A Near-Surface Structure Reconfiguration Strategy to Regulate Mn3+/Mn4+ and O2−/(O2)n− Redox for Stabilizing Lithium-Rich Oxide Cathode

Lithium-rich layered oxides (LROs) are one class of the most competitive high-capacity cathode materials due to their anion/cation synergistic redox activity. However, excessive oxidation of the oxygen sublattices can induce serious oxygen loss and structural imbalance. Hence, a near-surface reconfiguration strategy by fluorinating graphene is proposed to precisely regulate Mn³⁺/Mn⁴⁺ and O²⁻/(O₂)ⁿ⁻ redox couples for remarkably stabilizing high-capacity LROs and realizing the simultaneous reduction of the lattice stress, regulation of the Mn metal at a lower charge state, and construction of 3D Li⁺ diffusion channels. Combining with a highly conductive graphene-coating layer, the surface oxygen loss, transition metal dissolution, and electrolyte catalytic decomposition are suppressed. Benefiting from this synergy, the modified LROs disclose higher initial Coulombic efficiency and discharge-specific capacity and improve cyclability compared with pristine LROs. Further, it is revealed that the F⁻ impact becomes easier for the O sites at the lattice interface of C2/m and R$\overline{3}$m to sufficiently buffer lattice stress. Moreover, lithium ions coupled to the doped F atoms at the lattice interface migrate to the Ni-rich R$\overline{3}$m lattice sites with lower migration energies. This consolidated understanding will open new avenues to regulate reversible oxygen redox of LROs for high-energy-density lithium-ion batteries.     

Spintronic State-Induced Interface Reconfiguration of 2H-Perovskite Related Oxides for Pseudocapacitance Increase

Perovskite oxides are able to realize pseudocapacitive energy storage through oxygen anion intercalation. Herein, it is demonstrated that, based on the three 2H-perovskite related oxides Sr₆Co₅O_15-x, Sr₅Co₄O_12-x, and Sr₅Co₃NiO_12-x as the research objects, metal oxyhydroxides generated through surface reconfiguration during electrochemical processes can contribute extra capacity besides the oxygen-anion intercalation. This is because the electron spin state controlled by the transition metal valence state in the pseudo trigonal prisms for the 2H-perovskite structure will affect the Jahn–Teller (JT) distortion. The strong JT distortion of Co²⁺ and Ni³⁺ would elongate metal-O bonds, thereby helping the formation of metal oxyhydroxides on the surface of the pristine material. Among the three 2H-perovskite related oxides, the specific capacity of Sr₅Co₃NiO_12-x having the most Co²⁺ and Ni³⁺ contents showed the highest capacity increase. This study will provide a promising pathway to develop advanced perovskite-like oxide pseudocapacitive materials.