Electrolyte additives, electrolytes and lithium ion batteries

Abstract

The application relates to an electrolyte additive, an electrolyte and a lithium ion battery. The high-voltage electrolyte additive comprises a first additive, the structural formula of the first additive is at least one of structural formula I or structural formula II, in the structural formula I, m and n are both natural numbers not less than 0; R1-R4 are each independently selected from one of a C1-C20 alkyl group substituted or unsubstituted by halogen, a C1-C20 alkenyl group substituted or unsubstituted by halogen and a hydrogen atom; in the structural formula II, R5 and R6 are each independently selected from one of a C3-C12 cycloalkyl group, a C1-C20 alkyl group and a hydrogen atom; at least one of R5 and R6 is an alkyl group and combines with the adjacent carbon atom to form a cycloalkane. The scheme provided by the application can have higher stability, form a stable interface film and effectively improve the high-temperature cycle and storage performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte and a lithium ion battery. BACKGROUND

[0002] The ternary high-voltage electrolyte is a new type of battery electrolyte, which can improve the working voltage and specific capacity of the ternary lithium battery, and inhibit the structural phase transition of the positive electrode at high voltage (4.3V+). However, under high voltage conditions, the catalytic effect of nickel element in the ternary high-voltage electrolyte will accelerate the decomposition of the electrolyte, causing the electrolyte to oxidize and produce gas, especially LiPF6 in the electrolyte will degrade to generate phosphorus oxyfluoride and HF which is more destructive to the battery, at the same time, the cracks of the electrode sheet and the dissolved transition metal ions such as manganese and cobalt will also damage the SEI film of the negative electrode, resulting in serious impact on the capacity, cycle and safety of the battery in high temperature environment.

[0003] In the related art, an electrolyte additive is usually introduced into the electrolyte, which can generate an interface film with specific properties through oxidation or reduction reaction at the positive and negative electrode interfaces respectively, and can effectively improve the performance of the lithium ion battery. However, the stability of the interface film formed by the conventional electrolyte additive is usually not high enough, resulting in that the high temperature cycle and storage performance of the battery cannot be effectively improved. SUMMARY

[0004] To solve or partially solve the problems in the related art, the present application provides an electrolyte additive, an electrolyte and a lithium ion battery, which can have high stability, form a stable interface film and effectively improve the high temperature cycle and high temperature storage performance of the battery.

[0005] The first aspect of the present application provides an electrolyte additive, which comprises a first additive, the first additive is selected from at least one of the following structural formulae:

[0006]

[0007] In the structural formula one, m and n are both natural numbers not less than 0; R1-R4 are each independently selected from one of halogen-substituted or unsubstituted C1-C20 alkyl, halogen-substituted or unsubstituted C1-C20 alkenyl and hydrogen atom;

[0008] In the structural formula two, R5 and R6 are each independently selected from one of C3-C12 cycloalkyl, C1-C20 alkyl and hydrogen atom; at least one of R5 and R6 is alkyl, and combines with the adjacent carbon atom to form a cycloalkane.

[0009] As an optional embodiment, m and n are each independently selected from natural numbers from 0 to 9.

[0010] As an optional embodiment, the first additive comprises at least one of the compounds in structural formula I:

[0011]

[0012]

[0013] And / or, the first additive comprises the compound in structural formula II:

[0014]

[0015] As an optional embodiment, the high-voltage electrolyte additive further comprises a second additive, and the second additive is a fluoronitrobenzene compound.

[0016] As an optional embodiment, the structural formula of the second additive is as follows:

[0017]

[0018] In structural formula III, R5-R9 are each independently selected from one of C1-C20 alkyl substituted or unsubstituted, cyano, halogen atom, hydrogen atom.

[0019] As an optional embodiment, the second additive comprises at least one of the fluoronitrobenzene compounds as follows:

[0020]

[0021]

[0022] As an optional embodiment, the amount of the first additive and the second additive satisfies:

[0023] N / 90≤m1+m2≤N / 10

[0024] Wherein, the mass percentage of the first additive in the electrolyte is m1%; the mass percentage of the second additive in the electrolyte is m2%; when the content of each element is different, the percentage of the element with the largest content in the positive electrode active material is N%, and when the content of each element is the same, the percentage of the element with the largest contribution to the energy density is N%.

[0025] As an optional embodiment, m1 is 0.5-5; and / or, m2 is 0.3-5; and / or, when the positive electrode active material is selected from a nickel cobalt manganese lithium NCM material, the percentage of nickel in the nickel cobalt manganese lithium NCM material is N%, and N is 30-90.

[0026] The second aspect of the present application provides an electrolyte, comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises the aforementioned electrolyte additive.

[0027] The third aspect of the present application provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the aforementioned electrolyte.

[0028] As an optional embodiment, the positive electrode comprises a positive electrode current collector and a positive electrode active paste layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active paste layer comprises a positive electrode active material selected from one or more of lithium cobalt oxide LiCoO2, lithium nickel cobalt manganese oxide NCM, lithium iron phosphate LiFePO4 and lithium manganese oxide LiMn2O4.

[0029] As an optional embodiment, when the positive electrode active material is selected from a lithium nickel cobalt manganese oxide NCM material, the percentage of Ni in the lithium nickel cobalt manganese oxide NCM material is N%, wherein N is 30-90.

[0030] The technical solution provided by the present application can include the following beneficial effects:

[0031] The first additive in the present application comprises two cyclic anhydrides, which can efficiently remove trace water in the electrolyte, reduce the content of HF in the system, and prevent the destruction of the electrode material caused by excessive HF content. Further, the electrolyte additive of the present application comprises a compound formed by the saturation of two cyclic anhydrides with a multi-ring. This compound has high stability, so that the anhydride groups are not easily consumed by reaction with water. It can form a stable interface film on the positive electrode, isolate the direct contact between the electrolyte and the electrode interface, alleviate the consumption of the electrolyte, and reduce the irreversible loss of active lithium on the positive electrode interface under high temperature conditions, thereby improving the high temperature performance of the battery.

[0032] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and are not limited to the present application. DETAILED DESCRIPTION

[0033] The embodiments of the present application will be described in more detail below. Although the embodiments of the present application are shown, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0034] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or," as used herein, refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0035] It should be understood that although the terms "first," "second," "third," etc. can be used herein to describe various information, the information should not be limited by these terms. These terms are only used to distinguish one piece of information from another. For example, a first information can also be termed a second information, and, similarly, a second information can also be termed a first information, without departing from the scope of the present application. Therefore, the features defined with "first," "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically defined.

[0036] In the related art, an electrolyte additive is usually introduced into the electrolyte, which can generate an interface film with specific properties through oxidation or reduction reaction at the interface of the positive and negative electrodes, and can effectively improve the performance of the lithium ion battery. However, the stability of the interface film formed by the conventional electrolyte additive is usually not high enough, resulting in that the high-temperature cycle and storage performance of the battery cannot be effectively improved.

[0037] In view of the above problems, the embodiments of the present application provide an electrolyte additive, which can have high stability, form a stable interface film, and effectively improve the high-temperature cycle and storage performance of the battery.

[0038] The embodiments of the present application provide a high-voltage electrolyte additive, which comprises a first additive selected from at least one of the following structural formulas:

[0039]

[0040] In the structural formula one, m and n are both natural numbers not less than 0; R1-R4 are each independently selected from one of halogen-substituted or unsubstituted C1-C20 alkyl, halogen-substituted or unsubstituted C1-C20 alkenyl and hydrogen atom; in the structural formula two, R5 and R6 are each independently selected from one of C3-C12 cycloalkyl, C1-C20 alkyl and hydrogen atom; at least one of R5 and R6 is alkyl, and combines with the adjacent carbon atom to form a cycloalkane.

[0041] The first additive in the embodiments of the present application contains two cyclic anhydrides, and the two anhydride groups can effectively remove trace moisture in the electrolyte, reduce the content of HF in the system, and prevent excessive HF content from damaging the electrode material. Further, the electrolyte additive in the embodiments of the present application contains a compound formed by the condensation of two cyclic anhydrides through a saturated polycyclic ring. This compound has high stability, so that the anhydride groups are not easily consumed by reaction with water, can form a stable interfacial film on the positive electrode, isolate the direct contact between the electrolyte and the electrode interface, alleviate the consumption of the electrolyte, and reduce the irreversible loss of active lithium at the positive electrode interface under high temperature conditions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0042] As an optional embodiment, m and n are each independently selected from natural numbers from 0 to 9.

[0043] Specifically, m is selected from natural numbers from 0 to 9, n is selected from natural numbers from 0 to 9, and m and n can be the same or different.

[0044] The natural numbers selected for m and n determine the number of atoms on the polycyclic ring of the condensed two cyclic anhydrides. Different numbers of atoms on the ring result in different ring tensions, which affect the stability of the first additive. Therefore, the embodiments of the present application can select the values of m and n according to actual needs to adjust the stability of the film formation.

[0045] As an optional embodiment, the first additive contains at least one of the compounds in the following structural formula one:

[0046]

[0047]

[0048] And / or, the first additive contains a compound in the following structural formula two:

[0049]

[0050] Further, the first additive in the embodiments of the present application contains compound 1-12, and a combination of at least one of compound 1-1 to compound 1-11.

[0051] In the embodiments of the present application, compound 1-1 (condensed through a four-membered ring) has better improvement on the high-temperature cycle and storage performance of the battery than compound 1-10 (condensed through a five-membered ring) and compound 1-11 (condensed through a six-membered ring), because the stability of the anhydride with a cyclic structure is related to the size and tension of the ring, and the anhydride with moderate ring size and small ring tension has high structural stability. Further, the two anhydride groups can effectively neutralize the residual alkali in the positive active material, such as ternary material, reduce the high-temperature gas production of residual alkali, and there is no other substituent group on the ring, which can ensure the stability of the additive in the positive and negative electrode film-forming organic products.

[0052] As an optional embodiment, the high-voltage electrolyte additive further comprises a second additive, and the second additive is a fluoro-nitrobenzene compound.

[0053] The interface film generated by the first additive mainly comprises organic compounds, and the two anhydride groups in the structure cause the film to be thick, which has a large impedance to lithium ion transmission, and the film is formed on both the positive electrode and the negative electrode, thus significantly deteriorating the impedance of the positive electrode and the negative electrode.

[0054] The second additive in the embodiment of the present application contains a nitro group and F, can generate a low-impedance substance containing LiF on the surface of the positive electrode, and a substance containing LiN x O y The electrolyte generates a thin and stable CEI film, which can well protect the electrode from corrosion, reduce the decomposition of the electrolyte at the interface, and at the same time reduce the deterioration of the impedance of the positive electrode and the negative electrode by the first additive. Especially in the battery system with a high content of Ni (50% to 90%) in the ternary positive electrode material, the second additive can form an effective interface protection film on the surface of the positive electrode, effectively inhibiting the oxidation of the electrolyte by the high-nickel positive electrode material. Therefore, the second additive can synergize with the first additive and form an effective interface protection film, which can well protect the electrode from corrosion, reduce the decomposition of the electrolyte at the interface, and at the same time reduce the deterioration of the impedance of the positive electrode and the negative electrode by the first additive.

[0055] As a preferred embodiment, the structural formula of the second additive is as follows:

[0056]

[0057] In the third structural formula, R5-R9 are each independently selected from one of C1-C20 alkyl substituted or unsubstituted, cyano, halogen atom, hydrogen atom.

[0058] Specifically, any one of R5-R9 is selected from one of C1-C20 alkyl substituted or unsubstituted, cyano, halogen atom, and the selected groups of R5-R9 can be the same or different.

[0059] The halogen atom in the embodiment of the present application can be F, Cl, Br, and preferably F.

[0060] As a preferred embodiment, the second additive comprises at least one of the following compounds:

[0061]

[0062]

[0063] In the embodiments of the present application, the more fluorine atoms are substituted in the second additive, the greater the influence on the high-temperature cycle performance and storage performance of the battery, and the high-temperature cycle performance and storage performance of the battery can be significantly improved. This is because the more F is substituted, the more LiF is contained in the CEI film, and the CEI film rich in LiF has better toughness and higher thermal stability, which is beneficial to improve the cycle and storage performance of the battery.

[0064] As a preferred embodiment, the use amount of the first additive and the second additive satisfies:

[0065] N / 90≤m1+m2≤N / 10 wherein the mass percentage of the first additive in the electrolyte is m1 %; the mass percentage of the second additive in the electrolyte is m2 %; when the contents of elements in the positive electrode active material are different, the percentage of the element with the largest content is N %; when the contents of elements are the same, the percentage of the element with the largest contribution to the energy density is N %.

[0066] In the embodiments of the present application, the positive electrode comprises a positive electrode current collector and a positive electrode active paste layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active paste layer comprises a positive electrode active material selected from one or more of lithium cobalt oxide LiCoO2, lithium nickel cobalt manganese oxide NCM, lithium iron phosphate LiFePO4, and lithium manganese oxide LiMn2O4.

[0067] Further preferably, when the positive electrode active material is selected from a lithium nickel cobalt manganese oxide NCM material, when the contents of elements in the lithium nickel cobalt manganese oxide NCM material are different, the element with the largest content is Ni, and the percentage of Ni in the lithium nickel cobalt manganese oxide NCM material is N %, for example, the positive electrode active material is NCM523 or NCM622; when the contents of elements are the same, the element with the largest contribution to the energy density is Ni, and the percentage of Ni in the lithium nickel cobalt manganese oxide NCM material is N %, for example, the positive electrode active material is NCM111.

[0068] Specifically, in NCM811, the content of Ni is the largest and is 80 %, so that N is 80; in NCM622, the content of Ni is the largest and is 60 %, so that N is 60; in NCM523, the content of Ni is the largest and is 50 %, so that N is 50; in NCM111, the contents of elements are the same, Ni has the largest contribution to the energy density, and the content of Ni is 33.33 %, so that N is 33.33.

[0069] Taking lithium cobalt oxide LiCoO2 as an example, the element with the largest content is Co, and N % refers to the mass percentage of Co in the lithium cobalt oxide material.

[0070] Taking lithium iron phosphate LiFePO4 as an example, the element with the largest content is Fe, and N % refers to the mass percentage of Fe in the lithium cobalt oxide material.

[0071] For example, lithium manganate LiMn2O4, the element with the largest content is Mn, and N% refers to the mass percentage of Mn in the lithium cobaltate material. For lithium nickel cobalt manganate ternary material, the higher the content of Ni, the stronger the oxidizing property to the electrolyte, and the synergistic effect of the first additive and the second additive can effectively inhibit the influence of Ni in the ternary material on the oxidation of the electrolyte to produce gas; for lithium cobaltate LiCoO2 material, LiCoO2 material is prone to damage at high temperature, resulting in a large amount of Co dissolution, and the synergistic effect of the first additive and the second additive can effectively stabilize LiCoO2, reduce the damage of LiCoO2 material, reduce the oxidation of the electrolyte on the positive electrode to produce gas, and reduce the damage of Co dissolution on the negative electrode to SEI; for lithium iron phosphate LiFePO4 material, Fe in LiFePO4 material will dissolve a lot at high temperature and dissolve at the negative electrode, and the synergistic effect of the first additive and the second additive can stabilize the positive and negative electrode interface, improve the stability of the positive electrode material, reduce the dissolution of Fe, and reduce the damage of Fe dissolution on the negative electrode to SEI; for lithium manganate LiMn2O4 material, due to the poor stability of the material itself, Mn will dissolve a lot at high temperature and dissolve at the negative electrode, and Mn has strong destructive effect on SEI, resulting in irreversible capacity fading and gas production, and the synergistic effect of the first additive and the second additive can passivate the positive and negative electrode interface, reduce the damage of the positive electrode material, reduce the dissolution of Mn, and at the same time improve the stability of SEI, greatly reduce the negative influence of the dissolution of Mn on the negative electrode SEI. The inventors have found that in order to meet different business needs, different positive electrode materials can be selected, but different positive electrode materials will bring the above problems while meeting different needs, and the element with the largest content (or the element contributing most to the energy density) in the positive electrode material is the dominant factor. Through research, it is found that when N / 90≤m1+m2≤N / 10 is met, the synergistic effect of the first additive and the second additive can reach a balance with different positive electrode materials, reduce the influence of different positive electrode materials on the battery, and improve the comprehensive performance of the battery.

[0072] Preferably, m1 is 0.5-5.

[0073] In the embodiments of the present application, m1 can be 0.5, 1, 2, 5 or any value within the above defined range, which is not limited in the present application.

[0074] If m1 is too large, the impedance will be too large, and the cycle performance will be deteriorated; if m1 is too small, the protection effect will be poor.

[0075] Preferably, m2 is 0.3-5.

[0076] In the embodiments of the present application, m2 can be 0.3, 0.5, 1, 2, 5 or any value within the above defined range, which is not limited in the present application.

[0077] If m2 is too large, the viscosity of the electrolyte will increase significantly, and the kinetic attenuation will be serious; if m2 is too small, the protection effect and the impedance reduction effect will be poor.

[0078] The electrolyte additive provided by the embodiments of the present application at least includes a first additive and a second additive. The first additive contains two cyclic anhydrides, and the two anhydride groups can efficiently remove trace moisture in the electrolyte, reduce the content of HF in the system, and prevent the damage of excessive HF content to the electrode material. Further, the electrolyte additive provided by the embodiments of the present application contains a compound formed by the condensation of two cyclic anhydrides through a saturated polybasic ring. The compound has high stability, so that the anhydride groups are not easily consumed by reaction with water, can form a stable interface film on the positive electrode, isolate the direct contact between the electrolyte and the electrode interface, alleviate the consumption of the electrolyte, and reduce the irreversible loss of active lithium on the positive electrode interface under high-temperature conditions, thereby improving the high-temperature performance of the battery. The second additive contains nitro and F, can generate low-impedance substances containing LiF on the positive electrode surface, and contains LiNO x O y The generated CEI film is thin, dense and stable, can well protect the electrode from corrosion, reduce the decomposition of the electrolyte at the interface, and at the same time reduce the deterioration of the first additive to the impedance of the positive and negative electrodes. Especially in the battery system with a high content of Ni in the ternary positive electrode material, the second additive can form an effective interface protection film on the positive electrode surface. The first additive and the second additive can form a synergistic effect, which can well protect the electrode from corrosion, reduce the decomposition of the electrolyte at the interface, and at the same time reduce the deterioration of the first additive to the impedance of the positive and negative electrodes. The inventors have found that in order to meet different business needs, different positive electrode materials can be selected, but different positive electrode materials will bring the above-mentioned problems while meeting different needs, and the element with the largest content (or the element contributing most to the energy density) in the positive electrode material is the dominant factor. Through research, it has been found that when N / 90≤m1+m2≤N / 10 is met, the synergistic effect of the first additive and the second additive can be balanced with different positive electrode materials, the influence of different positive electrode materials on the battery can be reduced, and the comprehensive performance of the battery can be improved.

[0079] Corresponding to the foregoing application function implementation method embodiments, the present application also provides an electrolyte, a lithium ion battery and corresponding embodiments.

[0080] The embodiments of the present application also provide an electrolyte, which includes a lithium salt, a non-aqueous organic solvent and an additive, and the additive contains the foregoing electrolyte additive.

[0081] In the embodiments of the present application, the lithium salt is selected from at least one of an organic lithium salt or an inorganic lithium salt.

[0082] Preferably, the lithium salt is selected from at least one of a compound containing a fluorine element and a lithium element.

[0083] Preferably, the lithium salt is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluorosulfonate, lithium difluoro(trifluoromethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, lithium bisfluorimide sulfonate.

[0084] Preferably, the concentration of the lithium salt is 0.5M-1.5M. If the concentration of the lithium salt is too low, the conductivity of the electrolyte is low, which affects the rate and cycle performance of the entire battery system; if the concentration of the lithium salt is too high, the viscosity of the electrolyte is too large, which also affects the rate of the entire battery system.

[0085] Further preferably, the concentration of the lithium salt is 0.8M-1.3M.

[0086] In the embodiments of the present application, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, tetrahydrofuran.

[0087] The embodiments of the present application also provide a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the aforementioned electrolyte.

[0088] In the embodiments of the present application, the positive electrode comprises a positive electrode current collector and a positive electrode active paste layer on the positive electrode current collector, and the positive electrode active paste layer comprises a positive electrode active material; the negative electrode comprises a negative electrode current collector and a negative electrode active paste layer on the negative electrode current collector, and the negative electrode active paste layer comprises a negative electrode active material.

[0089] Preferably, the positive electrode active material is selected from one or more of lithium cobaltate LiCoO2, lithium nickel cobalt manganese ternary material, lithium iron phosphate LiFePO4, lithium manganate LiMn2O4.

[0090] Further preferably, when the positive electrode active material is selected from lithium nickel cobalt manganese NCM material, the percentage of Ni in the lithium nickel cobalt manganese NCM material is N%, and N is 30-90. For example, the positive electrode active material can be selected from NCM111, NCM523, NCM622.

[0091] Preferably, the negative electrode active material is selected from graphite and / or silicon, such as natural graphite, artificial graphite, mesophase carbon microbeads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O12-Li4Ti5O12, Li-Al alloy, which can all be used as negative electrode active materials. 12

[0092] ​For a further understanding of the present application, the application will be described with reference to the following examples, which are intended to be illustrative only and not limiting of the scope of the application.

[0093] I. Preparation of the battery

[0094] (1) Preparation of the electrolyte

[0095] EC / PC / EMC / DEC was mixed in a mass ratio of 1 / 1 / 2 / 6 as an organic solvent. After the additive PS, FEC was mixed uniformly, LiPF6 was added to obtain a mixed solution with a LiPF6 concentration of 1.1 mol / L, to obtain the electrolyte of Comparative Example 1 in Table 1, and then the first additive and the second additive were added to the mixed solution according to the formula in Table 1 to prepare the electrolyte of each example and comparative example. Among them, PS is 1,3-propanesulfonic acid lactone, and FEC is fluoroethylene carbonate.

[0096] (2) Preparation of the positive electrode sheet:

[0097] The positive electrode active material, the conductive agent CNT, and the binder polyvinylidene fluoride were mixed in a weight ratio of 97:1.5:1.5 in an N-methylpyrrolidone solvent to form a uniform positive electrode slurry. The slurry was coated on the positive electrode current collector Al foil, dried, cold-pressed to obtain the positive electrode sheet. Among them, the selection of the positive electrode active material and the percentage of the element with the largest content or the element with the largest energy density contribution in the positive electrode active material were set according to Table 1.

[0098] (3) Preparation of the negative electrode sheet:

[0099] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 95:2:2:1 in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry. The slurry was coated on the negative electrode current collector Cu foil, dried, cold-pressed to obtain the negative electrode sheet

[0100] (4) Preparation of the lithium ion battery:

[0101] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive and negative electrodes to play a separating role, and then the bare cell was wound. The bare cell was placed in an outer packaging bag, and the electrolyte in Table 1 was injected into the dried battery, and then the lithium ion battery was prepared after vacuum packaging, standing, formation, shaping, and other processes.

[0102] Table 1 Formula Table

[0103]

[0104]

[0105]

[0106] Note: NCM9055 is LiNi 0.90 Co 0.05 Mn 0.05 ; if N / (m1+m2) is in the range of 10-90, it means that N / 90≤m1+m2≤N / 10.

[0107] II. Performance test

[0108] (1) High-temperature cycle test of the battery

[0109] Test method: place the battery in an environment of 45±2 degrees, follow the standard charge-discharge cycle, cycle rate 1C, charge voltage 3.0-4.3V, and calculate the capacity retention rate of the battery after cycling. The calculation formula is as follows:

[0110] The capacity retention rate of the nth cycle (%) = (discharge capacity of the nth cycle) / (discharge capacity of the first cycle) * 100%.

[0111] (2) High-temperature storage test of the battery

[0112] Test method: charge the cell to 4.3V at 0.5C current at room temperature, place the fully charged battery in an environment of 85 degrees for 12 hours, measure the thickness expansion rate, recover to room temperature, and discharge to 3.0V at 0.5C current, and record the discharge capacity.

[0113] Battery test conditions are shown in Table 2

[0114] Table 2 test results

[0115]

[0116]

[0117]

[0118]

[0119] Based on the data in Table 1 and Table 2, by comparing Example 1 to Example 12, and Comparative Example 1, it can be known that when the first additive is selected from the additive provided in the present application, the high-temperature cycle and high-temperature storage performance of the battery can be effectively improved. And when the first additive is selected from compound 1-1, the improvement effect is best.

[0120] By comparing Example 1 with Example 13 to Example 27, it can be known that when the first additive and the second additive are used together, there is a synergistic effect, which can further improve the high-temperature performance of the battery. And when the second additive is selected from compound 2-15, the improvement effect is best.

[0121] Comparing Examples 27 to 30 shows that as the first additive content increases, the battery's high-temperature performance initially improves and then decreases. Furthermore, comparing Comparative Examples 3 to 7 shows that as the first additive content continues to increase, the battery's high-temperature performance deteriorates further. This may be because excessive first additive content leads to excessive impedance, which deteriorates the battery's cycling performance. Furthermore, if the first additive content is too low, the battery's high-temperature performance is not significantly improved. When the first additive content is between 0.5% and 5%, the battery's high-temperature performance is significantly improved.

[0122] By comparing Example 28 and Examples 31 to 34, it can be seen that when the content of the second additive increases, the degree of deterioration of the battery's high-temperature performance gradually increases. Further combined with Comparative Examples 8 to 11, it can be seen that as the content of the second additive continues to increase, the high-temperature performance of the battery further deteriorates. This may be because the second additive content is too high, the electrolyte viscosity increases significantly, the kinetic decay is serious, and thus the battery's cycle performance deteriorates; and if the second additive content is too low, the protection effect and impedance reduction effect are also poor. When the content of the second additive is 0.3% to 5%, the synergistic effect with the first additive is better. Further combined with Examples 35 to 40, it can be seen that when N / 90≤m1+m2≤N / 10 is satisfied, the battery's cycle performance can be further improved.

[0123] Although the present application has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for the elements thereof without departing from the scope of the present application. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present application without departing from the essential scope of the present application. Therefore, the present application is not intended to be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present application, but rather, the present application is intended to include all embodiments falling within the scope of the appended claims.

[0124] All ranges disclosed in this application are inclusive of the endpoints, and the endpoints are combinable with each other.

[0125] The embodiments of the present application have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to the technology in the market, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

1. An electrolyte additive characterized in that, The first additive is selected from at least one of the following structural formulas: Structural formula one Structural formula two In structural formula one, m and n are each a natural number not less than 0; R1-R4 are each independently selected from one of a C1-C20 alkyl group substituted or unsubstituted by halogen, a C1-C20 alkenyl group substituted or unsubstituted by halogen, and a hydrogen atom; In structural formula two, R5 and R6 are each independently selected from one of a C3-C12 cycloalkyl group, a C1-C20 alkyl group, and a hydrogen atom; at least one of R5 and R6 is an alkyl group and combines with the adjacent carbon atom to form a cycloalkyl group; The electrolyte additive further comprises a second additive, which is a fluoronitrobenzene compound; the structural formula of the second additive is as follows: Structural formula three In structural formula three, R5-R9 are each independently selected from one of a C1-C20 alkyl group substituted or unsubstituted by halogen, a cyano group, a halogen atom, and a hydrogen atom; The amount of the first additive and the second additive satisfies: N / 90≤m1+m2≤N / 10 Wherein, the mass percentage of the first additive in the electrolyte is m1%; the mass percentage of the second additive in the electrolyte is m2%; when the content of each element in the positive electrode active material is different, the percentage of the element with the largest content is N%; when the content of each element is the same, the percentage of the element with the largest contribution to the energy density is N%.

2. The electrolyte additive according to claim 1, characterized in that, m and n are each independently selected from a natural number of 0-9.

3. The electrolyte additive according to claim 1 or 2, characterized in that, The first additive comprises at least one of the following compounds of structural formula one: Compound 1-1 Compound 1-2 Compound 1-3 Compound 1-4 Compound 1-5 Compound 1-6 Compound 1-7 Compound 1-8 Compound 1-9 Compound 1-10 Compound 1-11 And / or, the first additive comprises a compound of the following structural formula two: Compound 1-12.

4. The electrolyte additive according to claim 1, characterized in that, The second additive comprises at least one of the following fluoronitrobenzene compounds: Compound 2-1 Compound 2-2 Compound 2-3 Compound 2-4 Compound 2-5 Compound 2-6 Compound 2-7 Compound 2-8 Compound 2-9 Compound 2-10 Compound 2-11 Compound 2-12 Compound 2-13 Compound 2-14 Compound 2-15.

5. The electrolyte additive according to claim 1, characterized in that, m1 is 0.5-5; and / or, m2 is 0.3-5; and / or, when the positive electrode active material is selected from a lithium nickel cobalt manganese oxide material, the percentage of Ni in the lithium nickel cobalt manganese oxide material is N%, and N is 30-90.

6. An electrolyte, characterized by The lithium battery comprises a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive comprises the electrolyte additive according to any one of claims 1-5.

7. A lithium-ion battery, characterized by The lithium battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte according to claim 6.

8. The lithium-ion battery of claim 7, wherein, The positive electrode comprises a positive electrode current collector and a positive electrode active paste layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active paste layer comprises a positive electrode active material selected from one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese oxide.

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