Electrolyte and secondary battery

Abstract

The invention provides an electrolyte and a secondary battery. The electrolyte comprises an electrolyte salt, an electrolyte additive and the balance of an organic solvent, and the electrolyte additive comprises a first additive and a second additive; wherein the first additive comprises an isocyanate compound, and the second additive comprises a lithium aluminum hydride-based compound and / or an aluminum hydride organic compound. The combination of the first additive and the second additive provided by the invention not only can efficiently remove trace moisture and hydrofluoric acid impurities in the electrolyte and improve the stability of electrolyte salt, but also can improve the film-forming stability and film-forming quality of an SEI (Solid Electrolyte Interphase) film and remarkably improve the cycle performance and high-temperature storage performance of a secondary battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and in particular relates to an electrolyte and a secondary battery. Background Art

[0002] Lithium-ion batteries have the characteristics of high discharge voltage, high energy density and low self-discharge. They have extremely broad application prospects in 3C products (a general term for computers, communications and consumer electronics), electric vehicles and energy storage fields.

[0003] In recent years, with the increasing global reliance on renewable energy sources (such as solar and wind power), demand for lithium-ion batteries in the power battery sector has skyrocketed. Simultaneously, market requirements for battery energy density and power performance have also become increasingly stringent. Reducing battery impedance while maintaining a certain energy density has become a technical challenge within the industry, and achieving a balance between these performance aspects in battery cells is difficult.

[0004] As an important component of lithium-ion batteries, the performance of the electrolyte directly affects the stability of the battery. Existing electrolytes have technical problems such as high impedance and short lifespan. One of the reasons is that a small amount of water inevitably enters the battery during the manufacturing process. After the electrolyte is subsequently injected, trace amounts of water will cause the lithium hexafluorophosphate to decompose, resulting in a decrease in the lithium salt content. At the same time, the decomposition of lithium hexafluorophosphate also produces hydrofluoric acid, which corrodes the SEI interface film that plays a passivating role, causing the electrochemical performance of the lithium-ion battery to deteriorate. Therefore, controlling the water content in the electrolyte is key to improving the performance and lifespan of lithium-ion batteries.

[0005] Based on the above research, how to optimize the composition of the electrolyte has important practical significance for improving the cycle life and storage performance of lithium-ion batteries. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention aims to provide an electrolyte and a secondary battery. The combination of the first and second additives provided by the present invention not only efficiently removes trace moisture and hydrofluoric acid impurities from the electrolyte, improving the stability of the electrolyte salt, but also enhances the stability and quality of the SEI film, significantly improving the cycling performance and high-temperature storage performance of the secondary battery.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electrolyte solution, comprising an electrolyte salt and an electrolyte additive, with the balance being an organic solvent, wherein the electrolyte additive comprises a first additive and a second additive;

[0009] Wherein, the first additive includes an isocyanate compound, and the second additive includes a lithium aluminum hydride-based compound and / or an aluminum hydride organic compound.

[0010] The present invention effectively solves the technical problems of high internal impedance and short cycle life of the battery caused by impurities such as trace water and hydrofluoric acid in the electrolyte by introducing a combined additive of isocyanate compounds and compounds containing aluminum elements and negative hydrogen ions into the electrolyte, thereby comprehensively improving the cycle stability and high-temperature performance of the secondary battery without significantly increasing the battery impedance.

[0011] Specifically, there is a synergistic effect between isocyanate compounds and compounds containing aluminum and hydrogen ions. On the one hand, the isocyanate group can react with the moisture absorbed in the secondary battery and the generated hydrofluoric acid, reducing the corrosion of the SEI film and the occurrence of side reactions, thereby reducing the internal impedance of the battery. On the other hand, the compound containing aluminum and hydrogen ions has a high reactivity and easily reacts with trace water and hydrofluoric acid in the electrolyte, thereby reducing damage to the SEI interface film. In addition, the above-mentioned compound containing aluminum and hydrogen ions can also react with the organic component LEDC ((CH2OCO2Li)2) in the SEI film to transform it into a more stable inorganic component Li2CO3, thereby improving the high-temperature stability of the SEI film and further improving the high-temperature performance of the secondary battery.

[0012] In this application, the term "SEI" stands for solid electrolyte interface. During the initial charge and discharge process of a liquid lithium-ion battery, the electrode material and electrolyte react at the solid-liquid interface, forming a passivation layer covering the surface of the electrode material. This passivation layer, a type of interface layer, has the characteristics of a solid electrolyte: an electronic insulator but an excellent conductor of lithium ions. Lithium ions can freely embed and de-embedding through this passivation layer, hence its name, "solid electrolyte interface."

[0013] Preferably, the lithium aluminum hydride-based compound includes any one or a combination of at least two of lithium aluminum hydride (LiAlH4), lithium tri(tert-butoxy)aluminum hydride (LTBA) or lithium aluminum hydride-boron trifluoride ether complex.

[0014] Preferably, the aluminum hydride organic compound includes diisobutylaluminum hydride (DIBAL-H) ​​and / or dimethoxyethoxyaluminum hydride.

[0015] In the present invention, lithium aluminum hydride is taken as an example, and the reaction formula of its reaction with water and the organic component LEDC in the SEI film is as follows:

[0016] LiAlH4+4H2O=LiOH+Al(OH)3+4H2(1);

[0017]

[0018] Preferably, based on the total mass of the electrolyte as 100%, the mass percentage of the second additive is 0.01%-0.2%, for example, it can be 0.01%, 0.015%, 0.02%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18% or 0.2%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0019] By regulating the mass percentage of the second additive, the present invention comprehensively improves the stability of the electrolyte and the quality of the SEI film, thereby reducing the internal impedance of the battery and improving the battery's cycling stability. Using a lower content of the second additive would reduce these effects; using a higher content would increase the electrolyte impedance.

[0020] Preferably, the isocyanate compound includes a monoisocyanate compound and / or a diisocyanate compound, the chemical formula of the monoisocyanate compound is O=C=NR, and the chemical formula of the diisocyanate compound is O=C=NRN=C=O, wherein R is selected from at least one of a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group.

[0021] Specifically, the alkyl group exemplarily includes any one of methyl, propyl, butyl or hexyl; the aryl group exemplarily includes any one of phenyl or biphenyl.

[0022] In the present invention, the substituted group includes at least one of a halogen atom or a sulfonyl group.

[0023] Preferably, the monoisocyanate compound includes any one of methyl isocyanate, n-butyl isocyanate, tert-butyl isocyanate, p-toluenesulfonyl isocyanate or 2-p-fluoroisocyanate, or a combination of at least two thereof.

[0024] Preferably, the diisocyanate compound includes any one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) or hexamethylene diisocyanate (HDI), or a combination of at least two thereof.

[0025] Preferably, based on the total mass of the electrolyte as 100%, the mass percentage of the first additive is 0.01%-0.2%, for example, it can be 0.01%, 0.015%, 0.02%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18% or 0.2%, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0026] By regulating the mass percentage of the first additive, the present invention effectively removes trace moisture and hydrofluoric acid impurities from the electrolyte, thereby improving the stability of the electrolyte salt. Using a lower content of the first additive would result in less pronounced effects. Using a higher content of the first additive would result in excessive isocyanate groups remaining in the electrolyte for a long time, leading to slow decomposition and deterioration of the overall performance of the secondary battery.

[0027] Preferably, the electrolyte additive further includes a third additive.

[0028] Preferably, the third additive includes any one or a combination of at least two of substituted or unsubstituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sultone compounds, nitrile compounds, aromatic compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds or borate compounds.

[0029] In the present invention, the substituted or unsubstituted cyclic carbonate compound illustratively includes at least one of a cyclic carbonate compound containing an unsaturated bond or a halogen-substituted cyclic carbonate compound.

[0030] Preferably, based on the total mass of the electrolyte as 100%, the mass percentage of the third additive is 0.1%-5%, for example, it can be 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4% or 5%, etc., and is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable.

[0031] Preferably, the electrolyte salt includes a lithium salt.

[0032] Preferably, the lithium salt includes any one or a combination of at least two of LiPF6, Li(FSO2)2N (LiFSI) or Li(CF3SO2)2N (LiTFSI), preferably LiPF6.

[0033] Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the electrolyte salt is 5%-20%, for example, it can be 5%, 8%, 10%, 12%, 15%, 18% or 20%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0034] Preferably, the organic solvent includes a carbonate solvent and / or a carboxylate solvent.

[0035] Preferably, the carbonate solvent includes any one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate or ethyl propyl carbonate, or a combination of at least two thereof.

[0036] Preferably, the carboxylate solvent includes any one of ethyl acetate, ethyl propionate, propyl propionate, methyl propionate or methyl acetate, or a combination of at least two thereof.

[0037] In a second aspect, the present invention provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the electrolyte comprises the electrolyte as described in the first aspect.

[0038] Preferably, the secondary battery satisfies the following: 0.6% ≤ (A + B) / C ≤ 20%, more preferably 3.33% ≤ (A + B) / C ≤ 10%, wherein A is the mass percentage of the first additive in the total electrolyte, B is the mass percentage of the second additive in the total electrolyte, and C is the electrolyte injection coefficient, expressed in g / Ah. C can be, for example, 2.0 g / Ah, 2.2 g / Ah, 2.5 g / Ah, 2.8 g / Ah, 3.0 g / Ah, 3.2 g / Ah, or 3.5 g / Ah. Therefore, the secondary battery can be, for example, 0.6%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0039] It should be noted that the "filling coefficient" refers to the ratio of the electrolyte filling volume to the rated capacity of the battery. In the present invention, the filling volume can be approximated as the electrolyte retention volume. The rated capacity of a battery refers to the amount of electricity discharged when the battery is discharged to the cutoff voltage under specified charge and discharge conditions.

[0040] In the present invention, the establishment of the equation 0.6%≤(A+B) / C≤20% only refers to the establishment of the index value relationship.

[0041] Preferably, the C satisfies: 2.0 g / Ah≤C≤3.5 g / Ah, for example, it can be 2.0 g / Ah, 2.2 g / Ah, 2.5 g / Ah, 2.8 g / Ah, 3.0 g / Ah, 3.2 g / Ah or 3.5 g / Ah, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0042] By regulating the content of the first additive, the content of the second additive, and the electrolyte injection coefficient to satisfy the above relationship, the present invention can achieve good cycle performance and high-temperature storage performance for the secondary battery by using a small amount of the first additive and the second additive combination, even when the battery injection coefficient C is low (for example, C ≤ 2.5g / Ah), that is, the electrolyte injection volume is small. This is mainly because the combination of the first additive and the second additive allows other electrolyte additives (such as vinylene carbonate) to generate more inorganic components, thereby improving the film formation stability and film quality of the SEI film.

[0043] If (A+B) / C is less than 0.6%, the combined additive content of the first and second additives is relatively low, and the absorption of moisture and hydrofluoric acid is not significant, with little impact on the overall performance of the secondary battery. If (A+B) / C is greater than 20%, the combined additive content is relatively high, and the excessive presence of isocyanate groups in the electrolyte over a long period of time will cause slow decomposition, which in turn degrades the electrochemical performance of the secondary battery.

[0044] Preferably, the active material of the positive electrode sheet includes at least one positive electrode material that can insert and remove lithium ions.

[0045] Preferably, the positive electrode material includes LiCoO2, LiNi x Co y Mn z O2、LiNi x Mn y O2, LiMn2O4, LiMnO2, Li2MnO4, Li 1+a Mn 1-x M x O2、LiCo 1-x M x O2、LiMn 1-x M x O4、Li2Mn 1-x O4, LiFePO4, LiMnPO4, LiCoPO4 or LiFe 1-x M x Any one or a combination of at least two of PO4, wherein M is selected from any one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V or Ti, 0≤a<0.2, 0≤x≤2, 0≤y≤2, 0≤z≤2.

[0046] Specifically, a can be, for example, 0, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15 or 0.18; x can be, for example, 0, 0.05, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2; y can be, for example, 0, 0.05, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2; z can be, for example, 0, 0.05, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2, and the like. The values ​​are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the active material of the negative electrode sheet includes at least one negative electrode material that can insert and remove lithium ions.

[0048] Preferably, the negative electrode material includes any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon-oxygen negative electrode, silicon-carbon negative electrode or metallic lithium, or a combination of at least two thereof.

[0049] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The present invention provides an electrolyte. By introducing a combined additive of an isocyanate compound and a compound containing aluminum and negative hydrogen ions into the electrolyte, the technical problems of high internal impedance and short cycle life of the battery caused by impurities such as trace water and hydrofluoric acid in the electrolyte are effectively solved, thereby comprehensively improving the cycle stability and high-temperature performance of the secondary battery without significantly increasing the battery impedance.

[0052] Specifically, there is a synergistic effect between isocyanate compounds and compounds containing aluminum and hydrogen ions. On the one hand, the isocyanate group can react with the moisture absorbed in the secondary battery and the generated hydrofluoric acid, reducing the corrosion of the SEI film and the occurrence of side reactions, thereby reducing the internal impedance of the battery. On the other hand, the compound containing aluminum and hydrogen ions has a high reactivity and easily reacts with trace water and hydrofluoric acid in the electrolyte, thereby reducing damage to the SEI interface film. In addition, the above-mentioned compound containing aluminum and hydrogen ions can also react with the organic component LEDC ((CH2OCO2Li)2) in the SEI film to transform it into a more stable inorganic component Li2CO3, thereby improving the high-temperature stability of the SEI film and further improving the high-temperature performance of the secondary battery. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0054] Example 1

[0055] This embodiment provides an electrolyte, which includes an electrolyte additive, a lithium salt, and an organic solvent.

[0056] The electrolyte additives include a first additive, a second additive, and a third additive, wherein the first additive is hexamethylene diisocyanate (HDI), the second additive is lithium aluminum hydride (LiAlH4), and the third additive is vinylene carbonate (VC).

[0057] Based on the total mass of the electrolyte as 100%, the mass percentage of the first additive is 0.05 wt%, the mass percentage of the second additive is 0.05 wt%, and the mass percentage of the third additive is 1 wt%. The lithium salt is lithium hexafluorophosphate, and the mass percentage of the lithium hexafluorophosphate is 14 wt%.

[0058] The organic solvent includes ethylene carbonate (EC), ethyl acetate (EA) and dimethyl carbonate (DMC), and the mass ratio of ethylene carbonate, ethyl acetate and dimethyl carbonate is 25:45:14.8.

[0059] This embodiment also provides a method for preparing the above electrolyte, which comprises the following steps:

[0060] In a glove box with qualified water and oxygen content, ethylene carbonate, ethyl acetate and dimethyl carbonate are first stirred and mixed according to the formula, and then lithium hexafluorophosphate is added and stirred evenly, and then the first additive, the second additive and the third additive are added and stirred evenly to obtain the electrolyte.

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 is that the electrolyte additives are composed as follows: the electrolyte additives include a first additive, a second additive, and a third additive. The first additive is hexamethylene diisocyanate (HDI); the second additive is lithium aluminum hydride (LiAlH4); and the third additive is vinylene carbonate (VC).

[0063] Based on the total mass of the electrolyte as 100%, the mass percentage of the first additive was 0.15 wt%, the mass percentage of the second additive was 0.15 wt%, and the mass percentage of the third additive was 1 wt%. The lithium salt was lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate was 13 wt%. The balance was an organic solvent. The mass ratio of ethylene carbonate, ethyl acetate, and dimethyl carbonate remained unchanged. All other conditions were the same as in Example 1.

[0064] Example 3

[0065] The difference between this embodiment and embodiment 1 is that the electrolyte additives are composed as follows: the electrolyte additives include a first additive, a second additive, and a third additive. The first additive is toluene diisocyanate (TDI); the second additive is lithium aluminum hydride (LiAlH4); and the third additive is vinylene carbonate (VC).

[0066] Based on the total mass of the electrolyte as 100%, the mass percentage of the first additive was 0.01 wt%, the mass percentage of the second additive was 0.01 wt%, and the mass percentage of the third additive was 1 wt%. The lithium salt was lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate was 18 wt%. The balance was an organic solvent. The mass ratio of ethylene carbonate, ethyl acetate, and dimethyl carbonate remained unchanged. All other conditions were the same as in Example 1.

[0067] Example 4

[0068] The difference between this embodiment and embodiment 1 is that the electrolyte additive composition is as follows: the electrolyte additive includes a first additive, a second additive, and a third additive. The first additive is hexamethylene diisocyanate (HDI); the second additive is lithium tri(tert-butoxy)aluminum hydride (LTBA); and the third additive is vinylene carbonate (VC).

[0069] Based on the total mass of the electrolyte as 100%, the mass percentage of the first additive was 0.2 wt%, the mass percentage of the second additive was 0.2 wt%, and the mass percentage of the third additive was 1 wt%. The lithium salt was lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate was 8 wt%. The balance was an organic solvent. The mass ratio of ethylene carbonate, ethyl acetate, and dimethyl carbonate remained unchanged. All other conditions were the same as in Example 1.

[0070] Example 5

[0071] The difference between this embodiment and embodiment 1 is that, except for adjusting the mass percentage of the first additive to 1 wt % and reducing the content of the organic solvent by the same mass ratio, the other aspects are the same as those of embodiment 1.

[0072] Example 6

[0073] The difference between this embodiment and embodiment 1 is that, except for adjusting the mass percentage of the second additive to 1 wt % and reducing the content of the organic solvent by the same mass ratio, the other aspects are the same as those of embodiment 1.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is that, except that the electrolyte additive is adjusted to not contain the first additive and an equal mass of the second additive is replaced, everything else is the same as Example 1.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that, except that the electrolyte additive is adjusted to not contain the second additive and an equal mass of the second additive is replaced by the first additive, everything else is the same as Example 1.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 1 is that the lithium aluminum hydride in the second additive is replaced by vinylene carbonate with an equal mass percentage, and the other contents are the same as those in Example 1.

[0080] Comparative Example 4

[0081] The difference between this comparative example and Example 1 is that, except that the electrolyte additives are adjusted to not contain the first additive and the second additive, and their equal mass is replaced with organic solvent, everything else is the same as Example 1.

[0082] Application Example 1

[0083] This application example provides a lithium-ion battery, which includes an artificial graphite negative electrode, a lithium iron phosphate positive electrode, a separator and the electrolyte provided in Example 1, wherein the electrolyte injection coefficient is 3.0, and the lithium-ion battery satisfies: (A+B) / C=3.33%.

[0084] This application example also provides a method for preparing the above-mentioned lithium-ion battery, the method comprising the following steps:

[0085] The positive electrode active material lithium iron phosphate (LiFePO4), conductive agent Super-P and binder PVDF were dissolved in solvent N-methylpyrrolidone at a mass ratio of 94:3.0:3.0 and mixed evenly to prepare the positive electrode slurry. The positive electrode slurry was evenly coated on the current collector aluminum foil with a coating amount of 18 mg / cm 2 , then dried at 85°C, cold pressed, trimmed, cut and slit, dried at 85°C under vacuum conditions for 4 hours, and welded to the tabs to produce a positive electrode sheet for a lithium-ion secondary battery that meets the requirements;

[0086] The negative electrode active material artificial graphite, conductive agent Super-P, thickener CMC and binder SBR were dissolved in solvent deionized water at a mass ratio of 96.5:1.0:1.0:1.5 and mixed evenly to prepare the negative electrode slurry. The negative electrode slurry was evenly coated on the current collector copper foil with a coating amount of 8.3 mg / cm 2 , then dried at 85°C, cold pressed, trimmed, cut and slit, dried at 110°C under vacuum conditions for 4 hours, and welded to the tabs to produce a negative electrode sheet for a lithium-ion secondary battery that meets the requirements;

[0087] The electrolyte, positive electrode sheet, negative electrode sheet and separator (PE film) obtained in Example 1 were laminated to form a battery with a thickness of 8 mm, a width of 60 mm and a length of 130 mm, and vacuum baked at 85°C for 10 h, injected with electrolyte, and allowed to stand for 24 h. Thereafter, the battery was charged to 3.65 V with a constant current of 0.1 C (200 mA), and then charged at a constant voltage of 3.65 V until the current dropped to 0.05 C (100 mA). Then, the battery was discharged to 2.5 V with a constant current of 0.1 C (200 mA), and the charge and discharge were repeated twice. Finally, the battery was charged to 3.3 V with a constant current of 0.1 C (200 mA) to obtain the lithium-ion battery.

[0088] Application Example 2

[0089] The difference between this application example and application example 1 is that the electrolyte used is the electrolyte provided in Example 2, the electrolyte injection coefficient is 3, and the lithium-ion battery satisfies: (A+B) / C=10%. The rest is the same as application example 1.

[0090] Application Example 3

[0091] The difference between this application example and application example 1 is that the electrolyte used is the electrolyte provided in Example 3, the electrolyte injection coefficient is 3.36, and the lithium-ion battery satisfies: (A+B) / C=0.6%. Other aspects are the same as application example 1.

[0092] Application Example 4

[0093] The difference between this application example and application example 1 is that the electrolyte used is the electrolyte provided in Example 4, the electrolyte injection coefficient is 2.0, and the lithium-ion battery satisfies: (A+B) / C=20%. Other aspects are the same as application example 1.

[0094] Application Example 5

[0095] The difference between this application example and application example 1 is that the electrolyte used is the electrolyte provided in Example 5, the electrolyte injection coefficient is 4.4, and the lithium-ion battery satisfies: (A+B) / C=25%. Other aspects are the same as application example 1.

[0096] Application Example 6

[0097] The difference between this application example and application example 1 is that the electrolyte used is the electrolyte provided in Example 6, the electrolyte injection coefficient is 4.4, and the lithium-ion battery satisfies: (A+B) / C=25%. Other aspects are the same as application example 1.

[0098] Comparative Application Examples 1 to 4 provide a lithium-ion battery. Comparative Application Examples 1 to 4 are the same as Application Example 1 except that the electrolytes provided in Comparative Examples 1 to 4 are used as electrolytes.

[0099] The lithium-ion batteries provided in the above application examples and comparative application examples were subjected to performance tests using the following methods:

[0100] (1) Storage performance test method:

[0101] At 25°C, the lithium ion secondary batteries prepared in the embodiment and the comparative example are first charged to 3.65V with a constant current of 1C, and further charged at a constant voltage of 3.65V to a current of 0.05C, and then discharged to 2.5V with a constant current of 1C. The discharge capacity is the discharge capacity of the lithium ion secondary battery before high-temperature storage; the lithium ion secondary battery is then charged to 3.65V with a constant current of 1C, and the lithium ion secondary battery is stored at 60°C for 30 days. After the storage is completed, the lithium ion secondary battery is placed in a 25°C environment, and then discharged to 2.5V with a constant current of 0.5C. The lithium ion secondary battery is then charged to 3.65V with a constant current of 1C, and further charged to a current of 1C with a constant voltage of 3.65V, and then discharged to 2.5V with a constant current of 1C. The last discharge capacity is the discharge capacity of the lithium ion secondary battery after high-temperature storage. Capacity retention rate of lithium ion secondary battery after high-temperature storage (%)=[discharge capacity of lithium ion secondary battery after high-temperature storage / discharge capacity of lithium ion secondary battery before high-temperature storage]×100%.

[0102] (2) Cyclic performance test method:

[0103] The fast-charge cycle performance of the lithium-ion secondary batteries prepared in the examples and comparative examples was tested. The specific method was as follows: at 45°C, the lithium-ion secondary batteries were first charged to 3.65V at a constant current of 4C (8000mA), then charged at a constant voltage of 3.65V to a current of 0.05C, and then discharged at a constant current of 1C (2000mA) to 2.5V. This constituted one charge-discharge cycle, and the discharge capacity was the discharge capacity of the first cycle. The lithium-ion secondary batteries were subjected to cyclic charge-discharge testing in this manner, and the discharge capacity after the 800th cycle was measured.

[0104] (3) High temperature storage gas production test:

[0105] After the high-temperature storage test, the lithium-ion battery was stored at 60°C for 30 days. After the storage period, the lithium-ion secondary battery was placed in a 25°C environment. The volume of the battery was tested using the water displacement method, and the thickness of the battery was measured using a micrometer. The lithium-ion secondary battery was then discharged to 2.5V at a constant current of 0.5C, and then charged to 3.65V at a constant current of 1C. It was further charged at a constant voltage of 3.65V to a current of 1C, and then discharged to 2.5V at a constant current of 1C. The last discharge capacity was the discharge capacity of the lithium-ion secondary battery after high-temperature storage. The battery volume expansion rate = (volume after storage / volume before storage - 1)%.

[0106] (4) DC internal resistance test:

[0107] At 25°C, the lithium-ion secondary batteries prepared in the examples and comparative examples were first charged to 3.65V at a constant current of 1C. They were then further charged at a constant voltage of 3.65V to a current of 0.05C. The batteries were then discharged at a constant current of 0.5C for 1 hour, maintaining a state of charge (SOC) of 50%. After standing for 10 minutes, the voltage V1 was recorded. The batteries were then discharged at a current of I (I = 5C) for 10 seconds, and the discharge end voltage V2 was recorded. The battery's discharge DC internal resistance (DCIR) is calculated as: DCIR = (V1 - V2) / I, expressed in mΩ.

[0108] The above test results are shown in Table 1.

[0109] Table 1

[0110]

[0111]

[0112] As can be seen from Table 1, the comparison of Application Example 1-Application Example 4 and Comparative Application Example 1-Comparative Application Example 4 shows that the first additive containing an isocyanate group in the electrolyte provided by the present invention and the second additive containing an aluminum element and a hydrogen anion have a synergistic effect, which can react with the moisture absorbed in the battery and the generated hydrofluoric acid impurities, thereby reducing the corrosion effect on the SEI film and the occurrence of side reactions, reducing the internal impedance of the lithium-ion battery, and improving the high-temperature cycle and storage performance of the lithium-ion battery.

[0113] From the comparison of Application Example 5 and Application Example 6, it can be seen that the present invention improves the comprehensive performance of lithium-ion batteries by regulating the content of the two additives and the injection coefficient of the electrolyte to an appropriate range. When the content of the first additive containing an isocyanate group or the second additive containing an aluminum element and a hydrogen anion is low, the improvement effect on the lithium-ion battery is not obvious. When the content of the first additive containing an isocyanate group or the second additive containing an aluminum element and a hydrogen anion is high, excess isocyanate groups and hydrogen anion compounds remain in the battery. Since they are easily decomposed at high temperatures, the internal resistance of the lithium-ion battery increases and the comprehensive performance deteriorates.

[0114] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises an electrolyte salt and an electrolyte additive, with the balance being an organic solvent, wherein the electrolyte additive comprises a first additive and a second additive; Wherein, the first additive includes an isocyanate compound, and the second additive includes a lithium aluminum hydride-based compound and / or an aluminum hydride organic compound.

2. The electrolyte according to claim 1, characterized in that The lithium aluminum hydride-based compound includes any one of lithium aluminum hydride, lithium tri(tert-butoxy)aluminum hydride, or lithium aluminum hydride-boron trifluoride ether complex, or a combination of at least two thereof; Preferably, the aluminum hydride organic compound comprises diisobutylaluminum hydride and / or dimethoxyethoxyaluminum hydride; Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the second additive is 0.01%-0.2%.

3. The electrolyte according to claim 1 or 2, characterized in that The isocyanate compound includes a monoisocyanate compound and / or a diisocyanate compound, the chemical formula of the monoisocyanate compound is O=C=NR, and the chemical formula of the diisocyanate compound is O=C=NRN=C=O, wherein R is selected from at least one of a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; Preferably, the monoisocyanate compound includes any one or a combination of at least two of methyl isocyanate, n-butyl isocyanate, tert-butyl isocyanate, p-toluenesulfonyl isocyanate or 2-p-fluoroisocyanate; Preferably, the diisocyanate compound includes any one of toluene diisocyanate, diphenylmethane diisocyanate or hexamethylene diisocyanate, or a combination of at least two thereof; Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the first additive is 0.01%-0.2%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The electrolyte additive further includes a third additive; Preferably, the third additive comprises any one or a combination of at least two of substituted or unsubstituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sultone compounds, nitrile compounds, aromatic compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds or borate compounds; Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the third additive is 0.1%-5%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte salt includes a lithium salt; Preferably, the lithium salt includes any one of LiPF6, Li(FSO2)2N or Li(CF3SO2)2N or a combination of at least two thereof, preferably LiPF6; Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the electrolyte salt is 5%-20%.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The organic solvent includes a carbonate solvent and / or a carboxylate solvent; Preferably, the carbonate solvent includes any one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate or ethyl propyl carbonate, or a combination of at least two thereof; Preferably, the carboxylate solvent includes any one of ethyl acetate, ethyl propionate, propyl propionate, methyl propionate or methyl acetate, or a combination of at least two thereof.

7. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the electrolyte comprises the electrolyte according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, wherein: The secondary battery satisfies: 0.6%≤(A+B) / C≤20%, wherein A is the mass percentage of the first additive in the total electrolyte, B is the mass percentage of the second additive in the total electrolyte, and C is the injection coefficient of the electrolyte, in g / Ah.

9. The secondary battery according to claim 8, characterized in that The C satisfies: 2.0g / Ah≤C≤3.5g / Ah.

10. The secondary battery according to any one of claims 7 to 9, characterized in that: The active material of the positive electrode sheet includes at least one positive electrode material that can insert and remove lithium ions; Preferably, the positive electrode material includes LiCoO2, LiNi x Co y Mn z O2、LiNi x Mn y O2, LiMn2O4, LiMnO2, Li2MnO4, Li 1+a Mn 1-x M x O2、LiCo 1-x M x O2、LiMn 1-x M x O4、Li2Mn 1-x O4, LiFePO4, LiMnPO4, LiCoPO4 or LiFe 1-x M x Any one or a combination of at least two of PO4, wherein M is selected from any one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V or Ti, 0≤a<0.2, 0≤x≤2, 0≤y≤2, 0≤z≤2; Preferably, the active material of the negative electrode sheet includes at least one negative electrode material that can insert and remove lithium ions; Preferably, the negative electrode material includes any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon-oxygen negative electrode, silicon-carbon negative electrode or metallic lithium, or a combination of at least two thereof.

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