Electrolyte, secondary battery and electric device

Abstract

Provided are a secondary battery, an electrolyte and an electric device. The secondary battery comprises a positive electrode sheet, an electrolyte, a separator and a negative electrode current collector, wherein the electrolyte comprises a non-aqueous solvent, an electrolyte salt and an additive, the non-aqueous solvent comprises an ether organic solvent, the additive comprises a first additive, and the first additive comprises one or more of a phosphite ester additive or a borate additive.

Description

Electrolyte, secondary battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310833096.9, filed on July 7, 2023, entitled “Electrolyte, Secondary Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Art

[0004] As the application of lithium-ion battery technology in markets such as consumer electronics, electric vehicles, and energy storage continues to expand, the problem of insufficient lithium resources has become increasingly prominent. Sodium-based batteries, due to the Earth's high sodium abundance, have gradually attracted attention and hold a strategically important position in cost-sensitive applications such as energy storage. Due to the higher reduction potential and greater relative molecular weight of metallic sodium compared to metallic lithium, the energy density of sodium-ion secondary batteries, which operate on similar principles, is significantly lower than that of lithium-ion batteries. The larger ionic radius of sodium ions also results in greater volume expansion when they are inserted into and removed from the positive and negative electrode materials, resulting in a decrease in the battery's cyclic reversibility. These factors significantly restrict the application and promotion of sodium-ion secondary batteries. With advances in electrolyte and additive technologies, as well as surface modification technologies, the long-standing problem of sodium dendrite growth caused by uneven metal surface deposition has been significantly improved, and product safety performance is expected to be significantly enhanced, bringing high-energy-density sodium metal anodes back into the spotlight.

[0005] However, due to the extremely high chemical activity of sodium metal, which easily reacts violently with the electrolyte to form a solid electrolyte interface film, the practical application of sodium metal anode faces huge challenges.

[0006] Summary of the Invention

[0007] The present application provides an electrolyte, a secondary battery and an electrical device to improve the cycle performance and coulombic efficiency of the secondary battery.

[0008] The first aspect of the present application provides a secondary battery comprising a positive electrode plate, an electrolyte, an isolation membrane and a negative electrode current collector, wherein the electrolyte comprises a non-aqueous solvent, an electrolyte salt and an additive, the non-aqueous solvent comprises an ether organic solvent, the additive comprises a first additive, and the first additive comprises one or more of a phosphite additive and a borate additive.

[0009] By introducing the aforementioned first additive into an ether-based organic solvent electrolyte, the first additive forms a film on the positive electrode surface, effectively reducing the oxidative decomposition of the ether solvent on the positive electrode surface and reducing the shuttle of the oxidative decomposition products between the positive and negative electrodes. Furthermore, the aforementioned first additive is relatively stable to sodium metal and can preferentially oxidize and decompose on the oxide positive electrode surface to form a CEI film containing boron or phosphorus compounds, thereby inhibiting the oxidative decomposition of the ether electrolyte on the positive electrode surface while also protecting the positive electrode structure from damage, thereby improving the battery's Coulombic efficiency and cycle performance. In particular, the trivalent boron atoms in the borate ester additive have vacant P orbitals, exhibiting overall Lewis acidity. These atoms can coordinate with anions to increase the transference number of lithium / sodium ions. Furthermore, they can coordinate with oxygen atoms in ether organic solvent molecules, reducing the charge density of oxygen in the solvent molecules and increasing the solvent's oxidation potential, further resisting oxidation of the ether organic solvent by the positive electrode active material.

[0010] In any embodiment of the first aspect, the secondary battery is a sodium ion secondary battery.

[0011] In any embodiment of the first aspect, the secondary battery is a negative electrode-free sodium secondary battery. Since the negative electrode side of the negative electrode-free sodium secondary battery does not pre-set sodium metal, it effectively alleviates the problem of decreased coulombic efficiency and cycle performance caused by the vigorous reaction between sodium metal and electrolyte.

[0012] In any embodiment of the first aspect, the negative electrode current collector includes a conductive substrate and an optional conductive layer, the conductive layer being disposed on at least one side of the conductive substrate, the conductive substrate comprising any one of bare copper, aluminum foil, aluminum alloy foil, and an aluminum-based composite current collector; the conductive layer optionally comprises a conductive agent and a binder, and further optionally, the conductive agent comprises graphite, graphene, carbon fiber, carbon black, soft carbon, hard carbon, multi-walled carbon nanotubes, or single-walled carbon nanotubes. The provision of the conductive layer further facilitates the deposition of sodium ions on the negative electrode current collector by electron reduction during charging to form a sodium metal negative electrode.

[0013] In any embodiment of the first aspect, the ether organic solvent includes one or more of ethylene glycol diethyl ether (DEE), ethylene glycol dimethyl ether (DME, 1,2-dimethoxyethane), diethylene glycol dimethyl ether (DEGDME, diethylene glycol dimethyl ether), tetraethylene glycol dimethyl ether (TEGDME), triethylene glycol dimethyl ether (TRGDME), ethylene glycol ethyl formate, ethylene glycol dibutyl ether (DBE), 1,3-dioxolane (DOL), 1,4-dioxane (1,4-dioxane), tetrahydrofuran (THF) or methyltetrahydrofuran. Each of the above ether organic solvents has a stable chemical structure, good fluidity, good solubility for additives, and is more conducive to the performance of the additives.

[0014] In any embodiment of the first aspect, the ether organic solvent optionally contains ethylene glycol diethyl ether. Ethylene glycol diethyl ether has a weaker interaction with anions and a stronger oxidation resistance, thus being more conducive to the performance of the additive.

[0015] In any embodiment of the first aspect, the mass content of ethylene glycol diethyl ether in the electrolyte is optionally greater than or equal to 30%, and optionally 40%-65%. By controlling the proportion of ethylene glycol diethyl ether in the electrolyte, the battery capacity overcharge can be effectively suppressed, and the battery's stability to the high-voltage positive electrode and the battery's coulombic efficiency can be improved.

[0016] In any embodiment of the first aspect, the phosphite additive includes one or more of tris(trimethylsilyl)phosphite (TMSP), trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributyl phosphite, or triphenyl phosphite. The phosphite additive can more efficiently oxidize and decompose on the surface of the oxide positive electrode to form a CEI film containing a phosphorus compound, more reliably inhibit the oxidative decomposition of the ether organic solvent on the positive electrode surface, and also protect the structure of the positive electrode from being damaged.

[0017] In any embodiment of the first aspect, the borate ester additive includes any one or more of tris(trimethylsilyl)borate (TMSB), trimethyl borate (TMB), triethyl borate (TEB), tripropyl borate (TPB), tributyl borate (TBB), or triphenyl borate. The borate ester additive can more efficiently oxidatively decompose on the surface of the oxide positive electrode to form a CEI film containing a boron compound, more reliably inhibit the oxidative decomposition of ether organic solvents on the positive electrode surface, and also protect the structure of the positive electrode from being damaged.

[0018] In any embodiment of the first aspect, the first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate. When either of the two substances is used as the first additive, the formed CEI film is more stable and has a more prominent protective effect on the positive electrode structure.

[0019] In any embodiment of the first aspect, the mass content of the first additive in the above-mentioned electrolyte is 0.2%-5%, and can be optionally 0.2%-3%. The first additive can be used to form a sufficient CEI film to protect the positive electrode, while avoiding the increase in internal resistance caused by excessive CEI film thickness, which affects the rate performance of the battery.

[0020] In any embodiment of the first aspect, the additive further comprises a second additive, and the second additive comprises a C2-C7 fluoroalkyl ether additive. By introducing the second additive into the electrolyte, the second additive forms a film on the surface of the negative electrode, which can effectively reduce the reduction of the above-mentioned oxidative decomposition products on the surface of the negative electrode, thereby inhibiting the oxidative decomposition products from shuttling back and forth between the positive and negative electrodes. Moreover, the second additive reacts relatively weakly with sodium metal, and the inorganic SEI components such as NaF generated by the reaction are distributed and formed into a film at the negative electrode, which can effectively inhibit the above-mentioned oxidative decomposition products from shuttling back and forth between the positive and negative electrodes, thereby achieving the purpose of effectively improving the coulombic efficiency and improving the battery cycle performance.

[0021] In any embodiment of the first aspect, the C2-C7 fluoroalkyl ether additives include 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane, 1,1,2,3,3,3 -pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, 2,2,3,3-tetrafluoro-1-methoxypropane, 1,1,2,3,3,3-pentafluoropropyl ethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3,3-pentafluoropropyldifluoromethyl ether or 2,2,2-trifluoroethyl ethyl ether. The above-mentioned C2-C7 fluoroalkyl ether additives react weakly with sodium metal, and the inorganic SEI components such as NaF generated by the reaction are distributed at the negative electrode, which can more effectively inhibit the shuttle of electrolyte oxidation decomposition products between the positive and negative electrodes, thereby better achieving the effect of inhibiting capacity overcharge.

[0022] In any embodiment of the first aspect, the C2-C7 fluoroalkyl ether additive may be one or more of methyl nonafluorobutyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. This achieves both high cycle performance and high capacity retention in the secondary battery.

[0023] In any embodiment of the first aspect, the mass content of the second additive in the electrolyte is 0.2%-5%, optionally 0.2%-2%. The second additive can form a sufficient SEI film to protect the negative electrode while preventing an excessive SEI film thickness from increasing internal resistance and affecting the rate performance of the battery.

[0024] In any embodiment of the first aspect, the electrolyte salt includes one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate (CF3COONa), sodium trifluoromethanesulfonate (CF3NaO3S, NaOTf) and sodium tetraphenylborate (NaBPh4). Sodium trifluoromethanesulfonate has a high solubility in ether organic solvents at low temperatures, and the efficiency of sodium metal deposition and stripping is high, so that the battery has good cycle performance at low temperatures, such as below -30°C. At room temperature, the side reaction between sodium trifluoromethanesulfonate and the sodium metal negative electrode is intensified, and the overall cycle performance of the battery deteriorates. The use of other electrolyte salts in the above electrolyte can improve the cycle performance of the secondary battery at room temperature.

[0025] In any embodiment of the first aspect, the electrolyte includes a first sodium salt and sodium trifluoromethanesulfonate, and the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, or sodium hexafluoroarsenate. This can improve both the low-temperature cycling performance and the room-temperature cycling performance of a secondary battery having the electrolyte.

[0026] In any embodiment of the first aspect, optionally, the mass content of sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%.

[0027] When the electrolyte of the present application includes sodium trifluoromethanesulfonate, sodium trifluoromethanesulfonate (NaOTf) has a high solubility in diethylene glycol dimethyl ether at low temperatures, in order to further improve the ionic conductivity of the electrolyte at low temperatures. In any embodiment of the first aspect, the ether organic solvent optionally contains diethylene glycol dimethyl ether, and the mass content of diethylene glycol dimethyl ether in the further electrolyte is optionally greater than or equal to 20%, optionally 25%-40%. Of course, if the electrolyte does not include sodium trifluoromethanesulfonate, the ether organic solvent may also contain diethylene glycol dimethyl ether.

[0028] In any embodiment of the first aspect, the mass content of sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%; thereby better improving the low-temperature cycle performance and room-temperature cycle performance of the secondary battery.

[0029] In any embodiment of the first aspect, optionally, the mass ratio of sodium trifluoromethanesulfonate to diethylene glycol dimethyl ether is denoted as X, where 0.05 ≤ X ≤ 0.2, and optionally 0.1 ≤ X ≤ 0.13, to further improve the ionic conductivity of the electrolyte at low temperatures.

[0030] In any embodiment of the first aspect, the positive electrode active material of the positive electrode sheet is a layered metal oxide. Optionally, the positive electrode active material includes one or more oxides with the chemical formula Na x Mn a Q b O 2-c-d F c where 0.5 < x ≤ 1, 0 < a, 0 < b, 0 ≤ c ≤ 0.2, -0.1 ≤ d ≤ 0.1, and Q includes one or more of the following elements: Li, B, Mg, Al, Si, K, Ca, Ti, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

[0031] A second aspect of the present application provides an electrolyte, including a non-aqueous solvent, an electrolyte salt, and an additive. Among them, the non-aqueous solvent includes an ether organic solvent, and the additive includes a first additive, and the first additive includes one or more of phosphite additives or borate additives.

[0032] Taking the positive electrode active material as an oxide as an example, the technical effects of the above electrolyte are described. By introducing the above first additive into the electrolyte of the ether organic solvent system, the first additive forms a film on the positive electrode surface, which can effectively reduce the oxidative decomposition of the ether solvent on the positive electrode surface and reduce the shuttling of the products generated by the oxidative decomposition between the positive and negative electrodes. And the above first additive is relatively stable to sodium metal and can preferentially oxidize and decompose on the surface of the oxide positive electrode to generate a CEI film containing boron or phosphorus compounds, inhibiting the oxidative decomposition of the ether electrolyte on the positive electrode surface and protecting the structure of the positive electrode from being damaged, thereby improving the Coulomb efficiency and cycle performance of the battery. Especially for the borate additives, the +3-valent boron atoms have empty P orbitals, which overall show Lewis acidity, can coordinate with anions to increase the migration number of sodium ions, and can also coordinate with oxygen atoms in the ether organic solvent molecules to reduce the charge density of oxygen in the solvent molecules and increase the solvent oxidation potential, further resisting the oxidation of the ether organic solvent by the positive electrode oxide.

[0033] In any embodiment of the second aspect, the ether organic solvent includes one or more of ethylene glycol diethyl ether (DEE), ethylene glycol dimethyl ether (DME, 1,2-dimethoxyethane), diethylene glycol dimethyl ether (DEGDME, diethylene glycol dimethyl ether), tetraethylene glycol dimethyl ether (TEGDME), triethylene glycol dimethyl ether (TRGDME), ethylene glycol ethyl formate, ethylene glycol dibutyl ether (DBE), 1,3-dioxolane (DOL), 1,4-dioxane (1,4-dioxane), tetrahydrofuran (THF), or methyltetrahydrofuran. Each of the above ether organic solvents has a stable chemical structure, good fluidity, and good solubility for additives, which is more conducive to the performance of the additives.

[0034] In any embodiment of the second aspect, the ether organic solvent optionally contains ethylene glycol diethyl ether. Ethylene glycol diethyl ether has a weaker interaction with anions and a stronger oxidation resistance, and is therefore more conducive to the performance of the additive.

[0035] In any embodiment of the second aspect, the mass content of ethylene glycol diethyl ether in the electrolyte is optionally greater than or equal to 30%, and optionally 40%-65%. By controlling the proportion of ethylene glycol diethyl ether in the electrolyte, the battery capacity overcharge can be effectively suppressed, and the battery's stability to the high-voltage positive electrode and the battery's coulombic efficiency can be improved.

[0036] In any embodiment of the second aspect, the phosphite additive includes one or more of tris(trimethylsilyl)phosphite (TMSP), trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributyl phosphite, or triphenyl phosphite. The phosphite additive can more efficiently oxidize and decompose on the surface of the oxide positive electrode to form a CEI film containing a phosphorus compound, more reliably inhibit the oxidative decomposition of the ether organic solvent on the positive electrode surface, and also protect the structure of the positive electrode from being damaged.

[0037] In any embodiment of the second aspect, the borate ester additive includes any one or more of tris(trimethylsilyl)borate (TMSB), trimethyl borate (TMB), triethyl borate (TEB), tripropyl borate (TPB), tributyl borate (TBB), or triphenyl borate. The borate ester additive can more efficiently oxidatively decompose on the surface of the oxide positive electrode to form a CEI film containing a boron compound, more reliably inhibit the oxidative decomposition of ether organic solvents on the positive electrode surface, and also protect the structure of the positive electrode from being damaged.

[0038] In any embodiment of the second aspect, the first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate. When either of the two substances is used as the first additive, the formed CEI film is more stable and has a more prominent protective effect on the positive electrode structure.

[0039] In any embodiment of the second aspect, the mass content of the first additive in the above-mentioned electrolyte is 0.2%-5%, and can be optionally 0.2%-3%. The first additive can be used to form a sufficient CEI film to protect the positive electrode, while avoiding the increase in internal resistance caused by excessive CEI film thickness, which affects the rate performance of the battery.

[0040] In any embodiment of the second aspect, the additive further comprises a second additive, and the second additive comprises a C2-C7 fluoroalkyl ether additive. By introducing the second additive into the electrolyte, the second additive forms a film on the surface of the negative electrode, which can effectively reduce the reduction of the above-mentioned oxidative decomposition products on the surface of the negative electrode, thereby inhibiting the shuttle of the oxidative decomposition products between the positive and negative electrodes. Moreover, the second additive reacts relatively weakly with sodium metal, and the inorganic SEI components such as NaF generated by the reaction are distributed at the negative electrode, which can effectively inhibit the shuttle of the above-mentioned oxidative decomposition products between the positive and negative electrodes, thereby achieving the purpose of effectively improving the coulombic efficiency and improving the battery cycle performance.

[0041] In any embodiment of the second aspect, the C2-C7 fluoroalkyl ether additives include 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane, 1,1,2,3,3,3 -pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, 2,2,3,3-tetrafluoro-1-methoxypropane, 1,1,2,3,3,3-pentafluoropropyl ethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3,3-pentafluoropropyldifluoromethyl ether or 2,2,2-trifluoroethyl ethyl ether. The above-mentioned C2-C7 fluoroalkyl ether additives react weakly with sodium metal, and the inorganic SEI components such as NaF generated by the reaction are distributed at the negative electrode, which can more effectively inhibit the shuttle of electrolyte oxidation decomposition products between the positive and negative electrodes, thereby better achieving the effect of inhibiting capacity overcharge.

[0042] In any embodiment of the second aspect, the C2-C7 fluoroalkyl ether additive may be one or more of methyl nonafluorobutyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. This achieves both high cycle performance and high capacity retention in the secondary battery.

[0043] In any embodiment of the second aspect, the mass content of the second additive in the electrolyte is 0.2%-5%, and optionally 0.2%-2%. This allows the second additive to form a sufficient SEI film to protect the negative electrode while preventing an excessively thick SEI film from increasing internal resistance and affecting the battery's rate performance.

[0044] In any embodiment of the second aspect, the electrolyte salt includes one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate (CF3COONa), sodium trifluoromethanesulfonate (CF3NaO3S, NaOTf) and sodium tetraphenylborate (NaBPh4). Sodium trifluoromethanesulfonate has a high solubility in ether organic solvents at low temperatures, and the sodium metal deposition and stripping efficiency is high, so that the battery has good cycle performance at low temperatures, such as below -30°C. At room temperature, the side reaction between sodium trifluoromethanesulfonate and the sodium metal negative electrode is intensified, and the overall cycle performance of the battery deteriorates. The use of other electrolyte salts in the above electrolyte can improve the cycle performance of the secondary battery at room temperature.

[0045] In any embodiment of the second aspect, the electrolyte includes a first sodium salt and sodium trifluoromethanesulfonate, and the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, or sodium hexafluoroarsenate. This can improve both the low-temperature cycling performance and the room-temperature cycling performance of a secondary battery having the electrolyte.

[0046] In any embodiment of the second aspect, optionally, the mass content of sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%.

[0047] When the electrolyte of the present application includes sodium trifluoromethanesulfonate, sodium trifluoromethanesulfonate (NaOTf) has a high solubility in diethylene glycol dimethyl ether at low temperatures, in order to further improve the ionic conductivity of the electrolyte at low temperatures. In any embodiment of the first aspect, the ether organic solvent optionally contains diethylene glycol dimethyl ether, and the mass content of diethylene glycol dimethyl ether in the further electrolyte is optionally greater than or equal to 20%, optionally 25%-40%. Of course, if the electrolyte does not include sodium trifluoromethanesulfonate, the ether organic solvent may also contain diethylene glycol dimethyl ether.

[0048] In any embodiment of the second aspect, the mass content of sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%; thereby better improving the low-temperature cycle performance and normal temperature cycle performance of the secondary battery.

[0049] In any embodiment of the second aspect, optionally, the mass ratio of sodium trifluoromethanesulfonate to diethylene glycol dimethyl ether is denoted as X, 0.05≤X≤0.2, and optionally 0.1≤X≤0.13, to further improve the ionic conductivity of the electrolyte at low temperatures.

[0050] A third aspect of the present application provides an electrical device, comprising a secondary battery, wherein the secondary battery is selected from any one of the secondary batteries of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0052] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0053] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0054] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0055] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0056] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0057] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0058] In the drawings, the drawings are not drawn to scale.

[0059] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0060] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0061] Below, the embodiments of the negative electrode sheet, secondary battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0062] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0064] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0065] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0066] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0067] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0068] [Secondary battery]

[0069] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged to activate the active materials after discharge and continue to be used.

[0070] Typically, a secondary battery includes a positive electrode sheet, a negative electrode current collector (or negative electrode sheet), a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions or sodium ions) are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct active ions.

[0071] The coulombic efficiency of secondary batteries decreases and the cycle performance is insufficient. To solve the above problems, the first embodiment of the present application provides a secondary battery, including a positive electrode plate, an electrolyte, a separator, and a negative electrode current collector, wherein the electrolyte includes a non-aqueous solvent, an electrolyte salt, and an additive, the non-aqueous solvent includes an ether organic solvent, and the additive includes a first additive, and the first additive includes one or more of a phosphite additive or a borate additive.

[0072] By introducing the above-mentioned first additive into the electrolyte of the ether organic solvent system, the first additive forms a film on the positive electrode surface, effectively reducing the oxidative decomposition of the ether electrolyte on the positive electrode surface and reducing the shuttling of the oxidative decomposition products between the positive and negative electrodes. Furthermore, the above-mentioned first additive is relatively stable to sodium metal and can preferentially oxidize and decompose on the surface of the oxide positive electrode to form a CEI film containing boron or phosphorus compounds, thereby inhibiting the oxidative decomposition of the ether electrolyte on the positive electrode surface while also protecting the positive electrode structure from damage, thereby improving the coulombic efficiency and cycle performance of the battery. In particular, the positive trivalent boron atoms in the borate ester additive have empty P orbitals and exhibit overall Lewis acidity. They can coordinate with anions to increase the transference number of lithium / sodium ions. They can also coordinate with oxygen atoms in ether organic solvent molecules, reducing the charge density of oxygen in the solvent molecules, increasing the solvent oxidation potential, and further resisting oxidation of the ether electrolyte by the positive electrode oxide.

[0073] The secondary battery of the present application can be a lithium ion secondary battery or a sodium ion secondary battery. In some embodiments, the secondary battery is a sodium ion secondary battery.

[0074] The sodium-ion secondary battery can be a conventional sodium-ion secondary battery with a negative electrode or a sodium-ion secondary battery without a negative electrode. The negative electrode of a conventional sodium-ion secondary battery with a negative electrode can be a conventional sodium metal negative electrode. To further achieve higher cell energy density, a negative-electrode-free sodium secondary battery has also been developed, which is achieved by in-situ deposition of the positive electrode material onto the negative electrode current collector through sodium removal.

[0075] A negative electrode-free sodium secondary battery refers to a battery in which a negative electrode active material layer is not actively provided on the negative electrode side during the battery manufacturing process. For example, a sodium metal or carbonaceous active material layer is not provided on the negative electrode through a coating or deposition process to form a negative electrode active material layer during the battery manufacturing process. During the first charge, sodium ions on the negative electrode side gain electrons, and metallic sodium is deposited on the current collector surface to form a sodium metal phase. During discharge, the metallic sodium can be converted into sodium ions and returned to the positive electrode, achieving cyclic charge and discharge. Compared to other sodium secondary batteries, negative electrode-free sodium secondary batteries can achieve higher energy density due to the lack of a negative electrode active material layer.

[0076] In some embodiments, in order to improve battery performance, the negative electrode side of the negative electrode-free sodium secondary battery can be provided with some conventional substances that can be used as negative electrode active materials, such as carbonaceous materials, metal oxides, alloys, etc. Although these materials have a certain capacity, due to the small amount of these materials, they are not used as the main negative electrode active material in the battery (when a carbonaceous material is used, the carbonaceous material can be considered as a conductive material), and no negative electrode active material layer that plays a role in sodium insertion (such as forming a conductive layer) is formed. Therefore, the sodium secondary battery constructed in this way can still be regarded as a negative electrode-free sodium secondary battery.

[0077] In some embodiments, the CB value of the negative electrode-free sodium secondary battery is less than or equal to 0.1. The CB value is the capacity per unit area of ​​the negative electrode plate in the secondary battery divided by the capacity per unit area of ​​the positive electrode plate. Because negative electrode-free batteries contain no or only a small amount of negative electrode active material, the capacity per unit area of ​​the negative electrode plate is relatively small, and the CB value of the secondary battery is less than or equal to 0.1.

[0078] In some embodiments of the present application, the secondary battery may be a negative electrode-free sodium metal secondary battery.

[0079] [Negative electrode current collector]

[0080] In some embodiments of the present application, the negative electrode current collector includes a conductive substrate and an optional conductive layer, wherein the conductive layer is provided on at least one side of the conductive substrate. In some embodiments, the conductive layer is provided on one surface or two opposing surfaces of the conductive substrate. The term "optional conductive layer" means that the conductive layer may or may not be provided.

[0081] Using a negative electrode current collector as the negative electrode for a negative electrode-free sodium secondary battery requires that sodium metal be deposited on the negative electrode current collector after the initial charge to form a negative electrode plate. Therefore, the post-generation of sodium metal can more effectively alleviate the problems caused by the reaction between sodium metal and the electrolyte.

[0082] In some embodiments, the conductive substrate comprises any one of bare copper, aluminum foil, aluminum alloy foil, and an aluminum-based composite current collector. The aluminum-based composite current collector comprises a polymer base film and aluminum foil and / or aluminum alloy foil formed on both sides of the polymer base film. Specifically, the aluminum-based composite current collector has a "sandwich" structure, with the polymer base film located in the middle and aluminum foil provided on both sides, or aluminum alloy foil provided on both sides. Alternatively, the polymer base film may have aluminum foil provided on one side and aluminum alloy foil provided on the other side. The polymer base film comprises any one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, and polycarbonate. The aluminum-based composite current collector has better ductility, which is beneficial for maintaining the integrity of the electrode during the sodium metal deposition / stripping process.

[0083] In some embodiments, the conductive layer includes a conductive agent and a binder. Further optionally, the conductive agent includes any one or more of conductive carbon, conductive polymer, and conductive ceramic material. The conductive carbon includes but is not limited to graphite, graphene, carbon fiber, carbon black, carbon dots, soft carbon, hard carbon, multi-walled carbon nanotubes, or single-walled carbon nanotubes.

[0084] In some embodiments, the conductive layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0085] In some embodiments, the negative electrode current collector can be prepared by the following method: the components for preparing the negative electrode current collector, such as the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a conductive slurry; the conductive slurry is coated on a substrate, and after drying, cold pressing and other processes, the negative electrode current collector can be obtained.

[0086] [Electrolyte]

[0087] Some embodiments of the present application provide an electrolyte solution including a non-aqueous solvent, an electrolyte salt, and an additive, wherein the non-aqueous solvent includes an ether organic solvent, the additive includes a first additive, and the first additive includes one or more of a phosphite additive or a borate additive.

[0088] When the secondary battery of some embodiments of the present application is a sodium ion secondary battery, since sodium metal has extremely high chemical activity and is prone to violent reaction with the electrolyte to produce a solid electrolyte interface film, the practical application of the sodium metal negative electrode faces huge challenges. For example, conventional electrolytes including carbonate additives such as FEC, DFEC, and VC will preferentially react with the sodium metal negative electrode during charging, making it difficult to form an effective protective layer on the positive electrode surface, resulting in a decrease in battery cycle stability. Conventional ether electrolytes and sodium salts can achieve highly reversible sodium metal deposition / stripping efficiency. However, the ether electrolyte itself has a low upper voltage window limit, especially when matched with a layered oxide positive electrode with a high ratio of transition metal elements, the catalytic effect of the surface transition metal elements further exacerbates the decomposition of the ether electrolyte. On the other hand, during the charging process, the products produced by the oxidative decomposition of the ether electrolyte (mainly the solvent therein) at the positive electrode shuttle to the sodium metal negative electrode, and then undergo a reduction reaction and return to the positive electrode to be oxidized. The back-and-forth redox shuttle formed in ether electrolytes greatly reduces the energy conversion efficiency of sodium-ion secondary batteries, thereby affecting the cycle performance of sodium-ion secondary batteries; and studies have found that the oxidative decomposition of ether electrolytes at the positive electrode will also cause the actual sodium-ion secondary charging capacity of the battery to be greater than the design capacity of the battery, resulting in capacity overcharge, which is reflected in the sodium-ion secondary battery as a decrease in the coulombic efficiency of the secondary battery.

[0089] By introducing the aforementioned first additive into an ether organic solvent system, the first additive forms a film on the positive electrode surface, effectively reducing the oxidative decomposition of the ether electrolyte on the positive electrode surface and reducing the shuttle of oxidative decomposition products between the positive and negative electrodes. Furthermore, the first additive is relatively stable to sodium metal and can preferentially oxidize and decompose on the oxide positive electrode surface to form a CEI film containing boron or phosphorus compounds. This inhibits the oxidative decomposition of the ether electrolyte on the positive electrode surface while also protecting the positive electrode structure from damage, thereby improving the battery's Coulombic efficiency and cycle performance. In particular, the trivalent boron atoms in the borate ester additive have vacant P orbitals, exhibiting overall Lewis acidity. This allows them to coordinate with anions to increase the transference number of lithium / sodium ions. They can also coordinate with oxygen atoms in ether organic solvent molecules, reducing the charge density of oxygen in the solvent molecules and increasing the solvent's oxidation potential, further resisting oxidation of the ether electrolyte by the positive electrode oxide.

[0090] The ether organic solvent of the present application can be selected from ether organic solvents commonly used in electrolytes. In some embodiments, the ether organic solvent includes one or more of ethylene glycol diethyl ether (DEE), ethylene glycol dimethyl ether (DME, 1,2-dimethoxyethane), diethylene glycol dimethyl ether (DEGDME, diethylene glycol dimethyl ether), tetraethylene glycol dimethyl ether (TEGDME), triethylene glycol dimethyl ether (TRGDME), ethylene glycol ethyl formate, ethylene glycol dibutyl ether (DBE), 1,3-dioxolane (DOL), 1,4-dioxane (1,4-dioxane), tetrahydrofuran (THF) or methyltetrahydrofuran. Each of the above ether organic solvents has a stable chemical structure, good fluidity, and good solubility for additives.

[0091] The antioxidant properties of the solvent in the electrolyte are determined by the interaction between the solvent molecules and the anions. Among the above-mentioned ether organic solvents, ethylene glycol diethyl ether has a weaker interaction with the anions and a stronger oxidation resistance. In some embodiments, the ether organic solvent optionally contains ethylene glycol diethyl ether. By controlling the proportion of ethylene glycol diethyl ether in the electrolyte, the oxidation resistance of the electrolyte to the positive electrode active material can be further effectively improved, and the capacity overcharge during battery charging can be more effectively suppressed, thereby improving the stability of the battery to the high-voltage positive electrode and the coulombic efficiency of the battery. Therefore, the mass content of ethylene glycol diethyl ether in the electrolyte is optionally greater than or equal to 30%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, and can be optionally 40%-65%.

[0092] The phosphite additive used in the present application can be a conventional phosphite additive for electrolytes. In some embodiments, the phosphite additive includes one or more of tris(trimethylsilyl)phosphite (TMSP), trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributyl phosphite, or triphenyl phosphite. The phosphite additive can more efficiently oxidize and decompose on the surface of the oxide positive electrode to form a CEI film containing phosphorus compounds, more reliably inhibit the oxidative decomposition of the ether electrolyte on the positive electrode surface, and also protect the positive electrode structure from being damaged.

[0093] The borate ester additive used in this application can be a conventional borate ester additive for electrolytes. In some embodiments, the borate ester additive includes any one or more of tris(trimethylsilyl)borate (TMSB), trimethyl borate (TMB), triethyl borate (TEB), tripropyl borate (TPB), tributyl borate (TBB), or triphenyl borate. These borate ester additives can more efficiently oxidize and decompose on the surface of the oxide positive electrode to form a CEI film containing boron compounds, more reliably inhibiting the oxidative decomposition of the ether electrolyte on the positive electrode surface while also protecting the positive electrode structure from damage.

[0094] In some embodiments, the first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate. When either of the two substances is used as the first additive, the formed CEI film is more stable and has a more prominent protective effect on the positive electrode structure.

[0095] In some embodiments, the mass content of the first additive in the above-mentioned electrolyte is 0.2%-5%, such as 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, and can be optionally 0.2%-3%. The first additive can be used to form a sufficient CEI film to protect the positive electrode, and the internal resistance caused by the excessive thickness of the CEI film is avoided, which affects the overcharge performance of the battery.

[0096] When the electrolyte of the present application is applied to a sodium metal battery system, sodium metal has extremely high chemical activity and tends to react violently with the electrolyte on the negative electrode side to produce a solid electrolyte interface film, thereby reducing the efficiency and cycle life of the battery; and this interface film is not stable. During the cycle process, as sodium metal is deposited and peeled off, this interface film is constantly broken and rebuilt, causing the internal resistance of the battery to continue to increase.

[0097] In order to solve the above problems, in some embodiments, the above additives also include a second additive, and the second additive includes a C2-C7 fluoroalkyl ether additive. By introducing the second additive into the electrolyte, the second additive forms a film on the surface of the negative electrode, which can effectively reduce the reduction of the product produced by the oxidation and decomposition of the ether electrolyte on the surface of the positive electrode on the surface of the negative electrode, thereby inhibiting the product from shuttling back and forth between the positive and negative electrodes. Moreover, the second additive reacts relatively weakly with sodium metal, and the inorganic SEI components such as NaF generated by the reaction are distributed and formed into a film at the negative electrode. The SEI film formed can effectively inhibit the products of the oxidation and decomposition of the ether electrolyte from shuttling back and forth between the positive and negative electrodes, thereby achieving a more effective effect of inhibiting capacity overcharge and further improving the coulombic efficiency of the battery, while also further improving the battery cycle performance.

[0098] In some embodiments, the C2-C7 fluoroalkyl ether additives used in the present application include but are not limited to 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane, 1,1,2,3,3 ,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 2,2,3,3-tetrafluoro-1-methoxypropane, 1,1,2,3,3,3-pentafluoropropyl ethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether or 2,2,2-trifluoroethyl ethyl ether.

[0099] The above-mentioned C2-C7 fluoroalkyl ether additives react weakly with sodium metal, and the inorganic SEI components such as NaF generated by the reaction are distributed at the negative electrode, which can effectively inhibit the oxidative decomposition products of the ether electrolyte from shuttling back and forth between the positive and negative electrodes, thereby better achieving the effect of inhibiting capacity overcharge and further improving the coulombic efficiency of the battery.

[0100] One of the main functions of the above-mentioned C2-C7 fluoroalkyl ether additives is to form an SEI film at the negative electrode. Therefore, the higher the film-forming activity, the more conducive it is to the formation of the SEI film. However, the higher the film-forming activity, the greater the consumption of the negative electrode capacity. Therefore, in order to take into account the high cycle performance and high capacity retention characteristics of the secondary battery, in some embodiments, the above-mentioned C2-C7 fluoroalkyl ether additives can be selected from one or more of methyl nonafluorobutyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0101] The amount of the second additive in the electrolyte can refer to conventional techniques. In some embodiments, the weight content of the second additive in the electrolyte is 0.2%-5%, such as 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, and can be optionally 0.2%-2%. The second additive can form a sufficient SEI film to protect the negative electrode while preventing the increase in internal resistance caused by excessive SEI film thickness, which would affect the battery's overcharge performance.

[0102] The electrolyte salt used in the present application can be selected from electrolyte salts commonly used in conventional secondary batteries. For example, in some embodiments, when the secondary battery is a lithium ion secondary battery, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0103] In some embodiments, when the electrolyte is used in a sodium ion secondary battery, the electrolyte salt includes one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate (CF3COONa), sodium trifluoromethanesulfonate (CF3NaO3S, NaOTf) and sodium tetraphenylborate (NaBPh4).

[0104] Among them, sodium trifluoromethanesulfonate has high solubility in ether organic solvents at low temperatures, and the sodium metal deposition and stripping efficiency is high, which makes the battery have good cycle performance at low temperatures (such as below -30°C). At room temperature, the side reaction between sodium trifluoromethanesulfonate and the sodium metal negative electrode is intensified, and the overall cycle performance of the battery deteriorates. Using other electrolyte salts in the above electrolytes can improve the cycle performance of secondary batteries at room temperature.

[0105] In some embodiments, the electrolyte optionally includes a first sodium salt and sodium trifluoromethanesulfonate, wherein the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, or sodium hexafluoroarsenate. This can improve both the low-temperature cycling performance and the normal-temperature cycling performance of a secondary battery having this electrolyte.

[0106] In some embodiments, optionally, the mass content of sodium trifluoromethanesulfonate in the electrolyte is 2%-10%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, optionally 2%-5%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, such as 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, optionally 5%-30%.

[0107] When the electrolyte of the present application includes sodium trifluoromethanesulfonate, sodium trifluoromethanesulfonate (NaOTf) has a high solubility in diethylene glycol dimethyl ether at low temperatures. In order to further improve the ionic conductivity of the electrolyte at low temperatures, in some embodiments, the ether organic solvent optionally contains diethylene glycol dimethyl ether, and the mass content of diethylene glycol dimethyl ether in the electrolyte is optionally greater than or equal to 20%, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and can be optionally 25%-40%. Of course, if the electrolyte does not include sodium trifluoromethanesulfonate, the ether organic solvent may also contain diethylene glycol dimethyl ether.

[0108] In some embodiments, the mass content of sodium trifluoromethanesulfonate in the electrolyte is 2%-10%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, such as 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, optionally 5%-30%; thereby better improving the low temperature cycle performance and normal temperature cycle performance of the secondary battery.

[0109] In some embodiments, to further improve the ionic conductivity of the electrolyte at low temperatures, the mass ratio of sodium trifluoromethanesulfonate to diethylene glycol dimethyl ether is optionally denoted as X, where 0.05 ≤ X ≤ 0.2. For example, the minimum value of X may be 0.05, 0.08, or 0.1, and the maximum value of X may be 0.12, 0.125, 0.13, 0.15, 0.17, or 0.2, and 0.1 ≤ X ≤ 0.13 may be selected. This improves the low-temperature cycling performance of the battery.

[0110] [Positive electrode]

[0111] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0112] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0113] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] When the secondary battery is a sodium ion secondary battery, the positive electrode active material of the positive electrode sheet is a layered metal oxide. In some embodiments, the above positive electrode active material includes one or more selected from the group consisting of oxides with the chemical formula Na x Mn a Q b O 2-c-d F c where 0.5 < x ≤ 1, 0 < a, 0 < b, 0 ≤ c ≤ 0.2, -0.1 ≤ d ≤ 0.1, and Q includes one or more of the following elements: Li, B, Mg, Al, Si, K, Ca, Ti, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi, such as NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0115] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0116] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0118] [Isolation film]

[0119] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0120] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0121] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0122] In some embodiments, the secondary battery includes a secondary battery cell, a battery module, or a battery pack, and may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0123] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0124] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery cell 5 with a square structure as an example.

[0125] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0126] In some embodiments, secondary battery cells may be assembled into a battery module. The battery module may contain one or more secondary battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0127] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary battery cells 5 may be secured together using fasteners.

[0128] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary battery cells 5 are accommodated in the accommodation space.

[0129] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0130] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0131] In addition, the present application also provides an electrical device, which includes the sodium ion secondary battery provided by the present application. The sodium ion secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0132] As the electrical device, a specific form of the secondary battery can be selected according to its usage requirements, such as a secondary battery cell, a battery module or a battery pack.

[0133] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0134] [Example]

[0135] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0136] Example 1

[0137] 1) Electrolyte

[0138] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm),

[0139] According to the electrolyte formula of Example 1, sodium trifluoromethanesulfonate (NaTOf) and sodium hexafluorophosphate (NaPF6) were dissolved in diethylene glycol dimethyl ether and ethylene glycol diethyl ether (DEE), and tris(trimethylsilyl) phosphite and methyl nonafluorobutyl ether were added and stirred evenly to prepare an electrolyte.

[0140] 2) Preparation of positive electrode sheet

[0141] The positive electrode active material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, binder polyvinylidene fluoride (PVDF), conductive agent conductive carbon black (Super-P) in N-methylpyrrolidone (NMP) solvent according to the mass ratio of 96:2:2 are mixed evenly to prepare positive electrode slurry, and the positive electrode active material is coated on the surface of aluminum foil by extrusion coating machine according to the unit area mass requirement and dried, and then the coated electrode is pressed by cold press at 2.5g / cm 3 The designed compaction is cold pressed to prepare the final positive electrode sheet.

[0142] 3) Preparation of negative electrode current collector

[0143] Single-walled carbon nanotubes and sodium alginate were added to deionized water and stirred to form a uniform slurry. The slurry was coated on aluminum foil and dried to form a conductive layer. The negative electrode current collector without a negative electrode structure was cut to obtain a conductive layer with a surface density of 25 g / m 2 .

[0144] 4) Isolation film

[0145] Polypropylene film is used as the isolation film.

[0146] 5) Preparation of batteries

[0147] The positive electrode sheet, separator, and negative electrode current collector are wound or stacked in sequence, with the separator positioned between the positive electrode sheet and the negative electrode current collector to provide insulation. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove water. The electrolyte is then injected and sealed to produce an uncharged battery. The uncharged battery then undergoes a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the sodium secondary battery product of Example 1.

[0148] The electrolyte compositions of Examples 2 to 30 and Comparative Examples 1 to 3 are shown in Table 1, and the rest are the same as in Example 1.

[0149]

[0150]

[0151]

[0152]

[0153]

[0154] The test results are recorded in Table 2.

[0155] Table 2

[0156] According to the data comparison of the embodiment and comparative examples 1 to 3, the combination of the first additive, the second additive and the ether organic solvent in the electrolyte of the present application has a significant effect on improving the low-temperature cycle performance, room-temperature cycle performance and coulombic efficiency of the sodium battery (the higher the coulombic efficiency, the more significant the improvement in capacity overcharge).

[0157] According to the data comparison of Examples 1 to 5, it can be seen that the change in the amount of the first additive has a direct impact on the low-temperature cycle performance and room-temperature cycle performance of the battery, but the coulombic efficiency does not change substantially. Whether the amount of the first additive is too low (Example 5) or the amount of the first additive is too high (Example 3), it will lead to a decrease in low-temperature cycle performance and room-temperature cycle performance. This may be because when the amount of the first additive is too low, the CEI film formed is insufficient, the protection effect on the positive electrode is insufficient, and thus the cycle performance is affected; when the amount of the first additive is too high, the CEI film formed is too thick, resulting in an increase in the internal resistance of the positive electrode, thereby affecting the cycle performance.

[0158] According to the data comparison of Example 1 and Examples 6 to 8, when tris(trimethylsilyl)phosphite or tris(trimethylsilyl)borate is selected as the first additive, the cycle performance and coulombic efficiency of the battery are particularly outstanding.

[0159] Comparison of the data from Examples 1 and 9 to 12 reveals that varying the dosage of the second additive affects both low-temperature cycling performance, room-temperature cycling performance, and coulombic efficiency. This suggests that the second additive affects both the cycling performance and overcharge performance of the battery. In particular, with respect to overcharge performance, within a certain dosage range, increasing the dosage of the second additive increases the coulombic efficiency of the battery, demonstrating a more pronounced improvement in overcharge performance. However, when the dosage of the second additive increases from 2% to 5%, while the coulombic efficiency remains above 90%, it also shows a downward trend. Further increasing to 7% further decreases the coulombic efficiency.

[0160] According to the data comparison of Examples 1, 13 to 16, it can be seen that when different fluoroalkyl additives are selected as the second additive, the cycle performance and coulombic efficiency of the battery are different, but all play a role in improving the cycle performance and coulombic efficiency.

[0161] According to the data comparison of Example 1 and Examples 17 to 21, it can be seen that, first, the use of sodium trifluoromethanesulfonate is beneficial to improving the low-temperature cycle performance of the battery; secondly, sodium trifluoromethanesulfonate has different effects on the low-temperature cycle performance and normal temperature cycle performance of the battery. Within a certain dosage range (for example, less than 5%), as the amount of sodium trifluoromethanesulfonate increases, the low-temperature cycle performance is significantly improved, but the normal temperature cycle performance decreases slightly; as the amount of sodium trifluoromethanesulfonate further increases (for example, increases to 10%), the low-temperature cycle performance does not improve, but the normal temperature cycle performance decreases significantly. This may be because sodium trifluoromethanesulfonate has a high solubility in ether organic solvents at low temperatures, and the sodium metal deposition and stripping efficiency is high, which makes the battery have better cycle performance at low temperatures, such as (below -30°C). At room temperature, the reaction between sodium trifluoromethanesulfonate and the sodium metal negative electrode intensifies, and the overall cycle performance of the battery deteriorates.

[0162] In addition, from the data comparison of Examples 1 and 17 to 19, it can be seen that when the mass ratio of sodium trifluoromethanesulfonate to diethylene glycol dimethyl ether increases within a certain range, the low-temperature cycle performance of the battery can also be improved. Moreover, according to the data comparison of Examples 22, 26 and 29 with other examples, the amount of diethylene glycol dimethyl ether has a key influence on the low-temperature cycle performance of the battery. This is probably because diethylene glycol dimethyl ether is a key solvent for dissolving sodium trifluoromethanesulfonate. When there is enough diethylene glycol dimethyl ether to fully dissolve sodium trifluoromethanesulfonate, the improvement effect of sodium trifluoromethanesulfonate on the low-temperature cycle performance of the battery can be fully exerted. According to the data comparison of Examples 25 and 27 with other examples, when diethylene glycol dimethyl ether is not contained or its content is too little, the battery storage efficiency will be lower, and the increase of electrolyte reaction products will accelerate battery attenuation, causing both low-temperature cycle performance and room-temperature cycle performance to deteriorate.

[0163] According to the data comparison of Example 1, Example 23 and Example 24, it can be seen that the composition of the sodium salt has a certain influence on the cycle performance and coulombic efficiency of the battery, but can play an improving role.

[0164] According to the data comparison of Example 28 with other examples and comparative examples, it can be seen that the second additive has a significant effect on the cycle performance and coulombic efficiency of the battery. When the second additive is not used, relying on the combination of the first additive and other components, the cycle performance and coulombic efficiency of Example 28 are significantly improved relative to the corresponding performance of Comparative Examples 2 and 3; when the second additive is continued to be added, the low-temperature cycle, high-temperature cycle and coulombic efficiency of Example 1 are greatly improved relative to Example 28.

[0165] In addition, it should be noted that the coulombic efficiency of Examples 28 and 29 is not as good as that of Comparative Example 1 because Comparative Example 1 uses the second additive, which precisely illustrates that the second additive can better improve the effect of capacity overcharge; however, the cycle performance of Examples 28 and 29 is still good, which illustrates that the first additive can better improve the effect of cycle performance (it also has the effect of improving coulombic efficiency, but the improvement to the cycle is more obvious).

[0166] According to the data comparison of Example 1, Example 25 and Example 30, it can be seen that when an equal amount of diethylene glycol dimethyl ether or ethylene glycol dimethyl ether is used to replace ethylene glycol diethyl ether, since the oxidation resistance of these two substances is not as good as ethylene glycol diethyl ether, the cycle performance and coulombic efficiency of Example 25 and Example 30 are not as good as Example 1.

[0167] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A secondary battery comprising a positive electrode sheet, an electrolyte, a separator and a negative electrode current collector, wherein: The electrolyte comprises a non-aqueous solvent, an electrolyte salt and an additive, wherein the non-aqueous solvent comprises an ether organic solvent, and the additive comprises: The first additive includes one or more of phosphite additives and borate additives.

2. The secondary battery according to claim 1, wherein The secondary battery is a sodium ion secondary battery; optionally, the secondary battery is a negative electrode-free sodium secondary battery; optionally, the negative electrode current collector includes a conductive substrate and an optional conductive layer, the conductive layer is arranged on at least one side of the conductive substrate, and the conductive substrate includes any one of bare copper, aluminum foil, aluminum alloy foil, and aluminum-based composite current collector; optionally, the conductive layer includes a conductive agent and a binder, and further optionally, the conductive agent includes graphite, graphene, carbon fiber, carbon black, carbon dots, soft carbon, hard carbon, multi-walled carbon nanotubes or single-walled carbon nanotubes.

3. The secondary battery according to claim 1 or 2, wherein: The ether organic solvent includes one or more of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol formate ethyl ether, ethylene glycol dibutyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran or methyltetrahydrofuran; optionally, the ether organic solvent contains ethylene glycol diethyl ether and / or diethylene glycol dimethyl ether, and optionally the mass content of ethylene glycol diethyl ether in the electrolyte is greater than or equal to 30%, and can be selected from 40% to 65%; optionally, the mass content of diethylene glycol dimethyl ether in the electrolyte is greater than or equal to 20%, and can be selected from 25% to 40%.

4. The secondary battery according to any one of claims 1 to 3, wherein The phosphite additive includes one or more of tris(trimethylsilyl)phosphite, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributyl phosphite or triphenyl phosphite.

5. The secondary battery according to any one of claims 1 to 4, wherein The borate ester additive includes any one or more of tri(trimethylsilyl)borate, trimethyl borate, triethyl borate, tripropyl borate, tributyl borate or triphenyl borate.

6. The secondary battery according to any one of claims 1 to 5, wherein The first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate; and / or the mass content of the first additive in the electrolyte is 0.2%-5%, optionally 0.2%-3%.

7. The secondary battery according to claim 1 or 2, wherein: The additives further include a second additive, wherein the second additive includes a C2-C7 fluoroalkyl ether additive.

8. The secondary battery according to claim 7, wherein The C2-C7 fluoroalkyl ether additives include 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane, 1,1,2,3,3,3-pentafluoropropyl-2 , 2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 2,2,3,3-tetrafluoro-1-methoxypropane, 1,1,2,3,3,3-pentafluoropropyl ethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether or 2,2,2-trifluoroethyl ethyl ether.

9. The secondary battery according to claim 7 or 8, wherein: The mass content of the second additive in the electrolyte is 0.2%-5%, and can be optionally 0.2%-2%.

10. The secondary battery according to any one of claims 1 to 9, wherein The electrolyte salt includes an electrolyte sodium salt; optionally, the electrolyte salt includes one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium trifluoromethanesulfonate or sodium tetraphenylborate; optionally, the electrolyte salt includes a first sodium salt and sodium trifluoromethanesulfonate, and the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate or sodium hexafluoroarsenate; optionally, the mass content of the sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%.

11. The secondary battery according to any one of claims 3 to 9, wherein In the electrolyte, the electrolyte salt includes a first sodium salt and sodium trifluoromethanesulfonate, and the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate or sodium hexafluoroarsenate; optionally, the mass content of the sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%; optionally, the mass ratio of the sodium trifluoromethanesulfonate to the diethylene glycol dimethyl ether is denoted as X, 0.05≤X≤0.2, and optionally 0.1≤X≤0.

13.

12. The secondary battery according to any one of claims 1 to 11, wherein The positive active material of the positive electrode plate is a layered metal oxide. Optionally, the positive active material includes one or more of the oxides with the chemical formula Na x Mn a Q b O 2-c- d F c , where 0.5 < x ≤ 1, 0 < a, 0 < b, 0 ≤ c ≤ 0.2, -0.1 ≤ d ≤ 0.1, and Q includes one or more of the following elements: Li, B, Mg, Al, Si, K, Ca, Ti, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, W, and Bi.

13. An electrolyte comprising a non-aqueous solvent, an electrolyte salt and an additive, wherein: The non-aqueous solvent includes an ether organic solvent, and the additive includes: The first additive includes one or more of phosphite additives and borate additives.

14. The electrolyte according to claim 13, wherein The ether organic solvent includes one or more of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol formate ethyl ether, ethylene glycol dibutyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran or methyltetrahydrofuran; optionally, the ether organic solvent contains ethylene glycol diethyl ether and / or diethylene glycol dimethyl ether, and optionally the mass content of ethylene glycol diethyl ether in the electrolyte is greater than or equal to 30%, and can be selected from 40% to 65%; optionally, the mass content of diethylene glycol dimethyl ether in the electrolyte is greater than or equal to 20%, and can be selected from 25% to 40%.

15. The electrolyte according to claim 13 or 14, wherein The phosphite additive includes one or more of tris(trimethylsilyl)phosphite, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributyl phosphite or triphenyl phosphite.

16. The electrolyte according to any one of claims 13 to 15, wherein The borate ester additive includes any one or more of tri(trimethylsilyl)borate, trimethyl borate, triethyl borate, tripropyl borate, tributyl borate or triphenyl borate.

17. The electrolyte according to any one of claims 13 to 16, wherein The first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate; and / or the mass content of the first additive in the electrolyte is 0.2%-5%, optionally 0.2%-3%.

18. The electrolyte according to any one of claims 13 to 17, wherein The additives further include a second additive, wherein the second additive includes a C2-C7 fluoroalkyl ether additive.

19. The electrolyte according to claim 18, wherein The C2-C7 fluoroalkyl ether additives include 1,1,2,2-tetrafluoroethyl methyl ether, 2,2,3,3-tetrafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis-(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, bis-(1,1,2,2-tetrafluoroethyl) ether, difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane, 1,1,2,3,3,3-pentafluoropropyl-2 , 2,2-trifluoroethyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 2,2,3,3-tetrafluoro-1-methoxypropane, 1,1,2,3,3,3-pentafluoropropyl ethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether or 2,2,2-trifluoroethyl ethyl ether.

20. The electrolyte according to claim 18 or 19, wherein The mass content of the second additive in the electrolyte is 0.2%-5%, and can be optionally 0.2%-2%.

21. The electrolyte according to any one of claims 13 to 20, wherein The electrolyte salt includes an electrolyte sodium salt; optionally, the electrolyte salt includes one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium trifluoromethanesulfonate or sodium tetraphenylborate; optionally, the electrolyte salt includes a first sodium salt and sodium trifluoromethanesulfonate, and the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate or sodium hexafluoroarsenate; optionally, the mass content of the sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%.

22. The electrolyte according to any one of claims 14 to 20, wherein In the electrolyte, the electrolyte salt includes a first sodium salt and sodium trifluoromethanesulfonate, and the first sodium salt includes any one or more of sodium hexafluorophosphate, sodium tetrafluoroborate or sodium hexafluoroarsenate; optionally, the mass content of the sodium trifluoromethanesulfonate in the electrolyte is 2%-10%; optionally, the mass content of the first sodium salt in the electrolyte is 3%-40%, optionally 5%-30%; optionally, the mass ratio of the sodium trifluoromethanesulfonate to the diethylene glycol dimethyl ether is denoted as X, 0.05≤X≤0.2, and optionally 0.1≤X≤0.

13.

23. An electrical device, comprising a secondary battery, wherein: The secondary battery is selected from the secondary battery according to any one of claims 1 to 12.

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