A three-dimensional Li 1.5 Na 1.5 V2(PO4)3 / NDs / CF x Cathode material and preparation method thereof

Abstract

This invention proposes a three-dimensional Li-type nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding site. 1.5 Na 1.5 V2(PO4)3 / NDs / CF x This invention relates to a cathode material and its preparation method, belonging to the technical field of cathode materials for lithium-ion batteries. The cathode material obtained by this invention exhibits good cycle stability when applied to the cathode of a lithium-ion battery. At 50 mA g... ‑1 The specific capacitance after 200 cycles at current density is 162 mA hg ‑1 ; at 1000mA g ‑1 At high current densities, it still achieves a significant 96 mA hg after 1000 cycles. ‑1 It exhibits long-term cycling stability and high capacity performance. The preparation method used in this invention has the advantages of simple process, easy implementation, and easy scale-up, and is expected to be mass-produced in the future.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery cathodes, and relates to a nanodiamond (NDs) and carbon fluoride (CF) X A method to jointly improve the positive electrode of the battery. Background Technology

[0002] Lithium-ion batteries, as an energy storage system with high energy density and long cycle life, have been widely used in various fields. However, the widespread use of lithium-ion batteries and the limited availability of lithium resources on Earth have led to a significant increase in their price. Among all the components of a lithium-ion battery, the cathode material, as the main source, has a significant impact on the overall performance and cost of the battery. The most common cathode materials in lithium-ion batteries include LiFPO4, LiCoO2, and LiNi. x Mn y Co 1-x-y O2, etc. However, their limited capacity and poor structural stability have hindered the further development of lithium-ion batteries. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an improved method for a novel lithium-ion battery cathode that enhances capacity, stabilizes cycle performance, and generates a robust solid electrolyte membrane (CEI) during cycling by selecting modifying materials and designing a special structure.

[0004] The specific technical solution of the present invention is as follows:

[0005] A three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and fluorinated carbon as the binding site 1.5 Na 1.5 V2(PO4)3 / NDs / CF x The preparation method of the positive electrode material is as follows:

[0006] 1) Hydrogen-treated nanodiamond powder (NDs) and carbon fluoride (CF) x Dissolved in deionized water and sonicated for 2 hours, solution A is obtained; the hydrogen-treated nanodiamond powder is nanodiamond powder that has been heat-treated in a hydrogen atmosphere.

[0007] 2) Take NH4VO3 and citric acid monohydrate (C6H) in a molar ratio of 1:1. 10 O8), dissolved in deionized water, heated and stirred at 80°C until a transparent blue solution B is formed;

[0008] 3) Add solution A from step 1) to solution B from step 2), and weigh out NaOH, LiOH, and NH4H2PO4 powders and add them to the solution; NaOH, LiOH, NH4VO3, NH4H2PO4, and C6H10 The molar ratio between O8 is 3:3:4:6:4;

[0009] 4) The solution is continuously stirred and heated to evaporate the water, and then dried in a drying oven;

[0010] 5) Grind the dried sample into a fine powder, preheat at 350℃ for 4 hours, and then heat in argon gas at 750℃~800℃ for 5 minutes. -1 Annealing at a heating rate of 8 h yielded a three-dimensional Li-type nanodiamond with fluorinated carbon as the substrate and fluorinated carbon as the binding site. 1.5 Na 1.5 V2(PO4)3 / NDs / CF x Positive electrode material.

[0011] The preparation steps of hydrogen-treated nanodiamond powder in step 1) are as follows:

[0012] Hydrogen-treated nanodiamond powder was obtained by heating nanodiamond powder to 500°C in a vacuum chamber under a hydrogen atmosphere and then cooling it to room temperature under a flow of hydrogen.

[0013] More preferably, the particle size of the nanodiamond powder is 5-10 nm.

[0014] Further preferably, the hydrogen flow rate is 50 sccm.

[0015] Preferably, the side length of the fluorinated carbon particles in step 1) is in the range of 1 to 30 μm.

[0016] Preferably, in step 3), the Li content in the obtained composite material is... 1.5 Na 1.5 V2(PO4)3, NDs and CF x The mass ratio of solution A to solution B is 1.80:0.005:0.03.

[0017] The method for preparing lithium-ion battery cathodes using the above-mentioned cathode materials is as follows:

[0018] 10 wt% binder, 80 wt% of the cathode material, and 10 wt% conductive agent are mixed, and solvent is added. The mixture is stirred with a magnetic stirrer to form a viscous fluid. The viscous fluid is then coated onto a current collector and dried under vacuum. Finally, it is cut into electrode shapes and compacted to obtain the cathode of a lithium-ion battery.

[0019] The cathode material obtained by the method of this invention uses CFx as a substrate and NDs as binding sites, with nanodiamonds distributed on CFx and Li. 1.5 Na 1.5 Three-dimensional Li is formed between V2(PO4)3. 1.5 Na 1.5 V2(PO4)3 / NDs / CFx Composite structure.

[0020] The beneficial effects of this invention are:

[0021] The cathode material prepared by this invention exhibits excellent electrochemical performance, and lithium-ion batteries made from it demonstrate good cycle stability. (At 50 mA g) -1 The specific capacitance after 200 cycles at current density is 162 mA hg -1 At 1000mA g -1 At high current densities, it still achieves a significant 96 mA hg after 1000 cycles. -1 This high capacity retention can be attributed to the fact that NDs facilitate the formation of a three-dimensional structure in the synthesized cathode material, and that a solid electrolyte film rich in NDs and LiF / NaF is generated during cycling, which enables the battery to maintain structural stability during continuous charge and discharge.

[0022] This invention applies nanodiamond to the synthesis of three-dimensional cathode materials. Its preparation method has the advantages of simple process, easy implementation and easy scale-up, and is expected to be mass-produced in the future. Attached Figure Description

[0023] Figure 1 Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the three-dimensional CFx / NDs / LNVP cathode material (LNDF) prepared for Example 1.

[0024] Figure 2 High-resolution transmission electron microscopy (HTEM) image of the three-dimensional CFx / NDs / LNVP cathode material (LNDF) prepared in Example 1.

[0025] Figure 3 The images shown are scanning electron microscope (SEM), transmission electron microscope (TEM), and high-resolution transmission electron microscope (HTEM) images of the LNF sample without nanodiamond material in Comparative Example 1.

[0026] Figure 4 The LNDF cathode prepared in Example 1 was applied to a lithium-ion battery at 50 mA g. -1 500mA g -1 1000mA g -1 The charge-discharge curves of the current density.

[0027] Figure 5 The charge-discharge cyclic voltammetry curve of the LNDF positive electrode prepared in Example 1.

[0028] Figure 6 The LNDF cathode prepared in Example 1 was used in a lithium-ion battery at 50 mA g. -1The charge-discharge plateau curve under constant current.

[0029] Figure 7 The LNDF cathode prepared in Example 1 was used in a lithium-ion battery at 1000 mA g. -1 Scanning electron microscopy and transmission electron microscopy images after 1000 charge-discharge cycles at high current density.

[0030] Figure 8 The LNDF cathode prepared in Example 1 was used in a lithium-ion battery at 1000 mA g. -1 High-resolution transmission electron microscopy image after 1000 charge-discharge cycles at high current density.

[0031] Figure 9 Comparative Example 1: The LNF cathode prepared without the addition of nanodiamond was applied to a lithium-ion battery at 1000 mA g. -1 Scanning electron microscopy and transmission electron microscopy images after 1000 charge-discharge cycles at high current density. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0033] Example 1: Fabrication of a 3D LNVP (LNVP / NDs / CFx) with CFx as the substrate and NDs as the bonding points.

[0034] 1) Hydrogen-treated nanodiamond powder with a particle size of 5-10 nm was heated to 500 °C in a vacuum chamber under a hydrogen atmosphere (purity 99.99%) and cooled to room temperature under a hydrogen flow to obtain hydrogen-treated nanodiamond powder; wherein the hydrogen flow rate was 50 sccm.

[0035] 2) 0.005g of hydrogen-treated nanodiamond powder (NDs) and 0.03g of CF x Dissolved in deionized water and sonicated for 2 hours; CF in this example x The side lengths range from 10 to 30 micrometers;

[0036] 3) Weigh out 0.97g (8.33mmol) NH4VO3 and 1.75g ​​(8.33mol) citric acid monohydrate (C6H) in a 1:1 molar ratio. 10 O8), dissolved in deionized water, heated and stirred at 80°C until a transparent blue solution is formed;

[0037] 4) Add the solution from step 2) to the solution from step 3). Add 0.25g (6.25mmol) NaOH, 0.15g (6.25mmol) LiOH, and 1.44g (12.5mmol) NH4H2PO4 powder to the solution, so that NaOH, LiOH, NH4VO3, NH4H2PO4, and C6H... 10 The molar ratio between O8 is 3:3:4:6:4;

[0038] 4) The solution is continuously stirred and heated until most of the water evaporates, and then dried in a drying oven;

[0039] 5) Grind the dried sample into a fine powder, preheat at 350℃ for 4 hours, and then heat it in argon gas at 750℃ for 5 minutes. -1 Annealing at a heating rate of 8 h yielded Li 1.5 Na 1.5 V2(PO4)3 / NDs / CF x (LNDF) composite material. Li in the composite material 1.5 Na 1.5 V2(PO4)3, NDs and / CF x The mass ratio is 1.80:0.005:0.03.

[0040] Comparative Example 1: Positive electrode without added nanodiamonds (LNF)

[0041] For comparison, the same method as in Example 1 was used in the comparative example, except that nano-diamond powder was not added. The resulting cathode material was designated as the comparative sample #LNF sample.

[0042] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the LNDF obtained in Example 1 are shown below. Figure 1 High-resolution transmission electron microscopy (HRTEM) image is shown below. Figure 2 ;like Figure 1 and Figure 2 As shown, the LNDF uses CF x Substrate, diamond-induced longitudinally aligned porous three-dimensional structure. SEM, TEM, and HRTEM images of the material sample #LNF without added nanodiamond in Comparative Example 1 are shown below. Figure 3 Compared to sample #LNDF, sample #LNF shows uneven carbon coating and disordered LNVP growth direction.

[0043] CF during heating x With C6H 10O8 reacts, while the addition of NDs causes the carbon coating of the cathode to form a three-dimensional porous structure. Furthermore, NDs induce the growth of LNVP precursors on the CFx substrate, and the presence of their functional groups also helps retain more F during the heating process. Analysis shows that using NDs improves the CFx... x With Li 1.5 Na 1.5 The V2(PO4)3 materials have more sufficient contact between each other, which helps with the final CF conversion. x A three-dimensional LNDF cathode material with NDs as the binding point and NDs as the substrate.

[0044] Example 2: Using LNDF as the positive electrode for use in lithium-ion battery components.

[0045] The positive electrode of the lithium-ion battery is composed of 80 wt% active material (LNDF material obtained in Example 1), 10 wt% binder (polyvinylidene fluoride, PVDF), and 10 wt% conductive agent (carbon black). After mixing and grinding the three components for 0.5 h, the mixture is placed in a container, and a certain amount of solvent (1-methyl-2-pyrrolidone, NMP) is added. The container is then placed on a magnetic stirrer and stirred at a constant speed for 12 h until the mixture becomes a viscous fluid. Using aluminum foil as the current collector, the above-mentioned viscous mixture is coated onto the current collector, ensuring a uniform coating density. The temperature of a vacuum drying oven is set to 120°C, and the above-mentioned aluminum foil coating is placed in the drying oven for 12 h. After 12 h, it is removed and ready for use. The prepared aluminum foil coating is cut into several electrode discs using a special cutting die. The active material on the electrode discs is then compacted using a pressing machine to ensure full contact with the current collector and prevent material detachment. The mass of the electrode discs is weighed for calculation of specific capacity parameters, etc.

[0046] Example 3: Fabrication and Performance Testing of Lithium-ion Batteries

[0047] The lithium-ion batteries assembled for testing were CR-2025 coin cells. Using the prepared LNDF as the positive electrode and a lithium sheet as the reference electrode, the batteries, along with their corresponding positive and negative electrode shells, gaskets, springs, separators, and electrolytes, were manufactured according to lithium-ion battery manufacturing specifications. The batteries were encapsulated in an anhydrous and oxygen-free environment, and their electrochemical performance was then tested using the Blue Electric testing system. The lithium-ion half-cells prepared using sample #LNF and sample #LNDF were labeled S1 and S2, respectively.

[0048] 1) Capacity curve test

[0049] Batteries S1 and S2 prepared in Example 1 were tested in the Blue Electricity Test System. At 25°C, they were charged to 4.4V at a specific current density; after charging, the batteries were allowed to rest for 3 minutes; then discharged to 2.0V at a specific current density. After discharging, the batteries were allowed to rest for 3 minutes and then charged to 4.4V at the same current density; after discharging, the batteries were allowed to rest for 3 minutes and then discharged again under the same conditions. 50mA g was tested at different current densities. -1 500mA g -1 1000mA g -1 Cyclic performance tests were performed on the half-cells of LNDF and LNF, respectively, and the results are as follows: Figure 4 As shown, at 50mA g -1 At low current density, after 200 cycles, the capacity of LNF is 130 mAh g. -1 LNDF has a capacity of 162 mAh g. -1 High reversible capacity, especially at higher current densities, such as 1000 mA g. -1 At a current density of [value missing], after 1000 cycles, the capacity of LNF is 48 mAh g. -1 LNDF has a capacity of 96 mAh g. -1 The high reversible capacity of LNDF is attributed to the presence of ND and more LiF and NaF in the CEI, which reduces side reactions between the cathode material and the electrolyte during cycling. This demonstrates that LNDF cathode material batteries possess high capacity and high stability.

[0050] 2) Charge-discharge cyclic voltammetry test

[0051] Cyclic voltammetry testing conditions included a test temperature controlled at 25℃, the use of an electrochemical workstation, and a scan rate set to 0.1 mV / s to 1 mV / s. For example... Figure 5 The LNDF cathode exhibited a sharper peak than the LNF cathode, indicating that the introduction of NDs is beneficial for enhancing the electron / ion transfer of the battery. With increasing scan rate, both LNF and LNDF cathodes maintained their characteristic redox peaks, but the polarization was amplified, while the polarization phenomenon of the LNDF cathode was alleviated. This suggests that the LNDF cathode has higher electronic conductivity and faster ion transport kinetics due to its unique structure and the addition of NDs.

[0052] 3) Constant current charge-discharge curve test

[0053] The constant-current charge-discharge voltage plateau curves of batteries S1 and S2 prepared using samples #LNF and #LNDF as cathode materials are shown below. Figure 6 As shown, the current density is 50 mA g. -1The voltage range is 2-4.4V. The charge / discharge capacity of the battery using LNDF as the positive electrode during the first cycle is 163(155) mA hg. -1 It is significantly higher than LNF's 135(125) mAh g. -1 The initial coulombic efficiency (ICE) of LNDF is 95%, higher than that of LNF (92%). After 200 cycles, LNDF achieves a capacity of 162 mAh g⁻¹. -1 This indicates a high capacity retention rate (100%). However, after 200 cycles, the charging capacity of the LNF cathode is low, at 130 mA hg. -1 This confirms that LNDF forms a more stable CEI film on its surface during cycling, enhancing electrochemical stability and reversibility.

Claims

1. A three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and fluorinated carbon as the binding site 1.5 Na 1.5 V2(PO4)3 / NDs / CF x The method for preparing the positive electrode material is characterized by, The steps of this method are as follows: 1) Hydrogen-treated nanodiamond powder (NDs) and fluorinated carbon (CF) x Dissolved in deionized water and sonicated for 2 hours, solution A is obtained; the hydrogen-treated nanodiamond powder is nanodiamond powder that has been heat-treated in a hydrogen atmosphere. 2) Take NH4VO3 and citric acid monohydrate C6H at a molar ratio of 1:

1. 10 O8, dissolved in deionized water, heated and stirred at 80°C until a transparent blue solution B is formed; 3) Add solution A from step 1) to solution B from step 2), and weigh out NaOH, LiOH, and NH4H2PO4 powders and add them to the solution; NaOH, LiOH, NH4VO3, NH4H2PO4, and C6H 10 The molar ratio between O8 is 3:3:4:6:4; 4) The solution is continuously stirred and heated to evaporate the water, and then dried in a drying oven; 5) Grind the dried sample into a fine powder, preheat at 350℃ for 4 hours, and then heat in argon gas at 750℃~800℃ for 5 minutes. -1 Annealing at a heating rate of 8 h yielded a three-dimensional Li-type nanodiamond with fluorinated carbon as the substrate and fluorinated carbon as the binding site. 1.5 Na 1.5 V2(PO4)3 / NDs / CF x Positive electrode material.

2. The three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding site as described in claim 1. 1.5 Na 1.5 The method for preparing V2(PO4)3 cathode material is characterized by, The preparation steps of hydrogen-treated nanodiamond powder in step 1) are as follows: Hydrogen-treated nanodiamond powder was obtained by heating nanodiamond powder to 500°C in a vacuum chamber under a hydrogen atmosphere and then cooling it to room temperature under a flow of hydrogen.

3. The three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding point as described in claim 2. 1.5 Na 1.5 The method for preparing V2(PO4)3 cathode material is characterized by, The particle size of the nanodiamond powder is 5-10 nm.

4. The three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding point as described in claim 2. 1.5 Na 1.5 The method for preparing V2(PO4)3 cathode material is characterized by, The hydrogen flow rate is 50 sccm.

5. The three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding point as described in claim 1. 1.5 Na 1.5 The method for preparing V2(PO4)3 cathode material is characterized by, In step 1), the side length of the fluorinated carbon particles ranges from 1 to 30 μm.

6. The three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding point as described in claim 1. 1.5 Na 1.5 The method for preparing V2(PO4)3 cathode material is characterized by, In step 3), according to the Li in the obtained composite material 1.5 Na 1.5 V2(PO4)3, NDs and CF x The mass ratio of solution A to solution B is 1.80:0.005:0.

03.

7. The three-dimensional Li₂ with fluorinated carbon as the substrate and nanodiamond as the binding site prepared by the method according to any one of claims 1 to 6. 1.5 Na 1.5 V2(PO4)3 / NDs / CF x The cathode material is characterized by, The cathode material uses CFx as a substrate and NDs as binding sites; nanodiamonds are distributed between CFx and Li. 1.5 Na 1.5 Three-dimensional Li forms between V2(PO4)3. 1.5 Na 1.5 V2(PO4)3 / NDs / CF x Composite structure.

8. The three-dimensional Li-based nanodiamond with fluorinated carbon as the substrate and nanodiamond as the binding site as described in claim 7. 1.5 Na 1.5 V2(PO4)3 / NDs / CF x Applications of cathode materials in lithium-ion battery cathodes.

9. The use according to claim 8, characterized in that, 10 wt% binder, 80 wt% of the cathode material, and 10 wt% conductive agent are mixed, and solvent is added. The mixture is stirred with a magnetic stirrer to form a viscous fluid. The viscous fluid is then coated onto a current collector and dried under vacuum. Finally, it is cut into electrode shapes and compacted to obtain the cathode of a lithium-ion battery.

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