Oxygen framework reconstruction by LiAlH4 treatment enabling stable cycling of high-voltage LiCoO2

LiCoO2 with a cut-off voltage of 4.6 V (versus Li/Li+) could increase by about 28% of energy density compared with the commercial 4.45 V LiCoO2 cathode. However, severe issues such as oxygen evolution and dramatic phase transition strangle the practical application of 4.6 V LiCoO2. We herein develop a one-step wet chemical coating method at room temperature to stabilize the interface of LiCoO2 under high voltage. Through the treatment of LiCoO2 particles by LiAlH4 solution, the oxygen framework of the surface was reconstructed forming a composite coating layer which is featured a morphology with an inside-out transition structure from order to disorder. Benifited from the Al-containing composite layer, an excellent cycling performance has been obtained on the treated commerical samples, delivering a capacity retention of 70.4% even after 1000 cycles. The key to the improvement of electrochemical performance is to restrain the loss of lattice oxygen which is further elucidated by the results from differential electrochemical mass spectroscopy (DEMS). The interface evolution in different depths was carefully investigated delineating the relationship between the fluorated interface and the enhanced performance. Since the introduction of aluminum hydroxide, it facilitates the capture of F- bringing the interface layer from oxide to more stable fluoride during the cycling. Combining with the first principles calculation results, the aluminum coating surface suppresses the evolution of surfacial oxygen confirmed by oxygen release energy, and the optimized models infer that the fluorinated layer can obviously stabilize the interface structure of LiCoO2. This study provides a direct coating method which confers a notable improvement on cycling stability of LiCoO2 under high voltage and enables the implementation of high energy storage applications.

Automated summary

By developing a one-step wet chemical coating method at room temperature, this study successfully stabilizes the interface of LiCoO2 under high voltage and achieves excellent cycling performance. The treated commercial samples show a capacity retention of 70.4% even after 1000 cycles. The key to the improvement in electrochemical performance lies in restraining the loss of lattice oxygen, which is effectively achieved by the Al-containing composite layer that stabilizes the interface structure of LiCoO2.