Addressing the Achilles' heel of pseudocapacitive materials: Long-term stability

Electrode materials with high energy densities and long-lasting performances are crucial to durable and reliable electrochemical energy storage devices for modern information technologies (eg, Internet of things). In terms of supercapacitors, their low energy densities could be enhanced by using pseudocapacitive electrodes, but meanwhile, their ultralong lifetimes are compromised by the limited charge-discharge cycling stabilities of pseudocapacitive materials. This review article discusses on the cycling instability issues of five common pseudocapacitive materials: conjugated polymers (or conducting polymers), metal oxides, metal nitrides, metal carbides, and metal sulfides. Specifically, the article includes the fundamentals of the failure modes of these materials, as well as thoroughly surveys the design rationales and technical details of the cycling-stability-boosting tactics for pseudocapacitive materials that reported in the literature. Additionally, promising opportunities, future challenges, and possible solutions associated with pseudocapacitive materials are discussed.