A comprehensive understanding of the charge/discharge behaviour of high-capacity anode active materials, e.g., Si and Li, is essential for the design and development of next-generation high-performance Li-based batteries. Here, we demonstrate the in situ scanning electron microscopy (in situ SEM) of Si anodes in a configuration analogous to actual lithium-ion batteries (LIBs) with an ionic liquid (IL) that is expected to be a functional LIB electrolyte in the future. We discovered that variations in the morphology of Si active materials during charge/discharge processes is strongly dependent on their size and shape. Even the diffusion of atomic Li into Si materials can be visualized using a back-scattering electron imaging technique. The electrode reactions were successfully recorded as video clips. This in situ SEM technique can simultaneously provide useful data on, for example, morphological variations and elemental distributions, as well as electrochemical data.
By exploiting characteristics such as negligible vapour pressure and ion-conductive nature of an ionic liquid (IL), we established an in situ scanning electron microscope (SEM) method to observe the electrode reaction in the IL-based Li-ion secondary battery (LIB). When 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide ([C2mim][FSA]) with lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) was used as the electrolyte, the Si negative electrode exhibited a clear morphology change during the charge process, without any solid electrolyte interphase (SEI) layer formation, while in the discharge process, the appearance was slightly changed, suggesting that a morphology change is irreversible in the charge-discharge process. On the other hand, the use of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][TFSA]) with Li[TFSA] did not induce a change in the Si negative electrode. It is interesting to note this distinct contrast, which could be attributed to SEI layer formation from the electrochemical breakdown of [C2mim](+) at the Si negative electrode|separator interface in the [C2mim][TFSA]-based LIB. This in situ SEM observation technique could reveal the effect of the IL species electron-microscopically on the Si negative electrode reaction.
Lithium manganate, LiMn 2 0 4 , applicable as a cathode material for lithium batteries has been synthesized by a redox mechanochemistry route. Gamma-Mn0 2 shows an excellent reaction ability with LiOH under grinding and the amorphous ground product can be crystallized to LiMn 2 0 4 at 400°C despite the requisition of the partial reduction of Mn0 2 to MnruMnrv0 5 • Contrary, Mn 2 0 3 shows a poor reactivity. The dissociation of the edge-sharing chains of Mn0 6-octahedra in yand ~-Mn0 2 and the increased reactivity of LiOH fused or activated under grinding is the proposed reaction mechanism. The ground products are slightly agglomerated by the moisture evolved from the hydroxide. However, the particle size can be controlled to be 300-500nm after the calcination at 800°C, when the grinding stress is limited not to be high. Unnecessarily high grinding stress induces the strong agglomeration to increase not only the size of agglomerates but the primary particle size. The synthesized LiMn 2 0 4 with the particle size of 3 70nm and the crystallite of 48nm provides the good cyclic charge-discharge characteristics, while the rechargeablity of LiMn 2 0 4 with 500nm and 68nm degrades within 3 cycles.
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