Kinetic Studies on the Synthesis of Monoclinic Li₃V₂(PO₄)₃via Solid-State Reaction

Abstract

The data obtained by thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (XRD) measurements of the stoichiometric mixture of LiNO, NHVO, and NHHPO were analyzed by both the Flynn-Wall-Ozawa (FWO) and Friedman-Reich-Levi (FRL) methods. The whole solid state reaction process could be divided into four stages corresponding to α values of 0.03-0.20, 0.30-0.60, 0.70-0.80, and 0.90-0.99. The nucleation of LiVPO (α = 0.70-0.80) is a determining step of the four-reaction processes, for which the mechanism of random nucleation and subsequent growth, described by the Avrami-Erofeev equation (n = 4) G(α) = [-ln(1 - α)], was assumed. Moreover, the Gibbs free energy of activation ΔG*, enthalpy of activation ΔH*, and entropy of activation ΔS* at maximum temperature of the peak for the determining step were 99.24 kJ·mol, 199.97 kJ·mol, and 136.30 J·mol·K, respectively. Finally, XRD analyses confirmed that the LiV(PO) synthesized by the precursor route is a pure phase.

Experimental Study on the Chemical Reaction Characteristics in the Calcination Process of an 811 Ternary Cathode Material

“…Experimental results showed that the electrochemical performance of the material is the best when the supply of lithium is 1.04 and the calcination temperature is 700 °C. Chen et al 14 found that the formation of the cathode material Li 3 V 2 (PO 4 ) 3 undergoes four stages of chemical reaction and determined that the most critical fourth-stage kinetic function is the Avrami–Erofeev equation, that is, random nucleation and subsequent growth mechanism. The enthalpy, entropy, and Gibbs free energy corresponding to that phase are also determined.…”

Rational Design and Facial Synthesis of Li3V2(PO4)3@C Nanocomposites Using Carbon with Different Dimensions for Ultrahigh-Rate Lithium-Ion Batteries

“…Among all of the cathode candidates, monoclinic lithium–vanadium phosphate, Li 3 V 2 (PO 4 ) 3 (LVP), has attracted extensive attention because of its high operating voltage, large theoretical specific capacity, and thermodynamically stable structure. − However, the practical application of LVP has been limited by its inferior electronic conductivity because of the two separated [VO 6 ] octahedral arrangement. , Various strategies have been adopted to overcome this problem: (1) Doping with metal ions. ,, Although the conductivity can be increased in some degree, introducing guest atoms into the crystal lattices of LVP may also be deleterious and not easy to control via this method. (2) Reducing the particle size. ,, According to the diffusion formula t = L 2 /2 D (where t is the diffusion time, L is the diffusion distance, and D is the diffusion coefficient), decreasing the particle size can significantly shorten the diffusion distance length, resulting in a fast Li + -ion transfer in LVP, thus much enhancing its power performance.…”