Xiao-Liang Wang

Amorphous Hierarchical Porous GeOx as High-Capacity Anodes for Li Ion Batteries with Very Long Cycling Life

Many researchers have focused in recent years on resolving the crucial problem of capacity fading in Li ion batteries when carbon anodes are replaced by other group-IV elements (Si, Ge, Sn) with much higher capacities. Some progress was achieved by using different nanostructures (mainly carbon coatings), with which the cycle numbers reached 100-200. However, obtaining longer stability via a simple process remains challenging. Here we demonstrate that a nanostructure of amorphous hierarchical porous GeO(x) whose primary particles are ~3.7 nm diameter has a very stable capacity of ~1250 mA h g(-1) for 600 cycles. Furthermore, we show that a full cell coupled with a Li(NiCoMn)(1/3)O(2) cathode exhibits high performance.

Graphene Enhances Li Storage Capacity of Porous Single-Crystalline Silicon Nanowires

We demonstrated that graphene significantly enhances the reversible capacity of porous silicon nanowires used as the anode in Li-ion batteries. We prepared our experimental nanomaterials, viz., graphene and porous single-crystalline silicon nanowires, respectively, using a liquid-phase graphite exfoliation method and an electroless HF/AgNO3 etching process. The Si porous nanowire/graphene electrode realized a charge capacity of 2470 mAh g(-1) that is much higher than the 1256 mAh g(-1) of porous Si nanowire/C-black electrode and 6.6 times the theoretical capacity of commercial graphite. This relatively high capacity could originate from the favorable charge-transportation characteristics of the combination of graphene with the porous Si 1D nanostructure.

Single-Crystal Intermetallic M-Sn (M = Fe, Cu, Co, Ni) Nanospheres as Negative Electrodes for Lithium-Ion Batteries

FeSn(2), Cu(6)Sn(5), CoSn(3), and Ni(3)Sn(4) single-crystalline nanospheres with a characteristic uniform particle size of approximately 40 nm have been synthesized via a modified polyol process, aiming at determining and understanding their intrinsic cycling performance as negative electrode materials for lithium-ion batteries. We find that, in this morphologically controlled condition, the reversible capacities follow FeSn(2) > Cu(6)Sn(5) approximately CoSn(3) > Ni(3)Sn(4), which is not directly decided by their theoretical capacities or lithium-driven volume changes. FeSn(2) exhibits the best electrochemical activity among these intermetallic nanospheres and an effective solid electrolyte interface, which explains its superior cycling performance. The small particle dimension also improves cycling stability and Li(+) diffusion.

Recent Advances in Inorganic Solid Electrolytes for Lithium Batteries

The review presents an overview of the recent advances in inorganic solid lithium ion conductors, which are of great interest as solid electrolytes in all-solid-state lithium batteries. It is focused on two major categories: crystalline electrolytes and glass-based electrolytes. Important systems such as thio-LISICON Li10SnP2S12, garnet Li7La3Zr2O12, perovskite Li3xLa(2/3)-xTiO3, NASICON Li1.3Al0.3Ti1.7(PO4)3 and glass-ceramic xLi2S•(1-x)P2S5 and their progress are described in great detail. Meanwhile, the review discusses different on-going strategies on enhancing conductivity, optimizing electrolyte/electrode interface and improving cell performance.

Nanospheres of a New Intermetallic FeSn5 Phase: Synthesis, Magnetic Properties and Anode Performance in Li-ion Batteries

We synthesized monodisperse nanospheres of an intermetallic FeSn(5) phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe(0.74)Sn(5) of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement. Importantly, FeSn(5), which is not yet established in the Fe-Sn phase diagram, exhibits a quasi-one dimensional crystal structure along the c-axis, thus leading to interesting anisotropic thermal expansion and magnetic properties. Magnetization measurements indicate that nanospheres are superparamagnetic above the blocking temperature T(B) = 300 K, which is associated with the higher magnetocrystalline anisotropy constant K = 3.33 kJ m(-3). The combination of the magnetization measurements and first-principles density functional theory calculations reveals the canted antiferromagnetic nature with significant spin fluctuation in lattice a-b plane. The low Fe concentration also leads Fe(0.74)Sn(5) to enhanced capacity as an anode in Li ion batteries.

CoSn5 Phase: Crystal Structure Resolving and Stable High Capacity as Anodes for Li Ion Batteries.

Tin alloys form a class of interesting high-energy-density anode materials for Li ion batteries, but the improvement of their cycling stability is elusive. Here, we provide new insight on this fatal issue by synthesizing novel CoSn5-phase nanospheres via a conversion chemistry route and directly comparing their cell behavior with that of recently found FeSn5-phase nanospheres. The CoSn5 phase is absent in previous Co-Sn phase diagrams. Co0.83Sn5 nanospheres show a much longer cycle life, which partially is related to milder evolution of their cycling profiles over time.

Carbon-coated Magnéli-phase TinO2n−1 nanobelts as anodes for Li-ion batteries and hybrid electrochemical cells

We describe a method for preparing carbon-coated Ti9O17 nanowires using H2Ti3O7 nanobelts as precursors to react with ethane and hydrogen at high-temperature. The carbon-coating layers play a key role in restraining the sintering growth of the core during the phase transformation from H2Ti3O7 to Magneli-phase TinO2n−1, and in retaining the morphology of nanobelts. We demonstrated that the initial reversible capacity of these Ti9O17 nanobelts attained 182u2002mAu2009hu2009g−1, a value even higher than the theoretical value of a-TiO2 (167u2002mAu2009hu2009g−1). Cyclic-voltammetry measurement supports the pseudocapacitive lithium-storage behavior of these Magneli-phase Ti9O17 nanobelts. Furthermore, the nanobelts exhibit high power density along with excellent cycling stability in their application as hybrid electrochemical cells.

The Development of Si and Ge-Based Nanomaterials for High Performance Lithium Ion Battery Anodes

Silicon and germanium are among the most promising anode materials for high performance lithium ion batteries, due to their unprecedented high capacities. In recent few years, increasingly enormous efforts have been dedicated to these two important anodes, leading to significant improvement in their cycling life, practical capacity, rate capability, and coulombic efficiency. Nanostructuring is playing a crucial role in enabling the improvement and will lead to their widespread use in various battery markets. Nanoscale particles can better tolerate the wild volume change upon cycling and maintain their integrity than micron-sized particles. They can also shorten the diffusion distance of lithium ions and electrons and thus have high capacity. Further, one-dimensional nanowires exhibit superior stress behavior and electron transport. Porous and hierarchical nanostructures can provide extra space to accommodate the volume change. Wisely manipulating these handles have produced impressively better-performing systems. Porous single-crystal silicon nanowires have shown more stable capacity than solid nanowires. Hierarchical porous amorphous (mathrm{{GeO}}_mathrm{x}) is another system with very long cycle life and high capacity.