Publication

Abstract : The cation-disordered lithium metal oxides display interesting electrochemical behavior quite distinct from the conventional cation-ordered layered structures. Comprehending the structure–property relations in these cation-disordered oxides is still in the preliminary stage. Herein, we report evidence of structural instabilities upon mechanical milling and electrochemical cycling of Li4FeMoO6. Remarkably, even under normal ball-milling conditions, the material becomes atomically disordered/the long-range order is severely affected. X-ray and electron diffraction studies reveal that pristine cationic disordered Li4FeMoO6 adopts the C2/m structure with stacking faults, whereas upon ball milling, a biphasic structure comprising a cubic phase (Fm3̅m + R3̅m) develops. With increasing milling time, these phases still coexist but as nanoscale domains (<5 nm); the 3 h ball-milled sample shows almost a 90.4% cubic (Fm3̅m) phase. Concomitant to ball milling, a dramatic improvement in charge–discharge capacities is also observed. The prepared sample Li4FeMoO6 showed a modest discharge capacity of 140 mA h g–1, whereas the 3 h ball-milled sample showed a discharge capacity of 359 mA h g–1, reaching 91.5% of its theoretical capacity. This unusual observation is a result of Li-ion percolation pathways (0-TM channels) introduced by the milling process.The cation-disordered lithium metal oxides display interesting electrochemical behavior quite distinct from the conventional cation-ordered layered structures. Comprehending the structure–property relations in these cation-disordered oxides is still in the preliminary stage. Herein, we report evidence of structural instabilities upon mechanical milling and electrochemical cycling of Li4FeMoO6. Remarkably, even under normal ball-milling conditions, the material becomes atomically disordered/the long-range order is severely affected. X-ray and electron diffraction studies reveal that pristine cationic disordered Li4FeMoO6 adopts the C2/m structure with stacking faults, whereas upon ball milling, a biphasic structure comprising a cubic phase (Fm3̅m + R3̅m) develops. With increasing milling time, these phases still coexist but as nanoscale domains (<5 nm); the 3 h ball-milled sample shows almost a 90.4% cubic (Fm3̅m) phase. Concomitant to ball milling, a dramatic improvement in charge–discharge capacities is also observed. The prepared sample Li4FeMoO6 showed a modest discharge capacity of 140 mA h g–1, whereas the 3 h ball-milled sample showed a discharge capacity of 359 mA h g–1, reaching 91.5% of its theoretical capacity. This unusual observation is a result of Li-ion percolation pathways (0-TM channels) introduced by the milling process.