprising the aforementioned electrochemical device.

[0113] For example, the above-mentioned power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0114] In order to further understand the present application, the present application is described below in conjunction with examples, which are only used to illustrate the present application and do not limit the scope of the present application.

[0115] I. Preparation of the battery

[0116] (1) Preparation of the electrolyte

[0117] EC / PC / EMC=2 / 1 / 7 by mass ratio were mixed as an organic solvent. After 3% of the additive FEC was uniformly mixed in the organic solvent, LiPF6 was added to obtain a mixed solution with a LiPF6 concentration of 1.1 mol / L, and then the first additive and the second additive were added to the mixed solution according to the formulation in Table 1 to prepare the electrolyte of each example and the comparative example. Among them, FEC is fluoroethylene carbonate.

[0118] (2) Preparation of the positive electrode sheet:

[0119] The positive electrode active material, the conductive agent CNT, and the binder polyvinylidene fluoride were mixed in a weight ratio of 97:1.5:1.5 in an N-methylpyrrolidone solvent to form a uniform positive electrode slurry. The slurry was coated on the positive electrode current collector Al foil, dried, cold-pressed to obtain the positive electrode sheet. Among them, the positive electrode active material was set according to Table 1.

[0120] (3) Preparation of the negative electrode sheet:

[0121] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 95:2:2:1 in a proper amount of deionized water solvent to form a uniform negative electrode slurry. The slurry was coated on the negative electrode current collector Cu foil, dried, cold-pressed to obtain the negative electrode sheet.

[0122] (4) Preparation of the lithium ion battery:

[0123] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order with the separator in the middle of the positive and negative electrodes to play a separating role, and then the bare battery cell is wound. The bare battery cell is placed in an outer packaging bag, and the electrolyte in Table 1 is injected into the dried battery, and after vacuum packaging, standing, formation, shaping and other processes, the preparation of the lithium ion battery is completed.

[0124] Table 1 formula table

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] II. Performance test

[0131] (1) High temperature cycle test of the battery

[0132] Test method: Place the battery in an environment of 45±2 degrees, and cycle according to the standard charge-discharge cycle with a cycle rate of 1C and a charge voltage of 3.0-4.3V. Calculate the capacity retention rate of the battery after cycling. The calculation formula is as follows:

[0133] The cycle capacity retention rate of the nth week (%) = (the cycle discharge capacity of the nth week) / (the first cycle discharge capacity) * 100%.

[0134] (2) High temperature storage test of the battery:

[0135] Test method: After the battery is divided and contained, it is charged to 4.3V at 0.5C current at room temperature. The full battery is placed in an environment of 85 degrees for 12 hours, and the thickness expansion rate is measured. After recovery to room temperature, discharge to 3.0V at 0.5C current, and record the discharge capacity.

[0136] The battery test conditions are shown in Table 2.

[0137] Table 2 test results

[0138]

[0139]

[0140]

[0141] With the data in Table 1 and Table 2, it can be known by comparing Example 1 to Example 8 that as the content of the first additive increases, the high-temperature cycle and storage performance of the battery improves, further combining Example 9 to Example 12, and Example 23 to Example 28, it can be known that continuing to add the second additive can further improve the high-temperature cycle and storage performance of the battery, indicating that the second additive and the first additive have a synergistic effect; further combining Comparative Example 4 and 5, it can be known that further increasing the content of the first additive or the second additive will reduce the high-temperature cycle and storage performance of the battery, because the content of the first additive or the second additive is too large, which will deteriorate the performance of the battery, and when 0.01≤Ya≤10, 0.01≤Yb≤5, the high-temperature performance of the battery can be effectively improved; further, when 1≤Ya≤8, 0.5≤Yb≤3, the high-temperature performance of the battery can be further effectively improved.

[0142] By comparing Example 10, Example 40 and Example 44, and Comparative Example 6 and 7, it can be known that when 0.01≤Ya≤10, 0.01≤Yb≤50, and 0.035≤M≤0.15, the high-temperature performance of the battery can be improved while ensuring the energy density of the battery.

[0143] By comparing Example 10, Example 40 and Example 44, and Comparative Example 6 and 7, it can be known that when 0.01≤Ya≤10, 0.01≤Yb≤50, and 0.025≤N≤0.12, the high-temperature performance of the battery can be improved while ensuring the energy density of the battery.

[0144] By comparing Example 9 to Example 12, Example 20 to Example 48, it can be known that when the first additive and the second additive satisfy 105≤(Ya+Yb) / (M*N)≤1200 between the positive and negative electrode material layers, the amount of the first additive and the second additive can be adapted to the area density of the positive and negative electrode material layers, so as to effectively protect the positive and negative electrodes and improve the high-temperature cycle performance of the battery.

[0145] Further comparing Example 9 to Example 12, Example 20 to Example 39, it can be known that when the first additive and the second additive satisfy 200≤(Ya+Yb) / (M*N)≤1000 between the positive and negative electrode material layers, the amount of the first additive and the second additive can be more adapted to the area density of the positive and negative electrode material layers, so as to more effectively protect the positive and negative electrodes and further improve the high-temperature cycle performance of the battery.

[0146] It can be seen by comparing Example 10, Example 49 to Example 51 that when the positive active material is selected as a lithium nickel manganese cobalt ternary material, the improvement in the high-temperature cycle performance of the battery is more effective compared to lithium cobaltate LiCoO2, lithium ferrophosphate LiFePO4, and lithium manganate LiMn2O4. This is because for a lithium nickel cobalt manganate ternary material, the higher the content of Ni, the stronger the oxidizing property to the electrolyte. The synergistic effect of the first additive and the second additive in the present application can effectively inhibit the influence of Ni in the ternary material on the oxidation of the electrolyte to produce gas, and therefore the first additive and the second additive have better adaptability to the lithium nickel cobalt manganate ternary material, and the performance improvement effect on the battery is more obvious.

[0147] III. EIS test of the battery

[0148] The lithium ion batteries of Comparative Example 1, Comparative Example 3, Comparative Example 2, and Example 10 were selected, and the cells were adjusted to 50% SOC, respectively. The parameters of the electrochemical workstation were set as a perturbation voltage of 5 mV, and the test frequency range was 0.04 Hz-100000 Hz. Three sets of tests were performed for each comparative example and example.

[0149] The test results are shown in Figure 1 The Base-1#, Base-2#, and Base-3# in the figure represent the three sets of test results of Comparative Example 1, Base+2% A-1#, Base+2% A-2#, and Base+2% A-3# represent the three sets of test results of Comparative Example 3, Base+1% B-1#, Base+1% B-2#, and Base+1% B-3# represent the three sets of test results of Comparative Example 2, and Base+2% A+1% B-1#, Base+2% A+1% B-2#, and Base+2% A+1% B-3# represent the three sets of test results of Example 10.

[0150] It is found by comparing Comparative Example 3 and Comparative Example 1 that the addition of the first additive has a significant increasing effect on the impedance of the battery. It is found by comparing Comparative Example 2 and Comparative Example 1 that the addition of the second additive has a significant decreasing effect on the impedance of the battery. And by simultaneously adding 2% of the first additive and 1% of the second additive, i.e., Example 10 and Comparative Example 1, due to the synergistic effect of the two, the second additive can balance the negative effect of the first additive on the impedance to a large extent, achieving the effect of improving the high temperature without significantly deteriorating the impedance.

[0151] While the application has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the application. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the application without departing from the central scope of the application. Therefore, the application is not intended to be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the application, but it is intended to cover in the appended claims all embodiments falling within the scope of the application.

[0152] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are combinable with each other.

[0153] Embodiments of the application have been described above, with the understanding that these embodiments are exemplary, but are not exhaustive, and are not limited to the embodiments disclosed. Many modifications and variations of the described embodiments will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms to be used in the description is not intended to limit the scope or breadth of the embodiments disclosed herein. Rather, the terms are chosen to best explain the principles of the embodiments, practical application, or improvement over the technology in the art, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An electrolyte, characterized by, The first additive includes a nitrogen-containing heterocyclic anhydride compound, and the second additive includes a borate compound, and the first additive and the second additive satisfy the following relationship with the positive and negative electrode material layer: 105 ≤ (Ya+Yb) / (M*N) ≤ 2000 The first additive accounts for Ya % of the mass percentage of the electrolyte, the second additive accounts for Yb % of the mass percentage of the electrolyte, the mass of the positive electrode material layer per unit area on the positive electrode sheet is M g / cm 2 , and the mass of the negative electrode material layer per unit area on the negative electrode sheet is N g / cm 2 . The structural formula of the nitrogen-containing heterocyclic anhydride compound is as follows: Formula 1 In Formula 1, X1 is one of C and N atoms, X2 is an N atom, R1 and R2 are each independently selected from one of a benzene ring, a cyano group, a halogen atom, a hydrogen atom, a C1-C10 alkyl group, a C1-C10 unsaturated alkyl group, a C1-C10 halogenated alkyl group, and a C1-C10 halogenated unsaturated alkyl group; 0.01 ≤ Ya ≤ 10, 0.01 ≤ Yb ≤ 5, 0.035 ≤ M ≤ 0.15, and 0.025 ≤ N ≤ 0.

12.

2. The electrolyte according to claim 1, characterized in that, The first additive and the second additive satisfy the following relationship with the positive and negative electrode material layer: 200 ≤ (Ya+Yb) / (M*N) ≤ 1000.

3. The electrolyte of claim 1, wherein R1 and R2 are each independently selected from one of a benzene ring, a cyano group, a halogen atom, a hydrogen atom, a C1-C3 alkyl group, a C1-C3 unsaturated alkyl group, a C1-C3 fluorinated alkyl group, and a C1-C10 fluorinated unsaturated alkyl group.

4. The electrolyte according to claim 3, characterized in that The first additive includes at least one nitrogen-containing heterocyclic anhydride compound as follows: Compound 1-1 Compound 1-2 Compound 1-3 Compound 1-4 Compound 1-5 Compound 1-6 Compound 1-7 Compound 1-8.

5. The electrolyte of claim 1, wherein, The borate compound has the following structural formula: Formula 2 In Formula 2, R3, R4, and R5 are each independently selected from one of a C1-C10 alkyl group, a C1-C10 unsaturated alkyl group, a C1-C10 perhalogenated or partially halogenated alkyl group, and a C1-C10 perhalogenated or partially halogenated unsaturated alkyl group.

6. The electrolyte of claim 5, wherein, R3, R4, and R5 are each independently selected from one of a C1-C5 perfluorinated or partially fluorinated alkyl group, and a C1-C5 perfluorinated or partially fluorinated unsaturated alkyl group.

7. The electrolyte of claim 5, wherein, The second additive includes at least one borate compound as follows: Compound 2-1 Compound 2-2 Compound 2-3 Compound 2-4 Compound 2-5 Compound 2-6 Compound 2-7 Compound 2-8 Compound 2-9 Compound 2-10.

8. The electrolyte of claim 1, wherein, 1 ≤ Ya ≤ 8; and / or, 0.5 ≤ Yb ≤ 3.

9. An electrochemical device, characterized by, The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte as claimed in any one of claims 1 to 8.

10. The electrochemical device of claim 9, wherein, The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer on at least one side of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

11. The electrochemical device of claim 10, wherein, The positive electrode active material is selected from one or more of lithium cobalt oxide LiCoO2, lithium nickel manganese cobalt ternary material, lithium iron phosphate LiFePO4, and lithium manganate LiMn2O4.

12. The electrochemical device of claim 11, wherein, The positive electrode active material is selected from lithium nickel manganese cobalt ternary material.

13. An electronic device, comprising: The electrochemical device includes the electrochemical device as claimed in any one of claims 9 to 12.

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