Effect of particle size on dc conductivity, activation energy and diffusion coefficient of lithium iron phosphate in Li-ion cells

Abstract

Available onlineKeywords: Activation energy dc conductivity ac impedance and diffusion coefficient A B S T R A C T Cathode materials in nano size improve the performance of batteries due to the increased reaction rate and short diffusion lengths. Lithium Iron Phosphate (LiFePO4) is a promising cathode material for Li-ion batteries. However, it has its own limitations such as low conductivity and low diffusion coefficient which lead to high impedance due to which its application is restricted in batteries. In the present work, increase of conductivity with decreasing particle size of LiFePO4/C is studied. Also, the dependence of conductivity and activation energy for hopping of small polaron in LiFePO4/C on variation of particle size is investigated. The micro sized cathode material is ball milled for different durations to reduce the particle size to nano level. The material is characterized for its structure and particle size. The resistivities/ dc conductivities of the pellets are measured using four probe technique at different temperatures, up to 150°C. The activation energies corresponding to different particle sizes are calculated using Arrhenius equation. CR2032 cells are fabricated and electrochemical characteristics, namely, ac impedance and diffusion coefficients, are studied.

Thermokinetic and conductivity analyzes of the high CO2 chemisorption on Li5AlO4 and alkaline carbonate impregnated Li5AlO4 samples: Effects produced by the use of CO2 partial pressures and oxygen addition

“…In fact, the E a values presented by Li 5 AlO 4 are similar to those reported by Al 2 O 3 for O 2 − conductivity [37] . Moreover, the activation energy values reported for Li-ion conductors are importantly lower ( ∼0.3 to 0.57 eV [38] ), in comparison to the values obtained here. Hence, as both E a can be associated to O 2 − mobility ( Fig.…”

Comparison of fresh and aged lithium iron phosphate cathodes using a tailored electrochemical strain microscopy technique

“…Using to describe the diffusion in a thin film [40] with a time constant τ = 2 ms and a depth of the probed volume of roughly R V = 10 nm leads to diffusion coefficients of about 2.5 × 10 −14 m 2 s −1 . This value is at the higher bound of experimental values given in the literature which range between 1 × 10 −14 to 1 × 10 −20 m 2 s −1 [74][75][76] and the lower bound of theoretically calculated diffusion coefficients. Theoretical work gives values ranging from 1 × 10 −11 to 1 × 10 −14 m 2 s −1 , which depends on the direction of the diffusion channels considered [56,57,65,77].…”

“…This faulty assumption affects the diffusion coefficients extracted from the experimental data. Additionally, the preparation of the material influences the diffusion coefficient [75,77]. The assumed 10 nm of probed depth is a reasonable assumption considering the sharp boundaries observed in the ESM signals.…”

Morphology-dependent space charge polarization and dielectric relaxation of CdO nanomorphotypes

“…Dielectric semiconductor materials with high activation energy indicate that the material is more resistive against electron transport and also have high dielectric polarization/ dielectric constant value. [40][41][42][43] As the resistance increase, the high dielectric polarization energy in the materials gets dissipated in the form of heat which causes large dielectric loss values in the material. In the present study, the higher activation energy in spherical morphology is due to its large grain resistance and dielectric loss values over flakes and parallelepiped morphotypes.…”