▎ 摘　　要

Crystal water of lithium-ion battery electrode active substances is electrochemically inert in reversible charge-discharge processes and may exert a positive effect on charge transfer, but these are still controversial in view of the absolutely adverse effects of adsorbed water/moisture. In this paper, hydrated, partial dehydration and anhydrous hydroxyl ferric phosphate Fe-5(PO4)(4)(OH)(3)center dot nH(2)O (n = 2, 1.3 and 0) and their graphene oxide (GO) doped composites of Fe-5(PO4)(4)(OH)(3)center dot nH(2)O/GO are separately prepared and applied as low-voltage lithium-ion battery (LIB) cathodes, aiming to prove a kinetic improvement mechanism of crystal water for the first time. Within 1.5-4.5 V vs. Li+/Li at 50 mA g(-1), pristine Fe-5(PO4)(4)(OH)(3)center dot nH(2)O and corresponding GO-doped composites deliver a reversible capacity of 128.7 (pristine n = 2), 63.5 (pristine n = 1.3), 46.5 (pristine n = 0), 155.1 (composite n = 2), 117.5 (composite = 1.3) and 98.0 mAh g(-1) (composite n = 0) in the 120th cycle, respectively. According to the theoretical capacity of Fe-5(PO4)(4)(OH)(3)center dot 2H(2)O (180 mAh g(-1)), it is the synergistic effect of intrinsic crystal water and additive GO that leads to the high performances of composite Fe-5(PO4)(4)(OH)(3)center dot 2H(2)O/GO (e.g., a reversible capacity similar to 140.6 mAh g(-1); 180 mA g(-1); the 250th cycle) for potential application purposes. (C) 2021 Elsevier Ltd. All rights reserved.