Electrolyte for low-temperature fast-charging lithium battery and application thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2026-01-19
- Publication Date
- 2026-06-02
Smart Images
Figure CN121546155B_ABST
Abstract
Description
Technical Field
[0001] This application relates to an electrolyte for low-temperature fast-charging lithium batteries and its application, belonging to the field of lithium-ion battery technology. Background Technology
[0002] With the increasing driving range of electric vehicles, the fast charging capability and low-temperature adaptability of lithium batteries have become key performance indicators restricting their further development. The core of achieving efficient fast charging lies in the battery system possessing extremely high ion conductivity (including the bulk electrolyte and interfacial film) and rapid interfacial reaction kinetics. This ensures that lithium ions can efficiently insert into / extract from the negative electrode during high-rate charging and discharging, avoiding lithium metal deposition due to kinetic limitations. Excellent low-temperature adaptability requires the electrolyte system to maintain low viscosity, high ionic conductivity, and low interfacial impedance at low temperatures, avoiding capacity reduction caused by electrolyte solidification, hindered ion migration, and increased interfacial impedance. However, while the widely used carbonate-based electrolyte system exhibits good overall performance at room temperature, its inherent physicochemical properties make it difficult to simultaneously support the demanding requirements of fast charging and low-temperature applications. In fast charging scenarios, the solvation structure of this system and the ion conductivity of the solid electrolyte interphase (SEI) film it forms are insufficient to support extremely high lithium-ion flux, resulting in a sharp increase in polarization voltage at the end of charging, significantly increasing the risk of lithium plating, endangering battery safety, and reducing cycle life. In low-temperature environments, due to its high freezing point and viscosity that increases sharply with decreasing temperature, the ionic conductivity decreases significantly, while the interfacial charge transfer impedance increases significantly, ultimately leading to a severe deterioration in battery capacity and power output performance.
[0003] To achieve the dual goals of fast charging and excellent low-temperature performance in lithium-ion batteries, electrolyte design faces unique and complex challenges. Chain-like carboxylic acid ester solvent systems, with their low viscosity, high dielectric constant, and low melting point, show significant potential in improving ionic conductivity and liquid phase window. However, these solvents themselves have poor compatibility with graphite (Gr) anodes, making it difficult to form a stable and effective SEI, resulting in poor battery cycle performance and low coulombic efficiency. Interface problems are particularly pronounced under the dual stresses of fast charging and low temperatures.
[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:
[0008] An electrolyte for low-temperature fast-charging lithium batteries includes a lithium salt, an organic solvent, and additives.
[0009] 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.
[0010] The additive is a cyclic ester compound with the following general structural formula: X is any one of carbon, sulfur, nitrogen, and phosphorus, and R3 and R4 are any combination of halogen, alkyl, silyl, alkoxy, siloxy, halogen-containing alkyl, halogen-containing silyl, phenyl, amino, halogen-containing amino, phosphoro, and halogen-containing phosphoro.
[0011] In the above scheme, the additive is a cyclic ester compound with strong reducing properties, and the organic solvent is a chain carboxylic acid ester compound. Combined with lithium salt, this results in an electrolyte with high ionic conductivity and a wide liquid range, achieving excellent low-temperature and rate performance. Specifically, based on the chain carboxylic acid ester system, the focus is on the research and design of additives with specific structures, and a more realistic and accurate additive reduction concept is proposed. The core of this concept lies in integrating the solvent environment and external electric field as intrinsic variables into the evaluation system of additive reduction capability. By directly comparing the differences in electron-gaining reduction tendencies between additive and solvent molecules, the interfacial competitive reduction behavior is accurately reflected. Based on this criterion, additives suitable for the chain carboxylic acid ester system can be efficiently formulated. These additives can serve as an important part of the solvation structure, and through preferential electron transfer of lithium ions at the interface, the additive decomposes preferentially over the solvent. This enables a significant transformation of the battery system from completely uncyclable to highly stable cycling, effectively enhancing interfacial lithium-ion transport kinetics, inhibiting continuous solvent decomposition, and thus achieving a low interfacial impedance and a stable SEI film rich in inorganic components, significantly improving the battery's low-temperature fast-charging performance.
[0012] Furthermore, as a preferred option:
[0013] The organic solvent is at least one selected from CH3COOCH3, CH3CH2COOCH3, CH3COOCH2CH3, CH3CH2COOCH2CH3, CH3CH2CH2COOCH3, CH3CH2CH2COOCH2CH3, CH3COOCH2CH2CH3, CH3CH2COOCH2CH2CH3, and CH3CH2CH2COOCH2CH2CH3. Preferably, CH3COOCH3, CH3CH2COOCH3, and CH3COOCH2CH3 are preferred.
[0014] The additive is at least one selected from the following: 4-chloromethyl-1,3-dioxacyclopenten-2-one, 4-bromomethyl-1,3-dioxacyclopenten-2-one, 4-iodomethyl-1,3-dioxacyclopenten-2-one, 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one, 4-iodomethyl-5-methyl-1,3-dioxacyclopenten-2-one, 4-amino-5-methyl-1,3-dioxacyclopenten-2-one, and 4-phospho-5-methyl-1,3-dioxacyclopenten-2-one. The affinity of the above additive for lithium ions, as well as its electron-donating ability in the solvated structure, must be higher than that of the solvent. More preferably, the additive is a mixture of 4-iodomethyl-5-methyl-1,3-dioxacyclopenten-2-one or 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, with a mixing mass ratio of 1:1 to 5. For example, the additive is 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-iodomethyl-5-methyl-1,3-dioxacyclopenten-2-one. A mixture of en-2-ones in a mass ratio of 1:1; or a mixture of 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one in a mass ratio of 3:1; or a mixture of 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one in a mass ratio of 5:1.
[0015] The additive is 5-15% of the total mass of the electrolyte.
[0016] The lithium salt concentration is 0.1~2 mol / L.
[0017] The lithium salt is at least one of lithium salts selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxaloyl)borate, lithium difluorooxaloyl borate, lithium tetrafluoroborate, lithium nitrate, and lithium difluorophosphate. For example, the lithium salt is a mixture of lithium hexafluorophosphate and lithium bis(oxaloyl)borate in a molar ratio of 1:1; or a mixture of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide in a molar ratio of 3:1; or a mixture of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate in a molar ratio of 1:1:1.
[0018] The electrolyte described above can be used in various lithium-ion battery systems, such as the Gr / Li battery in the half-cell series (Gr as the positive electrode and lithium metal as the negative electrode). Furthermore, the Gr / Li battery maintains a reversible specific capacity of at least 307.4 mAh / g and a capacity retention rate of over 80% within a voltage range of 0.005~1.0 V at a charge / discharge rate of 5 C, with an average coulombic efficiency exceeding 99.9%.
[0019] The above electrolyte can also be used in a full range of lithium batteries, such as ternary lithium batteries (cathode material: lithium nickel cobalt manganese oxide LiNi). 1-x Co x Mn y O2, where 0 ≤ x <1, 0≤ y <1, 0≤ x + y <1, lithium cobalt oxide batteries (positive electrode material is lithium cobalt oxide (LiCoO2), negative electrode material is Gr), lithium iron phosphate batteries (positive electrode material is lithium iron phosphate (LiFePO4), negative electrode material is Gr), etc. In addition, the LiFePO4 / Gr battery, within a voltage range of 2.5~3.65 V, still retains 0.34 Ah under 10 C charge-discharge, and maintains over 90% capacity retention after 1000 cycles, with an average coulombic efficiency as high as 99.9%, far exceeding the performance of ester-based electrolytes and other low-temperature fast-charging electrolytes in traditional lithium batteries. In this case, the lithium battery includes a positive electrode active material, a negative electrode active material, a separator, and the aforementioned electrolyte, giving the lithium battery a low-temperature fast-charging effect.
[0020] The positive electrode active material of the lithium battery is LiNi. 1-x Co x Mn y The cathode active material is any one of O2, LiCoO2, and LiFePO4, and the anode active material is any one of Gr, silicon-carbon composite, and lithium metal. A configuration with LiFePO4 as the cathode active material and Gr as the anode active material is preferred.
[0021] The lithium battery operates at a temperature of -40 to 25°C.
[0022] Compared with the prior art, the present invention has the following beneficial effects:
[0023] (1) This invention provides an electrolyte suitable for low-temperature fast-charging lithium batteries, which completely solves the problems of solidification and poor rate performance of traditional lithium battery ester-based electrolytes at low temperatures. The chain carboxylic acid ester is used as a solvent for lithium battery electrolytes, and with the addition of specific additives, the electrolyte has extremely high ionic conductivity and wide liquid range, promoting the progress of lithium batteries in the fields of low temperature and fast charging.
[0024] (2) This invention proposes a new additive compatibility concept. Compared with the traditional lowest unoccupied molecular orbital (LUMO) energy level and reduction potential, it takes into account more the environment of the solvation structure of the additive and the influence of the interfacial electric field. This screening concept can more accurately predict and clarify the reduction ability of the electrolyte in different solvents.
[0025] (3) The present invention is a high-performance electrolyte for low-temperature fast charging of lithium batteries, which combines the advantages of high ionic conductivity, strong reducing additives and low interfacial impedance, significantly improving the low-temperature fast charging performance and development potential of batteries. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application.
[0027] Figure 1 This is a comparison chart of the rate performance of Example 1 and Comparative Example 1.
[0028] (a) Rate performance of Example 1, (b) Rate performance of Comparative Example 1.
[0029] Figure 2 This is a comparison graph showing the cycle performance of Example 1 and Comparative Example 2.
[0030] (a) Cyclic performance curve of Example 1, (b) Cyclic performance curve of Comparative Example 2.
[0031] Figure 3 This is a comparison chart of the low-temperature performance of Example 1 and Comparative Example 3.
[0032] (a) Low-temperature performance curve of Example 1, (b) Low-temperature performance curve of Comparative Example 3.
[0033] Figure 4 This is a comparison chart of the rate performance of Example 2 and Comparative Example 4.
[0034] (a) Rate performance of Example 2, (b) Rate performance of Comparative Example 4.
[0035] Figure 5 This is a comparison graph showing the cycle performance of Example 2 and Comparative Example 5.
[0036] (a) Cyclic performance curve of Example 2, (b) Cyclic performance curve of Comparative Example 5.
[0037] Figure 6 This is a comparison chart of the low-temperature performance of Example 2 and Comparative Example 6.
[0038] (a) Low-temperature performance curve of Example 2, (b) Low-temperature performance curve of Comparative Example 6.
[0039] Figure 7 This is a charge-discharge curve for Comparative Example 7.
[0040] Figure 8 This is a schematic diagram illustrating the compatibility mechanism between the additives, lithium salts, and solvents in this application. Detailed Implementation
[0041] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the technical solutions in the embodiments of this application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit the technical solutions of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.
[0042] In the following embodiments:
[0043] Fabrication and testing of Gr / Li and LiFePO4 / Gr batteries:
[0044] (1) Positive electrode sheet: LiFePO4, PVDF binder and conductive carbon black are added to N-methylpyrrolidone (NMP) in a ratio of 9:0.5:0.5 and mixed evenly to obtain a slurry; then coated onto aluminum foil current collector, dried at 80 ℃, rolled and cut into round sheets with a diameter of 12 mm by a punching machine.
[0045] (2) Negative electrode sheet: Gr powder, PVDF binder and conductive carbon black are added to NMP at a ratio of 93:2:5 and mixed evenly to obtain a slurry; then coated onto copper foil current collector, dried at 80 ℃, rolled and cut into round sheets with a diameter of 14 mm by a punching machine.
[0046] (3) Electrolyte: The electrolyte prepared in the following examples and comparative examples.
[0047] (4) Diaphragm: Cut out a single-layer polyethylene diaphragm disc with a diameter of 19 mm using a punching machine.
[0048] (5) Battery assembly: In a glove box (O2<0.1 ppm, H2O<0.1 ppm), assemble the lithium battery in the following order: positive electrode shell-positive electrode disc-separator disc-negative electrode disc-stainless steel sheet-spring sheet-negative electrode shell, add the corresponding electrolyte, and finally seal to obtain the test battery.
[0049] (6) Battery test:
[0050] The rate testing conditions were as follows: Gr / Li (0.005-1.0 V) batteries were tested at room temperature (25 ℃) with 5 cycles at each rate of 0.1 C-0.5 C-1C-2 C-3 C-4 C-5 C; and 1 Ah LiFePO4 / Gr (2.5-3.65V) pouch batteries were tested at room temperature (25 ℃) with 5 cycles at each rate of 0.1 C-0.2 C-0.5 C-1 C-2 C-3 C-…-10 C.
[0051] The long-cycle test conditions, i.e., charge-discharge performance test conditions, are as follows: Gr / Li (0.005-1.0 V) batteries are cycled at 1C rate at room temperature (25 ℃); 1 Ah LiFePO4 / Gr (2.5-3.65 V) pouch batteries are cycled at 1C rate at room temperature (25 ℃).
[0052] The low-temperature testing conditions were as follows: Gr / Li (0.005-1.0 V) batteries were cycled at -40 °C at a rate of 0.1 C; 1 Ah LiFePO4 / Gr pouch cells (2.5-3.65 V) were cycled at -40 °C at a rate of 0.1 C. All results and conclusions have been described in the examples and comparative examples.
[0053] Example 1
[0054] This embodiment provides an electrolyte suitable for low-temperature fast-charging lithium batteries, the composition of which is as follows:
[0055] Lithium salt: Lithium hexafluorophosphate, concentration in electrolyte 1 mol / L.
[0056] Organic solvent: ethyl acetate.
[0057] Additive: 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, accounting for 10% by mass in the electrolyte.
[0058] The preparation method of the electrolyte described above is as follows:
[0059] Lithium hexafluorophosphate was slowly dissolved in ethyl acetate, and then the additive 4-chloromethyl-5-methyl-1,3-dioxane-2-one was added. The mixture was stirred until the solution was completely homogeneous and clear, thus obtaining an electrolyte suitable for low-temperature fast-charging lithium batteries.
[0060] The electrolyte from Example 1 was applied to a Gr / Li battery (Gr as the positive electrode material and lithium metal as the negative electrode material), and its electrochemical performance was tested.
[0061] Rate performance is shown in Figure 1As shown in Figure (a): at a high rate of 5 C, the discharge specific capacity of Example 1 can reach 307.4 mAh / g, the capacity retention rate is greater than 80%, and the average coulombic efficiency is as high as 99.9% or more.
[0062] Charge-discharge curves as follows Figure 2 As shown in (a): the battery can stably cycle 1380 times during a charge-discharge process at a rate of 1 C, with a capacity retention rate of up to 95% and an average coulombic efficiency of over 99.9%.
[0063] Low temperature performance curves are as follows Figure 3 As shown in (a): at -40 ℃, the discharge specific capacity is stable at around 298 mAh / g, and there is no significant decay during cycling. The capacity retention rate is 80% compared with room temperature.
[0064] Comparative Example 1
[0065] This comparative example is an ester-based electrolyte for conventional lithium batteries. Its preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in a 1:1 volume ratio of ethylene carbonate and methyl ethyl carbonate to achieve a lithium salt concentration of 1 mol / L. The solution is stirred until completely clear, thus obtaining the ester-based electrolyte for conventional lithium batteries.
[0066] The electrolyte from Comparative Example 1 was applied to a Gr / Li battery (Gr as the positive electrode material and lithium metal as the negative electrode material), and its rate performance is shown in [reference needed]. Figure 1 As shown in Figure (b), at the same 5 C rate, the capacity of Comparative Example 1 is only 63.9 Ah, with a capacity retention of only 18%, and the coulombic efficiency fluctuates greatly, far below the performance level of low-temperature fast charging electrolyte.
[0067] Comparative Example 2
[0068] This comparative example is an ester-based electrolyte for conventional lithium batteries. Its preparation process is as follows: lithium hexafluorophosphate is slowly dissolved in a 1:1 volume ratio of ethylene carbonate and diethyl carbonate, resulting in a lithium salt concentration of 1 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 2 was applied to a Gr / Li battery (Gr as the positive electrode material and lithium metal as the negative electrode material), and its cycle performance is shown in [reference needed]. Figure 2 As shown in Figure (b), the battery capacity continued to decrease during the same charge-discharge process at a rate of 1 C. After 300 cycles, the capacity retention rate was only 54%, and the average coulombic efficiency was only about 99.7%, which is far lower than the performance level of the low-temperature fast-charging electrolyte in Example 1.
[0070] Comparative Example 3
[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 1:1 volume ratio of ethylene carbonate and dimethyl carbonate 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 of Comparative Example 3 was applied to a Gr / Li battery (Gr as the positive electrode material and lithium metal as the negative electrode material), and its low-temperature performance curves are shown in [Figure 1]. Figure 3 As shown in Figure (b), at -40 °C, the discharge specific capacity is only 69.32 mAh / g, and the capacity retention is only 20% compared to room temperature. Its low-temperature performance is significantly lower than that of the present invention.
[0073] The above experimental results show that, compared with the ester-based electrolyte of traditional lithium batteries, the electrochemical performance of this application, such as rate performance and capacity retention, is significantly improved.
[0074] Example 2
[0075] This embodiment provides an electrolyte suitable for low-temperature fast-charging lithium batteries, the composition of which is as follows:
[0076] Lithium salt: Lithium bis(fluorosulfonyl)imide, concentration in electrolyte 1.5 mol / L.
[0077] Organic solvent: Methyl acetate.
[0078] Additives: 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, each accounting for 5% by mass in the electrolyte.
[0079] The preparation method of the electrolyte described above is as follows:
[0080] Lithium bis(fluorosulfonyl)imide is dissolved in methyl acetate, and then additives 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one are added. The mixture is stirred until the solution is completely homogeneous and clear to obtain an electrolyte suitable for low-temperature fast-charging lithium batteries.
[0081] The electrolyte from Example 2 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 electrochemical performance was tested.
[0082] Rate performance is shown in Figure 4 As shown in Figure (a), at a high rate of 10 C, the discharge capacity of Example 2 can reach 0.34 Ah, and there is no significant decay within 5 cycles, with an average coulombic efficiency of over 99.9%.
[0083] Charge-discharge curves as follows Figure 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%.
[0084] 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.
[0085] Comparative Example 4
[0086] 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 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.
[0087] 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 capability 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.
[0088] Comparative Example 5
[0089] 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.
[0090] 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.
[0091] Comparative Example 6
[0092] 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.
[0093] 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.
[0094] Comparative Example 7
[0095] 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.
[0096] 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.
[0097] The compatibility mechanism of the electrolyte additives in this application with lithium salts and solvents is as follows:
[0098] 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.
[0099] Figure 8This 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.
[0100] 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 low-temperature fast-charging graphite / lithium batteries, characterized in that, The composition is as follows: Lithium salt: Lithium hexafluorophosphate, concentration in electrolyte 1 mol / L; Organic solvent: ethyl acetate; Additive: 4-Chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, comprising 10% by mass in the electrolyte. The preparation method of the electrolyte described above is as follows: Lithium hexafluorophosphate is slowly dissolved in ethyl acetate, and then the additive 4-chloromethyl-5-methyl-1,3-dioxane-2-one is added. The mixture is stirred until the solution is completely homogeneous and clear to obtain an electrolyte suitable for low-temperature fast-charging graphite / lithium batteries.
2. An electrolyte for low-temperature fast-charging LiFePO4 / graphite batteries, characterized in that, The composition is as follows: Lithium salt: Lithium bis(fluorosulfonyl)imide, concentration in electrolyte 1.5 mol / L; Organic solvent: methyl acetate; Additives: 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, each comprising 5% by mass in the electrolyte. The preparation method of the electrolyte described above is as follows: Lithium bis(fluorosulfonyl)imide was dissolved in methyl acetate, and then additives 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one and 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one were added. The mixture was stirred until the solution was completely homogeneous and clear, thus obtaining an electrolyte suitable for low-temperature fast-charging LiFePO4 / graphite batteries.