Non-aqueous electrolytes, their preparation methods, and secondary batteries and electrical devices containing them.

Abstract

This application provides a non-aqueous electrolyte, a method for preparing the same, and a secondary battery and electrical device comprising the same. The non-aqueous electrolyte contains a non-aqueous solvent and lithium ions, a first cation, and a first anion dissolved therein, wherein the first cation is a metal cation other than lithium ions (Me). n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. ‑ The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion in the non-aqueous electrolyte is D2 ppm, both based on the total mass of the non-aqueous electrolyte. Furthermore, the non-aqueous electrolyte satisfies the following conditions: D1 is 0.1 to 1250, and D1 / D2 is 0.02 to 2. The non-aqueous electrolyte of this application enables the secondary battery to simultaneously achieve good cycle performance, safety performance, and kinetic performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a non-aqueous electrolyte, its preparation method, and a secondary battery and power-consuming device containing the electrolyte. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing application and promotion of rechargeable batteries, their comprehensive performance has received growing attention. For example, rechargeable batteries need to simultaneously meet requirements such as long cycle life, high safety performance, and good rate capability. Therefore, how to provide a rechargeable battery with excellent overall performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0003] The purpose of this application is to provide a non-aqueous electrolyte, its preparation method, and a secondary battery and power device containing the electrolyte, which enables the secondary battery to simultaneously achieve good cycle performance, safety performance and kinetic performance.

[0004] The first aspect of this application provides a non-aqueous electrolyte containing a non-aqueous solvent and lithium ions, a first cation, and a first anion dissolved therein, wherein the first cation is a metal cation other than lithium ions (Me). n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. - The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion 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: D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2.

[0005] During the research process, the inventors of this application unexpectedly discovered that when the mass concentration of the first cation D1 ppm and the mass concentration of the first anion D2 ppm in the non-aqueous electrolyte meet the conditions that D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2, the first cation not only does not deteriorate the electrochemical performance of the secondary battery, but also, under the synergistic effect of the first cation and the first anion, the non-aqueous electrolyte of this application can enable the secondary battery to simultaneously achieve good cycle performance, safety performance and kinetic performance.

[0006] In any embodiment of this application, Me n+ Standard reduction potential and Li + The difference in standard reduction potential is above 1.0V. Optionally, Me n+ Ni 2+ Co2+ Mn 2+ Al 3+ and Fe 2+ At least one of them. This allows for a better guarantee of Me. n+ It is reduced before lithium ions, thus better reducing the irreversible consumption of active lithium ions during the formation of the SEI film and improving the capacity retention rate of the secondary battery.

[0007] In any embodiment of this application, D1 is 100 to 1250, optionally 200 to 1250. Thus, the secondary battery can simultaneously achieve high capacity retention, low volume expansion, and good kinetic performance.

[0008] In any embodiment of this application, D1 / D2 is 0.35 to 2, optionally 0.5 to 1.5. This is beneficial for fully utilizing the synergistic effect between the first cation and the first anion, which not only broadens the electrochemical window of the non-aqueous electrolyte, but also forms a stable and low-resistance SEI film on the surface of the negative electrode active material. As a result, the secondary battery can simultaneously achieve good cycle performance, safety performance, and kinetic performance.

[0009] In any embodiment of this application, D2 is 1 to 2000, optionally 100 to 2000. Thus, the secondary battery can simultaneously achieve high capacity retention, low volume expansion, and good kinetic performance.

[0010] In any embodiment of this application, the non-aqueous electrolyte further contains a second anion, the second anion including perchlorate anion ClO4. - bis(trifluoromethanesulfonyl)imide anion N(SO₂CF₃)₂ - NO3 - and SO4 2- At least one of them, optionally including NO3 - and SO4 2- At least one of the following. The second anion helps to give the non-aqueous electrolyte higher thermal stability, thereby improving the high-temperature stability of the secondary battery; the second anion also contributes to BF4 - Becoming free ions reduces the association between cations and anions, thereby allowing BF4 to fully exert its potential. - It improves the capacity retention and kinetic performance of secondary batteries.

[0011] In any embodiment of this application, the mass concentration of the second anion in the non-aqueous electrolyte is D3ppm, which is based on the total mass of the non-aqueous electrolyte. Optionally, D3 is 1 to 3000, and more preferably 1 to 2000.

[0012] In any embodiment of this application, the mass concentration of the second anion in the non-aqueous electrolyte is D3ppm, optionally, the D2 / D3 ratio is 0.25 to 20, more preferably 0.5 to 5. This helps to fully utilize the synergistic effect between the first and second anions, thereby not only improving the thermal stability of the non-aqueous electrolyte, but also forming a stable and low-resistance SEI film on the surface of the negative electrode active material.

[0013] In any embodiment of this application, the non-aqueous electrolyte further contains a third anion, which includes hexafluorophosphate anion PF6. - 2, bis(fluorosulfonyl)imide anion N(SO₂F)₂ - Or a combination thereof.

[0014] In any embodiment of this application, optionally, the mass percentage of the third anion in the non-aqueous electrolyte is 8% to 20%, more preferably 9% to 15%, based on the total mass of the non-aqueous electrolyte.

[0015] Optionally, in any embodiment of this application, the third anion may also include the hexafluorophosphate anion PF6. - and difluorosulfonyl imide anion N(SO2F)2 - Alternatively, the hexafluorophosphate anion PF6 - and difluorosulfonyl imide anion N(SO2F)2 - The mass ratio α is 0.2 to 3, more preferably 0.5 to 1.5. Therefore, the non-aqueous electrolyte is less prone to hydrolysis, also exhibits higher thermal stability, and facilitates the formation of an interfacial film with lower impedance.

[0016] In any embodiment of this application, the non-aqueous electrolyte further contains a fourth anion, which includes difluorooxalate-borate anion (DFOB). - 2, oxalate-borate anion BOB - AsF6 hexafluoroarsenate anion - Trifluoromethanesulfonate anion CF3SO3 - difluorophosphate anion PO2F2 - Difluorodioxanol phosphate anion DODFP - and tetrafluorooxalate phosphate anion OTFP - At least one of the following. This can further improve the interfacial properties of the positive and / or negative electrodes, or improve the ionic conductivity or thermal stability of the non-aqueous electrolyte.

[0017] In any embodiment of this application, optionally, the mass percentage of the fourth anion in the non-aqueous electrolyte is less than 2%, more preferably less than 0.5%, based on the total mass of the non-aqueous electrolyte.

[0018] In any embodiment of this application, the fourth anion includes difluorophosphate anion PO2F2. - Optionally, the difluorophosphate anion PO2F2 - The mass ratio β of the third anion is 0.01 to 0.15, more preferably 0.01 to 0.1. This can improve the ionic conductivity of the non-aqueous electrolyte, improve the properties of the positive and / or negative electrode interfacial films, and help to construct stable and low-impedance positive and / or negative electrode interfacial films, thereby effectively reducing the decomposition of the non-aqueous electrolyte and further improving the kinetic and safety performance of the secondary battery.

[0019] In any embodiment of this application, the non-aqueous solvent comprises cyclic carbonate compounds and chain carbonate compounds. The mass percentage of the cyclic carbonate compound in the non-aqueous electrolyte is E1, and the mass percentage of the chain carbonate compound is E2, both based on the total mass of the non-aqueous electrolyte. E1 is 5% to 40%, optionally 10% to 30%, and E2 is 40% to 85%, optionally 60% to 80%. This helps the non-aqueous electrolyte to have suitable viscosity and ionic conductivity, thereby facilitating lithium-ion transport.

[0020] In any embodiment of this application, the non-aqueous solvent further includes ether compounds, including at least one selected from tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethoxymethane, and diethylene glycol dimethyl ether. This helps the non-aqueous electrolyte to have suitable viscosity and / or ionic conductivity, thereby facilitating lithium-ion transport.

[0021] In any embodiment of this application, the mass percentage of ether compounds in the non-aqueous electrolyte is E3, which is optionally 0.1% to 40% based on the total mass of the non-aqueous electrolyte, and more preferably 0.5% to 20%.

[0022] In any embodiment of this application, the non-aqueous electrolyte further contains a first additive, which is fluoroethylene carbonate. This effectively improves the cycle performance of the secondary battery.

[0023] In any embodiment of this application, the mass concentration of the first additive in the non-aqueous electrolyte is D4ppm, which is based on the total mass of the non-aqueous electrolyte. Optionally, D4 is 1 to 30,000, and more preferably 100 to 20,000.

[0024] In any embodiment of this application, the mass concentration of the first additive in the non-aqueous electrolyte is D4 ppm, optionally, the D4 / D2 ratio is 5 to 500, more preferably 5 to 100. This allows for the full utilization of FEC and BF4. - The synergistic effect between them will not only not significantly increase the gas production of the secondary battery, but will also further improve the cycle performance of the secondary battery.

[0025] In any embodiment of this application, the non-aqueous electrolyte further contains a second additive, which includes at least one selected from vinylene carbonate, lithium oxalate, vinyl sulfate, and 1,3-propanesulfonate lactone. The second additive helps to further improve the interfacial properties of the positive and / or negative electrodes, thereby further improving at least one of the cycle performance, safety performance, and kinetic performance of the secondary battery.

[0026] In any embodiment of this application, optionally, the mass percentage of the second additive in the non-aqueous electrolyte is less than 5%, more preferably less than 2.5%, based on the total mass of the non-aqueous electrolyte.

[0027] A second aspect of this application provides a method for preparing a non-aqueous electrolyte, comprising the following steps: mixing a non-aqueous solvent, a lithium salt, a soluble Me salt, a soluble tetrafluoroborate, and optional additives uniformly to obtain a non-aqueous electrolyte, wherein Me represents a metal element other than lithium, wherein the non-aqueous electrolyte contains a non-aqueous solvent and lithium ions, a first cation, and a first anion dissolved therein, wherein the first cation is a metal cation other than lithium ions, Me. n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. - The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion 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: D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2.

[0028] In any embodiment of this application, Me n+ Standard reduction potential and Li + The difference in standard reduction potential is above 1.0V. Optionally, Me n+ Ni 2+ Co 2+ Mn 2+ Al 3+ and Fe 2+ At least one of them.

[0029] In any embodiment of this application, the soluble Me salt includes 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(DFOB) n Me (BOB) n Me(AsF6) n Me(CF3SO3) n Me(PO2F2) n Me (DODFP) n and Me(OTFP) n At least one of them. This helps to adjust the mass concentration of metal cations and different anions in the non-aqueous electrolyte within the desired range.

[0030] In any embodiment of this application, the soluble tetrafluoroborate comprises Me(BF4). n At least one of LiBF4. This helps to adjust the mass concentration of the metal cation and the first anion in the non-aqueous electrolyte to the desired range.

[0031] In any embodiment of this application, the non-aqueous solvent includes cyclic carbonate compounds and chain carbonate compounds. Optionally, the non-aqueous solvent simultaneously includes cyclic carbonate compounds, chain carbonate compounds, and ether compounds. This helps to adjust the mass concentrations of metal cations and different anions in the non-aqueous electrolyte within the desired range.

[0032] In any embodiment of this application, the lithium salt comprises a first lithium salt, which includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or a combination thereof. Optionally, the lithium salt further includes a second lithium salt, which includes at least one of lithium difluorooxalateborate, lithium di(oxalateborate), lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium di(fluorodi(oxalate)phosphate, and lithium tetrafluorooxalate phosphate. This helps to adjust the mass concentrations of metal cations and different anions in the non-aqueous electrolyte within the desired range.

[0033] In any embodiment of this application, the additive includes at least one of a first additive and a second additive, wherein the first additive is fluoroethylene carbonate and the second additive includes at least one of vinylene carbonate, lithium oxalate, vinyl sulfate, and 1,3-propanesulfonate lactone.

[0034] A third aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte of the first aspect of this application or a non-aqueous electrolyte obtained by the preparation method of the second aspect of this application.

[0035] In any embodiment of this application, the positive electrode comprises a material with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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=1, g+h=2.

[0036] In any embodiment of this application, M may optionally be selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W.

[0037] In any embodiment of this application, A may optionally be selected from at least one of F, N, P and S, and more preferably, A may be selected from F.

[0038] In any embodiment of this application, optionally, 0 < b < 0.98, and more preferably, 0.50 ≤ b < 0.98.

[0039] In any embodiment of this application, c = 0 is optionally provided.

[0040] In any embodiment of this application, optionally, 0 < c ≤ 0.20, and more preferably, 0 < c ≤ 0.10.

[0041] In any embodiment of this application, optionally, d = 0 and 0 < e < 0.50, more preferably, d = 0 and 0 < e ≤ 0.10.

[0042] In any embodiment of this application, optionally, e = 0 and 0 < d < 0.50, more preferably, e = 0 and 0 < d ≤ 0.10.

[0043] In any embodiment of this application, optionally, 0 < d < 0.50 and 0 < e < 0.50, more preferably, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0044] The fourth aspect of this application provides an electrical device, including the secondary battery of the third aspect of this application.

[0045] The secondary battery of this application can simultaneously achieve good cycle performance, safety performance and dynamic performance. The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0048] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0049] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0050] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0051] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0052] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0053] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, discloses the non-aqueous electrolyte of this application, its preparation method, and embodiments of secondary batteries and electrical devices comprising it. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0060] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0062] With the application and promotion of secondary batteries, their comprehensive performance has received increasing attention. Non-aqueous electrolytes are one of the key factors affecting secondary battery performance. Currently, the most widely used commercial non-aqueous electrolyte system is a mixed carbonate solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has poor thermal stability at high temperatures, decomposing to form LiF and PF5 at higher temperatures. LiF increases interfacial impedance; PF5 has strong Lewis acidity, interacting with lone pairs of electrons on oxygen atoms in solvent molecules, causing solvent decomposition. Furthermore, PF5 is highly sensitive to trace amounts of water in the non-aqueous electrolyte, generating HF upon contact with water, thus increasing the acidity of the non-aqueous electrolyte. This easily corrodes the positive electrode active material and the positive electrode current collector, causing the dissolution of transition metal ions in the positive electrode active material and deteriorating the structural stability of the positive electrode active material, thereby affecting the service life of the secondary battery.

[0063] Furthermore, researchers generally consider other metal cations in non-aqueous electrolytes, besides lithium ions, to be foreign substances or impurities that can severely affect the electrochemical performance of secondary batteries. However, the inventors of this application unexpectedly discovered, after extensive research, that when the non-aqueous electrolyte simultaneously contains appropriate amounts of the metal cations Me described below... n+and tetrafluoroborate anion BF4 - At that time, the metal cation Me n+ Not only will it not deteriorate the electrochemical performance of the secondary battery, but it also enables the secondary battery using the non-aqueous electrolyte described in this application to simultaneously achieve good cycle performance, safety performance, and kinetic performance.

[0064] Non-aqueous electrolyte

[0065] Specifically, the first aspect of this application provides a non-aqueous electrolyte.

[0066] The non-aqueous electrolyte contains a non-aqueous solvent and dissolved lithium ions, a first cation, and a first anion, wherein the first cation is a metal cation other than lithium ions (Me). n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. - The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion 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: D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2.

[0067] It should be noted that the metal cation Me in the non-aqueous electrolyte of this application n+ The electrolyte is obtained by adding a soluble salt containing Me to a non-aqueous electrolyte and then dissociating it, rather than originating from impurity phases in the raw materials used in the preparation of the non-aqueous electrolyte. Furthermore, the improvement in the secondary battery performance primarily stems from the addition of the soluble salt containing Me during the preparation of the non-aqueous electrolyte and the resulting dissociated Me. n+ Instead of metal cations that dissolve from the positive electrode active material into the non-aqueous electrolyte during the use of a secondary battery.

[0068] During their research, the inventors of this application unexpectedly discovered that when the mass concentrations of the first cation (D1 ppm) and the first anion (D2 ppm) in the non-aqueous electrolyte satisfy the conditions that D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2, the first cation not only does not degrade the electrochemical performance of the secondary battery, but also, under the synergistic effect of the first cation and the first anion, the non-aqueous electrolyte of this application enables the secondary battery to simultaneously achieve good cycle performance, safety performance, and kinetic performance. Although the mechanism is not yet clear, the inventors of this application speculate that the possible reasons include at least the following points.

[0069] First, the metal cation Me n+ It is more electrochemically active than lithium ions, so it will be preferentially reduced before lithium ions, thereby reducing the irreversible consumption of active lithium ions during the formation of the SEI film and improving the capacity retention rate of the secondary battery.

[0070] Second, the metal cation Me n+ The metallic element formed by the reduction of the negative electrode has good electronic conductivity, which can promote electron transfer and cause a thicker SEI film to form on the surface of the negative electrode active material. This can reduce the interfacial side reactions between the negative electrode active material and the non-aqueous electrolyte, improve the capacity retention rate of the secondary battery, and reduce the volume expansion rate of the secondary battery.

[0071] Third, the tetrafluoroborate anion BF4 - It participates in the formation of the SEI film on the surface of the negative electrode active material, playing a role in modifying the SEI film and improving its composition, thereby facilitating the formation of a low-resistance SEI film and reducing the impedance of the secondary battery.

[0072] Fourth, the tetrafluoroborate anion BF4 - It exhibits high thermal stability, thereby improving the high-temperature stability of secondary batteries; BF4 - It also has a low charge transfer resistance Rct, which improves the low-temperature performance of the secondary battery.

[0073] Fifth, researchers generally believe that a thicker SEI film increases the impedance of the secondary battery and deteriorates its kinetic performance. However, the inventors of this application have surprisingly discovered that by setting the mass concentrations of the first cation (D1 ppm) and the first anion (D2 ppm) in the non-aqueous electrolyte to 0.1 to 1250 and the D1 / D2 ratio to 0.02 to 2, although a thicker SEI film is formed on the surface of the negative electrode active material, the impedance of the secondary battery is actually reduced, resulting in good kinetic performance and a longer lifespan for the secondary battery.

[0074] The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, ranging from 0.1 to 1250. When D1 is within a suitable range, the secondary battery can simultaneously achieve high capacity retention, low volume expansion, and good kinetic performance. If the mass concentration of the first cation is too low, it has almost no effect on improvement, failing to be reduced at the negative electrode to form a metallic element and thus unable to increase electronic conductivity or reduce irreversible consumption of active lithium ions. Consequently, it cannot effectively improve the capacity retention and reduce the volume expansion of the secondary battery. When the mass concentration of the first cation is too high, the SEI film on the surface of the negative electrode active material becomes too thick, resulting in poor kinetic performance of the secondary battery. Simultaneously, when the mass concentration of the first cation is too high, its negative impact on the SEI film outweighs its positive impact. In this case, excessive metal elements catalyze the decomposition of the SEI film. This process generates more gas, causing the secondary battery to expand and affecting its safety performance. Furthermore, the byproducts from the decomposition deposit on the SEI film surface hinder lithium-ion transport, increasing the secondary battery impedance. Moreover, to replenish the lost SEI film, the non-aqueous electrolyte and active lithium ions inside the battery are continuously consumed, thus irreversibly affecting the capacity retention rate of the secondary battery. Optionally, D1 can be 1 to 1250, 1 to 1200, 1 to 1000, 1 to 800, 1 to 700, 1 to 600, 1 to 500, 10 to 1250, 10 to 1200, 10 to 1000, 10 to 800, 10 to 700, 10 to 600, 10 to 500, 50 to 1250, 50 to 1200, 50 to 1000, 50 to 800, 50 to 700, 50 to 600, 50 to 500, 100 to 1250. 100 to 1200, 100 to 1000, 100 to 800, 100 to 700, 100 to 600, 100 to 500, 200 to 1250, 200 to 1200, 200 to 1000, 200 to 800, 200 to 700, 200 to 600, 200 to 500, 300 to 1250, 300 to 1200, 300 to 1000, 300 to 800, 300 to 700, 300 to 600 or 300 to 500.

[0075] In non-aqueous electrolytes, the mass concentrations of the first cation (D1 ppm) and the first anion (D2 ppm) must satisfy a D1 / D2 ratio of 0.02 to 2. This ratio is beneficial for fully utilizing the synergistic effect between the first cation and the first anion, not only broadening the electrochemical window of the non-aqueous electrolyte but also forming a stable and low-resistivity SEI film on the surface of the negative electrode active material. Thus, the secondary battery can simultaneously achieve good cycle performance, safety performance, and kinetic performance. When D1 / D2 is too small, the SEI film is mainly modified by the first anion, and the first cation has almost no effect, failing to effectively improve the capacity retention rate and reduce the volume expansion rate of the secondary battery. When the D1 / D2 ratio is too large, the SEI film becomes too thick, resulting in poor kinetic performance of the secondary battery. Simultaneously, when D1 / D2 is too large, the modifying effect of the first anion on the SEI film and its effect on reducing the negative electrode interface impedance will be less than the negative effect of the first cation on the SEI film. In this case, excessive metal elements will catalyze the decomposition of the SEI film. This process generates more gas, causing the secondary battery to expand and affecting its safety performance. Furthermore, the byproducts from the decomposition deposited on the SEI film surface hinder lithium-ion transport, increasing the secondary battery impedance. Moreover, to replenish the lost SEI film, the non-aqueous electrolyte and the active lithium ions inside the battery are continuously consumed, thus irreversibly affecting the capacity retention rate of the secondary battery. Optionally, D1 / D2 can be 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, 0.35 to 2, 0.35 to 1.8, 0.35 to 1.6, 0.35 to 1.4, 0.35 to 1.2, 0.35 to 1, 0.35 to 0.9, 0.35 to 0.8, 0.35 to 0.7, 0.35 to 0.6, 0.5 to 2, 0.5 to 1.8, 0.5 to 1.6, 0.5 to 1.5, 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.

[0076] In some embodiments, optionally, the mass concentration of the first anion in the non-aqueous electrolyte is D2 ppm, where D2 is between 1 and 2000. When D2 is within a suitable range, the secondary battery can simultaneously achieve high capacity retention, low volume expansion, and good kinetic performance. Furthermore, it avoids the following situations: when the mass concentration of the first anion is too low, it cannot modify the SEI film or improve its composition, resulting in high impedance and poor kinetic performance of the secondary battery; when the mass concentration of the first anion is too high, the SEI film is mainly modified by the first anion, failing to utilize the role of the first cation in increasing electronic conductivity and reducing irreversible consumption of active lithium ions after the first cation is reduced to form a metallic element at the negative electrode, which is detrimental to improving the capacity retention of the secondary battery; in addition, because the ionic conductivity of the first anion is low, when its mass concentration is too high, it is also detrimental to the formation of a stable SEI film on the surface of the negative electrode active material. Optionally, D2 can be 10 to 2000, 10 to 1800, 10 to 1600, 10 to 1400, 10 to 1200, 10 to 1000, 100 to 2000, 100 to 1800, 100 to 1600, 100 to 1400, 100 to 1200, 100 to 1000, 200 to 2000, 200 to 1800, 200 to 1600, 200 to 1400, 200 to 1200, 200 to 1000, 500 to 2000, 500 to 1800, 500 to 1600, 500 to 1400, 500 to 1200, or 500 to 1000.

[0077] In this application, the metal cation Me n+ The element Me represents a metal cation other than lithium ions, where n represents the valence of the metal cation. For example, optionally, Me represents at least one transition metal element or a metal element from Groups 5 to 7, where n represents 1, 2, 3, 4, 5, or 6. Alternatively, Me... n+ Standard reduction potential (vs. standard hydrogen electrode potential) and Li + The difference between the standard reduction potential (vs. the standard hydrogen electrode potential, i.e., -3.04V) is greater than 1.0V. n+ Standard reduction potential and Li + A difference in standard reduction potential greater than 1.0V can better guarantee Me n+ It is reduced before lithium ions, thus better reducing the irreversible consumption of active lithium ions during the formation of the SEI film and improving the capacity retention rate of the secondary battery.

[0078] Optionally, Me represents at least one of Ni, Co, Mn, Al, and Fe. More alternatively, Me n+ Ni 2+ Co 2+ Mn2 + Al 3+ and Fe 2+ At least one of them.

[0079] In some embodiments, the non-aqueous electrolyte may optionally contain a second anion, the second anion including perchlorate anion ClO4. - bis(trifluoromethanesulfonyl)imide anion N(SO₂CF₃)₂ - (abbreviated as TFSI) - NO3 - and SO4 2- At least one of them, more preferably including NO3 - and SO4 2- At least one of the following. The mass concentration of the second anion in the non-aqueous electrolyte is D3 ppm, which, based on the total mass of the non-aqueous electrolyte, optionally ranges from 1 to 3000. The second anion contributes to the high thermal stability of the non-aqueous electrolyte, thereby improving the high-temperature stability of the secondary battery; the second anion also contributes to BF4 - Becoming free ions reduces the association between cations and anions, thereby allowing BF4 to fully exert its potential. - Improvement of secondary battery capacity retention and kinetic performance. More preferably, D3 is 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.

[0080] In some embodiments, optionally, the mass concentrations of the first anion D2 ppm and the second anion D3 ppm also satisfy the following: D2 / D3 is 0.25 to 20. The inventors further discovered that when D2 / D3 is within a suitable range, it helps to fully utilize the synergistic effect between the first and second anions, thereby not only improving the thermal stability of the non-aqueous electrolyte but also forming a stable and low-resistance SEI film on the surface of the negative electrode active material. More optionally, D2 / D3 can 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.

[0081] In some embodiments, the non-aqueous electrolyte may optionally contain a third anion, the third anion including hexafluorophosphate anion PF6. - 2, bis(fluorosulfonyl)imide anion N(SO₂F)₂ - (abbreviated as FSI) - (or a combination thereof). Optionally, the mass percentage of the third anion in the non-aqueous electrolyte is 8% to 20%, more preferably 9% to 18%, and even more preferably 9% to 15%, based on the total mass of the non-aqueous electrolyte.

[0082] The non-aqueous electrolyte of this application uses a compound formed by the third anion and lithium ions as the main lithium salt, that is, lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide can be used as the main lithium salt. Lithium hexafluorophosphate has the characteristics of high ionic conductivity and is not easily corroded by the positive electrode current collector. As the main 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 F2NO4S2·Li, in which the N atom is connected to two electron-withdrawing sulfonyl groups, thereby fully delocalizing the charge on the N atom. As a result, lithium bis(fluorosulfonyl)imide has a low lattice energy and is easy to dissociate, which can improve the ionic conductivity and reduce the viscosity of the non-aqueous electrolyte. In addition, lithium bis(fluorosulfonyl)imide also has the characteristics of good high temperature resistance and is not easily hydrolyzed. It can form a thinner interface film with lower impedance and higher thermal stability on the surface of the negative electrode active material, thereby reducing the side reactions between the negative electrode active material and the non-aqueous electrolyte.

[0083] In some embodiments, the third anion includes the hexafluorophosphate anion PF6. - That is, this application can use lithium hexafluorophosphate (LiPF6) as the main lithium salt.

[0084] In some embodiments, the third anion includes the difluorosulfonamide anion N(SO₂F)₂. - That is, this application can use lithium bisfluorosulfonylimide (LiFSI) as the main lithium salt.

[0085] In some embodiments, the third anion also includes the hexafluorophosphate anion PF6. - and difluorosulfonyl imide anion N(SO2F)2 - That is, this application can use lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) together as the main lithium salt. Optionally, the hexafluorophosphate anion PF6 - and difluorosulfonyl imide anion N(SO2F)2 -The mass ratio α is 0.2 to 3, more preferably 0.3 to 2, 0.4 to 1.8, or 0.5 to 1.5. Therefore, the non-aqueous electrolyte is less prone to hydrolysis, while also exhibiting higher thermal stability and facilitating the formation of an interfacial film with lower impedance.

[0086] In some embodiments, the non-aqueous electrolyte may optionally contain a fourth anion, the fourth anion including difluorooxalate borate anion (DFOB). - 2, oxalate-borate anion BOB - AsF6 hexafluoroarsenate anion - Trifluoromethanesulfonate anion CF3SO3 - difluorophosphate anion PO2F2 - Difluorodioxanol phosphate anion DODFP - and tetrafluorooxalate phosphate anion OTFP - At least one of the following. This can further improve the interfacial properties of the positive and / or negative electrodes, or improve the ionic conductivity or thermal stability of the non-aqueous electrolyte. Optionally, the mass percentage of the fourth anion in the non-aqueous electrolyte is less than 2%, more preferably less than 0.5%, based on the total mass of the non-aqueous electrolyte.

[0087] Optionally, in some embodiments, the fourth anion includes difluorophosphate anion PO2F2. - This can improve the ionic conductivity of the non-aqueous electrolyte, enhance the properties of the positive and / or negative electrode interfacial films, and help construct stable and low-impedance positive and / or negative electrode interfacial films, thereby effectively reducing the decomposition of the non-aqueous electrolyte and further improving the kinetic and safety performance of the secondary battery. Optionally, the difluorophosphate anion PO2F2 - The mass ratio β of the third anion is 0.01 to 0.15, more preferably 0.01 to 0.1.

[0088] [additive]

[0089] In some embodiments, the non-aqueous electrolyte may optionally contain a first additive, which is fluoroethylene carbonate (FEC). The mass concentration of the first additive in the non-aqueous electrolyte is D4 ppm, and D4 may optionally be 1 to 30,000 based on the total mass of the non-aqueous electrolyte.

[0090] For secondary batteries, FEC can undergo reduction and decomposition reactions at higher potentials, forming a flexible SEI film on the surface of the negative electrode active material. Simultaneously, it can suppress the reduction and decomposition of organic solvents at lower potentials and inhibit the intercalation of organic solvents into the negative electrode active material. Therefore, when non-aqueous electrolytes contain FEC, the cycle performance of secondary batteries can be effectively improved. Furthermore, FEC is resistant to high-voltage oxidation, which is beneficial for matching high-voltage positive electrode active materials, thereby contributing to increased energy density of the secondary battery.

[0091] When the non-aqueous electrolyte contains FEC, it is beneficial to fully utilize the improving effect of FEC on the cycle performance and energy density of the secondary battery. Furthermore, FEC has a high dielectric constant, therefore, the presence of FEC in the non-aqueous electrolyte helps to enhance the activity of BF4 in the electrolyte. - Becoming free ions reduces the association between cations and anions, thereby allowing BF4 to fully exert its potential. - It improves the capacity retention and kinetic performance of secondary batteries. However, FEC decomposes to form HF, which can disrupt the structural stability of the positive electrode active material, increase gas production in the secondary battery, and deteriorate its storage performance. Therefore, its content should not be too high.

[0092] Alternatively, D4 can be 1 to 25000, 1 to 20000, 1 to 15000, 1 to 10000, 1 to 8000, 1 to 5000, 1 to 2000, 100 to 25000, 100 to 20000, 100 to 15000, 100 to 10000, 100 to 8000, 100 to 5000, or 100 to 2000.

[0093] In some embodiments, optionally, the mass concentrations of the first anion (D2 ppm) and the first additive (D4 ppm) satisfy a D4 / D2 ratio of 5 to 500. The inventors further discovered that when D4 / D2 is within a suitable range, FEC and BF4 can be fully utilized. - The synergistic effect between them will not only not significantly increase the gas production of the secondary battery, but will also further improve the cycle performance of the secondary battery. Alternatively, D4 / D2 can be 5 to 500, 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.

[0094] In some embodiments, the non-aqueous electrolyte may optionally contain a second additive, the second additive comprising at least one of vinylene carbonate (VC), lithium oxalate, vinyl sulfate (DTD), and 1,3-propanesulfonate lactone (PS). The second additive helps to further improve the interfacial properties of the positive and / or negative electrodes, thereby further improving at least one of the cycle performance, safety performance, and kinetic performance of the secondary battery. Optionally, the mass percentage of the second additive in the non-aqueous electrolyte is less than 5%, more preferably less than 2.5%, based on the total mass of the non-aqueous electrolyte.

[0095] In some embodiments, the non-aqueous electrolyte may optionally contain the first and second additives mentioned above, which helps to further improve the interfacial performance of the positive and / or negative electrodes, thereby further improving the cycle performance, safety performance and kinetic performance of the secondary battery.

[0096] [Non-aqueous solvent]

[0097] In this application, the non-aqueous solvent is mainly used to dissolve the lithium salt, causing it to form conductive ions, while simultaneously reducing the number of cations (e.g., lithium ions, metal cations Me) in the non-aqueous electrolyte. n+ Association of ions and anions (e.g., first anion, second anion, third anion, fourth anion, etc.).

[0098] In some embodiments, the non-aqueous solvent includes cyclic carbonate compounds and chain carbonate compounds. Cyclic carbonate compounds, due to their higher dielectric constant, can increase the ionic conductivity of the non-aqueous electrolyte, while chain carbonate compounds, due to their lower viscosity, can reduce the viscosity of the non-aqueous electrolyte. Therefore, when the non-aqueous solvent includes both cyclic and chain carbonate compounds, it helps the non-aqueous electrolyte to have suitable viscosity and ionic conductivity, thereby facilitating lithium-ion transport. As an example, the cyclic carbonate compound may include at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). As an example, the chain carbonate compound may include at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0099] In some embodiments, the non-aqueous solvent may further include solvents other than cyclic carbonate compounds and chain carbonate compounds, for example, at least one of carboxylic acid ester compounds, sulfone compounds, and ether compounds. As examples, carboxylic acid ester compounds may include 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 1,4-butyrolactone (GBL). As examples, sulfone compounds may include at least one of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). As examples, ether compounds include at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxolane (DOL), ethylene glycol monomethyl ether, ethylene glycol dimethyl ether (DME), tetraethylene glycol dimethyl ether, dimethoxymethane (DMM), and diethylene glycol dimethyl ether (DG). These solvents help non-aqueous electrolytes achieve suitable viscosity and / or ionic conductivity, thereby facilitating lithium-ion transport. Furthermore, these solvents also contribute to the presence of BF4 in non-aqueous electrolytes. - Becoming free ions reduces the association between cations and anions, thereby allowing BF4 to fully exert its potential. - It improves the capacity retention and kinetic performance of secondary batteries.

[0100] Optionally, in some embodiments, the non-aqueous solvent includes cyclic carbonate compounds, chain carbonate compounds, and ether compounds.

[0101] The mass percentage of cyclic carbonate compounds in the non-aqueous electrolyte is E1, the mass percentage of chain carbonate compounds is E2, and the mass percentage of ether compounds is E3, all based on the total mass of the non-aqueous electrolyte. In some embodiments, E1 is 5% to 40%. Optionally, E1 is 10% to 30%; E2 is 40% to 85%. Optionally, E2 is 60% to 80%; E3 is 0.1% to 40%, and optionally, E3 is 0.5% to 20%.

[0102] In this application, the components (e.g., the first cation, the first anion, the second anion, the third anion, the fourth anion, the first additive, the second additive, etc.) and their contents in the non-aqueous electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), or inductively coupled plasma optical emission spectrometry (ICP-OES).

[0103] It should be noted that during the non-aqueous electrolyte testing of this application, freshly prepared non-aqueous electrolyte can be used directly, or it can be obtained from a secondary battery. An exemplary method for obtaining non-aqueous electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cutoff voltage (for safety, the battery is generally left fully discharged), followed by centrifugation. A suitable amount of the centrifuged liquid is then taken as the non-aqueous electrolyte. Alternatively, the non-aqueous electrolyte can be obtained directly from the secondary battery's filling port.

[0104] Preparation method

[0105] The second aspect of this application provides a method for preparing a non-aqueous electrolyte, which can be used to obtain the non-aqueous electrolyte of the first aspect of this application.

[0106] Specifically, the preparation method of the non-aqueous electrolyte includes the following steps: mixing a non-aqueous solvent, a lithium salt, a soluble Me salt, a soluble tetrafluoroborate, and optional additives uniformly to obtain a non-aqueous electrolyte, where Me represents a metal element other than lithium. The non-aqueous electrolyte contains a non-aqueous solvent and lithium ions, a first cation, and a first anion dissolved therein, wherein the first cation is a metal cation other than lithium, Me. n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. - The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion 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: D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2.

[0107] Optionally, Me represents at least one of the transition metals and group 5 through 7 metals. Optionally, Me n+ Standard reduction potential (vs. standard hydrogen electrode potential) and Li + The difference between the standard reduction potential (vs. the standard hydrogen electrode potential, i.e., -3.04V) is greater than 1.0V. More preferably, Me represents at least one of Ni, Co, Mn, Al, and Fe. Alternatively, Me... n+ Ni 2+ Co 2+ Mn 2+ Al 3+ and Fe 2+ At least one of them.

[0108] There are no particular restrictions on the order in which the materials are added; for example, they can be added at the same time or in batches.

[0109] The soluble Me salt can be used with Me. n+ And the compound is soluble in the non-aqueous electrolyte. In some embodiments, the soluble Me salt optionally includes 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(DFOB) n Me (BOB) n Me(AsF6) n Me(CF3SO3) n Me(PO2F2) n Me (DODFP) n and Me(OTFP) n At least one of the following. More alternatively, the soluble Me salt includes Me(BF4). n Me(DFOB) n Me(NO3) n Me(SO4) n / 2 At least one of them. This helps to adjust the mass concentration of metal cations and different anions in the non-aqueous electrolyte within the desired range.

[0110] In some embodiments, the soluble tetrafluoroborate may optionally include Me(BF4). n At least one of LiBF4. This helps to adjust the mass concentration of the metal cation and the first anion in the non-aqueous electrolyte to the desired range.

[0111] In some embodiments, optionally, at least one of the soluble Me salt and the soluble tetrafluoroborate includes Me(BF4). n This helps secondary batteries to better balance good cycle performance, safety performance, and kinetic performance.

[0112] In some embodiments, the non-aqueous solvent comprises cyclic carbonate compounds and chain carbonate compounds. Optionally, the non-aqueous solvent may also comprise other solvents besides cyclic carbonate compounds and chain carbonate compounds, for example, at least one of carboxylic acid ester compounds, sulfone compounds, and ether compounds. More preferably, the non-aqueous solvent comprises cyclic carbonate compounds, chain carbonate compounds, and ether compounds simultaneously. Ether compounds help increase the degree of dissociation of soluble Me salts and soluble tetrafluoroborates in the non-aqueous electrolyte, thereby helping to adjust the mass concentrations of metal cations and different anions in the non-aqueous electrolyte within the desired range.

[0113] In some embodiments, the lithium salt comprises a first lithium salt, which comprises lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), or a combination thereof. The first lithium salt, as the main lithium salt, may have a mass percentage of 8% to 20%, optionally 9% to 18%, and more preferably 9% to 15%, based on the total mass of the non-aqueous electrolyte.

[0114] The non-aqueous electrolyte of this application uses lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide as the main lithium salt. Lithium hexafluorophosphate has the characteristics of high ionic conductivity and non-corrosion of the positive electrode current collector. As the main 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 F2NO4S2·Li, in which the N atom is connected to two electron-withdrawing sulfonyl groups, thereby fully delocalizing the charge on the N atom. As a result, lithium bis(fluorosulfonyl)imide has a low lattice energy and is easy to dissociate, which can improve the ionic conductivity and reduce the viscosity of the non-aqueous electrolyte. In addition, lithium bis(fluorosulfonyl)imide also has the characteristics of good high temperature resistance and non-hydrolysis resistance, which can form a thinner interface film with lower impedance and higher thermal stability on the surface of the negative electrode active material, thereby reducing the side reactions between the negative electrode active material and the non-aqueous electrolyte.

[0115] In some embodiments, the first lithium salt comprises lithium hexafluorophosphate (LiPF6).

[0116] In some embodiments, the first lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI).

[0117] In some embodiments, the first lithium salt comprises both lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI). Optionally, the mass ratio of lithium hexafluorophosphate to lithium bisfluorosulfonylimide is 0.2 to 3, more preferably 0.3 to 2, 0.4 to 1.8, or 0.5 to 1.5. Thus, the non-aqueous electrolyte is less prone to hydrolysis and also achieves higher thermal stability, while simultaneously contributing to the formation of an interface film with lower impedance.

[0118] In some embodiments, the lithium salt may optionally include a second lithium salt, which includes at least one of lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorodiooxalate phosphate (LiDODFP), and lithium tetrafluorooxalate phosphate (LiOTFP). The second lithium salt, as an auxiliary lithium salt, can further improve the interfacial properties of the positive and / or negative electrodes, or improve the ionic conductivity or thermal stability of the non-aqueous electrolyte. Optionally, the second lithium salt has a mass percentage content of less than 2% in the non-aqueous electrolyte, more preferably less than 0.5%, based on the total mass of the non-aqueous electrolyte.

[0119] In some embodiments, optionally, the second lithium salt comprises lithium difluorophosphate (LiPO2F2), lithium tetrafluorooxalate phosphate (LiOTFP), or a combination thereof; more preferably, the second lithium salt comprises lithium difluorophosphate (LiPO2F2). Lithium difluorophosphate exhibits high electrochemical stability, which can improve the ionic conductivity of non-aqueous electrolytes, enhance the properties of the positive and / or negative electrode interfacial films, and contribute to the construction of stable and low-resistance positive and / or negative electrode interfacial films, thereby effectively reducing the decomposition of non-aqueous electrolytes and further improving the kinetic and safety performance of the secondary battery. Optionally, the mass ratio of lithium difluorophosphate to the first lithium salt is 0.01 to 0.15, more preferably 0.01 to 0.1.

[0120] In some embodiments, the additive includes at least one of a first additive and a second additive, wherein the first additive is fluoroethylene carbonate (FEC) and the second additive includes at least one of vinylene carbonate (VC), lithium oxalate, vinyl sulfate (DTD), and 1,3-propanesulfonate lactone (PS).

[0121] By adjusting the types and amounts of raw materials in the non-aqueous electrolyte, it is helpful to regulate the degree of dissociation of lithium salt, soluble Me salt, and soluble tetrafluoroborate in the non-aqueous electrolyte, and to obtain a non-aqueous electrolyte that meets the required mass concentrations of metal cations and anions (e.g., first anion, second anion, third anion, fourth anion, etc.). The types and specific contents of each component in the resulting non-aqueous electrolyte are as described in the first aspect of the embodiments of this application.

[0122] Secondary batteries

[0123] A third aspect of this application provides a secondary battery, comprising an electrode assembly and a non-aqueous electrolyte. The non-aqueous electrolyte is the same as that of the first aspect of this application or a non-aqueous electrolyte obtained using the method of the second aspect of this application. This allows the secondary battery to simultaneously achieve good cycle performance, safety performance, and kinetic performance. The secondary battery of this application can be a lithium secondary battery, particularly a lithium-ion secondary battery.

[0124] The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is placed between the positive and negative electrodes and mainly serves to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through.

[0125] [Positive electrode plate]

[0126] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0127] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include at least one of 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 their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. These positive electrode active materials may be used alone or in combination of two or more.

[0128] In some embodiments, the positive electrode active material may optionally comprise a material with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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=1, g+h=2.

[0129] The molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The layered material can be selectively modified by M cation doping, A anion doping, or by simultaneous doping with M cation and A anion. The resulting layered material has a more stable crystal structure, which can further improve the electrochemical performance of the secondary battery, such as cycle performance and kinetic performance.

[0130] 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.

[0131] In some embodiments, A is selected from at least one of F, N, P, and S. Optionally, A is selected from F. After F doping modification, Li a Ni b Co c Mn d Al e M f O g A h The crystal structure is more stable, which enables secondary batteries to have better cycle performance and kinetic performance.

[0132] The values ​​of a, b, c, d, e, f, g, and h satisfy the following condition: that makes Li a Ni b Co c Mn d Al e M f O g A h Maintain electrical neutrality.

[0133] In some embodiments, 0 < b < 0.98. 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.

[0134] In some embodiments, c = 0.

[0135] In some embodiments, 0 < c ≤ 0.20. 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.

[0136] In some embodiments, d = 0 and 0 < e < 0.50. Alternatively, 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.

[0137] 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.

[0138] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Alternatively, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0139] In some embodiments, g = 2, h = 0.

[0140] In some embodiments, g = 0, h = 2.

[0141] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0142] As an example, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h Layered materials including but not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co0.05 Mn 0.15 O2, LiNi 0.7 Mn 0.3 O2, LiNi 0.69 Co 0.01 Mn 0.3 O2, LiNi 0.68 Co 0.02 Mn 0.3 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2, LiNi 0.61 Co 0.09 Mn 0.3 At least one of O2.

[0143] Li a Ni b Co c Mn d Al e M f O g A h It can be prepared according to conventional methods in the art. An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M-element precursor, and an A-element precursor are mixed and then sintered. The sintering atmosphere can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to actual conditions.

[0144] As examples, lithium sources include, but are not limited to, 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). As examples, nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As examples, cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As examples, manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As examples, aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As examples, precursors of element M include, but are not limited to, at least one of oxides, nitrate compounds, carbonate compounds, hydroxides, and acetate compounds of element M. As an example, the precursors of element A include, but are not limited to, at least one of 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 sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0145] In some embodiments, based on the total mass of the positive electrode film, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The layered material has a mass percentage content of 80% to 99%. For example, the molecular formula is Li. a Ni b Co c Mn d Al e M f O g A h The mass percentage of the layered material can be any range consisting of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher. Optionally, the molecular formula is Li. a Ni b Co c Mn d Al e M f O g A hThe mass percentage of the layered material is 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%.

[0146] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode film layer.

[0147] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode film layer.

[0148] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. An example of a polymer substrate may be polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0149] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0150] [Negative electrode plate]

[0151] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0152] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0153] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is less than 5% based on the total mass of the negative electrode film layer.

[0154] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is less than 5% based on the total mass of the negative electrode film layer.

[0155] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is less than 2% based on the total mass of the negative electrode film.

[0156] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0157] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0158] [Isolation membrane]

[0159] The separator is disposed between the positive electrode and the negative electrode, mainly to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0160] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0161] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0162] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and the non-aqueous electrolyte described above.

[0163] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0164] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1This is an example of a square-structured secondary battery 5.

[0165] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. A non-aqueous electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0166] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with a non-aqueous electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0167] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0168] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0169] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0170] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0171] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0172] Electrical appliances

[0173] A fourth aspect of this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in 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 may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0174] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0175] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0176] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0177] Example

[0178] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0179] The secondary batteries of Examples 1 to 30 and Comparative Examples 1 to 3 were all prepared according to the following method.

[0180] Preparation of positive electrode sheet

[0181] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0182] Preparation of negative electrode sheet

[0183] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0184] Separating membrane

[0185] Porous polyethylene (PE) membrane is used as the separator.

[0186] Preparation of non-aqueous electrolyte

[0187] The cyclic carbonate compound and the chain carbonate compound were mixed evenly according to the composition shown in Table 1 to obtain an organic solvent. Then, lithium salt, additives, soluble Me salt, and soluble tetrafluoroborate were added to the organic solvent according to the composition shown in Table 1 and mixed evenly to obtain a non-aqueous electrolyte. In Table 1, the amount of each component added is based on the total mass of the non-aqueous electrolyte.

[0188] Preparation of secondary batteries

[0189] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, and the above-mentioned non-aqueous electrolyte is added. After processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0190] Test section

[0191] (1) Composition and content test of non-aqueous electrolyte

[0192] Testing of metal cations: After fully discharging the prepared secondary battery, 10 ml of free electrolyte was taken out from the injection port and tested using an inductively coupled plasma atomic emission spectrometer (ICP-7400) from Thermo Fisher Scientific. The mass concentration of the first cation, D1 ppm, in the non-aqueous electrolyte was calculated based on the test results.

[0193] Anion testing: After fully discharging the prepared secondary battery, approximately 1.5 ml of free electrolyte was removed from the injection port for later use. The mass concentrations of the first anion (D2 ppm) and the second anion (D3 ppm) were measured using nuclear magnetic resonance spectroscopy.

[0194] The specific testing steps are as follows: In a nitrogen-filled glove box, add 500 μl of deuterated reagent to the NMR tube, and add 100 μl of the non-aqueous electrolyte sample to the NMR tube. Shake the NMR tube to dissolve the non-aqueous electrolyte in the deuterated reagent. The test is performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the NMR test and sample preparation are conducted in a nitrogen atmosphere (H2O content less than 0.1 ppm, O2 content less than 0.1 ppm). Simultaneously, all instruments involved in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours.

[0195] The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0196] (2) Cyclic performance test of secondary batteries at room temperature

[0197] At 25℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 25℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0198] (3) High-temperature cycle performance test of secondary batteries

[0199] At 45℃, the secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 45℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0200] (4) Initial DC internal resistance test of secondary battery

[0201] At 25℃, the secondary battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current is 0.05C, at which point the secondary battery is fully charged. The secondary battery is then discharged at a constant current of 0.5C and adjusted to 50% SOC, and the voltage of the secondary battery at this point is recorded as U1. The secondary battery is then discharged at a constant current of 4C I1 for 30 seconds, and the voltage at the end of the discharge is recorded as U2, using a 0.1-second sampling time. The initial DC internal resistance of the secondary battery is expressed as the DC internal resistance at 50% SOC, and the initial DC internal resistance (mΩ) of the secondary battery is given by (U1-U2) / I1.

[0202] (5) High-temperature storage performance test of secondary batteries

[0203] At 60℃, the secondary battery is charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reaches 0.05C. The volume of the secondary battery at this point is measured using the water displacement method and recorded as V0. The secondary battery is then placed in a 60℃ constant temperature chamber and stored for 30 days. After storage, its volume is measured again using the water displacement method and recorded as V1. The volume expansion rate (%) of the secondary battery after 30 days of storage at 60℃ is calculated as [(V1-V0) / V0]×100%.

[0204] Table 2 presents the test results for Examples 1 to 30 and Comparative Examples 1 to 3.

[0205] The inventors also investigated the effect of the first cation type on the performance of the secondary battery. The secondary batteries of Examples 31 to 36 were prepared using a method similar to that of Example 5, except that the types of soluble Me salt and soluble tetrafluoroborate were different, as detailed in Table 3. Table 4 shows the test results for Examples 31 to 36.

[0206]

[0207]

[0208]

[0209]

[0210]

[0211] Based on the test results of Examples 1 to 30, it can be seen that when the non-aqueous electrolyte contains the first cation and the first anion of this application, and the mass concentration of the first cation D1 ppm and the mass concentration of the first anion D2 ppm satisfy D1 = 0.1 to 1250 and D1 / D2 = 0.02 to 2, the first cation will not only not degrade the electrochemical performance of the secondary battery, but also, under the synergistic effect of the first cation and the first anion, the non-aqueous electrolyte of this application can enable the secondary battery to simultaneously have a high cycle capacity retention rate, a low internal resistance, and a low volume expansion rate.

[0212] Based on the test results of Comparative Examples 1 to 3, it can be seen that when the non-aqueous electrolyte contains only the first anion and no first cation or contains too much first cation, it cannot simultaneously improve the cycle performance, kinetic performance and storage performance of the secondary battery.

[0213] The test results from Examples 5, 22 to 24 also show that different types of lithium salts in the non-aqueous electrolyte have slightly different effects on improving the electrochemical performance of the secondary battery. In particular, when the lithium salt includes both lithium hexafluorophosphate and lithium bisfluorosulfonylimide, and more specifically, when the lithium salt further includes lithium difluorophosphate, it helps to improve the overall performance of the secondary battery.

[0214] Based on the test results of Examples 5, 25 to 30, it can be seen that when the non-aqueous electrolyte further contains the first additive and / or the second additive of this application, it helps to further improve at least one of the cycle performance, kinetic performance and storage performance of the secondary battery.

[0215] Based on the test results of Examples 5, 31 to 36, it can also be seen that when Me n+ Satisfy Men+ Standard reduction potential (vs. standard hydrogen electrode potential) and Li + The difference between the standard reduction potential (vs. the standard hydrogen electrode potential, i.e., -3.04V) and the standard reduction potential is greater than 1.0V, especially for Ni. 2+ Co 2+ Mn 2+ Al 3+ and Fe 2+ When at least one of these is used, it helps to better improve the overall performance of the secondary battery. Examples 35 and 36 respectively used Na... + and K + As the first cation, due to its standard reduction potential being similar to that of Li + The standard reduction potential is close, so its effect on increasing electronic conductivity and reducing irreversible consumption of active lithium ions is poor, resulting in a poor improvement effect on the overall performance of secondary batteries.

[0216] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A non-aqueous electrolyte comprising a non-aqueous solvent and lithium ions, a first cation, and a first anion dissolved therein, wherein, The first cation is a metal cation other than lithium ions (Me). n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. - The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion 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: D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2; Me n+ Standard reduction potential and Li + The difference in standard reduction potential is greater than 1.0V; The non-aqueous electrolyte also contains a second anion, which includes perchlorate anion ClO4. - bis(trifluoromethanesulfonyl)imide anion N(SO₂CF₃)₂ - NO3 - and SO4 2- At least one of them; 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. D3 ranges from 1 to 3000; D2 / D3 ranges from 0.25 to 20; The non-aqueous electrolyte is obtained by discharging the secondary battery to the discharge cutoff voltage after the secondary battery is prepared.

2. The non-aqueous electrolyte according to claim 1, characterized in that, Me n+ For Ni 2+ Co 2+ Mn 2+ Al 3+ and Fe 2+ At least one of them.

3. The non-aqueous electrolyte according to any one of claims 1-2, characterized in that, D1 is between 100 and 1250; and / or, D1 / D2 is 0.35 to 2; and / or, D2 ranges from 1 to 2000.

4. The non-aqueous electrolyte according to claim 3, characterized in that, D1 ranges from 200 to 1250.

5. The non-aqueous electrolyte according to claim 3, characterized in that, D1 / D2 is between 0.5 and 1.

5.

6. The non-aqueous electrolyte according to claim 3, characterized in that, D2 is between 100 and 2000.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The second anion includes NO3. - and SO4 2- At least one of them.

8. The non-aqueous electrolyte according to claim 1, characterized in that, D3 ranges from 1 to 2000.

9. The non-aqueous electrolyte according to claim 1, characterized in that, D2 / D3 is between 0.5 and 5.

10. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte also contains a third anion, which includes hexafluorophosphate anion PF6. - 2, bis(fluorosulfonyl)imide anion N(SO₂F)₂ - Or a combination thereof.

11. The non-aqueous electrolyte according to claim 10, characterized in that, The mass percentage of the third anion in the non-aqueous electrolyte is 8% to 20%, based on the total mass of the non-aqueous electrolyte.

12. The non-aqueous electrolyte according to claim 11, characterized in that, The mass percentage of the third anion in the non-aqueous electrolyte is 9% to 15%, based on the total mass of the non-aqueous electrolyte.

13. The non-aqueous electrolyte according to claim 10, characterized in that, The third anion also includes hexafluorophosphate anion PF6. - and difluorosulfonyl imide anion N(SO2F)2 - .

14. The non-aqueous electrolyte according to claim 13, characterized in that, The hexafluorophosphate anion PF6 - and difluorosulfonyl imide anion N(SO2F)2 - The mass ratio α is 0.2 to 3.

15. The non-aqueous electrolyte according to claim 14, characterized in that, α ranges from 0.5 to 1.

5.

16. The non-aqueous electrolyte according to claim 10, characterized in that, The non-aqueous electrolyte also contains a fourth anion, which includes difluorooxalate-borate anion (DFOB). - 2, oxalate-borate anion BOB - AsF6 hexafluoroarsenate anion - Trifluoromethanesulfonate anion CF3SO3 - difluorophosphate anion PO2F2 - Difluorodioxanol phosphate anion DODFP - and tetrafluorooxalate phosphate anion OTFP - At least one of them.

17. The non-aqueous electrolyte according to claim 16, characterized in that, The mass percentage of the fourth anion in the non-aqueous electrolyte is less than 2%, based on the total mass of the non-aqueous electrolyte.

18. The non-aqueous electrolyte according to claim 17, characterized in that, The mass percentage of the fourth anion in the non-aqueous electrolyte is less than 0.5%, based on the total mass of the non-aqueous electrolyte.

19. The non-aqueous electrolyte according to claim 16, characterized in that, The fourth anion includes difluorophosphate anion PO2F2. - .

20. The non-aqueous electrolyte according to claim 19, characterized in that, The difluorophosphate anion PO2F2 - The mass ratio β of the third anion is 0.01 to 0.

15.

21. The non-aqueous electrolyte according to claim 20, characterized in that, β ranges from 0.01 to 0.

1.

22. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous solvent includes cyclic carbonate compounds and chain carbonate compounds. The mass percentage of cyclic carbonate compounds in the non-aqueous electrolyte is E1, and the mass percentage of chain carbonate compounds is E2, both based on the total mass of the non-aqueous electrolyte. E1 ranges from 5% to 40%; E2 ranges from 40% to 85%.

23. The non-aqueous electrolyte according to claim 22, characterized in that, E1 ranges from 10% to 30%.

24. The non-aqueous electrolyte according to claim 22, characterized in that, E2 is 60% to 80%.

25. The non-aqueous electrolyte according to claim 22, characterized in that, The non-aqueous solvent also includes ether compounds, which include at least one selected from tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethoxymethane, and diethylene glycol dimethyl ether. The mass percentage of ether compounds in the non-aqueous electrolyte is E3, which ranges from 0.1% to 40% based on the total mass of the non-aqueous electrolyte.

26. The non-aqueous electrolyte according to claim 25, characterized in that, E3 ranges from 0.5% to 20%.

27. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte also contains a first additive, which is fluoroethylene carbonate. The mass concentration of the first additive in the non-aqueous electrolyte is D4 ppm, based on the total mass of the non-aqueous electrolyte. D4 is 1 to 30000; and / or, D4 / D2 ranges from 5 to 500.

28. The non-aqueous electrolyte according to claim 27, characterized in that, D4 ranges from 100 to 20000.

29. The non-aqueous electrolyte according to claim 27, characterized in that, D4 / D2 ranges from 5 to 100.

30. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte also contains a second additive, which includes at least one of vinylene carbonate, lithium oxalate, vinyl sulfate, and 1,3-propanesulfonate lactone. The mass percentage of the second additive in the non-aqueous electrolyte is less than 5%, based on the total mass of the non-aqueous electrolyte.

31. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage of the second additive in the non-aqueous electrolyte is less than 2.5%, based on the total mass of the non-aqueous electrolyte.

32. A method for preparing a non-aqueous electrolyte, comprising the following steps: A non-aqueous solvent, lithium salt, soluble Me salt, and soluble tetrafluoroborate, or a non-aqueous solvent, lithium salt, soluble Me salt, soluble tetrafluoroborate, and additives are mixed evenly and injected into an electrode assembly to form a secondary battery. The secondary battery is then discharged to the discharge cutoff voltage to obtain a non-aqueous electrolyte. Me represents a metallic element other than lithium. in, The non-aqueous electrolyte contains a non-aqueous solvent and dissolved lithium ions, a first cation, and a first anion, wherein the first cation is a metal cation other than lithium ions (Me). n+ 'n' represents the valence of the metal cation, and the first anion is tetrafluoroborate anion BF4. - The mass concentration of the first cation in the non-aqueous electrolyte is D1 ppm, and the mass concentration of the first anion 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: D1 is 0.1 to 1250 and D1 / D2 is 0.02 to 2; Me n+ Standard reduction potential and Li + The difference in standard reduction potential is greater than 1.0V; The non-aqueous electrolyte also contains a second anion, which includes perchlorate anion ClO4. - bis(trifluoromethanesulfonyl)imide anion N(SO₂CF₃)₂ - NO3 - and SO4 2- At least one of them; 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. D3 ranges from 1 to 3000; D2 / D3 ranges from 0.25 to 20.

33. The preparation method according to claim 32, characterized in that, Me n+ Ni 2+ Co 2+ Mn 2+ Al 3+ and Fe 2+ At least one of them.

34. The preparation method according to claim 33, characterized in that, The soluble Me salt includes 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(DFOB) n Me (BOB) n Me(AsF6) n Me(CF3SO3) n Me(PO2F2) n Me (DODFP) n and Me(OTFP) n At least one of them; and / or, The soluble tetrafluoroborate includes Me(BF4). n At least one of LiBF4; and / or, The non-aqueous solvent includes cyclic carbonate compounds and chain carbonate compounds; and / or, The lithium salt includes a first lithium salt, which includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or a combination thereof; and / or, The additive includes at least one of a first additive and a second additive, wherein the first additive is fluoroethylene carbonate and the second additive includes at least one of vinylene carbonate, lithium oxalate, vinyl sulfate, and 1,3-propanesulfonate lactone.

35. The preparation method according to claim 34, characterized in that, The non-aqueous solvent includes cyclic carbonate compounds, chain carbonate compounds, and ether compounds.

36. The preparation method according to claim 34, characterized in that, The lithium salt further includes a second lithium salt, which includes at least one of lithium difluorooxalate borate, lithium dioxalate borate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

37. A secondary battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, characterized in that, The non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1-31 or the non-aqueous electrolyte obtained by the preparation method according to any one of claims 32-36.

38. The secondary battery according to claim 37, characterized in that, The positive electrode sheet comprises Li a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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 = 1, g + h = 2.

39. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h In this context, M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W.

40. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h In this context, A is selected from at least one of F, N, P, and S.

41. The secondary battery according to claim 40, characterized in that, A is selected from F.

42. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mr d Al e M f O g A h China 0＜b＜0.98。 43. The secondary battery according to claim 42, characterized in that, 0.50≤b＜0.98。 44. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h In it, c = 0.

45. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h where 0 < c ≤ 0.

20.

46. ​​The secondary battery according to claim 45, characterized in that, 0＜c≤0.10。 47. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h Medium, d = 0 and 0 < e < 0.

50.

48. The secondary battery according to claim 47, characterized in that, d = 0 and 0 < e ≤ 0.

10.

49. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h Medium, e = 0 and 0 < d < 0.

50.

50. The secondary battery according to claim 49, characterized in that, e = 0 and 0 < d ≤ 0.

10.

51. The secondary battery according to claim 38, characterized in that, Li a Ni b Co c Mn d Al e M f O g A h Medium, 0<d<0.50 and 0<e<0.

50.

52. The secondary battery according to claim 51, characterized in that, 0 < d ≤ 0.30 and 0 < e ≤ 0.

10.

53. An electrical device comprising a secondary battery as described in any one of claims 37-52.

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