Lithium-sulfur battery positive electrode material and preparation method thereof

Abstract

The invention provides a lithium-sulfur battery positive electrode material and a preparation method thereof. The lithium-sulfur battery positive electrode material comprises a porous carbon material for accommodating sulfur and a metal sulfide loaded on the outer layer of the porous carbon material, wherein sulfur in the porous carbon material containing the sulfur comprises elemental sulfur with multiple pore channels and liquid metal in the pore channels of the elemental sulfur. The elemental sulfur with the multiple pore channels is adopted, so that the expansion of the electrode material can be reduced, and the ion conduction can be enhanced. The contact resistance between the carbon material and the elemental sulfur is reduced by the liquid metal in the elemental sulfur with multiple channels, and the contact area between the elemental sulfur and the conductor is increased, so that a catalytic effect is achieved on the elemental sulfur to form the polysulfide. Metal sulfides outside of carbon materials are capable of absorbing S<2-> formed in the discharging process. Through the synergistic adsorption catalysis effect of the liquid metal in the elemental sulfur with the pore channels and the metal sulfides wrapping outside the sulfur-loaded porous carbon, the electrode material is enabled to have high energy density and high cycling stability.

Description

technical field [0001] The invention belongs to the technical field of battery materials, and in particular relates to a lithium-sulfur battery cathode material and a preparation method thereof. Background technique [0002] With the rapid development of new energy vehicles and mobile electronic devices, there is an increasingly urgent need to develop batteries with higher energy density. In traditional lithium-ion batteries, limited by the theoretical capacity of the positive electrode active material, the limit value of its energy density is 250-300 Wh / Kg. It is difficult to meet the 700 Wh / Kg requirements of power electronic equipment such as new energy vehicles by relying on lithium ions. Demand, therefore, urgently requires the development of next-generation novel batteries. In the new energy storage system, the theoretical specific energy of a lithium-sulfur battery with metal lithium or lithium storage materials as the negative electrode and elemental sulfur or sulfu...

AI Technical Summary

Problems solved by technology

Therefore, the use of metal lithium anode and sulfur cathode materials in lithium-sulfur batteries will have the following problems: (1) elemental sulfur and its discharge products have poor electronic and ionic conductivity, making it difficult to reach the theoretical capacity, and the reversibility is also affected

(2) The densities of sulfur and lithium sulfide are 2.03 g / cm 3 and 2.03 g / cm 3 , there is up to 80% volume expansion / shrinkage during the charge and discharge process, which leads to the detachment of the active material from the conductive framework, resulting in capacity attenuation; (3) The process of reducing elemental sulfur to lithium sulfide is a multi-step reaction process, in which The intermediate product lithium polysulfide is easily soluble in the organic electrolyte, resulting in the loss of a part of the active material, and causing a great change in the structure and shape of the positive electrode. The active material is detached from the conductive agent after many cycles, which eventually leads to a decrease in cycle stability; (4) The surface of the metal lithium negative electrode is unstable, and the lithium polysulfide that is easy to diffuse to the negative electrode undergoes a self-discharge reaction during charging, and the self-discharged product migrates back to the positive electrode and is oxidized again, and so on (called "shuttle effect") , resulting in a decrease in the Coulombic efficiency of the battery and aggravating the capacity fading of the lithium-sulfur battery

However, the above-mentioned physical coating and chemical adsorption methods are relatively complicated, and still cannot solve the problems of volume expansion of elemental sulfur and poor ion and electronic conductivity.

And the above method can only achieve effective adsorption of polysulfides, but there is no strong affinity between it and polysulfides, and its surface does not have abundant active sites, so it cannot realize the effective conversion of polysulfides on its surface into low lithium sulfide

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