Graphite material with widened interlayer spacing and preparation method and application thereof

Abstract

The present disclosure provides a graphite material with widened interlayer spacing, wherein the interlayer spacing at the boundary of the graphite material crystal is 0.36-0.41 nm. The present disclosure also provides a preparation method of the graphite material, comprising: first, performing high-temperature heat treatment on graphene oxide in a multi-layer stack in an inert gas atmosphere, so that the graphene oxide is converted into a graphite phase, and the interlayer spacing at the crystal boundary of the graphite phase is widened; then, performing crushing and granulation on the graphite phase to obtain the graphite material with widened interlayer spacing; the interlayer spacing at the boundary of the graphite material is 0.36-0.41 nm. The present disclosure also provides a lithium ion battery, wherein the surface of the negative electrode of the lithium ion battery is coated with the graphite material as described above, or the graphite material obtained by the preparation method as described above.

Description

Technical Field

[0001] This disclosure belongs to the field of materials application technology, and in particular relates to a graphite material with widened interlayer spacing, its preparation method, and its application. Background Technology

[0002] The overuse of non-renewable fossil fuels has led to an energy crisis, threatening sustainable social and economic development. To address this challenge, research and development of renewable energy sources has become a focus of public attention. Since its invention in the 1970s, lithium-ion batteries have become an indispensable part of modern life. With their advantages such as high energy density, long cycle life, and no memory effect, lithium-ion batteries have become the primary power source for modern electronic devices and electric vehicles. However, with technological advancements and societal progress, the performance of existing lithium-ion batteries is gradually failing to meet market demands. Issues such as the safety, fast charging speed, and temperature sensitivity of lithium-ion batteries also require continuous technological innovation and improvement to resolve.

[0003] As a key component of lithium-ion batteries, the performance of the anode material is crucial in determining the rate capability and low-temperature performance of lithium-ion batteries. Currently, graphite anode materials can reversibly insert and extract lithium ions to form LiC6 compounds, making them ideal anode materials for lithium-ion batteries. However, the low lithium-ion diffusion rate of graphite under high current density and low-temperature conditions is a major factor affecting its application and a key challenge for commercialization in fast charging and low-temperature technologies.

[0004] Therefore, it is necessary to develop a graphite anode material with a fast lithium-ion diffusion channel, which enables lithium ions to be rapidly transferred from the edge of the graphite to the interior, thereby achieving high specific capacity and cycle stability of lithium-ion batteries under fast charging and low temperature conditions. Summary of the Invention

[0005] In view of this, in order to at least partially solve at least one of the aforementioned technical problems, this disclosure provides a graphite material with widened interlayer spacing, wherein the interlayer spacing at the boundaries within the graphite material crystal is 0.36~0.41 nanometers.

[0006] According to embodiments of this disclosure, the particle size of the graphite material is 5-10 micrometers.

[0007] According to embodiments of this disclosure, the bulk interlayer spacing within the crystal of the graphite material is 0.335-0.34 nanometers, and the oxygen content of the graphite material is 1%-3%.

[0008] In another aspect of this disclosure, a method for preparing the graphite material as described above is proposed, comprising:

[0009] In an inert gas atmosphere, graphene oxide stacked in multiple layers is heat-treated to transform the graphene oxide into the graphite phase and widen the interlayer spacing at the crystal boundaries of the graphite phase to 0.36~0.41 nanometers.

[0010] The graphite phase is then crushed and granulated to obtain a graphite material with widened interlayer spacing.

[0011] According to embodiments of this disclosure, heat treatment of graphene oxide includes:

[0012] The graphene oxide is subjected to a first heat treatment to decompose and remove the oxygen-containing groups in the graphene oxide.

[0013] A second heat treatment is performed on the multilayer graphene oxide to promote carbon atom hybridization and form an ordered graphite phase layered structure.

[0014] The temperature of the second heat treatment is higher than that of the first heat treatment.

[0015] According to embodiments of this disclosure, in the first heat treatment, the heating temperature is 600-1000°C; in the second heat treatment, the heating temperature is 2000-3000°C.

[0016] According to embodiments of this disclosure, the oxygen content of the graphene oxide is 1%-5%, and the number of graphene oxide layers is 0.5-20,000.

[0017] In another aspect of this disclosure, a lithium-ion battery is provided, wherein the negative electrode surface of the lithium-ion battery is coated with the graphite material as described above, or the graphite material obtained by the aforementioned preparation method.

[0018] According to embodiments of this disclosure, the lithium-ion diffusion rate of the negative electrode is 10. -8 ~10 -12 cm 2 s -1 The lithium-ion diffusion barrier of the negative electrode is 0.14 eV to 0.01 eV.

[0019] According to embodiments of this disclosure, the negative electrode to positive electrode capacity ratio of the lithium-ion battery is 1 to 1.2; the operating temperature of the lithium-ion battery is -40°C to 30°C.

[0020] According to embodiments of this disclosure, a graphite material with a widened interlayer spacing in its internal crystal structure is proposed. This widened interlayer spacing can eliminate anisotropy on the graphite surface. Specifically, when this graphite material with a widened interlayer spacing is used as the negative electrode material in a lithium-ion battery, the larger interlayer spacing makes the channels for lithium ion diffusion between layers more spacious, thereby reducing the resistance encountered by lithium ions during insertion and extraction. This means that lithium ions can move faster between the graphite layers, increasing the diffusion rate and allowing lithium ions to reach or leave the electrode surface more quickly, reducing polarization caused by concentration differences. Simultaneously, the wider interlayer channels also help reduce damage to the graphite structure during lithium ion insertion and extraction, improving the cycle stability of the battery and extending its lifespan. Attached Figure Description

[0021] Figure 1 This is a transmission electron microscope (HRTEM) image of the interlayer spacing widened graphite prepared in Example 1 of this disclosure.

[0022] Figure 2 The graph shows the diffusion rate of the interlayer spacing broadened graphite prepared in Example 1 of this disclosure as a function of lithium intercalation potential at 30°C.

[0023] Figure 3 The graph shows the diffusion rate of the interlayer spacing broadened graphite prepared in Example 1 of this disclosure as a function of lithium intercalation potential at -20°C.

[0024] Figure 4 Transmission electron microscopy image of the interlayer spacing widened graphite prepared in Example 2 of this disclosure;

[0025] Figure 5 Transmission electron microscopy image of the interlayer spacing widened graphite prepared in Example 3 of this disclosure;

[0026] Figure 6 Diffusion barrier maps of graphite with different lattice spacings prepared according to embodiments of this disclosure;

[0027] Figure 7 Transmission electron microscopy image of the interlayer spacing widened graphite prepared in Comparative Example 1 of this disclosure;

[0028] Figure 8 A comparison diagram of the capacity of full cells composed of graphite with widened interlayer spacing and ternary NCM obtained in Embodiments 1 and 2 of this disclosure;

[0029] Figure 9 This is a diagram showing the high-rate performance of a full cell composed of graphite with widened interlayer spacing and ternary NCM obtained in Embodiment 1 of this disclosure;

[0030] Figure 10 The diagram shows the cycle performance of a full cell composed of graphite with widened interlayer spacing and ternary NCM obtained in Embodiment 1 of this disclosure.

[0031] Figure 11 The charge-discharge curves of the full cell composed of graphite and ternary NCM with widened interlayer spacing obtained in Embodiment 1 of this disclosure are obtained at different temperature test temperatures. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0033] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0035] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0036] It should be noted that, unless otherwise defined, the technical or scientific terms used in this disclosure should have the ordinary meaning understood by a person with ordinary skill in the art to which this disclosure pertains. Where the terms "first," "second," etc., are used throughout, they are used only to distinguish similar objects and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly specifying the number of technical features indicated. It should be understood that the data described by "first," "second," etc., can be interchanged where appropriate.

[0037] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure.

[0038] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed in this disclosure.

[0040] In this disclosure, the term "bulk interlayer spacing" refers to the distance between adjacent graphite layers within a graphite crystal, specifically in a relatively intact region away from boundaries or defects. This distance is a relatively constant value in graphite crystals, with a bulk interlayer spacing of approximately 0.335 nanometers (or 3.35 Å). This distance is an important parameter of the graphite crystal structure, determining its physical and chemical properties, such as electrical conductivity, thermal conductivity, and the diffusion rate of lithium ions.

[0041] In this disclosure, the term "interlayer spacing at the boundary" means the distance between adjacent graphite layers near the boundary or defect of a graphite crystal. Due to the presence of boundaries or defects, the interlayer spacing in this region may differ from the bulk interlayer spacing. Graphite layers at the boundary may be affected by factors such as lattice distortion, stress concentration, or changes in chemical bonds, leading to variations in the interlayer spacing. These variations can affect the properties of graphite, especially in nanoscale or high-energy-density applications.

[0042] Graphite has a layered structure, with each layer consisting of carbon atoms arranged in a hexagonal lattice by strong covalent bonds, and the layers interacting with each other through relatively weak van der Waals forces. In realizing the technical concept of this disclosure, it was discovered that increasing the interlayer spacing of graphite through chemical treatment or physical methods can improve the diffusion rate of lithium ions in graphite, reduce electrode polarization, and improve charge-discharge performance, providing strong support for performance enhancement of lithium-ion batteries and other energy storage technologies. Therefore, this disclosure utilizes high-temperature heat treatment of multilayer stacked graphene oxide materials to widen the interlayer spacing at the graphite material boundaries, thereby improving its application as a negative electrode material for lithium-ion batteries.

[0043] This disclosure provides a graphite material with widened interlayer spacing, wherein the interlayer spacing at the boundary within the graphite material crystal is 0.36~0.41 nanometers, for example, it can be 0.36 nanometers, 0.365 nanometers, 0.37 nanometers, 0.375 nanometers, 0.38 nanometers, 0.385 nanometers, 0.39 nanometers, 0.395 nanometers, 0.40 nanometers, 0.405 nanometers, 0.41 nanometers, etc.

[0044] According to embodiments of this disclosure, a graphite material with a widened interlayer spacing in its internal crystal structure is proposed. This widened interlayer spacing can eliminate anisotropy on the graphite surface. Specifically, when this graphite material with a widened interlayer spacing is used as the negative electrode material in a lithium-ion battery, the larger interlayer spacing makes the channels for lithium ion diffusion between layers more spacious, thereby reducing the resistance encountered by lithium ions during insertion and extraction. This means that lithium ions can move faster between the graphite layers, increasing the diffusion rate and allowing lithium ions to reach or leave the electrode surface more quickly, reducing polarization caused by concentration differences. Simultaneously, the wider interlayer channels also help reduce damage to the graphite structure during lithium ion insertion and extraction, improving the cycle stability of the battery and extending its lifespan.

[0045] According to embodiments of this disclosure, the particle size of the graphite material is 5-10 micrometers, for example, it can be 5 micrometers, 5.5 micrometers, 6 micrometers, 6.5 micrometers, 7 micrometers, 7.5 micrometers, 8 micrometers, 8.5 micrometers, 9 micrometers, 9.5 micrometers, 10 micrometers, etc.

[0046] According to embodiments of this disclosure, the bulk interlayer spacing within the crystal of the graphite material is 0.335-0.34 nanometers, for example, it can be 0.335 nanometers, 0.336 nanometers, 0.337 nanometers, 0.338 nanometers, 0.339 nanometers, 0.34 nanometers, etc., and the oxygen content of the graphite material is 1%-3% by mass fraction.

[0047] In another aspect of this disclosure, a method for preparing graphite material as described above is proposed, comprising the following steps S101-S102:

[0048] Step S101: In an inert gas atmosphere, the multilayer stacked graphene oxide is heat-treated to transform the graphene oxide into the graphite phase and widen the interlayer spacing at the crystal boundary of the graphite phase to 0.36~0.41 nanometers.

[0049] Step S102: Then the graphite phase is crushed and granulated to obtain a graphite material with widened interlayer spacing.

[0050] According to embodiments of this disclosure, during high-temperature heat treatment, oxygen-containing functional groups such as epoxy and hydroxyl groups on the surface of graphene oxide decompose, generating gases such as carbon dioxide and water vapor. When the generation rate of these gases exceeds the rate at which they are released from the interlayer of graphene oxide, interlayer pressure is generated. This pressure may exceed the van der Waals forces between the graphene oxide layers, leading to a significant increase in the interlayer spacing. Simultaneously, during rapid thermal expansion, the increase in interlayer pressure and the thermal expansion effect of the crystal lattice work together to significantly widen the interlayer spacing.

[0051] According to embodiments of this disclosure, heat treatment of graphene oxide includes:

[0052] The graphene oxide is subjected to a first heat treatment to decompose and remove the oxygen-containing groups in the graphene oxide.

[0053] A second heat treatment is performed on the multilayer graphene oxide to promote carbon atom hybridization and form an ordered graphite phase layered structure.

[0054] The temperature of the second heat treatment is higher than that of the first heat treatment.

[0055] According to embodiments of this disclosure, in the first heat treatment, the heating temperature is 600-1000°C; in the second heat treatment, the heating temperature is 2000-3000°C.

[0056] According to embodiments of this disclosure, in the first heat treatment process, volatile impurities and unstable chemical groups, such as oxygen-containing groups, are removed from the graphene oxide material, generating a relatively disordered amorphous carbon structure. The heating temperature is 600℃~1000℃, for example, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc., preferably 700℃~900℃, for example, 700℃, 750℃, 800℃, 850℃, 900℃, etc.; in the second heat treatment, high... The heating temperature promotes the formation of sp² hybridization of carbon atoms, causing carbon atoms to arrange themselves into a hexagonal lattice in a two-dimensional plane and gradually form an ordered graphite phase layer structure. The heating temperature is 2000℃~3000℃, for example, 2000℃, 2100℃, 2200℃, 2300℃, 2400℃, 2500℃, 2600℃, 2700℃, 2800℃, 2900℃, 3000℃, etc., preferably 2500℃~2800℃, for example, 2500℃, 2600℃, 2700℃, 2800℃, etc.

[0057] In some specific embodiments, the material obtained by performing only the first heat treatment is not graphitized and cannot be used as a lithium-intercalated anode material. The absence of this first low-temperature heat treatment may affect the overall structure and performance of the material. The first heat treatment helps remove impurities, stabilize the graphite phase structure, and prepare for the subsequent second heat treatment. To ensure optimal material performance and structural stability, the graphite material preparation method proposed in this disclosure inevitably involves a two-stage heat treatment process.

[0058] According to embodiments of this disclosure, the oxygen content of the graphene oxide is 1%-5%, and the number of graphene oxide layers is 0.5-20,000.

[0059] According to embodiments of this disclosure, graphene oxide is rich in a large number of oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups, and its oxygen content is 1% to 5%, for example, it can be 1%, 2%, 3%, 4%, 5%, etc., preferably 2% to 4%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0060] According to embodiments of this disclosure, the high-temperature heat treatment of graphene oxide is carried out in an inert gas atmosphere to ensure the stability of the generated graphite material. The inert gas can be nitrogen or argon.

[0061] In another aspect of this disclosure, a lithium-ion battery is provided, wherein the negative electrode surface of the lithium-ion battery is coated with the graphite material as described above, or the graphite material obtained by the aforementioned preparation method.

[0062] According to embodiments of this disclosure, graphite with widened boundary layer spacing can eliminate the anisotropy of the graphite surface, allowing lithium ions to be rapidly transferred from the edges of the graphite to the interior, thus improving the lithium ion diffusion rate. When the graphite material proposed in this disclosure is used as the negative electrode of a lithium-ion battery, it exhibits a high lithium-ion diffusion rate and a low diffusion barrier. This graphite with widened boundary layer spacing, as a negative electrode material, enables the secondary battery to have a rapid lithium-ion transport channel under low-temperature and fast-charging conditions. When matched with commercial cathode materials, it can effectively improve the rate capability and cycle stability of the full battery under fast charging and low-temperature conditions.

[0063] In some specific embodiments, experimental results show that, as a negative electrode material for lithium-ion batteries, the graphite negative electrode, when assembled with a positive electrode containing lithium cobalt oxide, lithium iron phosphate, or ternary materials, exhibits excellent fast-charging and low-temperature performance in full-cell tests: the specific capacity retention rates at 2C, 5C, and 10C are 94%, 87.2%, and 78.3%, respectively. At 0℃, -20℃, -30℃, and -40℃, the battery capacity is maintained at 96.9%, 87.5%, 77.0%, and 51.8% of that at room temperature, respectively.

[0064] According to embodiments of this disclosure, the lithium-ion diffusion rate of the negative electrode is 10. -8~10 -12 cm 2 s -1 The lithium-ion diffusion barrier of the negative electrode is 0.14 eV~0.01 eV.

[0065] According to embodiments of this disclosure, graphite is composed of multiple layers of carbon atoms stacked in a hexagonal network structure, with the layers interacting through relatively weak van der Waals forces. This layered structure provides possible space for lithium-ion insertion and extraction. As the interlayer spacing of graphite increases, the channels for lithium-ion diffusion between layers become wider, thereby reducing the resistance encountered by lithium-ions during insertion and extraction. This means that lithium-ions can move more quickly between graphite layers, increasing the lithium-ion diffusion rate. Simultaneously, the widened interlayer spacing provides more diffusion channels for lithium-ions, reducing the resistance to lithium-ion diffusion between layers. Furthermore, the increased interlayer spacing effectively reduces the expansion and contraction of the graphite structure during lithium-ion insertion / extraction, thereby improving the battery's stability and cycle performance.

[0066] In some specific embodiments, the lithium-ion diffusion rate is obtained by constant current intermittent titration, and the test temperature can be controlled to decrease from 30°C to -20°C; the lithium-ion diffusion barrier is obtained by calculation combined with AC impedance spectroscopy.

[0067] In some specific embodiments, the positive electrode material of the lithium-ion battery can be a ternary positive electrode material such as lithium iron phosphate, lithium cobalt oxide, or nickel cobalt manganese oxide; the electrolyte in the electrolyte is lithium hexafluorophosphate, and the solvent is a carbonate such as ethylene carbonate, ethyl methyl carbonate, or dimethyl carbonate.

[0068] In some specific embodiments, the negative electrode of the lithium-ion battery also includes a conductive agent and a binder, wherein the conductive agent includes acetylene black, Super P, Ketjen Black, etc., and the binder includes polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, etc.

[0069] According to embodiments of this disclosure, the negative-to-positive capacity ratio of the lithium-ion battery is 1 to 1.2, for example, it can be 1, 1.1, 1.2, etc., more preferably 1.05 to 1.10; the operating temperature of the lithium-ion battery is -40°C to 30°C; the current density of the lithium-ion battery is 0.05 C to 10 C; and the high-rate performance test conditions of the lithium-ion battery are 1C to 10C.

[0070] According to embodiments of this disclosure, using graphite material with widened interlayer spacing as the negative electrode of the battery facilitates the rapid transfer of lithium ions from the edges of the graphite to the interior, effectively improving the diffusion kinetics of the lithium-ion battery and enhancing its performance under low-temperature and fast-charging conditions. The tested low-temperature range is -40°C to 0°C. A negative-to-positive electrode capacity ratio (N / P) of 1 to 1.2 allows for full utilization of the active materials in both electrodes, thereby increasing the actual capacity and energy density of the battery.

[0071] It should be noted that the described embodiments are merely some, not all, of the embodiments disclosed herein. Other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are all within the scope of protection of this disclosure.

[0072] Example 1

[0073] Under an argon atmosphere, multilayered graphene oxide was first pre-oxidized at 300℃ for 2 hours, then subjected to a first heat treatment at 1000℃ for 2 hours, followed by graphitization at 2900℃. Finally, after crushing and sieving, a graphite material with widened interlayer spacing was obtained, with a C / O ratio of 99 / 1 to 97 / 3. The number of stacked graphene oxide layers ranged from 5,000 to 20,000, and the C / O ratio was 70 / 30 to 90 / 10.

[0074] The graphite material obtained in Example 1 was characterized by transmission electron microscopy.

[0075] Figure 1 This is a transmission electron microscope (HRTEM) image of the interlayer widened graphite prepared in Example 1 of this disclosure.

[0076] like Figure 1 As shown, the bulk lattice spacing of this graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.38 nm.

[0077] The graphite material with broadened boundaries obtained in Example 1 was coated with a conductive agent and a binder in a ratio of 8:1:1 to form a film, which was then assembled into a coin cell. The lithium-ion diffusion rate was tested using constant current intermittent titration technology.

[0078] Figure 2 , Figure 3 The graphs show the diffusion rate of the interlayer spacing broadened graphite prepared in Example 1 of this disclosure as a function of lithium intercalation potential at 30°C and -20°C.

[0079] like Figure 2 ,3 As shown, under test conditions of 30℃, the diffusion rate of lithium ions during lithium intercalation is 10. -8 ~10 -11 cm 2 s -1 Under low-temperature testing conditions of -20°C, the diffusion rate of lithium ions during lithium intercalation is 10. -8 ~10 -12 cm 2 s -1 The larger interlayer spacing results in a higher lithium-ion diffusion rate for the negative electrode material obtained in Example 1.

[0080] Example 2

[0081] This embodiment provides a graphite anode material with widened interlayer spacing. The only difference from Embodiment 1 is that the multilayer stacked graphene oxide (pre-oxidized at 300°C for 2 hours) is first heat-treated at 900°C for 2 hours, and then graphitized at 2800°C to obtain graphite material 2. The remaining parameters and steps are consistent with those of Embodiment 1.

[0082] The graphite material obtained in Example 2 was characterized by transmission electron microscopy.

[0083] Figure 4 Transmission electron microscopy (TEM) image of the interlayer spacing widened graphite prepared in Example 2 of this disclosure.

[0084] like Figure 4 As shown, the bulk lattice spacing of this graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.41 nm.

[0085] Example 3

[0086] This embodiment provides a graphite anode material with widened interlayer spacing. The only difference from Embodiment 1 is that the multilayer stacked graphene oxide (pre-oxidized at 300°C for 2 hours) is first heat-treated at 800°C for 2 hours, and then graphitized at 2700°C. The other parameters and steps are the same as in Embodiment 1.

[0087] The graphite material obtained in Example 3 was characterized by transmission electron microscopy.

[0088] Figure 5 Transmission electron microscopy (TEM) image of the interlayer spacing widened graphite prepared in Example 3 of this disclosure.

[0089] like Figure 5 As shown, the bulk lattice spacing of this graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.41 nm.

[0090] Example 4

[0091] This embodiment provides a graphite anode material with widened interlayer spacing. The only difference from Embodiment 1 is that the multilayer stacked graphene oxide (pre-oxidized at 300°C for 2 hours) is first heat-treated at 700°C for 2 hours, and then graphitized at 2600°C. The other parameters and steps are the same as in Embodiment 1.

[0092] Theoretical calculations and simulations were performed on graphite materials with different lattice spacings, and variable-temperature AC impedance tests were conducted.

[0093] Figure 6 The diffusion barrier diagrams of graphite with different lattice spacings prepared according to embodiments of this disclosure are shown.

[0094] like Figure 6 As shown, when the lattice spacing is between 3.5 and 4.0, the larger the boundary layer spacing, the lower the diffusion barrier of lithium ions.

[0095] Comparative Example 1

[0096] This comparative example provides a graphite anode material with widened interlayer spacing. The difference from Example 1 is that the multilayer stacked graphene oxide (with 0.5-20,000 stacked layers) is replaced with a few-layer stacked graphene oxide with 0.1-0.5 million stacked layers. The remaining parameters and steps are the same as in Example 1.

[0097] Figure 7 Transmission electron microscopy (TEM) image of graphite with broadened interlayer thickness prepared in the comparative example of this disclosure.

[0098] As shown in the figure, the bulk lattice spacing of this graphite material is 0.335 nm, while the lattice spacing at the boundary is 0.348 nm. This indicates that when the number of stacked layers of the raw graphene oxide is too small, it is not conducive to lattice widening.

[0099] Performance testing

[0100] The graphite material with broadened boundaries obtained in Example 1 was mixed with a conductive agent (SP) and a binder (PVDF) in a mass ratio of 8:1:1 to form a slurry, which was then coated onto an electrode sheet with a thickness of approximately 250±10 micrometers. The electrode sheet loading was approximately 2.0±0.1 mg / cm². 2 .

[0101] It was used as the negative electrode and assembled with ternary lithium nickel cobalt manganese oxide or lithium cobalt oxide to form a coin cell, and its electrochemical performance was evaluated. The electrolyte was 1M LiPF6 / EC:EMC:DMC (1:1:1) provided by Tinci Materials, and the separator was a Celgard polypropylene separator. The assembly process was carried out in a Braun glove box to ensure that the oxygen and water ratio was below 0.1ppm. The battery was tested using the Newway Battery Testing System or the Blue Electric Battery Testing System.

[0102] Figure 8 This is a comparison chart of the capacities of full cells composed of graphite with increased interlayer spacing and ternary NCM obtained in Embodiment 1 and Comparative Example 1 of this disclosure.

[0103] like Figure 8 As shown, the full cell composed of a graphite anode with a boundary layer spacing of 0.38 nm and a ternary lithium nickel cobalt manganese oxide exhibits the best performance and capacity. This verifies that a certain number of stacked layers is required for graphene oxide materials to ensure stable widening of the interlayer spacing after heat treatment.

[0104] Figure 9 The high-rate performance diagram of the full cell composed of graphite and ternary NCM with widened interlayer spacing obtained in Embodiment 1 of this disclosure is shown. Figure 10 The diagram shows the cycle performance of a full cell composed of graphite with widened interlayer spacing and ternary NCM obtained in Embodiment 1 of this disclosure. Figure 11 The charge-discharge curves of the full cell composed of graphite and ternary NCM with widened interlayer spacing obtained in Embodiment 1 of this disclosure are obtained at different temperature test temperatures.

[0105] like Figure 9 As shown, the capacity retention rates at 2C, 5C, and 10C are 94%, 87.2%, and 78.3%, respectively. Figure 10 As shown, the cycle stability of this full cell is relatively good, approximately 90%~99%. Figure 11 As shown, the low-temperature performance test results of the full cell are excellent: at 0℃, -20℃, -30℃ and -40℃, the capacity is maintained at 96.9%, 87.5%, 77.0% and 51.8% of that at room temperature, respectively.

[0106] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A graphite material with widened interlayer spacing, characterized in that, The interlayer spacing at the boundaries within the graphite crystal is 0.36~0.41 nanometers; The bulk interlayer spacing within the crystals of the graphite material is 0.335-0.34 nanometers, and the oxygen content of the graphite material is 1%-3%.

2. The graphite material according to claim 1, wherein, The particle size of the graphite material is 5-10 micrometers.

3. A method for preparing a graphite material as described in any one of claims 1 or 2, comprising: In an inert gas atmosphere, multilayer stacked graphene oxide is heat-treated to transform the graphene oxide into the graphite phase and widen the interlayer spacing at the crystal boundaries of the graphite phase to 0.36~0.41 nanometers. The number of layers of the graphene oxide is 0.5-20,000. The graphite phase is then crushed and granulated to obtain a graphite material with widened interlayer spacing. The heat treatment of graphene oxide includes: The multilayer stacked graphene oxide is subjected to a first heat treatment to decompose and remove the oxygen-containing groups in the graphene oxide. The multilayered graphene oxide is subjected to a second heat treatment to promote carbon atom hybridization and form an ordered graphite phase layered structure. The temperature of the second heat treatment is higher than the temperature of the first heat treatment.

4. The preparation method according to claim 3, wherein, In the first heat treatment, the heating temperature is 600-1000℃; In the second heat treatment, the heating temperature is 2000-3000℃.

5. The preparation method according to claim 3, wherein, The oxygen content of the graphene oxide is 1%-5%.

6. A lithium-ion battery, characterized in that, The negative electrode surface of the lithium-ion battery is coated with the graphite material as described in claim 1 or 2, or the graphite material obtained by the preparation method of any one of claims 3 to 5.

7. The lithium-ion battery according to claim 6, wherein, The lithium-ion diffusion rate of the negative electrode is 10. -8 ~10 -12 cm 2 s -1 The lithium-ion diffusion barrier of the negative electrode is 0.14 eV to 0.01 eV.

8. The lithium-ion battery according to claim 6, wherein, The ratio of the negative electrode capacity to the positive electrode capacity of the lithium-ion battery is 1 to 1.2; The operating temperature of the lithium-ion battery is -40℃ to 30℃.

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