We report on the formation of composite silicon-based multiphase nanopowders as promising active-anode materials for highenergy-density, high-capacity-retention lithium-ion batteries. Simple synthetic routes have been developed for the preparation of core-shell Si and p-doped SiNi composite particles attached to carbon nanotubes. The particles were characterized by a variety of analytical and electrochemical methods. Environmental scanning-electron-microscopy and transmission-electron-microscopy images and electron-energy-loss-spectroscopy maps indicated formation of nanoparticles wrapped by carbon nanotubes and coated by nanometer-thick amorphous carbon. It was found that nickel diffuses to the bulk of silicon and forms either nickel-rich or nickel-depleted composite entities. The presence of boron in the synthesized composite powder has been detected by time-of-flight secondary-ion mass spectroscopy (TOFSIMS). Li/LiPF 6 EC:DEC/Si-C-MWCNT cells with anodes composed of about 80% coreshell Si-C composite (36% Si in the anode) ran for more than 1000 cycles with a degradation rate of 0.07%/cycle (beginning from cycle 25). The SiNi/MWCNT composite anode revealed a remarkably higher capacity-retention rate at initial cycles and higher C-rate capability. Li/SiNi/MWCNT cells ran for about 250 cycles demonstrating a reversible capacity of about 620 mAh/g Si at 120 μA/cm 2 and cycle 210, and 800 mAh/g Si at 50 μA/cm 2 at cycle 240. Given that lithium-ion batteries will be the preferred choice for EVs and plug-in applications for the next 10-15 years, the focus of research is on improving their safety and performance. New, highercapacity materials are required in order to address the need for greater energy density, longer cycle life and safer high-power operation. Silicon offers the highest gravimetric and volumetric capacity as an anode material (e.g. Li 22 Si 5 with nearly 4,200 mAh/g, 9,800 mAh/ml).1 The lithium-rich silicon compounds have high melting points. Their higher working potentials (vs. Li) eliminate the possibility of metallic-lithium deposition due to overcharge. Silicon is the second-most abundant element in the earth's crust, and it is environmentally benign.Unfortunately, silicon-based electrodes typically suffer from poor capacity retention. The capacity fade and large initial irreversible capacity of silicon anodes are caused by the extreme volume changes in silicon during lithiation/de-lithiation. This, in turn, causes a breakup of the electrode and electrical isolation of the active material. Volume expansion/contraction of silicon subjects its surface to a continuous reduction reaction of liquid electrolyte followed by the formation of a fresh solid electrolyte interphase (SEI). High irreversible capacity and poor faradaic efficiency (FE) arise from these phenomena. Tariq et al. presented, for the first time, in-operando tracking and 3D imaging of Si-electrode microstructure by X-ray tomography during lithiation. 2The lithiation-induced stress cracking was followed by electrodecurrent-collector del...

No abstract

We report here on the synthesis of SiNi-core carbon-shell nanoparticles and composite anodes reinforced by carbon nanotubes (CNTs). These anodes are inexpensive, environmentally friendly and easily scalable. The anodes can be synthesized by one-step pyrolysis of precursors dispersed in aqueous solutions without the use of hazardous HF acid. Carbon nanotubes (CNTs) are used as scaffolds both in the active anode powder and in the anode slurry, affording high electrical conductivity and high mechanical strength. The anodes exhibit capacities of over 1000mAh/ganode, for hundreds of cycles. The degradation mechanisms occurring on lithiation/delithiation of silicon-nickel nanocomposite anodes have been studied.

No abstract

No abstract