Controlling the morphology of nanostructured silicon is critical to improving the structural stability and electrochemical performance in lithium-ion batteries. The use of removable or sacrificial templates is an effective and easy route to synthesize hollow materials. Herein, we demonstrate the synthesis of mesoporous silicon hollow nanocubes (m-Si HCs) derived from a metal-organic framework (MOF) as an anode material with outstanding electrochemical properties. The m-Si HC architecture with the mesoporous external shell (∼15 nm) and internal void (∼60 nm) can effectively accommodate volume variations and relieve diffusion-induced stress/strain during repeated cycling. In addition, this cube architecture provides a high electrolyte contact area because of the exposed active site, which can promote the transportation of Li ions. The well-designed m-Si HC with carbon coating delivers a high reversible capacity of 1728 mAhg with an initial Coulombic efficiency of 80.1% after the first cycle and an excellent rate capability of >1050 mAhg even at a 15 C-rate. In particular, the m-Si HC anode effectively suppresses electrode swelling to ∼47% after 100 cycles and exhibits outstanding cycle stability of 850 mAhg after 800 cycles at a 1 C-rate. Moreover, a full cell (2.9 mAhcm) comprising a m-Si HC-graphite anode and LiCoO cathode exhibits remarkable cycle retention of 72% after 100 cycles at a 0.2 C-rate.

High-theoretical capacity and low working potential make silicon ideal anode for lithium ion batteries. However, the large volume change of silicon upon lithiation/delithiation poses a critical challenge for stable battery operations. Here, we introduce an unprecedented design, which takes advantage of large deformation and ensures the structural stability of the material by developing a two-dimensional silicon nanosheet coated with a thin carbon layer. During electrochemical cycling, this carbon coated silicon nanosheet exhibits unique deformation patterns, featuring accommodation of deformation in the thickness direction upon lithiation, while forming ripples upon delithiation, as demonstrated by in situ transmission electron microscopy observation and chemomechanical simulation. The ripple formation presents a unique mechanism for releasing the cycling induced stress, rendering the electrode much more stable and durable than the uncoated counterparts. This work demonstrates a general principle as how to take the advantage of the large deformation materials for designing high capacity electrode.

Nanostructured micrometer-sized Al-Si particles are synthesized via a facile selective etching process of Al-Si alloy powder. Subsequent thin Al2O3 layers are introduced on the Si foam surface via a selective thermal wet oxidation process of etched Al-Si particles. The resulting Si/Al2O3 foam anodes exhibit outstanding cycling stability (a capacity retention of 78% after 300 cycles at the C/5 rate) and excellent rate capability.

No abstract

X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometer (SSIMS) have been applied to characterize Si(111) surface treated with 40% NH4F solution. As-treated Si(111) surface is predominately terminated with monohydrides and free of contamination. The dynamics of etching process on ultra-clean atomically flat hydrogen-terminated Si(111) surface in 40% NH4F solution has been examined at various potentials including the open circuit potential (OCP) by using in situ electrochemical scanning tunneling microscopy (ECSTM). Two distinct mechanisms are observed:  (1) dihydride terminated step silicon atoms are dissolved much faster than the defect-free monohydride terminated ones; (2) dihydrides in the corner of {110} zigzag enclosed characteristic triangular pits lead to fast erosion of silicon atoms. Our results explain dynamic mechanics in formation of triangular pits on atomically flat silicon (111) surface in solution.

The electrochemical performance of Li-ion batteries (LIBs) can be highly tuned by various factors including the morphology of the anode material, the nature of the electrolyte, the binding material, and the percentage of conducting materials. Binding materials have been of particular interest to researchers over the decades as a means to further improve the cycle durability and columbic efficiency of LIBs. Such approaches include the introduction of different polymeric binders such as poly(acrylic acid) (PAA), carboxymethyl cellulose (CMC), and alginic acid (Alg) into the Si anode of LIBs. To achieve a better efficiency of LIBs, herein, we introduce a novel copolymer, poly(tert-butyl acrylate-co-triethoxyvinylsilane) (TBA-TEVS), as an efficient binder with stable cycle retention and excellent specific capacity. The binder forms a highly interconnected three-dimensional network upon thermal treatment as a result of de-protection of the tert-butyl group and the consequent inter-intra condensation reaction, which minimizes pulverization of the Si nanoparticles. Moreover, the siloxane group is expected to promote the formation of stable solid-electrolyte-interface (SEI) layers. A series of random copolymers were synthesized by varying the molar ratio of tert-butyl acrylate and triethoxyvinylsilane. Twenty-one percent of TEVS in the TBS-TEVS copolymer gave rise to a superior performance as a binder for Si anodes, where the anodes showed a stable specific capacity of 2551 mA h g(-1) over hundreds of cycles and an initial columbic efficiency (ICE) of 81.8%.

We demonstrate a simple but straightforward process for the synthesis of nanotube-type Si-based multicomponents by combining a coaxial electrospinning technique and subsequent metallothermic reduction reaction. Si-based multicomponent anodes consisting of Si, alumina and titanium silicide show several advantages for high-performance lithium-ion batteries. Alumina and titanium silicide, which have high mechanical properties, act as an effective buffer layer for the large volume change of Si, resulting in outstanding volume suppression behavior (volume expansion of only 14%). Moreover, electrically conductive titanium silicide layers located at the inner and outer layers of a Si nanotube exhibit a high initial coulombic efficiency of 88.5% and an extraordinary rate capability. Nanotubular structured Si-based multicomponents with mechanically and electrically improved components can be used as a promising alternative to conventional graphite anode materials. This synthetic route can be extended to other high capacity lithium-ion battery anode materials.

We synthesize Si foam particles via magnesiothermic reduction of silica foam. Three effective strategies, like control of the calcination conditions of silica foam, introduction of a heat scavenger and doping of electrically conductive layers, lead to significant improvement of the electrochemical properties of the Si foam anodes.