Ether nitrile mixed wide temperature range electrolyte, lithium secondary battery and preparation method thereof

Abstract

The application belongs to the field of lithium secondary batteries, and more particularly relates to an ether nitrile mixed wide temperature range electrolyte and a lithium secondary battery thereof. The ether nitrile mixed wide temperature range electrolyte comprises a lithium salt, a film forming additive, and a mixed solvent composed of an ether solvent and a nitrile solvent; wherein the ether solvent is cycloalkyl methyl ether and / or cycloalkyl ethyl ether; and the nitrile solvent is alpha-quaternary carbon nitrile. The application compounds a specific kind of ether solvent with a nitrile solvent, constructs a low-temperature and high-temperature dual synergistic mechanism between ether / nitrile molecules, enables the electrolyte to have high ion transmission capacity and fast interface charge transfer dynamics at low temperature, has good oxidation resistance and interface stability at high temperature, and has no gas production risk, effectively avoids impedance surge and swelling failure, can support the stable operation of the battery in a wide temperature range of-40 DEG C to 110 DEG C, and exhibits excellent cycle performance and capacity retention rate.

Description

Technical Field

[0001] This application belongs to the field of lithium secondary battery technology, and more specifically, relates to an ether-nitrile mixed wide-temperature-range electrolyte, a lithium secondary battery and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, aerospace, and energy storage systems for extreme cold / high temperature environments, the market urgently needs lithium secondary batteries that can operate stably over an extremely wide temperature range (-40℃ to 100℃). The electrolyte, as the core medium for conducting lithium ions, is crucial in determining the battery's operating temperature range.

[0003] Currently, commercial lithium-ion batteries mainly use carbonate electrolytes, which have good performance at room temperature, but significant bottlenecks emerge at extreme temperatures: at low temperatures, carbonate electrolytes are prone to crystallization and a surge in viscosity, leading to a sharp drop in ionic conductivity and the safety hazard of lithium plating at the negative electrode; at high temperatures, they have poor thermal stability, are prone to oxidation and decomposition, and generate gas, causing battery swelling and rapid capacity decay. Therefore, developing novel wide-temperature-range electrolyte systems that combine high and low temperature performance has become a research hotspot in this field.

[0004] To broaden the operating temperature range of lithium-ion batteries, researchers have attempted to combine ether-based solvents with nitrile solvents as novel solvent systems. However, existing ether-nitrile mixed electrolytes suffer from the following problems in practical applications: poor compatibility over a wide temperature range, leading to phase separation and system inhomogeneity; intensified interfacial side reactions during cycling, resulting in electrolyte decomposition and gas generation, damaging the SEI and CEI films at the positive and negative electrode interfaces, causing a surge in battery impedance, swelling failure, and a sharp deterioration in battery performance; furthermore, some ether-nitrile mixed systems exhibit significantly reduced solubility for lithium salts, making it difficult to form stable, high-concentration electrolytes, thus limiting their application in high-energy-density batteries.

[0005] Therefore, how to construct a uniform, stable ether-nitrile mixed electrolyte system with excellent high and low temperature performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide an ether-nitrile mixed wide-temperature-range electrolyte, a lithium secondary battery and its preparation method, aiming to solve the technical problems of existing lithium secondary batteries that cannot balance high and low temperature performance, positive and negative electrode interface instability and prominent safety hazards when working in a wide temperature environment.

[0007] To achieve the above objectives, in a first aspect, this application provides a wide-temperature-range electrolyte composed of an ether-nitrile mixture, comprising a lithium salt, a film-forming additive, and a mixed solvent composed of an ether solvent and a nitrile solvent; The ether solvents mentioned above are cycloalkyl methyl ethers and / or cycloalkyl diethyl ethers; The above-mentioned nitrile solvents are α-quaternary carbamates represented by formula (Ⅰ): R1, R2, and R3 are each independently selected from alkyl or haloalkyl groups.

[0008] Preferably, the cycloalkyl group in the above-mentioned cycloalkyl methyl ether is C3~C4. 10 cycloalkyl; and / or, The cycloalkyl group in the above cycloalkyl diethyl ether is C3~C4. 10 Cycloalkyl.

[0009] Preferably, R1, R2, and R3 are each independently selected from C1-C5 alkyl or C1-C5 fluoroalkyl.

[0010] More preferably, R1, R2, and R3 are each independently selected from C1-C3 alkyl or C1-C3 fluoroalkyl.

[0011] Preferably, the nitrile solvent is selected from one or more of 2,2-dimethylpropionitrile, 2,2-dimethylbutyronitrile, 2,2-dimethylpentanitrile, 2-methyl-2-ethylbutyronitrile, 2-methyl-2-ethylpentanitrile, 2,2-diethylbutyronitrile, 2,2-diethylpentanitrile, 2,2-dipropylpentanitrile, 2,3-dimethyl-2-ethylbutyronitrile, 2,2-dimethyl-3-fluoropropionitrile, 2-methyl-2-fluoromethyl-3-fluoropropionitrile, 2,2-dimethyl-3,3,3-trifluoropropionitrile, and 2-methyl-2-trifluoromethyl-3,3,3-trifluoropropionitrile.

[0012] Preferably, the volume ratio of the ether solvent to the nitrile solvent is 3:7 to 7:3.

[0013] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, and lithium difluorophosphate; and / or, The above film-forming additives are selected from one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, vinyl sulfate, and vinyl sulfite.

[0014] Preferably, the molar concentration of lithium salt in the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte is 0.5 mol / L to 2 mol / L; and / or, The mass fraction of film-forming additives in the above-mentioned ether nitrile mixed wide-temperature-range electrolyte is 0.5%~5%.

[0015] Secondly, this application provides a method for preparing the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte, comprising the following steps: S1. Mix the above-mentioned ether solvent and the above-mentioned nitrile solvent to obtain a mixed solvent; S2. Mix the above mixed solvent and the above lithium salt to obtain a lithium salt-containing solution; S3. Mix the above lithium salt solution and the above film-forming additive to obtain the above ether nitrile mixed wide-temperature-range electrolyte.

[0016] Thirdly, this application provides a lithium secondary battery comprising the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte.

[0017] Fourthly, this application provides an electrical device that includes the aforementioned lithium secondary battery.

[0018] In summary, the technical solutions conceived in this application have the following main technical advantages compared with the prior art: (1) The ether-nitrile mixed wide-temperature-range electrolyte provided in this application constructs a dual synergistic effect mechanism at low and high temperatures by compounding specific types of ether solvents with nitrile solvents. At low temperatures, cycloalkyl ether molecules react with Li + The weak coordination significantly lowers the desolvation energy barrier; simultaneously, the α-quaternary carbamate molecule optimizes the Li- through the intermolecular dipole-dipole interaction between its polar cyano group and the oxygen atom of the cycloalkyl ether. + The solvation structure of the electrolyte breaks the strong dipole association network of the α-quaternary carbamate molecules, synergistically suppressing the viscosity surge at low temperatures and endowing the electrolyte with high ion transport capability and rapid interfacial charge transfer kinetics. At high temperatures, the α-quaternary carbamate molecules, through the dipole-dipole interaction between the strong electron-withdrawing cyano group and the oxygen atom of the cycloalkyl ether molecule, can effectively change the electron cloud distribution of the cycloalkyl ether molecule and reduce its HOMO energy level, significantly suppressing high-temperature oxidative decomposition. At the same time, the rigid ring structure of the cycloalkyl ether molecule provides additional steric hindrance to the mixed system, further stabilizing the dipole arrangement between nitrile molecules, giving the electrolyte both good antioxidant capacity and interfacial stability, without the risk of gas generation, effectively avoiding impedance surge and swelling failure. Through the above-mentioned dual synergistic enhancement mechanism between ether / nitrile molecules, the electrolyte provided in this application can help the battery operate stably in a wide temperature range of -40℃ to 110℃, exhibiting excellent cycle performance and capacity retention.

[0019] (2) In the wide-temperature-range electrolyte of ether-nitrile mixture provided in this application, the cycloalkyl ether and α-quaternary carbide interact synergistically to change the electron cloud distribution and solvation state of the cycloalkyl ether, thereby significantly improving the high-temperature and high-pressure stability of the cycloalkyl ether solvent. At the same time, the steric shielding effect of α-quaternary carbide itself can slow down the direct contact between the cyano group and the electrode, and work synergistically with the film-forming additives to jointly construct a dense and highly ionicly conductive SEI film and CEI film at the positive and negative electrode interfaces, effectively inhibiting the continuous decomposition of the electrolyte at the electrode interface and the accumulation of by-reaction products, passivating the active sites on the electrode surface, thereby synergistically controlling the rapid impedance growth of the battery during high-temperature cycling, and inhibiting the redox decomposition and gas generation of each component of the electrolyte under high-temperature conditions.

[0020] (3) Compared with commercial electrolytes, the battery assembled using the ether-nitrile mixed wide temperature range electrolyte of this application can be stably cycled for more than 300 times at -40℃, showing excellent low temperature cycle stability; it can be stably cycled for more than 230 times at 80℃, showing excellent high temperature cycle stability; at the same time, it can effectively suppress interfacial side reactions at high temperatures, with a low impedance growth rate, and has good compatibility with high voltage cathode materials such as NMC811. Attached Figure Description

[0021] Figure 1 The cycling performance of the Li||NMC811 coin cells assembled in Embodiment 1 and Comparative Examples 1-2 of this application at 25°C and 1C rate is shown. Figure 2 The cycling performance of the Li||NMC811 coin cells assembled in Example 1 and Comparative Example 1 of this application at -40°C and 0.1C rate is shown. Figure 3 The cycling performance of the Li||NMC811 coin cells assembled in Embodiment 1 and Comparative Examples 1-2 of this application at 60°C and 1C rate is shown. Figure 4 This describes the cycle performance of the SiC||NMC811 pouch cell assembled in Example 1 of this application at 60°C and 1C rate. Figure 5 The cycling performance of the Li||NMC811 coin cells assembled in Embodiment 1 and Comparative Examples 1-2 of this application at 80°C and 1C rate is shown. Figure 6 The cycling performance of the Li||NMC811 coin cell assembled in Example 1 of this application under varying temperature (50°C to 110°C) and 1C rate is shown. Figure 7These are the electrochemical impedance spectra of the Li||NMC811 coin cells assembled in Examples 1 and 2 of this application; wherein content (a) is the electrochemical impedance spectrum of the battery before cycling at 60°C, and content (b) is the electrochemical impedance spectrum of the battery after cycling at 60°C 100 times. Figure 8 This describes the gas production of the Li||NMC811 pouch cells assembled in Embodiment 1 and Comparative Examples 1-2 of this application after being fully charged and stored at 60°C for 30 days. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In the description of this application, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this document indicates that the related objects are in an "or" relationship; for example, A / B means A or B.

[0024] In the description of the embodiments in this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0025] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.

[0026] The terms "group" and "chemical group" refer to specific segments or functional groups in a molecule.

[0027] The term "alkyl" refers to a saturated aliphatic hydrocarbon group having a specified number of carbon atoms, including both straight-chain and branched structures. For example, C1-C5 alkyl groups include alkyl groups having 1 to 5 carbon atoms in either a straight-chain or branched structure. Examples of C1-C5 alkyl groups include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, sec-butyl, isobutyl, or tert-butyl), and pentyl (e.g., n-pentyl, isopentyl, tert-pentyl, neopentyl).

[0028] The term "halogenated" or "halogen" refers to fluorine, chlorine, bromine, or iodine. In some embodiments, the halogenated or halogenated form is preferably fluorine or fluorinated.

[0029] The term "halogenated alkyl" refers to an alkyl group having one or more halogen substituents, such as halogenated methyl groups including but not limited to fluoromethyl (-CH2F), difluoromethyl (-CHF2), trifluoromethyl (-CF3), bromomethyl (-CH2Br), etc.

[0030] The term "C3~C" 10 "Cycloalkyl" refers to monocyclic or polycyclic alkyl groups having 3 to 10 carbon atoms. Examples include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, dicycloheptyl, cyclononyl, and cyclodecyl.

[0031] There has long been a technical bias in this field, suggesting that ether solvents and nitrile solvents, due to poor compatibility and incompatible interfacial reactions, cannot easily produce high-performance wide-temperature-range electrolytes through simple mixing. Based on these technical challenges, this invention provides a wide-temperature-range electrolyte composed of cycloalkyl methyl ether and / or cycloalkyl diethyl ether and α-quaternary carbamate as its core components. By selecting cyclic ether compounds with specific structures and nitrile compounds without active hydrogen on the α-carbon, this application unexpectedly discovered that the two exhibit good compatibility, effectively avoiding phase separation and side reactions. Simultaneously, it synergistically leverages the low-temperature advantages of ethers and the high-temperature stability of nitriles, effectively solving the aforementioned long-standing problems of existing ether-nitrile mixed electrolytes and achieving stable operation of lithium secondary batteries over a wide temperature range. Specifically, this application provides an ether-nitrile mixed wide-temperature-range electrolyte comprising a lithium salt, a film-forming additive, and a mixed solvent composed of an ether solvent and a nitrile solvent. The ether solvents mentioned above are cycloalkyl methyl ethers and / or cycloalkyl diethyl ethers; The above-mentioned nitrile solvents are α-quaternary carbamates represented by formula (Ⅰ): R1, R2, and R3 are each independently selected from alkyl or haloalkyl groups.

[0032] The ether-nitrile mixed wide-temperature-range electrolyte provided in this application constructs a unique synergistic mechanism between ether / nitrile molecules by compounding specific types of cycloalkyl ether solvents with α-quaternary carbamate solvents. At low temperatures, cycloalkyl ether molecules react with Li... + The interaction between them exhibits weak coordination, which can significantly reduce the desolvation energy barrier; simultaneously, the α-quaternary carbamate molecule generates intermolecular dipole-dipole interactions with the oxygen atoms of the cycloalkyl ether molecule through its polar cyano group, thus optimizing the Li... +On the one hand, the solvation structure effectively breaks the strong dipole association network of the α-quaternary carbide molecule itself, synergistically suppressing the viscosity surge of the mixed system under low temperature conditions. At high temperatures, in addition to its excellent high-temperature stability, the dipole-dipole interaction between the strong electron-withdrawing cyano group of the α-quaternary carbide molecule and the oxygen atom of the cycloalkyl ether molecule can effectively change the electron cloud distribution of the cycloalkyl ether molecule and reduce the HOMO energy level, significantly suppressing its tendency for oxidative decomposition under high temperature and pressure. Simultaneously, the rigid ring structure of the cycloalkyl ether molecule provides additional steric hindrance to the mixed system, further stabilizing the dipole arrangement between nitrile molecules. Through the above-mentioned dual synergistic enhancement mechanism between ether / nitrile molecules at low and high temperatures, the electrolyte provided in this application possesses high ion transport capacity and rapid interfacial charge transfer kinetics at low temperatures, and good oxidation resistance and interfacial stability at high temperatures, without the risk of gas generation, effectively avoiding impedance surge and swelling failure. This enables the battery to operate stably in a wide temperature range of -40℃ to 110℃, exhibiting excellent cycle performance and capacity retention.

[0033] In some embodiments, the cycloalkyl group in the above-mentioned cycloalkyl methyl ether is C3~C4. 10 Cycloalkyl group. In some embodiments, the cycloalkyl group in the above-mentioned cycloalkyl diethyl ether is C3~C4. 10 Naphthenic. For example, the above-mentioned ether solvents may be selected from one or more of cyclopropyl methyl ether, cyclobutyl methyl ether, cyclopentyl methyl ether, cyclohexyl methyl ether, cycloheptyl methyl ether, cyclooctyl methyl ether, cyclononyl methyl ether, cyclodecyl methyl ether, cyclopropyl ethyl ether, cyclobutyl ethyl ether, cyclopentyl ethyl ether, cyclohexyl ethyl ether, cycloheptyl ethyl ether, cyclooctyl ethyl ether, cyclononyl ethyl ether, and cyclodecyl ethyl ether.

[0034] In some embodiments, R1, R2, and R3 are each independently selected from C1-C5 alkyl or C1-C5 fluoroalkyl groups. For example, R1, R2, and R3 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, fluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3-fluoropropyl, 3,3,3-trifluoropropyl, 4-fluorobutyl, 5-fluoropentyl, etc.

[0035] In some embodiments, R1, R2, and R3 are each independently selected from C1-C3 alkyl or C1-C3 fluoroalkyl groups. In some specific embodiments of this application, the nitrile solvent is selected from one or more of 2,2-dimethylpropionitrile, 2,2-dimethylbutyronitrile, 2,2-dimethylpentanitrile, 2-methyl-2-ethylbutyronitrile, 2-methyl-2-ethylpentanitrile, 2,2-diethylbutyronitrile, 2,2-diethylpentanitrile, 2,2-dipropylpentanitrile, 2,3-dimethyl-2-ethylbutyronitrile, 2,2-dimethyl-3-fluoropropionitrile, 2-methyl-2-fluoromethyl-3-fluoropropionitrile, 2,2-dimethyl-3,3,3-trifluoropropionitrile, and 2-methyl-2-trifluoromethyl-3,3,3-trifluoropropionitrile.

[0036] In some embodiments, the volume ratio of the ether solvent to the nitrile solvent is 3:7 to 7:3. For example, the volume ratio of the ether solvent to the nitrile solvent can be 3:7, 4:6, 5:5, 6:4, 7:3, or any range of two of the above values.

[0037] In some embodiments, the lithium salt may be one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, and lithium difluorophosphate, but not limited to these.

[0038] In some embodiments, the molar concentration of lithium salt in the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte is 0.5 mol / L to 2 mol / L. For example, the molar concentration of lithium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or any combination of two of the above values.

[0039] In some embodiments, the film-forming additives described above may be one or more of, but not limited to, vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sulpholactone (PS), vinyl sulfate (DTD), and vinyl sulfite (ES).

[0040] In some embodiments, the mass fraction of the film-forming additive in the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte is 0.5% to 5%. For example, the mass fraction of the film-forming additive can be 0.5%, 1%, 2%, 3%, 4%, 5%, or any combination of two of the above values.

[0041] This application also provides a method for preparing the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte, comprising the following steps: S1. Mix the above-mentioned ether solvent and the above-mentioned nitrile solvent to obtain a mixed solvent; S2. Mix the above mixed solvent and the above lithium salt to obtain a lithium salt-containing solution; S3. Mix the above lithium salt solution and the above film-forming additive to obtain the above ether nitrile mixed wide-temperature-range electrolyte.

[0042] On the other hand, this application also provides a lithium secondary battery comprising the above-mentioned ether-nitrile mixed wide-temperature-range electrolyte.

[0043] In some embodiments, the aforementioned lithium secondary battery further includes a negative electrode and a positive electrode.

[0044] In some embodiments, the aforementioned lithium secondary batteries can also be assembled into battery modules. This application does not limit the number of lithium secondary batteries in a battery module; those skilled in the art can adjust this number according to the application and capacity of the battery module.

[0045] In some embodiments, the battery modules described above can be assembled into a battery pack. This application does not limit the number of battery modules in the battery pack; those skilled in the art can adjust the number according to the application and capacity of the battery modules.

[0046] Based on this, this application also provides an electrical device, which includes at least one of the above-mentioned lithium secondary battery, battery module or battery pack.

[0047] It should be understood that materials of the same or similar type, model, quality, properties, or function as the reagents and instruments used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0048] The following are examples and comparative examples: Example 1 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclopentyl methyl ether (an ether solvent) and 2,2-dimethylpropionitrile (a nitrile solvent) were mixed at a volume ratio of 1:1 to obtain a mixed solvent. Lithium difluorooxalate borate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Ethyl fluorocarbonate (a film-forming additive) was added to the clear solution to achieve a 5% mass fraction of ethylene fluorocarbonate in the electrolyte, and the mixture was thoroughly mixed to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0049] Comparative Example 1 The electrolyte provided in this comparative example has the same composition as in Example 1, except that it contains only ether solvents and no nitrile solvents.

[0050] Comparative Example 2 The electrolyte provided in this comparative example is a commercial carbonate electrolyte, and its preparation method includes the following steps: A homogeneous solution was prepared by dissolving lithium difluorooxalate borate and fluoroethylene carbonate in ethylene carbonate and diethyl carbonate to obtain a commercial carbonate electrolyte. The molar concentration of lithium difluorooxalate borate was 1 mol / L, the volume ratio of ethylene carbonate to diethyl carbonate was 1:1, and the mass fraction of fluoroethylene carbonate in the electrolyte was 5%.

[0051] The performance of the electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 was tested: (1) Electrochemical performance Electrolytes were assembled into Li||NMC811 coin cells and SiC||NMC811 pouch cells, wherein... The assembly process of Li||NMC811 button cell is as follows: button cells are assembled in a glove box with a water content of less than 0.01ppm and an oxygen content of less than 0.01ppm. The positive electrode uses an NMC811 sheet with a diameter of 8mm, the negative electrode uses a lithium metal sheet with a diameter of 12mm, and the electrolyte is the electrolyte mentioned above.

[0052] The assembly process of SiC||NMC811 pouch cell is as follows: The pouch cell is assembled in a glove box with a water content of less than 0.01ppm and an oxygen content of less than 0.01ppm. The positive electrode uses a 4cm×5cm NMC811 electrode, the negative electrode uses a 4.5cm×5.5cm SiC electrode, the separator uses a 5cm×6cm polypropylene separator, and the electrolyte is the same as described above.

[0053] The assembled Li||NMC811 button cells and SiC||NMC811 pouch cells were placed in a high and low temperature test chamber to control the test temperature and were subjected to cyclic testing using a charge and discharge tester. The test voltage for the Li||NMC811 button cells was 3~4.3V and the test voltage for the SiC||NMC811 pouch cells was 2.7~4.2V.

[0054] (2) Impedance before and after high temperature cycling The assembled Li||NMC811 coin cells were subjected to electrochemical impedance spectroscopy (EIS) testing. The EIS testing temperature was controlled at 60℃. The EIS spectra of the cells were measured before cycling at 60℃ and after 100 cycles at 60℃. The resistance growth rate of the cells before and after cycling was calculated.

[0055] (3) High-temperature storage gas production The electrolyte was used to assemble a Li||NMC811 pouch cell. The assembly process was as follows: the pouch cell was assembled in a glove box with a water content of less than 0.01 ppm and an oxygen content of less than 0.01 ppm. The positive electrode used a 4cm × 5cm NMC811 electrode, the negative electrode used a 4.5cm × 5.5cm lithium metal sheet, and the separator used a 5cm × 6cm polypropylene membrane. The electrolyte used was the same as described above. The assembled Li||NMC811 pouch cell was charged to 4.3V at 25℃ and then stored at 60℃ for 30 days. After storage, the pouch cell was removed and the gas production was observed. The degree of gas production was graded according to the change in height (ΔH) of the cell center before and after storage: mild (ΔH < 1cm), moderate (ΔH 1~3cm), and severe (ΔH > 3cm).

[0056] Figure 1 The cycling performance of the Li||NMC811 coin cells assembled in Example 1 and Comparative Examples 1 and 2 at 25°C and 1C rate is shown. It can be seen that the Li||NMC811 coin cell assembled in Comparative Example 1 experiences a sharp decrease in capacity during cycling, with a capacity retention of only 42% after 60 cycles; the Li||NMC811 coin cell assembled in Comparative Example 2 shows a capacity retention of 76% after 190 cycles; while the Li||NMC811 coin cell assembled in Example 1 still maintains a capacity retention of 81% after 600 cycles, exhibiting excellent cycling stability. This indicates that the ether-nitrile mixed wide-temperature-range electrolyte provided in this application is well-suited for high-voltage cathode materials such as NMC811.

[0057] Figure 2 The cycling performance of the Li||NMC811 coin cells assembled in Example 1 and Comparative Example 1 at -40°C and 0.1C rate is shown. It can be seen that the Li||NMC811 coin cell assembled in Comparative Example 1 experiences a sharp decrease in capacity during cycling, with a capacity retention of only 54% after 80 cycles; while the Li||NMC811 coin cell assembled in Example 1 shows no significant capacity decay after 300 cycles, exhibiting excellent low-temperature cycling stability.

[0058] Figure 3 The cycling performance of the Li||NMC811 coin cells assembled in Example 1 and Comparative Examples 1 and 2 at 60°C and 1C rate is shown. It can be seen that the capacity retention of the Li||NMC811 coin cell assembled in Comparative Example 1 decreased to 27% after 200 cycles; the capacity retention of the Li||NMC811 coin cell assembled in Comparative Example 2 decreased to 40% after 175 cycles; while the capacity retention of the Li||NMC811 coin cell assembled in Example 1 still reached 80% after 300 cycles, demonstrating excellent high-temperature cycling stability.

[0059] Figure 4 The cycling performance of the SiC||NMC811 pouch cell assembled in Example 1 at 60°C and 1C rate is shown. It can be seen that the SiC||NMC811 pouch cell assembled in Example 1 can stably cycle 1000 times, and the capacity retention rate after 938 cycles is 70%, exhibiting excellent high-temperature cycling stability. This indicates that the ether-nitrile mixed wide-temperature-range electrolyte provided in this application can be well adapted to various commercial anode materials.

[0060] Figure 5 The cycling performance of the Li||NMC811 coin cells assembled in Example 1 and Comparative Examples 1 and 2 at 80°C and 1C rate is shown. It can be seen that the capacity retention of the Li||NMC811 coin cell assembled in Comparative Example 1 decreases to 59% after 100 cycles; the capacity retention of the Li||NMC811 coin cell assembled in Comparative Example 2 decreases to 57% after 80 cycles; while the capacity retention of the Li||NMC811 coin cell assembled in Example 1 still reaches 75% after 230 cycles, demonstrating excellent high-temperature cycling stability.

[0061] Figure 6 The temperature cycling performance of the Li||NMC811 coin cell assembled in Example 1 at 50~110℃ and 1C rate is shown. It can be seen that the Li||NMC811 coin cell assembled in Example 1 can maintain a coulombic efficiency of over 96% and still stably exert its capacity at 110℃, demonstrating excellent ultra-high temperature operating capability.

[0062] Figure 7 The images show the electrochemical impedance spectroscopy (EIS) spectra of the Li||NMC811 coin cells assembled in Examples 1 and 1-2 before and after 100 cycles at 60°C. It can be seen that the charge transfer resistance (CRT) of the Li||NMC811 coin cell assembled in Comparative Example 1 was 20 Ω before cycling and 43 Ω after 100 cycles, representing a resistance increase rate of 115%. The CRT of the Li||NMC811 coin cell assembled in Comparative Example 2 was 13 Ω before cycling and 127 Ω after 100 cycles, representing a resistance increase rate as high as 877%. In contrast, the CRT of the Li||NMC811 coin cell assembled in Example 1 was 17 Ω before cycling and 27 Ω after 100 cycles, representing a resistance increase rate of only 58.8%, exhibiting the slowest impedance increase rate. This indicates that the ether-nitrile mixed wide-temperature-range electrolyte provided in this application can effectively suppress interfacial side reactions at high temperatures.

[0063] Figure 8These are comparative photographs showing the gas production of the Li||NMC811 pouch cells assembled in Example 1 and Comparative Examples 1 and 2 after being fully charged and stored at 60°C for 30 days. It can be seen that the Li||NMC811 pouch cell assembled in Comparative Example 1 exhibits moderate gas production (ΔH approximately 1.2 cm), the Li||NMC811 pouch cell assembled in Comparative Example 2 exhibits heavy gas production (ΔH approximately 3.4 cm), while the Li||NMC811 pouch cell assembled in Example 1 shows no significant gas production (ΔH < 1 cm). This indicates that the lithium secondary battery assembled using the ether-nitrile mixed wide-temperature-range electrolyte provided in this application has excellent high-temperature storage capabilities.

[0064] Comparative Example 3 The electrolyte provided in this comparative example has the same composition as in Example 1, except that it contains only nitrile solvents and no ether solvents.

[0065] Comparative Example 4 The electrolyte provided in this comparative example has the same composition as in Example 1, except that a chain ether solvent (ethylene glycol dimethyl ether DME) is used as the ether solvent.

[0066] Comparative Example 5 The electrolyte provided in this comparative example has the same composition as in Example 1, except that a cyclic ether solvent (tetrahydrofuran THF) is used as the ether solvent.

[0067] Example 2 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclopentyl ethyl ether (an ether solvent) and 2,2-dimethylbutyronitrile (a nitrile solvent) were mixed at a volume ratio of 1:1 to obtain a mixed solvent. Lithium difluorooxalate borate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Fluoroethylene carbonate was added to the clear solution to achieve a mass fraction of 5% fluoroethylene carbonate in the electrolyte, and the mixture was thoroughly mixed to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0068] Example 3 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclohexyl methyl ether (an ether solvent) and 2,2-dimethylpentanonitrile (a nitrile solvent) were mixed at a volume ratio of 3:7 to obtain a mixed solvent. Lithium hexafluorophosphate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Ethyl fluorocarbonate was added to the clear solution to make the mass fraction of ethylene fluorocarbonate in the electrolyte 5%, and the mixture was stirred evenly to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0069] Example 4 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclohexyl ethyl ether (an ether solvent) and 2-methyl-2-ethylbutyronitrile (a nitrile solvent) were mixed at a volume ratio of 7:3 to obtain a mixed solvent. Lithium difluorosulfonylimide was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Fluoroethylene carbonate was added to the clear solution to make the mass fraction of fluoroethylene carbonate in the electrolyte 5%, and the mixture was stirred evenly to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0070] Example 5 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cycloheptyl methyl ether (an ether solvent) and 2-methyl-2-ethylpentanonitrile (a nitrile solvent) were mixed at a volume ratio of 4:6 to obtain a mixed solvent. Lithium difluorooxalate borate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 0.5 mol / L. Ethyl fluorocarbonate was added to the clear solution to make the mass fraction of ethylene fluorocarbonate in the electrolyte 2%, and the mixture was stirred evenly to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0071] Example 6 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclooctyl methyl ether (an ether solvent) and 2,2-diethylbutyronitrile (a nitrile solvent) were mixed at a volume ratio of 6:4 to obtain a mixed solvent. Lithium difluorooxalate borate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 2 mol / L. Fluoroethylene carbonate was added to the clear solution to achieve a mass fraction of 0.5% in the electrolyte, and the mixture was thoroughly mixed to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0072] Example 7 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclopropyl methyl ether (an ether solvent) and 2,2-dipropylpentanonitrile (a nitrile solvent) were mixed at a volume ratio of 1:1 to obtain a mixed solvent. Lithium difluorooxalate borate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Ethyl fluorocarbonate was added to the clear solution to achieve a 5% mass fraction of ethylene fluorocarbonate in the electrolyte, and the mixture was thoroughly mixed to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0073] Example 8 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclobutyl ethyl ether solvent (an ether solvent) and 2,3-dimethyl-2-ethylbutyronitrile (a nitrile solvent) were mixed at a volume ratio of 4:6 to obtain a mixed solvent. Lithium hexafluorophosphate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Ethyl fluorocarbonate was added to the clear solution to make the mass fraction of ethylene fluorocarbonate in the electrolyte 5%, and the mixture was stirred evenly to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0074] Example 9 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclononyl methyl ether (an ether solvent) and 2,2-dimethyl-3-fluoropropionitrile (a nitrile solvent) were mixed at a volume ratio of 7:3 to obtain a mixed solvent. Lithium bis(trifluoromethanesulfonyl)imide was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 1 mol / L. Fluoroethylene carbonate was added to the clear solution to make the mass fraction of fluoroethylene carbonate in the electrolyte 5%, and the mixture was stirred evenly to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0075] Example 10 The method for preparing the ether-nitrile mixed wide-temperature-range electrolyte provided in this embodiment includes the following steps: In an argon-filled glove box, cyclodecyl ethyl ether (an ether solvent) and 2-methyl-2-fluoromethyl-3-fluoropropionitrile (a nitrile solvent) were mixed at a volume ratio of 1:1 to obtain a mixed solvent. Lithium difluorooxalate borate was added to the mixed solvent and stirred until completely dissolved to prepare a clear solution with a concentration of 2 mol / L. Fluoroethylene carbonate was added to the clear solution to make the mass fraction of fluoroethylene carbonate in the electrolyte 0.5%, and the mixture was stirred evenly to obtain a wide-temperature-range electrolyte of ether and nitrile mixture.

[0076] Using the assembly process described above, the electrolytes prepared in Examples 2-10 and Comparative Examples 3-5 were assembled into Li||NMC811 coin cells and Li||NMC811 pouch cells, respectively. The electrochemical performance of the Li||NMC811 coin cells was evaluated by testing their capacity retention at different temperatures and the resistance growth rate before and after cycling at 60°C. The high-temperature storage gas generation of the Li||NMC811 pouch cells was evaluated by testing the change in the height of the cell center after storage at 60°C for 30 days. The test results are shown in Table 1.

[0077]

[0078] The test results (Table 1) show that, compared with Comparative Example 1 (containing only ether solvents), Comparative Example 3 (containing only nitrile solvents), Comparative Example 4 (ether solvent is ethylene glycol dimethyl ether), and Comparative Example 5 (ether solvent is tetrahydrofuran), the embodiments of this application combine specific types of ether solvents with nitrile solvents. Through the unique dual synergistic effect mechanism between ether / nitrile molecules, the battery assembled based on the ether-nitrile mixed wide-temperature-range electrolyte can operate stably at ultra-low temperatures of -40℃ and ultra-high temperatures of 80℃, exhibiting excellent cycle performance and capacity retention. It can also be well adapted to high-voltage cathode materials such as NMC811, and its wide-temperature-range cycle performance is significantly better than that of the commercial electrolyte in Comparative Example 2.

[0079] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A wide-temperature-range electrolyte composed of ether and nitrile mixtures, characterized in that, This includes lithium salts, film-forming additives, and mixed solvents consisting of ether solvents and nitrile solvents; The ether solvent is a cycloalkyl methyl ether and / or a cycloalkyl diethyl ether; the cycloalkyl group in the cycloalkyl methyl ether is C3~C4. 10 cycloalkyl group, wherein the cycloalkyl group in the cycloalkyl diethyl ether is C3~C4. 10 cycloalkyl; The nitrile solvent is the α-quaternary carbamate shown in formula (Ⅰ): R1, R2, and R3 are each independently selected from C1-C5 alkyl or C1-C5 fluoroalkyl; The volume ratio of the ether solvent to the nitrile solvent is 3:7 to 7:

3.

2. The ether-nitrile mixed wide-temperature-range electrolyte according to claim 1, characterized in that, The nitrile solvent is selected from one or more of 2,2-dimethylpropionitrile, 2,2-dimethylbutyronitrile, 2,2-dimethylpentanitrile, 2-methyl-2-ethylbutyronitrile, 2-methyl-2-ethylpentanitrile, 2,2-diethylbutyronitrile, 2,2-diethylpentanitrile, 2,2-dipropylpentanitrile, 2,3-dimethyl-2-ethylbutyronitrile, 2,2-dimethyl-3-fluoropropionitrile, 2-methyl-2-fluoromethyl-3-fluoropropionitrile, 2,2-dimethyl-3,3,3-trifluoropropionitrile, and 2-methyl-2-trifluoromethyl-3,3,3-trifluoropropionitrile.

3. The ether-nitrile mixed wide-temperature-range electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, and lithium difluorophosphate; and / or, The film-forming additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, vinyl sulfate, and vinyl sulfite.

4. The ether-nitrile mixed wide-temperature-range electrolyte according to claim 1, characterized in that, The molar concentration of lithium salt in the ether-nitrile mixed wide-temperature-range electrolyte is 0.5 mol / L to 2 mol / L; and / or, The mass fraction of film-forming additives in the ether nitrile mixed wide-temperature-range electrolyte is 0.5% to 5%.

5. A method for preparing a wide-temperature-range electrolyte of ether nitrile mixture as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Mix the ether solvent and the nitrile solvent to obtain a mixed solvent; S2. Mix the mixed solvent and the lithium salt to obtain a lithium salt-containing solution; S3. Mix the lithium salt solution and the film-forming additive to obtain the ether nitrile mixed wide-temperature-range electrolyte.

6. A lithium secondary battery, characterized in that, Includes the ether nitrile mixed wide-temperature-range electrolyte according to any one of claims 1 to 4.

7. An electrical device, characterized in that, Includes the lithium secondary battery as described in claim 6.

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