Browsing by Author "Gao, Hongwei"

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Fast charging of commercial lithium-ion battery without lithium plating
(Elsevier BV, 2023-12) Thapa, Arun; Hedding, Noah; Gao, Hongwei
Rapid charging of lithium-ion batteries (LIBs) enables the devices or systems powered by the batteries to provide services at faster rates or higher frequencies. However, fast charging of LIBs can cause lithium plating, resulting in rapid capacity degradation and even thermal runaway or fire in the batteries. Fast charging and lithium plating in a LIB are anode-centric events. Therefore, an anode-centric electrochemical model is critical for deriving a fast charging protocol for LIBs. In this work, we developed an electric circuit model for the negative electrode using tests conducted on laboratory three-electrode lithium-ion cells, used the model to estimate the fast charging current, and compared the fast charging current derived using the model to the fast charging current obtained from measurement. The fast charging current obtained using the model agrees well with the measured fast charging current. Furthermore, we implemented this fast charging protocol on commercial 18650 LIBs for 350 cycles using custom-built charging hardware and software and achieved an 80 % state of charge in 29 min with acceptable temperature rise. The cell aging analysis revealed no significant capacity degradation nor lithium plating on the anode surface, as the protocol explicitly imposes control to protect the battery from lithium plating.
Low-frequency Inductive Loop and Its Origin in the Impedance Spectrum of a Graphite Anode
(The Electrochemical Society, 2022-11) Thapa, Arun; Gao, Hongwei
Graphite is a well-known anode material for commercial lithium-ion batteries, and its physical and electrochemical properties have been studied extensively. However, the origin of an inductive loop observed in the low-frequency region of the Nyquist complex plane impedance spectrum of the graphite anode has been widely debated and attributed to contrasting reasons. This paper investigates the impedance spectrum of the graphite anode at various states of charge (SoCs) using three-electrode galvanostatic Electrochemical Impedance Spectroscopy (EIS) and further explores the impedance response of the electrolyte as a function of frequency. The graphite anode EIS measurement displayed an inductive loop in the low-frequency region for almost entire SoCs, irrespective of the solid electrolyte interphase (SEI) age. To study the origin of this inductive loop in the graphite impedance spectrum, we fabricated a three-electrode pouch cell with graphite and NMC electrodes and estimated the electrolyte impedance in the frequency range from 1 MHz to 0.05 Hz. The electrolyte impedance at low frequencies exhibited inductive behavior, indicating a significant role of the electrolyte in the origin of the inductive characteristic in the low-frequency region of the graphite EIS spectrum.