Synergistic Effects of Cu(OH)₂-CuO Anodes for Multiple-Step Energy Storage of Li-Ion Microbatteries

Lithium-ion microbatteries (LIMBs) face challenges in achieving high power density without compromising energy density, due to limitations in assembly and kinetics. By overcoming LIMB electrode fabricated using a laser-assisted method, which significantly improves assembly precision and enhances reaction kinetics, the first anodization of Cu(OH)₂-CuO nanoneedle hybrids on Cu foil for a LIB anode is reported. By resolving the limitations of previous metal-hydroxide electrodes associated with conventional conversion reactions, the novel anode achieves an unprecedently-high initial capacity of 3065 mAh g^-1 which clearly exceeds the theoretical limit. X-ray Photoelectron Spectroscopy, Transmission Electron Microscopy, and in-situ Raman analysis revealed the nanoscale Cu-particles and LiOH in high-voltage reactions, alongside Cu_xH_y, Li₂O, and LiH in low-voltage hydride reactions. AIMD simulations additionally revealed the underlying atomistic mechanism. An in-plane LIMB using a laser-assisted method is further engineered, featuring in prelithiated Cu(OH)₂-CuO as the anode and LiNi_0.8Mn_0.1Co_0.1O₂ as the cathode. This LIMB operates between 2.0 and 4.5 V, delivering a reversible capacity of 6.61 mAh cm^-2 at 20 µA cm^-2 and retaining over 83% capacity after 500 cycles. This work advances overall understanding of lithium storage and offers key insights for the design of next-generation LIMBs.