Comparative study of 2D perovskite cathodes: impact of organic cation variation on electrochemical performance in lithium-ion batteries

In this study, two organic-inorganic hybrid perovskites, butylammonium copper chloride (BACC) and methylammonium copper chloride (MACC), were synthesized and evaluated as feasible active cathode materials for lithium-ion batteries. Both compounds were structurally and morphologically characterized using X-ray diffraction, scanning electron microscopy and infrared spectroscopy, revealing high crystalline structures and well-defined morphologies consistent with long-range order and unique features of conversion materials. The electrochemical performance of synthesized compounds as cathodes was assessed through cyclic voltammetry and galvanostatic charge/discharge measurements. Butylammonium copper chloride, with formula (C4H12N)2CuCl4, exhibited a remarkable specific discharge capacity of 200 mAh g-1 at 20 mA g-1 with capacity retention close to 65 %. Meanwhile, methylammonium copper chloride (CH3NH3)2CuCl4 delivered a specific capacity of 160 mAh g-1 at 20 mA g-1, maintaining 90.2 % capacity retention. Post-cycling XRD analysis was carried out on the cathodes after 100 cycles of operation at 50 mA g-1, providing evidence of structural changes during battery operation. These structural transformations account for the gradual capacity fading observed during prolonged cycling and demonstrate that a Coulombic efficiency close to 100 % does not necessarily imply structural reversibility. Overall, the results indicate that BACC and MACC should be regarded as model systems for fundamental studies of copper electrochemical chemistry in halogenated hybrid perovskites, rather than as competitive cathode materials for practical lithium-ion battery applications.