Preparation method and application of low-temperature-resistant ester-based electrolyte

Abstract

The application relates to a preparation method and application of a low-temperature-resistant ester-based electrolyte. The method comprises the following steps: firstly, dissolving lithium bistrifluoromethylsulfonylimide into a mixed solution of difluoropropionic acid ethyl ester and fluorinated ethylene carbonate to obtain solution A; secondly, dissolving lithium nitrate into ethylene glycol dimethyl ether to obtain solution B; and thirdly, adding solution B into solution A to obtain the low-temperature-resistant ester-based electrolyte. The weak-solvent electrolyte is composed of three solvents and two lithium salts, the carboxylic acid ester has a low melting point and a strong salt-dissolving capacity, the freezing point of the electrolyte can be significantly reduced, the electrolyte still has strong fluidity at low temperature, the migration rate of lithium ions at low temperature is improved, and the low-temperature performance of the battery is improved. The low-temperature-resistant ester-based electrolyte prepared by the application provides valuable insights for the next-generation electrolyte of lithium ion batteries operated under extreme conditions.

Description

Technical Field

[0001] This invention relates to methods for preparing and using electrolytes, and more specifically to methods for preparing and using a low-temperature resistant ester-based electrolyte. Background Technology

[0002] The significant performance degradation of lithium-ion batteries at low temperatures has become a key limiting factor for their application in electric vehicles, energy storage in cold regions, and aerospace. Studies show that at -20℃ and below, problems such as decreased battery capacity, intensified polarization, and deteriorated rate performance are particularly prominent, with insufficient electrolyte performance being the core cause of low-temperature failure. Increased electrolyte viscosity, decreased ionic conductivity, and limited lithium-ion desolvation kinetics at low temperatures severely hinder charge transport processes and induce safety hazards such as lithium deposition at the negative electrode. Lithium iron phosphate / graphite (LFP / Gr) batteries are widely recognized for their excellent cycle performance. However, traditional EC-based electrolytes suffer from high viscosity and are prone to freezing at low temperatures, and lithium-ion desolvation presents a high energy barrier, making their practical application still very challenging. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing and applying a low-temperature resistant ester-based electrolyte.

[0004] A method for preparing a low-temperature resistant ester-based electrolyte, specifically comprising the following steps:

[0005] 1. Dissolve lithium bis(trifluoromethanesulfonyl)imide in a mixture of ethyl difluoropropionate and fluoroethylene carbonate to obtain solution A;

[0006] 2. Dissolve lithium nitrate in ethylene glycol dimethyl ether to obtain solution B;

[0007] 3. Under stirring conditions, solution B is added dropwise to solution A and stirred until homogeneous to obtain a low-temperature resistant ester-based electrolyte.

[0008] The principles and advantages of this invention:

[0009] This invention provides a weakly solvated electrolyte composed of three solvents and two lithium salts. The carboxylic acid ester has a low melting point and strong salt-dissolving ability, significantly lowering the electrolyte's freezing point and maintaining strong fluidity at low temperatures. This enhances the migration rate of lithium ions at low temperatures, thus improving the battery's low-temperature performance. Fluoroethylene carbonate is used because its high dielectric constant allows for good dissociation of lithium salts at low temperatures, optimizing interfacial transport and stabilizing the solid electrolyte interface (SEI) at low temperatures. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is chosen as the lithium salt in this system due to its high ionic conductivity, good thermal stability, and wide electrochemical window. A small amount of lithium nitrate is added as a lithium salt additive. The high donor number of lithium nitrate preferentially decomposes on the electrode surface, generating a dense SEI film rich in Li₂O and Li₃N, effectively suppressing continuous electrolyte consumption and preventing lithium dendrite growth, thus avoiding the risk of internal short circuits in the battery. Adding an appropriate amount can also reduce the electrolyte interfacial impedance, thereby improving the battery's charge / discharge efficiency and capacity retention at low temperatures to some extent. A small amount of ether solvent is used to dissolve lithium nitrate. LFP / Gr batteries using this electrolyte exhibit excellent cycle stability; the assembled coin cells have a discharge specific capacity of 150 mAh / g at room temperature and 81.7% capacity retention after 600 cycles. This significantly improves cycle stability and provides excellent performance at both room temperature and low temperatures.

[0010] The low-temperature resistant ester-based electrolyte prepared by this invention provides valuable insights into next-generation electrolytes for lithium-ion batteries operating under extreme conditions. Attached Figure Description

[0011] Figure 1 The Raman spectrum of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1;

[0012] Figure 2 The Raman spectrum of the DFAE electrolyte prepared in Comparative Example 1;

[0013] Figure 3 XPS spectrum of C1s of CEI generated by the decomposition of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 at the LFP cathode;

[0014] Figure 4 The XPS spectrum of N1s of CEI generated by the decomposition of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 at the LFP cathode;

[0015] Figure 5 XPS spectrum of F1s of CEI generated by the decomposition of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 at the LFP cathode;

[0016] Figure 6 The left image of panel a shows the LFP positive electrode of the LFP||Gr full cell assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 after 600 cycles, and the right image shows the Gr negative electrode; the left image of panel b shows the LFP positive electrode of the LFP||Gr full cell assembled using the DFAE electrolyte prepared in Comparative Example 1 after 600 cycles, and the right image shows the Gr negative electrode.

[0017] Figure 7 The Nyquist curves of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the DFAE electrolyte prepared in Control Example 1 are shown.

[0018] Figure 8 The graph shows the cycling performance of LFP||Gr full cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the commercial electrolyte of Control Example 2 at 1C.

[0019] Figure 9 The rate performance of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the commercial electrolyte of Control Example 2 at -25°C was measured.

[0020] Figure 10 The cycling performance of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the commercial electrolyte of Control Example 2 at -25°C was measured.

[0021] Figure 11 The rate performance of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolytes DFAE-L, DFAE-L1, and DFAE-L2 prepared in Examples 1-3 at 25°C was measured. Detailed Implementation

[0022] Specific Implementation Method 1: This implementation method is a method for preparing a low-temperature resistant ester-based electrolyte, specifically carried out according to the following steps:

[0023] 1. Dissolve lithium bis(trifluoromethanesulfonyl)imide in a mixture of ethyl difluoropropionate and fluoroethylene carbonate to obtain solution A;

[0024] 2. Dissolve lithium nitrate in ethylene glycol dimethyl ether to obtain solution B;

[0025] 3. Under stirring conditions, solution B is added dropwise to solution A and stirred until homogeneous to obtain a low-temperature resistant ester-based electrolyte.

[0026] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that steps one, two, and three are all completed inside a glove box; the H2O concentration inside the glove box is <0.01ppm, and the O2 concentration is <0.01ppm. The other steps are the same as in Specific Implementation Method One.

[0027] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to the volume ratio of the mixture of ethyl difluoropropionate and fluoroethylene carbonate in step 1 is (0.2g~0.3g):(0.8mL~1mL). The other steps are the same as in Specific Implementation Method 1 or 2.

[0028] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to the volume ratio of the mixture of ethyl difluoropropionate and fluoroethylene carbonate in step one is 0.287 g: 0.9 mL. The other steps are the same as in Specific Implementation Methods One to Three.

[0029] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the volume ratio of ethyl difluoropropionate to ethylene fluorocarbonate in the mixture of ethyl difluoropropionate and ethylene fluorocarbonate in step one is (0.6~0.8):(0.1~0.3). The other steps are the same as in Specific Implementation Methods One to Four.

[0030] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the volume ratio of ethyl difluoropropionate to ethylene fluorocarbonate in the mixture of ethyl difluoropropionate and ethylene fluorocarbonate in step one is 0.7:0.2. The other steps are the same as in Specific Implementation Methods One to Five.

[0031] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the volume ratio of ethyl difluoropropionate to ethylene fluorocarbonate in the mixture of ethyl difluoropropionate and ethylene fluorocarbonate in step one is 0.8:0.1. The other steps are the same as in Specific Implementation Methods One to Six.

[0032] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the mass ratio of lithium nitrate to the volume ratio of ethylene glycol dimethyl ether in step two is (0.06g~0.07g):1mL. The other steps are the same as in Specific Implementation Methods One to Seven.

[0033] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods One to Eight is that the volume ratio of solution B to solution A in step three is 0.1:(0.8~1). The other steps are the same as in Specific Implementation Methods One to Eight.

[0034] Specific Implementation Method 10: This implementation method describes the application of the low-temperature resistant ester-based electrolyte in lithium-ion batteries.

[0035] The beneficial effects of the present invention are verified using the following embodiments:

[0036] Example 1: A method for preparing a low-temperature resistant ester-based electrolyte, specifically comprising the following steps:

[0037] 1. Dissolve 0.287 g of lithium bis(trifluoromethanesulfonyl)imide in a mixture of 0.7 mL of ethyl difluoropropionate (EDFP) and 0.2 mL of fluoroethylene carbonate (FEC) to obtain solution A;

[0038] 2. Dissolve 0.069g of lithium nitrate in 1mL of dimethyl ethylene glycol (DME) to obtain solution B;

[0039] 3. Under stirring conditions, solution B is added dropwise to solution A and stirred until homogeneous to obtain a low-temperature resistant ester-based electrolyte (denoted as DFAE-L).

[0040] The volume ratio of solution B to solution A in step three is 0.1:0.9;

[0041] Steps one, two, and three are all completed inside a glove box; the glove box contains H2O < 0.01 ppm and O2 < 0.01 ppm.

[0042] Example 2: The difference between this example and Example 1 is that in step one, 0.287g of lithium bis(trifluoromethanesulfonyl)imide was dissolved in a mixture of 0.6mL of ethyl difluoropropionate (EDFP) and 0.3mL of fluoroethylene carbonate (FEC) to obtain solution A; the low-temperature resistant ester-based electrolyte obtained in step three is designated DFAE-L1. All other steps and parameters are the same as in Example 1.

[0043] Example 3: The difference between this example and Example 1 is that in step one, 0.287g of lithium bis(trifluoromethanesulfonyl)imide was dissolved in a mixture of 0.8mL of ethyl difluoropropionate (EDFP) and 0.1mL of fluoroethylene carbonate (FEC) to obtain solution A; the low-temperature resistant ester-based electrolyte obtained in step three is designated DFAE-L2. All other steps and parameters are the same as in Example 1.

[0044] Comparing with Example 1: The preparation method of DFAE electrolyte is specifically carried out according to the following steps:

[0045] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), 0.287 g of lithium bis(trifluoromethanesulfonyl)imide was dissolved in a mixture of 0.7 mL of ethyl difluoropropionate (EDFP), 0.2 mL of fluoroethylene carbonate (FEC), and 0.1 mL of dimethoxyethane (DME) to obtain the DFAE electrolyte, denoted as DFAE.

[0046] Compare with Example 2: Purchase commercial electrolyte (provide the manufacturer and model if possible), which is the Based.

[0047] Figure 1 The Raman spectrum of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1;

[0048] Figure 2 The Raman spectrum of the DFAE electrolyte prepared in Comparative Example 1;

[0049] from Figure 1 and Figure 2 It can be seen that the proportion of aggregates (AGG) in the electrolyte DFAE-L is larger, indicating that solvent molecules decompose preferentially to form a dense and stable SEI; while the proportion of contact ion pairs (CIP) in the DFAE electrolyte is higher, indicating that anions decompose preferentially to form a loose and unstable SEI, which leads to rapid lithium salt consumption, short battery cycle life, and low coulombic efficiency.

[0050] The assembly of LFP||Li half-cells is carried out according to the following steps:

[0051] ① Before the materials are officially placed in the glove box, all pretreatment work needs to be completed.

[0052] The positive LFP electrode and the negative lithium electrode need to be pre-cut to the specified diameter (6mm for lithium iron phosphate (LFP) and 7mm for lithium (Li) electrode), and vacuum dried at 120°C for 12 hours. The lithium negative electrode is dried at 80°C for 12 hours. A PP membrane, model Celgard2320, is used as the separator and dried at 60°C for 12 hours to avoid introducing trace amounts of moisture. All materials are then transferred through a glove box transfer chamber using a vacuum-argon purging cycle to ensure that no outside air is brought into the chamber.

[0053] ② After entering the glove box, first place the negative electrode shell on the workbench as the starting reference for stacking. First, place the spring clips and gaskets inside the negative electrode shell, then place the lithium negative electrode sheet inside, ensuring the coated side faces upwards and the copper foil makes good contact with the gaskets. It should also be placed as centrally as possible to avoid subsequent short circuits or uneven stress. Then, using a pipette, slowly add 35 μL of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 to the central region of the negative electrode. Next, smoothly cover the lithium negative electrode with the separator, and then use a pipette to slowly add 35 μL of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 to the central region of the separator. Immediately afterwards, place the LFP positive electrode sheet on top of the separator, typically requiring its active material layer to face the separator and the aluminum foil to face upwards. The entire battery structure is now assembled, but not yet sealed.

[0054] ③ Next, a sealing machine is needed to perform a sealing operation:

[0055] The assembled battery is placed in a sealing mold and pressed under a set pressure to cause plastic deformation of the positive and negative shells and achieve hermetically sealed packaging. After packaging, the battery should be subjected to a simple visual inspection to confirm that there is no leakage or obvious deformation. The assembled battery needs to stand for 12 hours to allow the electrolyte to fully wet the electrode pore structure and reach an interface equilibrium state before testing can be carried out.

[0056] Following the above method, the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 was replaced with DFAE-L1, DFAE-L2, DFAE electrolyte, or Based on assembling LFP||Li half-cells.

[0057] The LFP||Li half-cells assembled in the glove box were placed in a -30℃ low-temperature oven and run for 5 cycles each at different rates of 0.05C, 0.1C, 0.2C, 0.5C, and 0.1C on the Xinwei (brand) battery test rack at a voltage range of 2.5~4V. Then, the cells were run for 40 cycles at a rate of 0.1C. After that, the cells were removed and disassembled in the glove box. The positive electrode (LFP) was taken out and repeatedly cleaned with DMC solvent. After drying, the cells were sealed and prepared as samples.

[0058] XPS (X-ray Photoelectron Spectroscopy) is a core method for surface chemical analysis in battery electrode research. It is mainly used to analyze the elemental composition and chemical state of the material surface, and is especially crucial in the study of interface films (SEI / CEI).

[0059] Step 1, Sample loading: (1) Fix the sample on the sample stage (conductive adhesive or clamp); (2) Ensure good grounding (avoid charge accumulation); Step 2: Vacuuming; Step 3: Fine scanning of key elements; Step 4: Perform peak fitting on the scanned spectrum to obtain the data in the figure, see Figures 3-5 As shown;

[0060] Figure 3 XPS spectrum of C1s of CEI generated by the decomposition of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 at the LFP cathode;

[0061] Figure 4 The XPS spectrum of N1s of CEI generated by the decomposition of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 at the LFP cathode;

[0062] Figure 5 XPS spectrum of F1s of CEI generated by the decomposition of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 at the LFP cathode;

[0063] from Figures 3-5 It can be seen that the introduction of LiNO3 inhibits the accumulation of excessive organic decomposition products in the interfacial film and promotes the formation of a higher proportion of inorganic-enriched interfacial layer. The LiF signal is significantly more prominent. LiF is widely considered one of the most favorable inorganic components in lithium-ion battery interfacial films, helping to inhibit the continuous decomposition of the electrolyte and possessing high mechanical strength and good interfacial chemical stability. This improves the density and integrity of the interfacial film, thereby reducing the probability of side reactions during electrolyte-electrode contact. Therefore, a higher proportion of LiF in DFAE-L is crucial for maintaining a stable interface at low temperatures. The obvious signals of CN and Li-NX nitrogen-containing inorganic species indicate that LiNO3 is not merely an "inert additive" but actually participates in the interfacial chemical evolution during low-temperature cycling. The formation of these nitrogen-containing components usually implies NO... 3- Reduction or reconstruction occurs in the interfacial reaction, and nitrogen-containing inorganic phases with high ion transport capacity may be formed.

[0064] The assembly of the LFP||Gr full cell is completed according to the following steps:

[0065] ① Before the materials are officially placed in the glove box, all pretreatment work needs to be completed.

[0066] The positive LFP electrode and the negative graphite electrode need to be pre-cut to the specified diameter (6mm for lithium iron phosphate (LFP) and 7mm for graphite electrode (Gr negative electrode), and then vacuum-dried at 120℃ for 12 hours. The graphite negative electrode is dried at 80℃ for 12 hours. A PP membrane, model Celgard2320, is used as the separator and dried at 60℃ for 12 hours to avoid introducing trace amounts of moisture. All materials are then transferred through a glove box transfer chamber using a vacuum-argon purging cycle to ensure that no outside air is brought into the chamber.

[0067] ② After entering the glove box, first place the negative electrode shell on the workbench as the starting reference for stacking. First, place the spring clips and gaskets inside the negative electrode shell, then place the graphite negative electrode sheet inside, ensuring the coated side faces upwards and the copper foil makes good contact with the gaskets. It should also be placed as centrally as possible to avoid subsequent short circuits or uneven stress. Then, use a pipette to slowly add 35 μL of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 to the central region of the negative electrode. Next, smoothly cover the graphite negative electrode with the separator, and then use a pipette to slowly add 35 μL of the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 to the central region of the separator. Immediately afterwards, place the LFP positive electrode sheet on top of the separator, typically requiring its active material layer to face the separator and the aluminum foil to face upwards. The entire battery structure is now assembled, but not yet sealed.

[0068] ③ Next, a sealing machine is needed to perform a sealing operation:

[0069] The assembled battery is placed in a sealing mold and pressed under a set pressure to cause plastic deformation of the positive and negative shells and achieve hermetically sealed packaging. After packaging, the battery should be subjected to a simple visual inspection to confirm that there is no leakage or obvious deformation. The assembled battery needs to stand for 12 hours to allow the electrolyte to fully wet the electrode pore structure and reach an interface equilibrium state before testing can be carried out.

[0070] Both the positive LFP electrode and the negative graphite electrode (Gr electrode) were purchased from Zhejiang Nandu Energy Technology Co., Ltd.

[0071] Figure 6 The left image of panel a shows the LFP positive electrode of the LFP||Gr full cell assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 after 600 cycles, and the right image shows the Gr negative electrode; the left image of panel b shows the LFP positive electrode of the LFP||Gr full cell assembled using the DFAE electrolyte prepared in Comparative Example 1 after 600 cycles, and the right image shows the Gr negative electrode.

[0072] Combination Figure 5According to the LiF measured by XPS, LiNO3 in the DFAE-L assembled LFP||Gr full cell participates in the first solvation sheath layer of lithium ions. Compared with the battery assembled with DFAE electrolyte, it exhibits a more uniform film formation effect on both the positive and negative electrodes, forming inorganic-rich CEI and SEI films. In contrast, the DFAE control sample without LiNO3 showed more obvious cracks and local non-uniform film layers on both the positive and negative electrodes, which is not conducive to the cycle life of the battery.

[0073] Figure 7 The Nyquist curves of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the DFAE electrolyte prepared in Control Example 1 are shown.

[0074] Comparing the two sets of data reveals that the semi-circular diameter of the DFAE-L electrolyte system is significantly smaller than that of the control DFAE system, indicating that its charge transfer impedance is much lower than that of the DFAE electrolyte. The DFAE system exhibits high interfacial reaction resistance and relatively sluggish electrochemical reaction kinetics; while in the DFAE-L system, Li... + The transport barrier at the electrode-electrolyte interface is significantly reduced, and the interfacial conductivity is significantly improved. This phenomenon directly reflects that the DFAE-L electrolyte optimizes the SEI film structure and interfacial properties, reduces interfacial reaction resistance, and enables Li... + The embedding and extraction process is smoother, which also improves Li + The migration efficiency within the active material is improved. The prepared DFAE-L low-temperature resistant ester-based electrolyte can significantly reduce the charge transfer impedance and diffusion impedance of LFP||Li half-cells, optimize the charge transport behavior at the electrode and electrolyte interface, and enhance the Li... + Migration rate and electrochemical reaction kinetics.

[0075] Figure 8 The graph shows the cycling performance of LFP||Gr full cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the commercial electrolyte of Control Example 2 at 1C.

[0076] Figure 8 This indicates that DFAE-L has low impedance during transmission, which is beneficial for Li + The migration.

[0077] The LFP||Gr full cell with DFAE-L electrolyte exhibited excellent long-term cycling stability. Its initial discharge specific capacity at 1C rate was 148.68 mAh g⁻¹. -1 After 600 cycles, it maintained 121.69 mAh g. -1The capacity retention rate reached 81.85%, while the base-based battery exhibited faster capacity decay and poor cycle stability. This indicates that commercial carbonate electrolytes struggle to maintain stable kinetics and interfacial states in high-load LFP||Gr battery systems. In contrast, DFAE-L, in battery systems where both graphite anode and LFP cathode are present, can achieve both high capacity output and long cycle life.

[0078] Figure 9 The rate performance of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the commercial electrolyte of Control Example 2 at -25°C was measured.

[0079] from Figure 9 As can be seen from the rate performance of LFP||Li batteries at -30°C, the battery assembled with DFAE-L electrolyte maintains the highest capacity throughout the entire rate range. When the rate recovers to 0.1C, the capacity recovery of DFAE-L is more significant, indicating that it has better rate performance and reversible recovery capability at low temperatures compared to LFP||Li half-cells assembled with the base electrolyte. The LFP||Li battery with DFAE-L electrolyte exhibits excellent rate performance. At 0.1C, its initial discharge specific capacity is 94.54 mAh g⁻¹. -1 The discharge specific capacity at a 0.5 C rate is 44 mAh g. -1 The initial discharge specific capacity of the base battery at a 0.1 C rate is 84.68 mAh g. -1 The discharge specific capacity at 0.5 C rate is 26.33 mAh g. -1 This demonstrates that the DFAE-L battery system can balance high capacity output and long cycle life.

[0080] Figure 10 The cycling performance of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolyte DFAE-L prepared in Example 1 and the commercial electrolyte of Control Example 2 at -25°C was measured.

[0081] from Figure 10 It is evident that at a low temperature of -30°C and a rate of 0.1C, the discharge capacity of the DFAE-L battery is significantly higher than that of the Based battery. The battery assembled with the DFAE-L electrolyte exhibits lower viscosity and higher ionic conductivity, significantly improving low-temperature ion transport kinetics. Simultaneously, it promotes the formation of a dense and stable SEI film rich in LiF, reducing interfacial impedance and suppressing side reactions. Furthermore, the battery assembled with the DFAE-L electrolyte demonstrates excellent desolvation capability and charge transfer kinetics, effectively enhancing lithium insertion / extraction reversibility, thereby achieving more stable cycle performance.

[0082] Figure 11 The rate performance of LFP||Li half-cells assembled using the low-temperature resistant ester-based electrolytes DFAE-L, DFAE-L1, and DFAE-L2 prepared in Examples 1-3 at 25°C was measured.

[0083] from Figure 11 It can be seen that the LFP||Li battery assembled by DFAE-L exhibits higher discharge capacity at a high rate of 2C, and its capacity recovers well after rate switching. This proves that the electrolyte system has superior ion transport capability, ensuring Li remains within acceptable limits even at high rates. + It exhibits rapid migration; secondly, its solvation structure is more conducive to the desolvation process, reducing the interfacial charge transfer resistance; and thirdly, its overall polarization is smaller, allowing the electrode to fully utilize the active material under high current, thus exhibiting higher capacity.

Claims

1. A method for preparing a low-temperature resistant ester-based electrolyte, characterized in that... The preparation method is specifically carried out according to the following steps:

1. Dissolve lithium bis(trifluoromethanesulfonyl)imide in a mixture of ethyl difluoropropionate and fluoroethylene carbonate to obtain solution A; 2. Dissolve lithium nitrate in ethylene glycol dimethyl ether to obtain solution B; 3. Under stirring conditions, solution B is added dropwise to solution A and stirred until homogeneous to obtain a low-temperature resistant ester-based electrolyte.

2. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 1, characterized in that... Steps one, two, and three are all completed inside a glove box; the glove box contains H2O < 0.01 ppm and O2 < 0.01 ppm.

3. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 1, characterized in that... The mass ratio of lithium bis(trifluoromethanesulfonyl)imide in step one to the volume ratio of the mixture of ethyl difluoropropionate and fluoroethylene carbonate is (0.2g~0.3g):(0.8mL~1mL).

4. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 3, characterized in that... The mass ratio of lithium bis(trifluoromethanesulfonyl)imide in step one to the volume ratio of the mixture of ethyl difluoropropionate and fluoroethylene carbonate is 0.287 g: 0.9 mL.

5. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 1, characterized in that... The volume ratio of ethyl difluoropropionate to ethylene fluorocarbonate in the mixture of ethyl difluoropropionate and ethylene fluorocarbonate described in step one is (0.6~0.8):(0.1~0.3).

6. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 5, characterized in that... In the mixture of ethyl difluoropropionate and ethylene fluorocarbonate described in step one, the volume ratio of ethyl difluoropropionate to ethylene fluorocarbonate is 0.7:0.

2.

7. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 5, characterized in that... In step one, the volume ratio of ethyl difluoropropionate to ethylene fluorocarbonate in the mixture is 0.8:0.

1.

8. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 5, characterized in that... The mass ratio of lithium nitrate to ethylene glycol dimethyl ether in step two is (0.06g~0.07g):1mL.

9. The method for preparing a low-temperature resistant ester-based electrolyte according to claim 1, characterized in that... The volume ratio of solution B to solution A in step three is 0.1:(0.8~1).

10. The application of the low-temperature resistant ester-based electrolyte prepared by the preparation method according to claim 1, characterized in that... The low-temperature resistant ester-based electrolyte is used in lithium-ion batteries.

Images