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In-situ Probing Interfacial Kinetics for Studying the Electrochemical Properties of Active Nano/micro-Particles and the State of Li-ion Batteries

Abstract

It is critical to monitor the state of health (SOH) of the Li-ion batteries to ensure a safe operation and to extend the service life of the batteries in electric vehicles. In this work, we demonstrated that the equivalent capacitance (Cp) and resistance (Rp) of the electrode interface derived using a first-order RC equivalent circuit under a large galvanostatic pulse (LGPM) condition can be correlated to SOH. For both the cathode and the anode, the interfacial kinetics of Li-ions were analyzed to study the electrochemical properties of active particles. The RC parameters of the equivalent circuit were correlated to the diffusion kinetics of Li-ions near the interface between the electrolyte and the active nano/micro-particles during fast charging/discharging. For fresh LiFePO4 (LFP)/Li half-cells, the values and the change of Cp and Rp were explained using the hypothesis of interparticle ion transport under a non-equilibrium condition. For graphite/Li half-cells, the buffering of Li-ions by the solid-electrolyte interphase (SEI) layer was speculated to affect Cp and Rp under a non-equilibrium condition. In commercial LFP/graphite batteries, and the Cp values of unhealthy batteries were found to be higher than that of healthy batteries. In further tests, the Cp values of the half cells with graphite anode recovered from the unhealthy batteries were found to be higher than those of the half cells with graphite from the healthy batteries. The half cells with LFP from the unhealthy batteries behaved similarly to that with LFP from the healthy batteries. With additional analysis on the microstructure, we proposed that the deterioration of the LFP/graphite batteries was mostly due to the formation of a thicker SEI on the graphite anode. The method developed in this work can be integrated in EVs at a low calculation cost. More importantly, we gained a better understanding on the interfacial kinetics of Li-ions during a non-equilibrium process.

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Publication details

The article was received on 19 Aug 2017, accepted on 03 Oct 2017 and first published on 04 Oct 2017


Article type: Paper
DOI: 10.1039/C7TA07332A
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
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    In-situ Probing Interfacial Kinetics for Studying the Electrochemical Properties of Active Nano/micro-Particles and the State of Li-ion Batteries

    W. Ren, H. Chen, R. Qiao, Y. lin and F. Pan, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA07332A

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