Galvanostatic Intermittent Titration Technique Reinvented: Part II. Experiments
Stephen Dongmin Kang, Jimmy Jiahong Kuo, Nidhi Kapate, Jihyun Hong, Joonsuk Park, William C. Chueh
Abstract
Following a critical review of the galvanostatic intermittent titration technique in Part I, here we experimentally demonstrate how to extract chemical diffusivity with a modified method. We prepare dense bulk samples that ensure diffusion-limitation. We utilize the scaling with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msqrt> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>relax</mml:mi> </mml:mrow> </mml:msub> <mml:mo>+</mml:mo> <mml:mi>τ</mml:mi> </mml:mrow> </mml:msqrt> <mml:mo>−</mml:mo> <mml:msqrt> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>relax</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msqrt> </mml:math> ( t relax : relaxation time; τ : pulse duration), avoiding problems with composition-dependent overpotentials. The equilibrium Nernst voltage is measured separately using small porous particles. This separation between the diffusion measurement and the titration procedure is critical for performing each measurement in a reliable setting. We report the chemical diffusion coefficients of Li x Ni 1/3 Mn 1/3 Co 1/3 O 2 and their activation energy. We extract ionic conductivity and compare it with total conductivity to confirm ion-limitation in chemical diffusion. The measurements suggest that the time scale for diffusion in typical Li-ion battery particles could be much shorter than that of the intercalation/deintercalation processes at the particle surface (Biot number less than 0.1).