Manganese Tetraphosphide (MnP4) as a High Capacity Anode for Lithium‐Ion and Sodium‐Ion Batteries

Abstract

AbstractPhosphorus‐rich 6‐MnP4 nanoparticles are synthesized via high energy mechanical milling (HEMM) and their electrochemical properties as an anode for lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) are investigated focusing on the electrochemical activity and reaction mechanism. The 6‐MnP4 nanoparticles with a triclinic structure (P‐1) are successfully synthesized by HEMM and they are composed of 5 to 20 nm‐sized crystallites. During the lithiation process, the MnP4 phase undertakes the sequential alloying (MnP4 + 7 Li+ + 7 e− → Li7MnP4) and conversion (Li7MnP4 + 5 Li+ + 5 e− → Mn0 + 4 Li3P) reactions. On the other hand, the MnP4 nanoparticles are directly converted to Mn0 and Na3P without the formation of an intermediate Na–Mn–P alloy phase during sodiation process. The MnP4 electrode shows high initial discharge and charge capacity (1876 and 1615 mAh g−1 for LIBs, and 1234 and 1028 mAh g−1 for SIBs) and high initial Coulombic efficiency (86% for LIBs and 83% for SIBs), indicating a promising candidate for high capacity anodes. In addition, the long‐term cyclability and high rate capability of MnP4 can be further improved through the formation of MnP4/graphene nanocomposites and vanadium substituted Mn0.75V0.25P4 solid solutions.