Sufficient Utilization of Mn2+/Mn3+/Mn4+ Redox in NASICON Phosphate Cathodes towards High‐Energy Na‐Ions Batteries

Abstract Na superionic conductor of Na 3 MnTi(PO 4 ) 3 only containing high earth‐abundance elements is regarded as one of the most promising cathodes for the applicable Na‐ion batteries due to its desirable cycling stability and high safety. However, the voltage hysteresis caused by Mn 2+ ions resided in Na + vacancies has led to significant capacity loss associated with Mn reaction centers between 2.5–4.2 V. Herein, the sodium excess strategy based on charge compensation is applied to suppress the undesirable voltage hysteresis, thereby achieving sufficient utilization of the Mn 2+ /Mn 3+ and Mn 3+ /Mn 4+ redox couples. These findings indicate that the sodium excess Na 3.5 MnTi 0.5 Ti 0.5 (PO 4 ) 3 cathode with Ti 4+ reduction has a lowest Mn 2+ occupation on the Na + vacancies in its initial composition, which can improve the kinetics properties, finally contributing to a suppressed voltage hysteresis. Based on these findings, it is further applied the sodium excess route on a Mn‐richer phosphate cathode, which enables the suppressed voltage hysteresis and more reversible capacity. Consequently, this developed Na 3.6 Mn 1.15 Ti 0.85 (PO 4 ) 3 cathode achieved a high energy density over 380 Wh kg −1 (based on active substance mass of cathode) in full‐cell configurations, which is not only superior to most of the phosphate cathodes, but also delivers more application potential than the typical oxides cathodes for Na‐ion batteries.