Na2MnSiO4 as a positive electrode material for sodium secondary batteries using an ionic liquid electrolyte

Sodium manganese orthosilicate, Na2MnSiO4, was synthesized by a sol–gel method and investigated for use as a positive electrode material for Na secondary batteries using Na[FSA]–[C3C1pyrr][FSA] (FSA = bis(fluorosulfonyl)amide anion and C3C1pyrr = N-methyl-N-propylpyrrolidinium cation) ionic liquid electrolyte in the temperature range 298–363 K. Carbon coating and elevation of operational temperatures significantly improved the electrode performance. A reversible capacity of 125 mAh g− 1 (90% of the theoretical value based on a one-electron transfer process) was found at a rate of C/10 (13.9 mA g− 1) within 2.0–4.0 V at 363 K, with an acceptably high rate capability. Na2MnSiO4 became amorphous upon the electrochemical removal of sodium, exhibiting a similar behavior as its lithium equivalent. Both Na2MnSiO4 and its desodiated form (Na0.8MnSiO4) possess remarkable thermal stability, suggesting their safety characteristic.