Gel electrolyte and semi-solid lithium ion battery thereof

Abstract

Provided are a gel electrolyte and a semi-solid lithium ion battery thereof. The gel electrolyte is obtained by polymerizing an electrolyte containing a gel precursor material, wherein the electrolyte comprises a first additive, and the gel precursor material comprises a gelator and a thermal initiator; the first additive comprises a compound shown in structural formula 1, and the gelator comprises compounds shown in structural formula 2, structural formula 3 and structural formula 4. The gel electrolyte satisfies the following relational expressions: 0.1≤j / k≤1, 0.1≤j≤3, and 3≤k≤10. The gel electrolyte can form an interfacial film with better thermal stability on an interface between positive and negative electrodes, and has the characteristic of being non-swelling and non-leaking, which enhances the safety performance of the lithium ion battery.

Description

Gel electrolyte and its semi-solid lithium-ion battery Technical Field

[0001] The present invention belongs to the technical field of semi-solid lithium ion batteries, and in particular relates to a gel electrolyte and a semi-solid lithium ion battery thereof. Background Art

[0002] With the development of the lithium-ion battery industry and the continued increase in battery energy density, news reports of serious safety incidents such as thermal runaway have gradually increased. Safety issues have become a technical bottleneck restricting the wider and more in-depth application of lithium-ion batteries and a major concern for consumers. The root cause is that the widely used lithium-ion batteries generally use small molecule organic solvents with low boiling points and low flash points. Under the influence of mechanical abuse, electrical abuse, thermal abuse, etc., they are prone to violent gas production and heat release, and even thermal runaway, posing a serious safety hazard.

[0003] Academician Ouyang Minggao and his team have identified three mechanisms for thermal runaway in lithium-ion batteries: First, structural damage to the cathode of high-energy-density batteries releases reactive oxygen species; second, active lithium is released from the anode due to rapid charging or overcharging; and third, internal short circuits caused by high-temperature melting or mechanical puncture of the separator. Thermal runaway begins with a self-exothermic reaction within the battery. When the solid electrolyte interface (SEI) on the positive and negative electrode surfaces begins to irreversibly decompose, the high-energy lithium-intercalated anode reacts with the organic solvent, marking the beginning of the self-exothermic phase.

[0004] Gel electrolytes are made by adding organic polymer monomers (i.e., gel factors) to liquid electrolytes. Under the action of thermal initiators, they form a three-dimensional network of polymers, transforming the liquid electrolyte into a gel electrolyte. This prevents electrolyte leakage, enhances mechanical strength, and thus improves battery safety. However, relying on a single approach alone cannot improve the intrinsic safety of lithium-ion batteries. The accumulated heat from the self-exothermic reactions within the battery can also cause the gel to desorb and vaporize the solvent, reducing battery safety. Therefore, in existing commercial lithium-ion battery systems, improving the SEI through electrolytes and improving the stability of gel electrolytes are urgent issues that need to be addressed.

[0005] Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the heat accumulated by the self-exothermic reaction inside the existing lithium-ion battery will cause the gel to desorb and vaporize the solvent, thereby reducing the safety performance of the battery. The present application provides a gel electrolyte and a semi-solid lithium-ion battery thereof.

[0007] To solve the above technical problems, the present application provides a gel electrolyte, which is obtained by polymerization of an electrolyte containing a gel precursor material, wherein the electrolyte includes a first additive, the gel precursor material includes a gel factor and a thermal initiator, the first additive includes a compound represented by structural formula 1, and the gel factor includes compounds represented by structural formulas 2, 3, and 4.

[0008] wherein n is 0 or 1, A is selected from C or O, and X is selected from R1 and R2 are each independently selected from H, R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0009] w is an integer from 0 to 11, y is an integer from 1 to 8, and z is an integer from 1 to 8;

[0010] The gel electrolyte satisfies the following relationship:

[0011] 0.1≤j / k≤1, and 0.1≤j≤3, 3≤k≤10;

[0012] Wherein, j is the mass content of the first additive in the electrolyte, in %;

[0013] k is the mass content of the gel factor in the electrolyte, in %.

[0014] Preferably, the gel electrolyte satisfies the following relationship: 0.15≤j / k≤0.4.

[0015] Preferably, in the gel factor, the mass content of the compound represented by structural formula 2 in the electrolyte is 1% to 6%, the mass content of the compound represented by structural formula 3 in the electrolyte is 1% to 8%, and the mass content of the compound represented by structural formula 4 in the electrolyte is 1% to 3%.

[0016] Preferably, based on the total mass of the electrolyte being 100%, the mass content j% of the first additive in the electrolyte is 1 to 3%;

[0017] The mass content k% of the gel factor in the electrolyte is 5-10%.

[0018] Preferably, the compound represented by structural formula 1 is selected from one or more of the following compounds:

[0019] Preferably, the compound represented by structural formula 2 is selected from one or more of the following compounds:

[0020] The compound represented by structural formula 3 is selected from one or more of the following compounds:

[0021] The compound represented by structural formula 4 is selected from one or more of the following compounds:

[0022] Preferably, the electrolyte further comprises a film-forming additive and a low-resistance additive, and the total mass content of the film-forming additive, the low-resistance additive and the thermal initiator is 1% to 20% based on the total mass of the electrolyte as 100%;

[0023] The film-forming additive includes one or more of cyclic carbonate compounds, cyclic sulfonate compounds, nitrile compounds, phosphate compounds, and borate compounds;

[0024] The low-impedance additive includes one or more of vinylene carbonate, vinyl sulfate, propylene sulfate, lithium difluorooxalatoborate, and lithium difluorophosphate;

[0025] The thermal initiator includes an azo compound.

[0026] Preferably, the cyclic sulfonate compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone or 1,3-propene sultone;

[0027] The cyclic carbonate compound is selected from vinylene carbonate, ethylene carbonate, fluoroethylene carbonate or structure

[0028] At least one of the compounds represented by formula 5,

[0029] In the structural formula 5, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

[0030] The phosphate compound is selected from at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite or the compound shown in Structural Formula 6:

[0031] In the structural formula 6, R 31 、R 32 、R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(Cm H 2m+1 )3, m is a natural number from 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group;

[0032] The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0033] The nitrile compound is selected from at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile;

[0034] The thermal initiator is azobisisobutyronitrile.

[0035] Preferably, the electrolyte further comprises a non-aqueous organic solvent and an electrolyte salt, wherein the electrolyte salt comprises lithium hexafluorophosphate, at least one of LiPO2F2, LiBF4, LiBOB, LiCF3SO3, LiDFOB, LiC(SO2CF3)3, LiN(SO2F)2, and LiClO4;

[0036] The molar concentration of the electrolyte salt in the electrolyte is 0.8 mol / L to 1.35 mol / L;

[0037] The non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylate solvents and sulfone solvents; based on the total mass of the electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 70% to 90%.

[0038] In a second aspect, the present application provides a semi-solid lithium-ion battery comprising a positive electrode, a negative electrode and the gel electrolyte described above.

[0039] The gel electrolyte provided by the present application, when the mass content j of the first additive in the electrolyte and the mass content k of the gel factor in the electrolyte meet the conditions 0.1≤j / k≤1, and 0.1≤j≤3, 3≤k≤10, the compound represented by structural formula 1 in the electrolyte can form an interface film with good thermal stability on the electrode surface during the first electrochemical reaction of the battery, and the interface film is resistant to Lewis Acid corrosion, not easy to dissolve and decompose at high temperature, the stable interface film formed effectively increases the starting temperature of the battery's self-heating, avoids the desorption of the gel electrolyte and vaporization of the solvent due to heat accumulation, thereby improving the high temperature performance and safety performance of the lithium-ion battery. At the same time, the gel factor polymerizes with the help of a thermal initiator to form a polymer gel network. The gel network "binds" the electrolyte to make it semi-solid, solidifies the electrolyte and reduces leakage and rapid gas production caused by solvent volatilization. At the same time, the filling and supporting effects also make the diaphragm have higher heat-resistant deformation strength; it can give full play to the synergistic effect between the compound shown in structural formula 1 and the gel factor, form an interface film with better thermal stability at the positive and negative electrode interfaces, and at the same time has the characteristics of no gas expansion and no leakage, thereby improving the safety performance of the lithium-ion battery. DETAILED DESCRIPTION

[0040] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] The present application provides a gel electrolyte, characterized in that the gel electrolyte is obtained by polymerization of an electrolyte containing a gel precursor material, the electrolyte includes a first additive, the gel precursor material includes a gel factor and a thermal initiator, the first additive includes a compound represented by structural formula 1, and the gel factor includes compounds represented by structural formulas 2, 3, and 4.

[0042] wherein n is 0 or 1, A is selected from C or O, and X is selected from R1 and R2 are each independently selected from H, R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0043] w is an integer from 0 to 11, y is an integer from 1 to 8, and z is an integer from 1 to 8;

[0044] The gel electrolyte satisfies the following relationship:

[0045] 0.1≤j / k≤1, and 0.1≤j≤3, 3≤k≤10;

[0046] Wherein, j is the mass content of the first additive in the electrolyte, in %;

[0047] k is the mass content of the gel factor in the electrolyte, in %.

[0048] The inventors found that the compound shown in structural formula 1 and the gel precursor material are added to the electrolyte, and the performance of the gel electrolyte containing the compound shown in structural formula 1 is directly related to the content k of the gel factor. If the gel factor content k is too low, the glass transition temperature of the formed polymer is low, and it is easy to melt and creep during the thermal abuse test, and it is difficult to solve the problems of rapid gas production and leakage, and the safety performance is reduced; if the gel factor content k is too high, the viscosity of the electrolyte is too high, which is not conducive to the diffusion and transfer of the compound of structural formula 1 in the electrolyte (or: the viscosity of the electrolyte is too high to affect the wetting effect, and the aging time is insufficient), resulting in uneven film formation at the positive and negative electrode interfaces and reduced safety performance; when the mass content j of the first additive in the electrolyte and the mass content k of the gel factor in the electrolyte meet the conditions 0.1≤j / k≤1, and 0.1≤j≤3, 3≤k≤10, the compound shown in structural formula 1 in the electrolyte can be used in the first During the electrochemical reaction, an interface film with good thermal stability is formed on the electrode surface, and the interface film is resistant to Lewis acid corrosion and is not easily dissolved and decomposed at high temperatures. The formed stable interface film effectively increases the starting temperature of the battery's self-heating, avoids the desorption of the gel electrolyte and vaporization of the solvent due to heat accumulation, thereby improving the high-temperature performance and safety performance of the lithium-ion battery. At the same time, the gel factor polymerizes with the help of a thermal initiator to form a polymer gel network. The gel network "binds" the electrolyte to make it semi-solid, solidifies the electrolyte and reduces leakage and rapid gas production caused by solvent volatilization. At the same time, the filling and supporting effects also make the diaphragm have higher heat-resistant deformation strength; it can give full play to the synergistic effect between the compound shown in structural formula 1 and the gel factor, form an interface film with better thermal stability at the positive and negative electrode interfaces, and at the same time has the characteristics of no swelling and no leakage, thereby improving the safety performance of the lithium-ion battery.

[0049] Specifically, if j / k is less than 0.1, it may be that the gel factor content k is too high, and the electrolyte viscosity is too high, which is not conducive to the diffusion and transfer of the compound of structural formula 1 in the electrolyte (or: the electrolyte viscosity is too high, affecting the wetting effect, and the aging time is insufficient), resulting in uneven film formation at the positive and negative electrode interfaces and reduced safety performance; or the content of the first additive is too low, and an interface film with good thermal stability cannot be formed on the electrode surface, reducing the high temperature performance and safety performance of the battery. If j / k is greater than 1, it may be that the gel factor content k is too low, the polymer formed has a low glass transition temperature, and is prone to melting creep during thermal abuse testing, making it difficult to solve the problems of rapid gas production and leakage, and the battery safety performance is reduced. It may be that the content of the first additive is too high, the viscosity of the electrolyte is too high, and the interface film formed at the positive and negative electrode interfaces is uneven and too thick, and the battery safety performance is reduced.

[0050] It can be understood that, under the premise of 0.1≤j≤3, 3≤k≤10, the value of j / k can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc., as long as the relationship 0.1≤j / k≤1, and 0.1≤j≤3, 3≤k≤10 is satisfied.

[0051] In some preferred embodiments, the gel electrolyte satisfies the following relationship: 0.15≤j / k≤0.4.

[0052] The gel electrolyte satisfies the relationship 0.15≤j / k≤0.4. A lithium-ion battery having the gel electrolyte can give full play to the synergistic effect between the compound shown in structural formula 1 and the gel factor, can form an interface film with better thermal stability at the positive and negative electrode interfaces, and has the characteristics of no bloating and no leakage, and the battery has higher safety performance.

[0053] In some embodiments, in the gel factor, the mass content of the compound represented by structural formula 2 in the electrolyte is 1% to 6%, the mass content of the compound represented by structural formula 3 in the electrolyte is 1% to 8%, and the mass content of the compound represented by structural formula 4 in the electrolyte is 1% to 3%.

[0054] The present application provides a gel factor in a gel precursor material of a gel electrolyte, which contains the compound shown in structural formula 2, the compound shown in structural formula 3, and the compound shown in structural formula 4, respectively. This is conducive to polymerization under the action of a thermal initiator to form a polymer gel network, solidify the electrolyte, and reduce leakage and rapid gas production caused by solvent volatilization. At the same time, the filling and supporting effects also make the diaphragm have higher heat-resistant deformation strength, and at the same time, cooperate with the compound shown in structural formula 1 to improve the safety performance of the battery. Specifically, in the gel factor, if the mass content of the compound shown in structural formula 2 is less than 1%, or the mass content of the compound shown in structural formula 3 is less than 1%, or the mass content of the compound shown in structural formula 4 is less than 1%, it is not conducive to the formation of a polymer gel network. If the mass content of the compound shown in structural formula 2, structural formula 3, or structural formula 4 is too high, the viscosity of the electrolyte increases, and the formed polymer gel network has a poor swelling effect on the electrolyte.

[0055] In some preferred embodiments, based on the total mass of the electrolyte being 100%, the mass content j% of the first additive in the electrolyte is 1-3%;

[0056] The mass content k% of the gel factor in the electrolyte is 5-10%.

[0057] The mass content of the first additive and the gel factor in the electrolyte is within the above range, which helps to form a structurally stable interface film at the interface of the positive and negative electrodes. At the same time, the polymer gel network formed by the gel factor under the action of the thermal initiator has high stability, which converts the liquid electrolyte into a gel electrolyte, solves the problems of rapid gas production and leakage of the battery, and synergistically improves the safety performance of the battery.

[0058] In some embodiments, the compound represented by structural formula 1 is selected from one or more of the following compounds:

[0059] It is understandable that the above-mentioned compounds 1 to 22 are only some of the types listed in the compound shown in structural formula 1. It should be noted that as long as the compounds meet the requirements of structural formula 1, they can cooperate with the gel factor to form a stable interfacial film at the positive and negative electrode interfaces, and at the same time have the characteristics of no inflation and no leakage, thereby improving battery safety.

[0060] In some embodiments, the compound represented by structural formula 2 is selected from one or more of the following compounds:

[0061] The compound represented by structural formula 3 is selected from one or more of the following compounds:

[0062] The compound represented by structural formula 4 is selected from one or more of the following compounds:

[0063] It can be understood that the above-mentioned compounds A1 to A4 are only some of the types listed among the compounds shown in Structural Formula 2, compounds B1 to B3 are only some of the types listed among the compounds shown in Structural Formula 3, and compounds C1 to C3 are only some of the types listed among the compounds shown in Structural Formula 4. It should be noted that as long as the compounds shown in Structural Formula 2, Structural Formula 3, and Structural Formula 4 meet the requirements, they all fall within the scope of protection of this application.

[0064] In the compound of Structural Formula 2, w ranges from 0 to 11. This application lists w as 1, 3, 5, and 7. It is understood that w can also take other values, such as 2, 4, 6, 8, etc., as long as w is within the range of 0 to 11. Similarly, in the compound of Structural Formula 3, y can be 1, 2, 4, 5, 6, 8, etc., as long as y is within the range of 1 to 8. Similarly, in the compound of Structural Formula 4, z can be 1, 2, 4, 5, 6, 8, etc., as long as z is within the range of 1 to 8.

[0065] In some embodiments, the film-forming additive includes one or more of cyclic carbonate compounds, cyclic sulfonate compounds, nitrile compounds, phosphate compounds, and borate compounds.

[0066] In a preferred embodiment, the sulfonate compound is selected from at least one of methylene disulfonate, 1,3-propane sultone, 1,4-butane sultone or 1,3-propene sultone;

[0067] The cyclic carbonate compound is selected from at least one of vinyl ethylene carbonate, fluoroethylene carbonate or the compound shown in structural formula 5.

[0068] In the structural formula 5, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

[0069] The phosphate compound is selected from at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite or the compound shown in Structural Formula 6:

[0070] In the structural formula 6, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, C1-C5 unsaturated hydrocarbon group, halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group;

[0071] The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate. In a preferred embodiment, the compound shown in Structural Formula 5 includes the following compounds:

[0072] In a preferred embodiment, the phosphate compound shown in the structural formula 6 may be at least one of tris(trimethylsilyl)phosphate, tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0073] The film-forming additive can cooperate with the compound shown in structural formula 1 to help form a stable interface film at the interface of the positive and negative electrodes, thereby improving the electrical performance and safety performance of the battery.

[0074] In some embodiments, the low impedance additive includes one or more of vinylene carbonate, vinyl sulfate, propylene sulfate, lithium difluorooxalatoborate, and lithium difluorophosphate.

[0075] Low-impedance additives are beneficial for reducing battery impedance and improving battery performance.

[0076] In some embodiments, the thermal initiator includes an azo compound.

[0077] In some preferred embodiments, the thermal initiator is azobisisobutyronitrile.

[0078] In some embodiments, the electrolyte further comprises a film-forming additive and a low-resistance additive. Based on the total mass of the electrolyte being 100%, the total mass content of the film-forming additive, the low-resistance additive and the thermal initiator is 1% to 20%.

[0079] In some embodiments, based on the total mass of the electrolyte being 100%, the mass content of the thermal initiator is 0.2% to 1.5%.

[0080] In some embodiments, the electrolyte further comprises an electrolyte salt, wherein the electrolyte salt comprises lithium hexafluorophosphate, at least one of LiPO2F2, LiBF4, LiBOB, LiCF3SO3, LiDFOB, LiC(SO2CF3)3, LiN(SO2F)2, and LiClO4;

[0081] The molar concentration of the electrolyte salt in the electrolyte is 0.8 mol / L to 1.35 mol / L;

[0082] In some embodiments, the electrolyte further includes a non-aqueous organic solvent, and the non-aqueous organic solvent includes at least one of an ether solvent, a nitrile solvent, a carbonate solvent, a carboxylate solvent, and a sulfone solvent.

[0083] In some embodiments, the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether with 3 to 10 carbon atoms and a cyclic ether with 3 to 6 carbon atoms. The cyclic ether may be, but is not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), a crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether may be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have low viscosity and can impart high ionic conductivity. One ether compound can be used alone, or two or more can be used in any combination and ratio. There is no special restriction on the amount of ether compound added, and it is arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present application. The volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more in the non-aqueous solvent volume ratio of 100%. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of the ether compounds can be made to meet the above range. When the amount of ether compound added is within the above preferred range, it is easy to ensure the improvement effect of ion conductivity brought about by the increase in lithium ion dissociation degree and the decrease in viscosity of the chain ether. In addition, when the negative electrode active material is a carbon material, the phenomenon of co-embedding of chain ether and lithium ions can be suppressed, so that the input and output characteristics and charge and discharge rate characteristics can reach an appropriate range.

[0084] In some embodiments, the nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

[0085] In some embodiments, the carbonate solvent includes a cyclic carbonate or a chain carbonate. The cyclic carbonate can be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate can be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. However, when using one alone, the lower limit of its content is generally 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the decrease in conductivity due to the decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, and it is easy to achieve a good range of high current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. In addition, the upper limit is generally 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolyte can be improved, thereby contributing to the stability during high temperature storage. The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolyte, is usually more than 15% by volume, preferably more than 20% by volume, and more preferably more than 25% by volume. In addition, usually the volume ratio is less than 90%, preferably less than 85% by volume, and more preferably less than 80% by volume. By making the content of linear carbonate in the above-mentioned scope, it is easy to make the viscosity of nonaqueous electrolyte reach appropriate range, suppress the reduction of ionic conductivity, and then contribute to the output characteristics of nonaqueous electrolyte battery reach good scope. When using two or more linear carbonates in combination, make the total amount of linear carbonate meet the above-mentioned scope.

[0086] In certain embodiments, also can preferably use the linear carbonates with fluorine atoms (hereinafter referred to as " fluorinated linear carbonate ").The number of the fluorine atoms possessed by fluorinated linear carbonate is as long as being more than 1 then has no particular restrictions, but is generally below 6, preferably below 4.When fluorinated linear carbonate has a plurality of fluorine atoms, these fluorine atoms can be bonded on the same carbon, also can be bonded on different carbons.As fluorinated linear carbonate, can enumerate, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives etc.

[0087] Carboxylate solvents include cyclic carboxylates and / or chain carbonates. Examples of cyclic carboxylates include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0088] In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone. Preferably, in the case of a cyclic sulfone, the compound generally has 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of a chain sulfone, the compound generally has 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no particular limitation on the amount of sulfone solvent added, and it can be any amount that does not significantly impair the effect of the lithium-ion battery of the present invention. The volume ratio relative to the total amount of solvent in the non-aqueous electrolyte is generally 0.3% or more, preferably 0.5% or more, and more preferably 1% or more. Furthermore, the volume ratio is generally 40% or less, preferably 35% or less, and more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvents can be adjusted to meet the above range. When the amount of sulfone solvent added is within the above range, an electrolyte solution with excellent high-temperature storage stability tends to be obtained.

[0089] In a preferred embodiment, the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate.

[0090] In some preferred embodiments, the non-aqueous organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, and propyl propionate.

[0091] In some embodiments, based on the total mass of the electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 70% to 90%.

[0092] In a second aspect, the present application provides a semi-solid lithium-ion battery comprising a positive electrode, a negative electrode and the gel electrolyte described above.

[0093] The semi-solid lithium-ion battery containing the above-mentioned gel electrolyte can form an interface film with better thermal stability at the interface of the positive and negative electrodes during the charge and discharge process. At the same time, gel factors and thermal initiators are additionally added to the liquid electrolyte, and the polymerization reaction forms a gel network that "binds" the electrolyte to make it semi-solid. At the same time, it fills the pores of the diaphragm and strengthens the heat deformation resistance of the diaphragm, so that the battery has the characteristics of no inflation and no leakage, thereby improving the intrinsic safety of the lithium-ion battery.

[0094] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer covers a surface of the positive electrode current collector.

[0095] The positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0096] In some embodiments, the positive electrode material layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductor, and the positive electrode active material, the positive electrode binder, and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0097] The positive electrode active materials include ternary materials, lithium iron phosphate, lithium cobalt oxide, etc., which are existing technologies and will not be described in detail here.

[0098] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0099] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0100] Silicon compounds SiO x It can be silicon oxide or silicon monoxide; silicates include lithium silicate.

[0101] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, and will not be further described here. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0102] In some embodiments, the negative electrode material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent, which are blended together to form the negative electrode material layer. The negative electrode binder and negative electrode conductive agent may be the same as the positive electrode binder and positive electrode conductive agent, respectively, and are not further described here.

[0103] In some embodiments, the negative electrode active material includes graphite, silicon-based materials, and the like.

[0104] The silicon-based material is selected from a composite material formed by silicon or a silicon compound and graphite, wherein the silicon element includes at least one of nano silicon particles, silicon nanotubes, silicon nanowires, micro silicon particles and silicon thin films; the silicon compound includes SiO x Or at least one of silicate compounds, wherein 0<x≤2.

[0105] In some embodiments, the battery further includes a separator, which is located between the positive electrode and the negative electrode.

[0106] The diaphragm can be an existing conventional diaphragm, which can be a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, an inorganic-organic composite diaphragm, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and three-layer PP / PE / PP diaphragms.

[0107] The present invention is further described below with reference to the following examples.

[0108] The compounds involved in the following examples and comparative examples are shown in Table 1 below:

[0109] Table 1

[0110] Table 2 Parameter design of examples and comparative examples

[0111] Example 1

[0112] The gel electrolyte and semi-solid lithium ion battery disclosed in the present invention are specifically described, including the following steps:

[0113] 1) Preparation of electrolyte

[0114] Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:PC:EMC=1:1:1, and then 1 mol / L lithium hexafluorophosphate (LiPF6) is added, and then the mass content of the first additive is 2% based on the total mass of the electrolyte is added, and the mass content of the gel factor is 6%, and then other additives with a mass content of 8% are added, wherein the other additives include film-forming additives, which are mixed in a mass ratio of fluoroethylene carbonate:succinonitrile:hexanetrinitrile=4:1:1, a low-impedance additive using a mass content of 1% lithium difluorooxalatoborate and a thermal initiator using a mass content of 1% azobisisobutyronitrile, and the mass ratio of film-forming additive:low-impedance additive:thermal initiator is 6:2:2.

[0115] The mass ratio of compound A2:compound B3:compound C2 in the gel factor is 2:3:1.

[0116] 2) Preparation of the Positive Electrode Plate: Aluminum-doped or coated lithium cobalt oxide, conductive carbon black Super-P, and a binder, polyvinylidene fluoride (PVDF), are uniformly mixed and then dispersed in N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The slurry is evenly coated on both sides of aluminum foil, dried, rolled, and vacuum-dried to form a positive electrode material layer. Aluminum lead wires are then ultrasonically welded to form the positive electrode plate. The plate thickness is 120-150 μm, and the mass percentage of Al in the positive electrode material layer is 0.2%.

[0117] 3) Preparation of negative plate

[0118] The negative electrode active material, artificial graphite, conductive carbon black Super-P, and binders styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC), are mixed in a mass ratio of 94:1:2.5:2.5 and dispersed in deionized water to create a negative electrode slurry. The slurry is then coated on both sides of a copper foil, dried, rolled, and vacuum-dried. Nickel lead wires are then ultrasonically welded to create the negative electrode plate, which is 120-150 μm thick.

[0119] 4) Preparation of battery cells

[0120] A three-layer separator with a thickness of 20 μm was placed between the positive plate and the negative plate, and then the sandwich structure consisting of the positive plate, negative plate and separator was wound. The wound body was flattened and placed in an aluminum foil packaging bag, and vacuum-baked at 75°C for 48 hours to obtain a battery cell ready for liquid injection.

[0121] 5) Battery filling

[0122] In a glove box with a dew point controlled below -40°C, the prepared electrolyte was injected into the battery cell, vacuum-sealed, and left to stand for 24 hours.

[0123] 6) Cell Formation and Gelation: After the cells were allowed to rest at 75°C ± 2°C for 2 hours, the initiator AIBN caused the gelling factor to undergo a thermal polymerization reaction, gelling the electrolyte. The cells were then hot-pressed for the first charge according to the following steps: 0.1C constant current charging to 3.2V, 0.2C constant current charging to 3.65V, and 0.5C constant current charging to 4.15V. The cells were then vacuum-sealed a second time, charged at 0.2C constant current to 4.48V, and then discharged at 0.2C constant current to 3.0V.

[0124] Examples 2 to 26

[0125] Examples 2 to 26 are used to illustrate the gel electrolyte and semi-solid lithium-ion battery disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0126] The types and contents of the compound represented by structural formula 1, the types and contents of the compound represented by structural formula 2, the types and contents of the compound represented by structural formula 3, and the types and contents of the compound represented by structural formula 4 shown in Examples 2 to 26 in Table 2 were used.

[0127] Comparative Examples 1 to 7

[0128] Comparative Examples 1 to 7 are used to compare and illustrate the gel electrolyte and semi-solid lithium-ion battery disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0129] The types and contents of the compound represented by structural formula 1, the types and contents of the compound represented by structural formula 2, the types and contents of the compound represented by structural formula 3, and the types and contents of the compound represented by structural formula 4 shown in comparative examples 1 to 7 in Table 2 were used.

[0130] Safety performance test:

[0131] Battery Thermal Shock Test: This test is conducted in accordance with the relevant standards "GB 31241-2022 Safety Technical Specification for Lithium-ion Batteries and Battery Packs for Portable Electronic Products" or "GB 38031-2020 Safety Requirements for Storage Batteries for Electric Vehicles." Freshly prepared soft-pack battery cells are charged to full charge at a constant current and constant voltage of 0.3C. The cells are then placed in an explosion-proof thermal shock test chamber and heated from ambient temperature to 136°C at a linear rate of 5°C / min, with an error tolerance of ±1°C. This temperature is maintained for 30 minutes, after which heating is stopped and the test is considered complete after the cells cool naturally to 80°C. If the battery catches fire or explodes during the test, it is considered a failure and the test is repeated at a 2°C lower temperature until it passes. If the battery does not catch fire or explode, it is considered a passing temperature and the test is repeated at a 2°C higher temperature until it fails. The highest temperature at which the battery passes the test is defined as the limiting passing temperature.

[0132] During the entire test process, the changes in battery voltage and surface temperature are monitored, and the voltage curve and temperature curve are recorded to facilitate the analysis of the voltage drop inflection point and the escape window. The time from the battery entering the constant temperature stage to the voltage drop is defined as the voltage drop inflection point. The smaller the voltage drop inflection point, the worse the thermal stability of the battery, and vice versa, the better the thermal stability. The length of time from the beginning of the voltage drop to the occurrence of fire or explosion in the battery is defined as the escape window. The smaller the escape window, the higher the thermal risk of the battery, and vice versa, the smaller the thermal risk of the battery. Among the various performance indicators of the above embodiments and comparative examples, in order to make a reasonable comparison of the voltage drop inflection point and the escape window, each group selected a 136°C thermal shock test. Specific test results are shown in Tables 3-5.

[0133] (1) The test results obtained in Examples 1 to 18 and Comparative Examples 1 to 7 are shown in Table 3.

[0134] Table 3

[0135] It can be seen from Tables 1, 2, and 3 that, by comparing Comparative Examples 1-3, 5, and 6 with Examples 1-8, when the gel factor in Comparative Examples 1-3 contains no compound represented by Structural Formula 2, or contains no compound represented by Structural Formula 3, or contains no compound represented by Structural Formula 4, the formation of the polymer gel network is affected, and the prepared batteries undergo a thermal shock test with a low limit passing temperature, a small voltage drop inflection point, and a low escape window; the total mass content of the gel factor in Comparative Examples 5 and 6 is lower than 3% or higher than 10%, and the voltage drop inflection point of the prepared batteries is smaller and the escape window is lower; this indicates that the gel factor must contain the compound represented by Structural Formula 2, the compound represented by Structural Formula 3, and the compound represented by Structural Formula 4 at the same time, and the total mass content of the gel factor in the electrolyte is in the range of 3% to 10%, and the gel factor polymerizes with the help of a thermal initiator to form a polymer gel network, solidify the electrolyte, and reduce leakage and rapid gas production caused by solvent volatilization. Comparative Example 4 is compared with Example 1. The content j of the compound represented by Structural Formula 1 in the electrolyte is less than 0.1%. The prepared battery undergoes a thermal shock test, and the limit passing temperature is low, the voltage drop inflection point is small, and the escape window is low. This indicates that the mass content of the compound represented by Structural Formula 1 in the electrolyte is in the range of 0.1% to 3%. The compound represented by Structural Formula 1 can form an interface film with good thermal stability on the electrode surface during the first electrochemical reaction of the battery, effectively increasing the starting temperature of the battery's self-heating, avoiding desorption of the gel electrolyte and vaporization of the solvent due to heat accumulation, thereby improving the high temperature performance and safety performance of the lithium-ion battery.

[0136] Comparison of Comparative Example 7 with Examples 1-8 shows that when the mass content of the compound represented by Structural Formula 1 in the electrolyte is in the range of 0.1% to 3%, and the total mass content of the gel factor in the electrolyte is in the range of 3% to 10%, and the condition 0.1≤j / k≤1 is satisfied, the compound represented by Structural Formula 1 and the gel factor can give full play to the synergistic effect, forming an interface film with better thermal stability at the interface of the positive and negative electrodes, and at the same time having the characteristics of no bloating and no leakage, thereby improving the safety performance of the lithium-ion battery.

[0137] Comparing Examples 1-8, the mass content j of the compound represented by structural formula 1 added to the electrolyte is in the range of 1 to 3%, and the mass content k of the gel factor is in the range of 5 to 10%. The prepared batteries undergo a thermal shock test, and the limit passing temperature is higher, the voltage drop inflection point is larger, and the escape window is higher. Comparing Examples 1-8 with Examples 15-18, the gel electrolyte satisfies the relationship 0.15≤j / k≤0.4, and the battery has higher safety performance.

[0138] Comparison between Examples 9-14 and Examples 1-8 and 15-18 shows that the mass content of the compound represented by structural formula 2 in the gel factor in the electrolyte is 1% to 6%, the mass content of the compound represented by structural formula 3 in the electrolyte is 1% to 8%, and the mass content of the compound represented by structural formula 4 in the electrolyte is in the range of 1% to 3%, which is conducive to polymerization under the action of a thermal initiator to form a polymer gel network, solidify the electrolyte and reduce leakage and rapid gas production caused by solvent volatilization. At the same time, the filling and supporting effects also make the diaphragm have higher heat-resistant deformation strength, and at the same time, synergize with the compound represented by structural formula 1 to improve the safety performance of the battery.

[0139] (2) The test results obtained in Examples 1 and 19 to 23 are entered in Table 4.

[0140] Table 4

[0141] It can be seen from Tables 1-2 and 4 that as long as the compound added to the electrolyte satisfies the structure of the compound shown in Structural Formula 1, it can cooperate with the gel factor to form an interface film with better thermal stability at the positive and negative electrode interfaces, and at the same time has the characteristics of no swelling and no leakage, thereby improving the safety performance of lithium-ion batteries.

[0142] (3) The test results obtained in Examples 1 and 24 to 26 are entered in Table 5.

[0143] Table 5

[0144] It can be seen from Tables 1-2 and 5 that the gel factor added to the electrolyte, as long as it satisfies the structure of the compound shown in Structural Formula 2, the structure of the compound shown in Structural Formula 3, and the structure of the compound shown in Structural Formula 4, can cooperate with the compound shown in Structural Formula 1 to form an interface film with better thermal stability at the positive and negative electrode interfaces, and at the same time has the characteristics of no inflation and no leakage, thereby improving the safety performance of the lithium-ion battery.

[0145] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gel electrolyte, characterized in that: The gel electrolyte is obtained by polymerizing an electrolyte containing a gel precursor material, the electrolyte includes a first additive, the gel precursor material includes a gel factor and a thermal initiator, the first additive includes a compound shown in structural formula 1, and the gel factor includes compounds shown in structural formula 2, structural formula 3 and structural formula 4. Wherein n is 0 or 1, A is selected from C or O, and X is selected from R1 and R2 are each independently selected from H, R1 and R2 are not simultaneously selected from H, and at least one sulfur atom is contained in X, R1 and R2; w is an integer from 0 to 11, y is an integer from 1 to 8, and z is an integer from 1 to 8; The gel electrolyte satisfies the following relationship: 0.1≤j / k≤1, and 0.1≤j≤3, 3≤k≤10; Wherein, j is the mass content of the first additive in the electrolyte, in %; k is the mass content of the gel factor in the electrolyte, in %.

2. A gel electrolyte according to claim 1, characterized in that: The gel electrolyte satisfies the following relationship: 0.15≤j / k≤0.

4.

3. A gel electrolyte according to claim 1, characterized in that: In the gel factor, the mass content of the compound represented by structural formula 2 in the electrolyte is 1% to 6%, the mass content of the compound represented by structural formula 3 in the electrolyte is 1% to 8%, and the mass content of the compound represented by structural formula 4 in the electrolyte is 1% to 3%.

4. A gel electrolyte according to claim 1, characterized in that: Based on the total mass of the electrolyte being 100%, the mass content j% of the first additive in the electrolyte is 1 to 3%; The mass content k% of the gel factor in the electrolyte is 5-10%.

5. A gel electrolyte according to claim 1, characterized in that: The compound represented by the structural formula 1 is selected from one or more of the following compounds:

6. A gel electrolyte according to claim 1, characterized in that: The compound represented by structural formula 2 is selected from one or more of the following compounds: The compound represented by structural formula 3 is selected from one or more of the following compounds: The compound represented by structural formula 4 is selected from one or more of the following compounds:

7. A gel electrolyte according to claim 1, characterized in that: The electrolyte further comprises a film-forming additive and a low-resistance additive. Taking the total mass of the electrolyte as 100%, the total mass content of the film-forming additive, the low-resistance additive and the thermal initiator is 1% to 20%.

8. A gel electrolyte according to claim 7, characterized in that: The film-forming additive includes one or more of cyclic carbonate compounds, cyclic sulfonate compounds, nitrile compounds, phosphate compounds, and borate compounds.

9. A gel electrolyte according to claim 8, characterized in that: The cyclic sulfonate compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone or 1,3-propylene sultone; The cyclic carbonate compound is selected from at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate or the compound shown in structural formula 5. In the structural formula 5, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group; The phosphate compound is selected from at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite or the compound shown in Structural Formula 6: In the structural formula 6, R 31 , R 32 , R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 , R 32 , R 33 At least one of them is an unsaturated hydrocarbon group; The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate; The nitrile compound is selected from at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

10. A gel electrolyte according to claim 7, characterized in that: The low impedance additive includes one or more of vinylene carbonate, vinyl sulfate, propylene sulfate, lithium difluorooxalatoborate, and lithium difluorophosphate; The thermal initiator includes azo compounds.

11. A gel electrolyte according to claim 10, characterized in that: The thermal initiator is azobisisobutyronitrile.

12. A gel electrolyte according to claim 1, characterized in that: The electrolyte solution further includes a non-aqueous organic solvent and an electrolyte salt, wherein the electrolyte salt includes at least one of lithium hexafluorophosphate, LiPO2F2, LiBF4, LiBOB, LiCF3SO3, LiDFOB, LiC(SO2CF3)3, LiN(SO2F)2, and LiClO4; The molar concentration of the electrolyte salt in the electrolyte is 0.8 mol / L to 1.35 mol / L; The non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylate solvents and sulfone solvents; based on the total mass of the electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 70% to 90%.

13. A semi-solid lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and the gel electrolyte according to any one of claims 1 to 12.

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