Abstract
LiCoPO4 (LCP) exists in three different structural modifications: LCP-Pnma (olivine structure), LCP-Pn21a (KNiPO4 structure type), and LCP-Cmcm (Na2CrO4 structure type). The synthesis of the LCP-Cmcm polymorph has been reported via high pressure/temperature solid-state methods and by microwave-assisted solvothermal synthesis. Phase transitions from both LCP-Pn21a and LCP-Cmcm to LCP-Pnma upon heating indicates a metastable behavior. However, a precise study of the structural changes during the heating process and the magnetic properties of LCP-Cmcm are hitherto unknown. Herein, we present the synthesis and characterization of LCP-Cmcm via a rapid and facile soft-chemistry approach using two different kinetically controlled pathways, solvothermal and polyol syntheses, both of which only require relatively low temperatures (~200 °C). Additionally, by polyol, method a dumbbell-like morphology is obtained without the use of any additional surfactant or template. A temperature-dependent in situ powder XRD shows a transition from LCP-Cmcm at room temperature to LCP-Pnma and finally to LCP-Pn21a at 575 and 725 °C, respectively. In addition to that, the determination of the magnetic susceptibility as a function of temperature indicates a long-range antiferromagnetic order below TN = 11 K at 10 kOe and 9.1 K at 25 kOe. The magnetization curves suggests the presence of a metamagnetic transition.
Highlights
Since their introduction by Whittingham [1] and commercialization in the early 1990s by Sony® [2], Li-ion batteries (LIB) have become a breakthrough technology in portable electronics
20–40 in 3–4 length, 3–4 nm in(Figure thickness
A dumbbell-like morphology could be obtained by a simple one-step synthesis without the use of additional surfactants or templates
Summary
Since their introduction by Whittingham [1] and commercialization in the early 1990s by Sony® [2], Li-ion batteries (LIB) have become a breakthrough technology in portable electronics. The third modification is LCP-Cmcm, which adapts the Na2 CrO4 -type structure (Figure 1c) This structure was first reported by Amador and co-workers[19] resulting from a high-pressure and high-temperature solid-state synthesis (6 GPa, 900 ◦ C). Manthiram et al [21,22] claimed two conditions to be necessary for the formation of LCP-Cmcm: the use of fresh dried tetraethylene glycol (TTEG) as a solvent and the use of cobalt oxalate as a cobalt precursor. This synthesis was performed in a closed system using a temperature of 260 ◦ C and a pressure below 30 bar.
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