High-temperature and high-pressure electrolyte additive, electrolyte containing high-temperature and high-pressure electrolyte additive and lithium ion battery

Abstract

The invention discloses a high-temperature and high-pressure electrolyte additive, an electrolyte containing the high-temperature and high-pressure electrolyte additive and a lithium ion battery. The electrolyte additive is selected from at least one of cyclic borate compounds. According to the invention, after the cyclic borate compound (such as bis (pinacol) diboron or 3-(trifluoromethyl) phenylboronic acid pinacol ester compound) is applied to the high-nickel lithium ion battery as the electrolyte additive, the battery can still maintain the capacity greater than or equal to 88% at the working voltage of 2.8-4.5 V (55 DEG C, and 300 cycles), meanwhile, the rate capability of the battery is improved, and the service life of the battery is prolonged. Compared with a battery without the cyclic borate compound additive, the cyclic borate compound additive is greatly improved under the same battery test condition. The cyclic borate additive is added into the electrolyte, so that the cycle performance of the lithium ion battery at high temperature and high voltage can be improved, and the rate capability of the battery can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery electrolytes, and relates to a high-temperature and high-pressure electrolyte additive, an electrolyte containing the same, and a lithium-ion battery. Specifically, it relates to an electrolyte for a high-temperature and high-pressure lithium-ion battery and a lithium-ion battery thereof, which is suitable for improving the rate performance and cycle performance of lithium-ion batteries under high temperature and high pressure. Background Art

[0002] With the rapid development of electric vehicles, the demand for high specific energy, safe and reliable lithium-ion batteries is increasing. x Co y Mn 1-x-y O2 (NCM) layered oxides are ideal cathodes for high-energy lithium-ion batteries due to their high voltage platform and considerable specific capacity. However, high-nickel active materials have defects such as poor cycle performance and poor thermal stability in carbonate-based electrolyte systems, especially under harsh conditions (such as high temperature and high cut-off voltage), which greatly limits their commercial application. The above problems of high-nickel active materials are mainly due to the instability of the material itself and the interface: on the one hand, the degree of Li / Ni mixing increases during the cycle, resulting in the destruction of the layered structure and the attenuation of the capacity of the electrode material during the cycle; at the same time, Ni in the high delithiation state 4+ Tends to be reduced to form Ni 3+ , which easily releases oxygen, resulting in poor thermal stability of the material. Furthermore, the electrode / electrolyte interface is unstable in actual electrochemical environments and susceptible to corrosion by free acids in the electrolyte, leading to problems such as low battery capacity retention and poor high-temperature performance. Therefore, improving the cycle life of high-nickel-based lithium-ion batteries under high-temperature and high-voltage conditions is a major issue that needs to be addressed.

[0003] In order to solve the above problems of high-nickel electrode materials, there are currently three main approaches: one is to dope cations (Al, Mg, Ti, Zr, etc.) or anions (F) into the material lattice to inhibit Li / Ni mixing, thereby improving the stability of the material structure and thus improving the cycle performance of the material; the second is to coat the surface of the electrode material with a protective layer of uniform thickness and good conductivity, by physically isolating the direct contact between the electrolyte and the electrode material to reduce acid corrosion of the electrode; the third is to add suitable electrolyte additives to oxidatively decompose on the surface of the electrode material to form a dense protective film, thereby inhibiting further oxidative decomposition of the electrolyte on the positive electrode surface, thereby improving the interfacial stability of the positive electrode material and improving the cycle stability of high-nickel materials. Although researchers have conducted a lot of research on this, there are still shortcomings, because the cycle problem of lithium-ion batteries under high voltage is not only in the positive electrode itself, but also closely related to the electrolyte. Summary of the Invention

[0004] To address the above technical issues, the present invention provides a high-temperature, high-voltage resistant electrolyte additive, an electrolyte containing the same, and a lithium-ion battery thereof. The electrolyte of the present invention includes a cyclic borate electrolyte additive. After adding this additive, the electrolyte will prematurely oxidize to form a film on the electrode surface, inhibiting electrolyte decomposition and effectively preventing hydrofluoric acid corrosion on the high-nickel electrode surface, thereby protecting the crystal structure of the electrode material and improving the cycle performance and rate performance of high-nickel lithium-ion batteries at high temperatures and high voltages.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] An electrolyte comprises an additive; wherein the additive is selected from at least one cyclic borate compound.

[0007] According to an embodiment of the present invention, the cyclic borate ester compound is selected from at least one compound having a structure shown in Formula I to Formula IV;

[0008]

[0009] Wherein, R1, R2, R3, R4, R5, R6, R7, W1, W2, W3, W4, W5, W6, W7, W8, W9 are the same or different and are independently selected from alkyl, alkenyl, aromatic or halogen, preferably halogen, C 1-6 Alkyl, C 2-6 Alkenyl, C 3-16 Saturated or partially saturated cycloalkyl and its derivatives, C 3-16 Saturated or partially saturated heterocycloalkyl and its derivatives, C in which some or all of H are substituted by halogen 1-6 Alkyl; wherein, when R3, R4, W4, and W5 are carbon elements, they may be connected to form a five-membered ring or a six-membered ring, and one or more carbon elements on the five-membered ring or the six-membered ring may be substituted by a N element.

[0010] According to an embodiment of the present invention, the additive is selected from at least one compound having the following structural formula:

[0011]

[0012]

[0013] Preferably, the additive is selected from at least one of bis(pinacol)diboron, neopentyl glycol diborate, bis(hexenyl glycolate)diboron, 3-(trifluoromethyl)phenylboronic acid pinacol ester, 2,4-bis(trifluoromethyl)phenylboronic acid pinacol ester and 1,5-dimethyl-1H-pyrazole-4-boronic acid pinacol ester.

[0014] According to an exemplary embodiment of the present invention, the cyclic borate ester compound is preferably bis(pinacolato)diboron having a structure shown in Formula 1 or 3-(trifluoromethyl)phenylboronic acid pinacol ester having a structure shown in Formula 2:

[0015]

[0016]

[0017] According to an embodiment of the present invention, the electrolyte further comprises an organic solvent. Preferably, the organic solvent is selected from at least one of a chain carbonate and a cyclic carbonate, preferably at least two of a chain carbonate and a cyclic carbonate. Preferably, the chain carbonate is selected from at least one of the compounds of formula V, and the cyclic carbonate is selected from the compounds of formula VI:

[0018]

[0019] Wherein, R8, R9 are independently selected from C 1-6 Alkyl, exemplified by methyl, ethyl or propyl;

[0020] R 10 , R 11 , R 12 , R 13 Independently selected from H, C 1-6 Alkyl; exemplified by H, methyl, ethyl or propyl.

[0021] According to an exemplary embodiment of the present invention, the compound with the structure shown in Formula V is selected from dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0022] According to an exemplary embodiment of the present invention, the compound with the structure represented by Formula VI is selected from ethylene carbonate and propylene carbonate.

[0023] According to an exemplary embodiment of the present invention, the organic solvent is preferably any one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethyl methyl carbonate (DMC), preferably two or three of the above organic solvents.

[0024] According to an embodiment of the present invention, the electrolyte further comprises a lithium salt. For example, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium perchlorate (LiClO4), lithium methanesulfonate (LiCH3SO3), and lithium trifluoromethanesulfonate (LiCF3SO3).

[0025] According to an embodiment of the present invention, the amount of the additive is 0.2wt% to 10wt% of the total mass of the electrolyte, exemplified by 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 2.0wt%, 5.0wt%, and 10wt%.

[0026] According to an embodiment of the present invention, the amount of the organic solvent used accounts for 10 to 90 wt % of the total mass of the electrolyte.

[0027] According to an embodiment of the present invention, the total molar concentration of the lithium salt in the electrolyte is 0.5 to 1.3 mol·L -1 , exemplified by 1.0 mol·L -1 .

[0028] The present invention also provides the use of the above additive in lithium-ion batteries, preferably in high-nickel-based lithium-ion batteries.

[0029] The present invention also provides a lithium ion battery containing the above electrolyte and / or additive.

[0030] According to an embodiment of the present invention, the lithium-ion battery further includes a positive electrode and a negative electrode.

[0031] Preferably, the material of the positive electrode is a high nickel layered oxide; the chemical formula of the high nickel layered oxide is LiNi x Co y M 1-x-y O2, where M is Mn or Al, x ≥ 0.6, 0 <y≤0.4,1-x-y≥0。

[0032] Preferably, the cut-off operating voltage of the lithium-ion battery is 4.5V; and the capacity of the lithium-ion battery after 300 cycles at 0.5C is ≥88%.

[0033] Optionally, the operating temperature of the lithium-ion battery is 25 or 55°C.

[0034] Optionally, the operating voltage of the lithium-ion battery is 2.8-4.5V.

[0035] According to an embodiment of the present invention, the material of the negative electrode is a lithium sheet, a graphite-like carbon material or a silicon-based material.

[0036] Beneficial effects of the present invention:

[0037] The present invention uses cyclic borate compounds (such as bis(pinacolato)diboron or 3-(trifluoromethyl)phenylboronic acid pinacolato compounds) as electrolyte additives to improve the rate performance and high-temperature and high-pressure cycling stability of high-nickel lithium-ion batteries at high voltages. When the electrolyte of the present invention is applied to a high-nickel lithium-ion battery, the battery can maintain a capacity greater than or equal to 88% after an operating voltage of 2.8-4.5V (55°C, 300 cycles), while also improving the battery's rate performance. This performance is significantly improved compared to batteries without the cyclic borate compound additive under the same battery testing conditions. By adding the cyclic borate additive to the electrolyte, the present invention enables the high-nickel lithium-ion battery to have better electrochemical performance.

[0038] Definition and Explanation:

[0039] C 1-6 Selected from C1, C2, C3, C4, C5, C6; C 2-6 Selected from C2, C3, C4, C5, C6; C 3-16 Selected from C3, C4, C5, C6, C7, C8, C9, C 10 、C 11 、C 12 、C 13 、C 14 、C 15 、C 16 ;

[0040] As used herein, the term "alkyl" refers to a linear or branched monovalent hydrocarbon group. Non-limiting examples include methyl, ethyl, propyl, butyl, 2-methyl-propyl, 1,1-dimethylethyl, pentyl, and hexyl.

[0041] As used herein, the term "1 to a plurality of" means more than one, for example, 1, 2, 3, 4, 5 or more.

[0042] The term "cycloalkyl" refers to a saturated or partially unsaturated monocyclic or polycyclic cyclic hydrocarbon group, and the carbocyclic ring can contain 3 to 20 carbon atoms, preferably 3 to 12 (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) carbon atoms, more preferably 3 to 6 carbon atoms. The carbocyclic ring can be monocyclic or polycyclic, and it can be a saturated cycloalkyl or can optionally contain one, two or more double bonds and / or triple bonds on its ring, thereby forming a so-called cycloalkenyl or cycloalkynyl. In the case of having multiple rings, the carbocyclic rings can form spirocyclic, fused ring and bridged ring structures. For example, non-limiting examples of monocyclic carbocyclic rings include cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cyclohexadienyl, cycloheptyl, cycloheptatrienyl, cyclooctyl, cyclooctatetraenyl, etc.; non-limiting examples of polycyclic carbocyclic rings include decalinyl or isobornyl.

[0043] The term "heterocycle" refers to a saturated or partially unsaturated monocyclic or polycyclic hydrocarbon substituent containing 3 to 20 ring atoms, one or more of which is a heteroatom or atomic group selected from N, O, NH, S, S(O) or S(O)2, but excluding the ring portion of -OO-, -OS- or -SS-, and the remaining ring atoms are carbon. Preferably, it contains 3 to 12 ring atoms, 1-4 of which are heteroatoms (e.g., 1, 2, 3, and 4); more preferably, it contains 3 to 6 ring atoms (e.g., 3, 4, 5, 6). The heterocyclic group can be connected to the rest of the molecule through any one of the carbon atoms or a nitrogen atom (if present) or an oxygen or sulfur atom (particularly in the case of forming an onium salt). The heterocyclic group can include fused or bridged rings and / or spirocyclic rings. Non-limiting examples of monocyclic heterocyclic groups include azetidinyl, oxetanyl, pyrrolidinyl, imidazolidinyl, tetrahydrofuranyl, tetrahydrothienyl, dihydroimidazolyl, dihydrofuranyl, dihydropyrazolyl, dihydropyrrolyl, dioxolyl, tetrahydropyranyl, pyrrolinyl, piperidinyl, piperazinyl, morpholinyl, thiomorpholinyl, dithianyl, trithianyl, homopiperazinyl, diazepanyl etc., preferably piperidinyl, pyrrolidinyl. Polycyclic heterocyclic groups include spirocyclic, fused ring and bridged heterocyclic groups, and can also be benzo-fused heterocyclic groups such as dihydroisoquinolinyl. The heterocyclic group can be bicyclic, and its non-limiting examples include hexahydrocyclopenta [c] pyrrole -2 (1H) - base, hexahydro pyrrolo [1,2-a] pyrazine -2 (1H) - base. The heterocyclyl group may also be partially unsaturated, i.e. it may contain one or more double bonds, non-limiting examples of which include dihydrofuranyl, dihydropyranyl, 2,5-dihydro-1H-pyrrolyl, 4H-[1,3,4]thiadiazinyl, 4,5-dihydrooxazolyl or 4H-[1,4]thiazinyl.

[0044] The heterocyclyl group may be optionally substituted or unsubstituted. When substituted, the substituents are preferably one or more groups independently selected from alkyl, alkenyl, alkynyl, alkoxy, alkylthio, alkylamino, halogen, mercapto, hydroxy, nitro, cyano, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, cycloalkoxy, heterocycloalkoxy, cycloalkylthio, heterocycloalkylthio, oxo, carboxyl or carboxylate.

[0045] As used herein, the term "heteroaryl / heteroaromatic ring" refers to a heteroaromatic system comprising 1 to 4 heteroatoms, 5 to 20 ring atoms, wherein the heteroatoms are selected from oxygen, sulfur, nitrogen and phosphorus. Heteroaryl is preferably 5 to 10 yuan (e.g., 5, 6, 7, 8, 9 or 10 yuan), more preferably 5 yuan or 6 yuan. Non-limiting examples of heteroaryl include, but are not limited to, thienyl, furyl, pyrrolyl, oxazolyl, thiazolyl, imidazolyl, pyrazolyl, isoxazolyl, isothiazolyl, oxadiazolyl, triazolyl, thiadiazolyl, thia-4H-pyrazolyl, etc. and their benzo derivatives, such as benzofuranyl, benzothienyl, benzoxazolyl, benzisoxazolyl, benzimidazolyl, benzotriazolyl, indazolyl, indolyl, , isoindolyl, etc.; or pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, etc., and benzo derivatives thereof, such as quinolyl, quinazolinyl, isoquinolyl, etc.; or acinyl, indolizinyl, purinyl, etc. and benzo derivatives thereof; or cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, naphthyridinyl, pteridinyl, carbazolyl, acridinyl, phenazinyl, phenothiazinyl and / or phenoxazinyl, etc.

[0046] The heteroaryl group / heteroaromatic ring may be optionally substituted or unsubstituted. When substituted, the substituents are preferably one, two or more groups independently selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, alkylthio, alkylamino, halogen, mercapto, hydroxy, nitro, cyano, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, cycloalkoxy, heterocycloalkoxy, cycloalkylthio, heterocycloalkylthio, carboxyl or carboxylate. DETAILED DESCRIPTION

[0047] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0048] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0049] Example 1

[0050] In the embodiment, for LiNi 0.6 Co 0.2 Mn 0.2 O2 / Li battery related tests.

[0051] LiNi 0.6 Co 0.2 Mn 0.2 The O2 / Li battery is prepared using a conventional button cell manufacturing process. The specific method is as follows:

[0052] By mixing LiCo 0.6 Ni 0.2 Mn 0.2 The positive electrode slurry was prepared by mixing O2 powder (80 wt%), carbon black (10 wt%), polyvinylidene fluoride (PVDF 10 wt%) and N-methylpyrrolidone (NMP). The mixed slurry was coated on aluminum foil using an automatic coating machine, and the coated electrode was placed in a 100°C vacuum oven to dry overnight. The next day, the large electrode was rolled and cut into 16 mm small discs at room temperature. The cut small discs were then placed in a vacuum oven at 100°C for 12 hours. The dried electrode was assembled into a 2025 button cell in an argon-filled glove box (moisture <5 ppm, oxygen <5 ppm) with a separator (Celgard 2325), electrolyte, lithium sheet, and positive and negative electrode casings.

[0053] The electrolyte composition is as follows:

[0054] The concentration of lithium salt LiPF6 is 1.0 mol·L -1 The organic solvent is a mixed solvent of EC:EMC:DMC in a volume ratio of 1:1:1, which is defined as base; an additive bis(pinacolato)diboron (BPCD) is added to the base, and the additive accounts for 0.2wt% of the total mass of the electrolyte.

[0055] Example 2

[0056] The only difference between this embodiment and embodiment 1 is that the additive bis(pinacolato)diboron accounts for 0.5 wt % of the total mass of the electrolyte. The electrolyte prepared above is added into a button cell.

[0057] Example 3

[0058] The only difference between this embodiment and embodiment 1 is that the additive bis(pinacolato)diboron accounts for 1.0 wt % of the total mass of the electrolyte. The electrolyte prepared above is added into a button cell.

[0059] Example 4

[0060] The only difference between this embodiment and embodiment 1 is that the additive is 3-(trifluoromethyl)phenylboronic acid pinacol ester (TD), and the additive accounts for 0.5 wt % of the total mass of the electrolyte. The electrolyte prepared above is added to a button cell.

[0061] Example 5

[0062] The only difference between this embodiment and embodiment 1 is that the additive is 3-(trifluoromethyl)phenylboronic acid pinacol ester (TD), and the additive accounts for 1.0 wt % of the total mass of the electrolyte. The electrolyte prepared above is added to a button cell.

[0063] Example 6

[0064] The only difference between this embodiment and embodiment 1 is that the additive is 3-(trifluoromethyl)phenylboronic acid pinacol ester (TD), and the additive accounts for 2.0 wt % of the total mass of the electrolyte. The electrolyte prepared above is added to a button cell.

[0065] Comparative Example 1

[0066] The only difference between this comparative example and Example 1 is that the electrolyte composition is base. The electrolyte prepared above is added to a button cell.

[0067] The batteries prepared in Examples 1-6 and Comparative Example 1 were subjected to cycle performance tests at room temperature. The test results are shown in Table 1. The test process is as follows:

[0068] 0.1C constant current charge to 4.5V, 0.1C constant current discharge to 2.8V, cycle 3 weeks, 0.5C constant current charge to 4.5V, 0.5C constant current discharge to 2.8V, cycle 500 weeks.

[0069] Table 1

[0070] serial number 0.1C first discharge capacity (mAh / g) Battery capacity retention rate after 500 (300) cycles at 0.5C (%) Example 1 (normal temperature) 193.4 87.9 Example 2 (normal temperature) 195.3 89.8 Example 3 (normal temperature) 196.2 88.4 Example 4 (normal temperature) 189.7 88.9 Example 5 (normal temperature) 196.8 90.1 Example 6 (normal temperature) 195.6 88.3 Comparative Example 1 (normal temperature) 197.1 73.4

[0071] The high temperature cycle performance test was conducted on the batteries prepared in Examples 2, 5 and Comparative Example 1. The test results are shown in Table 2. The test process is as follows:

[0072] The battery was charged to 4.5V at 0.1C constant current and discharged to 2.8V at 0.1C constant current for 3 cycles in a constant temperature box at 55℃; then charged to 4.5V at 0.5C constant current and discharged to 2.8V at 0.5C constant current for 300 cycles.

[0073] Table 2

[0074] serial number 0.1C first discharge capacity (mAh / g) Battery capacity retention after 300 cycles at 0.5C (%) Example 2 (high temperature) 202.5 88.6 Example 5 (high temperature) 208.4 88.0 Comparative Example 1 (high temperature) 196.1 64.5

[0075] Example 7

[0076] The rate performance test of the batteries prepared in Example 2, Example 5 and Comparative Example 1 was carried out at room temperature. The test results are shown in Table 3. The test process is as follows:

[0077] 0.1C constant current charge to 4.5V, 0.1C constant current discharge to 2.8V, cycle 10 weeks, 0.2C constant current charge to 4.5V, 0.2C constant current discharge to 2.8V, cycle 10 weeks, 0.5C constant current charge to 4.5V, 0.5C constant current discharge to 2.8V, cycle 10 weeks, 1C constant current charge to 4.5V, 1C constant current discharge to 2.8V, cycle 10 weeks, 2C constant current charge to 4.5V, 2C constant current discharge to 2.8V, cycle 10 weeks, 5C constant current charge to 4.5V, 5C constant current discharge to 2.8V, cycle 10 weeks.

[0078] Table 3

[0079]

[0080] As can be seen from the results in Tables 1-2, compared to the lithium ion battery prepared in Comparative Example 1 without the addition of a cyclic borate ester additive, at room temperature or high temperature of 0.5°C, when the operating voltage is 4.5V, the lithium ion batteries prepared in Examples 1-5 of the present invention after adding cyclic borate esters such as bis(pinacolato)diboron (BPCD) and 3-(trifluoromethyl)phenylboronic acid pinacol ester (TD) additives can significantly improve the cycle performance of the lithium ion battery, and the battery capacity retention rate is also significantly improved. At the same time, it can be seen from Table 3 that the electrolyte obtained after adding bis(pinacolato)diboron (BPCD) or 3-(trifluoromethyl)phenylboronic acid pinacol ester (TD) additives to the electrolyte can also improve the rate performance of the lithium ion battery using the electrolyte when operating at 4.5V, especially at high rates (2C-5C), the rate cycle discharge capacity of the lithium ion batteries of Examples 2 and 5 is significantly higher than that of Comparative Example 1. This shows that the cyclic borate ester additive of the present invention is added to the electrolyte to form a more stable protective layer on the electrode surface, which inhibits the decomposition of the electrolyte; at the same time, the boron element in the additive and the PF6 - or F - It can stabilize the electrolyte and reduce the corrosion of HF on the electrode materials, so as to improve the crystal structure stability of the electrode active materials and thus improve the cycle performance of lithium-ion batteries.

[0081] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes an additive; wherein the additive is selected from at least one cyclic borate-containing compound.

2. The electrolyte according to claim 1, characterized in that The cyclic borate ester compound is selected from at least one compound having a structure shown in Formula I to Formula IV; Wherein, R1, R2, R3, R4, R5, R6, R7, W1, W2, W3, W4, W5, W6, W7, W8, W9 are the same or different and are independently selected from alkyl, alkenyl, aromatic or halogen, preferably halogen, C 1-6 Alkyl, C 2-6 Alkenyl, C 3-16 Saturated or partially saturated cycloalkyl and its derivatives, C 3-16 Saturated or partially saturated heterocycloalkyl and its derivatives, C in which some or all of H are substituted by halogen 1-6 Alkyl; wherein, when R3, R4, W4, and W5 are carbon elements, they may be connected to form a five-membered ring or a six-membered ring, and one or more carbon elements on the five-membered ring or the six-membered ring may be substituted by a N element.

3. The electrolyte according to claim 1 or 2, characterized in that The additive is selected from at least one compound having the following structural formula:

4. The electrolyte according to any one of claims 1 to 3, characterized in that The additive is preferably bis(pinacolato)diboron or 3-(trifluoromethyl)phenylboronic acid pinacol ester.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further comprises an organic solvent. Preferably, the organic solvent is selected from at least one of chain carbonates and cyclic carbonates, and preferably at least two of chain carbonates and cyclic carbonates. Preferably, the linear carbonate is selected from at least one of the compounds represented by formula V, and the cyclic carbonate is selected from at least one of the compounds represented by formula VI; Wherein, R8, R9 are independently selected from C 1-6 Alkyl, exemplified by methyl, ethyl or propyl; R 10 , R 11 , R 12 , R 13 Independently selected from H, C 1-6 Alkyl groups are exemplified by H, methyl, ethyl or propyl. Preferably, the compound with the structure represented by formula V is selected from dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and the compound with the structure represented by formula VI is selected from ethylene carbonate and propylene carbonate.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The electrolyte further comprises a lithium salt, preferably at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium perchlorate, lithium methanesulfonate, and lithium trifluoromethanesulfonate.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The amount of the additive is 0.2 wt% to 10 wt% of the total mass of the electrolyte; Preferably, the amount of the organic solvent is 10 wt% to 90 wt% of the total mass of the electrolyte; Preferably, the total molar concentration of the lithium salt in the electrolyte is 0.5 mol·L -1 ~1.3 mol·L -1 .

8. A lithium-ion battery, characterized in that: The electrolyte comprises the electrolyte and / or additive according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that The lithium-ion battery further comprises a positive electrode and a negative electrode. Preferably, the material of the positive electrode is a high nickel layered oxide; the chemical formula of the high nickel layered oxide is LiNi x Co y M 1-x-y O2, where M is Mn or Al, x ≥ 0.6, 0 <y≤0.4,1-x-y≥0; Preferably, the negative electrode is made of a lithium sheet, a graphite-like carbon material or a silicon-based material.

10. The lithium-ion battery according to claim 8 or 9, characterized in that The cut-off operating voltage of the lithium-ion battery is 4.5V; and the capacity of the lithium-ion battery after 300 cycles at 0.5C and 55°C is ≥88%.

Images