Achieving a Deeply Desodiated Stabilized Cathode Material by the High Entropy Strategy for Sodium-ion Batteries.

Manganese-based layered oxides are currently of significant interest as cathode materials for sodium-ion batteries due to their low toxicity and high specific capacity. However, the practical applications are impeded by sluggish intrinsic Na+ migration and poor structure stability as a result of Jahn-Teller distortion and complicated phase transition. In this study, a high-entropy strategy is proposed to enhance the high-voltage capacity and cycling stability. The designed P2-Na0.67Mn0.6Cu0.08Ni0.09Fe0.18Ti0.05O2 achieves a deeply desodiation and delivers charging capacity of 158.1 mAh g-1 corresponding to 0.61 Na with a high initial Coulombic efficiency of 98.2 %. The charge compensation is attributed to the cationic and anionic redox reactions conjunctively. Moreover, the crystal structure is effectively stabilized, leading to a slight variation of lattice parameters. This research carries implications for the expedited development of low-cost, high-energy-density cathode materials for sodium-ion batteries.

Constructing An Oxyhalide Interface for 4.8†V-Tolerant High-Nickel Cathodes in All-Solid-State Lithium-Ion Batteries.

All-solid-state lithium batteries (ASSBs) have received increasing attentions as one promising candidate for the next-generation energy storage devices. Among various solid electrolytes, sulfide-based ASSBs combined with layered oxide cathodes have emerged due to the high energy density and safety performance, even at high-voltage conditions. However, the interface compatibility issues remain to be solved at the interface between the oxide cathode and sulfide electrolyte. To circumvent this issue, we propose a simple but effective approach to magic the adverse surface alkali into a uniform oxyhalide coating on LiNi0.8Co0.1Mn0.1O2 (NCM811) via a controllable gas-solid reaction. Due to the enhancement of the close contact at interface, the ASSBs exhibit improved kinetic performance across a broad temperature range, especially at the freezing point. Besides, owing to the high-voltage tolerance of the protective layer, ASSBs demonstrate excellent cyclic stability under high cutoff voltages (500 cycles~94.0 % at 4.5 V, 200 cycles~80.4 % at 4.8 V). This work provides insights into using a high voltage stable oxyhalide coating strategy to enhance the development of high energy density ASSBs.

Atomic-Resolution In Situ Exploration of the Phase Transition Triggered Failure in a Single-Crystalline Ni-Rich Cathode.

Single-crystalline cathode materials LiNixCoyMn1-y-zO2 (x ≥ 0.6) are important candidates for obtaining better cyclic stability and achieving high energy densities of Li-ion batteries. However, it is liable to initiate phase transitions inside the grains during electrochemical cycling, and the processes and regions of these phase transitions have remained unknown. In this research, we conducted an intrinsic study, investigating the chemicals and microstructural evolution of single-crystalline LiNi0.83Co0.11Mn0.06O2 using in situ biasing transmission electron microscopy at an atomic scale. We observed that the layered structure on the surface of the single-crystalline material was degraded during the charging process, resulting in continuous phase transitions and the formation of surface oxygen vacancies, which can reduce both the structural and thermal stability of the material. Uneven delithiation led to the formation of high-density defects and discontinuous inactive electrochemical phases, such as local antiphase boundaries and the rock salt phase, in the bulk of the material. The non-uniformity of the structure and the coexistence of active and inactive phases introduce significant tensile stress, which can lead to intragranular cracks inside the grains. As the number of cycles increases, the structural degradation caused by the intragranular phase transition will further increase, ultimately affecting the cycling capacity and stability of the battery. This work has broad implications for creating lithium-ion batteries that are effective and long-lasting.

From Oxygen Redox to Sulfur Redox: A Paradigm for Li-Rich Layered Cathodes.

The utilization of anionic redox chemistry provides an opportunity to further improve the energy density of Li-ion batteries, particularly for Li-rich layered oxides. However, oxygen-based hosts still suffer from unfavorable structural rearrangement, including the oxygen release and transition metal (TM)-ion migration, in association with the tenuous framework rooted in the ionicity of the TM-O bonding. An intrinsic solution, by using a sulfur-based host with strong TM-S covalency, is proposed here to buffer the lattice distortion upon the highly activating sulfur redox process, and it achieves howling success in stabilizing the host frameworks. Experimental results demonstrate the prolonged preservation of the layered sulfur lattice, especially the honeycomb superlattice, during the Li+ extraction/insertion process in contrast to the large structural degeneration in Li-rich oxides. Moreover, the Li-rich sulfide cathodes exhibited a negligible overpotential of 0.08 V and a voltage drop of 0.13 mV/cycle, while maintaining a substantial reversible capacity upon cycling. These superior electrochemical performances can be unambiguously ascribed to the much shorter trajectories of sulfur in comparison to those of oxygen revealed by molecular dynamics simulations at a large scale (∼30 nm) and a long time scale (∼300 ps) via high-dimensional neural network potentials during the delithiation process. Our findings highlight the importance of stabilizing host frameworks and establish general guidance for designing Li-rich cathodes with durable anionic redox chemistry.