Water-Soluble Binders For Sulfur Cathode Materials In Rechargeable Lithium Batteries

With the rapid development of high-energy rechargeable batteries, rechargeable lithium-sulfur batteries have attracted more attention. Among the components in the sulfur cathode, the binder plays an important role in improving its electrochemical performance, especially in regards of cycle performances. In this work, three water-soluble binders are applied in sulfur cathode to investigate the effects on the electrochemical performance of lithium-sulfur batteries in detail.A new binder, carbonyl-β-cyclodextrin, is prepared through partial oxidation, and some of its physical properties, including viscosity, pH and bonding property are studied detailedly. FT-IR shows that some of hydroxyl groups inβ-cyclodextrin molecule are oxidized to carbonyl groups, which greatly enhances its solubility in water and the solubility is 165g/100g (H2O). The shearing strength is up to 0.197MPa, showing a great bonding property, and CV result indicates that this binder remains stable between 1V and 3V and no electrochemical reaction can be observed. And then it is applied as the binder in sulfur composite. The sulfur cathode expresses a high reversible specific capacity of 694.5mAh/g and remains 655.3mAh/g even after 50 cycles. The results show that sulfur cathode using carbonyl-β-cyclodextrin expresses a higher specific capacity and better stability than that using PTFE or PVDF as the binder. The SEM indicates that a homogeneous distribution can be observed in the cathode after 50 cycles, and no severe aggregation can be found in the cathode.Arabic gum and sodium alginate are also initially studied as binders of sulfur composite cathodes to study their effects on the electrochemical performances. Sulfur composite cathode using Arabic gum as the binder shows a high specific capacity of 666.7mAh/g in the first cycle and remains 603.2mAh/g even after 50 cycles. Sodium alginate is also introduced in the sulfur cathode as a binder. And specific capacity of sulfur composite using sodium alginate as the binder is only 482.1mAh/g after 50 cycles.From these experiments, it can be concluded that carbonyl-β-cyclodextrin has a good potential application prospect due to its high water solubility, good convenience, low price, environmental friendness and stable electrochemical performances.