It is reported that silicon (Si) anodes with a smaller crystallite size show better electrochemical performance in lithium‐ion batteries (LIBs); Si particles with different diameters are also used. However, it is yet to be clarified whether the better performance is attributed to crystallite size or particle diameter. The effect of Si crystallite size on its anode performance using Si particles having the same diameter and different crystallite sizes is investigated. Longer cycle life is obtained for smaller crystallite size, due to the small amount of the amorphous Li‐rich Li—Si phase formed during charging. The phase is likely to form in a greater amount in Si particles with larger crystallite size, leading to degradation of the Si electrode at an early stage. Furthermore, Si electrodes with larger crystallite size show superior rate performance because of the high Li diffusion rate into the broader grain boundary; on the other hand, Si with smaller crystallite size should limit Li diffusion due to the narrower grain boundary. Therefore, smaller crystallite size helps improve the cycle life but deteriorates the rate performance of LIBs.
Silicides are attractive novel active
materials for use in the
negative-electrodes of next-generation lithium-ion batteries that
use certain ionic-liquid electrolytes; however, the reaction mechanism
of the above combination is yet to be clarified. Possible reactions
at the silicide electrode are as follows: deposition and dissolution
of Li metal on the electrode, lithiation and delithiation of Si, which
would result from the phase separation of the silicide, and alloying
and dealloying of the silicide with Li. Herein, we examined these
possibilities using various analysis methods. The results revealed
that the lithiation and delithiation of silicide occurred.
Lithium-ion batteries
are used in various extreme environments,
such as cold regions and outer space; thus, improvements in energy
density, safety, and cycle life in these environments are urgently
required. We investigated changes in the charge and discharge properties
of Si-based electrodes in ionic liquid electrolytes with decreasing
temperature and the cycle life at low temperature. The reversible
capacity at low temperature was determined by the properties of the
surface film on the electrodes and/or the ionic conductivity of the
electrolytes. The electrode coated with a surface film formed at a
low temperature exhibited insufficient capacity. In contrast, a Si-only
electrode precoated with the surface film at room temperature exhibited
a cycle life at low temperatures in ionic liquid electrolytes longer
than that in conventional organic liquid electrolytes. Doping phosphorus
into Si led to improved cycling performance, and its impact was more
noticeable at lower temperatures.
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