Mitigating Jahn-Teller Effects: First-Principles and experimental study of aluminium-doped manganese-based NASICON...

Manganese-based structures have been widely studied as candidates for cathode materials in sodium-ion batteries (SIBs) owing to their low-cost and environmental-friendly properties. However, due to the orbital properties of Mn³⁺, the Jahn-Teller effect occurs frequently during the electrode reaction, leading to irreversible phase transition of the structure with capacity degradation. Here, we mitigated this critical issue by a theory-guided synthesis of aluminium-doped manganese-based NASICON-type phosphate cathode Na₄MnAl(PO₄)₃. Using density functional theory, we have predicted its electrode properties, including the phase stability, voltage plateau and ionic diffusion properties, which results supported favor physicochemical properties and fast kinetics behavior. Moreover, Na₄MnAl(PO₄)₃ exhibited structural stability and small volume change (6.2 %) during theoretical cycling process, and the detrimental Jahn-Teller effect was effectively suppressed analyzed by Bader charge. With two effective redox pairs, i.e., Mn⁴⁺/Mn³⁺ (4.1 V) and Mn³⁺/Mn²⁺ (3.6 V), Na₄MnAl(PO₄)₃ achieved a capacity retention of 85.08 % after 500 cycles at 5C. Moreover, this cathode was well compatible to hard carbon and achieved 81.8 % capacity retention after 200 cycles at 1C. This work suggests its high energy density and excellent cycling stability, which provides a critical reference from theoretical design to experimental study for the manganese-based phosphate cathode for high-performance SIBs.