Conducting nitrogen-incorporated ultrananocrystalline diamond coating for highly structural stable anode materials in lithium ion battery

In lithium ion battery (LIB), the structural changes and degradation of electrode materials during intercalation/deintercalation, leading to reversible capacity loss and short cycle life, have plagued LIB from advancing forward. In order to overcome these hurdles, a novel conducting nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) is proposed to coat on the model electrode material of natural graphite (NG) by microwave plasma-enhanced chemical vapor deposition (MPCVD), demonstrates the superior improvement on electrode stability. The electrochemical results of the N-UNCD coated NG anode reveal excellent cyclability, rate capability and conductivity over a hundred cycles as compared to the pristine NG. Furthermore, the underlying high structural stability of the N-UNCD coating for the anode material and the failure mechanism of the pristine NG anode is fully elucidated by combining diffraction and imaging techniques based on in-situ synchrotron X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM). These results show that the amorphization of NG originates from the accumulation of internal stress by periodic volume changes, which leads to mechanical fading with loss of strength and toughness. However, the N-UNCD film serves as a strong buffer layer to accommodate the volume changes, and also maintains the mechanical integrity of the pristine anode by suppressing from the continuous damage and the thickening of the solid electrolyte interphase during charging/discharging. Optimally, our investigations systematically explain the failure mechanism of the pristine anode and shed light on constructing a high capability and long cycle N-UNCD coated anode for LIBs.