3D current collector based on cellulose-carbon nanotube nanocomposites for all-solid-state batteries

Abstract

Recently, lithium-ion batteries (LIBs) have been employed in various applications as a clean power source. In particular, all-solid-state batteries (ASSBs) using non-flammable organic solid electrolytes have attracted extensive interest because they have increased safety and energy density compared to conventional LIBs. Among the many building blocks in an ASSB, the current collector is a bridging element between the LIB electrodes and external circuits and has been developed to achieve enhanced performance in terms of maximum capacity, rate capability, and cycle stability. However, controllable, reproducible, and efficient current collectors have yet to be developed without using complex and costly methods. Herein, we report three dimensional (3D) current collectors for a cathode electrode in ASSBs using an eco-friendly sustainable fabrication method without generating environmentally toxic or harmful chemicals. The 3D hybrid current collector was prepared by bar-coating a 1.5 μm-thick conductive layer with cellulose-SWCNT (C-CNT) nanocomposites on a conventional aluminum (Al) foil. The dispersed C-CNT aqueous solution was fabricated from natural pulp and SWCNT powder using a high-power shaking process. Structural analysis of the dried C-CNT films confirmed that the entanglement and dispersion of C-CNT nanowires determined the mechanical and electrical properties. Moreover, the generated 3D porous structure with the randomly entangled nanowires increased the surface roughness of the C-CNT layer, resulting in improved contact resistance and adhesion bonding strength to the solid-sate cathode active materials in an ASSB. Compared with cells based on a flat Al current collector, the ASSB using a C-CNT layer of 23 wt% SWCNTs (apparent density of 1.16 g cm⁻³ and electrical conductivity of 180.4 S cm⁻¹) achieved 20% increased discharging capacitance at a C-rate of 0.1C, 163% increased capacity retention at a high C-rate of 1.0C, and 36% increased cycle stability after a 100 cycle test at 0.33C. In addition, the influence of a 3D microstructure on a current collecting layer using C-CNT nanocomposites was carefully analyzed using an adhesion test, cyclic voltammetry, and electrochemical impedance spectroscopy.