Zhengping Ding

Hierarchical Nanocomposite of Hollow N-Doped Carbon Spheres Decorated with Ultrathin WS2 Nanosheets for High-Performance Lithium-Ion Battery Anode

Hierarchical nanocomposite of ultrathin WS2 nanosheets uniformly attached on the surface of hollow nitrogen-doped carbon spheres (WS2@HNCSs) were successfully fabricated via a facile synthesis strategy. When evaluated as an anode material for LIBs, the hierarchical WS2@HNCSs exhibit a high specific capacity of 801.4 mA h g(-1) at 0.1 A g(-1), excellent rate capability (545.6 mA h g(-1) at a high current density of 2 A g(-1)), and great cycling stability with a capacity retention of 95.8% after 150 cycles at 0.5 A g(-1). The Li-ion storage properties of our WS2@HNCSs nanocomposite are much better than those of the previously most reported WS2-based anode materials. The impressive electrochemical performance is attributed to the robust nanostructure and the favorable synergistic effect between the ultrathin (3-5 layers) WS2 nanosheets and the highly conductive hollow N-doped carbon spheres. The hierarchical hybrid can simultaneously facilitate fast electron/ion transfer, effectively accommodate mechanical stress from cycling, restrain agglomeration, and enable full utilization of the active materials. These characteristics make WS2@HNCSs a promising anode material for high-performance LIBs.

The Effect of Boron Doping on Structure and Electrochemical Performance of Lithium-Rich Layered Oxide Materials

Polyanion doping shows great potential to improve electrochemical performance of Li-rich layered oxide (LLO) materials. Here, by optimizing the doping content and annealing temperature, we obtained boron-doped LLO materials Li1.2Mn0.54Ni0.13Co0.13BxO2 (x = 0.04 and 0.06) with comprehensively improved performance (94% capacity retention after 100 cycles at 60 mA/g current density and a rate capability much higher compared to that of the pristine sample) at annealing temperatures of 750 and 650 °C, respectively, which are much lower than the traditional annealing temperature of similar material systems without boron. The scenario of the complex crystallization process was captured using Cs-corrected high-angle annular dark field scanning transmission electron microscopic (HAADF-STEM) imaging techniques. The existence of layered, NiO-type, and spinel-like structures in a single particle induced by boron doping and optimization of annealing temperature is believed to contribute to the remarkable improvement of cycling stability and rate capability.

Understanding the Enhanced Kinetics of Gradient-Chemical-Doped Lithium-Rich Cathode Material

Although chemical doping has been extensively employed to improve the electrochemical performance of Li-rich layered oxide (LLO) cathodes for Li ion batteries, the correlation between the electrochemical kinetics and local structure and chemistry of these materials after chemical doping is still not fully understood. Herein, gradient surface Si/Sn-doped LLOs with improved kinetics are demonstrated. The atomic local structure and surface chemistry are determined using electron microscopy and spectroscopy techniques, and remarkably, the correlation of local structure-enhanced kinetics is clearly described in this work. The experimental results suggest that Si/Sn substitution decreases the TMO2 slab thickness and enlarges the interslab spacing, and the concentration gradient of Si/Sn affects the magnitude of these structural changes. The expanded interslab spacing accounts for the enhanced Li+ diffusivity and rate performance observed in Si/Sn-doped materials. The improved understanding of the local structure-enhanced kinetic relationship for doped LLOs demonstrates the potential for the design and development of other high-rate intercalated electrode materials.

Understanding the Improved Kinetics and Cyclability of a Li2MnSiO4 Cathode with Calcium Substitution

Limited practical capacity and poor cyclability caused by sluggish kinetics and structural instability are essential aspects that constrain the potential application of Li2MnSiO4 cathode materials. Herein, Li2Mn1- xCa xSiO4/C nanoplates are synthesized using a diethylene-glycol-assisted solvothermal method, targeting to circumvent its drawbacks. Compared with the pristine material, the Ca-substituted material exhibits enhanced electrochemical kinetics and improved cycle life performance. In combination with experimental studies and first-principles calculations, we reveal that Ca incorporation enhances electronic conductivity and the Li-ion diffusion coefficient of the Ca-substituted material, and it improves the structural stability by reducing the lattice distortion. It also shrinks the crystal size and alleviates structure collapse to enhance cycling performance. It is demonstrated that Ca can alleviate the two detrimental factors and shed lights on the further searching for suitable dopants.

Tuning anisotropic ion transport in mesocrystalline lithium orthosilicate nanostructures with preferentially exposed facets

Li2TMSiO4 (TM = Mn, Fe, Co, etc.) is regarded as a new class of cathode materials for next generation Li-ion batteries because of the theoretical possibility of reversible deintercalation of two Li ions from the structure (ca. 330 mA hg−1). Nevertheless, the silicate cathode still suffers from low electronic conductivity, slow Li ion diffusion and structural instability upon deep cycling. To solve these problems, for the first time, we propose a rational design of mesocrystalline Li2FeSiO4 hollow discoids with an ordered single-crystal-like structure and highly exposed (001) facets. The Li2FeSiO4 mesocrystals display a near theoretical discharge capacity, superior rate capability and good cycling stability. The enhanced Li storage performance is ascribed to the unique structural features with a large surface area generated from the hollow mesocrystal structure and a shortened Li+ diffusion path along (001) exposed facets. This new facile, elegant synthesis method that enables the manipulation of crystal growth and subsequent improvements in the electronic and ionic kinetics and structural integrity should have a positive impact on the research and development of silicate materials as promising cathodes for next generation Li-ion batteries.Batteries: Getting more lithium from electrodesA battery-electrode material that achieves the excellent performance predicted by theory has been synthesised by researchers in China and Canada. A lithium-ion battery is charged by removing lithium from one electrode and storing it in a second. The energy is released when a circuit is connected and the lithium ions flow back the other way, thus producing a current. Li2FeSiO4 is a new electrode material that is exciting battery researchers because it theoretically has a large capacity for the removal of two lithium ions. A team led by Weifeng Wei from the Central South University in Changsha has now developed a simple method for creating hollow Li2FeSiO4 discoids. They show that this material exhibits near theoretical discharge capacity plus good stability as the battery is repeatedly charged and discharged.Mesocrystalline Li2FeSiO4hollow discoids with an ordered single-crystal-like structure and highly exposed (001) facets have been successfully synthesized as a lithium-ion cathode. Li2FeSiO4@C mesocrystals display a near theoretical discharge capacity, superior rate capability and good cycling stability due to their unique structural features with a large surface area generated from the hollow mesocrystal structure and a shortened Li+ diffusion path along (001) exposed facets.

Crystallographic Habit Tuning of Li2MnSiO4 Nanoplates for High-Capacity Lithium Battery Cathodes

Li2MnSiO4 has attracted significant attention as a cathode material for lithium ion batteries because of its high theoretical capacity (330 mA h g-1 with two Li+ ions per formula unit), low cost, and environmentally friendly nature. However, its intrinsically poor Li diffusion, low electronic conductivity, and structural instability preclude its use in practical applications. Herein, elongated hexagonal prism-shaped Li2MnSiO4 nanoplates with preferentially exposed {001} and {210} facets have been successfully synthesized via a solvothermal method. Density functional theory calculations and experimental characterization reveal that the formation mechanism involves the decomposition of solid precursors to nanosheets, self-assembly into nanoplates, and Ostwald ripening. Hydroxyl-containing solvents such as ethylene glycol and diethylene glycol play a crucial role as capping agents in tuning the preferential growth. Li2MnSiO4@C nanoplates demonstrate a near theoretical discharge capacity of 326.7 mA h g-1 at 0.05 C (1 C = 160 mA h g-1), superior rate capability, and good cycling stability. The enhanced electrochemical performance is ascribed to the electrochemically active {001} and {210} exposed facets, which provide short and fast Li+ diffusion pathways along the [001] and [100] axes, a conformal carbon nanocoating, and a nanoscaled platelike structure, which offers a large electrode/electrolyte contact interface for Li+ extraction/insertion processes.