CN103811740B - A kind of nucleocapsid structure Li xv 2o 5/ LiV 3o 8intercalation materials of li ions and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of nucleocapsid structure Li _xv ₂o ₅/ LiV ₃o ₈intercalation materials of li ions and preparation method thereof.By LiV ₃o ₈be placed in tube furnace and heat-treat reduction and can form Li _xv ₂o ₅/ LiV ₃o ₈core-shell material, can effective Li in control objectives product by the flow controlling reducing gas _xv ₂o ₅outer field thickness.Li _xv ₂o ₅the introducing energy available protecting LiV of shell ₃o ₈, significantly can improve the interfacial electrochemistry character of electrode simultaneously, thus increase substantially the chemical property of material.The Li of preparation _xv ₂o ₅/ LiV ₃o ₈compound intercalation materials of li ions has excellent stable circulation performance and high rate performance.The method technological process is short, simple to operate, with low cost, is easy to realize suitability for industrialized production.

Description

A core-shell structure LixV2O5/LiV3O8 lithium intercalation material and its preparation method

technical field

The invention belongs to the technical field of high-energy battery materials, and in particular relates to a high-performance composite lithium vanadate cathode material with a core-shell structure and a preparation method thereof.

Background technique

Vanadium oxy compounds have become a research hotspot in recent years because of their relatively low cost, simple synthesis method, and high specific capacity. my country is rich in vanadium resources, but the development of vanadium mines is mainly concentrated on primary products, and the comprehensive utilization of vanadium resources is not high, which restricts the development of vanadium industry. Therefore, the development of high-capacity vanadium-based compounds as new lithium-ion battery intercalation materials is of great significance for optimizing the utilization of vanadium resources in my country and promoting economic development. Among the vanadium-based lithium intercalation materials, LiV ₃ O ₈ is the most researched. The material has a monoclinic structure and belongs to the P2 ₁ /m point group. The LiV ₃ O ₈ unit is a sandwich cake structure in which lithium ions are sandwiched between two layers ^of V ₃ O ₈ . The special structure makes the material have better structural stability in the process of lithium ion deintercalation.

The study found that the discharge capacity and cycle life of LiV ₃ O ₈ are closely related to the synthesis method of the material and the subsequent heat treatment process. The traditional high-temperature solid-state method generally mixes Li ₂ CO ₃ and V ₂ O ₅ uniformly according to the stoichiometric ratio, and sinters them at 650°C. The discharge capacity is about 180mAh g ^-1 . Si et al [Journal of Alloys and Compounds, 486(2009) 400] used urea as fuel to prepare LiV ₃ O ₈ with a capacity of up to 340mAh/g by low-temperature combustion method, which was lower than 250mAh g ^-1 after 30 cycles. Zhou et al [Solid State Ionics, 179(2008) 1763] prepared LiV ₃ O ₈ by EDTA-assisted sol-gel method combined with solid-state sintering process. The first discharge capacity is 251.7mAh/g, and the average capacity decay rate per cycle is 0.43%. Meanwhile, the rate performance of LiV ₃ O ₈ is poor. Liu et al[J.Power Sources,192(2009)668] prepared single crystal LiV ₃ O ₈ nanorods, the capacity was as high as 348mAh g ^{-1 for the first time at 20mA g -1} _, ^but dropped ^to 200mAh g -1 at 100mA g ^{-1 1} or so. Pan et al [J.Mater.Chem,21(2011)10077] synthesized LiV ₃ O ₈ nanosheets, the discharge capacity at 100mA g ^-1 was about 260mAh g ^-1 , and at 300 and 1000mA g ^-1 , respectively, decreased to 194 and 166mAh g ^-1 , and the capacity fading increases. How to further improve the cycle stability and rate performance of LiV ₃ O ₈ is the focus of current research.

Researchers have successively carried out a lot of research on doping and surface coating modification, aiming to further improve the electrochemical performance of LiV ₃ O ₈ . The study confirmed that the dissolution of V leads to the change of the material structure during the charging and discharging process, which is an important reason for the capacity fading of LiV ₃ O ₈ . Therefore, coating a layer of inactive material on the target material to prevent the dissolution of V and inhibiting the volume expansion of the material during charge and discharge will improve its electrochemical performance. In addition, the coating layer will effectively reduce the reactivity of the interface between the material and the electrolyte, inhibit the occurrence of side reactions, and stabilize the electrode. At present, the carbon coating layer, polyaniline (PAn), AlPO ₄ , AlF ₃ and Al ₂ O ₃ are successively used to modify the surface of LiV ₃ O ₈ , which effectively improves the cycle performance of the material. However, since the V in LiV ₃ O ₈ has a valence of +5 and has a strong oxidizing ability, the cladding layer can easily induce structural changes in the matrix material during the sintering process, which affects the electrochemical performance. Idris et al [Compos.Sci.Technol.,71(2011)343] found that the reversible capacity of carbon-coated LiV ₃ O ₈ nanoflakes dropped from 335mAh g ^-1 before coating to 227mAh g ^-1 . The reversible capacity of polyaniline-coated LiV ₃ O ₈ decreased from 283mAh·g ^-1 to 243mAh·g ^-1 [J.Power Sources,64(2012)47].

The present invention designs an in-situ transformation method, using LiV ₃ O ₈ as the substrate, through simple reducing atmosphere treatment, a thin layer of Li _x V ₂ O ₅ is directly formed on the surface of LiV ₃ O ₈ , thereby forming a one-step Li _x V ₂ O ₅ /LiV ₃ O ₈ composites with core-shell structure. Compared with pristine LiV ₃ O ₈ , the cycle stability and rate capability of the composite are significantly improved.

Contents of the invention

The object of the present invention is to propose a lithium ion battery positive electrode material with a core-shell structure and a preparation method thereof with high capacity, long life and high rate. The preparation method is a new and simple in _- situ conversion method. ₈ as the matrix, an ultra-thin Li _x V ₂ O ₅ layer was directly generated on the surface of LiV ₃ O ₈ by heat treatment in a reducing atmosphere, thus realizing a step of the core-shell structure Li _x V ₂ O ₅ /LiV ₃ O ₈ composite Preparation method; solves the problems of short cycle life and poor rate performance of such materials in the prior art.

A lithium intercalation material with a core-shell structure Li _x V ₂ O ₅ /LiV ₃ O ₈ is a composite nanomaterial with LiV ₃ O ₈ as the core and Li _x V ₂ O ₅ as the outer shell with 0<x<1.

The nanostructure is one of nanoparticle, nanosheet, nanowire, nanorod and nanosphere.

A preparation method of a core-shell structure Li _x V ₂ O ₅ /LiV ₃ O ₈ lithium intercalation material, taking the LiV ₃ O ₈ material and placing it in a protective gas, then heating up, switching the protective gas to a reducing gas for treatment, Naturally cooled to room temperature, the core-shell structure material of Li _x V ₂ O ₅ wrapped LiV ₃ O ₈ was obtained.

The protective gas is one of argon and nitrogen. The heating rate is 1-15°C/min. Raise the temperature and heat to 300-600°C. The reducing gas is a mixed gas of _H2 and Ar, or a mixed gas of CO and _CO2 . The volume fraction of _H2 in the mixed gas of _H2 and Ar is 3-20%; the volume fraction of CO in the mixed gas of CO and _CO2 is 5-20%. The flow rate of the injected reducing gas is 50-500 cm ³ /min. The heat treatment time after injecting the reducing gas is 1-60 minutes.

Principle of the present invention:

The capacity fading of LiV ₃ O ₈ is closely related to the vanadium dissolution that occurs during the intercalation and deintercalation of lithium ions. The dissolution of vanadium leads to changes in the structure of the material. Due to the limitation of the crystal structure, LiV ₃ O ₈ has a low lithium ion diffusion coefficient, resulting in poor rate performance. Appropriate surface modification can inhibit the dissolution of vanadium during charge and discharge, stabilize the crystal structure of the material, and prolong the cycle life. The study found that the lithium ion diffusion coefficient of Li _x V ₂ O ₅ is about 2 orders of magnitude higher than that of LiV ₃ O ₈ , and the rate performance of this material is better than that of LiV ₃ O ₈ . Based on this, the present invention utilizes the reduction reaction of pentavalent vanadium in LiV ₃ O ₈ and reducing gas at high temperature, and a self-transformation reaction occurs on the surface of LiV ₃ O ₈ to form a uniform Li _x V ₂ O ₅ shell and form a core shell structure. _The thickness of the final _{LixV2O5 shell} can be controlled by controlling the amount of injected reducing gas. The outer layer of Li _x V ₂ O ₅ can not only effectively inhibit the dissolution of vanadium in the matrix material LiV ₃ O ₈ during charge and discharge, protect the electrode, but also greatly improve the interface electrochemical properties of the composite electrode, thereby improving the rate performance and Cycle stability.

Advantages and positive effects of the present invention

The present invention has following salient features:

1): Compared with other coating methods, the present invention does not introduce other impurity elements, and the self-transformation reaction of LiV ₃ O ₈ can ensure that the product is not affected by other impurity ions, and at the same time overcomes the inadequacy of ordinary coating methods. The lack of uniformity and the lack of tight contact between the coating layer and the base material can realize the uniform and tight coating of the Li _x V ₂ O ₅ layer, thereby significantly improving the cycle stability of the material.

2): The thickness of the outer layer Li _x V ₂ O ₅ in the core-shell composite can be effectively controlled by the injection of reducing gas. Since Li _x V ₂ O ₅ also has a good ability to intercalate lithium, this method will not obviously Reduce the reversible capacity of the composite.

3): Compared with LiV ₃ O ₈ , Li _x V ₂ O ₅ has a higher lithium ion diffusion coefficient. Therefore, the core-shell structure of Li _x V ₂ O ₅ /LiV ₃ O ₈ can effectively improve the interface electrochemical properties of the electrode, thereby obtaining better rate performance.

Positive effect of the present invention:

Compared with the original LiV ₃ O ₈ , the core-shell structure Li _x V ₂ O ₅ /LiV ₃ O ₈ composite material synthesized by the present invention has significantly improved cycle performance and rate performance. The invention will provide method support for in-depth research and future industrial application of vanadate materials. At the same time, the idea of generating Li _x V ₂ O ₅ /LiV ₃ O ₈ composite materials with core-shell structure in one step by heat treatment in a reducing atmosphere proposed by the present invention will provide a reference for the coating research of other positive electrode materials.

Description of drawings

Fig. 1 is respectively the XRD curve of the target material that embodiment 1, embodiment 2, embodiment 3, embodiment 4 and embodiment 5 prepare;

Fig. 2 is respectively the high-resolution transmission electron microscope picture of the target material that embodiment 3, embodiment 5 prepare;

Figure 3 is the cyclic voltammetry curves of the target materials prepared in Example 1 and Example 3 at 1.5-4.0V, and the scan rate is 0.1mV/s;

Figure 4 is the cycle capacity diagrams of the target materials prepared in Example 1, Example 2, Example 3 and Example 4 at 1C rate (300mA g ^-1 );

Fig. 5 is respectively the cycle capacity diagram of the target materials prepared in Example 1, Example 2, Example 3 and Example 4 at different magnifications;

Fig. 6 is a diagram of the cycle capacity of the target material prepared in Example 5 at 1C rate (300mA g ^-1 ).

Detailed ways

The present invention will be further described below by way of examples, rather than limiting the present invention.

Example 1:

Weigh 2.5g flake LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 120cm ³ /min. After half an hour, heat to 450°C at a heating rate of 15°C/min for 10 minutes, close the tube furnace, and cool naturally to room temperature to obtain unreduced gas-treated LiV ₃ O ₈ for comparative studies. The crystal structure of the material is shown in Example 1 in FIG. 1 . It can be seen from the XRD curve that the prepared product belongs to the monoclinic crystal system and the point group P2 ₁ /m.

Mix the prepared target material, conductive agent Super P, and binder PVDF uniformly in a certain mass ratio (80:10:10), use tetrahydrofuran (THF) as the solvent, stir thoroughly for 6 hours, and use a film applicator to quickly spread the slurry Spread evenly on aluminum foil. After the solvent evaporates, place the coated pole piece in a vacuum drying oven at 110°C for 12 hours. The pole piece is made into a small disc with a diameter of 12mm. With the metal lithium sheet as the negative electrode, the EC:DMC (1:1, v/v) mixed solution of 1mol/L LiPF ₆ produced by Guangzhou Tianci Company is used as the electrolyte, and the buckle is assembled in an inert gas glove box (produced by UNILAB MBRAUN Germany). Type half-cell (CR2016), the operating system of the glove box is high-purity argon. After the half-cell was assembled, it was left to stand for 5 hours, and its electrochemical data was tested at room temperature with a Xinwei battery charging and discharging instrument. Adopt constant current charge and discharge mode, the voltage range is 1.5 ~ 4.0V. The cyclic voltammetry test was carried out at Shanghai Chenhua Electrochemical Workstation with a scan rate of 0.1mV/s. Figure 3 records the cyclic voltammetry curve of the material. It can be seen from the figure that the LiV ₃ O ₈ electrode has many pairs of obvious redox pairs, corresponding to the intercalation and extraction processes of lithium ions. Example 1 in Figure 4 documents the cycling performance of the material. It can be seen from the figure that the initial discharge specific capacity of LiV ₃ O ₈ nanosheets at 1C rate (300mA/g) is 178mAh g ^-1 , and it drops to 120mAh·g ^-1 after 100 cycles. Example 1 in Figure 5 documents the rate capability of the material. The initial discharge capacities of the material are 278.7mAh g ^-1 , 181.0mAh g ^-1 and 50.2mAh·g ^-1 at 0.1C, 1C and 5C rates. It can be seen that the rate performance of untreated LiV ₃ O ₈ nanosheets is not good.

Example 2

Weigh 2.52g flake LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 120cm ³ /min. After half an hour, heat to 450°C at a heating rate of 15°C/min for 10 minutes, and immediately switch the argon flow to H ₂ /Ar (H ₂ volume 5%) Mixed gas, the H ₂ /Ar mixed gas flow rate is 60cm ³ /min, stop the gas injection after 1 minute of treatment, close the tube furnace, and naturally cool to room temperature to obtain the target material. Its crystal structure is shown in Example 2 in FIG. 1 . It can be seen from the XRD curve that the prepared product belongs to the monoclinic crystal system, the P2 ₁ /m point group, and no obvious impurity diffraction peaks, indicating that the heat treatment in the 1min H ₂ /Ar mixed gas generated LiV ₃ O ₈ surface Li The content of _x V ₂ O ₅ is very small, below the detection limit of XRD diffraction.

The manufacturing process and testing of the half-cell are the same as in Example 1. Example 2 in Figure 4 documents the cycle performance of the target material. It can be seen from the figure that the initial discharge specific capacity of the material is 165.1mAh g ^-1 at 1C rate, and it maintains at 154.7mAh·g ^-1 and 155.1mAh·g ^-1 after 100 and 200 cycles, respectively. Compared with LiV ₃ O ₈ without H ₂ /Ar gas treatment in Example 1, the heat treatment for 1 min in this example significantly improved the cycle performance of the target material. Example 2 in Figure 5 records the rate capability of the target material. The initial discharge capacities of the material at 0.1C and 5C rates are 277.1mAh g ^-1 and 80.3mAh·g ^-1 , respectively. The rate performance of the material has been improved, which may be due to the reduction reaction of LiV ₃ O ₈ on the surface with H ₂ to generate a small amount of Li _x V ₂ O ₅ , forming a core-shell structure of Li _x V ₂ O ₅ /LiV ₃ O ₈ composite materials. The Li _x V ₂ O ₅ shell can significantly improve the interface electrochemical properties of the composite electrode.

Example 3

Weigh 2.52g flake LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 120cm ³ /min. After half an hour, heat to 450°C at a heating rate of 15°C/min for 10 minutes, and immediately switch the argon flow to H ₂ /Ar (H ₂ volume 5%) Mixed gas, the flow rate of H ₂ /Ar mixed gas is 60cm ³ /min, the gas injection is stopped after 5 minutes of treatment, the tube furnace is closed, and the target material is obtained by natural cooling to room temperature. Its crystal structure is shown in Example 3 in FIG. 1 . It can be seen from the XRD curve that the prepared product belongs to the monoclinic crystal system, the P2 ₁ /m point group, and there is no obvious impurity diffraction peak, indicating that the heat treatment of 5min H ₂ /Ar mixed gas generates Li _x on the surface of LiV ₃ O ₈ There is also very little V ₂ O ₅ , and its content is below the detection limit of XRD diffraction.

The manufacturing process and testing of the half-cell are the same as in Example 1. Figure 2(a) is the HRTEM image of the target material. There are two different types of diffraction lattice regions inside and outside on the figure, the main diffraction lattice (d=0.38nm) corresponds to the {003} crystal plane of the LiV ₃ O ₈ matrix, the outer layer is thinner (~12nm), and the diffraction lattice (d=0.22nm) corresponds to the {601} crystal plane of Li _x V ₂ O ₅ , and the results confirm the existence of Li _x V ₂ O ₅ /LiV ₃ O ₈ core-shell structure. From the CV comparison in Figure 3, it is found that compared with LiV ₃ O ₈ not treated in a reducing atmosphere, the target material prepared in this example also has an obvious reduction peak at 3.25V, which is the characteristic of the Li _x V ₂ O ₅ electrode. typical features. Example 3 in Figure 4 documents the cycle performance of the target material. It can be seen from the figure that the initial discharge specific capacity of the material is 195.4mAh g ^-1 at 1C rate, and it maintains at 168.5mAh·g ^-1 and 163.4mAh·g ^-1 after 100 and 200 cycles, respectively. Compared with the materials in Example 1 and Example 2, the electrochemical performance of the electrode in this example has been further improved after 5 minutes of thermal reduction treatment. Example 3 in Figure 5 records the rate capability of the target material. The initial discharge capacities of the material at 0.1C and 5C rates are 278.1mAh g ^-1 and 152.1mAh·g ^-1 , respectively, and the rate performance has been significantly improved. The research confirmed that LiV ₃ O ₈ on the surface reacted with H ₂ to produce a small amount of Li _x V ₂ O ₅ , forming a Li _x V ₂ O ₅ /LiV ₃ O ₈ composite with a core-shell structure. The existence of a thin coating of Li _x V ₂ O ₅ can not only effectively protect the stability of LiV ₃ O ₈ during charge and discharge, but also significantly improve the interfacial electrochemical properties of the electrode.

Example 4

Weigh 2.52g flake LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 120cm ³ /min. After half an hour, heat to 450°C at a heating rate of 15°C/min for 10 minutes, and immediately switch the argon flow to H ₂ /Ar (H ₂ volume 5%) Mixed gas, the flow rate of H ₂ /Ar mixed gas is 60cm ³ /min, the gas injection is stopped after 10 minutes of treatment, the tube furnace is closed, and the target material is obtained by natural cooling to room temperature. Its crystal structure is shown in Example 4 in FIG. 1 . It can be seen from the XRD curve that the prepared product belongs to the monoclinic crystal system, the P2 ₁ /m point group, and no obvious impurity diffraction peaks, indicating that the heat treatment of 10min H ₂ /Ar mixed gas generates Li _x on the surface of LiV ₃ O ₈ The amount of V ₂ O ₅ is still below the detection limit of XRD diffraction.

The manufacturing process and testing of the half-cell are the same as in Example 1. Example 4 in Figure 4 documents the cycle performance of the target material. It can be seen from the figure that the initial discharge specific capacity of the material is 176.4mAh g ^-1 at 1C rate, and it maintains at 156.7mAh·g ^-1 and 131.9mAh·g ^-1 after 100 and 200 cycles, respectively. Compared with LiV ₃ O ₈ which was not treated with H ₂ /Ar gas in Example 1, this example effectively improves the cycle performance of the target material, but compared with Example 2 and Example 3, the cycle performance decreases with the prolongation of the treatment time reduce. Example 4 in Figure 5 records the rate capability of the target material. The initial discharge capacities of the material at 0.1C and 5C rates are 279.3mAh g ^-1 and 115.2mAh·g ^-1 , respectively. Compared with Example 1 and Example 2, the rate performance of the material prepared in this example is improved, but worse than that in Example 3. It shows that the more Li _x V ₂ O ₅ generated on the surface of LiV ₃ O ₈ is not the better.

Example 5

Weigh 2.52g flake LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 120cm ³ /min. After half an hour, simultaneously heat to 450°C at a heating rate of 15°C/min for 10 minutes, and immediately switch the argon flow to H ₂ /Ar (H ₂ volume 5% ) mixed gas, the flow rate of H ₂ /Ar mixed gas was 60cm ³ /min, the gas injection was stopped after 30 minutes of treatment, the tube furnace was closed, and the target material was obtained by natural cooling to room temperature. Its crystal structure is shown in Example 5 in FIG. 1 . From the XRD curve, it can be seen that the prepared product belongs to the monoclinic crystal system, the P2 ₁ /m point group, and a new diffraction peak appears at the same time, which is consistent with the Li _0.7 V ₂ O ₅ standard spectrum. The results confirm that Li _x V appears in the target material. ₂ O ₅ phase, this example can further illustrate that Li _x V ₂ O ₅ /LiV ₃ O ₈ with core-shell structure can be obtained by heat treatment with reducing gas. Example 2, example 3, in example 4, XRD fails to detect the diffraction peak of Li _x V ₂ O ₅ phases because the amount of Li _x V ₂ O ₅ generated is small, and the detection limit of the instrument has not been reached (generally, the ratio is lower than 5% instruments are difficult to detect).

The manufacturing process and testing of the half-cell are the same as in Example 1. Figure 2(b) is the HRTEM image of the target material. The figure also shows two different types of diffraction lattice regions inside and outside. The main diffraction lattice (d=0.38nm) corresponds to the {003} crystal plane of the LiV ₃ O ₈ matrix, and the diffraction lattice of the outer layer (d=0.22nm ) corresponds to the {601} crystal plane of Li _x V ₂ O ₅ , compared with example 3, the thickness of the outer layer Li _x V ₂ O ₅ increases significantly (~28nm) with the prolongation of heat treatment time, and the results also confirm that the Li x V 2 O 5 Existence of _x V ₂ O ₅ /LiV ₃ O ₈ core-shell structure. Figure 6 records the cycling performance of the target material at 1C rate. The initial discharge capacity of the material was 152.4mAh g ^-1 , and it remained at 138.2mAh·g ^-1 and 116.2mAh·g ^-1 after 100 and 200 cycles, respectively. Compared with the material that was not heat-treated in reducing atmosphere in Example 1, the cycle performance and reversible capacity have been improved, but compared with the heat treatment of 5 minutes in Example 3, the performance is significantly reduced, which further shows that too long heat treatment is not conducive to the performance of the target material. electrochemical performance.

Example 6

Weigh 2.52g of rod-shaped LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 300cm ³ /min. After half an hour, heat to 550°C at a heating rate of 10°C/min for 10 minutes, and immediately switch the argon gas flow to H ₂ /Ar (H ₂ volume ratio 10% ) mixed gas, the flow rate of H ₂ /Ar mixed gas was 60cm ³ /min, the gas injection was stopped after 5 minutes of treatment, the tube furnace was turned off, and the target material was obtained by natural cooling to room temperature.

The manufacturing process and testing of the half-cell are the same as in Example 1, and the performance is similar to that of the material prepared in Example 3.

Example 7

Weigh 2.52g of rod-shaped LiV ₃ O ₈ nanomaterials and place them in a tube furnace. Continuously inject argon protective gas at a flow rate of 150cm ³ /min. After half an hour, heat to 550°C at a heating rate of 10°C/min for 10 minutes, and immediately switch the argon flow to CO/CO ₂ (CO volume 10%) mixture Gas, the gas flow rate is 100cm ³ /min, the gas injection is stopped after 5 minutes of treatment, the tube furnace is closed, and the target material is obtained by natural cooling to room temperature.

The manufacturing process and testing of the half-cell are the same as in Example 1, and the performance is similar to that of the material prepared in Example 3.

Claims (10)

1. A Li _x V ₂ O ₅ /LiV ₃ O ₈ lithium intercalation material with a core-shell structure, characterized in that it uses LiV ₃ O ₈ as the core, Li _x V ₂ O ₅ , 0<x<1 as the shell composite nanomaterials. 2. The material according to claim 1, wherein the composite nanomaterial is one of nanosheets, nanowires, nanorods, and nanospheres. 3. A preparation method for a core-shell structure Li _x V ₂ O ₅ /LiV ₃ O ₈ lithium intercalation material, characterized in that the LiV ₃ O ₈ material is placed in a protective gas, then heated up, and the protective gas is switched to After reducing gas and further heat treatment, it is naturally cooled to room temperature to obtain Li _x V ₂ O ₅ , 0<x<1, a core-shell structure material wrapped with LiV ₃ O ₈ . 4. The preparation method according to claim 3, wherein the protective gas is one of argon and nitrogen. 5. The preparation method according to claim 3, characterized in that the heating rate is 1-15°C/min. 6. The preparation method according to claim 3 or 5, characterized in that the temperature is raised to 300-600°C. 7. The preparation method according to claim 3, characterized in that, the reducing gas is a mixed gas of _H2 and Ar, or a mixed gas of CO and _CO2 . 8. The preparation method according to claim 7, characterized in that, the volume fraction of H in the mixed gas of H and Ar is 3-20%; the volume fraction of _CO in the mixed gas of _CO and _CO is 5-20% %. 9. The preparation method according to claim 3, 7 or 8, characterized in that the flow rate of the injected reducing gas is 50-500 cm ³ /min. 10. The preparation method according to claim 3, characterized in that the heat treatment time after injecting the reducing gas is 1-60 min.