A non-aqueous electrolyte for lithium-ion batteries and the lithium-ion battery thereof.

Abstract

This invention discloses a non-aqueous electrolyte for lithium-ion batteries, comprising an organic solvent, a lithium salt, conventional additives, and special additives, wherein the special additives are cyclic boric anhydride compounds and isothiocyanate compounds. The electrolyte of this invention can significantly improve the cycle life, high-temperature performance, and rate performance of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a non-aqueous electrolyte for lithium-ion batteries and the lithium-ion battery thereof. Background Technology

[0002] In recent years, with the rapid development of 3C digital products, electric vehicles, and energy storage systems, people have placed higher demands on the energy density of lithium-ion batteries. Therefore, cathode materials are gradually being developed towards higher voltage to further improve their specific capacity and energy density.

[0003] Under high voltage, the cathode material structure is unstable and has high oxidation activity, easily catalyzing the oxidative decomposition of the electrolyte and generating a large amount of gas. Furthermore, during cycling, transition metal ions from the cathode easily dissolve into the electrolyte, reducing and depositing at the anode, damaging the SEI film and hindering Li... + The migration of these molecules exacerbates the occurrence of side reactions at the electrode / electrolyte interface, leading to accelerated capacity decay and deterioration of cell performance.

[0004] Developing new electrolyte additives is one of the economical and effective methods to solve the above problems and improve the performance of lithium-ion batteries. However, the additives used in existing technologies have disadvantages such as requiring large amounts, being difficult to synthesize, and being expensive, which are not conducive to industrial production and commercial application.

[0005] Therefore, existing technologies still have shortcomings, and new additives need to be developed to improve the performance of lithium-ion batteries. Summary of the Invention

[0006] This invention addresses the problems in the prior art by disclosing a non-aqueous electrolyte for lithium-ion batteries and a lithium-ion battery thereof. The electrolyte contains cyclic boric anhydride and thiocyanate compounds, which can significantly improve the cycle life, high-temperature performance, and rate performance of lithium-ion batteries.

[0007] This invention is achieved through the following technical solution: This invention provides a non-aqueous electrolyte for lithium-ion batteries, comprising an organic solvent, a lithium salt, conventional additives, and special additives. The special additives are cyclic boric anhydride compounds as shown in structural formula I and isothiocyanate compounds as shown in structural formula II.

[0008] R1, R2, R3, and R4 are each independently selected from one of trimethylsilyl, trimethylsiloxy, unsubstituted or substituted alkane or alkoxy groups of C1 to C10, unsubstituted or substituted alkenyl groups of C2 to C10, unsubstituted or substituted alkynyl groups of C2 to C10, and unsubstituted or substituted aryl groups of C6 to C10. When substituted, the substituent can be a halogen atom or a cyano group, and n is 1 or 2.

[0009] The electrolyte additives in this invention include cyclic boric anhydride and isothiocyanate compounds, both of which have higher HOMO values ​​and lower LUMO values ​​than the solvent. They preferentially undergo redox reactions in the solvent and participate in the formation of the interfacial passivation film. In the cyclic boric anhydride compounds of this invention, the boron (B) is in an electron-deficient state and readily reacts with the ferrous (F) radical. - and PF6 - The combination of these compounds can suppress the decomposition of LiPF6 to produce HF, which is beneficial to improving the thermal stability of LiPF6 and reducing damage to the positive electrode material. When cyclic boric anhydride compounds are used together with isothiocyanate compounds, the BO bonds in the cyclic boric anhydride compounds break under the action of isothiocyanate compounds, thereby opening the ring structure and generating a polymer protective film containing S and B. This film tightly covers the surface of the positive and negative electrode materials, forming a thin and uniform SEI / CEI film with good stability and ionic conductivity. This film can further effectively suppress the dissolution of transition metal ions, prevent the deposition of positive electrode oxidation products on the negative electrode, and significantly improve the cell's cycle performance, high-temperature performance, and rate performance.

[0010] As a further embodiment, R1, R2, R3 and R4 are each independently selected from one of trimethylsilyl, trimethylsiloxy, unsubstituted or substituted alkane or alkoxy groups of C1 to C4, unsubstituted or substituted alkenyl groups of C2 to C4, unsubstituted or substituted alkynyl groups of C2 to C4, and unsubstituted or substituted aryl groups of C6 to C10, wherein when substituted, the substituent can be a halogen atom or a cyano group, and n is 1 or 2.

[0011] As a further option, structural formula I is selected from at least one of compounds having the following structures: .

[0012] As a further option, structural formula II is selected from at least one of compounds having the following structures:

[0013] As a further embodiment, the cyclic boric anhydride compound is selected from compounds 1-1 and / or 1-2, and the isothiocyanate compound is selected from compounds 2-3 and / or 2-4. Trimethylsilyl groups can participate in film formation, resulting in a film composition rich in silicates, exhibiting good lithium-ion conductivity, and reducing the internal resistance of the battery cell.

[0014] As a further option, the special additive is selected from compounds 1-1 and 2-3.

[0015] As a further embodiment, the organic solvent accounts for 60% to 85% of the total mass of the electrolyte.

[0016] As a further embodiment, the organic solvent includes any one or a combination of two or more of the following: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl trifluoroethyl carbonate (FEMC), diethyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), propyl acetate (PA), ethyl acetate (EA), ethyl butyrate (EB), γ-butyrolactone (GBL), γ-valerolactone (GVL), and δ-valerolactone (DVL).

[0017] As a further embodiment, the organic solvent is a combination of three or more selected from ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The combined use of cyclic and chain carbonates can achieve higher electrical conductivity and lower viscosity, thereby improving performance.

[0018] As a further embodiment, the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

[0019] As a further option, the lithium salt includes lithium hexafluorophosphate (LiPF6).

[0020] As a further embodiment, the lithium salt also includes any one or a combination of two or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate borate) (LiBOB), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0021] As a further embodiment, the lithium salt includes a combination of at least two of LiPF6, LiPO2F2 and LiFSI.

[0022] As a further embodiment, the total mass of the conventional additives and special additives is 3% to 20% of the total mass of the electrolyte.

[0023] As a further embodiment, the cyclic boric anhydride compounds and thiocyanate compounds account for 0.1% to 3% of the total mass of the electrolyte, respectively. When the amount added is too small, the SEI and CEI films formed by these substances are not uniform and dense enough, resulting in poor stability and hindering long cycle life. When the amount added is too large, it will increase the viscosity of the electrolyte and reduce its conductivity. In addition, the excessively thick interfacial film may lead to increased interfacial impedance, which in turn degrades the cell performance.

[0024] As a further embodiment, the cyclic boric anhydride compounds and thiocyanate compounds account for 0.5% to 2% of the total mass of the electrolyte, respectively.

[0025] As a further embodiment, the conventional additives include any one or a combination of two or more of the following: fluoroethylene carbonate (FEC), 1,3-propanesulfonyl lactone (PS), 1,3-sulfonyl lactone (PST), 1,4-butanesulfonyl lactone (BS), vinyl sulfate (DTD), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), tris(trimethylsilane)borate (TMSB), tris(trimethylsilane)phosphate (TMSP), adiponitrile (ADN), succinic anhydride (SN), ethylene glycol dipropionitrile ether (DENE), 1,3,6-hexanetrionitrile (HTCN), succinic anhydride (SA), maleic anhydride (MA), citrate anhydride (CTA), and methanedisulfonate (MMDS).

[0026] A second aspect of the present invention is to provide a lithium-ion battery, the lithium-ion battery comprising the above-mentioned non-aqueous electrolyte for lithium-ion batteries.

[0027] As a further embodiment, the lithium-ion battery also includes a positive electrode, a negative electrode, and a separator.

[0028] As a further option, the active material in the positive electrode is LiCO2, LiMn2O4, LiFePO4, or LiNi. x Co y Mn z M 1-x-y-z O2 or LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from one or more of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 1≥x≥0.5, 0.5≥y≥0, 0.5≥z≥0, and x+y+z≤1, and the values ​​of x, y and z satisfy the valence equilibrium of the general formula.

[0029] As a further option, the active material in the negative electrode is one or more of natural graphite, artificial graphite, and silicon-carbon composite materials.

[0030] A third aspect of the present invention is to provide an electrochemical device or electrical appliance having the lithium-ion battery.

[0031] As a further embodiment, the electrochemical device can be used in end-consumer products, including but not limited to mobile phones, laptops, pen input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, and portable printers.

[0032] As a further embodiment, the electrochemical device can be used in electrical equipment, including large and small electrical equipment. Small electrical equipment includes consumer products, wearable electronic devices, or portable electronic devices; large electrical equipment includes transportation equipment. Transportation equipment includes, but is not limited to, vehicles such as automobiles, motorcycles, electric bicycles, buses, subways, high-speed trains, airplanes, and ships. Wearable electronic devices or portable electronic devices include, but are not limited to, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, drones, motors, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0033] The features and beneficial effects of this invention are as follows: (1) The electrolyte additives in this invention include cyclic boric anhydride and isothiocyanate compounds, both of which have higher HOMO values ​​and lower LUMO values ​​than the solvent. The solvent preferentially undergoes redox reactions and participates in the formation of the interfacial passivation film.

[0034] (2) In the cyclic boric anhydride compounds of the present invention, B is in an electron-deficient state and readily reacts with F. - and PF6 - This combination can suppress the decomposition of LiPF6 to produce HF, which is beneficial to improving the thermal stability of LiPF6 and reducing damage to the cathode material.

[0035] (3) When cyclic boric anhydride compounds are used together with isothiocyanate compounds, the BO bonds in the cyclic boric anhydride compounds break under the action of isothiocyanate compounds, thereby opening the ring structure and generating a polymer protective film containing S and B, which tightly covers the surface of the positive and negative electrode materials. The resulting SEI / CEI film is thin and uniform, with good stability and ionic conductivity, which can further effectively inhibit the dissolution of transition metal ions, prevent the deposition of positive electrode oxidation products on the negative electrode, and significantly improve the cell cycle performance, high temperature performance and rate performance. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 The EDS test results of the negative electrode of the lithium-ion battery prepared in Comparative Example 3 after cycling at 45°C for 200 cls are shown.

[0038] Figure 2 The EDS test results of the negative electrode of the lithium-ion battery prepared in Example 7 after cycling at 45°C for 200cls are shown. Detailed Implementation

[0039] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0040] Example 1 1. Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a ratio of EC:PC:DEC:EMC = 3:1:2:4. After thorough mixing, 13.5 wt% LiPF6 and 1 wt% LiPO2F2 were added sequentially. After complete dissolution, conventional and special additives were added. The conventional additives were 0.5 wt% VC and 1 wt% FEC, and the special additives were 1 wt% cyclic boric anhydride compound 1-1 and 1 wt% isothiocyanate compound 2-1. After thorough mixing and dissolution, the mixture was ready for use.

[0041] 2. Preparation of the positive electrode The positive electrode active material NCM811, conductive carbon black (Super-P), carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:0.7:0.7:1.6, and then dispersed in N-methyl-2-pyrrolidone (NMP). After thorough stirring, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated onto the positive electrode current collector Al foil, dried, and then rolled and die-cut to obtain a positive electrode sheet that meets the requirements.

[0042] 3. Preparation of the negative electrode Artificial graphite (anode active material), conductive carbon black (Super-P), styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 95:1.2:2:1.8 and then dispersed in deionized water to obtain anode slurry. The anode slurry was uniformly coated onto Cu foil (anode current collector), dried, and then rolled and die-cut to obtain anode sheets that met the requirements.

[0043] 4. Preparation of lithium-ion batteries The positive and negative electrode sheets and the separator prepared by the above method are stacked in sequence, with the separator located in the middle of the positive and negative electrode sheets. The stacked cells are fixed with tape, and then cold-pressed and packaged to form a lithium-ion battery with a thickness of 4.6 mm, a length of 85 mm, and a width of 50 mm. The cells are vacuum baked at 80°C for 24 h to obtain cells ready for electrolyte injection. The prepared electrolyte is injected into the cells in a glove box with the dew point controlled below -40°C. After standing at high temperature for 24 h and standing at room temperature for 12 h, formation, secondary sealing, and capacity testing are performed to complete the battery manufacturing.

[0044] Example 2 The difference from Example 1 is that the special cyclic boric anhydride additive added to the electrolyte is 1 wt% of compound 1-2, and the rest are the same.

[0045] Example 3 The difference from Example 1 is that the special cyclic boric anhydride additive added to the electrolyte is 1 wt% of compounds 1-3, and the rest are the same.

[0046] Example 4 The difference from Example 1 is that the special cyclic boric anhydride additive added to the electrolyte is 1 wt% of compounds 1-4, and the rest are the same.

[0047] Example 5 The difference from Example 1 is that the special isothiocyanate additive added to the electrolyte is 1 wt% of compound 2-2, and the rest are the same.

[0048] Example 6 The difference from Example 1 is that the special isothiocyanate additive added to the electrolyte is 1 wt% of compound 2-3, while the rest are the same.

[0049] Example 7 The difference from Example 1 is that the special isothiocyanate additive added to the electrolyte is 1 wt% of compound 2-4, while the rest are the same.

[0050] Example 8 The difference from Example 1 is that the special cyclic boric anhydride additive added to the electrolyte is 0.5 wt% of compound 1-1, and the rest are the same.

[0051] Example 9 The difference from Example 1 is that the special cyclic boric anhydride additive added to the electrolyte is 2 wt% of compound 1-1, and the rest are the same.

[0052] Example 10 The difference from Example 1 is that the special isothiocyanate additive added to the electrolyte is 0.5 wt% of compound 2-3, and the rest are the same.

[0053] Example 11 The difference from Example 1 is that the special isothiocyanate additive added to the electrolyte is 2 wt% of compound 2-3, and the rest are the same.

[0054] Comparative Example 1 The difference from Example 1 is that the electrolyte does not contain any special additives of cyclic boric anhydride, that is, it does not contain 1 wt% of compound 1-1, but all other aspects are the same.

[0055] Comparative Example 2 The difference from Example 1 is that the electrolyte does not contain any special isothiocyanate additives, that is, it does not contain 1 wt% of compound 2-1, but all other aspects are the same.

[0056] Comparative Example 3 The difference from Example 1 is that the electrolyte does not contain any special additives, namely, it does not contain 1 wt% of cyclic boric anhydride compound 1-1 and 1 wt% of isothiocyanate compound 2-1, but all other components are the same.

[0057] Comparative Example 4 The difference from Example 1 is that the electrolyte does not contain any special additives of cyclic boric anhydride, i.e., it does not contain compound 1-1, but it does contain 1 wt% of TMSB (tris(trimethylsilane)borate) additive, and the rest are the same.

[0058] Comparative Example 5 The difference from Example 1 is that the electrolyte does not contain any special isothiocyanate additives, i.e., it does not contain compound 2-1, but it does contain 1 wt% PPDI (terephthalic diisocyanate) additive, and the rest are the same.

[0059] Lithium-ion battery performance testing The lithium-ion batteries prepared in Comparative Examples 1-5 and Examples 1-11 were subjected to performance tests.

[0060] 1) Room temperature cycling performance test: At 25℃, charge to 4.25V with constant current and constant voltage at 0.33C, cut off current at 0.05C, and then discharge to 3.0V with constant current at 0.33C. Record the initial discharge capacity as C0. Repeat the charge and discharge 500 times and record the discharge capacity on the 500th cycle as C1. Calculate the capacity retention rate of room temperature cycling according to the following formula: Capacity retention rate = C1 / C0 × 100%.

[0061] 2) High-temperature cycling performance test: In a 45℃ constant temperature chamber, charge to 4.25V with constant current and constant voltage at 0.33C, cut off current at 0.05C, and then discharge to 3.0V with constant current at 0.33C. Record the initial discharge capacity as C0. Repeat the charge and discharge cycle 500 times and record the discharge capacity on the 500th cycle as C1. Calculate the capacity retention rate of high-temperature cycling using the following formula: Capacity retention rate = C1 / C0 × 100%.

[0062] 3) Performance test after 4 hours of storage at 85℃: At 25℃, the battery was charged to 4.25V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. Then, it was discharged to 3.0V at a constant current of 0.2C, and the initial discharge capacity was recorded as C0. At 25℃, the battery was charged to 4.25V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. The room temperature thickness T0 of the fully charged battery was measured. The fully charged battery was then transferred to 85℃ and left to stand for 4 hours. After storage, the hot thickness T1 was measured. Then, the battery was left to stand at 25℃ for 2 hours, and then discharged to 3.0V at a constant current of 0.2C. The discharge capacity was recorded as C1. The thickness expansion rate after 4 hours of storage at 85℃ is calculated as (T1-T0) / T0 × 100%, and the capacity retention rate is calculated as C1 / C0 × 100%.

[0063] 4) Rate performance test: At 25℃, charge to 4.25V with a constant current and constant voltage of 0.5C, cut off current of 0.05C, and then discharge to 3.0V with a constant current of XC (where X=0.2, 2). Record the discharge capacities of 0.2C and 2C as C0 and C1, respectively. 2C discharge ratio = C1 / C0×100%.

[0064] Lithium-ion battery EDS test The lithium-ion batteries prepared in Comparative Example 3 and Example 7 were subjected to a 45°C cycle test. After 200 cls of cycling, the cells were discharged to 3.0V and then removed for disassembly. The negative electrode sheet was soaked in pure DMC solvent for 10 min, then cut into 2 mm × 4 mm rectangles, and attached to the sample stage with conductive adhesive. EDS testing was performed using a HITACHI (SU8100) scanning electron microscope.

[0065] The performance test data of the lithium battery are shown in Table 1.

[0066] Table 1. Lithium-ion battery performance test results

[0067] As shown in Comparative Examples 1-3 and Examples 1-11, the addition of cyclic boric anhydride compounds and thiocyanate compounds to the electrolyte significantly improves the cycle performance, high-temperature performance, and rate performance of lithium-ion batteries. Furthermore, the combined effect of both compounds is superior to their individual use. This is because, when used in combination, the BO bonds in the cyclic boric anhydride compounds break under the influence of the isothiocyanate compounds, thereby opening the ring structure and generating a polymer protective film containing sulfur (S) and boron (B). This film exhibits better stability and ionic conductivity, which is beneficial for improving the cycle performance, high-temperature performance, and rate performance of the battery cell.

[0068] As shown in Comparative Examples 1-3 and Examples 1-11, the optimal dosage range for cyclic boric anhydride compounds and thiocyanate compounds is 0.5wt%-2wt%. Electrolytes within this range can significantly improve the cycle performance, high-temperature performance, and rate performance of lithium-ion batteries. When the dosage is too low, the SEI and CEI films formed by these substances are not uniform and dense enough, resulting in poor stability and hindering long cycle life. When the dosage is too high, it will increase the viscosity of the electrolyte and reduce the conductivity. In addition, an excessively thick interfacial film may lead to increased interfacial impedance, which in turn degrades the cell performance.

[0069] Examples 1-7 explored the effects of cyclic boric anhydride compounds and isothiocyanate compounds with different structures. We observed that compounds 1-1, 1-2, 2-3, and 2-4 showed superior performance (Examples 1, 2, 6, and 7). We believe this advantage stems from the synergistic effect of the siloxane and cyano groups, as well as the higher isothiocyanate functionality. Furthermore, when the special additive was selected from compounds 1-1 and 2-3 (i.e., Example 6), the lithium battery exhibited optimal performance. Therefore, the most preferred special additive is the combination of compounds 1-1 and 2-3.

[0070] As shown in Comparative Examples 1, 4, and 1, adding TMSB to the electrolyte can improve the performance of lithium-ion batteries, but the effect is not as good as that of compound 1-1. The reason for this may be that TMSB is a linear BO compound, while compound 1 is a cyclic BO compound with multiple BO bonds in its structure. Through BO ring opening, it participates in the formation of the interfacial film, resulting in a thinner and more uniform and dense CEI / SEI film, thus improving the performance more significantly.

[0071] As shown in Comparative Examples 2, 5, and 7, adding PPDI to the electrolyte can improve the cycle performance, high-temperature performance, and rate performance of lithium-ion batteries, but the improvement effect of additive 2-4 is more significant. This is because additive 2-4 is an isothiocyanate group; compared to N=C=O, the S in N=C=S can effectively reduce film-forming resistance and improve film stability, thereby further improving cycle performance, high-temperature performance, and rate performance.

[0072] from Figure 1 and Figure 2 The comparison shows that in lithium-ion batteries without special additives, namely cyclic boric anhydride compounds and thiocyanate compounds, the SEI film does not contain B and S elements. After 200 battery cycles, a large amount of transition metal ions such as Co and Mn from the positive electrode dissolve out, are reduced at the negative electrode, damage the SEI film, and hinder Li... + The migration of oxygen leads to increased polarization at the negative electrode and accelerated capacity decay. However, in lithium-ion batteries with added cyclic boric anhydride and thiocyanate compounds, B and S elements are uniformly distributed on the surface of the negative electrode, indicating that these two special additives participate in the formation of the interfacial film, improving its stability and ionic conductivity. This effectively inhibits the dissolution of transition metal ions from the positive electrode, prevents the deposition of positive electrode oxidation products on the negative electrode, and slows down the occurrence of side reactions at the electrode / electrolyte interface, thereby ensuring a long cycle life of the lithium battery and improving its high-temperature and rate performance.

[0073] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte for lithium-ion batteries, characterized in that, It includes organic solvents, lithium salts, conventional additives, and special additives, wherein the special additives are cyclic boric anhydride compounds as shown in structural formula I and isothiocyanate compounds as shown in structural formula II: Structural Formula I Structural Form II R1, R2, R3 and R4 are each independently selected from one of trimethylsilyl, trimethylsiloxy, unsubstituted or substituted alkane or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C10, wherein when substituted, the substituent is a halogen atom or a cyano group, and n is 1 or 2; The total mass of the conventional additives and special additives is 3% to 20% of the total mass of the electrolyte; The cyclic boric anhydride compounds and thiocyanate compounds account for 0.1% to 3% of the total mass of the electrolyte, respectively. The conventional additives include any one or a combination of two or more of the following: fluoroethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, ethylene sulfate, vinylene carbonate, ethylene ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinic anhydride, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, succinic anhydride, maleic anhydride, citrate anhydride, and methanedisulfonate.

2. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, R1, R2, R3 and R4 are each independently selected from one of trimethylsilyl, trimethylsiloxy, unsubstituted or substituted alkane or alkoxy group of C1 to C4, unsubstituted or substituted alkenyl group of C2 to C4, unsubstituted or substituted alkynyl group of C2 to C4, and unsubstituted or substituted aryl group of C6 to C10, wherein when substituted, the substituent is a halogen atom or a cyano group, and n is 1 or 2.

3. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The structural formula I is selected from at least one of the following compounds: Compound 1-1 Compounds 1-2 Compounds 1-3 Compounds 1-4.

4. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The structural formula II is selected from at least one of the following compounds: 。 5. A non-aqueous electrolyte for lithium-ion batteries according to claim 3 or 4, characterized in that, The cyclic boric anhydride compounds are selected from compounds 1-1 and / or compounds 1-2, and the isothiocyanate compounds are selected from compounds 2-3 and / or compounds 2-4.

6. The non-aqueous electrolyte for lithium-ion batteries according to claim 5, characterized in that, The special additives are selected from compounds 1-1 and 2-3.

7. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The organic solvent includes any one or a combination of two or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

8. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The organic solvent is a combination of three or more of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

9. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The lithium salt includes lithium hexafluorophosphate.

10. A non-aqueous electrolyte for lithium-ion batteries according to claim 9, characterized in that, The lithium salt further includes any one or a combination of two or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

11. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The lithium salt comprises a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, and lithium difluorosulfonylimide.

12. The non-aqueous electrolyte for lithium-ion batteries according to claim 1, characterized in that, The cyclic boric anhydride compounds and thiocyanate compounds account for 0.5% to 2% of the total mass of the electrolyte, respectively.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte according to any one of claims 1-12.

14. A lithium-ion battery according to claim 13, characterized in that, The lithium-ion battery also includes a positive electrode, a negative electrode, and a separator; The active material in the positive electrode is LiCoO2, LiMn2O4, LiFePO4, or LiNi. x Co y Mn z M 1-x-y-z O2 or LiNi x Co y Al z N 1-x-y-z One or more of O2; wherein M and N are independently selected from one or more of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 1≥x≥0.5, 0.5≥y≥0, 0.5≥z≥0, and x+y+z≤1; The active material in the negative electrode is one or more of natural graphite, artificial graphite, and silicon-carbon composite materials.

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