Lithium ion electrolyte and preparation method thereof as well as lithium ion battery and preparation method thereof

Abstract

The invention discloses a lithium ion electrolyte and a preparation method thereof as well as a lithium ion battery and a preparation method thereof. The lithium ion electrolyte comprises the following components: a lithium salt with the concentration of 1-1.5 mol / L, a fluoroborate-containing additive with the mass percent of 1-5%, a surfactant with the mass percent of 0.05-1% and the balance of a mixed solvent system, the mixed solvent system comprises tris (2, 2, 2-trifluoroethyl) phosphate, 1, 3-dioxolame and tetrahydrofuran; the preparation method of the lithium ion electrolyte comprises the following steps: preparing a mixed solvent system, adding a lithium salt and stirring; adding a fluoroborate-containing additive and a surfactant, stirring, and filtering; the lithium ion battery comprises a lithium ion electrolyte, a positive plate and a negative plate, the preparation method of the lithium ion battery comprises the following steps: assembling the positive plate, the diaphragm and the negative plate into a battery cell, and injecting the lithium ion electrolyte into the battery cell. The low-temperature discharge performance and the low-temperature cycle performance of the lithium ion battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-ion electrolyte and its preparation method, and a lithium-ion battery and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, are widely used in many fields of modern society, such as electric vehicles, portable electronic devices, and energy storage systems. However, the poor low-temperature performance of lithium-ion batteries has always been a key factor restricting their wider application in cold environments. Under low-temperature conditions, lithium-ion batteries typically experience problems such as capacity decay, reduced charge and discharge efficiency, and increased internal resistance. For example, in northern winters, the driving range of electric vehicles is significantly reduced, and electronic devices such as mobile phones are prone to automatic shutdown, causing great inconvenience to users and limiting the application of lithium-ion batteries in special scenarios such as polar scientific expeditions and energy storage for communication base stations in cold regions. The main reasons for the performance degradation of traditional lithium-ion batteries at low temperatures include: increased electrolyte viscosity, leading to a slower lithium-ion migration rate; and increased electrode / electrolyte interface impedance, affecting charge transfer efficiency. Therefore, improving the low-temperature performance of lithium-ion batteries has significant practical importance and market demand. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a lithium-ion electrolyte and its preparation method, and a lithium-ion battery and its preparation method.

[0004] The technical solution adopted by the present invention to solve its technical problem is as follows: a lithium-ion electrolyte is proposed, which includes the following components: lithium salt with a concentration of 1 mol / L to 1.5 mol / L, fluorinated borate ester additives with a mass percentage of 1% to 5%, surfactants with a mass percentage of 0.05% to 1%, and the remainder being a mixed solvent system; the mixed solvent system includes tris(2,2,2-trifluoroethyl) phosphate, 1,3-dioxolane and tetrahydrofuran in a volume ratio of (3-5):(1-3):(2-6).

[0005] Preferably, the fluoroboronic acid ester additive is a boronic acid ester modified with lithium bis(fluorosulfonyl)imide.

[0006] Preferably, the surfactant is polyethylene glycol dodecyl ether or fatty alcohol polyoxyethylene ether.

[0007] Preferably, the lithium salt is LiPF6, LiTFSI, LiFSI, or LiBF4.

[0008] The present invention also proposes a method for preparing the above-mentioned lithium-ion electrolyte, which includes the following steps: S1. Tris(2,2,2-trifluoroethyl) phosphate, 1,3-dioxolane and tetrahydrofuran are mixed in a volume ratio of (3-5):(1-3):(2-6), and stirred for the first time in an inert gas atmosphere. Then lithium salt is added and stirred for the second time to obtain a mixed solvent. S2. Fluoroboronic acid ester additives and surfactants are added sequentially to the mixed solvent, stirred evenly, and then filtered through a filter membrane to obtain lithium-ion electrolyte.

[0009] Preferably, in step S1, the first stirring is carried out at a speed of 200 r / min to 300 r / min for 3 to 5 hours; and / or, the second stirring is carried out at a speed of 200 r / min to 300 r / min for 8 to 12 hours; and / or, the inert gas is argon or helium.

[0010] Preferably, in step S2, the pore size of the filter membrane is 0.1~0.8μm.

[0011] The present invention also proposes a lithium-ion battery, which includes the above-mentioned lithium-ion electrolyte, positive electrode and negative electrode. The positive electrode sheet includes a positive current collector and a positive electrode slurry loaded on the positive current collector, the positive electrode slurry including a positive electrode material; the negative electrode sheet includes a negative current collector and a negative electrode slurry loaded on the negative current collector, the negative electrode slurry including a negative electrode material.

[0012] Preferably, both the positive electrode current collector and the negative electrode current collector have a porous structure, with the pore size of the positive electrode current collector and the negative electrode current collector being 50~200μm and the porosity being 50~65% respectively. The cathode material includes at least one of lithium iron phosphate and lithium phosphate; and / or, The negative electrode material includes at least one of graphite and carbon nanomaterials.

[0013] The present invention also proposes a method for preparing the above-mentioned lithium-ion battery, which includes the following steps: assembling a positive electrode, a separator and a negative electrode into a battery cell, and then injecting the above-mentioned lithium-ion electrolyte into the battery cell to obtain a lithium-ion battery.

[0014] The beneficial effects of this invention are: The lithium-ion electrolyte of the present invention uses a mixed solvent system containing tris(2,2,2-trifluoroethyl) phosphate, 1,3-dioxolane and tetrahydrofuran, which dissolves lithium salt and adds fluoroboronic acid ester additives and surfactants, so that lithium ions can maintain a high migration rate at low temperature, improve the low-temperature charge and discharge performance of the battery, and improve the cycle stability of the battery.

[0015] The method for preparing the lithium-ion electrolyte of the present invention involves first mixing a mixed solvent system with a lithium salt, and then adding fluoroboronic acid ester additives and surfactants. The method is simple and feasible, the process conditions are easy to achieve, and it is suitable for large-scale production.

[0016] The lithium-ion battery of the present invention uses an improved lithium-ion electrolyte to increase the migration rate of lithium ions between the positive and negative electrodes, thereby effectively improving the low-temperature discharge performance and low-temperature cycle performance of the lithium-ion battery.

[0017] The method for preparing a lithium-ion battery according to the present invention involves assembling a positive electrode, a separator, and a negative electrode, and then injecting a lithium-ion electrolyte. The preparation method is simple and easy to operate. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is the low-temperature discharge performance curve of the lithium-ion battery of Embodiment 1 of the present invention; Figure 2 This is the low-temperature cycling performance curve of the lithium-ion battery of Embodiment 1 of the present invention; Figure 3 These are low-temperature discharge performance comparison curves of lithium-ion batteries from Example 1 and Comparative Examples 1-4. Detailed Implementation

[0019] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the invention and do not constitute a limitation on the scope of protection of this invention.

[0020] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0021] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0022] This invention proposes a lithium-ion electrolyte comprising the following components: a lithium salt at a concentration of 1 mol / L to 1.5 mol / L, a fluoroboronic acid ester additive at a mass percentage of 1% to 5%, a surfactant at a mass percentage of 0.05% to 1%, and the remainder being a mixed solvent system. The mixed solvent system comprises tris(2,2,2-trifluoroethyl) phosphate (TFEP), 1,3-dioxolane (DOL), and tetrahydrofuran (THF) in a volume ratio of (3-5):(1-3):(2-6).

[0023] Understandably, the concentration of lithium salt can be selected from 1 mol / L, 1.2 mol / L, 1.3 mol / L, or 1.5 mol / L, preferably 1.0 mol / L-1.2 mol / L. The mass percentage of fluoroborate ester additives can be selected from 1%, 2%, 3%, 4%, or 5%, preferably 1%-3%. The mass percentage of surfactants can be selected from 0.05%, 0.1%, 0.5%, 0.8%, or 1%, preferably 0.1%-0.5%. The volume ratio between TFEP, DOL, and THF in the mixed solvent system can be selected from 3:2:5, 4:2:4, 5:2:3, 4:3:3, or 3:1:6, etc.

[0024] Unlike traditional single-solvent systems or common mixed-solvent systems, the mixed-solvent system of this invention introduces a low-melting-point, high-dielectric-constant organic solvent. TFEP, with its low melting point (approximately -80°C), significantly lowers the freezing point of the mixed solvent, thereby improving the fluidity of the electrolyte at low temperatures and reducing viscosity. Simultaneously, the high dielectric constant of TFEP helps enhance the dissociation of lithium salts, increasing ionic conductivity. Furthermore, DOL and THF possess excellent lithium-ion solvation capabilities, promoting lithium-ion transport. This unique mixed-solvent system maintains a high ion migration rate at low temperatures, thus improving the charge-discharge performance of the battery.

[0025] Preferably, the fluorinated borate ester additive can be a bis(fluorosulfonyl)imide lithium (LiFSI) modified borate ester. At low temperatures, the fluorinated borate ester additive can form a stable interfacial film with high lithium-ion conductivity on the electrode surface. On the one hand, it can reduce the charge transfer resistance at the electrode / electrolyte interface, promoting rapid lithium-ion transfer at the interface; on the other hand, this interfacial film can effectively inhibit electrolyte decomposition and improve the cycle stability of the battery.

[0026] In some embodiments, the surfactant is polyethylene glycol dodecyl ether or fatty alcohol polyoxyethylene ether. Adding a small amount of surfactant can improve the wettability of the electrolyte to the electrode material, further increasing the diffusion rate of lithium ions in the electrode pores.

[0027] In some embodiments, the lithium salt may be LiPF6 (lithium hexafluorophosphate), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), or LiBF4 (lithium tetrafluoroborate).

[0028] The electrolyte, as a liquid medium, contains dissolved lithium salts and forms an ion transport network in the organic solvent, providing the necessary environment for the movement of lithium ions between the positive and negative electrodes.

[0029] The lithium-ion electrolyte of this invention uses a mixed solvent system containing TFEP, DOL and THF, which dissolves lithium salt and adds special additives (containing fluoroboronic acid esters and surfactants) to enable lithium ions to maintain a high migration rate at low temperatures, improve the low-temperature charge and discharge performance of the battery, and enhance the cycle stability of the battery.

[0030] The present invention also proposes a method for preparing the above-mentioned lithium-ion electrolyte, comprising the following steps: S1. Tris(2,2,2-trifluoroethyl) phosphate, 1,3-dioxolane and tetrahydrofuran are mixed in a volume ratio of (3-5):(1-3):(2-6), and stirred for the first time in an inert gas atmosphere. Then lithium salt is added and stirred for the second time to obtain a mixed solvent.

[0031] Specifically, step S1 includes: taking TFEP, DOL and THF in a volume ratio of (3-5):(1-3):(2-6), adding them to a dry reaction vessel, and stirring for the first time under the protection of an inert gas to ensure thorough and uniform mixing; then adding an appropriate amount of lithium salt, with its concentration controlled at 1mol / L~1.5mol / L, and stirring for the second time until the lithium salt is completely dissolved to obtain a mixed solvent.

[0032] In step S1, the inert gas is argon or helium. The first stirring is carried out at a speed of 200-300 rpm for 3-5 hours, and the second stirring is carried out at a speed of 200-300 rpm for 8-12 hours. Understandably, the stirring speeds for the first and second stirring can be independently selected as 200 rpm, 230 rpm, 250 rpm, 280 rpm, or 300 rpm, etc. The stirring time for the first stirring can be selected as 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours, etc., and the stirring time for the second stirring can be selected as 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours, etc.

[0033] S2. Fluoroboronic acid ester additives and surfactants are added sequentially to the above mixed solvent, stirred evenly, and then filtered through a filter membrane to obtain lithium-ion electrolyte.

[0034] In step S2, the components of the fluoroboronic acid ester additives and surfactants are the same as described above and will not be repeated here. The pore size of the filter membrane can be 0.1μm~0.8μm, such as 0.1μm, 0.22μm, 0.5μm or 0.8μm. The filter membrane is made of polytetrafluoroethylene (PTFE) or polypropylene (PP) to avoid reaction between the filter membrane and the electrolyte components, thus ensuring the electrochemical stability of the electrolyte.

[0035] The method for preparing the lithium-ion electrolyte of the present invention involves first mixing a mixed solvent system with a lithium salt, and then adding fluoroboronic acid ester additives and surfactants. The method is simple and feasible, the process conditions are easy to achieve, and it is suitable for large-scale production.

[0036] This invention also proposes a lithium-ion battery, comprising the aforementioned lithium-ion electrolyte, a positive electrode, and a negative electrode. The positive electrode includes a positive current collector and a positive electrode slurry loaded on the positive current collector; the positive electrode slurry includes a positive electrode material. The negative electrode includes a negative current collector and a negative electrode slurry loaded on the negative current collector; the negative electrode slurry includes a negative electrode material. The lithium-ion battery also includes a separator disposed between the positive and negative electrode sheets; the separator may be made of polypropylene (PP) or polyethylene (PE). The lithium-ion electrolyte wets the positive electrode, the negative electrode, and the separator.

[0037] Preferably, both the positive and negative current collectors have a porous structure, and the pore size of each current collector is independently 30μm to 300μm, such as 30μm, 60μm, 100μm, 200μm or 300μm, preferably 50μm to 200μm; the porosity is independently 40% to 80%, such as 40%, 50%, 60%, 70% or 80%, preferably 50% to 65%.

[0038] A three-dimensional porous electrode current collector is utilized. This current collector possesses a highly ordered porous network, allowing the electrode material in the electrode slurry to be uniformly loaded within and onto the surface of the porous current collector, forming a three-dimensional electrode structure. At low temperatures, this structure significantly increases the contact area between the electrolyte and the electrode material, shortening the lithium-ion diffusion path and thus improving the power performance and low-temperature charge-discharge efficiency of lithium-ion batteries. Simultaneously, the three-dimensional structure also enhances the mechanical stability of the electrode material, reducing volume changes during charge-discharge processes.

[0039] The cathode material in the cathode slurry includes at least one of lithium iron phosphate (LiFePO4) and lithium phosphate (Li3PO4). In some embodiments, the cathode material includes a first host material, which is lithium iron phosphate, and a lithium phosphate coating is deposited on the surface of the first host material. The first host material is doped with metal ions at an atomic percentage of 0.1% to 5%. The atomic percentage of the metal ions can be 0.1%, 0.5%, 1%, 2%, or 5%, preferably 0.5% to 2%. The metal ions may include at least one of magnesium ions, zirconium ions, and calcium ions.

[0040] In cathode materials, an ultrathin ion-conducting coating, namely a lithium phosphate coating, is deposited on the surface of the first host material. The thickness of this coating is precisely controlled between a few nanometers and tens of nanometers, effectively improving the interfacial properties of the cathode material. For example, the thickness of the lithium phosphate coating can be 5nm to 30nm, specifically 5nm, 10nm, 15nm, 20nm, or 30nm. At low temperatures, the lithium phosphate coating can act as a fast channel for lithium-ion transport, reducing the migration resistance of lithium ions on the cathode material surface. Simultaneously, the crystal structure of the cathode material can be optimized by doping the first host material with a small amount of metal ions, altering the lattice parameters and increasing the diffusion coefficient of lithium ions within the crystal lattice. For instance, doping lithium iron phosphate with 0.5% to 2% magnesium ions can increase the lithium-ion diffusion coefficient by 1-2 orders of magnitude at low temperatures.

[0041] The negative electrode material in the negative electrode slurry includes at least one of graphite and carbon nanomaterials. In some embodiments, the negative electrode material includes a second host material, which is graphite, and carbon nanomaterials are dispersed on the surface and inside the second host material. The mass percentage of carbon nanomaterials in the negative electrode material is 5% to 20%, such as 5%, 8%, 12%, 15%, or 20%.

[0042] In some embodiments, the carbon nanomaterials in the anode material include at least one of graphene quantum dots (GQDs), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon nanohorns (CNHs). Carbon nanomaterials have high specific surface area and good low-temperature performance. Composite carbon nanomaterials with graphite as the second host material can effectively improve the low-temperature performance of the anode material.

[0043] In the electrode material of the present invention, the first main material of the positive electrode material has a surface coating and is doped with metal ions, which can improve the interfacial performance of the positive electrode material and increase the diffusion rate of lithium ions in the positive electrode material; the second main material of the negative electrode material has carbon nanomaterials dispersed on both the surface and inside, which can effectively improve the low-temperature performance of the negative electrode material.

[0044] Furthermore, the preparation method of the above-mentioned electrode materials (including positive electrode materials and negative electrode materials) includes the following steps: S1. Preparation of cathode material: A lithium phosphate coating is formed by surface deposition on the first host material, followed by metal ion doping to obtain the cathode material. The first host material is lithium iron phosphate.

[0045] In surface deposition, lithium and phosphorus precursors are used, and a lithium phosphate coating is formed by 20 to 150 deposition cycles on the surface of a first host material in a reactive gas atmosphere. The number of deposition cycles can be selected based on the thickness of each deposition and the desired coating thickness. For example, if the thickness of each deposition cycle is approximately 0.2 nm, then 25 deposition cycles are required to obtain a 5 nm thick lithium phosphate coating.

[0046] In some embodiments, the lithium precursor includes at least one of lithium tert-butoxide, lithium isopropoxide, lithium n-butoxide, and lithium tert-pentoxide, and the phosphorus precursor includes at least one of tris(dimethylamino)phosphine, tris(dimethylamino)iminophosphine, and bis(trimethylsilyl)aminophosphine, and the reaction gas is oxygen or ozone.

[0047] In some embodiments, the surface deposition temperature is 200°C to 300°C, and can be selected from 200°C, 230°C, 250°C, 280°C, or 300°C; the pressure is 130Pa to 1300Pa, and can be selected from 130Pa, 300Pa, 600Pa, 900Pa, or 1300Pa. The surface deposition method can employ existing technologies, such as atomic layer deposition (ALD) or atomic layer sputtering (ALS), and surface deposition can be performed in the corresponding deposition equipment.

[0048] In metal ion doping, the first host material is added to a metal salt solution and stirred, then filtered and washed. The resulting filter cake is calcined to obtain the cathode material. The metal salt solution is prepared by dissolving a metal salt in deionized water, and its concentration can be 0.01 mol / L to 0.05 mol / L, such as 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, or 0.05 mol / L. The metal salt in the solution includes at least one of magnesium nitrate, calcium nitrate, and zirconium nitrate.

[0049] Specifically, metal ion doping includes: adding the first host material LiFePO4 to a metal salt solution and stirring at room temperature for 2-4 hours to allow the metal ions in the metal salt solution to be uniformly adsorbed on the surface of the first host material; after the stirring at room temperature is completed, the mixture (suspension) of the metal salt solution and the first host material is transferred to a Buchner funnel for filtration (vacuum filtration), then the filter cake is washed with deionized water to remove the residual metal salt solution on the surface of the filter cake, then the moisture in the filter cake is dried, and finally high-temperature calcination is performed to complete the metal ion doping and obtain the cathode material.

[0050] The specific filtration procedure is as follows: Install the Buchner funnel on the filtration flask beforehand, and line the funnel with a layer of qualitative filter paper matching the funnel size. Moisten the filter paper with a small amount of deionized water, ensuring a tight seal between the filter paper and the bottom of the funnel to prevent solid particles from leaking out during filtration. Turn on the vacuum pump and slowly pour the stirred suspension into the Buchner funnel. The negative pressure forces the liquid to quickly pass through the filter paper into the filtration flask, while the LiFePO4 solid particles are trapped on the filter paper. If there is too much liquid in the funnel during this process, pause pouring and wait for the liquid level to drop before continuing to avoid overflow. After all the suspension has been transferred, keep the vacuum pump running for 1-2 minutes to remove as much residual liquid as possible from the filter cake, reducing the burden of subsequent washing.

[0051] After filtration, the washing procedure is as follows: Use a pipette to draw an appropriate amount of deionized water and slowly and evenly pour it onto the filter cake, ensuring the water flow covers the entire surface while avoiding excessive impact that could loosen or disintegrate the cake. Simultaneously add water and perform vacuum filtration. After the washing water has completely filtered out, repeat the washing process 2-3 times to thoroughly remove residual metal salts and other impurities. After each wash, collect a small amount of filtrate for testing. This can be done by adding an appropriate amount of carbonate solution and observing whether a white precipitate forms. If no precipitate forms, the washing is complete; if precipitate still forms, continue washing until no metal ions are detectable in the filtrate. After the final wash, keep the vacuum pump running for 3-5 minutes to remove as much moisture as possible from the filter cake, preparing for subsequent high-temperature calcination.

[0052] In some embodiments, the calcination temperature can be 700℃~800℃, and can be selected from 700℃, 730℃, 750℃, 770℃ or 800℃, etc.; the calcination time can be 4~6 hours, and can be selected from 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, etc.

[0053] S2. Preparation of negative electrode material: A composite solution containing carbon nanomaterials is prepared. The second host material is mixed with the composite solution, and a co-precipitation treatment is performed to allow the carbon nanomaterials to adhere to the second host material. Then, a pyrolysis treatment is performed to obtain the negative electrode material. The second host material is graphite.

[0054] In some embodiments, the step of preparing a composite solution containing carbon nanomaterials includes: adding carbon nanomaterials to deionized water to prepare a mixture with a concentration of 0.5 mg / mL to 1 mg / mL, adding an appropriate amount of dispersant, magnetically stirring, and then ultrasonically treating to obtain a uniformly dispersed composite solution. The concentration of the mixture can be 0.5 mg / mL, 0.8 mg / mL, or 1 mg / mL, etc.

[0055] In some embodiments, the carbon nanomaterials include GQDs and CNTs, with a mass ratio of GQDs to CNTs of 1:(2-4), such as 1:2, 1:3, or 1:4. The particle size of the GQDs can be 2nm-10nm, such as 2nm, 4nm, 6nm, 8nm, or 10nm. The diameter of the CNTs can be 10nm-20nm, such as 10nm, 12nm, 15nm, 18nm, or 20nm; the length of the CNTs can be 5μm-10μm, such as 5μm, 7μm, 9μm, or 10μm. The mass percentage of the carbon nanomaterials in the final anode material can be 10%-15%, such as 10%, 12%, 13%, or 15%.

[0056] The dispersant can be sodium dodecylbenzenesulfonate, and the amount of dispersant added can be 4%-6% of the total mass of carbon nanomaterials, such as 4%, 5%, or 6%. Magnetic stirring time can be 20-40 minutes, such as 20, 25, 30, 35, or 40 minutes. Ultrasonic treatment can be performed using an ultrasonic cell disruptor, and the ultrasonic treatment time can be 0.5-1.5 hours, such as 0.5 hours, 1 hour, or 1.5 hours. The ultrasonic power can be 200W-400W, such as 200W, 300W, or 400W, with a 3-second operation followed by a 2-second pause.

[0057] In some embodiments, before the second host material is mixed with the composite solution, the second host material is pretreated. The pretreatment includes: adding the second host material to an acidic solvent for acid washing to remove impurities (such as metal ions and oxides) from its surface; then repeatedly centrifuging and washing with deionized water until the pH of the filtrate is neutral, and then vacuum drying.

[0058] The second main material is natural graphite powder or artificial graphite powder, and its particle size can be 5μm-20μm, such as 5μm, 10μm, 15μm, or 20μm. The acidic solvent can be hydrochloric acid solution with a concentration of 1mol / L-2mol / L, such as 1mol / L, 1.5mol / L, or 2mol / L. Acid washing can be performed by stirring at 50-70℃ for 1.5-2.5 hours, where the temperature can be 50℃, 55℃, 60℃, 65℃, or 70℃, and the time can be 1.5 hours, 2 hours, or 2.5 hours. Vacuum drying can be performed in a vacuum drying oven at 70-90℃ for 10-14 hours, where the temperature can be 70℃, 75℃, 80℃, 85℃, or 90℃, and the time can be 10 hours, 11 hours, 12 hours, 13 hours, or 14 hours.

[0059] Further, the step of mixing the second host material with the composite solution includes: adding the pretreated second host material to the composite solution and magnetically stirring to ensure the second host material is fully impregnated. The solid-liquid ratio of the second host material to the composite solution can be 1:(8-12) (g / mL), such as 1:8, 1:10, or 1:12. The magnetic stirring temperature can be 25-35℃, such as 25℃, 30℃, or 35℃, and the stirring time can be 1.5-2.5 hours, such as 1.5 hours, 2 hours, or 2.5 hours.

[0060] The coprecipitation process includes: adding an aluminum salt, then adding an alkaline solvent, adjusting the pH to alkaline, reacting to form a colloid, centrifuging to collect the precipitate, washing and drying to obtain the precursor material. The aluminum salt can be an aluminum nitrate solution, an aluminum sulfate solution, an aluminum chloride solution, or an aluminum acetate solution.

[0061] Specifically, the co-precipitation treatment includes: slowly adding aluminum salt with a concentration of 0.05 mol / L to 0.15 mol / L to a mixture of the second host material and the composite solution, stirring for 20-40 minutes, and then adding alkaline solvent with a concentration of 0.5 mol / L to 1.5 mol / L dropwise to adjust the pH of the system to 8-9. At this point, the aluminum ions of the aluminum salt hydrolyze to generate aluminum hydroxide colloid, which anchors the carbon nanomaterials on the surface and pores of the second host material through adsorption. After the addition is complete, constant temperature stirring is performed to promote complete precipitation reaction; the mixture after reaction is centrifuged, the precipitate is collected, and the precipitate is repeatedly washed with deionized water until the pH of the filtrate is neutral to remove residual alkaline solvent and dispersant in the precipitate, and then washed once with anhydrous ethanol to reduce agglomeration during the subsequent drying process; finally, the washed precipitate is vacuum dried to remove water and anhydrous ethanol to obtain the dried precursor material.

[0062] The aluminum salt is added at a rate of 2%-4% of the mass percentage of the second main material, such as 2%, 3%, or 4%. Ammonia can be used as the alkaline solvent. The constant temperature stirring temperature is 40℃-60℃, such as 40℃, 50℃, or 60℃, for 0.5-1.5 hours, such as 0.5 hours, 1 hour, or 1.5 hours. The centrifugation speed is 3000 r / min-7000 r / min, such as 3000 r / min, 5000 r / min, or 7000 r / min, for 8-12 minutes, such as 8 minutes, 10 minutes, or 12 minutes. The vacuum drying temperature is 50℃-70℃, such as 50℃, 60℃, or 70℃, for 7-9 hours, such as 7 hours, 8 hours, or 9 hours.

[0063] In some embodiments, the pyrolysis treatment includes two stages: first, heating to 550℃-650℃ at a rate of 4℃ / min-6℃ / min and holding at that temperature for 1.5-2.5 hours; then heating to 850℃-950℃ at a rate of 2℃ / min-4℃ / min and holding at that temperature for 3.5-4.5 hours. The heating rate during the 550℃-650℃ (e.g., 600℃) holding stage can be 4℃ / min, 5℃ / min, or 6℃ / min, and the holding time can be 1.5 hours, 2 hours, or 2.5 hours, etc. This holding stage primarily removes organic impurities (such as residual dispersants) and decomposition products (alumina) of aluminum hydroxide colloids from the precursor material. The heating rate in the high-temperature stage of 850℃-950℃ (e.g., 900℃) can be 4℃ / min, 5℃ / min, or 6℃ / min, and the holding time can be 3.5 hours, 4 hours, or 4.5 hours. This high-temperature stage promotes the graphitization degree of carbon nanomaterials on the surface of the second host material, graphite. At the same time, through thermal diffusion, some carbon nanomaterials enter the internal pores of graphite particles to form a stable composite structure.

[0064] After the pyrolysis process is completed, cooling is performed, including: turning off the heating device (such as a tube furnace), maintaining an inert gas (such as argon) atmosphere until the heating device cools naturally to room temperature, and then removing the product.

[0065] Further, the product undergoes post-processing, including grinding and sieving, to obtain the final negative electrode material. Specifically, grinding can be done gently using an agate mortar, and sieving is performed through a 150-250 mesh sieve.

[0066] Through the above steps, the initial anchoring of carbon nanomaterials is achieved through the colloidal adsorption effect of chemical co-precipitation. Combined with the diffusion and stabilization effects of high-temperature pyrolysis, the carbon nanomaterials are ensured to be uniformly dispersed in the second host material, the graphite matrix, ultimately forming a composite structure with both high conductivity and low-temperature lithium-ion transport capability. Specifically, the carbon nanomaterials GQDs possess abundant edge active sites, enabling rapid adsorption and transport of lithium ions at low temperatures, while CNTs can construct an efficient electron transport network, improving the conductivity of the anode material. The composite structure of carbon nanomaterials and the second host material effectively reduces the internal resistance of the anode material at low temperatures, improving the lithium-ion insertion and extraction efficiency.

[0067] In other embodiments, in step S2, other methods can be used to attach the carbon nanomaterials to the second host material. Specifically, the step of preparing the composite solution containing carbon nanomaterials includes: adding the carbon nanomaterials to a dispersant and ultrasonically treating it for 2-3 hours to uniformly disperse the carbon nanomaterials and form a composite solution. The carbon nanomaterials include GQDs and CNTs, and the mass ratio between GQDs and CNTs can be 1:(2-4), such as 1:2, 1:3, or 1:4; the dispersant is ethanol.

[0068] Further, the step of mixing the second host material with the composite solution includes: adding graphite powder, the second host material, to the composite solution, mixing under stirring, and then evaporating a dispersant to allow the carbon nanomaterials to adhere to the second host material, thus obtaining a mixture. The evaporation temperature of the dispersant can be 60℃-80℃, such as 60℃, 70℃, or 80℃. Further still, the resulting mixture is subjected to pyrolysis treatment to form a negative electrode material. The pyrolysis treatment temperature is 900℃-1000℃, such as 900℃, 950℃, or 1000℃, and the time is 2-3 hours, such as 2 hours, 2.5 hours, or 3 hours.

[0069] In the electrode material preparation method of the present invention, by performing surface deposition and metal ion doping on the first host material of the positive electrode material, the migration resistance of lithium ions on the surface of the positive electrode material can be reduced and the diffusion coefficient of lithium ions in the positive electrode material can be improved; by performing co-precipitation treatment and pyrolysis treatment on the second host material of the negative electrode material, the carbon nanomaterial is ensured to be uniformly dispersed in the second host material, effectively reducing the internal resistance of the negative electrode material at low temperature and improving the insertion and extraction efficiency of lithium ions.

[0070] The positive electrode slurry also includes a first conductive agent and a first binder, and the negative electrode slurry also includes a second conductive agent and a second binder. The volume ratio of the positive electrode material, the first conductive agent, and the first binder is (7-9):(0.5-1.5):(0.5-1.5), for example, 8:1:1, 7:1.5:1.5, 9:0.5:0.5, etc. The volume ratio of the negative electrode material, the second conductive agent, and the second binder is (80-90):(4-6):(6-14), for example, 85:5:10, 80:6:14, 90:4:6, etc.

[0071] In some embodiments, the first conductive agent and the second conductive agent each independently include at least one of acetylene black, conductive carbon black, and carbon nanotubes. For example, the first conductive agent is acetylene black, and the second conductive agent is conductive carbon black. The first binder and the second binder each independently include at least one of polyvinylidene fluoride, styrene-butadiene rubber, and polyacrylic acid. For example, the first binder is polyvinylidene fluoride, and the second binder is styrene-butadiene rubber.

[0072] Furthermore, the method for preparing the electrode sheets (including positive and negative electrode sheets) includes the following steps: R1. Preparation of the positive electrode: R1.1 The above-mentioned positive electrode material is mixed with the first conductive agent and the first binder, and an appropriate amount of the first solvent is added. After stirring, a positive electrode slurry is obtained. The compositions of the first conductive agent and the first binder are as described above and will not be repeated here. The volume ratio of the positive electrode material, the first conductive agent, and the first binder is (7-9):(0.5-1.5):(0.5-1.5). The first solvent is used to dissolve the first binder, polyvinylidene fluoride, and to control the properties of the positive electrode slurry. The amount of the first solvent added can be selected according to actual needs (such as the viscosity of the positive electrode slurry), and this invention does not impose specific limitations. The first solvent can be N-methylpyrrolidone (NMP) solvent.

[0073] R1.2 The positive electrode slurry is coated onto the porous positive electrode current collector described above, then dried and stamped to obtain the positive electrode sheet. The positive electrode current collector can be an aluminum foil current collector. Drying is performed under vacuum at 80℃-100℃ for 12-16 hours. The drying temperature can be 80℃, 90℃, or 100℃, and the drying time can be 12 hours, 14 hours, or 16 hours, etc.

[0074] R2. Preparation of the negative electrode: R2.1 The above-mentioned negative electrode material is mixed with the second conductive agent and the second binder, and an appropriate amount of the second solvent is added. After stirring, a negative electrode slurry is obtained. The compositions of the second conductive agent and the second binder are as described above and will not be repeated here. The volume ratio of the negative electrode material, the second conductive agent, and the second binder is (80-90):(4-6):(6-14). The second solvent can be deionized water.

[0075] R2.2 The negative electrode slurry is coated onto the porous negative electrode current collector described above, then dried and stamped to obtain the negative electrode sheet. The negative electrode current collector can be a copper foil current collector. Drying is performed under vacuum at 60℃-80℃ for 8-12 hours. The drying temperature can be 60℃, 70℃, or 80℃, and the drying time can be 8 hours, 10 hours, or 12 hours, etc.

[0076] In the electrode sheet preparation method of the present invention, the electrode material is mixed with a conductive agent and a binder to form an electrode slurry, and then the electrode slurry is loaded onto a porous electrode current collector and dried under vacuum to form an electrode sheet. The preparation method is simple, feasible and easy to operate.

[0077] The lithium-ion battery of the present invention uses an improved lithium-ion electrolyte to increase the migration rate of lithium ions between the positive and negative electrodes, thereby effectively improving the low-temperature discharge performance and low-temperature cycle performance of the lithium-ion battery.

[0078] This invention also proposes a method for preparing the aforementioned lithium-ion battery, comprising the following steps: assembling a positive electrode, a separator, and a negative electrode into a battery cell, and then injecting the aforementioned lithium-ion electrolyte into the battery cell to obtain a lithium-ion battery. The positive electrode, separator, and negative electrode are assembled into a battery cell in sequence, which can employ a winding or stacking assembly process. This assembly process can refer to existing technologies, and its process parameters can be selected according to actual needs, without specific limitations here. During the assembly process, good contact between the electrode and the separator is ensured.

[0079] The method for preparing a lithium-ion battery according to the present invention involves assembling a positive electrode, a separator, and a negative electrode, and then injecting a lithium-ion electrolyte. The preparation method is simple and easy to operate.

[0080] This invention relates to novel lithium-ion electrolyte formulations and their preparation methods, modified electrode materials and their preparation methods, and integrated battery structures and their preparation methods. It aims to fundamentally solve core problems such as hindered ion transport, deterioration of electrode kinetic performance, and surge in interface impedance under low-temperature conditions, and achieves high-capacity output and efficient charge-discharge stability of lithium-ion batteries under extremely cold conditions of -30℃ to -40℃.

[0081] The following is an illustration through specific examples: Example 1 A lithium-ion electrolyte comprises the following components: a lithium salt at a concentration of 1.2 mol / L, a fluorinated borate ester additive at a mass percentage of 2.5%, a surfactant at a mass percentage of 0.3%, and the remainder being a mixed solvent system. The mixed solvent system comprises TFEP, DOL, and THF in a volume ratio of 3:2:5; the fluorinated borate ester additive is a LiFSI-modified borate ester; the surfactant is polyethylene glycol dodecyl ether; and the lithium salt is LiPF6.

[0082] A method for preparing the above-mentioned lithium-ion electrolyte includes the following steps: S1. Take TFEP, DOL, and THF in a volume ratio of 3:2:5 and add them to a dry reactor. Stir for the first time under argon atmosphere. Then add an appropriate amount of lithium salt, with the concentration controlled at 1.2 mol / L, and stir for the second time until the lithium salt is completely dissolved to obtain a mixed solvent. The first stirring is carried out at a speed of 250 r / min for 4 hours, and the second stirring is carried out at a speed of 250 r / min for 10 hours.

[0083] S2. Fluoroboronic acid ester additives and surfactants are added sequentially to the above mixed solvent. After stirring evenly, the mixture is filtered through a filter membrane to obtain a lithium-ion electrolyte. The pore size of the filter membrane can be 0.22 μm, and the filter membrane is composed of polytetrafluoroethylene.

[0084] A lithium-ion battery includes the aforementioned lithium-ion electrolyte, a positive electrode, and a negative electrode. The positive electrode includes a positive current collector and a positive electrode slurry loaded on the positive current collector; the positive electrode slurry includes a positive electrode material. The negative electrode includes a negative current collector and a negative electrode slurry loaded on the negative current collector; the negative electrode slurry includes a negative electrode material. The lithium-ion battery also includes a separator disposed between the positive and negative electrode sheets; the separator may be made of polypropylene. The lithium-ion electrolyte wets the positive electrode, the negative electrode, and the separator.

[0085] Both the positive and negative current collectors have porous structures, with a pore size of 100 μm and a porosity of 60%.

[0086] The cathode material includes a first host material, which is lithium iron phosphate. A lithium iron phosphate coating with a thickness of 5 nm is deposited on the surface of the first host material. The first host material is doped with 1.5% metal ions, including magnesium ions and zirconium ions.

[0087] The negative electrode material includes a second host material, which is graphite. Carbon nanomaterials are dispersed on the surface and inside the second host material. The carbon nanomaterials include GQDs and CNTs. The mass percentage of carbon nanomaterials in the negative electrode material is 10%.

[0088] Furthermore, the preparation method of the above-mentioned electrode materials (including positive electrode materials and negative electrode materials) includes the following steps: S1. Preparation of cathode material: A lithium phosphate coating is formed by surface deposition on the first host material, followed by metal ion doping to obtain the cathode material. The first host material is lithium iron phosphate.

[0089] Surface deposition involves using lithium and phosphorus precursors, and performing 25 deposition cycles on the surface of a first host material in a reaction gas atmosphere. Each cycle deposits a thickness of approximately 0.2 nm, forming a 5 nm thick lithium phosphate coating. The lithium precursors include lithium tert-butoxide and lithium isopropoxide, the phosphorus precursor is tris(dimethylamino)phosphine, and the reaction gas is oxygen. Surface deposition is performed in the reaction chamber of an ALD device at a temperature of 250°C and a pressure of 600 Pa.

[0090] Metal ion doping involves: adding the first host material, LiFePO4, to a 0.03 mol / L metal salt solution and stirring at room temperature for 3 hours; after stirring at room temperature, transferring the mixture of the metal salt solution and the first host material (suspension) to a Buchner funnel for filtration (vacuum filtration); washing the filter cake with deionized water; drying the filter cake; and finally calcining at high temperature to complete metal ion doping and obtain the cathode material. The metal salt solution is prepared by dissolving metal salts in deionized water, and the metal salts in the solution include magnesium nitrate and calcium nitrate. The calcination temperature is 750℃, and the time is 5 hours.

[0091] S2. Preparation of negative electrode material: A composite solution containing carbon nanomaterials is prepared. The second host material is mixed with the composite solution, and a co-precipitation treatment is performed to allow the carbon nanomaterials to adhere to the second host material. Then, a pyrolysis treatment is performed to obtain the negative electrode material. The second host material is natural graphite powder with a particle size of 15 μm.

[0092] The steps for preparing a composite solution containing carbon nanomaterials include: adding carbon nanomaterials to deionized water to prepare a mixture with a concentration of 0.8 mg / mL; adding an appropriate amount of dispersant; magnetically stirring for 30 minutes; and then sonicating for 1 hour using an ultrasonic cell disruptor at a power of 300 W, with a 3-second operation followed by a 2-second pause, to obtain a uniformly dispersed composite solution. The carbon nanomaterials consist of GQDs and CNTs in a mass ratio of 1:3, with GQDs having a particle size of 6 nm, CNTs having a diameter of 15 nm, and CNTs having a length of 8 μm. The mass percentage of carbon nanomaterials in the final negative electrode material is 13%. The dispersant is sodium dodecylbenzenesulfonate, added at 5% of the total mass of the carbon nanomaterials.

[0093] Before mixing the second main material with the composite solution, the second main material is pretreated. The pretreatment includes: adding the second main material to a 1 mol / L hydrochloric acid solution for acid washing, stirring at 60°C for 2 hours; then repeatedly centrifuging and washing with deionized water until the pH of the filtrate is neutral, and then drying in a vacuum drying oven at 80°C for 12 hours.

[0094] Furthermore, the step of mixing the second host material with the composite solution includes: adding the pretreated second host material to the composite solution and magnetically stirring at 30°C for 2 hours. The solid-liquid ratio of the second host material to the composite solution can be 1:10 (g / mL).

[0095] The coprecipitation treatment included: slowly adding a 0.1 mol / L aluminum nitrate solution dropwise to a mixture of the second host material and the composite solution, stirring for 30 minutes, then adding a 1.0 mol / L ammonia solution dropwise to adjust the pH of the system to 8.5; subsequently, stirring at 50°C for 1 hour, then centrifuging the resulting mixture at 7000 r / min for 10 minutes, collecting the precipitate, repeatedly washing the precipitate with deionized water until the pH of the filtrate was neutral, and then washing once with anhydrous ethanol; finally, vacuum drying the washed precipitate at 60°C for 8 hours to obtain the dried precursor material. The amount of aluminum nitrate solution added was 3% of the mass percentage of the second host material.

[0096] The pyrolysis treatment consists of two stages: first, the temperature is increased to 600℃ at a rate of 5℃ / min and held for 2 hours; then, the temperature is increased to 900℃ at a rate of 3℃ / min and held for 4 hours.

[0097] After the pyrolysis process, cooling is performed, including: turning off the heating device (tube furnace), maintaining an argon atmosphere until the heating device cools naturally to room temperature, and then removing the product. The product is then post-processed, including: gently grinding the product with an agate mortar and pestle, and then passing it through a 150-250 mesh sieve to obtain the final anode material.

[0098] The positive electrode slurry further includes a first conductive agent and a first binder, and the negative electrode slurry further includes a second conductive agent and a second binder. The volume ratio of the positive electrode material, the first conductive agent, and the first binder is 8:1:1. The volume ratio of the negative electrode material, the second conductive agent, and the second binder is 85:5:10. The first conductive agent is acetylene black, and the second conductive agent is conductive carbon black. The first binder is polyvinylidene fluoride, and the second binder is styrene-butadiene rubber.

[0099] Furthermore, the method for preparing the electrode sheets (including positive and negative electrode sheets) includes the following steps: R1. Preparation of the positive electrode: R1.1 The above-mentioned positive electrode material is mixed with the first conductive agent and the first binder in a volume ratio of 8:1:1, and an appropriate amount of the first solvent is added. After stirring, a positive electrode slurry is obtained. The first solvent is NMP solvent.

[0100] R1.2. The positive electrode slurry is coated onto the above-mentioned porous positive electrode current collector, then vacuum dried at 90°C for 14 hours and stamped to obtain the positive electrode sheet. The positive electrode current collector is an aluminum foil current collector.

[0101] R2. Preparation of the negative electrode: R2.1. The above-mentioned negative electrode material is mixed with the second conductive agent and the second binder at a volume ratio of 85:5:10, and an appropriate amount of the second solvent is added. After stirring, a negative electrode slurry is obtained. The second solvent is deionized water.

[0102] R2.2. The negative electrode slurry is coated onto the above-mentioned porous negative electrode current collector, then vacuum dried at 70°C for 10 hours and stamped to obtain the negative electrode sheet. The negative electrode current collector can be a copper foil current collector.

[0103] A method for preparing the above-mentioned lithium-ion battery includes the following steps: assembling a positive electrode, a separator, and a negative electrode into a battery cell, and then injecting the above-mentioned lithium-ion electrolyte into the battery cell to obtain a lithium-ion battery. The positive electrode, separator, and negative electrode are assembled into the battery cell in sequence using a winding assembly process.

[0104] Example 2 The difference between this embodiment and Embodiment 1 is that the lithium-ion electrolyte comprises the following components: a lithium salt with a concentration of 1.0 mol / L, a 1.5% (w / w) fluoroboronic acid ester additive, a 0.1% (w / w) surfactant, and the remainder being a mixed solvent system. The mixed solvent system comprises TFEP, DOL, and THF in a volume ratio of 4:2:4; the fluoroboronic acid ester additive is a LiFSI-modified borate ester; the surfactant is a fatty alcohol polyoxyethylene ether; and the lithium salt is LiTFSI.

[0105] The rest is the same as in Example 1, and will not be repeated here.

[0106] Example 3 The difference between this embodiment and Example 1 is that the lithium-ion electrolyte comprises the following components: a lithium salt with a concentration of 1.4 mol / L, a 4% (w / w) fluorinated borate ester additive, a 0.8% (w / w) surfactant, and the remainder being a mixed solvent system. The mixed solvent system comprises TFEP, DOL, and THF in a volume ratio of 5:2:3; the fluorinated borate ester additive is a LiFSI-modified borate ester; the surfactant is polyethylene glycol dodecyl ether; and the lithium salt is LiFSI.

[0107] The rest is the same as in Example 1, and will not be repeated here.

[0108] Comparative Example 1 The difference between this comparative example and Example 1 is that a conventional lithium-ion electrolyte, namely the electrolyte system of "ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethyl methyl carbonate (EMC) + lithium hexafluorophosphate (LiPF6)," is used, and the system contains no special additives. The rest is the same as in Example 1 and will not be repeated here.

[0109] Comparative Example 2 The difference between this comparative example and Example 1 is that a conventional cathode material (lithium iron phosphate) is used, which has not undergone surface deposition and metal ion doping. The rest is the same as in Example 1 and will not be repeated here.

[0110] Comparative Example 3 The difference between this comparative example and Example 1 is that a conventional negative electrode material (graphite material) is used, without composite carbon nanomaterials. The rest is the same as Example 1 and will not be repeated here.

[0111] Comparative Example 4 The difference between this comparative example and Example 1 is that a conventional planar current collector (non-porous current collector) is used. Everything else is the same as in Example 1 and will not be repeated here.

[0112] Performance testing: The lithium-ion battery of Example 1 was subjected to 1C discharge performance tests at 25°C, -30°C, and -40°C, respectively. The test results are as follows: Figure 1 As shown. The lithium-ion battery of Example 1 was subjected to 0.5C cycle performance tests at -30℃ and -40℃, respectively. The test results are as follows. Figure 2 As shown. The lithium-ion batteries of Example 1 and Comparative Examples 1-4 were subjected to a -40°C low-temperature discharge performance test. The test results are as follows. Figure 3 As shown.

[0113] according to Figure 1 It can be seen that the lithium-ion battery of Example 1 has a low-temperature discharge efficiency (capacity retention rate) of up to 70% at -30℃ and a low-temperature discharge efficiency of up to 68% at -40℃, demonstrating that the lithium-ion battery of the present invention has excellent low-temperature discharge performance. Figure 2 It can be seen that the lithium-ion battery of Example 1 has a cycle life of 1050 cycles and a capacity retention rate of 80% at -30℃, while it has a cycle life of 950 cycles and a capacity retention rate of 80% at -40℃. This shows that the lithium-ion battery of the present invention has excellent cycle performance at low temperatures.

[0114] according to Figure 3 It can be seen that the low-temperature capacity retention rate of Comparative Example 1 is only 58%, the low-temperature discharge efficiency of Comparative Example 2 is only 57%, the low-temperature capacity retention rate of Comparative Example 3 is only 56%, and the low-temperature capacity retention rate of Comparative Example 4 is only 55%; while the low-temperature capacity retention rate of Example 1 of the present invention is 68%, which is significantly better than the low-temperature discharge performance of Comparative Examples 1-4.

[0115] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0116] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A lithium-ion electrolyte, characterized in that, It comprises the following components: lithium salt with a concentration of 1 mol / L to 1.5 mol / L, fluorinated borate ester additives with a mass percentage of 1% to 5%, surfactants with a mass percentage of 0.05% to 1%, and the remainder being a mixed solvent system; the mixed solvent system comprises tris(2,2,2-trifluoroethyl) phosphate, 1,3-dioxolane and tetrahydrofuran in a volume ratio of (3-5):(1-3):(2-6).

2. The lithium-ion electrolyte according to claim 1, characterized in that, The fluorinated borate ester additive is a borate ester modified with lithium bis(fluorosulfonyl)imide.

3. The lithium-ion electrolyte according to claim 1, characterized in that, The surfactant is polyethylene glycol dodecyl ether or fatty alcohol polyoxyethylene ether.

4. The lithium-ion electrolyte according to claim 1, characterized in that, The lithium salt is LiPF6, LiTFSI, LiFSI, or LiBF4.

5. A method for preparing the lithium-ion electrolyte according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Tris(2,2,2-trifluoroethyl) phosphate, 1,3-dioxolane and tetrahydrofuran are mixed in a volume ratio of (3-5):(1-3):(2-6), and stirred for the first time in an inert gas atmosphere. Then lithium salt is added and stirred for the second time to obtain a mixed solvent. S2. The fluorinated borate ester additive and the surfactant are added sequentially to the mixed solvent, stirred evenly, and then filtered through a filter membrane to obtain a lithium-ion electrolyte.

6. The method for preparing the lithium-ion electrolyte according to claim 5, characterized in that, In step S1, the first stirring is performed at a speed of 200 r / min to 300 r / min for 3 to 5 hours; and / or, The second stirring is performed at a speed of 200 rpm to 300 rpm for 8 to 12 hours; and / or, The inert gas is argon or helium.

7. The method for preparing the lithium-ion electrolyte according to claim 5, characterized in that, In step S2, the pore size of the filter membrane is 0.1~0.8μm.

8. A lithium-ion battery, characterized in that, Includes the lithium-ion electrolyte, positive electrode, and negative electrode as described in any one of claims 1 to 4; The positive electrode sheet includes a positive current collector and a positive electrode slurry loaded on the positive current collector, the positive electrode slurry including a positive electrode material; the negative electrode sheet includes a negative current collector and a negative electrode slurry loaded on the negative current collector, the negative electrode slurry including a negative electrode material.

9. The lithium-ion battery according to claim 8, characterized in that, Both the positive electrode current collector and the negative electrode current collector have a porous structure, and the pore size of the positive electrode current collector and the negative electrode current collector are each independently 50~200μm, and the porosity is each independently 50~65%. The cathode material includes at least one of lithium iron phosphate and lithium phosphate; and / or, The negative electrode material includes at least one of graphite and carbon nanomaterials.

10. A method for preparing a lithium-ion battery, characterized in that, The process includes the following steps: assembling a positive electrode, a separator, and a negative electrode into a battery cell, and then injecting the lithium-ion electrolyte according to any one of claims 1 to 4 into the battery cell to obtain a lithium-ion battery.

Images