Direct and modified ionothermal synthesis of LiMnPO4 with tunable morphology for rechargeable Li-ion batteries

Abstract

Low temperature solvothermal synthesis routes are increasingly being pursued as energy-savvy ways, as opposed to conventional solid-state synthesis, to produce electrode materials. This current work reports ionothermal synthesis, using pristine ionic liquids (ILs) as reacting media, to produce LiMnPO₄ (LMP) in the temperature range of 220–250 °C at ambient pressure. The role of various processing parameters and different types of ionic liquids on the structure and morphology of LiMnPO₄ has been reported. Further, ionothermal synthesis can be modified by altering the nature of reacting media by addition of partially miscible solvent to ionic liquids. Here, in addition, we demonstrate three modified versions of ionothermal synthesis, namely (a) water-micelles (nano-reactors) entrapped in ILs, yielding nanoparticles, (b) carbon-assisted IL synthesis as a one-step production of carbon-coated LiMnPO₄ and (c) diol-assisted ionothermal synthesis forming platelet-morphology. The resulting IL-synthesized LiMnPO₄ olivines were found to deliver reversible capacity close to 100 mA h g⁻¹ (at a rate of C/20) with excellent cycling stability involving standard two-phase lithium (de)insertion mechanism.