Li-ion battery materials: present and future

Nanostructured silicon is promising for high capacity anodes in lithium batteries. The specific capacity of silicon is an order of magnitude higher than that of conventional graphite anodes, but the large volume change of silicon during lithiation and delithiation and the resulting poor cyclability has prevented its commercial application. This challenge could potentially be overcome by silicon nanostructures that can provide facile strain relaxation to prevent electrode pulverization, maintain effective electrical contact, and have the additional benefits of short lithium diffusion distances and enhanced mass transport. In this review, we present an overview of rechargeable lithium batteries and the challenges and opportunities for silicon anodes, then survey the performance of various morphologies of nanostructured silicon (thin film, nanowires/nanotubes, nanoparticles, and mesoporous materials) and their nanocomposites. Other factors that affect the performance of nanostructured silicon anodes, including solvent composition, additives, binders, and substrates, are also examined. Finally, we summarize the key lessons from the successes so far and offer perspectives and future challenges to enable the applications of silicon nanoanodes in practical lithium batteries at large scale.

https://www.rsc.org/suppdata/EE/C0/C0EE00281J/C0EE00281J.PDF

Nanostructured silicon for high capacity lithium battery anodes

To utilize high-capacity Si anodes in next-generation Li-ion batteries, the physical and chemical transformations during the Li–Si reaction must be better understood. Here, in situ transmission electron microscopy is used to observe the lithiation/delithiation of amorphous Si nanospheres; amorphous Si is an important anode material that has been less studied than crystalline Si. Unexpectedly, the experiments reveal that the first lithiation occurs via a two-phase mechanism, which is contrary to previous understanding and has important consequences for mechanical stress evolution during lithiation. On the basis of kinetics measurements, this behavior is suggested to be due to the rate-limiting effect of Si–Si bond breaking. In addition, the results show that amorphous Si has more favorable kinetics and fracture behavior when reacting with Li than does crystalline Si, making it advantageous to use in battery electrodes. Amorphous spheres up to 870 nm in diameter do not fracture upon lithiation; this is much...

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In Situ TEM of Two-Phase Lithiation of Amorphous Silicon Nanospheres

Growing market demand for portable energy storage has triggered significant research on high-capacity lithium-ion (Li-ion) battery anodes. Various elements have been utilized in innovative structures to enable these anodes, which can potentially increase the energy density and decrease the cost of Li-ion batteries. In this review, electrode and material parameters are considered in anode fabrication. The periodic table is then used to explore how the choice of anode material affects rate performance, cycle stability, Li-ion insertion/extraction potentials, voltage hysteresis, volumetric and specific capacities, and other critical parameters. Silicon (Si), germanium (Ge), and tin (Sn) anodes receive more attention in literature and in this review, but other elements, such as antimony (Sb), lead (Pb), magnesium (Mg), aluminum (Al), gallium (Ga), phosphorus (P), arsenic (As), bismuth (Bi), and zinc (Zn) are also discussed. Among conversion anodes focus is placed on oxides, nitrides, phosphides, and hydrides. Nanostructured carbon (C) receives separate consideration. Issues in high- capacity research, such as volume change, insufficient coulombic efficiency, and solid electrolyte interphase (SEI) layer stability are elucidated. Finally, advanced carbon composites utilizing carbon nanotubes (CNT), graphene, and size preserving external shells are discussed, including high mass loading (thick) electrodes and electrodes capable of providing load-bearing properties.

High‐Capacity Anode Materials for Lithium‐Ion Batteries: Choice of Elements and Structures for Active Particles

In situ transmission electron microscopy (TEM) is used to study the electrochemical lithiation of high-capacity crystalline Si nanoparticles for use in Li-ion battery anodes. The lithiation reaction slows down as it progresses into the particle interior, and analysis suggests that this behavior is due not to diffusion limitation but instead to the influence of mechanical stress on the driving force for reaction.

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Y. X. Yao

Papers

Determination of the diffusion coefficient of lithium ions in nano-Si