Electrolyte solution, secondary battery, and electric device

Abstract

The invention provides a secondary battery, an electrolyte and an electric device. The secondary battery comprises a positive pole piece, an electrolyte, an isolating membrane and a negative pole current collector, the electrolyte comprises a non-aqueous solvent, 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 ester additive.

Description

Technical Field

[0001] 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

[0002] As the application of lithium-ion battery technology in consumer electronics, electric vehicles, energy storage and other markets gradually expands, the problem of insufficient lithium resources has also begun to emerge. Sodium-based batteries have gradually attracted attention because the earth has a sufficiently high abundance of sodium, and they have an important strategic position in cost-sensitive application fields such as energy storage. Due to the higher reduction potential and larger relative molecular mass of metallic sodium compared to metallic lithium, the energy density of sodium-ion secondary batteries with similar working principles is significantly lower than that of lithium-ion batteries; the larger ionic radius of sodium ions also causes greater volume expansion when they are embedded and extracted from positive and negative electrode materials, resulting in a decrease in the cycle reversibility of the battery, which significantly restricts the application and promotion of sodium-ion secondary batteries. With the development and progress of electrolyte and additive technology and surface modification technology, the problem of sodium dendrite growth caused by uneven deposition on metal surfaces that has long plagued the academic community has been significantly improved, and the product safety performance is expected to be significantly improved, making high-energy-density sodium metal negative electrodes re-enter people's field of vision.

[0003] However, the practical application of sodium metal anodes faces great challenges because sodium metal has extremely high chemical activity and is prone to violent reactions with electrolytes to produce solid electrolyte interface films. Summary of the invention

[0004] 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.

[0005] The first aspect of the present application provides a secondary battery, including a positive electrode plate, an electrolyte, an isolation membrane and a negative electrode current collector, the electrolyte including a non-aqueous solvent, an electrolyte salt and an additive, the non-aqueous solvent including an ether organic solvent, the additive including a first additive, and the first additive including one or more of a phosphite additive and a borate additive.

[0006] 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, 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-mentioned 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 while also protecting the structure of the positive electrode from being destroyed, thereby improving the coulomb efficiency and cycle performance of the battery. In particular, the positive trivalent boron atom in the borate ester additive has an empty P orbital, which is Lewis acidic as a whole, can coordinate with anions to increase the migration number of lithium / sodium ions, and can also coordinate with oxygen atoms in ether organic solvent molecules, reduce the charge density of oxygen in the solvent molecules, and increase the solvent oxidation potential, further resisting the oxidation of the positive electrode active material to the ether organic solvent.

[0007] In any embodiment of the first aspect, the secondary battery is a sodium ion secondary battery.

[0008] 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, the problem of decreased coulombic efficiency and cycle performance caused by the violent reaction of sodium metal with the electrolyte is effectively alleviated.

[0009] In any embodiment of the first aspect, 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; the conductive layer optionally includes a conductive agent and a binder, and further optionally, the conductive agent includes 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 is more conducive to the sodium ions being reduced and deposited by electrons on the negative electrode current collector during charging to form a sodium metal negative electrode.

[0010] 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 formate ethyl ether, ethylene glycol dibutyl ether (DBE), 1,3-dioxolane (DOL), 1,4-dioxane (1,4-dioxane), tetrahydrofuran (THF) or methyltetrahydrofuran. The chemical structure of each of the above ether organic solvents is stable, the fluidity is good, the solubility of the additive is good, and it is more conducive to the effect of the additive.

[0011] In any embodiment of the first aspect, the ether organic solvent optionally contains ethylene glycol diethyl ether. Ethylene glycol diethyl ether has weaker interaction with anions and stronger oxidation resistance, thus being more conducive to the performance of the additive therein.

[0012] 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 can be optionally 40%-65%. By controlling the proportion of ethylene glycol diethyl ether in the electrolyte, the overcharge of the battery capacity can be effectively suppressed, and the stability of the battery to the high voltage positive electrode and the coulombic efficiency of the battery can be improved.

[0013] 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 generate a CEI film containing phosphorus compounds, 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 destroyed.

[0014] 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 oxidize and decompose on the surface of the oxide positive electrode to generate a CEI film containing a boron 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 destroyed.

[0015] In any embodiment of the first aspect, the first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate. When any 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.

[0016] 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, and the internal resistance is increased due to the excessive thickness of the CEI film, which affects the rate performance of the battery.

[0017] In any embodiment of the first aspect, the additive further includes 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 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 in the negative electrode to form a film, 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, while improving the battery cycle performance.

[0018] In any embodiment of the first aspect, the C2-C7 fluoroalkyl ether additive includes 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. 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 shuttle of electrolyte oxidation decomposition products between the positive and negative electrodes, thereby better achieving the effect of inhibiting capacity overcharge.

[0019] In any embodiment of the first aspect, the C2-C7 fluoroalkyl ether additive may 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, which takes into account the high cycle performance and high capacity retention characteristics of the secondary battery.

[0020] In any embodiment of the first aspect, the mass content of the second additive in the electrolyte is 0.2%-5%, and can be 0.2%-2%. The second additive can be used to form a sufficient SEI film to protect the negative electrode, and the increase in internal resistance caused by excessive SEI film thickness is avoided, which affects the rate performance of the battery.

[0021] 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 is deteriorated. The use of other electrolyte salts in the above electrolyte can improve the cycle performance of the secondary battery at room temperature.

[0022] 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. Thus, the low-temperature cycle performance and normal-temperature cycle performance of the secondary battery having the electrolyte can be improved.

[0023] 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%.

[0024] 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%, 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.

[0025] 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 normal temperature cycle performance of the secondary battery.

[0026] 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.

[0027] 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 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.

[0028] The 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.

[0029] Taking the positive electrode active material as an oxide as an example to illustrate the technical effects of the above electrolyte. 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 back and forth 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 also protecting the structure of the positive electrode from being damaged, thereby improving the Coulomb efficiency and cycle performance of the battery. In particular, the trivalent boron atom in the borate additive has an empty P orbital and overall shows Lewis acidity, which can coordinate with anions to increase the transference number of sodium ions, and can also coordinate with the oxygen atom in the ether organic solvent molecule to reduce the charge density of oxygen in the solvent molecule, increase the solvent oxidation potential, and further resist the oxidation of the ether organic solvent by the positive electrode oxide.

[0030] 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 formate ethyl ether, ethylene glycol dibutyl ether (DBE), 1,3-dioxolane (DOL), 1,4-dioxane (1,4-dioxane), tetrahydrofuran (THF) or methyltetrahydrofuran. The chemical structure of each of the above ether organic solvents is stable, the fluidity is good, the solubility of the additive is good, and it is more conducive to the effect of the additive.

[0031] In any embodiment of the second aspect, optionally, the ether organic solvent contains ethylene glycol diethyl ether. Ethylene glycol diethyl ether has weaker interaction with anions and stronger oxidation resistance, and is therefore more conducive to the performance of the additive.

[0032] 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 can be optionally 40%-65%. By controlling the proportion of ethylene glycol diethyl ether in the electrolyte, the overcharge of the battery capacity can be effectively suppressed, and the stability of the battery to the high voltage positive electrode and the coulombic efficiency of the battery can be improved.

[0033] 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 generate a CEI film containing phosphorus compounds, 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 destroyed.

[0034] 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 oxidize and decompose on the surface of the oxide positive electrode to generate a CEI film containing a boron 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 destroyed.

[0035] In any embodiment of the second aspect, the first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate. When any 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.

[0036] 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, and the internal resistance is increased due to excessive CEI film thickness, which affects the rate performance of the battery.

[0037] In any embodiment of the second aspect, the additive further includes 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 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.

[0038] In any embodiment of the second aspect, the C2-C7 fluoroalkyl ether additive includes 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. 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 shuttle of electrolyte oxidation decomposition products between the positive and negative electrodes, thereby better achieving the effect of inhibiting capacity overcharge.

[0039] In any embodiment of the second aspect, the C2-C7 fluoroalkyl ether additive may 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, which takes into account the high cycle performance and high capacity retention characteristics of the secondary battery.

[0040] In any embodiment of the second aspect, the mass content of the second additive in the electrolyte is 0.2%-5%, and can be 0.2%-2%. The second additive can be used to form a sufficient SEI film to protect the negative electrode, and the increase in internal resistance caused by excessive SEI film thickness is avoided, which affects the rate performance of the battery.

[0041] 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 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 is deteriorated. The use of other electrolyte salts in the above electrolyte can improve the cycle performance of the secondary battery at room temperature.

[0042] 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. Thus, the low-temperature cycle performance and normal-temperature cycle performance of the secondary battery having the electrolyte can be improved.

[0043] 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%.

[0044] 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%, 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.

[0045] 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.

[0046] 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, so as to further improve the ionic conductivity of the electrolyte at low temperature.

[0047] 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

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. 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 paying creative work.

[0049] Figure 1 Schematic diagram of a secondary battery according to one embodiment of the present application.

[0050] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0051] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0052] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0053] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0054] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0055] In the drawings, the drawings are not drawn to scale.

[0056] Description of reference numerals:

[0057] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0058] The following detailed description and drawings of the embodiments of the present application are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0059] Below, the embodiments of the negative electrode plate, secondary battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the 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 structure 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 descriptions 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.

[0060] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0062] 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.

[0063] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means 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), which means 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.

[0064] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0065] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0066] [Secondary battery]

[0067] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can continue to be used by recharging the active materials after the battery is discharged.

[0068] Normally, a secondary battery includes a positive electrode sheet, a negative current collector (or negative electrode sheet), a separator and an electrolyte. During the battery charging and discharging process, active ions (such as lithium ions or sodium ions) are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged 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.

[0069] The coulombic efficiency of the secondary battery is reduced and the cycle performance is insufficient. In order 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.

[0070] 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, which can effectively reduce the oxidative decomposition of the ether electrolyte on the positive electrode surface and reduce the shuttle of the oxidative decomposition products between the positive and negative electrodes. In addition, 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 generate a CEI film containing boron or phosphorus compounds, inhibiting the oxidative decomposition of the ether electrolyte on the positive electrode surface while also protecting the structure of the positive electrode from being destroyed, thereby improving the coulomb efficiency and cycle performance of the battery. In particular, the positive trivalent boron atom in the borate ester additive has an empty P orbital, which is Lewis acidic as a whole, can coordinate with anions to increase the migration number of lithium / sodium ions, and can also coordinate with oxygen atoms in ether organic solvent molecules, reduce the charge density of oxygen in the solvent molecules, and increase the solvent oxidation potential, further resisting the oxidation of the positive electrode oxide to the ether electrolyte.

[0071] The secondary battery of the present application may be a lithium ion secondary battery or a sodium ion secondary battery. In some embodiments, the secondary battery is a sodium ion secondary battery.

[0072] The above-mentioned sodium ion secondary battery can be a conventional sodium ion secondary battery with a negative electrode, or a sodium secondary battery without a negative electrode. The negative electrode of the conventional sodium ion secondary battery with a negative electrode can be a conventional sodium metal negative electrode. In order to further obtain a higher battery cell energy density, a negative electrode-free sodium secondary battery in which the positive electrode material is de-sodiumized and in-situ deposited onto the negative electrode current collector is also studied.

[0073] A negative electrode-free sodium secondary battery refers to a battery that does not actively set a negative electrode active material layer on the negative electrode side during the manufacturing process of the battery. For example, a sodium metal or carbonaceous active material layer is not set at the negative electrode through coating or deposition to form a negative electrode active material layer during the manufacturing process of the battery. During the first charge, the sodium ions obtain electrons on the negative electrode side and metallic sodium is deposited on the surface of the current collector to form a sodium metal phase. During discharge, the metallic sodium can be converted into sodium ions and return to the positive electrode to achieve cyclic charge and discharge. Compared with 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.

[0074] In some embodiments, in order to improve battery performance, some conventional substances that can be used as negative electrode active materials, such as carbonaceous materials, metal oxides, alloys, etc., can be set on the negative electrode side of the negative electrode-free sodium secondary battery. 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 materials 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. The sodium secondary battery thus constructed can still be regarded as a sodium secondary battery without a negative electrode.

[0075] 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 unit area capacity of the negative electrode plate in the secondary battery divided by the unit area capacity of the positive electrode plate. Since the negative electrode-free battery does not contain or contains only a small amount of negative electrode active material, the unit area capacity of the negative electrode plate is small, and the CB value of the secondary battery is less than or equal to 0.1.

[0076] In some embodiments of the present application, the secondary battery may be a negative electrode-free sodium metal secondary battery.

[0077] [Negative electrode current collector]

[0078] In some embodiments of the present application, the negative electrode current collector includes a conductive substrate and an optional conductive layer, and 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 opposite surfaces of the conductive substrate. The above optional conductive layer means that the conductive layer may be provided or not provided.

[0079] When using the negative electrode current collector as the negative electrode of the negative electrode-free sodium secondary battery, sodium metal needs to be deposited on the negative electrode current collector to form a negative electrode sheet after the first charge. Therefore, the post-generation of sodium metal can more effectively alleviate the problems caused by the reaction of sodium metal with the electrolyte.

[0080] In some embodiments, the conductive substrate includes any one of bare copper, aluminum foil, aluminum alloy foil, and aluminum-based composite current collector. The aluminum-based composite current collector includes 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 is a "sandwich" structure, the polymer base film is located in the middle, and aluminum foil is provided on both sides, or aluminum alloy foil is provided on both sides. It can also be that aluminum foil is provided on one side of the polymer base film and aluminum alloy foil is provided on the other side. The polymer base film includes 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 conducive to maintaining the integrity of the electrode during the sodium metal deposition / stripping process.

[0081] In some embodiments, the conductive layer includes a conductive agent and a binder, and 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.

[0082] In some embodiments, the conductive layer may further include a binder. As an 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).

[0083] 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.

[0084] [Electrolyte]

[0085] Some embodiments of the present application provide an electrolyte comprising a non-aqueous solvent, an electrolyte salt and an additive, wherein 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 or a borate additive.

[0086] 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 easy to react violently 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 including 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 oxidation and 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 pairs formed in ether electrolytes greatly reduce 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.

[0087] The electrolyte introduces the first additive into the ether organic solvent system, and the first additive forms a film on the positive electrode surface, which can effectively reduce the oxidative decomposition of the ether electrolyte on the positive electrode surface and reduce the shuttle of the oxidative decomposition products between the positive and negative electrodes. In addition, the 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 while also protecting the structure of the positive electrode from being destroyed, thereby improving the coulomb efficiency and cycle performance of the battery. In particular, the positive trivalent boron atom in the borate ester additive has an empty P orbital, which is Lewis acidic as a whole, can coordinate with anions to increase the migration number of lithium / sodium ions, and can also coordinate with oxygen atoms in ether organic solvent molecules, reduce the charge density of oxygen in the solvent molecules, and increase the solvent oxidation potential, further resisting the oxidation of the positive electrode oxide to the ether electrolyte.

[0088] The ether organic solvent of the present application can be selected from the ether organic solvents commonly used in the electrolyte. 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 formate ethyl ether, ethylene glycol dibutyl ether (DBE), 1,3-dioxolane (DOL), 1,4-dioxane (1,4-dioxane), tetrahydrofuran (THF) or methyltetrahydrofuran. The chemical structure of each of the above ether organic solvents is stable, the fluidity is good, and the solubility of the additive is good.

[0089] The antioxidant property of the solvent in the electrolyte is determined by the interaction between the solvent molecules and the anions. In the above-mentioned ether organic solvents, the interaction between ethylene glycol diethyl ether and the anions is weaker, and its oxidation resistance is stronger. In some embodiments, optionally, the ether organic solvent 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, and the stability of the battery to the high voltage positive electrode and the coulomb efficiency of the battery can be improved. 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%.

[0090] The phosphite additive used in the present application may be a conventional phosphite additive for electrolyte. 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 generate 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 structure of the positive electrode from being destroyed.

[0091] The borate ester additive used in the present application may be a conventional borate ester additive for electrolyte. 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. The borate ester additive can more efficiently oxidize and decompose on the surface of the oxide positive electrode to generate a CEI film containing a boron compound, more reliably inhibit the oxidative decomposition of the ether electrolyte on the positive electrode surface, and also protect the structure of the positive electrode from being destroyed.

[0092] In some embodiments, the first additive includes tris(trimethylsilyl)phosphite and / or tris(trimethylsilyl)borate. When any of the above 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.

[0093] 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.

[0094] When the electrolyte of the present application is applied to a sodium metal battery system, due to the extremely high chemical activity of sodium metal, it is easy 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, along with the deposition and peeling of sodium metal, this interface film is constantly broken and rebuilt, causing the internal resistance of the battery to continue to increase.

[0095] 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 in the negative electrode to form a film. The SEI film formed can effectively inhibit the products of the oxidation and decomposition of the above 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.

[0096] 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.

[0097] 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 shuttling of the oxidation decomposition products of the ether electrolyte between the positive and negative electrodes, thereby better achieving the effect of inhibiting capacity overcharge and further improving the coulombic efficiency of the battery.

[0098] 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 both 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 methyl nonafluorobutyl ether, ethyl perfluorobutyl ether, ethyl nonafluorobutyl ether 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or more.

[0099] The amount of the second additive in the electrolyte can refer to conventional technology. In some embodiments, the mass 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 0.2%-2%. The second additive can be used to form a sufficient SEI film to protect the negative electrode, and avoid the increase of internal resistance due to excessive thickness of the SEI film, which affects the improvement of the capacity overcharge performance of the battery.

[0100] 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.

[0101] 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).

[0102] Among them, 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 (below -30°C). At room temperature, the side reaction between sodium trifluoromethanesulfonate and the sodium metal negative electrode intensifies, and the overall cycle performance of the battery deteriorates. The use of other electrolyte salts in the above electrolytes can improve the cycle performance of secondary batteries at room temperature.

[0103] In some embodiments, the electrolyte optionally 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, thereby improving both the low-temperature cycle performance and the normal-temperature cycle performance of the secondary battery having the electrolyte.

[0104] 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%.

[0105] 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.

[0106] 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.

[0107] In some embodiments, in order to further improve the ionic conductivity of the electrolyte at low temperature, optionally, the mass ratio of sodium trifluoromethanesulfonate to diethylene glycol dimethyl ether is recorded as X, 0.05≤X≤0.2, for example, the minimum value of X can be 0.05, 0.08 or 0.1, and the maximum value of X can be 0.12, 0.125, 0.13, 0.15, 0.17 or 0.2, and 0.1≤X≤0.13 can be selected. Thereby improving the low temperature cycle performance of the battery.

[0108] [Positive electrode]

[0109] The positive electrode plate 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.

[0110] 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.

[0111] 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.).

[0112] When the secondary battery is a sodium ion secondary battery, the positive electrode active material of the positive electrode plate 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.

[0113] 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.

[0114] 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.

[0115] In some embodiments, the positive electrode sheet can be prepared in the following manner: 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.

[0116] [Isolation film]

[0117] 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 stability and mechanical stability can be selected.

[0118] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0119] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0120] In some embodiments, the secondary battery includes a secondary battery cell, a battery module, or a battery pack, and may include an outer package that can be used to encapsulate the electrode assembly and the electrolyte.

[0121] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0122] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery cell 5 is a square structure as an example.

[0123] In some embodiments, reference Figure 2, the outer packaging may include a shell 51 and a cover plate 53. Among them, 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 form 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.

[0124] In some embodiments, secondary battery cells may be assembled into a battery module. The number of secondary battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0125] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary battery cells 5 may be fixed by fasteners.

[0126] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary battery cells 5 are received in the receiving space.

[0127] 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 according to the application and capacity of the battery pack.

[0128] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0129] In addition, the present application also provides an electrical device, which includes a sodium ion secondary battery provided in 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 are not limited thereto.

[0130] 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.

[0131] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0132] [Example]

[0133] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0134] Example 1

[0135] 1) Electrolyte

[0136] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm),

[0137] According to the electrolyte formula of Example 1, sodium trifluoromethanesulfonate (NaTOf) and sodium hexafluorophosphate (NaPF6) are dissolved in diethylene glycol dimethyl ether and ethylene glycol diethyl ether (DEE), and tri(trimethylsilyl)phosphite and methyl nonafluorobutyl ether are added and stirred evenly to prepare an electrolyte.

[0138] 2) Preparation of positive electrode

[0139] The positive electrode active material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2, binder polyvinylidene fluoride (PVDF), and conductive agent conductive carbon black (Super-P) were mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 96:2:2 to prepare positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil by an extrusion coater according to the mass requirement of the positive electrode active material per unit area and dried. The coated electrode was then pressed by a cold press at a pressure of 2.5 g / cm 3 The designed compaction is then cold pressed to prepare the final positive electrode sheet.

[0140] 3) Preparation of negative electrode current collector

[0141] Single-walled carbon nanotubes and sodium alginate were added to deionized water and stirred into 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 .

[0142] 4) Isolation film

[0143] Polypropylene film is used as the isolation film.

[0144] 5) Preparation of batteries

[0145] The positive electrode sheet, the separator, and the negative electrode current collector are wound or stacked in order, and the separator is placed between the positive electrode sheet and the negative electrode current collector to play an isolating role. The bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the above-mentioned electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the sodium secondary battery product of Example 1.

[0146] 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 Example 1.

[0147]

[0148]

[0149]

[0150]

[0151]

[0152] The test results are recorded in Table 2.

[0153] Table 2

[0154]

[0155]

[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 (the higher the coulombic efficiency, the more significant the improvement in capacity overcharge) of the sodium battery.

[0157] According to the data comparison of Examples 1 to 5, the change in the amount of the first additive has a direct impact on the low-temperature cycle performance and normal temperature cycle performance of the battery, but the coulomb efficiency has basically not changed. 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 normal 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 of the positive electrode is insufficient, and 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, which in turn affects 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] According to the data comparison of Example 1 and Examples 9 to 12, when the dosage of the second additive changes, the low-temperature cycle performance, the normal-temperature cycle performance and the coulombic efficiency are all affected, which indicates that the second additive affects both the cycle performance and the capacity overcharge performance of the battery. Especially for the capacity overcharge performance, within a certain dosage range, as the dosage of the second additive increases, the coulombic efficiency of the battery increases, indicating that the improvement effect of the capacity overcharge performance of the battery tends to be obvious; however, when the dosage of the second additive increases from 2% to 5%, although the coulombic efficiency remains above 90%, it also shows a downward trend. When it continues to increase to 7%, the coulombic efficiency shows a further downward trend.

[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 conducive 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 stripping storage efficiency is high, so that the battery has good 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, it can be seen that the amount of diethylene glycol dimethyl ether used has a key influence on the low-temperature cycle performance of the battery. This may be 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 low, and the increase of electrolyte reaction products will accelerate the battery attenuation, so that both the low-temperature cycle performance and the normal temperature cycle performance are degraded.

[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 between Example 28 and 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 performances of Comparative Examples 2 and 3; after continuing to add the second additive, 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. This precisely illustrates that the second additive can better improve the effect of overcharge capacity; however, the cycle performance of Examples 28 and 29 is still good, illustrating that the first additive can better improve the effect of cycle performance (it also has the effect of improving coulombic efficiency, but the improvement in 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 coulomb 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 parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned 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 includes all technical solutions falling 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 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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