Sulfur-carbon compound and preparation method therefor, and electrode material and lithium-sulfur battery containing sulfur-carbon compound

Abstract

The invention relates to the technical field of a lithium ion battery, and particularly to a sulfur-carbon compound for a lithium-sulfur battery. The sulfur-carbon compound comprises carbon nanoparticles, sulfur loaded in the carbon nanoparticles and silicon dioxide template existing in the carbon nanoparticles in a residual manner, wherein the content of sulfur accounts for 40-70% of the content of the sulfur-carbon compound based on mass percent; and the content of the silicon dioxide template accounts for 0.3-3% of the content of the sulfur-carbon compound based on mass percent. The residual silicon dioxide template in the sulfur-carbon compound is dispersed in the carbon nanoparticles so as to reduce the aperture of the carbon nanoparticles; therefore, the carbon nanoparticles have a relatively high capture capability for polysulfide lithium that is an intermediate product of an electrochemical reaction in use; meanwhile, the residual silicon dioxide template can effectively prevent a flying shuttle effect of polysulfide lithium; and the invention also relates to a preparation method for the sulfur-carbon compound, and an electrode material and the lithium-sulfur battery containing the sulfur-carbon compound.

Description

technical field [0001] The invention relates to the technical field of lithium-ion batteries, in particular to a sulfur-carbon composite for lithium-sulfur batteries, a preparation method thereof, an electrode material prepared by using the sulfur-carbon composite, and a lithium-sulfur battery. Background technique [0002] Lithium-sulfur battery is a kind of lithium battery, which is a secondary battery with metal lithium as the negative electrode and sulfur element as the positive electrode; when the lithium-sulfur battery is discharged, the negative electrode reaction is that lithium loses electrons and becomes lithium ions, and the positive electrode reaction is sulfur and lithium. Ions and electrons react to form sulfides, and the potential difference between the positive and negative electrodes is the discharge voltage provided by the lithium-sulfur battery. The specific energy of lithium-sulfur batteries can theoretically reach 2600Wh / kg, which is far greater than any...

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Problems solved by technology

[0003] However, there are still some problems hindering its practical application in lithium-sulfur batteries. The specific problems are as follows: 1. 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; 2. Lithium polysulfides, the intermediate discharge products of lithium-sulfur batteries, will dissolve into the organic electrolyte, increase the viscosity of the electrolyte, and reduce the ion conductivity; and lithium polysulfides It can migrate between the positive and negative electrodes, resulting in the loss of active materials and the waste of electric energy; and the dissolved lithium polysulfides will diffuse across the separator to the negative electrode, react with the negative electrode, and destroy the solid electrolyte interface film (SEI film) of the negative electrode; 3. The final discharge product of lithium-sulfur batteries, Li 2 S n (n=1~2) Electronic insulation and insoluble in organic electrolyte, will be deposited on the surface of the conductive framework; part of the lithium sulfide is detached from the conductive framework, and cannot be converted into sulfur or high-order polysulfides through a reversible charging process. Resulted in a great attenuation of capacity; 4. The densities of sulfur and lithium sulfide are 2.07g cm -3 and 1.66g cm -3 , there is a volume expansion / contraction of up to 79% during charge and discharge. This expansion will lead to changes in the morphology and structure of the positive electrode, which in turn will lead to the detachment of sulfur from the conductive framework, resulting in capacity attenuation; and this volume effect in It is not obvious under the button battery, but the volume effect will be enlarged in the large battery, which will cause significant capacity fading, and may even cause damage to the battery. The huge volume change will destroy the electrode structure

However, the sulfur-carbon composites synthesized in the prior art are always unable to avoid the problem of polysulfides dissolving into the electrolyte, resulting in poor cycle stability of lithium-sulfur batteries made using the sulfur-carbon composites, which cannot meet actual needs

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