Preparation method of lithium-sulfur battery cathode

Abstract

The invention relates to a preparation method of a lithium-sulfur battery positive electrode, and the preparation method of a Fe3C@C / S composite material comprises the following steps: dropwise addinga mixed solution B into a mixed solution A, and performing uniform mixing to obtain a mixed solution C; freeze-drying the mixed solution C to obtain a freeze-dried product, wherein the mixed solutionA comprises urea, metal salt, a surfactant and water, the metal salt comprises ferric salt and / or ferrous salt, and the mixed solution B comprises glucose compounds, silicon dioxide, acid and water;carbonizing the freeze-dried product, and separating out a Fe3C@C composite material; uniformly mixing the Fe3C@C composite material with a sulfur-containing compound, and carrying out heat treatmentto obtain the Fe3C@C / S composite material. The Fe3C@C composite material can accelerate the oxidation-reduction reaction of polysulfide, effectively inhibit shuttling of polysulfide and generation ofa surface passivation layer, and finally obtain a high-surface-capacity lithium-sulfur battery at a low temperature.

Description

technical field [0001] The invention relates to the technical field of batteries, in particular to a method for preparing a positive electrode of a lithium-sulfur battery. Background technique [0002] Lithium-sulfur batteries have a high theoretical specific energy (2600 Wh kg -1 ), is considered to be one of the new secondary battery systems most likely to be practical after lithium-ion batteries. However, it has been 60 years since the lithium-sulfur battery was invented, and it has not yet achieved a real scale application, mainly due to the following two reasons: [0003] (1) Low areal capacity and high E / S ratio: Due to the electronic and ion insulating properties of elemental sulfur and the discharge product lithium sulfide itself, a large amount of conductive agent needs to be added to the positive electrode, resulting in the majority of lithium-sulfur battery positive electrode materials. Sulfur content < 64%, sulfur loading per unit area < 2 mg cm -2 , the...

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Problems solved by technology

However, when the sulfur loading is increased, more polysulfides will be enriched on the surface of the sulfur carrier during the discharge process, resulting in a slow redox conversion of polysulfides and a rapid passivation of the carrier surface (generated Li 2 S 2 / Li 2 S passivation layer), which reduces the effective reactive active sites and exacerbates the shuttle effect, which leads to rapid capacity fading of Li-S batteries

[0004] (2) Poor low-temperature performance: When exposed to extreme environments, excellent low-temperature performance is essential for practical secondary batteries

However, secondary batteries usually have poor electrochemical performance at low temperatures due to low ion diffusion and electrochemical reaction kinetics

For lithium-sulfur batteries, the low operating temperature also reduces the thermodynamic diffusion of polysulfides, triggers the enrichment of polysulfides on the surface of the carrier, and further causes severe shuttling of polysulfides.

[0005] In addition, there are currently few studies on low-temperature lithium-sulfur batteries, especially high-area-capacity lithium-sulfur batteries at low temperatures have not been reported.

The reported low-temperature lithium-sulfur batteries are all obtained under low-load conditions, and the sulfur load is generally between 1 and 3 mg cm -2 , the resulting low-temperature lithium-sulfur batteries have an areal capacity lower than the 4 mAh cm of current commercial lithium-ion batteries -2 , has no practical application value

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