Electrolyte and lithium ion battery

Abstract

This invention belongs to the field of electrochemistry, specifically relating to an electrolyte and a lithium-ion battery. The electrolyte of this invention comprises a first additive, which includes a compound of formula I and a compound of formula II. In this invention, the compound of formula I is beneficial for maintaining the stability of the positive electrode, while the compound of formula II is beneficial for protecting the negative electrode and inhibiting electrolyte decomposition. Furthermore, the compounds of formula I and formula II have a synergistic effect in improving the cycle stability of the lithium-ion battery.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to an electrolyte and a lithium-ion battery. Background Technology

[0002] With the increasing popularity of new energy vehicles, higher and higher demands are being placed on the energy density of lithium-ion batteries (LIBs). This necessitates the use of ternary materials to improve battery energy density, while simultaneously combining them with silicon anodes to further enhance the cell's energy density. However, considering the actual operating conditions of new energy vehicles and the increasingly harsh real-world temperatures, increasingly stringent high-temperature requirements are also being placed on batteries.

[0003] After high-voltage charging, ternary materials undergo a hydrogenation reaction on the surface of the oxide cathode. This process is mainly due to the transfer of hydrogen atoms (in the form of protons H) from the electrolyte solvent. + and electronic e - Hydrogenation occurs when hydrogen atoms are partially delithiated from the oxide cathode surface. This hydrogenation reaction alters the surface structure of the cathode material, affecting the electrochemical behavior and stability of the battery. Specifically, when the battery is under high voltage, the partially delithiated oxide cathode surface reacts with carbonate solvents (such as ethylene carbonate EC and ethyl methyl carbonate EMC) in the electrolyte. The CH bonds (especially the -CH2- groups) in these solvents are easily broken, and the released hydrogen atoms transfer to the oxide cathode surface, protonating the lattice oxygen. Simultaneously, electrons reduce nearby high-valence transition metals (such as nickel Ni). This process not only leads to surface hydrogenation of the cathode material but also induces lattice expansion, thus affecting the chemical-mechanical stability of the cathode material. Silicon, due to its high energy density, is currently the most promising anode material for lithium-ion batteries. However, the significant volume changes of silicon particles during cycling cause continuous damage to the solid electrolyte interface (SEI), resulting in decreased cycle performance. Since the work function of silicon is significantly higher than that of graphite, its storage performance deteriorates significantly under high-temperature conditions. Therefore, high temperature is the biggest bottleneck in silicon-containing anodes.

[0004] Therefore, there is an urgent need to develop an electrolyte that can improve the stability of lithium-ion batteries. Summary of the Invention

[0005] To address the above problems, this invention provides an electrolyte and a lithium-ion battery. The electrolyte of this invention contains a first additive, which comprises a compound of formula I and a compound of formula II: the compound of formula I can reduce the hydrogenation reaction at the positive electrode interface and form a CEI film on the positive electrode side by oxidation, thus maintaining the stability of the positive electrode; the compound of formula II can enhance the mechanical strength and flexibility of the SEI film on the negative electrode surface, reduce the damage and shedding of the SEI film, protect the negative electrode, and inhibit electrolyte decomposition; furthermore, the compounds of formula I and formula II have a synergistic effect, thereby improving the cycle stability of the lithium-ion battery.

[0006] Specifically, the electrolyte provided by the present invention comprises a first additive, which comprises compounds of formula I and formula II:

[0007] Wherein, X1 is O or NR1, and R1 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R1 is a substituted benzene ring, the substituent is one or more halogen atoms; Where X2 is O or NR2, and R2 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R2 is a substituted benzene ring, the substituent is one or more halogen atoms; Wherein, X3 is O or NR3, and R3 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R3 is a substituted benzene ring, the substituent is one or more halogen atoms; Among them, at least one of X1, X2 and X3 is not 0; The unsaturation degree within the rings containing X1, X2, and X3 is α, where 1 ≤ α ≤ 3; Wherein, R0 is a C6-C14 aromatic ring or a 5-14 membered heteroaromatic ring; the degree of intra-ring unsaturation of R0 is β, 1≤β≤7; Wherein, R4 is hydrogen, halogen, cyano, trifluoromethyl, substituted C6-C10 aryl, unsubstituted C6-C10 aryl, substituted phosphate ester, unsubstituted phosphate ester, substituted phosphite ester, or unsubstituted phosphite ester; when R4 is a substituted C6-C10 aryl, substituted phosphate ester, or substituted phosphite ester, the substituent is one or more halogen atoms; Among them, R7, R8, R9, R 10 Each group is independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon double bonds, and substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon triple bonds; when R7, R8, R9, or R 10When the substituent is a substituted C1-C6 alkyl group, a substituted C1-C6 alkoxy group, a substituted C2-C6 group containing an unsaturated carbon-carbon double bond, or a substituted C2-C6 group containing an unsaturated carbon-carbon triple bond, the substituent is independently selected from one or more of halogen, methacryloxy, methoxy, and trimethylsilyl. Among them, R7, R8, R9, R 10 Independent bonding or linked into a ring; The degree of unsaturation of the compound of formula II is γ, where γ ≥ 1.

[0008] In one or more embodiments, X1 is NR1, X3 is NR3, and R1 and R3 are each independently a substituted or unsubstituted benzene ring.

[0009] In one or more embodiments, the compound of formula I does not contain a -CH2- bond.

[0010] In one or more embodiments, X1 is 0, X2 is 0, and X3 is NR3.

[0011] In one or more embodiments, X1 is NR1, X2 is 0, and X3 is NR3.

[0012] In one or more implementations, R7, R8, R9, R 10 It contains at least one substituted or unsubstituted C2-C6 group with an unsaturated carbon-carbon double bond.

[0013] In one or more embodiments, R0 is a benzene ring, a naphthalene ring, a pyrrole ring, a furan ring, or an indole.

[0014] In one or more embodiments, X1 is NR1, X2 is O, X3 is NR3, and R1 and R3 are each independently a substituted or unsubstituted benzene ring.

[0015] In one or more embodiments, the compound of formula I is selected from one or more of the following structural formulas: .

[0016] In one or more embodiments, the compound of formula II is selected from one or more of the following structural formulas: .

[0017] In one or more embodiments, the electrolyte contains a compound of formula I in an amount of A wt%, where 0.25 ≤ A ≤ 1.5.

[0018] In one or more embodiments, the content of the compound of formula II in the electrolyte is B wt%, 0.05≤B≤5.

[0019] In one or more embodiments, the electrolyte further comprises a second additive, the second additive being fluoroethylene carbonate and / or difluoroethylene carbonate.

[0020] In one or more embodiments, the electrolyte further comprises a third additive selected from one or more of ethylene carbonate, vinylene carbonate, 1,3-propane sulpholactone, mannitol sulfate, 1,3-dioxane, 1,4-dioxane, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, vinyl sulfate, 1,3-propane sulpholactone, propenyl-1,3-sulfonyl lactone, 2,4-butane sulpholactone, methanedisulfonate, 1,3-propanedisulfonic anhydride, ethylene sulfite, and propargyl phosphate.

[0021] In one or more embodiments, the electrolyte further comprises a solvent selected from one or more of cyclic carbonates, linear carbonates, cyclic carboxylic esters, linear carboxylic esters, sulfones, phosphate esters, and phosphites; preferably, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, dimethyl sulfoxide, sulfolane, diphenyl sulfone, triethyl phosphate, and methyl ethyl phosphite.

[0022] In one or more embodiments, the electrolyte further comprises a lithium salt selected from one or more of lithium hexafluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, and lithium tri(trifluoromethylsulfonyl)methyl.

[0023] In one or more embodiments, the content of the second additive in the electrolyte is C wt%, 2.5≤C≤16, and 0.02≤A / C≤0.56.

[0024] In one or more embodiments, the content of the third additive in the electrolyte is 0.5wt% to 10wt%.

[0025] In one or more embodiments, the solvent content in the electrolyte is 70.5 wt% to 86.5 wt%.

[0026] In one or more embodiments, the content of the lithium salt in the electrolyte is 10.0 wt% to 14.5 wt%.

[0027] The present invention provides a lithium-ion battery comprising the electrolyte described in any embodiment of the present invention.

[0028] In one or more embodiments, the lithium-ion battery includes a silicon anode sheet, the silicon anode sheet includes a negative electrode material layer, and the negative electrode material layer includes a silicon anode active material.

[0029] In one or more embodiments, the silicon anode active material is selected from one or more of silicon-carbon materials, silicon-oxygen materials, or lithium-silicon alloy materials.

[0030] In one or more embodiments, the specific surface area of ​​the silicon anode active material is Y m 2 / g, 0.98≤Y≤1.88, and 0.2≤(A+B) / Y≤5.7. Detailed Implementation

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0033] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0034] In this document, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0035] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0036] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0037] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0038] The electrolyte provided by this invention comprises a first additive comprising compounds of formula I and formula II:

[0039] Wherein, R0 is a C6-C14 aromatic ring or a 5-14 membered heteroaromatic ring; the degree of intra-ring unsaturation of R0 is β, 1≤β≤7; Wherein, X1 is O or NR1, R1 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R1 is a substituted benzene ring, the substituent is one or more halogen atoms; wherein, X2 is O or NR2, R2 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R2 is a substituted benzene ring, the substituent is one or more halogen atoms; wherein, X3 is O or NR3, R3 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R3 is a substituted benzene ring, the substituent is one or more halogen atoms; where at least one of X1, X2, and X3 is not O; where the degree of intra-ring unsaturation of the rings containing X1, X2, and X3 is α, 1≤α≤3; Wherein, R4 is hydrogen, halogen, cyano, trifluoromethyl, substituted C6-C10 aryl, unsubstituted C6-C10 aryl, substituted phosphate ester, unsubstituted phosphate ester, substituted phosphite ester, or unsubstituted phosphite ester; when R4 is a substituted C6-C10 aryl, a substituted phosphate ester, or a substituted phosphite ester, the substituent is one or more halogen atoms; Among them, R7, R8, R9, R 10Each group is independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon double bonds, and substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon triple bonds; when R7, R8, R9, or R 10 When the substituent is a substituted C1-C6 alkyl group, a substituted C1-C6 alkoxy group, a substituted C2-C6 group containing an unsaturated carbon-carbon double bond, or a substituted C2-C6 group containing an unsaturated carbon-carbon triple bond, the substituent is independently selected from one or more of halogen, methacryloxy, methoxy, and trimethylsilyl; wherein, R7, R8, R9, R 10 Independent bonding or linked into a ring; The degree of unsaturation of the compound of formula II is γ, where γ ≥ 1.

[0040] The compound of Formula I of this invention does not contain methylene (-CH2-) groups, which can prevent hydrogen atoms in the structure from migrating to the positive electrode surface and causing hydrogenation reaction of the positive electrode material, maintain the stability of the positive electrode particles, suppress crosstalk from the positive electrode to the negative electrode, reduce self-discharge caused by voltage drop during storage, and improve the storage stability of the battery; at the same time, it has a high HOMO energy level, which can be oxidized on the positive electrode side to form a CEI film rich in inorganic components such as Li3N, LiF, and Li2CO3 as well as cross-linked organic components.

[0041] The compound of Formula II in this invention is a silane additive containing unsaturated bonds. It can undergo oxidation reactions before other electrolyte components, reducing electrolyte decomposition on the cathode side, altering the CEI structure, inhibiting the dissolution of transition metals from the cathode, and improving the structural stability of the nickel-rich cathode. Simultaneously, it can also form a stable protective barrier on the negative electrode. Specifically, firstly, the central element silicon can react with the hydroxyl groups (—OH) on the surface of the silicon negative electrode to generate a Si-O-Si chemical bond polymer network, enhancing the mechanical strength and flexibility of the SEI film. This allows it to adapt to the significant volume expansion of the silicon negative electrode during charging and discharging, reducing SEI film damage and detachment, thereby protecting the negative electrode and inhibiting electrolyte decomposition. Secondly, unsaturated bonds such as double or triple bonds can undergo electrochemical polymerization during charging and discharging, forming a uniform and dense protective film on the negative electrode surface, adhering to the surface of silicon particles to form a stable and... The SEI film, which exhibits stronger adhesion to silicon, differs fundamentally from interface films formed by traditional additives. It is more stable, denser, and firmly bonded to the electrode, effectively inhibiting the continuous decomposition of the electrolyte. Furthermore, the additive of Formula II of this invention can eliminate HF in the electrolyte and stabilize PF5 through the generated silanes, improving the stability of LiPF6-based electrolytes. Finally, the additive of Formula II of this invention is insensitive to electric fields, can stably adsorb on the electrode surface, and is unaffected by potential changes; it can prevent solvent molecules from entering the inner Helmholtz layer, thus ensuring the stability of PF6. -Anions accumulate at the interface, inducing anion reactions and participating in the formation of the SEI film.

[0042] In this invention, the compounds of formula I and formula II have a synergistic effect. The compound of formula I reduces the hydrogenation reaction of the solvent at the positive electrode, while the compound of formula II forms an in-situ electropolymerization film structure at the negative electrode. At the same time, the Si-O-Si bonds formed inhibit interphase electron transitions and regulate the electron transport behavior at the negative electrode, thereby improving the storage performance under high voltage.

[0043] The compound of formula II of this invention does not use the -CN group because the cyano group is an electron-rich structure that easily forms a six-membered ring with the double bond at the γ position. This is not conducive to the electron-gaining electropolymerization of the double bond at the negative electrode, and it cannot effectively form an organic polymer that adheres to the surface of the negative electrode material. At the same time, it cannot form an organic polymer silicide to ensure better bonding and interaction with the surface of the silicon material. On the contrary, the double bond that does not undergo electropolymerization at the negative electrode may be oxidized at the positive electrode, generating gas, which is not conducive to cycle and storage performance.

[0044] This invention uses compounds of formula I and formula II. First, silane additives containing unsaturated bonds are used to form polymeric silicides at the negative electrode. This ensures better bonding and adhesion between the SEI film and silicon and graphite particles, while the polymer can adapt to large volume changes, preventing the formation of fresh interfaces and continuous side reactions with the electrolyte. Second, the use of compound I eliminates the need for active hydrogen to undergo hydrogenation at the ternary positive electrode and contains N-unsaturated heterocycles, which can be oxidized at the positive electrode to generate organic nitrogen-containing compounds and Li3N. This is beneficial for film formation at the positive electrode to prevent ternary lattice phase transitions, and the formed Li3N structure can reduce RCEI and decrease lithium-ion shuttle resistance.

[0045] In this invention, when X1 is NR1 and X3 is NR3, R1 and R3 are each independently a substituted or unsubstituted benzene ring.

[0046] In this invention, X1 is O, X2 is O, and X3 is NR3. In this invention, X1 is NR1, X2 is O, and X3 is NR3, and R1 and R3 can each be independently substituted or unsubstituted benzene rings.

[0047] In this invention, X1 is NR1, X2 is 0, and X3 is NR3.

[0048] In this invention, R7, R8, R9, R 10 It contains at least one substituted or unsubstituted C2-C6 group with an unsaturated carbon-carbon double bond.

[0049] In this invention, R0 is a benzene ring, naphthalene ring, pyrrole ring, furan ring, or indole.

[0050] In this invention, the compound of formula I is selected from one or more of the following structural formulas: .

[0051] Preferably, the compound of formula I is selected from one or more of the following structural formulas: .

[0052] In this invention, the compound of formula II is selected from one or more of the following structural formulas: .

[0053] Preferably, the compound of formula II is selected from one or more of the following structural formulas: .

[0054] In the electrolyte of this invention, the content of compound I can be A wt%, 0.25≤A≤1.5.

[0055] In the electrolyte of this invention, the content of compound II can be B wt%, 0.05≤B≤5. In this invention, when the content of compound II is within the above range, the improvement effect gradually becomes more obvious and reaches the optimal value as the content of compound II increases. However, when it exceeds the optimal value, the excess free compound II will react with lithium salt on the surface of the ternary cathode in the electrolyte to generate silanol byproducts containing active hydrogen, which is detrimental to storage performance.

[0056] In this invention, the electrolyte may further contain a second additive, which may be fluoroethylene carbonate and / or difluoroethylene carbonate.

[0057] In this invention, the electrolyte may further contain a third additive, which may be selected from one or more of the following: ethylene carbonate, vinylene carbonate, 1,3-propane sulpholactone, mannitol sulfate, 1,3-dioxane, 1,4-dioxane, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, vinyl sulfate, 1,3-propane sulpholactone, propenyl-1,3-sulfonyl lactone, 2,4-butane sulpholactone, methanedisulfonate, 1,3-propanedisulfonic anhydride, ethylene sulfite, and propargyl phosphate.

[0058] In this invention, the electrolyte may further contain a solvent, which may be one or more selected from cyclic carbonates, linear carbonates, cyclic carboxylic acid esters, linear carboxylic acid esters, sulfones, phosphate esters, and phosphites; preferably, the solvent may be one or more selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, dimethyl sulfoxide, sulfolane, diphenyl sulfone, triethyl phosphate, and methyl ethyl phosphite.

[0059] In this invention, the electrolyte further comprises a lithium salt, which may be one or more selected from lithium hexafluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, and lithium tri(trifluoromethanesulfonyl)methyl. In the electrolyte of this invention, the content of the second additive may be Cwt%, 2.5≤C≤16, and 0.02≤A / C≤0.56. In the electrolyte of this invention, the content of the third additive may be 0.5wt%~10wt%. In the electrolyte of this invention, the content of the solvent may be 70.5wt%~86.5wt%. In the electrolyte of this invention, the content of the lithium salt may be 10.0wt%~14.5wt%.

[0060] This invention provides a lithium-ion battery comprising the electrolyte described in any embodiment of the invention. The lithium-ion battery of this invention comprises a silicon anode sheet, which may include a negative electrode material layer, and the negative electrode material layer may include a silicon anode active material. In this invention, the silicon anode active material may be one or more selected from silicon-carbon materials, silicon-oxygen materials, or lithium-silicon alloy materials.

[0061] In this invention, the specific surface area of ​​the silicon anode active material can be Y m 2 / g, 0.98≤Y≤1.88, and 0.2≤(A+B) / Y≤5.7. In this invention, (A+B) / Y is within the above range. With the increase of the ratio, the combined use of compound I and compound II can achieve the optimal improvement effect at both the positive and negative electrodes. It can suppress the redox reaction of active hydrogen in the solvent on the positive electrode side with a high oxidation state, which leads to the transformation of the layered structure and structural collapse. At the same time, compound II participates in the formation of SEI film, suppresses silicon volume expansion, and reduces side reactions between the fresh interface and the electrolyte. When the optimal value is exceeded, with the increase of the ratio, the dosage is too high, which is over-designed and is not conducive to the improvement of storage performance.

[0062] In this invention, the content of silicon anode active material can be X%, 3≤X≤15. The content of silicon anode active material is the content of silicon anode active material in the anode active material, for example, silicon anode active material / (silicon anode active material + graphite material).

[0063] Because the cyano group is an electron-rich structure, it easily forms a six-membered ring with the double bond at the γ position, which is not conducive to the electron-gaining electropolymerization of the double bond at the negative electrode. It cannot effectively form organic polymers that adhere to the surface of the negative electrode material, nor can it form organic polymeric silicides to ensure better bonding and interaction with the silicon material surface. On the contrary, double bonds that do not undergo electropolymerization at the negative electrode may be oxidized at the positive electrode, producing gas, which is detrimental to cycle and storage performance.

[0064] This invention uses silane additives containing unsaturated bonds, which can form polymeric silicides at the negative electrode. This ensures better bonding and adhesion between the SEI film and silicon and graphite particles, while the polymer can adapt to large volume changes, preventing the formation of fresh interfaces and continuous side reactions with the electrolyte. The additives with a Si-N directly linked structure prevent active hydrogen from undergoing hydrogenation reactions at the ternary positive electrode, and contain N-unsaturated heterocycles that can be oxidized at the positive electrode to generate organic nitrogen-containing compounds and Li3N. This is beneficial for film formation at the positive electrode and prevents ternary lattice phase transitions. At the same time, the formed Li3N structure can reduce RCEI and decrease lithium-ion shuttle resistance.

[0065] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention can solve the problems of hydrogen atoms generated by the breaking of CH bonds in the solvent migrating to the surface of the high oxidation state cathode and undergoing hydrogenation reaction on the cathode side, leading to lattice phase transformation and dissolution of transition metals. At the same time, it solves the problem of poor high-temperature performance caused by the high work function of silicon materials, thereby achieving the purpose of improving high-temperature storage.

[0066] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. Unless otherwise stated, the methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art.

[0067] Preparation Example 1

[0068] In an argon-atmospheric glove box with a water content of <10 ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed in a mass ratio of 3:5:2 and mixed thoroughly to obtain an organic solvent. Then, 12.5 wt% LiPF6 was added to the organic solvent and mixed thoroughly to obtain a basic electrolyte. A first additive consisting of compound I of structural formula 1 and compound II of structural formula 21 was added to the basic electrolyte to obtain the final electrolyte. In the electrolyte, the content of compound I was 0.25 wt%, the content of compound II was 0.60 wt%, the content of LiPF6 was 13.75 wt%, and the content of organic solvent was 85.40 wt%.

[0069] Preparation Example 2

[0070] The other conditions in this preparation example are the same as those in Preparation Example 1, except that in this preparation example, the compound of Formula I is replaced by the compound of Formula 6 instead of Formula 1, the content of the compound of Formula I in the electrolyte is 0.50 wt%, and the content of the organic solvent is 85.15 wt%.

[0071] Preparation Example 3

[0072] The other conditions in this preparation example are the same as those in Preparation Example 1, except that in this preparation example, the compound of Formula I is replaced by the compound of Formula 11, the content of the compound of Formula I in the electrolyte is 0.85 wt%, and the content of the organic solvent is 84.8 wt%.

[0073] Preparation Example 4

[0074] The preparation examples are the same as those in Preparation Example 1, except that the compound of Formula I is replaced by Formula 14, the content of the compound of Formula I in the electrolyte is 1.5 wt%, and the content of the organic solvent is 84.15 wt%.

[0075] Preparation Example 5

[0076] The preparation examples are otherwise the same as those in Preparation Example 3, except that in this preparation example, the compound of Formula II is replaced by Formula 15 instead of Formula 21, the content of Compound II in the electrolyte is 0.05 wt%, and the content of organic solvent is 85.35 wt%.

[0077] Preparation Example 6

[0078] The other conditions in this preparation example are the same as those in Preparation Example 3, except that in this preparation example, compound II is replaced by structural formula 18 instead of structural formula 21, the content of compound II in the electrolyte is 2.50 wt%, and the content of organic solvent is 82.9 wt%.

[0079] Preparation Example 7

[0080] The other conditions in this preparation example are the same as those in Preparation Example 3, except that in this preparation example, compound II is replaced by structural formula 24 instead of structural formula 21, the content of compound II in the electrolyte is 5.00 wt%, and the content of organic solvent is 80.4 wt%.

[0081] Preparation Example 8

[0082] The preparation examples are the same as those in Preparation Example 1, except that in this preparation example, compound I is replaced by structural formula 10 and compound II is replaced by structural formula 19. In the electrolyte, the content of compound I is 0.50 wt%, the content of compound II is 0.60 wt%, and the content of organic solvent is 85.15 wt%.

[0083] Preparation Example 9

[0084] The other conditions in this preparation example are the same as those in Preparation Example 8, except that the content of compound I is 1.30 wt%, the content of compound II is 2.00 wt%, and the content of organic solvent is 82.95 wt%.

[0085] Comparative Preparation Example 1

[0086] The preparation conditions in this comparative example are the same as those in Preparation Example 1, except that the compound of Formula I is replaced by Formula 11, the content of Compound I in the electrolyte is 0.10 wt%, and the content of organic solvent is 85.55 wt%.

[0087] Comparative Example 2

[0088] The preparation conditions in this comparative example are the same as those in Preparation Example 1, except that the compound of Formula I is replaced by Formula 11, the content of Compound I in the electrolyte is 2.00 wt%, and the content of organic solvent is 83.65 wt%.

[0089] Comparative Example 3

[0090] The preparation conditions in this comparative example are the same as those in Preparation Example 1. The only difference is that in this comparative preparation example, compound I is replaced by structural formula 10 and compound II is replaced by structural formula 15. In the electrolyte, the content of compound I is 0.85 wt%, the content of compound II is 0.02 wt%, and the content of organic solvent is 85.38 wt%.

[0091] Comparative Example 4

[0092] The preparation conditions in this comparative example are the same as those in Preparation Example 1. The only difference is that in this comparative preparation example, compound I is replaced by structural formula 10 and compound II is replaced by structural formula 15. In the electrolyte, the content of compound I is 0.25 wt%, the content of compound II is 7.00 wt%, and the content of organic solvent is 79 wt%.

[0093] Comparative Example 5

[0094] The preparation conditions in this comparative example are the same as those in preparation example 3, except that the content of compound I is 0.28 wt%, the content of compound II is 0.05 wt%, and the content of organic solvent is 85.92 wt%.

[0095] Comparative Example 6

[0096] The preparation conditions in this comparative example are the same as those in preparation example 3, except that the content of compound I is 1.30 wt%, the content of compound II is 4.50 wt%, and the content of organic solvent is 80.45 wt%.

[0097] Preparation Example 10

[0098] In an argon-atmospheric glove box with a water content of <10 ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed in a mass ratio of 3:5:2 and mixed thoroughly to obtain an organic solvent. Then, 12.5 wt% LiPF6 was added to the organic solvent and mixed thoroughly to obtain a basic electrolyte. A first additive consisting of compound I of structural formula 11 and compound II of structural formula 21 was added to the basic electrolyte, and a second additive FEC was added to obtain the electrolyte. In the electrolyte, the content of compound I was 0.25 wt%, the content of compound II was 0.60 wt%, the content of the second additive FEC was 2.5 wt%, the mass ratio of compound I to the second additive was 0.1, the content of LiPF6 was 12.5 wt%, and the content of the organic solvent was 84.15 wt%.

[0099] Preparation Example 11

[0100] The other conditions in this preparation example are the same as those in Preparation Example 10, except that the second additive in this preparation example is FEC and DFEC. In the electrolyte, the content of FEC is 3 wt%, the content of DFEC is 2 wt%, the content of organic solvent is 81.65 wt%, and the mass ratio of compound I to the second additive is 0.05.

[0101] Preparation Example 12

[0102] The other conditions in this preparation example are the same as those in Preparation Example 10, except that the second additive in this preparation example is DFEC, the content of DFEC in the electrolyte is 10 wt%, the content of organic solvent is 76.65 wt%, and the mass ratio of compound I to the second additive is 0.025.

[0103] Preparation Example 13

[0104] The other conditions in this preparation example are the same as those in Preparation Example 10, except that the second additive in this preparation example is FEC and DFEC. In the electrolyte, the content of compound I is 1.2 wt%, the content of FEC is 1.5 wt%, the content of DFEC is 1 wt%, the content of organic solvent is 83.2 wt%, and the mass ratio of compound I to the second additive is 0.48.

[0105] Preparation Example 14

[0106] The other conditions in this preparation example are the same as those in Preparation Example 10, except that the second additive in this preparation example is FEC and DFEC. In the electrolyte, the content of compound I is 1.2 wt%, the content of FEC is 8 wt%, the content of DFEC is 7 wt%, the content of organic solvent is 70.7 wt%, and the mass ratio of compound I to the second additive is 0.08.

[0107] Test Example 1

[0108] Positive electrode sheet: using LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added and stirred until homogeneous, resulting in a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 120°C to obtain a positive electrode precursor with a single-sided coating of positive electrode material. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode precursor with a double-sided coating of positive electrode material. After cold pressing and slitting, the positive electrode sheet (NCM611) was obtained, with a compaction density of 3.55 g / cm³. 3 The areal density of both sides is 340 mg / cm³.2 .

[0109] Negative electrode sheet: Silicon-carbon active material, graphite active material, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 5:91:2:2. Deionized water is added, and the mixture is stirred evenly to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry is uniformly coated on one surface of a copper foil with a thickness of 8μm for the negative electrode current collector and dried at 120℃ to obtain a negative electrode sheet precursor with a single-sided coating of negative electrode material. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet precursor with a double-sided coating of negative electrode material. After cold pressing and slitting, a negative electrode sheet (silicon / graphite negative electrode sheet) is obtained, wherein the compaction density of the negative electrode sheet is 1.63 g / cm³. 3 The areal density of both sides is 190 mg / cm³. 2 .

[0110] Lithium-ion battery preparation: The positive electrode, separator (10μm polypropylene porous film), and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound into an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, baked at 80°C to remove moisture, and then injected with the electrolytes prepared in Preparation Examples 1-14 and Comparative Examples 1-6. After vacuum sealing, standing, formation, and shaping processes, the lithium-ion batteries corresponding to Examples 1-14 and Comparative Examples 1-6 are obtained. The electrolytes prepared in Preparation Examples 1-14 and Comparative Examples 1-6 correspond one-to-one with the lithium-ion batteries corresponding to Examples 1-14 and Comparative Examples 1-6. The specific surface area of ​​the silicon negative electrode active material of the corresponding negative electrode is shown in Table 1-2.

[0111] Performance testing: The lithium-ion battery was charged at 25℃ with 1C to 4.4V, CV to 0.05C, rested for 30 minutes, and then discharged at 1C constant current to 2.8V. This cycle was repeated for 3 weeks, and the discharge capacity of the third cycle was recorded as the first discharge capacity. The battery was charged to 100% SOC and stored at 60℃. The discharge capacity on the 30th day of storage was recorded. The 60℃ storage capacity retention rate (%) = 30th day discharge capacity / first discharge capacity × 100%. The 60℃ storage capacity retention rate is shown in Tables 1 and 2.

[0112] in: The content of compound I in the electrolyte is A wt% The content of compound II in the electrolyte is B wt% The content of the second additive in the electrolyte is C wt% The ratio of the content of compound I and the second additive is A / C; Specific surface area Y m of silicon anode active material 2 / g, the ratio of the sum of the contents of additives of formula I and formula II to the specific surface area of ​​the silicon anode active material is (A+B) / Y.

[0113] Table 1

[0114] As shown in Table 1, Example 3 and Comparative Examples 1-2, when the content of Compound I is within the range of this invention, the storage capacity retention gradually increases with the increase of Compound I content. However, when it exceeds a certain value, the improvement effect is no longer advantageous with the increase of Compound I content, and the storage capacity retention gradually decreases instead. The Compound I of this invention does not contain a methyl (-CH2-) group and has a higher HOMO energy level. It can be oxidized on the positive electrode side to form a CEI film rich in Li3N, Li2CO3 and other components, preventing hydrogen atoms in the structure from migrating to the positive electrode surface and causing hydrogenation reaction of the positive electrode material. This reduces self-discharge caused by voltage drop during storage and improves the storage stability of the battery.

[0115] Table 2

[0116] As shown in Table 2, Compound I possesses an electron-rich structure. When electron-deficient Lewis acids such as PF5 and POF3 are present in the electrolyte, the Gibbs free energy for the formation of a new complex by Compound I with electron-deficient structures is negative, indicating that the reaction proceeds in the forward direction. Compound I can promptly capture electron-deficient structures in the electrolyte, thereby achieving the acid removal effect. When a second additive is present, the first additive can inhibit the acid-producing reaction of the second additive. This ensures that the second additive forms a LiF structure on the surface of silicon particles, promoting the formation of amorphous silicon inside the particles, while simultaneously inhibiting the corrosion of the cathode material and dissolution of the SEI film by HF generated by the second additive catalyzed by PF5 at high temperatures.

[0117] Furthermore, as shown in Table 2, when FEC and DFEC are used in combination, DFEC can reduce the HF generation effect of FEC. That is, the combination of the two fluorinated additives can promote the formation of amorphous silicon inside the silicon material, regulate the internal crystal structure of the silicon material, and inhibit the expansion of silicon. The maximum improvement effect can be achieved by combining an appropriate amount of Formula I compound.

Claims

1. An electrolyte, characterized in that, The electrolyte contains a first additive, which comprises compounds of formula I and formula II: Wherein, X1 is O or NR1, and R1 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R1 is a substituted benzene ring, the substituent is one or more halogen atoms; Where X2 is O or NR2, and R2 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R2 is a substituted benzene ring, the substituent is one or more halogen atoms; Wherein, X3 is O or NR3, and R3 is H, a substituted benzene ring, or an unsubstituted benzene ring; when R3 is a substituted benzene ring, the substituent is one or more halogen atoms; Among them, at least one of X1, X2 and X3 is not 0; The unsaturation degree within the rings containing X1, X2, and X3 is α, where 1 ≤ α ≤ 3; Wherein, R0 is a C6-C14 aromatic ring or a 5-14 membered heteroaromatic ring; the degree of intra-ring unsaturation of R0 is β, 1≤β≤7; Wherein, R4 is hydrogen, halogen, cyano, trifluoromethyl, substituted C6-C10 aryl, unsubstituted C6-C10 aryl, substituted phosphate ester, unsubstituted phosphate ester, substituted phosphite ester, or unsubstituted phosphite ester; when R4 is a substituted C6-C10 aryl, substituted phosphate ester, or substituted phosphite ester, the substituent is one or more halogen atoms; Among them, R7, R8, R9, R 10 Each group is independently selected from substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups, substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon double bonds, and substituted or unsubstituted C2-C6 groups containing unsaturated carbon-carbon triple bonds; when R7, R8, R9, or R 10 When the substituent is a substituted C1-C6 alkyl group, a substituted C1-C6 alkoxy group, a substituted C2-C6 group containing an unsaturated carbon-carbon double bond, or a substituted C2-C6 group containing an unsaturated carbon-carbon triple bond, the substituent is independently selected from one or more of halogen, methacryloxy, methoxy, and trimethylsilyl. Among them, R7, R8, R9, R 10 Independent bonding or linked into a ring; The degree of unsaturation of the compound of formula II is γ, where γ ≥ 1.

2. The electrolyte as described in claim 1, characterized in that, X1 is NR1, X3 is NR3, and R1 and R3 are each independently substituted or unsubstituted benzene rings.

3. The electrolyte as described in claim 1, characterized in that, The electrolyte has one or more of the following characteristics: Compound I does not contain -CH2- bonds; X1 is 0, X2 is 0, and X3 is NR3, or X1 is NR1, X2 is 0, and X3 is NR3; R7, R8, R9, R 10 It contains at least one substituted or unsubstituted C2-C6 group with an unsaturated carbon-carbon double bond; R0 can be a benzene ring, naphthalene ring, pyrrole ring, furan ring, or indole.

4. The electrolyte as described in claim 1, characterized in that, X1 is NR1, X2 is O, X3 is NR3, and R1 and R3 are each independently substituted or unsubstituted benzene rings.

5. The electrolyte as described in claim 1, characterized in that, Compounds of Formula I are selected from one or more of the following structural formulas: 。 6. The electrolyte as described in claim 1, characterized in that, Compounds of formula II are selected from one or more of the following structural formulas: 。 7. The electrolyte as described in claim 1, characterized in that, The electrolyte has one or more of the following characteristics: In the electrolyte, the content of the compound of formula I is A wt%, 0.25≤A≤1.5; In the electrolyte, the content of compound of formula II is B wt%, 0.05≤B≤5; The electrolyte further contains a second additive, which is fluoroethylene carbonate and / or difluoroethylene carbonate. The electrolyte further comprises a third additive selected from one or more of the following: ethylene carbonate, vinylene carbonate, 1,3-propane sulpholactone, mannitol sulfate, 1,3-dioxane, 1,4-dioxane, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, vinyl sulfate, 1,3-propane sulpholactone, propenyl-1,3-sulfonyl lactone, 2,4-butane sulpholactone, methanedisulfonate, 1,3-propanedisulfonic anhydride, ethylene sulfite, and triargyl phosphate. The electrolyte further comprises a solvent selected from one or more of cyclic carbonates, linear carbonates, cyclic carboxylic acid esters, linear carboxylic acid esters, sulfones, phosphate esters, and phosphites; preferably, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, dimethyl sulfoxide, sulfolane, diphenyl sulfone, triethyl phosphate, and methyl ethyl phosphite; The electrolyte further comprises a lithium salt selected from one or more of lithium hexafluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium di(trifluoromethylsulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, and lithium di(pentafluoroethylsulfonyl)imide or lithium tri(trifluoromethylsulfonyl)methyl.

8. The electrolyte as described in claim 7, characterized in that, In the electrolyte, the content of the second additive is C wt%, 2.5≤C≤16, and 0.02≤A / C≤0.56; The content of the third additive in the electrolyte is 0.5wt%~10wt%; The solvent in the electrolyte contains 70.5 wt% to 86.5 wt%. The content of lithium salt in the electrolyte is 10.0wt%~14.5wt%.

9. A lithium-ion battery comprising the electrolyte according to any one of claims 1-8.

10. The lithium-ion battery as described in claim 9, characterized in that, The lithium-ion battery includes a silicon anode sheet, the silicon anode sheet includes a negative electrode material layer, and the negative electrode material layer includes a silicon anode active material. Preferably, the silicon anode active material is selected from one or more of silicon-carbon materials, silicon-oxygen materials, or lithium-silicon alloy materials; Preferably, the specific surface area of ​​the silicon anode active material is Y m 2 / g, 0.98≤Y≤1.88, and 0.2≤(A+B) / Y≤5.7.

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