Stabilizing lattice oxygen in slightly Li-enriched nickel oxide cathodes toward high-energy batteries

Abstract

•The slight lithium-enrichment strategy revives the lithium nickel oxide cathode •A double-tilt electrochemical cell enables tracking of surface structural changes •Detrimental phase transition is inhibited by trapping O2 in lattice •Trapped O2 nonuniformly distributes in particle surface revealed by EELS line scan Lattice oxygen release (LOR), which promotes surface structural degradation and electrolyte decomposition, is a major contributor to capacity fade and thermal runaway in layered oxide cathodes. Despite decades of research, it is still a great challenge to stabilize the lattice oxygen, especially in deeply delithiated cathodes. Here, we demonstrate an Li-enrichment strategy to revive lithium nickel oxide (LNO), a high-energy cathode (>900 Wh kg−1) long plagued by poor cycle performance and thermal instability. In a slightly Li-enriched LNO (Li1.04Ni0.96O2) prepared by a specially designed molten-salt synthesis, spatially resolved (operando) characterizations reveal intralayer Ni migration upon delithiation, and this leads to the formation of vacancy clusters to trap the electrochemically oxidized oxygen in the near-surface lattice. Thus, the detrimental effects of LOR are effectively suppressed. The Li-rich LNO cathode greatly outperforms the traditional Li-deficient LNO cathodes modified by conventional approaches such as doping and surface coating. Our findings open up new opportunities for building better batteries. Lattice oxygen release (LOR), which promotes surface structural degradation and electrolyte decomposition, is a major contributor to capacity fade and thermal runaway in layered oxide cathodes. Despite decades of research, it is still a great challenge to stabilize the lattice oxygen, especially in deeply delithiated cathodes. Here, we demonstrate an Li-enrichment strategy to revive lithium nickel oxide (LNO), a high-energy cathode (>900 Wh kg−1) long plagued by poor cycle performance and thermal instability. In a slightly Li-enriched LNO (Li1.04Ni0.96O2) prepared by a specially designed molten-salt synthesis, spatially resolved (operando) characterizations reveal intralayer Ni migration upon delithiation, and this leads to the formation of vacancy clusters to trap the electrochemically oxidized oxygen in the near-surface lattice. Thus, the detrimental effects of LOR are effectively suppressed. The Li-rich LNO cathode greatly outperforms the traditional Li-deficient LNO cathodes modified by conventional approaches such as doping and surface coating. Our findings open up new opportunities for building better batteries.