Visualizing the roles of graphene for excellent lithium storage

Graphene has been extensively used in hybrid electrodes for its notable improvement of lithium storage properties. However, direct visualization of the roles of graphene and the origin for the enhancement at the nanoscale are highly inadequate, which are difficult to be obtained by ex situ methods. Here, we use in situ transmission electron microscopy to visualize the roles of graphene during lithiation using a NiO/graphene hybrid as a model material. We witness that graphene has three roles in a strong-coupled NiO/graphene hybrid: (1) it increases the Li+ diffusion rate by two orders of magnitude; (2) it strongly improves Li+ reaction kinetics with NiO at high current densities and facilitates the homogeneous lithiation of NiO; (3) it severely restricts the expansion of NiO near the interface, ensuring stable electrical contact between graphene and NiO during extended cycling. Combined with the electrochemical measurements and first-principles calculations, this study further verifies the interface-induced graphene enhancement and distinctly provides valuable insights for excellent lithium storage by constructing interfacial binding between graphene and active materials to make full use of graphene.