SWNT Networks with Polythiophene Carboxylate Links for High-Performance Silicon Monoxide Electrodes

Carboxylated polythiophenes, such as poly[3-(potassium-4-butanoate) thiophene] (PPBT), play a critical role in securely connecting single-walled carbon nanotube (SWNT) electrical networks onto the surface of carbon-coated silicon monoxide (c-SiO_x). These connections are a function of the materials' surface chemistries and resultant physical/chemical bonding through favorable molecular interactions. Specifically, the PPBT π-conjugated backbone and alkyl side chain carboxylate moieties (COO-), respectively, physically interact with the SWNT and c-SiO_x carbon layer π-electron-rich surfaces, and chemically bind to surface hydroxyl (-OH) species of the c-SiO_x electroactive materials to form a carboxylate bond. This approach effectively captured pulverized particles that form during battery operation and beneficially suppressed the thickness change that electrodes typically undergo. The resultant electrodes exhibited superior electrochemical performance, which was ascribed to stable SEI layer formation, reduced electrode resistance, and improved electrode kinetics. Moreover, electrodes fabricated by blending 30 wt % of c-SiO_x with graphite using <3 wt % binder exhibited remarkable performance in both coin-type half-cell and pouch-type full-cell systems. The concept that introduces robust SWNT electrical networks with PPBT carboxylate linkages suggests a feasible approach for the design of practical, high-performance, and high-capacity anodes for battery applications.