Electrolyte solution additive, electrolyte solution, and electrochemical energy storage device

Abstract

The present application relates to an electrolyte solution additive, an electrolyte solution, and an electrochemical energy storage device. The electrolyte solution additive comprises a fluoroaluminate compound and a nitrile compound, wherein the mass ratio of the fluoroaluminate compound to the nitrile compound is 0.01-20. In the solution provided in the present application, both positive and negative electrode interfaces of a battery can be simultaneously passivated, and film-forming products have high thermodynamic and electrochemical stability, thereby meeting the requirements for high energy density performance of the battery.

Description

Electrolyte additive, electrolyte and electrochemical energy storage device

[0001] The present application claims priority to the Chinese patent application No. 202411259445.1, filed on September 10, 2024, and entitled "Electrolyte additive, electrolyte and electrochemical energy storage device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte and an electrochemical energy storage device. BACKGROUND

[0003] Lithium ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, electric vehicles and other fields due to their high specific energy, no memory effect, long cycle life and other advantages. These fields have increasingly high requirements for the energy density of lithium ion batteries.

[0004] In related technologies, the energy density of the battery is mainly improved by optimizing the electrolyte. This method usually uses carbonate additives and lithium salt additives to passivate the negative electrode interface and improve the cycle performance of the battery.

[0005] However, the above-mentioned carbonate additives and lithium salt additives cannot passivate the positive electrode interface, and the film formed will increase the interface impedance, making it difficult to meet the demand for high energy density performance of the battery. SUMMARY

[0006] To solve or partially solve the problems in the related art, the present application provides an electrolyte additive, an electrolyte and an electrochemical energy storage device, which can passivate the positive and negative electrode interfaces of the battery at the same time, and the film product has high thermodynamic and electrochemical stability, which can meet the demand for high energy density performance of the battery.

[0007] The first aspect of the present application provides an electrolyte additive, comprising a fluorinated aluminate compound and a nitrile compound, and the mass ratio of the fluorinated aluminate compound to the nitrile compound is 0.01-20.

[0008] As an optional embodiment, the fluorinated aluminate compound is selected from at least one of the following structural formula I, structural formula II and structural formula III:

[0009] wherein R1, R2, R3, R4, R5 and R6 are respectively selected from one or more fluorine atom-substituted alkanes, alkenes and alkynes having 1-6 carbon atoms; and M is selected from at least one of Li, Na and K.

[0010] As an optional embodiment, the fluorinated aluminate compound is selected from at least one of the following compounds:

[0011] As an optional embodiment, the fluorinated aluminate compound accounts for 0.1% to 10% of the mass percentage of the electrolyte solution.

[0012] As an optional embodiment, the fluorinated aluminate compound accounts for 1% to 10% of the mass percentage of the electrolyte solution.

[0013] As an optional embodiment, the nitrile compound accounts for 0.5% to 10% of the mass percentage of the electrolyte solution.

[0014] As an optional embodiment, the nitrile compound accounts for 7% to 10% of the mass percentage of the electrolyte solution.

[0015] As an optional embodiment, the nitrile compound is selected from at least one of di-nitrile, tri-nitrile, and tetra-nitrile.

[0016] As an optional embodiment, the nitrile compound is selected from at least one of butanedinitrile, pentanedinitrile, hexanedinitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,3,6-hexanetristitnitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,4,6-hexanetetranitrile, 1,2,4,5-benzene tetranitrile, 2,3,5,6-pyrazine tetranitrile, and ether tetranitrile.

[0017] As an optional embodiment, the electrolyte additive further comprises at least one of a carbonate compound, a metal salt compound, and a sulfur-oxygen double bond compound.

[0018] As an optional embodiment, the carbonate compound is selected from at least one of fluoroethylene carbonate FEC, bis-fluoroethylene carbonate DFEC, vinylene carbonate VC, and vinyl ethylene carbonate VEC.

[0019] As an optional embodiment, the carbonate compound accounts for 11% to 30% of the mass percentage of the electrolyte solution.

[0020] As an optional embodiment, the metal salt compound is selected from at least one of di-oxalate borate MBOB, di-fluoro-oxalate borate MDFOB, tetra-fluoroborate MBF4, di-fluoro-phosphate MPO2F2, and di-fluoro-oxalate phosphate MDODFP.

[0021] As an optional embodiment, the metal salt compound accounts for 0.1% to 7% of the mass percentage of the electrolyte; and / or, the sulfur-oxygen double bond compound is at least one selected from 1,3-propane sulfonic acid endolactone PS, 1,3-propylene sulfonic acid endolactone PST, vinyl sulfite DTD, 1,4-butane sulfonic acid endolactone BS, ethylene sulfite ES and vinyl ethylene sulfite VES.

[0022] As an optional embodiment, the sulfur-oxygen double bond compound accounts for 0.1% to 5% of the mass percentage of the electrolyte.

[0023] The second aspect of the present application provides an electrolyte, comprising an electrolyte salt, an organic solvent and an additive, wherein the additive is the aforementioned electrolyte additive.

[0024] The third aspect of the present application provides an electrochemical energy storage device, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the aforementioned electrolyte.

[0025] As an optional embodiment, the negative electrode comprises a current collector and a negative electrode active material coated on the current collector, wherein the negative electrode active material is at least one selected from a carbon-based material, a silicon-based material, an alkali metal and a material that can be alloyed with the alkali metal.

[0026] As an optional embodiment, the negative electrode active material is selected from a silicon-based material.

[0027] As an optional embodiment, the mass percentage of the fluorinated aluminate compound in the electrolyte is a, the mass percentage of the silicon-based material in the negative electrode active material is b, and a / b is 0.0015 to 1.

[0028] As an optional embodiment, the mass percentage of the silicon-based material in the negative electrode active material is 10% to 60%.

[0029] As an optional embodiment, the positive electrode active material of the positive electrode is at least one selected from lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum, lithium iron phosphate, lithium manganese iron phosphate, lithium-rich manganese-based, Na x TMO2, wherein TM is a transition metal atom, and 0X≤1.

[0030] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. DETAILED DESCRIPTION

[0031] Embodiments of the present application will be described in more detail by referring to the drawings. Although embodiments of the present application are shown in the drawings, it is understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0032] The terminology used in the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0033] It should be understood that although the terms "first", "second", "third", etc. can be employed in this application to describe various information, such information should not be limited by these terms. These terms are only used to distinguish one piece of information from another. For example, a first information can also be termed a second information, and, similarly, a second information can also be termed a first information, without departing from the scope of the present application. Therefore, the characteristics defined with "first", "second" can explicitly or implicitly include one or more of the characteristics. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0034] The electrolyte additive provided by the embodiments of the present application comprises a fluoroaluminate compound and a nitrile compound, and the mass ratio of the fluoroaluminate compound to the nitrile compound is 0.01-20.

[0035] In the embodiments of the present application, the nitrile compound in the electrolyte additive can passivate the surface of the positive active material, and the positive electrode interface passivation effect is further improved with the increase of the addition amount. However, the nitrile compound has the following problems: first, the nitrile compound can only act on the active sites of the transition metal of the positive active material, resulting in incomplete passivation of the positive electrode interface (point passivation in local area); second, the addition amount of the nitrile compound is too large, and the positive electrode interface passivation effect is further improved limitedly, and due to the reduction of the excessive nitrile compound at the negative electrode and the damage to the SEI film, the compatibility of the negative electrode interface is poor, which will deteriorate the cycle performance. After adding the fluoroaluminate compound, the fluoroaluminate compound can synergize with the nitrile compound, the fluoroaluminate compound can form a complete and dense CEI film on the positive electrode, and the positive electrode is coated, which makes up for the deficiency of the nitrile compound; in addition, the fluoroaluminate compound can form an SEI film on the negative electrode, which can avoid the reduction of the nitrile compound at the negative electrode and the damage to the SEI film. Therefore, by simultaneously adding the fluoroaluminate compound and the nitrile compound, not only can the passivation of the high-voltage positive electrode interface be further realized, and the attenuation of the positive electrode material can be inhibited, but also the problem of poor compatibility of the nitrile compound to the negative electrode interface can be inhibited, so as to simultaneously improve the passivation effect of the positive and negative electrode interfaces.

[0036] Specifically, the fluoroaluminate compound realizes the synergistic effect with the nitrile compound through the following functions: first, the fluoroaluminate compound can participate in film formation on the positive and negative electrodes, and the film formation products are mainly LiF and lithium aluminate compounds. Such compounds have strong thermal stability and chemical stability, can better inhibit the generation of positive and negative electrode interface by-products, and can make the positive and negative electrode protection films (such as SEI film and CEI film) have a wider electrochemical window, which can simultaneously resist higher voltage (resist oxidation) and lower voltage (resist reduction), and ensure that the battery can work or store stably in a wider voltage range; second, the fluoroaluminate compound has a water removal function, and can be hydrolyzed to generate LiF and aluminum hydroxide, thereby inhibiting the generation of HF in the electrolyte and its damage to the active material, SEI and CEI; third, the aluminate of the fluoroaluminate compound can coordinate with the dissolved transition metal of the positive electrode to form insoluble substances, thereby complexing the dissolved transition metal of the positive electrode and reducing the influence of the transition metal deposited on the negative electrode on the damage to the SEI. Fourth, the fluoroaluminate compound can also thermally polymerize to generate polyfluoroaluminate lithium, which not only has good mechanical properties, but also has high ionic conductivity, which is conducive to lithium ion transmission and improves the kinetic performance of the battery.

[0037] In addition, the mass ratio of the fluorinated aluminate compound and the nitrile compound can be the ratio of the mass percentage of the fluorinated aluminate compound to the mass percentage of the nitrile compound in the electrolyte, and can be 0.1 / 10, 0.1 / 5, 0.5 / 7, 1 / 9, 1 / 7, 2 / 7, 5 / 9, 5 / 7, 10 / 7, 10 / 6, 10 / 3, 10 / 2, 10 / 1, 10 / 0.5, or any value within the above defined range, which is not limited in the present application.

[0038] When the mass ratio of the fluorinated aluminate compound and the nitrile compound is less than 0.01, the content of the fluorinated aluminate compound is too low, and the effect is not significant; when the mass ratio of the fluorinated aluminate compound and the nitrile compound is greater than 20, the content of the fluorinated aluminate compound is too high, which can cause the negative electrode film impedance to be too high, deteriorate the negative electrode film impedance, easily lithiumize during charging, and the content of the nitrile compound is too low, which can not completely passivate the positive electrode.

[0039] As an optional embodiment, the fluorinated aluminate compound is selected from at least one of the following structural formula I, structural formula II, and structural formula III:

[0040] wherein R1, R2, R3, R4, R5, and R6 are respectively selected from one or more fluorine atom-substituted alkanes, alkenes, and alkynes with 1-6 carbon atoms; and M is selected from at least one of Li, Na, and K.

[0041] The structural formula of the fluorinated aluminate compound provided in the embodiments of the present application is rich in F elements, the formed CEI film and SEI film contain a large amount of MF with good chemical and thermal stability, are easy to polymerize into a film, the film product is a fast lithium ion conductor, can remove water and acid, and has a wide chemical window.

[0042] As a preferred embodiment, the fluorinated aluminate compound is selected from at least one of the following compounds:

[0043] The structural formula of the fluorinated aluminate compound provided in the embodiments of the present application is rich in F elements, the formed CEI film and SEI film contain a large amount of MF with good chemical and thermal stability, are easy to polymerize into a film, the film product is a fast lithium ion conductor, can remove water and acid, and has a wide chemical window.

[0044] As an optional embodiment, the mass percentage of the fluorinated aluminate compound in the electrolyte is 0.1% to 10%.

[0045] In the embodiments of the present application, the mass percentage of the fluorinated aluminate compound in the electrolyte can be 0.1%, 0.5%, 2%, 5%, 10% or any value within the above defined range, which is not limited in the present application.

[0046] When the content of the fluorinated aluminate compound is too low, the effect is not significant; when the content of the fluorinated aluminate compound is too high, it will lead to too high negative film forming impedance, deteriorate the negative film forming impedance, and easily lithiumize during charging.

[0047] As a preferred embodiment, the mass percentage of the fluorinated aluminate compound in the electrolyte is 1% to 10%.

[0048] In the embodiments of the present application, the mass percentage of the fluorinated aluminate compound in the electrolyte can be 1%, 3%, 5%, 10% or any value within the above defined range, which is not limited in the present application.

[0049] When the mass percentage of the fluorinated aluminate compound in the electrolyte is limited to the above range, the excellent cycle performance and safety performance of the battery can be ensured.

[0050] As an optional embodiment, the mass percentage of the nitrile compound in the electrolyte is 0.5% to 10%.

[0051] In the embodiments of the present application, the mass percentage of the nitrile compound in the electrolyte can be 0.5%, 1%, 2%, 5%, 10% or any value within the above defined range, which is not limited in the present application.

[0052] When the content of the nitrile compound is too low, it will lead to incomplete passivation of the positive electrode; when the content of the nitrile compound is too high, the further improvement of the passivation effect of the positive electrode interface is limited, and due to the reduction of the excessive nitrile compound at the negative electrode and the damage to the SEI film, the negative electrode interface compatibility is poor, which will deteriorate the cycle performance.

[0053] As a preferred embodiment, the mass percentage of the nitrile compound in the electrolyte is 7% to 10%.

[0054] In the embodiments of the present application, the mass percentage of the nitrile compound in the electrolyte can be 7%, 9%, 10% or any value within the above defined range, which is not limited in the present application.

[0055] When the mass percentage of the nitrile compound in the electrolyte is limited to the above range, the excellent cycle performance and safety performance of the battery can be ensured.

[0056] Further, when the fluorinated aluminate compound accounts for 1% to 10% of the mass percentage of the electrolyte, and the nitrile compound accounts for 7% to 10% of the mass percentage of the electrolyte, the mass ratio of the fluorinated aluminate compound to the nitrile compound can be 0.5 / 10, 1 / 10, 7 / 10, 10 / 10, 3 / 5, 7 / 5, 9 / 5, or any value within the above defined range, which is not limited in the present application.

[0057] As a preferred embodiment, the nitrile compound is selected from at least one of di-nitrile, tri-nitrile, and tetra-nitrile.

[0058] The nitrile compound in the embodiments of the present application can be a poly-nitrile compound, which contains a-CN functional group and Co 3+ The combination of the-CN functional group and Co has a lower binding energy, and is more likely to be enriched on the positive electrode surface. At the same time, the cyan group functional group on the positive electrode surface coordinates with the high-valence transition metal atom, and cooperates with the film forming product of the fluorinated aluminate compound on the positive electrode surface, thereby reducing the side reaction of the positive electrode and the electrolyte. Similarly, in the LiMn2O4, LiMnO2, Li2MnO4, LiFePO4 system, the-CN functional group can also inhibit the dissolution of transition metal ions in the positive electrode, and form a more stable SEI film on the negative electrode, thereby inhibiting the destruction of the negative electrode side by transition metal ions.

[0059] As a preferred embodiment, the nitrile compound is selected from at least one of butanedinitrile SN, pentanedinitrile, hexanedinitrile AND, trans-butenedinitrile, trans-hexenedinitrile, 1,3,6-hexanetrimethanitrile HTCN, 1,2-bis(2-cyanoethoxy)ethane DENE, 1,3,4,6-hexanetetranitrile, 1,2,4,5-benzotetramethanitrile, 2,3,5,6-pyrazinetetranitrile, and ether tetranitrile.

[0060] The viscosity of the nitrile compound selected in the embodiments of the present application is moderate, the positive electrode passivation effect is good, and the compatibility with the negative electrode is relatively good.

[0061] As an optional embodiment, the electrolyte additive further comprises at least one of a carbonate compound, a metal salt compound, and a sulfur-oxygen double bond compound.

[0062] In the embodiments of the present application, the negative electrode film forming effect of the carbonate compound is good, which can improve the cycle performance and initial efficiency of the battery; the metal salt compound can form a film on the positive and negative electrode interface at the same time, thereby improving the cycle and storage performance of the battery; the film forming effect of the sulfur-oxygen double bond compound is good, the film forming resistance is low, and the cost is low, which can comprehensively improve the cycle, storage, floating, and other electrical properties and safety performance of the battery.

[0063] As a preferred embodiment, the carbonate compound is selected from at least one of fluorinated ethylene carbonate FEC, difluorinated ethylene carbonate DFEC, vinylene carbonate VC, and vinyl ethylene carbonate VEC.

[0064] In a preferred embodiment, the carbonate compound accounts for 1% to 30% of the electrolyte by mass.

[0065] In the embodiments of this application, the mass percentage of carbonate compound in the electrolyte can be 1%, 5%, 10%, 20%, 30%, or any value within the above-defined range, and this application does not limit it in this regard.

[0066] As a preferred embodiment, the metal salt compound is selected from at least one of bis(oxalate)borate MBOB, difluoro(oxalate)borate MDFOB, tetrafluoroborate MBF4, difluorophosphate MPO2F2, and difluoro(oxalate)phosphate MDOFP.

[0067] In a preferred embodiment, the metal salt compound accounts for 0.1% to 7% of the mass of the electrolyte.

[0068] In the embodiments of this application, the mass percentage of the metal salt compound in the electrolyte can be 0.1%, 2%, 4%, 5%, 7% or any value within the above-defined range, and this application does not limit it in this regard.

[0069] As a preferred embodiment, the sulfur-oxygen double bond compound is selected from at least one of 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), vinyl sulfate (DTD), 1,4-butanesulfonate lactone (BS), ethylene sulfite (ES), and ethylene sulfite (VES).

[0070] In a preferred embodiment, the sulfur-oxygen double bond compound accounts for 0.1% to 5% of the mass percentage of the electrolyte.

[0071] In the embodiments of this application, the mass percentage of the sulfur-oxygen double bond compound in the electrolyte can be 0.1%, 2%, 4%, 5%, or any value within the above-defined range, and this application does not limit it in this regard.

[0072] Corresponding to the aforementioned application function implementation method embodiments, this application also provides an electrolyte, an electrochemical energy storage device, and corresponding embodiments.

[0073] This application provides an electrolyte comprising an electrolyte salt, an organic solvent, and an additive, wherein the additive is the aforementioned electrolyte additive.

[0074] In the embodiments of this application, the organic solvent is selected from at least one of ethylene carbonate EC, propylene carbonate PC, ethyl propionate EP, propyl propionate PP, dimethyl carbonate DMC, ethyl methyl carbonate EMC, diethyl carbonate DEC, ethyl difluorocarbonate DFEA, dimethyl fluorocarbonate FDMC, ethyl fluorocarbonate FEMC, and diethyl fluorocarbonate FDEC.

[0075] In the embodiments of the present application, the electrolyte salt is selected from at least one of NPF6 and NFSI. Wherein, N is an alkali metal, such as Li and Na, and the concentration is 0.8 mol / L-1.5 mol / L, preferably 1.0 mol / L-1.2 mol / L.

[0076] The embodiments of the present application also provide an electrochemical energy storage device, comprising a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the aforementioned electrolyte.

[0077] As an optional embodiment, the positive electrode active material is selected from at least one of lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum, lithium iron phosphate, lithium manganese iron phosphate, lithium-rich manganese-based, Na x at least one of TMO2 (TM is a transition metal atom, 0X≤1).

[0078] As an optional embodiment, the negative electrode comprises a current collector and a negative electrode active material coated on the current collector, and the negative electrode active material is selected from at least one of a carbon-based material, a silicon-based material, an alkali metal and a material that can be alloyed with an alkali metal. Preferably, the alkali metal is Li, Na or K.

[0079] Preferably, the carbon-based material is selected from at least one of artificial graphite, natural graphite, hard carbon, and the like.

[0080] Further, the negative electrode active material is selected from a silicon-based material, such as silicon-carbon and silicon-oxygen materials.

[0081] Further, the mass percentage of the fluorinated aluminate compound in the electrolyte is a, and the mass percentage of the silicon-based material in the negative electrode active material is b, and a / b is 0.0015-1.

[0082] In the embodiments of the present application, a / b can be 0.0015, 0.1, 0.15, 1 or any value within the above defined range, which is not limited by the present application.

[0083] Further, the mass percentage of the silicon-based material in the negative electrode active material is 10%-60%.

[0084] In the embodiments of the present application, the mass percentage of the silicon-based material in the negative electrode active material can be 10%, 15%, 20%, 40%, 60% or any value within the above defined range, which is not limited by the present application.

[0085] In order to further understand the present application, the present application is described below in conjunction with the embodiments, which are only used to illustrate the present application and not to limit the scope of the present application.

[0086] I. Preparation of the battery

[0087] (1) Preparation of the positive electrode sheet:

[0088] The positive active material LCO, conductive agent CNT, and binder polyvinylidene fluoride were mixed in a weight ratio of 97:1.5:1.5 in an N-methylpyrrolidone solvent, and stirred sufficiently to form a uniform positive electrode slurry. The slurry was coated on a positive electrode current collector Al foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0089] (2) Preparation of a negative electrode sheet:

[0090] a. The negative active material graphite, silicon-carbon, conductive agent acetylene black, binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 80:15:2:2:1 in an appropriate amount of deionized water solvent, and stirred sufficiently to form a uniform negative electrode slurry. The slurry was coated on a negative electrode current collector Cu foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0091] b. The negative electrode sheets were prepared by the above step a according to the different Si components and contents in Table 5.

[0092] (3) Preparation of an electrolyte:

[0093] a. EC / PC / PP = 1 / 3 / 6 by mass ratio (the whole organic solvent was normalized to 100%) were mixed as the organic solvent. The additives in the additive formulation of the examples and comparative examples in Table 1 were added to the organic solvent, and after being mixed uniformly, LiPF6 was added to obtain a mixed solution with a LiPF6 concentration of 1.15 mol / L as the electrolyte.

[0094] a. EC / PC / PP = 1 / 3 / 6 by mass ratio (the whole organic solvent was normalized to 100%) were mixed as the organic solvent. The additives in the additive formulation of the examples and comparative examples in Table 1 were added to the organic solvent, and after being mixed uniformly, LiPF6 was added to obtain a mixed solution with a LiPF6 concentration of 1.15 mol / L as the electrolyte.

[0095] c. EC / PC / PP = 1 / 3 / 6 by mass ratio (the whole organic solvent was normalized to 100%) were mixed as the organic solvent. The additives in the additive formulation of the examples in Table 5 were added to the organic solvent, and after being mixed uniformly, LiPF6 was added to obtain a mixed solution with a LiPF6 concentration of 1.15 mol / L as the electrolyte.

[0096] (4) Preparation of a lithium ion battery:

[0097] a) Stack the positive electrode sheet, separator, and negative electrode sheet obtained in step a) in sequence, placing the separator between the positive and negative electrodes for isolation. Then, wind them into the bare battery cell. Place the bare battery cell in an outer packaging bag and dry it at high temperature until the water content of the electrode sheet is less than 100 ppm. Then, inject the electrolyte obtained in step a) and proceed through vacuum sealing, settling, formation, and shaping processes to complete the preparation of the lithium-ion battery.

[0098] b. Stack the positive electrode sheet, separator, and negative electrode sheet obtained in step a in sequence, placing the separator between the positive and negative electrodes to provide isolation. Then, wind them into the bare battery cell. Place the bare battery cell in an outer packaging bag and dry it at high temperature until the water content of the electrode sheet is less than 100 ppm. Then, inject the electrolyte obtained in step b. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery is completed.

[0099] c. Stack the positive electrode sheet, separator, and negative electrode sheet obtained in step b in sequence, placing the separator between the positive and negative electrodes to provide isolation. Then, wind them into the bare cell. Place the bare cell in an outer packaging bag and dry it at high temperature until the water content of the electrode sheet is less than 100 ppm. Then, inject the electrolyte obtained in step c. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery is completed.

[0100] II. Performance Testing

[0101] The batteries obtained from all the above embodiments and comparative examples were subjected to the following performance tests. The test results of the batteries obtained from lithium-ion battery manufacturing step a are shown in Table 2, the test results of the batteries obtained from lithium-ion battery manufacturing step b are shown in Table 4, and the test results of the batteries obtained from lithium-ion battery manufacturing step c are shown in Table 6.

[0102] Battery testing

[0103] (1) 25℃ Cyclic Test

[0104] Test Method: The battery was placed in an environment of 25±2 degrees Celsius and subjected to standard charge-discharge cycles at a charging rate of 3C, a discharging rate of 1C, and a charging voltage of 3.0V~4.51V. The capacity retention rate and battery thickness expansion rate were calculated after the cycles (thickness testing was performed using a PPG battery thickness gauge, with a weight set to 700g). The calculation formula is as follows:

[0105] The capacity retention rate (%) of the nth cycle = (discharge capacity of the nth cycle) / (discharge capacity of the first cycle) * 100%; the thickness expansion rate (%) of the nth cycle = (cell thickness after the nth cycle) / (test thickness before the cycle) * 100%.

[0106] (2) 45℃ Cyclic Test

[0107] Test method: The battery was placed in an environment of 45±2 degrees, and the capacity retention rate and thickness expansion rate of the battery after cycling were calculated according to the standard charge-discharge cycle, with a charge rate of 3C, a discharge rate of 1C, a charge voltage of 3.0V-4.51V. The calculation formula is as follows:

[0108] The nth cycle capacity retention rate (%) = (the nth cycle discharge capacity) / (the first cycle discharge capacity) * 100%; the nth cycle thickness expansion rate (%) = (the thickness of the battery after the nth cycle) / (the thickness before cycling) * 100%.

[0109] (3) 45°C intermittent cycle test

[0110] Test method: The battery was placed in an environment of 45±2 degrees, and the capacity retention rate and thickness expansion rate of the battery after cycling were calculated according to the standard charge-discharge cycle, with a charge rate of 3C, a discharge rate of 1C, a charge voltage of 3.0V-4.51V. The calculation formula is as follows:

[0111] The nth cycle capacity retention rate (%) = (the nth cycle discharge capacity) / (the first cycle discharge capacity) * 100%; the nth cycle thickness expansion rate (%) = (the thickness of the battery after the nth cycle) / (the thickness before cycling) * 100%.

[0112] (4) 45°C float test

[0113] Test method: The battery was placed in an environment of 45±2 degrees, and the capacity retention rate and thickness expansion rate of the battery after cycling were calculated according to the standard charge-discharge cycle, with a charge rate of 3C, a discharge rate of 1C, a charge voltage of 3.0V-4.51V. The calculation formula is as follows:

[0114] The thickness expansion rate (%) = (the thickness of the battery after 45D continuous charging - the thickness of the battery before testing) / (the thickness of the battery before testing) * 100%.

[0115] (5) Overcharge test

[0116] Test method: Place the battery in a high-low temperature chamber at 25±2 degrees. Charge the battery at room temperature at 1C constant current to 4.51V (constant voltage charge to 0.05C), stand for 5min, then 1C constant current and constant voltage charge to 10V, continue charging for 40H, record the voltage, internal resistance and weight of the battery, and record the number of 10 battery tests that meet the requirements. Note: leakage, fire, combustion are judged as unqualified.

[0117] (6) Hot box test

[0118] Test method: Place the battery in a high-low temperature chamber at 25±2 degrees. Charge the battery at room temperature at 1C constant current to 4.51V (constant voltage charge to 0.05C), stand for 2h, then place the battery in a high-low temperature chamber, place the battery in a hot box within 1h, then heat the hot box to 150℃ at a rate of 5℃ / min, hold for 60min, record the voltage, internal resistance and weight of the battery, and record the number of 10 battery tests that meet the requirements. Note: leakage, fire, combustion are judged as unqualified.

[0119] Table 1 Note: The mass percentage of organic solvent in the electrolyte corresponding to Table 1 is EC:PC:PP=10:30:60 (normalized to 100%), and the additives also include PS accounting for 4% of the mass percentage of the electrolyte and FEC accounting for 15% of the mass percentage of the electrolyte.

[0120] Table 2

[0121] According to the data in Table 1 and Table 2, by comparing Comparative Example 1 and Comparative Example 2, it is found that in the case of adding only nitrile compounds and a small amount of other additives (such as FEC and PS), even if the content of nitrile compounds is increased, the cycle performance and safety performance of lithium ion batteries are still poor, and the main reason may be that the protection of the positive and negative electrode interface, especially the negative electrode interface, is insufficient.

[0122] By comparing Example 1 to Example 10, and Comparative Example 2, it is found that when a small amount of fluorinated aluminate compound is further added, the cycle performance, float test, and safety performance of the battery are all significantly improved, which is mainly due to the good passivation effect of the fluorinated aluminate compound on the positive and negative electrode interfaces. By comparing Example 15 and 20, and Comparative Example 5 and 7, it is found that when the mass ratio of the fluorinated aluminate compound to the nitrile compound is too small (e.g., less than 0.01), the content of the fluorinated aluminate compound is too low to effectively passivate the negative electrode interface and significantly inhibit the destruction of the SEI film by the high content of the nitrile compound, resulting in poor cycle performance and safety performance of the battery. When the mass ratio of the fluorinated aluminate compound to the nitrile compound is too high (e.g., greater than 20), too much fluorinated aluminate compound results in too high a film formation impedance, significantly deteriorating the room temperature cycle, while the low content of the nitrile compound cannot effectively passivate the positive electrode interface, and the two cannot play a synergistic role, resulting in poor electrical performance and safety performance. When the mass ratio of the fluorinated aluminate compound to the nitrile compound is 0.01 to 20, the cycle performance and safety performance of the battery are good.

[0123] By comparing Example 7 and Example 11, and Comparative Examples 1-3, it is found that when the additive only contains a fluorinated aluminate compound or only contains a nitrile compound, the performance of the battery is worse than when the additive contains both a fluorinated aluminate compound and a nitrile compound, which is because the fluorinated aluminate compound and the nitrile compound have a synergistic effect, and the addition of the fluorinated aluminate compound and the nitrile compound not only further achieves passivation of the high-voltage positive electrode interface and inhibition of the degradation of the positive electrode material, but also inhibits the poor compatibility of the nitrile compound with the negative electrode interface, thereby simultaneously improving the passivation effect on the positive and negative electrode interfaces.

[0124] By comparing Example 1 to Example 10, it is found that when the fluorinated aluminate compound is selected as compound 11 as the additive, the cycle performance, float test, and safety performance of the battery are the best, which is because compound 11 has more F atoms, which can form SEI films and CEI films with higher content of LiF, and its cyclic structure is conducive to its polymerization to generate a polymer film of fast ion conductor, which can ensure high mechanical properties, chemical stability, and ionic conductivity.

[0125] It is found by comparing Example 7, Examples 11 to 14, and Comparative Examples 2 and 4 that, as the content of the fluoroaluminate compound increases, the high-temperature performance is improved, but the room-temperature cycle is relatively deteriorated, mainly because too much aluminate compound leads to too high impedance of the film formed, and lithium precipitation is prone to occur during the room-temperature cycle. The mass percentage of the fluoroaluminate compound in the electrolyte is 0.1% to 10%. Further, when the mass percentage of the fluoroaluminate compound in the electrolyte is 1% to 10%, the battery has more excellent cycle performance and safety performance. It is found by comparing Example 14, Example 19, Example 20, and Example 23, and Comparative Examples 5 and 6 that, as the content of the nitrile compound increases, the high-temperature performance of the battery is improved, but the room-temperature performance is deteriorated, which is due to the increase in the content of the nitrile compound, the increase in the viscosity, and the destruction of the SEI film. The mass percentage of the nitrile compound in the electrolyte is 0.5% to 10%. Further, it is found by comparing Example 13, Example 17, and Example 22 that, when the mass percentage of the fluoroaluminate compound in the electrolyte is 1% to 10%, and the mass percentage of the nitrile compound in the electrolyte is 7% to 10%, the battery has more excellent cycle performance and safety performance.

[0126] Table 3 Note: The mass percentage of the organic solvent in the electrolyte is EC:PC:PP = 10:30:60.

[0127] Table 4

[0128] According to the data in Table 3 and Table 4, after the fluoroaluminate compound and the nitrile compound are used in combination, and further addition of the carbonate compound, the sulfur-oxygen double bond compound, and the lithium salt compound, the cycle performance, the float test, and the safety performance of the battery are further improved, which is mainly due to the fact that the carbonate compound, the sulfur-oxygen double bond compound, and the lithium salt compound as additives further passivate the positive and negative electrode interfaces, and inhibit the side reactions at the positive and negative electrode interfaces. In addition, the improvement effect of the electrical performance and the safety performance of the battery is not significant when only one of the carbonate compound, the sulfur-oxygen double bond compound, and the lithium salt compound is added, mainly because the passivation effect of the positive and negative electrode interfaces is insufficient, and the effect is better when multiple combinations are used. In addition, too little amount of the carbonate compound, the sulfur-oxygen double bond compound, and the lithium salt compound will lead to insufficient film protection, and too much amount will lead to a relatively thick film, and the improvement effect on the electrical performance and the safety performance is not obvious.

[0129] Table 5 Note: In the electrolyte, the mass percentage of organic solvent is EC:PC:PP = 10:30:60 (normalized to 100%), and the additives further include 4% PS, 15% FEC, 0.5% VC, 1% DTD, 0.5% LiDFOB, 0.5% LiBOB, 2% ADN, 2% SN, 1% DENE, and 2% HTCN.

[0130] Table 6

[0131] According to the data in Tables 5 and 6, under the synergistic effect of the fluoroaluminate compound and the nitrile compound, the battery cell can still have good cycle, floating, and safety performance under different Si components and contents, and the electrolyte additive of the embodiments of the present application can be applied to various types of silicon negative electrode batteries.

[0132] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles, practical application, or improvement of the technology in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. An electrolyte additive characterized in that, The fluorinated aluminates compound and the nitrile compound are in a mass ratio of 0.01-20.

2. The electrolyte additive according to claim 1, characterized in that, The fluoroaluminate compound is selected from at least one of the following structural formula I, structural formula II, structural formula III: R1, R2, R3, R4, R5, R6 are respectively selected from one or more fluorine atom-substituted alkane, alkene, alkyne with 1-6 carbon atoms; M is selected from at least one of Li, Na, K.

3. The electrolyte additive according to claim 2, characterized in that, The fluoroaluminate compound is selected from at least one of the following compounds:

4. The electrolyte additive according to claim 1, characterized in that, The fluorinated aluminates compound accounts for 0.1%-10% of the mass percentage of the electrolyte.

5. The electrolyte additive according to claim 4, characterized in that The fluorinated aluminates compound accounts for 1%-10% of the mass percentage of the electrolyte.

6. The electrolyte additive according to claim 1, characterized in that, The nitrile compound accounts for 0.5%-10% of the mass percentage of the electrolyte.

7. The electrolyte additive according to claim 6, characterized in that The nitrile compound accounts for 7%-10% of the mass percentage of the electrolyte.

8. The electrolyte additive according to claim 1, characterized in that, The nitrile compound is selected from at least one of di-nitrile, tri-nitrile, tetra-nitrile.

9. The electrolyte additive according to claim 8, characterized in that The nitrile compound is selected from at least one of butanedinitrile, pentanedinitrile, hexanedinitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,3,6-hexanetrimethanitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,4,6-hexanetetranitrile, 1,2,4,5-benzene tetramethanitrile, 2,3,5,6-pyrazine tetranitrile, ether tetranitrile.

10. The electrolyte additive according to any one of claims 1 to 9, characterized in that The electrolyte additive further comprises at least one of carbonate compound, metal salt compound, sulfur-oxygen double bond compound.

11. The electrolyte additive according to claim 10, characterized in that The carbonate compound is selected from at least one of fluorinated ethylene carbonate FEC, difluorinated ethylene carbonate DFEC, vinylene carbonate VC, vinyl ethylene carbonate VEC; and / or, the carbonate compound accounts for 1%-30% of the mass percentage of the electrolyte.

12. The electrolyte additive according to claim 10, characterized in that, The metal salt compound is selected from at least one of di-oxalate borate MBOB, difluoro-oxalate borate MDFOB, tetrafluoroborate MBF4, difluorophosphate MPO2F2 and difluoro-oxalate phosphate MDODFP; and / or, the metal salt compound accounts for 0.1%-7% of the mass percentage of the electrolyte.

13. The electrolyte additive of claim 10, wherein The sulfur-oxygen double bond compound is selected from at least one of 1,3-propane sulfonate endolactone PS, 1,3-propylene sulfonate endolactone PST, vinyl sulfite DTD, 1,4-butane sulfonate endolactone BS, ethylene sulfite ES and vinyl ethylene sulfite VES; and / or, the sulfur-oxygen double bond compound accounts for 0.1%-5% of the mass percentage of the electrolyte.

14. An electrolyte, characterized by The electrolyte comprises electrolyte salt, organic solvent and additive, the additive is the electrolyte additive according to any one of claims 1-13.

15. An electrochemical energy storage device, characterized by The electrolyte comprises electrolyte salt, organic solvent and additive, the additive is the electrolyte additive according to any one of claims 1-13.

16. The electrochemical energy storage device of claim 15, wherein, The negative electrode comprises current collector and negative electrode active material coated on the current collector, the negative electrode active material is selected from at least one of carbon-based material, silicon-based material, alkali metal, material alloyable with alkali metal.

17. The electrochemical device of claim 16, wherein, The negative electrode active material is selected from silicon-based material.

18. The electrochemical device of claim 17, wherein, The fluorinated aluminates compound accounts for a mass percentage of the electrolyte, the silicon-based material accounts for b mass percentage of the negative electrode active material, a / b is 0.0015-1.

19. The electrochemical device of claim 17 or 18, wherein, The silicon-based material accounts for 10%-60% of the mass percentage of the negative electrode active material.

20. The electrochemical device of claim 15, wherein, The positive electrode active material of the positive electrode is selected from lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum, lithium iron phosphate, lithium manganese iron phosphate, lithium-rich manganese-based, Na x at least one of TMO2, wherein TM is a transition metal atom, and 0 < X < 1.

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