Soft carbon in non-aqueous rechargeable batteries: a review of its synthesis, carbonization mechanism, characterization, and multifarious applications

Abstract

Soft carbon is a special class of carbon materials having tunable physical properties that makes it suitable for various battery applications. The precursors containing large polyaromatic hydrocarbons undergo mesophase formation via complex organic rearrangements, which endows soft carbon with unique attributes. Soft carbon is considered an ideal and upscalable matrix for Si-based anodes due to its non-overlapping potential zone of lithiation with Si/SiO_x, interfacial cohesion, structural stability, and spatial connection. It is considered superior to other carbonaceous materials in confining polysulfides and enabling a higher loading of sulphur in Li–S batteries. It is the best anode for K-storage because of its ideal diffusion/adsorption balance, a good matrix for Na storage due to its enormous expandability, and an emerging material for anion storage as it contains graphitic microdomains. Soft carbon behaves as a multifunctional coating agent, capable of mitigating the poor electronic conductivity of polyanionic cathodes, alleviating interfacial instabilities of graphite anodes, and providing high voltage protection to spinel oxide and anion-storing cathodes. It is also employed in three-dimensional carbon fiber electrodes, where it plays multifaceted roles as a binder, conductive additive, and coating agent. Further, carbon-based current collectors can be prepared from soft carbon. In summary, this review summarizes all the attributes of soft carbon for use in rechargeable batteries.