Electrolyte, electrochemical apparatus and electronic apparatus

Abstract

An electrolyte, an electrochemical apparatus and an electronic apparatus. The electrolyte contains lithium difluorooxalate borate and a first additive. On the basis of the mass of the electrolyte, the mass percentage content of lithium difluorooxalate borate is A%, and the mass percentage content of the first additive is B%, wherein 0.025≤B / A≤15 and 0.2≤A+B≤8. The first additive is selected from at least one of a compound of formula I and a compound of formula II; R1-R9 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, R is selected from hydrogen, hydroxyl, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R and R1-R9 is selected from alkenyl; R10-R21 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R10-R21 is selected from alkenyl. The lithium difluorooxalate borate in the electrolyte is used together with the first additive, thus improving the high-temperature cycle and storage performance of batteries.

Description

Electrolytes, electrochemical devices and electronic devices Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to an electrolyte, an electrochemical device, and an electronic device. Background Technology

[0002] In high-nickel cathode active materials, nickel can achieve Ni 2+ →Ni 3+ / Ni 4+ The reversible transformation of nickel allows the positive electrode active material to achieve a high reversible specific capacity, thus enabling it to achieve high energy density. However, excessive nickel content can cause structural damage and microcracks in the positive electrode active material due to anisotropic volume changes during cycling. This increases the contact area between the electrode active material and the electrolyte, leading to side reactions and reducing the cycle stability of the positive electrode active material. Lithium difluorooxalate borate, as an additive, can form a high-ionic-conductivity CEI / SEI film rich in LiF on the positive and negative electrode surfaces, improving the interface between the positive and negative electrode active materials and the electrolyte, thereby improving the cycle stability of the battery. However, it is prone to decomposition at high temperatures, worsening gas generation during high-temperature storage and also affecting the high-temperature cycle performance of the battery. Summary of the Invention

[0003] In order to improve the problem of gas generation during high-temperature storage of batteries and to enhance the high-temperature cycle performance of batteries, this application provides the following electrolyte, electrochemical device and electronic device.

[0004] The first aspect of this application provides an electrolyte containing lithium difluorooxalate borate and a first additive. Based on the mass of the electrolyte, the mass percentage of lithium difluorooxalate borate is A%, and the mass percentage of the first additive is B%, with a tolerance of 0.025 ≤ B / A ≤ 15 and 0.2 ≤ A + B ≤ 8. The first additive is selected from at least one compound of formula I and formula II.

[0005] R1-R9 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, R is selected from hydrogen, hydroxyl, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R and R1-R9 is selected from alkenyl; R10-R21 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R10-R21 is selected from alkenyl.

[0006] In some optional embodiments of the first aspect of this application, the first additive comprises at least one of the following compounds:

[0007] In some optional embodiments of the first aspect of this application, the mass percentage A% of lithium difluorooxalate borate satisfies 0.1≤A≤5, preferably 0.2≤A≤3.

[0008] In some optional embodiments of the first aspect of this application, the mass percentage B% of the first additive satisfies 0.05≤B≤3, preferably 0.1≤B≤2.

[0009] In some optional embodiments of the first aspect of this application, 0.5 ≤ B / A ≤ 10.

[0010] In some optional embodiments of the first aspect of this application, the electrolyte further includes a second additive, which includes at least one of vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, or fluoroethylene carbonate; the mass percentage of the second additive is D% based on the mass of the electrolyte, 0.1≤D≤15, preferably 2≤D≤8.

[0011] The second aspect of this application provides an electrochemical device, including the electrolyte and positive electrode provided in the first aspect of this application. The positive electrode includes a positive electrode material layer, which includes nickel. Based on the total mass of the positive electrode material layer, the mass percentage of nickel is M%, and 0.53≤100(A+B) / M≤15.87.

[0012] In some optional embodiments of the second aspect of this application, the mass percentage of nickel, M%, satisfies 28.87 ≤ M ≤ 57.1.

[0013] In some optional embodiments of the second aspect of this application, 0.19 ≤ 100*B / M ≤ 8.66.

[0014] In some optional embodiments of the second aspect of this application, the positive electrode material layer comprises lithium nickel cobalt manganese oxide, wherein the mass percentage of cobalt in the lithium nickel cobalt manganese oxide is E% based on the total mass of the positive electrode material layer, 2.85≤E≤19, 2≤M / E≤18.

[0015] A third aspect of this application provides an electronic device that includes the electrochemical device of the second aspect of this application.

[0016] The one or more technical solutions provided in the embodiments of this application have at least the following beneficial effects:

[0017] The electrolyte provided in the first aspect of this application contains lithium difluorooxalate borate and a first additive. Lithium difluorooxalate borate can form a high-ionic-conductivity CEI / SEI film rich in lithium fluoride on the positive and negative electrode surfaces, improving the interface between the positive electrode active material and the electrolyte, thereby improving the cycle stability of the battery. However, its thermal stability is poor; it decomposes to generate carbon dioxide gas when the temperature exceeds its thermal stability threshold. Simultaneously, byproducts such as BF4- generated during decomposition may damage the solid electrolyte film between the electrode and the electrolyte, reducing the battery's cycle life and capacity retention. The unsaturated bonds in the first additive facilitate polymerization at the positive and negative electrode interface, forming a uniform and dense CEI / SEI film, preventing further decomposition of the electrolyte on the positive electrode side, improving interface stability, reducing gas release, and thus improving gas generation during storage at high temperatures, reducing the risk of lithium difluorooxalate borate deteriorating during storage. On the other hand, Si-O-Si bonds can replace F through a bimolecular nucleophilic substitution reaction. - This process removes HF, a common byproduct in the electrolyte, prevents gas accumulation, inhibits the risk of reaction between HF and the cathode interface, suppresses the dissolution of transition metal ions in high-nickel cathode materials, and maintains the stability of the cathode interface. The combined use of lithium difluorooxalate borate and the first additive can improve the high-temperature cycling and storage performance of the battery.

[0018] The electrochemical device provided in the second aspect of this application has excellent high-temperature cycling stability and storage performance.

[0019] The electronic device provided in the third aspect of this application has an extended service life, improved reliability in high-temperature environments, optimized energy efficiency, enhanced safety, and the ability to maintain long-term storage performance. Detailed Implementation

[0020] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0021] This application provides an electrolyte containing lithium difluorooxalate borate and a first additive. Based on the mass of the electrolyte, the mass percentage of lithium difluorooxalate borate is A%, the mass percentage of the first additive is B%, and the mass percentages are 0.025 ≤ B / A ≤ 15 and 0.2 ≤ A + B ≤ 8. The first additive is selected from at least one compound of formula I and formula II.

[0022] R1-R9 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, R is selected from hydrogen, hydroxyl, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R and R1-R9 is selected from alkenyl; R10-R21 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R10-R21 is selected from alkenyl.

[0023] For example, the value of B / A can be 0.025, 0.05, 0.083, 0.1, 0.167, 0.5, 1, 2, 3, 4, 5, 10, 12, 15 or a range of any two of these values.

[0024] The value of A+B can be 0.2, 0.3, 0.6, 0.7, 1.05, 1.1, 1.5, 2.05, 2.2, 3, 3.5, 4, 5, 5.5, 6, 6.5, 7, 8, or a range of any two values ​​selected from these values.

[0025] The electrolyte provided in the first aspect of this application contains lithium difluorooxalate borate and a first additive. Lithium difluorooxalate borate can form a high-ionic-conductivity CEI / SEI film rich in lithium fluoride on the positive and negative electrode surfaces, improving the interface between the positive electrode active material and the electrolyte, thereby improving the cycle stability of the battery. However, its thermal stability is poor; it decomposes to generate carbon dioxide gas when the temperature exceeds its thermal stability threshold. Simultaneously, byproducts such as BF4- generated during decomposition may damage the solid electrolyte film between the electrode and the electrolyte, reducing the battery's cycle life and capacity retention. The unsaturated bonds in the first additive readily undergo polymerization at the positive and negative electrode interfaces. By controlling the mass percentage of lithium difluorooxalate borate and the first additive to satisfy the aforementioned specific relationship, a uniform and dense CEI / SEI film can be formed at the positive and negative electrode interfaces, preventing further decomposition of the electrolyte on the positive electrode side, improving interface stability, reducing gas release, thereby improving gas generation during storage at high temperatures and reducing the risk of lithium difluorooxalate borate deteriorating during storage.

[0026] In some optional embodiments of the first aspect of this application, the first additive comprises at least one of the following compounds:

[0027] In some optional embodiments of the first aspect of this application, the mass percentage A% of lithium difluorooxalate borate satisfies 0.1 ≤ A ≤ 5. Exemplarily, the value of A can be 0.1, 0.5, 1, 2, 3, 4, 5 or a range selected from any two of these values.

[0028] Preferably, 0.2 ≤ A ≤ 3. For example, the value of A can be 0.2, 0.4, 0.8, 1.2, 1.8, 2.4, 3 or a range selected from any two of these values.

[0029] In some optional embodiments of the first aspect of this application, the mass percentage content B% of the first additive satisfies 0.05≤B≤3. Exemplarily, the value of B can be 0.05, 0.1, 0.3, 0.5, 1, 1.5, 2, 2.5, 3 or a range selected from any two of these values.

[0030] Preferably, 0.1 ≤ B ≤ 2. For example, the value of B can be 0.1, 0.3, 0.5, 0.9, 1.3, 1.5, 1.7, 2 or a range of any two values ​​selected therefrom.

[0031] In some optional embodiments of the first aspect of this application, wherein 0.5 ≤ B / A ≤ 10, and exemplarily, the value of B / A can be 0.5, 0.6, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range selected from any two of these values.

[0032] In some optional embodiments of the first aspect of this application, the electrolyte further includes a second additive, the ester additive including at least one selected from vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, or fluoroethylene carbonate; the mass percentage of the second additive is D% based on the mass of the electrolyte, 0.1 ≤ D ≤ 15, and exemplarily, the value of D can be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, or a range selected from any two of these values.

[0033] Preferably, 2≤D≤8. For example, the value of D can be 2, 3, 4, 5, 6, 7, 8 or a range of any two of these values.

[0034] A second aspect of this application provides an electrochemical device comprising an electrolyte and a positive electrode sheet as provided in the first aspect of this application. The positive electrode sheet includes a positive electrode material layer comprising nickel. Based on the total mass of the positive electrode material layer, the mass percentage of nickel is M%, and the value is 0.53 ≤ 100(A+B) / M ≤ 15.87. For example, the value of 100(A+B) / M can be 0.53, 0.58, 0.87, 1.32, 1.44, 1.73, 2.02, 2.63, 2.92, 3.03, 3.17, 3.95, 4.33, 5.20, 5.91, 6.35, 7, 8, 8.66, 10.10, 11.54, 14.43, 15.87, or a range selected from any two of these values.

[0035] The Si-O-Si bond in the first additive can replace F through a bimolecular nucleophilic substitution reaction. - This process removes HF (hydrofluoric acid), a common byproduct in the electrolyte, prevents gas accumulation, inhibits the risk of reaction between HF and the positive electrode interface, suppresses the dissolution of transition metal ions in the high-nickel positive electrode material, and maintains the stability of the positive electrode interface. The use of lithium difluorooxalate borate together with the first additive, and ensuring that the sum of their mass percentages satisfies the above-mentioned relationship with the mass percentage of nickel in the positive electrode material layer, can improve the high-temperature cycling and storage performance of the battery.

[0036] In some optional embodiments of the second aspect of this application, the mass percentage of nickel, M%, satisfies 28.87 ≤ M ≤ 57.1.

[0037] In some optional embodiments of the second aspect of this application, 0.19 ≤ 100*B / M ≤ 8.66, and exemplarily, the value of 100*B / M can be 0.19, 0.29, 0.88, 0.97, 1.32, 1.44, 1.73, 2, 3, 4, 5, 5.77, 6, 7, 8, 8.66 or a range selected from any two of these values.

[0038] In some optional embodiments of the second aspect of this application, the positive electrode material layer comprises lithium nickel cobalt manganese oxide, wherein the mass percentage of cobalt in the lithium nickel cobalt manganese oxide is E% based on the total mass of the positive electrode material layer, 2.85≤E≤19, 2≤M / E≤18.

[0039] A third aspect of this application provides an electronic device that includes the electrochemical device of the second aspect of this application.

[0040] The electrochemical device provided in the second aspect of this application has excellent high-temperature cycling stability and storage performance.

[0041] The electronic device provided in the third aspect of this application has an extended service life, improved reliability in high-temperature environments, optimized energy efficiency, enhanced safety, and the ability to maintain long-term storage performance.

[0042] The cathode material of this application includes lithium nickel cobalt manganese oxide. This application does not impose any particular limitation on the preparation method of lithium nickel cobalt manganese oxide, as long as it achieves the purpose of this application. For example, the preparation method of lithium nickel cobalt manganese oxide may include, but is not limited to, the following steps: uniformly mixing a cobalt-containing compound, a nickel-containing compound, a manganese-containing compound, and a lithium-containing compound, followed by heat treatment in an air atmosphere to obtain lithium nickel cobalt manganese oxide. The nickel-containing compound may include, but is not limited to, at least one of NiCO3, NiO, Ni(OH)2, NiSO4, Ni(NO3)2, or Ni(CH3COO)2; the cobalt-containing compound may include, but is not limited to, at least one of CoSO4, Co(NO3)2, or Co(CH3COO)2LiCoO2; the manganese-containing compound may include, but is not limited to, at least one of MnSO4, Mn(NO3)2, or Mn(CH3COO)2; and the lithium-containing compound may include, but is not limited to, at least one of LiCH3COO, Li2CO3, LiOH, or LiNO3. This application does not impose any particular restrictions on the temperature, time, and heating rate of the heat treatment, as long as the purpose of this application can be achieved. For example, the heat treatment temperature is 650°C to 850°C, the time is 22h to 26h, and the heating rate is 2°C / min to 8°C / min.

[0043] In this application, the mass percentage content B of nickel and the mass percentage content E of cobalt in the cathode material layer can be controlled by adjusting the mass ratio of cobalt-containing compounds, nickel-containing compounds, and manganese-containing compounds during the preparation of lithium nickel cobalt manganese oxide. For example, when the mass percentage content of nickel remains constant, decreasing the amount of manganese-containing compound and increasing the amount of cobalt-containing compound changes the mass ratio of cobalt-containing compounds, nickel-containing compounds, and manganese-containing compounds, resulting in an increase in the mass percentage content of cobalt and a decrease in the mass percentage content of manganese; conversely, increasing the amount of manganese-containing compound and decreasing the amount of cobalt-containing compound changes the mass ratio of cobalt-containing compounds, nickel-containing compounds, and manganese-containing compounds, resulting in a decrease in the mass percentage content of cobalt and an increase in the mass percentage content of manganese. When the mass percentage of cobalt remains constant, decreasing the amount of manganese-containing compound and increasing the amount of nickel-containing compound alters the mass ratio of cobalt-containing, nickel-containing, and manganese-containing compounds, resulting in an increase in the mass percentage of nickel and a decrease in the mass percentage of manganese. Conversely, increasing the amount of manganese-containing compound and decreasing the amount of nickel-containing compound alters the mass ratio of cobalt-containing, nickel-containing, and manganese-containing compounds, resulting in a decrease in the mass percentage of nickel and an increase in the mass percentage of manganese.

[0044] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0045] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0046] In this application, the positive electrode material layer includes a positive electrode material, which includes lithium nickel cobalt manganese oxide. The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. This application does not impose any particular limitation on the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode material layer can be (93 to 97):(1 to 3):(2 to 5).

[0047] This application does not impose any particular limitation on the adhesive, as long as it can achieve the purpose of this application. For example, the adhesive may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a copolymer of styrene and acrylate, a copolymer of styrene and butadiene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0048] This application does not impose any particular limitation on the conductive agent, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. In this application, the conductive carbon black includes at least one of acetylene black and Ketjen black.

[0049] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0050] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0051] In this application, the electrochemical device also includes a separator membrane. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0052] In some embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0053] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0054] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0055] In some embodiments of the present application, the inorganic layer may further comprise a thickener and a wetting agent. There are no particular restrictions on the types of the thickener and the wetting agent in the present application, as long as the object of the present application can be achieved. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose; the wetting agent may include, but is not limited to, at least one of dimethyl siloxane, sodium dodecyl sulfate, trialkyl phosphate, methyl decanoate or dodecyl acetate.

[0056] In the present application, there is no particular restriction on the thickness of the separator, as long as the object of the present application can be achieved. For example, the thickness of the separator may be 4 μm to 30 μm.

[0057] In the present application, the electrochemical device further comprises a negative electrode pole piece, and the negative electrode pole piece comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above statement "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be disposed on one surface of the negative electrode current collector along its own thickness direction, or may be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" herein may be the entire region of the surface of the negative electrode current collector, or may be a partial region of the surface of the negative electrode current collector, and there is no particular restriction in the present application, as long as the object of the present application can be achieved.

[0058] There is no particular restriction on the negative electrode current collector in the present application, as long as the object of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector. Illustratively, the composite current collector may be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0059] The negative electrode material layer of the present application comprises a negative electrode material. There is no particular restriction on the type of the negative electrode material in the present application, as long as the object of the present application can be achieved. For example, the negative electrode material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO x (0<x<2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with spinel structure 12 , Li-Al alloy or metallic lithium.

[0060] There is no particular restriction on the thickness of the negative electrode current collector and the negative electrode material layer in the present application, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0061] In some embodiments of this application, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of conductive agents, binders, and thickeners, as long as they achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), waterborne acrylic resin, or carboxymethyl cellulose (CMC). The conductive agent may include, but is not limited to, at least one of conductive carbon black, sheet graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. In this application, the conductive carbon black includes at least one of acetylene black and Ketjen black. The thickener may include, but is not limited to, at least one of carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose, or lithium carboxymethyl cellulose.

[0062] This application does not impose any particular limitation on the mass ratio of negative electrode material, binder, and thickener in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the mass ratio of negative electrode material, binder, and thickener in the negative electrode material layer can be (93 to 97):(1 to 3):(2 to 5).

[0063] The electrochemical device also includes a housing for accommodating the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of electrochemical devices. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, the housing can be a rigid housing or a flexible housing. The material of the rigid housing can be metal; this application does not limit the type of metal and can use known metal rigid housings, as long as they achieve the purpose of this application. The flexible housing can be a metal-plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0064] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the electrochemical device may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. Alternatively, stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0065] [Specific Implementation Examples]

[0066] The following specific embodiments and comparative examples illustrate the implementation of this application in more detail, but this application is not limited to these embodiments as long as it does not depart from its spirit. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0067] I. Test Methods and Equipment

[0068] 1.1 Ni and Co element content test

[0069] After discharging the lithium-ion battery to 3V at 0.2C, the positive electrode was removed. The positive electrode was cut into 10 small discs with a diameter of 16mm. The positive electrode material layer was scraped off from the current collector of each small disc using a knife, yielding powder. 0.2g of the powder was weighed and digested with 10mL of aqua regia. The solution was then diluted to a volumetric flask with deionized water. An inductively coupled plasma analyzer (ICP, model AVIO-200) was used, with the RF generator frequency set to 40.68MHz, the argon secondary pressure to 0.6MPa, the RF power to 1400W, and the pump speed to 1.0mL / min. The content of each element in the positive electrode material layer of each small disc was measured. The average content of each element from the 10 small discs was taken to obtain the content of Co and Ni elements in the positive electrode material layer. The aqua regia was obtained by mixing concentrated nitric acid and concentrated hydrochloric acid in a 1:1 volume ratio.

[0070] 1.2 Electrolyte composition testing

[0071] The lithium-ion battery was discharged to 3V at 0.2C and then disassembled to obtain positive and negative electrode plates. These plates were then centrifuged in centrifuge tubes to obtain the electrolyte. The mass percentage of each substance (e.g., Formula I compound, additives, and lithium salt additives) in the centrifuged electrolyte was determined using gas chromatography-mass spectrometry (GC-MS).

[0072] 1.3 High-Temperature Cyclic Performance Test

[0073] At 60℃, a lithium-ion battery is charged at a constant current of 1C to 4.35V, then charged at a constant voltage of 4.35V to 0.05C, and finally discharged at a constant current of 10C to 3V. This constitutes one charge-discharge cycle. This cycle is repeated 500 times. The discharge capacity after one cycle is recorded as the initial discharge capacity C0, and the discharge capacity after 400 cycles is recorded as C1. The cycle capacity retention rate after 400 cycles at 60℃ characterizes the high-temperature cycle performance of the lithium-ion battery. A higher cycle capacity retention rate after 500 cycles at 60℃ indicates better high-temperature cycle performance. Cycle capacity retention rate (%) = C1 / C0 × 100%.

[0074] In the high-temperature cycling performance test of this application embodiment, each charge-discharge cycle is an ultra-high rate charge-discharge cycle, and the test conditions are more stringent than those of general conventional test conditions.

[0075] 1.4 High-Temperature Circulating Gas Generation Performance Test

[0076] Before testing, the initial thickness d0 of the secondary battery was measured using a micrometer at 25°C. At 60°C, the lithium-ion battery was charged at a constant current of 1C to 4.35V, then charged at a constant voltage of 0.05C at 4.35V, and finally discharged at a constant current of 6C to 3V. This constitutes one charge-discharge cycle. This cycle was repeated 500 times. The thickness d1 of the lithium-ion battery after 500 cycles was then measured using a micrometer. The thickness expansion rate after 500 cycles at 60°C characterizes the high-temperature gas generation performance of the lithium-ion battery. A smaller expansion rate after 500 cycles at 60°C indicates better high-temperature storage performance. Cyclic gas generation thickness expansion rate (%) = (d1 - d0) / d0 × 100%.

[0077] 1.5 High-Temperature Storage Performance Test

[0078] Before testing, the initial thickness d0 of the secondary battery was measured using a micrometer at 25°C. At 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.35V, and then charged at a constant voltage of 0.05C at 4.35V, resulting in a fully charged state. The lithium-ion battery was then placed in a 60°C constant temperature chamber for high-temperature storage for 15 days. The thickness d2 of the lithium-ion battery after storage was then measured using a micrometer. The thickness expansion rate after 15 days of storage at 60°C characterizes the high-temperature storage performance of the lithium-ion battery. The smaller the thickness expansion rate after 15 days of storage at 60°C, the better the high-temperature storage performance of the lithium-ion battery. High-temperature storage thickness expansion rate (%) = (d2 - d0) / d0 × 100%.

[0079] Example 1

[0080] <Preparation of the positive electrode>

[0081] LiNi 0.6 Co 0.1 Mn 0.3O2, conductive carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was formed. The positive electrode slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 120°C to obtain a single-sided coated positive electrode sheet. The coating weight of the positive electrode material layer was 267.8 mg / 1540 mm². 2 The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with dimensions of 74mm × 867mm for later use. The compaction density of the positive electrode material layer is 4.15 g / cm³. 3 .

[0082] <Preparation of Negative Electrode Sheets>

[0083] Artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed at a mass ratio of 95:2:3. Deionized water was then added as a solvent to prepare a slurry with a solid content of 70 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was then uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The foil was dried at 120°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃ and cold pressing, the sheet is cut and tabs are welded to obtain a negative electrode sheet with dimensions of 78mm × 875mm for later use. The compaction density of the negative electrode material layer is 1.74 g / cm³. 3 .

[0084] <Preparation of Electrolyte>

[0085] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of 10:30:60 to obtain a base solvent. Compound of formula I-1, lithium difluorooxalate borate, and lithium salt LiPF6 were then added and stirred until homogeneous to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage of lithium difluorooxalate borate (A%) was 1%, the mass percentage of the first additive (B%) was 0.5%, the mass percentage of lithium salt LiPF6 was 12.5%, and the remainder was the base solvent.

[0086] <Isolation membrane>

[0087] A 15μm thick porous polyethylene polymer film (manufacturer: Celgard Diaphragm Company, USA) was used as the separator.

[0088] <Preparation of Lithium-ion Batteries>

[0089] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form the electrode assembly. This assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, and shaping processes to obtain the lithium-ion battery. The formation temperature is 70°C, and the settling time is 2 hours.

[0090] Examples 2 to 21

[0091] Except for adjusting the mass percentage of lithium difluorooxalate borate, the type and mass percentage of the first additive according to Table 1 in the <Preparation of Electrolyte>, and changing the mass percentage of the base solvent accordingly, the mass ratio of each component of the base solvent and the mass percentage of lithium salt remain unchanged, and the rest are the same as in Example 1.

[0092] Examples 22 to 29

[0093] Except for the addition of the second additive according to Table 1 in the <Preparation of Electrolyte>, and the adjustment of the type and mass percentage of the second additive, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1.

[0094] Examples 30 to 37

[0095] Except for adjusting the relevant preparation parameters (including the ratio of nickel and cobalt in the nickel oxide and lithium nickel cobalt manganese oxide in the positive electrode material layer) according to Table 1 in the <Preparation of Positive Electrode>, adjusting the mass percentage content of lithium difluorooxalate borate and the mass percentage content of the first additive, the rest are the same as in Example 1.

[0096] Comparative Example 1

[0097] Except that the first additive is not added in the <Preparation of Electrolyte>, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt remains unchanged, everything else is the same as in Example 1.

[0098] Comparative Example 2

[0099] Except that lithium difluorooxalate borate is not added in the <Preparation of Electrolyte>, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt remains unchanged, everything else is the same as in Example 1.

[0100] Comparative Example 3

[0101] Except for adjusting the mass percentages of the first additive and lithium difluorooxalate borate according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the base solvent accordingly, keeping the mass ratio of each component of the base solvent unchanged, and keeping the mass percentage of the lithium salt unchanged, everything else is the same as in Example 1.

[0102] Comparative Example 4

[0103] Except for adjusting the mass percentages of the first additive and lithium difluorooxalate borate according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the base solvent accordingly, keeping the mass ratio of each component of the base solvent unchanged, and keeping the mass percentage of the lithium salt unchanged, everything else is the same as in Example 1.

[0104] Comparative Example 5

[0105] Except for adjusting the mass percentages of the first additive and lithium difluorooxalate borate according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the base solvent accordingly, keeping the mass ratio of each component of the base solvent unchanged, and keeping the mass percentage of the lithium salt unchanged, everything else is the same as in Example 1.

[0106] Table 1 Battery fabrication parameters for each embodiment and comparative example

[0107] Table 2 Performance test data for each embodiment and comparative example

[0108] Analyze the data from Tables 1 and 2:

[0109] In Examples 1 to 21, the electrolytes all included lithium difluorooxalate borate and a first additive. The sum of the mass percentages of lithium difluorooxalate borate and the first additive, A+B, all conformed to the preset range of 0.2≤A+B≤8, and the mass percentage ratio of the first additive to lithium difluorooxalate borate, B / A, all conformed to the preset range of 0.025≤B / A≤15. The cycle capacity retention rates of Examples 1 to 21 were all higher than those of Comparative Examples 1 to 5, while the cycle gas production thickness expansion rate and the high-temperature storage thickness expansion rate were both lower than those of Comparative Examples 1 to 5.

[0110] Comparative Example 1, excluding the first additive, features the same mass percentage of lithium difluorooxalate borate as the sum of the mass percentages of lithium difluorooxalate borate and the first additive (A+B) in Example 1. Example 1 exhibits a significantly higher cycle capacity retention rate than Comparative Example 1, and the cycle gas generation thickness expansion rate and high-temperature storage thickness expansion rate of Example 1 are both much lower than those of Comparative Example 1. This indicates that adding the first additive in the presence of lithium difluorooxalate borate improves the high-temperature cycle performance and stability of the battery, reduces gas generation during high-temperature storage, and enhances the battery's high-temperature performance.

[0111] Comparative Example 2 does not include lithium difluorooxalate borate. In Example 1, where the mass percentage of the first additive is the same as the sum of the mass percentages of lithium difluorooxalate borate and the first additive (A+B), Example 1 exhibits a significantly higher cycle capacity retention rate than Comparative Example 2. Furthermore, the cycle gas generation thickness expansion rate and high-temperature storage thickness expansion rate of Example 1 are both significantly lower than those of Comparative Example 2. This indicates that adding lithium difluorooxalate borate in the presence of the first additive can improve the high-temperature cycle performance of the battery, enhance battery cycle stability, reduce high-temperature storage gas generation, and improve the battery's high-temperature performance.

[0112] Compared to Comparative Example 1, which did not contain the first additive, Comparative Example 2 showed a weaker improvement in high-temperature cycling performance without lithium difluorooxalate borate. This demonstrates that lithium difluorooxalate borate and the first additive in the electrolyte of the battery (especially the positive electrode material layer which includes nickel) can work synergistically to improve the high-temperature performance of the battery and reduce gas generation during high-temperature storage.

[0113] In Comparative Example 3, the values ​​of B / A and A+B both exceeded the preset range; in Comparative Example 4, A+B exceeded the preset range; and in Comparative Example 5, B / A exceeded the preset range. Compared with Comparative Examples 3 to 5, Examples 1 to 6 all affected the optimization effect on the high-temperature stability performance of the battery when at least one value of B / A and A+B in the battery fluid was not within the corresponding preset range.

[0114] Examples 1 and 7 to 10 show that in the battery electrolyte, the first additive selected from one of the structural formulas I and II, or two or more of the structural formulas I and II, has a similar and better effect on improving the cycle capacity retention rate of the battery at high temperature, and also effectively suppresses battery cycle gas generation and high temperature storage expansion.

[0115] Compared with Example 6, Examples 1 to 5 show that: Examples 1 to 5 (where the value of A satisfies 0.1≤A≤5) further improve the cycle capacity retention rate of the battery at high temperature by at least 4.7%, further reduce the cycle gas generation thickness expansion rate by at least 4.3%, and further reduce the high temperature storage thickness expansion rate by at least 2.6% compared with Example 6 (which exceeds the range of 0.1≤A≤5).

[0116] Compared with Examples 1, 4-5 and Examples 2-3, it is shown that when the mass percentage A% of lithium difluorooxalate borate is further narrowed and the value satisfies 0.2≤A≤3, the high-temperature cycle performance and high-temperature storage performance of the battery are further improved. Specifically, the cycle capacity retention rate of the battery at high temperature is further improved to more than 70%, the cycle gas production thickness expansion rate is in the range of 15% to 26%, and the high-temperature storage thickness expansion rate is further reduced to less than 30%.

[0117] Compared with Example 15, Examples 11 to 14 show that: Examples 11 to 14 (where the value of B satisfies 0.05≤B≤3) have a higher cycle capacity retention rate at high temperature by at least 3.1%, a lower cycle gas generation thickness expansion rate by at least 2.1%, and a lower high-temperature storage thickness expansion rate by at least 1.5% compared with Example 15 (which exceeds the range of 0.05≤B≤3).

[0118] Compared with Examples 11-12, Examples 13-14 show that when the range of the mass percentage content B% of the first additive is further narrowed and the condition 0.1≤B≤2 is met, the high-temperature cycle performance and high-temperature storage performance of the battery are further improved. Specifically, the cycle capacity retention rate of the battery at high temperature is at a relatively high level of around 70%, and the cycle gas generation thickness expansion rate and the high-temperature storage thickness expansion rate are further reduced.

[0119] Compared with Examples 16-17, Examples 18-19 show that when the ratio of the mass percentage of the first additive B% to the mass percentage of lithium difluorooxalate borate A% is further narrowed and satisfies 0.5≤B / A≤10, the high-temperature cycle performance and high-temperature storage performance of the battery are further improved. Specifically, the cycle capacity retention rate of the battery at high temperature is further improved to more than 70%, the cycle gas generation thickness expansion rate is less than 25%, and the high-temperature storage thickness expansion rate is further reduced to less than 30%.

[0120] The electrolytes in Examples 22 to 29 all included a second additive, and the mass percentage (D%) of the second additive all fell within the preset range of 0.1 ≤ D ≤ 15. The cycle capacity retention rates of Examples 22 to 29 all exceeded 80%, showing a significant improvement compared to Example 1. The cycle gas production thickness expansion rate and high-temperature storage thickness expansion rate of Examples 22 to 29 both decreased to below 15% or even below 10%, significantly lower than those of Example 1.

[0121] Compared with Examples 22 and 26, Examples 23-25 ​​show that when the range of the mass percentage D% of the second additive is further narrowed and 2≤D≤8 is satisfied, the high-temperature cycle performance and high-temperature storage performance of the battery are further improved. Specifically, the cycle capacity retention rate of the battery at high temperature is further increased to about 89%, and the cycle gas generation thickness expansion rate and the high-temperature storage thickness expansion rate are further reduced to below 9%.

[0122] Examples 23 and 27 to 29 show that the second additive, selected from one or more of vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, or fluoroethylene carbonate, has a similar and better effect on improving the high-temperature performance of the battery, and can effectively suppress the expansion of the battery during high-temperature cycling and storage. Specifically, the cycle capacity retention rate at high temperature is above 85%, the cycle gas production thickness expansion rate is in the range of 8.5% to 11.6%, and the high-temperature storage thickness expansion rate is in the range of 8.6% to 12.9%.

[0123] Examples 30 to 37 show that when the mass percentage of nickel in the positive electrode (M%), the mass percentage of lithium difluorooxalate borate in the electrolyte (A%), and the mass percentage of the first additive (B%) satisfy 28.87 ≤ M ≤ 57.1 and 0.53 ≤ 100(A+B) / M ≤ 15.87, the battery exhibits superior high-temperature cycle performance and high-temperature storage performance. The nickel oxides in the positive electrode material layer include lithium nickel cobalt manganese oxide and lithium nickel oxide.

[0124] Except for Example 32, in Examples 30 to 37, the relationship between the mass percentage of the first additive B% in the electrolyte and the mass percentage of nickel M% in the positive electrode, 100*B / M, satisfies the preset range of 0.19≤100*B / M≤8.66. Compared with Example 32, it has a higher cycle capacity retention rate at high temperature, a lower cycle thickness expansion and a lower high-temperature storage thickness expansion rate.

[0125] In Examples 31 and 32, the cathode materials did not contain lithium nickel cobalt manganese oxide and did not contain cobalt. Examples 30, 33 to 37, compared to Examples 31-32, show that cathode material layers containing lithium nickel cobalt manganese oxide (containing cobalt) exhibit better performance, especially when the mass percentage of cobalt (E%) satisfies 2.85 ≤ E ≤ 19 and the ratio of nickel mass percentage to cobalt mass percentage (M / E) satisfies 2 ≤ M / E ≤ 18. This results in superior high-temperature cycle capacity retention, lower cycle thickness expansion, and lower high-temperature storage thickness expansion. It is evident that when the electrolyte contains a mixture of lithium difluorooxalate borate and the first additive, the cathode material containing lithium nickel cobalt manganese oxide is superior to the cathode material containing only lithium nickel oxide in terms of improving high-temperature stability. The stabilizing layered structure of cobalt can improve the thermal stability, structural stability, electrochemical performance, and cycle life of nickel-cobalt-manganese ternary materials, while reducing side reactions and improving the overall safety and performance of the battery.

[0126] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0127] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0128] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte contains lithium difluorooxalate borate and a first additive. Based on the mass of the electrolyte, the mass percentage of lithium difluorooxalate borate is A%, the mass percentage of the first additive is B%, and 0.025≤B / A≤15, 0.2≤A+B≤8. The first additive is selected from at least one of the compounds of formula I and formula II: R1-R9 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, R is selected from hydrogen, hydroxyl, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R and R1-R9 is selected from alkenyl; R10-R21 are each independently selected from hydrogen, C1-C5 alkyl or C2-C10 alkenyl, and at least one of R10-R21 is selected from alkenyl.

2. The electrolyte according to claim 1, wherein, The first additive includes at least one of the following compounds:

3. The electrolyte according to claim 1, wherein, The mass percentage A% of lithium difluorooxalate borate satisfies 0.1≤A≤5, preferably 0.2≤A≤3.

4. The electrolyte according to claim 1, wherein, The mass percentage B% of the first additive satisfies 0.05≤B≤3, preferably 0.1≤B≤2.

5. The electrolyte according to claim 1, wherein, 0.5≤B / A≤10.

6. The electrolyte according to any one of claims 1 to 5, wherein, The electrolyte further includes a second additive, which includes at least one of vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, or fluoroethylene carbonate; based on the mass of the electrolyte, the mass percentage of the second additive is D%, 0.1≤D≤15, preferably 2≤D≤8.

7. An electrochemical device, characterized in that, Includes the electrolyte and positive electrode sheet as described in any one of claims 1 to 6, wherein the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes nickel, and the mass percentage of nickel is M% based on the total mass of the positive electrode material layer, 0.53≤100(A+B) / M≤15.

87.

8. The electrochemical device according to claim 7, wherein, The mass percentage of nickel, M%, satisfies 28.87 ≤ M ≤ 57.

1.

9. The electrochemical device according to claim 7, wherein, 0.19≤100*B / M≤8.

66.

10. The electrochemical device according to claim 7, wherein, The cathode material layer comprises lithium nickel cobalt manganese oxide. Based on the total mass of the cathode material layer, the mass percentage of cobalt in the lithium nickel cobalt manganese oxide is E%, 2.85≤E≤19, 2≤M / E≤18.

11. An electronic device comprising the electrochemical device according to any one of claims 7-10.

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