In-situ reconstructed surface/inner-structure synergistic design enabling 4.6 V LiCoO2 cathode for all-solid-state thin-film battery

Abstract

Developing high-voltage LiCoO₂ cathode film is a promising approach to meet high-energy density demands for intelligent microdevices. However, the electrochemical performance of bare LiCoO₂ is compromised beyond 4.55 V due to irreversible phase transitions, cobalt dissolution, and intergranular cracking. Meanwhile, vacuum physical deposition technology and interface compatibility pose challenges to achieving higher capacity integrated into a narrow space. Herein we proposed an in-situ reconstructed surface/inner-structure synergistic modification prototype strategy to achieve a superior high-voltage LiCoO₂ through a facile in-situ magnetron sputtering. This sandwich structure design enables a synergistic effect of internal titanium body-doping and external LiCoPO₄ compact layer to strengthen stability under high voltage. Consequently, the triggered defects and strong PO coordination are substantially beneficial for stabilizing Li⁺ channels, inhibiting Co migration, as well as enhancing diffusion kinetics. Strain field analysis reveals that the mitigated lattice deformation along (104) preferential orientation is beneficial for alleviating volumetric strain even at an operating voltage of up to 4.6 V. Additionally, the induced body and surface atom rearrangement regulates the band structure and reduces oxygen redox activity. Therefore, the as-designed high-voltage LiCoO₂-based all-solid-state thin-film battery achieves superior cycle stability with 75 % capacity retention after 500 cycles at 1 C under 10 °C.