Wide-temperature-range electrolyte, preparation method and application thereof

Abstract

The application belongs to the field of lithium ion battery electrolyte, and discloses a wide-temperature-range electrolyte and a preparation method and application thereof. The wide-temperature-range electrolyte is prepared by mixing lithium difluoroborate powder, diethylene glycol dibutyl ether, 3-methoxypropionitrile and fluoroethylene carbonate. The 3-methoxypropionitrile controls the solvation structure to discharge diethylene glycol dibutyl ether, and cooperates with fluoroethylene carbonate and lithium difluoroborate to form a solid electrolyte interface layer rich in inorganic components, realizes efficient ion transmission and interface stability of the lithium ion battery in a wide temperature range of-20 DEG C to 60 DEG C, significantly improves the cycle life, and has important industrial application value for lithium ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolytes, specifically relating to a wide-temperature-range electrolyte, its preparation method, and its application. Background Technology

[0002] Over the past 30 years, lithium-ion batteries have been widely used and have garnered significant public attention. Since Sony launched the first lithium-ion battery in 1991, it has been extensively used in portable electronic devices, electric vehicles, and large-scale energy storage stations. Despite years of technological development, lithium-ion batteries have become quite mature, but their operating temperature is limited to room temperature. With the expanding application scenarios, lithium-ion batteries need to operate over a wider temperature range; portable electronic devices typically require normal operation between -20°C and 60°C. However, currently available lithium-ion battery products still cannot perform well in such extreme environments. Therefore, there is an urgent need to develop new lithium-ion battery products suitable for wide-temperature operation.

[0003] In practical applications, lithium-ion batteries typically employ external heating / cooling systems to ensure consistent capacity and reliable power output across a suitable temperature range. However, these systems inevitably introduce a non-negligible increase in weight, leading to reduced energy density and increased complexity of the battery device. Clearly, optimizing the electrolyte system is the simplest and most effective way to achieve normal operation of lithium-ion batteries across a wide temperature range.

[0004] While commercially available electrolyte systems exhibit excellent cycle performance at room temperature, severe side reactions occur at high temperatures of 30-60°C. Furthermore, at low temperatures of -20 to 0°C, the battery's internal impedance rises sharply due to the electrolyte's weak desolvation capability, making it unsuitable for use over a wide temperature range. Summary of the Invention

[0005] The purpose of this invention is to provide a wide-temperature-range electrolyte and its preparation method, which eliminates unstable solvents and forms an inorganic component-rich interface layer by regulating the solvation structure, thereby achieving the cycle stability and safety of lithium-ion batteries in a wide temperature range.

[0006] Another objective of this invention is to provide an application of a wide-temperature-range electrolyte in lithium-ion batteries.

[0007] The technical solution of the present invention is as follows:

[0008] This invention provides a wide-temperature-range electrolyte, which is a mixture of solvent, lithium salt and additive. The solvent is one or more of diethylene glycol dibutyl ether (DGDE) or 3-methoxypropionitrile (MPN), the additive is fluoroethylene carbonate (FEC), and the lithium salt is LiODFB.

[0009] The wide temperature range in the wide temperature range electrolyte refers to the temperature range of -20~60℃.

[0010] The volume ratio of solvent to additive in the wide-temperature-range electrolyte is 8~10:1.

[0011] The molar concentration of the lithium salt in the wide-temperature-range electrolyte is 0.8~1.2 mol / L.

[0012] This invention provides a method for preparing the wide-temperature-range electrolyte, the method comprising the following steps:

[0013] A wide-temperature-range electrolyte is obtained by mixing lithium salt, solvent and additives.

[0014] The mixing process takes place at a temperature of 40-50°C.

[0015] This invention provides an application of the wide-temperature-range electrolyte in lithium-ion batteries.

[0016] A method for preparing a lithium-ion battery, the method comprising the following steps:

[0017] The positive electrode, negative electrode, and separator are assembled, and a wide-temperature-range electrolyte is injected to obtain the lithium-ion battery.

[0018] The active material of the positive electrode is lithium iron phosphate, and the thickness of the positive electrode is 50-200 μm.

[0019] The active material of the negative electrode is graphite, and the thickness of the negative electrode is 50-150 μm.

[0020] The assembly method is either stacking or winding.

[0021] The DGDE used in this invention has a longer side chain and, compared to ethylene glycol dimethyl ether, a higher boiling point and flash point, allowing it to maintain low viscosity at low temperatures and ensuring Li + It still has a high mobility at -20℃, while its low volatility suppresses battery expansion at high temperatures.

[0022] When MPN enters the first solvation shell of lithium ions, its strongly electronegative groups can squeeze out some easily oxidized DGDE molecules from the solvation center through steric hindrance and charge shielding. This results in more stable MPN or anions being near the positive electrode surface during charging, thereby inhibiting the oxidative decomposition of ether solvents under high temperature and high pressure.

[0023] At high temperatures, LiODFB preferentially decomposes on the positive electrode surface over the solvent, forming a CEI film rich in borates to prevent continuous oxidation of the electrolyte. At low temperatures, its decomposition products have lower charge transfer resistance, which can reduce the desolvation ability of lithium ions, making the battery easier to discharge at low temperatures.

[0024] FEC promotes the formation of a LiF-rich inorganic SEI layer on the negative electrode surface through a defluorination reaction. LiF has high mechanical strength and chemical stability, which can effectively isolate DGDE from active graphite and prevent ether molecules from embedding into the graphite layer, thus preventing structural damage.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The DGDE used in this invention has a melting point close to -60°C and maintains good fluidity in the electrolyte at low temperatures; simultaneously, due to the interaction between ether and nitrile solvents with Li... + The binding energy of the lithium ion is weaker and more flexible than that of highly polar carbonates, which effectively reduces the lithium ion desolvation energy barrier, thereby reducing the interfacial charge transfer impedance and enabling the battery to have excellent low-temperature start-up capability.

[0027] 2. Compared with low-boiling-point DME or traditional ester solvents, DGDE and MPN both have higher boiling and flash points, which reduces the risk of internal pressure increase and thermal runaway in the battery under high-temperature conditions. Combined with the good thermal stability of LiODFB, the lithium-ion battery described in this invention can achieve stable cycling within the -20 to 60°C window.

[0028] 3. Through the synergistic effect of FEC and LiODFB, SEI film and positive electrode interface film rich in inorganic components such as LiF are preferentially formed on the positive and negative electrode surfaces, effectively inhibiting the continuous decomposition of electrolyte, lithium dendrite growth and capacity decay.

[0029] 4. The synergistic effect of LiODFB and MPN constructs a CEI layer rich in borate species on the positive electrode side, which inhibits the oxidative decomposition of ether solvents under high voltage and improves battery cycle life. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0032] Example 1

[0033] A method for preparing a wide-temperature-range electrolyte includes the following steps:

[0034] LiODFB powder was placed in a glass reagent bottle, and then DGDE and FEC were added in a volume ratio of 10:1. The mixture was stirred at 45°C for 10 hours until the LiODFB powder was fully dissolved and the molar concentration of LiODFB was 1 mol / L, thus obtaining the wide-temperature-range electrolyte.

[0035] Example 2

[0036] A method for preparing a wide-temperature-range electrolyte includes the following steps:

[0037] LiODFB powder was placed in a glass reagent bottle, and then DGDE, MPN and FEC were added in a volume ratio of 8:2:1. The mixture was stirred at 45°C for 10 hours until the LiODFB powder was fully dissolved and the molar concentration of LiODFB was 1 mol / L, thus obtaining the wide temperature range electrolyte.

[0038] Example 3

[0039] A method for preparing a wide-temperature-range electrolyte includes the following steps:

[0040] The difference between the preparation method in this embodiment and that in Example 2 is that the volume ratio of DGDE, MPN and FEC is changed from 8:2:1 to 6:4:1.

[0041] Example 4

[0042] A method for preparing a wide-temperature-range electrolyte includes the following steps:

[0043] The difference between the preparation method in this embodiment and that in Example 2 is that the volume ratio of DGDE, MPN and FEC is changed from 8:2:1 to 4:6:1.

[0044] Example 5

[0045] A method for preparing a wide-temperature-range electrolyte includes the following steps:

[0046] The difference between the preparation method in this embodiment and that in Example 2 is that the volume ratio of DGDE, MPN and FEC is changed from 8:2:1 to 2:8:1.

[0047] Comparative Example 1

[0048] An electrolyte preparation method includes the following steps:

[0049] LiPF6 powder was placed in a glass reagent bottle, and then EC, DMC and EMC were added in a volume ratio of 8:2:1. The mixture was stirred at 45°C for 10 hours until the LiPF6 powder was fully dissolved and the molar mass of LiPF6 was 1 mol / L, thus obtaining the electrolyte.

[0050] Comparative Example 2

[0051] An electrolyte preparation method includes the following steps:

[0052] The preparation method of this comparative example differs from that of Example 1 in that LiODFB is replaced with LiPF6.

[0053] Comparative Example 3

[0054] An electrolyte preparation method includes the following steps:

[0055] The preparation method of this comparative example differs from that of Example 3 in that FEC was not added.

[0056] Application Example 1

[0057] A method for preparing a lithium-ion battery, comprising the following steps:

[0058] The positive electrode, negative electrode, and separator are assembled by winding, and the electrolyte prepared in each embodiment and comparative example is injected to obtain a lithium-ion battery.

[0059] The steps of the method for preparing the positive electrode are as follows:

[0060] S1. Weigh 95wt% of positive electrode active material lithium iron phosphate (LFP), 3wt% of polyvinylidene fluoride (PVDF), 0.5wt% of polyvinylpyrrolidone (PVP) and 1.5wt% of conductive carbon black (SP) and stir and mix for 1h to obtain positive electrode mixed powder. During the process, the rotation speed is controlled at 1000r / min and the stirring temperature is 60℃.

[0061] S2. Add 44% N-methylpyrrolidone (NMP), 0.5% PVP, and 1.5% SP of the total weight of the positive electrode mixed powder to the mixed powder, and stir for 1.5 hours, during which the stirring speed is controlled at 1000 r / min and the stirring temperature is 50℃.

[0062] S3. Add 6% NMP (by weight of the total positive electrode mixed powder) to the product obtained in S2 and stir for 2.5 h, controlling the rotation speed at 2000 r / min and the stirring temperature at 35℃, to obtain the positive electrode slurry.

[0063] S4. The positive electrode slurry is uniformly coated onto the current collector using a coating machine at a temperature range of 60-120℃ to obtain an LFP active material sheet with a thickness of 170 μm. After rolling, an LFP positive electrode sheet with a thickness of 150 μm is obtained.

[0064] The steps for preparing the negative electrode are as follows:

[0065] S1. Weigh 94wt% of graphite, 1wt% of carboxymethyl cellulose, 3wt% SP and 2wt% styrene-butadiene rubber (SBR) and stir for 1h, during which the speed is controlled at 750r / min and the stirring temperature is 35℃ to obtain the negative electrode mixed powder.

[0066] S2. Add 40% of the weight of the negative electrode mixed powder to the negative electrode mixed powder, stir and mix for 1.5 hours, during which the speed is controlled at 750 r / min and the stirring temperature is 35℃;

[0067] S3. Add 40% deionized water (by weight of negative electrode powder) and 3% SBR (by weight of negative electrode powder) to the product obtained in S2 and stir for 2.5 hours, during which the stirring speed is controlled at 1000 r / min and the stirring temperature is 10-60℃; thus, the negative electrode slurry is obtained.

[0068] S4. The negative electrode slurry is uniformly coated onto the current collector using a coating machine at a temperature range of 60-120℃ to obtain an active material sheet with a thickness of 130μm, which is then rolled to obtain a negative electrode sheet with a thickness of 110μm.

[0069] Test Example 1

[0070] The lithium-ion battery from Application Example 1 was tested using a Xinwei charge / discharge machine according to standard GB / T 31486-2024. The tests included -20℃ DC internal resistance during discharge, -20℃ 1C capacity retention during discharge, capacity recovery after 7 days of storage at 60℃, and cycle life at 45℃. In the -20℃ DC internal resistance test, the state of charge (SOC) was 50%. In the 45℃ cycle life test, the capacity decay to 80% SOH was used as the termination condition. The test results are shown in Table 1 below.

[0071] Table 1 Performance Test Table

[0072]

[0073] Examples 1-5 and Comparative Example 2 show significantly improved DC internal resistance at -20°C and cycle life at 45°C compared to Comparative Example 1. This indicates that the solvent system used in this invention has lower low-temperature internal resistance and higher high-temperature cycle life than the conventional solvent system used in the comparative example. The conventional carbonate solvent system has high viscosity and hindered ion transport at low temperatures, resulting in insufficient interfacial film stability. Therefore, its low-temperature internal resistance and high-temperature cycle life are weaker than those of the examples and Comparative Example 2. Examples 1-5 show a significant improvement in 45°C cycle life compared to Comparative Example 2. This indicates that even with the solvent system described in this invention, the poor thermal stability and weak film-forming ability of LiPF6 salt limit the low-temperature ion transport and cycle life of the battery. The LiODFB used in the examples has higher temperature adaptability than LiPF6, so its DC internal resistance at -20°C and cycle life at 45°C are better than those of Comparative Example 2. Comparative Example 3 did not add FEC. Without FEC, the interfacial film is loose and unstable, leading to a decrease in overall electrochemical performance, which is significantly weaker than that of Examples 1-5.

[0074] In Examples 1-5, as the MPN ratio gradually increases, the low-temperature DC internal resistance of the electrolyte continuously decreases. Example 4 achieves the best results in both low-temperature internal resistance at -20℃ and high-temperature cycle life at 45℃. This indicates that introducing an appropriate amount of MPN can effectively control the Li... + The solvation structure improves ion transport kinetics; at the same time, this system uses DGDE with a higher boiling point, whose molecular chain length is longer than that of common DME, and its oxidation stability is significantly improved, thus effectively solving the problems of low boiling point, easy volatility and easy decomposition at high temperature of traditional ether solvents. However, when the proportion of DGDE is too low, the oxidation decomposition at high temperature is aggravated, resulting in a significant shortening of cycle life.

[0075] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0076] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A wide-temperature-range electrolyte, characterized in that, The wide-temperature-range electrolyte is a mixture of solvent, lithium salt and additive. The solvent is one or more of diethylene glycol dibutyl ether or 3-methoxypropionitrile, the additive is fluoroethylene carbonate, and the lithium salt is LiODFB.

2. The wide-temperature-range electrolyte according to claim 1, characterized in that, The volume ratio of solvent to additive in the wide-temperature-range electrolyte is 8~10:

1.

3. The wide-temperature-range electrolyte according to claim 1, characterized in that, The molar concentration of the lithium salt in the wide-temperature-range electrolyte is 0.8~1.2 mol / L.

4. A method for preparing a wide-temperature-range electrolyte as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: A wide-temperature-range electrolyte is obtained by mixing lithium salt, solvent and additives.

5. The method for preparing a wide-temperature-range electrolyte according to claim 4, characterized in that, The mixing process is carried out at a temperature of 40~50℃.

6. The application of the wide-temperature-range electrolyte as described in claim 1 in lithium-ion batteries.

7. A method for preparing a lithium-ion battery, characterized in that, The preparation method includes the following steps: The positive electrode, negative electrode, and separator are assembled and injected with the wide-temperature-range electrolyte as described in claim 1 to obtain the lithium-ion battery.

8. The method for preparing a lithium-ion battery according to claim 7, characterized in that, The active material of the positive electrode is lithium iron phosphate, and the thickness of the positive electrode is 50-200 μm.

9. The method for preparing a lithium-ion battery according to claim 7, characterized in that, The active material of the negative electrode is graphite, and the thickness of the negative electrode is 50-150 μm.

10. The method for preparing a lithium-ion battery according to claim 7, characterized in that, The assembly method is either stacking or winding.

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