Three-dimensional Hollow Carbon Fiber Foam Sulfur Positives from Cotton Prepared from Metals

With the rapid development of mobile electronic devices, electric vehicles and renewable energy sources, the demand for high-capacity batteries has become increasingly urgent, and the development of new high-energy-density electrochemical energy storage systems has received great attention. Lithium-sulfur batteries have a high theoretical specific capacity (1675 mAh g-1) and energy density (2600 Wh kg-1). At the same time, because of its many advantages, such as abundant reserves and low prices, lithium sulfur batteries are regarded as the most promising next generation. One of the high energy electrochemical energy storage systems. However, based on the multi-electron reaction of lithium-sulfur batteries, the reaction complexity determines that during the charge-discharge process, polysulfide intermediates that are soluble in the electrolyte will be formed, resulting in a "shuttle effect", resulting in irreversible capacity loss, and due to sulfur Poor conductivity leads to a bottleneck in the short cycle life and rapid capacity decay of the sulfur cathode.

Carbon materials have excellent electrical conductivity, rich pore structure, and extremely high chemical stability. Therefore, the development of carbon/sulfur composite electrode materials is considered as one of the effective ways to improve the performance of lithium-sulfur batteries. However, in most carbon/sulfur composite electrodes reported in most research work, the areal density of sulfur is relatively low (less than 2 mg cm-2), resulting in a lower surface capacity of the carbon/sulfur composite electrode, even lower than that of commercial lithium ion battery 4.0. The level of mAh cm-2 severely restricts the practical application of lithium-sulfur batteries.

Recently, the Institute of Advanced Carbon Materials, Institute of Metal Research, Chinese Academy of Sciences, used natural cotton as a precursor, and after high-temperature carbonization, prepared a three-dimensional hollow carbon fiber foam with high conductivity, and then put sulfur/multi-walled carbon nanotubes/carbon black nanoclusters. A three-dimensional hollow carbon fiber foamed sulphur positive electrode with a surface density of up to 21.2 mg cm-2 was obtained by filling in the interstitial spaces of the fibers. The carbon/sulfur composite electrode can provide a multi-stage conductive network with both short-range and long-range, thereby achieving higher sulfur utilization. At the same time, this work proposes a new idea to suppress the “shuttle effect”: the use of hollow carbon fiber foams has a high liquid absorption rate for electrolytes, which allows them to absorb electrolytes while also limiting polysulfides dissolved in the electrolytes. In the positive electrode region, the diffusion of polysulfides to the negative electrode is prevented, thereby effectively suppressing the "shuttle effect" and ensuring good cycle stability. Therefore, the composite electrode with a sulfur surface density of 21.2 mg cm-2 has an initial surface capacity of up to 23.32 mAh cm-2, and after cycling 150 times, a 70% capacity retention rate can be achieved. This work not only demonstrated the preparation of high-conductivity carbon materials using natural materials as raw materials, but also proposed a new idea for inhibiting the "shuttle effect" of lithium-sulfur batteries, opening up a new path for the development of high-capacity, high-surface capacity lithium-sulfur batteries. .

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