Coordination Chemistry Guides the Design of Mn-Rich Phosphate Cathodes with Fewer Structure Defects.

Mn-rich phosphate of Na3.3Mn1.15Ti0.85(PO4)3 (NMTP), only containing high-abundance elements, was considered a promising cathode for Na-ion batteries (NIBs) owing to its 2.3-electron reactions and high working voltage based on Mn2+/Mn3+/Mn4+ redox couples between 2.5 and 4.2 V. However, excessive Mn content provides more chances for Mn2+ delocalization to sodium vacancies (Mn/Na□) to generate intrinsic antisite defects (IASDs), which leads to more serious voltage hysteresis in charge/discharge profiles, limiting the energy density of the NMTP system. Herein, we propose to introduce dopants with low valence and electronegativity into the titanium sites of NMTP to regulate Mn-O coordination chemistry. Following this rule, monovalent and low-electronegativity Li+ dopants are selected to build an enhanced Mn-O framework with a Na-rich environment, effectively reducing Mn/Na□ IASDs during the synthesis of materials. Benefited from facilitated Na+ diffusion kinetics because of the less Mn/Na□ IASD-affected pathway in the structure, Li+-doped NMTP (NMTLiP) shows suppressed voltage hysteresis behavior, achieving an energy density increase from 331 to 426 W h kg-1. This current work provides directional guidance from a coordination chemistry regulation perspective to suppress structure defects in Mn-rich phosphate cathodes toward high-energy NIBs.