Preparation method of lithium battery negative electrode material and lithium battery negative electrode material

Abstract

This invention provides a method for preparing a lithium-ion battery anode material. The method includes: dispersing carbon nanotubes in a solvent to form multiple carbon nanotube dispersions; adding a zinc source, a complexing agent, and a dispersant to each carbon nanotube dispersion and dispersing them to form multiple mixed dispersions; wherein the target zinc-to-carbon mass ratio of the multiple mixed dispersions forms a preset gradient; adding an oxygen source to each mixed dispersion for a hydrothermal reaction, followed by washing and drying to form multiple composite filter cakes; dispersing graphene with each composite filter cake in a solvent to form multiple composite dispersions; and performing layered filtration on the multiple composite dispersions according to the preset gradient arrangement to form a lithium-ion battery anode material with a dual reverse gradient structure. This invention effectively improves the uniformity of the lithium-ion battery charging and discharging process.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a method for preparing a lithium battery anode material and the lithium battery anode material itself. Background Technology

[0002] Lithium metal is a core anode candidate material for next-generation high-energy-density lithium metal batteries (LMBs) due to its ultra-high theoretical specific capacity of 3860 mAh / g, low redox potential of -3.04 V, and lightweight properties of 0.534 g / cm³. It can meet the requirements of new energy vehicles and high-end energy storage equipment for long range and high safety.

[0003] However, lithium metal anodes suffer from three major pain points that severely hinder their industrial application:

[0004] One issue is dendrite growth. Due to uneven lithium-ion deposition, dendritic lithium dendrites can form during the deposition process. These dendritic lithium dendrites may puncture the separator, leading to battery short circuits and thermal runaway. Secondly, there is the problem of dead lithium formation. Due to the uneven dissolution of lithium metal during discharge, lithium near the current collector side will dissolve rapidly, resulting in "lithium islands" remaining on the separator side, which become inactive dead lithium. The formation of dead lithium can lead to problems such as reduced capacity and reduced cycle life. Thirdly, there is the issue of volume deformation. Without a designed lithium-ion distribution framework, the lithium will expand / contract dramatically during charging and discharging due to its "hostless" nature, which will damage the stability of the electrode structure and the solid electrolyte interface (SEI) and further exacerbate side reactions. Summary of the Invention

[0005] The method for preparing lithium battery anode materials and the lithium battery anode materials provided by this invention can effectively improve the uniformity of the lithium battery charging and discharging process by reverse designing the nucleation site gradient and the conductivity gradient.

[0006] In a first aspect, the present invention provides a method for preparing a lithium battery anode material, the method comprising: Carbon nanotubes are dispersed in a solvent to form multiple carbon nanotube dispersions. A zinc source, a complexing agent, and a dispersant are added to each carbon nanotube dispersion and dispersed to form multiple mixed dispersions; wherein the target zinc-carbon mass ratio of the multiple mixed dispersions forms a preset gradient. An oxygen source is added to each part of the mixed dispersion to carry out a hydrothermal reaction, followed by washing and drying to form multiple composite filter cakes. Graphene and each part of the composite filter cake are dispersed in a solvent to form multiple composite dispersions; Multiple composite dispersions are layered and filtered according to a preset gradient to form a lithium battery anode material with a dual inverse gradient structure.

[0007] Optionally, the step of performing stratified filtration of multiple composite dispersions according to a preset gradient includes: After completing the filtration of the composite dispersion corresponding to the current target zinc-carbon mass ratio and forming a composite membrane layer, the next composite dispersion corresponding to the target zinc-carbon mass ratio is added to the composite membrane layer, and the next composite dispersion corresponding to the target zinc-carbon mass ratio is used as the composite dispersion corresponding to the current target zinc-carbon mass ratio for the next filtration.

[0008] Optionally, the step of performing stratified filtration of multiple composite dispersions according to a preset gradient includes: Multiple composite dispersions were subjected to stratified filtration in order of increasing target zinc-carbon mass ratio.

[0009] Optionally, the step of adding a zinc source, a complexing agent, and a dispersant to each portion of carbon nanotube dispersion and dispersing them to form multiple mixed dispersions includes: Zinc source, complexing agent and dispersant were added to each carbon nanotube dispersion and dispersed to form multiple mixed dispersions. The target zinc-carbon mass ratio of the multiple mixed dispersions was controlled between 1% and 25%.

[0010] Optionally, dispersing carbon nanotubes in a solvent to form multiple carbon nanotube dispersions includes: Deionized water was added to the aqueous slurry containing carbon nanotubes to form a solution to be dispersed. The solution to be dispersed is subjected to multiple dispersion treatments, wherein each dispersion treatment includes sequential mechanical stirring and ultrasonic treatment.

[0011] Optionally, the step of adding a zinc source, a complexing agent, and a dispersant to each portion of carbon nanotube dispersion and then dispersing them includes: Zinc chloride as a zinc source, urea as a complexing agent, and citric acid as a dispersant were added to each carbon nanotube dispersion to form a mixture to be dispersed. The mixture to be dispersed is mechanically stirred to form a mixed dispersion.

[0012] Optionally, the addition of an oxygen source to each portion of the mixed dispersion for hydrothermal reaction includes: Ammonia water is used as an oxygen source and added to each part of the mixed dispersion until the pH value of each part of the mixed dispersion reaches 8-9. Urea was added to the mixed dispersion containing ammonia and then placed in a hydrothermal reactor. The hydrothermal reactor was then placed at a temperature of 160-200°C and reacted continuously for 8-24 hours.

[0013] Optionally, dispersing the graphene with each portion of the composite filter cake in a solvent includes: Graphene and deionized water are added to each composite filter to form multiple composite solutions to be dispersed. Multiple portions of the composite solution to be dispersed are mechanically stirred to form multiple composite dispersions.

[0014] Optionally, the step of adding an oxygen source to each portion of the mixed dispersion for a hydrothermal reaction, followed by washing and drying, includes: The mixed dispersion after the hydrothermal reaction was completed was washed multiple times by centrifugation with anhydrous ethanol to remove impurities.

[0015] In a second aspect, the present invention provides a lithium battery anode material, prepared by the method described in any one of the foregoing claims, wherein the lithium battery anode material comprises: Multiple composite material film layers are sequentially arranged, wherein each composite material film layer includes zinc oxide, carbon nanotubes and graphene, and the target zinc-carbon mass ratio of zinc oxide and carbon nanotubes has a preset gradient.

[0016] In the technical solution provided by this invention, carbon nanotubes and graphene are formed into an interwoven structure with surface and line, which has high mechanical strength and flexibility, and can buffer the volume expansion during lithium deposition / dissolution (expansion rate ≤10%), thus preventing the electrode structure from breaking. At the same time, zinc oxide generated by hydrothermal reaction is used as nucleation sites in the 3D framework structure of carbon nanotubes and graphene. This ensures that zinc oxide and the 3D framework structure form a tight physical-chemical bond, avoiding detachment during cycling and ensuring the long-term effectiveness of the gradient structure. Furthermore, through the preset gradient of the target zinc-carbon mass ratio of zinc oxide and carbon nanotubes, the nucleation ability gradient and the conductivity gradient are mutually inverse, so that the electrode maintains structural integrity under high rate (10C) and long cycle (500 cycles). Attached Figure Description

[0017] Figure 1 This invention provides a method for preparing a lithium battery anode material according to an embodiment of the present invention. Figure 2 This is an X-ray diffraction pattern of a lithium battery anode material prepared by a method according to another embodiment of the present invention. Figure 3 This is a SEM image of the framework formed by graphene and carbon nanotubes in the preparation method of lithium battery anode material according to another embodiment of the present invention. Figure 4 The dispersion structure of zinc oxide in the preparation method of lithium battery negative electrode material according to another embodiment of the present invention; Figure 5This is a TEM image of a lithium battery anode material prepared by a method for preparing lithium battery anode material according to another embodiment of the present invention. Figure 6 This is a TEM image of a lithium battery anode material prepared by a method for preparing lithium battery anode material according to another embodiment of the present invention. Figure 7 This is an HRTEM image of a lithium battery anode material prepared by a method according to another embodiment of the present invention. Figure 8 This is an XPS full spectrum of a lithium battery anode material prepared by a method according to another embodiment of the present invention. Figure 9 XPS spectrum of zinc element in lithium battery anode material prepared by another embodiment of the present invention; Figure 10 XPS spectrum of carbon in lithium battery anode material prepared by another embodiment of the present invention; Figure 11 XPS spectrum of oxygen element in lithium battery anode material formed by the preparation method of lithium battery anode material according to another embodiment of the present invention; Figure 12 The Fourier transform infrared spectrum of the lithium battery anode material prepared by the preparation method of the lithium battery anode material according to another embodiment of the present invention; Figure 13 Mass content distribution of lithium battery anode materials with different target zinc-to-carbon mass ratios formed by the preparation method of lithium battery anode materials according to another embodiment of the present invention; Figure 14 The conductivity distribution of lithium battery anode materials with different target zinc-to-carbon mass ratios formed by the preparation method of lithium battery anode material according to another embodiment of the present invention; Figure 15 The method for preparing lithium battery anode material according to another embodiment of the present invention forms the particle and layered stacked morphology of lithium battery anode material in SEM observation; Figure 16 The distribution image of C, N, Zn, and O elements in the lithium battery anode material is formed according to another embodiment of the preparation method of the lithium battery anode material of the present invention. Figure 17 The overpotential test diagram of the lithium battery anode material is formed according to another embodiment of the preparation method of the lithium battery anode material of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a method for preparing a lithium battery anode material, such as... Figure 1 As shown, the method includes: Carbon nanotubes are dispersed in a solvent to form multiple carbon nanotube dispersions. In some embodiments, the solvent may be, for example, deionized water. As a preferred embodiment, each portion of carbon nanotube dispersion may be prepared by taking 0.02 g of aqueous carbon nanotube slurry by mass, adding 100 ml of deionized water, mechanically stirring for 30 min, and then sonicating for 30 min. This mechanical stirring and sonication process is repeated alternately at least five times to ensure uniform dispersion of the carbon nanotubes and prevent agglomeration, thereby obtaining a stable carbon nanotube dispersion. The carbon nanotubes may be, for example, single-walled carbon nanotubes.

[0020] A zinc source, a complexing agent, and a dispersant are added to each carbon nanotube dispersion and dispersed to form multiple mixed dispersions; wherein the target zinc-carbon mass ratio of the multiple mixed dispersions forms a preset gradient. In some embodiments, the carbon nanotubes in the multiple portions of carbon nanotubes have the same mass fraction. In preparing the mixed dispersion, different masses of a zinc source, such as zinc chloride, can be added to each of the multiple carbon nanotube dispersions. To ensure stable bonding and uniform dispersion of the carbon nanotubes and the zinc source, a complexing agent and a dispersant are also added to the carbon nanotube dispersion. The zinc source, complexing agent, and dispersant can be dispersed, for example, by mechanical stirring. The target zinc-carbon mass ratio refers to the mass ratio of zinc oxide to carbon in the lithium-ion battery anode material formed after the subsequent hydrothermal reaction and the addition of graphene, where the mass of carbon includes the sum of the masses of carbon nanotubes and graphene.

[0021] An oxygen source is added to each part of the mixed dispersion to carry out a hydrothermal reaction, followed by washing and drying to form multiple composite filter cakes. In some embodiments, since zinc oxide has superior performance as a nucleation site for lithium ions, it is necessary to convert the zinc source in the mixed dispersion into close-packed hexagonal zinc oxide (ZnO) to form 200 nm particle size. This lithium-affinity property guides uniform lithium ion deposition and reduces the nucleation overpotential. The mixed dispersion is converted into zinc oxide by adding an oxygen source and performing a hydrothermal reaction. As a preferred embodiment, urea can be used as the oxygen source. During the hydrothermal reaction, urea decomposes to produce OH-. -- , with Zn 2+ The reaction generates zinc oxide nanoparticles, which are then in situ loaded onto the surface of carbon nanotubes to form a ZnO-CNT composite material. As a preferred embodiment, the pH of the mixed dispersion can be adjusted before the hydrothermal reaction; for example, ammonia can be used to adjust the pH of the mixed dispersion.

[0022] Graphene and each part of the composite filter cake are dispersed in a solvent to form multiple composite dispersions; In some embodiments, each composite filter cake is mixed and dispersed with graphene to form a composite dispersion. The addition of graphene is beneficial to forming an interwoven structure, so as to suppress the volume expansion of lithium ions.

[0023] Multiple composite dispersions are layered and filtered according to a preset gradient to form a lithium battery anode material with a dual inverse gradient structure.

[0024] In some embodiments, during the stratified filtration process, the composite dispersion corresponding to the lowest target zinc-carbon mass ratio is first filtered, and then the target zinc-carbon mass ratio of the composite dispersion is increased sequentially for each filtration, thereby forming a reverse gradient distribution in which the target zinc-carbon mass ratio is low at the top and high at the bottom, and the conductivity is high at the top and low at the bottom.

[0025] The lithium battery anode material formed in the technical solution provided by this invention can effectively suppress dendrite growth through a synergistic mechanism under charging conditions; and the Li in the electrolyte under charging conditions... + It passes through the diaphragm and reaches the top of the composite membrane; due to the fewer nucleation sites at the top and the more nucleation sites at the bottom, a nucleation gradient is formed, and Li + Guided by differences in lithophile affinity, electrons preferentially migrate towards the bottom (current collector side). The composite film exhibits high conductivity at the top and low conductivity at the bottom, creating a conductivity gradient. As electrons transport from the current collector to the top, the conduction efficiency is similar to that of Li. + The migration efficiency is dynamically matched to avoid Li-induced degradation due to localized electron accumulation. + Rapid deposition; based on this state, Li +The lithium metal layer is deposited uniformly at the bottom and middle layers to form a dense layer, rather than growing in a "dendritic" manner, thus avoiding the risk of dendrites piercing the separator from the root. Furthermore, under discharge conditions, lithium metal needs to be converted back into Li. + Upon entering the electrolyte, the high conductivity at the top of the composite membrane leads to rapid electron transport, preferentially dissolving lithium metal near the membrane side. The low conductivity at the bottom slows down the lithium metal dissolution rate, balancing the dissolution rate at the top and preventing the phenomenon of "rapid dissolution at the bottom and isolated islands at the top." Simultaneously, the lithium-affinity properties of ZnO assist Li... + Rapid diffusion further enhances the uniformity of dissolution; as lithium metal dissolves gradually and uniformly from top to bottom, there are no residual "lithium islands", and the amount of dead lithium generated is significantly reduced. After testing, the coulombic efficiency remained at 100% (200 cycles) under constant current charge and discharge test at 0.5C.

[0026] Meanwhile, the interwoven structure of carbon nanotubes and graphene has high mechanical strength and flexibility, which can buffer the volume expansion during lithium deposition / dissolution (expansion rate ≤10%) and prevent the electrode structure from breaking; and zinc oxide nanoparticles are loaded onto the surface of carbon nanotubes through hydrothermal in-situ growth, forming a tight physical-chemical bond with graphene, with no shedding during cycling, ensuring the long-term effectiveness of the gradient structure. Based on the aforementioned theory, in this embodiment of the invention, the nucleation gradient and the conduction gradient are matched in opposite directions to avoid performance degradation caused by the failure of a single gradient, so that the electrode can maintain structural integrity under high magnification (10C) and long cycling (500 cycles).

[0027] As an optional implementation, the step of performing stratified filtration of multiple composite dispersions according to a preset gradient arrangement includes: After completing the filtration of the composite dispersion corresponding to the current target zinc-carbon mass ratio and forming a composite membrane layer, the next composite dispersion corresponding to the target zinc-carbon mass ratio is added to the composite membrane layer, and the next composite dispersion corresponding to the target zinc-carbon mass ratio is used as the composite dispersion corresponding to the current target zinc-carbon mass ratio for the next filtration.

[0028] In some embodiments, for the filtration process of multiple composite dispersions, after each composite membrane layer corresponding to a target zinc-carbon mass ratio is completed by filtration, a new composite dispersion is added on the basis of the composite membrane layer and filtration is performed again. Through multiple filtrations, the resulting lithium battery anode material has a reverse gradient structure with a target zinc-carbon mass ratio that is low at the top and high at the bottom, and conductivity that is high at the top and low at the bottom.

[0029] As an optional implementation, the step of performing stratified filtration of multiple composite dispersions according to a preset gradient arrangement includes: Multiple composite dispersions were subjected to stratified filtration in order of increasing target zinc-carbon mass ratio.

[0030] In some embodiments, for example, taking the filtration of multiple composite dispersions with target zinc-carbon mass ratios of 1wt%, 3wt%, 5wt%, and 10wt% as an example, the composite dispersion with a target zinc-carbon mass ratio of 1wt% should be filtered first, then the composite dispersion with a target zinc-carbon mass ratio of 3wt% should be added and filtered, and then the composite dispersions with target zinc-carbon mass ratios of 5wt% and 5wt% should be filtered in sequence.

[0031] As an optional implementation, the step of adding a zinc source, a complexing agent, and a dispersant to each portion of carbon nanotube dispersion and dispersing them to form multiple mixed dispersions includes: Zinc source, complexing agent and dispersant were added to each carbon nanotube dispersion and dispersed to form multiple mixed dispersions. The target zinc-carbon mass ratio of the multiple mixed dispersions was controlled between 1% and 25%.

[0032] As an optional implementation, dispersing carbon nanotubes in a solvent to form multiple carbon nanotube dispersions includes: Deionized water was added to the aqueous slurry containing carbon nanotubes to form a solution to be dispersed. The solution to be dispersed is subjected to multiple dispersion treatments, wherein each dispersion treatment includes sequential mechanical stirring and ultrasonic treatment.

[0033] In some embodiments, for example, mechanical stirring for 30 minutes followed by ultrasonic treatment for 30 minutes is performed before each dispersion treatment. The mechanical stirring and ultrasonic treatment are alternated 5 times to ensure uniform dispersion of carbon nanotubes, avoid agglomeration, and obtain a stable carbon nanotube dispersion.

[0034] As an optional implementation, the step of adding a zinc source, a complexing agent, and a dispersant to each portion of carbon nanotube dispersion and then dispersing them includes: Zinc chloride as a zinc source, urea as a complexing agent, and citric acid as a dispersant were added to each carbon nanotube dispersion to form a mixture to be dispersed. The mixture to be dispersed is mechanically stirred to form a mixed dispersion.

[0035] In some embodiments, when forming the mixed dispersion, for example, 0.168 g ZnCl2, 0.336 g urea (complexing agent), and 0.05 g citric acid (dispersant) can be added sequentially to the carbon nanotube dispersion, followed by mechanical stirring for 2 hours to form a homogeneous mixed dispersion with a target zinc-to-carbon mass ratio of 10 wt%. For multiple portions of the mixed dispersion, the corresponding target zinc-to-carbon mass ratios are 1 wt%, 3 wt%, 5 wt%, and 10 wt%, respectively.

[0036] As an optional implementation, the addition of an oxygen source to each portion of the mixed dispersion for hydrothermal reaction includes: Ammonia water is used as an oxygen source and added to each part of the mixed dispersion until the pH value of each part of the mixed dispersion reaches 8-9. Urea was added to the mixed dispersion containing ammonia and then placed in a hydrothermal reactor. The hydrothermal reactor was then placed at a temperature of 160-200°C and reacted continuously for 8-24 hours.

[0037] In some embodiments, ammonia is added to each group of mixed dispersions to adjust the pH to 8-9, followed by the addition of urea and transfer to a reaction vessel, which is then placed in an electrically heated constant-temperature drying oven and kept at 180°C for 12 hours. During the hydrothermal process, urea decomposes to produce OH-. - , with Zn² + The reaction generates ZnO nanoparticles, which are then loaded in situ onto the surface of carbon nanotubes to form a ZnO-CNT composite material.

[0038] As an optional implementation, dispersing the graphene with each portion of the composite filter cake in a solvent includes: Graphene and deionized water are added to each composite filter to form multiple composite solutions to be dispersed. Multiple portions of the composite solution to be dispersed are mechanically stirred to form multiple composite dispersions.

[0039] In some embodiments, when forming the composite dispersion, 0.98g of reduced graphene oxide is added to each group of ZnO-CNT filter cakes, deionized water is added and ultrasonically dispersed for 30min, and then mechanically stirred for 2 hours to allow graphene and ZnO-CNT to fully interweave and form a ZnO-CNT-G composite dispersion.

[0040] As an optional implementation, the step of adding an oxygen source to each portion of the mixed dispersion for a hydrothermal reaction, followed by washing and drying, includes: The mixed dispersion after the hydrothermal reaction was completed was washed multiple times by centrifugation with anhydrous ethanol to remove impurities.

[0041] In some embodiments, the mixed dispersion after hydrothermal reaction is washed three times with anhydrous ethanol (8000 rpm, 10 min each time) to remove unreacted salts, citric acid and other impurities, and then filtered to obtain ZnO-CNT filter cake.

[0042] This invention also provides a lithium battery anode material, prepared by the method described in any one of the foregoing embodiments, wherein the lithium battery anode material comprises: Multiple composite material film layers are sequentially arranged, wherein each composite material film layer includes zinc oxide, carbon nanotubes and graphene, and the target zinc-carbon mass ratio of zinc oxide and carbon nanotubes has a preset gradient.

[0043] The following is a structural and performance description of the lithium battery anode materials prepared by the technical solutions provided in the foregoing embodiments of the present invention, as detailed below. like Figure 2 As shown, to elucidate the chemical state of zinc species, CNT-G and ZnO-CNT-G composites with different ZnO loadings (1, 3, 5, and 10 wt%) were characterized by XRD. Figure 2 As shown, the XRD pattern of the lithium battery anode material prepared by the aforementioned method, namely the ZnO-CNT-G composite material, shows obvious ZnO diffraction peaks at 2θ = 31.96°, 34.66°, and 36.54°, corresponding to the (100), (002), and (101) crystal planes of hexagonal ZnO, respectively. These diffraction peaks are not observed in the graphene and carbon nanotube composite material without zinc oxide loading, i.e., CNT-G. These characteristic peaks confirm the successful formation of wurtzite ZnO crystals in the composite matrix.

[0044] like Figures 3-4 As shown, the surface morphology of ZnO-CNT-G composites with different Zn / C ratios was analyzed using a Hitachi S-8100 field emission scanning electron microscope (FE-SEM). Samples were prepared by ethanol dispersion, drop coating, drying, and gold sputtering to ensure optimal imaging conditions. Figures 3-4 The SEM images shown indicate that particles of approximately 200 nm in size are uniformly dispersed in the graphene-carbon nanotube matrix in the ZnO-CNT-G composite material, confirming the successful introduction of ZnO.

[0045] like Figures 5-6 As shown, the three-dimensional structure of the ZnO-CNT-G composite material was investigated using a FEITecnaiG2F20 cryo-transmission electron microscope (TEM) to resolve its nanoscale structural features. Figures 5-6 As shown, the ZnO-CNT-G composite material exhibits a well-integrated structure, consisting of graphene-carbon nanotubes and ZnO nanoparticles (approximately 200 nm) modified onto them.

[0046] like Figure 7 As shown, the high-resolution TEM image reveals clear lattice fringes with spacings of 0.260 nm and 0.246 nm, corresponding to the (002) and (101) crystal planes of wurtzite ZnO, confirming its hexagonal close-packed crystal structure.

[0047] like Figures 8-11 As shown, the chemical bonding states of C, O, and Zn in the ZnO-CNT-G composite material were characterized by X-ray photoelectron spectroscopy (XPS) using a Thermo Fisher Scientific ESCALAB250Xi system. Figure 8 As shown, XPS analysis of the 10 at.% ZnO-CNT-G composite material indicates that its elemental composition is 11.75 at.% Zn, 45.13 at.% C, and 13.25 at.% O, which is highly consistent with the nominal stoichiometry of the precursor material. Figure 9 The Zn 2p XPS spectrum shows characteristic doublets of 2p1 / 2 and 2p3 / 2 spin orbitals, and their binding energy and intensity ratio confirm that Zn... 2+ The oxidation state. Figure 10 The C1s XPS spectrum shows a persistent CO and C=O bond configuration, indicating that the carbon skeleton in the ZnO-CNT-G composite material has undergone partial oxidation. Figure 11 As shown, the Zn:O atomic ratio obtained by XPS quantitative analysis is close to 1:1, strongly indicating that zinc exists mainly as the ZnO phase in the composite material, and no metallic Zn or other zinc compounds were detected. Figure 12 As shown, Fourier transform infrared (FTIR) spectroscopy was performed on pristine CNT-G and ZnO-CNT-G composites with different ZnO loadings (1–10 wt%) using a Bruker ALPHA spectrometer to characterize their surface functional groups. Figure 12 As shown, at 3400cm - The broad absorption band near ¹ corresponds to the OH stretching vibration, indicating the presence of surface hydroxyl groups or adsorbed water molecules. This characteristic signal typically originates from adsorbed water or intrinsic functional groups (such as hydroxyl groups (–OH)) on the graphene oxide (GO) substrate in the composite material. At 1600 cm⁻¹ -1 The nearby medium-intensity sharp peaks are characteristic of the C=C stretching vibrations in the graphene / sp² carbon framework and carbon nanotubes (CNTs), confirming the retention of the conjugated carbon structure in the composite material. (1200–1000 cm⁻¹) -1 The absorption bands appearing between these bands are attributed to C–O stretching vibrations (such as epoxy and alkoxy groups), representing typical oxygen-containing functional groups in graphene oxide or its reduction products. The characteristic FTIR signal of ZnO appears in the low-frequency region (400–600 cm⁻¹). -1), which corresponds to lattice vibrations involving Zn-O stretching and bending modes, and is a distinct characteristic peak of the ZnO crystal domain.

[0048] like Figure 13 As shown, the designed ZnO content in the ZnO-CNT-G composite material is displayed. Figure 14 This indicates that the conductivity gradually decreases with increasing ZnO loading, from the highest conductivity of the original CNT-G to the lowest conductivity of 10% ZnO-CNT-G. This controllable conductivity gradient is crucial for regulating lithium deposition uniformity and preventing dendrite formation that leads to catastrophic battery failure and capacity decay. A dual-gradient ZnO-CNT-G three-dimensional structure was prepared by continuous vacuum filtration of 1–10 wt% ZnO composite materials. Figure 15 As shown, cross-sectional SEM reveals a dense graphene-carbon nanotube network and tubular ZnO deposits, confirming an inverse correlation between nucleation sites (increasing from bottom to top) and conductivity (decreasing from bottom to top). This synergistic effect modulates the Li... + Flux prevents dendrite formation, which can lead to safety hazards and rapid capacity decay in lithium metal batteries.

[0049] like Figure 16 As shown, energy-dispersive X-ray spectroscopy (EDS) analysis of the cross-section of the dual-gradient ZnO-CNT-G three-dimensional composite material was performed using a Bruker Quantax 200 system to quantify the spatial distribution of Zn, O, and C. EDS analysis revealed a Zn concentration of 0.33 at.% and a C content of 54.17 at.%, with the elemental distribution map showing a decreasing Zn concentration gradient from the top to the bottom surface. This result clearly validates the designed dual-reverse gradient structure in the ZnO-CNT-G composite material, where ZnO nucleation sites and electrical conductivity exhibit spatially reversed distribution characteristics.

[0050] like Figure 17 As shown, to evaluate the synergistic effect of ZnO nucleation sites and dual-gradient conductivity on lithium deposition uniformity (which is crucial for mitigating dendrite-induced safety failure), at 0.2 mA / cm²... 2 The nucleation overpotential of the following samples was tested at a current density of (i) homogeneous ZnO-CNT-G composite material (0–10 wt% ZnO); (ii) structure-optimized dual-gradient three-dimensional matrix; and (iii) standard copper foil (baseline). Figure 17The nucleation overpotentials of CNT-G, ZnO-CNT-G composites with different ZnO loadings (1, 3, 5, and 10 wt%), and the dual-gradient ZnO-CNT-G structure were compared, demonstrating the latter's superior performance in reducing the lithium deposition energy barrier. Testing revealed a characteristic voltage curve for lithium deposition on bare copper foil: an initial sharp drop followed by a recovery to a stable plateau. The nucleation overpotential, defined as the difference between the plateau voltage and the lowest valley (74 mV), reflects the high energy barrier for lithium nucleation on the unmodified substrate. The nucleation overpotential for lithium deposition on CNT-G was 47 mV, while the nucleation energy barrier of ZnO-CNT-G increased to 71 mV after introducing 1 wt% ZnO. Further increasing the ZnO content to 5 wt% and 10 wt% resulted in a moderate decrease in overpotential to 67 mV and 65 mV, respectively, indicating a non-monotonic relationship between ZnO loading and nucleation efficiency. Notably, the 3wt% ZnO-CNT-G composite material achieved an extremely low nucleation overpotential of 39 mV, a 17% reduction compared to the original CNT-G (47 mV), indicating an optimal balance between nucleation sites and charge transport. The dual-gradient ZnO-CNT-G three-dimensional structure, through the synergistic combination of inversely correlated conductivity and nucleation site distribution, achieved an optimal nucleation overpotential of 40 mV. This unique design enables bottom-up lithium deposition during charging and simultaneously promotes top-down lithium dissolution during discharging, thereby fundamentally solving the dendrite-induced safety hazards and cycle instability problems that plague lithium metal batteries through spatially controlled lithium deposition / stripping behavior.

[0051] To test the electrochemical properties of the prepared lithium battery anode material, LiFePO4 was used as the positive electrode, and two different types of materials were used as anodes (ZnO-CNT-G / Li composite materials with different ZnO contents, and ZnO-CNT-G / Li composite lithium metal with nucleation-conduction dual reverse gradient three-dimensional structure). Full cells were assembled and cyclic voltammetry (CV) tests were performed. The tests showed that a pair of redox peaks were observed in the voltage range of 2.5 to 4.5 V: specifically, the oxidation peak was located at 3.78 V and the reduction peak was located at 3.18 V.

[0052] Furthermore, electrochemical impedance spectroscopy (EIS) was tested on ZnO-CNT-G / Li composite materials with different zinc oxide contents, as well as on a full cell of a nucleation-conductivity dual reverse gradient three-dimensional structure ZnO-CNT-G / Li composite lithium metal anode paired with LiFePO4. The intercept of the high-frequency region with the X-axis represents the internal resistance (Rs) of the battery, and the semicircles correspond to the lithium ion transport impedance (RSEI) and charge transfer impedance (Rct) through the solid electrolyte interphase (SEI) layer, respectively. The tests revealed that, compared with the curves of CNT-G / Li, 1wt% ZnO-CNT-G / Li, and 10wt% ZnO-CNT-G / Li composite materials, the EIS spectrum of the nucleation-conductivity dual reverse gradient three-dimensional structure ZnO-CNT-G / Li composite lithium metal anode exhibited the smallest slope, indicating that the introduction of different contents of ZnO nucleating particles through gradient structuring reduced the conductivity of the material to some extent. The synergistic effect of the concentration gradient of ZnO nucleation sites and the conductivity gradient of CNT-G in the double-inverted structure provides efficient charge transport and Li + The dual diffusion pathway helps improve battery cycle life and rate performance.

[0053] Furthermore, to evaluate the coulombic efficiency of the nucleation-conductivity dual-gradient three-dimensional ZnO-CNT-G / Li composite lithium metal anode paired with LiFePO4, a full cell was assembled using the gradient-structured anode and LiFePO4 cathode. Constant current charge-discharge tests were conducted at 0.5C to obtain its electrochemical potential-capacity curves. This configuration allows for direct comparison of the interface stability and ion transport efficiency between the gradient-structured anode and a conventional lithium metal electrode. The dual-gradient design effectively mitigates lithium dendrite growth while maintaining stable SEI formation, as confirmed by the stable voltage plateau observed in the cyclic voltammetry test. The test revealed flat charge-discharge potential plateaus at 3.6V and 3.3V. The stable charge-discharge process enabled the nucleation-conductivity dual-gradient three-dimensional ZnO-CNT-G composite lithium metal anode to maintain an average coulombic efficiency of up to 100% after 20 cycles.

[0054] To further investigate the electrochemical performance of the dual reverse gradient ZnO-CNT-G / Li lithium metal composite anode, a full cell was assembled using LiFePO4 as the cathode and the nucleation-conduction dual reverse gradient three-dimensional ZnO-CNT-G / Li as the anode, and its charge-discharge cycle performance was evaluated. At 0.5C, the initial specific capacity was 141.5 mAh / g, and after 200 charge-discharge cycles, the specific capacity was 138.3 mAh / g, with a capacity retention of 97.7% and a coulombic efficiency of 100%. In contrast, full cells using ZnO-CNT-G / Li anodes with uniformly distributed ZnO nucleation particles (1%, 3%, 5%, and 10%) showed a decrease in specific capacity after 120 charge-discharge cycles, from 139 mAh / g to 133.6 mAh / g, from 141 mAh / g to 128.8 mAh / g, from 152.7 mAh / g to 125.6 mAh / g, and from 151.3 mAh / g to 143.5 mAh / g, respectively, with corresponding capacity retention rates of 96%, 91.3%, 82.2%, and 95%. Comparative data analysis indicates that the nucleation-conductivity dual reverse gradient three-dimensional structure ZnO-CNT-G / Li composite material exhibits higher structural stability.

[0055] A full cell was assembled using LiFePO4 as the positive electrode and a nucleation-conductivity dual reverse gradient three-dimensional ZnO-CNT-G / Li composite lithium metal as the negative electrode. The battery was cycled 10 times each at 0.5C, 1C, 2C, 3C, 4C, 5C, 8C, and 10C rates, and then cycled 10 times at 0.5C to restore the baseline state. In terms of rate performance, the specific capacities of the full cell based on the nucleation-conductivity dual reverse gradient three-dimensional ZnO-CNT-G / Li composite lithium metal at 0.5C, 1C, 2C, 3C, 5C, and 8C discharge rates were 155.5 mAh / g, 152.6 mAh / g, 144.1 mAh / g, 127.9 mAh / g, 111.5 mAh / g, and 109.1 mAh / g, respectively. After restoring to the 0.5C rate, the specific capacity remained at 153.9 mAh / g, with a capacity retention of 98.9%. This performance, accompanied by negligible structural degradation, resulted in a specific capacity exceeding that of batteries using ZnO-CNT-G / Li anodes with 1%, 5%, or 10% ZnO content. To evaluate the coulombic efficiency of ZnO(10%)-CNT-G, a half-cell was constructed using ZnO(10%)-CNT-G and lithium metal as electrodes. At 0.5 mA / cm²... -2 The constant current density and 0.5 mAh / cm² -2Cyclic charge-discharge tests were conducted at a fixed discharge capacity, and potential-time curves were obtained. The ZnO(10%)-CNT-G electrode was able to cycle stably for more than 600 hours, indicating that the deposition and dissolution of lithium metal within the electrode have excellent stability. Furthermore, the potential-capacity curve after 300 cycles exhibited a flat charge-discharge plateau of 60 mV, highlighting the electrode's superior electrochemical performance.

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a lithium battery anode material, characterized in that, The method includes: Carbon nanotubes are dispersed in a solvent to form multiple carbon nanotube dispersions. A zinc source, a complexing agent, and a dispersant are added to each carbon nanotube dispersion and dispersed to form multiple mixed dispersions; wherein the target zinc-carbon mass ratio of the multiple mixed dispersions forms a preset gradient. An oxygen source is added to each part of the mixed dispersion to carry out a hydrothermal reaction, followed by washing and drying to form multiple composite filter cakes. Graphene and each part of the composite filter cake are dispersed in a solvent to form multiple composite dispersions; Multiple composite dispersions are layered and filtered according to a preset gradient to form a lithium battery anode material with a dual inverse gradient structure.

2. The method according to claim 1, characterized in that, The step of performing stratified filtration of multiple composite dispersions according to a preset gradient includes: After completing the filtration of the composite dispersion corresponding to the current target zinc-carbon mass ratio and forming a composite membrane layer, the next composite dispersion corresponding to the target zinc-carbon mass ratio is added to the composite membrane layer, and the next composite dispersion corresponding to the target zinc-carbon mass ratio is used as the composite dispersion corresponding to the current target zinc-carbon mass ratio for the next filtration.

3. The method according to claim 1, characterized in that, The step of performing stratified filtration of multiple composite dispersions according to a preset gradient includes: Multiple composite dispersions were subjected to stratified filtration in order of increasing target zinc-carbon mass ratio.

4. The method according to claim 1, characterized in that, The step of adding a zinc source, a complexing agent, and a dispersant to each carbon nanotube dispersion and dispersing them to form multiple mixed dispersions includes: Zinc source, complexing agent and dispersant were added to each carbon nanotube dispersion and dispersed to form multiple mixed dispersions. The target zinc-carbon mass ratio of the multiple mixed dispersions was controlled between 1% and 25%.

5. The method according to claim 1, characterized in that, The process of dispersing carbon nanotubes in a solvent to form multiple carbon nanotube dispersions includes: Deionized water was added to the aqueous slurry containing carbon nanotubes to form a solution to be dispersed. The solution to be dispersed is subjected to multiple dispersion treatments, wherein each dispersion treatment includes sequential mechanical stirring and ultrasonic treatment.

6. The method according to claim 1, characterized in that, The step of adding a zinc source, a complexing agent, and a dispersant to each carbon nanotube dispersion and then dispersing them includes: Zinc chloride as a zinc source, urea as a complexing agent, and citric acid as a dispersant were added to each carbon nanotube dispersion to form a mixture to be dispersed. The mixture to be dispersed is mechanically stirred to form a mixed dispersion.

7. The method according to claim 1, characterized in that, The process of adding an oxygen source to each portion of the mixed dispersion for hydrothermal reaction includes: Ammonia water is used as an oxygen source and added to each part of the mixed dispersion until the pH value of each part of the mixed dispersion reaches 8-9. Urea was added to the mixed dispersion containing ammonia and then placed in a hydrothermal reactor. The hydrothermal reactor was then placed at a temperature of 160-200℃ and reacted continuously for 8-24 hours.

8. The method according to claim 1, characterized in that, The dispersion of graphene with each portion of the composite filter cake in a solvent includes: Graphene and deionized water are added to each composite filter to form multiple composite solutions to be dispersed. Multiple portions of the composite solution to be dispersed are mechanically stirred to form multiple composite dispersions.

9. The method according to claim 1, characterized in that, The process of adding an oxygen source to each portion of the mixed dispersion for hydrothermal reaction, followed by washing and drying, includes: The mixed dispersion after the hydrothermal reaction was completed was washed multiple times by centrifugation with anhydrous ethanol to remove impurities.

10. A lithium battery anode material, characterized in that, The lithium battery anode material is prepared by the method described in any one of claims 1-9, and comprises: Multiple composite material film layers are sequentially arranged, wherein each composite material film layer includes zinc oxide, carbon nanotubes and graphene, and the target zinc-carbon mass ratio of zinc oxide and carbon nanotubes has a preset gradient.

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