A Three-Dimensional Hybrid Carbon-Microelectromechanical System on a Graphite-Coated Stainless Steel Substrate as a High-Performance Anode for Lithium-Ion Batteries

Three-dimensional (3D) microbatteries provide higher capacities owing to their additional volume when compared to a thin-film electrode configuration. Here for the first time, we report a carbon-microelectromechanical system approach to fabricate 3D carbon microelectrode arrays on a graphite-coated stainless steel (SS) current collector. A thin layer of graphite coating on SS wafer through pencil tracing at the base of the 3D micropillars not only provides an efficient conducting path but also significantly improves the cycle life and reversible storage capability by eliminating detrimental side reactions. The as-fabricated 3D hybrid carbon microelectrode arrays delivered significantly higher reversible capacities of 920 and 624 mAh g-1 at current densities of 37.2 and 500 mA g-1, respectively. A detailed investigation is carried out to demonstrate the advantage of graphite coating on the base while comparing the performance of 3D carbon electrodes on the bare SS. Excellent cycling stability with >99% capacity retention even after 100 cycles of galvanostatic charge-discharge confirms the commercial feasibility of such 3D hybrid carbon microelectrode arrays for high-performance Li-ion batteries. Furthermore, the dimensional stability of the 3D hybrid carbon microelectrodes is confirmed by the postcycle analysis after 100 cycles. In addition, a diffusion-limited model utilizing the finite element method is deployed to estimate time-dependent Li-ion transport across the hybrid microelectrodes, which reveals that the Li-ion diffusion is substantially improved when compared to that in conventional commercial planar electrodes.