Superior cycling performance of a novel NKVO@polypyrrole composite anode for aqueous rechargeable lithium-ion batteries

Abstract

An aqueous rechargeable lithium-ion battery (ARLB) system has been assembled using as-prepared polypyrrole (PPy) to coat Na_0.8K_0.2K₆O₁₅ (NKVO) anode coupled with LiMn₂O₄ cathode, both immersed in an aqueous LiNO₃ solution. The chemical polymerization techniques have been employed to uniformly coat the surface of NKVO with PPy. The phase of NKVO@PPy composite has been characterized by X-ray diffraction; for quantifying PPy content, the thermal gravimetric analysis was performed. Spectroscopy techniques have been used to visualize the microscale morphological changes on the particle surface of NKVO caused by PPy coating. The staircase cyclic voltammetry and galvanic charge–discharge tests have been conducted at various current rates in the voltage range of −1 to 1 V vs. saturated calomel electrode (SCE). The PPy coated NKVO material showed a similar intercalation/deintercalation mechanism to that of pristine NKVO. When subjected to cyclic performance evaluation at a higher rate of 4 A g⁻¹, PPy-coated NKVO@PPy exhibited a preliminary discharge capacity of 115 mA h g⁻¹ and 64.5 mA h g⁻¹ following 400 cycles of charge–discharge with a retention rate of 55.6%, whereas the uncoated NKVO showed only 18.8% capacity retention rate. The significantly improved cyclic capacity retention has been attributed to the PPy coating, which acted as a protective layer preventing the unwanted side reactions, buffering the volume change and simultaneously increasing the electrical conductivity of pristine NKVO electrode during charge–discharge cycles. The decent performance demonstrated that NKVO@PPy is a promising electrode material for ARLB.