A lithium ion battery and a preparation method thereof

Abstract

This application relates to a lithium-ion battery and its preparation method, comprising the following components: a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte; the positive electrode sheet includes a pretreated positive current collector, a graphene-cyclodextrin crosslinked polymer slurry, and a positive electrode material slurry; the negative electrode sheet includes a pretreated negative current collector and a negative electrode material slurry; the positive electrode material slurry includes LiFePO4@Y-Lu co-doped lithium manganese-based core-shell positive electrode material, acetylene black, and PVDF; the negative electrode material slurry includes a silicon suboxide / graphene / carbon nanotube composite negative electrode material and PVDF. This lithium-ion battery exhibits a 5C rate discharge performance >94% and a capacity retention rate >84% after 500 cycles.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage due to their high energy density and long cycle life. However, with the continuous improvement of application requirements, traditional lithium-ion batteries still have the following problems in fast charging scenarios: Insufficient rate performance: significant polarization during high-rate charging and discharging, resulting in a decrease in capacity retention and difficulty in meeting the needs of fast charging; Short cycle life: the positive electrode structure is prone to distortion during long-term charging and discharging, leading to rapid capacity decay and limited lifespan.

[0003] Existing technologies typically employ methods such as element doping or surface coating for improvement, but a single modification method is insufficient to simultaneously achieve high-rate performance and long cycle life, and the overall electrochemical performance of the battery still needs to be improved. Summary of the Invention

[0004] This invention provides a lithium-ion battery and its preparation method, which improves the rate performance and service life of lithium-ion batteries.

[0005] In a first aspect, this application provides a lithium-ion battery comprising the following components: a positive electrode, a separator, a negative electrode, and an electrolyte; the positive electrode comprises a pretreated positive current collector, a graphene-cyclodextrin crosslinked polymer slurry, and a positive electrode material slurry; the negative electrode comprises a pretreated negative current collector and a negative electrode material slurry; the positive electrode material slurry comprises LiFePO4@Y-Lu co-doped lithium manganese-based core-shell positive electrode material, acetylene black, and PVDF; the negative electrode material slurry comprises a silicon suboxide / graphene / carbon nanotube composite negative electrode material and PVDF.

[0006] By adopting the above technical solution, this application provides a lithium-ion battery with a 5C rate discharge performance >94% and a capacity retention rate >84% after 500 cycles. This is likely because, on the one hand, Y-Lu co-doping plays a synergistic role; Y element expands the lattice spacing to promote lithium-ion diffusion, while Lu element enhances lattice stability, and the combination of the two optimizes ion transport and structural stability. On the other hand, the LiFePO4 coating layer forms a stable ion-conducting interface on the surface of the cathode material, reducing side reactions between the cathode material and the electrolyte. Furthermore, this improves rate performance and cycle stability.

[0007] Optionally, in the positive electrode slurry of the positive electrode sheet, the raw materials for preparing the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell positive electrode material include a Y-Lu co-doped lithium manganese-based core.

[0008] Optionally, the preparation method of the Y-Lu co-doped lithium manganese-based core includes the following steps: a1: NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, Y(NO3)3·6H2O and Lu(NO3)3·6H2O are dissolved together in water to obtain a mixed salt solution; a2: Under the conditions of 55-65℃, inert gas protection, and stirring, the mixed salt solution and precipitant solution obtained in step a1 are added to the reaction vessel, the pH value is adjusted to 11.0, stirred and aged for 10-14 hours, filtered, the precipitate is collected, the precipitate is washed until neutral, dried, and the hydroxide precursor is obtained. a3: The hydroxide precursor prepared in step a2 is mixed with Li2CO3, dried, calcined, cooled, pulverized, washed, dried, and sieved to obtain a Y-Lu co-doped lithium manganese-based core.

[0009] Optionally, in step a1, the molar ratio of Y(NO3)3·6H2O and Lu(NO3)3·6H2O is (1.25-3):1.

[0010] By adopting the above technical solution and adjusting the amounts of Y(NO3)3·6H2O and Lu(NO3)3·6H2O according to the above molar ratio, when the molar ratio of Y(NO3)3·6H2O and Lu(NO3)3·6H2O is (1.25-3):1, the lithium-ion battery has a lower battery DCR and better rate performance and cycle stability.

[0011] Optionally, in step a1, the molar ratio of NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, Y(NO3)3·6H2O and Lu(NO3)3·6H2O is (0.08-0.12):(0.08-0.12):(0.35-0.45):(0.005-0.007):(0.002-0.004).

[0012] Optionally, in step a2, the precipitant solution is an aqueous solution containing 0.5-1.5 mol / L NaOH and 0.5-1.5 mol / L NH3·H2O, and the volume ratio of the precipitant solution to the mixed salt solution is 1:(0.5-1.5).

[0013] Optionally, the molar ratio of Li2CO3 in step a3 to the total metal ions in the mixed salt solution in step a1 is (0.48-0.56):1.

[0014] Optionally, the preparation method of the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material in the cathode material slurry of the cathode sheet includes the following steps: b1: Dissolve ferrous oxalate, lithium dihydrogen phosphate and citric acid in water, stir at 55-65℃ until completely dissolved, add ascorbic acid and continue stirring for 20-40 min to obtain LiFePO4 sol; b2: Add the Y-Lu co-doped lithium manganese-based core to ethanol and sonicate to obtain a Y-Lu co-doped lithium manganese-based core suspension. Add the LiFePO4 sol obtained in step b1 to the Y-Lu co-doped lithium manganese-based core suspension and stir to obtain a mixed slurry. Dry the mixed slurry to obtain the precursor powder. b3: The precursor powder was calcined in an inert gas atmosphere, cooled, and sieved to obtain LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material.

[0015] Optionally, in step b2, the mass ratio of LiFePO4 sol and Y-Lu co-doped lithium manganese-based core is (19-21):3.

[0016] Optionally, the preparation method of the silicon suboxide / graphene / carbon nanotube composite negative electrode material in the negative electrode slurry of the negative electrode sheet includes the following steps: c1: Calcine sub-silicon oxide under an inert gas atmosphere, cool, and pulverize to obtain pretreated sub-silicon oxide; c2: Multi-walled carbon nanotubes were added to an aqueous solution of sodium dodecylbenzenesulfonate and ultrasonically dispersed to obtain a carbon nanotube dispersion. c3: Add graphene oxide to water and disperse it by ultrasonication to obtain a graphene oxide dispersion; c4: Mix the carbon nanotube dispersion obtained in step c2 with the graphene oxide dispersion obtained in step c3, and sonicate to obtain a carbon nanotube / graphene hybrid dispersion. c5: The pretreated silicon suboxide obtained in step c1 is mixed with the carbon nanotube / graphene hybrid dispersion obtained in step c4, sucrose is added, and the mixture is sonicated and dried to obtain a composite precursor. The composite precursor is then calcined in an inert gas atmosphere and cooled to obtain a silicon suboxide / graphene / carbon nanotube composite anode material.

[0017] Optionally, in step c5, the mass ratio of pretreated silica suboxide to carbon nanotube / graphene hybrid dispersion is (9-17):3.

[0018] By adopting the above technical solution and adjusting the amounts of pretreated silica and carbon nanotube / graphene hybrid dispersion according to the above mass ratio, when the mass ratio of pretreated silica to carbon nanotube / graphene hybrid dispersion is (9-17):3, the internal resistance of the battery can be reduced, the rate performance can be improved, and the cycle stability can be enhanced. This may be because, within this mass ratio range, the three-dimensional conductive network formed by the carbon nanotube / graphene hybrid dispersion achieves an optimal ratio with silica, which not only ensures the rapid transport of electrons and ions, but also effectively suppresses the volume expansion of silica through the buffering effect of carbon materials, thereby synergistically improving the conductivity, structural stability, and cycle life of the negative electrode.

[0019] Optionally, in step c5, sucrose accounts for 8-12% of the mass of the pretreated silica.

[0020] In a second aspect, this application provides a method for preparing the lithium-ion battery described in the first aspect, comprising the following steps: S1: Positive current collector pretreatment: The aluminum foil is pretreated to obtain the pretreated positive current collector; S2: Negative electrode current collector pretreatment: The copper foil is pretreated to obtain the pretreated negative electrode current collector; S3: Preparation of graphene-cyclodextrin crosslinked polymer slurry: Graphene and cyclodextrin crosslinked polymer were dispersed in water to obtain graphene-cyclodextrin crosslinked polymer slurry; S4: Preparation of cathode material slurry: The cathode material is dispersed in N-methylpyrrolidone to obtain cathode material slurry; S5: Preparation of negative electrode material slurry: The negative electrode material is dispersed in N-methylpyrrolidone to obtain the negative electrode material slurry; S6: Preparation of positive electrode sheet: The graphene-cyclodextrin crosslinked polymer slurry obtained in step S3 is coated onto the pretreated positive electrode current collector obtained in step S1, dried, and then coated with the positive electrode material slurry obtained in step S4. After drying and rolling, a positive electrode sheet is obtained. S7: Preparation of negative electrode sheet: The negative electrode material slurry obtained in step S5 is coated on the pretreated negative electrode current collector obtained in step S2, and then dried and rolled to obtain a negative electrode sheet; S8: Lithium-ion battery preparation: Assemble the positive electrode sheet prepared in step S6, the negative electrode sheet prepared in step S7, and the separator, and inject electrolyte to obtain a lithium-ion battery.

[0021] Optionally, in step S1, the pretreatment of the positive current collector involves wiping the surface of the aluminum foil with oxalic acid solution, then wiping the surface of the aluminum foil with potassium permanganate solution, and drying it to obtain the pretreated positive current collector.

[0022] Optionally, in step S2, the pretreatment of the negative electrode current collector involves wiping the surface of the copper foil with citric acid solution and drying it to obtain the pretreated negative electrode current collector.

[0023] Optionally, in step S3, the viscosity of the graphene-cyclodextrin crosslinked polymer slurry is 50-500 mPa·s.

[0024] Optionally, in step S4, the viscosity of the positive electrode material slurry is 4000-6000 mPa·s.

[0025] Optionally, in step S5, the viscosity of the negative electrode material slurry is 2000-4000 mPa·s.

[0026] Optionally, in step S6, the double-sided coating density of the positive electrode material slurry on the pretreated positive electrode current collector is 70-80 mg / cm³. 2 .

[0027] Optionally, in step S7, the double-sided coating density of the negative electrode material slurry on the pretreated negative electrode current collector is 13-16 mg / cm³. 2 .

[0028] Optionally, in step S8, the diaphragm is a PE diaphragm.

[0029] In summary, the present invention has at least one of the following beneficial technical effects: 1. This application provides a lithium-ion battery with a 5C rate discharge performance >94% and a capacity retention rate >84% after 500 cycles. On one hand, Y-Lu co-doping plays a synergistic role; Y expands the lattice spacing to promote lithium-ion diffusion, while Lu enhances lattice stability. The combination of these two elements optimizes ion transport and structural stability. On the other hand, the LiFePO4 coating layer forms a stable ion-conducting interface on the surface of the cathode material, reducing side reactions between the cathode material and the electrolyte. Furthermore, this improves rate performance and cycle stability.

[0030] 2. This application provides a method for preparing a lithium-ion battery, which optimizes the electrode interface structure and ion transport channels by pretreatment of the positive electrode current collector, construction of a graphene-cyclodextrin crosslinked polymer intermediate layer and control of slurry viscosity, thereby improving rate performance and cycle stability. Detailed Implementation

[0031] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Specific conditions not specified in the examples shall be carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0032] The silicon suboxide was purchased from Yumu (Ningbo) New Materials Co., Ltd. (YM-SiO-W10), the multi-walled carbon nanotubes were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (C761800), and the graphene oxide was purchased from Shanghai Liantian Materials Technology Co., Ltd.

[0033] The diaphragms used in the following embodiments and comparative examples are PE diaphragms.

[0034] Preparation Example 1 Preparation of Yttrium-lutetium (Y-Lu) co-doped lithium manganese-based core a1: Dissolve 0.104 mol of NiSO4·6H2O, 0.104 mol of CoSO4·7H2O, 0.400 mol of MnSO4·H2O, 0.006 mol of Y(NO3)3·6H2O and 0.003 mol of Lu(NO3)3·6H2O in 500 mL of deionized water to obtain a mixed salt solution; a2: Under nitrogen protection and stirring speed of 1000 rpm at 60℃, the mixed salt solution and precipitant solution obtained in step a1 were added dropwise to the reaction vessel. The precipitant solution was an aqueous solution containing 1.0 mol / L NaOH and 1.0 mol / L NH3·H2O. The volume ratio of the precipitant solution to the mixed salt solution was 1:1. The pH of the reaction system was controlled at 11.0. After the addition was completed, the mixture was stirred and aged for 12 h. The mixture was filtered, the precipitate was collected, washed until neutral, washed twice with anhydrous ethanol, and dried under vacuum (20 kPa absolute pressure) at 80℃ for 12 h to obtain the hydroxide precursor. a3: The hydroxide precursor obtained in step a2 was mixed with 0.32 mol of Li2CO3 and ball-milled for 4 h with anhydrous ethanol as the medium. After drying, it was placed in an air atmosphere and pre-calcined by heating to 450 °C at 3 °C / min and holding for 5 h, followed by high-temperature sintering by heating to 850 °C at 5 °C / min and holding for 8 h. After cooling to room temperature in the furnace, it was pulverized, washed with deionized water, dried, and sieved to obtain a Y-Lu co-doped lithium manganese-based core.

[0035] Preparation Example 2 The difference between Preparation Example 2 and Preparation Example 1 is that in step a1, the total molar amount of Y(NO3)3·6H2O and Lu(NO3)3·6H2O remains unchanged, and the molar ratio of Y(NO3)3·6H2O to Lu(NO3)3·6H2O is 5:4.

[0036] Preparation Example 3 The difference between Preparation Example 3 and Preparation Example 1 is that in step a1, the total molar amount of Y(NO3)3·6H2O and Lu(NO3)3·6H2O remains unchanged, and the molar ratio of Y(NO3)3·6H2O to Lu(NO3)3·6H2O is 7:2.

[0037] Preparation Example 4 Preparation of LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material b1: Dissolve 7.16g ferrous oxalate, 5.15g lithium dihydrogen phosphate and 12.6g citric acid in 200mL deionized water, stir in a 60℃ water bath until completely dissolved, add 1.0g ascorbic acid, and continue stirring for 30min to obtain LiFePO4 sol; b2: Add 30g of the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 1 to 150mL of anhydrous ethanol and disperse ultrasonically (power 200W, 30min) to obtain a Y-Lu co-doped lithium manganese-based core suspension. Slowly add 200g of LiFePO4 sol obtained in step b1 to the Y-Lu co-doped lithium manganese-based core suspension while stirring at 1000rpm. After the addition is complete, continue stirring for 6h to obtain a mixed slurry. Spray dry the mixed slurry (inlet air temperature 180℃, outlet air temperature 90℃, atomizer speed 15000rpm) to obtain precursor powder. b3: The precursor powder was placed in a tube furnace and high-purity nitrogen gas (flow rate 200 mL / min, oxygen content <10 ppm) was introduced. The temperature was increased to 350℃ at 2℃ / min and held for 2 h. Then the temperature was increased to 580℃ at 2℃ / min and held for 4 h. Then the temperature was increased to 620℃ at 2℃ / min and held for 2 h. The furnace was cooled to room temperature and passed through a 400-mesh sieve to obtain LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material.

[0038] Preparation Example 5 The difference between Preparation Example 5 and Preparation Example 4 is that, in step b2, the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 1 is replaced with the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 2.

[0039] Preparation Example 6 The difference between Preparation Example 6 and Preparation Example 4 is that, in step b2, the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 1 is replaced with the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 3.

[0040] Preparation Example 7 Preparation of silicon suboxide / graphene / carbon nanotube composite anode materials c1: Place silicon suboxide in an argon atmosphere and heat it to 800°C at a heating rate of 2°C / min. Hold it at this temperature for 3 hours, cool it down, and then remove it. Pulverize it with an air jet mill to obtain pretreated silicon suboxide. c2: Multi-walled carbon nanotubes were added to deionized water containing 1 wt% sodium dodecylbenzenesulfonate and ultrasonically dispersed for 2 h (500 W power, ice water bath) to obtain a carbon nanotube dispersion with a concentration of 2 mg / mL. c3: Add graphene oxide to deionized water and ultrasonically disperse for 1 hour (power 300W) to obtain a graphene oxide dispersion with a concentration of 2 mg / mL. c4: Mix the carbon nanotube dispersion obtained in step c2 with the graphene oxide dispersion obtained in step c3 at a mass ratio of 1:2, and sonicate for 40 min to obtain a carbon nanotube / graphene hybrid dispersion. c5: The pretreated silica obtained in step c1 is mixed with the carbon nanotube / graphene hybrid dispersion obtained in step c4 at a weight ratio of 80:20. Sucrose accounting for 10% of the mass of the pretreated silica is added, and the mixture is sonicated for 40 min. The mixture is then spray-dried (inlet air temperature 180℃, outlet air temperature 80℃) to obtain a composite precursor. The composite precursor is placed in a tube furnace and heated to 700℃ at 3℃ / min under an argon / hydrogen mixed atmosphere (90:10). The temperature is maintained for 3 h and then naturally cooled to room temperature to obtain a silica / graphene / carbon nanotube composite anode material.

[0041] Preparation Example 8 The difference between Preparation Example 8 and Preparation Example 7 is that, in step c5, the total mass of the pretreated silica and carbon nanotube / graphene hybrid dispersion remains unchanged, and the mass ratio of the pretreated silica and carbon nanotube / graphene hybrid dispersion is 75:25.

[0042] Preparation Example 9 The difference between Preparation Example 9 and Preparation Example 7 is that, in step c5, the total mass of the pretreated silica and carbon nanotube / graphene hybrid dispersion remains unchanged, and the mass ratio of the pretreated silica and carbon nanotube / graphene hybrid dispersion is 85:15.

[0043] Preparation Example 10 Preparation of electrolyte In an argon-filled glove box (water content <1 ppm, oxygen content <1 ppm), 60 g of dimethyl carbonate, 20 g of ethylene carbonate, and 20 g of ethyl propionate were mixed to obtain a mixed organic solvent. 15.8 g of lithium hexafluorophosphate and 5.0 g of lithium difluorosulfonylimide were added to the mixed organic solvent, and the mixture was stirred at room temperature and 300 rpm for 3 h to obtain a premixed electrolyte. Then, 1.0 g of lithium difluorooxalate borate, 1.0 g of lithium difluorophosphate, 3.0 g of fluoroethylene carbonate, 2.0 g of adiponitrile, 1.5 g of ethylene sulfate, and 0.5 g of 1,3-propenesulfonyl lactone were added to the premixed electrolyte, and the mixture was stirred at 25 °C and 400 rpm for 1.5 h to obtain the electrolyte.

[0044] Comparative Preparation Example 1 The difference between Preparation Example 1 and Preparation Example 2 is that in step a1, Y(NO3)3·6H2O is replaced with Lu(NO3)3·6H2O in equimolar amounts.

[0045] Accordingly, step a3 is as follows: The hydroxide precursor obtained in step a2 is mixed with 0.32 mol of Li2CO3, ball-milled for 4 h with anhydrous ethanol as the medium, dried, and placed in an air atmosphere. It is then pre-calcined by heating to 450 °C at 3 °C / min and holding for 5 h, followed by high-temperature sintering by heating to 850 °C at 5 °C / min and holding for 8 h. The resulting product is pulverized, washed with deionized water, dried, and sieved to obtain a Lu-doped lithium manganese-based core.

[0046] Comparative Preparation Example 2 The difference between Preparation Example 2 and Preparation Example 1 is that in step a1, Lu(NO3)3·6H2O is replaced with Y(NO3)3·6H2O in equal molar amounts.

[0047] Accordingly, step a3 is as follows: The hydroxide precursor obtained in step a2 is mixed with 0.32 mol of Li2CO3, ball-milled for 4 h with anhydrous ethanol as the medium, dried, and placed in an air atmosphere. It is then pre-calcined by heating to 450 °C at 3 °C / min and holding for 5 h, followed by high-temperature sintering by heating to 850 °C at 5 °C / min and holding for 8 h. After cooling to room temperature in the furnace, it is pulverized, washed with deionized water, dried, and sieved to obtain a Y-doped lithium manganese-based core.

[0048] Comparative preparation example 3 The difference between Preparation Example 3 and Preparation Example 1 is that in step a1, Lu(NO3)3·6H2O is replaced with Zr(NO3)4·5H2O in equal molar amounts.

[0049] Accordingly, step a3 is as follows: The hydroxide precursor obtained in step a2 is mixed with 0.32 mol of Li2CO3, ball-milled for 4 h with anhydrous ethanol as the medium, dried, and placed in an air atmosphere. It is then pre-calcined by heating to 450 °C at 3 °C / min and holding for 5 h, followed by high-temperature sintering by heating to 850 °C at 5 °C / min and holding for 8 h. After cooling to room temperature in the furnace, it is pulverized, washed with deionized water, dried, and sieved to obtain a Y-Zr co-doped lithium manganese-based core.

[0050] Comparative preparation example 4 The difference between Comparative Preparation Example 4 and Preparation Example 4 is that, in step b2, the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 1 is replaced by the Lu-doped lithium manganese-based core prepared in Comparative Preparation Example 1.

[0051] Accordingly, step b3 is as follows: the precursor powder is placed in a tube furnace, high-purity nitrogen gas (flow rate 200 mL / min, oxygen content <10 ppm) is introduced, the temperature is increased to 350℃ at 2℃ / min and held for 2 h; then the temperature is increased to 580℃ at 2℃ / min and held for 4 h; then the temperature is increased to 620℃ at 1℃ / min and held for 2 h, and then cooled to room temperature with the furnace, and passed through a 400-mesh sieve to obtain LiFePO4@Lu doped lithium manganese-based core-shell cathode material.

[0052] Comparative preparation example 5 The difference between Preparation Example 5 and Preparation Example 4 is that, in step b2, the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 1 is replaced by the Y-doped lithium manganese-based core prepared in Comparative Preparation Example 2.

[0053] Accordingly, step b3 is as follows: the precursor powder is placed in a tube furnace, high-purity nitrogen gas (flow rate 200 mL / min, oxygen content <10 ppm) is introduced, the temperature is increased to 350℃ at 2℃ / min and held for 2 h; then the temperature is increased to 580℃ at 2℃ / min and held for 4 h; then the temperature is increased to 620℃ at 1℃ / min and held for 2 h, and then cooled to room temperature with the furnace, and passed through a 400-mesh sieve to obtain LiFePO4@Y doped lithium manganese-based core-shell cathode material.

[0054] Comparative preparation example 6 The difference between Preparation Example 6 and Preparation Example 4 is that, in step b2, the Y-Lu co-doped lithium manganese-based core prepared in Preparation Example 1 is replaced by the Y-Zr co-doped lithium manganese-based core prepared in Comparative Preparation Example 3.

[0055] Accordingly, step b3 is as follows: the precursor powder is placed in a tube furnace, high-purity nitrogen gas (flow rate 200 mL / min, oxygen content <10 ppm) is introduced, the temperature is increased to 350℃ at 2℃ / min and held for 2 h; then the temperature is increased to 580℃ at 2℃ / min and held for 4 h; then the temperature is increased to 620℃ at 1℃ / min and held for 2 h, and then cooled to room temperature with the furnace, and passed through a 400-mesh sieve to obtain LiFePO4@Y-Zr co-doped lithium manganese-based core-shell cathode material.

[0056] Example 1

[0057] Example 1 provides a method for preparing a lithium-ion battery, comprising the following steps: S1: Positive current collector pretreatment: First, wipe the aluminum foil surface with a 0.1% oxalic acid solution. While the oxalic acid solution is still wet, immediately wipe the aluminum foil surface with a 0.5% potassium permanganate solution. After drying, the pretreated positive current collector is obtained. S2: Negative electrode current collector pretreatment: Wipe the copper foil surface with a 0.8% (w / w) citric acid solution, and dry it to obtain the pretreated negative electrode current collector; S3: Preparation of graphene-cyclodextrin crosslinked polymer slurry: Graphene and cyclodextrin crosslinked polymer were dispersed in water at a mass ratio of 1:1 to prepare a graphene-cyclodextrin crosslinked polymer slurry with a viscosity of 400 mPa·s. The cyclodextrin crosslinked polymer was prepared by the crosslinking reaction of epichlorohydrin and β-cyclodextrin. The preparation method was as follows: β-cyclodextrin was dissolved in a 20% sodium hydroxide solution, and 35 mL of epichlorohydrin was added dropwise at a certain rate while continuously stirring. After the slurry viscosity reached 6000 mPa·s, stirring was stopped, and the reaction continued until a gel-like solid mass appeared. The slurry was then removed, washed with water and acetone until no chloride ions were present, filtered, dried, and ground to obtain the cyclodextrin crosslinked polymer. S4: Preparation of cathode material slurry: The cathode material was dispersed in N-methylpyrrolidone to prepare a cathode material slurry with a viscosity of 5000 mPa·s; the cathode material consisted of 98 wt% of LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Preparation Example 4, 0.5 wt% of acetylene black and 1.5 wt% of PVDF; S5: Preparation of negative electrode material slurry: The negative electrode material was dispersed in N-methylpyrrolidone to prepare a negative electrode material slurry with a viscosity of 3000 mPa·s; the negative electrode material consisted of 98 wt% of silicon suboxide / graphene / carbon nanotube composite negative electrode material prepared by the preparation method of Preparation Example 7 and 2 wt% of PVDF. S6: Preparation of the positive electrode sheet: The graphene-cyclodextrin crosslinked polymer slurry obtained in step S3 is first coated onto the pretreated positive electrode current collector obtained in step S1. After drying, a 1 μm thick graphene-cyclodextrin crosslinked polymer layer is formed. Then, the positive electrode material slurry obtained in step S4 is coated on top, with a double-sided coating areal density of 75 mg / cm³. 2 After drying and rolling, a positive electrode sheet is obtained; S7: Preparation of the negative electrode sheet: The negative electrode material slurry obtained in step S5 is coated onto the pretreated negative electrode current collector obtained in step S2, with a double-sided coating density of 14.5 mg / cm³. 2 After drying and rolling, a negative electrode sheet is obtained; S8: Lithium-ion battery preparation: The positive electrode sheet prepared in step S6, the negative electrode sheet prepared in step S7, and the separator are assembled, and the electrolyte prepared by the preparation method of preparation example 10 is injected to obtain a lithium-ion battery.

[0058] Example 2

[0059] Example 2 provides a lithium-ion battery, which differs from Example 1 in that, in step S4, the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Example 4 is replaced by the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Example 5.

[0060] Other preparation methods are the same as in Example 1.

[0061] Example 3

[0062] Example 3 provides a lithium-ion battery, which differs from Example 1 in that, in step S4, the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Example 4 is replaced by the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Example 6.

[0063] Other preparation methods are the same as in Example 1.

[0064] Example 4

[0065] Example 4 provides a lithium-ion battery, which differs from Example 1 in that, in step S5, the silicon suboxide / graphene / carbon nanotube composite anode material prepared by the preparation method of Example 7 is replaced by the silicon suboxide / graphene / carbon nanotube composite anode material prepared by the preparation method of Example 8.

[0066] Other preparation methods are the same as in Example 1.

[0067] Example 5

[0068] Example 5 provides a lithium-ion battery, which differs from Example 1 in that, in step S5, the silicon suboxide / graphene / carbon nanotube composite anode material prepared by the preparation method of Example 7 is replaced by the silicon suboxide / graphene / carbon nanotube composite anode material prepared by the preparation method of Example 9.

[0069] Other preparation methods are the same as in Example 1.

[0070] Comparative Example 1 Comparative Example 1 provides a lithium-ion battery, which differs from Example 1 in that, in step S4, the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Example 4 is replaced by the same mass of the LiFePO4@Lu doped lithium manganese-based core-shell cathode material prepared by the preparation method of Comparative Example 4.

[0071] Other preparation methods are the same as in Example 1.

[0072] Comparative Example 2 Comparative Example 2 provides a lithium-ion battery, which differs from Example 1 in that, in step S4, the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Preparation Example 4 is replaced by the LiFePO4@Y doped lithium manganese-based core-shell cathode material prepared by the preparation method of Comparative Example 5.

[0073] Other preparation methods are the same as in Example 1.

[0074] Comparative Example 3 Comparative Example 3 provides a lithium-ion battery, which differs from Example 1 in that, in step S4, the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Preparation Example 4 is replaced by the LiFePO4@Y-Zr co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Comparative Example 6.

[0075] Other preparation methods are the same as in Example 1.

[0076] Comparative Example 4 Comparative Example 4 provides a lithium-ion battery, which differs from Example 1 in that, in step S4, the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material prepared by the preparation method of Example 4 is replaced by the Y-Lu co-doped lithium manganese-based core prepared by the preparation method of Example 1.

[0077] Other preparation methods are the same as in Example 1.

[0078] Performance testing 1. Battery Discharge Rate Test The battery rate discharge was tested according to GB / T 31486-2015. Under conditions of 25℃±2℃, the lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-4 were charged at a constant current of 1C to 3.8V, then charged at a constant voltage of 3.8V to a cutoff current of 0.05C, allowed to stand for 30 minutes, and then discharged at a constant current of 1C to 2.5V. This process was repeated three times, and the average discharge capacity was taken as the standard capacity value C1. The batteries were then charged at a constant current of 1C to 3.8V, charged at a constant voltage of 3.8V to 0.05C, allowed to stand for 30 minutes, and then discharged at a rate of 5C to 2.5V to obtain the capacity value C2 at the 5C rate. The battery 5C rate retention rate was calculated as C2 / C1×100%. Specific results are shown in Table 1.

[0079] 2. Battery room temperature cycle test Battery cycling at room temperature was tested according to GB / T 31484-2015. At 25℃±2℃, the lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-4 were charged at a constant current of 1C to 3.8V, then charged at a constant voltage of 3.8V to a cutoff current of 0.05C, rested for 30 minutes, and then discharged at a constant current of 1C to 2.5V, rested for 30 minutes. The initial cycle discharge capacity was measured. This cycle was repeated for 500 charge / discharge cycles. The discharge capacity after the 500th cycle was measured, and the capacity retention rate after the 500th cycle was calculated using the following formula: Capacity retention rate after the 500th cycle (%) = (Discharge capacity after the 500th cycle / Discharge capacity after the first cycle) × 100%. Specific results are shown in Table 1.

[0080] Table 1

[0081] Conclusion Analysis and Summary As shown in Examples 1-3 and Table 1, adjusting the molar ratio of Y(NO3)3·6H2O and Lu(NO3)3·6H2O in the cathode material can affect the internal resistance, rate performance, and cycle stability of the lithium-ion battery. In Example 1, when the molar ratio of Y(NO3)3·6H2O to Lu(NO3)3·6H2O is 2:1, the prepared lithium-ion battery exhibits the best 5C rate discharge performance and the best capacity retention rate after 500 cycles compared to Examples 2 and 3.

[0082] Based on Examples 1, 4-5, and Table 1, it can be seen that adjusting the mass ratio of pretreated silica to carbon nanotube / graphene hybrid dispersion in the negative electrode material can affect the internal resistance, rate performance, and cycle stability of lithium-ion batteries. In Example 1, when the mass ratio of pretreated silica to carbon nanotube / graphene hybrid dispersion is 80:20, the prepared lithium-ion battery exhibits the best 5C rate discharge performance and the best capacity retention after 500 cycles compared to Examples 4 and 5.

[0083] Based on Example 1, Comparative Examples 1-2, and Table 1, it can be seen that in Comparative Example 1, replacing equimolar amounts of Y(NO3)3·6H2O with Lu(NO3)3·6H2O, and in Comparative Example 2, replacing equimolar amounts of Lu(NO3)3·6H2O with Y(NO3)3·6H2O, both resulted in a deterioration in the 5C rate discharge performance and capacity retention after 500 cycles of the prepared lithium-ion batteries. This may be because single doping cannot simultaneously address ion transport and structural stability: Lu doping alone results in insufficient lattice spacing expansion, hindering lithium-ion diffusion; Y doping alone leads to excessive lattice expansion, making long-term cycling prone to collapse. Y-Lu co-doping optimizes lattice parameters through synergistic effects, simultaneously achieving rapid ion transport and high structural stability.

[0084] Based on Example 1, Comparative Example 3, and Table 1, it can be seen that in Comparative Example 3, replacing Lu(NO3)3·6H2O with an equimolar amount of Zr(NO3)4·5H2O resulted in a deterioration in the 5C rate discharge performance and capacity retention after 500 cycles of the prepared lithium-ion battery. This may be because Zr... 4+ The ionic radius and valence of Lu 3+ Significant differences exist; heterovalent substitution leads to increased lattice distortion and defects, hindering lithium-ion transport. Meanwhile, Zr lacks the 4f electron effect of Lu, and the synergistic effect of the Y-Zr combination is weaker than that of the Y-Lu combination, resulting in decreased rate performance and cycle stability.

[0085] Based on Example 1, Comparative Example 4, and Table 1, it can be seen that in Comparative Example 4, replacing the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material with an equal mass of Y-Lu co-doped lithium manganese-based core significantly deteriorated the 5C rate discharge performance and capacity retention after 500 cycles of the prepared lithium-ion battery. This may be because the absence of the LiFePO4 coating layer leads to the loss of interfacial stability of the cathode material, causing severe side reactions due to direct contact between the core and the electrolyte, resulting in a significant increase in interfacial impedance and polarization; at the same time, lithium-ion transport in the bare core is hindered, structural damage and metal dissolution are accelerated, leading to a significant decrease in battery rate performance and cycle life.

[0086] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the products, methods and principles of this application should be covered within the scope of protection of this application.

Claims

1. A lithium-ion battery, characterized in that, It includes the following components: positive electrode, separator, negative electrode, and electrolyte; The positive electrode sheet includes a pretreated positive electrode current collector, a graphene-cyclodextrin crosslinked polymer slurry, and a positive electrode material slurry; The negative electrode sheet includes a pretreated negative electrode current collector and a negative electrode material slurry; The cathode material slurry includes LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material, acetylene black, and PVDF; The negative electrode material slurry includes a silicon suboxide / graphene / carbon nanotube composite negative electrode material and PVDF.

2. The lithium-ion battery according to claim 1, characterized in that, The raw materials for preparing the LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material in the cathode slurry of the cathode sheet include a Y-Lu co-doped lithium manganese-based core.

3. The lithium-ion battery according to claim 2, characterized in that, The preparation method of the Y-Lu co-doped lithium manganese-based core includes the following steps: a1: NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, Y(NO3)3·6H2O and Lu(NO3)3·6H2O are dissolved together in water to obtain a mixed salt solution; a2: Under the conditions of 55-65℃, inert gas protection, and stirring, the mixed salt solution and precipitant solution obtained in step a1 are added to the reaction vessel, the pH value is adjusted to 11.0, stirred and aged for 10-14 hours, filtered, the precipitate is collected, the precipitate is washed until neutral, dried, and the hydroxide precursor is obtained. a3: The hydroxide precursor prepared in step a2 is mixed with Li2CO3, dried, calcined, cooled, pulverized, washed, dried, and sieved to obtain a Y-Lu co-doped lithium manganese-based core.

4. The lithium-ion battery according to claim 3, characterized in that, In step a1, the molar ratio of Y(NO3)3·6H2O and Lu(NO3)3·6H2O is (1.25-3):

1.

5. The lithium-ion battery according to claim 3, characterized in that, In step a2, the precipitant solution is an aqueous solution containing 0.5-1.5 mol / L NaOH and 0.5-1.5 mol / L NH3·H2O, and the volume ratio of the precipitant solution to the mixed salt solution is 1:(0.5-1.5).

6. The lithium-ion battery according to claim 3, characterized in that, The molar ratio of Li2CO3 in step a3 to the total metal ions in the mixed salt solution in step a1 is (0.48-0.56):

1.

7. The lithium-ion battery according to claim 1, characterized in that, The preparation method of LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material in the cathode material slurry of the cathode sheet includes the following steps: b1: Dissolve ferrous oxalate, lithium dihydrogen phosphate and citric acid in water, stir at 55-65℃ until completely dissolved, add ascorbic acid and continue stirring for 20-40 min to obtain LiFePO4 sol; b2: Add the Y-Lu co-doped lithium manganese-based core to ethanol and sonicate to obtain a Y-Lu co-doped lithium manganese-based core suspension. Add the LiFePO4 sol obtained in step b1 to the Y-Lu co-doped lithium manganese-based core suspension and stir to obtain a mixed slurry. Dry the mixed slurry to obtain the precursor powder. b3: The precursor powder was calcined in an inert gas atmosphere, cooled, and sieved to obtain LiFePO4@Y-Lu co-doped lithium manganese-based core-shell cathode material.

8. The lithium-ion battery according to claim 1, characterized in that, The preparation method of the silicon suboxide / graphene / carbon nanotube composite anode material in the anode material slurry of the anode sheet includes the following steps: c1: Calcine sub-silicon oxide under an inert gas atmosphere, cool, and pulverize to obtain pretreated sub-silicon oxide; c2: Multi-walled carbon nanotubes were added to an aqueous solution of sodium dodecylbenzenesulfonate and ultrasonically dispersed to obtain a carbon nanotube dispersion. c3: Add graphene oxide to water and disperse it by ultrasonication to obtain a graphene oxide dispersion; c4: Mix the carbon nanotube dispersion obtained in step c2 with the graphene oxide dispersion obtained in step c3, and sonicate to obtain a carbon nanotube / graphene hybrid dispersion. c5: The pretreated silicon suboxide obtained in step c1 is mixed with the carbon nanotube / graphene hybrid dispersion obtained in step c4, sucrose is added, and the mixture is sonicated and dried to obtain a composite precursor. The composite precursor is then calcined in an inert gas atmosphere and cooled to obtain a silicon suboxide / graphene / carbon nanotube composite anode material.

9. The lithium-ion battery according to claim 8, characterized in that, In step c5, the mass ratio of pretreated silica suboxide to carbon nanotube / graphene hybrid dispersion is (9-17):

3.

10. A method for preparing a lithium-ion battery according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Positive current collector pretreatment: The aluminum foil is pretreated to obtain the pretreated positive current collector; S2: Negative electrode current collector pretreatment: The copper foil is pretreated to obtain the pretreated negative electrode current collector; S3: Preparation of graphene-cyclodextrin crosslinked polymer slurry: Graphene and cyclodextrin crosslinked polymer were dispersed in water to obtain graphene-cyclodextrin crosslinked polymer slurry; S4: Preparation of cathode material slurry: The cathode material is dispersed in N-methylpyrrolidone to obtain cathode material slurry; S5: Preparation of negative electrode material slurry: The negative electrode material is dispersed in N-methylpyrrolidone to obtain the negative electrode material slurry; S6: Preparation of positive electrode sheet: The graphene-cyclodextrin crosslinked polymer slurry obtained in step S3 is coated onto the pretreated positive electrode current collector obtained in step S1, dried, and then coated with the positive electrode material slurry obtained in step S4. After drying and rolling, a positive electrode sheet is obtained. S7: Preparation of negative electrode sheet: The negative electrode material slurry obtained in step S5 is coated on the pretreated negative electrode current collector obtained in step S2, and then dried and rolled to obtain a negative electrode sheet; S8: Lithium-ion battery preparation: Assemble the positive electrode sheet prepared in step S6, the negative electrode sheet prepared in step S7, and the separator, and inject electrolyte to obtain a lithium-ion battery.

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