Balancing interlayer spacing, pore structures and conductivity endows hard carbon with high capacity for rechargeable aluminum batteries

As a key configuration, hard carbon (HC) is widely regarded as a promising cathode for rechargeable aluminum batteries (RABs), because of its enlarged interlayer spacing and well-developed pore structures. However, the trade-off between the pore structure, interlayer spacing and conductivity easily leads to an unsatisfactory electrochemical performance in terms of capacity and cycling stability. Hence, N-doped hard carbon (P-M) is synthesized at a relatively low temperature (700 °C) and anion intercalation associated with the energy storage process is investigated. The results demonstrate that the introduction of a N-doping agent not only expands the layer spacing and creates rich pore structures, but also boosts the conductivity. Compared with HC without N-doping, the expanded interlayer spacing in P-M can increase ion storage ability, and the rich pore channels contribute to electron transfer. Besides, compared with HC annealed at a higher temperature (900 °C), the enhanced conductivity in P-M is conducive to accelerating ion diffusion. Benefiting from these structure merits, the optimized P-M cathode delivers a high capacity (323 mA h g