Electrolyte, battery, battery pack, and electric device

Abstract

The application provides an electrolyte, a battery, a battery pack and an electric device. The electrolyte comprises a solvent, and the solvent comprises an aromatic nitrile solvent. The structure of the aromatic nitrile solvent is shown in formula I: formula I, wherein R1 is selected from any one of difluoromethylene and monofluoromethylene; R2-R6 are each independently selected from substituted or unsubstituted methyl, hydrogen or fluorine. The application can improve the stability of the electrolyte under low-temperature working conditions and the desolvation efficiency, and improve the cycle performance of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to an electrolyte, a battery, a battery pack, and an electrical device. Background Technology

[0002] Secondary batteries are widely used in new energy vehicles, energy storage systems and consumer electronics. Under low temperature conditions, secondary batteries usually adopt a non-aqueous electrolyte system with carbonate solvents as the main component.

[0003] However, carbonate solvents have a stronger coordination effect with active ions such as lithium ions at low temperatures, which can restrict the desolvation process and lead to an increase in charge transfer impedance. At the same time, their crystallization tendency is enhanced, the stability of the electrolyte decreases, and thus weakens the ion transport efficiency and capacity retention.

[0004] Therefore, how to improve the stability and desolvation efficiency of the electrolyte in low-temperature environments, improve the cycle performance of the battery, and take into account the stability of the system has become an urgent technical problem to be solved. Summary of the Invention

[0005] This application provides an electrolyte, a battery, a battery pack, and an electrical device, which can improve the stability and desolvation efficiency of the electrolyte under low-temperature conditions and improve the cycle performance of the battery.

[0006] In a first aspect, embodiments of this application provide an electrolyte comprising a solvent, wherein the solvent comprises an aromatic nitrile solvent, and the structure of the aromatic nitrile solvent is shown in Formula I:

[0007] Formula I,

[0008] In Formula I, R1 is selected from either difluoromethylene or monofluoromethylene; R2-R6 are each independently selected from substituted or unsubstituted methyl, hydrogen, or fluorine.

[0009] In one possible implementation, R2-R3 are each independently selected from methyl or fluoromethyl.

[0010] In one possible implementation, R4-R6 are each independently selected from hydrogen.

[0011] In one possible embodiment, the aromatic nitrile solvent includes one or more of the following: 2-fluoro-o-methylphenylacetonitrile, 2-fluoro-o-(fluoromethyl)phenylacetonitrile, 2-fluoro-o-(difluoromethyl)phenylacetonitrile, 2-fluoro-o-(trifluoromethyl)phenylacetonitrile, 2,2-difluoro-o-methylphenylacetonitrile, 2,2-difluoro-o-(fluoromethyl)phenylacetonitrile, 2,2-difluoro-o-(difluoromethyl)phenylacetonitrile, 2,2-difluoro-o-(trifluoromethyl)phenylacetonitrile, and 2,2-difluoro-o-(trifluoromethyl)tetrafluorophenylacetonitrile.

[0012] In one possible implementation, the aromatic nitrile solvent in the solvent has a mass percentage of 20% to 40%, preferably 22.5% to 35%.

[0013] In one possible embodiment, the solvent further includes carbonate solvents and / or carboxylic acid ester solvents; preferably, the carbonate solvents include cyclic carbonate solvents and / or linear carbonate solvents; preferably, the carboxylic acid ester solvents include one or more of ethyl acetate, methyl propionate, and ethyl propionate; preferably, the carbonate solvents include linear carbonate solvents, and the mass percentage of the cyclic carbonate solvent in the solvent is 20% to 30%; preferably, the carbonate solvents include cyclic carbonate solvents, and the sum of the mass percentage of the linear carbonate solvent and the mass percentage of the carboxylic acid ester solvent in the solvent is 25% to 50%.

[0014] In one possible embodiment, the electrolyte further includes an electrolyte salt and / or additives; preferably, the mass percentage of the additives in the electrolyte is 0.5% to 3.0%; preferably, the molar volume ratio of the electrolyte salt to the solvent is 0.6 mol / L to 1.5 mol / L; preferably, the electrolyte salt includes a lithium salt, which includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, and tris(trifluoromethanesulfonyl)methyl lithium; preferably, the additives include one or more of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, propanesulfonate lactone, butanesulfonate lactone, adiponitrile, succinitrile, lithium bis(oxalato)borate, and lithium difluorooxalato)borate.

[0015] Secondly, a battery comprising the electrolyte described above.

[0016] Thirdly, a battery pack comprising at least two batteries as described above.

[0017] Fourthly, an electrical device comprising the aforementioned battery or battery pack.

[0018] The present application provides an electrolyte, battery, battery pack, and electrical device. By introducing a specific structure of aromatic nitrile solvent into the solvent of the electrolyte and limiting its substituent composition, the interaction between the solvent and active ions can be regulated, improving the active ion transport performance and desolvation efficiency at low temperatures, thereby reducing the charge transfer impedance under low-temperature conditions and improving the stability of the electrolyte and the cycle capacity retention capability of the battery. Detailed Implementation

[0019] To enable those skilled in the art to better understand the solutions of this invention, the following provides a more detailed description of this application. The specific embodiments listed below are merely descriptions of the principles and features of this invention; the examples are only for explaining the invention and are not intended to limit its scope. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0020] Currently, carbonate solvents (such as ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate) in non-aqueous electrolyte systems exhibit strong coordination properties, allowing their carbonyl oxygen atoms to form strong interactions with active ions such as lithium ions. While this strong coordination facilitates the dissolution of electrolyte salts like lithium salts and improves the ionic conductivity of the electrolyte, it also results in excessively high binding energies between active ions and solvent molecules. Especially at low temperatures, active ions need to overcome a high energy barrier to escape from the solvation sheath and enter the electrode material. Simultaneously, their crystallization tendency increases, leading to slow active ion transport rates and decreased cycle performance.

[0021] In view of this, embodiments of the present invention provide an electrolyte comprising a solvent, the solvent comprising an aromatic nitrile solvent, the structure of which is shown in Formula I:

[0022] Formula I,

[0023] In Formula I, R1 is selected from either difluoromethylene or monofluoromethylene; R2-R6 are each independently selected from substituted or unsubstituted methyl, hydrogen, or fluorine.

[0024] According to the inventors' research, an electrolyte with the above composition can improve the stability and desolvation efficiency of the electrolyte under low-temperature conditions, thereby improving the cycle performance of the battery.

[0025] The reasons for this are as follows: In aromatic nitrile solvents, the cyano group (-C≡N), as a typical linear monodentate ligand, has a lone pair of electrons from its sp-hybridized nitrogen atom that coordinates with active ions such as lithium ions. Due to the combined effect of the conjugated electron-withdrawing effect (-C effect) of the benzene ring, the bond energy of the coordination bond between the nitrogen in the cyano group and the active ion is significantly weaker than that of the coordination bond between the carbonyl oxygen in carbonate and carboxylic ester solvents and the active ion. At the same time, the fluorine substituent in R1 may also participate in coordination competition through secondary weak interactions between fluorine and the active ion, making the coordination site exhibit dynamic instability and rapid exchange kinetics. Furthermore, the fluorine atom in the fluorine substituent in R1 has a van der Waals radius much larger than that of the hydrogen atom, which can further increase the volume of the side chain. In addition, the benzene ring provides a rigid planar framework, and its large volume will hinder the coordination of other solvent molecules around the active ion in the electrolyte. When the active ion attempts to coordinate with other solvent molecules, the rigid benzene ring will generate significant steric hindrance, physically preventing the close packing of other solvent molecules (such as straight-chain carbonates) around the active ion. This results in weakening the coordination strength between active ions and solvents, as well as improving the low-temperature stability of the electrolyte. It can also increase the desolvation rate of active ions and enhance the low-temperature cycling performance of the electrolyte.

[0026] In this embodiment of the invention, the specific structure of the aromatic nitrile solvent and the mass percentage of the aromatic nitrile solvent in the solvent can be tested according to the following method:

[0027] S1. Take the above electrolyte, dissolve it in deuterated chloroform (CDCl3) solvent, and use tetramethylsilane (TMS) as an internal standard. 13 12C nuclear magnetic resonance (NMR) 19 F NMR and 1 Combined H NMR detection;

[0028] S2, 13 C NMR test parameters: scan frequency not less than 100MHz, relaxation delay D1 set to 2~5 seconds, sampling number not less than 1024 times to ensure signal-to-noise ratio;

[0029] 13 C NMR spectra should be located using the nitrile carbon signal as a general structural anchor. All target compounds show a nitrile carbon (-C≡N) signal in the δ 117 ppm to 120 ppm range. This signal is a single peak and is not affected by fluorine atom coupling, which can be used to confirm the presence of phenylacetonitrile.

[0030] Observe the chemical shift and splitting pattern of the benzylic carbon (i.e., the carbon atom directly connected to the benzene ring and the cyano group): If the carbon exhibits a sharp singlet at δ 25ppm~30ppm without fluorine-coupled splitting, then R1 is determined to be -(CH2)-; if it exhibits a clear doublet at δ 75ppm~85ppm, and the carbon-fluorine one-bond coupling constant is high... 1 If JCF is approximately 180~190 Hz, then R1 is determined to be -(CFH)-.

[0031] S3, proceed 19 F NMR determination is used to achieve precise localization and quantification of fluorine-containing functional groups. Recommended measurement parameters are: scan frequency of 376 MHz or 564 MHz, and sampling number of no less than 256 times.

[0032] exist 19 In the 1H NMR spectrum, various fluorine signals should be analyzed according to chemical shift zones: when R2 is -(CF3), a singlet or broad singlet appears in the δ -60ppm to -65ppm range, and its integrated area corresponds to 3 fluorine atoms; when R1 is -(CF2)-, a triplet or symmetrical multiplet appears in the δ -110ppm to -120ppm range, and its integrated area corresponds to 2 fluorine atoms; when R1 is -(CFH)-, a doublet coupled to hydrogen nuclei appears in the δ -120ppm to -135ppm range, and its hydrogen-fluorine double bond coupling constant... 2 JHF is approximately 46 Hz ~ 48 Hz;

[0033] S4, proceed 1 H-NMR measurements were performed as supplementary verification of the above structure. 1 H-NMR parameters are set to 400 MHz or 600 MHz, with a scan width of 16 ppm;

[0034] exist 1In the H-NMR spectrum, the first step should be to look for the ortho-methyl signal when R2 is -(CH3) in the δ 2.30ppm~2.45ppm range. This signal is a single peak, and the integrated area corresponds to 3 hydrogen atoms. If R2 is -(CF3), then there should be no methyl proton signal in this region. Subsequently, the benzylic proton region was observed: when R1 is -(CH2)-, a single peak is visible at δ 3.70ppm~3.80ppm with an integral area of ​​2H; when R1 is -(CFH)-, a quartet is visible at δ 5.90ppm~6.20ppm with an integral area of ​​1H. This proton is significantly shifted to a lower field due to its direct attachment to the fluorinated carbon; when R1 is -(CF2)-, there should be no corresponding proton signal in either of the above two regions; the aromatic ring proton signal (when R3-R6 are H) is concentrated at δ 7.20ppm~7.80ppm, exhibiting multiple peaks; if a certain position is substituted by fluorine, causing the corresponding proton to disappear, the substitution site of the fluorine atom on the benzene ring can be inferred from the reduction in peak area and the change in splitting mode.

[0035] S5. When the data from the three spectra above are consistent and there are no contradictory signals, the structure of the aromatic nitrile solvent can be confirmed.

[0036] S6, Simultaneous Combination 13 C NMR, 19 F NMR and 1 By converting the integral area, molecular weight, and corresponding nucleus number of each spectrum in the H NMR three-spectrum analysis, we can obtain the types of cyclic carbonate solvents, linear carbonate solvents, and carboxylic acid ester solvents. We can also obtain the molar ratio of cyclic carbonate solvents: linear carbonate solvents: carboxylic acid ester solvents: aromatic nitrile solvents, and thus obtain the mass percentage of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and aromatic nitrile solvents in the solvent.

[0037] In some embodiments, R2-R3 are each independently selected from methyl or fluoromethyl, i.e., R2 can be selected from methyl or fluoromethyl, and R3 can be selected from methyl or fluoromethyl, wherein the fluoromethyl can be any of monofluoromethyl, difluoromethyl, or trifluoromethyl. The electron-donating inductive effect (+I effect) of the ortho-methyl group makes the bond energy of the nitrogen-active ion coordination bond in the cyano group significantly weaker than the coordination bond energy of the carbonyl oxygen-active ion in carbonate and carboxylic acid solvents. At the same time, the ortho-methyl group can hinder the rotation of the originally free cyano group, forcing the molecule to adopt a non-coplanar twisted conformation. Furthermore, the fluorine atom in the fluoromethyl group has a van der Waals radius much larger than that of the hydrogen atom, which can further increase the volume of the side chain and generate significant steric hindrance. This physically prevents other solvent molecules (such as straight-chain carbonates) from packing tightly around the active ion, thereby further reducing the interaction between the solvent and the active ion and improving the desolvation efficiency.

[0038] In some embodiments, R4-R6 are each independently selected from hydrogen, i.e., R4 can be selected from hydrogen, R5 can be selected from hydrogen, and R6 can be selected from hydrogen. Fewer lateral substitutions result in a more regular spatial configuration of the solvent molecules, and the solvation shell around the active ions is more likely to rearrange and desorb, thus being more conducive to rapid desolvation at low temperatures and improving the low-temperature stability of the electrolyte.

[0039] In some embodiments, the aromatic nitrile solvent includes one or more of 2-fluoroo-methylphenylacetonitrile, 2-fluoroo-(fluoromethyl)phenylacetonitrile, 2-fluoroo-(difluoromethyl)phenylacetonitrile, 2-fluoroo-(trifluoromethyl)phenylacetonitrile, 2,2-difluoroo-methylphenylacetonitrile, 2,2-difluoroo-(fluoromethyl)phenylacetonitrile, 2,2-difluoroo-(difluoromethyl)phenylacetonitrile, 2,2-difluoroo-(trifluoromethyl)phenylacetonitrile, and 2,2-difluoroo-(trifluoromethyl)tetrafluorophenylacetonitrile. The conjugated structure formed by the aromatic ring and nitrile group gives the molecule both a certain degree of polarity and a low coordination strength. The ortho-methyl or polyfluorine substitution further changes the spatial configuration and electronic distribution, making it easier for the solvated structure formed after the electrolyte salt dissociates to rearrange and release at the electrode interface. This can suppress the crystallization tendency common in carbonate systems under low temperature conditions, reduce local compositional imbalance, thereby reducing interfacial charge transfer impedance and low temperature stability of the electrolyte, improving the migration efficiency and intercalation / deintercalation kinetics of active ions such as lithium ions, and improving the low temperature cycle performance of the battery.

[0040] In some embodiments, the mass percentage of aromatic nitrile solvent in the solvent is 20% to 40%, for example, it can be 20%, 22.5%, 25%, 30%, 35%, 40%, or any combination thereof. Aromatic nitrile solvents can partially replace strong coordination solvents, reduce the binding strength between active ions and solvents, and make it easier for active ions to remove the solvation shell at the electrode interface; at the same time, it can further avoid excessively loose solvation structures or imbalances in system viscosity and solubility.

[0041] In some specific embodiments, the mass percentage of aromatic nitrile solvent in the solvent is 22.5% to 35%. Aromatic nitrile solvent can form a more stable synergistic solvation system with other solvents, which is beneficial to the full dissociation of electrolyte salt, can further significantly inhibit low-temperature crystallization, and improve desolvation efficiency.

[0042] In some embodiments, the solvent may also include one or more of carbonate solvents and carboxylic acid ester solvents to form a multi-component synergistic solvent system, which, while improving desolvation efficiency, further maintains the solvation structure and balances the viscosity and solubility of the solvent system.

[0043] In some specific embodiments, the carbonate solvent includes one or more of cyclic carbonate solvents and linear carbonate solvents. The higher dielectric constant of cyclic carbonate solvents helps to promote electrolyte salt dissociation and reduce ion association, thereby improving the initial ionic conductivity of the electrolyte. The low viscosity of linear carbonate solvents can further improve the low-temperature fluidity of the electrolyte and reduce the resistance to active ion migration, allowing the electrolyte to maintain good transport capacity at low temperatures. At the same time, the flexible bending properties of its conformation play a role in diluting and homogenizing the electrolyte at the microscopic level, breaking down the high concentration barrier in the microscopic local area and preventing the electrolyte from solidifying. In addition, the unique asymmetric structure of aromatic nitrile solvents and the steric hindrance generated by the rigid benzene ring undermine the long-range order of cyclic carbonates, effectively inhibiting solvent crystallization and precipitation behavior at low temperatures. This synergistic design of multi-component anti-crystallization, homogenization, and solubilization effects ensures a thermodynamically stable liquid phase of the electrolyte over a wide temperature range, which is beneficial to improving the low-temperature cycle performance of the battery.

[0044] Cyclic carbonate solvents include one or more of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC); linear carbonate solvents include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (EMC).

[0045] In some specific embodiments, the carboxylic acid ester solvents include one or more of ethyl acetate (EA), methyl propionate (MP), and ethyl propionate (EP), which can further adjust the solvation structure and system polarity, and synergistically improve the ion migration performance at low temperatures with aromatic nitrile solvents and carbonate solvents.

[0046] In some specific embodiments, the mass percentage of cyclic carbonate solvent in the solvent is 20% to 30%, for example, it can be 20%, 22.5%, 25%, 27.5%, 30%, or any combination thereof. This is more conducive to improving the dissociation ability and stability of the electrolyte salt, while reducing the viscosity of the electrolyte, improving the low-temperature stability and desolvation efficiency of the electrolyte, and improving the low-temperature cycle performance of the battery.

[0047] In some specific embodiments, the sum of the mass percentages of linear carbonate solvents and carboxylic acid ester solvents in the solvent is 25% to 50%, meaning the total mass of carboxylic acid ester solvents and linear carbonate solvents in the solution accounts for 25% to 50% of the total mass of the solvent. For example, it can be a range of 25%, 30%, 35%, 40%, 45%, 50%, or any combination thereof. This can further reduce the overall viscosity of the system and improve low-temperature wettability, thereby reducing desolvation resistance.

[0048] In some embodiments, the electrolyte further includes one or more of an electrolyte salt and additives. The electrolyte salt can provide a source of migratory active ions and together with the aromatic nitrile solvent, constitute an ion conduction system. The additives can optimize the electrolyte system and suppress side reactions.

[0049] In some specific embodiments, the mass percentage of the additive in the electrolyte is 0.5% to 3.0%, for example, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.0%, 3.0%, or any combination thereof. This helps to balance the adjustment of the interfacial film composition and suppress the occurrence of side reactions.

[0050] In some specific embodiments, the molar volume ratio of electrolyte salt to solvent is 0.6 mol / L to 1.5 mol / L, for example, it can be 0.6 mol / L, 0.9 mol / L, 1.2 mol / L, 1.5 mol / L, or any combination thereof. This can further reduce electrolyte viscosity and desolvation resistance while ensuring sufficient ion concentration, thereby reducing transport resistance at low temperatures.

[0051] In some specific embodiments, the electrolyte salt includes lithium salts, including one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiSO3CF3), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), and tris(trifluoromethanesulfonyl)methyl lithium (LiC(CF3SO2)3). These lithium salts can ensure good dissociation and electrochemical stability, and can further improve the low-temperature stability of the electrolyte while improving the desolvation efficiency.

[0052] In some specific embodiments, the additives include one or more of vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), propanesulfonate lactone, butanesulfonate lactone, adiponitrile, succinitrile, lithium bis(oxalato)borate (LiBOB), and lithium difluorooxalato)borate (LiODFB). This facilitates preferential reduction and decomposition at the negative electrode surface, forming a dense and stable solid electrolyte interphase (SEI) film, thereby reducing interfacial impedance. Furthermore, adiponitrile and succinitrile can further modulate the solvation structure and improve low-temperature rate performance.

[0053] In this embodiment of the invention, the type of electrolyte salt and the molar volume ratio of electrolyte salt to solvent can be determined by the following method: Ion chromatography (IC) can be used to determine the cations and anions of the electrolyte salt, thus obtaining the type of electrolyte salt. Simultaneously, the content of cations and anions in the electrolyte can be measured. Specifically, the battery can be disassembled in a glove box, the electrolyte taken, diluted with a diluent such as acetonitrile, and the content of cations and anions after dilution can be tested by ion chromatography. Then, the content of cations and anions in the electrolyte can be obtained by conversion according to the specific dilution factor. 13 C NMR, 19 F NMR and 1 The types and contents of each solvent are determined by H NMR, and then the molar volume ratio of electrolyte salt to solvent is obtained. Among them, ion chromatography (IC) is a conventional test method in this field and there are no restrictions on it.

[0054] In this embodiment of the invention, the type of additive and the mass percentage of the additive in the electrolyte can be determined by the following method: Take the above-mentioned electrolyte, firstly distinguish the types of additives such as VC, VEC, FEC, sulfur-containing, phosphorus-based, and fluoronitrile by high performance liquid chromatography based on the retention time of each additive standard, and then complete the qualitative confirmation by analyzing the molecular skeleton structure by nuclear magnetic resonance spectroscopy. Then, use high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) to collect the specific elemental chromatographic signals of fluorinated, sulfur-based, and phosphorus-based additives containing F, S, and P characteristic heteroatoms to establish external standard curves for accurate quantification. For unsaturated carbonate additives without characteristic heteroatoms, the external standard method of liquid phase detector is used for quantification. Combine the sample weight and dilution factor to calculate the mass percentage of each type of additive in the electrolyte.

[0055] This invention also provides a battery comprising the electrolyte described above, which has advantages corresponding to the electrolyte described above, and will not be described in detail hereafter.

[0056] Generally, a battery includes a cell and a casing that encapsulates the cell. The electrolyte is injected into the cell within the casing. The cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of positive electrode, separator, and negative electrode stacked sequentially and then wound together.

[0057] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0058] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0059] Specifically, the diaphragm can be a polymer membrane, which can be a conventional diaphragm material in the art, for example, the diaphragm includes polyethylene (PE) membrane and / or polypropylene (PP) membrane.

[0060] In this embodiment of the invention, conventional positive electrode sheets in the art can be used, and there are no particular limitations. For example, the positive electrode sheet may include a positive current collector and a positive active layer located on at least one side surface of the positive current collector. Specifically, the positive active layer may be provided on one side surface of the positive current collector, or the positive active layers may be provided on both opposite sides of the positive current collector in the thickness direction (i.e., the two surfaces of the positive current collector).

[0061] Generally, the positive electrode active layer may include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, all of which can be conventional materials in the art. For example, the positive electrode active material may include one or more of lithium nickel oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and positive electrode ternary materials. The positive electrode ternary material may include nickel cobalt manganese ternary materials (NCM) and / or nickel cobalt aluminum ternary materials (NCA). The positive electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0062] Generally, in the positive electrode active layer, the mass percentage of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass percentage of the positive electrode conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof. The mass percentage of the positive electrode binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0063] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0064] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the positive electrode active layer, such as the positive electrode active material, positive electrode conductive agent, and positive electrode binder, can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0065] In this embodiment of the invention, conventional negative electrode sheets in the art can be used, and there are no particular limitations. For example, the negative electrode sheet includes a negative current collector and a negative active layer located on at least one side surface of the negative current collector. Specifically, the negative active layer can be provided on one side surface of the negative current collector, or negative active layers can be provided on both opposite sides of the negative current collector in the thickness direction.

[0066] Specifically, the negative electrode active layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include graphite, which may include natural graphite and / or artificial graphite; the negative electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the negative electrode binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0067] Generally, in the negative electrode active layer, the mass percentage of the negative electrode active material (i.e., the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active layer) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass percentage of the negative electrode conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; the mass percentage of the negative electrode binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0068] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0069] In this embodiment of the invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, negative electrode conductive agent, and negative electrode binder, can be dispersed in a solvent, such as water (specifically deionized water), to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0070] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator, negative electrode and separator can be stacked in sequence to obtain a battery cell. Then the battery cell is placed in a casing (outer packaging) and after conventional battery assembly processes such as baking, electrolyte injection (i.e., injecting the above-mentioned electrolyte), aging, formation and aging, a battery is obtained. In the battery preparation process, the baking, electrolyte injection (i.e., injecting electrolyte), aging, formation and aging processes involved are all conventional operations in the art and are not particularly limited.

[0071] This invention also provides a battery pack comprising at least two batteries as described above. This battery pack has advantages corresponding to the batteries described above, which will not be repeated here.

[0072] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0073] This invention also provides an electrical device, including the battery or battery pack described above. This electrical device has advantages corresponding to the battery pack described above, which will not be elaborated further.

[0074] The electrical equipment in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars, car chassis), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on them.

[0075] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0076] In the embodiments of the present invention, the aromatic nitrile solvents used can all be prepared according to the following steps:

[0077] Place o-methylbenzyl chloride (≥99%) into a three-necked reactor equipped with a stirrer, stir and heat to 65°C, add industrial-grade sodium cyanide solution in batches, control the dropping temperature to ≤80°C, after the dropping is completed, heat to 90°C, keep the reaction at this temperature for 100 min, take online or offline samples during the reaction, terminate the reaction when the o-methylbenzyl chloride residue is ≤0.5%, cool to room temperature, let stand and separate the layers, wash the organic phase twice with 5% sodium carbonate solution, then wash with deionized water until neutral, distill under reduced pressure (pressure -0.095MPa~-0.098MPa), collect the fraction at 115°C~120°C;

[0078] Then, it was dissolved in 500 ml of anhydrous tetrahydrofuran (THF), and industrial-grade sodium hydride was added in batches at -20℃ to 0℃. The mixture was kept at this temperature for 30 minutes. Then, N-fluorobis(phenyl)sulfonamide (NFSI) was added, and the temperature was slowly raised to 60℃ to 70℃ to carry out the substitution reaction. The reaction was then quenched with saturated ammonium chloride (NH4Cl), extracted with ethyl acetate, washed with sodium carbonate (Na2CO3), and dried.

[0079] Products with different degrees of substitution were obtained by controlling the substitution reaction time.

[0080] In this embodiment of the invention, after preparing aromatic nitrile solvents with different degrees of substitution according to the above steps, the aromatic nitrile solvent with the desired degree of substitution can be determined according to the following method:

[0081] After preparing the products with different degrees of substitution, they were dissolved in deuterated chloroform (CDCl3) solvent, and tetramethylsilane (TMS) was used as an internal standard. 13 C10 nuclear magnetic resonance (NMR) 19 F NMR and 1 Combined H NMR detection;

[0082] S1、 13 C NMR: The scanning frequency is not less than 100MHz, the relaxation delay D1 is set to 2~5 seconds, and the number of samplings is not less than 1024 to ensure the signal-to-noise ratio;

[0083] 13 C NMR spectra should be located using the nitrile carbon signal as a general structural anchor. All target compounds show a nitrile carbon (-C≡N) signal in the δ 117 ppm to 120 ppm range. This signal is a single peak and is not affected by fluorine atom coupling, which can be used to confirm the presence of phenylacetonitrile.

[0084] Observe the chemical shift and splitting pattern of the benzylic carbon (i.e., the carbon atom directly connected to the benzene ring and the cyano group): If the carbon exhibits a sharp singlet at δ 25ppm~30ppm without fluorine-coupled splitting, then R1 is determined to be -(CH2)-; if it exhibits a clear doublet at δ 75ppm~85ppm, and the carbon-fluorine one-bond coupling constant is high... 1 If JCF is approximately 180~190 Hz, then R1 is determined to be -(CFH)-.

[0085] S2, proceed 19 F NMR determination is used to achieve precise localization and quantification of fluorine-containing functional groups. Recommended measurement parameters are: scan frequency of 376 MHz or 564 MHz, and sampling number of no less than 256 times.

[0086] exist 19In the 1H NMR spectrum, various fluorine signals should be analyzed according to chemical shift zones: when R2 is -(CF3), a singlet or broad singlet appears in the δ -60ppm to -65ppm range, and its integrated area corresponds to 3 fluorine atoms; when R1 is -(CF2)-, a triplet or symmetrical multiplet appears in the δ -110ppm to -120ppm range, and its integrated area corresponds to 2 fluorine atoms; when R1 is -(CFH)-, a doublet coupled to hydrogen nuclei appears in the δ -120ppm to -135ppm range, and its hydrogen-fluorine double bond coupling constant... 2 JHF is approximately 46 Hz ~ 48 Hz;

[0087] S3, proceed 1 H-NMR measurements were performed as supplementary verification of the above structure. 1 The H-NMR parameters were set to 400 MHz or 600 MHz, with a scan width of 16 ppm.

[0088] exist 1 In the H-NMR spectrum, the first step should be to look for the ortho-methyl signal when R2 is -(CH3) in the δ 2.30ppm~2.45ppm range. This signal is a single peak, and the integrated area corresponds to 3 hydrogen atoms. If R2 is -(CF3), then there should be no methyl proton signal in this region. Subsequently, the benzylic proton region was observed: when R1 is -(CH2)-, a single peak is visible at δ 3.70ppm~3.80ppm with an integral area of ​​2H; when R1 is -(CFH)-, a quartet is visible at δ 5.90ppm~6.20ppm with an integral area of ​​1H. This proton is significantly shifted to a lower field due to its direct attachment to the fluorinated carbon; when R1 is -(CF2)-, there should be no corresponding proton signal in either of the above two regions; the aromatic ring proton signal (when R3-R6 are H) is concentrated at δ 7.20ppm~7.80ppm, exhibiting multiple peaks; if a certain position is substituted by fluorine, causing the corresponding proton to disappear, the substitution site of the fluorine atom on the benzene ring can be inferred from the reduction in peak area and the change in splitting mode.

[0089] Based on the above three spectra data, when these three data are consistent with each other and there are no contradictory signals, the aromatic nitrile solvent with the required degree of substitution can be confirmed.

[0090] Example 1

[0091] This invention provides an electrolyte, the specific preparation steps of which are as follows:

[0092] Preparation of electrolyte

[0093] In the preparation process of the above-mentioned aromatic nitrile solvents, online or offline real-time monitoring is performed to obtain the aromatic nitrile solvent M1 with the desired degree of substitution, as shown in Formula II:

[0094] Formula II,

[0095] EC, EMC, DMC, and M1 were mixed evenly in a mass ratio of 30:30:15:25. Then, VC (1% by mass of the electrolyte) and 1.0 mol / L LiPF6 were added and mixed evenly to obtain the electrolyte.

[0096] Example 2-Example 22

[0097] The difference from Example 1 is that the types of solvent components (M2 used in Examples 4-6 and 19-20 is as shown in Formula III, and M3 used in Examples 7-9 and 21-22 is as shown in Formula IV), the mass ratio of each component of the solvent, the mass percentage content and type of additives, the type of electrolyte salt and its molar volume ratio with the solvent are different, as detailed in Table 1. The remaining steps and conditions are the same as in Example 1.

[0098] Formula III,

[0099] Formula IV.

[0100] Table 1. Composition of the electrolyte

[0101]

[0102] Test case

[0103] I. Battery Preparation

[0104] 1. Preparation of positive electrode sheet

[0105] Lithium iron phosphate, carbon black, and PVDF were mixed in a mass ratio of 100:0.8:2.3, and NMP was added. The mixture was stirred evenly to prepare a positive electrode slurry.

[0106] The positive electrode slurry is coated on both sides of the aluminum foil. After drying and rolling, a positive electrode active layer is formed on both sides of the aluminum foil, thus obtaining the positive electrode sheet.

[0107] 2. Preparation of negative electrode sheet

[0108] Graphite, carbon black, SBR, and CMC are mixed in a mass ratio of 100:0.8:1.5:1.7, and deionized water is added. The mixture is stirred evenly to prepare a negative electrode slurry.

[0109] The negative electrode slurry is coated on both the front and back surfaces of a copper foil. After drying and rolling, a negative electrode active layer is formed on both the front and back surfaces of the copper foil, thus producing a negative electrode sheet.

[0110] 3. Battery assembly

[0111] A battery cell is obtained by stacking the negative electrode, separator, positive electrode, and separator in sequence, wherein the separator is a PE separator.

[0112] The cells are packaged in aluminum-plastic film and then subjected to baking, vacuum electrolyte injection (i.e., injection of the electrolyte prepared above, with an injection coefficient of 3.5 g / Ah), aging (standing at 25℃ for 24 h), formation (forming at 0.1 C to 3.8 V), aging (45℃), and capacity testing (capacity testing at 0.33 C to the voltage range of 2.5 V-3.65 V). Qualified lithium-ion batteries with a capacity retention rate of ≥95% (room temperature 1C discharge capacity 2Ah) are selected.

[0113] II. Testing Methods

[0114] 1. Low-temperature stability test of electrolyte: In a room-temperature drying room, the above electrolyte was injected into colorless transparent glass bottles with a capacity of 150ml, 50ml into each bottle, and then a graphite negative electrode sheet with a size of 5cm×5cm was placed into each bottle.

[0115] Subsequently, the glass bottles were transferred to a constant temperature chamber with an observation window. The temperature of the constant temperature chamber was controlled at -20℃, and the system was kept at this temperature for 3 hours to ensure that the system reached thermal equilibrium. External observation was conducted through the observation window of the constant temperature chamber to record whether the electrolyte remained clear and transparent. If the electrolyte remained clear and transparent, it was determined that the electrolyte had good low-temperature stability. Specific data are shown in Table 2.

[0116] 2. Low-temperature desolvation efficiency test of electrolyte: Take the fully charged soft-pack batteries mentioned above and conduct electrochemical impedance tests at five temperature gradients: -30℃, -25℃, -20℃, -15℃, and -10℃. Before the test, the batteries are kept at a constant temperature for 5 hours at each target temperature to ensure uniform internal temperature of the batteries.

[0117] Electrochemical workstation (CHI660E) was used to conduct tests under open-circuit potential (OCV) conditions with a perturbation amplitude of 5-10 mV (rms) and a frequency scan range of 100 kHz to 10 mHz. After the test, the charge transfer resistance Rct at each temperature point was obtained. Based on the Arrhenius equation, the temperature-Rct curve was fitted, and the slope of the curve was taken as the apparent activation energy. The lower the apparent activation energy, the higher the desolvation efficiency of the electrolyte. Specific data are shown in Table 2.

[0118] 3. Low-temperature cycle performance test of the battery: Take the above-mentioned soft-pack battery and place it in a -20℃ high and low temperature constant temperature chamber for 5 hours. Then set the charge and discharge cutoff voltage to 2.5 V-3.65 V and perform constant current charge and discharge cycle test for 300 cycles at a 1 C rate. Record the discharge capacity of the first cycle and the last 300 cycles. The low-temperature cycle performance of the battery is expressed as the capacity retention rate after 300 cycles, which is equal to the discharge capacity of the 300th cycle / the discharge capacity of the first cycle. See Table 2 for specific data.

[0119] Table 2 Performance of Electrolyte and Battery

[0120]

[0121] Compared to Comparative Examples 1-2, the electrolytes in Examples 1-22 include solvents, which include aromatic nitrile solvents, the structures of which are shown in Formula I:

[0122] Formula I,

[0123] In Formula I, R1 is selected from either difluoromethylene or monofluoromethylene; R2-R6 are each independently selected from substituted or unsubstituted methyl, hydrogen, or fluorine, which can improve the stability of the electrolyte and the desolvation efficiency under low temperature conditions, and improve the cycle performance of the battery.

[0124] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. An electrolyte, characterized in that, The solvent includes aromatic nitrile solvents, the structure of which is shown in Formula I: Formula I, In Formula I, R1 is selected from either difluoromethylene or monofluoromethylene; R2-R6 are each independently selected from substituted or unsubstituted methyl, hydrogen, or fluorine.

2. The electrolyte according to claim 1, characterized in that, R2-R3 are each independently selected from methyl or fluoromethyl.

3. The electrolyte according to claim 1 or 2, characterized in that, R4-R6 are each independently selected from hydrogen.

4. The electrolyte according to any one of claims 1-3, characterized in that, The aromatic nitrile solvents include one or more of the following: 2-fluoro-o-methylphenylacetonitrile, 2-fluoro-o-(fluoromethyl)phenylacetonitrile, 2-fluoro-o-(difluoromethyl)phenylacetonitrile, 2-fluoro-o-(trifluoromethyl)phenylacetonitrile, 2,2-difluoro-o-methylphenylacetonitrile, 2,2-difluoro-o-(fluoromethyl)phenylacetonitrile, 2,2-difluoro-o-(difluoromethyl)phenylacetonitrile, 2,2-difluoro-o-(trifluoromethyl)phenylacetonitrile, and 2,2-difluoro-o-(trifluoromethyl)tetrafluorophenylacetonitrile.

5. The electrolyte according to any one of claims 1-4, characterized in that, The aromatic nitrile solvent in the solvent has a mass percentage of 20% to 40%, preferably 22.5% to 35%.

6. The electrolyte according to any one of claims 1-5, characterized in that, The solvent also includes carbonate solvents and / or carboxylic acid ester solvents; Preferably, the carbonate solvent includes cyclic carbonate solvents and / or linear carbonate solvents; Preferably, the carboxylic acid ester solvent includes one or more of ethyl acetate, methyl propionate, and ethyl propionate; Preferably, the carbonate solvent includes a linear carbonate solvent, and the mass percentage of the cyclic carbonate solvent in the solvent is 20% to 30%. Preferably, the carbonate solvent includes cyclic carbonate solvents, and the sum of the mass percentage of the linear carbonate solvent and the mass percentage of the carboxylic acid ester solvent in the solvent is 25% to 50%.

7. The electrolyte according to any one of claims 1-6, characterized in that, The electrolyte also includes electrolyte salts and / or additives; Preferably, the mass percentage of the additive in the electrolyte is 0.5% to 3.0%; Preferably, the molar volume ratio of the electrolyte salt to the solvent is 0.6 mol / L to 1.5 mol / L; Preferably, the electrolyte salt includes a lithium salt, which includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, and tris(trifluoromethanesulfonyl)methyllithium. Preferably, the additive includes one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, propanesulfonate lactone, butanesulfonate lactone, adiponitrile, succinic acid, lithium bis(oxalato)borate, and lithium difluorooxalato)borate.

8. A battery, characterized in that, Includes the electrolyte according to any one of claims 1-7.

9. A battery pack, characterized in that, It includes at least two batteries as described in claim 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 8 or the battery pack as described in claim 9.

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