Abstract
The overpotential of Li-ion batteries is one of the most relevant characteristics influencing the power and energy densities of these battery systems. However, the intrinsic complexity and multi-influencing factors make it challenging to analyze the overpotential precisely. To decompose the total overpotential of a battery into various individual components, a pseudo-two-dimensional (P2D) model has been adopted and used for electrochemical simulations of a graphite-based porous electrode/Li battery. Analytical expressions for the total overpotential have been mathematically derived and split up into four terms, associated with the electrolyte concentration overpotential, the Li concentration overpotential in the solid, the kinetic overpotential, and the ohmic overpotential. All these four terms have been separately analyzed and are found to be strongly dependent on the physical/chemical battery parameters and the reaction-rate distribution inside the porous electrode. The reaction-rate distribution of the porous electrode is generally non-uniform and shows dynamic changes during (dis)charging, resulting in fluctuations in the four overpotential components. In addition, the disappearance of the phase-change information in the voltage curve of the graphite-based porous electrode/Li battery under moderate and high C-rates is ascribed to the Li concentration overpotential among solid particles, resulting from the non-uniform reaction-rate distribution. • Analytical overpotential expressions are derived from P2D model. • Four overpotential components contribute to the total battery overpotential. • Four overpotential components are coupled together by the reaction rate distribution. • Fluctuations in overpotential components are related to the reaction rate distribution.
Highlights
Li-ion batteries (LIB) have been successfully applied in portable electronic devices, electric vehicles (EV), and hybrid electric vehicles (HEV) due to their high energy and power density, high coulombic and energy efficiency, and low cost [1]
The open-circuit voltage (OCV) of the battery shows several plateaus and slope regions, which are related to the two-phase and onephase during Li-intercalation in the graphite electrode [44,45]
Switching off the current periodically followed by relaxations at moderate C-rates makes the stages appear again at the end of relaxations, as indicated by the open-circle dash lines of GITT measurement in Fig. S2, where the currents of 0.1, 0.2 and 0.5C are used during the current pulses
Summary
Li-ion batteries (LIB) have been successfully applied in portable electronic devices, electric vehicles (EV), and hybrid electric vehicles (HEV) due to their high energy and power density, high coulombic and energy efficiency, and low cost [1]. Li-ion diffusion inside the electrodes is frequently considered as the rate-determining step for LIB [4,7,11] Besides these internal battery properties, some external factors, such as the applied current density [12,13], temperature [14], State-of-Charge (SoC) [15], and State-of-Health (SoH) [15,16,17] affect the overpotential. The reaction-rate distribution inside the porous electrode, an important factor influencing overpotential components and battery performance, is non-uniform in real applications [33,34,35] and simula tions [36,37], and is determined by numerous battery parameters [36,37,38]. The results in the present paper help to understand the overpotential in P2D-modeled Li-ion batteries and provide insights for further improve ment and optimization
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