Preparation method of positive electrode material of lithium sulfur battery

Abstract

The invention belongs to the technical field of lithium sulfur batteries, and particularly relates to a preparation method of a positive electrode material of a lithium sulfur battery. The preparation method comprises the following steps: adding a carbon nano tube into a nitrogen source substance solution with the mass concentration not less than 10%, mixing uniformly, transferring into a hydrothermal/solvent thermal reaction kettle for heat preservation, cooling, and washing and drying a reaction product so as to obtain a carbon nitride nano tube; dissolving sulfur into an organic solvent so as to obtain a sulfur contained organic solution, then adding the carbon nitride nano tube obtained in the step 1 into the sulfur contained organic solution, carrying out ultrasonic dispersion for more than 0.5 hour, and performing ultrasound treatment continuously while dropwise adding an extracting agent, wherein the mass ratio of the extracting agent to the organic solvent is (0.5-10) to 1; and then drying, and carrying out freeze drying on a product after the solvent is evaporated by more than a half. Compared with the prior art, the carbon-sulfur compound obtained by the method is good in circulation stability.

Description

technical field [0001] The invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a preparation method of a positive electrode material of a lithium-sulfur battery. Background technique [0002] Lithium-sulfur battery is a secondary battery with metallic lithium as the negative electrode and elemental sulfur as the positive electrode. During discharge, the negative electrode reacts as lithium loses electrons and becomes lithium ions, and the positive electrode reacts as sulfur reacts with lithium ions and electrons to form sulfide. The potential difference of the negative electrode reaction is the discharge voltage provided by the lithium-sulfur battery. The specific energy of lithium-sulfur batteries can theoretically reach 2600Wh / Kg, which is much larger than any commercial secondary batteries used at this stage. In addition to the advantages of high energy density, lithium-sulfur batteries also have the advantages of less envir...

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Problems solved by technology

[0004] First, the electronic conductivity and ionic conductivity of elemental sulfur are poor, and the conductivity of sulfur materials at room temperature is extremely low (5.0×10 -30 S cm -1 ), the final product of the reaction Li 2 S 2 and Li 2 S is also an electronic insulator, which is not conducive to the high rate performance of the battery;

[0005] Second, the intermediate discharge products of lithium-sulfur batteries will dissolve into the organic electrolyte, increasing the viscosity of the electrolyte and reducing the ion conductivity.

[0006] Third, the final discharge product of lithium-sulfur batteries, Li 2 S n (n=1~2) Electronic insulation and insoluble in the electrolyte, deposited on the surface of the conductive framework; part of the lithium sulfide detached from the conductive framework, unable to react into sulfur or high-order polysulfides through a reversible charging process, resulting in Great attenuation of capacity

[0007] Fourth, the densities of sulfur and lithium sulfide are 2.07 g cm -3 and 1.66g cm -3 , there is a volume expansion / contraction of up to 79% during the charge and discharge process, which will lead to changes in the morphology and structure of the positive electrode, resulting in the detachment of sulfur from the conductive framework, resulting in capacity attenuation; this volume effect is in the button battery It is not significant, but in large batteries, the volume effect will be enlarged, which will cause significant capacity fading, which may cause damage to the battery, and the huge volume change will destroy the electrode structure

[0010] However, the cycle stability of the carbon-sulfur complex synthesized by the method in the prior art is not good, and cannot meet the actual needs

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