Garnet solid electrolytes have attracted great interest due to their wide electrochemistry window and high ion conductivity. However, the lithiophobic Li 2 CO 3 generated on the garnet surface results in a huge interfacial resistance and interface incompatibility. Herein, different from the extensive removal or conversion strategies, the Li 2 CO 3 on the surface of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) is directly used as a lithiophobic layer to suppress Li dendrite growth, and the lithophilic Li-In-F composite is used as the anode. The Li symmetrical half-cell with a Li 2 CO 3 interlayer is stably cycled for 6500 h without Li dendrite formation, a much longer time than for the half-cell without a Li 2 CO 3 interlayer (2334 h), showing a much higher interfacial stability. Moreover, the full cell based on LiFePO 4 and LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode shows a stable cycling performance and high rate capability (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , 94%@100th cycle@1C; LiFePO 4 , 90%@500th cycle@2C). This study provides a distinct way of converting disadvantages into advantages and solving the Li|LLZTO interfacial issues.

LiCoO2 (LCO) is ideal for 3C electronics due to its high tap density. However, the excessive O → Co charge transfer at high delithiation leads to irreversible Co reduction, O release, and structural degradation, deteriorating the high-voltage performance of LCO. Herein, we propose to regulate the intrinsic Fermi level via uneven trace Zr/Mg doping. First, the increase of electron density in the Fermi level mitigates both the O oxidation/coupled Co reduction through alleviating the O → Co charge transfer, restraining the formations of Co2+ and O2. This elevates Co redox activity and reduces O redox activity. In addition, the structural evolution of the cathode at delithiation is simplified. The modulated LCO delivers a high discharge capacity and a high cycling stability with 4.5 and 4.6 V ceilings. This study sheds new light on the modulation of Co/O redox chemistry and the reliable large-scale production of high-voltage LiCoO2.

P2-type Na0.67Mn0.5Fe0.5O2 (MF) has attracted great interest as a promising cathode material for sodium-ion batteries (SIBs) due to its high specific capacity and low cost. However, its poor cyclic stability and rate performance hinder its practical applications, which is largely related to lattice oxygen instability. Here, we propose to coat the cathode of SIBs with Li2ZrO3, which realizes the “three-in-one” modification of Li2ZrO3 coating and Li+, Zr4+ co-doping. The synergy of Li2ZrO3 coating and Li+/Zr4+ doping improves both the cycle stability and rate performance, and the underlying modification mechanism is revealed by a series of characterization methods. The doping of Zr4+ increases the interlayer spacing of MF, reduces the diffusion barrier of Na+, and reduces the ratio of Mn3+/Mn4+, thus inhibiting the Jahn–Teller effect. The Li2ZrO3 coating layer inhibits the side reaction between the cathode and the electrolyte. The synergy of Li2ZrO3 coating and Li+, Zr4+ co-doping enhances the stability of lattice oxygen and the reversibility of anionic redox, which improves the cycle stability and rate performance. This study provides some insights into stabilizing the lattice oxygen in layered oxide cathodes for high-performance SIBs.

High-voltage LiCoO2 (LCO) attracts great interest because of its large specific capacity, but it suffers from oxygen release, structural degradation, and quick capacity drop. These daunting issues root from the inferior thermodynamics and kinetics of the triggered oxygen anion redox (OAR) at high voltages. Herein, a tuned redox mechanism with almost only Co redox is demonstrated by atomically engineered high-spin LCO. The high-spin Co network reduces the Co/O band overlap, eliminates the adverse phase transition of O3 → H1–3, delays the exceeding of the O 2p band over the Fermi level, and suppresses excessive O → Co charge transfer at high voltages. This function intrinsically promotes Co redox and restrains O redox, fundamentally addressing the issues of O2 release and coupled detrimental Co reduction. Moreover, the chemomechanical heterogeneity caused by different kinetics of Co/O redox centers and the inferior rate performance limited by slow O redox kinetics is simultaneously improved owing to the suppression of slow OAR and the excitation of fast Co redox. The modulated LCO delivers ultrahigh rate capacities of 216 mAh g–1 (1C) and 195 mAh g–1(5C), as well as high capacity retentions of 90.4% (@100 cycles) and 86.9% (@500 cycles). This work sheds new light on the design for a wide range of O redox cathodes.