Quick-charging electrolyte additive, quick-charging electrolyte containing same and secondary battery

Abstract

The invention provides a fast-charging electrolyte additive, a fast-charging electrolyte containing the fast-charging electrolyte additive and a secondary battery. The fast charging electrolyte additive includes a boric acid ester compound having a sulfonyl group. The borate compound additive provided by the invention can form a stable SEI film on the surface of a negative electrode material, and is beneficial to promoting dissociation of lithium salt and inhibiting decomposition of an electrolyte, so that the interface stability, the ion transmission performance and the oxidation stability of the electrolyte are comprehensively improved, and the fast charging performance and the high-voltage performance of a lithium ion battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and in particular relates to a fast-charge electrolyte additive, a fast-charge electrolyte containing the same, and a secondary battery. Background Art

[0002] Electrolyte is an important component of lithium-ion batteries, among which the development of ethylene carbonate (EC)-based electrolyte was the key to the commercialization of lithium-ion batteries in 1991. However, the energy market has put forward more, higher, and even more stringent requirements and demands for the improvement of battery energy density and the refinement of application scenarios, which makes traditional electrolytes prone to serious side reactions under extreme working conditions, leading to the failure of lithium-ion batteries. For example, traditional electrolytes are prone to continuous reaction and decomposition on the surface of repeatedly cracked / crushed high-specific-capacity silicon-based negative electrode materials, causing the electrolyte to dry up and the capacity to decay suddenly. At the same time, under high voltage conditions, traditional electrolytes are prone to oxidation reactions on the surface of the oxide positive electrode, and the solvent dehydrogenation reaction is also caused by the dehydrogenation reaction of the solvent. + Easy with PF6 - The reaction forms HF and corrodes the positive electrode. In addition, when the conventional EC-based electrolyte is operated at high rate conditions, Li + -EC interaction is strong, making it difficult to desolvate at the battery negative electrode interface, forming a highly polarized interface that leads to a decrease in battery capacity or the formation of lithium dendrites.

[0003] In addition, the commonly used electrolyte solvents have a high organic component after film formation and a low lithium fluoride inorganic component, as well as poor kinetic performance and SEI film stability. They lack flame retardant function, which in turn affects the safety of lithium-ion batteries. At present, the electrolyte additives disclosed in the prior art (such as 1,3-propane sultone, 1,3-propylene sultone and vinylene carbonate, etc.) can play a role in protecting the negative electrode material to a certain extent, but the SEI film they form has high impedance characteristics, which further limits the power performance of lithium-ion batteries. What's more, the existing technology also has shortcomings in improving the dissociation efficiency of lithium salts and enhancing the oxidation stability of electrolytes, making it difficult to meet the growing demand for high-performance batteries.

[0004] Therefore, in this field, how to optimize the electrolyte components has important practical significance for improving the energy density, fast charging capability and other functions of lithium-ion batteries. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to provide a fast-charge electrolyte additive, a fast-charge electrolyte, and a secondary battery containing the same. The borate compound additive provided by the present invention can form a stable SEI film on the surface of the negative electrode material, while also helping to promote the dissociation of lithium salts and inhibit the decomposition of the electrolyte, thereby comprehensively improving the interfacial stability, ion transport performance, and oxidative stability of the electrolyte, thereby improving the fast-charge performance and high-voltage performance of lithium-ion batteries.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a fast charge electrolyte additive, wherein the fast charge electrolyte additive comprises a borate compound having the structure shown in formula (1):

[0008]

[0009] wherein L1 is selected from substituted or unsubstituted pyrazole groups, substituted or unsubstituted C6-C 10 any one of an aryl group or a substituted or unsubstituted pyrrolopyridine group, and L2 is selected from a substituted or unsubstituted C6-C 10 Aryl.

[0010] In the present invention, the C6-C 10 The aryl group illustratively includes at least one of a phenyl group and a naphthyl group.

[0011] The present invention effectively solves the technical problems of poor oxidation resistance, low ionic conductivity and high interface impedance between the electrolyte and the negative electrode material by introducing a borate compound additive having a sulfonyl group into the electrolyte, thereby comprehensively improving the cycle stability and rate performance of the electrolyte at high voltage.

[0012] Specifically, the sulfonyl group in the additive structure can be preferentially reduced on the surface of the negative electrode material to form a low-impedance polymer film, thereby better protecting the interface of the silicon-based negative electrode material and reducing the interface impedance between it and the electrolyte, thereby improving the cycle performance of the lithium-ion battery at high voltage; secondly, the borate group in the additive has a certain Lewis acidity and can complex PF6 - Anion or F -anions, thereby promoting the dissociation of lithium salts, thereby improving the ionic conductivity of the electrolyte; finally, the borate groups contained in the additive can form stable complexes with Lewis basic solvents such as ethylene carbonate (EC) through BO bond coordination, inhibiting the dehydrogenation reaction of EC solvents under high pressure, reducing the generation of gaseous by-products (CO2 and C2H4), and ultimately improving the oxidation stability of EC-based electrolytes, widening the oxidation potential window of lithium-ion batteries by 0.1V-0.3V, thereby significantly improving the safety and energy density of lithium-ion batteries.

[0013] Further preferably, the fast charge electrolyte additive includes a compound having the structure shown in formula (2) and / or a compound having the structure shown in formula (3):

[0014]

[0015]

[0016] Wherein, R1 and R2 are each independently selected from any one of a hydrogen atom or an unsubstituted C1-C3 alkyl group, R3 and R4 are each independently selected from any one of a substituted or unsubstituted phenyl group, and R5 is selected from any one of a halogen atom or a cyano group.

[0017] Preferably, the substituted group comprises a C1-C3 alkyl group.

[0018] In the present invention, the C1-C3 alkyl group exemplarily includes any one of methyl, ethyl, n-propyl or isopropyl.

[0019] Among them, the strong electron-withdrawing effect of the cyano group itself enhances the Lewis acidity of the borate group, making it more effective in complexing PF6 - Anions and F - Anions further promote the dissociation of lithium salts, thereby improving the ionic conductivity of the electrolyte.

[0020] In addition, the present invention further preferably contains a substituted or unsubstituted phenylsulfonyl pyrazole group, which is conducive to forming a passivation film on the positive electrode surface and further improving the high-voltage cycle performance and safety of the electrolyte.

[0021] Preferably, the halogen atom includes any one of a fluorine atom and a chlorine atom.

[0022] More preferably, the fast charge electrolyte additive is at least one of the following compounds:

[0023]

[0024] In a second aspect, the present invention provides a fast-charge electrolyte, comprising an electrolyte salt, an organic solvent, and an electrolyte additive, wherein the electrolyte additive comprises a first additive, and the first additive comprises the fast-charge electrolyte additive as described in the first aspect.

[0025] Preferably, based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the first additive in the fast charge electrolyte is 1%-3%, preferably 1.8%-2.2%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8% or 3%, etc., not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0026] The present invention improves the cyclic stability and rate performance of the electrolyte at high voltage by regulating the mass percentage of the first additive. If a lower content of the first additive is used, the above-mentioned effects will not be obvious, the negative electrode material cannot be better protected, and there will be no good improvement effect on the rate performance of the secondary battery, and the operating voltage window of the electrolyte cannot be effectively widened. If a higher content of the first additive is used, the viscosity of the electrolyte will increase, and the formed SEI film will become thicker, resulting in an increase in the ion transmission distance and a deterioration in the rate performance of the secondary battery.

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

[0028] Preferably, the second additive comprises a lithium salt additive.

[0029] Preferably, the lithium salt additive includes at least one of LiFSI, LiTFSI or LiNO3.

[0030] Preferably, based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the second additive in the fast charge electrolyte is 0.2%-2%, preferably 0.7%-0.9%, for example, it can be 0.2%, 0.4%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8% or 2%, etc., not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0031] By regulating the mass percentage of the second additive, the present invention can further enhance the high-temperature stability of the electrolyte and the mechanical strength of the SEI film, thereby achieving better overall performance. Using a lower content of the second additive can result in poor electrochemical performance of the lithium-ion battery at high temperatures. Using a higher content of the second additive can lead to problems such as corrosion of aluminum foil at high voltages.

[0032] Preferably, the electrolyte additive further includes a third additive.

[0033] Preferably, the third additive includes a nitrile additive and / or a sulfate additive.

[0034] Preferably, based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the third additive in the fast charge electrolyte is 0.5%-2.5%, preferably 0.7%-2%, for example, it can be 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.8%, 2%, 2.2% or 2.5%, etc., not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0035] Preferably, the nitrile additive includes acetonitrile.

[0036] Preferably, based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the nitrile additive in the fast charge electrolyte is 0.5%-1.5%, preferably 0.9%-1.1%, for example, it can be 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%, etc., not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0037] The present invention regulates the mass percentage of the nitrile additive so that it can complex the free acid (such as HF) in the electrolyte through the cyano group, thereby inhibiting the acid corrosion of the electrolyte. If the nitrile additive is used at a lower content, the high-voltage stability of the electrolyte will be poor. If the nitrile additive is used at a higher content, the stability of the SEI film may be deteriorated, thereby deteriorating the cycle performance of the lithium-ion battery.

[0038] Preferably, the sulfate ester additive includes vinyl sulfate.

[0039] Preferably, based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the sulfate ester additive in the fast charge electrolyte is 0.5%-1%, preferably 0.7%-0.9%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0040] The present invention regulates the mass percentage of sulfate ester additives, enabling their use in combination with the borate ester compounds, thereby further reducing the interfacial impedance between the electrolyte and the negative electrode material. Using a lower content of sulfate ester additives can exacerbate the expansion and capacity decay of lithium-ion batteries in high-temperature environments. Using a higher content of sulfate ester additives can affect the electrochemical stability of the electrolyte, increasing the internal resistance of the lithium-ion battery and reducing the overall performance of the battery.

[0041] Preferably, the electrolyte additive further includes a fourth additive.

[0042] Preferably, the fourth additive includes vinylene carbonate and / or fluoroethylene carbonate.

[0043] Preferably, based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the fourth additive in the fast charge electrolyte is 1%-5%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8% or 5%, etc., not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0044] In the present invention, the carbonate additive and the borate compound additive provided by the present invention have a synergistic effect, specifically as follows: during the charge and discharge process of the lithium-ion battery, the carbonate additive can preferentially react on the electrode surface to form a lithium fluoride (LiF)-rich SEI film, while the low-resistance polymer film formed by the borate compound additive can cooperate with the SEI film, further improving the structural stability and interfacial stability of the SEI film, thereby effectively inhibiting the decomposition of the electrolyte and avoiding corrosion of the electrode material.

[0045] Preferably, the electrolyte salt includes a lithium salt.

[0046] In the present invention, the lithium salt exemplarily includes at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroborate (LiBF6) or lithium bis(oxalatoborate) (LiBOB).

[0047] Preferably, the molar concentration of the electrolyte salt in the fast charge electrolyte is 1 mol / L-1.5 mol / L, preferably 1 mol / L-1.2 mol / L, for example, it can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, etc., and is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0048] Preferably, the organic solvent comprises a combination of a linear carbonate solvent and a cyclic carbonate solvent.

[0049] Preferably, the linear carbonate solvent includes any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or methyl propyl carbonate, or a combination of at least two thereof.

[0050] Preferably, the cyclic carbonate solvent includes any one of ethylene carbonate, fluoroethylene carbonate or propylene carbonate, or a combination of at least two thereof.

[0051] Preferably, the volume ratio of the linear carbonate solvent to the cyclic carbonate solvent is (60-80):(20-40), for example, it can be 60:40, 62:38, 65:35, 68:32, 70:30, 72:28, 75:25, 78:22 or 80:20, etc., and is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0052] Further preferably, the organic solvent comprises a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0053] Further preferably, the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 30:30:40.

[0054] In the present invention, ethylene carbonate has a higher dielectric constant, which helps the dissociation of lithium salts, and dimethyl carbonate and ethyl methyl carbonate have the advantage of low viscosity. By further optimizing the volume ratio of the three solvents, the lithium ion migration rate of the electrolyte is comprehensively improved.

[0055] In a third 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 fast-charge electrolyte additive as described in the first aspect or the fast-charge electrolyte as described in the second aspect.

[0056] In the present invention, the active material of the positive electrode sheet exemplarily includes a ternary positive electrode material.

[0057] In the present invention, the active material of the negative electrode sheet exemplarily includes silicon-carbon material.

[0058] The fast-charge electrolyte provided by the present invention can further enhance the electrochemical performance of lithium-ion batteries at high voltage and high rate.

[0059] 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.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The present invention provides a fast-charging electrolyte additive, which effectively solves the technical problems of poor oxidation resistance of the electrolyte, low ionic conductivity, and high interface impedance between the electrolyte and the negative electrode material, thereby comprehensively improving the cycle stability and rate performance of the electrolyte at high voltage.

[0062] Specifically, the sulfonyl group in the additive structure can be preferentially reduced on the surface of the negative electrode material to form a low-impedance polymer film, thereby better protecting the interface of the silicon-based negative electrode material and reducing the interface impedance between it and the electrolyte, thereby improving the cycle performance of the lithium-ion battery at high voltage; secondly, the borate group in the additive has a certain Lewis acidity and can complex PF6 - or F - anions, thereby promoting the dissociation of lithium salts, thereby improving the ionic conductivity of the electrolyte; finally, the borate groups contained in the additive can form stable complexes with Lewis basic solvents such as ethylene carbonate (EC) through BO bond coordination, inhibiting the dehydrogenation reaction of EC solvents under high pressure, reducing the generation of gaseous by-products (CO2 and C2H4), and ultimately improving the oxidation stability of EC-based electrolytes, widening the oxidation potential window of lithium-ion batteries by 0.1V-0.3V, thereby significantly improving the safety and energy density of lithium-ion batteries. DETAILED DESCRIPTION

[0063] 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.

[0064] The structural formulas of Compound A in the following Examples 1 to 5 and 7 to 12 are shown below:

[0065]

[0066] The structural formula of compound B in Example 6 is shown below:

[0067]

[0068] Example 1

[0069] This embodiment provides a fast-charge electrolyte additive and a fast-charge electrolyte containing the same. The fast-charge electrolyte includes the electrolyte additive, a lithium salt, and an organic solvent.

[0070] The electrolyte additives include a first additive, a second additive, a third additive, and a fourth additive, wherein the first additive is compound A; the second additive is LiFSI; the third additive includes acetonitrile and vinyl sulfate; and the fourth additive includes vinylene carbonate.

[0071] Based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the first additive is 2wt%, the mass percentage of the second additive is 0.8wt%, the mass percentage of the third additive is 1.8wt%, and the mass percentage of the fourth additive is 1.5wt%.

[0072] In the third additive, based on the total mass of the fast-charge electrolyte being 100%, the mass percentage of acetonitrile is 1 wt %, and the mass percentage of vinyl sulfate is 0.8 wt %.

[0073] The lithium salt is lithium hexafluorophosphate, and the molar concentration of lithium hexafluorophosphate in the fast charge electrolyte is 1.1 mol / L.

[0074] The organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 30:30:40.

[0075] This embodiment also provides a method for preparing the above-mentioned fast-charge electrolyte, which comprises the following steps:

[0076] In a glove box with qualified water and oxygen content, ethylene carbonate, dimethyl carbonate and ethyl methyl 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, the third additive and the fourth additive are added and stirred evenly to obtain the fast charge electrolyte.

[0077] Example 2

[0078] This embodiment differs from Embodiment 1 in that the electrolyte additives are composed of the following: a first additive, a second additive, a third additive, and a fourth additive. The first additive is Compound A; the second additive is LiFSI; the third additive includes acetonitrile and vinyl sulfate; and the fourth additive includes vinylene carbonate.

[0079] Based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the first additive is 1.8wt%, the mass percentage of the second additive is 0.9wt%, the mass percentage of the third additive is 2wt%, and the mass percentage of the fourth additive is 1.2wt%.

[0080] In the third additive, based on the total mass of the fast-charge electrolyte being 100%, the mass percentage of acetonitrile is 1.1 wt %, and the mass percentage of vinyl sulfate is 0.9 wt %. Other contents are the same as those in Example 1.

[0081] Example 3

[0082] This embodiment differs from Embodiment 1 in that the electrolyte additives are composed of the following: a first additive, a second additive, a third additive, and a fourth additive. The first additive is Compound A; the second additive is LiFSI; the third additive includes acetonitrile and vinyl sulfate; and the fourth additive includes vinylene carbonate.

[0083] Based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the first additive is 2.2wt%, the mass percentage of the second additive is 0.7wt%, the mass percentage of the third additive is 1.6wt%, and the mass percentage of the fourth additive is 2wt%.

[0084] In the third additive, based on the total mass of the fast-charge electrolyte being 100%, the mass percentage of acetonitrile is 0.9 wt %, and the mass percentage of vinyl sulfate is 0.7 wt %. Other contents are the same as those in Example 1.

[0085] Example 4

[0086] This embodiment provides a fast-charge electrolyte additive and a fast-charge electrolyte containing the same. The fast-charge electrolyte includes the electrolyte additive, a lithium salt, and an organic solvent.

[0087] The electrolyte additives include a first additive, a second additive, a third additive, and a fourth additive, wherein the first additive is compound A, the second additive is LiTFSI, the third additive is acetonitrile, and the fourth additive includes fluoroethylene carbonate.

[0088] Based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the first additive is 1wt%, the mass percentage of the second additive is 1.8wt%, the mass percentage of the third additive is 0.5wt%, and the mass percentage of the fourth additive is 1wt%.

[0089] The lithium salt is lithium hexafluorophosphate, and the molar concentration of lithium hexafluorophosphate in the fast charge electrolyte is 1 mol / L.

[0090] The organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 30:30:40.

[0091] The preparation method of the fast-charge electrolyte provided in this embodiment is the same as that in Example 1.

[0092] Example 5

[0093] This embodiment provides a fast-charge electrolyte additive and a fast-charge electrolyte containing the same. The fast-charge electrolyte includes the electrolyte additive, a lithium salt, and an organic solvent.

[0094] The electrolyte additives include a first additive, a second additive, a third additive, and a fourth additive, wherein the first additive is compound A, the second additive is LiTFSI, the third additive is vinyl sulfate, and the fourth additive includes fluoroethylene carbonate.

[0095] Based on the total mass of the fast charge electrolyte as 100%, the mass percentage of the first additive is 2.8wt%, the mass percentage of the second additive is 0.3wt%, the mass percentage of the third additive is 1wt%, and the mass percentage of the fourth additive is 2.5wt%.

[0096] The lithium salt is lithium hexafluorophosphate, and the molar concentration of lithium hexafluorophosphate in the fast charge electrolyte is 1.5 mol / L.

[0097] The organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 30:30:40.

[0098] The preparation method of the fast-charge electrolyte provided in this embodiment is the same as that in Example 1.

[0099] Example 6

[0100] The difference between this embodiment and embodiment 1 is that compound A in the first additive is replaced by compound B with the same mass percentage, and the rest is the same as embodiment 1.

[0101] Example 7

[0102] The difference between this embodiment and embodiment 1 is that, except for adjusting the mass percentage of the first additive in the electrolyte additive to 0.5wt%, and increasing the contents of the second additive, the third additive and the fourth additive in equal mass proportions, everything else is the same as embodiment 1.

[0103] Example 8

[0104] The difference between this embodiment and embodiment 1 is that, except for adjusting the mass percentage of the first additive in the electrolyte additive to 6 wt %, and reducing the contents of the second additive, the third additive and the fourth additive in equal mass proportions, everything else is the same as embodiment 1.

[0105] Example 9

[0106] The difference between this embodiment and embodiment 1 is that, except for adjusting the mass percentage of the second additive in the electrolyte additive to 0.05wt%, and increasing the contents of the first additive, the third additive and the fourth additive in equal mass proportions, everything else is the same as embodiment 1.

[0107] Example 10

[0108] The difference between this embodiment and embodiment 1 is that, except for adjusting the mass percentage of the second additive in the electrolyte additive to 5wt%, and reducing the contents of the first additive, the third additive and the fourth additive in equal mass proportions, everything else is the same as embodiment 1.

[0109] Example 11

[0110] The difference between this embodiment and Example 1 is that, except for adjusting the mass percentage of the third additive in the electrolyte additive to 0.2wt%, the mass ratio of acetonitrile and vinyl sulfate remains unchanged, and the contents of the first additive, the second additive and the fourth additive are increased in equal mass proportions, everything else is the same as Example 1.

[0111] Example 12

[0112] The difference between this embodiment and Example 1 is that, except for adjusting the mass percentage of the third additive in the electrolyte additive to 5wt%, the mass ratio of acetonitrile and vinyl sulfate remains unchanged, and the contents of the first additive, the second additive and the fourth additive are reduced in equal mass proportions, everything else is the same as Example 1.

[0113] Comparative Example 1

[0114] 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.

[0115] Comparative Example 2

[0116] 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 third additive is replaced, everything else is the same as Example 1.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 1 is that the compound A in the first additive is replaced with 1-benzenesulfonylpyrazole (CAS No.: 108128-27-4) with an equal mass percentage, and the other contents are the same as those in Example 1.

[0119] Comparative Example 4

[0120] The difference between this comparative example and Example 1 is that the compound A in the first additive is replaced with 4-pyrazoleboronic acid pinacol ester (CAS No.: 269410-08-4) of equal weight percentage, and the rest is the same as Example 1.

[0121] Comparative Example 5

[0122] 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 first additive is replaced with an organic solvent, everything else is the same as Example 1.

[0123] Application Examples 1-12 and Comparative Application Examples 1-5

[0124] The electrolytes provided in Examples 1 to 12 and Comparative Examples 1 to 5 were assembled to obtain lithium-ion batteries. The specific preparation method is as follows:

[0125] Preparation of negative electrode sheet:

[0126] Silicon-carbon negative electrode material (silicon content of 48%), conductive carbon black Super-P, single-walled carbon nanotubes (SWCNTs) and polyacrylic acid binder (PAA) are mixed and stirred evenly with water in a mass ratio of 83.5:8:0.5:8 to obtain a negative electrode slurry, and the solid content is controlled to be 30%. The negative electrode slurry is then coated on a copper foil current collector through a coating process, and then vacuum dried and cold pressed to obtain a negative electrode sheet.

[0127] Preparation of positive electrode:

[0128] The ternary cathode material NCM811 (LiNi 0.9 Co 0.05 Mn 0.05 The active material O2, polyvinylidene fluoride binder (PVDF) and conductive carbon black Super-P are mixed and stirred evenly with N-methylpyrrolidone solvent in a mass ratio of 96:1.8:2.2 to obtain a positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil through a coating process, and then dried and cold pressed to obtain a positive electrode sheet.

[0129] Preparation of lithium-ion batteries:

[0130] The positive electrode sheet, separator (including a polyethylene-based film and a ceramic coating provided on one side of the polyethylene-based film) and negative electrode sheet are stacked in order, with the separator located between the positive electrode sheet and the negative electrode sheet to thereby serve as an isolation layer, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with the electrolyte provided in the above embodiments and comparative examples. After vacuum packaging, standing, formation and shaping, a lithium-ion battery is obtained.

[0131] Test conditions

[0132] The lithium ion batteries prepared in the above examples and comparative examples were subjected to electrochemical performance tests respectively, and the test methods were as follows:

[0133] (1) 60℃ high temperature storage performance

[0134] ① Standard charge and discharge: At 25℃, charge the lithium-ion battery to 4.35V at a constant current and constant voltage rate of 0.33C, let it stand for 10 minutes, then discharge the lithium-ion battery to 2.5V at a constant current rate of 0.33C, let it stand for 10 minutes.

[0135] ② Initial performance test: Test the performance of lithium-ion batteries using battery testing equipment at room temperature (25°C). Perform three charge and discharge cycles at a standard rate of 0.33C. Record the capacity at the third discharge cycle, and the capacity before storage as C0.

[0136] ③ High-temperature storage: At room temperature (25°C), charge the lithium-ion battery to 4.35V at a constant current and constant voltage rate of 0.33C, let it stand for 30 minutes, measure the thickness of the battery cell, and record it as t1; then place the battery cell in a 60°C oven for high-temperature storage for 7 days.

[0137] ④ Performance test after storage: After the storage time is reached, take the lithium-ion battery out of the oven and place it at room temperature for 2h-4h to restore the temperature of the lithium-ion battery to room temperature. Test the thickness of the battery cell and record the thickness as t2. Perform a constant current discharge of the lithium-ion battery at a rate of 0.33C to 2.5V and let it stand for 10min. The discharge capacity is the maintenance capacity, recorded as C1. Then perform a standard charge and discharge cycle of the lithium-ion battery at a rate of 0.33C for 3 times and record the capacity of the third discharge. The capacity after storage is recorded as C2.

[0138] Capacity recovery rate = C2 / C0×100%.

[0139] (2) Capacity retention after 1000 cycles at 1C / 1C rate at room temperature

[0140] At 25°C, the lithium-ion battery is charged to 4.35V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C, and allowed to stand for 10 minutes. Then, the lithium-ion battery is discharged to 2.5V at a constant current rate of 1C and allowed to stand for 10 minutes. This is considered one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times according to the above method, and the capacity retention rate of the lithium-ion battery after 1000 charge and discharge cycles at 1C / 1C is calculated.

[0141] Capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0142] (3) Capacity retention after 1000 cycles at 1C / 1C rate at 45°C

[0143] At 45°C, the lithium-ion battery is charged to 4.35V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C, and allowed to stand for 10 minutes. Then, the lithium-ion battery is discharged to 2.5V at a constant current rate of 1C and allowed to stand for 10 minutes. This is considered one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times according to the above method, and the capacity retention rate of the lithium-ion battery after 1000 charge and discharge cycles at 1C / 1C is calculated.

[0144] Capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0145] (4) Room temperature 6C rate performance - constant current charging ratio

[0146] At 25°C, the lithium-ion battery was discharged at a constant current rate of 1C to 2.5V and allowed to stand for 10 minutes. The lithium-ion battery was then charged at a constant current and constant voltage rate of 6C to 4.35V with a cut-off current of 0.05C. The battery was allowed to stand for 10 minutes. The constant current charging capacity of the lithium-ion battery was recorded as Q1, and the total constant current and constant voltage charging capacity was recorded as Q2. The constant current charging ratio of the 6C rate charging was calculated according to the following formula: constant current charging ratio of 6C rate charging = (constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2) × 100%.

[0147] (5) Battery cell thermal runaway ARC test

[0148] Start the ARC adiabatic thermal runaway test (the test sample is heated from room temperature to 45±2°C in the chamber, and after 90 minutes, the temperature rise rate of the lithium-ion battery is detected). If the temperature rise exceeds 0.2°C within 10 minutes (i.e., the self-heating temperature rise rate, referred to as SHR, SHR>0.02°C / min), it is considered that a self-exothermic reaction has occurred inside the lithium-ion battery, and the adiabatic environment is maintained until the lithium-ion battery thermal runaway occurs; if the temperature rise does not exceed 0.2°C within 10 minutes (i.e., SHR≤0.02°C / min), continue to the next step temperature rise test; each temperature step is 5°C, and the steps are repeated at each temperature step. The ARC test temperature range is 45°C-300°C, the starting temperature of self-heating is T1 (temperature rise rate SHR>0.02°C / min), and the starting temperature of thermal runaway is T2 (temperature rise rate SHR>1°C / min).

[0149] The above test results are shown in Table 1.

[0150] Table 1

[0151]

[0152]

[0153] As can be seen from Table 1, compared with Comparative Application Examples 1-2 and Comparative Application Example 5, the borate compound additive with a specific structure having a sulfonyl group provided in Application Examples 1-6 of the present invention effectively solves the technical problems of poor oxidation resistance of the electrolyte, low ionic conductivity, and high interface impedance between the electrolyte and the negative electrode material, thereby comprehensively improving the cycle stability and rate performance of the electrolyte at high voltage. In addition, the borate group contained in the additive and Lewis alkaline solvents such as ethylene carbonate (EC) can form a stable complex through BO bond coordination, inhibiting the dehydrogenation reaction of the EC solvent under high pressure, and ultimately improving the oxidation stability of the EC-based electrolyte, thereby significantly improving the safety of the lithium-ion battery.

[0154] By comparing Application Example 1, Application Example 7 and Application Example 8, it can be seen that the present invention optimizes the mass percentage of the first additive in the electrolyte additive to better protect the negative electrode material, thereby comprehensively improving the electrochemical performance of the lithium-ion battery under high voltage and high rate.

[0155] By comparing Application Example 1, Application Example 9 and Application Example 10, it can be seen that the present invention can further improve the high-temperature stability of the electrolyte and the mechanical strength of the SEI film by optimizing the mass percentage of the second additive in the electrolyte additive, thereby improving the overall performance of the lithium-ion battery.

[0156] By comparing Application Example 1, Application Example 11 and Application Example 12, it can be seen that the present invention optimizes the interface performance between the electrolyte and the negative electrode material and improves the high-voltage stability of the electrolyte by optimizing the mass percentage of the third additive in the electrolyte additive.

[0157] From Comparative Application Example 1, Comparative Application Example 3 and Comparative Application Example 4, it can be seen that the present invention further enhances the comprehensive performance of the electrolyte under high pressure and high temperature by optimizing the structure of the compound in the first additive, thereby improving the cycle performance and thermal safety performance of the lithium-ion battery under different environments.

[0158] 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. A fast-charge electrolyte additive, characterized in that: The fast charge electrolyte additive includes a borate compound having the structure shown in formula (1): wherein L1 is selected from substituted or unsubstituted pyrazole groups, substituted or unsubstituted C6-C 10 any one of an aryl group or a substituted or unsubstituted pyrrolopyridine group, and L2 is selected from a substituted or unsubstituted C6-C 10 Aryl.

2. The fast-charge electrolyte additive according to claim 1, characterized in that The fast-charge electrolyte additive includes a compound having a structure represented by formula (2) and / or a compound having a structure represented by formula (3): wherein R1 and R2 are each independently selected from a hydrogen atom or an unsubstituted C1-C3 alkyl group, R3 and R4 are each independently selected from a substituted or unsubstituted phenyl group, and R5 is selected from a halogen atom or a cyano group; The substituted groups include C1-C3 alkyl groups.

3. The fast-charge electrolyte additive according to claim 2, characterized in that The halogen atom includes either a fluorine atom or a chlorine atom.

4. The fast-charge electrolyte additive according to any one of claims 1 to 3, characterized in that The fast charge electrolyte additive is at least one of the following compounds:

5. A fast-charging electrolyte, characterized in that: The fast-charge electrolyte includes an electrolyte salt, an organic solvent, and an electrolyte additive. The electrolyte additive includes a first additive. The first additive includes the fast-charge electrolyte additive according to any one of claims 1 to 4.

6. The fast-charge electrolyte according to claim 5, characterized in that Based on the total mass of the fast-charge electrolyte being 100%, the mass percentage of the first additive in the fast-charge electrolyte is 1%-3%, preferably 1.8%-2.2%.

7. The fast-charge electrolyte according to claim 5 or 6, characterized in that: The electrolyte additive further includes a second additive; Preferably, the second additive comprises a lithium salt additive; Preferably, the lithium salt additive includes at least one of LiFSI, LiTFSI or LiNO3; Preferably, based on the total mass of the fast charge electrolyte being 100%, the mass percentage of the second additive in the fast charge electrolyte is 0.2%-2%, preferably 0.7%-0.9%; Preferably, the electrolyte additive further includes a third additive; Preferably, the third additive includes a nitrile additive and / or a sulfate additive; Preferably, based on the total mass of the fast charge electrolyte being 100%, the mass percentage of the third additive in the fast charge electrolyte is 0.5%-2.5%, preferably 0.7%-2%; Preferably, the nitrile additive comprises acetonitrile; Preferably, based on the total mass of the fast charge electrolyte being 100%, the mass percentage of the nitrile additive in the fast charge electrolyte is 0.5%-1.5%, preferably 0.9%-1.1%; Preferably, the sulfate ester additive includes vinyl sulfate; Preferably, based on the total mass of the fast-charge electrolyte being 100%, the mass percentage of the sulfate ester additive in the fast-charge electrolyte is 0.5%-1%, preferably 0.7%-0.9%.

8. The fast-charge electrolyte according to any one of claims 5 to 7, characterized in that The electrolyte additive further includes a fourth additive; Preferably, the fourth additive comprises vinylene carbonate and / or fluoroethylene carbonate; Preferably, based on the total mass of the fast-charge electrolyte being 100%, the mass percentage of the fourth additive in the fast-charge electrolyte is 1%-5%.

9. The fast-charge electrolyte according to any one of claims 5 to 8, characterized in that The electrolyte salt includes a lithium salt; Preferably, the molar concentration of the electrolyte salt in the fast charge electrolyte is 1 mol / L-1.5 mol / L, preferably 1 mol / L-1.2 mol / L; Preferably, the organic solvent comprises a combination of a linear carbonate solvent and a cyclic carbonate solvent; Preferably, the linear carbonate solvent comprises any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or methyl propyl carbonate; Preferably, the cyclic carbonate solvent includes any one or a combination of at least two of ethylene carbonate, fluoroethylene carbonate or propylene carbonate; Preferably, the volume ratio of the linear carbonate solvent to the cyclic carbonate solvent is (60-80):(20-40); Preferably, the organic solvent comprises a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; Preferably, the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 30:30:

40.

10. A secondary battery, characterized in that: The secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, and the electrolyte includes the fast-charge electrolyte additive according to any one of claims 1 to 4 or the fast-charge electrolyte according to any one of claims 5 to 9.

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