Effect of precipitators on the morphologies and electrochemical properties of Li1.2Mn0.54Ni0.13Co0.13O2 via rapid nucleation and post-solvothermal method

A Simple Gas-Solid Treatment for Surface Modification of Li-Rich Oxides Cathodes

Li-rich layered oxides with high capacity are expected to be the next generation of cathode materials. However, the irreversible and sluggish anionic redox reaction leads to the O₂ loss in the surface as well as the capacity and voltage fading. In the present study, a simple gas-solid treatment with ferrous oxalate has been proposed to uniformly coat a thin spinel phase layer with oxygen vacancy and simultaneously realize Fe-ion substitution in the surface. The integration of oxygen vacancy and spinel phase suppresses irreversible O₂ release, prevents electrolyte corrosion, and promotes Li-ion diffusion. In addition, the surface doping of Fe-ion can further stabilize the structure. Accordingly, the treated Feox-2 % cathode exhibits superior capacity retention of 86.4 % and 85.5 % at 1 C and 2 C to that (75.3 % and 75.0 %) of the pristine sample after 300 cycles, respectively. Then, the voltage fading is significantly suppressed to 0.0011 V per cycle at 2 C especially. The encouraging results may play a significant role in paving the practical application of Li-rich layered oxides cathode.

Synergetic effect of high Ni ratio and low oxygen defect interface zone of single crystals on the capacity retention of lithium rich layered oxides

Li-rich layered oxides (LLOs) are promising cathode materials for Li-ion batteries owing to their high capacities (>250 mAh g^-1), however, they suffered from severe capacity and voltage fading caused by irreversible oxygen loss and phase changes. Herein, the structural stability of single crystalline and polycrystalline Li_1.14Ni_0.32Mn_0.44Co_0.04O₂ was compared in detail. It was found that the stability of oxidized oxygen ions on the near surface was improved in single crystals, which retarded oxygen loss from surface and surficial phase changes, possibly owing to the facet regulating and low surface curvature. In addition, the formation-migration of Mn³⁺, one of the crucial factors that caused capacity fading of LLOs, can be mitigated by increasing Ni³⁺ ratio. Under the synergistic effect of low oxygen defects on the near surface and high Ni³⁺ ratio, stable cycling performances and higher thermal stability were obtained.

Synergistic Effect of Mn3+ Formation-Migration and Oxygen Loss on the Near Surface and Bulk Structural Changes in Single Crystalline Lithium-Rich Oxides

Micron-sized single crystal particles could be used to intensify structural changes between bulk and surface area during the charge-discharge process owing to their long-range order. In this study, the effects of Mn³⁺ formation-migration and oxygen loss on the structure change from the bulk side to the near surface in single crystalline Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ were decoupled by regulating the voltage windows of 2-4.5, 3-4.8, and 2-4.8 V because Mn³⁺ formation-migration and oxygen loss mainly occurred below 3 V and beyond 4.5 V, respectively. It is found that oxygen vacancies and phase transformation can be retarded by suppressing the formation-migration of Mn³⁺. Finally, we also conducted an important insight that boron ion doping in tetrahedral site could be used to suppress Mn³⁺ migration from octahedral site to tetrahedral site and disrupt the synergistic effect of Mn³⁺ migration and oxygen loss.

Simple Glycerol-Assisted and Morphology-Controllable Solvothermal Synthesis of Lithium-Ion Battery-Layered Li1.2Mn0.54Ni0.13Co0.13O2 Cathode Materials

High-performance lithium-rich-layered oxide is regarded as a promising candidate for lithium-ion battery (LIB) cathode materials because of its outstanding high specific capacity. Despite in-depth research over the past decade, there are still a number of serious problems limiting its commercialization. Here, we report a simple morphological design and size-controllable material preparation strategy to enhance the electrochemical performance of LIB cathode materials. We use a simple solvothermal method to obtain a carbonate precursor material with different morphologies by adjusting the solvent ratio of the system, which will be conveniently formed into Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ by calcination. Moreover, further relation between the morphology and electrochemical performance of cathode materials is systematically investigated. The microsphere cathode material with suitable size exhibits superior electrochemical performances among all samples in terms of initial reversible capacity (280.4 mA h g^-1 at 0.1 C) and cycle performance (87.67% retention after 200 cycles at 1 C). Even at 5 C, a high discharge capacity of 150.8 mA h g^-1 can be obtained. In addition, this work provides a feasible and effective approach to controllable synthesis of stable structures and high-performance oxide electrode materials for LIBs.

Enhanced Cathode Performance: Mixed Al2O3 and LiAlO2 Coating of Li1.2Ni0.13Co0.13Mn0.54O2

Li-rich, manganese-based cathode materials are attractive candidates for Li-ion batteries because of their excellent capacity, but poor rate and cycle performance have limited their commercial applications. Herein, Li-rich, manganese-based cathode materials were modified with aluminum isopropoxide as an aluminum source modifier using a sol-gel technique followed by a wet chemical method. To investigate the structure, morphology, electronic state, and elemental composition of both pristine- and surface-modified Li_1.2Ni_0.13Co_0.13Mn_0.54O₂, various characterizations were performed. Based on density functional theory simulations and the results of electrochemical tests, the surface of the modified cathode material was found to contain at least part of the LiAlO₂ phase. This was attributed to the aluminum isopropoxide reacting with a Li₂CO₃/LiOH byproduct on the material surface to form LiAlO₂ with a three-dimensional Li-ion channel structure. Electrochemical testing revealed that a 3 wt % aluminum isopropoxide coating of cathode materials exhibited excellent electrochemical performance. Furthermore, the initial Coulombic efficiency and discharge capacity at 0.1 C were up to 88.55% and 272.7 mAh g^-1, respectively. A final discharge capacity of 186.4 mAh g^-1 was achieved, corresponding to a capacity retention of 83.55% after 300 cycles at 0.5 C. This was attributed to LiAlO₂ partially accelerating the diffusion of Li ions and Al₂O₃ aiding the avoidance of side reactions in the mixed coating layer by partially protecting the structure.

Sodium Doping to Enhance Electrochemical Performance of Overlithiated Oxide Cathode Materials for Li-Ion Batteries via Li/Na Ion-Exchange Method

Overlithiated oxide cathode materials show high capacity but poor cycle stability and voltage attenuation. In this work, a concentration difference driven molten salt ion exchange strategy is used to replace a small quantity of lithium ions by sodium ions. With the entry of sodium ions, the interplanar spacing is increased and the structure is stabilized. The electrochemical properties of materials have been improved obviously. The powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and transmission electron microscopy are used to detect the entry of sodium ions and structural changes. The modified materials display high discharge specific capacity, excellent cycling performance, and reduced voltage attenuation.

Microsphere Na0.65[Ni0.17Co0.11Mn0.72]O2 Cathode Material for High-Performance Sodium-Ion Batteries

P2-type layered oxides have been considered promising candidates as cathodes for sodium-ion batteries (SIBs) owing to their high capacity and high rate capability. However, because of the difficulty involved in forming hierarchical microstructures, it remains challenging to develop high energy density P2-type layered oxides with good electrochemical performance and high electrode density. In this study, we demonstrate the feasibility of P2-type Na_0.65[Ni_0.17Co_0.11Mn_0.72]O₂ as a very efficient cathode material for high energy density SIBs by synthesizing a micron-sized hierarchical structure via the coprecipitation route. The as-prepared P2-type microsphere cathode constructed from nanoscale primary particles provides a sufficient interface between the electrodes and the electrolyte solution, which enables to shorten the transport pathways for Na⁺ ions and electrons. Simultaneously, the hierarchical microstructure enhances the structural stability and high tap density (∼1.18 g cm^-3). Benefiting from these merits, the proposed P2-type microsphere Na_0.65[Ni_0.17Co_0.11Mn_0.72]O₂ displays a high discharge capacity of 187 mA h g^-1 at 12 mA g^-1 and an exceptional cycle retention of 74.7% after 500 cycles, even at the high current density of 600 mA g^-1. In addition, the high tap density of this P2-type microsphere enhances the density of composite cathodes, which translates to a high volumetric energy density of 340 W h L^-1 based on the overall volume of the cathode active mass and the aluminum foil current collector.

The effect of lithium content on the structure, morphology and electrochemical performance of Li-rich cathode materials Li1+x(Ni1/6Co1/6Mn4/6)1−xO2

Among the Li-rich cathode materials investigated, the x = 0.167 sample exhibits the highest electrochemical performances.