Guiding Design of Mn‐Rich Phosphate Cathodes with Less Intrinsic Anti‐Site Defects

The serious voltage hysteresis phenomenon in Na3MnTi(PO4)3 has received extensive research interests, which is determined by the intrinsic‐anti‐site‐defects (IASDs) of Mn2+ resided in Na vacancies (Mn/Na□) in structure. However, a general guideline to decrease IASDs is still lacking for design of higher‐performance Na3MnTi(PO4)3 system. Herein, we find that generation of Mn/Na□ IASDs in Na3MnTi(PO4)3 system is mainly related to Na vacancies and weaker Mn‐O bonds in structure. The more of Na vacancies, the more probability for Mn2+ occupation on Na sites. Meanwhile the weaker Mn‐O bond, the more probaility for Mn2+ delocalization/migration to other sites, finally leading to the Mn/Na□ IASDs. To decrease Mn/Na□ IASDs, we propose to introduce dopants with lower valence (vs. Ti4+), lower electronegativity (vs. Ti4+) and good solid solubility in Na3MnTi(PO4)3 system. Based on the guiding rule, we have selected several doping cations (including Cr3+, Ti3+, Fe3+, V3+) to construct a Na‐rich environment and enhance Mn‐O strength. Among various dopants, the substitution of V3+ for Ti4+ leads to the strongest Mn‐O interaction, thus demonstrating the most effective suppression of Mn/Na□ IASDs. With these discoveries, we further developed a series of V doped Mn‐richer phosphate cathodes, Na3.3+yMn1.15VyTi0.85‐y(PO4)3 (0.1≤y≤0.25) as the promising candidates for Na‐ion batteries.