Enhancement of electrochemical performance of Al-doped LiVPO4F using AlF3 as aluminum source

Elemental doping is one of the most effective strategies to improve the electrochemical performance of electrode materials for lithium ion batteries. The Al-doped LiV(1-x)AlxPO(4)F (x = 0, 0.01, 0.02, named as AF-0, AF-1, AF-2, respectively) cathode materials are prepared by a soft chemical lithiation process using AlF3 as aluminum source. For comparison, LiV0.99Al0.01PO4F sample is also synthesized by using Al2O3 as Al precursor (named as AO-1). The X-ray diffraction analysis shows that parts of V sites are substituted by Al atoms, without changing the primary triclinic structure of LiVPO4F. A higher purified LiV0.99Al0.01PO4F sample with less monoclinic Li3V2(PO4)(3) is obtained by using AlF3 as aluminum source than that prepared by employing Al2O3. The charge-discharge tests show that AF-0, AF(-)1, AF-2, AO-1 can deliver specific discharge capacity of 132, 131, 132, 127 mAh g(-1), respectively. The AF-1 sample possesses the best cyclic performance, maintaining the capacity retention of 96.9% after 50 cycles at 0.5 C rate. Although the capacity decreases for all samples as the current density increasing, the Al-doped samples show less discount than the undoped one. Furthermore, AF-1 performs the best electrochemical performance, delivering 118, 98 mAh g(-1) at 3, 6 C, respectively. CV test sindicate that the as-prepared Al-doped samples show lower polarization and higher discharge potential plateaus than the pristine one, and the AF-1 functions better than AO-1. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.