MXene interfaces reconstruct graphite, composite materials, electrode sheets, batteries, and electrical devices.

Abstract

This invention discloses an MXene interface-reconstructed graphite, a composite material, an electrode sheet, a battery, and an electrical device. The MXene sheet forms an MXene interface layer on the base surface of the graphite layer, and the MXene interface-reconstructed graphite has a sandwich-like MXene-graphite-MXene heterostructure. Ah-level batteries with the MXene interface-reconstructed graphite anode of this invention exhibit ultra-long durability, high energy density, and excellent rate performance, superior to pure graphite anodes.

Description

Technical Field

[0001] This utility model belongs to the field of materials, and in particular relates to an MXene interface reconstructed graphite, composite material, electrode sheet, battery and electrical device. Background Technology

[0002] Commercial lithium-ion batteries (LIBs) have attracted worldwide attention as a power source for electric vehicles due to their high energy density, long cycle life, and cost-effectiveness. Generally, LIBs are made of graphite anodes and transition metal oxide / phosphide cathodes in an organic electrolyte, exhibiting energy densities of 140-280 Wh / kg under ambient temperature conditions. 1 High energy density. However, under extreme conditions such as sub-zero temperatures and high rates, LIBs typically exhibit poor electrochemical performance due to high electrochemical polarization at the electrolyte / electrode interface and the inhomogeneous reaction current associated with the inevitable formation of lithium dendrites at the graphite edges. The presence of lithium dendrites further inhibits Li-Electrode synthesis. + The insertion of lithium dendrites into the graphite interlayers severely exacerbates the polarization and uncontrollable growth of lithium dendrites, which largely hinders the practical application of LIBs in certain scenarios.

[0003] To address the issues of large electrochemical polarization and uncontrollable lithium dendrite formation, researchers have explored several strategies, including promoting Li... + Migration and enhancement of Li in the solid electrolyte interphase (SEI) layer + The diffusion coefficient in the negative electrode is as follows: (1) Using advanced electrolytes such as locally high concentration electrolytes (LHCE), the formation of anion-derived interfaces with high ionic conductivity is promoted, thereby improving the reversibility of the lithium plating layer; (2) Constructing artificial interface layers (such as inorganic layers) to reduce the Li at the interface between the electrolyte and graphite. + Solvent removal energy barrier, accelerating interfacial reaction kinetics; (3) Uniform Li by adding hard carbon or amorphous carbon with high specific surface area to the graphite anode. + Distribution and suppression of lithium metal deposition. Although these strategies can alleviate electrochemical polarization and lithium dendrite formation to some extent, eliminating lithium dendrites in graphite anodes under extreme conditions, such as low temperature (<0°C) and high rate (>4C, the target of the US Advanced Battery Consortium), remains a significant challenge. Utility Model Content

[0004] This paper addresses the technical problem that limits the practical application of graphite anode materials in existing commercial lithium-ion batteries due to the degradation of electrochemical performance and safety issues caused by the formation of lithium dendrites in low-temperature or high-rate environments.

[0005] The first aspect of this utility model provides an MXene interface reconstructed graphite, wherein MXene sheets form an MXene interface layer on the base surface of a graphite layer, and the MXene interface reconstructed graphite has a sandwich-like MXene-graphite-MXene heterostructure.

[0006] In some embodiments, the MXene sheets are used to form the MXene interface layer on the base surface of the graphite layer through electrostatic adsorption.

[0007] In some embodiments, the size of the MXene sheets described above is between 0.5 and 4 micrometers.

[0008] In some embodiments, the thickness of the MXene sheet is between 1 and 10 nm, preferably between 1 and 3 nm.

[0009] In some embodiments, the particle size range of the MXene interface-reconstructed graphite is between 100 and 1000 micrometers; In some embodiments, the transition metal element contained in the MXene sheets is selected from one of Ti, V, Nb, Ta, Zr, W, Mo, and Cr; preferably, the MXene is Ti3C2T. x .

[0010] In some embodiments, the thickness of the MXene interface layer is between 1 and 10 nm, preferably between 1 and 3 nm; In some embodiments, the thickness of the MXene interface layer is the thickness of a single MXene sheet or several MXene sheets; preferably, the MXene sheet is a single-atom layer of MXene.

[0011] A second aspect of this invention provides a composite material comprising: the aforementioned MXene interface-reconstructed graphite, and metallic lithium on the surface of the MXene interface-reconstructed graphite.

[0012] In some embodiments, the aforementioned metallic lithium is on the surface of the MXene interface layer.

[0013] In some embodiments, the crystal structure of the aforementioned lithium metal is body-centered cubic. In some embodiments, the exposed crystal plane of the lithium metal is the (110) crystal plane; In some embodiments, the lattice spacing of the lithium metal is 2.48 Å.

[0014] In some embodiments, the lithium metal exhibits a pebble-like particle morphology.

[0015] A third aspect of this invention provides an electrode sheet containing the aforementioned MXene interface reconstructed graphite; or, the aforementioned composite material.

[0016] The fourth aspect of this utility model provides a battery comprising the aforementioned electrode sheets.

[0017] The fifth aspect of this utility model is an electrical device comprising the aforementioned battery.

[0018] The beneficial technical effects of this invention are as follows: This invention provides an effective strategy for reconstructing the carbon-to-MXene interface in a graphite electrode to eliminate lithium dendrites in commercial lithium-ion batteries under extreme conditions. The outermost MXene interface layer not only effectively reduces the nucleation barrier of Li in the anode, but also has good lattice compatibility with the deposited lithium, which helps to grow densely packed bcc-Li (body-centered cubic lithium metal) horizontally along the (110) plane under extreme conditions. The Ah-level battery with the MXene interface-reconstructed graphite anode has ultra-long durability, high energy density, and excellent rate performance, which is superior to that of pure graphite anodes. Attached Figure Description

[0019] Figure 1 (a) is a schematic diagram of MXene-reconstructed graphite synthesis; (bd) shows the surface zeta potential test results of graphite (b), APS-graphite (c) and MXene (d).

[0020] Figure 2 (a) is a schematic diagram of the structure of the MXene-configured graphite of this invention, showing that layered graphite is sandwiched between two MXene interface layers to form a unique sandwich structure; (b) is the Fourier transform infrared (FTIR) spectrum of graphite and APS graphite.

[0021] Figure 3 (a) Optical photographs of the MXene-graphite mixture (left) and the MXene interface-reconstructed graphite (right) dispersion; (b) Thermogravimetric analysis (TGA) curves of MXene-reconstructed graphite in air.

[0022] Figure 4 (a) is a transmission electron microscope (TEM) image of MXene sheets, showing that their average size distribution is in the range of 0.5-4 μm; (b) is an atomic force microscope (TEM) image of MXene sheets, showing that the thickness of the MXene nanosheets is about 2 nm; (c) is a scanning electron microscope (SEM) image of MXene interface reconstructed graphite observed from the side; (d) is a particle size distribution diagram of MXene interface reconstructed graphite and graphite.

[0023] Figure 5(a) and (b) are high-resolution transmission electron microscopy (HRTEM) and corresponding FFT images (insets) of the MXene interface reconstructed graphite according to this invention, revealing that the MXene interface layer is located on the graphite surface.

[0024] Figure 6 (a) is a cross-sectional transmission electron microscope (TEM) image of the graphite reconstructed by the MXene interface of this invention and an EDS line scan analysis of C (b) and Ti (c) elements along the yellow line in a. The image shows that the C element is mainly in the middle, while the Ti element appears on both sides, which clearly indicates that the graphite reconstructed by the MXene interface of this invention has a sandwich-like MXene-graphite-MXene heterostructure.

[0025] Figure 7 (a) MXene Ti3C2T of graphite reconstructed by Li atoms at the MXene interface of this novel x The adsorption energy at the interface is 3.41 eV is pure graphite ( (a) is about 3 times that of 1.03eV; (b) the nucleation overpotential of the lithium plating layer on the graphite reconstructed at the MXene interface is 12mV, which is much lower than that of pure graphite (42mV).

[0026] Figure 8 For MXene Ti3C2T x The interface shows 0.3 (a), 0.5 (b), and 0.7 (c) mAh cm⁻¹ 2 Low-temperature TEM images and corresponding FFT patterns at different deposition capacities (inset).

[0027] Figure 9 Experimental testing of the MXene interface lithium deposition mechanism on the graphite anode material reconstructed by the MXene interface of this invention; (a) MXene Ti3C2T x Schematic diagrams of lithium nucleation, horizontal stacking, and planar growth at the interface; (b, c) Lithium deposition capacities of 0.3 (b) and 1.0 (c) mAh cm⁻¹ 2 Low-temperature TEM images, where red, blue, and yellow regions represent crystalline Li metal, LiF, and Li2O nanocrystals, respectively. Inset: Fast Fourier Transform pattern obtained from the deposited lithium metal region; (d) is a magnified image of the blue box region in Figure c, showing a good crystal structure; (e) is an atomic resolution transmission electron microscope image of the box-shaped region in Figure d, showing the interplanar spacing between the (110) facets as 2.48 Å; (f) the (110), (200), (211), and (310) planes of lithium with MXene Ti3C2T xLattice mismatch between the hexagonal crystal planes of the interface, illustration: Li and MXeneTi3C2T x Lattice matching diagrams between different crystal planes at the interface; (g) in lithium, MXene Ti3C2T x The adsorption energy of lithium atoms grown horizontally or vertically on graphene and copper substrates.

[0028] Figure 10 For 0.5mA cm 2 Low-temperature TEM characterization of lithium deposited on a carbon layer at a current density of 1 mAh cm⁻¹, showing a lithium deposition capacity of 1 mAh cm⁻¹. 2 .

[0029] Figure 11 For (a, b), at a capacity level of 10mAh cm 2 MXene Ti3C2T x In-situ XRD patterns of the (110) plane (a) and (200) plane (b) of Li during Li deposition; (c) Intensity of the Li (110) and (200) planes as capacity increases.

[0030] Figure 12 (a) Viscosities of MXene interface-reconstructed graphite slurries with different solid contents in Example 3. The results show that the MXene interface-reconstructed graphite slurry has a viscosity as high as 3451 mPa·s. 1 (a) is the viscosity of the slurry containing MXene interface-reconstructed graphite and graphite when the solid content is 42%.

[0031] Figure 13 (a) is a schematic diagram of the peel strength test of the MXene-reconstructed graphite electrode in Example 3; (b) is the peel strength-peel elongation curve of the MXene-reconstructed graphite and pure graphite electrodes, showing that the average peel strength of the MXene-reconstructed graphite electrode is 11.9 Nm. 1 .

[0032] Figure 14 (a) represents the powder conductivity of MXene and common graphite anode additives; (b) represents the conductivity of the modified graphite anode of Example 3 of this utility model.

[0033] Figure 15 (a) The curve obtained by galvanostatic intermittent titration technique (GITT) in Embodiment 3 of this utility model. The average apparent Li of the graphite anode obtained at 20℃+ The diffusion coefficient and the mass loading of the negative electrode are approximately 3 mg cm⁻¹. 2 (a) and approximately 12 mg cm 2 (b). c, in At 20°C, the mass loading is approximately 12 mg cm⁻¹. 2 The DRT curve corresponding to the negative electrode.

[0034] Figure 16 (a) High-resolution F1s XPS spectra of MXene-reconstructed graphite (a) and pure graphite (b) after one cycle, showing the peak ratio (Ig) of MXene-reconstructed graphite. LiF / I C-F The increase compared to pure graphite indicates that the SEI layer of the MXene interface-reconstructed graphite anode is rich in LiF, which is beneficial for the rapid transport of lithium ions.

[0035] Figure 17 This is a schematic diagram of the graphite and modified graphite of this utility model; wherein, (a) graphite; (b) a mechanical mixture of graphene and graphite; (c) MXene interface-reconstructed graphite; (d) a mechanical mixture of 1% MXene and graphite; and (e) a mechanical mixture of 5% MXene and graphite.

[0036] Figure 18 The electrochemical performance of the MXene interface-reconstructed graphite anode in Embodiment 3 of this utility model is shown; wherein (a) is the activation energy of lithium-ion diffusion in the SEI film of the MXene interface-reconstructed graphite anode; and (b) is the electrochemical performance of the graphite anode in Embodiment 3 ... dQ / dV curves of the half-cell at 20℃; (c) At 20℃, the DCM curve shows a low slope, indicating a small surface area for lithium deposition on the MXene interface; (de)Ah-level soft-pack batteries at 40℃ and... Cycling performance within a temperature range of 20℃ and corresponding constant current / constant voltage charging stages: the MXene interface-reconstructed graphite anode exhibits excellent low-temperature performance; (f) After 100 cycles at 20℃, the MXene interface reconstructed the graphite anode and the physical photographs and SEM images of the graphite anode, showing dendrite-free morphology.

[0037] Figure 19 Reconstructing the graphite anode for the (ae)MXene interface SEM images at 20℃ under different states of charge (SoC) show that the deposited lithium exhibits a smooth and uniform morphology; (fj) graphite anode in SEM images at different states of charge (SoC) at 20℃ show the formation of a large number of lithium dendrites.

[0038] Figure 20 In Embodiment 3 of this utility model, the MXene interface is reconstructed for the graphite anode. XRD patterns of lithium deposited at 20℃ and 200% SoC conditions show that its I (110) / I (200) The diffraction peak intensity ratio is as high as 3.8, which is nearly 4 times that of pure graphite (1.1).

[0039] Figure 21 In Embodiment 3 of this utility model, the MXene interface is used to reconstruct the graphite anode (left) and graphite anode (right). Macroscopic photographs and SEM images after 100 lithium deposition / stripping cycles at 20℃ and 1C rate show that the surface of the MXene interface-reconstructed graphite anode remains smooth with no silvery-white dead lithium formation, while obvious dead lithium appears on the surface of the graphite anode.

[0040] Figure 22 SEM images of the negative electrode material under different lithium deposition amounts at room temperature in Embodiment 3 of this utility model. SEM image of pure MXene deposition: (a) 0.5 mAh cm⁻¹ 2 (b) 1mAh cm 2 (c) 3mAh cm 2 (d) 5mAh cm 2 SEM image of MXene-configured graphite deposition: (e) 0.5 mAh cm⁻¹ 2 (f) 1mAh cm 2 (g) 3mAh cm 2 ;(h)5mAh cm 2 SEM images of MXene (1%)-graphite deposition: (i) 0.5 mAh cm⁻¹ 2 (j) 1mAh cm 2 ;(k)3mAh cm 2 (l) 5mAh cm 2SEM image of MXene (5%)-graphite deposition: (m) 0.5 mAh cm⁻¹ 2 ;(n)1mAh cm 2 ;(o)3mAh cm 2 (p) 5mAh cm 2 SEM image of graphene-graphite deposition: (q) 0.5 mAh cm⁻¹ 2 ;(r)1mAh cm 2 ;(s)3mAh cm 2 ;(t)5mAh cm 2 SEM image of Graphite deposition: (u) 0.5mAh cm⁻¹ 2 (v) 1mAh cm 2 (w) 3mAh cm 2 (x) 5mAh cm 2 .

[0041] Figure 23 In embodiment 3 of this utility model SEM images of the anode material at different lithium deposition amounts under 20℃ low-temperature conditions. SEM image of pure MXene deposition: (a) 0.5mAh cm⁻¹ 2 (b) 1mAh cm 2 (c) 3mAh cm 2 (d) 5mAh cm 2 SEM image of MXene-configured graphite deposition: (e) 0.5 mAh cm⁻¹ 2 (f) 1mAh cm 2 (g) 3mAh cm 2 ;(h)5mAh cm 2 SEM images of MXene (1%)-graphite deposition: (i) 0.5 mAh cm⁻¹ 2 (j) 1mAh cm 2 ;(k)3mAh cm 2 (l) 5mAh cm 2 SEM image of MXene (5%)-graphite deposition: (m) 0.5 mAh cm⁻¹ 2 ;(n)1mAh cm 2 ;(o)3mAh cm 2 (p) 5mAh cm 2 Graphene SEM image of graphite deposition: (q) 0.5 mAh cm⁻¹ 2 ;(r)1mAhcm 2 ;(s)3mAh cm 2 ;(t)5mAh cm 2 SEM image of Graphite deposition: (u) 0.5mAh cm⁻¹ 2 (v) 1mAh cm 2 (w) 3mAh cm 2 (x) 5mAh cm 2 .

[0042] Figure 24 for dQ / dV plots of graphite and modified graphite at 20℃. (a) MXene-configured graphite; (b) MXene (1%)-graphite; (c) MXene (5%)-graphite; (d) Graphene-graphite; (e) Graphite; (f) Statistical results of voltage difference between charge and discharge platforms.

[0043] Figure 25This invention relates to the electrochemical performance of an Ah-level pouch cell with an MXene interface-reconstructed graphite anode under extreme conditions in Embodiment 3 of this invention; wherein, (a) is a schematic diagram of the MXene interface-reconstructed graphite||NCM811 pouch cell structure and the design of an in-situ pressure monitoring device; (bc) in At 20℃, the stress fluctuation and long-cycle performance of the MXene interface-reconstructed graphite anode pouch cell showed that the stress fluctuation was negligible and the cycle stability was excellent. After 1200 cycles at 20℃, the capacity retention of MXene-modified graphite was 2.2 times that of unmodified graphite; (d) the energy density comparison of the pouch cell and the performance comparison with other pouch cells reported in the literature show that it has the advantages of high performance in pouch cells. It has the highest energy density retention rate over a wide temperature range of 20℃ to 40℃.

[0044] Figure 26 In embodiment 3 of this utility model Long-cycle performance of graphite and modified graphite at 1C rate under low temperature conditions of 20℃.

[0045] Figure 27 The invention relates to a pouch cell with MXene interface reconstructed graphite, MXene-graphite mixture, and graphite anode, which exhibits long-cycle performance at 25°C and 10°C.

[0046] Figure 28 This invention reconstructs multiple functions of the MXene interface in graphite using the MXene interface of this utility model. Detailed Implementation

[0047] The technical solution of this utility model is illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in this utility model do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of this utility model. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or defining the scope of implementation of this utility model. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of implementation of this utility model.

[0048] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0049] Example 1 This embodiment provides an interface-reconstructed graphite anode material and method, such as Figure 1 As shown in (a), the implementation steps include: 1) Graphite Amination: Graphite material is amination treated to introduce amino functional groups onto its surface, resulting in amination-treated graphite. During this process, a large number of positively charged amino (-NH2) groups are introduced onto the graphite surface. In this embodiment, aminopropyltrimethoxysilane (APS) is grafted onto the graphite, thereby generating positively charged amino (-NH2) groups on the graphite surface.

[0050] 2) Electrostatic adsorption: Electrostatic interaction between positively charged modified graphite and negatively charged MXene. In this embodiment, the aminated modified graphite (APS-graphite) and MXene are mixed and dispersed in an aqueous solvent, then separated into solid and liquid phases, and dried. The MXene is obtained by etching the A layer of the MAX phase with a fluorinated etching solution, followed by cleaning, stripping, and solid-liquid separation. In some embodiments, the fluorinated etching solution is a hydrofluoric acid (HF) solution or a mixture of fluoride salt and acid. The resulting MXene has a two-dimensional sheet morphology and its surface contains abundant hydroxyl (-OH) and oxygen (-O) functional groups, making the MXene sheet surface negatively charged. Figure 1 b to d show the surface zeta potentials of graphite, APS-graphite, and MXene, respectively. The results show that the zeta potential of APS-graphite is +6.5 mV, while that of MXene is... 29.7mV means that the MXene layer will spontaneously adsorb onto the APS-graphite surface through electrostatic interactions.

[0051] When negatively charged MXene and positively charged aminated graphite are mixed in solution, a two-dimensional ultrathin MXene layer spontaneously adsorbs onto the graphite surface through electrostatic interactions, thus forming a unique sandwich structure, such as... Figure 2 As shown in Figure a, graphite is sandwiched between two MXene interface layers, forming a heterostructure of MXene-graphite-MXene (this invention is referred to as MXene interface reconstructed graphite). Fourier transform infrared spectra of graphite and APS-graphite are also shown. Figure 2 b) Tests showed that the wavelength range was 4000 to 600 cm. 1 Among them, 1594, 1350, 1086 and 760 cm 1 The main characteristic peaks at the point were identified as stretching or bending vibrations of -NH2, CN, Si-O-Si, and Si-H / -NH2, respectively, indicating that the APS component had been successfully grafted onto the graphite surface.

[0052] like Figure 2As shown in the schematic diagram, an MXene interface layer is formed by adhering numerous single or multiple MXene sheets to a graphite substrate. Therefore, the MXene interface layer has an ultrathin thickness, the same as that of a single or multiple MXene sheets. The thickness of the MXene sheets can be measured using atomic force microscopy (AFM) (approximately 1-10 nm). Preferably, the thickness of the MXene interface layer is between 1 and 10 nm. When a single MXene sheet is a single-atom-layer MXene, AFM testing shows that the thickness of the MXene sheet is approximately 1-3 nm. In this embodiment of the invention, the thickness of the MXene sheet is only 2 nm. Figure 4 b). That is, when the MXene interface layer consists of only a single atomic layer of MXene adhered to the graphite substrate, the ultrathin thickness of the MXene interface layer of the MXene interface reconstructed graphite of this invention is 1~3nm.

[0053] Example 2 This embodiment provides a specific MXene interface reconstruction graphite and its implementation method, wherein MXene is Ti3C2T x Ti3C2 was prepared by etching the Al layer in Ti3AlC2 using MAX phase Ti3AlC2 as a precursor (produced by Jinan Sanchuan New Material Technology Co., Ltd.) and lithium fluoride (LiF) and hydrochloric acid (HCl) as etchants. More specific preparation steps include: immersing 1g of Ti3AlC2 powder in a mixture containing 40mL of 12M HCl and 3.2g of LiF, and heating at 35℃ for 24 hours with magnetic stirring. The suspension was then repeatedly washed with deionized water and ultrasonically for several hours, and centrifuged to obtain Ti3C2T. x Dispersion.

[0054] The method for reconstructing the interface using graphite includes the following steps: (1) Graphite amination: 1 g of graphite particles were dispersed in 100 mL of APS aqueous solution (0.15 mg / mL). 1 The mixture was stirred at 60°C for 12 hours, and then washed with deionized water for several cycles to synthesize APS-modified graphite (APS-graphite).

[0055] (2) MXene interface reconstruction: 50 mL of MXene aqueous solution (0.2 mg / mL) was prepared. 1 Add dropwise to 100 mL of APS-modified graphite ink solution (10 mg / mL) 1 Stirring for 2 hours in a solution yields an MXene interface-reconstructed graphite dispersion. After solid-liquid separation and vacuum drying, the resulting MXene interface-reconstructed graphite is obtained.

[0056] Figure 3 Image a compares optical photographs of the MXene-graphite mixture (left) and the MXene-interface-reconstructed graphite dispersion (right), showing obvious precipitation due to the electrostatic interaction between MXene and APS-modified graphite. Thermogravimetric analysis (TGA) of the MXene-reconstructed graphite in air shows that it is completely oxidized to titanium dioxide (TiO2) at 1400℃, with a weight loss of 98.72%. Based on the relative molar masses of MXene and TiO2, the MXene content can be estimated to be approximately ~1%. Figure 3 b).

[0057] To better illustrate the unique sandwich structure of the MXene interface-reconstructed graphite of this invention, the morphology of the product was characterized. A scanning electron microscope (SEM) image of the MXene interface-reconstructed graphite, viewed from the side, clearly shows that the MXene interface-reconstructed graphite possesses a sandwich-like MXene-graphite-MXene structure. Figure 4 c). The planar dimensions of MXene sheets are between 0.5 and 4 μm. Figure 4 a) Thickness is approximately 2nm ( Figure 4 b); The particle size of the graphite particles ranges from 100 micrometers to 1000 micrometers, with an average particle size of approximately ~307 μm. Figure 4 c) The negatively charged MXene sheets are significantly smaller than graphite particles, and the vast majority of MXene sheets are adsorbed onto the positively charged APS-graphite basal surface. This is evidenced by the particle size distribution of the MXene-reconstructed graphite (average particle size ~312 μm), which is close to that of graphite. Figure 4 c).

[0058] High-resolution transmission electron microscopy (HRTEM) clearly shows that the MXene interface layer is located on the surface of graphite and forms a sandwich structure. Figure 5 Furthermore, the MXene interface layer (shown by the orange-yellow dashed line) is extremely thin, only about 1 nm thick, indicating that the MXene interface layer is a single-atom layer of MXene. This is further supported by cross-sectional transmission electron microscopy (TEM) images (…). Figure 6 The image clearly shows the elemental distribution of Ti on both sides and C in the middle, confirming that the MXene interface reconstruction graphite of this invention has a sandwich-like MXene-graphite-MXene heterostructure. The MXene sheets are mainly adhered to the graphite substrate, providing effective interface reconstruction for the graphite interface.

[0059] Density functional theory (DFT) calculations show that this interfacial reconstruction from carbon to MXene will significantly increase the adsorption energy of Li. 3.41 eV, approximately the same as pure graphite ( 3 times that of 1.03 eV Figure 7 Experimental results show that the nucleation overpotential (|η) at the MXene interface n |) is only 12 mV, about a quarter of that of pure graphite (42 mV). Based on classical nucleation theory ( Δ Gn*∝z|η n |, where z is the charge of the cation), due to the Li nucleation energy barrier ( ΔG n *) Proportional to the overpotential, the MXene interface will undoubtedly reduce the Li nucleation energy barrier, effectively promoting uniform nucleation of Li on the reconstructed graphite anode material at the MXene interface.

[0060] To gain a deeper understanding of MXene (Ti3C2T) x The behavior of lithium deposition on the interface, at concentrations ranging from 0.3 to 0.7 mAh cm⁻¹ 2 Cryo-TEM was performed after different deposition capacities. Figure 8 and Figure 9 b, c). For example... Figure 9 As shown in b, at 0.3mAh cm 2 At the current deposition capacity, isolated grains with diameters of 10-20 nm were observed on the interface layer. When the deposition capacity increased to 1.0 mAh cm⁻¹, [further details needed]. 2 At that time, a large amount of metallic lithium grew uniformly on the MXene interface layer, without visible dendritic lithium ( Figure 9 c). Notably, the deposited lithium metal is entirely body-centered cubic (bcc) Li, with most of the exposed crystal planes being (110) planes and a lattice spacing of 2.48 Å. Figure 9 d, e). This contrasts with the dendritic lithium that grows randomly along multiple planes (110), (200), or (211) on the surface of the carbon layer ( Figure 10 The preferential growth of lithium along the (110) plane at the MXene interface was further demonstrated by in-situ X-ray diffraction (XRD) measurements. As the lithium deposition capacity increased to 10 mAh cm⁻¹, the preferential growth of lithium along the (110) plane was further demonstrated. 2 The strength of the (110) surface gradually increases. Figure 11 This does not exist in the case of graphite and Cu-Li anodes.

[0061] To further elucidate the horizontal or vertical stacking of lithium atoms at the MXene interface during lithium deposition, DFT calculations were performed. Figure 9 In g, MXene Ti3C2T accumulates horizontally. x The adsorption energy is 3.05 eV, much higher than pure Li ( 1.65 eV), graphene ( 1.46 eV) and copper ( The adsorption energy is 2.33 eV. Conversely, for vertical accumulation, MXeneTi3C2T x The adsorption energy is -0.33 eV, which is much lower than that of pure Li ( 1.01eV), graphene ( 1.54eV) and copper ( The adsorption energy is 1.01 eV. Driven by the difference in adsorption energy, lithium exhibits a significant horizontal growth trend at the MXene interface, which may solve the technical challenge of vertical growth of dendritic lithium on pure lithium and many other substrates.

[0062] To further understand the Li deposition mechanism at the MXene interface, the lattice compatibility between lithium electrodeposited along different planes and reconstructed graphite at the MXene interface was calculated using the Bramfitt two-dimensional mismatch formula:

[0063] In the formula This represents the exposed plane of the two-dimensional (2D) material and the ( ) of the Li metal. hkl Lattice mismatch between crystal planes This indicates that the two-dimensional material is along the low refractive index direction. uvw ] 2D The interatomic spacing. Li (represents) hkl The interatomic spacing along the low refractive index direction in a plane, where θ is the direction of low refractive index. uvw ] 2D and[ uvw ] Li The angle between them. Calculation results show that the (110) crystal plane of Li and MXene Ti3C2T x The lattice mismatch between the hexagonal crystal planes is only 7.5%, far lower than that of other Li planes, such as (200) plane (36.5%), (211) plane (32.4%), and (310) plane (70.7%). Figure 9 f), indicating that Li atoms readily pack into dense clusters along the (110) close-packed plane. The plane at the MXene interface is consistent with the results of the aforementioned low-temperature TEM and XRD analyses. In contrast, the lattice mismatch between the (110) crystal plane of Li and the hexagonal crystal plane of graphite is as high as 39.6%, which is ~5 times that of the MXene interface. Clearly, the MXene interface reconstruction can effectively regulate the lithium deposition behavior in the graphite anode.

[0064] In some other embodiments of this invention, by adjusting the reaction parameters, the mass content of MXene can be controlled to be preferably ≤2 wt.%; preferably, between 1 and 2 wt.%; more preferably, between 1 and 1.5 wt.%; and even more preferably, between 1 and 1.2 wt.%.

[0065] Example 3 This embodiment provides an electrode sheet containing the MXene interface reconstructed graphite anode material of this invention, a lithium metal / graphite composite material, a battery, and its electrochemical performance.

[0066] Electrode preparation method: A negative electrode sheet using MXene interface-reconstructed graphite as the negative electrode material was prepared using a classic slurry method. Specifically, 98 wt% MXene interface-reconstructed graphite, 1 wt% carboxymethyl cellulose (CMC) binder, and 1 wt% conductive agent SuperP were sequentially dispersed in deionized water to form a uniform slurry. The slurry was then coated on both sides of a copper foil (6 μm) and vacuum dried at 80 °C for 15 hours to produce the MXene interface-reconstructed graphite negative electrode. After calendering, the negative electrode was cut into rectangular blocks for assembling pouch cells.

[0067] Comparative example: Using graphite, 1% graphene and graphene-mechanical hybrid anode (Graphene-graphite), 1% MXene and graphene-mechanical hybrid anode (MXene(1%)-graphite), and 5% MXene and graphene-mechanical hybrid anode (MXene(5%)-graphite) as comparisons, we further explored the fundamental reasons for the improved electrochemical performance of MXene-configured graphite under extreme conditions.

[0068] In the process of preparing MXene interface reconstructed graphite slurry, by adjusting the amount of MXene interface reconstructed graphite added, this embodiment also studied the viscosity change of the slurry with a solid content of 37% to 42%. Figure 12 When the solid content of the MXene interface-reconstructed graphite electrode slurry is around 37%, the viscosity of the slurry is 3451 mPa·s. 1 It is within the range conducive to good electrode manufacturing (2000-4000 mPa·s) 1 However, the solid content of this MXene interface-reconstructed graphite slurry is much lower than that of commercial graphite electrodes (approximately 42%). If the solid content of the MXene interface-reconstructed graphite is set to approximately 42%, the viscosity increases dramatically to 11291 mPa·s. 1It is much higher than the viscosity of graphite slurry (2437 mPa·s). 1 The high viscosity of MXene-reconstructed graphite is attributed to the abundance of functional groups in MXene, which interact with water or carboxymethyl cellulose (CMC) binders through hydrogen bonding. According to literature (… J. Power Sources (2018, 397, 223), we evaluated the exfoliation strength of the MXene interface-reconstructed graphite electrode. The exfoliation strength-exfoliation elongation curves show ( Figure 13 The average exfoliation strength of the MXene interface-reconstructed graphite electrode was 11.9 N / m. 1 Approximately 7.6 Nm for a graphite electrode. 1 1.5 times that of [previous study]. Based on the high viscosity and good peel strength of the slurry, our study achieved a mass loading of up to 19.3 mg cm⁻¹. 1 The MXene interface is used to reconstruct the graphite electrode.

[0069] In other embodiments, the mass load of the MXene interface-reconstructed graphite electrode can be easily adjusted to 9, 10, 11, 12, 14, 16, 17, 18, 19, or 20 mg cm⁻¹ depending on the cell design. 2 .

[0070] It should be noted that, in order to obtain lithium-ion batteries with good low-temperature and high-rate performance, graphite electrodes typically have a density of ≤8 mg cm⁻¹. 2 The optimal active mass loading is crucial because excessive mass loading significantly impacts electron transfer and ion diffusion capabilities, leading to large electrochemical polarization. In contrast, our MXene-interface-reconstructed graphite electrode exhibits ~19.3 mg cm⁻¹ active mass. 2 High-quality loads, due to their high viscosity, can not only be easily manufactured using traditional slurry methods, but also exhibit high electrical conductivity, excellent low-temperature performance, high rate performance, and high energy density.

[0071] The electrochemical performance of lithium-ion batteries is closely related to the transport rates of electrons and ions within the battery. For example... Figure 14 As shown in figure a, MXene exhibits excellent electronic conductivity (4545 S cm⁻¹). 1 ), approximately graphite (262S cm), 1 17 times that of graphene (359Scm) 1It is 12 times that of the MXene-configured graphite electrode. Correspondingly, the electronic conductivity of the MXene-configured graphite electrode is 1084 S cm⁻¹. 1 It is approximately 2-2.5 times that of graphene and graphene-graphite. Furthermore, as the MXene content increases to 5%, the electronic conductivity of the MXene(5%)-graphite electrode also increases to 1736 S cm⁻¹. 1 This further confirms that introducing high-conductivity MXene into the graphite anode can effectively increase the electronic conductivity of the composite electrode.

[0072] To evaluate the ion diffusion coefficient of modified graphite electrodes, half-cells were assembled using graphite or modified graphite as the positive electrode and lithium metal as the negative electrode. The cells were activated at 0.1C for two cycles at room temperature, and then the half-cells were tested at low temperatures using the GITT (giant galvanostatic titration) method. The diffusion coefficient at 20℃. Figure 15 As shown in a, for a mass loading of approximately 3 mg cm⁻¹ 2 The electrodes, MXene interface reconstructed graphite in Average Li at 20℃ + The diffusion coefficient is 8.7 × 10⁻⁶. 11 cm 2 s 1 It is an MXene-graphite composite material or mixture (3.8 × 10⁻⁶). 11 cm 2 s 1 This difference is twice that of [previous electrode mass loading]. This difference increases significantly with increasing mass loading in the electrode. At up to approximately 12 mg cm⁻¹ 2 Under a mass load of approximately 12 mg cm² s, MXene interface reconstructs graphite. - ¹) average Li + The diffusion coefficient is 2.87 × 10⁻⁶. 11 cm 2 s 1 Compared to MXene-graphite composites or mixtures (0.17 × 10⁻⁶), 11 cm 2 s 1 ) about 16 times higher ( Figure 15 b). For example Figure 15 The relaxation time distribution (DRT) measurement results shown in c further confirm this, where in At 20℃, the MXene interface reconstructs the graphite anode with Li + Diffusion (R) diff-Gr The related peak value (approximately 48 s) is 971 Ω s. 1 This is significantly lower than that of MXene-graphite composites or mixtures (6962 Ω s). 1 This clearly demonstrates that MXene interface-reconstructed graphite exhibits high Li content at low temperatures. + Diffusion coefficient.

[0073] On the one hand, the high ion diffusion coefficient of the MXene-configured graphite electrode originates from the reaction between the MXene interface and lithium to generate LiF-riched material with a high ion diffusion rate (where the ion surface diffusion rate of LiF is ~3×10⁻⁶). 3 Scm 1 ) SEI membrane ( Figure 16 On the other hand, such as Figure 17 Graphene-graphite, MXene (1%)-graphite, and MXene (5%)-graphite completely encapsulate graphite. This layered encapsulation structure creates a steric hindrance effect on lithium-ion transport, significantly increasing the ion transport path. Meanwhile, MXene-configured graphite... Figure 17 In c), the MXene sheets mainly adhere to the base surface of graphite and do not obstruct the insertion and extraction of ions at the edge surfaces.

[0074] In addition, the activation energy of the MXene interface reconstructed graphite electrode (49.0 kJ mol) 1 , Figure 18 a) Lower than graphite (58.5 kJmol) 1 Therefore, in At a typical low temperature of 20°C, the half-cell with the MXene interface-reconstructed graphite anode exhibited significantly lower electrochemical polarization than that of the pure graphite anode (223 mV). Figure 18 b, The potential difference between the lithiation / delithiation peaks is 138mV. At 20℃, the MXene interface-reconstructed graphite anode exhibits a capacity of 298 mAh g. 1 High specific capacity, accounting for 365 mAh g at room temperature. l 81% of ).

[0075] To further investigate the reasons for the enhanced electrochemical performance of the MXene interface-reconstructed graphite anode at low temperatures, in-situ dynamic capacitance (DCM) measurements were performed. At 20℃, the onset time of lithium deposition in the MXene-reconstructed graphite anode was 19549 seconds, much later than that of the pure graphite anode (14449 seconds). This indicates that the MXene interface can effectively delay the initial lithium deposition time. Furthermore, the slope of the capacitance Cs change of the MXene-reconstructed graphite anode with respect to lithium deposition time was low, at 0.8 × 10⁻⁶. 6 It is only one-fifth the size of the graphite anode (4.2 × 10⁻⁶). 6 , Figure 18 c). According to the literature on DCM experiments, the slope is positively correlated with the electrochemically active surface area of ​​lithium plating on the electrode. This is further evidenced by SEM images of graphite reconstructed from 100% discharge to 200% state of charge (SoC) at the MXene interface, where all electrode surfaces are smooth. Figure 19 In contrast, numerous lithium dendrites were observed on the pure graphite electrode, similar to those reported in graphite anodes under extreme conditions. Notably, excessive lithium deposition on the MXene-reconstructed graphite anode (200% SoC) is shown in the XRD pattern (…). Figure 20 The high I / O is provided in version 3.8. (110) / I (200) The value is almost three times that of pure graphite anodes (1.1), which is very consistent with the dominant (110) observations obtained from the low-temperature TEM images and DFT calculations above. According to reported lithium anodes, the densest filled (110) plane of Li has the lowest migration barrier of 0.11 Jm. 2 It exhibits good reversibility. After 100 lithium-ion deposition / stripping cycles, the MXene interface-reconstructed graphite anode surface remains smooth, without any silvery-white dead lithium, which is mainly present on pure graphite. Figure 21 ).

[0076] This embodiment further evaluates the performance of the modified graphite anode at room temperature ( Figure 22 ) and low temperature ( Figure 23 The morphology of lithium nucleation and growth under the above conditions was determined. The above half-cells were subjected to 0.5 mA / cm² conditions. 2 Current density deposition of 0.5-5 mAh cm⁻¹ 2 The capacity of lithium metal was measured, the electrode sheet was then disassembled, washed and dried, and finally the microstructure was observed using SEM. For example... Figure 22 As shown, metallic lithium grows horizontally along two-dimensional nanosheets at room temperature, subsequently forming pebble-shaped lithium particles that eventually cover the entire electrode surface. MXene-configured graphite at 1 mAh cm⁻¹ 2 No obvious lithium deposition was observed on the surface at 3 mAh cm⁻¹ 2 Flat, plate-like metallic lithium was observed. Unlike MXene-configured graphite, MXene(1%)-graphite exhibited similar behavior at 3 mAh cm⁻¹. 2 Horizontally grown metallic lithium with a diameter greater than 20 μm was deposited; MXene (5%)-graphite was deposited in 1 mAh cm⁻¹. 2 Horizontally grown metallic lithium had already been deposited at that time. Graphene-graphite and graphite anodes, however, showed up at 1 mAh cm⁻¹. 2 Lithium dendrites had already precipitated. At a low temperature of 20℃, MXene in 1mAh cm⁻¹ 2 Spherical lithium metal particles with a diameter of approximately 2 μm were formed on the surface, and the metal particles on MXene gradually increased in size with increasing deposition amount. Similar to room temperature, MXene-configured graphite exhibited high performance at 1 mAh cm⁻¹. 2 No significant metallic lithium was observed on the surface at 1 mAh cm⁻¹. 2 Pebble-like metallic lithium was formed on the surface, and MXene was added to the graphite anode at 1 mAh cm⁻¹. 2 Both exhibited a dense deposition morphology. However, obvious lithium dendrites precipitated on graphene-graphite and graphite anodes. In summary, unlike the lithium dendrite precipitation on the surface of graphene-modified graphite and pure graphite, controllable lithium deposition on graphite anodes can be achieved at both room temperature and room temperature via the MXene interface.

[0077] In addition, modified graphite half-cells in The dQ / dV graph at 0.05C under a low temperature of 20℃ shows that ( Figure 24The voltage difference between the charging and discharging platforms of MXene-configurated graphite was 26.8 mV, which is lower than that of MXene(1%)-graphite (33.4 mV), MXene(5%)-graphite (46.5 mV), Graphene-graphite (49.7 mV), and Graphite (58.3 mV). This confirms that MXene-configurated graphite can effectively alleviate electrochemical polarization inside the battery.

[0078] In summary, when lithium ions are deposited as metallic lithium on the surface of reconstructed graphite at the MXene interface, a metallic lithium / graphite composite material is obtained. Metallic lithium preferentially deposits and grows along the two-dimensional MXene sheets at the MXene interface layer, gradually forming pebble-like lithium particles, eventually covering the entire electrode surface.

[0079] Example 4 Based on the above research, this embodiment combines graphite and modified graphite with the cathode material LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was used to assemble Ah-level pouch batteries ( Figure 25 a, c), and using a constant current (CC)-constant voltage (CV) charging protocol, long-cycle performance at low temperatures was tested. As is well known, stress variation is an important factor in evaluating commercial lithium-ion batteries. An in-situ pressure monitoring device was also assembled in this embodiment ( Figure 25 a) to evaluate stress fluctuations in pouch cells with MXene interface-reconstructed graphite anodes. At 20℃, a small stress fluctuation with an average pressure increment of 0.12 kPa was observed. Figure 25 b), which is 5% of the volume change of the pure graphite anode cell (2.37 kPa), clearly demonstrates that the volume change of our pouch cell during low-temperature cycling is negligible. This low stress fluctuation is beneficial for long-term cycling performance under extreme conditions, including low temperature and high rate. When at 1C@ When cycling at 20°C, the energy density reaches as high as 273 Wh kg. 1 The cycling energy density at room temperature is 324 Wh / kg. 1 It is worth noting that after 1200 cycles at low temperature, the capacity retention rate is as high as 93%. Figure 25 c). In contrast, under the same test conditions, the pouch cell with a pure graphite anode exhibited a relatively low energy density (191 Wh kg). 1) and capacity retention (43%), compared to existing lithium-ion batteries under similar conditions (144-176 Wh / kg). 1 , Figure 25 d). Furthermore, at a high rate of 10C and 25°C at room temperature, our pouch cell still exhibited a remarkable 94% capacity retention and 287Wh / kg capacity after 1200 cycles. 1 High energy density ( Figure 25 d), which is superior to pure graphite anode batteries and reported lithium-ion batteries (180-265 Wh / kg). 1 ).

[0080] like Figure 26 As shown, in At 20°C and 1C rate, the MXene interface-reconstructed graphite pouch cell can stably cycle 1200 times, with a capacity retention rate (93%) significantly better than MXene (1%)-graphite (71%), MXene (5%)-graphite (63%), Graphene-graphite (54%), and Graphite (55%). Furthermore, at room temperature (25°C) and a high rate of 10C, the MXene interface-reconstructed graphite pouch cell still exhibits a significant capacity retention rate of 94% after 1100 cycles, superior to cells with MXene-graphite hybrids (81%) and graphite anodes (54%). Figure 27 ).

[0081] In summary, the MXene interface in MXene-configured graphite is a multi-functional interface. Figure 28 The main functions include: ① The MXene interface can enhance the electronic conductivity of the negative electrode (1084 S cm⁻¹). 1 ); ② The MXene interface has high adsorption performance for lithium ions ( 3.41eV), which can effectively reduce the nucleation barrier of Li in the negative electrode; ③ The MXene interface can induce the formation of LiF-riched SEI film, which can promote the transport of lithium ions; ④ The MXene interface has good lattice compatibility with the deposited lithium, which is conducive to the generation of body-centered cubic Li with horizontal growth and dense packing along the (110) crystal plane under extreme conditions.

[0082] It should be noted that the graphite used in this embodiment is commercially available natural flake graphite. The use of other types of graphite, or negative electrode materials with a graphite structure, is also included in the scope of this invention. Since MXene is a two-dimensional material with similar material properties, the MXene Ti3C2T in this embodiment... x It can be replaced with MXene material M composed of other elements. n+1 X n T x In this context, the transition metal element M is selected from one or more of the elements Ti, V, Nb, Ta, Zr, W, Mo, and Cr; the nonmetal element X is selected from one or more of the elements C, N, and B; T represents a surface group (such as -F, -Cl, -OH, -O, etc.); and 1 ≤ n ≤4, 0< x ≤2, by using T x The surface has the meaning of functional groups.

[0083] In materials science, "basal plane" often specifically refers to the crystal plane parallel to the main layer in a layered crystal, such as the graphite basal plane, which is the crystal plane parallel to the direction of the graphite layer; in contrast to "cylindrical plane" or "end face" (such as the (100) and (110) planes of graphite, which are crystal planes perpendicular to the edge of the layer).

[0084] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the present invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the present invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the present invention, as well as various different choices and variations. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A MXene interfacial restructured graphite, characterized in that, MXene sheets form an MXene interface layer on the base surface of the graphite layer, and the MXene interface reconstructs the graphite to have a sandwich-like MXene-graphite-MXene heterostructure.

2. The MXene interfacial restructured graphite of claim 1, wherein, The MXene sheets form the MXene interface layer on the base surface of the graphite layer through electrostatic adsorption.

3. The MXene interfacial restructured graphite of claim 1, wherein, The size of the MXene sheets is between 0.5 and 4 micrometers; And / or, the thickness of the MXene sheet is between 1 and 10 nm.

4. The MXene interfacial reconstructed graphite of claim 3, wherein, The thickness of the MXene sheet is between 1 and 3 nm.

5. The MXene interfacial restructured graphite of claim 1, wherein, The particle size range of the MXene interface-reconstructed graphite is between 100 and 1000 micrometers; And / or, the transition metal element contained in the MXene sheet is selected from one of Ti, V, Nb, Ta, Zr, W, Mo, and Cr.

6. The MXene interfacial reconstructed graphite of claim 5, wherein, The MXene is Ti3C2T x .

7. The MXene interfacial reconstructed graphite of any one of claims 1-6, wherein, The thickness of the MXene interface layer is between 1 and 10 nm; And / or, the thickness of the MXene interface layer is the thickness of a single MXene sheet or several MXene sheets.

8. The MXene interfacial reconstructed graphite of claim 7, wherein, The thickness of the MXene interface layer is 1 to 3 nm; And / or, the MXene sheet is a single-atom layer MXene.

9. A composite material, characterized by It includes MXene interface-reconstructed graphite as described in any one of claims 1 to 8, and metallic lithium on the surface of the MXene interface-reconstructed graphite.

10. The composite material of claim 9, wherein, The lithium metal is on the surface of the MXene interface layer.

11. The composite material of claim 10, wherein, The lithium metal has a body-centered cubic lattice structure. And / or, the exposed crystal plane of the lithium metal is the (110) crystal plane; And / or, the lattice spacing of the lithium metal is 2.48 Å; And / or, the lithium metal has a microscopic morphology of pebble-like particles.

12. An electrode tab, characterized by The composite material containing MXene interface reconstructed graphite as claimed in any one of claims 1 to 8; or, a composite material as claimed in any one of claims 9 to 11.

13. A battery, characterized by It contains the electrode sheet as described in claim 12.

14. An electrical device, characterized by It contains the battery as described in claim 13.

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