Preparation method of anti-lithiation graphite with amorphous carbon edge structure and application thereof in lithium ion battery field

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a preparation method of anti-lithium precipitation graphite with amorphous carbon edge structure and application of the anti-lithium precipitation graphite in the field of lithium ion batteries. 3 The application utilizes the non-uniform oxidation mechanism of graphite edges in carbon dioxide and the sp 3 Carbon atom in-situ formation mechanism to construct a graphite structure capable of spontaneously reducing local polarization, thereby realizing optimization of local high lithium ion flux, and then improving the rate performance and cycle life of the lithium ion battery as a whole by increasing the anti-lithium precipitation capacity of the graphite material itself.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a method for preparing lithium-resistant graphite with an amorphous carbon edge structure and its application in the field of lithium-ion batteries. Background Technology

[0002] Graphite is the core anode material for lithium-ion batteries. Its low cost, high stability, and excellent lithium-ion intercalation / deintercalation performance make it widely used in consumer electronics, electric vehicles, and energy storage, supporting the dominant position of lithium-ion batteries in the energy storage field. However, graphite is prone to lithium plating under extreme conditions (low temperature, fast charging), leading to battery capacity decay, shortened lifespan, and even safety hazards, severely limiting the performance improvement of lithium-ion batteries. Anti-lithium plating graphite, by optimizing the graphite structure and reducing the lithium-ion migration barrier, can effectively suppress lithium plating, ensuring the cycle stability and safety of lithium-ion batteries under extreme conditions. This has significant industrial value and application significance for promoting the development of high-performance lithium-ion batteries and expanding their application scenarios.

[0003] In existing technologies, to improve the performance of lithium-ion batteries and solve the problem of lithium deposition in graphite, the core focus is on graphite structure modification and performance optimization, resulting in multiple technical approaches: one is to construct an amorphous carbon structure from graphite, utilizing amorphous carbon (sp... 3 Highly active sites of hybrid carbon and suitable Li / Li ratio + First, the adsorption energy is optimized to improve the local lithium-ion flux and alleviate lithium-ion aggregation polarization. Second, three mainstream methods are used to regulate the graphite structure to improve lithium-ion transport performance: chemical activation (acid / alkali high-temperature etching), physical activation (oxidizing gas atmosphere high-temperature etching), and vapor deposition. Third, the graphite interface is modified to reduce the migration energy barrier of lithium ions in graphite and solid interface, thereby reducing the possibility of lithium metal nucleation and deposition.

[0004] However, existing technologies for improving the performance of lithium-ion batteries and solving the problem of lithium plating in graphite still have many problems and are difficult to achieve efficient anti-lithiation effect: (1) Existing graphite structure modification methods have obvious limitations. Chemical activation methods are prone to introducing heteroatoms, and the washing process is difficult to completely remove them (such as the invention patent with publication number CN119306216A), which affects battery performance; physical activation methods are mainly used to remove residual impurities in precursors or activated carbon industry, and have limited effect on graphite anti-lithiation modification; vapor deposition methods have not yet achieved effective control of the intrinsic structure of graphite and cannot play an anti-lithiation role. (2) The core technology bottleneck has not been broken through. Existing methods cannot solve the limitation of lithium-ion transport by the intrinsic structure of graphite with ordered multi-layer stacking, and it is difficult to effectively reduce the local lithium-ion flux and fundamentally suppress the problem of lithium plating in graphite. (3) It is difficult to balance the comprehensive performance of modified graphite. Although some modification methods can improve lithium-ion transport to a certain extent, they will sacrifice the specific capacity or cycle stability of graphite and cannot meet the application requirements of high-performance lithium-ion batteries. In summary, there is an urgent need for a novel method for preparing lithium-resistant graphite to overcome existing technological bottlenecks and achieve a synergistic improvement in both the lithium-resistant properties and overall electrochemical performance of graphite. Summary of the Invention

[0005] The present invention aims to provide a method for preparing lithium-resistant graphite with an amorphous carbon edge structure and its application in the field of lithium-ion batteries, so as to solve the technical problem that the existing ordered multi-layer stacked structure of graphite materials cannot solve the limitation of lithium-ion transport, thus making it difficult to reduce local lithium-ion flux or suppress graphite lithium deposition.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing lithium-resistant graphite with an amorphous carbon edge structure, comprising the following steps: Step S1: Place the graphite carbon precursor in a heated container and preheat it to the reaction temperature under an inert gas atmosphere; Step S2: Introduce carbon dioxide gas into the preheated precursor and react it. After the reaction is complete, allow it to cool naturally to room temperature to obtain lithium-resistant graphite with an amorphous carbon edge structure.

[0007] Preferably, the precursor is mesophase carbon microspheres (MCMB) with highly anisotropic graphite edges, and the particle size D of the MCMB precursor particles is... 50 The surface area ranges from 2 to 30 μm, and the specific surface area ranges from 0.5 to 2 m². 2 / g.

[0008] Preferably, the heatable container is a tube furnace or a rotary furnace.

[0009] Preferably, the reaction temperature is 800~1000℃, and the heating rate in both stages is 5~15℃ / min.

[0010] Preferably, the flow rate of carbon dioxide gas is 0.2~2 L / min, and the reaction time is 0.5~5 h.

[0011] Preferably, the carbon dioxide gas is high-purity carbon dioxide, or a mixture of carbon dioxide and an inert gas; the inert gas is either high-purity argon or high-purity nitrogen. This facilitates the full surface reaction of the precursor.

[0012] Preferably, when the carbon dioxide gas is a mixture of carbon dioxide and an inert gas, the carbon dioxide content in the mixture is greater than 20 vol.

[0013] Preferably, this solution also provides an anti-lithium plating graphite with an amorphous carbon edge structure, wherein the anti-lithium plating graphite particles with an amorphous carbon structure have a disordered edge structure on the outside at a depth > 200 nm; the edge graphite structure is a stack of a few lamellar layers (less than 10 layers) and has obvious sp. 3 Hybrid structure, surface Raman D / G peak ratio greater than 0.35, and overall particle specific surface area less than 10 m² 2 / g.

[0014] Preferably, this solution also provides an application of lithium-ion battery-resistant graphite with an amorphous carbon edge structure, including the preparation of a graphite-lithium half-cell using the aforementioned lithium-ion battery-resistant graphite with an amorphous carbon edge structure as an electrode. This facilitates the testing of the electrochemical performance of the extended-layer graphite.

[0015] Preferably, the electrolyte used in the graphite-lithium half-cell is a mixture of 1M LiPF6 solution and 1 vol% VC solution, wherein the solvent in the LiPF6 solution is a mixture of EC, EMC and DMC in equal volume ratio.

[0016] The principle of this scheme is: This scheme utilizes the heterogeneous oxidation mechanism of graphite edges in carbon dioxide and sp 3 The in-situ carbon atom formation mechanism constructs a graphite structure that can spontaneously reduce local polarization, thereby optimizing local high lithium-ion flux. Furthermore, by increasing the graphite material's resistance to lithium plating, the overall rate performance and cycle life of lithium-ion batteries are improved.

[0017] Compared with the prior art, the advantages of the present invention are: 1. The preparation method of the lithium-resistant graphite with amorphous carbon structure described in this invention, without changing the internal structure of the mesophase carbon microsphere precursor and without introducing heteroatoms, uses high-temperature physical activation of carbon dioxide to construct an amorphous structure in situ in the outer structure (depth > 200 nm) by adjusting the reaction parameters.

[0018] 2. The lithium-resistant graphite with an amorphous carbon structure obtained by this invention has more adsorption sites, and the sp3 hybrid carbon atoms in the amorphous structure have higher electronic activity than the sp2 hybrid carbon atoms. Therefore, it can optimize the interfacial chemical process during the formation process, increase the proportion of inorganic components in the solid electrolyte interface (SEI) and their spatial distribution in the interface, and improve the stability of the SEI interface under long-term cycling.

[0019] 3. The lithium-resistant graphite with an amorphous carbon structure obtained in this invention undergoes mild oxidation with carbon dioxide to achieve a few-layer stacked edge structure. This results in the formation of nanoscale pore structures at the edges, while simultaneously generating sp3 hybrid carbon atom structures in situ at the edges. Under conditions of high overall lithium-ion flux and low temperature, this edge structure can suppress the generation of high local lithium-ion flux sites at the particle interface, optimize mass transfer kinetics, effectively suppress overpotential lithium deposition due to polarization, and reduce lithium dendrite formation.

[0020] 4. Since the reaction process between the oxidizing gas carbon dioxide and the mesophase carbon microsphere precursor is mild and the increase in specific surface area is limited, the initial coulombic efficiency loss of lithium-ion batteries caused by the increase in graphite active sites in this invention is only 2%~5%. The initial coulombic efficiency loss can be further reduced by increasing the compaction density.

[0021] 5. This technical solution is simple and easy to promote to ton-scale production. Combined with a low-freezing-point multi-carbonate-based electrolyte, it can solve the problem of commercial lithium-ion batteries failing to operate normally under extreme conditions at the electrode material side. Attached Figure Description

[0022] Figure 1 The image shows a comparison of scanning electron microscope (SEM) images of Comparative Example 3 (artificial graphite precursor) and Comparative Example 4 (artificial graphite particles after full reaction).

[0023] Figure 2 The results show the comparison of multi-site Raman scattering patterns of Comparative Example 1 (precursor particles), Example 1, and Example 3 (lithium-resistant graphite particles) of the present invention.

[0024] Figure 3 The images shown are scanning electron microscope (SEM) images of Comparative Example 1 (precursor particles) and Example 1 (lithium-resistant graphite particles) of the present invention.

[0025] Figure 4 The high-resolution transmission electron microscope (HRTEM) images of Comparative Example 1 (precursor particles) and Example 1 (lithium-resistant graphite particles) of the present invention are shown as a comparison.

[0026] Figure 5The X-ray diffraction (XRD) spectra of Comparative Example 1 (precursor particles) and Example 1 (lithium-resistant graphite particles) of the present invention are compared.

[0027] Figure 6 The nitrogen adsorption-desorption curves of Comparative Example 1 (precursor particles) and Example 1 (lithium-resistant graphite particles) are compared.

[0028] Figure 7 The electrochemical mass transfer kinetics test results of Comparative Example 1 (precursor half-cell) and Example 1 (lithium-resistant graphite half-cell) of the present invention are compared. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials and reagents used can all be obtained commercially.

[0030] Example 1 This solution provides a lithium-resistant graphite with an amorphous carbon edge structure, and the preparation method includes the following steps: Step S1: Take 4g of commercial graphite mesophase carbon microspheres (MCMB) as a precursor, place them in a tube furnace, and heat them to the reaction temperature at 15℃ / min under argon protection (1000℃ in this example). Step S2: Switch the inert gas to high-purity carbon dioxide (inlet rate is 0.2 L / min), react at 1000℃ for 3 hours, stop the carbon dioxide inlet, cool to room temperature, and obtain MCMB with amorphous carbon structure (A-MCMB-1000-3).

[0031] This solution also provides an application of lithium-ion battery-resistant graphite with an amorphous carbon edge structure, including the following: (a) Electrode preparation: NMP solvent was added at a mass ratio of 92:4:4 (negative electrode material: super-P conductive agent: PVDF binder) to obtain electrode slurry, which was coated onto commercial carbon-coated copper foil current collector. After heating to volatilize NMP, φ14 mm electrode sheets were cut for later use.

[0032] (II) Battery Assembly: Assemble the above electrode sheets into a 2025 coin cell. The half cell includes a positive electrode shell, electrode sheets, separator, lithium metal, gasket, spring sheet and negative electrode shell. The electrolyte content is 60 μL~80 μL. The lithium metal is a 0.1 mm thick commercial lithium metal disc with a diameter of φ16 mm. The separator is a Celgard 2500 separator cut into a circle with a diameter of φ19 mm. The electrolyte formula is: 1M LiPF6in EC:EMC:DMC (1:1:1 vol) + 1 vol%VC.

[0033] (III) The assembly process includes: placing the A-MCMB-1000-3 electrode sheet, separator, and lithium metal sheet into the positive electrode shell of the 2025 model battery in sequence, adding 60 μL~80 μL of electrolyte to wet the inside, then placing the gasket and spring sheet, and pressing them together with a pressing machine to obtain the 2025 model expanded graphite||lithium half-cell, denoted as A-MCMB-1, with a loading capacity of 3 mg / cm³. 2 .

[0034] Battery testing: All batteries underwent initial formation at 0.05C discharge and 0.1C charge, followed by three cycles at a constant current of 0.1C, after which various electrochemical tests were performed. In this embodiment, 3C rate performance testing and 0.5C cycle performance testing were conducted.

[0035] Example 2 This embodiment is basically the same as Embodiment 1, except that: during the material preparation process, a mixture of carbon dioxide and high-purity nitrogen is introduced at a rate of 2 L / min, wherein the carbon dioxide content in the mixture is 50 vol%; the reaction temperature is 800℃ and the reaction time is 1 h. The half-cell formation method is the same, and it is prepared for use after 3 cycles at 0.1C.

[0036] Example 3 This embodiment is basically the same as Embodiment 1, except that: during the material preparation process, a mixed gas of carbon dioxide and high-purity nitrogen is introduced at a rate of 1 L / min, wherein the carbon dioxide content in the mixed gas is 20 vol%; the reaction temperature is 950℃, and the reaction time is 3 h. The half-cell formation method is the same, and it is prepared for use after 3 cycles at 0.1C.

[0037] Comparative Example 1 This comparative example does not involve reacting the precursor; instead, commercial mesophase carbon microspheres (MCMB) are used directly as the electrode material for electrode preparation and subsequent steps. The half-cell formation method is the same, and the cells are cycled at 0.1C for 3 cycles before being put into use.

[0038] Comparative Example 2 This comparative example is basically the same as Example 1, except that a mixed gas of carbon dioxide and high-purity nitrogen is introduced, in which carbon dioxide accounts for 5 vol%. The resulting material is only characterized.

[0039] Comparative Example 3 This comparative example focuses on commercially available artificial graphite and performs relevant material characterization.

[0040] Comparative Example 4 This comparative example is basically the same as Example 1, except that artificial graphite from Comparative Example 3 is used as the precursor. The resulting material is only characterized.

[0041] Experimental Example 1: Comparison of materials with amorphous carbon edge structure and lithium plating resistant graphite, and performance comparison of assembled lithium-ion half-cells. To aid in understanding this technical method, its practical application effects and technical features are described. The experimental results and related analyses of the above comparative examples and embodiments are presented in further detail.

[0042] Examples 1-2 and Comparative Examples 1-4 D / G As shown in Table 1.

[0043] Table 1. Ig obtained from Raman diffraction in Examples 1-2 and Comparative Examples 1-4 D / G

[0044] The above addresses different material particles I D / G This demonstrates that the highly anisotropic structure of MCMB is advantageous for its role as a precursor in forming amorphous structures. Furthermore, SEM images of the artificial graphite precursor before and after the reaction further illustrate the difference in its structural reactivity. Figure 1 ).

[0045] For MCMB-related reactions, the multisite Raman spectra of Examples 1, 2, and Comparative Example 1 are as follows: Figure 2 As shown. The results indicate that the average D band to G band ratio (D peak to G peak intensity ratio, I) at different sites in Comparative Example 1 is: D / G The value of D band was 0.33, while it was 0.35 and 0.80 in Examples 1 and 2, respectively. The relative increase in D band indicates the effective formation of amorphous structures during the physical activation of carbon dioxide.

[0046] Furthermore, such as Figure 3 and Figure 4 As shown, the SEM and corresponding HRTEM of Comparative Example 1 and Example 1 directly demonstrate that their edge structures exhibit incompletely close-packed sheet structures in the edge space at a scale of at least 200 nm. Figure 4 a~ Figure 4 c), and the 2nm precision HRTEM of Example 1 confirmed the 1-3nm amorphous structure edges generated due to the carbon dioxide physical activation process. Figure 4 d). The X-ray diffraction patterns of the two materials ( Figure 5 This further illustrates that the overall graphitization degree of Example 1 did not change, and the increase in its (100) and (110) diffraction peaks indicates an increase in the proportion of additional edge stacking structures. The increase in active sites caused by the above changes in morphology and physical properties can be attributed to... Figure 6 Quantification of nitrogen adsorption-desorption curves.

[0047] Compared to Examples 2 and 3, the actual specific surface area of ​​Example 1 was still controlled at 10 m² under higher temperatures and activation times. 2 / g or less (actually approximately 6.38 m 2 The average initial coulombic efficiency (ACE) from multiple repeated experiments (Table 2) demonstrates that the implementation of this technique may not cause a significant decrease in the crucial initial coulombic efficiency required for lithium-ion battery applications. This demonstrates the effectiveness of this technique in altering the inherent edge structure of mesophase carbon microspheres.

[0048] Table 2. Average initial coulombic efficiency and 3C cycle performance of Examples 1-3 and Comparative Example 1

[0049] Experimental Example 2: Performance Comparison of the Obtained Batteries To further illustrate the beneficial effects of this technique in addressing the critical technical challenge of preventing lithium plating in graphite within the lithium-ion battery field, electrochemical tests from actual experiments are presented here. This is based on the electron transfer kinetics of lithium-ion batteries (Butler-Volmor equation). j ∝ i 0sinh(F η / RT) In the formula, j Let F, R, and T be the lithium-ion flux, F, R, and T, respectively, representing the Faraday constant, the gas constant, and the temperature. i 0 represents the exchange current density of the graphite material. η This is an overpotential. During the experiment, a fixed small current can be used to test the small flux. η This allows for the calculation of its mass transfer kinetics. After complete lithium insertion with a small current, conventional LiC6-state graphite can be obtained. Since the graphite is already fully lithiated, the additional 50% capacity occurs at the graphite interface. Figure 7As can be seen, under the same lithium-ion flux, the half-cell prepared in Example 1 exhibits a more near-zero equilibrium lithium deposition potential and a lower nucleation overpotential. Specifically, the lower equilibrium lithium deposition potential in Example 1 indicates that the electrode particle structure in Example 1 is beneficial in reducing the polarization of the graphite surface, while the lower nucleation overpotential in Example 1 indicates a higher surface exchange current density, thus leading to a lower nucleation overpotential.

[0050] The changes in the overall performance of the half-cell further confirm the beneficial effects of this technique on improving lithium-ion performance and overall stability: In Table 2, the actual capacity retention of Comparative Example 1 under 3C constant current charge / discharge conditions is only 27% of its actual capacity. This result indicates that due to the kinematic limitations of the selected graphite particle size (D50 = 15.6 μm), the slow interfacial process, and the resulting polarization effect, graphite is difficult to fully intercalate lithium near 0V. However, the graphite prepared by this method showed a certain degree of performance improvement in Examples 1-3. Among them, the capacity retention rates of Examples 1-3 at 3C rate reached 51%, 39%, and 40%, respectively, which were significantly higher than those of Comparative Example 1. This demonstrates the beneficial effect of this method on the mass transfer process at the graphite interface. At the same time, the cycle stability of Examples 1-3 was also improved compared to Comparative Example 1. After 64 cycles at 3C rate, the capacity retention rate of Comparative Example 1 was only 10%, indicating that due to its large surface polarization effect, significant lithium plating occurred during cycling, resulting in a decrease in capacity. Examples 1-3 all showed improved capacity retention after cycling, which further demonstrates the feasibility and beneficial effects of the graphite material prepared by this invention in the field of lithium-ion battery technology.

[0051] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing lithium-resistant graphite with an amorphous carbon edge structure, characterized in that: Includes the following steps: Step S1: Place the graphite carbon precursor in a heated container and preheat it to the reaction temperature under an inert gas atmosphere; Step S2: Introduce carbon dioxide gas into the preheated precursor and react it. After the reaction is complete, allow it to cool naturally to room temperature to obtain lithium-resistant graphite with an amorphous carbon edge structure.

2. The method for preparing lithium-resistant graphite with an amorphous carbon edge structure according to claim 1, characterized in that: The precursor is mesophase carbon microspheres (MCMB) with highly anisotropic graphite edges, and the particle size D of the MCMB precursor particles is... 50 The surface area ranges from 2 to 30 μm, and the specific surface area ranges from 0.5 to 2 m². 2 / g.

3. The method for preparing lithium-resistant graphite with an amorphous carbon edge structure according to claim 2, characterized in that: The heated container is a tube furnace or a rotary furnace.

4. The method for preparing lithium-resistant graphite with an amorphous carbon edge structure according to claim 1, characterized in that: The reaction temperature is 800~1000℃, and the heating rate in both stages is 5~15℃ / min.

5. A method for preparing lithium-resistant graphite with an amorphous carbon edge structure according to claim 4, characterized in that: The flow rate of carbon dioxide gas is 0.2~2 L / min, and the reaction time is 0.5~5 h.

6. The method for preparing lithium-resistant graphite with an amorphous carbon edge structure according to claim 5, characterized in that: The carbon dioxide gas is high-purity carbon dioxide, or a mixture of carbon dioxide and an inert gas; the inert gas is either high-purity argon or high-purity nitrogen.

7. The method for preparing lithium-resistant graphite with an amorphous carbon edge structure according to claim 6, characterized in that: When the carbon dioxide gas is a mixture of carbon dioxide and inert gases, the carbon dioxide content in the mixture is greater than 20 vol.

8. A lithium-resistant graphite with an amorphous carbon edge structure, characterized in that: Prepared by the method described in any one of claims 1 to 7.

9. The application of a lithium-ion battery-resistant graphite with an amorphous carbon edge structure, characterized in that: This includes using the lithium-resistant graphite with an amorphous carbon edge structure as described in claim 8 as an electrode to prepare a graphite-lithium half-cell.

10. The application of the lithium-ion battery-resistant graphite with an amorphous carbon edge structure according to claim 9, characterized in that: The electrolyte used in the graphite-lithium half-cell is a mixture of 1M LiPF6 solution and 1 vol% VC solution, wherein the solvent in the LiPF6 solution is a mixture of EC, EMC and DMC in equal volume ratio.

Images