Manganese Local Environment Modulation via SiO 4 Substitution to Boost Sodium Storage Performance of Na 4 MnCr(PO 4 ) 3 .

Manganese-based Na superionic conductors (NASICONs) Na 4 MnCr(PO 4 ) 3 with three-electron reaction are attractive cathode materials for sodium-ion batteries. However, the irreversible distortion of Mn local structure leads to sluggish electrode kinetics, voltage hysteresis, and poor cycling stability. Here, SiO 4 is introduced to substitute PO 4 to modulate the local environment of Mn to activate the redox activity and stabilize the reversibility of Na 4 MnCr(PO 4 ) 2.9 (SiO 4 ) 0.1 (NMCP-Si). A combined experimental and theoretical investigation have been undertaken to reveal the evolution of electronic structures and Na storage properties associated with SiO 4 substitution. The NMCP-Si exhibits much-enhanced rate capability and cycling stability, being attributed to the unique Jahn-Teller distortion (Mn 3+ ) that facilitates sodium de/insertion kinetics by optimizing the Na ion diffusion channels. This work addresses the challenge of stabilizing the structure of Mn-based NASICONs and represents a breakthrough in understanding how to improve the Na + conductivity by regulating local structure.