In Situ X-ray Diffraction of LiCoO2 in Thin-Film Batteries under High-Voltage Charging

LiCoO2 has been used as the cathode material employed in lithium-ion batteries since their development, and efforts to improve its performance are still in progress. For example, complete use of lithium provides a theoretical capacity as high as 274 mAh g(-1); however, charge-discharge cycling with such a high capacity leads to rapid degradation. The degradation mechanism has been intensively studied in order to increase the practical capacity. Although phase transitions taking place in high-voltage charging have been considered to affect the cycling performance, side reactions induced by the high-voltage charging always overlap to blur the effects of phase transitions on the electrode properties. This study has unveiled the relation between the phase transition and electrode properties by employing a solid electrolyte that suppresses the side reactions efficiently. Electrochemical impedance spectroscopy combined with in situ X-ray diffraction shows clear correlation between phase transition from O-3 to H1-3 and a drastic increase in the electrode resistance. The increasing resistance is attributable to formation of narrow interlayers with a gallery height of 4.2 angstrom that impede lithium-ion diffusion.

Automated summary

LiCoO2 is commonly used as the cathode material in lithium-ion batteries due to its high theoretical capacity, but degradation occurs with high capacity cycling. This study has shed light on the relationship between phase transitions and electrode properties, aiding the improvement of battery performance.