Electrolyte compound additive for spontaneously constructing high ionic conductance SEI layer, electrolyte and secondary battery

Abstract

The invention provides a compound additive for an electrolyte. A <-> is selected from one of boron-containing inorganic anions or nitrogen-containing organic anions; r1-R4 and X are respectively and independently selected from one of a hydrogen atom, a halogen atom, a C1-C7 alkyl chain or a C1-C7 alkyl chain with a substituent group, a C1-C7 alkoxy chain or a C1-C7 alkoxy chain with a substituent group, a C2-C7 olefin chain or a C2-C7 olefin chain with a substituent group; y is selected from a sulfur atom or an oxygen atom, and A-in the formula 1 and X in the formula 2 respectively contain at least one halogen atom. The electrolyte additive shows high ionic conductivity and good interface mechanical performance, and interface charge transfer impedance is remarkably reduced; meanwhile, the dendritic crystal growth puncture problem at the interface is effectively inhibited, and the cycle life and the safety performance of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary battery electrolyte, in particular to an electrolyte complex additive for spontaneously constructing a high-ionic-conductivity SEI layer, an electrolyte and a secondary battery. BACKGROUND

[0002] The rapid development of mobile devices, electric vehicles and other devices has driven the rapid development and technological innovation of global power energy and energy storage markets. In particular, the research and development of high-energy-density secondary batteries aims to improve the energy density of the battery while maintaining long cycle stability. Existing secondary batteries still face many problems that need to be solved. For example, lithium metal secondary batteries, lithium metal anodes often undergo uneven deposition and uncontrollable dendrite growth during repeated charging and discharging, which can further cause serious volume expansion, dendrite puncture short circuit and even fire. In addition, lithium metal will produce metal fatigue after multiple cycles, which is an important reason for the failure of lithium metal anodes and the reduction of battery cycle life. Therefore, improving the stability and cycle life of metal anodes from the metal anode side is an important means to improve the electrochemical performance and cycle life of secondary batteries.

[0003] One of the most effective and easy-to-operate methods to improve the stability of metal anodes and thus improve the electrochemical performance of the battery is through electrolyte regulation. Additive regulation is the most economical and effective means of electrolyte regulation, and a small amount of additive can bring about significant performance improvement. Additives can affect lithium ion diffusion and lithium deposition growth through coordination with other components in the electrolyte, such as Chinese patent (CN117317374B) which provides an electrolyte additive centered on a benzene ring, which is beneficial to combine with nucleophilic reagents, thereby reducing the viscosity of the electrolyte and improving the wettability of the electrolyte, and itself decomposes to participate in SEI film formation. Electrolyte additives can also construct SEI films rich in inorganic matter by preferentially decomposing, thereby isolating the anode from further contact with the electrolyte, suppressing side reactions and improving anode stability. For example, Chinese patent (CN118054084B) discloses an electrolyte additive containing a nitrogen-based initiator and a halogen-substituted vinyl ether, which can generate a double-layer SEI film to alleviate the reconstruction of the electrode / electrolyte interface to stabilize the lithium metal anode.

[0004] However, the electrolyte additives provided in the existing disclosed patents mainly construct a single SEI layer to isolate the electrode from further contact with the electrolyte and reduce undesirable side reactions, but the existing solutions ignore the kinetic effects at the SEI interface. They focus on regulating the uniform deposition of lithium ions to suppress dendrites. However, the rapid transport of lithium ions at the SEI interface is ignored, which has an important influence on the dynamic performance and electrochemical performance of the battery.

[0005] In view of this, by regulating the electrolyte additive to construct an SEI layer with high lithium ion conductivity, the ion kinetic performance at the interface is improved, thereby regulating the lithium ion deposition and growth behavior, so as to improve the stability of the negative electrode and the electrochemical performance of the battery. It is an innovative, simple and efficient, important means with industrialization prospect and economic benefit. SUMMARY

[0006] The present application is directed to the deficiencies of the prior art, and the present application proposes an electrolyte complex additive for spontaneously constructing a high ion conductive SEI layer, an electrolyte and a secondary battery. The electrolyte additive in the present application can spontaneously decompose at the negative electrode and generate a composite inorganic SEI layer rich in elements such as fluorine (F), phosphorus (P), nitrogen (N), sulfur (S), boron (B) (for example, containing LiF, Li3N, Li3PO4, Li2S, etc.), generating an inorganic layer with high ion conductivity gradient. It has a unique ion transport channel and exhibits high ion conductivity, significantly reducing the interface charge transfer impedance; at the same time, it exhibits good interface mechanical properties, and the high rigidity of the inorganic component effectively inhibits the problem of dendrite growth penetration at the interface, improving the cycle life and safety performance of the battery. The electrolyte additive A and the electrolyte additive B are used in combination, and the type and amount control method is various. A small amount of addition can meet the battery performance requirements in various use environments, has a wide application prospect, and exhibits good economic benefits.

[0007] The present application is realized by the following technical solutions: In a first aspect, the present application provides an electrolyte complex additive, comprising electrolyte additive A and electrolyte additive B, each having a general structure as shown in formula 1 and formula 2;

[0008] A in the formula 1 - is selected from one of a boron (B)-containing inorganic anion or a nitrogen (N)-containing organic anion; R1 in the formula 1, R2~R4 in the formula 2, and X are each independently selected from one of a hydrogen atom, a halogen atom, a C1~C7 alkyl chain or a C1~C7 alkyl chain with a substituent, a C1~C7 alkoxy chain or a C1~C7 alkoxy chain with a substituent, a C2~C7 alkene chain or a C2~C7 alkene chain with a substituent; the substituent group is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a mercapto group, a silane group; Y in the formula 2 is selected from a sulfur (S) atom or an oxygen (O) atom; and A -at least one halogen atom, at least one halogen atom in X of formula 2.

[0009] The present application aims at the problems of poor kinetic performance and poor lithium ion conduction performance at the interface of the SEI layer in the prior art, and proposes an electrolyte complex additive for spontaneously constructing a high ionic conduction SEI layer, an electrolyte and a secondary battery. The cationic group in the electrolyte additive A has a structure of triphenyl phosphorus, three benzene rings are directly connected to the phosphorus atom at the center, the three-dimensional structure effectively regulates the flux of small molecule solvents and ions, and is conducive to the uniform growth of SEI and the uniform deposition of lithium. And the electronic structure of the triphenyl phosphorus group is reconstructed, which is conducive to the preferential decomposition to generate an SEI film. The electrolyte additive B is partially rigid, the -N-C(=Y)-N- chain in the substituent group increases the flexibility of the molecule, allows intramolecular rotation, reduces the rigidity of the electrolyte additive B, and the flexible chain part arranges in three-dimensional space with the electrolyte additive A, occupies the gap position of the electrolyte additive A, and can further regulate the uniform charge flux. At the same time, the substituent part in the electrolyte additive A and the electrolyte additive B changes the electron cloud distribution of the electrolyte additive due to the high electronegativity of the halogen atom, regulates the reaction activity and the spontaneous decomposition film forming ability of the electrolyte additive A and the electrolyte additive B when they are compounded, which helps to reduce the viscosity of the electrolyte while improving the ion transference rate. In addition, when the two electrolyte additives are applied at the same time, the benzene ring of the triphenyl phosphorus may have π-π stacking with the benzene ring in the electrolyte additive B, which enhances the stability of the complex system. At the same time, the R2~R4 groups in the electrolyte additive B and the lone pair electrons of the phosphorus atom in the electrolyte additive A may form a weak hydrogen bond, creating a dynamic network, further optimizing the ion transport path. This network maintains rigidity and allows ion hopping, improving conductivity without sacrificing stability. At the same time, the electrolyte additive A and the electrolyte additive B both have the ability to spontaneously decompose at the negative electrode. The electrolyte additive A with the structure of formula 1 adopts an inorganic anion group containing boron or an organic anion group containing nitrogen, so that it has a lower reduction potential and can be preferentially reduced and decomposed on the surface of the negative electrode. At the same time, the electrolyte additive B with the structure of formula 2 is a compound rich in sulfur or oxygen elements, which has excellent film forming stability and interface regulation ability. The nitrogen (N) atom in its molecular structure can spontaneously form an inorganic phase containing Li3N at the negative electrode, greatly improving the ionic conductivity of the negative electrode. The sulfur (S) or oxygen (O) atom in the defined Y can form a strong coordination with the active sites on the surface of the negative electrode, inducing the generation of a dense SEI layer rich in inorganic components such as Li2S / Li2O, significantly improving the interface ion transport efficiency and mechanical stability. In addition, the reduction product of the electrolyte additive B has a low interface impedance, which can effectively inhibit solvent co-intercalation and lithium dendrite growth, and cooperates with the electrolyte additive A to construct a gradient SEI structure. At the same time, the present application also limits A- At least one halogen atom, at least one halogen atom in X of electrolyte additive B, on this basis, further strengthen the above-mentioned synergistic effect, halogen atoms, such as fluorine atoms introduced in the molecule of electrolyte additive A can release halogen anions or halogen-containing active species in situ. These species can react with the by-products produced by the decomposition of lithium salt in the electrolyte, effectively removing these harmful substances, thereby improving the chemical stability of the entire electrolyte system from the source. More importantly, the released halogen ions can participate in the construction of the SEI layer to generate lithium fluoride and other thermodynamically stable, high interfacial energy inorganic nanocrystals. At the same time, the halogen atoms also introduced in the molecule of electrolyte additive B will contribute halogen components during the spontaneous reduction into film. This makes the two additives, when decomposed, can "inject" rich LiF or other lithium halide crystal nuclei into the initially formed SEI layer from different spatial and temporal scales. The synergistic decomposition mechanism of the two additives realizes the self-assembly of the SEI layer in the cycle, is suitable for various negative electrode systems, has high ionic conductivity, significantly reduces the interface charge transfer impedance; at the same time, it shows good interface mechanical properties, and the high-rigidity inorganic components effectively inhibit the problem of dendrite growth puncture at the interface, improve the cycle life and safety performance of the battery; meet the battery performance requirements in various use environments, have wide application prospect and good economic benefit.

[0010] As a further solution, A - When the A - Satisfies one of formula 3 or formula 4;

[0011] Y1~Y4 are each independently selected from one of halogen atoms, C1~C7 alkyl chains or C1~C7 alkyl chains with substituents, C1~C7 alkoxy chains or C1~C7 alkoxy chains with substituents, C2~C7 alkene chains or C2~C7 alkene chains with substituents; the substituents are selected from one or more of halogen atoms, hydroxyl groups, amino groups, carboxyl groups, ester groups, amide groups, acyloxy groups, nitro groups, cyano groups, ether oxygen groups, phosphate groups, phosphite groups, sulfonate groups, sulfonyl groups, sulfoxide groups, sulfhydryl groups, silane groups.

[0012] m is 1 or 2; when m is 2, the structure of formula 4 is symmetrically structured around boron (B); when m is 1, Y5~Y6 are each independently selected from one of a halogen atom, a C1~C7 alkyl chain or a C1~C7 alkyl chain with a substituent, a C1~C7 alkoxy chain or a C1~C7 alkoxy chain with a substituent, a C2~C7 alkene chain or a C2~C7 alkene chain with a substituent; the substituent is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a sulfhydryl group, a silane group.

[0013] As a further preferred aspect, A in the electrolyte additive A - is selected from a boron (B)-containing inorganic anion, the A - satisfies one of formula 3 or formula 4; Y1~Y4 in formula 3 are each independently selected from one of a halogen atom, a C1~C2 alkyl chain substituted with a halogen atom; m in formula 4 is 1 and Y5 and Y6 are each independently selected from one of a halogen atom, a C1~C2 alkyl chain substituted with a halogen atom.

[0014] As a further preferred aspect, A in the electrolyte additive A - is selected from a boron (B)-containing inorganic anion, the A - satisfies one of formula 3 or formula 4; Y1~Y4 in formula 3 are each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted with a fluorine atom; m in formula 4 is 1 and Y5 and Y6 are each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted with a fluorine atom.

[0015] As an exemplary aspect, A in the electrolyte additive A - is exemplarily selected from one of formula 5~formula 9:

[0016] As a further aspect, A in the electrolyte additive A - is selected from one of a nitrogen (N)-containing organic anion, the A - satisfies one of formula 10;

[0017] wherein Z1to Z2are each independently selected from one of a halogen atom, a C1to C7alkyl chain or a C1to C7alkyl chain substituted with a substituent, a C1to C7alkoxy chain or a C1to C7alkoxy chain substituted with a substituent, a C2to C7alkene chain or a C2to C7alkene chain substituted with a substituent; the substituent is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a sulfhydryl group, a silane group, and at least one of Z1and Z2contains a halogen atom.

[0018] As a further preferred aspect, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - As a further preferred aspect, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - satisfies one of Formula 10; and Z1to Z2are each independently selected from one of a halogen atom, a C1to C2alkyl chain substituted with a halogen atom.

[0019] As an exemplary aspect, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - As an exemplary aspect, A in the electrolyte additive A is selected from one of Formulae 11 to 13:

[0020] As a further preferred aspect, R1in the electrolyte additive A is selected from one of a halogen atom, a C1to C2alkyl chain substituted with a halogen atom.

[0021] As a further preferred aspect, R1in the electrolyte additive A is selected from one of a fluorine atom, a C1to C2alkyl chain substituted with a fluorine atom.

[0022] As a further preferred exemplary aspect, the cationic portion of Formula 1 in the electrolyte additive A is selected from one of Formulae 14 to 22:

[0023] As a further preferred aspect, R1in the electrolyte additive A is selected from one of a halogen atom, a C1to C2alkyl chain substituted with a halogen atom; and A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - As a further preferred aspect, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - As a further preferred aspect, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - As a further preferred aspect, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. -satisfies one of Formula 3 or Formula 4, Y1-Y4 in Formula 3 are each independently selected from one of a halogen atom, a C1-C2 alkyl chain substituted with a halogen atom group; m in Formula 4 is 1 and Y5 and Y6 are each independently selected from one of a halogen atom, a C1-C2 alkyl chain substituted with a halogen atom.

[0024] The present application can further limit R1 in electrolyte additive A, the substituent in anion group, by introducing specific halogen groups as strong electron-withdrawing groups, to achieve precise control of molecular energy level, reduction potential and decomposition path, thereby optimizing its chemical behavior at the electrode interface and the composition and structure of the final SEI film. The present application further limits R1 and the substituent in the anion of the electrolyte additive (such as Y1-Y6, Z1-Z2) to be selected from halogen atoms or short-chain halogenated alkyl groups. The above groups can significantly lower the lowest unoccupied molecular orbital energy level of additive A molecules. This makes the molecule more likely to gain electrons under the action of an electric field, thereby having a more negative reduction potential, thereby more conducive to its preferential reduction decomposition on the negative electrode surface over conventional solvent molecules such as carbonates. On the one hand, it avoids the continuous side reactions of solvent molecules, reducing the generation of by-products in the lithium salt decomposition process. On the other hand, with the substitution of the above substituent, the mechanical properties and ionic conductivity of the SEI film formed can be better balanced. For example, when more halogen-containing substituents are used, taking fluorine atoms as an example, fluorine is released during the reduction process and participates in the formation of LiF. LiF is a key component for building SEI skeletons with high mechanical strength and high stability, greatly enhancing the density, chemical stability, high ionic conductivity and mechanical strength of the SEI layer, and inhibiting the continuous decomposition of the electrolyte and the germination and growth of lithium dendrites.

[0025] As a further preferred aspect, R1 in the electrolyte additive A is selected from one of a fluorine atom or a C1-C2 alkyl chain substituted with a fluorine atom; A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - When A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion, A in the electrolyte additive A is selected from one of a boron (B)-containing inorganic anion. - satisfies one of Formula 3 or Formula 4, Y1-Y4 in Formula 3 are each independently selected from one of a fluorine atom, a C1-C2 alkyl chain substituted with a fluorine atom group; m in Formula 4 is 1 and Y5 and Y6 are each independently selected from one of a fluorine atom, a C1-C2 alkyl chain substituted with a fluorine atom. - When A in the electrolyte additive A is selected from one of a boron (B)-containing inorganic anion, A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion. - satisfies one of Formula 3 or Formula 4, Y1-Y4 in Formula 3 are each independently selected from one of a fluorine atom, a C1-C2 alkyl chain substituted with a fluorine atom group; m in Formula 4 is 1 and Y5 and Y6 are each independently selected from one of a fluorine atom, a C1-C2 alkyl chain substituted with a fluorine atom.

[0026] As a further preferred embodiment, R2~R4 in the electrolyte additive B are hydrogen atoms, X are each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted with a fluorine atom, and Y is a sulfur atom.

[0027] As a further preferred embodiment, R2~R4 in the electrolyte additive B are hydrogen atoms, X are each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted with a fluorine atom, and Y is a sulfur atom.

[0028] By further limiting Y in the electrolyte additive B to be sulfur, the migration barrier of lithium ions in the crystal lattice of sulfur is relatively low due to the larger radius of sulfur than oxygen, which is more conducive to the rapid transport of lithium ions. Therefore, the SEI inorganic phase constructed by sulfur can provide more excellent bulk ion conduction capability for the high ionic conduction SEI layer pursued by the present application, thereby significantly reducing the interface impedance and improving the rate performance of the battery.

[0029] As a further preferred embodiment, the electrolyte additive B is selected from one or more of the following formulae 23~46:

[0030] As a further preferred embodiment, the electrolyte additive B is selected from one or more of the following formulae 23~46:

[0031] As a further preferred embodiment, the electrolyte additive B is selected from one or more of the following formulae 23~46:

[0032] The application can further optimize the molar ratio of the electrolyte additive A and the electrolyte additive B, at this time, the electrolyte additive A with a higher molar ratio can form more LiF, Li3PO4, Li2S, Li3N and other components at the negative electrode, and the SEI film layer obtained at this time has higher mechanical strength, effectively inhibiting the problem of lithium dendrite puncture. At the same time, the formation of Li2S makes the SEI film layer more dense, and Li2S can cooperate with the inorganic SEI component with high ionic conductivity formed by the electrolyte additive B to obtain higher ionic conductivity on the basis of being dense and having sufficient mechanical strength, and the electrolyte additive B is a key component for improving ionic conductivity in the application, and the benzene ring in the molecular structure of the electrolyte additive B gives it a good planar conjugated structure and electron delocalization, so that it is adsorbed on the high active point of the electrode surface; and the N element contained in the electrolyte additive B is more than that in the electrolyte additive A, which can generate components such as Li3N in a reducing environment. Li3N is one of the important ultra-fast lithium ion conductors, and its ionic conductivity is much higher than that of other common SEI film components. However, too much Li3N will reduce the mechanical properties of the material itself and the chemical stability is insufficient, and decomposition may occur under long-term cycling or high voltage. The application limits the molar ratio of the electrolyte additive A and the electrolyte additive B to a certain range, which is a precise optimization according to the contribution of different electrolyte additives, makes up for the defects of using a single additive in the function of the SEI film layer, and plays a synergistic role.

[0033] As a further preferred aspect, the electrolyte complex additive comprises the electrolyte additive A containing boron (B) inorganic anions, the electrolyte additive A containing nitrogen (N) organic anions and the electrolyte additive B; the molar ratio of the electrolyte additive A containing boron (B) inorganic anions to the electrolyte additive A containing nitrogen (N) organic anions is (0.2~2.5):1.

[0034] As a further preferred aspect, the electrolyte complex additive comprises the electrolyte additive A containing boron (B) inorganic anions, the electrolyte additive A containing nitrogen (N) organic anions and the electrolyte additive B; the molar ratio of the electrolyte additive A containing boron (B) inorganic anions to the electrolyte additive A containing nitrogen (N) organic anions is (0.5~2):1.

[0035] The application can further limit the type of electrolyte additive A selected in the electrolyte complex additive. When the electrolyte additive A containing inorganic anion of boron (B) and the electrolyte additive A containing organic anion of nitrogen (N) are both present and the molar ratio of the two is controlled within a certain range, the proportion of the SEI component containing boron in the inner layer of SEI and the inorganic components such as LiF, Li3N and Li2S can be more reasonably controlled. The SEI film has sufficient structural strength to inhibit dendrites, while maintaining a very high number of lithium ion transfer, and the interface impedance is significantly lower than that of the traditional system.

[0036] As a preferred example, the electrolyte complex additive comprises the electrolyte additive A of formula 47, formula 48 and the electrolyte additive B of formula 26 as follows:

[0037] The electrolyte additive A of formula 47 in the electrolyte complex additive is (fluoromethyl)triphenylphosphonium tetrafluoroborate, the electrolyte additive A of formula 48 in the electrolyte complex additive is (fluoromethyl)triphenylphosphonium bis-trifluoromethanesulfonimide, and the electrolyte additive B of formula 26 in the electrolyte complex additive is [4-(trifluoromethyl)phenyl]thiourea.

[0038] In a second aspect, the application further provides an electrolyte, which comprises an alkali metal salt, a solvent, and the electrolyte complex additive described in the first aspect.

[0039] As a further solution, the metal salt is selected from one or more of organic metal salt and inorganic metal salt.

[0040] As a further solution, the solvent is selected from one or more of ether solvent, ester solvent, sulfone solvent, ionic liquid.

[0041] As a further preferred solution, the inorganic metal salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide.

[0042] As a further preferred solution, the organic metal salt is selected from one or more of lithium bis-trifluoromethylsulfonimide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro(dioxalato)phosphate, lithium bis(pentafluoroethylsulfonyl)imide.

[0043] As a further preferred solution, the concentration of the metal salt in the electrolyte is 0.6-2 mol / L.

[0044] As a further solution, the solvent is selected from one or more of carbonate solvent, carboxylate solvent, phosphate solvent, ether solvent, sulfone solvent.

[0045] As a further preferred example, the carbonate solvent is selected from one or more of methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, fluoroethylene carbonate, ethylene carbonate, vinylene carbonate, propylene carbonate, 1,2-propylene carbonate.

[0046] As a further preferred example, the carboxylic acid ester solvent is selected from one or more of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate.

[0047] As a further preferred example, the phosphate ester solvent is selected from one or more of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triphenyl phosphate.

[0048] As a further preferred example, the ether solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, dipropylene glycol butyl ether, propylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, cyclopentyl methyl ether, diethyl ether, dipropyl ether, butyne glycol dipropoxy ether, propargyl ether.

[0049] As a further preferred example, the sulfone solvent is selected from one or more of tetramethylene sulfone, 3-methyltetramethylene sulfone, 2,4-dimethyltetramethylene sulfone, 3-ethyltetramethylene sulfone, cyclopropane sulfone, 3-methylcyclopropane sulfone, dimethyl sulfone, diethyl sulfone, phenyl ethyl sulfone, phenyl propyl sulfone, sulfonamide, diphenyl sulfone.

[0050] As a further preferred example, the mass ratio of the electrolyte complex additive in the electrolyte is 0.2-2wt%.

[0051] As a further preferred example, the solvent in the electrolyte is selected from one or more of ethylene carbonate and / or diethyl carbonate, the metal salt is selected from one or more of lithium hexafluorophosphate, and the electrolyte complex additive is selected from at least one of the electrolyte additive A and at least one of the electrolyte additive B.

[0052] In a third aspect, the present application also provides a secondary battery, which is one or more of metal secondary batteries, comprising the electrolyte complex additive or the electrolyte.

[0053] As a further example, the secondary battery is selected from one or more of lithium secondary batteries, sodium secondary batteries, and potassium secondary batteries.

[0054] As a further example, the secondary battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte.

[0055] As a further preferred example, the secondary battery is a lithium secondary battery.

[0056] As a further preferred scheme, the lithium secondary battery is a Li||NCM811 battery, the positive electrode of the Li||NCM811 battery is NCM811, the negative electrode is lithium metal, and the separator is Celgard 2325.

[0057] As a still further preferred scheme, the charge-discharge window of the Li||NCM811 battery is 2.8-4.3V.

[0058] The characteristics and benefits of the present application are: (1) In the present application, the electrolyte complex additive can generate a dense SEI protective layer at the negative electrode interface preferentially and spontaneously compared with the electrolyte solvent, which isolates the further contact of the electrolyte with the negative electrode and the adverse side reactions, and effectively inhibits dendrite growth, greatly improving the stability of the negative electrode and the cycle life of the battery.

[0059] (2) The electrolyte complex additive provided by the present application can contain a plurality of high electronegativity elements in the structure, which promotes the diversification of inorganic components of the SEI composition. In addition, the inorganic components such as Li3N, Li3PO4 and Li2S in the SEI are good ion conductors, which is beneficial to improve the kinetic performance of the SEI layer, promote the transmission of ions, and effectively reduce the uneven accumulation of ions and dendrite growth at the interface.

[0060] (3) The method provided by the present application only needs a small amount of additive, and the mass fraction is only 0.2-2wt%, which can significantly improve the battery performance, and can be used in combination, and the types and metering control methods are numerous, which can meet the battery performance requirements in various use environments, has a wide application prospect, and shows good economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0062] Figure 1 The comparison chart of electrochemical impedance data of Li||Li batteries of Example 1 and Comparative Example 7.

[0063] Figure 2 The XPS chart of the battery pole piece of the battery prepared in Example 1 after cycle. DETAILED DESCRIPTION

[0064] In order to facilitate the understanding of the present application, the present application will be described more fully below, and the embodiments of the present application are given, but the scope of the present application is not limited thereto.

[0065] As a specific example of the implementation of the present application, the detailed case is provided as follows.

[0066] The chemical raw materials involved in the following examples and comparative examples are all prior art, and are all obtained by commercial purchase (purchased from Sichuan Aokai Technology Co., Ltd.). The experimental devices, testing devices and the like involved in the following examples and comparative examples are all conventional devices in the art, and are not particularly required and limited.

[0067] Example 1: (1) Preparation of electrolyte: In an argon-filled glove box (moisture, oxygen content <1 ppm), ethylene carbonate, diethyl carbonate were mixed uniformly in a volume ratio of 1:1, then 1 mol / L lithium hexafluorophosphate in the electrolyte was added, and finally the electrolyte complex additive was added. The mass of the electrolyte complex additive is 1 wt.% of the mass of the electrolyte. The molar ratio of the electrolyte additive A of formula 47, the electrolyte additive A of formula 48, and the electrolyte additive B of formula 26 is 1:1:1 (i.e. the molar ratio of the electrolyte additive A to the electrolyte additive B is 2:1). After mixing uniformly, the electrolyte is obtained.

[0068]

[0069] (2) Preparation of lithium secondary battery: Preparation of Li||Li battery: The metal Li electrode was used as the positive electrode and the negative electrode, and was assembled in the order of positive electrode, separator, negative electrode. Then the electrolyte prepared in (1) was injected, followed by vacuum packaging, standing, and formation to obtain a Li||Li battery (button cell CR2032), which was subjected to electrochemical cycle test at room temperature.

[0070] Preparation of Li||Cu battery The metal Li electrode was used as the negative electrode, and the commercial copper foil was used as the positive electrode. The positive electrode, the separator, and the negative electrode were assembled in order. Then the electrolyte prepared in (1) was injected, followed by vacuum packaging, standing, and formation to obtain a Li||Cu battery (button cell CR2032), which was subjected to electrochemical cycle test at room temperature.

[0071] Preparation of Li||811 battery The metal Li electrode was used as the negative electrode, and NCM811 was used as the positive electrode. NCM811, conductive agent Super P, and binder polyvinylidene fluoride were mixed and dispersed in a solvent N-methyl pyrrolidone at a certain ratio, and then the uniformly mixed slurry was coated on the current collector aluminum foil, transferred to a vacuum drying oven and vacuum dried at 120°C for 12h; and then the positive electrode sheet (diameter 11mm) was obtained by cutting. Assembled in the order of negative electrode, separator, and positive electrode, and injected with electrolyte, followed by vacuum packaging, standing, and formation, to obtain Li||NCM811 battery (button cell CR2032), which was subjected to electrochemical cycle test at room temperature.

[0072] Example 2: Different from Example 1, the molar ratio of electrolyte additive A of Formula 47, electrolyte additive A of Formula 48, and electrolyte additive B of Formula 26 was 0.5:1:1, and the others were the same as Example 1.

[0073] Example 3: Different from Example 1, the molar ratio of electrolyte additive A of Formula 47, electrolyte additive A of Formula 48, and electrolyte additive B of Formula 26 was 1:0.5:1, and the others were the same as Example 1.

[0074] Example 4: Different from Example 1, the molar ratio of electrolyte additive A of Formula 47, electrolyte additive A of Formula 48, and electrolyte additive B of Formula 26 was 1:1:2, and the others were the same as Example 1.

[0075] Example 5: Different from Example 1, the molar ratio of electrolyte additive A of Formula 47, electrolyte additive A of Formula 48, and electrolyte additive B of Formula 26 was 1:1:4, and the others were the same as Example 1.

[0076] Example 6: Different from Example 1, the electrolyte additive was obtained by mixing uniformly electrolyte additive A of Formula 49, electrolyte additive A of Formula 50, and electrolyte additive B of Formula 23 at a molar ratio of 1:1:1, and the others were the same as Example 1.

[0077]

[0078] Example 7: Different from Example 1, the electrolyte additive was obtained by mixing uniformly electrolyte additive A of Formula 51, electrolyte additive A of Formula 52, and electrolyte additive B of Formula 23 at a molar ratio of 1:1:1, and the others were the same as Example 1.

[0079]

[0080] Example 8: Different from Example 1, the molar ratio of electrolyte additive A of Formula 47, electrolyte additive A of Formula 48, and electrolyte additive B of Formula 26 is 1.1:0.5:1.

[0081] Example 9: Different from Example 1, the electrolyte additive is composed of electrolyte additive A of Formula 53, electrolyte additive A of Formula 54, and electrolyte additive B of Formula 30 in a molar ratio of 1:1:1, and the electrolyte is obtained after uniform mixing, and the other conditions are the same as in Example 1.

[0082]

[0083] Example 10: Different from Example 1, the electrolyte additive B is shown in Formula 38, and the other conditions are the same as in Example 1.

[0084]

[0085] Comparative Example 1: Different from Example 1, the electrolyte additive is only electrolyte additive A of Formula 47, and the amount of electrolyte additive is 1 wt% of the electrolyte. The other conditions are the same as in Example 1.

[0086] Comparative Example 2: Different from Example 1, the electrolyte additive is only electrolyte additive A of Formula 48, and the amount of electrolyte additive is 1 wt% of the electrolyte. The other conditions are the same as in Example 1.

[0087] Comparative Example 3: Different from Example 1, the electrolyte additive is only electrolyte additive B of Formula 26, and the amount of electrolyte additive is 1 wt% of the electrolyte. The other conditions are the same as in Example 1.

[0088] Comparative Example 4: Different from Example 1, the electrolyte additive is different in that the additive A is replaced by an additive whose anion part does not satisfy Formula 1, and the compound of Formula 55 and electrolyte additive B of Formula 26 are used as electrolyte complex additives, the molar ratio of the compound of Formula 55 and the electrolyte additive B of Formula 26 is 1:2, and the total mass of the electrolyte complex additive is 1 wt% of the total mass of the electrolyte. The other conditions are the same as in Example 1.

[0089]

[0090] Comparative Example 5: Different from Example 1, the electrolyte additive B is replaced by a compound that only partially matches the general formula of Formula 2, i.e., the compound of Formula 56, which does not have the group defined by the invention at the para position of the haloalkyl group on the benzene ring, and the amount and ratio of the electrolyte additive remain unchanged. The other conditions are the same as in Example 1.

[0091]

[0092] Comparative Example 6: Different from Example 1, electrolyte additive B is replaced by an additive only partially matching the general formula of Formula 2, i.e. a compound of Formula 57 as follows, while the amount and ratio of the electrolyte additive remain unchanged. The rest is the same as Example 1.

[0093]

[0094] Comparative Example 7: Different from Example 1, no electrolyte additive is used. The rest is the same as Example 1.

[0095] Comparative Example 8: Different from Example 1, the electrolyte additive is replaced by a compound that does not contain a cation, specifically Formula 58 as follows, and the molar ratio of the compound of Formula 58 to the electrolyte additive B of Formula 26 is 2:1.

[0096]

[0097] Comparative Example 9: Different from Example 1, the two electrolyte additives of electrolyte additive A in Example 1 are replaced by a compound of Formula 59 as shown, and the molar ratio of the compound of Formula 59 to the electrolyte additive B of Formula 26 is 2:1. The rest is the same as Example 1.

[0098]

[0099] The electrolyte additives used in Examples 1-10 and Comparative Examples 1-9 are applied to the same battery system, and the kinetic and electrochemical properties of the above-mentioned batteries are tested as follows: (1) Li||Li battery cycle test After the prepared Li||Li battery is left for 8 hours, it is first discharged at a current density of 0.5 mA / cm 2 to 1 mAh / cm 2 , then charged at a current density of 0.5 mA / cm 2 to 1 mAh / cm 2 cutoff, which is one cycle. Cycle test is performed and lithium deposition overpotential and battery cycle life are obtained.

[0100] (2) Li||Cu battery cycle test After the prepared Li||Cu battery is left for 8 hours, it is first discharged at a current density of 0.5 mA / cm 2 to 1 mAh / cm 2 , left for 1 minute, then charged at a current density of 0.5 mA / cm 2 to 1 V cutoff, which is one cycle.

[0101] Coulombic efficiency (CE) = (charge specific capacity of constant current charging to 1 V cut-off process / discharge specific capacity of constant current discharging process (1 mAh / cm 2 ) x 100%.

[0102] The first cycle coulombic efficiency is the initial cycle coulombic efficiency (ICE).

[0103] The sum of N cycle coulombic efficiency / N is the average coulombic efficiency of N cycles (ACE).

[0104] (3) Li||NCM811 battery cycle test The Li||NCM811 battery is tested by constant current charging and discharging. First, constant current charging to 4.3 V, standing for 1 minute, then constant current discharging to 2.8 V at the same current density, standing for one minute, which is one cycle. First, cycle two times at a current density of 0.2C, then cycle test at a larger current density. The discharge specific capacity / charge specific capacity of the first cycle is the initial cycle coulombic efficiency ICE of the full battery. Under the same current density, the discharge specific capacity of the Nth cycle / the discharge specific capacity of the first cycle x 100% is the capacity retention rate of N cycles.

[0105] Specifically: The initial cycle coulombic efficiency ICE of Li||Cu battery = the charge specific capacity / the discharge specific capacity of the first cycle x 100%; The average coulombic efficiency ACE of Li||Cu battery N cycles = the sum of N cycle coulombic efficiency / N x 100%; The initial cycle coulombic efficiency ICE of Li||NCM811 battery = the discharge specific capacity / the charge specific capacity of the first cycle x 100%; The N cycle capacity retention rate of Li||NCM811 = the discharge specific capacity of N cycles / the discharge specific capacity of the first cycle x 100%.

[0106] The test results of examples 1-10 and comparative examples 1-9 are shown in Tables 1-3:

[0107]

[0108]

[0109] As can be seen from the comparison of Examples 1-10 and Comparative Examples 1-9, the electrolyte additive used in the present application can spontaneously and preferentially decompose at the negative electrode to form a compact SEI layer, effectively inhibiting the electrolyte loss and adverse side reactions caused by further contact between the electrolyte and the negative electrode, improving the stability and cycle life of the negative electrode, and the electrochemical performance of the battery. More importantly, the structure of the electrolyte additive contains multiple high electronegativity elements, which promotes the diversification of inorganic components of the SEI composition. In addition, inorganic components such as Li3N, Li3PO4, and Li2S in the SEI are good ion conductors, which is beneficial to improve the kinetic performance of the SEI layer, promote ion transport, and effectively reduce the inhomogeneous accumulation and dendrite growth of ions at the interface.

[0110] Specifically, as can be seen from the electrochemical impedance test data, such as Figure 1 and Table 1, when the electrolyte additive and the compounding use method provided by the present application are used, the Li||Li symmetric battery has a lower interface impedance (the impedance group presents two semicircles, the first semicircle represents the impedance of the SEI layer formation process at the negative electrode interface, and represents the resistance of the SEI layer formation; the second semicircle represents the impedance of the lithium ion transport process at the interface, and represents the resistance of the SEI layer to lithium ion transport). Examples 1-10 as a whole show a much better interface kinetic performance than Comparative Examples 1-9, mainly reflected in lower interface impedance and nucleation potential. The SEI formation impedance in the Li||Li battery is less than 48Ω, the charge transfer impedance in the Li||Li battery is less than 43Ω, the lithium nucleation overpotential in the first circle of the Li||Li battery is less than 40 mV, and the lithium growth overpotential in the first circle of the Li||Li battery is less than 29 mV.

[0111] At the same time, Examples 1-10 as a whole also show a much better electrochemical performance than Comparative Examples 1-9, such as higher coulombic efficiency of the Li||Cu battery, and higher discharge specific capacity and capacity retention rate of the full battery, which are significantly better than the comparative examples.

[0112] As can be seen from the comparison of Example 1 and Comparative Examples 1-3 and Comparative Example 7, when no electrolyte additive is used, or only one of the electrolyte additives A or one of the electrolyte additives B is used, the performance of the battery is significantly deteriorated due to the inability to build a complete and functionally balanced composite SEI film.

[0113] As can be seen from Comparative Example 1, although the long-term cycle coulombic efficiency of the Li||Cu battery of Comparative Example 1 is acceptable, with an average coulombic efficiency of 92.9% for 200 cycles as shown in Table 2, indicating that the SEI film formed has a certain stability, the first cycle lithium nucleation overpotential of the Li||Li battery thereof is as high as 72 mV, which is much higher than 30 mV of Example 1. This proves that the single boron-containing additive mainly forms an SEI layer mainly containing boron elements, and since the cationic group in the electrolyte additive A has a structure of triphenylphosphine, the three benzene rings are directly connected to the central phosphorus atom, the benzene ring has a planar structure as an aromatic ring and forms a highly rigid π-π conjugated system, the rotation of the benzene ring is limited, resulting in a strong rigidity of the whole molecule and a high stability, so the molecule has a certain degree of close packing in the electrolyte, but the viscosity of the electrolyte system is increased; although the SEI layer is dense and stable, the ion conduction ability is insufficient, resulting in a higher energy barrier to be overcome by lithium ions during initial deposition, which is not conducive to uniform lithium deposition, thereby affecting the interface kinetics performance. At the same time, it also reflects in the lower first cycle specific capacity of the full battery, which is 190.5 mAh / g as shown in Table 3.

[0114] As can be seen from Comparative Example 2, the first cycle coulombic efficiency of the Li||Cu battery of Comparative Example 2 is extremely low, only 72.3%, and the average coulombic efficiency for 200 cycles is only 92.4%. This shows that, based on the use of the electrolyte additive A containing a triphenylphosphine structure alone, the use of only a single electrolyte additive A containing a bis-trifluoromethanesulfonylimide anion as an electrolyte additive may generate a large amount of unstable and / or highly resistive interface components during reduction, which seriously consumes active lithium and electrolyte, resulting in a large irreversible capacity of the battery and poor cycle stability.

[0115] As can be seen from Comparative Example 3, the coulombic efficiency of the Li||Cu battery prepared in Comparative Example 3 is 88.9%, the average coulombic efficiency for 200 cycles is 93.2%, and the capacity retention rate of the full battery is only 93.5%, all of which are at a low level. This shows that the single electrolyte additive B, although it can provide Li3N and Li2S and other ultra-fast ion conductors to improve the kinetics, may fail to form an SEI skeleton with high mechanical strength due to the lack of electrolyte additive A. Without the support of high-mechanical-strength components such as LiF and Li3PO4, the mechanical stability of the SEI film is insufficient, which cannot effectively inhibit the growth of lithium dendrites and the rupture of the SEI film during long-term cycling, resulting in that the coulombic efficiency cannot be further improved and the capacity continues to decay.

[0116] Comparative Example 7 proves that the SEI film is unstable and has poor ionic conductivity without the electrolyte additives, and cannot meet the needs of high-performance lithium metal batteries due to extremely high interfacial impedance, extremely high nucleation overpotential, extremely low coulombic efficiency, and rapid capacity decay without the electrolyte additives.

[0117] As can be seen from the above Example 1 and Comparative Examples 1-3 and 7, the synergistic decomposition mechanism of the two additives realizes the self-assembly of the SEI layer in the cycle, is suitable for various negative electrode systems, has high ionic conductivity, significantly reduces the interfacial charge transfer impedance, and at the same time exhibits good interfacial mechanical properties. The high-rigidity inorganic component effectively inhibits the problem of dendrite growth puncture at the interface, improves the cycle life and safety performance of the battery, meets the performance requirements of the battery in various use environments, has a wide application prospect, and exhibits good economic benefits.

[0118] As can be seen from the comparison of Example 1 and Comparative Example 4, when the compound of formula 55 is used instead of the combination of the electrolyte additive A and the electrolyte additive B of the present application, although the cationic part of the compound of formula 55 meets the structural general formula of the electrolyte additive A, the anionic part of the compound of formula 55 does not meet the structure defined in the present patent. At this time, due to the lack of the specific molecular structure and electronic properties of the inorganic anion containing boron (B) or the organic anion containing nitrogen (N) defined in the present application, the iodine anion in Comparative Example 4 cannot be reduced to form Li3BO3 and other SEI film layers containing boron under reducing conditions, nor can it generate sufficient LiF and Li3N as the organic anion containing nitrogen in Example 1. The possible reduction product of Comparative Example 4 is lithium iodide, which cannot form a stable and continuous solid protective layer on the electrode surface. This leads to fundamental differences in the reduction decomposition behavior and the composition of the final SEI film, and cannot achieve the synergistic effect expected by the present application, resulting in a significant reduction in the effect of synergistically constructing a high-performance SEI film.

[0119] As can be seen from the comparison of Example 1 and Comparative Example 5, when the electrolyte additive B is selected to partially meet the structural general formula of the additive B, the distribution of the electron cloud of the electrolyte additive A cannot be changed due to the lack of the -N-C(=Y)-N- structure, the reaction activity and spontaneous decomposition ability of the electrolyte additive A and the electrolyte additive B cannot be controlled when they are compounded, and the content of Li2S and Li3N, which are the superfast ionic conductors pursued by the present application, is greatly reduced under reducing conditions, which is not conducive to improving the ionic conductivity of the negative electrode. At the same time, due to the lack of flexible segments, the structure exhibits higher rigidity, which is not conducive to the improvement of ionic mobility.

[0120] As can be seen from the comparison of Example 1 and Comparative Example 6, when the electrolyte additive is selected to partially satisfy the structural general formula of the electrolyte additive B, but lacks the Ph-X part, because the molecular structure lacks the key interface adsorption and function conduction skeleton, it cannot be effectively positioned at the electrode interface and play the preset synergistic film forming function, and it also lacks the structural stability effect generated by the π-π stacking action between the electrolyte additive A and the electrolyte additive B. The thioureido group of Comparative Example 6 has a smaller molecular size and weaker hydrophobicity, and has weak interaction with the electrode surface. The concentration and stability of the compound at the interface are greatly reduced, resulting in low and uneven film forming efficiency; the battery performance is significantly reduced.

[0121] As can be seen from the comparison of Example 1 and Comparative Example 8, when the electrolyte additive A in the electrolyte complex additive is replaced by the compound of formula 58, compared with the compound defined in the application, formula 58 is not the A - An ionic compound composed of anions and phosphorus-containing cations, at this time, due to the fundamental differences in molecular polarity, adsorption behavior on the electrode surface, and reduction decomposition mechanism, it cannot achieve the purpose of improving the stability of the negative electrode and the electrochemical performance of the battery at the same time.

[0122] As can be seen from the comparison of Example 1 and Comparative Example 9, when the electrolyte additive A in the electrolyte complex additive does not contain halogen atoms, at this time, due to the lack of halogen anions or halogen-containing active species, the by-products generated by the decomposition of lithium salts in the electrolyte cannot be effectively removed, the chemical stability of the electrolyte system is reduced, the SEI layer cannot be well constructed, and the amount of inorganic nanocrystalline grains with high interface energy and thermodynamic stability such as lithium fluoride is reduced, which has an adverse effect on the stability and ionic conductivity of the electrolyte system. At this time, the electrolyte additive A cannot work with the electrolyte additive B to improve the mechanical properties and ionic conductivity of the interface.

[0123] As can be seen from the comparison of Example 1 and Examples 2-9, Example 1 has a lower SEI formation resistance, which indicates that the additive provided by the application can preferentially or spontaneously participate in the formation of the SEI layer, avoiding the electrolyte loss and adverse side reactions caused by the further contact of lithium metal with the electrolyte, thereby improving the stability of the negative electrode. In addition, Example 1 shows lower lithium ion interface transmission impedance, indicating that the SEI layer formed by the additive has high ionic conductivity, which can promote the transmission of lithium ions at the interface, thereby improving the lithium ion interface transmission kinetics and inhibiting the accumulation and uneven deposition of lithium ions due to slow diffusion kinetics, and effectively inhibiting the generation of lithium dendrites.

[0124] As can be seen from the comparison of Example 1 and Comparative Example 9, when the electrolyte additive A in the electrolyte complex additive does not contain halogen atoms, at this time, due to the lack of halogen anions or halogen-containing active species, the by-products generated by the decomposition of lithium salts in the electrolyte cannot be effectively removed, the chemical stability of the electrolyte system is reduced, the SEI layer cannot be well constructed, and the amount of inorganic nanocrystalline grains with high interface energy and thermodynamic stability such as lithium fluoride is reduced, which has an adverse effect on the stability and ionic conductivity of the electrolyte system. At this time, the electrolyte additive A cannot work with the electrolyte additive B to improve the mechanical properties and ionic conductivity of the interface. Figure 2As can be seen from the XPS test, the use of the additive provided by the present application can generate SEI with high ionic conductivity at the electrode interface, and the specific components include Li3N, Li3PO4, Li2S, etc.

[0125] As can be seen from the comparison of Examples 1-3 and Examples 4-5, the present application can further optimize the molar ratio of electrolyte additive A and electrolyte additive B in the electrolyte additive. When further optimized, the higher molar ratio of electrolyte additive A can form more LiF, Li3PO4, Li2S, etc. components in the negative electrode, and the SEI film obtained at this time has higher mechanical strength, effectively inhibiting the puncture problem of lithium dendrites. At the same time, the formation of Li2S makes the SEI film more dense, and Li2S can cooperate with the high ionic conductivity inorganic SEI component formed by electrolyte additive B to obtain higher ionic conductivity on the basis of density and sufficient mechanical strength. Electrolyte additive B is a key component for improving ionic conductivity in the present application, and the benzene ring in its molecular structure gives it a good planar conjugated structure and electron delocalization, so it can preferentially adsorb on the high activity point of the electrode surface; and the N element contained therein can generate components such as Li3N in a reducing environment. Li3N is one of the important ultra-fast lithium ion conductors, and its ionic conductivity is much higher than that of other common SEI film components. However, too much Li3N can reduce the mechanical properties of the material itself and lack chemical stability, and may decompose under long-term cycling or high voltage. The present application limits the molar ratio of electrolyte additive A and electrolyte additive B to a certain range, which is a precise optimization according to the contribution of different electrolyte additives, makes up for the defects of single additive in the function of SEI film, and plays a synergistic role.

[0126] As can be seen from Examples 1-5 and Example 8, the present application can limit the type of electrolyte additive A selected in the electrolyte additive. When the electrolyte additive A containing boron (B) inorganic anion and the electrolyte additive A containing nitrogen (N) organic anion are used at the same time, and by controlling the molar ratio of the two within a certain range, the ratio of boron-containing SEI components to LiF, Li3N, Li2S, etc. inorganic components in the inner layer of SEI can be further more reasonably controlled. It ensures that the SEI film has sufficient structural strength to inhibit dendrites, while maintaining a very high lithium ion transference number, and its interface impedance is significantly lower than that of the traditional system.

[0127] As can be seen from the comparison of Example 1 and Example 10, when Y in electrolyte additive B is further defined as sulfur, the migration barrier of lithium ions in the crystal lattice thereof is relatively low due to the larger radius of sulfur than oxygen, which is more conducive to the rapid transport of lithium ions. Therefore, the SEI inorganic phase constructed by sulfur can provide more excellent bulk ion conduction capability for the high-ion-conductivity SEI layer pursued by the present application, thereby significantly reducing the interface impedance and improving the rate performance of the battery.

[0128] As can be seen from the comparison of Example 1 and Example 7, when the carbon chain length of the substituent group in electrolyte additive A and electrolyte additive B is further optimized in the present application, the steric hindrance of the compound structure of the electrolyte additive is smaller due to the shorter length of the carbon chain, the molecule is relatively compact, and the adsorption and arrangement on the lithium surface are more compact, which is further conducive to the formation of a dense SEI, thereby reducing the charge transfer impedance while improving the ion transport capability of the battery. When the carbon chain length is too long, the space steric hindrance of the electrolyte additive is large, the film formed at the interface is likely to be thicker but the compactness is significantly reduced, which hinders the transport of lithium ions. At the same time, the electron-donating effect and the space shielding of the long alkyl chain weaken the interaction between the phosphonium center and the electrolyte anion, which reduces the contribution to the improvement of the lithium ion migration number, resulting in a decrease in ion conductivity.

[0129] As can be seen from the comparison of Example 1 and Example 6, when the electrolyte additive A and electrolyte additive B in the present application are further preferred to be groups substituted with halogen-substituted higher electronegativity groups, the energy level, reduction potential and decomposition path of the molecule can be precisely controlled, thereby optimizing the chemical behavior thereof at the electrode interface and the composition and structure of the final SEI film. When the substituent group in electrolyte additive A in the present application is further preferred to be a group containing a halogen atom, the above group can significantly reduce the lowest unoccupied molecular orbital energy level of the additive molecule. The molecule is more likely to obtain electrons under the action of an electric field, thereby having a more negative reduction potential, so as to preferentially undergo reduction and decomposition on the negative electrode surface compared with conventional solvent molecules such as carbonates, which on the one hand avoids the continuous side reaction of the solvent molecules and reduces the generation of by-products, and on the other hand, the above substituent group can better balance the mechanical properties and ion conductivity of the formed SEI film.

[0130] As can be seen from the comparison of Example 1 and Example 9, when R1 in electrolyte additive A is further simultaneously optimized to be selected from a fluorine atom or a C1-C2 alkyl group substituted with a fluorine atom, and A - is selected from one of nitrogen (N)-containing organic anions, the A -satisfies one of Formula 10; and Z1~Z2 are each independently selected from one of a fluorine atom, a fluorine atom-substituted C1~C2 alkyl group; A in the electrolyte additive A - when the A is selected from one of a boron (B)-containing inorganic anion, the A - satisfies one of Formula 3 or Formula 4; when m is 1 and Y1~Y4 in Formula 3 and Y5 and Y6 in Formula 4 are each independently selected from one of a fluorine atom, a fluorine atom-substituted C1~C2 alkyl group, due to the strong electron-withdrawing group, precise regulation of the molecular energy level, reduction potential and decomposition path is achieved, thereby optimizing its chemical behavior at the electrode interface and the composition and structure of the final SEI film. The present application further selects the substituents (such as Y1-Y6, Z1-Z2) in R1 and the anion in the electrolyte additive from halogen atoms or short-chain halogenated alkyl groups. When the above groups can significantly reduce the lowest unoccupied molecular orbital energy level of the additive A molecule. The molecule is more likely to obtain an electron under the action of an electric field, thereby having a more negative reduction potential, thereby more conducive to its preferential reduction decomposition on the negative electrode surface over conventional solvent molecules such as carbonates, on the one hand, avoiding the continuous side reactions of solvent molecules, reducing the generation of by-products in the lithium salt decomposition process, on the other hand, the above substituents can better balance the mechanical properties and ion conductivity of the formed SEI film, for example, when more halogen-containing substituents are used, for example, fluorine atoms, due to the release of fluorine source during the reduction process, which participates in the formation of LiF. LiF is a key component for building a high-mechanical-strength, high-stability SEI skeleton, which greatly enhances the compactness, chemical stability, high ionic conductivity and mechanical strength of the SEI layer, and inhibits the continuous decomposition of the electrolyte and the germination and growth of lithium dendrites.

[0131] Therefore, by combining Example 1 and Examples 6~7, Example 9, it can be seen that when the present application simultaneously limits the R1 substituent group, Y1~Y6 in the electrolyte additive A, X in the electrolyte additive B to be a fluorine atom or a fluorine atom-substituted C1~C2 alkyl group, and R2~R4 in the electrolyte additive B to be hydrogen, further higher inhibition of dendrite puncture mechanical properties can be obtained while having higher ion conductivity from the electron-withdrawing effect of the electrolyte additive and the formation of a variety of gradient conductive SEI films, etc.

[0132] The above conclusion is effectively verified by the cycle test of Example 1 in the present application through the Li||Li symmetrical battery as shown in Table 1. The Example 1 using the electrolyte additive and the compounding use method provided by the present application exhibits the lowest lithium nucleation overpotential and growth potential, which is derived from the high kinetic characteristics and high lithium ion transmission performance of the SEI. In summary, the use of the electrolyte additive provided by the present application can spontaneously participate in the construction of the SEI layer with high ionic conductivity, improve the interface kinetics, promote the rapid diffusion of lithium ions, thereby inhibit the dendrite growth, protect the lithium metal negative electrode, and improve the cycle life of the battery.

[0133] As can be seen from the coulombic efficiency of the Li||Cu battery in Table 2, the Example using the additive and the compounding method provided by the present application has higher coulombic efficiency compared with the comparative example not using any additive or only using the conventional additive. The low nucleation overpotential is conducive to the uniform deposition and growth of lithium. Higher coulombic efficiency again indicates that the generated SEI has high diffusion of lithium ions and low diffusion resistance, which ensures the stripping of a high proportion of active lithium and reduces the generation of “dead lithium”, again verifying the high ionic conductivity and high kinetic characteristics of the SEI layer.

[0134] We further verify the application potential of the additive provided by the present application in the full battery. As shown in Table 3, the initial efficiency of the Li||NCM811 full battery using the additive described in the present application is greatly improved, and the discharge specific capacity is significantly improved (0.2C, the first circle discharge specific capacity of the Li||NCM811 battery without using the additive described in the present application is only 188.0 mAh / g, while the first circle discharge specific capacity of the battery using the additive of the present application is increased to 206.8 mAh / g). In addition, Example 1 exhibits higher capacity retention rate (the capacity almost does not attenuate after 50 cycles), which indicates that the electrolyte additive and the compounding use method provided by the present application effectively protect the negative electrode, and also have a certain protective effect on the structural stability of the positive electrode. This is mainly because the benzene ring group has high stability, and the N, P, S, O and other elements in the additive can coordinate with other components in the electrolyte to adjust the solvation structure of the electrolyte, thereby improving the electrochemical performance of the full battery.

[0135] In summary, the present application successfully constructs a gradient SEI layer with high ionic conductivity and excellent mechanical stability through the synergistic compounding of the electrolyte additive A and the electrolyte additive B with a specific structure. The SEI layer can effectively regulate the lithium ion deposition behavior, inhibit the dendrite growth, and improve the interface stability, and is suitable for various negative electrode systems (such as lithium metal, silicon-carbon, etc.). The method only needs a small amount of addition (0.2-2 wt%), which can significantly improve the cycle life, coulombic efficiency and safety performance of the battery. The process is simple, the cost is controllable, and has a high industrial application prospect and economic benefit.

[0136] Each technical feature of the above-described embodiments can be combined with any other technical feature, and for the sake of brevity, not all possible combinations are described, but it is understood that the scope of the present specification includes all possible combinations. Although the above has shown and described the embodiments of the present application, it is understood that the above-described embodiments are exemplary, and the present application is not limited thereto, and those skilled in the art can make modifications, changes, substitutions and variations of the above-described embodiments within the scope of the present application. Furthermore, those skilled in the art can combine and combine the features of different embodiments or examples described in the specification and the features of different embodiments or examples, without contradiction.

Claims

1. An electrolyte compounding additive, characterized in that, The electrolyte additive A and the electrolyte additive B, respectively, have a general structure formula as formula 1 and formula 2: ; A in the formula 1 - one selected from a boron (B) containing inorganic anion or a nitrogen (N) containing organic anion; R1in the formula 1, R2~R4in the formula 2, X are each independently selected from one of a hydrogen atom, a halogen atom, a C1~C7 alkyl chain or a C1~C7 alkyl chain with a substituent, a C1~C7 alkoxy chain or a C1~C7 alkoxy chain with a substituent, a C2~C7 alkene chain or a C2~C7 alkene chain with a substituent; the substituent is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a sulfhydryl group, a silane group; Y in the formula 2 is selected from a sulfur (S) atom or an oxygen (O) atom; and A in the formula 1 - at least one halogen atom, at least one halogen atom in X of the formula 2.

2. The electrolyte compounding additive according to claim 1, characterized in that, A in the electrolyte additive A - when A is selected from inorganic anions containing boron (B), the A - satisfies one of formula 3 or formula 4; ; Y1~Y4 are each independently selected from one of a halogen atom, a C1~C7 alkyl chain or a C1~C7 alkyl chain with a substituent, a C1~C7 alkoxy chain or a C1~C7 alkoxy chain with a substituent, a C2~C7 alkene chain or a C2~C7 alkene chain with a substituent; the substituent is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a sulfhydryl group, a silane group; m is 1 or 2; when m is 2, the structure of formula 4 is a symmetric structure centered on boron (B); when m is 1, Y5~Y6 are each independently selected from one of a halogen atom, a C1~C7 alkyl chain or a C1~C7 alkyl chain with a substituent, a C1~C7 alkoxy chain or a C1~C7 alkoxy chain with a substituent, a C2~C7 alkene chain or a C2~C7 alkene chain with a substituent; the substituent is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a sulfhydryl group, a silane group; Preferably, A in the electrolyte additive A - When A is selected from a boron (B) containing inorganic anion, A - satisfies one of Formula 3 or Formula 4; Y1~Y4 in Formula 3 are each independently selected from one of a halogen atom, a C1~C2 alkyl chain substituted with a halogen atom group; m in Formula 4 is 1 and Y5 and Y6 are each independently selected from one of a halogen atom, a C1~C2 alkyl chain substituted with a halogen atom group; Further preferably, A in the electrolyte additive A - When A is selected from a boron (B) containing inorganic anion, A - satisfies one of Formula 3 or Formula 4; Y1~Y4 in Formula 3 are each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted with a fluorine atom; m in Formula 4 is 1 and Y5 and Y6 are each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted with a fluorine atom.

3. The electrolyte compounding additive according to claim 1, characterized in that, A in the electrolyte additive A - when selected from one of the nitrogen (N) containing organic anions, the A - satisfies one of formula 10; ; Z1~Z2 are each independently selected from one of a halogen atom, a C1~C7 alkyl chain or a C1~C7 alkyl chain with a substituent, a C1~C7 alkoxy chain or a C1~C7 alkoxy chain with a substituent, a C2~C7 alkene chain or a C2~C7 alkene chain with a substituent; the substituent is selected from one or more of a halogen atom, a hydroxyl group, an amino group, a carboxyl group, an ester group, an amide group, an acyloxy group, a nitro group, a cyano group, an ether oxygen group, a phosphate group, a phosphite group, a sulfonate group, a sulfonyl group, a sulfoxide group, a sulfhydryl group, a silane group, and at least one halogen atom is contained in Z1 and Z2; Preferably, A in the electrolyte additive A - When A is selected from one of the nitrogen (N) -containing organic anions, the A - satisfies one of formula 10; and Z1~Z2are each independently selected from one of a halogen atom, a C1~C2alkyl chain substituted with a halogen atom.

4. The electrolyte compounding additive according to claim 1, characterized in that, R1 in the electrolyte additive A is selected from one of a halogen atom, a C1~C2 alkyl chain substituted by a halogen atom; Preferably, R1 in the electrolyte additive A is selected from one of a fluorine atom, a C1~C2 alkyl chain substituted by a fluorine atom.

5. The electrolyte compounding additive according to claim 1, characterized in that, R1in the electrolyte additive A is selected from one of a halogen atom or a C1-C2 alkyl chain substituted with a halogen atom; A in the electrolyte additive A - when the A is selected from one of a nitrogen (N)-containing organic anion, the A - satisfies one of Formula 10, and Z1-Z2are each independently selected from one of a halogen atom, a C1-C2 alkyl chain substituted with a halogen atom; A in the electrolyte additive A - when the A is selected from one of a boron (B)-containing inorganic anion, the A - satisfies one of Formula 3 or Formula 4, Y1-Y4in Formula 3 are each independently selected from one of a halogen atom, a C1-C2 alkyl chain substituted with a halogen atom group; m in Formula 4 is 1 and Y5and Y6are each independently selected from one of a halogen atom, a C1-C2 alkyl chain substituted with a halogen atom.

6. The electrolyte compounding additive according to claim 1, characterized in that, R1in the electrolyte additive A is selected from one of a fluorine atom or a C1-C2 alkyl chain substituted with a fluorine atom; A - when A in the electrolyte additive A is selected from one of a nitrogen (N)-containing organic anion, A - satisfies one of Formula 10, and Z1-Z2are each independently selected from one of a fluorine atom or a C1-C2 alkyl chain substituted with a fluorine atom; A - when A in the electrolyte additive A is selected from one of a boron (B)-containing inorganic anion, A - satisfies one of Formula 3 or Formula 4, Y1-Y4in Formula 3 are each independently selected from one of a fluorine atom or a C1-C2 alkyl chain substituted with a fluorine atom group; m in Formula 4 is 1 and Y5 and Y6 are each independently selected from one of a fluorine atom or a C1-C2 alkyl chain substituted with a fluorine atom.

7. The electrolyte compounding additive according to claim 1, characterized in that, R2~R4 in the electrolyte additive B are hydrogen atoms, X is each independently selected from one of a halogen atom, a C1~C2 alkyl chain substituted by a halogen atom, Y is selected from one of sulfur (S) and oxygen (O); Preferably, R2~R4 in the electrolyte additive B are hydrogen atoms, X is each independently selected from one of a fluorine atom, a C1~C2 alkyl chain substituted by a fluorine atom, Y is a sulfur atom.

8. The electrolyte compounding additive according to claim 1, characterized in that, The electrolyte additive A and the electrolyte additive B in the electrolyte compound additive are selected from at least one of the electrolyte additive A and at least one of the electrolyte additive B, and the molar ratio of the electrolyte additive A to the electrolyte additive B in the electrolyte compound additive is (0.2~2.5):1; Preferably, the molar ratio of the electrolyte additive A to the electrolyte additive B in the electrolyte compound additive is (1.5~2.5):1; Preferably, the electrolyte complex additive comprises an electrolyte additive A containing inorganic anion of boron (B), an electrolyte additive A containing organic anion of nitrogen (N) and an electrolyte additive B; the molar ratio of the electrolyte additive A containing inorganic anion of boron (B) to the electrolyte additive A containing organic anion of nitrogen (N) is (0.2~2.5):1; Preferably, the electrolyte complex additive comprises an electrolyte additive A containing inorganic anion of boron (B), an electrolyte additive A containing organic anion of nitrogen (N) and an electrolyte additive B; the molar ratio of the electrolyte additive A containing inorganic anion of boron (B) to the electrolyte additive A containing organic anion of nitrogen (N) is (0.5~2):

1.

9. An electrolyte, characterized by The electrolyte comprises an alkali metal salt, a solvent and the electrolyte complex additive according to any one of claims 1~7. Preferably, the mass ratio of the electrolyte complex additive in the electrolyte is 0.2~2wt%.

10. A secondary battery characterized by comprising: The secondary battery is one or more of metal secondary batteries, comprising the electrolyte complex additive according to any one of claims 1~7 or the electrolyte according to claim 8.

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