Large Alkylammonium\nCation Based 2D-3D Hybrid Perovskite\nwith Fast Charge Conduction for a Li-Ion Battery Anode

Organic–inorganic hybrid perovskites (PSKs) function\nas\nefficient anodes for Li-ion batteries (LIBs) due to their facile alloying–dealloying\nreactions between Li and Pb. A large alkyl chain containing an organic\ncation, specifically, 3-bromopropylamine hydrobromide (BPA), is used\nto synthesize a 2D-3D hybrid PSK (CsMABPAPbIBr). The bulkiness of\nBPA inhibits its incorporation in the 3D octahedral cages, creating\na pseudoquantum well wherein the low band gap inorganic PbX<sub>6</sub><sup>4–</sup> (X: Br/I) octahedra serve as the potential wells,\nand the high band gap organic layers serve as potential barriers.\nThis mixed-dimensional structure affords a greater number of accessible\nsites for Li<sup>+</sup> ions, superior electrical conductivity and\nchemical stability relative to the control 3D PSK (CsMAPbIBr), thereby\nimproving capacity, rate capability, and operational lifespan. Li-ion\ncells with the 2D-3D hybrid PSK-carbon nanotubes (CNTs) composite\nexhibited an initial discharge capacity of 221 mAh g<sup>–1</sup>, 84% capacity retention after 100 cycles and an energy density of\n508 Wh kg<sup>–1</sup>, significantly enhanced compared to\nthe 3D PSK-CNTs. The charge storage mechanism is largely dominated\nby pseudocapacitive-surface-controlled redox reactions, and the improved\nresistance to capacity fade demonstrated by the 2D-3D PSK is attributed\nto the ability of the organic cations (BPA) to serve as a strain-absorbing\noverlayer. These results highlight the potential of 2D-3D PSKs for\ndeveloping energy-dense long-lived LIBs for practical applications.