Xiaowu Liu

Nitrogen-Doped Ordered Mesoporous Anatase TiO2 Nanofibers as Anode Materials for High Performance Sodium-Ion Batteries

Nitrogen-doped ordered mesoporous TiO2 nanofibers (N-MTO) have been fabricated by electrospinning and subsequent nitridation treatment. The N-doping in TiO2 leads to the formation of Ti(3+) , resulting in the improved electron conductivity of TiO2 . In addition, one-dimensional (1D) N-MTO nanostructure possesses very short diffusion length of Na(+) /e(-) in N-MTO, easy access of electrolyte, and high conductivity transport of electrons along the percolating fibers. The N-MTO shows excellent sodium storage performance.

Carbon‐Coated Germanium Nanowires on Carbon Nanofibers as Self‐Supported Electrodes for Flexible Lithium‐Ion Batteries

A hybrid structure with carbon-coated germanium nanowires grown on the surface of carbon nanofibers is fabricated using an in situ vapor-liquid-solid process. It is used as a self-supported and flexible anode for Li-ion batteries.

N-doped porous hollow carbon nanofibers fabricated using electrospun polymer templates and their sodium storage properties

N-doped hollow porous carbon nanofibers (P-HCNFs) were prepared through pyrolyzation of hollow polypyrrole (PPy) nanofibers fabricated using electrospun polycaprolactone (PCL) nanofibers as a sacrificial template. When used as anode material for NIBs, P-HCNFs exhibit a reversible capacity of 160 mA h g−1 after 100 cycles at a current density of 0.05 A g−1. An improved rate capability is also obtained at even higher charge–discharge rates. When cycled at a current density of 2 A g−1, the electrode can still show a reversible capacity of 80 mA h g−1. The N-doped sites, one-dimensional nanotube structure, and functionalized surface of P-HCNFs are capable of rapidly and reversibly accommodating sodium ions through surface adsorption and redox reactions. Therefore, P-HCNF is a promising anode material for next-generation NIBs.

General Strategy for Fabricating Sandwich-like Graphene-Based Hybrid Films for Highly Reversible Lithium Storage.

We report a general strategy for the fabrication of freestanding sandwich-like graphene-based hybrid films by electrostatic adsorption and following reduction reaction. We demonstrate that by rational control of pH value in precursors, graphene oxide (GO) sheets can form three-dimensional (3D) sandwich frameworks with nanoparticles decorated between the layers of graphene. In our proof-of-concept study, we prepared the graphene/Si/graphene (G@Si@G) sandwich-like films. When used as negative electrode materials for lithium-ion batteries, it exhibits superior lithium-ion storage performance (∼1800 mA h g(-1) after 40 cycles at 100 mA g(-1)). Importantly, with this simple and general method, we also successfully synthesized graphene/Fe2O3/graphene and graphene/TiO2/graphene hybrid films, showing improved electrochemical performance. The good electrochemical property results from the enhanced electron transport rate, and the 3D flexible matrix to buffer volume changes during cycling. In addition, the porous sandwich structure consisting of plate-like graphene with high surface area provides effective electrolyte infiltration and promotes diffusion rate of Li(+), leading to an improved rate capability.

Phosphorus-doped porous carbon derived from rice husk as anode for lithium ion batteries

We developed a simple and scalable chemical method to obtain phosphorus-doped porous carbon (P-PC–RH) by optimized acid treatment and thermal annealing of rice husk with triphenylphosphine (TPP). After doping with phosphorus (doping level of ∼4.14 at% P), the P-PC–RH electrode increases by almost half the reversible capacity (757 mA h g−1 after 100 cycles at 100 mA g−1) of porous carbon without phosphorus doping (PC–RH-x, x = 2, 4, 6). When cycled at a high current of 2000 mA g−1, it still delivers a reversible specific capacity of 382 mA h g−1. The improved electrochemical performance of P-PC–RH is attributed to the synergetic effect of the 3D interconnected porous structure and phosphorus doping, which can maintain perfect electrical conductivity throughout the electrode and enhance electrochemical activities for lithium storage.

Highly reversible lithium storage in a 3D macroporous Ge@C composite

A porous Ge@C composite was synthesized by magnesiothermic reduction reaction of GeO2, Mg powder and glucose followed by an etching process with HCl solution. Compared to a porous Ge electrode, the porous Ge@C composite electrode delivers better cycling stability (∼100% capacity retention after 100 cycles at the 0.2 C rate) and higher rate capability (440 mA h g−1 at 1800 mA g−1). The improved electrochemical performance results from the synergistic effect of the 3D interconnected porous structure and the carbon shells. The local pores could buffer the volume change and the conductive carbon shell could prevent the aggregation of Ge as well as enhance the electronic conductivity of the whole electrode.

Facile synthesis of germanium–reduced graphene oxide composite as anode for high performance lithium-ion batteries

Germanium is a promising anode material for lithium ion batteries (LIBs) due to its high specific capacity, but it still suffers from poor cyclability. A simple method was developed to synthesize Ge–reduced graphene oxide nanocomposites using organic germanium as a precursor. The nanocomposites exhibit improved electrochemical performance with a reversible specific capacity of 814 mA h g−1 after 50 cycles at a current density of 0.1 A g−1. When cycled at a high current density of 2 A g−1, they still deliver a reversible specific capacity of 690 mA h g−1 after 150 cycles. The improved electrochemical performance is attributed to the unique nanostructure (0D electroactive particles in 2D mixed conducting matrix), which conferred a variety of advantages: high flexibility of the graphene sheets for accommodating the volume change, good electrochemical coupling and short transport length for ions and electrons, enabling low contact resistances.

Anchoring Nitrogen‐doped TiO2 Nanocrystals on Nitrogen‐doped 3D Graphene Frameworks for Enhanced Lithium Storage

An advanced architecture design of nitrogen-doped TiO2 anchored on nitrogen-doped 3D graphene framework composites (denoted as N-TiO2 /N-3D GFs) have been fabricated by a facile template process and further NH3 treatment. The 3D graphene framework allows the electrolyte to penetrate into the inverse opal structure, and possesses high electronic conductivity. The close contact between the N-TiO2 and the graphene suppresses the growth and aggregation of TiO2 nanoparticles during heating process, leading to decreased Li+ diffusion length. The N-doping in both TiO2 and the graphene matrix could improve the electronic conductivity on the TiO2 particle surface and between adjacent particles. As expected, when used as an anode for Li-ion batteries (LIBs), the N-TiO2 /N-3D GFs composite delivers an excellent reversible capacity of 165 mA h g-1 after 200 cycles at 100 mA g-1 and an outstanding rate capability of 114 mA h g-1 after 1000 cycles at 1 Ag-1 . With rational design, this strategy could be extended to other electrode materials that may hold great promise for the development of high energy storage systems.

Germanium encapsulated in sulfur and nitrogen co-doped 3D porous carbon as an ultra-long-cycle life anode for lithium ion batteries

Germanium (Ge) has been considered as a promising anode material for Li-ion batteries because of its theoretical capacity (1600 mA h g−1). However, its poor electrochemical performances resulting from the large volume variation during Li–Ge alloy/dealloy processes prevent its practical application. Herein, we designed a 3D core/shell structure by encapsulation of Ge in a sulfur (S) and nitrogen (N) co-doped three-dimensionally (3D) interconnected macroporous carbon matrix (denoted as Ge@S,N-3DPC). The 3D porous structure can not only buffer the volume change during alloy/dealloy processes, but also facilitate the electrolyte to soak in, offering fast ion/electron pathways. Whats more, the co-doping of S and N in carbon could introduce more defects and active sites, which can also help to improve the interfacial adsorption and electrochemical behaviors. When used as an anode material for LIBs, the Ge@S,N-3DPC shows excellent electrochemical performances (1000 mA h g−1 at 200 mA g−1), outstanding cycling stability (94% capacity retention after 300 cycles) and high rate capability (358 mA h g−1 at 10 A g−1). This work develops a general strategy to improve the electrochemical performance of these alloy-type electrode materials with huge volume change in the energy storage area.

Energy Storage: Nitrogen-Doped Ordered Mesoporous Anatase TiO2 Nanofibers as Anode Materials for High Performance Sodium-Ion Batteries (Small 26/2016).

On page 3522, Y. Yu and co-workers fabricate nitrogen-doped ordered mesoporous TiO2 nanofibers (denoted as N-MTO) by electrospinning and subsequent nitridation treatment. Nitrogen atoms are successfully doped into the TiO2 lattice, accompanied by the formation of Ti(3+) and oxygen vacancies, contributing to the improvement of electronic conductivity of TiO2 . When used as an anode for a sodium-ion battery, the N-MTO demonstrates excellent rate capability and superior long cycling performance.