Synergistic effect of uniform lattice cation/anion doping to improve structural and electrochemical performance stability for Li-rich cathode materials

Improving the long-term electrochemical performances of Li-rich cathode material by encapsulating a three-in-one nanolayer

With large specific capacity, wide voltage window, and high energy density, Li-rich layered oxides have been considered as a promising cathode candidate for advanced lithium-ion batteries (LIBs). However, their commercial application is challenging due to severe capacity degradation and voltage fading caused by irreversible oxygen evolution and phase transition upon repeated cycling. This work proposes an effective strategy to improve the long-term electrochemical performances of Li_1.2Mn_0.56Ni_0.17Co_0.07O₂ (LMNCO) by constructing multifunctional nanolayers composed of element-doping, layered-spinel heterostructural connection, and fast ion conductor shell via a facile method. The Li_0.09B_0.97PO₄ (LBPO) coating shell acts as a fast ion carrier and physical screen to promote Li⁺ diffusion and isolate side reactions at the cathode-electrolyte interface; moreover, two-phase transitional region provides three-dimensional channel to facilitate Li⁺ transport and inhibit phase transition. Besides, B³⁺ and PO₄^3--doping collaborates with oxygen vacancies to stabilize lattice oxygen and restrain oxygen evolution from the bulk active cathode. The optimized LMNCO@LBPO material exhibits a superior capacity retention of 78.6%, higher than that of the pristine sample (49.3%), with the mitigated voltage fading of 0.73 mV per cycle after 500 cycles at 1 C. This study opens up an avenue for the surface modification to the electrochemical properties and perspective application of Li-rich cathodes in high-performance LIBs.

Recent Advances in Biomass-Derived Carbon Materials for Sodium-Ion Energy Storage Devices

Compared with currently prevailing Li-ion technologies, sodium-ion energy storage devices play a supremely important role in grid-scale storage due to the advantages of rich abundance and low cost of sodium resources. As one of the crucial components of the sodium-ion battery and sodium-ion capacitor, electrode materials based on biomass-derived carbons have attracted enormous attention in the past few years owing to their excellent performance, inherent structural advantages, cost-effectiveness, renewability, etc. Here, a systematic summary of recent progress on various biomass-derived carbons used for sodium-ion energy storage (e.g., sodium-ion storage principle, the classification of bio-microstructure) is presented. Current research on the design principles of the structure and composition of biomass-derived carbons for improving sodium-ion storage will be highlighted. The prospects and challenges related to this will also be discussed. This review attempts to present a comprehensive account of the recent progress and design principle of biomass-derived carbons as sodium-ion storage materials and provide guidance in future rational tailoring of biomass-derived carbons.

Sulfuration of Li-Rich Mn-Based Cathode Materials for Multianionic Redox and Stabilized Coordination Environment

Lithium-rich transition metal oxides (LLOs) can deliver high specific capacity over 250 mAh g^-1 , stemming from additional contribution of oxygen redox. However, the formation of O^{(2- n )-} (0 < n < 2) species and even oxygen gas during the deep oxidation stage leads to progressive structural transformation that cause voltage decay/hysteresis, sluggish kinetics, and poor thermostability, preventing real-world application of LLOs. Therefore, the substantive key relies on enhancing the anionic redox stability in LLOs. Here, a sulfuration procedure of LLOs (S-LLOs) is proposed, in which sulfur anions are incorporated into oxygen sites in the lattice structure and form polyanions on the surface. Proved by structural characterizations and density functional theory (DFT) calculations, sulfur anions in the interior lattice can reversibly participate in the redox process and enhance the integral coordination stability by mitigating undesired oxygen redox. Moreover, S polyanions at the surface form a protecting layer for interfacial stability. The electrochemical measurements indicate that S-LLO demonstrates a high discharge capacity of 307.8 mAh g^-1 , an outstanding capacity retention rate of 91.5% after 200 cycles, along with excellent voltage maintenance, rate capability, and thermostability. The sulfuration process of LLOs with multianionic redox mechanism highlights a promising strategy to design novel high-energy-density cathode materials with superior cycling performance.