A lithium-ion battery negative electrode material with a lithium lanthanum zirconium oxide solid electrolyte coated with graphite and a preparation method thereof

Abstract

The present invention relates to a lithium ion battery negative electrode material of lithium lanthanum zirconium oxide solid electrolyte coated graphite and a preparation method thereof, belonging to the technical field of lithium ion batteries. The method comprises first coating natural graphite with dopamine in a solution; then uniformly mixing the dopamine-coated graphite, lithium nitrate, lanthanum nitrate hexahydrate, zirconium oxychloride octahydrate, citric acid monohydrate, etc. in deionized water; and subjecting the powder obtained after evaporating the solution to high-temperature heat treatment to obtain lithium lanthanum zirconium oxide solid electrolyte coated graphite. The method uses dopamine to pre-coat natural graphite, and utilizes the amphiphilic properties of dopamine to uniformly coat the lithium lanthanum zirconium oxide solid electrolyte on the surface of natural graphite without segregation, thereby ensuring the rate performance of the material while greatly improving the cycle performance of the material, solving the shortcomings of existing modification technologies such as insignificant improvement in cycle life and negative impact on rate performance.

Description

Technical Field

[0001] The present invention relates to a lithium ion battery negative electrode material of lithium lanthanum zirconium oxide solid electrolyte coated with graphite and a preparation method thereof, belonging to the technical field of lithium ion batteries. Background Art

[0002] Lithium-ion secondary batteries, due to their green and environmentally friendly, high energy density, and reusability, can provide a feasible strategy for energy security and efficient and sustainable operation of new energy, and have extremely high application value and research value.

[0003] Graphite-based anode materials have been used extensively in lithium-ion battery systems to this day and are currently the most widely used anode material. Graphite anodes offer advantages such as high capacity density, low potential, good conductivity, and abundant resources. They will remain the primary anode material of choice for lithium-ion batteries for a long time to come.

[0004] Natural graphite is widely available and inexpensive, making it an important material for the negative electrode of lithium-ion batteries. However, natural graphite negative electrode materials still have the following disadvantages: (1) Natural graphite has anisotropy, which is not conducive to the diffusion of lithium ions. (2) There are many surface defects and poor compatibility with the electrolyte. (3) Cracks will form between the layers due to the insertion and extraction of lithium ions, thereby increasing the Li + Diffusion resistance. (4) The lower electrode potential causes lithium deposition at the negative electrode during high-rate charging. Currently, traditional graphite negative electrodes can no longer meet the demand for high-performance lithium-ion batteries in social development. Therefore, many researchers have been committed to natural graphite modification technology. The main modification technologies include coating modification, surface treatment, element doping, etc.

[0005] Coating is a simple and effective modification method. Coating natural graphite with metals and their oxides can improve the cycling stability and rate performance of graphite anodes. Lithium lanthanum zirconium oxide solid electrolytes, with their excellent ionic conductivity and electrochemical stability, hold promise for improving the performance of natural graphite. However, conventional methods for coating natural graphite with lithium lanthanum zirconium oxide solid electrolytes have segregation issues, preventing them from achieving the desired results. Summary of the Invention

[0006] In view of this, the present invention aims to provide a lithium-ion battery negative electrode material comprising graphite coated with a lithium lanthanum zirconium oxide solid electrolyte and a preparation method thereof. Dopamine is used to promote the uniform coating of the lithium lanthanum zirconium oxide solid electrolyte on the surface of natural graphite, thereby improving the capacity and cycle stability of natural graphite.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for preparing a negative electrode material for a lithium-ion battery comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite, the method comprising the following steps:

[0009] (1) dissolving dopamine hydrochloride in a mixed solution of water and ethanol, and then adding natural graphite and stirring to uniformly disperse the mixture to obtain a dispersion;

[0010] (2) adjusting the dispersion to be weakly alkaline, stirring to polymerize and adsorb dopamine on the surface of natural graphite, filtering, collecting the powder and vacuum drying to obtain dopamine-coated graphite;

[0011] (3) dispersing the dopamine-coated graphite in deionized water, adding lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate, and then adding citric acid monohydrate to obtain a mixed reaction system;

[0012] (4) heating and stirring until the solution in the mixed reaction system is evaporated to dryness, and vacuum drying the evaporated material to obtain a precursor material;

[0013] (5) The precursor material is transferred to a tube furnace and heat treated under a protective gas atmosphere to obtain a lithium ion battery negative electrode material with a lithium lanthanum zirconium oxide solid electrolyte coated with graphite.

[0014] Preferably, in step (1), the mass ratio of dopamine hydrochloride to natural graphite is 0.02 to 0.04:1.

[0015] Preferably, in step (1), the volume ratio of water to ethanol is 1:1 to 1.5.

[0016] Preferably, in step (2), NH3·H2O is added dropwise to adjust the pH value of the dispersion to 8.3-8.5.

[0017] Preferably, in step (2), the stirring rate is 200-300 rpm and the stirring time is 24-32 h.

[0018] Preferably, in step (2), deionized water and anhydrous ethanol are used alternately for filtration and washing until neutrality occurs.

[0019] Preferably, in step (2), the vacuum drying temperature is 60-80° C. and the time is 6-10 h.

[0020] Preferably, in step (3), lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate are prepared according to the conditions of lithium lanthanum zirconium oxide (Li7La3Zr2O 12 ) is added in a chemical dosage ratio, and an additional 10% to 12% excess lithium nitrate is added, corresponding to a lithium lanthanum zirconium oxide mass of 3% to 10% of the mass of natural graphite. A certain amount of lithium nitrate is added to compensate for lithium loss during the subsequent heating process.

[0021] Preferably, in step (3), the molar amount of citric acid monohydrate is 1.5 to 2 times that of the cations in the mixed reaction system.

[0022] Preferably, in step (4), the heating and stirring temperature is 70-90° C., and the stirring rate is 200-300 rpm.

[0023] Preferably, in step (4), the vacuum drying temperature is 60-80° C. and the time is 6-10 h.

[0024] Preferably, in step (5), the protective gas is nitrogen or an inert gas (a gas element corresponding to all Group 0 elements on the periodic table).

[0025] Preferably, in step (5), the heat treatment temperature is 850-950°C, the treatment time is 5-7h, and the heating rate is 5-10°C / min.

[0026] A lithium-ion battery negative electrode material with a lithium lanthanum zirconium oxide solid electrolyte coated with graphite is prepared by the above method.

[0027] A lithium-ion battery, wherein the negative electrode material of the battery is a lithium-lanthanum-zirconium-oxygen solid electrolyte-coated graphite lithium-ion battery negative electrode material described in the present invention.

[0028] Beneficial effects

[0029] The present invention involves dissolving dopamine hydrochloride in a mixed solution of water and ethanol, then adding natural graphite to react and generate dopamine-coated graphite. The dopamine-coated graphite is then mixed with lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate according to a specific method, followed by high-temperature heat treatment, to produce a lithium-ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte-coated graphite. The method pre-coates natural graphite with dopamine, leveraging the amphiphilic nature of dopamine to uniformly coat the surface of the natural graphite with the lithium lanthanum zirconium oxide solid electrolyte without segregation. This significantly improves the material's cycle performance while maintaining its rate performance, addressing shortcomings of existing modification technologies such as limited cycle life improvement and negative impacts on rate performance. The negative electrode material prepared by the method achieves a specific capacity exceeding 340 mAh / g, and its cycle capacity remains essentially unchanged after 450 cycles at 1C. The ratio of dopamine, lithium lanthanum zirconium oxide, and natural graphite used during the preparation process, as well as the temperature and time during the heat treatment, can influence the structure and performance of the negative electrode material.

[0030] The preparation method of the present invention is simple and safe, has low cost, and has good continuity, and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the SEM image of the final product in Example 1.

[0032] Figure 2 This is the EDS diagram of the final product in Example 1.

[0033] Figure 3-4 This is the XRD pattern of the final product in Example 1.

[0034] Figure 5 Graph showing the cycle performance of the final product in Example 1 and Comparative Example 1.

[0035] Figure 6 The first week charge and discharge curves of the final products in Example 1 and Comparative Example 1 are shown.

[0036] Figure 7 This is the cycle performance diagram of the final product in Example 2.

[0037] Figure 8 This is the SEM image of the final product in Comparative Example 2.

[0038] Figure 9 This is the cycle performance diagram of the final product in comparison 2.

[0039] Figure 10 This is the XRD pattern of the final product in Comparative Example 2.

[0040] Figure 11 This is the cycle performance diagram of the final product in Comparative Example 3. DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below with reference to specific embodiments.

[0042] In the following examples and comparative examples:

[0043] Battery assembly and testing. A slurry of the final product (Super P: sodium polyacrylate) mixed in a mass ratio of 8:1:1 was coated onto copper foil to form a negative electrode sheet. A lithium metal sheet served as the positive electrode, Ceglard 2500 was used as the separator, and LB315 was used as the electrolyte. The battery was then left to rest for 8 hours before being cycled at a 1C rate. The test voltage range was 0.005V-1.5V, with a 1C current density defined as 300mA / g.

[0044] Example 1

[0045] (1) Dissolve 0.1 g of dopamine hydrochloride in a mixture of water and ethanol in a volume ratio of 1:1, then add 5 g of natural graphite and stir evenly.

[0046] (2) NH3·H2O was added dropwise to the above solution to adjust the pH to 8.3. The mixed solution was magnetically stirred at 200 rpm for 24 h to polymerize dopamine. The reaction solution was filtered and washed alternately with deionized water and anhydrous ethanol until neutral. The powder was collected and dried in a vacuum oven at 70°C for 10 h to obtain dopamine-coated graphite.

[0047] (3) The dopamine-coated graphite was dispersed in deionized water, and lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate were added to the water in a stoichiometric ratio, with the corresponding mass of lithium, lanthanum, zirconium and oxygen being 10% of that of the natural graphite. An additional 10% of lithium nitrate was then added, followed by citric acid monohydrate at twice the molar amount of the cations.

[0048] (4) The mixed solution was magnetically stirred at 300 rpm at 80°C until the solution was evaporated to dryness, and then the evaporated material was placed in an oven at 80°C for vacuum drying for 10 h.

[0049] (5) The dried mixed material was transferred to a tube furnace and heated to 900°C at a heating rate of 5°C / min under argon gas protection for 7 hours to obtain lithium lanthanum zirconium oxide solid electrolyte coated graphite.

[0050] The SEM test results of the final product are as follows Figure 1 As shown, the results show that the morphology of the natural graphite material after co-coating with lithium lanthanum zirconium oxygen solid electrolyte has not changed significantly, and the original spherical graphite morphology characteristics are retained.

[0051] The EDS test results of the final product are as follows Figure 2 As shown, the results show that the lithium lanthanum zirconium oxide solid electrolyte is evenly distributed on the graphite surface, indicating that the lithium lanthanum zirconium oxide solid electrolyte successfully coats natural graphite.

[0052] The XRD test results of the final product are as follows Figure 3-4 As shown in Figure 3, the results show that the XRD diffraction pattern of natural graphite was not significantly changed after heat treatment.

[0053] The electrochemical performance test results of the final product are as follows Figure 5 、 6 As shown, the results show that the final product has a first-week charging capacity of 342.6 mAh / g and a first-week coulombic efficiency of 67.0%; in terms of cycle performance, the final product has a capacity of 339.9 mAh / g after 450 cycles at a current density of 1C, and a capacity retention rate of 99.4%.

[0054] Example 2

[0055] In step (2), the corresponding mass of lithium lanthanum zirconium oxide is 3% of natural graphite, and the rest is the same as in Example 1.

[0056] The SEM, EDS and XRD test results of the final product are similar to those in Example 1.

[0057] The electrochemical performance test results of the final product are as follows Figure 7 As shown, the 3% lithium lanthanum zirconium oxide solid electrolyte coated with graphite was cycled for 700 weeks at a rate of 1C, and the capacity remained at 290mAh / g.

[0058] Comparative Example 1

[0059] The same battery assembly and testing were performed using natural graphite.

[0060] The electrochemical performance test results of the final product are as follows Figure 5 、 6 As shown, the results show that the final product has a first-week charging capacity of 350.7 mAh / g and a first-week coulombic efficiency of 65%; in terms of cycle performance, the final product has a capacity of 111.5 mAh / g after 450 cycles at a current density of 1C, and a capacity retention rate of 31.8%.

[0061] Comparative Example 2

[0062] Without using dopamine, natural graphite is directly coated with lithium lanthanum zirconium oxide solid electrolyte.

[0063] (1) 5 g of natural graphite was dispersed in deionized water. Lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate were added to the water in a stoichiometric ratio, with the corresponding mass of lithium, lanthanum, zirconium and oxygen being 10% of the added natural graphite. An additional 10% of lithium nitrate was then added, followed by citric acid monohydrate at twice the molar amount of the cations.

[0064] (2) The mixed solution was magnetically stirred at 300 rpm at 80°C until the solution was evaporated to dryness, and then the evaporated material was placed in an oven at 80°C for vacuum drying for 10 h.

[0065] (3) The dried mixed material was transferred to a tube furnace and heated to 900°C at a heating rate of 5°C / min under argon gas protection for 7 hours to obtain lithium lanthanum zirconium oxide solid electrolyte coated graphite.

[0066] The SEM test results of the final product are as follows Figure 8 As shown, the results show that there are segregated particles on the surface of the natural graphite material after direct co-coating of lithium lanthanum zirconium oxygen solid electrolyte, and the natural graphite cannot be uniformly coated.

[0067] The electrochemical performance test results of the final product are as follows Figure 9 As shown, the results show that the final product has a first-week charging capacity of 378.9 mAh / g and a first-week coulombic efficiency of 66.8%; in terms of cycle performance, the capacity of the final product decays rapidly at a current density of 1C and cannot work normally.

[0068] The EDS test results of the final product are as follows Figure 10 As shown, the results indicate that the lithium lanthanum zirconium oxide solid electrolyte obtained without dopamine is evenly distributed on the graphite surface, which is because the lithium lanthanum zirconium oxide solid electrolyte is segregated on the graphite surface.

[0069] Comparative Example 3

[0070] Using excess dopamine coated 5% lithium lanthanum zirconium oxide solid electrolyte

[0071] (1) Dissolve 0.5 g of dopamine hydrochloride in a mixture of water and ethanol in a volume ratio of 1:1, then add 5 g of natural graphite and stir evenly.

[0072] (2) NH3·H2O was added dropwise to the above solution to adjust the pH to 8.3, and the mixed solution was magnetically stirred at 200 rpm for 24 h to polymerize dopamine. The reaction solution was filtered and washed alternately with deionized water and anhydrous ethanol until neutral. The powder was collected and placed in an oven at 70°C for 10 h under vacuum to obtain dopamine-coated graphite.

[0073] (3) The dopamine-coated graphite was dispersed in deionized water, and lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate were added to the water in a stoichiometric ratio, with the corresponding mass of lithium, lanthanum, zirconium and oxygen being 5% of the added natural graphite. An additional 10% of lithium nitrate was then added, followed by citric acid monohydrate at twice the molar amount of the cations.

[0074] (4) The mixed solution was magnetically stirred at 300 rpm at 80°C until the solution was evaporated to dryness, and then the evaporated material was placed in an oven at 80°C for vacuum drying for 10 h.

[0075] (5) The dried mixed material was transferred to a tube furnace and heated to 900°C at a heating rate of 5°C / min under argon gas protection for 7 hours to obtain lithium lanthanum zirconium oxide solid electrolyte coated graphite.

[0076] The electrochemical performance test results of the final product are as follows Figure 11 As shown, the results show that the capacity of the final product decays rapidly at a current density of 1C and cannot work normally.

[0077] In summary, the invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be deemed to be within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite, characterized in that: The method steps include: (1) dissolving dopamine hydrochloride in a mixed solution of water and ethanol, adding natural graphite and stirring to disperse the mixture uniformly to obtain a dispersion; (2) adjusting the dispersion to be weakly alkaline, stirring to allow dopamine to polymerize and adsorb on the surface of natural graphite, filtering, collecting the powder and vacuum drying to obtain dopamine-coated graphite; (3) dispersing the dopamine-coated graphite in deionized water, adding lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate, and then adding citric acid monohydrate to obtain a mixed reaction system; (4) heating and stirring until the solution in the mixed reaction system is evaporated to dryness, and vacuum drying the evaporated material to obtain a precursor material; (5) transferring the precursor material into a tube furnace and performing heat treatment under a protective gas atmosphere to obtain a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite; Wherein, in step (1), the mass ratio of dopamine hydrochloride to natural graphite is 0.02~0.04:

1.

2. The method for preparing a lithium ion battery negative electrode material of a lithium lanthanum zirconium oxide solid electrolyte coated graphite according to claim 1, wherein: In step (1), the volume ratio of water to ethanol is 1:1~1.

5.

3. The method for preparing a negative electrode material for a lithium-ion battery comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (2), NH3∙H2O is added dropwise to adjust the pH value of the dispersion to 8.3-8.

5.

4. The method for preparing a lithium ion battery negative electrode material of a lithium lanthanum zirconium oxide solid electrolyte coated graphite according to claim 1, characterized in that: In step (2), the stirring rate is 200-300 rpm and the time is 24-32 h.

5. The method for preparing a lithium ion battery negative electrode material of a lithium lanthanum zirconium oxide solid electrolyte coated graphite according to claim 1, characterized in that: In step (2), deionized water and anhydrous ethanol are used alternately for filtration and washing until the mixture becomes neutral.

6. The method for preparing a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (2), the vacuum drying temperature is 60-80°C and the time is 6-10 hours.

7. The method for preparing a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (3), lithium nitrate, lanthanum nitrate hexahydrate, and zirconium oxychloride octahydrate are added according to the chemical dosage ratio of lithium lanthanum zirconium oxide, and an excess of 10% to 12% of lithium nitrate is additionally added, and the corresponding mass of lithium lanthanum zirconium oxide is 3% to 10% of the mass of natural graphite.

8. The method for preparing a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (3), the molar amount of citric acid monohydrate is 1.5 to 2 times that of the cation in the mixed reaction system.

9. The method for preparing a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (4), the heating and stirring temperature is 70-90°C, and the stirring rate is 200-300 rpm.

10. The method for preparing a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (4), the vacuum drying temperature is 60-80°C and the time is 6-10 hours.

11. The method for preparing a negative electrode material for a lithium-ion battery comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (5), the protective gas is nitrogen or an inert gas.

12. The method for preparing a lithium ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite according to claim 1, wherein: In step (5), the heat treatment temperature is 850~950℃, the treatment time is 5~7h, and the heating rate is 5~10℃ / min.

13. A lithium-ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite, characterized in that: The material is prepared by the method according to any one of claims 1 to 12.

14. A lithium-ion battery, characterized in that: The negative electrode material of the battery is a lithium-ion battery negative electrode material comprising a lithium lanthanum zirconium oxide solid electrolyte coated with graphite as described in claim 13.

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