Aluminum battery offers a new possibility for low cost and large-scale stationary storage of electricity because it can be made with cheap materials and exhibits high theoretical mass specific capacity and power density. Among many cathodic materials, graphite/graphene may be one of the most promising cathode materials for aluminum-ion battery. A suitable three-dimensional structure of the cathode is an important factor for the high performance of battery. In this paper, a binder-free cathode is prepared by dropcasting small ultrasonicated graphite flakes (u-GF) on carbon fiber cloth (CFC) which provides a three-dimensional network skeleton for the new cathode. Al|EMImCl-1.3AlCl 3 |u-GF@CFC battery exhibits a high discharge specific capacity of ~140 mAh g −1 at 100 mA g −1 . The battery has good rate performance and cycling stability: the capacity still exceeds 100 mAh g −1 at 600 mA g −1 with a high coulomb efficiency of 98% and maintains 60 mAh g −1 at 3000 mA g −1 over 300 cycles.
Tin-based hybrid flow batteries have demonstrated dendrite-free morphology and superior performance in terms of cycle life and energy density. However, the quick accumulation of electrodeposits near the electrode/membrane interface blocks the ion transport pathway during the charging of the battery, resulting to a very limited areal capacity (especially at high current density) that significantly hinders its deployment in long-duration storage applications. Herein, a conductivity-activity dual-gradient design is disclosed by electrically passivating the carbon felt near the membrane/electrode interface and chemically activating the carbon felt near the electrode/current collector interface. In consequence, the tin metals are preferentially plated at the region near electrode/current collector, preventing the ion transport pathway from being easily blocked. The resultant gradient electrode demonstrated an unprecedentedly high areal capacity of 268 mAh cm −2 at a current density of as high as 80 mA cm −2 . Numerical modeling and experimental characterizations show that the dual-gradient electrode differs from conventional electrodes with regard to their reaction current density distribution and electrodeposit distribution during charging. This work demonstrates a new design strategy of 3D electrodes for hybrid flow batteries to induce a desirable distribution of electrodeposits and achieve a high areal capacity at commercially relevant current densities.
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