Archetypical 2D sheet-like Cu2MoS4 for all-solid-state symmetric pseudocapacitors with ultra-steady performance efficiency

Abstract

Presently, the development of ultra-efficient electrode materials is necessary for the advancement of supercapacitor device technologies. In this context, herein, a sluggish nucleation and growth kinetic strategy was developed for the synthesis of square-shaped 2D sheet-like Cu₂MoS₄ with rich phase purity, low crystallinity, good elemental stoichiometry, and multi-oxidation state characteristics of its metal components. The electrochemical studies of Cu₂MoS₄ (as positive and negative electrode material) validated its rich redox physiognomies, excellent kinetic reversibility of its redox reactions, no evident iR drop, high supercapacitive energy storage, ∼89% contribution of diffusion-controlled electrochemical processes to the overall charge storage, very low charge transfer (∼0.45 Ω) and series resistance (∼0.5 Ω), potential-independent charge transfer and series resistance, and signature of lower Warburg resistance, signifying facilitated ion dissimilation during the redox reactions in the 2D sheet-like microstructure of the material. According to the electrochemical analyses, the fabricated 1.6 V Cu₂MoS₄‖Cu₂MoS₄ all-solid-state symmetric pseudocapacitor (ASSSPC) device demonstrated pseudocapacitive charge storage, high areal and mass-specific capacitance/capacity, no distinctive iR drop, very low charge-transfer (∼1.23 Ω) and series resistance (1.01 Ω), and fundamentally low Warburg resistance, demonstrating poorly constrained ion mobilization throughout the electrodes during the redox processes. The Cu₂MoS₄‖Cu₂MoS₄ ASSSPC device also showed an extremely low relaxation time (∼0.5 ms), remarkably high energy and power density (∼30 W h kg⁻¹ at ∼1882 W kg⁻¹), rate energy and power density (∼11 W h kg⁻¹ at ∼5649 W kg⁻¹), and retained ∼97.1% of its specific capacity after 10 500 repetitive charge–discharge cycles. The rich performance efficiency of the Cu₂MoS₄‖Cu₂MoS₄ ASSSPC device is ascribed to the following reasons: (i) the salient electromicrostructural physiognomies of the 2D layered sheet-like Cu₂MoS₄ for charge conduction and ion dissimilation, (ii) presence of redox-active multi-metal ions for augmented number of redox reactions followed by charge transfer, and (iii) striking electrochemical and electromicrostructural compatibility between the same positive and negative electrode material for facilitating charge transfer and highly efficient pseudocapacitive charge storage.