The Li[Li 0.23 Co 0.3 Mn 0.47 ]O 2 cathode material was prepared by a sol-gel method. Combinative X-ray diffraction (XRD) and Raman scattering studies showed that the material was a solid solution rather than a composite of nano Li 2 MnO 3 and LiCoO 2 . The material had a high discharge capacity of 250 mAh g -1 in the voltage window of 2.0-4.8 V. However, the capacity retention was poor. The material showed different electrochemical mechanisms in the first charge and subsequent cycles. Galvanostatic intermittent titration technique (GITT) study showed that the Li + diffusion coefficients during the first charge were as small as 10 -19 cm 2 s -1 because of the high kinetic barriers associated with the concurrent Li + extraction, oxygen loss, and structural rearrangement. The Li + diffusion coefficients increased to 10 -14 cm 2 s -1 after the first charge. However, they were still much smaller than those of typical layered materials such as LiCoO 2 and Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 . Electrochemical impedance spectroscopy (EIS) study showed that the large interface impedance at high potential seriously hindered the electrode performance of the material. A lower charge cutoff voltage of 4.6 V was the most suitable for this material considering that the correponding reversible capacity (∼200 mAh g -1 ) was attractive for high energy density lithium ion batteries.

We present first-principles calculations of silicene/graphene and germanene/graphene bilayers. Various supercell models are constructed in the calculations in order to reduce the strain of the lattice-mismatched bilayer systems. Our energetics analysis and electronic structure results suggest that graphene can be used as a substrate to synthesize monolayer silicene and germanene. Multiple phases of single crystalline silicene and germanene with different orientations relative to the substrate could coexist at room temperature. The weak interaction between the overlayer and the substrate preserves the low-buckled structure of silicene and germanene, as well as their linear energy bands. The gap induced by breaking the sublattice symmetry in silicene on graphene can be up to 57 meV.

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A carbon-coated MgTi(PO) polyanion material was prepared by the sol-gel method and then studied as the negative electrode materials for lithium-ion and sodium-ion batteries. The material showed a specific capacity of 268.6 mAh g in the voltage window of 0.01-3.0 V vs Na/Na. Due to the fast diffusion of Na in the NASICON framework, the material exhibited superior rate capability with a specific capacity of 94.4 mAh g at a current density of 5A g. Additionally, 99.1% capacity retention was achieved after 300 cycles, demonstrating excellent cycle stability. By comparison, MgTi(PO) delivered 629.2 mAh g in 0.01-3.0 V vs Li/Li, much higher than that of the sodium-ion cells. During the first discharge, the material decomposed to Ti/Mg nanoparticles, which were encapsulated in an amorphous SEI and LiPO matrix. Li ions were stored in the LiPO matrix and the SEI film formed/decomposed in subsequent cycles, contributing to the large Li capacity of MgTi(PO). However, the lithium-ion cells exhibited inferior rate capability and cycle stability compared to the sodium-ion cells due to the sluggish electrochemical kinetics of the electrode.