Manganese Local Environment Modulation via SiO₄ Substitution to Boost Sodium Storage Performance of Na₄ MnCr(PO₄ )₃

Manganese-based Na superionic conductors (NASICONs) Na₄ MnCr(PO₄ )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, SiO₄ is introduced to substitute PO₄ to modulate the local environment of Mn to activate the redox activity and stabilize the reversibility of Na₄ MnCr(PO₄ )_2.9 (SiO₄ )_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 SiO₄ substitution. The NMCP-Si exhibits much-enhanced rate capability and cycling stability, being attributed to the unique Jahn-Teller distortion (Mn³⁺ ) 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.