Electrolyte solution, secondary battery, and electric device

Abstract

The invention provides an electrolyte, a secondary battery and an electric device. The electrolyte comprises sodium salt and metal ions with the ion radius larger than that of the sodium ions. The electrolyte can effectively inhibit sodium dendrites, and is beneficial to improving the cycle performance and high-temperature storage performance of the battery.

Description

Electrolyte, secondary battery and electrical device Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] The performance of electrolytes has a key impact on the performance of secondary batteries. Currently, electrolytes have many defects and cannot meet the application needs of the new generation of electrochemical systems.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide an electrolyte that can effectively inhibit sodium dendrites, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0006] In a first aspect of the present application, an electrolyte for a sodium secondary battery is provided, wherein the electrolyte comprises a sodium salt and a metal ion having an ionic radius larger than that of a sodium ion.

[0007] The ionic radius of metal ions is larger than that of sodium ions. On the one hand, they can form a steric hindrance effect on sodium ions, preventing the growth of sodium dendrites. On the other hand, metal ions can form a charge shielding effect, improving the current density of sodium ion deposition, promoting uniform deposition of sodium ions, and forming a synergistic effect with the steric hindrance effect to inhibit the growth of sodium dendrites, avoid internal short circuits in the battery, and improve the battery's cycle performance and high-temperature storage performance.

[0008] In any embodiment, the metal ion comprises K + , Ca 2+ 、Sr 2+ 、Ba 2+ One or more of, optionally including K + .

[0009] The aforementioned metal ions all satisfy the requirement that their ionic radius is greater than that of sodium ions, effectively inhibiting the growth of sodium dendrites and improving the battery's cycling performance and high-temperature storage performance. Furthermore, when the reduced state of the aforementioned metal ions is used as an electrode, its standard electrode potential is lower than that of sodium. This prevents the metal ions from being reduced to metal atoms for deposition during the battery's charging process, thus avoiding or minimizing the impact on sodium ion deposition.

[0010] In any embodiment, the electrolyte comprises PF6- 、NO3 - 、ClO3 - One or more of .

[0011] In any embodiment, the electrolyte includes one or more of potassium hexafluorophosphate, calcium hexafluorophosphate, strontium hexafluorophosphate, barium hexafluorophosphate, potassium nitrate, calcium nitrate, strontium nitrate, barium nitrate, potassium perchlorate, calcium perchlorate, strontium perchlorate, and barium perchlorate, and optionally includes one or more of potassium hexafluorophosphate, potassium nitrate, and calcium hexafluorophosphate.

[0012] The above substances not only have steric effects and charge shielding effects, but are also compatible with sodium salts in the electrolyte, thus avoiding or reducing the negative effects brought about by the addition of the above substances.

[0013] In any embodiment, the concentration of the metal ions in the electrolyte is 0.005 mol / L to 0.3 mol / L, and can be optionally 0.01 mol / L to 0.1 mol / L.

[0014] Controlling the metal ion concentration in the electrolyte to an appropriate level can prevent or reduce the metal ion concentration from being too low, which prevents it from fully functioning, and can also prevent or reduce the effect of excessive metal ion concentration on the deposition of sodium ions, which can increase battery polarization and hinder battery performance. An appropriate concentration of metal ions is conducive to the uniform deposition of sodium ions. Further controlling the metal ion concentration in the electrolyte to 0.01 mol / L to 0.1 mol / L can significantly improve the battery's high-temperature storage performance.

[0015] In any embodiment, the sodium salt includes one or more of sodium chloride, sodium bromide, sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium acetate, sodium trifluoroacetate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium tetrafluoroborate, and sodium tetraphenylborate, and optionally includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium tetrafluoroborate.

[0016] The electrolytes including the above sodium salts all have excellent battery cycle performance and high-temperature storage performance.

[0017] In any embodiment, the concentration of the sodium salt in the electrolyte is 0.1 mol / L to 1.8 mol / L, and can be optionally 0.5 mol / L to 1.5 mol / L.

[0018] Controlling the sodium salt concentration in the electrolyte to an appropriate level can, on the one hand, prevent or reduce the low sodium salt concentration that leads to a low concentration of dissociated sodium ions in the electrolyte, which in turn reduces the sodium ion conductivity; on the other hand, it can prevent or reduce the high sodium salt concentration that leads to an increase in electrolyte viscosity, which in turn reduces the sodium ion conductivity rate. A suitable sodium salt concentration is beneficial for improving sodium ion conductivity. Further controlling the sodium salt concentration in the electrolyte to 0.5 mol / L to 1.5 mol / L can further significantly improve the battery's cycling performance and high-temperature storage performance.

[0019] In any embodiment, the electrolyte further includes an ether solvent, and the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, and optionally includes one or more of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and diethylene glycol dibutyl ether.

[0020] The above-mentioned ether solvents have excellent anti-reduction properties, which can effectively reduce the side reactions between sodium metal and solvents, and further improve the high-temperature storage performance of the battery.

[0021] In any embodiment, the ether solvent includes at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, and optionally includes at least two of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0022] The ether solvents include at least two of the above-mentioned ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, which are beneficial to further significantly improve the cycle performance and high-temperature storage performance of the battery.

[0023] In any embodiment, the electrolyte further includes a fluoroether compound, which includes one or more of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl methyl ether (TME), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), tris(trifluoroethoxy)methane (TFEO), methyl nonafluorobutyl ether (MFE), 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE), and optionally includes one or more of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

[0024] The above-mentioned fluoroether compounds are inert fluoroether compounds, which are located in the outermost layer of the sodium ion solvation structure. Moreover, the above-mentioned fluoroether compounds have low reactivity and are not easy to react with sodium metal, thereby improving the interface stability between the electrolyte and sodium metal, and improving the cycle performance and high-temperature storage performance of the battery.

[0025] In any embodiment, based on the total mass of the ether solvent and the fluoroether compound, the mass content of the fluoroether compound is 2% to 30%, optionally 5% to 20%.

[0026] Controlling the mass content of the fluoroether compound within an appropriate range is beneficial to improving the battery's cycle performance and high-temperature storage performance. Further controlling the mass content of the fluoroether compound to 5% to 20% is beneficial to further significantly improving the battery's cycle performance and high-temperature storage performance.

[0027] In any embodiment, the sodium salt comprises sodium hexafluorophosphate, and the metal ion comprises K + The ether solvent includes ethylene glycol dimethyl ether, and the fluoroether compound includes 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0028] The electrolyte containing sodium salt, metal ions, ether solvents and fluoroether compounds is beneficial to improving the cycle performance and high-temperature storage performance of the battery and improving the performance of the battery.

[0029] A second aspect of the present application provides a secondary battery comprising the electrolyte of the first aspect.

[0030] In any embodiment, the secondary battery is a negative electrode-less sodium secondary battery.

[0031] Anode-free sodium secondary batteries have high energy density.

[0032] In any embodiment, the secondary battery further includes a negative electrode plate, the negative electrode plate includes a negative electrode collector and a primer layer provided on at least one surface of the negative electrode collector, the primer layer including one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0033] The above-mentioned primer layer not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the surface of the current collector, thereby improving the coulombic efficiency and cycle performance of the battery.

[0034] In any embodiment, the surface density of the primer layer is 0.5 g / m 2 ~35g / m 2 .

[0035] Surface density is 0.5g / m 2 ~35g / m 2 The bottom coating is beneficial to the uniform distribution of nucleation sites in the negative electrode-free secondary battery, promoting the uniform deposition of metals without affecting the electron transport behavior.

[0036] In any embodiment, the primer layer has a thickness of 0.2 μm to 50 μm.

[0037] Controlling the thickness of the bottom coating layer to be 0.2 μm to 50 μm can provide enough nucleation sites for the negative electrode-free secondary battery, which is beneficial to the uniform deposition of metal ions and inhibits dendrites.

[0038] A third aspect of the present application provides an electrical device comprising the secondary battery according to the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0040] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0041] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0042] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0043] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0044] 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.

[0045] 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 cover plate. DETAILED DESCRIPTION

[0046] Below, the embodiments of the electrolyte, 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 may be 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.

[0047] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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).

[0053] Dendrite growth in batteries not only poses a safety hazard but also severely impacts battery performance. For example, in sodium batteries, uneven current distribution often leads to dendrite growth, and the electrolyte lacks the mechanical strength to prevent it. Therefore, a new electrolyte design is needed to meet the demands of next-generation electrochemistry.

[0054] [Electrolyte]

[0055] Based on this, the present application proposes an electrolyte for a sodium secondary battery, the electrolyte comprising a sodium salt and metal ions having an ion radius larger than that of sodium ions.

[0056] As used herein, the term "sodium salt" refers to a salt composed of sodium ions and anions that is liquid at or near room temperature. Room temperature refers to 25°C ± 5°C. Examples include, but are not limited to, one or more of sodium perchlorate, sodium hexafluorophosphate, sodium acetate, sodium trifluoroacetate, and sodium trifluoromethanesulfonate.

[0057] In this article, the term "ionic radius" refers to the average distance from the nucleus to the outermost electron. The ionic radius generally increases with increasing atomic number.

[0058] The ionic radius of metal ions is larger than that of sodium ions. On the one hand, they can form a steric hindrance effect on sodium ions, preventing the growth of sodium dendrites. On the other hand, metal ions can form a charge shielding effect, improving the current density of sodium ion deposition, promoting uniform deposition of sodium ions, and forming a synergistic effect with the steric hindrance effect to inhibit the growth of sodium dendrites, avoid internal short circuits in the battery, and improve the battery's cycle performance and high-temperature storage performance.

[0059] In some embodiments, the metal ion comprises K + , Ca 2+ 、Sr 2+ 、Ba 2+ One or more of, optionally including K + .

[0060] In this article, Na + The ionic radius is 0.097nm, K + The ionic radius of Ca is 0.133 nm. 2+ The ionic radius of Sr is 0.099nm. 2+ The ionic radius of Ba is 0.112nm. 2+ The ionic radius is 0.134 nm.

[0061] In this article, Na + The reduced state of potassium ion is used as an electrode, and its standard electrode potential is -2.711V; the reduced state of potassium ion is used as an electrode, and its standard electrode potential is -2.923V; the reduced state of calcium ion is used as an electrode, and its standard electrode potential is -2.76V; 2+ The reduced state of Ba is used as an electrode, and its standard electrode potential is -2.89V; 2+ The reduced state is used as an electrode, and its standard electrode potential is -2.90V.

[0062] As used herein, the term "metal ion reduced state" refers to a metal ion that is reduced to a metal atom.

[0063] In this article, the term "standard electrode potential" refers to the standard potential of the electrode, that is, the electrode potential when all substances participating in the electrode reaction are in a standard state with an activity of 1.

[0064] In some embodiments, the metal ion comprises K + In some embodiments, the metal ion comprises Ca 2+ In some embodiments, the metal ion comprises Ba 2+ In some embodiments, the metal ion comprises Sr 2+ .

[0065] The aforementioned metal ions all satisfy the requirement that their ionic radius is greater than that of sodium ions, effectively inhibiting the growth of sodium dendrites and improving the battery's cycling performance and high-temperature storage performance. Furthermore, when the reduced state of the aforementioned metal ions is used as an electrode, its standard electrode potential is lower than that of sodium. This prevents the metal ions from being reduced to metal atoms for deposition during the battery's charging process, thus avoiding or minimizing the impact on sodium ion deposition.

[0066] In some embodiments, the electrolyte comprises PF6 - 、NO3 - 、ClO3 - One or more of .

[0067] In some embodiments, the electrolyte comprises PF6 - In some embodiments, the electrolyte includes NO3 - In some embodiments, the electrolyte comprises ClO3 - .

[0068] In some embodiments, the electrolyte includes one or more of potassium hexafluorophosphate, calcium hexafluorophosphate, strontium hexafluorophosphate, barium hexafluorophosphate, potassium nitrate, calcium nitrate, strontium nitrate, barium nitrate, potassium perchlorate, calcium perchlorate, strontium perchlorate, and barium perchlorate, and optionally includes one or more of potassium hexafluorophosphate, potassium nitrate, and calcium hexafluorophosphate.

[0069] In some embodiments, the electrolyte comprises potassium hexafluorophosphate. In some embodiments, the electrolyte comprises calcium nitrate. In some embodiments, the electrolyte comprises strontium perchlorate. In some embodiments, the electrolyte comprises potassium hexafluorophosphate and calcium nitrate. In some embodiments, the electrolyte comprises potassium hexafluorophosphate and calcium hexafluorophosphate.

[0070] The above substances not only have steric effects and charge shielding effects, but are also compatible with sodium salts in the electrolyte, thus avoiding or reducing the negative effects brought about by the addition of the above substances.

[0071] In some embodiments, the concentration of metal ions in the electrolyte is 0.005 mol / L to 0.3 mol / L, and can be optionally 0.01 mol / L to 0.1 mol / L.

[0072] In some embodiments, the concentration of metal ions in the electrolyte may be selected as 0.005 mol / L, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.22 mol / L, 0.25 mol / L, 0.27 mol / L, 0.3 mol / L, or a value in the range consisting of any two of the above points.

[0073] Controlling the metal ion concentration in the electrolyte to an appropriate level can prevent or reduce the metal ion concentration from being too low, which prevents it from fully functioning, and can also prevent or reduce the effect of excessive metal ion concentration on the deposition of sodium ions, which can increase battery polarization and hinder battery performance. An appropriate concentration of metal ions is conducive to the uniform deposition of sodium ions. Further controlling the metal ion concentration in the electrolyte to 0.01 mol / L to 0.1 mol / L can significantly improve the battery's high-temperature storage performance.

[0074] In some embodiments, the sodium salt includes one or more of sodium chloride, sodium bromide, sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium acetate, sodium trifluoroacetate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium tetrafluoroborate, and sodium tetraphenylborate, and optionally includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium tetrafluoroborate.

[0075] In some embodiments, the sodium salt comprises sodium chloride. In some embodiments, the sodium salt comprises sodium tetrafluoroborate. In some embodiments, the sodium salt comprises sodium trifluoroacetate. In some embodiments, the sodium salt comprises sodium chloride. In some embodiments, the sodium salt comprises sodium tetrafluoroborate.

[0076] The electrolytes including the above sodium salts all have excellent battery cycle performance and high-temperature storage performance.

[0077] In some embodiments, the concentration of the sodium salt in the electrolyte is 0.1 mol / L to 1.8 mol / L, and can be optionally 0.5 mol / L to 1.5 mol / L.

[0078] In some embodiments, the concentration of sodium salt in the electrolyte is 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, or a value in a range consisting of any two of the above points.

[0079] Controlling the sodium salt concentration in the electrolyte to an appropriate level can, on the one hand, prevent or reduce the low sodium salt concentration that leads to a low concentration of dissociated sodium ions in the electrolyte, which in turn reduces the sodium ion conductivity; on the other hand, it can prevent or reduce the high sodium salt concentration that leads to an increase in electrolyte viscosity, which in turn reduces the sodium ion conductivity rate. A suitable sodium salt concentration is beneficial for improving sodium ion conductivity. Further controlling the sodium salt concentration in the electrolyte to 0.5 mol / L to 1.5 mol / L can further significantly improve the battery's cycling performance and high-temperature storage performance.

[0080] In some embodiments, the electrolyte further includes an ether solvent, and the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, and optionally includes one or more of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and diethylene glycol dibutyl ether.

[0081] In some embodiments, the ether solvent comprises ethylene glycol diethyl ether. In some embodiments, the ether solvent comprises diethylene glycol dimethyl ether. In some embodiments, the ether solvent comprises tetraethylene glycol dimethyl ether. In some embodiments, the ether solvent comprises ethylene glycol dimethyl ether. In some embodiments, the ether solvent comprises ethylene glycol dimethyl ether. In some embodiments, the ether solvent comprises tetrahydrofuran.

[0082] The above-mentioned ether solvents have excellent anti-reduction properties, which can effectively reduce the side reactions between sodium metal and solvents, and further improve the high-temperature storage performance of the battery.

[0083] In some embodiments, the ether solvent includes at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, and optionally includes at least two of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0084] In some embodiments, the ether solvent includes ethylene glycol dimethyl ether and diethylene glycol dimethyl ether. In some embodiments, the ether solvent includes ethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. In some embodiments, the ether solvent includes ethylene glycol dibutyl ether and diethylene glycol dimethyl ether. In some embodiments, the ether solvent includes ethylene glycol dimethyl ether and tetrahydrofuran.

[0085] The ether solvents include at least two of the above-mentioned ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, which are beneficial to further significantly improve the cycle performance and high-temperature storage performance of the battery.

[0086] In some embodiments, the electrolyte further includes a fluoroether compound, the fluoroether compound including one or more of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl methyl ether (TME), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), tris(trifluoroethoxy)methane (TFEO), methyl nonafluorobutyl ether (MFE), 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE), and optionally including one or more of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

[0087] In some embodiments, the fluoroether compound includes 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. In some embodiments, the fluoroether compound includes bis(2,2,2-trifluoroethyl) ether. In some embodiments, the fluoroether compound includes tris(trifluoroethoxy)methane. In some embodiments, the fluoroether compound includes 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether. In some embodiments, the fluoroether compound includes 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

[0088] The above-mentioned fluoroether compounds are inert fluoroether compounds, which are located in the outermost layer of the sodium ion solvation structure. Moreover, the above-mentioned fluoroether compounds have low reactivity and are not easy to react with sodium metal, thereby improving the interface stability between the electrolyte and sodium metal, and improving the cycle performance and high-temperature storage performance of the battery.

[0089] In some embodiments, based on the total mass of the ether solvent and the fluoroether compound, the mass content of the fluoroether compound is 2% to 30%, optionally 5% to 20%.

[0090] In some embodiments, the mass content of the fluoroether compound is 2%, 4%, 5%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, or a value in the range consisting of any two of the above points, based on the total mass of the ether solvent and the fluoroether compound.

[0091] Controlling the mass content of the fluoroether compound within an appropriate range is beneficial to improving the battery's cycle performance and high-temperature storage performance. Further controlling the mass content of the fluoroether compound to 5% to 20% is beneficial to further significantly improving the battery's cycle performance and high-temperature storage performance.

[0092] In some embodiments, the sodium salt comprises sodium hexafluorophosphate and the metal ion comprises K + , ether solvents include ethylene glycol dimethyl ether, and fluoroether compounds include 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0093] The electrolyte containing sodium salt, metal ions, ether solvents and fluoroether compounds is beneficial to improving the cycle performance and high-temperature storage performance of the battery and improving the performance of the battery.

[0094] [Positive electrode]

[0095] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on at least a portion of the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, which may include at least one of a layered transition metal oxide, a polyanionic compound, and a Prussian blue compound.

[0096] The transition metal in the layered transition metal oxide can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Optionally, the layered transition metal oxide is, for example, NaxMO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0<x≤1.

[0097] Polyanionic compounds can be metal ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The metal ion can be selected from sodium ion, lithium ion, potassium ion, and zinc ion; the transition metal can be selected from at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be selected from at least one of P, S, and Si; n represents (YO4) n- valence.

[0098] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0099] The positive electrode active material layer may further include a conductive agent to improve the conductivity of the positive electrode. The conductive agent may be selected from one or more of Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0100] The positive electrode active material layer may further include a binder to firmly bond the positive electrode active material and optional conductive agent to the positive electrode current collector. The binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0101] The positive electrode current collector can be a conductive carbon sheet, metal foil, carbon-coated metal foil, porous metal plate, or a composite current collector. The conductive carbon material of the conductive carbon sheet can be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foil, carbon-coated metal foil, and porous metal plate can each be independently selected from at least one of copper, aluminum, nickel, and stainless steel. The composite current collector can be a composite of metal foil and a polymer-based film.

[0102] 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0103] [Negative electrode]

[0104] The negative electrode plate may only include a negative electrode current collector without including a negative electrode active material. The negative electrode plate may also be formed by pre-depositing a metal phase on the negative electrode current collector.

[0105] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] In some embodiments, the negative electrode plate includes a negative electrode current collector and a primer layer disposed on at least one surface of the negative electrode current collector, wherein the primer layer includes one or more of carbon nanotubes, graphite, graphene, carbon black, aluminum oxide, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

[0107] As used herein, the term "carbon nanotube" refers to a seamless hollow cylinder formed by rolling up a single or multiple layers of graphene, with a diameter less than 100 nm and a length greater than 100 nm. Examples of carbon nanotubes include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0108] The above-mentioned primer layer not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the surface of the current collector, thereby improving the cycle performance and safety of the battery.

[0109] In some embodiments, the basecoat layer has an areal density of 0.5 g / m 2 ~35g / m 2 .

[0110] In some embodiments, the surface density of the base coating can be 0.5 g / m 2 , 1g / m 2 , 5g / m 2 , 10g / m 2 , 15g / m 2 , 20g / m 2 , 25g / m 2 , 30g / m 2 , 35g / m 2 , or a value in the range formed by any two of the above points.

[0111] Surface density is 5g / m 2 ~50g / m 2 The undercoat layer is beneficial to the uniform distribution of nucleation sites and promotes the uniform deposition of metal without affecting the transport behavior of electrons.

[0112] In some embodiments, the primer layer has a thickness of 0.2 μm to 50 μm.

[0113] In some embodiments, the thickness of the primer layer may be 0.2 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or a value in a range consisting of any two of the above points.

[0114] Controlling the thickness of the base coating to be 2 μm to 100 μm can provide enough nucleation sites to facilitate uniform deposition of metal ions and inhibit dendrites.

[0115] [Isolation film]

[0116] 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.

[0117] In some embodiments, the material of the separator can be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. 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.

[0118] 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.

[0119] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0120] 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.

[0121] [Secondary battery]

[0122] A secondary battery includes an electrolyte in some embodiments.

[0123] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 is an example of a square-structured battery cell 5 , and FIG2 is an exploded view of the battery cell 5 .

[0124] In some embodiments, the secondary battery further includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0125] In some embodiments, the secondary battery includes at least one of a lithium battery and a sodium battery.

[0126] In some embodiments, the secondary battery includes at least one of a potassium battery, a magnesium battery, and a zinc battery.

[0127] In some embodiments, the secondary battery is a negative electrode-less sodium battery.

[0128] 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 gain electrons on the anode side, 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 return 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.

[0129] In some embodiments, to improve battery performance, the negative electrode side of the negative electrode-free sodium secondary battery may 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 materials in the battery and are therefore not considered to form a negative electrode active material layer that plays a sodium intercalation role. The sodium secondary battery thus constructed can still be considered a negative electrode-free sodium secondary battery.

[0130] In some embodiments, the CB value of the negative electrode-free sodium secondary battery is less than or equal to 0.1.

[0131] The CB value is the capacity per unit area of ​​the negative electrode in a secondary battery divided by the capacity per unit area of ​​the positive electrode. Since a battery without a negative electrode contains no or only a small amount of negative electrode active material, the capacity per unit area of ​​the negative electrode is relatively small, and the CB value of a secondary battery is less than or equal to 0.1.

[0132] In some embodiments, referring to FIG2 , 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 separator 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 number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0133] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0134] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0135] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0136] 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.

[0137] 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.

[0138] [Electrical devices]

[0139] In one embodiment of the present application, an electric device is provided, comprising at least one of a secondary battery according to any embodiment, a battery module according to any embodiment, or a battery pack according to any embodiment.

[0140] The electrical device includes at least one of the secondary batteries, battery modules, or battery packs provided in this application. The secondary batteries, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units 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.

[0141] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0142] 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.

[0143] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0144] Example

[0145] 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.

[0146] 1. Preparation method

[0147] Example 1

[0148] 1) Electrolyte

[0149] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), 22.2% ethylene glycol dimethyl ether (DME) and 77.8% ethylene glycol diethyl ether were mixed to obtain a mixed solvent. Sodium hexafluorophosphate (SHP) and potassium hexafluorophosphate (KHP) containing potassium metal ions were then added and dissolved in the mixed solvent. The mixture was stirred to obtain a concentration of 1 mol / L for the sodium hexafluorophosphate and 0.03 mol / L for the potassium metal ions, thereby preparing an electrolyte.

[0150] 2) Preparation of positive electrode sheet

[0151] 10wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone. 10wt% carbon black conductive agent and 80wt% Na4Fe3(PO4)2P2O7 positive electrode active material were added and stirred to form a positive electrode slurry. The slurry was evenly coated on the surface of the current collector aluminum foil to form a positive electrode film. The film was then transferred to a vacuum drying oven for complete drying. The dried electrode was then roll-pressed and punched to form the positive electrode sheet.

[0152] 3) Preparation of negative electrode sheet

[0153] 5g of CMC was dissolved in 1000mL of deionized water, followed by the addition of 5g of single-walled carbon nanotubes. After ultrasonic dispersion, the slurry was prepared and coated on the surface of copper foil. Finally, the slurry was transferred to a vacuum drying oven for complete drying, followed by slitting and die-cutting to produce negative electrode sheets without anode structure.

[0154] 4) Isolation film

[0155] Polypropylene film is used as the isolation film.

[0156] 5) Preparation of batteries

[0157] The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator acting as an insulator between the positive and negative electrode sheets. Tabs were welded to the bare cell and placed in an aluminum casing. The bare cell was baked at 80°C to remove water, and then the electrolyte was injected and sealed to obtain an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the negative-electrode-free sodium secondary battery product of Example 1.

[0158] Examples 2-3

[0159] The battery preparation methods in Examples 2 to 3 are basically similar to those in Example 1, but the types of ether solvents or metal ions are adjusted. The specific parameters are shown in Table 1.

[0160] Example 4

[0161] The battery preparation method in Example 4 is basically similar to that in Example 1, except that a fluoroether compound is introduced into the electrolyte. The preparation method of the electrolyte is as follows:

[0162] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), 20% ethylene glycol dimethyl ether (DME), 70% ethylene glycol diethyl ether, and 10% 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) were mixed to obtain a mixed solvent. Sodium hexafluorophosphate (SHP) and potassium hexafluorophosphate (KHP) containing potassium metal ions were dissolved in the mixed solvent and stirred to obtain a concentration of 1 mol / L for the sodium hexafluorophosphate and 0.03 mol / L for the potassium ions, respectively, to prepare an electrolyte.

[0163] Examples 5 to 31

[0164] The battery preparation methods in Examples 5 to 31 are basically similar to those in Example 4, except that the concentration of metal ions, the type of metal ions, the type of ether solvent, the type of fluoroether compound, the concentration of fluoroether compound, the type of sodium salt, and the concentration of sodium salt are adjusted. The specific parameters are shown in Table 1.

[0165] Comparative Example 1

[0166] The battery preparation method in Comparative Example 1 is basically similar to that in Example 1, but there are no metal ions in the electrolyte. The specific parameters are shown in Table 1.

[0167] Comparative Example 2

[0168] The battery preparation method in Comparative Example 2 is basically similar to that in Comparative Example 1, but a fluoroether compound is added to the electrolyte. The specific parameters are shown in Table 1.

[0169] Comparative Example 3

[0170] The battery preparation method in Comparative Example 3 is basically similar to that in Comparative Example 2, but the type of the electrolyte ether solvent is adjusted. The specific parameters are shown in Table 1.

[0171] Comparative Example 4

[0172] The battery preparation method in Comparative Example 4 is basically similar to that in Example 1, but the metal ions are adjusted to magnesium ions (Mg 2+ The ionic radius of Mg is 0.066nm, 2+ The reduced state is used as the electrode, and its standard electrode potential is -2.375 V). The specific parameters are shown in Table 1.

[0173] 2. Performance Testing

[0174] 1. Battery performance test

[0175] 1) Storage capacity retention test

[0176] At 25°C, the prepared battery was charged to 3.7V at a constant current of 0.2C, then charged at a constant voltage of 3.7V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.2C to obtain the discharge capacity before storage (Cd1); then the battery was charged to 3.7V at a constant current of 0.2C again, and then charged at a constant voltage of 3.7V until the current dropped to 0.05C. The battery was then stored in a 60°C constant temperature box for 30 days. After being taken out, the battery was placed at 25°C and charged to 3.7V at a constant current of 0.2C, then charged at a constant voltage of 3.7V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.2C to obtain the discharge capacity after storage (Cd2). The battery capacity retention rate after storage at 60°C for 30 days was calculated according to the following formula:

[0177] Storage capacity retention rate=discharge capacity after storage (Cd2) / discharge capacity before storage (Cd1).

[0178] 2) Cyclic performance test

[0179] The cycling performance test process is as follows: at 25°C, the prepared battery was allowed to stand for 30 minutes, then discharged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, allowed to stand for 1 hour, and then discharged at a constant current of 0.33C to 2.5V to obtain the initial capacity (C0); after standing for 1 hour, the battery was again charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, allowed to stand for 1 hour, and then discharged at a constant current of 0.33C to 2.5V to obtain the process capacity (C1). The above steps were repeated for the same battery, and the process capacity (Cn) of the battery after the 100th cycle was recorded at the same time. The capacity retention rate after 100 cycles = Cn / C1×100%. The test process of the comparative example and other embodiments is the same as above.

[0180] 3) Sodium dendrite test

[0181] After n cycles, the battery was disassembled in an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), and the surface morphology of the negative electrode was visually observed to determine whether sodium dendrites had formed. A negative electrode with no white spots was considered to have no sodium dendrites, a negative electrode with sporadic white spots was considered to have mild sodium dendrites, and a negative electrode with dense white spots was considered to have severe sodium dendrites. The test procedures for the comparative example and other examples were the same as above.

[0182] 3. Analysis of test results of various embodiments and comparative examples

[0183] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0184] Table 1

[0185] Table 2

[0186] According to the above results, the electrolytes in Examples 1 to 31 include sodium salts and metal ions with an ion radius larger than that of sodium ions.

[0187] From the comparison of Examples 1 to 31 with Comparative Examples 1 to 3, it can be seen that the electrolyte includes metal ions with an ionic radius larger than that of sodium ions, which effectively inhibits the formation of sodium dendrites. At the same time, it is beneficial to improve the battery's cycle capacity retention rate and the capacity retention rate after storage at 60°C for 30 days, thereby improving the battery performance.

[0188] From the comparison of Examples 1 to 31 with Comparative Examples 1 to 4, it can be seen that compared with the electrolyte including magnesium hexafluorophosphate, the electrolyte in the present application includes potassium hexafluorophosphate, calcium hexafluorophosphate, calcium nitrate or strontium nitrate, which effectively inhibits the formation of sodium dendrites, and is beneficial to improving the battery's cycle capacity retention rate and the capacity retention rate after storage at 60°C for 30 days, thereby improving the battery performance.

[0189] Comparison of Examples 4 to 8 with Example 9 shows that controlling the metal ion concentration in the electrolyte to 0.005 mol / L to 0.3 mol / L is beneficial to improving the battery's cycle capacity retention rate and the capacity retention rate after 30 days of storage at 60°C. Comparison of Examples 4, 6 to 7 with Examples 5 and 8 shows that further controlling the metal ion concentration in the electrolyte to 0.01 mol / L to 0.1 mol / L is beneficial to further significantly improving the battery's capacity retention rate after 30 days of storage at 60°C.

[0190] From the comparison of Examples 4, 10 to 13 with Example 1, it can be seen that the addition of the fluoroether compound is beneficial to improving the cycle capacity retention rate of the battery and the capacity retention rate after storage at 60°C for 30 days, and inhibiting the sodium dendrites of the battery. From Examples 4, 10 to 13, it can be seen that based on the total mass of the ether solvent and the fluoroether compound, the mass content of the fluoroether compound is controlled to be 2% to 30%, and the battery has excellent cycle capacity retention rate and capacity retention rate after storage at 60°C for 30 days, and effectively inhibits sodium dendrites. From the comparison of Examples 4, 11 to 12 with Examples 5 and 13, it can be seen that based on the total mass of the ether solvent and the fluoroether compound, the mass content of the fluoroether compound is further controlled to be 5% to 20%, which is beneficial to further significantly improve the cycle capacity retention rate of the battery and the capacity retention rate after storage at 60°C for 30 days.

[0191] As can be seen from Examples 4 and 14 to 18, controlling the concentration of sodium salt in the electrolyte to 0.1 mol / L to 1.8 mol / L enables the battery to have excellent cycle capacity retention and capacity retention after 30 days of storage at 60°C, and effectively suppresses sodium dendrites. As can be seen from the comparison of Examples 4 and 14 to 16 with Examples 17 to 18, further controlling the concentration of sodium salt in the electrolyte to 0.5 mol / L to 1.5 mol / L is conducive to further significantly improving the cycle capacity retention and capacity retention after 30 days of storage at 60°C of the battery.

[0192] It can be seen from Examples 4 and 19 to 21 that the electrolyte includes one of potassium hexafluorophosphate, calcium hexafluorophosphate, calcium nitrate, and strontium nitrate, and the batteries thereof have excellent cycle capacity retention and capacity retention after storage at 60°C for 30 days, and effectively suppress sodium dendrites.

[0193] From the comparison of Examples 1 to 2, 4, 22 to 26 with Example 27, it can be seen that controlling the ether solvent in the electrolyte to be selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether or diethylene glycol dimethyl ether is beneficial to improving the battery's cycle capacity retention rate and the capacity retention rate after storage at 60°C for 30 days, as well as inhibiting the sodium dendrite phenomenon of the battery.

[0194] From the comparison between Example 4 and Examples 24 and 26, and Example 22 and Examples 24 to 25, it can be seen that controlling the ether solvent in the electrolyte to be selected from at least two of ethylene glycol dimethyl ether, ethylene glycol diethyl ether and diethylene glycol dimethyl ether is beneficial to further significantly improve the battery's cycle capacity retention rate and the capacity retention rate after storage at 60°C for 30 days.

[0195] As can be seen from Examples 4, 28 to 29, the sodium salt includes one of sodium hexafluorophosphate, sodium perchlorate and sodium bis(fluorosulfonyl)imide, and the batteries thereof have excellent cycle capacity retention and capacity retention at 60°C for 30 days, and effectively suppress sodium dendrites. As can be seen from the comparison between Example 1 and Example 3, and Example 4 and Example 19, compared with the sodium salt including Ca 2+ metal ions, including K + The metal ions are beneficial to further improve the battery's cycle capacity retention rate and the capacity retention rate after storage at 60°C for 30 days.

[0196] It can be seen from Examples 4 and 30 to 31 that the sodium salt includes one of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl methyl ether, and the batteries thereof have excellent cycle capacity retention and capacity retention after storage at 60°C for 30 days, and effectively suppress sodium dendrites.

[0197] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte for a sodium secondary battery, characterized in that: The electrolyte includes a sodium salt and metal ions whose ion radius is larger than that of sodium ions.

2. The electrolyte according to claim 1, characterized in that The metal ions include K + , Ca 2+ , Sr 2+ , Ba 2+ One or more of, optionally including K + .

3. The electrolyte according to claim 1 or 2, characterized in that The electrolyte includes PF6 - 、NO3 - 、ClO3 - One or more of .

4. The electrolyte according to any one of claims 1 to 3, characterized in that The electrolyte includes one or more of potassium hexafluorophosphate, calcium hexafluorophosphate, strontium hexafluorophosphate, barium hexafluorophosphate, potassium nitrate, calcium nitrate, strontium nitrate, barium nitrate, potassium perchlorate, calcium perchlorate, strontium perchlorate, and barium perchlorate, and optionally includes one or more of potassium hexafluorophosphate, potassium nitrate, and calcium hexafluorophosphate.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The concentration of the metal ions in the electrolyte is 0.005 mol / L to 0.3 mol / L, and can be optionally 0.01 mol / L to 0.1 mol / L.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The sodium salt includes one or more of sodium chloride, sodium bromide, sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium acetate, sodium trifluoroacetate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium tetrafluoroborate, and sodium tetraphenylborate, and optionally includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium tetrafluoroborate.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The concentration of the sodium salt in the electrolyte is 0.1 mol / L to 1.8 mol / L, and can be optionally 0.5 mol / L to 1.5 mol / L.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The electrolyte also includes an ether solvent, which includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, and can optionally include one or more of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and diethylene glycol dibutyl ether.

9. The electrolyte according to claim 8, characterized in that The ether solvent includes at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran, methyltetrahydrofuran and 1,3-dioxolane, and optionally includes at least two of ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

10. The electrolyte according to any one of claims 1 to 9, characterized in that The electrolyte also includes a fluoroether compound, which includes one or more of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tris(trifluoroethoxy)methane, methyl nonafluorobutyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and optionally includes one or more of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

11. The electrolyte according to claim 10, characterized in that Based on the total mass of the ether solvent and the fluoroether compound, the mass content of the fluoroether compound is 2% to 30%, and can be optionally 5% to 20%.

12. The electrolyte according to claim 10 or 11, characterized in that: The sodium salt includes sodium hexafluorophosphate, and the metal ion includes K + The ether solvent includes ethylene glycol dimethyl ether, and the fluoroether compound includes 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

13. A secondary battery, characterized in that: The electrolyte comprising the electrolyte described in any one of claims 1 to 12.

14. The secondary battery according to claim 13, characterized in that: The secondary battery is a negative electrode-free sodium secondary battery.

15. The secondary battery according to claim 13 or 14, characterized in that: The secondary battery also includes a negative electrode plate, which includes a negative electrode collector and a primer layer arranged on at least one surface of the negative electrode collector, and the primer layer includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.

16. The secondary battery according to claim 15, characterized in that: The surface density of the primer layer is 0.5 g / m 2 ~35g / m 2 .

17. The secondary battery according to claim 15 or 16, characterized in that: The thickness of the primer layer is 0.2 μm to 50 μm.

18. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 15 to 17.

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