P-type binary copper oxide semiconductor films for various O₂ flow rates and total pressures (P_t) were prepared using the reactive magnetron sputtering method. Their morphologies and structures were detected by X-ray diffraction, Raman spectrometry, and SEM. A phase diagram with Cu₂O, Cu₄O₃, CuO, and their mixture was established. Moreover, based on Kelvin Probe Force Microscopy (KPFM) and conductive AFM (C-AFM), by measuring the contact potential difference (V_CPD) and the field emission property, the work function and the carrier concentration were obtained, which can be used to distinguish the different types of copper oxide states. The band gaps of the Cu₂O, Cu₄O₃, and CuO thin films were observed to be (2.51 ± 0.02) eV, (1.65 ± 0.1) eV, and (1.42 ± 0.01) eV, respectively. The resistivities of Cu₂O, Cu₄O₃, and CuO thin films are (3.7 ± 0.3) × 10³ Ω·cm, (1.1 ± 0.3) × 10³ Ω·cm, and (1.6 ± 6) × 10¹ Ω·cm, respectively. All the measured results above are consistent.

In this paper, we adopt first-principles calculations based on density functional theory and kinetic Monte Carlo simulations to investigate the adsorption and diffusion of lithium in bilayer graphene (BLG) as anodes in lithium-ion batteries. Based on energy barriers directly obtained from first-principles calculations for single-Li and two-Li intercalated BLG, a new equation was deduced for predicting energy barriers considering ${\mathrm{Li}}^{{}^{\prime }}\mathrm{s}$ interactions for multi-Li intercalated BLG. Our calculated results indicate that Li energetically prefers to intercalate within rather than adsorb outside the BLG. Additionally, lithium exists in a cationic state in the BLG. More excitingly, ultrafast Li diffusion coefficient ($\sim {10}^{-5}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) within AB-stacked BLG near room temperature was obtained, which reproduces the ultrafast Li diffusion coefficient measured in recent experiment. However, ultrafast Li diffusion was not found within AA-stacked BLG near room temperature. The analyses of potential distribution indicate that the stacking structure of BLG greatly affects its height of potential well within BLG, which directly leads to the large difference in Li diffusion. Furthermore, it is found that both the interaction among Li ions and the stacking structure cause Li diffusion within AB-stacked BLG to exhibit directional preference. Finally, the temperature dependence of Li diffusion is described by the Arrhenius law. These findings suggest that the stacking structure of BLG has an important influence on Li diffusion within BLG, and changing the stacking structure of BLG is one possible way to greatly improve Li diffusion rate within BLG. At last, it is suggested that AB-stacked BLG can be regarded as an excellent candidate for anode material in lithium-ion batteries.

The Li⁺ diffusion coefficients in Li⁺-adsorbed graphene systems were determined by combining first-principle calculations based on density functional theory with Kinetic Monte Carlo simulations. The calculated results indicate that the interactions between Li ions have a very important influence on lithium diffusion. Based on energy barriers directly obtained from first-principle calculations for single-Li⁺ and two-Li⁺ adsorbed systems, a new equation predicting energy barriers with more than two Li ions was deduced. Furthermore, it is found that the temperature dependence of Li⁺ diffusion coefficients fits well to the Arrhenius equation, rather than meeting the equation from electrochemical impedance spectroscopy applied to estimate experimental diffusion coefficients. Moreover, the calculated results also reveal that Li⁺ concentration dependence of diffusion coefficients roughly fits to the equation from electrochemical impedance spectroscopy in a low concentration region; however, it seriously deviates from the equation in a high concentration region. So, the equation from electrochemical impedance spectroscopy technique could not be simply used to estimate the Li⁺ diffusion coefficient for all Li⁺-adsorbed graphene systems with various Li⁺ concentrations. Our work suggests that interactions between Li ions, and among Li ion and host atoms will influence the Li⁺ diffusion, which determines that the Li⁺ intercalation dependence of Li⁺ diffusion coefficient should be changed and complex.

Intercalation of lithium in few-layer phosphorene has aroused great concern because of the prospects of few-layer phosphorene as an anode material for high-performance lithium-ion batteries (LIBs). In this paper, we adopt first-principles calculations to explore in detail the effects of stacking structure of bilayer black phosphorene (BBP) on the adsorption and diffusion of lithium in BBP. Our calculated results indicate that Li energetically prefers to intercalate within rather than adsorb outside BBP, and it exists in a cationic state. Moreover, the stacking structure of BBP has very important effects on Li adsorption, the open-circuit voltage, and Li diffusion in BBP. Additionally, Li diffusion in BBP exhibits directional preference, with diffusing along the zigzag direction being easier. The analyses of the potential distribution indicate that the puckered honeycomb structure of monolayer phosphorene and the stacking structure of BBP greatly cause low-potential channels along the zigzag direction, which directly lead to the directional preference in Li diffusion. More interestingly, our results suggest that BBP with AC stacking is the most beneficial for Li adsorption and diffusion. These findings suggest that changing the stacking structure of BBP is one possible way to rationally design the anode material in high charge/discharge rate LIBs based on BBP.