Precursor pre-oxidation enables highly exposed plane {010} for high-rate Li-rich layered oxide cathode materials

Structure engineering with sodium doping for cobalt-free Li-rich layered oxide toward improving electrochemical stability

Structure engineering of the Li-rich layered cathodes to overcome insufficient structural stability and the rapid decay of capacity and voltage is crucial for commercializing of the materials for the lithium-ion batteries. Alkali metal element doping at the lithium sites has proven to be a feasible approach to boost the performance of the Li-rich layered oxides. Herein, the Na+-doping strategy in the lithium slabs is introduced to modify the structure of the cobalt-free layered Li-rich oxide, Li1.2Ni0.2Mn0.6O2. It is revealed that the doped Na+ ions can promote the activation of the Li2MnO3 phase, endowing the materials with high initial discharge capacity of 284.2 mAh g-1 at 0.1C. Due to the pillaring effect of the doped Na+ ions in the lithium slabs and the induced formation of oxygen vacancies, the electrochemical stability of the material is significantly improved, providing a capacity retention of 94.0 % after 100 cycles at 0.5C. The voltage decay per cycle is only 2.0 mV, less than 3.2 mV of the Li1.2Ni0.2Mn0.6O2. The results suggest that the facile strategy of introducing Na+ ions into the lithium slabs is an efficient approach for optimizing structure design of the Li-rich layered oxides for the lithium-ion batteries.

Optimized In Situ Doping Strategy Stabling Single-Crystal Ultrahigh-Nickel Layered Cathode Materials

Single-crystal Ni-rich cathodes offer promising prospects in mitigating intergranular microcracks and side reaction issues commonly encountered in conventional polycrystalline cathodes. However, the utilization of micrometer-sized single-crystal particles has raised concerns about sluggish Li+ diffusion kinetics and unfavorable structural degradation, particularly in high Ni content cathodes. Herein, we present an innovative in situ doping strategy to regulate the dominant growth of characteristic planes in the single-crystal precursor, leading to enhanced mechanical properties and effectively tackling the challenges posed by ultrahigh-nickel layered cathodes. Compared with the traditional dry-doping method, our in situ doping approach possesses a more homogeneous and consistent modifying effect from the inside out, ensuring the uniform distribution of doping ions with large radius (Nb, Zr, W, etc). This mitigates the generally unsatisfactory substitution effect, thereby minimizing undesirable coating layers induced by different solubilities during the calcination process. Additionally, the uniformly dispersed ions from this in situ doping are beneficial for alleviating the two-phase coexistence of H2/H3 and optimizing the Li+ concentration gradient during cycling, thus inhibiting the formation of intragranular cracks and interfacial deterioration. Consequently, the in situ doped cathodes demonstrate exceptional cycle retention and rate performance under various harsh testing conditions. Our optimized in situ doping strategy not only expands the application prospects of elemental doping but also offers a promising research direction for developing high-energy-density single-crystal cathodes with extended lifetime.

Anion-Cation Dual-Ion Multisite Doping Stabilizes the Crystal Structure of Li-Rich Layered Oxides

Li-rich layered oxide (LLOs) cathode materials are gaining increasing attention as lithium-ion batteries (LIBs) pursue greater energy density. However, LLOs still suffer from severe capacity fading and voltage decay due to their unstable crystal structure. Hence, the anion-cation dual-ion multisite doping strategy based on Mg and S atoms is used to stabilize the crystal structures of LLOs. Mg substitutes Li atoms in the Li and transition-metal (TM) layers, while S atoms occupy tetrahedral interstitial sites and lattice O sites, all of which contribute to the crystal structure stability of LLOs. Theoretical calculations show that Mg/S dual-ion multisite doping successfully reduces the energy levels of the TM 3d-O 2p and isolated O 2p orbitals, which effectively stabilizes the lattice oxygen. Therefore, multisite-doped samples exhibit promising electrochemical performance. This strategy provides a new approach to enhance the crystal structure stability of LLOs for the design of high-energy-density Li-ion batteries.

Recent advances in lithium-rich manganese-based cathodes for high energy density lithium-ion batteries

The development of society challenges the limit of lithium-ion batteries (LIBs) in terms of energy density and safety. Lithium-rich manganese oxide (LRMO) is regarded as one of the most promising cathode materials owing to its advantages of high voltage and specific capacity (more than 250 mA h g^-1) as well as low cost. However, the problems of fast voltage/capacity fading, poor rate performance and the low initial Coulombic efficiency severely hinder its practical application. In this paper, we review the latest research advances of LRMO cathode materials, including crystal structure, electrochemical reaction mechanism, existing problems and modification strategies. In this review, we pay more attention to recent progress in modification methods, including surface modification, doping, morphology and structure design, binder and electrolyte additives, and integration strategies. It not only includes widely studied strategies such as composition and process optimization, coating, defect engineering, and surface treatment, but also introduces many relatively novel modification methods, such as novel coatings, grain boundary coating, gradient design, single crystal, ion exchange method, solid-state batteries and entropy stabilization strategy. Finally, we summarize the existing problems in the development of LRMO and put forward some perspectives on the further research.

Engineering Crystal Orientation of Cathode for Advanced Lithium-ion Batteries: A Minireview

Engineering crystal orientation has attracted widespread attention since it is related to the cyclability and rate performance of cathode materials for lithium-ion batteries (LIBs). Regulating the crystal directional growth with optimal exposed crystal facets is an effective strategy to improve the performance of cathode materials, but still lacks sufficient attention in research field. Herein, we briefly introduce the characterization techniques and identification methods for crystal facets, then summarize and illuminate the major methods for regulating crystal orientation and their internal mechanism. Furthermore, the optimization strategies for layered-, spinel-, and olivine-structure cathodes are discussed based on the characteristic of crystal structure, and the relationship between exposure of special crystal facets and lithium storage performance is deeply analyzed, which could guide the rational design of cathodes for LIBs.

Improving Fast Charging-Discharging Performances of Ni-Rich LiNi0.8Co0.1Mn0.1O2 Cathode Material by Electronic Conductor LaNiO3 Crystallites

Fast charging-discharging is one of the important requirements for next-generation high-energy Li-ion batteries, nevertheless, electrons transport in the active oxide materials is limited. Thus, carbon coating of active materials is a common method to supply the routes for electron transport, but it is difficult to synthesize the oxide-carbon composite for LiNiO₂-based materials which need to be calcined in an oxygen-rich atmosphere. In this work, LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) coated with electronic conductor LaNiO₃ (LNO) crystallites is demonstrated for the first time as fast charging-discharging and high energy cathodes for Li-ion batteries. The LaNiO₃ succeeds in providing an exceptional fast charging-discharging behavior and initial coulombic efficiency in comparison with pristine NCM811. Consequently, the NCM811@3LNO electrode presents a higher capacity at 0.1 C (approximately 246 mAh g⁻¹) and a significantly improved high rate performance (a discharge specific capacity of 130.62 mAh g⁻¹ at 10 C), twice that of pristine NCM811. Additionally, cycling stability is also improved for the composite material. This work provides a new possibility of active oxide cathodes for high energy/power Li-ion batteries by electronic conductor LaNiO₃ coating.

Dual-Site Doping Strategy for Enhancing the Structural Stability of Lithium-Rich Layered Oxides

Lithium-rich layered oxide (LLO) cathode materials are considered to be one of the most promising next-generation candidates of cathode materials for lithium-ion batteries due to their high specific capacity. However, some inherent defects of LLOs hinder their practical application due to the oxygen loss and structure collapse resulting from intrinsic anion and cation redox reactions, such as poor cycle stability, sluggish Li⁺ kinetics, and voltage decay. Herein, we put forward a facile synergistic strategy to respond to these shortcomings of LLOs via dual-site doping with cerium (Ce) and boron (B) ions. The doped Ce ions occupy the octahedral sites, which not only enlarge the cell volume but also stabilize the layered framework and introduce abundant oxygen vacancies for LLOs, while B ions occupy the tetrahedral sites in the lattice, which block the migration path of transition metal (TM) ions and reduce the oxygen loss using the strong B-O bond. Based on this dual-site doping effect, after 100 cycles at 1 C, the dual-site doped materials exhibit excellent structural stability with a capacity retention of 91.15% (vs 75.12%) and also greatly suppress the voltage decay in LLOs with a voltage retention of 93.60% (vs 87.83%).

Systematic evaluation of lithium-excess polyanionic compounds as multi-electron reaction cathodes

Polyanion cathodes with multi-electron redox always facilitate wider application in a metal ion-based battery system because of their high capacity and safety. However, the irreversible phase transformation and interfacial deterioration remain major impediments. Herein, using monoclinic Li₃V₂(PO₄)₃ as a model, the impact of excess lithium on its electrochemical properties are demonstrated. It was determined that a maximum of 5% excess lithium could be incorporated into the monoclinic structure, and a further overdose of lithium led to the formation of secondary phase Li₃PO₄. The excess Li⁺ ions are located at both octahedral and interstitial sites, which enable enhanced redox kinetics that are mainly attributed to accelerated ionic movement induced by alternate diffusion behavior of Li⁺ ions in a three-dimensional permeation path. Moreover, Li-excess local configurations can stabilize the lattice oxygen and provide a favorable cathode-electrolyte interface, which synergistically relieves the structural degradation during electrochemical cycling, thus guaranteeing exceptional cycling stability (e.g., 82.5% after 1000 cycles at 1000 mA g^-1). These findings provide a comprehensive understanding of defect/electronic structure/ion transport and the intrinsic properties of polyanionic Li₃V₂(PO₄)₃ and may help to pave the way for other highly stable electrodes for rechargeable batteries.