Wuxing Zhang

Nitrogen-doped porous carbon nanofiber webs as anodes for lithium ion batteries with a superhigh capacity and rate capability.

Nitrogen-doped carbon nanofiber webs (CNFWs) with high surface areas are successfully prepared by carbonization-activation of polypyrrole nanofiber webs with KOH. The as-obtained CNFWs exhibit a superhigh reversible capacity of 943 mAh g(-1) at a current density of 2 A g(-1) even after 600 cycles, which is ascribed to the novel porous nanostructure and high-level nitrogen doping.

Biomass derived hard carbon used as a high performance anode material for sodium ion batteries

A porous hard carbon material was synthesized by the simple pyrolysis of H3PO4-treated biomass, i.e., pomelo peels, at 700 °C in N2. The as-obtained hard carbon had a 3D connected porous structure and a large specific surface area of 1272 m2 g−1. XPS analysis showed that the carbon material was functionalized by O-containing and P-containing groups. The porous hard carbon was used as an anode for sodium ion batteries and exhibited good cycling stability and rate capability, delivering a capacity of 181 mA h g−1 at 200 mA g−1 after 220 cycles and retaining a capacity of 71 mA h g−1 at 5 A g−1. The sodium storage mechanisms of the porous hard carbon can be explained by Na+ intercalation into the disordered graphene layers, redox reaction of the surface O-containing functional groups and Na+ storage in the nanoscale pores. However, the porous hard carbon demonstrated a low coulombic efficiency of 27%, resulting from the formation of a solid electrolyte interphase film and the side reactions of surface phosphorus groups.

Morphosynthesis of a hierarchical MoO2 nanoarchitecture as a binder-free anode for lithium-ion batteries

A simple and cost-effective morphogenetic route has been developed for the fabrication of a hierarchically nanostructured “cellulose” MoO2 monolith in large qualities, whereby the cotton texture acts as both a template and a stabilizer. The MoO2 monolith possesses hierarchical porosity and an interconnected framework, which is demonstrated to be useful as a binder-free anode in rechargeable lithium-ion batteries with both high specific capacity of 719.1 mA h g−1 and good reversibility. Our single-component anode for lithium-storage devices also benefits from a simplified fabrication process and reduced manufacturing cost, in comparison with conventional multicomponent electrodes that are fabricated from a mixture of polymer binders and active materials. The present morphogenetic strategy is facile but effective, and therefore it is very promising for large-scale industrial production. It can be extended to prepare other metal oxides with elaborate textural characteristics.

Coral-like α-MnS composites with N-doped carbon as anode materials for high-performance lithium-ion batteries

Coral-like α-MnS composites with nitrogen-doped carbon (NC) were designed as anode materials for lithium-ion batteries. A facile two-step method was developed to synthesize the composites. Hydrothermally obtained polyvinyl pyrrolidone (PVP) capped (NH4)2Mn2(SO4)3 was used as a precursor. The α-MnS–NC composites were attained by heating the precursor at different temperatures for an appropriate time in a N2 atmosphere. The microstructure and morphology were carefully investigated by means of field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). As anode materials, the α-MnS–NC composites exhibit large reversible capacity, excellent cyclic stability and high rate capability. At a current density of 500 mA g−1, the discharge capacity reaches as high as 878 mA h g−1 at the first cycle and remains at 699 mA h g−1 even after 400 cycles.

Synthesis of hierarchical MoS2 and its electrochemical performance as an anode material for lithium-ion batteries

A facile process is developed to synthesize MoS2 in basic solutions via a hydrothermal route by employing ammonium heptamolybdate and thiourea as starting materials and post-annealing in a N2 atmosphere at 450 °C for 5 h. The morphologies of the MoS2 products can be tuned from porous flowers to dense spheres by addition of NaOH. Experimental results show that the MoS2 products have good crystallinity. A formation mechanism of the MoS2 is proposed in which the dense MoS2 spheres are evolved from the porous MoS2 flowers through growth along the 〈00l〉 direction of the nanosheets. Based on the growth mechanism, the microstructure of MoS2 can be successfully controlled by adjustment of the S/Mo ratio or addition of a surfactant in the recipe. Electrochemical measurements demonstrate that the flower-like MoS2 shows better electrochemical performance than MoS2 spheres as anode materials for Li-ion batteries, which deliver a high reversible capacity of 900 mA h g−1 at a current density of 100 mA g−1, excellent cycling stability and rate capability.

Controllable Synthesis of Hollow Bipyramid β-MnO2 and Its High Electrochemical Performance for Lithium Storage

Three types of MnO2 nanostructures, viz., α-MnO2 nanotubes, hollow β-MnO2 bipyramids, and solid β-MnO2 bipyramids, have been synthesized via a simple template-free hydrothermal method. Cyclic voltammetry and galvanostatic charge/discharge measurements demonstrate that the hollow β-MnO2 bipyramids exhibit the highest specific capacity and the best cyclability; the capacity retains 213 mAh g(-1) at a current density of 100 mA g(-1) after 150 cycles. XRD patterns of the lithiated β-MnO2 electrodes clearly show the expansion of lattice volume caused by lithiation, but the structure keeps stable during lithium insertion/extraction process. We suggest that the excellent performance for β-MnO2 can be attributed to its unique electrochemical reaction, compact tunnel-structure and hollow architecture. The hollow architecture can accommodate the volume change during charge/discharge process and improve effective diffusion paths for both lithium ions and electrons.

Facile synthesis of mesoporous 0.4Li2MnO3·0.6LiNi2/3Mn1/3O2 foams with superior performance for lithium-ion batteries

Mesoporous 0.4Li2MnO3·0.6LiNi2/3Mn1/3O2 foams with a pore diameter of ca. 3 nm have been fabricated by a gel-combustion method. The sintering temperature is optimized to as low as 600 °C by considering the balance of crystallization and particle size. The as-obtained mesoporous 0.4Li2MnO3·0.6LiNi2/3Mn1/3O2 foams show excellent rate capability and cyclability. At a current density of 15 mA g−1, the specific discharge capacity is 291 mA h g−1 for the first cycle and the capacity retention is 92.3% over 100 cycles. Even at 200 mA g−1, the capacity is as high as 208 mA h g−1. The improved rate capability and cyclability can be ascribed to the mesoporous structure. The mesoporous structure has a large contact surface between the electrode and electrolyte, which facilitates the Li+-ion diffusion and enhances the ability of accommodation for continuous structural transition during charge and discharge cycling.

Hollow K0.27MnO2 Nanospheres as Cathode for High-Performance Aqueous Sodium Ion Batteries.

Hollow K0.27MnO2 nanospheres as cathode material were designed for aqueous sodium ion batteries (SIBs) using polystyrene (PS) as a template. The samples were systematically studied by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. As cathode materials for aqueous SIBs, the hollow structure can effectively improve the sodium storage property. A coin cell with hollow K0.27MnO2 as cathode and NaTi2(PO4)3 as anode exhibits a specific capacity of 84.9 mA h g(-1) at 150 mA g(-1), and the capacity of 56.6 mA h g(-1) is still maintained at an extremely high current density of 600 mA g(-1). For full cell measurement at the current density of 200 mA g(-1), 83% capacity retention also can be attained after 100 cycles. The as-designed hollow K0.27MnO2 nanospheres demonstrate long cyclability and high rate capability, which grant the potential for application in advanced aqueous SIBs.

Nanostructured alkali cation incorporated δ-MnO2 cathode materials for aqueous sodium-ion batteries

Nanostructured δ-MnO2 incorporated with alkali cations (A-δ-MnO2, A = K+, Na+) has been synthesized and evaluated as a cathode material for aqueous sodium-ion batteries. It is observed that Na+ ions are easier than K+ ions to intercalate into the layered δ-MnO2 due to their smaller ion radius. The incorporation of K+ and Na+ into δ-MnO2 shows a great influence on the electrochemical performance of the layered δ-MnO2. The full cell with (K, Na)-co-incorporated δ-MnO2 (K : Na : Mn = 0.15 : 0.26 : 1) hierarchical nanospheres as the cathode and NaTi2(PO4)3 as the anode exhibits a specific capacity of 74.6 mA h g−1 at 150 mA g−1, and the capacity remains at ∼62% at a high current density of 600 mA g−1. The electrochemical cycling does not induce observable structural degradation even after 200 cycles. K-incorporated and (K, Na)-co-incorporated δ-MnO2 electrodes have superior capacity and rate capability, which can be ascribed to their hierarchical structure and adequate crystallinity.

Mechanism of Capacity Fade in Sodium Storage and the Strategies of Improvement for FeS2 Anode

Pyrite FeS2 has attracted extensive interest as anode material for sodium-ion batteries due to its high capacity, low cost, and abundant resource. However, the micron-sized FeS2 usually suffers from poor cyclability, which stems from structure collapse, exfoliation of active materials, and sulfur dissolution. Here, we use a synergistic approach to enhance the sodium storage performance of the micron-sized FeS2 through voltage control (0.5-3 V), binder choice, and graphene coating. The FeS2 electrode with the synergistic approach exhibits high specific capacity (524 mA h g-1), long cycle life (87.8% capacity retention after 800 cycles), and excellent rate capability (323 mA h g-1 at 5 A g-1). The results prove that a synergistic approach can be applied in the micron-sized sulfides to achieve high electrochemical performance.