Bimetal phosphide inlaid carbon hollow nanocage as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a bimetallic phosphide embedded carbon hollow nanocage and a preparation method and application thereof. The preparation method comprises the following steps: dispersing a nickel-cobalt Prussian blue derivative in a liquid medium, preparing dispersion liquid, adding dopamine hydrochloride into the dispersion liquid, and preparing nickel-cobalt prussian blue wrapped by the polydopamine; calcining the nickel-cobalt Prussian blue derivative wrapped by the polydopamine to prepare a nickel-cobalt bimetallic particle embedded carbon hollow nanocage; taking hydrogen phosphide as a phosphating agent, and carrying out one-step phosphating on the carbon hollow nanocage inlaid with the bimetallic particles to prepare the carbon hollow nanocage inlaid with the bimetallic phosphide; preparing a dispersion liquid from a bimetallic phosphide embedded carbon hollow nanocage, carbon black and polyvinylidene fluoride, then coating a polypropylene diaphragm with the dispersion liquid, and performing drying to prepare a multifunctional diaphragm. The comprehensive performance of the lithium-sulfur battery is remarkably improved.

Description

technical field [0001] The invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a double-metal phosphide-embedded carbon hollow nanocage and a preparation method and application thereof. Background technique [0002] Lithium-sulfur batteries are generally composed of four parts: metal lithium negative electrode, sulfur positive electrode, electrolyte and separator. It is a type of high-energy-density battery system that realizes the conversion of electrical energy and chemical energy by breaking the sulfur-sulfur bond. It has a low cost , environmental friendliness and other advantages, the theoretical specific capacity and energy density are 1675mAh h -1 and 2600Wh kg -1 , which is more than five times the theoretical energy density of commercialized lithium-ion batteries. [0003] However, lithium-sulfur batteries still have some problems: [0004] (1) S and Li 2 S 2 / Li 2 S is an electronic insulating material, so it wil...

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Problems solved by technology

[0004] (1) S and Li 2 S 2 / Li 2 S is an electronic insulating material, so it will generate a large internal resistance during the battery charge and discharge cycle, which will reduce the activity of the reaction; the current solution is mainly to compound S with various carbon materials with good conductivity. To a certain extent, it will also greatly reduce the loading of S; in addition, due to Li 2 S has poor conductivity, and it is difficult to completely convert S on the electrode into Li 2 S, so it is usually difficult to obtain the theoretical specific capacity;

[0005] (2) Since S (2.03g cm -3 ) and Li 2 S (1.66g cm -3 ) There is a density difference between them, so in a fully discharged state, sulfur will experience a volume expansion of up to 80%. Severe volume expansion will lead to the shedding and failure of the electrode material, which will cause a sharp decline in battery performance and limit the capacity of the battery. Further application of high-loaded sulfur cathodes;

[0006] (3) The working mechanism of lithium-sulfur batteries is a "solid-liquid-solid" process. Polysulfide intermediates usually have good solubility in organic solvents, which makes the positive electrode materials continuously flow into the electrolyte during the cycle. Dissolution, resulting in irreversible capacity; in addition, due to the solubility of S in organic solvents is better than that of Li 2 S, resulting in faster conversion of S to polysulfides than polysulfides to Li 2 The conversion of S, which further increases the content of polysulfides in the electrolyte; at the same time, due to the reduction of polysulfides dissolved in the electrolyte into Li 2 S usually covers the surface of the positive electrode, which reduces the conductivity of the positive electrode;

[0007] (4) Shuttle effect: Since polysulfides can be better dissolved in the organic ether electrolyte, they can easily diffuse to the surface of the negative electrode, thereby directly reacting with the metal lithium sheet of the negative electrode, resulting in loss of capacity, and Li produced by the reaction 2 S has poor conductivity, which will also affect the cycle stability of the negative electrode to a certain extent; the current main research is devoted to improving the conductivity of the positive electrode and polar materials to inhibit the shuttle effect, such as adding a large amount of conductive carbon materials, polar metals, etc. Compounds, etc., however, the additional cathode sulfur host material more or less reduces the energy density of the cathode

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