Electrochemical Enhancement of Lithium‐Ion Diffusion in Polypyrrole‐Modified Sulfurized Polyacrylonitrile Nanotubes for Solid‐to‐Solid Free‐Standing Lithium–Sulfur Cathodes
Yikun Yi, Feng Hai, Jingyu Guo, Xin Gao, Wenting Chen, Xiaolu Tian, Wei Tang, Weibo Hua, Mingtao Li
Abstract
The energy density of lithium-sulfurized polyacrylonitrile (Li-SPAN) batteries has chronically suffered from low sulfur content. Although a free-standing electrode can significantly reduce noncapacity mass contribution, the slow bulk reaction kinetics still constrain the electrochemical performance. In this regard, a novel electrochemically active additive, polypyrrole (PPy), is introduced to construct PAN nanotubes as a sulfur carrier. This hollow channel greatly facilitates charge transport within the electrode and increases the sulfur content. Both electrochemical tests and simulations show that the SPANPPy-1% cathode possesses a larger lithium-ion diffusion coefficient and a more homogeneous phase interface than the SPAN cathode. Consequently, significantly improved capabilities and rate properties are achieved, as well as decent exportations under high-sulfur-loading or lean-electrolyte conditions. In-situ and semi-situ characterizations are further performed to demonstrate the nucleation growth of lithium sulfide and the evolution of the electrode surface structure. This type of electrochemically active additive provides a well-supported implementation of high-energy-density Li-S batteries.