Non-aqueous electrolyte and secondary battery

Abstract

The invention provides a non-aqueous electrolyte and a secondary battery, the non-aqueous electrolyte comprises a compound as shown in a structural formula 1 and a compound as shown in a structural formula 2: in the structural formula 1, R1, R2 and R3 are independently selected from one of C1-C6 alkyl and halogen atom substituted C1-C6 alkyl, and X is selected from B, P or P = O; k in the structural formula 2 and the structural formula II is 1 or 2, and R4 is selected from one of a C2-C6 sulfonate group, a C2-C6 saturated alkyl group, a C2-C6 unsaturated alkyl group and a C2-C6 alkoxy group. The non-aqueous electrolyte provided by the invention can effectively inhibit the gas production rate and capacity attenuation in the battery using process of the electrolyte, and ensures good positive and negative electrode film forming effects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a non-aqueous electrolyte and a secondary battery. BACKGROUND

[0002] In recent years, lithium ion secondary batteries have developed rapidly and are widely used in consumer electronics, electric tools, new energy vehicles and energy storage power stations. However, due to the instability of mainstream liquid electrolyte, gas will be generated during use, which will cause the battery to bulge, the pressure relief valve to open, and other conditions that seriously affect the safety of use. In addition, electrolyte decomposition gas is often accompanied by capacity decay of the battery, increasing the use cost of lithium ion batteries. Suppressing the gas generation and capacity decay of the battery during use is a crucial link in the development of high-performance liquid lithium ion batteries. Non-patent document j.electacta.2017.08.027 mentions using trimethyl borate as an additive for high-voltage lithium nickel manganese oxide cathodes to improve gas generation and cycle capacity. However, trimethyl borate is unstable in electrolyte and can easily cause electrolyte discoloration and deterioration. Phosphoric acid triethyl ester can be used to suppress thermal decomposition gas generation and improve the thermal safety of lithium ion batteries due to its high flash point and phosphorus atom oxygen radical capture properties, but it has obvious capacity degradation in batteries. Traditional borate / phosphate esters have certain defects, making them difficult to be commercialized.

[0003] Therefore, how to overcome the defects of traditional borate / phosphate esters, suppress the gas generation and cycle capacity decay of the battery during use, and at the same time consider good impedance characteristics, is a technical problem that needs to be solved. SUMMARY

[0004] Therefore, how to overcome the defects of traditional borate / phosphate esters, suppress the gas generation and cycle capacity decay of the battery during use, and at the same time consider good impedance characteristics, is a technical problem that needs to be solved.

[0005] Another purpose of the present application is to provide a secondary battery.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a non-aqueous electrolyte, comprising a first additive and a second additive, the first additive comprising a compound represented by structural formula 1, and the second additive comprising a compound represented by structural formula 2: Structural formula 1, In structural formula 1, R1, R2 and R3 are each independently selected from one of C1-C6 hydrocarbyl and halogen atom-substituted C1-C6 hydrocarbyl, and X is selected from B, P or P=O. Structure 2, In Structure II, k is 1 or 2, and R4 is selected from one of C2-C6 sulfonate group, C2-C6 saturated hydrocarbon group, C2-C6 unsaturated hydrocarbon group, and C2-C6 alkoxy group.

[0007] The non-aqueous electrolyte described in the present application can at least bring the following beneficial effects: Adding the borate / phosphate compound with cage structure shown in Structure 1 to the electrolyte can effectively inhibit the gas production and capacity attenuation of the electrolyte during battery use, and improve the thermal safety performance; at the same time, using the borate / phosphate compound shown in Structure 1 in combination with the compound shown in Structure 2 can ensure good positive and negative electrode film forming effect.

[0008] Specifically, the borate compound, such as trimethyl borate, has certain positive electrode film forming effect, and can well inhibit the gas production of the battery during use, but it is not stable in the electrolyte and can easily cause the electrolyte to discolor and deteriorate. The reason is that the whole electron deficiency causes it to exhibit Lewis acid characteristics, catalyzing the electrolyte decomposition and polymerization to produce color. At the same time, the flash point of trimethyl borate is low, and a high content in the battery will cause the safety performance to decrease. The cage structure borate compound containing N atom provided in the present application can exist stably in the electrolyte because the N atom provides lone pair electrons to the borate structure, which significantly weakens the Lewis acidity of the borate structure, and the Lewis base property of the N atom can further stabilize the lithium salt anion. Thus, the cage structure borate compound can exist stably in the electrolyte. Moreover, the cyclic structure containing N atom strengthens its film forming effect, and a solid electrolyte film with lower impedance and more stability can be obtained, which improves the thermal safety performance to a certain extent. The phosphate / phosphite compound, such as triethyl phosphate, can capture active oxygen at the positive electrode, stabilize the positive electrode structure, and improve the safety performance, but the solid electrolyte film formed by it is not stable. For example, the alkyl phosphate component has a loose and porous structure, low ionic conductivity, and poor shielding effect on electrons, which cannot prevent the continuous decomposition of the electrolyte, causing the capacity to decrease in the later stage. More seriously, triethyl phosphate is easy to co-embed with lithium ions into the interlayer of graphite, causing the graphite structure to expand and the layered structure to peel off, resulting in accelerated capacity attenuation. The cage structure phosphate / phosphite compound containing N atom provided in the present application retains the ability of the phosphate / phosphite group to capture active oxygen and improve the thermal safety performance, and the large molecular structure with cyclic rigidity is difficult to co-embed with the layered negative electrode such as graphite, avoiding capacity degradation. At the same time, the cyclic cage structure and N atom provide strong positive electrode film forming capacity, generating a dense interface film containing Li3N component with strong ionic conductivity.

[0009] The compound shown in Structural Formula 1 possesses excellent positive electrode film-forming properties, capable of generating robust inorganic lithium salts containing B / P and a Li3N component with high ionic conductivity at the positive electrode. This effectively isolates the reaction between the electrolyte and the positive electrode, suppresses gas generation and capacity decay, and maintains good impedance characteristics, making it a highly effective positive electrode film-forming additive. However, the compound shown in Structural Formula 1 does not provide excellent protection for the negative electrode through its reduction products. Furthermore, its high film-forming activity makes it prone to excessive consumption at the negative electrode during the first charge, hindering the subsequent film quality at the positive electrode. The inventors discovered that using the compound shown in Structural Formula 1 in combination with the compound shown in Structural Formula 2 ensures good film-forming effects at both the positive and negative electrodes. This is likely because the sulfur-containing additive in the compound shown in Structural Formula 2 has an earlier film-forming potential at the negative electrode than the compound shown in Structural Formula 1, allowing it to preferentially coat the negative electrode with a primary film containing sulfur-containing lithium salts and organic polymers. This suppresses the consumption of the compound shown in Structural Formula 1 at the negative electrode, ensuring the film quality of the compound shown in Structural Formula 1 at the positive electrode. The synergistic effect of the compounds shown in structural formula 1 and structural formula 2 ensures good film formation effect on both positive and negative electrodes.

[0010] In some embodiments, in the structural formula I, R1, R2 and R3 are each independently selected from one of the following: a C2-C6 alkenyl group, a C2-C6 alkenyl group substituted with a halogen atom, a C2-C6 alkynyl group, and a C2-C6 alkynyl group substituted with a halogen atom, and X is P=O.

[0011] In some embodiments, the compound represented by structural formula 1 includes at least one of compounds 1 to 12, optionally compound 5: .

[0013] In some embodiments, the compound represented by structural formula 2 includes at least one of compounds I to VIII, and may be compound III: .

[0014] In some embodiments, the compound represented by structural formula 1 is present in the non-aqueous electrolyte at a mass percentage of a, where 0.05% ≤ a ≤ 3%.

[0015] In some implementations, 'a' satisfies: 0.1% ≤ a ≤ 2%.

[0016] In some embodiments, the compound represented by structural formula 2 is present in the non-aqueous electrolyte at a mass percentage of b, where 0.05% ≤ b ≤ 3%.

[0017] In some implementations, b satisfies: 0.1% ≤ b ≤ 2%.

[0018] In some implementations, a and b satisfy the following relationship: 0.05 ≤ a / b ≤ 9.

[0019] In some embodiments, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of vinylene carbonate, lithium difluorophosphate, and lithium difluorooxalate borate.

[0020] In some embodiments, the non-aqueous electrolyte further includes a non-aqueous organic solvent, which includes at least one of linear carbonate solvents or carboxylic acid ester solvents.

[0021] In some embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0022] In some embodiments, the carboxylic acid ester solvent includes at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, and ethyl difluoroacetate.

[0023] In some embodiments, the non-aqueous electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, and lithium fluorosulfonate.

[0024] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.3 to 1.5 mol / L.

[0025] A second aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte described in this application.

[0026] In some embodiments, the negative electrode includes a negative electrode active material, which includes at least one of graphite, hard carbon, graphite, and composite materials, wherein the composite material is a composite of graphite and silicon.

[0027] The secondary battery described in this application has at least the beneficial effects of the non-aqueous electrolyte described in this application.

[0028] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0029] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings. in: Figure 1 This is a comparison chart of the stability test results of the non-aqueous electrolytes in Examples 30-32 and Comparative Examples 8-9, where: Figure a shows the stability test results of the non-aqueous electrolyte in Comparative Example 8. b is the graph showing the stability test results of the non-aqueous electrolyte in Comparative Example 9; c is a graph showing the stability test results of the non-aqueous electrolyte in Example 30; d is a graph showing the stability test results of the non-aqueous electrolyte in Example 31; e is a graph showing the stability test results of the non-aqueous electrolyte in Example 32. Detailed Implementation

[0030] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0031] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0032] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0033] When the term “and / or” is used in a list containing two or more items, it means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression “A and / or B” is intended to mean A or B or A and B, that is, A only, B only, or a combination of A and B.

[0034] In this application, Cx-Cy refers to the presence of x to y carbon atoms in the corresponding group. Taking C1-C6 hydrocarbon groups as an example, it means that the hydrocarbon group contains 1, 2, 3, 4, 5, or 6 carbon atoms.

[0035] <Non-aqueous electrolyte> The non-aqueous electrolyte of this application embodiment includes a first additive and a second additive. The first additive includes a compound represented by structural formula 1, and the second additive includes a compound represented by structural formula 2. Structural Formula 1, In structural formula 1, R1, R2 and R3 are each independently selected from one of C1-C6 hydrocarbon groups or C1-C6 hydrocarbon groups substituted with halogen atoms, and X is selected from B, P or P=O. Structural Formula 2, In structural formula II, k is 1 or 2, and R4 is selected from one of the following: C2-C6 sulfonate group, C2-C6 saturated hydrocarbon group, C2-C6 unsaturated hydrocarbon group, and C2-C6 alkoxy group.

[0036] The non-aqueous electrolyte of this application embodiment can bring at least the following beneficial effects: Adding a borate / phosphate compound with a cage-like structure, as shown in Formula 1, to a non-aqueous electrolyte can effectively suppress gas production and capacity decay during battery use and improve thermal safety performance. At the same time, the use of the borate / phosphate compound shown in Formula 1 in combination with the compound shown in Formula 2 can ensure good film formation on both the positive and negative electrodes.

[0037] Specifically, borate ester compounds, such as trimethyl borate, possess certain positive electrode film-forming effects and can effectively suppress gas generation during battery use. However, they are unstable in the electrolyte, easily causing discoloration and deterioration. This is because their overall electron deficiency leads to Lewis acid characteristics, catalyzing electrolyte decomposition and polymerization, resulting in color. Furthermore, trimethyl borate has a low flash point, and excessive amounts in the battery can lead to decreased safety performance. The cage-like borate ester compound containing nitrogen atoms provided in this application significantly weakens the Lewis acidity of the borate ester structure due to the lone pair electrons provided by the nitrogen atom. The Lewis base properties of the nitrogen atom further stabilize the lithium salt anion, allowing the cage-like borate ester compound to exist stably in the electrolyte. Moreover, the ring structure containing nitrogen atoms enhances its film-forming effect, resulting in a solid electrolyte film with lower impedance and greater stability, thus improving thermal safety performance to some extent. Phosphate / phosphite compounds, such as triethyl phosphate, can capture reactive oxygen species at the positive electrode, stabilizing the positive electrode structure and improving safety performance. However, the solid electrolyte membrane formed by these compounds is unstable. For example, the alkyl phosphate components exhibit a loose and porous structure with low ionic conductivity and poor electron shielding, failing to prevent continuous electrolyte decomposition and leading to a decrease in capacity over time. More seriously, triethyl phosphate readily intercalates with lithium ions between graphite layers, causing graphite structural expansion and layered exfoliation, resulting in accelerated capacity decay. The cage-like phosphate / phosphite compound containing nitrogen atoms provided in this application retains the ability of the phosphate / phosphite groups to capture reactive oxygen species and improve thermal safety performance. At the same time, the large, rigid cyclic molecular structure makes it difficult for it to co-intercalate with layered negative electrodes such as graphite, avoiding capacity degradation. Furthermore, the cyclic cage structure and nitrogen atoms provide strong positive electrode film-forming ability, generating a dense interfacial film containing components such as Li3N with strong ion-conducting capacity.

[0038] The compound shown in Structural Formula 1 possesses excellent positive electrode film-forming properties, capable of generating robust inorganic lithium salts containing B / P and a Li3N component with high ionic conductivity at the positive electrode. This effectively isolates the reaction between the electrolyte and the positive electrode, suppresses gas generation and capacity decay, and maintains good impedance characteristics, making it a highly effective positive electrode film-forming additive. However, the compound shown in Structural Formula 1 does not provide excellent protection for the negative electrode through its reduction products. Furthermore, its high film-forming activity makes it prone to excessive consumption at the negative electrode during the first charge, hindering the subsequent film quality at the positive electrode. The inventors discovered that using the compound shown in Structural Formula 1 in combination with the compound shown in Structural Formula 2 ensures good film-forming effects at both the positive and negative electrodes. This is likely because the sulfur-containing additive in the compound shown in Structural Formula 2 has an earlier film-forming potential at the negative electrode than the compound shown in Structural Formula 1, allowing it to preferentially coat the negative electrode with a primary film containing sulfur-containing lithium salts and organic polymers. This suppresses the consumption of the compound shown in Structural Formula 1 at the negative electrode, ensuring the film quality of the compound shown in Structural Formula 1 at the positive electrode. The synergistic effect of the compounds shown in structural formula 1 and structural formula 2 ensures good film formation effect on both positive and negative electrodes.

[0039] As an alternative example, the first additive is a compound represented by structural formula 1, and the second additive is a compound represented by structural formula 2.

[0040] For example, in the structural formula 1, the C1-C6 hydrocarbon groups include C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, and C6 aryl, etc.

[0041] in: C1-C6 alkyl groups include, but are not limited to, methyl groups. ), ethyl ( ), n-propyl ( ), isopropyl ( ), n-butyl ( ), isobutyl ( ), sec-butyl ( ), tert-butyl ( ), pentyl ( ), hexyl ( ), cyclopropyl ( ), cyclobutyl ( ), cyclopentyl ( ) or cyclohexyl ( One of them, etc.

[0042] C2-C6 alkenyl groups include, but are not limited to, vinyl groups. ), allyl ( ), 1-propenyl ( ), butenyl ( ), 2-Butenyl ( One of the following: cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, etc.

[0043] C2-C6 alkynyl groups include, but are not limited to, ethynyl groups ( ), 1-propynyl ( ), 3-methyl-1-butynyl ( One of the following: , cyclopropynyl, etc.

[0044] C6 aryl group is phenyl ( ).

[0045] For example, the halogen atom in structural formula 1 includes one of F, Cl, Br, and I.

[0046] It should be noted that when R1, R2 and R3 in structural formula 1 are each independently selected from C1-C6 hydrocarbon groups substituted with halogen atoms, they are C1-C6 hydrocarbon groups substituted with the aforementioned halogen atoms as substituents.

[0047] In some embodiments, in structural formula I, R1, R2, and R3 are each independently selected from one of the following: a C2-C6 alkenyl group, a halogen-substituted C2-C6 alkenyl group, a C2-C6 alkynyl group, or a halogen-substituted C2-C6 alkynyl group, where X is P=O. Selecting these groups allows for the construction of a three-dimensional cage-like structure, improving the compound's film-forming ability at interfaces.

[0048] In some embodiments, the compound represented by structural formula 1 includes at least one of compound 1 to compound 12: .

[0050] The compounds shown in structural formula 1, from compound 1 to compound 12, can have a good film-forming effect on the positive electrode side, suppressing gas generation and cycle capacity decay under high temperature conditions.

[0051] As an alternative example, the compound shown in structural formula 1 is compound 5. Compared to the other compounds in compounds 1-12, compound 5 has a moderate electronic structure of phosphate ester, neither acting as a significant electron acceptor nor providing lone pairs of electrons, resulting in more uniform film formation and better interfacial impedance at the interface.

[0052] In the embodiments of this application, the compound represented by structural formula 1 can be synthesized by known methods, such as by esterification of boric acid / phosphoric acid / phosphorous acid with triethanolamine / triethanolamine homologues or derivatives. For example, in the preparation of compound 5, the molar ratio of phosphoric acid to triethanolamine is 1:1. Triethylamine diluted 1:1 with deionized water is placed in a three-necked flask and cooled to 0-5°C in a water bath. While stirring continuously, a 50wt% phosphoric acid solution diluted with deionized water is slowly added dropwise, ensuring the reaction temperature remains below 30°C. The addition continues until the system is neutral or weakly acidic. The reaction solution is then transferred to a round-bottom flask and concentrated under reduced pressure using a rotary evaporator at a water bath temperature of 60-70°C to remove most of the water and solvent, yielding a viscous product. This product is purified by recrystallization or column chromatography and finally dried in a vacuum drying oven to obtain the target compound.

[0053]

[0054] In some embodiments, the compound represented by structural formula 2 includes at least one of compounds I to VIII: .

[0055] The compounds shown in structural formula 2, from compounds I to VIII, can preferentially form a film at the negative electrode, thus suppressing the consumption of the additives shown in structural formula 1 at the negative electrode.

[0056] As an alternative example, the compound shown in structural formula 2 is compound III. Compared to the other compounds in compounds I-VIII, compound III has a bifunctional structure (i.e., containing two sulfonate groups that can effectively form films), which further enhances the film-forming effect and has lower impedance.

[0057] In the embodiments of this application, the compound shown in structural formula 2 can be obtained commercially or synthesized by known synthetic methods.

[0058] In some embodiments, the mass percentage of the compound represented by Formula 1 in the non-aqueous electrolyte is a, where 0.05% ≤ a ≤ 3%. When the mass content of the compound represented by Formula 1 in the non-aqueous electrolyte is within the above range, it can provide good positive electrode film formation, improve the thermal stability of the positive electrode side film, and does not significantly degrade the viscosity of the electrolyte.

[0059] For example, the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte includes, but is not limited to, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, or 2.9%.

[0060] As an optional example, 'a' satisfies: 0.1% ≤ a ≤ 2%. When the mass content of the compound shown in Formula 1 in a non-aqueous electrolyte is within the above range, it can ensure good positive electrode film formation without significantly degrading the impedance of the positive electrode interface.

[0061] In some embodiments, the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte is b, where 0.05% ≤ b ≤ 3%. When the mass content of the compound represented by structural formula 2 in the non-aqueous electrolyte is within the above range, it can provide good negative electrode film formation.

[0062] For example, the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte includes, but is not limited to, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, or 2.9%.

[0063] As an optional example, b satisfies: 0.1% ≤ b ≤ 2%. When the mass content of the compound shown in Formula 2 in the non-aqueous electrolyte is within the above range, it can ensure a good negative electrode film formation effect, suppress the consumption of the additive shown in Formula 1 at the negative electrode interface, and at the same time, it will not significantly degrade the negative electrode interface impedance.

[0064] In some implementations, a and b satisfy the following relationship: 0.05 ≤ a / b ≤ 9.

[0065] In the embodiments of this application, the mass content of the compound shown in structural formula 1 in the non-aqueous electrolyte and the mass content of the compound shown in structural formula 2 in the non-aqueous electrolyte satisfy the above relationship. The consumption of the additives shown in structural formula 1 and structural formula 2 can be controlled, so that the two additives can play a better synergistic role, avoiding excessive film formation or insufficient protection at the positive and negative electrodes, thereby forming a good solid electrolyte film at both the positive and negative electrodes, ensuring good impedance characteristics and thermal stability.

[0066] For example, the values ​​of a / b mentioned above include, but are not limited to, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 or 8.5, and can be selected from 0.1 to 5.

[0067] In some embodiments, the non-aqueous electrolyte further includes auxiliary additives, including at least one selected from vinylene carbonate, lithium difluorophosphate, and lithium difluorooxalate borate. Adding auxiliary additives to the electrolyte can further suppress gas generation during high-temperature standby and improve high-temperature cycling capacity.

[0068] For example, the mass percentage of the vinylene carbonate in the non-aqueous electrolyte is 0.1% to 1%, including but not limited to 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, and optionally 0.5%.

[0069] For example, the mass percentage of lithium difluorophosphate in the non-aqueous electrolyte is 0.1% to 1%, including but not limited to 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, and optionally 0.7%.

[0070] For example, the mass percentage of lithium difluorooxalate borate in the non-aqueous electrolyte is 0.1% to 1%, including but not limited to 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, and optionally 0.5%.

[0071] In some embodiments, the non-aqueous electrolyte further includes a non-aqueous organic solvent.

[0072] In some embodiments, the non-aqueous organic solvent includes, but is not limited to, at least one of linear carbonate solvents or carboxylic acid ester solvents.

[0073] For example, the linear carbonate solvent includes, but is not limited to, at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0074] For example, the carboxylic acid ester solvent includes, but is not limited to, at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, and ethyl difluoroacetate.

[0075] In some embodiments, the non-aqueous electrolyte also includes lithium salts.

[0076] For example, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, and lithium fluorosulfonate, and may be lithium hexafluorophosphate.

[0077] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.3 to 1.5 mol / L, including but not limited to 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L.

[0078] Secondary batteries The secondary battery of this application embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte of this application embodiment.

[0079] In some embodiments, the secondary battery includes a lithium-ion battery, which may be selected as a lithium-ion battery.

[0080] In some embodiments, the negative electrode includes a negative electrode active material, which includes, but is not limited to, at least one of graphite, hard carbon, graphite and composite materials, wherein the composite material is a composite of graphite and silicon.

[0081] For example, in the composite material, the graphite content is 60-95% by mass, including but not limited to 65%, 70%, 75%, 80%, 85% or 90%.

[0082] It should be noted that, in the embodiments of this application, there are no restrictions on the specific selection of other components of the negative electrode, the positive electrode, the separator, etc., which can be any other components of the negative electrode, the positive electrode, the separator, etc. known in the art that can be used for secondary batteries, especially lithium-ion batteries.

[0083] The secondary battery of this application embodiment has at least the beneficial effects of the non-aqueous electrolyte of this application embodiment.

[0084] The following non-limiting embodiments further illustrate certain features of the present technology.

[0085] I. Examples and Comparative Examples The following embodiments and some comparative examples involve the first additive as shown in Table 1.

[0086] Table 1 Partial list of first additives

[0087] The second additives involved in the following embodiments and some comparative examples are shown in Table 2.

[0088] Table 2 Partial list of second additives

[0089] Example 1 The non-aqueous electrolyte in this embodiment is composed of lithium salt, non-aqueous organic solvent, first additive, second additive, and auxiliary additives. Wherein: The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.05 mol / L; The non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 30:40:30; The first additive is compound 5, and the mass percentage of the first additive in the non-aqueous electrolyte is a, where a = 1.5%. The first additive is compound III, and the second additive has a mass percentage of b in the non-aqueous electrolyte, where b = 1.5%. a / b = 1.5% / 1.5% = 1.00; The auxiliary additives consist of vinylene carbonate, lithium difluorophosphate, and lithium difluorooxalate borate, wherein the mass percentage of vinylene carbonate in the non-aqueous electrolyte is 0.5%, the mass percentage of lithium difluorophosphate in the non-aqueous electrolyte is 0.7%, and the mass percentage of lithium difluorooxalate borate in the non-aqueous electrolyte is 0.5%.

[0090] The preparation method of the non-aqueous electrolyte in this embodiment is as follows: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed in a volume ratio of EC:EMC:DMC = 30:40:30. After mixing, lithium hexafluorophosphate (LiPF6) with a concentration of 1.05 mol / L was added, followed by the first additive, the second additive, and auxiliary additives ethylene carbonate, lithium difluorophosphate, and lithium difluorooxalate borate, which were then mixed thoroughly.

[0091] Examples 2-46 and Comparative Examples 1-9 are basically the same as Example 1, except that the selection and amount of the non-aqueous electrolyte components are different, as shown in Table 3.

[0092] Table 3. Selection and dosage of some substances in the electrolytes of each embodiment and comparative example.

[0093] Note: In Table 3, " / " represents "not present".

[0094] II. Performance Testing 1. Electrolyte stability test The non-aqueous electrolytes of Comparative Examples 8-9 and Examples 30-32 were shaken well and then sealed in dry Al bottles for storage in a constant temperature incubator at 45°C for 30 days. After storage, the electrolytes were transferred to glass tubes, and photographs were taken from above. The results are as follows. Figure 1 As shown.

[0095] from Figure 1 It can be seen that the nitrogen-containing cage-like additive designed in this application (i.e., the compound shown in structural formula 1) has higher stability in the electrolyte under high temperature environment compared with the traditional trimethyl borate / triethyl phosphate, and is less likely to cause electrolyte reaction and discoloration.

[0096] 2. Battery performance test The non-aqueous electrolytes of each embodiment and comparative example were used to prepare lithium-ion batteries, and the performance of the prepared lithium-ion batteries was tested.

[0097] in: The method for preparing a lithium-ion battery includes the following steps: (1) Preparation of positive electrode: The positive electrode active material LiNi was mixed in a mass ratio of 96.2:1.5:0.5:1.8. 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (Super P), single-walled carbon nanotube conductive agent, and binder polyvinylidene fluoride were mixed to obtain a mixture; then, the mixture was dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry; then, the positive electrode slurry was uniformly coated on the opposite two surfaces of an aluminum foil with a thickness of 15 micrometers, and after drying, rolling and vacuum drying, aluminum leads were welded on using an ultrasonic welding machine to obtain a positive electrode plate with a coating thickness of 120 μm.

[0098] (2) Anode preparation: Artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber binder and carboxymethyl cellulose are mixed in a mass ratio of 95.2:1:2.4:1.4 to obtain a mixture; then, the mixture is dispersed in deionized water to obtain anode slurry; then, the anode slurry is coated on the opposite two surfaces of a copper foil with a thickness of 12 micrometers, dried, rolled and vacuum dried, and nickel leads are welded on with an ultrasonic welding machine to obtain the anode.

[0099] (3) Selection of diaphragm: The diaphragm consists of a composite base membrane and a ceramic particle coating applied to its opposite two sides. The composite base membrane is a composite membrane in which polypropylene, polyethylene and polypropylene are stacked in sequence, and the total thickness of the composite base membrane is 15 micrometers. The ceramic particles are alumina, and the thickness of the ceramic particle coating on one side of the composite base membrane is 2 micrometers.

[0100] (4) Battery assembly: A separator is placed between the positive electrode plate (i.e., the positive electrode prepared in step (1) above) and the negative electrode plate (i.e., the negative electrode prepared in step (2) above). Then, the sandwich structure composed of the positive electrode plate, the negative electrode plate and the separator is wound up. The wound body is flattened and placed in a square aluminum-plastic shell. The leads of the positive and negative electrodes are welded to nickel tabs and aluminum tabs respectively. The shell is sealed and vacuumed to obtain the battery cell to be injected with electrolyte. The non-aqueous electrolyte prepared in the above embodiments or comparative examples is injected into the battery cell through the injection hole. The amount of electrolyte should be sufficient to fill the gaps in the battery cell.

[0101] Then, perform the first charging routine as follows: charge at a constant current of 0.05C for 3 hours, charge at a constant current of 0.2C for 2 hours, charge at a constant current of 0.5C for 2 hours, let stand for 1 hour, shape and seal, then charge at a constant current of 0.2C to 4.25V, let stand for 0.5 hours, and then discharge at a constant current of 0.2C to 3.0V.

[0102] The battery performance testing method is as follows: (1) Initial DCIR The battery was placed in a 25°C constant temperature test chamber and left to stand for 4 hours. Then, it was run at a constant temperature, charged at 0.5 C to the upper limit voltage, with a cutoff current of 0.05 C, left to stand for 10 minutes, and then discharged at a constant current of 0.5 C with a cutoff capacity of 0.5 C. After standing for 30 minutes, it was discharged at a constant current of 2 C I for 10 seconds, and the discharge start voltage U1 and discharge cutoff voltage U2 were recorded.

[0103] Initial DCIR = (U1-U2) / I*1000, in milliohms.

[0104] (2) Gas production rate during high-temperature storage Charge the battery at 0.5 C to the upper limit voltage and cut-off voltage at 0.05 C. Test the initial volume Vinitial. Then place it in a 60℃ constant temperature test chamber. After n days, take out the test volume Vn.

[0105] High-temperature gas production rate over n days = (Vn - Vinitial) / Vinitial * 100%.

[0106] (3) High-temperature cycling capacity retention Place the battery in a 45℃ constant temperature test chamber, charge it at 0.2C constant current and constant voltage to the upper limit voltage, let it rest for 5 minutes, discharge it at 0.2C constant current to the lower limit voltage, and let it rest for 5 minutes. After repeating this cycle twice, perform the following cycle: charge it at 3C constant current to the upper limit voltage, then switch to 1C constant current and constant voltage charging to the upper limit voltage, cut off the current at 0.05C, let it rest for 10 minutes, discharge it at 1C constant current to the lower limit voltage, and let it rest for 10 minutes. Record the discharge capacity as C1. Repeat this cycle, and record the discharge capacity after n cycles as Cn.

[0107] High-temperature cycling capacity retention rate (n cycles) = Cn / C1 * 100%.

[0108] (4) Thermal shock test Three batteries prepared with electrolytes from the same embodiment or comparative example were tested in each group. The batteries were placed in an explosion-proof test chamber and heated from room temperature (25°C) at a temperature rise rate of 5°C / min. When the temperature of the test chamber reached 140°C, it was kept at a constant temperature for 30 minutes. The batteries passed the test if they did not catch fire or explode.

[0109] The battery performance test results are shown in Table 4.

[0110] Table 4 Battery performance test results

[0111] As can be seen from Table 4, the non-aqueous electrolytes of the embodiments of this application have lower initial DCIR and high-temperature storage gas generation rate, as well as better high-temperature cycling performance and thermal safety performance compared with the comparative example under the same conditions.

[0112] Specifically: Comparing Examples 1, 10 and 1-4, it can be seen that, under the premise that the content of the first additive is the same and the content of the second additive is the same (using compound III of structural formula 2 of this application), regardless of whether auxiliary additives are used, the first additive using compound 5 of structural formula 1 of this application can achieve lower initial DCIR and high-temperature storage gas production rate, as well as better high-temperature cycling performance and thermal safety performance compared to trimethyl borate or triethyl phosphate.

[0113] Comparing Example 1 and Comparative Examples 5-7, it can be seen that under the same conditions, when the non-aqueous electrolyte lacks at least one of the compounds shown in Structural Formula 1 and Structural Formula 2 of this application, even with the presence of auxiliary additives, the performance of all batteries decreases significantly. This indicates that the synergistic effect of the compounds shown in Structural Formula 1 and Structural Formula 2 of this application can significantly improve the performance of the battery.

[0114] Comparative Examples 30-32 and Comparative Examples 8-9 show that, without auxiliary additives and with the same values ​​for a and b, the compounds shown in Structural Formula 1 and Compound I of Structural Formula 2 of this application can significantly reduce the initial DCIR and high-temperature storage gas production rate, and improve high-temperature cycling performance and thermal safety performance, compared with trimethyl borate or triethyl phosphate and Compound I of Structural Formula 2.

[0115] Comparing Examples 1-13 and Examples 41-46, it can be seen that the content a of compound 5 of structural formula 1, compound III of structural formula 2, and the value of a / b are within the range defined in this application. Compared with outside the range, the improvement effect on battery performance is more obvious. However, even if some of them are outside the range of this application, due to the use of compound 5 of structural formula 1 and compound III of structural formula 2, the battery still has better overall performance than Comparative Examples 1-4.

[0116] Comparing Examples 1, 14-29, and 33-40, it can be seen that under the same conditions, changing the compound of structural formula 2, changing the compound of structural formula 1, or both can also improve battery performance, although the improvement effect is slightly lower than that of Example 1. This is because, compared to compound 5, most other compounds may have a slight advantage in suppressing gas generation or improving high-temperature cycle capacity retention, but their initial DICR deteriorates to varying degrees compared to compound 5. Therefore, while meeting performance requirements, compound 5 still exhibits the best overall performance.

[0117] Comparing Examples 1 and 10, Examples 2 and 11, Examples 8 and 13, and Examples 3 and 12, it can be seen that the auxiliary additives can at least further reduce the gas production rate of high-temperature storage and improve the high-temperature cycling performance.

[0118] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0119] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0120] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes a first additive and a second additive, wherein the first additive comprises a compound represented by structural formula 1, and the second additive comprises a compound represented by structural formula 2. Structural Formula 1, In structural formula 1, R1, R2 and R3 are each independently selected from one of C1-C6 hydrocarbon groups or C1-C6 hydrocarbon groups substituted with halogen atoms, and X is selected from B, P or P=O. Structural Formula 2, In structural formula II, k is 1 or 2, and R4 is selected from one of the following: C2-C6 sulfonate group, C2-C6 saturated hydrocarbon group, C2-C6 unsaturated hydrocarbon group, and C2-C6 alkoxy group.

2. The non-aqueous electrolyte according to claim 1, characterized in that, In the structural formula I, R1, R2 and R3 are each independently selected from one of the following: C2-C6 alkenyl, halogen-substituted C2-C6 alkenyl, C2-C6 alkynyl, and halogen-substituted C2-C6 alkynyl, and X is P=O.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The compound represented by structural formula 1 includes at least one of compounds 1 to 12, and may be compound 5: 。 4. The non-aqueous electrolyte according to claim 1, characterized in that, The compound represented by structural formula 2 includes at least one of compounds I to VIII, and may be compound III: 。 5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that, The compound represented by structural formula 1 has a mass percentage of a in the non-aqueous electrolyte, where 0.05% ≤ a ≤ 3%. And / or, the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte is b, 0.05% ≤ b ≤ 3%.

6. The non-aqueous electrolyte according to claim 5, characterized in that, The condition 'a' satisfies: 0.1% ≤ a ≤ 2%; And / or, the b satisfies: 0.1% ≤ b ≤ 2%; And / or, a and b satisfy the following relationship: 0.05 ≤ a / b ≤ 9.

7. The non-aqueous electrolyte according to any one of claims 1 to 5, characterized in that, The non-aqueous electrolyte also includes auxiliary additives, which include at least one of vinylene carbonate, lithium difluorophosphate, and lithium difluorooxalate borate. And / or, the non-aqueous electrolyte further includes a non-aqueous organic solvent, which includes at least one of linear carbonate solvents or carboxylic acid ester solvents; And / or, the non-aqueous electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, and lithium fluorosulfonate.

8. The non-aqueous electrolyte according to claim 7, characterized in that, The linear carbonate solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; And / or, the carboxylic acid ester solvent includes at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, and ethyl difluoroacetate; And / or, the concentration of the lithium salt in the non-aqueous electrolyte is 0.3 to 1.5 mol / L.

9. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is a non-aqueous electrolyte as described in any one of claims 1 to 8.

10. The secondary battery according to claim 9, characterized in that, The negative electrode includes a negative electrode active material, which includes at least one of graphite, hard carbon, graphite and composite materials, wherein the composite material is a composite material of graphite and silicon.

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