Wide-temperature-range lithium ion battery electrolyte and preparation method thereof

Abstract

This invention discloses a wide-temperature-range lithium-ion battery electrolyte and its preparation method, relating to the field of lithium-ion battery materials technology. The preparation method includes: dissolving a sulfonylimide-based lithium salt in a mixed solvent of dimethyl carbonate and ethyl methyl carbonate at -5℃ to 10℃ to obtain a pre-solvated solution; heating to 5~30℃ and adding lithium hexafluorophosphate in batches; adding a cyclic fluorinated carbonate regulator followed by ultrasonic activation and temperature control at 25~50℃; and finally, aging at 35~45℃ followed by filtration and degassing. This invention reconstructs the lithium-ion mass transfer solvation shell through spatiotemporal control of lithium salt dissolution, cascade gradient temperature control, and specific power ultrasonic activation, significantly reducing the desolvation energy barrier at extreme low temperatures and constructing a thermodynamically stable inorganic-rich dual-interface protective film at high temperatures, thereby greatly expanding the stable operating temperature range of the battery.

Description

Technical Field

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

[0002] Existing lithium-ion battery electrolytes, under low-temperature conditions, experience a significant decrease in ionic conductivity and a sharp increase in interfacial impedance due to increased solvent viscosity and reduced salt dissociation. This leads to rapid capacity decay and even lithium deposition on the negative electrode surface. During high-temperature operation or storage, the solvent and lithium salt are prone to thermal decomposition, resulting in thickening and damage to the solid electrolyte interphase (SEI) and positive electrode electrolyte interphase (CEI) films, and even corrosion of the aluminum current collector, shortening the battery's cycle life and deteriorating safety. Therefore, it is difficult to meet the requirement of stable operation over a wide temperature range of -40℃ to 60℃. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a wide-temperature-range lithium-ion battery electrolyte and its preparation method, the specific technical solution of which is as follows: A method for preparing a wide-temperature-range lithium-ion battery electrolyte includes the following steps: S1. Under an inert atmosphere, dimethyl carbonate and ethyl methyl carbonate are mixed and cooled to -5~10℃. Then, a sulfonylimide main lithium salt is added and stirred until completely dissolved to obtain a presolvated solution. S2. Under continuous stirring, the presolventized liquid is heated to 5~30℃, and then lithium hexafluorophosphate is added in batches; S3. Add a cyclic fluorocarbonate regulator to the system obtained in step S2, activate the system and control the temperature of the system to rise to 25~50℃, and keep it at that temperature for 20~60 min; S4. The system obtained in step S3 is kept at 35~45℃ for 4~12 hours for aging, then filtered and degassed to obtain the final product.

[0004] Preferably: In step S1, the stirring speed is 300~500 rpm and the stirring time is 1~2 hours; In step S2, the heating rate is 0.2~1.5℃ / min, and the batch addition is done in 3~5 batches over 30~60 min.

[0005] In step S3, the activation process is ultrasonic activation, and the frequency of ultrasonic activation is 20~40 kHz, and the power is 100~200 W.

[0006] Preferably, in step S3, vinylene carbonate is also added to the system, and the amount added is 0.5% to 1% of the total mass of the electrolyte.

[0007] Preferably, the molar ratio of the sulfonamide-based lithium salt to lithium hexafluorophosphate is (0.3~0.5):(0.6~0.8); and the total molar concentration of the sulfonamide-based lithium salt and lithium hexafluorophosphate in the electrolyte is 1.0~1.2 mol / L.

[0008] Preferably, the volume ratio of dimethyl carbonate to ethyl methyl carbonate is (4~6):(4~6); the volume fraction of the cyclic fluorocarbonate regulator in the total solvent volume is 5%~15%.

[0009] Preferably, the sulfonylimide main lithium salt is lithium bisfluorosulfonylimide, and the cyclic fluorocarbonate regulator is fluoroethylene carbonate; or the sulfonylimide main lithium salt is modified lithium bisfluorosulfonylimide, and the cyclic fluorocarbonate regulator is a silicon-fluorine hybrid fluoride ester regulator.

[0010] Preferably, the sulfonylimide main lithium salt is modified bis(fluorosulfonylimide) lithium, which is prepared by the following steps: dissolving bis(fluorosulfonylimide) lithium and lithium difluorooxalate borate in anhydrous acetonitrile solvent, and stirring the reaction at 45~55℃ for 2~4 hours; after the reaction is completed, removing the anhydrous acetonitrile solvent and recrystallizing under conditions of 50~55℃ and a vacuum degree of -0.095 MPa or higher, and then drying under vacuum to obtain the final product.

[0011] Preferably, the cyclic fluorinated carbonate regulator is a silicon-fluorine hybrid fluorinated ester regulator, which is prepared by the following steps: 4-hydroxymethyl ethylene carbonate and vinyltrimethoxysilane are mixed in a molar ratio of 1:(0.9~1.1), and reacted at 65~75°C for 4~8 hours in the presence of an acidic catalyst, and then purified by vacuum distillation.

[0012] The present invention also provides a wide-temperature-range lithium-ion battery electrolyte, which is prepared by any of the preparation methods described above.

[0013] Preferably, the electrolyte has a water content of ≤10 ppm and a free acid content (calculated as HF) of ≤20 ppm.

[0014] The preparation method provided by this invention reconstructs the mass transfer resistance of lithium ions through spatiotemporal control of the lithium salt dissolution sequence, cascaded gradient temperature control, and targeted physical field activation, achieving efficient synergy between the main lithium salt anion and the regulator. This approach significantly reduces the desolvation barrier at low temperatures, increases the lithium ion transport number and ionic conductivity, and suppresses low-temperature lithium plating and dendrite growth, effectively solving the problem of excessive interfacial impedance in batteries at low temperatures. Simultaneously, at high temperatures, it can synergistically passivate the aluminum current collector, constructing a thermodynamically stable inorganic-rich protective film that effectively suppresses catalytic side reactions and thermal decomposition of the solvent and lithium salt at high voltage and high temperature. This overcomes the technical defects of conventional dual-salt systems where performance cannot be balanced or even deteriorates under wide-temperature operation, significantly extending the battery's wide-temperature-range cycle life. Detailed Implementation

[0015] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0016] This embodiment provides a method for preparing a wide-temperature-range lithium-ion battery electrolyte. Through temperature control steps, a specific order of component addition, and a physical activation process, the reconstruction of the solvation shell within the system is guided to meet the requirements for wide-temperature-range use. The preparation method specifically includes the following steps: Step 1: Low-temperature pre-dissolution In a glove box or vacuum environment protected by argon or other high-purity inert atmosphere, mix the linear carbonate solvents dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) uniformly according to a preset ratio. Cool the temperature of the mixed solvent to -5℃ to 10℃.

[0017] While maintaining this low temperature range, a sulfonamide-based lithium salt is added to the mixed solvent, and stirring is used to ensure complete dissolution at low temperature, thereby obtaining a uniform and transparent presolvated liquid. In this step, the low temperature suppresses thermal motion, inducing the sulfonamide-based lithium salt to preferentially coordinate with the low-viscosity linear carbonate solvent, constructing a locally high-concentration presolvated network.

[0018] Step 2: Gradual addition of the main salt While maintaining continuous stirring, the presolventized liquid obtained in step one is heated under controlled temperature until the system temperature rises steadily to 5℃~30℃.

[0019] During this heating process, another core main salt, lithium hexafluorophosphate (… The anions are added to the system in batches, slowly. During the batch addition, the local temperature and heat release of the system need to be monitored and controlled to avoid hot spots. This gradient temperature control and batch feeding process can smoothly drive the outer anions to participate in the lithium-ion (lithium-ion) process. In the first solvation shell of the ion, weak solvation structures such as contact ion pairs (CIPs) and aggregates (AGGs) are induced to form.

[0020] Step 3: Add regulatory components and activate Add a predetermined amount of cyclic fluorocarbonate regulator to the mixed system in step two after the main salt has been dissolved.

[0021] After the feed is completed, a specific activation treatment is applied to the entire mixing system. During the activation treatment, the temperature of the system is controlled to rise and stabilize within the range of 25℃ to 50℃, and maintained at this temperature for 20 to 60 minutes. This activation treatment imparts energy across the reaction activation energy to the regulator molecules, enabling them to participate in the pre-assembly of the in-situ interface precursor and the final optimization of the solvation shell.

[0022] Step 4: Aging and Post-processing After the material system in step three is activated and heated, it is transferred to a curing device with constant temperature control. The system temperature is controlled within the range of 35℃ to 45℃ for static curing, which lasts for 4 to 12 hours.

[0023] After maturation, the material is cooled to room temperature, filtered to remove any trace suspended matter or insoluble impurities, and a vacuum degassing process is applied to remove trace amounts of moisture, bubbles, and low-boiling-point residual gases introduced during mixing. Finally, it is packaged to obtain a qualified wide-temperature-range lithium-ion battery electrolyte.

[0024] The preparation method provided in this embodiment reconstructs the mass transfer resistance of lithium ions by controlling the spatiotemporal dissolution sequence of lithium salts, cascaded gradient temperature control, and targeted physical field activation, achieving efficient synergy between the main lithium salt anion and the regulator. This scheme significantly reduces the desolvation barrier at low temperatures, increases the transport number and ionic conductivity of lithium ions, and suppresses low-temperature lithium plating and dendrite growth, effectively solving the problem of excessive interfacial impedance in batteries at low temperatures. Simultaneously, at high temperatures, it can synergistically passivate the aluminum current collector, constructing a thermodynamically stable inorganic-rich protective film, effectively suppressing catalytic side reactions and thermal decomposition of the solvent and lithium salt at high voltage and high temperature. This overcomes the technical defects of conventional dual-salt systems where performance cannot be balanced or even deteriorates under wide-temperature operation, significantly extending the battery's wide-temperature-range cycle life.

[0025] Furthermore, this embodiment limits the core actions in the preparation process, such as stirring, heating, feeding, and activation, and determines the optimal ratio range of each component.

[0026] In the low-temperature pre-dissolution process of step one, after the mixed solvent is cooled and adjusted to the preset low-temperature range, the sulfonylimide main lithium salt is added and stirring is started. The stirring speed is controlled between 300 and 500 rpm, and this stirring speed is maintained for 1 to 2 hours. Under the combined action of the low temperature of -5℃ to 10℃ (preferably 0 to 5℃) and the shear force of the specific stirring speed, the sulfonylimide main lithium salt can be completely dissolved, forming a pre-solventized liquid with uniform dispersion at the molecular level.

[0027] In the gradient addition of the main salt in step two, to create a stable thermodynamic environment for the subsequent ordered competitive coordination of anions, the heating rate of the system needs to be finely controlled, limited to between 0.2 and 1.5 °C / min. Meanwhile, the core main salt, lithium hexafluorophosphate (… The solution should not be poured in all at once, but rather added slowly and intermittently in 3-5 batches over a total time of 30-60 minutes to the continuously stirred pre-solventized liquid. This batch-by-batch addition method, combined with slow temperature control, allows for... The heat generated during dissolution is dissipated rapidly and evenly, preventing localized overheating that could trigger side reactions in the solvent or lithium salt.

[0028] In the activation process of step three, this embodiment employs a specific physical field to drive the pre-assembly of the interfacial precursor of the regulator. Specifically, the activation process utilizes ultrasonic activation. The ultrasonic activation frequency is set to 20–40 kHz, and the ultrasonic input power is controlled at 100–200 W. Under this specific ultrasonic cavitation effect and microjets, the system is continuously held at a temperature range of 25°C–50°C for 20–60 min, which significantly reduces the intermolecular association energy barrier, allowing the regulator molecules and lithium salt anions to rapidly adjust and optimize their spatial configuration at the microscopic level.

[0029] Furthermore, to establish multiple protection mechanisms during final battery operation, while adding cyclic fluorocarbonate regulators to the system in step three, vinylene carbonate can also be introduced into the system. The amount of vinylene carbonate added accounts for 0.5% to 1% of the total mass of the final electrolyte, and it can participate in the subsequent interfacial film-forming reaction as an auxiliary film-forming agent.

[0030] From an overall formulation perspective, to ensure the electrolyte exhibits excellent wide-temperature conductivity and electrochemical stability, each core component in the electrolyte system satisfies a specific quantitative dependence relationship. Among these, the sulfonylimide-based lithium salt serves as the first main salt, and lithium hexafluorophosphate serves as the second main salt. The molar ratio between the two lithium salts was controlled at (0.3~0.5):(0.6~0.8); simultaneously, the total molar concentration of the two lithium salts in the electrolyte was controlled at 1.0~1.2 mol / L. Regarding the solvent ratio, the volume ratio between the two main linear carbonate solvents, dimethyl carbonate (DMC) and ethylmethyl carbonate (EMC), was controlled at (4~6):(4~6); the volume fraction of the introduced third regulating component, cyclic fluorocarbonate regulator, accounted for 5%~15% of the total solvent volume.

[0031] Furthermore, to achieve optimal wide-temperature adaptability in different application scenarios, this embodiment provides two exclusive pairings in the material selection of the preparation process. These two combinations, under specific cascaded temperature control and ultrasonic activation processes, can trigger different interface construction and stabilization mechanisms.

[0032] Combination 1: Conventional dual-salt compound synergistic scheme In this combination, the sulfonylimide main lithium salt added in step one is specifically selected as lithium bis(fluorosulfonylimide). In step three, the cyclic fluorocarbonate regulator added is specifically selected as fluoroethylene carbonate ( ). This combination depends on With lithium hexafluorophosphate ( The adaptive reconstruction of the solvation shell is completed under the temperature-controlled process of steps one to four, utilizing... Mild activation under ultrasonication synergistically constructs a protective film with wide temperature range characteristics.

[0033] Combination 2: Hybrid Complexation Scheme of Modified Components To further extend the stable operating boundary under extreme temperatures, in this combination, the sulfonylimide main lithium salt added in step one is modified bis(fluorosulfonylimide) lithium (… In step three, the cyclic fluorocarbonate regulator added is a silicon-fluorine hybrid fluorinated ester regulator with temperature-responsive characteristics. ).

[0034] When the second combination is selected, the modified lithium bis(fluorosulfonyl)imide (m-LiFSI) is prepared by the following in-situ chemical modification steps: In an inert atmosphere glove box filled with high-purity argon and with strictly controlled moisture and oxygen content both less than 0.1 ppm, 0.4 mol of lithium bisfluorosulfonylimide (LiFSI) powder and 0.05–0.10 mol of lithium difluorooxalate borate (LiODFB) were weighed and completely dissolved in anhydrous acetonitrile to prepare a homogeneous precursor solution. Then, a magnetic stirrer was turned on, and the system was maintained at 45–55°C using a constant-temperature oil bath for 2–4 hours to allow the anions of LiFSI to undergo local coordination and recombination with the boron centers of LiODFB. After the reaction, the reaction solution was filtered through a multi-stage filter to remove trace amounts of suspended insoluble matter. The filtrate was then subjected to high vacuum at 50–55°C and a vacuum greater than -0.095 MPa to remove the acetonitrile solvent and promote recrystallization. The final collected white solid powder is the modified lithium bisfluorosulfonylimide (m-LiFSI). This modified lithium salt, by introducing a covalently / coordinally locked polynuclear boron-based anion acceptor structure, greatly promotes the charge dissociation of lithium ions and enhances their coordination activity in low-viscosity linear carbonates.

[0035] When the second combination is selected, the silicon-fluorine hybrid fluorinated ester regulator (m-FEC) is prepared by the following chemical grafting steps: Weigh out predetermined amounts of 4-hydroxymethyl ethylene carbonate and vinyltrimethoxysilane, and mix them in a near equimolar ratio of 1:(0.9~1.1) in a dry single-necked or three-necked reaction flask. Then, add p-toluenesulfonic acid as an acidic catalyst to the reaction flask, controlling the amount of p-toluenesulfonic acid added to be between 0.5% and 1.0% of the total mass of 4-hydroxymethyl ethylene carbonate. Place the reaction system in a constant-temperature oil bath or heating mantle, controlling the reaction temperature to be stable within the range of 65℃~75℃, while simultaneously turning on mechanical or strong magnetic stirring. Maintain the reaction for 4~8 hours under nitrogen protection, quantitatively grafting vinylsiloxane groups onto the carbonate side chains through the dealcoholization condensation reaction of side-chain hydroxyl groups and siloxy groups. After the reaction is complete, the entire reaction solution is transferred to a vacuum distillation apparatus and subjected to vacuum distillation at a vacuum level of less than -0.095 MPa and a temperature of 80℃~90℃. The core high-boiling-point fraction is collected to obtain a highly pure, clear liquid, namely the silicon-fluorine hybrid fluorinated ester regulator (m-FEC). This regulator, through the grafting of short-chain vinylsiloxane structures, possesses unique interfacial adaptive crosslinking properties during subsequent physical field activation and thermal ripening processes.

[0036] This embodiment also provides a wide-temperature-range lithium-ion battery electrolyte product manufactured by the above method. Because this electrolyte achieves lithium-ion dissolution at the molecular level through spatiotemporal control of the lithium salt dissolution order, cascaded gradient temperature control, and targeted physical field activation treatment... The coordination reconstruction of the solvated shell results in extremely high purity, excellent conductivity at extreme low temperatures, and an extremely wide electrochemical stability window.

[0037] After preparation, the physical and chemical characteristics of this wide-temperature-range lithium-ion battery electrolyte meet the quality control requirements. Specifically, the internal water content of the electrolyte is controlled below 10 ppm, determined using the Karl Fischer coulometric method; the free acid content (calculated as HF) is controlled below 20 ppm, determined using an automatic potentiometric titrator. Furthermore, the weakly solvated network structure induced by the process allows the electrolyte to maintain an ionic conductivity above 1.2 mS / cm even at extreme low temperatures of -40°C, as measured using electrochemical impedance spectroscopy (EIS) with a conductivity meter. Simultaneously, at room temperature (25°C), the electrolyte exhibits an electrochemical stability window of 4.5 V (relative to...). The above measurements were performed using cyclic voltammetry (CV) or linear voltammetry (LSV).

[0038] This embodiment also provides a product entity—a lithium-ion battery—that uses the aforementioned wide-temperature-range electrolyte. The internal core structure of this lithium-ion battery mainly consists of a positive electrode, a negative electrode, a separator placed between the positive and negative electrodes, and an injected electrolyte.

[0039] In the battery assembly, the positive electrode includes a positive current collector (such as aluminum foil) and a positive active material coated on the surface of the positive current collector. The positive active material can be selected from lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), or lithium cobalt oxide (NCA). ) or lithium iron phosphate ( High-voltage, high-capacity positive electrode materials, such as copper foil, are used. The negative electrode includes a negative electrode current collector (e.g., copper foil) and a negative electrode active material coated on the surface of the current collector. The negative electrode active material can be selected from artificial graphite, natural graphite, hard carbon, silicon-based negative electrode, or lithium metal sheet. The separator is sandwiched between the positive and negative electrodes to isolate electron conduction and provide lithium-ion channels. The separator can be selected from polyethylene (PE) monolayer membrane, polypropylene (PP) monolayer membrane, multilayer PP / PE / PP composite microporous membrane, or a modified separator with an alumina nano-ceramic layer coated on the surface. The wide-temperature-range lithium-ion battery electrolyte prepared above is vacuum-filled into the microporous gaps between the positive electrode, negative electrode, and separator, and synergistically participates in the formation of a highly thermodynamically stable interface protective film during the first charge-discharge formation process of the battery.

[0040] Specific embodiments are provided below. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0041] Preparation Example 1 In a high-purity inert gas glove box filled with high-purity argon gas and with moisture and oxygen content maintained below 0.1 ppm, 74.8 g of lithium bis(fluorosulfonyl)imide (LiFSI) powder and 14.4 g of lithium difluorooxalate borate (LiODFB) solid powder were weighed and poured into a 500 mL three-necked flask. Then, 250 mL of anhydrous acetonitrile was added as a solvent, and magnetic stirring was started and carried out at room temperature for 30 minutes to completely dissolve the precursor, obtaining a colorless and transparent precursor solution. While maintaining continuous stirring, the temperature of the material in the three-necked flask was heated to 50°C using a constant-temperature water bath. This temperature was maintained, and magnetic stirring was continued for 3 hours to initiate anionic coordination recombination. After the reaction was complete, the reaction solution was filtered through a 0.22 μm PTFE precision microporous membrane, and the filtrate was collected and transferred to a single-necked vacuum distillation flask. The flask was connected to a rotary vacuum drying system, and acetonitrile solvent was removed by continuous vacuum distillation under conditions of -0.096 MPa and an external oil bath temperature of 50°C. High-temperature recrystallization was then carried out until the solvent was completely dried. Finally, a white crystalline powder was collected at the bottom of the flask, which is the modified lithium difluorosulfonyl imide (m-LiFSI). It was then sealed in a cool, inert atmosphere for later use.

[0042] Preparation Example 2 In a nitrogen-protected, dry reaction vessel, 118.1 g of 4-hydroxymethyl ethylene carbonate and 148.2 g of vinyltrimethoxysilane were weighed and poured together into a 500 mL four-necked glass reaction vessel equipped with a reflux condenser and a mechanical stirrer. Then, 1.3 g of dried p-toluenesulfonic acid was added as an acidic catalyst. The mechanical stirrer shaft was connected and the speed adjusted to 250 rpm. The heating mantle was turned on, and the temperature of the material in the reaction vessel was heated to 70°C. The reaction was maintained at this temperature with continuous stirring for 6 hours to carry out the dealcoholization condensation reaction. During the reaction, circulating cooling water at 5°C was circulated through the condenser to reflux the raw materials. After the reaction, the heating was turned off, and the material was allowed to cool to room temperature. The liquid in the reaction vessel was transferred to a distillation flask in a vacuum distillation apparatus. A rotary vane vacuum pump was turned on, and the vacuum level inside the system was stabilized at -0.095 MPa. Slowly increase the temperature of the heating mantle to perform vacuum distillation, remove the byproduct methanol and trace amounts of low-boiling unreacted substances, and finally collect the clear liquid corresponding to the high-boiling fraction to obtain a colorless and transparent liquid, which is the silicon-fluorine hybrid fluorinated ester regulator (m-FEC), and store it in a silica gel desiccator in a sealed container.

[0043] Example 1

[0044] In a glove box for electrolyte preparation under argon protection (water and oxygen content both less than 0.1 ppm), 450 mL of dimethyl carbonate (DMC) and 450 mL of ethyl methyl carbonate (EMC) were measured and introduced into a 2 L jacketed stainless steel reactor. The cryogenic cooling circulator connected to the stainless steel reactor was turned on to lower the temperature of the heat transfer fluid in the jacket until the temperature of the mixed solvent inside the stainless steel reactor dropped to 3°C. Maintaining the low temperature of 3°C and with the anchor-type agitator inside the reactor turned on and the speed adjusted to 400 rpm, 74.8 g of lithium difluorosulfonylimide (… Slowly pour the solid powder into the reactor. Stir continuously at 400 rpm for 1.5 hours, observing the material in the reactor until the solid powder is completely dissolved, obtaining a uniform and transparent presolvated liquid.

[0045] Next, keeping the agitator running continuously at 400 rpm, the heating program was started, and the temperature of the heat transfer oil in the outer jacket was adjusted to raise the temperature of the presolventized liquid in the reactor to 20℃ at a steady heating rate of 0.8℃ / min. While maintaining a constant temperature of 20℃ and continuous stirring, 106.3 g of lithium hexafluorophosphate (… The crystalline powder was divided into four batches over a total time of 40 minutes. One batch was added to the reactor every 10 minutes. During this period, the thermometer inside the reactor was closely monitored, and the overall temperature of the material was controlled to fluctuate slightly within the range of 20~25℃ by fine-tuning the jacket cooling water.

[0046] After the lithium hexafluorophosphate is completely dissolved, 100 mL of fluoroethylene carbonate is measured and poured into the reactor at once. Then, add 10 g of vinylene carbonate (VC). After the addition is complete, turn on the ultrasonic dispersion device embedded in the flange, set the ultrasonic frequency to 30 kHz, and adjust the output power to 150 W. While the ultrasonic physical field is activating, control the jacket circulating oil to raise the material temperature in the reactor to 45°C, and maintain this temperature for 45 min under continuous ultrasonic activation.

[0047] After ultrasonic activation, the ultrasonic dispersion device is turned off, and the entire material in the reactor is transferred through pipeline to a sealed horizontal constant-temperature curing tank. The jacket temperature of the curing tank is maintained at 40℃, and the electrolyte is allowed to stand and cure for 8 hours under this atmospheric pressure static environment. After the curing time is completed, the circulation pump is turned on, and the cured liquid is circulated and filtered through a 0.45μm PTFE corrosion-resistant filter. The filtrate is then introduced into a sealed vacuum degassing vessel, where it is continuously degassed for 30 minutes under a vacuum of -0.09 MPa to remove trace amounts of water and mixed air bubbles. Finally, it is packaged to obtain the finished wide-temperature-range lithium-ion battery electrolyte.

[0048] Example 2

[0049] The only difference between this embodiment and Example 1 is that, in lithium difluorosulfonylimide ( In the dissolution stage, the solid powder was replaced with the white microcrystalline powder modified lithium bisfluorosulfonylimide (prepared in Example 1). 74.8g. The proportions of the remaining carbonate solvents, the low-temperature dissolution process, and lithium hexafluorophosphate (…). Four batches of ) were separately added, as well as fluoroethylene carbonate ( The subsequent process steps and dosages, such as the addition of vinylene carbonate (VC), ultrasonic physical field activation, high-temperature curing, fine filtration and vacuum degassing, are exactly the same as in Example 1.

[0050] Example 3

[0051] The only difference between this embodiment and Example 1 is that, in the stage of adding functional additives, fluoroethylene carbonate ( ) 100 mL was replaced with the clear liquid silicon-fluorine hybrid fluorinated ester regulator prepared in Preparation Example 2 ( 100 mL. The remaining dimethyl carbonate and ethyl methyl carbonate were prepared by solvation, and lithium difluorosulfonyl imide (… The dissolution of lithium hexafluorophosphate ( ) The batch addition of vinylene carbonate (VC), the mixing and blending of VC, the ultrasonic field heat preservation activation, and the subsequent static heat preservation curing, vacuum degassing and packaging processes and corresponding material usage are all exactly the same as in Example 1.

[0052] Example 4

[0053] In an argon-protected glove box, the modified lithium bis(fluorosulfonyl)imide prepared in Preparation Example 1 was added to a mixed solvent of 450 mL dimethyl carbonate and 450 mL ethylmethyl carbonate, maintained at 3°C. 74.8 g of lithium hexafluorophosphate was stirred at 400 rpm for 1.5 hours until completely dissolved. The temperature was then steadily increased to 20°C, and 106.3 g of lithium hexafluorophosphate was added in four batches. After complete dissolution, the silicon-fluorine hybrid fluorinated ester regulator prepared in Preparation Example 2 was directly poured into the vector reactor. 100 mL of ethylene carbonate (VC) and 10 g of vinylene carbonate (VC) were added. The subsequent purification and packaging processes, including 30 kHz ultrasonic physical field activation, 40°C static heat preservation, precision filter filtration, and degassing under reduced pressure, were exactly the same as in Example 1.

[0054] Example 5

[0055] The only difference between this embodiment and Example 1 is that, when preparing the mixed solvent, the amount of dimethyl carbonate (DMC) is adjusted to 550 mL and the amount of ethyl methyl carbonate (EMC) is adjusted to 350 mL. At a low temperature of 3°C and a rotation speed of 400 rpm, the modified lithium difluorosulfonylimide (DMC) prepared in Example 1 is added to the solvent. 74.8 g of lithium hexafluorophosphate was added and stirred for 1.5 hours to dissolve. The temperature was then steadily raised to 20°C, and lithium hexafluorophosphate was added in four batches. 106.3 g. After complete dissolution, the silicon-fluorine hybrid fluorinated ester regulator prepared in Example 2 was poured into the vector reactor. 100 mL of ethylene carbonate (VC) and 10 g of vinylene carbonate (VC). The subsequent steps of 45°C heating and ultrasonication, 40°C static curing, precision filtration, and vacuum degassing and packaging were exactly the same as in Example 1.

[0056] Comparative Example 1 In this comparative example, the solvent ratio, lithium difluorosulfonylimide ( Low-temperature dissolution of lithium hexafluorophosphate ( ) Four batches of ) were separately added, as well as fluoroethylene carbonate ( The amounts of vinylene carbonate (VC) added were exactly the same as in Example 1. The difference was that after all components were added, the mixture was continuously stirred at 45°C with a mechanical stirrer at 400 rpm for 45 min, and then transferred to a curing tank for static curing at 40°C for 8 hours, followed by routine filtration and degassing.

[0057] Comparative Example 2 In this comparative example, the solvent dosage, low-temperature dissolution of lithium salt, batch addition of lithium hexafluorophosphate, additive addition, and the 30 kHz ultrasonic physical field activation process at 45°C are all exactly the same as in Example 1. The difference is that after ultrasonic activation for 45 min, the ultrasonically activated liquid is directly circulated and filtered through a 0.45 μm polytetrafluoroethylene filter at room temperature, and continuously degassed under a vacuum of -0.09 MPa for 30 min before being packaged as a finished product.

[0058] Comparative Example 3 In this comparative example, lithium bis(fluorosulfonyl)imide was not added to a stainless steel reactor in a mixed solvent of 450 mL dimethyl carbonate and 450 mL ethyl methyl carbonate maintained at 3°C. After directly heating to 20°C, lithium hexafluorophosphate was added in batches over 40 minutes. 181.2 g. After complete dissolution, pour in fluoroethylene carbonate ( 100 mL of ethylene carbonate (VC) and 10 g of VC were used. The subsequent heating and ultrasonic activation, isothermal curing, precision filtration and vacuum degassing processes were exactly the same as in Example 1.

[0059] Comparative Example 4 In this comparative example, the modified lithium bis(fluorosulfonyl)imide prepared in Example 1 was prepared by low-temperature dissolution in a mixed solvent. 74.8 g was then added in batches at room temperature to lithium hexafluorophosphate ( 106.3 g. After complete dissolution, fluoroethylene carbonate (FEC) was directly poured into the reactor. 100 mL of [unspecified ingredient] and 10 g of vinylene carbonate (VC). Subsequent heating and ultrasonic activation, isothermal ripening, precision filtration, and vacuum degassing processes were identical to those in Example 1. Comparative Example 5 In this comparative example, lithium bis(fluorosulfonyl)imide was dissolved at low temperature in a mixed solvent. 74.8 g was then added in batches at room temperature to lithium hexafluorophosphate ( 106.3 g. After complete dissolution, the silicon-fluorine hybrid fluorinated ester regulator prepared in Preparation Example 2 was directly poured into the vector reactor. 100 mL of ethylene carbonate (VC) and 10 g of VC were used. The subsequent heating and ultrasonic activation, isothermal curing, precision filtration and vacuum degassing processes were exactly the same as in Example 1.

[0060] To verify the physicochemical properties of the wide-temperature-range lithium-ion battery electrolyte described in this embodiment and its comprehensive electrochemical performance in physical battery devices, comparative tests were conducted on the electrolyte products prepared in Examples 1-5 and Comparative Examples 1-5 and the assembled batteries.

[0061] The test items and test methods are as follows: 1. Water content and free acid test: The water content of each electrolyte product was determined by a Karl Fischer coulometric titrator at 25°C; the free acid content was calculated by titrating the electrolyte with standard sodium methoxide solution using an anhydrous ethanol as solvent and an automatic potentiometric titrator, and the content was converted to HF.

[0062] 2. -40℃ Ionic Conductivity Test: Each electrolyte product was sealed in a conductivity cell and placed in an ultra-low temperature constant temperature chamber at -40℃ for 4 hours. An electrochemical workstation was used to perform alternating current impedance (EIS) testing within the frequency range of 100 kHz to 1 Hz. The bulk solution resistance was obtained by finding the intersection of the high-frequency region of the impedance spectrum with the real axis, and the ionic conductivity at -40℃ was calculated using the cell constant.

[0063] 3. Electrochemical Window Voltage Measurement at 25℃: Linear voltammetry (LSV) measurements were performed using a three-electrode system at 25℃. A platinum sheet was used as the working electrode, and lithium metal sheets were used as the counter and reference electrodes. The scan rate was 5 mV / s, and the current density reached 0.1 mA / s. The potential corresponding to this time is defined as the oxidative decomposition voltage of the electrolyte, i.e., the electrochemical stability window.

[0064] 4. Battery coin cell charge / discharge test (-40℃ capacity retention): Each electrolyte group was assembled with an artificial graphite anode, a lithium metal cathode, and a polyethylene separator to form CR2032 coin cells. The cells were activated and formed by three charge-discharge cycles at 25℃ and a 0.1C rate. Subsequently, the fully charged cells were placed at -40℃ for 4 hours and discharged at a constant current rate of 0.2C to 2.0 V. The discharge capacity was recorded, and the percentage of this capacity relative to the 0.2C discharge capacity at 25℃ was calculated; this is the -40℃ capacity retention rate.

[0065] 5. Battery pouch cycle test (60℃, 1000 cycles retention rate): Each group of electrolytes was separately injected into the ternary material ( A 1 Ah industrial standard soft-pack battery with graphite as the positive electrode and artificial graphite as the negative electrode was used. After formation and settling, the battery was placed in a constant temperature explosion-proof chamber at 60℃ and subjected to continuous long-term cycle testing of 1C charge / 1C discharge within a voltage range of 2.8~4.2V. The ratio of the discharge capacity after the 1000th cycle to the discharge capacity of the first cycle was recorded, which is the capacity retention rate after 1000 cycles at 60℃.

[0066] The test data of various performance indicators of each embodiment and comparative example are shown in Table 1 and Table 2.

[0067] Table 1: Electrolyte and Battery Performance Test Data from Examples

[0068] Table 2: Performance Test Data of Comparative Electrolytes and Batteries

[0069] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a wide-temperature-range lithium-ion battery electrolyte, characterized in that, Includes the following steps: S1. Under an inert atmosphere, dimethyl carbonate and ethyl methyl carbonate are mixed and cooled to -5~10℃. Then, a sulfonylimide main lithium salt is added and stirred until completely dissolved to obtain a presolvated solution. S2. Under continuous stirring, the presolventized liquid is heated to 5~30℃, and then lithium hexafluorophosphate is added in batches; S3. Add a cyclic fluorocarbonate regulator to the system obtained in step S2, activate the system and control the temperature of the system to rise to 25~50℃, and keep it at that temperature for 20~60 min; S4. The system obtained in step S3 is kept at 35~45℃ for 4~12 hours for aging, then filtered and degassed to obtain the final product.

2. The preparation method according to claim 1, characterized in that: In step S1, the stirring speed is 300~500 rpm and the stirring time is 1~2 hours; In step S2, the heating rate is 0.2~1.5℃ / min, and the batch addition is done in 3~5 batches over 30~60 min; In step S3, the activation process is ultrasonic activation, and the frequency of ultrasonic activation is 20~40 kHz, and the power is 100~200 W.

3. The preparation method according to claim 1, characterized in that, In step S3, vinylene carbonate is also added to the system, and the amount added is 0.5% to 1% of the total mass of the electrolyte.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The molar ratio of the sulfonylimide main lithium salt to lithium hexafluorophosphate is (0.3~0.5):(0.6~0.8); the total molar concentration of the sulfonylimide main lithium salt and lithium hexafluorophosphate in the electrolyte is 1.0~1.2 mol / L.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The volume ratio of dimethyl carbonate to ethyl methyl carbonate is (4~6):(4~6); the volume fraction of the cyclic fluorocarbonate regulator in the total solvent volume is 5%~15%.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The sulfonylimide main lithium salt is lithium difluorosulfonylimide, and the cyclic fluorinated carbonate regulator is fluoroethylene carbonate; or the sulfonylimide main lithium salt is modified lithium difluorosulfonylimide, and the cyclic fluorinated carbonate regulator is a silicon-fluorine hybrid fluorinated ester regulator.

7. The preparation method according to claim 6, characterized in that, The sulfonylimide main lithium salt is modified bis(fluorosulfonylimide) lithium, which is prepared by the following steps: dissolving bis(fluorosulfonylimide) lithium and lithium difluorooxalate borate in anhydrous acetonitrile solvent, and stirring the reaction at 45~55℃ for 2~4 hours; after the reaction is completed, removing the anhydrous acetonitrile solvent and recrystallizing under conditions of 50~55℃ and a vacuum degree of -0.095 MPa or higher, and then drying under vacuum to obtain the final product.

8. The preparation method according to claim 6, characterized in that, The cyclic fluorinated carbonate regulator is a silicon-fluorine hybrid fluorinated ester regulator, which is prepared by the following steps: 4-hydroxymethyl ethylene carbonate and vinyltrimethoxysilane are mixed in a molar ratio of 1:(0.9~1.1), and reacted at 65~75℃ for 4~8 hours in the presence of an acidic catalyst. The mixture is then purified by vacuum distillation.

9. A wide-temperature-range lithium-ion battery electrolyte, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. The wide-temperature-range lithium-ion battery electrolyte according to claim 9, characterized in that, The electrolyte has a water content of ≤10 ppm and a free acid content (calculated as HF) of ≤20 ppm.

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