Magnetic properties and vanadium oxidation state in α-Li3V2(PO4)3/C composite: Magnetization and ESR measurements

Here we present the magnetization and electron spin resonance (ESR) measurements of α-Li3V2(PO4)3/C composite, which can be potentially used as a cathode material in a lithium ion battery. Magnetization measurements of α-Li3V2(PO4)3/C indicate that the investigated sample is in paramagnetic state and exhibits Curie-Weiss like behavior above T = 50K. The negative value of the Curie-Weiss temperature θCW = −22 K suggests the presence of the antiferromagnetic interactions between magnetic spins of V3+ ions (3 d2, S = 1). At the same time, the presence of the magnetic phase transition was not observed in the investigated temperature range from 2 K up to room temperature. The nonlinear behavior of the field dependence of the magnetization was observed only at T = 2 K suggesting the possible magnetic ordering below this temperature. ESR measurements were performed both for as-prepared α-Li3V2(PO4)3/C composite and for α-Li3V2(PO4)3/C sample after Li deintercalation and intercalation processes. The complete reduction of vanadium ions to the initial valence state V3+ after the first charge/discharge cycle was determined indicating the reversible intercalation of all lithium ions to the structure during the first delithiation/lithiation cycle in the investigated α-Li3V2(PO4)3/C composite.