Black Phosphorus-Graphite Material Composites with a Low Activation Energy of Interfacial Conductivity

The reaction kinetics of electrochemical lithiation/delithiation in a composite consisting of black phosphorus and cup-stacked carbon nanotube (BP-CSCNT) were investigated. Two semicircles were observed in Nyquist plots at the high and low frequency regions, which were attributed to the resistance of lithium-ion transport through the surface film and the resistance of the alloying/dealloying reaction (charge-transfer resistance), respectively. The activation energy using the charge transfer reaction was evaluated from the temperature-dependence of the interfacial conductivity. Even with the use of ethylene carbonate-based and propylene carbonate electrolytes, the activation energy was calculated to be 25–26 kJ mol⁻¹, which is much smaller than that obtained with graphite electrodes and cathode materials. These results indicate that the ionic charge transfer process in BP-CSCNT composite electrodes is not coupled with the desolvation process and suggest that the charge transfer in BP-CSCNT is exceptionally fast compared to that in other insertion materials