| Lithium iron(II) phosphate, also known as lithium ferrophosphate (LiFePO4, LFP), has been the subject of many recent energy storage studies. As a battery cathode material, LFP has many advantages for commercial applications. Compared to its competitors like LiMn2O4 and the ubiquitous but carcinogenic LiCoO2, LFP (specific energy = 600 Wh/kg) exhibits low toxicity, low cost, good thermal stability, and excellent electrochemical performance at high charge/discharge rates. As part of the efforts to understand and improve LFP, a great amount of research has been committed towards developing, characterizing, and electrochemically testing chemical relatives of this phase. In this work, chemical relatives of LFP belonging to the Li3PO4-Fe3(PO4) 2-InPO4 phase system were investigated. This has lead to the discovery of lithium iron(II) indium phosphate [LiFeIn(PO4) 2, LFIP]. Structural studies on LFIP using laboratory and synchrotron X-ray, neutron, and electron diffraction techniques have demonstrated this phase to crystallize in the orthorhombic space group Pbca with lattice parameters a = 9.276(1) A, b = 13.757(2) A, and c = 9.476(1) A. Unlike LFP, this new material does not perform well as a battery cathode as found by chemical delithiation tests, electrochemical cycling, and bond-valence sum difference maps of Li+ diffusion pathways. LFIP has also been characterized by magnetic and optical measurements. The material does not order magnetically above 2 K, is paramagnetic with weak antiferromagnetic interactions, and has an effective magnetic moment of 5.39 microB/Fe. LFIP has a band-gap energy of 2.94 eV and d orbital ligand field splitting energies of 0.75 eV and 0.99 eV. Based on our synthesis results, a preliminary assessment of the Li3PO4-Fe3(PO4) 2-InPO4 phase system is presented. |
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