Preparation method of Ti < 3 > C < 2 >-Ni < 2 > P composite material with heterogeneous interface structure and application of Ti < 3 > C < 2 >-Ni < 2 > P composite material in lithium-sulfur battery

Abstract

The invention provides a preparation method of a Ti < 3 > C < 2 >-Ni < 2 > P composite material with a heterogeneous interface structure and application of the Ti < 3 > C < 2 >-Ni < 2 > P composite material to a lithium-sulfur battery to improve adsorption and conversion capacity to polysulfide and solve the problems of shuttling and slow dynamics of the polysulfide. The Ti3C2-coated Ni2P composite material is obtained by adopting a template method and a gas phase phosphating method, Ni2P particles are uniformly loaded on a Ti3C2 substrate, the agglomeration problem of the Ni2P particles is effectively solved, meanwhile, the nano particles are used as interlayer spacers and can effectively prevent Ti3C2 sheet layers from being stacked, mutual assistance in structure is achieved through ingenious combination of the nano particles and the Ti3C2 sheet layers, and the composite material has the advantages of being simple in preparation process, low in cost and the like. And the built stable structure generates a built-in electric field through electron flow across a heterogeneous interface, so that energy barriers in the sulfur conversion process can be effectively reduced, and rapid ion transmission can be realized. Besides, the dispersed Ni2P particles have good adsorption and catalysis effects on LiPSs and can effectively limit the shuttle effect, and the structure of Ti3C2 also provides a large specific surface area, so that not only can a continuous rapid electron transport channel be provided, but also adsorption and rapid conversion of Ni2P on LiPSs can be enhanced. According to the Ti < 3 > C < 2 >-Ni < 2 > P heterogeneous interface structure constructed by the method, the conversion kinetics of LiPSs is improved, and the shuttle effect of the LiPSs is effectively relieved.

Description

Technical Field

[0001] The present invention relates to the field of construction and design of positive electrode materials for lithium-sulfur batteries, and in particular to the technical field of improving the performance of positive electrode materials at heterogeneous structure interfaces in lithium-sulfur batteries. Background Art

[0002] With the continuous development of science and technology and manufacturing industry, the society's demand for energy is increasing. The reserves of major fossil energy such as oil and coal are limited and non-renewable, so the development of renewable green energy is particularly important. At present, the commercialization process of lithium-ion batteries has been developed for decades and has been widely used in modern portable devices and new energy vehicles. However, the actual energy density of the existing lithium-ion battery system is only 200-300 Wh / kg, which is far from meeting the needs of major development and limits the application of multiple scenarios. Therefore, lithium-sulfur batteries use lithium metal (theoretical capacity 3860 mAh / g) as the negative electrode and elemental sulfur (theoretical capacity 1675 mAh / g) as the positive electrode. The actual energy density can reach 500-800 Wh / kg, which is a highly potential next-generation battery. In addition, the positive electrode material sulfur is non-toxic, low-cost, abundant in reserves, and environmentally friendly, which has great research significance and broad application prospects.

[0003] Although lithium-sulfur batteries have the advantage of high energy density, there are also some problems with sulfur positive electrode materials that limit their further development. The main problems are: (1) The poor conductivity of sulfur and its discharge products affects the recycling of active materials and leads to slow reaction kinetics, which seriously limits the high-rate discharge performance of lithium-sulfur batteries; (2) During the reaction process, lithium-sulfur batteries will produce lithium polysulfide active products that are easily soluble in ether electrolytes, which constantly shuttle between the positive and negative electrodes, affecting the cycle performance of lithium-sulfur batteries and causing irreversible capacity loss. (3) The charging and discharging process of lithium-sulfur batteries is accompanied by multi-phase transformation. This "solid-liquid-solid" phase change requires the positive electrode material to undergo a large volume expansion, which seriously affects the structural stability of the positive electrode material. It also leads to slower reaction kinetics between phases, causing irreversible damage to battery performance.

[0004] In response to the above problems, the key to solving the problems is to rationally design positive electrode materials with high conductivity, high catalytic activity and high structural stability. It is also the key to promoting the further development of lithium-sulfur batteries and their practical application. This has also become the main focus of this patent research. Summary of the invention

[0005] The first object of the present invention is to provide a Ti3C2@Ni2P composite material with structural mutual assistance and heterogeneous interface, and the key features of using this technology are: The separation of two-dimensional Ti3C2 sheets provides a substrate for Ni2P loading and also provides good electrical conductivity; The loading of nano-Ni2P prevents the stacking of Ti3C2 sheets, exposing more active sites, which is beneficial to the anchoring and conversion of polysulfides; The Ti3C2@Ni2P composite material constitutes a heterogeneous interface and generates a built-in electric field, which reduces the conversion energy barrier of polysulfides and improves the kinetics of redox reactions, thereby improving the electrochemical performance of lithium-sulfur batteries.

[0006] In view of the above existing technical problems, the second object of the present invention is to provide a method for preparing a Ti3C2@Ni2P composite material with a heterogeneous interface structure, comprising the following steps: (1) Preparation of Ti3C2 MXene nanosheets: Ti3AlC2 powder, LiF and HCl solution were mixed and etched in a mass ratio of 1:1.6:7, and the reaction was washed with deionized water. The washed precipitate was dispersed in deionized water, and the upper green suspension was used as a single few-layer Ti3C2 MXene dispersion after ultrasonic centrifugation and collected.

[0007] (2) Preparation of Ti3C2@Ni2P: Ti3C2 MXene dispersion was added to NiCl2·6H2O aqueous solution, followed by vigorous stirring and the precursor product was collected by centrifugation, washing, and freeze drying. The above Ni-impregnated product was then calcined to obtain the product Ti3C2@Ni. Ti3C2@Ni and NaH2PO2 were then placed in the downstream and upstream of a tube furnace for calcination, respectively, and the obtained product was then washed with deionized water and dried to obtain Ti3C2@Ni2P.

[0008] (3) Preparation of S / Ti3C2@Ni2P composite material: The active material Ti3C2@Ni2P and sulfur powder were mixed by melt diffusion method and melted to form the positive electrode material.

[0009] The etching temperature in step (1) is 40-50°C, the reaction time is 24-36 h, and the pH of the solution after washing is ≥6; The concentration of NiCl2·6H2O aqueous solution in step (2) should be 0.1 g mL -1 ; Step (2) The mixed atmosphere should be argon and hydrogen in a ratio of 9:1, the calcination temperature should be 300-400 °C, and the calcination time should be 2-3 h; In step (2), the calcination atmosphere should be argon, the mass ratio of Ti3C2@Ni to NaH2PO2 should be 1:10, the calcination temperature should be 300-400 °C, and the calcination time should be 2-3 h; In step (3), the mixing ratio of Ti3C2@Ni2P and sulfur powder is less than 1, the melting temperature is 120-180 °C, and the melting time is 9-15 h; The third object of the present invention is to provide a Ti3C2@Ni2P with a heterogeneous interface structure having high conductivity and high adsorption catalytic activity as a positive electrode material for lithium-sulfur batteries. Compared with traditional sulfur positive electrode materials, the present invention has the following advantages: two-dimensional Ti3C2 provides a storage site for sulfur, and provides high conductivity and a flexible substrate that can adapt to the volume change of sulfur during the reaction.

[0010] Nano-Ni2P particles can rapidly adsorb polysulfides and catalyze their conversion, inhibit shuttling and reduce the redox reaction energy barrier.

[0011] The heterostructure constructed by Ti3C2@Ni2P can promote the diffusion of lithium ions and enhance the catalytic activity, thereby improving the cycle performance of lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 X-ray diffraction diagram of the heterostructure Ti3C2@Ni2P of the cathode material of the present invention; Figure 2 This is a scanning electron microscope image of the heterostructure Ti3C2@Ni2P of the cathode material of the present invention; Figure 3 The cyclic voltammogram of the heterostructure Ti3C2@Ni2P of the cathode material of the present invention; Implementation

[0013] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation examples. The specific implementation examples described herein are only applicable to explaining the application itself and are not intended to limit the present application.

[0014] The specific preparation method of the present invention is as follows: (1) Preparation of Ti3C2 MXene nanosheets: 1 g Ti3AlC2 powder is added to 1.6 g LiF and 20 mL 9.0 mol L -1 The reaction precipitate was etched in a mixed solution of hydrochloric acid and washed with water. The precipitate was redispersed in water and centrifuged. The upper green suspension Ti3C2 MXene dispersion was collected. (2) Preparation of Ti3C2@Ni2P: 30 mL of 0.1 g mL-1 NiCl2·6H2O aqueous solution was added to 100 mg of Ti3C2 MXene dispersion, followed by vigorous stirring and the precursor product was collected by centrifugation, washing, and freeze drying. The above-mentioned Ni-impregnated product was then calcined to obtain the product Ti3C2@Ni. The above-mentioned Ni-impregnated product was then placed in a reducing atmosphere with an argon and hydrogen composition of 9:1 at 2 ℃ min -1The product Ti3C2@Ni was obtained by heating at a rate of 1:10 at 300 °C for 2 hours. Subsequently, Ti3C2@Ni and NaH2PO2 were placed in the downstream and upstream of the tube furnace at a mass ratio of 1:10 and kept at 300 °C for 2 hours under an argon environment. The obtained product was then washed with deionized water and dried to obtain Ti3C2@Ni2P. (3) Preparation of S / Ti3C2@Ni2P composite material: Ti3C2@Ni2P and sulfur powder were melted at a mass ratio of 3:7 and used as the positive electrode material.

[0015] In the embodiment of the present invention, Ni2P is in situ grown on the Ti3C2 sheet to construct a heterostructure consisting of Ti3C2 two-dimensional sheets and Ni2P semiconductors. This structure not only combines the high conductivity and high catalytic performance of Ti3C2 and Ni2P, but also the heterostructure can promote faster transmission of lithium ions and reduce the reaction energy barrier of polysulfides, thereby effectively improving the electrochemical performance of lithium-sulfur batteries.

[0016] Figure 1 As shown, the Ti3C2@Ni2P in the present invention has good crystallinity, the structure of Ti3C2 after phosphating is well preserved, and the obvious (002) plane characteristic peak is retained. At the same time, the existence of a series of characteristic peaks of Ni2P proves its successful synthesis.

[0017] Figure 2 As shown, Ni2P particles with relatively uniform distribution are clearly observed on the Ti3C2 flakes, and the Ti3C2@Ni2P composite material exhibits high dispersion of flakes and nanoparticles.

[0018] Figure 3 As shown, compared with lithium-sulfur batteries assembled with single-component positive electrode materials, lithium-sulfur batteries assembled with Ti3C2@Ni2P composite materials have stronger reaction activity and lower redox reaction polarization.

[0019] The present invention is not limited to the above-mentioned embodiments. For those skilled in the art, several improvements and modifications can be made without departing from the present invention, and these improvements and modifications are deemed to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professionals in the field.

Claims

1. A method for preparing a Ti3C2@Ni2P composite material with a heterogeneous interface structure and its application in a lithium-sulfur battery, comprising the following steps: (1) Preparation of Ti3C2 MXene nanosheets: Ti3AlC2 powder, LiF and HCl solution are mixed and etched in a mass ratio of 1:1.6:7, and the reaction is washed with deionized water, and the washed precipitate is dispersed in deionized water. After ultrasonic centrifugation, the upper green suspension is used as a single few-layer Ti3C2 MXene dispersion and collected. (2) Preparation of Ti3C2@Ni2P: Ti3C2 MXene dispersion is added to NiCl2·6H2O aqueous solution, followed by vigorous stirring and the precursor product is collected by centrifugation, washing and freeze drying. Then the above-mentioned Ni-impregnated product is calcined to obtain the product Ti3C2@Ni. Subsequently, Ti3C2@Ni and NaH2PO2 are placed in the downstream and upstream of a tube furnace respectively for calcination, and then the obtained product is washed with deionized water and dried to obtain Ti3C2@Ni2P. (3) Preparation of S / Ti3C2@Ni2P composite material: The active material Ti3C2@Ni2P and sulfur powder were mixed by melt diffusion method and melted to form the positive electrode material.

2. The preparation method according to claim 1, characterized in that Ni2P nanoparticles were successfully synthesized in situ on MXene sheets, and a structurally complementary heterostructure interface was constructed, which effectively reduced the energy barrier in the sulfur conversion process and achieved rapid ion transport. At the same time, Ni2P improved the adsorption and conversion of polysulfides, effectively alleviating the LiPSs shuttle effect.

3. The preparation method according to claim 1, characterized in that The etching temperature in step (1) is 40-50°C, the reaction time is 24-36 h, and the pH of the solution after washing is ≥6.

4. The preparation method according to claim 1, characterized in that The concentration of the NiCl2·6H2O aqueous solution in step (2) is 0.1 g mL -1 .

5. The preparation method according to claim 1, characterized in that: In step (2), the mixed atmosphere should be argon and hydrogen in a ratio of 9:1, the calcination temperature should be 300-400 °C, and the calcination time should be 2-3 h.

6. The preparation method according to claim 1, characterized in that: In step (2), the calcination atmosphere should be argon, the mass ratio of Ti3C2@Ni and NaH2PO2 should be 1:10, the calcination temperature should be 300-400 °C, and the calcination time should be 2-3 h.

7. The preparation method according to claim 1, characterized in that: In step (3), the mixing ratio of Ti3C2@Ni2P and sulfur powder is less than 1, the melting temperature is 120-180°C, and the melting time is 9-15 h.

8. The Ti3C2@Ni2P positive electrode material obtained by the preparation method according to claims 1-7 has excellent electrochemical performance; the Ti3C2@Ni2P preparation method and its application as a positive electrode material in lithium-sulfur batteries.

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