2D single-crystalline LiCoO₂ nanosheets developed for high-performance battery-supercapacitor hybrid devices

A team led by Prof. Wu Zhongshuai has developed novel 2D atomically thin (001)-oriented single-crystalline LiCoO₂ nanosheets with longer Li⁺ intercalation distance and (001) planes dominated surface for high-performance battery-supercapacitor hybrid devices. This study was published in ACS Energy Letters.

Shorter Li⁺ intercalation distance or lower intercalation energy barrier enables fast diffusion in Li⁺ intercalation process. However, it has been found that nanosize effect in nanocrystalline LiCoO₂ affects surface-redox and Li⁺ intercalation processes simultaneously.

As the crystallite size decreases, more Li⁺ intercalation processes are replaced by surface-redox processes, which brings about decreased platform capacity, low initial coulombic efficiency, and poor cycle performance. Therefore, the nanosize effect restricts the application of nanostructured LiCoO₂ in "double high" battery-supercapacitor hybrid devices.

To solve this problem, Prof. Wu's team attempted to regulate the nanosize effect by precisely controlling the Li⁺ intercalation process and surface-redox process.

The team synthesized micro-sized atomically thin single-crystalline LCO nanosheets (SC-LCO) and nanocrystalline LCO nanosheets (NC-LCO).

Compared with NC-LCO, SC-LCO presented longer Li⁺ intercalation distance and decreased side reactions. Both coulombic efficiency and discharge capacity of SC-LCO at 1C (194 mAh g^-1, 92%) were higher than those of NC-LCO (173 mAh g^-1, 86%).

The specific capacity of SC-LCO maintained 151 mAh g^-1 (83%) after cycling for 500 cycles, which preceded NC-LCO (84 mAh g^-1, 63%).

Moreover, the team fabricated a battery-supercapacitor hybrid device with SC-LCO, which achieved high-energy and high-power, demonstrating the practical applicability of this nanosheets.