Non-aqueous electrolyte, as well as secondary batteries and electrical devices containing this electrolyte

Abstract

A non-aqueous electrolyte containing a non-aqueous solvent and dissolved lithium ions, first cations, and first anions, wherein the first cation is a metal cation Men+ distinct from the lithium ion, where n represents a chemical valence of the metal cation; wherein the first anion is a difluorooxalate borate anion DFOB-; wherein the mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm and the mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, each based on the total mass of the non-aqueous electrolyte; and wherein the non-aqueous electrolyte satisfies the condition that D1 is between 0.5 and 870 and that D1 / D2 is between 0.02 and 2.

Description

TECHNICAL AREA This application relates to the field of battery technologies and specifically to a non-aqueous electrolyte, as well as to a secondary battery and an electrical device containing it. BACKGROUND In recent years, secondary batteries have become widespread in energy storage systems for power generation, such as hydroelectric, thermal, wind, and solar power plants, as well as in many other areas including power tools, e-bikes, e-motorcycles, electric vehicles, military equipment, and aerospace. With the increasing use and prevalence of secondary batteries, their overall performance has become increasingly important. For example, secondary batteries must exhibit a long cycle life, high safety performance, and good rate performance. Therefore, the question of how to provide a secondary battery with good overall performance is a technical problem that urgently needs to be addressed. SUMMARY One objective of this application is to provide a non-aqueous electrolyte as well as a secondary battery and an electrical device containing this electrolyte, so that the secondary battery has good cycle stability, safety performance and kinetic performance. A first aspect of this application relates to a non-aqueous electrolyte containing a non-aqueous solvent and dissolved lithium ions, first cations and first anions, wherein the first cation is a metal cation Men+, distinct from the lithium ion, where n represents the chemical valence of the metal cation; the first anion is a difluorooxalate borate anion DFOB-; the mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm and the mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, both based on the total mass of the non-aqueous electrolyte; and the non-aqueous electrolyte satisfies the condition that D1 is 0.5 to 870 and D1 / D2 is 0.02 to 2. The inventors of this application surprisingly discovered during their research that if the mass concentration D1 ppm of the first cations and the mass concentration D2 ppm of the first anions in the non-aqueous electrolyte meet the conditions that D1 is between 0.5 and 870 and that D1 / D2 is between 0.02 and 2, the first cations do not impair the electrochemical performance of the secondary battery, and that the non-aqueous electrolyte in this application also enables good cycle stability, safety performance, and kinetic performance of the secondary battery through the synergistic effect of the first cations and first anions. In each embodiment of this application, the difference between a standard reduction potential of Men+ and a standard reduction potential of Li+ is 1.0 V or more, and optionally Men+ represents at least one of Ni2+, Co2+, Mn2+, Al3+, and Fe2+. This better ensures that Men+ is reduced before the lithium ions, thereby further reducing the irreversible consumption of active lithium ions during SEI film formation and improving the capacity retention rate of the secondary battery. In each embodiment of this application, D1 is 100 to 870 and optionally 200 to 870. This allows the secondary battery to have a high capacity retention rate, a low volume swell rate, and good kinetic performance. In each embodiment of this application, D1 / D2 is 0.3 to 2 and optionally 0.3 to 1.2. This is conducive to the full exploitation of the synergy effect between the first cations and the first anions, enabling the secondary battery to exhibit good cycle stability, safety performance, and kinetic performance. In each embodiment of this application, D2 is 1 to 3000 and optionally 100 to 2000. This allows the secondary battery to have a high capacity retention rate, a low volume swell rate, and good kinetic performance. In each embodiment of this application, the non-aqueous electrolyte additionally contains second anions, wherein the second anion is a tetrafluoroborate anion BF4-. The mass concentration of the second anions in the non-aqueous electrolyte is D3 ppm, based on the total mass of the non-aqueous electrolyte. Optionally, D3 is 1 to 3000 and more optionally 1 to 2000. This can improve the high-temperature stability and low-temperature performance of the secondary battery. In each embodiment of this application, D2 / D3 is optionally 0.4 to 20 and more optionally 1 to 10. This helps to fully exploit the synergy effect between BF4 and DFOB, thereby not only widening the electrochemical window of the non-aqueous electrolyte but also forming a stable, low-impedance SEI film on the surface of an active material of the negative electrode. In each embodiment of this application, the non-aqueous electrolyte additionally contains third anions, wherein the third anion comprises at least one of the perchlorate anion ClO4-, the bis(trifluoromethanesulfonyl)imide anion N(SO2CF3)2-, NO3-, and SO42-, and optionally at least one of NO3- and SO42-. The mass concentration of the third anions in the non-aqueous electrolyte is D4 ppm, based on the total mass of the non-aqueous electrolyte. Optionally, D4 is 1 to 3000 ppm, and optionally 1 to 2000 ppm. The third anions contribute to the high thermal stability of the non-aqueous electrolyte and thereby improve the high-temperature stability of the secondary battery. The third anions additionally support DFOB- in becoming free ions to reduce the association of anions and cations, thus fully exploiting the effect of DFOB- on improving the capacity retention rate and kinetic performance of the secondary battery. In each embodiment of this application, the mass concentration of the third anions in the non-aqueous electrolyte is D4 ppm. Optionally, D2 / D4 is 0.4 to 20 and optionally 0.8 to 5. This helps to fully exploit the synergistic effect between the first and third anions, thereby not only improving the thermal stability of the non-aqueous electrolyte but also forming a stable, low-impedance SEI film on the surface of the active material of the negative electrode. In each embodiment of this application, the non-aqueous electrolyte additionally contains fourth anions, wherein the fourth anion comprises hexafluorophosphate anion PF6-, bis(fluorosulfonyl)imide anion N(SO2F)2- or a combination thereof. In each embodiment of this application, the mass fraction of the fourth anions in the non-aqueous electrolyte is optionally 8% to 20% and more, optionally 9% to 15%, based on the total mass of the non-aqueous electrolyte. In each embodiment of this application, the fourth anions optionally comprise both hexafluorophosphate anions PF6 and bis(fluorosulfonyl)imide anions N(SO2F)2, and optionally a mass ratio α of the hexafluorophosphate anions PF6 and the bis(fluorosulfonyl)imide anions N(SO2F)2 lies between 0.2 and 3, and optionally between 0.5 and 1.5. In this way, the non-aqueous electrolyte is not susceptible to hydrolysis and can exhibit higher thermal stability and contribute to the formation of an interfacial film with a lower impedance. In each embodiment of this application, the non-aqueous electrolyte additionally contains fifth anions, wherein the fifth anion comprises at least one of the dioxalate borate anion BOB-, hexafluoroarsenate(V) anion AsF6-, trifluoromethanesulfonate anion CF3SO3-, difluorophosphate anion PO2F2-, difluorodioxalate phosphate anion DODFP-, and tetrafluorooxalate phosphate anion OTFP-. This further improves the interfacial performance of the positive and / or negative electrode or the ionic conductivity or thermal stability of the non-aqueous electrolyte. In each embodiment of this application, the mass fraction of the fifth anions in the non-aqueous electrolyte is optionally 2% or less and more optionally 0.5% or less, based on the total mass of the non-aqueous electrolyte. In each embodiment of this application, the fifth anions comprise difluorophosphate anions PO₂F₂⁻. Optionally, the mass ratio β of the difluorophosphate anions PO₂F₂⁻ and the fourth anions is 0.01 to 0.15, and optionally 0.01 to 0.1. This can increase the ionic conductivity of the non-aqueous electrolyte, improve the properties of a positive electrode interfacial film and / or a negative electrode interfacial film, and contribute to constructing a stable, low-impedance positive electrode interfacial film and / or a stable, low-impedance negative electrode interfacial film, thereby effectively reducing the decomposition of the non-aqueous electrolyte and further improving the kinetic and safety performance of the secondary battery. In each embodiment of this application, the non-aqueous solvent comprises a cyclic carbonate compound and a linear carbonate compound, wherein in the non-aqueous electrolyte the mass fraction of the cyclic carbonate compound is E1 and the mass fraction of the linear carbonate compound is E2, both based on the total mass of the non-aqueous electrolyte; E1 is 5% to 40% and optionally 10% to 30%; and E2 is 40% to 85% and optionally 60% to 80%. This helps the non-aqueous electrolyte to achieve a suitable viscosity and ionic conductivity, which in turn facilitates the transport of lithium ions. In each embodiment of this application, the non-aqueous solvent additionally contains an ether compound, wherein the ether compound comprises at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol monomethyl ether, dimethoxyethane, tetraethylene glycol dimethyl ether, dimethoxymethane, and diglyme. The ether compound helps the non-aqueous electrolyte to achieve a suitable viscosity and / or ionic conductivity, which in turn facilitates the transport of lithium ions. In each embodiment of this application, the mass fraction of the ether compound in the non-aqueous electrolyte is E3, based on the total mass of the non-aqueous electrolyte; and optionally E3 is 0.1% to 40% and more, optionally 0.5% to 20%. In each embodiment of this application, the non-aqueous electrolyte additionally contains a first additive, wherein the first additive is fluoroethylene carbonate. This can effectively improve the cycle life of the secondary battery. In each embodiment of this application, the mass concentration of the first additive in the non-aqueous electrolyte D5 is ppm, based on the total mass of the non-aqueous electrolyte; and optionally D5 is 1 to 30,000 and more, optionally 100 to 20,000. In each embodiment of this application, the mass concentration of the first additive in the non-aqueous electrolyte D5 is ppm; and optionally D5 / D2 is 5 to 500 and optionally 5 to 100. This allows the synergy effect between FEC and DFOB to be fully exploited, further improving the cycle stability of the secondary battery without significantly increasing gas formation in the secondary battery. In each embodiment of this application, the non-aqueous electrolyte additionally contains a second additive, wherein the second additive comprises at least one of vinylidene carbonate, lithium oxalate, vinyl sulfate, and 1,3-propanesultone. The second additive contributes to further improving the interfacial performance of the positive and / or negative electrode, thereby further improving at least one of the cycle life, safety performance, and kinetic performance of the secondary battery. In each embodiment of this application, the mass fraction of the second additive in the non-aqueous electrolyte is optionally 5% or less and more optionally 2.5% or less, based on the total mass of the non-aqueous electrolyte. An unclaimed aspect of this application relates to a method for producing a non-aqueous electrolyte. The method comprises the following step: mixing a non-aqueous solvent, a lithium salt, a soluble Me salt, a soluble difluorooxalate borate, and an optional additive to a homogeneous mass to obtain a non-aqueous electrolyte, wherein Me is a metal element other than lithium; wherein the non-aqueous electrolyte contains the non-aqueous solvent and dissolved lithium ions, first cations, and first anions, wherein the first cation is a metal cation Men+, distinct from the lithium ion, where n represents a chemical valence of the metal cation; and the first anion is a difluorooxalate borate anion DFOB-.The mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm and the mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, both based on the total mass of the non-aqueous electrolyte; and the non-aqueous electrolyte satisfies the condition that D1 is 0.5 to 870 and D1 / D2 is 0.02 to 2. In each embodiment of this application, the difference between a standard reduction potential of Men+ and a standard reduction potential of Li+ is 1.0 V or more, and optionally Men+ represents at least one of Ni2+, Co2+, Mn2+, Al3+ and Fe2+. In each embodiment of this application, the soluble Me salt comprises at least one of Me(DFOB)n, Me(BF4)n, Me(ClO4)n, Me[N(SO2CF3)2]n, Me(NO3)n, Me(SO4)n / 2, Me(PF6)n, Me[N(SO2F)2]n, Me(BOB)n, Me(AsF6)n, Me(CF3SO3)n, Me(PO2F2)n, Me(DODFP)n, and Me(OTFP)n. This helps to regulate the mass concentrations of the metal cations and various anions in the non-aqueous electrolyte within the desired ranges. In each embodiment of this application, the soluble difluorooxalate borate comprises at least one of Me(DFOB)n and LiDFOB. This helps to regulate the mass concentrations of the metal cations and the first anions in the non-aqueous electrolyte within the desired ranges. In each embodiment of this application, the non-aqueous solvent comprises a cyclic carbonate compound and a linear carbonate compound, and optionally, the non-aqueous solvent comprises a cyclic carbonate compound, a linear carbonate compound, and an ether compound. This helps to regulate the mass concentrations of the metal cations and various anions in the non-aqueous electrolyte within the desired ranges. In each embodiment of this application, the lithium salt comprises a first lithium salt, wherein the first lithium salt comprises lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or a combination thereof, and optionally the lithium salt further comprises a second lithium salt, wherein the second lithium salt comprises at least one of lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate. This helps to regulate the mass concentrations of the metal cations and various anions in the non-aqueous electrolyte within the desired ranges. In each embodiment of this application, the additive comprises at least one of a first additive and a second additive, wherein the first additive is fluoroethylene carbonate and the second additive comprises at least one of vinylidene carbonate, lithium oxalate, vinyl sulfate and 1,3-propanesultone. A third aspect of this application relates to a secondary battery comprising a positive electrode plate, a negative electrode plate and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to the first aspect of this application or a non-aqueous electrolyte obtained using the manufacturing process according to the unclaimed aspect of this application. In each embodiment of this application, the positive electrode plate comprises a layer material having the molecular formula LiaNibCocMndAleMfOgAh, wherein M represents a doping cation at a transition metal site, A represents a doping anion at an oxygen site, wherein 0.8 ≤ a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, 0 ≤ e ≤ 1, 0 ≤ f ≤ 0.2, 0 ≤ g ≤ 2, 0 ≤ h ≤ 2, b + c + d + e + f + f = 1 and g + h = 2. In each embodiment of this application, M is optionally at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W. In each embodiment of this application, A is optionally selected from at least one of F, N, P and S, and more optionally, A is selected from F. In each embodiment of this application, optionally 0 < b < 0.98 and more optionally 0.50 ≤ b < 0.98. In every embodiment of this application, c = 0 is optional. In each embodiment of this application, optionally 0 < c ≤ 0.20 and more optionally 0 < c ≤ 0.10. In each embodiment of this application, optionally d = 0 and 0 < e < 0.50 and more optionally d = 0 and 0 < e ≤ 0.10. In each embodiment of this application, optionally e = 0 and 0 < d < 0.50 and more optionally e = 0 and 0 < d ≤ 0.10. In each embodiment of this application, optionally 0 < d < 0.50 and 0 < e < 0.50 and more optionally 0 < d ≤ 0.30 and 0 < e ≤ 0.10. A fourth aspect of this application relates to an electrical device comprising the secondary battery according to the third aspect of this application. The secondary battery in this application can exhibit good cycle stability, safety performance, and kinetic performance. The electrical device in this application incorporates the secondary battery provided in this application and thus offers at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS To describe the technical solutions of the embodiments of this application more clearly, the accompanying drawings illustrating these embodiments are briefly described below. Obviously, the accompanying drawings in the following descriptions show only some embodiments of this application, and those skilled in the art can derive other drawings from them without much creative effort. Fig. 1 is a schematic diagram of an embodiment of a secondary battery in this application. Fig. 2 is a schematic exploded view of the embodiment of the secondary battery in Fig. 1. Fig. 3 is a schematic diagram of an embodiment of a battery module in this application. Fig. 4 is a schematic diagram of an embodiment of a battery pack in this application. Fig. 5 is a schematic exploded view of the embodiment of the battery pack in Fig. 4.Figure 6 is a schematic diagram of an embodiment of an electrical device that uses the secondary battery in this application as a power source. The figures in the accompanying drawings are not necessarily shown to scale. The reference symbols are as follows: 1. Battery pack; 2. Upper housing part; 3. Lower housing part; 4. Battery module; 5. Secondary battery; 51. Housing; 52. Electrode assembly; and 53. Cover plate. DESCRIPTION OF THE EXECUTION FORMS In the following, embodiments of a non-aqueous electrolyte, a secondary battery, and an electrical device containing these are disclosed in detail in this application with appropriate reference to the accompanying drawings. However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of known facts and repeated descriptions of actually identical structures have been omitted. This is to avoid unnecessarily lengthening the following description and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following descriptions are intended to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims. The “ranges” disclosed in this application are defined in the form of lower and upper limits. A particular range is defined by a selected lower limit and a selected upper limit, the selected lower and upper limits defining the boundaries of that particular range. The ranges defined by this method may or may not include end values, and any combinations may be used; that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60–120 and 80–110 are specified for a particular parameter, it can be assumed that the ranges 60–110 and 80–120 are also possible. Furthermore, if the minimum values ​​of a range are specified as 1 and 2, and the maximum values ​​of the range as 3, 4, and 5, then all of the following ranges may be considered: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5.In this application, unless otherwise specified, a range of values ​​of "ab" is shorthand for any combination of real numbers between a and b, where both a and b are real numbers. For example, a range of values ​​of "0-5" means that all real numbers in the range of "0-5" are listed here, and "0-5" is simply shorthand for any combination of these values. Furthermore, a parameter expressed as an integer greater than or equal to 2 is equivalent to disclosing that the parameter is, for example, an integer between 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. Unless otherwise stated, all embodiments and optional embodiments of this application may be combined to form new technical solutions, and such technical solutions should be considered to be contained in the disclosure of this application. Unless otherwise stated, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application. Unless otherwise specified, all steps in this application may be performed in the order described or in any order, preferably in the order described. For example, a method comprising steps (a) and (b) means that the method may comprise steps (a) and (b) in the specified order or steps (b) and (a) in the specified order. For example, the foregoing method may further comprise step (c), which means that step (c) may be inserted at any point in the method; for example, the method may comprise steps (a), (b) and (c), steps (a), (c) and (b), steps (c), (a) and (b), or the like. Unless otherwise stated, the terms "comprise" and "contain" used in this application are inclusive or may be exclusive. For example, the terms "comprise" and "contain" may mean that other, unlisted components may also be included, or that only the listed components are included. Unless otherwise stated, the term "or" in this application is inclusive. For example, the expression "A or B" means "A, B, or both A and B." More precisely, each of the following conditions satisfies the "A or B" condition: A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present). In this application, the term “a multitude of” means two or more than two and the term “a multitude of types” means two or more than two types. With the application and proliferation of secondary batteries, their overall performance has become increasingly important. Non-aqueous electrolytes are one of the key factors influencing secondary battery performance. Currently, the most widely used non-aqueous electrolyte system is a mixed carbonate solution containing lithium hexafluorophosphate. However, lithium hexafluorophosphate exhibits low thermal stability in high-temperature environments and decomposes at high temperatures to form LiF and PF3. LiF increases interfacial impedance. PF5 has a strong Lewis acidity and interacts with the lone pairs of electrons on an oxygen atom in a solvent molecule, thereby decomposing the solvent. Furthermore, PF5 is highly sensitive to trace amounts of water in a non-aqueous electrolyte and forms RF upon contact with water.This increases the acidity of the non-aqueous electrolyte, leading to slight corrosion of the active material of the positive electrode and the current collector of the positive electrode, to the dissolution of transition metal ions in the active material of the positive electrode, and to a deterioration of the structural stability of the active material of the positive electrode, which affects the service life of secondary batteries. Furthermore, researchers currently generally consider all metal cations other than lithium ions in a non-aqueous electrolyte to be foreign substances or impurities that seriously impair the electrochemical performance of the secondary battery. However, the inventors of this application have surprisingly found through extensive research that when a non-aqueous electrolyte contains suitable amounts of both the metal cations Men+ and the difluorooxalate borate anion DFOB-, as described below, the metal cations Men+ do not impair the electrochemical performance of the secondary battery. Instead, they enable the secondary battery using the non-aqueous electrolyte in this application to exhibit good cycle stability, safety performance, and kinetic performance. Non-aqueous electrolyte The first aspect of this application relates in particular to a non-aqueous electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent and dissolved lithium ions, first cations and first anions, wherein the first cation is a metal cation Men+ distinct from the lithium ion, where n represents the chemical valence of the metal cation; the first anion is a difluorooxalate borate anion DFOB-; the mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm and the mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, both based on the total mass of the non-aqueous electrolyte; and the non-aqueous electrolyte satisfies the condition that D1 is 0.5 to 870 and D1 / D2 is 0.02 to 2. It should be noted that the metal cations Men+ in the non-aqueous electrolyte in this application are obtained by adding a soluble salt containing the element Me to the non-aqueous electrolyte and by dissociation of the soluble salt, but do not originate from impurity phases in the respective raw materials used to produce the non-aqueous electrolyte. Furthermore, the performance improvement of the secondary battery is mainly attributable to the soluble salt containing the element Me, which was added during the production of the non-aqueous electrolyte, and to the Men+ dissociated from it, and not to the metal cations that were dissolved into the non-aqueous electrolyte from an active material of the positive electrode during use of the secondary battery. The inventors of this application surprisingly discovered during their research that if the mass concentration D1 ppm of the first cations and the mass concentration D2 ppm of the first anions in the non-aqueous electrolyte meet the conditions that D1 is between 0.5 and 870 and that D1 / D2 is between 0.02 and 2, the first cations do not impair the electrochemical performance of the secondary battery. Furthermore, the non-aqueous electrolyte in this application, through the synergistic effect of the first cations and first anions, also enables good cycle stability, safety performance, and kinetic performance of the secondary battery. Although the mechanism is not fully understood, the inventors of this application suggest that the possible reasons include at least the following. Firstly, the metal cations Men+ are more active than the lithium ions with respect to their electrochemical activity and are therefore reduced before the lithium ions, thereby reducing the irreversible consumption of active lithium ions during SEI film formation and improving the capacity retention rate of the secondary battery. Secondly, the metal element formed by the reduction of the metal cations Men+ at the negative electrode exhibits a higher electronic conductivity and can facilitate electron transfer and the formation of a thicker SEI film on the surface of the active material of the negative electrode, thereby reducing side reactions at the interface between the active material of the negative electrode and the non-aqueous electrolyte, improving the capacity retention rate of the secondary battery, and reducing the volume swelling rate of the secondary battery. Thirdly, the difluorooxalate borate anions DFOB- participate in the formation of an SEI film on the surface of the active material of the negative electrode, in order to take on the role of modifying the SEI film and improving the composition of the SEI film, thereby facilitating the formation of a low impedance SEI film and reducing the impedance of the secondary battery. Fourth, the difluorooxalate borate anion (DFOB) contains an oxalate group, and this oxalate group is oxidized to carbon dioxide gas upon heating. Therefore, if the secondary battery is used improperly, such as by overcharging or short-circuiting, the internal pressure of the battery increases due to the carbon dioxide gas produced. This can cause a safety valve in the battery to open quickly, preventing the secondary battery from catching fire or even exploding, thus improving the safety performance of the secondary battery. Fifth, researchers generally assume that a thicker SEI film increases the impedance of the secondary battery and degrades its kinetic performance. However, the inventors of this application have surprisingly found that when the mass concentration D1 ppm of the first cations and the mass concentration D2 ppm of the first anions in the non-aqueous electrolyte meet the condition that D1 is 0.5 to 870 and D1 / D2 is 0.02 to 2, the impedance of the secondary battery is reduced despite the formation of a thicker SEI film on the surface of the active material of the negative electrode, and the secondary battery thus exhibits good kinetic performance and a long lifetime. The mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm, and D1 ranges from 0.5 to 870. If D1 is within the correct range, the secondary battery can exhibit a high capacity retention rate, a low volume swelling rate, and good kinetic performance. If the mass concentration of the first cations is too low, little improvement is achieved. This is because the first cations cannot be reduced to form a metallic element at the negative electrode, and consequently, neither the electronic conductivity can be increased nor the irreversible consumption of active lithium ions reduced. As a result, neither the capacity retention rate nor the volume swelling rate of the secondary battery can be effectively increased.If the mass concentration of the first cations is too high, the SEI film on the surface of the active material of the negative electrode becomes too thick, resulting in poor kinetic performance of the secondary battery. Furthermore, at excessively high mass concentrations of the first cations, their negative effect on the SEI film outweighs any positive effects. In this case, too much metal element catalyzes the decomposition of the SEI film.This process first produces a large amount of gas, causing the secondary battery to swell, which impairs its safety performance; secondly, byproducts generated during decomposition are deposited on the surface of the SEI film and impede lithium ion transport, thereby increasing the impedance of the secondary battery; and thirdly, active lithium ions in the non-aqueous electrolyte and in the battery are continuously consumed to replenish the lost SEI film, which has irreversible effects on the capacity retention rate of the secondary battery. Optionally, D1 can be configured for 1 to 870, 1 to 800, 1 to 700, 1 to 600, 1 to 500, 10 to 870, 10 to 800, 10 to 700, 10 to 600, 10 to 500, 50 to 870, 50 to 800, 50 to 700, 50 to 600, 50 to 500, 100 to 870, 100 to 800, 100 to 700, 100 to 600, 100 to 500, 200 to 870, 200 to 800, 200 to 700, 200 to 600, 200 to 500, 300 to 870 300 to 800, 300 to 700, 300 to 600 or 300 to 500.The mass concentration D1 ppm of the first cations and the mass concentration D2 ppm of the first anions in the non-aqueous electrolyte further satisfy the condition that D1 / D2 is between 0.02 and 2. This is conducive to the full exploitation of the synergistic effect between the first cations and the first anions, enabling the secondary battery to exhibit good cycle stability, safety performance, and kinetic performance. If D1 / D2 is too low, the SEI film is primarily modified by the first anions. Consequently, the first cations can contribute little improvement, and neither the capacity retention rate nor the volume swelling rate of the secondary battery can be effectively increased or decreased. If D1 / D2 is too high, the SEI film is too thick, and the kinetic performance of the secondary battery is poor.If the D1 / D2 ratio is too large, the improvement provided by the first anions in modifying the SEI film and reducing the interfacial impedance of the negative electrode is less significant compared to the negative effects of the first cations on the SEI film. In this case, too much metal element catalyzes the decomposition of the SEI film. This process first generates a large amount of gas, causing the secondary battery to swell and impairing its safety performance; second, byproducts generated during decomposition are deposited on the surface of the SEI film, hindering lithium ion transport and increasing the impedance of the secondary battery; and third, active lithium ions in the non-aqueous electrolyte and the battery are continuously consumed to replenish the lost SEI film, irreversibly affecting the capacity retention rate of the secondary battery.Optionally, D1 / D2 is 0.1 to 2, 0.1 to 1.8, 0.1 to 1.6, 0.1 to 1.4, 0.1 to 1.2, 0.1 to 1, 0.1 to 0.9, 0.1 to 0.8, 0.1 to 0.7, 0.1 to 0.6, 0.2 to 2, 0.2 to 1.8, 0.2 to 1.6, 0.2 to 1.4, 0.2 to 1.2, 0.2 to 1, 0.2 to 0.9, 0.2 to 0.8, 0.2 to 0.7, 0.2 to 0.6, 0.3 to 2, 0.3 to 1.8, 0.3 to 1.6, 0.3 to 1.4, 0.3 to 1.2, 0.3 to 1, 0.3 to 0.9, 0.3 to 0.8, 0.3 to 0.7, 0.3 to 0.6, 0.5 to 2, 0.5 to 1.8, 0.5 to 1.6, 0.5 to 1.4, 0.5 to 1.2, 0.5 to 1, 0.5 to 0.9 or 0.5 to 0.8. In some embodiments, the mass concentration of the first anions in the non-aqueous electrolyte D2 is ppm, where D2 is optionally from 1 to 3000. If D2 is within the correct range, the secondary battery can exhibit a high capacity retention rate, a low volume swelling rate, and good kinetic performance. Furthermore, the following situations can be effectively avoided: If the mass concentration of the first anions is too low, the first anions cannot perform their function of modifying the SEI film and improving its composition, resulting in high impedance and low kinetic performance of the secondary battery.If the mass concentration of the first anions is too high, the SEI film is primarily modified by these anions, preventing the first cations from fulfilling their function of increasing electronic conductivity and reducing the irreversible consumption of active lithium ions when they are reduced at the negative electrode to form a metallic cell. Consequently, increasing the capacity retention rate of the secondary battery is hindered. Furthermore, the first anions are not oxidation-resistant, and an excessive amount of them impairs the storage performance of the secondary battery, particularly in high-temperature environments.More optional are D2 10 to 3000, 10 to 2500, 10 to 2000, 10 to 1500, 10 to 1000, 100 to 3000, 100 to 2500, 100 to 2000, 100 to 1500, 100 to 1000, 200 to 3000, 200 to 2500, 200 to 2000, 200 to 1500, 200 to 1000, 500 to 3000, 500 to 2500, 500 to 2000, 500 to 1500 or 500 to 1000. In this application, the metal cation Men+ represents a metal cation other than the lithium ion, and n is the chemical valence of the metal cation. Optionally, for example, the element Me represents at least one of the transition metal elements and the metal elements of groups 5 to 7, and n is 1, 2, 3, 4, 5, or 6. Optionally, the difference between a standard reduction potential of Men+ (vs. the standard hydrogen electrode potential) and a standard reduction potential of Li+ (vs. the standard hydrogen electrode potential: -3.04 V) is 1.0 V or more. A difference of 1.0 V or more between the standard reduction potential of Men+ and the standard reduction potential of Li+ can better ensure that Men+ is reduced before the lithium ions, thereby better reducing the irreversible consumption of active lithium ions during SEI film formation and improving the capacity retention rate of the secondary battery. Optionally, Me represents at least one of Ni, Co, Mn, Al, and Fe. More optionally, Men+ represents at least one of Ni2+, Co2+, Mn2+, Al3+, and Fe2+. In some embodiments, the non-aqueous electrolyte may optionally contain a second anion, wherein the second anion is a tetrafluoroborate anion, BF4-. The mass concentration of the second anion in the non-aqueous electrolyte is D3 ppm, based on the total mass of the non-aqueous electrolyte. Optionally, D3 is 1 to 3000. BF4- has high thermal stability and can therefore improve the high-temperature stability of the secondary battery. BF4- also has a low charge transfer resistance, Rct, and can therefore improve the low-temperature performance of the secondary battery. BF4- can improve both the high-temperature stability and low-temperature performance of the secondary battery and widen the electrochemical window of the non-aqueous electrolyte. However, the ionic conductivity of BF4- is low, and a high proportion of BF4- is not conducive to the formation of a stable SEI film on the surface of the active material of the negative electrode.Therefore, the proportion of BF4 should not be too large. More optional are D3 1 to 2500, 1 to 2000, 1 to 1500, 1 to 1000, 1 to 500, 50 to 3000, 50 to 2500, 50 to 2000, 50 to 1500, 50 to 1000, 50 to 500, 100 to 3000, 100 to 2500, 100 to 2000, 100 to 1500, 100 to 1000, 100 to 500, 200 to 3000, 200 to 2500, 200 to 2000, 200 to 1500, 200 to 1000 or 200 to 500. In some embodiments, the mass concentration D2 ppm of the first anions and the mass concentration D3 ppm of the second anions optionally additionally fulfill the condition that D2 / D3 is between 0.4 and 20. Through further investigations, the inventors have found that a D2 / D3 value within a suitable range contributes to fully exploiting the synergistic effect between BF4 and DFOB, thereby not only widening the electrochemical window of the non-aqueous electrolyte but also forming a stable, low-impedance SEI film on the surface of an active material of the negative electrode. Optionally, D2 / D3 can also be 0.5 to 20, 0.5 to 15, 0.5 to 10, 0.5 to 8, 0.5 to 6, 0.5 to 4, 0.5 to 2, 0.8 to 15, 0.8 to 10, 0.8 to 8, 0.8 to 6, 0.8 to 4, 0.8 to 2, 1 to 15, 1 to 10, 1 to 8, 1 to 6, 1 to 4 or 1 to 2. In some embodiments, the non-aqueous electrolyte may optionally contain additional third anions, wherein the third anion comprises at least one of the following: perchlorate anion ClO4-, bis(trifluoromethanesulfonyl)imide anion N(SO2CF3)2- (abbreviated TFSI-), NO3-, and SO42-, and optionally includes at least one of NO3- and SO42-. The mass concentration of the third anions in the non-aqueous electrolyte is D4 ppm, based on the total mass of the non-aqueous electrolyte. Optionally, D4 is 1 to 3000. The third anions contribute to the high thermal stability of the non-aqueous electrolyte and thereby improve the high-temperature stability of the secondary battery. The third anions additionally support DFOB- in becoming free ions to reduce the association of anions and cations, thus fully exploiting the effect of DFOB- on improving the capacity retention rate and kinetic performance of the secondary battery.More optional are D4 1 to 2500, 1 to 2000, 1 to 1500, 1 to 1000, 1 to 500, 50 to 3000, 50 to 2500, 50 to 2000, 50 to 1500, 50 to 1000, 50 to 500, 100 to 3000, 100 to 2500, 100 to 2000, 100 to 1500, 100 to 1000, 100 to 500, 200 to 3000, 200 to 2500, 200 to 2000, 200 to 1500, 200 to 1000 or 200 to 500. In some embodiments, the mass concentration D2 ppm of the first anions and the mass concentration D4 ppm of the third anions optionally additionally satisfy the condition that D2 / D4 is between 0.4 and 20. Through further investigations, the inventors have found that a D2 / D4 value within a suitable range contributes to fully exploiting the synergistic effect between the first and third anions, thereby not only improving the thermal stability of the non-aqueous electrolyte but also forming a stable, low-impedance SEI film on the surface of an active material of the negative electrode. Optionally, D2 / D4 can also be 0.5 to 20, 0.5 to 15, 0.5 to 10, 0.5 to 8, 0.5 to 6, 0.5 to 5, 0.5 to 4, 0.5 to 3, 0.5 to 2, 0.8 to 15, 0.8 to 10, 0.8 to 8, 0.8 to 6, 0.8 to 5, 0.8 to 4, 0.8 to 3 or 0.8 to 2. In some embodiments, the non-aqueous electrolyte can optionally contain both the second and third anions, as described above. The mass concentration of the second anions in the non-aqueous electrolyte is D3 ppm, and the mass concentration of the third anions in the non-aqueous electrolyte is D4 ppm, both based on the total mass of the non-aqueous electrolyte. Optionally, D3 and D4 are 1 to 3000 ppm. This not only widens the electrochemical window of the non-aqueous electrolyte and improves its thermal stability, but also forms a stable, low-impedance SEI film on the surface of the negative electrode's active material, thereby further improving the cycle life, safety performance, and kinetic performance of the secondary battery. More optionally, the non-aqueous electrolyte fulfills the condition that D2 / D3 is 0.4 to 20 and D2 / D4 is 0.4 to 20. In some embodiments, the non-aqueous electrolyte may optionally contain additional fourth anions, wherein the fourth anion comprises the hexafluorophosphate anion PF6-, the bis(fluorosulfonyl)imide anion N(SO2F)2- (abbreviated FSI-), or a combination thereof. Optionally, the mass fraction of the fourth anions in the non-aqueous electrolyte is 8% to 20%, optionally 9% to 18%, and further optionally 9% to 15%, based on the total mass of the non-aqueous electrolyte. In the non-aqueous electrolyte of this application, a compound formed from the fourth anions and lithium ions is used as the primary lithium salt. More specifically, lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide can be used as the primary lithium salt in this application. Lithium hexafluorophosphate has high ionic conductivity and is less prone to corroding a current collector of the positive electrode, and can improve the overall ionic conductivity and thermal stability of the non-aqueous electrolyte when used as the primary lithium salt. The chemical formula of lithium bis(fluorosulfonyl)imide is F₂NO₄S₂Li, in which the nitrogen atom is bonded to two electron-withdrawing sulfonyl groups.This allows the charge on the nitrogen atom to be completely delocalized, resulting in a low lattice energy and easy dissociation for lithium bis(fluorosulfonyl)imide. This improves the ionic conductivity of the non-aqueous electrolyte and reduces its viscosity. Furthermore, lithium bis(fluorosulfonyl)imide exhibits good high-temperature stability and is not prone to hydrolysis, enabling it to form a thinner, but thermally more stable, lower-impedance interfacial film on the surface of the negative electrode active material. This reduces side reactions between the negative electrode active material and the non-aqueous electrolyte. In some embodiments, the fourth anion comprises the hexafluorophosphate anion PF6-. More precisely, lithium hexafluorophosphate (LiPF6) can be used as the primary lithium salt in this application. In some embodiments, the fourth anion comprises the bis(fluorosulfonyl)imide anion N(SO2F)2-. More precisely, lithium bis(fluorosulfonyl)imide (LiFSI) can be used as the primary lithium salt in this application. In some embodiments, the fourth anions comprise both hexafluorophosphate anions PF6- and bis(fluorosulfonyl)imide anions N(SO2F)2-. More precisely, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) can be used together as the primary lithium salt in this application. Optionally, the mass ratio α of the hexafluorophosphate anions PF6- and the bis(fluorosulfonyl)imide anions N(SO2F)2- is between 0.2 and 3, more optionally between 0.3 and 2, between 0.4 and 1.8, or between 0.5 and 1.5. In this way, the non-aqueous electrolyte is not susceptible to hydrolysis and can exhibit higher thermal stability and contribute to the formation of an interfacial film with a lower impedance. In some embodiments, the non-aqueous electrolyte may optionally contain fifth anions, wherein the fifth anion comprises at least one of the following: dioxalate borate anion (BOB), hexafluoroarsenate(V) anion (AsF6), trifluoromethanesulfonate anion (CF3SO3), difluorophosphate anion (PO2F2), difluorodioxalate phosphate anion (DODFP), and tetrafluorooxalate phosphate anion (OTFP). This may further improve the interfacial performance of the positive and / or negative electrode, or the ionic conductivity or thermal stability of the non-aqueous electrolyte. Optionally, the mass fraction of the fifth anions in the non-aqueous electrolyte is 2% or less, and more optionally 0.5% or less, based on the total mass of the non-aqueous electrolyte. Optionally, in some embodiments, the fifth anions comprise difluorophosphate anions PO₂F₂⁻. This can increase the ionic conductivity of the non-aqueous electrolyte, improve the properties of a positive electrode and / or negative electrode interfacial film, and contribute to the construction of a stable, low-impedance positive electrode and / or negative electrode interfacial film, thereby effectively reducing the decomposition of the non-aqueous electrolyte and further improving the kinetic and safety performance of the secondary battery. Optionally, the mass ratio β of the difluorophosphate anions PO₂F₂⁻ and the fourth anions is 0.01 to 0.15, and optionally 0.01 to 0.1. [Additive] In some embodiments, the non-aqueous electrolyte may optionally contain a first additive, wherein the first additive is fluoroethylene carbonate (FEC). The mass concentration of the first additive in the non-aqueous electrolyte is D5 ppm, based on the total mass of the non-aqueous electrolyte. Optionally, D5 is 1 to 30,000 ppm. In secondary batteries, FEC can undergo reductive decomposition reactions at high potential to form a flexible SEI film on the surface of the negative electrode's active material. This inhibits the reductive decomposition of the lower-potential non-aqueous solvent and its intercalation into the negative electrode's active material. Therefore, if the non-aqueous electrolyte contains FEC, the cycle life of the secondary battery can be effectively improved. Furthermore, FEC is resistant to oxidation at high voltages and thus better matches the positive electrode's active material at high voltages, facilitating improvements in the secondary battery's energy density. The non-aqueous electrolyte containing FEC helps to fully exploit the effect of FEC on improving the cycle stability and energy density of the secondary battery. Furthermore, FEC has a high dielectric constant. Therefore, the non-aqueous electrolyte containing FEC supports the formation of free ions (DFOB) within the electrolyte, reducing the association of anions and cations and thus fully exploiting the effect of DFOB on improving the capacity retention rate and kinetic performance of the secondary battery. However, the decomposition of FEC produces radiofrequency (HF), which destroys the structural stability of the active material of the positive electrode and increases gas formation in the secondary battery, thereby degrading its storage performance. Therefore, the proportion of FEC should not be too high. More optional D5 is 1 to 25,000, 1 to 20,000, 1 to 15,000, 1 to 10,000, 1 to 8,000, 1 to 5,000, 1 to 2,000, 100 to 25,000, 100 to 20,000, 100 to 15,000, 100 to 10,000, 100 to 8,000, 100 to 5,000 or 100 to 2,000. In some embodiments, the mass concentration D2 ppm of the first anions and the mass concentration D5 ppm of the first additive optionally satisfy the condition that D5 / D2 is between 5 and 500. Through further investigations, the inventors have found that D5 / D2 lies within a suitable range to fully exploit the synergistic effect between FEC and DFOB, thereby further improving the cycle stability of the secondary battery without significantly increasing gas formation. More optionally, D5 / D2 is 5 to 400, 5 to 300, 5 to 200, 5 to 150, 5 to 100, 5 to 75, 5 to 50, or 5 to 40. In some embodiments, the non-aqueous electrolyte may optionally contain a second additive, comprising at least one of vinylidene carbonate (VC), lithium oxalate, vinyl sulfate (DTD), and 1,3-propanesultone (PS). The second additive contributes to further improving the interfacial performance of the positive and / or negative electrode, thereby further enhancing at least one of the cycle life, safety performance, and kinetic performance of the secondary battery. Optionally, the mass fraction of the second additive in the non-aqueous electrolyte is 5% or less, and more optionally 2.5% or less, based on the total mass of the non-aqueous electrolyte. In some embodiments, the non-aqueous electrolyte can optionally contain either the first additive or the second additive. This helps to further improve the interfacial performance of the positive electrode and / or the negative electrode, thereby further improving the cycle stability, safety performance, and kinetic performance of the secondary battery. [Non-aqueous solvent] In this application, the non-aqueous solvent is primarily configured to dissolve the lithium salt so that the lithium salt forms conductive ions, and to reduce the association of cations (e.g., lithium ions and metal cations Men+) and anions (e.g., first anions, second anions, third anions, fourth anions, and fifth anions) in the non-aqueous electrolyte. In some embodiments, the non-aqueous solvent comprises a cyclic carbonate compound and a linear carbonate compound. Due to its high dielectric constant, the cyclic carbonate compound can increase the ionic conductivity of the non-aqueous electrolyte, and the linear carbonate compound can decrease the viscosity of the non-aqueous electrolyte due to its low viscosity. Thus, the non-aqueous solvent containing the cyclic and linear carbonate compounds helps the non-aqueous electrolyte achieve a suitable viscosity and ionic conductivity, which in turn facilitates the transport of lithium ions. For example, the cyclic carbonate compound can comprise at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).For example, the linear carbonate compound can comprise at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC) and ethylene propyl carbonate (EPC). In some embodiments, the non-aqueous solvent may additionally comprise a solvent other than the cyclic carbonate compound and the linear carbonate compound. For example, the non-aqueous solvent may additionally comprise at least one carboxylate compound, sulfone compound, and ether compound. For example, the carboxylate compound may comprise at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), and gamma-butyrolactone (GBL). For example, the sulfone compound may comprise at least one of sulfolane (SF), methylsulfonylmethane (MSM), ethyl methanesulfonate (EMS), and ethylsulfonylethane (ESE).For example, the ether compounds include at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxolane (DOL), ethylene glycol monomethyl ether, dimethoxyethane (DME), tetraethylene glycol dimethyl ether, dimethoxymethane (DMM), and diglyme (DG). These solvents help the non-aqueous electrolyte achieve a suitable viscosity and / or ionic conductivity, which in turn facilitates the transport of lithium ions. Furthermore, these solvents also contribute to the conversion of DFOB to free ions in the non-aqueous electrolyte, reducing the association of anions and cations and thus fully exploiting the effect of DFOB on improving the capacity retention rate and kinetic performance of the secondary battery. Optionally, in some embodiments, the non-aqueous solvent comprises a cyclic carbonate compound, a linear carbonate compound, and an ether compound. In the non-aqueous electrolyte, the mass fraction of the cyclic carbonate compound E1, the mass fraction of the linear carbonate compound E2, and the mass fraction of the ether compound E3 are each based on the total mass of the non-aqueous electrolyte. In some embodiments, E1 is 5% to 40%, and optionally 10% to 30%; E2 is 40% to 85%, and optionally 60% to 80%; and E3 is 0.1% to 40%, and optionally 0.5% to 20%. In this application, any composition (e.g., the first cations, first anions, second anions, third anions, fourth anions, fifth anions, first additives, and second additives) and their percentage fraction in the non-aqueous electrolyte can be determined using a method known in the art. For example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance (NMR), and inductively coupled plasma optical emission spectrometry (ICP-OES) can be used for the determination. It should be noted that for the testing of the non-aqueous electrolyte in this application, a freshly prepared non-aqueous electrolyte can be used directly, or a non-aqueous electrolyte can be obtained from a secondary battery. An exemplary method for obtaining a non-aqueous electrolyte from a secondary battery comprises the following steps: discharging the secondary battery to a discharge cut-off voltage (generally, completely discharging the battery for safety reasons), performing centrifugation, and using a suitable quantity of the centrifuged electrolyte as the non-aqueous electrolyte. Alternatively, the non-aqueous electrolyte can be obtained directly from an injection port of the secondary battery. Manufacturing process An unclaimed aspect of this application relates to a manufacturing process of a non-aqueous electrolyte, and the manufacturing process of a non-aqueous electrolyte according to the second aspect of this application can be used to obtain the non-aqueous electrolyte according to the first aspect of this application. In particular, the manufacturing process of a non-aqueous electrolyte comprises the following step: mixing a non-aqueous solvent, a lithium salt, a soluble Me salt, a soluble difluorooxalate borate and an optional additive to a homogeneous mass to obtain a non-aqueous electrolyte, wherein Me is a metallic element other than lithium.The non-aqueous electrolyte contains the non-aqueous solvent and dissolved lithium ions, first cations, and first anions, wherein the first cation is a metal cation Men+ distinct from the lithium ion, where n represents a chemical valence of the metal cation; the first anion is a difluorooxalate borate anion DFOB-; the mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm and the mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, each based on the total mass of the non-aqueous electrolyte; and the non-aqueous electrolyte satisfies the condition that D1 is 0.5 to 870 and that D1 / D2 is 0.02 to 2. Optionally, the element Me represents at least one of the transition metal elements and the metal elements of groups 5 to 7. Optionally, the difference between a standard reduction potential of Men+ (relative to the standard hydrogen electrode potential) and a standard reduction potential of Li+ (relative to the standard hydrogen electrode potential: -3.04 V) is 1.0 V or more. More optionally, Me represents at least one of Ni, Co, Mn, Al, and Fe. Optionally, Men+ represents at least one of Ni2+, Co2+, Mn2+, Al3+, and Fe2+. The materials are not restricted to a specific order of addition. They can, for example, be added simultaneously or in batches. A compound containing Men+ and soluble in the non-aqueous electrolyte can be used as a soluble Me salt. In some embodiments, the soluble Me salt optionally comprises at least one of Me(DFOB)n, Me(BF4)n, Me(ClO4)n, Me[N(SO2CF3)2]n, Me(NO3)n, Me(SO4)n / 2, Me(PF6)n, Me[N(SO2F)2]n, Me(BOB)n, Me(AsF6)n, Me(CF3SO3)n, Me(PO2F2)n, Me(DODFP)n, and Me(OTFP)n. More optionally, the soluble Me salt comprises at least one of Me(DFOB)n, Me(BF4)n, Me(NO3)n, and Me(SO4)n / 2. This helps to regulate the mass concentrations of the metal cations and various anions in the non-aqueous electrolyte within the desired ranges. In some embodiments, the soluble difluorooxalate borate comprises at least one of Me(DFOB)n and LiDFOB. This helps to regulate the mass concentrations of the metal cations and the first anions in the non-aqueous electrolyte within the desired ranges. In some embodiments, at least one of the soluble mesine salt and the soluble difluorooxalate borate Me(DFOB)n is optionally included. This helps the secondary battery achieve a better balance between good cycle stability, safety performance, and kinetic performance. In some embodiments, the non-aqueous solvent comprises a cyclic carbonate compound and a linear carbonate compound. Optionally, the non-aqueous solvent may additionally comprise a solvent other than the cyclic carbonate compound and the linear carbonate compound. For example, the non-aqueous solvent may additionally comprise at least one carboxylate compound, sulfone compound, and ether compound. More optionally, the non-aqueous solvent comprises a cyclic carbonate compound, a linear carbonate compound, and an ether compound. The ether compound contributes to increasing the degree of dissociation of the soluble mexic acid salt and the soluble difluorooxalate borate in the non-aqueous electrolyte, thereby regulating the mass concentrations of the metal cations and various anions in the non-aqueous electrolyte within the desired ranges. In some embodiments, the lithium salt comprises a first lithium salt, and the first lithium salt comprises lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), or a combination thereof. The first lithium salt is used as the primary lithium salt and may have a mass fraction of 8% to 20%, optionally 9% to 18%, and optionally 9% to 15% in the non-aqueous electrolyte, based on the total mass of the non-aqueous electrolyte. In the non-aqueous electrolyte described in this application, lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide are used as the primary lithium salt. Lithium hexafluorophosphate has high ionic conductivity and is less prone to corroding the current collector of the positive electrode. When used as the primary lithium salt, it can improve the overall ionic conductivity and thermal stability of the non-aqueous electrolyte. The chemical formula of lithium bis(fluorosulfonyl)imide is F₂NO₄S₂Li, in which the nitrogen atom is bonded to two electron-withdrawing sulfonyl groups. This allows the charge on the nitrogen atom to be completely delocalized, resulting in a low lattice energy and easy dissociation for lithium bis(fluorosulfonyl)imide. This improves the ionic conductivity and reduces the viscosity of the non-aqueous electrolyte.Furthermore, lithium bis(fluorosulfonyl)imide also exhibits good high-temperature resistance and does not tend to hydrolyze, so it can form a thinner but thermally more stable interfacial film with lower impedance on the surface of the active material of the negative electrode, thereby reducing side reactions between the active material of the negative electrode and the non-aqueous electrolyte. In some embodiments, the first lithium salt comprises lithium hexafluorophosphate (LiPF6). In some embodiments, the first lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI). In some embodiments, the first lithium salt comprises both lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). Optionally, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 0.2 to 3, and optionally 0.3 to 2, 0.4 to 1.8, or 0.5 to 1.5. In this way, the non-aqueous electrolyte is not susceptible to hydrolysis and can exhibit higher thermal stability, contributing to the formation of an interfacial film with lower impedance. In some embodiments, the lithium salt may optionally contain a second lithium salt, and the second lithium salt contains at least one of lithium bis(oxalato)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiDODFP), and lithium tetrafluoro(oxalato)phosphate (LiOTFP). As an additional lithium salt, the second lithium salt may further improve the interfacial performance of a positive and / or negative electrode or the ionic conductivity or thermal stability of the non-aqueous electrolyte. Optionally, the mass fraction of the second lithium salt in the non-aqueous electrolyte is 2% or less, and more optionally 0.5% or less, based on the total mass of the non-aqueous electrolyte. In some embodiments, the second lithium salt optionally comprises lithium difluorophosphate (LiPO₂F₂), lithium tetrafluoro(oxalato)phosphate (LiOTFP), or a combination thereof, and more optionally, the second lithium salt comprises lithium difluorophosphate (LiPO₂F₂). Lithium difluorophosphate has high electrochemical stability and can therefore increase the ionic conductivity of the non-aqueous electrolyte, improve the properties of a positive electrode and / or a negative electrode interfacial film, and contribute to constructing a stable, low-impedance positive electrode and / or negative electrode interfacial film, thereby effectively reducing the decomposition of the non-aqueous electrolyte and further improving the kinetic and safety performance of the secondary battery.Optionally, the mass ratio of lithium difluorophosphate and the first lithium salt is 0.01 to 0.15 and more, optionally 0.01 to 0.1. In some embodiments, the additive comprises at least one of a first additive and a second additive, wherein the first additive is fluoroethylene carbonate (FEC) and the second additive comprises at least one of vinylidene carbonate (VC), lithium oxalate, vinyl sulfate (DTD) and 1,3-propanesultone (PS). By adjusting the type and quantity of the raw materials in the non-aqueous electrolyte, the degree of dissociation of the lithium salt, the soluble mesium salt, and the soluble difluorooxalate borate anion in the non-aqueous electrolyte can be adjusted, thereby obtaining a non-aqueous electrolyte with the required mass concentrations of the metal cations and anions (for example, the first anions, second anions, third anions, fourth anions, and fifth anions). The resulting non-aqueous electrolyte has the same type of composition and the same specific composition ratio as the non-aqueous electrolyte in the first aspect of the embodiments of this application. Secondary battery A third aspect of this application relates to a secondary battery. The secondary battery comprises an electrode arrangement and a non-aqueous electrolyte. The non-aqueous electrolyte is either the non-aqueous electrolyte according to the first aspect of this application or a non-aqueous electrolyte obtained using the method according to the second aspect of this application. In this way, the secondary battery can exhibit good cycle stability, safety performance, and kinetic performance. The secondary battery in this application can be a lithium secondary battery, and in particular a lithium-ion secondary battery. The electrode assembly comprises a positive electrode plate, a negative electrode plate, and a separator. The separator is positioned between the positive and negative electrode plates, primarily to prevent a short circuit between them and to allow lithium ions to pass through. [Positive electrode plate] In some embodiments, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector. The positive electrode film layer comprises the active material of the positive electrode, which may be a known active material for secondary batteries. For example, the active material of the positive electrode may comprise at least one lithium transition metal oxide, lithium-containing phosphate with an olivine structure, and their respective modified compounds. Examples of the lithium transition metal oxide may include at least one lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and corresponding modified compounds thereof.Examples of lithium-containing phosphate with an olivine structure can include at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and corresponding modified compounds thereof. One of these positive electrode active materials can be used alone, or two or more can be used in combination. In some embodiments, the active material of the positive electrode optionally comprises a layer material with the molecular formula LiaNibCocMndAleMfOgAh, wherein M represents a doping cation at a transition metal site, A represents a doping anion at an oxygen site, wherein 0.8 ≤ a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, 0 ≤ e ≤ 1, 0 ≤ f ≤ 0.2, 0 ≤ g ≤ 2, 0 ≤ h ≤ 2, b + c + d + e + f + f = 1 and g + h = 2. The layer material with the molecular formula LiaNibCocMndAleMfOgAh is optionally modified by doping with cations M, doping with anions A, or both. The resulting doped layer material exhibits a more stable crystal structure and can further improve the electrochemical performance of the secondary battery, such as cycle stability and kinetic performance. In some embodiments, M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W. In some embodiments, A is selected from at least one of F, N, P, and S. Optionally, A is selected from F. After modification by F doping, LiaNibCocMndAleMfOgAheine exhibits a more stable crystal structure, resulting in improved cycle stability and kinetic performance of the secondary battery. The values ​​of a, b, c, d, e, f, g and h satisfy the following conditions, so that LiaNibCocMndAlcMfOgAh maintains electrical neutrality. In some embodiments, 0 < b < 0.98 applies. Optionally, 0.50 ≤ b < 0.98, 0.55 ≤ b < 0.98, 0.60 ≤ b < 0.98, 0.65 ≤ b < 0.98, 0.70 ≤ b < 0.98, 0.75 ≤ b < 0.98 or 0.80 ≤ b < 0.98 applies. In some embodiments, c = 0. In some embodiments, 0 < c ≤ 0.20 applies. Optionally, 0 < c ≤ 0.15, 0 < c ≤ 0.10, 0 < c ≤ 0.09, 0 < c ≤ 0.08, 0 < c ≤ 0.07, 0 < c ≤ 0.06, 0 < c ≤ 0.05, 0 < c ≤ 0.04, 0 < c ≤ 0.03, 0 < c ≤ 0.02, or 0 < c ≤ 0.01 applies. Cobalt is rare in the Earth's crust, difficult to mine, and expensive. Therefore, low or no cobalt content has become an unavoidable development trend for active materials of positive electrodes. However, cobalt significantly contributes to the lithium-ion diffusion rate of active materials for positive electrodes, and a low or no cobalt content reduces the lithium-ion diffusion rate of these materials, impairing the cycle life of secondary batteries. Researchers have worked to increase the lithium-ion diffusion rate of active materials with low or no cobalt content, but so far no satisfactory solution has been found. The inventors of this application surprisingly discovered during their research that DFOB can form a low-impedance protective film on the surface of the positive electrode active material in a non-aqueous electrolyte, and that the boron atom in DFOB can readily bond with the oxygen atom in the positive electrode active material to reduce the charge transfer resistance of the active material and thus the diffusion resistance of lithium ions in the bulk phase of the active material. Therefore, if the non-aqueous electrolyte contains a suitable amount of DFOB, the positive electrode active material with low or no cobalt content can exhibit a significantly improved lithium-ion diffusion rate.The surface can be replenished with lithium ions in a timely manner within the bulk phase of the active material of the positive electrode with low or no cobalt content, thereby avoiding excessive deintercalation of lithium on the surface of the active material of the positive electrode with low or no cobalt content, thus stabilizing the crystal structure of the active material of the positive electrode with low or no cobalt content.The crystal structure of the active material of the positive electrode with low or no cobalt content is more stable, which significantly reduces the likelihood that excessive deintercalation of lithium at the surface of the active material of the positive electrode with low or no cobalt content will lead to unstable structural, chemical or electrochemical properties of the active material of the positive electrode, such as irreversible deformation and an increase in lattice defects of the active material of the positive electrode. In some embodiments, d = 0 and 0 < e < 0.50. Optionally, d = 0 and 0 < e ≤ 0.45, d = 0 and 0 < e ≤ 0.40, d = 0 and 0 < e ≤ 0.35, d = 0 and 0 < e ≤ 0.30, d = 0 and 0 < e ≤ 0.25, d = 0 and 0 < e ≤ 0.20, d = 0 and 0 < e ≤ 0.15 or d = 0 and 0 < e ≤ 0.10. In some embodiments, e = 0 and 0 < d < 0.50. Optionally, e = 0 and 0 < d ≤ 0.45, e = 0 and 0 < d ≤ 0.40, e = 0 and 0 < d ≤ 0.35, e = 0 and 0 < d ≤ 0.30, e = 0 and 0 < d ≤ 0.25, e = 0 and 0 < d ≤ 0.20, e = 0 and 0 < d ≤ 0.15 or e = 0 and 0 < d ≤ 0.10. In some embodiments, 0 < d < 0.50 and 0 < e < 0.50 apply. Optionally, 0 < d ≤ 0.30 and 0 < e ≤ 0.10 apply. In some embodiments, g = 2 and h = 0. In some embodiments, g = 0 and h = 2. In some embodiments, 0 < g < 2, 0 < h < 2 and g + h = 2. For example, the layer material with the molecular formula LiaNibCocMndAleMfOgAh comprises at least one of LiNi0.8Co0.1Mn0,1O2, LiNi0,6Co0,2Mn0,2O2, LiNi0,5Co0,2Mn0,3O2, LiNi0,8C0,05Mn0.15O2, LiNi0,7Mn0,3O2, LiNi0,69Co0,01Mn0,3O2, LiNi0,68Co0,02Mn0,3O2, LiNi0,65Co0.05Mn0,3O2, LiNi0,63Co0.07Mn0,3O2, and LiNi0,61Co0,09Mn0,3O2, but is not limited to them. LiaNibCocMndAleMfOgAh can be produced using a conventional manufacturing process. An example of such a process is as follows: sintering a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an element M precursor, and an element A precursor after mixing to obtain LiaNibCocMndAleMfOgAh. The sintering atmosphere can be oxygen-containing, for example, air or oxygen. The O2 concentration of a sintering atmosphere is, for example, 70% to 100%. The sintering temperature and time can be adjusted depending on the specific situation. The lithium source includes, for example, at least one of lithium oxide (Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate (LiH₂PO₄), lithium acetate (CH₃COOLi), lithium hydroxide (LiOH), lithium carbonate (Li₂CO₃), and lithium nitrate (LiNO₃), but is not limited to these. The nickel source includes, for example, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate, but is not limited to these. The cobalt source includes, for example, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate, but is not limited to these. The manganese source includes, for example, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate, but is not limited to these. The aluminum source includes, for example, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate, but is not limited to these.The precursor of element M comprises, for example, at least one of the oxides, nitric acid compounds, carbonic acid compounds, hydroxide compounds, and acetic acid compounds of element M. The precursor of element A comprises, for example, at least one of the following: ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfide, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur. In some embodiments, the mass fraction of the layer material with the molecular formula LiaNibCocMndAleMfOgAh is 80% to 99%, based on the total mass of the positive electrode film layer. For example, the mass fraction of the layer material with the molecular formula LiaNibCocMndAleMfOgAh can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or within a range defined by any of these values. Optionally, the mass fraction of the layer material with the molecular formula LiaNibCocMndAleMfOgAh can be 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97% or 95% to 97%. In some embodiments, the positive electrode film layer optionally comprises a conductive element of the positive electrode. The conductive element of the positive electrode is not limited to a specific type in this application. For example, the conductive element of the positive electrode comprises at least one of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass fraction of the conductive element of the positive electrode is 5% or less, based on the total mass of the positive electrode film layer. In some embodiments, the positive electrode film layer optionally comprises a positive electrode binder. The positive electrode binder is not limited to a specific type in this application. For example, the positive electrode binder may comprise at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene propylene terpolymer, vinylidene fluoride-hexafluoropropylene tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, the mass fraction of the positive electrode binder is 5% or less, based on the total mass of the positive electrode film layer. In some embodiments, the current collector of the positive electrode can be a metal foil current collector or a composite current collector. For example, the metal foil can be aluminum foil. The composite current collector can comprise a polymer material matrix and a metal material layer formed on at least one surface of the polymer material matrix. For example, the metal material can comprise at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. For example, the polymer material matrix can comprise polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), or the like. The positive electrode film layer is typically formed by applying a positive electrode paste to the current collector of the positive electrode, followed by drying and cold pressing. The positive electrode paste is typically formed by dispersing the active material of the positive electrode, the optional conductive agent, the optional binder, and all other components in a solvent and stirring until a homogeneous mass is achieved. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP). [Negative electrode plate] In some embodiments, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector. The active material of the negative electrode can be a known active material for negative electrodes used in secondary batteries. For example, the active material of the negative electrode includes, but is not limited to, at least one of natural graphite, synthetic graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate. The silicon-based material can include at least one of elemental silicon, a silicon-oxygen compound, a silicon-carbon compound, a silicon-nitrogen compound, and a silicon alloy. The tin-based material can include at least one of elemental tin, tin oxide, and a tin alloy. This application is not limited to these materials, and other conventional, well-known materials that can be used as active materials for the negative electrode of a secondary battery may also be used.One of these active materials of the negative electrode can be used alone, or two or more of them can be used in combination. In some embodiments, the negative electrode film layer optionally comprises a conductive element of the negative electrode. The conductive element of the negative electrode is not limited to a specific type in this application. For example, the conductive material of the negative electrode may comprise at least one of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass fraction of the conductive element of the negative electrode is 5% or less, based on the total mass of the negative electrode film layer. In some embodiments, the negative electrode film layer optionally comprises a negative electrode binder. The negative electrode binder is not limited to a specific type in this application. For example, the negative electrode binder may comprise at least one of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethylacrylic acid PMAA, and sodium polyacrylic acid PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass fraction of the negative electrode binder is 5% or less, based on the total mass of the negative electrode film layer. In some embodiments, the negative electrode film layer optionally comprises a further additive. For example, the further additive may comprise a thickening agent, such as sodium carboxymethylcellulose (CMC-Na) or PTC thermistor material. In some embodiments, the mass fraction of the further additive is 2% or less, based on the total mass of the negative electrode film layer. In some embodiments, the negative electrode current collector can be a metal foil current collector or a composite current collector. For example, the metal foil can be a copper foil. The composite current collector can comprise a polymer matrix and a metal layer formed on at least one surface of the polymer matrix. For example, the metal material can comprise at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, or a silver alloy. For example, the polymer matrix can comprise polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), or the like. The negative electrode film layer is typically formed by applying a negative electrode paste to the current collector of the negative electrode, followed by drying and cold pressing. The negative electrode paste is generally formed by dispersing the negative electrode active material, optional conductor, optional binder, and optional other additive in a solvent and stirring until a homogeneous mass is achieved. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. [Separator] The separator is arranged between the positive and negative electrode plates, primarily to prevent a short circuit between the positive and negative electrodes and to allow lithium ions to pass through. The separator is not limited to a specific type in this application and can be any known porous separator with good chemical and mechanical stability. In some embodiments, the separator material may comprise at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film. If the separator is a multi-layer composite thin film, all layers may consist of the same or different materials. In some embodiments, the positive electrode plate, the separator and the negative electrode plate can be processed into an electrode assembly by winding or laminating. In some embodiments, the secondary battery may include an outer casing. The outer casing may be used to package the electrode assembly and the non-aqueous electrolyte. In some embodiments, the outer packaging of the secondary battery can be a hard shell, for example, a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft packaging, for example, a soft bag. The material of the soft bag can be plastic, for example, at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), or the like. This application does not particularly restrict the shape of the secondary battery, and the secondary battery can be cylindrical, rectangular, or any other shape. Fig. 1 shows a rectangular secondary battery 5 as an example. In some embodiments, as shown in Fig. 2, the outer packaging may comprise a housing 51 and a cover plate 53. The housing 51 may include a base plate and a side plate connected to the base plate, the base plate and the side plate enclosing a receiving space. The housing 51 has an opening that communicates with the receiving space, and the cover plate 53 is configured to cover the opening to seal the receiving space. The positive electrode plate, the negative electrode plate, and the separator may be processed into an electrode assembly 52 by winding or laminating. The electrode assembly 52 is packed into the receiving space. The non-aqueous electrolyte penetrates the electrode assembly 52. ​​The secondary battery 5 may comprise one or more electrode assemblies 52, the number of which can be adjusted as required. The manufacturing process for secondary batteries in this application is generally known. In some embodiments, the positive electrode plate, the separator, the negative electrode plate, and the non-aqueous electrolyte can be assembled to form a secondary battery. For example, the positive electrode plate, the separator, and the negative electrode plate can be processed into an electrode assembly by winding or laminating; and the electrode assembly is placed in an outer packaging, subsequently dried, filled with the non-aqueous electrolyte, then vacuum-sealed, allowed to rest, formed, shaped, and subjected to further processes to obtain a secondary battery. In some embodiments of this application, such secondary batteries can be combined to assemble a battery module. The battery module can comprise a plurality of secondary batteries, the number of which can be adapted depending on the application and capacity of the battery module. Fig. 3 is a schematic diagram of a battery module 4 as an example. As shown in Fig. 3, a plurality of secondary batteries 5 can be arranged sequentially along the longitudinal axis of the battery module 4. Of course, the batteries can also be arranged in other ways. Additionally, the plurality of secondary batteries 5 can be secured using fastening elements. Optionally, the battery module 4 can additionally include a housing with a receiving space, and the multiple secondary batteries 5 are housed in the receiving space. In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted based on the use and capacity of the battery pack. Figures 4 and 5 are schematic representations of a battery pack 1 as an example. As shown in Figures 4 and 5, the battery pack 1 can comprise a battery housing and a plurality of battery modules 4 arranged within the battery housing. The battery housing comprises a housing top 2 and a housing bottom 3. The housing top 2 is configured to cover the housing bottom 3 to form an enclosed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged within the battery housing in any configuration. Electrical device A fourth aspect of this application relates to an electrical device. The electrical device comprises at least one of the secondary battery, battery module, and battery pack according to this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (e.g., a mobile phone or a notebook computer), an electric vehicle (e.g., a battery-powered electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, or an electric truck), an electric train, a ship, a satellite, an energy storage system, and the like. The secondary battery, battery module or battery pack can be selected for the electrical device according to the requirements for the use of the device. Figure 6 is a schematic diagram of an electrical device as an example. This electrical device is a battery-powered electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. To meet the electrical device's requirements for high power and high energy density, a battery pack or battery module can be used. In another example, the electrical device could be a mobile phone, a tablet computer, a notebook computer, or the like. The electrical device typically needs to be lightweight and thin, and a secondary battery can be used as a power source. Examples The content disclosed in this application is described in detail in the following examples. These examples serve only for illustration, as various modifications and changes made without altering the scope of the content disclosed in this application will be obvious to those skilled in the art. Unless otherwise stated, all parts, proportions, and ratios given in the following examples are based on mass. All reagents used in the examples are commercially available or prepared by conventional means and can be used directly without further treatment. All equipment used in the examples is commercially available. In examples 1 to 36 and comparative examples 1 to 4, all secondary batteries were manufactured according to the following procedure. Production of the positive electrode plate An active material for the positive electrode, LiNi0.65Co0.05Mn0.3O2, a conductive agent, Super P, and a binder, polyvinylidene fluoride (PVDF), were thoroughly mixed and stirred in a suitable amount of solvent (NMP) in a weight ratio of 97.5:1.4:1.1 to form a homogeneous positive electrode paste. The positive electrode paste was uniformly applied to the surface of an aluminum foil as the current collector of the positive electrode, then dried and cold-pressed to obtain a positive electrode plate. Production of the negative electrode plate An active material of the negative electrode made of graphite, a binder made of styrene-butadiene rubber (SBR), a thickening agent made of sodium carboxymethylcellulose (CMC-Na) and a conductive agent made of carbon black (Super P) were thoroughly mixed and stirred in a suitable amount of the solvent deionized water in a mass ratio of 96.2:1.8:1.2:0.8 to form a uniform paste of the negative electrode. The negative electrode paste was applied evenly to the surface of a copper foil as the current collector of the negative electrode, then dried and cold-pressed to obtain a negative electrode plate. separator A porous polyethylene (PE) film was used as a separator. Production of the non-aqueous electrolyte A cyclic carbonate compound and a linear carbonate compound, composed according to the composition shown in Table 1, were mixed uniformly to obtain an organic solvent. Subsequently, a lithium salt, additives, a soluble mesodium salt, and soluble difluorooxalate borate, also composed according to the composition shown in Table 1, were added to the organic solvent and mixed uniformly to obtain a non-aqueous electrolyte. In Table 1, the amount of each composition is based on the total mass of the non-aqueous electrolyte. Production of the secondary battery The positive electrode plate, separator, and negative electrode plate were stacked and wound in the specified order to form an electrode assembly. The electrode assembly was placed in an outer packaging, and the previously prepared non-aqueous electrolyte was added, followed by sealing, resting, forming, maturation, and other processes to obtain a secondary battery. Tests (1) Test for compositions of non-aqueous electrolytes and their quantities Metal cation test: After the secondary battery prepared above was completely discharged, 10 ml of free electrolyte were extracted from the injection port. An inductively coupled plasma optical emission spectrometer, model ICAP-7400 from Thermo Fisher Scientific, was used for the test. The mass concentration D1 ppm of the first cations in the non-aqueous electrolyte was calculated based on the test results. Anion test: After the secondary battery produced above was completely discharged, 1.5 ml of free electrolyte was withdrawn from the injection port for later use. The electrolyte was tested by nuclear magnetic resonance spectrometry for the mass concentration D2 ppm of the first anion, the mass concentration D3 ppm of the second anion, and the mass concentration D4 ppm of the third anion. The specific steps of the test were as follows: 500 µl of deuterated reagent were placed in a magnetic resonance (MRI) tube in a nitrogen-filled glove box, 100 µl of non-aqueous electrolyte was withdrawn and added to the MRI tube, and the MRI tube was shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The test was performed using an Oxford Instruments X-Pulse benchtop MRI spectrometer. Since the non-aqueous electrolyte is very sensitive to water, both the nuclear magnetic resonance test and the sample preparation were carried out in a nitrogen atmosphere (with an H2O content of less than 0.1 ppm and an O2 content of less than 0.1 ppm), and the equipment associated with the test was pre-washed with pure water and dried for 48 hours or longer in a vacuum environment at 60 °C. The deuterated reagent was prepared in the following step: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using 4A molecular sieves at 25 °C or higher for at least 3 days to ensure that the water content of all reagents was below 3 ppm. A Metrohm 831 KF coulometer from Switzerland was used as a moisture meter. Subsequently, 10 mL of dried DMSO-d6 and 300 µL of dried internal standard trifluoromethylbenzene were withdrawn from the nitrogen-filled glove compartment and mixed uniformly to obtain a first solution. 10 mL of dried deuterated acetonitrile and 300 µL of dried internal standard trifluoromethylbenzene were withdrawn and mixed uniformly to obtain a second solution, and the first and second solutions were then mixed uniformly to obtain a deuterated reagent. (2) Cycle stability test of secondary batteries at room temperature At 25°C, the secondary battery was charged to 4.3V at a constant current of 1C and then charged to 0.05C at a constant voltage. At this point, the secondary battery was fully charged, and the charge capacity at this time was recorded as the first cycle charge capacity. The secondary battery was allowed to rest for 5 minutes and then discharged to 2.8V at a constant current of 1C. This was one charge and discharge cycle, and the discharge capacity at this time was recorded as the first cycle discharge capacity. The secondary battery was subjected to a charge and discharge cycle test according to the preceding procedure, and the discharge capacity of each cycle was recorded. Secondary battery capacity retention rate (%) of the 600th cycle at 25°C = 600th cycle discharge capacity / first cycle discharge capacity × 100% (3) Cycle stability test of secondary batteries at high temperatures At 45°C, the secondary battery was charged to 4.3 V at a constant current of 1C and then charged to 0.05 C at a constant voltage. At this point, the secondary battery was fully charged, and the charge capacity at this time was recorded as the first cycle charge capacity. The secondary battery was allowed to rest for 5 minutes and then discharged to 2.8 V at a constant current of 1C. This was one charge and discharge cycle, and the discharge capacity at this time was recorded as the first cycle discharge capacity. The secondary battery was subjected to a charge and discharge cycle test according to the above procedure, and the discharge capacity of each cycle was recorded. Secondary battery capacity retention rate (%) of the 600th cycle at 45°C = 600th cycle discharge capacity / first cycle discharge capacity × 100% (4) Test for the initial internal DC resistance of secondary batteries At 25 °C, the secondary battery was charged to 4.3 V with a constant current of 1 C and then charged to 0.05 C with a constant voltage. At this point, the secondary battery was fully charged. The secondary battery was then discharged to 50% state of charge (SOC) with a constant current of 0.5 C. At this point, the voltage of the secondary battery was recorded as U1. The secondary battery was then discharged to 4 C with a constant current I1 for 30 seconds, with a measurement taken every 0.1 seconds. The voltage at the end of the discharge was recorded as U2. The internal DC resistance of the secondary battery at the initial discharge and a 50% SOC was used to determine the initial internal DC resistance of the secondary battery. The initial internal DC resistance (mΩ) of the secondary battery was (U1 - U2) / I1. (5) Test of the storage performance of secondary batteries at high temperatures At 60°C, the secondary battery was charged to 4.3 V with a constant current of 1C and then to 0.05 C with a constant voltage. At this point, the volume of the secondary battery was tested using the dehydration method and recorded as V0. The secondary battery was then placed in a 60°C thermostat and stored there for 30 days. At this point, the volume of the secondary battery was again tested using the dehydration method and recorded as V1. Volume swelling rate (%) of the secondary battery after 30 days of storage at 60°C = (V1 - V0) / V0 × 100% Table 2 shows the test results for examples 1 to 36 and comparison examples 1 to 4. Table 1 Table 1 Example 1EC20 %DMC65.400 %LiPF612.50 %FEC2.0 %Mn(BF4)20.02 %Mn(NO3)20.03 %LiDFOB0 %Mn(DFOB)20.05 % Example 2EC20 %DMC65.39 %LiPF612.50FEC2.0 %Mn(BF4)20.02 %Mn(NO3)20.04 %LiDFOB0 %Mn(DFOB)20.05 % Example 3EC20 %DMC65.38 %LiPF612.50 %FEC2.0 %Mn(BF4)20.02 %Mn(NO3)20.05 %LiDFOB0 %Mn(DFOB)20.05 % Example 4EC20 %DMC65.37 %LiPF612.50 %FEC2.0 %Mn(BF4)20.02 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 5EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 6EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %Mn(BF4)20.04 %Mn(NO3)20.05 %LiDFOB0 %Mn(DFOB)20.05 % Example 7EC20 %DMC65.35 %LiPF612.50 %FEC2.0 %Mn(BF4)20.05 %Mo(NO3)20.05 %LiDFOB0 %Mn(DFOB)20.05 % Example 8EC20 %DMC65.34 %LiPF612.50 %FEC2.0 %Mn(BF4)20.06 %Mn(NO3)20.05 %LiDFOB0 %Mn(DFOB)20.05 % Example 9EC20 %DMC65.29 %LiPF612.50 %FEC2.0 %Mn(BF4)20.08 %Mn(NO3)20.08 %LiDFOB0 %Mn(DFOB)20.05 % Example 10EC20 %DMC65.25 %LiPF612.50 %FEC2.0 %Mn(BF4)20.10 %Mn(NO3)20.10 %LiDFOB0 %Mn(DFOB)20.05 % Example 11EC20 %DMC65.19 %LiPF612.50 %FEC2.0 %Mn(BF4)20.13 %Mn(NO3)20.13 %LiDFOB0 %Mn(DFOB)20.05 % Example 12EC20 %DMC65.35 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0.01 %Mn(DFOB)20.05 % Example 13EC20 %DMC65.34 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0.02 %Mn(DFOB)20.05 % Example 14EC20 %DMC65.33 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0.03 %Mn(DFOB)20.05 % Example 15EC20 %DMC65.31 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0.05 %Mn(DFOB)20.05 % Example 16EC20 %DMC65.26 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0.10 %Mn(DFOB)20.05 % Example 17EC20 %DMC65.11 %LiPF612.50 %FEC2.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0.25 %Mn(DFOB)20.05 % Example 18EC20 %DMC65.40 %LiPF612.50 %FEC2.0 %Mn(BF4)20.05 %Mn(NO3)20 %LiDFOB0 %Mn(DFOB)20.05 % Example 19EC20 %DMC65.37 %LiPF612.50 %FEC2.0 %Mn(BF4)20.08 %Mn(NO3)20 %LiDFOB0 %Mn(DFOB)20.05 % Example 20EC20 %DMC65.35 %LiPF612.50 %FEC2.0 %Mn(BF4)20.10 %Mn(NO3)20 %LiDFOB0 %Mn(DFOB)20.05 % Example 21EC20 %DMC65.42 %LiPF612.50 %FEC2.0 %Mn(BF4)20 %Mn(NO3)20.03 %LiDFOB0 %Mn(DFOB)20.05 % Example 22EC20 %DMC65.40 %LiPF612.50 %FEC2.0 %Mn(BF4)20 %Mn(NO3)20.05 %LiDFOB0 %Mn(DFOB)20.05 % Example 23EC20 %DMC65.37 %LiPF612.50 %FEC2.0 %Mn(BF4)20 %Mn(NO3)20.08 %LiDFOB0 %Mn(DFOB)20.05 % Example 24EC20 %DMC64.86 %LiPF612.50 %FEC + VC= 4:1(m:m)2.5 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 25EC20 %DMC64.86 %LiPF612.50 %FEC + DTD= 4:1(m:m)2.5 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 26EC20 %DMC64.86 %LiPF612.50 %FEC + PS =4:1(m:m)2.5 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 27EC20 %DMC67.36 %LiPF612.50 %FEC0.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 28EC20 %DMC66.86 %LiPF612.50 %FEC0.5 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 29EC20 %DMC66.36 %LiPF612.50 %FEC1.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 30EC20 %DMC64.36 %LiPF612.50 %FEC3.0 %Mn(BF4)20.03 %Mn(NO3)20.06 %LiDFOB0 %Mn(DFOB)20.05 % Example 3 1EC20%DMC65.36%LiPF612.50%FEC2.0%Ni(BF4)20.03%Ni(NO3):0.06%LiDFOB0%Ni(DFOB)20.05% Example 32EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %Co(BF4)20.03 %Co(NO3)20.06 %LiDFOB0%Co(DFOB)20.05 % Example 33EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %Fe(BF4)20.03 %Fe(NO3)20.06 %LiDFOB0%Fe(DFOB)20.05 % Example 34EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %Al(BF4)30.03 %Al(NO3)30.06 %LiDFOB0 %Al(DFOB)30.05 % Example 35EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %NaBF40.03 %NaNO30.06 %LiDFOB0 %NaDFOB0.05 % Example 36EC20 %DMC65.36 %LiPF612.50 %FEC2.0 %KBF40.03 %KNO30.06 %LiDFOB0%KDFOB0.05 % Comparison example: 1EC 20% DMC 65.50% LiPF 612.50% FEC 2.0% Mn(BF4) 20% Mn(NO3) 20% LiDFOB 0% Mn(DFOB) 20% Comparison example: 2EC 20% DMC 65.50% LiPF 612.50% FEC 2.0% Mn(BF4) 20% Mo(NO3) 20% LiDFOB 0.05% Mn(DFOB) 20% Comparison example: 3EC 20% DMC 65.05% LiPF 612.50% FEC 2.0% Mn(BF4) 20.20% Mo(NO3) 20.20% LiDFOB 0.05% Mn(DFOB) 20% Comparison example: 4EC 20% DMC 65.00% LiPF 612.50% FEC 2.0% Mn(BF4) 20.20% Mn(NO3) 20.20% LiDFOB 0.05% Mn(DFOB) 20.05% The test results of Examples 1 to 30 show that if the non-aqueous electrolyte contains the first cations and the first anions in this application and the mass concentration D1 ppm of the first cations and the mass concentration D2 ppm of the first anions meet the condition that D1 is between 0.5 and 870 and that D1 / D2 is between 0.02 and 2, the first cations do not impair the electrochemical performance of the secondary battery and that, due to the synergistic effect of the first cations and first anions, the non-aqueous electrolyte in this application also enables a high capacity retention rate over the cycles, a low internal resistance and a low volume swelling rate of the secondary battery. The test results of comparison examples 1 to 4 show that if the non-aqueous electrolyte contains only the first anions but no first cations, or if the non-aqueous electrolyte contains too many first cations, the cycle stability, kinetic performance and storage performance of the secondary battery cannot all be improved. The test results of Examples 24 to 30 also show that the non-aqueous electrolyte, which in this application additionally contains the first additive and / or the second additive, contributes to further improving at least one of the cycle stability, kinetic performance and storage performance of the secondary battery. The test results from Examples 5 and 31 to 36 also show that if Men+ satisfies the condition that the difference between the standard reduction potential of Men+ (vs. the standard hydrogen electrode potential) and the standard reduction potential of Li+ (vs. the standard hydrogen electrode potential: -3.04 V) is 1.0 V or more, and in particular if Men+ is at least one of Ni2+, Co2+, Mn2+, Al3+, and Fe2+, the overall performance of the secondary battery is improved. In Examples 35 and 36, Na+ and K+ were each used as the first cations, and their standard reduction potentials were close to the standard reduction potential of Li+. Therefore, Na+ and K+ have only a small effect on increasing the electronic conductivity and reducing the irreversible consumption of active lithium ions, and thus only a small effect on improving the overall performance of the secondary battery. It should be noted that this application is not limited to the embodiments described above. The embodiments described above are merely examples, and embodiments exhibiting essentially the same designs and effects as the technical idea within the technical solutions of this application are all included within the technical scope of this application. Furthermore, without departing from the essence of this application, various modifications of the embodiments that may be conceived by those skilled in the art in this field, as well as other embodiments constructed by combining some of the components of the embodiments, are also included within the scope of this application.

Claims

A non-aqueous electrolyte containing a non-aqueous solvent and dissolved lithium ions, first cations, and first anions, wherein the first cation is a metal cation Men+ distinct from the lithium ion, where n represents a chemical valence of the metal cation; wherein the first anion is a difluorooxalate borate anion DFOB-; wherein the mass concentration of the first cations in the non-aqueous electrolyte is D1 ppm and the mass concentration of the first anions in the non-aqueous electrolyte is D2 ppm, each based on the total mass of the non-aqueous electrolyte; and wherein the non-aqueous electrolyte satisfies the condition that D1 is between 0.5 and 870 and that D1 / D2 is between 0.02 and 2. Non-aqueous electrolyte according to claim 1, wherein the difference between a standard reduction potential of Men+ and a standard reduction potential of Li+ is 1.0 V or more, and Men+ optionally represents at least one of Ni2+, Co2+, Mn2+, Al3+ and Fe2+. Non-aqueous electrolyte according to claim 1 or 2, wherein D1 is between 100 and 870 and optionally between 200 and 870; D1 / D2 is between 0.3 and 2 and optionally between 0.3 and 1.2; and / or D2 is between 1 and 3000 and optionally between 100 and 2000. A non-aqueous electrolyte according to any one of claims 1 to 3, wherein the non-aqueous electrolyte additionally contains second anions, wherein the second anion is a tetrafluoroborate anion BF4- and the mass concentration of the second anions in the non-aqueous electrolyte is D3 ppm, based on the total mass of the non-aqueous electrolyte; wherein D3 is optionally between 1 and 3000 and more, optionally between 1 and 2000; and / or optionally D2 / D3 is between 0.4 and 20 and more, optionally between 1 and 10. A non-aqueous electrolyte according to any one of claims 1 to 4, wherein the non-aqueous electrolyte additionally contains third anions, wherein the third anion comprises at least one of the perchlorate anion ClO4-, the bis(trifluoromethanesulfonyl)imide anion N(SO2CF3)2-, NO3- and SO42- and optionally at least one of NO3- and SO42-; and the mass concentration of the third anions in the non-aqueous electrolyte is D4 ppm, based on the total mass of the non-aqueous electrolyte; wherein optionally D4 is between 1 and 3000 and more, optionally between 1 and 2000; and / or optionally D2 / D4 is between 0.4 and 20 and more, optionally between 0.8 and 5. A non-aqueous electrolyte according to any one of claims 1 to 5, wherein the non-aqueous electrolyte further comprises fourth anions, wherein the fourth anion comprises hexafluorophosphate anion PF6-, bis(fluorosulfonyl)imide anion N(SO2F)2- or a combination thereof; wherein the mass fraction of the fourth anions in the non-aqueous electrolyte is optionally 8% to 20% and more optionally 9% to 15%, based on the total mass of the non-aqueous electrolyte; and the fourth anions optionally comprise both hexafluorophosphate anions PF6- and bis(fluorosulfonyl)imide anions N(SO2F)2- and more optionally a mass ratio α of the hexafluorophosphate anions PF6- and the bis(fluorosulfonyl)imide anions N(SO2F)2- is between 0.2 and 3 and more optionally between 0.5 and 1.

5. Non-aqueous electrolyte according to claim 6, wherein the non-aqueous electrolyte additionally contains fifth anions, the fifth anion comprising at least one of dioxalate borate anion BOB-, hexafluoroarsenate(V) anion AsF6-, trifluoromethanesulfonate anion CF3SO3-, difluorophosphate anion PO2F2-, difluorodioxalate phosphate anion DODFP- and tetrafluorooxalate phosphate anion OTFP-; and the mass fraction of the fifth anions in the non-aqueous electrolyte is optionally 2% or less and more optionally 0.5% or less, based on the total mass of the non-aqueous electrolyte. Non-aqueous electrolyte according to claim 7, wherein the fifth anions comprise difluorophosphate anions PO2F2-; and a mass ratio β of the difluorophosphate anions PO2F2- and the fourth anions is optionally 0.01 to 0.15 and more optionally 0.01 to 0.

1. A non-aqueous electrolyte according to any one of claims 1 to 8, wherein the non-aqueous solvent comprises a cyclic carbonate compound and a linear carbonate compound, wherein in the non-aqueous electrolyte the mass fraction of the cyclic carbonate compound is E1 and the mass fraction of the linear carbonate compound is E2, both based on the total mass of the non-aqueous electrolyte; wherein E1 is between 5% and 40% and optionally between 10% and 30%; and wherein E2 is between 40% and 85% and optionally between 60% and 80%. Non-aqueous electrolyte according to claim 9, wherein the non-aqueous solvent further comprises an ether compound, wherein the ether compound comprises at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol monomethyl ether, dimethoxyethane, tetraethylene glycol dimethyl ether, dimethoxymethane and diglyme, and the mass fraction of the ether compound in the non-aqueous electrolyte is E3, based on the total mass of the non-aqueous electrolyte; and E3 is optionally between 0.1% and 40% and more optionally between 0.5% and 20%. A non-aqueous electrolyte according to any one of claims 1 to 10, wherein the non-aqueous electrolyte further comprises a first additive, wherein the first additive is fluoroethylene carbonate and the mass concentration of the first additive in the non-aqueous electrolyte is D5 ppm, based on the total mass of the non-aqueous electrolyte; wherein D5 is optionally between 1 and 30,000 and more, optionally between 100 and 20,000; and / or optionally D5 / D2 is between 5 and 500 and more, optionally between 5 and 100. A non-aqueous electrolyte according to any one of claims 1 to 11, wherein the non-aqueous electrolyte further comprises a second additive, the second additive comprising at least one of vinylidene carbonate, lithium oxalate, vinyl sulfate and 1,3-propanesultone; and the mass fraction of the second additive in the non-aqueous electrolyte is optionally 5% or less and more optionally 2.5% or less, based on the total mass of the non-aqueous electrolyte. Secondary battery comprising a positive electrode plate, a negative electrode plate and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1 to 12. Secondary battery according to claim 13, wherein the positive electrode plate comprises a layer material with the molecular formula LiaNi3CocMndAleMfOgAhum, wherein M represents a doping cation at a transition metal site, A represents a doping anion at an oxygen site, wherein 0.8 ≤ a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, 0 ≤ e ≤ 1, 0 ≤ f ≤ 0.2, 0 ≤ g ≤ 2, 0 ≤ h ≤ 2, b + c + d + e + f + f = 1 and g + h = 2; and optionally LiaNibCocMndAleMfOgAh at least one of the following conditions (1) to (8) is satisfied: (1) M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W; (2) A is selected from at least one of the elements F, N, P and S, and optionally A is selected from F; (3) 0 < b < 0.98 and optionally 0.50 ≤ b < 0.98; (4) c = 0; (5) 0 < c ≤ 0.20 and optionally 0 < c ≤ 0.10; (6) d = 0 and 0 < e < 0.50, and optionally d = 0 and 0 < e ≤ 0.10; (7) e = 0 and 0 < d < 0.50, and optionally e = 0 and 0 < d ≤ 0.10;and (8) 0 < d < 0.50 and 0 < e < 0.50, and optionally 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

15. Electrical device comprising the secondary battery according to claim 13 or 14.;

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