The nanostructure of nickel oxide was controlled using two different synthesis methods and its influence on cyclability, charge/discharge capacity and mass transport of Li+ ions at the Li-ion battery anode was examined. Effective diffusion coefficients were calculated using the current pulse relaxation technique and a new model was derived and applied to deconvolute the mass transport of Li+ through the NiO and Li2O+Ni phases. The NiO phase diffusion coefficients were found to be independent of the material geometry; however, the diffusion coefficient of Li+ in the Li2O+Ni phase was strongly dependent on the electrode geometry. Results suggest that controlled nanosized crystallites of NiO are preferred as they result in smaller average grain boundary sizes for the Li2O+Ni phase formed during cell charging. This has several benefits including better accessibility of the Li2O+Ni phase during discharge, yielding improved cycle life, a decreased Li+ path length leading to lower tortuosity and a larger grain boundary area allowing more in-plane Li+ transport.