Lithiation and Delithiation of Silicon Oxycarbide Single Particles with a Unique Microstructure

Single particles (11 and 13 mu m diameter) of a silicon oxycarbide (Si-O-C) glass were electrochemically analyzed using a microelectrode technique. A micromanipulator-guided nickel-plated rhodium-platinum microfilament (25 mu m diameter, 13 wt % rhodium) was used to maintain electrical contact to a single Si-O-C glass particle in an organic solution containing 1 mol dm(-3) LiClO(4). The cyclic voltammograms of a single Si-O-C glass particle (11 mu m diameter) featured a characteristic sharp peak at ca. 0.1 V vs Li/Li(+), along with a broad peak and a shoulder, in the anodic reaction. This result indicates that there are several electrochemically active sites for lithium storage in the single Si-O-C glass particle. The first lithiation and delithiation capacities of a single Si-O-C glass particle (13 mu m diameter) were 1.67 nA h and 1.12 nAh, respectively, at 5 nA (4C rate) in the potential range 0.01-2.5 V vs Li/Li(+), leading to a Coulombic efficiency of 67%. These results are in good agreement with those observed in typical porous composite electrodes. The 13 mu m diameter particle gives 75% of the full-delithiation capacity even at 100 nA (80C rate), demonstrating that its intrinsic delithiation rate capability is suitable for practical purposes. Assuming that the Tafel equation is applicable to the delithiation of the single Si-O-C glass particle, the charge-transfer resistance tended to increase as lithium was released.