Insights into self-induced electrochemical activation of carbon cathode

Abstract

Continuous capacity increase in electrochemical cycling, termed as electrochemical activation, is a frequently observed but rarely systematically studied phenomenon. Such phenomenon is noted in a preliminary study of carbon cathode for dual ion battery, showing gradual discharge capacity growth from 186 mAh g−1 (the 1st) to 320 mAh g−1 (the 300th). Systematical characterizations are carried out to investigate this phenomenon occurred on the carbon cathode, hydrothermally reduced graphene oxide (HrGO). The electrochemical activation comes from surface area increment, originated from multilayer reduced graphene oxide rolls formation and accumulation and structural order increase in cycling. The formation of rolls is plausibly a result of strain release of reduced graphene layers after electrochemical interaction with PF6−. Additionally, charge storage mechanism of HrGO is revealed. At active surface sites of HrGO, PF6− is consistently stored in a pseudocapacitive manner. In contrast, at well-crystallized domains, pseudocapacitive PF6− uptake occurs at low voltage region while PF6− intercalation dominates at higher potentials. Supportive lithium storage also contributes to total capacity. Comprehensively, this work offers valuable insights of electrochemical activation and carbon cathodes’ electrochemical behaviors and will facilitate the construction of high-capacity carbon cathodes.