Synthesis and characterization of olivine LiNiPO_4 for aqueous rechargeable battery

摘要

LiNiPO_4 belongs to a family of olivine type compounds, with members LiMPO_4 where M=Fe, Mn, Co or Ni are transition metals. The lithium nickel phosphate was prepared and characterized in order to evaluate a new potential cathode material for our ongoing research in aqueous rechargeable batteries. Annealing the final product is critical in obtaining the stoichiometric LiNiPO_4 pure phase; conventional cooling to a room temperature leads to an indication of Li_3PO_4 and NiO secondary phases as impurities. The synchrotron infrared radiation (SR-IR) as a source for IR spectroscopy pins down the differences in the chemical bonding for annealed and conventional cooled LiNiPO_4 samples. The cyclic voltammetric and galvanostatic studies showed annealed LiNiPO_4 is electrochemically active from which lithium ions can be de-intercalated during oxidation process leading to an amorphous NiPO_4 and a minor product of nickel(II) hydroxide (β-NiOOH). During subsequent reduction, lithium ions are not fully intercalated, however, the structure is reversible and adequate for multiple cycles. The high potential in LiNiPO_4 looks to be very attractive in terms of high energy density, given the efficiency is improved.