Electrolyte for low-temperature fast-charging lithium battery and application

Abstract

The invention provides an electrolyte for a low-temperature fast-charging lithium battery and application, and belongs to the technical field of lithium ion batteries. Comprising a lithium salt, an organic solvent and an additive, the concentration of the lithium salt is 0.1-2 mol / L, the organic solvent is a chain carboxylic ester compound, the additive is a cyclic ester compound, and the additive accounts for 5-15% of the total mass of the electrolyte. When the battery pack is applied to the lithium battery, low-temperature fast charging of the lithium battery can be realized.

Description

TECHNICAL FIELD

[0001] The application relates to an electrolyte for a low-temperature fast-charging lithium battery and an application thereof, and belongs to the technical field of lithium ion batteries. BACKGROUND

[0002] With the improvement of the cruising range of electric vehicles, the fast-charging capability of lithium batteries and the adaptability to low-temperature environments have become key performance indicators restricting the further development thereof. The core of realizing efficient fast charging lies in that the battery system needs to have extremely high ion conduction capability (including bulk electrolyte and interface film) and fast interface reaction kinetics, so as to ensure that lithium ions can be efficiently embedded / detached from the negative electrode at a high rate, and avoid the precipitation of lithium metal caused by kinetic limitations. Excellent low-temperature adaptability requires that the electrolyte system still maintains low viscosity, high ion conductivity and low interface impedance at low temperatures, so as to avoid the capacity reduction caused by the solidification of electrolyte, the obstruction of ion migration and the increase of interface impedance. However, the currently widely used carbonate electrolyte system, although having good comprehensive performance at room temperature, its inherent physical and chemical properties are difficult to simultaneously meet the stringent requirements of fast charging and low-temperature application. In the fast charging scenario, the solvation structure of the system and the ion conduction capability of the solid-state electrolyte interface film (SEI) formed thereby are insufficient, which cannot support extremely high lithium ion flux, resulting in a sharp rise in polarization voltage at the end of charging, significantly increasing the risk of lithium precipitation, endangering the safety of the battery and reducing the cycle life; in a low-temperature environment, due to its high freezing point and viscosity which sharply increases with the decrease of temperature, the ion conductivity is greatly reduced, and the interface charge transfer impedance is significantly increased, eventually leading to serious deterioration of the battery capacity and power output performance.

[0003] In view of the dual targets of simultaneously realizing fast charging and excellent low-temperature performance of lithium batteries, the electrolyte design faces unique and complex challenges. The chain carboxylic acid ester solvent system has the potential of significantly improving ion conductivity and liquid phase window due to its low viscosity, high dielectric constant and low melting point characteristics. However, this kind of solvent itself has poor compatibility with graphite (Gr) negative electrode, and is difficult to form a stable and effective SEI, resulting in poor battery cycle performance and low coulombic efficiency, especially under the double stress of fast charging and low temperature, the interface problem is more prominent.

[0004] Currently, some novel electrolytes have been developed for low-temperature fast charging, but they all have obvious drawbacks. For example, the fast-charging Gr anode disclosed in "Lin, Hu, et al. "Tailoring Graphite Interfacial Chemistry with Medium Concentration Weakly Solvating Electrolyte toward Fast-charging and Low-temperature Lithium-ion Batteries." Nano Energy (2025): 111266." can only release a specific capacity of 113 mAh / g under 5 C charge-discharge conditions. The battery disclosed in "Zhang, Heng, et al. "Tailoring electrolyte solvation of dimethyl sulfite with fluoride dominant via electrolyte engineering for enabling low-temperature batteries." EnergyStorage Materials 74 (2025): 103955." can only release a specific capacity of 125.7 mAh / g under low-temperature conditions.

[0005] It is evident that traditional ester-based electrolytes for lithium batteries suffer from drawbacks such as low ionic conductivity, narrow liquid range, and susceptibility to side reactions. These drawbacks lead to electrolyte solidification, poor rate performance, and short cycle life in low-temperature fast-charging applications. Meanwhile, chain-like carboxylic esters, while possessing high ionic conductivity, suffer from poor compatibility with the negative electrode, limiting their application. Current research on low-temperature fast-charging electrolytes falls far short of meeting the demands of lithium batteries. Summary of the Invention

[0006] In view of this, this application provides an electrolyte for low-temperature fast-charging lithium batteries, which not only takes into account high ionic conductivity and wide liquid range, but also effectively achieves safe and stable low-temperature fast charging effect.

[0007] Specifically, this application is implemented through the following scheme: An electrolyte for low-temperature fast-charging lithium batteries includes a lithium salt, an organic solvent, and additives. The organic solvent is a chain-like carboxylic acid ester compound with the following general structural formula: R1 and R2 are any combination of methyl, ethyl, and propyl. The additive is a cyclic ester compound with the following general structural formula: X is any one of carbon, sulfur, nitrogen, phosphorus, and R3 and R4 are any combination of halogen, alkyl, silicon, alkoxy, siloxy, halogen-containing alkyl, halogen-containing silicon, phenyl, amino, halogen-containing amino, phosphorus, and halogen-containing phosphorus.

[0008] In the above scheme, the additive is a cyclic ester compound with strong reducing properties, and the organic solvent is a chain carboxylic ester compound, which is combined with lithium salt to make the electrolyte have high ionic conductivity and wide liquid range, and good low temperature and rate performance is achieved. Among them, based on the chain carboxylic ester system, an additive with a specific structure is developed and designed, and a more true and accurate additive reduction concept is proposed. The core of this concept is to take the solvent environment and the external electric field as the intrinsic variable, and integrate it into the evaluation system of the additive reduction ability, by directly comparing the difference in electron reduction tendency between the additive and the solvent molecule, the interface competitive reduction behavior is truly reflected. Based on this criterion, the additive suitable for the chain carboxylic ester system can be efficiently matched, which can be an important part of the solvation structure, and through the preferential electron transfer of lithium ions at the interface, the additive is preferentially decomposed to the solvent, so that the battery system can be changed from completely unable to cycle to very stable cycle, thereby effectively enhancing the interface lithium ion transmission dynamics, inhibiting the continuous decomposition of the solvent, thereby realizing low interface impedance and stable SEI film rich in inorganic components, and significantly improving the low temperature and fast charging performance of the battery.

[0009] Further, as preferred: The organic solvent is at least one of CH3COOCH3, CH3CH2COOCH3, CH3COOCH2CH3, CH3CH2COOCH2CH3, CH3CH2CH2COOCH3, CH3CH2CH2COOCH2CH3, CH3COOCH2CH2CH3, CH3CH2COOCH2CH2CH3, and CH3CH2CH2COOCH2CH2CH3. And CH3COOCH3, CH3CH2COOCH3, and CH3COOCH2CH3 are preferred.

[0010] The additive is at least one of 4-chloromethyl-1,3-dioxol-2-one, 4-bromomethyl-1,3-dioxol-2-one, 4-iodomethyl-1,3-dioxol-2-one, 4-chloromethyl-5-methyl-1,3-dioxol-2-one, 4-bromomethyl-5-methyl-1,3-dioxol-2-one, 4-iodomethyl-5-methyl-1,3-dioxol-2-one, 4-amino-5-methyl-1,3-dioxol-2-one, and 4-phospho-5-methyl-1,3-dioxol-2-one. The affinity of the above-mentioned additive to lithium ions and the electron-accepting ability of the additive in the solvation structure are both required to be higher than that of the solvent. More preferably, the additive is a mixture of 4-iodomethyl-5-methyl-1,3-dioxol-2-one and 4-bromomethyl-5-methyl-1,3-dioxol-2-one or a mixture of 4-chloromethyl-5-methyl-1,3-dioxol-2-one, with a mass ratio of 1:1 to 5. For example, the additive is a mixture of 4-chloromethyl-5-methyl-1,3-dioxol-2-one and 4-iodomethyl-5-methyl-1,3-dioxol-2-one, with a mass ratio of 1:1; or a mixture of 4-chloromethyl-5-methyl-1,3-dioxol-2-one and 4-bromomethyl-5-methyl-1,3-dioxol-2-one, with a mass ratio of 3:1; or a mixture of 4-chloromethyl-5-methyl-1,3-dioxol-2-one and 4-bromomethyl-5-methyl-1,3-dioxol-2-one, with a mass ratio of 5:1.

[0011] The additive is 5% to 15% of the total mass of the electrolyte.

[0012] The lithium salt concentration is 0.1 to 2 mol / L.

[0013] The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium nitrate, and lithium difluorophosphate. For example, the lithium salt is a mixture of lithium hexafluorophosphate and lithium bis(oxalato)borate, with a molar ratio of 1:1; or a mixture of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, with a molar ratio of 3:1; or a mixture of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate, with a molar ratio of 1:1:1.

[0014] The electrolyte can be applied to various lithium ion battery systems, such as Gr / Li batteries (Gr as the positive electrode and lithium metal as the negative electrode) in the half-cell series. In addition, the Gr / Li battery still has a reversible specific capacity of at least 307.4 mAh / g and a capacity retention rate of more than 80% at a 5 C charge-discharge rate in a voltage range of 0.005-1.0 V, and the average coulombic efficiency can reach more than 99.9%.

[0015] The electrolyte can also be applied to full-cell series of lithium batteries, such as ternary lithium batteries (positive electrode material: lithium nickel manganese cobalt oxide LiNi 1-x Co x Mn y O2, wherein 0≤ x <1, 0≤ y <1, 0≤ x + y <1, and the negative electrode material is Gr), lithium cobalt oxide batteries (positive electrode material: lithium cobalt oxide (LiCoO2), and negative electrode material: Gr), lithium iron phosphate batteries (positive electrode material: lithium iron phosphate (LiFePO4), and negative electrode material: Gr), etc. In addition, the LiFePO4 / Gr battery still has a capacity retention rate of more than 90% after 1000 cycles at a 10 C charge-discharge rate in a voltage range of 2.5-3.65 V, and the average coulombic efficiency is as high as 99.9%, which is much better than the performance of traditional lithium battery ester-based electrolyte and other low-temperature fast-charging electrolyte. At this time, the lithium battery includes a positive electrode active material, a negative electrode active material, a separator, and the above-mentioned electrolyte, which gives the lithium battery a low-temperature fast-charging effect.

[0016] The positive electrode active material of the lithium battery is any one of LiNi 1-x Co x Mn y O2, LiCoO2, and LiFePO4, and the negative electrode active material is any one of Gr, silicon-carbon composite, and lithium metal. It is preferable that the positive electrode active material is LiFePO4 and the negative electrode active material is Gr.

[0017] The working temperature of the lithium battery is -40-25 ℃.

[0018] Compared with the prior art, the present application has the following beneficial effects: (1) The present application provides an electrolyte suitable for low-temperature fast-charging lithium batteries, which completely solves the problem of solidification of traditional lithium battery ester-based electrolyte at low temperature and poor rate performance. Chain carboxylic acid ester is used as a solvent for lithium battery electrolyte, and specific additives are used to make the electrolyte have extremely high ionic conductivity and wide liquid range, which promotes the progress of lithium batteries in the field of low temperature and fast charging.

[0019] (2) The application proposes a new additive compatibility concept, compared with the traditional lowest unoccupied molecular orbital (LUMO) energy level and reduction potential, the solvent structure environment and the influence of the interface electric field where the additive is located are considered more, and the screening concept can more accurately predict and clarify the reduction ability of the electrolyte in different solvents.

[0020] (3) The application is a high-performance lithium battery low-temperature fast-charging electrolyte, which combines the advantages of high ionic conductivity, strong reducing additive and low interface impedance, and significantly improves the low-temperature fast-charging performance and development potential of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application.

[0022] Figure 1 The rate performance comparison chart of Example 1 and Comparative Example 1 is shown in Figure 1, (a) Rate performance of Example 1, (b) rate performance of Comparative Example 1.

[0023] Figure 2 The cycle performance comparison chart of Example 1 and Comparative Example 2 is shown in Figure 2, (a) Cycle performance curve of Example 1, (b) cycle performance curve of Comparative Example 2.

[0024] Figure 3 The low-temperature performance comparison chart of Example 1 and Comparative Example 3 is shown in Figure 3, (a) Low-temperature performance curve of Example 1, (b) low-temperature performance curve of Comparative Example 3.

[0025] Figure 4 The rate performance comparison chart of Example 2 and Comparative Example 4 is shown in Figure 4, (a) Rate performance of Example 2, (b) rate performance of Comparative Example 4.

[0026] Figure 5 The cycle performance comparison chart of Example 2 and Comparative Example 5 is shown in Figure 5, (a) Cycle performance curve of Example 2, (b) cycle performance curve of Comparative Example 5.

[0027] Figure 6 The low-temperature performance comparison chart of Example 2 and Comparative Example 6 is shown in Figure 6, (a) Low-temperature performance curve of Example 2, (b) low-temperature performance curve of Comparative Example 6.

[0028] Figure 7 The charge-discharge curve chart of Comparative Example 7 is shown in Figure 7.

[0029] Figure 8 The figure is a schematic diagram of the compatibility mechanism of the additive, lithium salt and solvent in the present application. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, the technical solutions in the embodiments of the present application will be further described in detail below with reference to the drawings in the embodiments of the present application. 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 technical solutions of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0031] In the following examples: Preparation and testing of Gr / Li and LiFePO4 / Gr batteries: (1) Positive electrode sheet: LiFePO4, binder PVDF, and conductive carbon black were added to N-methyl pyrrolidone (NMP) at a ratio of 9:0.5:0.5, and mixed uniformly to obtain a slurry; then coated on an aluminum foil current collector, dried at 80°C, and after rolling, punched into a 12 mm diameter disc using a sheet punching machine.

[0032] (2) Negative electrode sheet: Gr powder, binder PVDF, and conductive carbon black were added to NMP at a ratio of 93:2:5, and mixed uniformly to obtain a slurry; then coated on a copper foil current collector, dried at 80°C, and after rolling, punched into a 14 mm diameter disc using a sheet punching machine.

[0033] (3) Electrolyte: The electrolyte prepared in the following examples and comparative examples.

[0034] (4) Separator: A 19 mm diameter aluminum oxide coated polyethylene single layer separator disc was punched out using a sheet punching machine.

[0035] (5) Battery assembly: In a glove box (O2<0.1 ppm, H2O<0.1 ppm), lithium batteries were assembled in the order of positive shell-positive disc-separator disc-negative disc-stainless steel sheet-spring sheet-negative shell, and the corresponding electrolyte was added, and finally packaged to obtain test batteries.

[0036] (6) Battery testing: The rate test conditions are that the Gr / Li (0.005-1.0 V) battery is cycled at 0.1 C-0.5 C-1 C-2 C-3 C-4 C-5 C rate at room temperature (25 DEG C) for 5 cycles at each rate; and the 1 Ah LiFePO4 / Gr (2.5-3.65 V) soft package battery is cycled at 0.1 C-0.2 C-0.5 C-1 C-2 C-3 C-…-10 C rate at room temperature (25 DEG C) for 5 cycles at each rate.

[0037] The long cycle, i.e. charge-discharge performance test conditions are that the Gr / Li (0.005-1.0 V) battery is cycled at 1 C rate at room temperature (25 DEG C); and the 1 Ah LiFePO4 / Gr (2.5-3.65 V) soft package battery is cycled at 1 C rate at room temperature (25 DEG C).

[0038] The low temperature test conditions are that the Gr / Li (0.005-1.0 V) battery is cycled at 0.1 C rate at -40 DEG C; and the 1 Ah LiFePO4 / Gr soft package battery (2.5-3.65 V) is cycled at 0.1 C rate at -40 DEG C. All the result analysis and conclusions are described in the examples and comparative examples.

[0039] Example 1

[0040] The example provides an electrolyte suitable for low-temperature fast-charging lithium battery, which is composed of: Lithium salt: lithium hexafluorophosphate, the concentration in the electrolyte is 1 mol / L.

[0041] Organic solvent: ethyl acetate.

[0042] Additive: 4-chloromethyl-5-methyl-1,3-dioxol-2-one, the mass ratio in the electrolyte is 10%.

[0043] The preparation method of the electrolyte composed of the above components is as follows: Dissolve lithium hexafluorophosphate slowly in ethyl acetate, then add additive 4-chloromethyl-5-methyl-1,3-dioxol-2-one, stir until the solution is completely uniform and clear, and the electrolyte suitable for low-temperature fast-charging lithium battery is obtained.

[0044] The electrolyte of example 1 is applied to Gr / Li battery (the positive electrode material is Gr, and the negative electrode material is lithium metal), and the electrochemical performance is detected.

[0045] The rate performance is shown in Figure 1The discharge specific capacity of Example 1 can reach 307.4 mAh / g at a high rate of 5 C, the capacity retention rate is greater than 80%, and the average coulombic efficiency is as high as 99.9%.

[0046] The charge-discharge curve is shown in (a) of FIG. 1. Figure 2 The battery can be stably cycled for 1380 cycles at a rate of 1 C, the capacity retention rate is as high as 95%, and the average coulombic efficiency is as high as 99.9%.

[0047] The low-temperature performance curve is shown in (a) of FIG. 3. Figure 3 The discharge specific capacity is stable at about 298 mAh / g at -40°C, and there is no obvious decay during the cycle, and the capacity retention rate is 80% compared with room temperature.

[0048] Comparative Example 1

[0049] The comparative example is an ester-based electrolyte for a traditional lithium battery. The preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1:1, so that the concentration of lithium salt lithium hexafluorophosphate is 1 mol / L. Stir until the electrolyte is completely clear, and the ester-based electrolyte for a traditional lithium battery is obtained.

[0050] The electrolyte of Comparative Example 1 is applied to a Gr / Li battery (the positive electrode material is Gr, and the negative electrode material is lithium metal), and the rate performance is shown in (b) of FIG. 1. Figure 1 The capacity of Comparative Example 1 is only 63.9 Ah at a rate of 5 C, the capacity retention rate is only 18%, and the coulombic efficiency fluctuates greatly, which is far from the performance level of the low-temperature fast-charging electrolyte.

[0051] Comparative Example 2

[0052] The comparative example is an ester-based electrolyte for a traditional lithium battery. The preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, so that the concentration of lithium salt lithium hexafluorophosphate is 1 mol / L. Stir until the electrolyte is completely clear, and the ester-based electrolyte for a traditional lithium battery is obtained.

[0053] The electrolyte of Comparative Example 2 is applied to a Gr / Li battery (the positive electrode material is Gr, and the negative electrode material is lithium metal), and the cycle performance is shown in (b) of FIG. 2. Figure 2 The capacity of the battery continuously decays during the charge-discharge process at a rate of 1 C, and the capacity retention rate is only 54% when cycled to 300 cycles, and the average coulombic efficiency is only about 99.7%, which is far lower than the performance level of the low-temperature fast-charging electrolyte in Example 1.

[0054] Comparative Example 3

[0055] The comparative example is an ester-based electrolyte for a conventional lithium battery. The preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, so that the concentration of lithium salt lithium hexafluorophosphate is 1.5 mol / L. Stir until the electrolyte is completely clear, and the ester-based electrolyte for a conventional lithium battery is obtained.

[0056] The electrolyte of comparative example 3 is applied to a Gr / Li battery (the positive electrode material is Gr, and the negative electrode material is lithium metal), and the low-temperature performance curve is shown in FIG. (b) of Figure 3 At -40 ℃, the specific discharge capacity is only 69.32 mAh / g, and the capacity retention rate at room temperature is only 20%. The low-temperature performance is significantly lower than that of the present application.

[0057] The above experimental results show that the electrochemical performance such as rate performance and capacity retention of the present application is greatly improved compared with the ester-based electrolyte for a conventional lithium battery.

[0058] Example 2

[0059] The present example provides an electrolyte suitable for a low-temperature fast-charging lithium battery, which is composed of: Lithium salt: lithium bis(fluorosulfonyl)imide, the concentration in the electrolyte is 1.5 mol / L.

[0060] Organic solvent: methyl acetate.

[0061] Additives: 4-bromomethyl-5-methyl-1,3-dioxol-2-one and 4-chloromethyl-5-methyl-1,3-dioxol-2-one, each accounting for 5% by mass in the electrolyte.

[0062] The preparation method of the above-mentioned electrolyte is as follows: Dissolve lithium bis(fluorosulfonyl)imide in methyl acetate, then add additives 4-bromomethyl-5-methyl-1,3-dioxol-2-one and 4-chloromethyl-5-methyl-1,3-dioxol-2-one, and stir until the solution is completely uniform and clear. The electrolyte suitable for a low-temperature fast-charging lithium battery is obtained.

[0063] The electrolyte of example 2 is applied to a 1 Ah LiFePO4 / Gr soft pack battery (the positive electrode material is LiFePO4, and the negative electrode material is Gr), and the electrochemical performance is detected.

[0064] The rate performance is shown in FIG. (a) of Figure 4 At a large rate of 10 C, the discharge capacity of example 2 can reach 0.34 Ah, and there is no obvious decay within 5 cycles, and the average coulombic efficiency is as high as more than 99.9%.

[0065] The charge-discharge curve is as followsFigure 5 As shown in (a), the battery can stably cycle 928 times during a charge-discharge process at a rate of 1 C, with a capacity retention rate of up to 97% and an average coulombic efficiency of over 99.9%.

[0066] Low temperature performance curves are as follows Figure 6 As shown in (a) in the figure: at -40 ℃, the discharge capacity is stable at around 0.42 Ah and there is no decay during cycling. The capacity retention rate is 40% compared with room temperature, and the average coulombic efficiency is as high as 99.9% or more.

[0067] Comparative Example 4

[0068] This comparative example is an ester-based electrolyte for conventional lithium batteries. The preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in a 1:1 volume ratio of ethylene carbonate and dimethyl carbonate, resulting in a lithium salt hexafluorophosphate concentration of 1.5 mol / L. The solution is stirred until completely clear, thus obtaining the ester-based electrolyte for conventional lithium batteries.

[0069] The electrolyte from Comparative Example 4 was applied to a 1 Ah LiFePO4 / Gr pouch cell (LiFePO4 as the positive electrode material and Gr as the negative electrode material), and its rate performance was as follows: Figure 4 As shown in Figure (b): its rate performance is shown in [Figure number missing]. Figure 4 As shown in Figure (b), at the same 10 C high rate, the capacity of Comparative Example 4 is only 0.07 Ah, the capacity retention rate is only 7%, and the coulombic efficiency fluctuates greatly, which is far from the performance level of the low temperature fast charging electrolyte of the present invention.

[0070] Comparative Example 5

[0071] This comparative example is an ester-based electrolyte for conventional lithium batteries. The preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in a mixed solution of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate (volume ratio 1:1:1) to achieve a lithium salt concentration of 1.5 mol / L. The solution is stirred until completely clear, thus obtaining the ester-based electrolyte for conventional lithium batteries.

[0072] The electrolyte from Comparative Example 5 was applied to a 1 Ah LiFePO4 / Gr pouch cell (LiFePO4 as the positive electrode and Gr as the negative electrode). The cycle performance curves are shown below. Figure 5 As shown in Figure (b), at the same 1 C rate, the capacity retention rate is only 80% after 423 cycles, the reversible capacity decay is severe, and the average coulombic efficiency is only 99.7%. This indicates that the ester-based electrolyte of traditional lithium batteries can no longer meet the requirements of fast charging performance.

[0073] Comparative Example 6

[0074] This comparative example is an ester-based electrolyte for conventional lithium batteries. The preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in a mixed solution of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate (volume ratio 1:1:1) to achieve a lithium salt concentration of 1.5 mol / L. The solution is stirred until completely clear, thus obtaining the ester-based electrolyte for conventional lithium batteries.

[0075] The electrolyte from Comparative Example 6 was applied to a 1 Ah LiFePO4 / Gr pouch cell (LiFePO4 as the positive electrode and Gr as the negative electrode). Its low-temperature performance curves are shown in [Figure Number]. Figure 6 As shown in Figure (b), under the same condition of -40 °C, the ester-based electrolyte of traditional lithium batteries can hardly release its capacity, proving that the interfacial impedance is extremely high and cannot meet the requirements for operation under low temperature conditions. Its performance level is far lower than that of the low-temperature fast-charging electrolyte of the present invention.

[0076] Comparative Example 7

[0077] This comparative example is a carboxylic acid ester-based electrolyte without any additives. Its preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in ethyl acetate to achieve a lithium salt concentration of 1.5 mol / L. The solution is stirred until completely clear, thus obtaining the carboxylic acid ester-based electrolyte without any additives.

[0078] The electrolyte of Comparative Example 7 was applied to a Gr / Li battery (Gr as the positive electrode material and lithium metal as the negative electrode material), and its charge-discharge curves are shown in [Figure 1]. Figure 7 As shown, without additives, the battery can only perform the first charge-discharge cycle and cannot perform normal charge-discharge cycles afterward, proving that the interface impedance is extremely high without additives, reflecting the importance of the selection of additives in this invention.

[0079] The compatibility mechanism of the electrolyte additives in this application with lithium salts and solvents is as follows: The mechanism of this compatibility involves two parameters, T and R. First, T describes the affinity between the additive and lithium ions under an electric field, reflecting the additive's ability to participate in the solvation structure. Second, R describes the additive's ability to gain electrons in the solvation structure under an electric field. When both T and R of an additive are higher than those of the solvent, it can preferentially decompose before the solvent, forming a stable SEI film with low interfacial impedance and rich in inorganic components.

[0080] Figure 8 This is a comparison graph of the predicted results and experimental results of this criterion. For example, when the solvent is ethyl acetate, both parameters of the green additives (i.e., additives that are effective in the experimental results) are higher than those of ethyl acetate, while the parameters of the red additives (i.e., additives that are ineffective in the experimental results) are not all higher than those of ethyl acetate. The results of the above examples confirm the above-described compatibility mechanism.

[0081] The above-described embodiments are merely illustrative of several feasible implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention, nor are the embodiments intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. An electrolyte for a low-temperature fast-charging lithium battery, comprising a lithium salt, an organic solvent and an additive, characterized in that: the organic solvent is at least one of CH3COOCH3, CH3CH2COOCH3, CH3COOCH2CH3, CH3CH2COOCH2CH3, CH3CH2CH2COOCH3, CH3CH2CH2COOCH2CH3, CH3COOCH2CH2CH3, CH3CH2COOCH2CH2CH3, CH3CH2CH2COOCH2CH2CH3; the additive is at least one of 4-chloromethyl-1,3-dioxol-2-one, 4-bromomethyl-1,3-dioxol-2-one, 4-iodomethyl-1,3-dioxol-2-one, 4-chloromethyl-5-methyl-1,3-dioxol-2-one, 4-bromomethyl-5-methyl-1,3-dioxol-2-one, 4-iodomethyl-5-methyl-1,3-dioxol-2-one, 4-amino-5-methyl-1,3-dioxol-2-one, 4-phospho-5-methyl-1,3-dioxol-2-one. The additive is a mixture of 4-iodomethyl-5-methyl-1,3-dioxol-2-one or 4-bromomethyl-5-methyl-1,3-dioxol-2-one and 4-chloromethyl-5-methyl-1,3-dioxol-2-one, with a mixing mass ratio of 1:1 to 5. The additive is 5 to 15% of the total mass of the electrolyte. 2.The electrolyte for a low-temperature fast-charging lithium battery according to claim 1, characterized in that: The lithium salt concentration is 0.1 to 2 mol / L. 3.The electrolyte for a low-temperature fast-charging lithium battery according to claim 1, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium nitrate and lithium difluorophosphate. 4.The electrolyte for a low-temperature fast-charging lithium battery according to claim 1, characterized in that:

6. A lithium battery using the electrolyte of claim 1. 5.The electrolyte for a low-temperature fast-charging lithium battery according to claim 1, characterized in that: The lithium battery is a half-cell series or a full-cell series. The working temperature of the lithium battery is -40 to 25℃.

7. The lithium battery of claim 6, wherein: ​ 8. The lithium battery of claim 6, wherein: ​

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