Electrolyte for Li-S battery, preparation method thereof, and Li-S battery containing same

Abstract

The invention discloses an electrolyte for a Li-S battery. The electrolyte mainly comprises electrolyte salts and an organic solvent, wherein the electrolyte salts contain lithium polysulfide, and the molecular formula of the lithium polysulfide is Li2Sn. A preparation method of the electrolyte comprises the following steps of adding lithium metal or Li2Sn and elemental sulfur into the organic solvent according to a molar ratio and carrying out reaction at room temperature and under the protection of an inert atmosphere to generate the electrolyte, wherein lithium salts, shuttle inhibitors and the like can be selectively added to the electrolyte. The invention further discloses a Li-S battery containing the electrolyte; a negative active material is the lithium metal or lithium-containing alloy; a positive active material is at least one of the elemental sulfur, organic sulfides and carbon-sulfur polymer, and the positive pole is composed of the positive active material, a conductive agent and a binding agent which are mixed in a certain mass ratio; and the dosage of the electrolyte is about 0.04 mL relative to every milligram of sulfur. The Li-S battery disclosed by the invention has the advantages that the sources of raw materials are broad, the energy density of the Li-S battery can be increased, and the cycle life of the Li-S battery can be prolonged.

Description

technical field [0001] The invention relates to an electrolyte, its preparation and a secondary battery, in particular to an electrolyte for a Li-S battery, a Li-S battery and a preparation method for the electrolyte. Background technique [0002] Due to the continuous development of the automobile industry, the demand for high-energy-density secondary batteries has gradually increased, and lithium-sulfur batteries have begun to enter people's field of vision. The theoretical specific energy of lithium-sulfur batteries is as high as 2600Wh / Kg, while the theoretical specific capacity of elemental sulfur is as high as 1680 mAh / g. At the same time, sulfur reserves are abundant, cheap, and environmentally friendly. Although rechargeable lithium-sulfur batteries have many advantages over traditional lithium-ion batteries, their current disadvantages such as low energy density and short cycle life limit their large-scale application. [0003] The low energy density and short cyc...

AI Technical Summary

Problems solved by technology

[0003] The low energy density and short cycle life of lithium-sulfur batteries are mainly due to the following reasons: First, elemental sulfur, the active material of the positive electrode, is an insulator, so a large amount of conductive agent needs to be added to the positive electrode, although this can improve the performance of the positive electrode to a certain extent , but the addition of inactive materials reduces the energy density of the battery

Second, due to the intermediate product of the electrochemical reaction of the lithium-sulfur battery, the high-valence polysulfide lithium has high solubility in the organic electrolyte, and the polysulfide lithium cannot be completely converted into a solid product at the end of the discharge, and only a small amount of active material is present at the end of the charge. It can be oxidized to elemental sulfur, and a large amount of active materials exist in the electrolyte in the form of high-valent polysulfide lithium, so the discharge capacity of existing lithium-sulfur batteries is much lower than the theoretical capacity

At present, the main solution to this problem in China is to use a new structure of carbon conductive agent, hoping to provide high specific surface area and super adsorption capacity with the help of the rich pore structure of conductive carbon, and limit the dissolution of lithium polysulfide from the positive electrode structure, but So far, there is still no ideal carbon structure that can fundamentally solve the dissolution problem of lithium polysulfide

Third, metal lithium, the active material of the negative electrode, continuously reacts with the organic solvent during charging and discharging, resulting in the depletion of the electrolyte. At the same time, the decomposition products of the solvent will be deposited on the negative electrode and the positive electrode, resulting in the passivation of the electrode, and the lithium metal is repeatedly depleted during the battery cycle. Dissolution and deposition of lead to surface chalking

Fourth, the electrolyte salt will oxidize the positive electrode active material to generate Li x SO y , leading to the irreversible loss of active materials, which reduces the energy density and cycle life of the battery

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