Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and {001} planes, and octahedra with exposed {111}planes - is synthesized using a very simple one-step hydrothermal method. The three kinds of Co(3)O(4) exhibit significantly different electrochemical performances and the effect of different exposed crystal planes on the electrochemical performance of Co(3)O(4) is comprehensively studied.

Decreasing Li/Ni disorder has been a challenging problem for layered oxide materials, where disorder seriously restricts their electrochemical performances for lithium-ion batteries (LIBs). Element doping is a great strategy that has been widely used to stabilize the structure of the cathode material of an LIB and improve its electrochemical performance. On the basis of the results of previous studies, we hypothesized that the element of Ca, which has a lower valence state and larger radius compared to Ni, would be an ideal doping element to decrease the Li/Ni disorder of LiMO materials and enhance their electrochemical performances. A Ni-rich LiNiMnCoO cathode material was selected as the bare material, which usually shows severe Li/Ni disorder and serious capacity attenuation at a high cutoff voltage. So, a series of Ca-doped LiNiCoMnCaO (x = 0-8%) samples were synthesized by a traditional solid-state method. As hypothesized, neutron diffraction showed that Ca-doped LiNiCoMnO possessed a lower degree of Li/Ni disorder, and potentiostatic intermittent titration results showed a faster diffusion coefficient of Li compared with that of LiNiMnCoO. The Ca-doped LiNiMnCoO samples exhibited higher discharge capacities and better cycle stabilities and rate capabilities, especially under a high cutoff voltage with 4.5 V. In addition, the problems of polarization and voltage reduction of LiNiMnCoO were also alleviated by doping with Ca. More importantly, we infer that it is crucial to choose an appropriate doping element and our findings will help in the research of other layered oxide materials.

The facet-dependent performance has aroused great interest in the fields of catalyst, lithium ion battery and electrochemical sensor. In this study, the well-defined Co 3 O 4 cubes with exposed (001) plane and octahedrons with exposed (111) plane have been successfully synthesized and the facet-dependent electrocatalytic performance of Co 3 O 4 for rechargeable Li−O 2 battery has been comprehensively investigated by the combination of experiments and theoretical calculations. The Li−O 2 battery cathode catalyzed by Co 3 O 4 octahedron with exposed (111) plane shows much higher specific capacity, cycling performance, and rate capability than Co 3 O 4 cube with exposed (001) plane, which may be largely attributed to the richer Co 2+ and more active sites on (111) plane of Co 3 O 4 octahedrons. The DFT-based first-principles calculations further indicate that Co 3 O 4 (111) has a lower activation barrier of O 2 desorption in oxygen evolution reaction (OER) than Co 3 O 4 (001), which is very important to refresh active sites of catalyst and generate a better cyclic performance. Also, our calculations indicate that Co 3 O 4 (111) surface has a stronger absorption ability for Li 2 O 2 than Co 3 O 4 (001), which may be an explanation for a larger initial capacity in Co 3 O 4 (111) plane by experimental observation.

Lithium-rich Li(1.13)Ni(0.30)Mn(0.57)O2 has been functionally modified with fast Li(+)-ion conducting Li2SiO3via a facile and novel method, based on the reaction between Ni(0.35)Mn(0.65)C2O4·xH2O and Si(OC2H5)4. Due to the unique Li2SiO3 coating layer which greatly improves the Li(+) ion diffusion rate, Li2SiO3@Li(1.13)Ni(0.30)Mn(0.57)O2 exhibits outstanding rate capability, cycle stability and low polarization.