Wide-temperature-range electrolyte suitable for alkali metal ion battery and application

Abstract

The invention belongs to the technical field of alkali metal ion batteries, and particularly relates to a wide-temperature-range electrolyte suitable for an alkali metal ion battery and application. The wide-temperature-range electrolyte suitable for the alkali metal ion battery provided by the invention comprises electrolyte salt, an organic solvent and a film-forming additive, and further comprises monoglyceride and a bridge solvent for dissolving the monoglyceride, the interaction of the monoglyceride and the organic solvent can inhibit the reductive decomposition of the organic solvent and inhibit the co-intercalation effect of the organic solvent and alkali metal ions. According to the invention, by adding the monoglyceride and the bridge solvent for dissolving the monoglyceride and optimizing the formula, the problem that the organic solvent is incompatible with the graphite negative electrode is effectively solved, the electrolyte with wide temperature range performance and good compatibility with the graphite negative electrode is prepared, and stable operation of the battery in a relatively wide temperature range of-40 DEG C to 60 DEG C is ensured.

Description

Technical Field

[0001] The present application belongs to the technical field of alkali metal ion batteries, and more specifically, relates to a wide temperature range electrolyte suitable for alkali metal ion batteries and its application. Background Art

[0002] Lithium-ion batteries (LIBs) are widely used in portable electronic devices, electric vehicles, energy storage grids and other fields due to their high energy density, long cycle life, environmental protection, and no memory effect. At the same time, the continuous advancement and iterative improvement of technology, as well as the reduction of costs and the increase of energy density, have enabled LIBs to maintain their competitive advantage in electrochemical energy storage for a long time. However, as the scope of battery application scenarios continues to expand, people are paying more and more attention to the applicability and safety of batteries in a large operating temperature range. Commercial LIBs usually operate best in a narrow temperature range of -15℃~35℃. In extremely cold areas at high altitudes or high latitudes, LIBs usually need to work for a long time at temperatures below -30℃; in hot environments such as deserts, they need to work at high temperatures of 50℃ and above. At present, most commercial electrolytes are EC-based electrolytes, but the high melting point of EC (melting point is 36.4℃) makes the commercial electrolyte easy to solidify or even crystallize at low temperatures. At the same time, EC is very easy to undergo oxidative decomposition with the positive electrode material at a high voltage of 4.4V, making the commercial electrolyte unable to meet the application requirements under harsh conditions such as high temperature, high pressure, and low temperature, limiting the application of the battery.

[0003] Solvents such as propylene carbonate and ethylene glycol dimethyl ether have a wider liquid temperature range, but they are incompatible with graphite negative electrodes and are easily co-embedded with lithium ions in the graphite interlayer, causing the structure of the graphite material to collapse, resulting in reduced battery capacity and rapid decay.

[0004] Therefore, the development of EC-free electrolytes with wide temperature range performance and good compatibility with graphite anode is crucial for developing wide temperature range batteries and improving battery safety, stability and reliability. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of this application is to provide a wide temperature range electrolyte and application suitable for alkali metal ion batteries, aiming to solve the problems that the existing electrolyte is easy to freeze at low temperatures (-50°C and below), the compatibility of organic solvents in the electrolyte with the graphite negative electrode is poor, and the capacity of batteries assembled based on the existing electrolyte is low and decays quickly.

[0006] To achieve the above objectives, in a first aspect, the present 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, and also includes a monoglyceride and a bridge solvent for dissolving the monoglyceride; The interaction between the monoglyceride and the organic solvent can inhibit the reduction decomposition of the organic solvent and inhibit the co-intercalation effect of the organic solvent and the alkali metal ions.

[0007] Preferably, the monoglyceride is one or more of glyceryl monostearate, glyceryl monolaurate, glyceryl monopalmitate, glyceryl monolinoleate and glyceryl monooleate.

[0008] Preferably, the bridge solvent is one or more of tetrahydrofuran, tetrahydropyran and chloroform.

[0009] Preferably, the added amount of the above monoglyceride is 1wt%~5wt% of the total mass of the wide temperature range electrolyte; more preferably 1wt%~2wt%.

[0010] Preferably, the electrolyte salt is a lithium salt or a potassium salt.

[0011] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate.

[0012] Preferably, the potassium salt is one or more of potassium hexafluorophosphate, potassium perchlorate and potassium trifluoromethanesulfonate.

[0013] Preferably, the organic solvent is one or more of propylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, diethyl carbonate, ethyl methyl carbonate, trimethyl phosphate, triethyl phosphate, methyl propionate, methyl butyrate and 2-methyltetrahydrofuran.

[0014] Preferably, the film-forming additive is one or more of fluoroethylene carbonate, vinylene carbonate and vinylethylene carbonate.

[0015] Preferably, in the above-mentioned wide temperature range electrolyte, the molar concentration of the electrolyte salt is 0.8~1.2 mol / L.

[0016] Preferably, the molar ratio of the organic solvent to the bridge solvent is greater than 1:1; more preferably (1.25-3):1.

[0017] Preferably, the molar ratio of the organic solvent, the bridge solvent and the film-forming additive is (5-6):(3-4):(1-2).

[0018] In a second aspect, 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.

[0019] Preferably, the negative electrode is a carbon-based negative electrode or a silicon-carbon negative electrode.

[0020] In general, the above technical solutions conceived by this application have the following technical advantages compared with the prior art: (1) The wide temperature range electrolyte for alkali metal ion batteries provided in the present application includes an electrolyte salt, an organic solvent and a film-forming additive, and also includes a monoglyceride and a bridge solvent for dissolving the monoglyceride. By adding monoglyceride and a bridge solvent, the present application can prepare an EC-free electrolyte with wide temperature range performance. The electrolyte does not freeze at -60°C, and the ionic conductivity at -60°C to 60°C is higher than that of commercial EC-based electrolytes. In addition, the monoglyceride in the electrolyte can interact with the organic solvent at the interface of the graphite negative electrode, weaken the affinity between the alkali metal ions and the organic solvent, and increase 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 reduce the desolvation energy barrier of the alkali metal ions, so that the alkali metal ions can be reversibly deintercalated into the graphite negative electrode. Combining the above effects, the electrolyte provided in the present application effectively solves the problem of poor compatibility between the organic solvent and the graphite negative electrode, and prepares an EC-free electrolyte with wide temperature range performance and good compatibility with the graphite negative electrode.

[0021] (2) This application can effectively improve the capacity of the battery at low temperatures by adjusting the addition ratio of electrolyte salts, organic solvents, monoglycerides, bridge solvents and other components in the wide temperature range electrolyte through formula optimization, so that the battery can operate stably in a wider temperature range (such as -40℃~60℃, or even -50℃~100℃), effectively solving the problem of low capacity and rapid attenuation of the battery at low temperatures. At the same time, it can effectively improve the initial charge and discharge efficiency and long cycle performance of the battery, and can achieve stable cycling of the battery for 1,000 times or more at room temperature.

[0022] (3) Compared with commercial EC-based electrolytes and existing wide-temperature range electrolytes, the wide-temperature range electrolyte provided in the present application does not freeze at low temperatures (-60°C) and has higher conductivity; at the same time, it still has good cycle stability at high temperatures (100°C). The electrolyte is compatible with the graphite negative electrode and also exhibits good wide-temperature adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The conductivity of the electrolytes prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present application at different temperatures; Figure 2 The first charge and discharge voltage-capacity curve of the Li||graphite battery assembled in Example 1 and Comparative Example 1 of the present application; Figure 3 The long cycle performance of the Li||graphite battery assembled in Example 1, Comparative Example 1 and Comparative Example 2 of the present application at 25°C and 0.5C rate; Figure 4 The cyclic voltammetry curve of the Li||graphite battery assembled in Example 1 and Comparative Example 1 of the present application at a scan rate of 0.1 mV / S; Figure 5 The long cycle performance of the graphite||LFP soft pack battery assembled in Example 1 and Comparative Example 1 of the present application at 25°C and 1C rate; Figure 6 The discharge curve of the graphite||LFP soft-pack battery assembled in Example 1 and Comparative Example 1 of the present application at low temperature (-50°C~-20°C) and 0.1C rate after charging at 25°C; Figure 7 This is a charge and discharge curve diagram of the graphite||LFP soft-pack battery assembled in Example 1 and Comparative Example 1 of the present application at high temperature (60°C~100°C) and 1C rate. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] In the description of this application, it should be understood that the term "and / or" is a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The symbol " / " herein indicates that the associated objects are in an or relationship, for example, A / B means A or B.

[0026] In the description of the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0027] In the description of the embodiments of the present application, unless otherwise specified, “plurality” means two or more than two.

[0028] The term "monoglyceride" refers to a mono-fatty acid glyceride.

[0029] Traditional commercial electrolytes are mostly EC-based electrolytes, and the high melting point of EC and the fact that it is easily oxidized on the positive electrode side make the existing EC-based electrolytes unable to meet the application requirements under a variety of harsh conditions such as high temperature, high pressure, and low temperature. By selecting organic solvents with a wide liquid range and good antioxidant properties, such as propylene carbonate, ethylene glycol dimethyl ether, etc., the freezing point of the electrolyte can be lowered, and the liquid range of the electrolyte can be expanded, providing the possibility for the battery to work in extreme environments. However, these solvents will co-embed the graphite negative electrode with the alkali metal ions, resulting in the inability of the alkali metal ions to be normally and reversibly de-embedded from the graphite, resulting in poor battery cycle performance. Based on this, the present 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 bridge solvent for dissolving the monoglyceride; Among them, the interaction between monoglyceride and organic solvent can weaken the affinity between alkali metal and organic solvent and reduce the desolvation energy barrier of alkali metal ions, thereby inhibiting the reductive decomposition of organic solvent and inhibiting the co-embedding effect of organic solvent and alkali metal ions.

[0030] The inventors of the present application unexpectedly discovered through experiments that by adding monoglyceride and a bridge solvent capable of dissolving the monoglyceride to the electrolyte, an EC-free electrolyte with wide temperature range performance can be prepared, the electrolyte still does not freeze at -60°C, and the ionic conductivity at -60°C to 60°C is higher than that of commercial EC-based electrolytes. In addition, the monoglyceride dissolved in the electrolyte can weaken the affinity between the alkali metal ions and the organic solvent, increase the lowest unoccupied molecular orbital (LUMO) energy level of the organic solvent molecules, and make it difficult for the organic solvent to be reduced and decomposed. At the same time, it can also reduce the desolvation energy barrier of the alkali metal ions, so that the alkali metal ions can be reversibly deintercalated into the graphite negative electrode, which effectively improves the compatibility of the organic solvent and the graphite negative electrode, making the electrolyte compatible with the graphite negative electrode.

[0031] In some embodiments, the monoglyceride is one or more of glyceryl monostearate (GMS), glyceryl monomolylate (GMO), glyceryl monopalmitate (GPP), glyceryl monolinoleate and glyceryl monooleate (GML). In a preferred embodiment, the monoglyceride is glyceryl monostearate.

[0032] In some embodiments, the bridge solvent is one or more of tetrahydrofuran, tetrahydropyran and chloroform.

[0033] It is understandable that the wide temperature range electrolyte provided in the present application is suitable for various alkali metal ion batteries, including commonly used lithium ion batteries and potassium ion batteries. It should be understood that the wide temperature range electrolyte provided in the present application can also be applied to sodium ion batteries, and the corresponding electrolyte salts used in the wide temperature range electrolyte are lithium salts, potassium salts or sodium salts. The wide temperature range electrolyte provided in the present application can be applied to different alkali metal ion batteries only by adjusting the type of electrolyte salt, and has good universality.

[0034] When the wide temperature range electrolyte provided in the present application is applied to a lithium-ion battery, the lithium salt thereof may be, but is not limited to, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate, etc.

[0035] When the wide temperature range electrolyte provided in the present application is applied to a lithium ion battery, the potassium salt therein may be, but is not limited to, potassium hexafluorophosphate, potassium perchlorate, potassium trifluoromethanesulfonate, and the like.

[0036] In some embodiments, the organic solvent is an organic solvent having a melting point less than or equal to -40°C and a boiling point greater than or equal to 60°C. In a preferred embodiment, 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), ethyl methyl carbonate (EMC), trimethyl phosphate (TMP), triethyl phosphate (TEP), methyl propionate (MP), methyl butyrate (MB) and 2-methyltetrahydrofuran (2-MeTHF).

[0037] The present application can form a stable SEI film with excellent performance on the electrode surface by adding an appropriate amount of film-forming additives, thereby alleviating the problem of incompatibility between organic solvents and graphite negative electrodes. The above-mentioned film-forming additives include but are not limited to fluoroethylene carbonate (FEC), vinylene carbonate (VC) and vinyl ethylene carbonate (VCE). Among them, fluoroethylene carbonate can also inhibit the decomposition and gas production of the electrolyte at high temperature to a certain extent, thereby improving the high temperature stability and safety of the battery.

[0038] In some embodiments, in the wide temperature range electrolyte, the molar concentration of the electrolyte salt is 0.8 mol / L to 1.2 mol / L.

[0039] 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 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 cycling performance of the battery assembled with the electrolyte solution prepared based on this formula 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 cycling performance of the battery assembled with the electrolyte solution prepared based on this formula 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.

[0040] 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).

[0041] In some embodiments, the addition amount of the above-mentioned monoglyceride is 1 wt% - 5 wt% of the total mass of the wide-temperature electrolyte solution, preferably 1 wt% - 2 wt%, 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.

[0042] The present application also provides a preparation method of the above-mentioned wide-temperature electrolyte solution, including the following steps: According to the ratio, heat and mix the electrolyte salt, monoglyceride, bridging solvent, organic solvent, and film-forming additive evenly to prepare a clear and transparent electrolyte solution, that is, the wide-temperature electrolyte solution.

[0043] In some embodiments, the temperature of the above-mentioned heating is 30°C - 40°C.

[0044] 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 electrolyte solution.

[0045] 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 O 2 , where 0 < x < 1 and 0 < y < 1.

[0046] In some embodiments, the above-mentioned negative electrode is a carbon-based negative electrode or a silicon-carbon negative electrode.

[0047] 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.

[0048] When the wide temperature range electrolyte provided in this application is used to assemble lithium-ion batteries, it can improve the interface stability of the graphite negative electrode, improve the initial charge and discharge efficiency and long cycle performance of the battery, and enable it to stably cycle 1,000 times or more at room temperature. At the same time, it can improve the capacity of the battery at low temperatures, so that the lithium-ion battery can operate stably in a wider temperature range (such as -40°C~60°C, or even -50°C~100°C), effectively solving the problems of the existing electrolyte being easy to freeze at low temperatures (-50°C and below), the poor compatibility of organic solvents with graphite negative electrodes, and the low capacity and rapid decay of the battery, providing a reference for the development of EC-free high-performance lithium-ion batteries.

[0049] It should be understood that materials of the same or similar type, model, quality, nature or function as the reagents and instruments used in the following examples can be used to implement the present application. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0050] The following are examples and comparative examples: Example 1 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment with a water content and an oxygen content of less than 0.1 ppm, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the 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 1wt% of the total mass of the electrolyte.

[0051] The conductivity of the prepared wide temperature range electrolyte was tested: The electrolyte was placed at different temperatures and allowed to stand for 5 minutes, and then the conductivity of the electrolyte at different temperatures was measured using a conductivity meter.

[0052] The assembly process of the secondary lithium-ion battery (Li|| graphite battery) provided in this embodiment is as follows: The button-type battery is 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, wherein the positive electrode is graphite, the negative electrode is a lithium metal sheet, and the electrolyte is the above-mentioned wide temperature range electrolyte.

[0053] The assembly process of the lithium-ion full battery (graphite||LFP soft pack battery) provided in this embodiment is as follows: The soft-pack battery is assembled in a glove box with a water content of less than 0.1ppm and an oxygen content of less than 0.1ppm, wherein the positive electrode is a 3.5mm×3.5mm commercial lithium iron phosphate (LFP) electrode, the negative electrode is a 4mm×4mm commercial graphite electrode, the diaphragm is a 5mm×5mm PP diaphragm, and the electrolyte is the above-mentioned wide temperature range electrolyte.

[0054] Electrochemical tests on assembled Li||graphite batteries and graphite||LFP soft pack batteries: 1) Cycle performance test: The above batteries were placed in a blue battery test system for cycle testing, where the test voltage of the Li||graphite battery was 0.01~2V, and the test voltage of the graphite||LFP soft pack was 2.35~3.65V.

[0055] 2) Cyclic voltammetry test: The test was carried out on a CHI660E workstation with a scan rate of 0.1 mV / S, an initial voltage of the battery voltage, a high potential of 2.5 V, a low potential of 0.005 V, and a cut-off voltage of 2.5 V.

[0056] Comparative Example 1 (without adding monoglyceride) The preparation of the electrolyte provided in this comparative example comprises the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide is dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is an electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 1 mol / L, and the molar ratio of propylene carbonate, tetrahydrofuran and fluoroethylene carbonate is 6:3:1.

[0057] The conductivity of the prepared electrolyte was tested using the method provided in Example 1.

[0058] The same method as in Example 1 was used to assemble Li||graphite batteries and graphite||LFP soft-pack batteries, and electrochemical tests were performed.

[0059] Comparative Example 2 (commercial electrolyte) This comparative example uses a commercial electrolyte, which is lithium hexafluorophosphate LiPF 6 The lithium hexafluorophosphate is dissolved in ethylene carbonate and ethyl methyl carbonate to prepare a clear and transparent electrolyte, wherein the molar concentration of lithium hexafluorophosphate is 1 mol / L, and the molar ratio of ethylene carbonate to ethyl methyl carbonate is 3:7.

[0060] The conductivity of the prepared electrolyte was tested using the method provided in Example 1.

[0061] The same method as in Example 1 was used to assemble Li||graphite batteries and graphite||LFP soft-pack batteries, and electrochemical tests were performed.

[0062] Figure 1 The figure shows the ionic conductivities of the electrolytes prepared in Example 1, Comparative Example 1 and Comparative Example 2 at temperatures between -60°C and 60°C. It can be seen that the electrolyte prepared in Example 1 exhibits relatively high ionic conductivity in the range of -60°C to 60°C, while the commercial electrolyte of Comparative Example 2 freezes at around -30°C, and its ionic conductivity at low temperatures is much lower than that of Example 1.

[0063] Figure 2 The first charge and discharge voltage-capacity curves of the Li||graphite battery assembled in Example 1 and Comparative Example 1 are shown. It can be seen that the battery assembled in Comparative Example 1 without adding glycerol monostearate undergoes continuous reduction and decomposition of the solvent at around 0.5V, and a typical Li + -Organic solvent co-embedding platform, solvent co-embedding leads to overcharging of graphite anode, and the initial charge and discharge efficiency is only 65.92%. Monostearate is added to the electrolyte prepared in Example 1, which can effectively inhibit the reduction decomposition and co-embedding of the solvent, effectively improve the compatibility of the solvent and graphite, and realize Li + The graphite negative electrode can be reversibly deintercalated, thereby improving 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%.

[0064] Figure 3 The figure shows 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 capacity retention rate of the Li|| graphite battery assembled in Example 1 is 80% after 320 cycles, showing excellent cycle stability; while the Li|| graphite battery assembled in Comparative Example 1 fails after about 100 cycles, and the capacity of the Li|| graphite battery assembled in Comparative Example 2 drops sharply after 130 cycles.

[0065] Figure 4 The cyclic voltammetry curves of the Li|| graphite battery assembled in Example 1 and Comparative Example 1 are shown. It can be seen that at a scan rate of 0.1mV / s, the graphite electrode of Comparative Example 1 has an obvious irreversible reduction peak at around 0.5V during the initial cathode scan. This phenomenon is consistent with the changes in the initial charge and discharge curves of the battery, reflecting the reduction and decomposition of the solvent and its co-embedding in the graphite negative electrode. The solvent reduction peak of the CV curve of Example 1 disappears, and a pair of current peaks appear at 0~0.3V at the graphite negative electrode, which is a typical Li + Characteristics of reversibly deintercalated graphite anode.

[0066] Figure 5The figure shows the long cycle performance of the graphite||LFP soft-pack battery 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 soft-pack battery assembled in Comparative Example 1 drops to 73% after 200 cycles, while the capacity retention rate of the graphite||LFP soft-pack battery assembled in Example 1 can still reach 80% after 850 cycles, which has excellent cycle performance.

[0067] Figure 6 The figure shows the performance of the graphite||LFP soft-pack battery with an initial capacity of 1Ah assembled in Example 1 and Comparative Example 1 at low temperature (-50°C~-20°C) after charging at 25°C. It can be seen that the discharge platform of the graphite||LFP soft-pack battery assembled in Example 1 is about 3.25V at room temperature after charging at 25°C, and the discharge platform gradually decreases with decreasing temperature. The battery can provide a high capacity of 0.72Ah at a low temperature of -20°C and a rate of 0.1C; and can also provide a capacity of 0.44Ah at an ultra-low temperature of -50°C and a rate of 0.1C.

[0068] Figure 7 The graphite||LFP soft pack battery with an initial capacity of 1Ah assembled in Example 1 and Comparative Example 1 is shown as the charge and discharge curve at high temperature (60°C~100°C) and 1C rate. It can be seen that the discharge capacity of the graphite||LFP soft pack battery assembled in Example 1 is 0.8Ah at a high temperature of 60°C and a rate of 1C, and it can still provide a reversible capacity of 0.64Ah at an ultra-high temperature of 100°C and a rate of 1C. Therefore, the graphite||LFP soft pack battery assembled using the electrolyte provided in Example 1 of the present application has a wide temperature adaptability and has good cycle stability in a wide temperature range of -50°C to 100°C.

[0069] Example 2 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the wide temperature range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran and fluoroethylene carbonate is 6:3:1, and the addition amount of glyceryl monostearate accounts for 1.25wt% of the total mass of the electrolyte.

[0070] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0071] Example 3 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the wide temperature range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran and fluoroethylene carbonate is 6:3:1, and the addition amount of glyceryl monostearate accounts for 1.5wt% of the total mass of the electrolyte.

[0072] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0073] Example 4 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 30°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the wide temperature range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran and fluoroethylene carbonate is 5:3:2, and the addition amount of glyceryl monostearate accounts for 1wt% of the total mass of the electrolyte.

[0074] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0075] Example 5 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 30°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the wide temperature range electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran and fluoroethylene carbonate is 5:4:1, and the addition amount of glyceryl monostearate accounts for 1wt% of the total mass of the electrolyte.

[0076] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0077] Example 6 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium tetrafluoroborate and glyceryl monostearate are dissolved in ethylene glycol dimethyl ether, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium tetrafluoroborate in the 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 addition amount of glyceryl monostearate accounts for 1wt% of the total mass of the electrolyte.

[0078] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0079] Example 7 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium hexafluorophosphate and glyceryl monostearate are dissolved in propylene carbonate, 1,3-dioxolane, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium hexafluorophosphate in the 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 addition amount of glyceryl monostearate accounts for 1wt% of the total mass of the electrolyte.

[0080] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0081] Example 8 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: In a dry, low-oxygen environment, lithium hexafluorophosphate and glyceryl monostearate are dissolved in trimethyl phosphate, tetrahydrofuran and vinylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the wide temperature range electrolyte is 1 mol / L, the molar ratio of trimethyl phosphate, tetrahydrofuran and vinylene carbonate is 6:3:1, and the addition amount of glyceryl monostearate accounts for 1wt% of the total mass of the electrolyte.

[0082] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0083] Example 9 The preparation of the wide temperature range electrolyte provided in this embodiment includes the following steps: 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 certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is a wide temperature range electrolyte. The molar concentration of lithium perchlorate in the 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 addition amount of glyceryl monostearate accounts for 1wt% of the total mass of the electrolyte.

[0084] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0085] Comparative Example 3 (Replacing Monoglyceride with Sorbitol Stearate) The preparation of the electrolyte provided in this comparative example comprises the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and sorbitol stearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is an electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 1 mol / L, the molar ratio of propylene carbonate, tetrahydrofuran and fluoroethylene carbonate is 5:4:1, and the addition amount of sorbitol stearate accounts for 1wt% of the total mass of the electrolyte.

[0086] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0087] Comparative Example 4 (the molar ratio of the organic solvent to the bridge solvent is 4:5) The preparation of the electrolyte provided in this comparative example comprises the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate, tetrahydrofuran and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is an electrolyte. The molar concentration of lithium bis(fluorosulfonyl)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 1wt% of the total mass of the electrolyte.

[0088] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0089] Comparative Example 5 (no bridge solvent added) The preparation of the electrolyte provided in this comparative example comprises the following steps: In a dry, low-oxygen environment, lithium bis(fluorosulfonyl)imide and glyceryl monostearate are dissolved in propylene carbonate and fluoroethylene carbonate in a certain proportion, and stirred at 40°C to obtain a clear and transparent solution, which is an electrolyte. The molar concentration of lithium bis(fluorosulfonyl)imide in the 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 1wt% of the total mass of the electrolyte.

[0090] The graphite||LFP soft-pack battery was assembled in the same manner as in Example 1, and electrochemical tests were performed. The results are shown in Table 1.

[0091] Table 1 Capacity retention rate of graphite||LFP soft pack batteries assembled in examples and comparative examples at different temperatures

[0092] It can be seen from Table 1 that the graphite||LFP soft-pack battery assembled with the wide temperature range electrolyte prepared in the embodiment has a wide temperature adaptability and has good cycle stability in a wide temperature range of -40°C to 60°C. The reason for this may be that the electrolyte provided in the present application adds glyceryl monostearate and a solvent capable of dissolving the component, so that glyceryl monostearate can interact with organic solvents such as propylene carbonate at the interface of the graphite negative electrode, thereby weakening the Li + - The affinity between organic solvents leads to an increase in the lowest unoccupied molecular orbital (LUMO) energy level of organic solvent molecules, making it difficult for organic solvents to be reduced and decomposed; at the same time, it can reduce Li + The desolvation barrier of Li + The reversible deintercalation of the graphite negative electrode achieves full compatibility between the organic solvent and the graphite negative electrode, thereby improving the interface stability and cycle stability of the graphite negative electrode. The electrolyte provided in this application has a wide range of applications, excellent wide temperature range performance, and can maintain good rate performance and cycle stability at room temperature.

[0093] The graphite||LFP soft-pack battery assembled with the electrolyte prepared in Comparative Example 3 has a first-cycle charge and discharge efficiency of only 50%, and its cycle performance at -40°C and -20°C is poor. This shows that the addition of sorbitol stearate, which has a structure and properties similar to those of glyceryl monostearate, to the electrolyte cannot effectively inhibit the co-embedding of the solvent into the graphite negative electrode, and cannot make Li + The reversible deintercalation of the graphite negative electrode cannot achieve complete compatibility between the solvent and the graphite negative electrode, and thus cannot improve the wide temperature range cycling performance of the graphite||LFP soft-pack battery.

[0094] The capacity retention rate of the graphite||LFP soft-pack battery assembled with the electrolyte prepared in Comparative Example 5 at low temperature (-40°C, -20°C), room temperature (25°C) and high temperature (60°C) is low. The reason for this may be that the glyceryl monostearate added to the electrolyte formula is not effectively dissolved, so the Li+ / -20% electrolyte cannot be effectively reduced through the interaction between glyceryl monostearate and the organic solvent. + The desolvation barrier inhibits the organic solvent and Li + Co-intercalation into graphite anode and reduction and decomposition of organic solvent on the anode side.

[0095] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A wide temperature range electrolyte suitable for alkali metal ion batteries, characterized in that: The invention comprises an electrolyte salt, an organic solvent and a film-forming additive, and also comprises a monoglyceride and a bridge solvent for dissolving the monoglyceride; The interaction between the monoglyceride and the organic solvent can inhibit the reduction decomposition of the organic solvent and inhibit the co-intercalation effect of the organic solvent and the alkali metal ions.

2. The wide temperature range electrolyte according to claim 1, characterized in that: The monoglyceride is one or more of glyceryl monostearate, glyceryl monolaurate, glyceryl monopalmitate, glyceryl monolinoleate and glyceryl monooleate; and / or, The bridge 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 added amount of the monoglyceride is 1wt% to 5wt% 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 of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide and lithium nitrate; 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 organic solvent is one or more of propylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,3-dioxolane, diethyl carbonate, ethyl methyl carbonate, trimethyl phosphate, triethyl phosphate, methyl propionate, methyl butyrate and 2-methyltetrahydrofuran.

6. 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 vinylethylene carbonate.

7. The wide temperature range electrolyte according to any one of claims 1 to 6, 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 bridge solvent is greater than 1:1, preferably (1.25-3):

1.

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

9. An alkali metal ion battery, characterized in that: It comprises a positive electrode, a negative electrode and a wide temperature range electrolyte as claimed in any one of claims 1 to 8.

10. The alkali metal ion battery according to claim 9, characterized in that: The negative electrode is a carbon-based negative electrode or a silicon-carbon negative electrode.

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