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

Abstract

Abstract The serious voltage hysteresis phenomenon in Na 3 MnTi(PO 4 ) 3 has received extensive research interests, which is determined by the intrinsic‐antisite‐defects (IASDs) of Mn 2+ resided in Na vacancies (Mn/Na □ ) in structure. However, a general guideline to decrease IASDs is still lacking for the design of a higher‐performance Na 3 MnTi(PO 4 ) 3 system. Herein, we find that generation of Mn/Na□ IASDs in Na 3 MnTi(PO 4 ) 3 system is mainly related to Na vacancies and weaker Mn─O bonds in structure. The more Na vacancies, the more probability for Mn 2+ occupation on Na sites. Meanwhile, the weaker Mn─O bond, the more probability for Mn 2+ 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. Ti 4+ ), lower electronegativity (vs. Ti 4+ ), and good solid solubility in Na 3 MnTi(PO 4 ) 3 system. Based on the guiding rule, we have selected several doping cations (including Cr 3+ , Ti 3+ , Fe 3+ , and V 3+ ) to construct a Na‐rich environment and enhance Mn─O strength. Among various dopants, the substitution of V 3+ for Ti 4+ 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, Na 3.3+ y Mn 1.15 V y Ti 0.85‐ y (PO 4 ) 3 (0.1 ≤ y ≤ 0.25) as the promising candidates for Na‐ion batteries.