Impact of Post-Synthesis heat treatment avoidance on cobalt carbonate hydroxide as a Battery-Type electrode material

Abstract

In this study, the electrochemical energy storage properties of one-dimensional (1D) hierarchical nanowire array (NWA) of cobalt carbonate hydroxide hydrate (Co6(CO3)2(OH)8·H2O) (CCH) is explored. The 1D nanostructure is advantageous due to their better charge/ion transport properties. The material was synthesized via. simple, and facile hydrothermal approach. The highlighting feature of this work lies in its post-synthesis process, where the authors deliberately avoided the post-synthesis heat treatment process to utilize the hydrated (x‧H2O) part associated with the lattice water which eventually led CCH in a unique robust crystal structure. Here, the authors have explored multifaceted aspects of 1D CCH NWAs, including the nanowire synthesis, their growth mechanism, and pseudocapacitive charge storage properties. The authors propose a novel charge storage mechanism, insertion pseudocapacitance, which depends on the (de)intercalation of cations (e.g., Li+, Na+, K+, and H+), where tunnels play a significant role in charge storage properties. In this type of charge-storage mechanism, cationic diffusion occur from the interior of the crystalline framework along with the surface-confined phenomena. The electrochemical energy storage performance in terms of specific capacity (Csp) is found to be 243.55 mAhg−1 @ 5 mVs−1 scan rate and 161.465 mAhg−1 at 2500 mAg−1 current density. The material exhibited excellent capacity retention of ∼ 95 % and ∼ 86 % at significantly higher current densities of 20,000 mAg−1 and 100,000 mAg−1, respectively. This work tries to establish the structure-electrochemical property correlation of the CCH which has an exceptional crystal structure that is deduced ∼ 20 years after its first report. Therefore, the authors emphasize exploring the fundamental understanding of the CCH from the crystallographic point of view and its relevance to electrochemical energy storage. This work will help in exploring the next-generation metal carbonate hydroxide hydrate-based (MCH) materials.