A wide-temperature-range electrolyte suitable for alkali metal ion batteries and its application

Abstract

This application belongs to the field of alkali metal ion battery technology, and more specifically, relates to a wide-temperature-range electrolyte suitable for alkali metal ion batteries and its application. The wide-temperature-range electrolyte for alkali metal ion batteries provided in this application includes an electrolyte salt, an organic solvent, and a film-forming additive, further including a monoglyceride and a bridging solvent for dissolving the monoglyceride; the interaction between the monoglyceride and the organic solvent can inhibit the reductive decomposition of the organic solvent and suppress the co-intercalation effect between the organic solvent and alkali metal ions. By adding a monoglyceride and a bridging solvent for dissolving the monoglyceride, and through formulation optimization, this application effectively solves the problem of incompatibility between organic solvents and graphite anodes, preparing an electrolyte with wide-temperature-range performance and good compatibility with graphite anodes, ensuring stable battery operation within a wide temperature range of -40℃ to 60℃.

Description

Technical Field

[0001] This application belongs to the field of alkali metal ion battery technology, and more specifically, relates to a wide-temperature-range electrolyte suitable for alkali metal ion batteries and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are widely used in portable electronic devices, electric vehicles, and energy storage grids due to their advantages such as high energy density, long cycle life, environmental friendliness, and lack of memory effect. Meanwhile, continuous technological advancements and iterations, along with cost reductions and energy density increases, have enabled LIBs to maintain their competitive advantage in electrochemical energy storage for a considerable period. However, as the range of battery applications continues to expand, increasing attention is being paid to the suitability and safety of batteries across a wide operating temperature range. Commercial LIBs typically operate optimally within a narrow temperature range of -15°C to 35°C. In extremely cold regions at high altitudes or latitudes, LIBs often need to operate for extended periods at temperatures below -30°C; in hot environments such as deserts, they require operation at temperatures of 50°C and above. Currently, most commercial electrolytes are EC-based, but the high melting point of EC (36.4°C) makes this commercial electrolyte prone to solidification and even crystallization at low temperatures. Meanwhile, EC is prone to oxidation and decomposition with the positive electrode material at a high voltage of 4.4V, which makes this commercial electrolyte unable to meet the application requirements under harsh conditions such as high temperature, high pressure, and low temperature, thus limiting the application of the battery.

[0003] Solvents such as propylene carbonate and dimethyl ethylene glycol have a wider liquid temperature range, but they are incompatible with graphite anodes and tend to co-intercalate with lithium ions between graphite layers, causing the structure of the graphite material to collapse, resulting in a decrease in battery capacity and rapid degradation.

[0004] Therefore, developing an EC-free electrolyte with wide temperature range performance and good compatibility with graphite anodes is crucial for developing wide temperature range batteries and improving their safety, stability and reliability. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this application is to provide a wide temperature range electrolyte suitable for alkali metal ion batteries and its application, aiming to solve the problems that existing electrolytes are prone to freezing at low temperatures (-50°C and below), have poor compatibility between organic solvents in the electrolyte and graphite anodes, and have low capacity and rapid capacity decay of batteries assembled based on existing electrolytes.

[0006] To achieve the above objectives, in a first aspect, this application provides a wide-temperature-range electrolyte suitable for alkali metal ion batteries, comprising an electrolyte salt, an organic solvent and a film-forming additive, and further comprising a monoglyceride and a bridging solvent for dissolving the monoglyceride.

[0007] The interaction between the monoglyceride and the organic solvent can suppress the reductive decomposition of the organic solvent and the co-intercalation effect between the organic solvent and alkali metal ions.

[0008] Preferably, the above-mentioned monoglyceride is one or more of glyceryl monostearate, glyceryl monosilyl ester, glyceryl monopalmitate, glyceryl monolinoleate, and glyceryl monooleate.

[0009] Preferably, the bridging solvent is one or more of tetrahydrofuran, tetrahydropyran, and chloroform.

[0010] Preferably, the amount of the above-mentioned monoglyceride added is 1wt% to 5wt% of the total mass of the wide temperature range electrolyte; more preferably, it is 1wt% to 2wt%.

[0011] Preferably, the electrolyte salt is a lithium salt or a potassium salt.

[0012] Preferably, the lithium salt is one or more selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bisfluorosulfonylimide, lithium difluorooxalate borate, lithium bisoxalate borate, lithium perchlorate, lithium bistrifluoromethanesulfonylimide, and lithium nitrophosphate.

[0013] Preferably, the potassium salt is one or more of potassium hexafluorophosphate, potassium perchlorate, and potassium trifluoromethanesulfonate.

[0014] Preferably, the organic solvent is one or more selected from propylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, diethyl carbonate, methyl ethyl carbonate, trimethyl phosphate, triethyl phosphate, methyl propionate, methyl butyrate, and 2-methyltetrahydrofuran.

[0015] Preferably, the film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate, and ethylene ethylene carbonate.

[0016] Preferably, in the above-mentioned wide-temperature-range electrolyte, the molar concentration of the electrolyte salt is 0.8~1.2 mol / L.

[0017] Preferably, the molar ratio of the organic solvent and the bridging solvent is greater than 1:1; more preferably (1.25~3):1.

[0018] Preferably, the molar ratio of the organic solvent, the bridging solvent and the film-forming additive is (5~6):(3~4):(1~2).

[0019] Secondly, this application also provides an alkali metal ion battery, which includes a positive electrode, a negative electrode, and the aforementioned wide-temperature-range electrolyte.

[0020] Preferably, the above-mentioned negative electrode is a carbon-based negative electrode or a silicon-carbon negative electrode.

[0021] In summary, the technical solutions conceived in this application have the following main technical advantages compared with the prior art:

[0022] (1) The wide-temperature-range electrolyte for alkali metal ion batteries provided in this application includes an electrolyte salt, an organic solvent, and a film-forming additive, as well as a monoglyceride and a bridging solvent for dissolving the monoglyceride. By adding the monoglyceride and the bridging solvent, this application can prepare an EC-free electrolyte with wide-temperature-range performance. This electrolyte does not freeze at -60°C, and its ionic conductivity from -60°C to 60°C is higher than that of commercial EC-based electrolytes. In addition, the monoglyceride in this electrolyte can interact with the organic solvent at the graphite anode interface, weakening the affinity between alkali metal ions and organic solvents, and raising the lowest unoccupied molecular orbital (LUMO) energy level of the organic solvent molecules, making it difficult for the organic solvent to be reduced and decomposed. At the same time, it can also lower the desolvation energy barrier of alkali metal ions, enabling the reversible insertion and extraction of alkali metal ions from the graphite anode. Combining the above effects, the electrolyte provided in this application effectively solves the problem of poor compatibility between organic solvents and graphite anodes, and prepares an EC-free electrolyte with wide-temperature-range performance and good compatibility with graphite anodes.

[0023] (2) This application improves the battery capacity at low temperatures by adjusting the proportions of electrolyte salts, organic solvents, monoglycerides, and bridging solvents in a wide-temperature-range electrolyte. This optimization of the formulation effectively enhances the battery's capacity at low temperatures, enabling it to operate stably over a wider temperature range (e.g., -40℃ to 60℃, or even -50℃ to 100℃), effectively solving the problem of low capacity and rapid capacity decay at low temperatures. Simultaneously, it effectively improves the battery's initial charge-discharge efficiency and long-cycle performance, enabling the battery to achieve stable cycling of 1000 times or more at room temperature.

[0024] (3) Compared with commercial EC-based electrolytes and existing wide-temperature-range electrolytes, the wide-temperature-range electrolyte provided in this application does not freeze at low temperature (-60℃) and has high conductivity; at the same time, it still has good cycle stability at high temperature (100℃). The electrolyte is compatible with graphite anodes and also exhibits good wide-temperature adaptability. Attached Figure Description

[0025] Figure 1 The conductivity of the electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this application at different temperatures;

[0026] Figure 2 This is a first charge / discharge voltage-capacity curve of the Li|| graphite battery assembled in Example 1 and Comparative Example 1 of this application;

[0027] Figure 3The long-cycle performance of the Li|| graphite batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 of this application at 25°C and 0.5C rate is shown.

[0028] Figure 4 The cyclic voltammetry curves of the Li|| graphite batteries assembled in Example 1 and Comparative Example 1 of this application at a scan rate of 0.1 mV / S are shown.

[0029] Figure 5 The graphite||LFP pouch cell assembled in Example 1 and Comparative Example 1 of this application demonstrates its long-cycle performance at 25°C and 1C rate.

[0030] Figure 6 The graphite LFP pouch cells assembled in Example 1 and Comparative Example 1 of this application are shown as discharge curves at low temperature (-50℃~-20℃) and 0.1C rate after being charged at 25℃.

[0031] Figure 7 The graphite LFP pouch cells assembled in Example 1 and Comparative Example 1 of this application are shown as charge-discharge curves at high temperature (60℃~100℃) and 1C rate. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0036] The term "monoglyceride" refers to monoglycerides of fatty acids.

[0037] Traditional commercial electrolytes are mostly EC-based electrolytes. However, the high melting point and easy oxidation of EC on the positive electrode side make existing EC-based electrolytes unsuitable for applications under harsh conditions such as high temperature, high pressure, and low temperature. By selecting organic solvents with a wide liquid range and good oxidation resistance, such as propylene carbonate and ethylene glycol dimethyl ether, the freezing point of the electrolyte can be lowered, and the liquid range of the electrolyte can be expanded, making it possible for the battery to operate in extreme environments. However, these solvents can co-intercalate with alkali metal ions in the graphite anode, causing the alkali metal ions to be unable to reversibly intercalate and deintercalate in graphite, resulting in poor battery cycle performance. Based on this, this application provides a wide-temperature-range electrolyte suitable for alkali metal ion batteries, which includes an electrolyte salt, an organic solvent, and a film-forming additive; it also includes a monoglyceride and a bridging solvent for dissolving the monoglyceride;

[0038] Among them, the interaction between monoglycerides and organic solvents can weaken the affinity between alkali metals and organic solvents, lower the desolvation energy barrier of alkali metal ions, thereby inhibiting the reductive decomposition of organic solvents and suppressing the co-intercalation effect between organic solvents and alkali metal ions.

[0039] The inventors of this application accidentally discovered through experiments that by adding monoglycerides and a bridging solvent capable of dissolving the monoglycerides to the electrolyte, an EC-free electrolyte with a wide temperature range can be prepared. This electrolyte remains unfrozen at -60°C, and its ionic conductivity from -60°C to 60°C is higher than that of commercial EC-based electrolytes. Furthermore, the monoglycerides dissolved in this electrolyte weaken the affinity between alkali metal ions and organic solvents, raising the lowest unoccupied molecular orbital (LUMO) energy level of organic solvent molecules, making the organic solvent difficult to reduce and decompose. Simultaneously, it lowers the desolvation energy barrier of alkali metal ions, enabling reversible insertion / extraction of alkali metal ions into and out of the graphite anode. All of these factors effectively improve the compatibility between the organic solvent and the graphite anode, resulting in good compatibility between the electrolyte and the graphite anode.

[0040] In some embodiments, the monoglyceride is one or more of glyceryl monostearate (GMS), glyceryl monosilyl ester (GMO), glyceryl monopalmitate (GPP), glyceryl monolinoleate, and glyceryl monooleate (GML). In a preferred embodiment, the monoglyceride is glyceryl monostearate.

[0041] In some embodiments, the bridging solvent is one or more of tetrahydrofuran, tetrahydropyran, and chloroform.

[0042] It is understood that the wide-temperature-range electrolyte provided in this application is suitable for various alkali metal ion batteries, including commonly used lithium-ion batteries and potassium-ion batteries. It should also be understood that the wide-temperature-range electrolyte provided in this application can also be used in sodium-ion batteries, with the corresponding electrolyte salts being lithium salt, potassium salt, or sodium salt. The wide-temperature-range electrolyte provided in this application can be applied to different alkali metal ion batteries simply by adjusting the type of electrolyte salt, demonstrating good versatility.

[0043] When the wide-temperature-range electrolyte provided in this application is applied to lithium-ion batteries, the lithium salt may be, but is not limited to, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bisfluorosulfonylimide, lithium difluorooxalate borate, lithium bisoxalate borate, lithium perchlorate, lithium bistrifluoromethanesulfonylimide, and lithium nitrophosphate.

[0044] When the wide-temperature-range electrolyte provided in this application is applied to lithium-ion batteries, the potassium salt may be, but is not limited to, potassium hexafluorophosphate, potassium perchlorate, and potassium trifluoromethanesulfonate.

[0045] In some embodiments, the organic solvent is an organic solvent with a melting point less than or equal to -40°C and a boiling point greater than or equal to 60°C. In preferred embodiments, the organic solvent is one or more of propylene carbonate (PC), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), 1,3-dioxolane (DOL), diethyl carbonate (DEC), methyl methyl carbonate (EMC), trimethyl phosphate (TMP), triethyl phosphate (TEP), methyl propionate (MP), methyl butyrate (MB), and 2-methyltetrahydrofuran (2-MeTHF).

[0046] This application utilizes appropriate film-forming additives to form a high-performance and stable SEI film on the electrode surface, mitigating the incompatibility issue between organic solvents and graphite anodes. These film-forming additives include, but are not limited to, fluoroethylene carbonate (FEC), vinylene carbonate (VC), and ethylene ethylene carbonate (VCE). FEC can also, to some extent, inhibit electrolyte decomposition and gas generation at high temperatures, improving the battery's high-temperature stability and safety.

[0047] In some embodiments, the molar concentration of the electrolyte salt in the above-mentioned wide-temperature-range electrolyte is 0.8 mol / L to 1.2 mol / L.

[0048] In some embodiments, the molar ratio of the above-mentioned organic solvent to the above-mentioned bridging solvent is greater than 1:1, preferably (1.25 - 3):1, more preferably (1.25 - 2):1, and an electrolyte solution with wide-temperature-range performance can be prepared. The inventors of the present application found through experiments that when the molar ratio of the above-mentioned organic solvent to the above-mentioned bridging solvent is less than 1:1, the cycle performance of the battery assembled with the electrolyte solution prepared based on this formulation deteriorates at high temperatures; when the molar ratio of the above-mentioned organic solvent to the above-mentioned bridging solvent is greater than 3:1, the cycle performance of the battery assembled with the electrolyte solution prepared based on this formulation is poor. This may be because the addition amount of the organic solvent is too small, resulting in a limited dissolution amount of monoglyceride, thus unable to effectively improve the problem of poor compatibility between the organic solvent and the graphite negative electrode.

[0049] In some embodiments, the molar ratio of the above-mentioned organic solvent, the above-mentioned bridging solvent and the above-mentioned film-forming additive is (5 - 6):(3 - 4):(1 - 2).

[0050] In some embodiments, the addition amount of the above-mentioned monoglyceride is 1wt% - 5wt% of the total mass of the wide-temperature-range electrolyte solution, preferably 1wt% - 2wt%, which can make the monoglyceride fully dissolve in the above-mentioned bridging solvent and effectively improve the problem of poor compatibility between the organic solvent and the graphite negative electrode.

[0051] The present application also provides a preparation method for the above-mentioned wide-temperature-range electrolyte solution, including the following steps:

[0052] Heat and mix the electrolyte salt, monoglyceride, bridging solvent, organic solvent and film-forming additive according to the ratio to prepare a clear and transparent electrolyte solution, that is, the wide-temperature-range electrolyte solution.

[0053] In some embodiments, the temperature of the above-mentioned heating is 30°C - 40°C.

[0054] On the other hand, the present application also provides an alkali metal ion battery, which includes a positive electrode, a negative electrode and the above-mentioned wide-temperature-range electrolyte solution.

[0055] In some embodiments, the material of the above-mentioned positive electrode can be lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickel manganate, lithium-rich manganese-based or layered ternary material LiNi x Co y Mn 1-x-y O2, where 0 < x < 1 and 0 < y < 1.

[0056] In some embodiments, the above-mentioned negative electrode is a carbon-based negative electrode or a silicon-carbon negative electrode.

[0057] In some embodiments, the above-mentioned carbon-based negative electrode is one or more of natural graphite, artificial graphite, soft carbon, hard carbon and mesocarbon microbeads.

[0058] When the wide-temperature-range electrolyte provided in this application is used to assemble lithium-ion batteries, it can improve the interfacial stability of the graphite anode, enhance the initial charge-discharge efficiency and long-cycle performance of the battery, enabling it to cycle stably for 1000 cycles or more at room temperature. Simultaneously, it can improve the battery capacity at low temperatures, allowing the lithium-ion battery to operate stably over a wider temperature range (such as -40℃ to 60℃, or even -50℃ to 100℃). This effectively solves the problems of existing electrolytes easily freezing at low temperatures (-50℃ and below), poor compatibility between organic solvents and graphite anodes, and low battery capacity and rapid capacity decay, providing a reference for the development of EC-free high-performance lithium-ion batteries.

[0059] 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.

[0060] The following are examples and comparative examples:

[0061] Example 1

[0062] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0063] In a dry, low-oxygen environment with both water and oxygen content less than 0.1 ppm, lithium difluorosulfonyl imide and glyceryl monostearate were dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium difluorosulfonyl imide in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 6:3:1, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0064] The conductivity of the prepared wide-temperature-range electrolyte was tested:

[0065] The electrolyte was placed at different temperatures and allowed to stand for 5 minutes. Then, the conductivity of the electrolyte at different temperatures was measured using a conductivity meter.

[0066] The assembly process of the secondary lithium-ion battery (Li|| graphite battery) provided in this embodiment is as follows:

[0067] A coin cell battery was assembled in a glove box with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm. The positive electrode was graphite, the negative electrode was a lithium metal sheet, and the electrolyte was the wide-temperature-range electrolyte mentioned above.

[0068] The assembly process of the lithium-ion full battery (graphite||LFP soft-pack battery) provided in this embodiment is as follows:

[0069] The soft-pack battery was assembled in a glove box with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm. The positive electrode was a 3.5 mm × 3.5 mm commercial lithium iron phosphate (LFP) electrode, the negative electrode was a 4 mm × 4 mm commercial graphite electrode, the separator was a 5 mm × 5 mm PP separator, and the electrolyte was the wide-temperature-range electrolyte mentioned above.

[0070] Electrochemical tests were performed on the assembled Li|| graphite battery and graphite|| LFP pouch cell:

[0071] 1) Cyclic performance test: The above batteries were placed in the Blue Battery Test System for cyclic testing. The test voltage for Li|| graphite batteries was 0.01~2V, and the test voltage for graphite|| LFP soft packs was 2.35~3.65V.

[0072] 2) Cyclic voltammetry test: The test was conducted on a CHI660E workstation with a scan rate of 0.1 mV / s, an initial voltage equal to the battery voltage, a high potential of 2.5 V, a low potential of 0.005 V, and a cutoff voltage of 2.5 V.

[0073] Comparative Example 1 (without added monoglycerides)

[0074] The preparation of the electrolyte provided in this comparative example includes the following steps:

[0075] Lithium difluorosulfonylimide was dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion under dry, low-oxygen conditions. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the electrolyte. The molar concentration of lithium difluorosulfonylimide in this electrolyte is 1 mol / L, and the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 6:3:1.

[0076] The conductivity of the prepared electrolyte was tested using the method provided in Example 1.

[0077] The Li|| graphite battery and the graphite|| LFP pouch cell were assembled using the same method as in Example 1, and electrochemical tests were performed.

[0078] Comparative Example 2 (Commercial Electrolyte)

[0079] This comparative example uses a commercial electrolyte, which is a clear and transparent electrolyte prepared by dissolving lithium hexafluorophosphate (LiPF6) in ethylene carbonate and methyl ethyl carbonate, wherein the molar concentration of lithium hexafluorophosphate is 1 mol / L and the molar ratio of ethylene carbonate to methyl ethyl carbonate is 3:7.

[0080] The conductivity of the prepared electrolyte was tested using the method provided in Example 1.

[0081] The Li|| graphite battery and the graphite|| LFP pouch cell were assembled using the same method as in Example 1, and electrochemical tests were performed.

[0082] Figure 1 The table shows the ionic conductivity of the electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 at temperatures ranging from -60°C to 60°C. It can be seen that the electrolyte prepared in Example 1 exhibits high ionic conductivity in the range of -60°C to 60°C, while the commercial electrolyte in Comparative Example 2 freezes at around -30°C, and its ionic conductivity at low temperatures is much lower than that of Example 1.

[0083] Figure 2 The figure shows the first charge-discharge voltage-capacity curves of the Li|| graphite batteries assembled in Example 1 and Comparative Example 1. It can be seen that the battery assembled in Comparative Example 1 without the addition of glyceryl monostearate undergoes continuous solvent reduction decomposition around 0.5V, and typical Li|| graphite decomposition occurs around 0.5V. + - The organic solvent co-intercalation platform leads to overcharging of the graphite anode, resulting in an initial charge-discharge efficiency of only 65.92%. The electrolyte prepared in Example 1, with the addition of glyceryl monostearate, effectively inhibits solvent reductive decomposition and co-intercalation, significantly improving the compatibility between the solvent and graphite, and achieving Li... + Reversible insertion and extraction of graphite anodes improves the initial efficiency of the battery. The initial charge and discharge efficiency of the Li|| graphite battery assembled in Example 1 can reach 92.77%.

[0084] Figure 3 The figures show the long-cycle performance of the Li|| graphite batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 at 25°C and 0.5C rate. It can be seen that the Li|| graphite battery assembled in Example 1 retains 80% of its capacity after 320 cycles, exhibiting excellent cycle stability. However, the Li|| graphite battery assembled in Comparative Example 1 fails after about 100 cycles, and the Li|| graphite battery assembled in Comparative Example 2 experiences a sharp decrease in capacity after 130 cycles.

[0085] Figure 4 The cyclic voltammograms of the Li|| graphite batteries assembled in Example 1 and Comparative Example 1 are shown. It can be seen that at a scan rate of 0.1 mV / s, the graphite electrode of Comparative Example 1 exhibits a significant irreversible reduction peak around 0.5 V during the initial cathode scan. This phenomenon is consistent with the initial charge-discharge curve changes of the battery, reflecting the reduction decomposition of the solvent and its co-intercalation in the graphite anode. In Example 1, the solvent reduction peak disappears from the CV curve, and a pair of current peaks appear at the graphite anode between 0 and 0.3 V. This is typical of Li|| graphite batteries. +Features of reversible graphite anode with intercalation / deintercalation.

[0086] Figure 5 The figure shows the long-term cycle performance of the graphite||LFP pouch cells with an initial capacity of 1Ah assembled in Example 1 and Comparative Example 1 at 25°C and 1C rate. It can be seen that the capacity retention rate of the graphite||LFP pouch cell assembled in Comparative Example 1 decreased to 73% after 200 cycles, while the capacity retention rate of the graphite||LFP pouch cell assembled in Example 1 can still reach 80% after 850 cycles, showing excellent cycle performance.

[0087] Figure 6 The image shows the performance of the graphite||LFP pouch cells with an initial capacity of 1Ah assembled in Example 1 and Comparative Example 1 at low temperatures (-50°C to -20°C) after charging at 25°C. It can be seen that the graphite||LFP pouch cell assembled in Example 1, after charging at 25°C, has a discharge plateau of approximately 3.25V at room temperature. As the temperature decreases, the discharge plateau gradually declines. Specifically, this battery can provide a high capacity of 0.72Ah at a low temperature of -20°C and a 0.1C rate; and it can also provide a capacity of 0.44Ah at an ultra-low temperature of -50°C and a 0.1C rate.

[0088] Figure 7 The figures show the charge-discharge curves of graphite||LFP pouch cells with an initial capacity of 1Ah assembled in Example 1 and Comparative Example 1 at high temperatures (60°C~100°C) and a 1C rate. It can be seen that the graphite||LFP pouch cell assembled in Example 1 has a discharge capacity of 0.8Ah at 60°C and a 1C rate, and still provides a reversible capacity of 0.64Ah at an ultra-high temperature of 100°C and a 1C rate. Therefore, the graphite||LFP pouch cell assembled using the electrolyte provided in Example 1 of this application has a wide temperature adaptability and good cycle stability within a wide temperature range of -50°C to 100°C.

[0089] Example 2

[0090] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0091] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and glyceryl monostearate were dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium difluorosulfonyl imide in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 6:3:1, and the amount of glyceryl monostearate added accounts for 1.25 wt% of the total mass of the electrolyte.

[0092] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0093] Example 3

[0094] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0095] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and glyceryl monostearate were dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium difluorosulfonyl imide in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 6:3:1, and the amount of glyceryl monostearate added accounts for 1.5 wt% of the total mass of the electrolyte.

[0096] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0097] Example 4

[0098] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0099] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution is stirred at 30°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium difluorosulfonyl imide in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 5:3:2, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0100] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0101] Example 5

[0102] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0103] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution is stirred at 30°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium difluorosulfonyl imide in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 5:4:1, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0104] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0105] Example 6

[0106] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0107] Lithium tetrafluoroborate and glyceryl monostearate were dissolved in ethylene glycol dimethyl ether, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion under dry, low-oxygen conditions. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium tetrafluoroborate in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of ethylene glycol dimethyl ether, tetrahydrofuran, and fluoroethylene carbonate is 5:3:2, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0108] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0109] Example 7

[0110] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0111] In a dry, low-oxygen environment, lithium hexafluorophosphate and glyceryl monostearate were dissolved in propylene carbonate, 1,3-dioxolane, tetrahydrofuran, and fluoroethylene carbonate in a specific ratio. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium hexafluorophosphate in this wide-temperature-range electrolyte is 0.8 mol / L, the molar ratio of propylene carbonate, 1,3-dioxolane, tetrahydrofuran, and fluoroethylene carbonate is 3:2:4:1, and the amount of glyceryl monostearate added is 1 wt% of the total mass of the electrolyte.

[0112] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0113] Example 8

[0114] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0115] In a dry, low-oxygen environment, lithium hexafluorophosphate and glyceryl monostearate are dissolved in trimethyl phosphate, tetrahydrofuran, and vinylene carbonate in a certain proportion. The solution is stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium difluorosulfonylimide in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of trimethyl phosphate, tetrahydrofuran, and vinylene carbonate is 6:3:1, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0116] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0117] Example 9

[0118] The preparation of the wide-temperature-range electrolyte provided in this embodiment includes the following steps:

[0119] In a dry, low-oxygen environment, lithium perchlorate and glyceryl monostearate are dissolved in trimethyl phosphate, ethylene glycol dimethyl ether, tetrahydrofuran, and fluoroethylene carbonate in a specific ratio. The solution is stirred at 40°C to obtain a clear and transparent solution, which is the wide-temperature-range electrolyte. The molar concentration of lithium perchlorate in this wide-temperature-range electrolyte is 1 mol / L, the molar ratio of trimethyl phosphate, ethylene glycol dimethyl ether, tetrahydrofuran, and fluoroethylene carbonate is 4:2:3:1, and the amount of glyceryl monostearate added is 1 wt% of the total mass of the electrolyte.

[0120] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0121] Comparative Example 3 (with monoglyceride replaced by sorbitan stearate)

[0122] The preparation of the electrolyte provided in this comparative example includes the following steps:

[0123] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and sorbitan stearate were dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the electrolyte. The molar concentration of lithium difluorosulfonyl imide in the electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 5:4:1, and the amount of sorbitan stearate added accounts for 1 wt% of the total mass of the electrolyte.

[0124] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0125] Comparative Example 4 (molar ratio of organic solvent to bridging solvent is 4:5)

[0126] The preparation of the electrolyte provided in this comparative example includes the following steps:

[0127] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and glyceryl monostearate were dissolved in propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate in a certain proportion. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the electrolyte. The molar concentration of lithium difluorosulfonyl imide in the electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran, and fluoroethylene carbonate is 4:5:1, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0128] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0129] Comparative Example 5 (without added bridge solvent)

[0130] The preparation of the electrolyte provided in this comparative example includes the following steps:

[0131] In a dry, low-oxygen environment, lithium difluorosulfonyl imide and glyceryl monostearate were dissolved in propylene carbonate and fluoroethylene carbonate in a certain proportion. The solution was stirred at 40°C to obtain a clear and transparent solution, which is the electrolyte. The molar concentration of lithium difluorosulfonyl imide in this electrolyte is 1 mol / L, the molar ratio of propylene carbonate to fluoroethylene carbonate is 9:1, and the amount of glyceryl monostearate added accounts for 1 wt% of the total mass of the electrolyte.

[0132] The graphite||LFP pouch cell was assembled using the same method as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0133] Table 1. Capacity retention of assembled graphite||LFP pouch cells in the examples and comparative examples at different temperatures.

[0134]

[0135] As shown in Table 1, the graphite||LFP pouch cells assembled using the wide-temperature-range electrolyte prepared in the examples exhibit a wide temperature adaptability, demonstrating good cycle stability across a broad temperature range of -40°C to 60°C. The reason for this may be that the electrolyte provided in this application, by adding glyceryl monostearate and a solvent capable of dissolving this component, allows glyceryl monostearate to interact with organic solvents such as propylene carbonate at the graphite anode interface, thereby reducing the Li... + - The affinity between organic solvents leads to an increase in the lowest unoccupied molecular orbital (LUMO) energy level of the organic solvent molecules, making them difficult to reduce and decompose; at the same time, it can reduce the Li + The desolvation energy barrier of Li makes Li +The reversible intercalation / deintercalation of the graphite anode achieves complete compatibility between the organic solvent and the graphite anode through a combined effect, thereby improving the interfacial stability and cycle stability of the graphite anode. The electrolyte provided in this application has a wide range of applications, excellent wide-temperature performance, and can maintain good rate performance and cycle stability at room temperature.

[0136] The graphite||LFP pouch cell assembled using the electrolyte prepared in Comparative Example 3 exhibited a first-cycle charge-discharge efficiency of only 50%, and poor cycle performance at -40℃ and -20℃. This indicates that adding sorbitan stearate, which has a structure and properties similar to glyceryl monostearate, to the electrolyte cannot effectively inhibit solvent co-intercalation into the graphite anode, nor can it allow Li... + Reversible insertion / extraction of graphite anodes cannot achieve complete compatibility between the solvent and the graphite anode, thus failing to improve the wide-temperature-range cycling performance of graphite||LFP pouch cells.

[0137] The graphite||LFP pouch cells assembled using the electrolyte prepared in Comparative Example 5 exhibited low capacity retention at low temperatures (-40℃, -20℃), room temperature (25℃), and high temperatures (60℃). The reason for this is likely that the glyceryl monostearate added to the electrolyte formulation was not effectively dissolved, thus failing to effectively reduce Li- concentration through the interaction between glyceryl monostearate and the organic solvent. + The desolvation energy barrier inhibits the reaction of organic solvents and Li + The graphite anode is co-embedded with organic solvents, and the reduction and decomposition of organic solvents occur on the anode side.

[0138] 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 suitable for alkali metal ion batteries, characterized in that, It includes electrolyte salts, organic solvents and film-forming additives, as well as monoglycerides and bridging solvents for dissolving the monoglycerides; The interaction between the monoglyceride and the organic solvent can suppress the reductive decomposition of the organic solvent and the co-intercalation effect of the organic solvent and alkali metal ions. The negative electrode of the alkali metal ion battery is a carbon-based negative electrode or a silicon-carbon negative electrode; the organic solvent is one or more of propylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, diethyl carbonate, methyl ethyl carbonate, trimethyl phosphate, triethyl phosphate, methyl propionate, methyl butyrate, and 2-methyltetrahydrofuran; the molar ratio of the organic solvent to the bridging solvent is greater than 1:

1.

2. The wide-temperature-range electrolyte according to claim 1, characterized in that, The monoglyceride is one or more selected from glyceryl monostearate, glyceryl monosilyl ester, glyceryl monopalmitate, glyceryl monolinoleate, and glyceryl monooleate; and / or, The bridging solvent is one or more of tetrahydrofuran, tetrahydropyran, and chloroform.

3. The wide-temperature-range electrolyte according to claim 1 or 2, characterized in that, The amount of monoglyceride added is 1 wt% to 5 wt% of the total mass of the wide-temperature-range electrolyte.

4. The wide-temperature-range electrolyte according to claim 1, characterized in that, The electrolyte salt is a lithium salt or a potassium salt; The lithium salt is one or more selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrophosphate; and / or, The potassium salt is one or more of potassium hexafluorophosphate, potassium perchlorate, and potassium trifluoromethanesulfonate.

5. The wide-temperature-range electrolyte according to claim 1, characterized in that, The film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate, and ethylene ethylene carbonate.

6. The wide-temperature-range electrolyte according to any one of claims 1 to 5, characterized in that, In the wide-temperature-range electrolyte, the molar concentration of the electrolyte salt is 0.8~1.2 mol / L; and / or, The molar ratio of the organic solvent to the bridging solvent is (1.25~3):

1.

7. The wide-temperature-range electrolyte according to claim 6, characterized in that, The molar ratio of the organic solvent, the bridging solvent, and the film-forming additive is (5~6):(3~4):(1~2).

8. An alkali metal ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a wide-temperature-range electrolyte as described in any one of claims 1 to 7.

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