Abstract
Sodium-ion batteries (SIBs) have recently been proclaimed as the frontrunner 'post lithium' energy storage technology. This is because SIBs share similar performance metrics with lithium-ion batteries, and sodium is 1000 times more abundant than lithium. In order to understand the electrochemical characteristics of SIBs and improve present-day designs, physics-based models are necessary. Herein, a physics-based, pseudo-two-dimensional (P2D) model is introduced for SIBs for the first time. The P2D SIB model is based on Na3V2(PO4)2F3 (NVPF) and hard carbon (HC) as positive and negative electrodes, respectively. Charge transfer in the NVPF and HC electrodes is described by concentration-dependent diffusion coefficients and kinetic rate constants. Parametrization of the model is based on experimental data and genetic algorithm optimization. It is shown that the model is highly accurate in predicting the discharge profiles of full cell HC//NVPF SIBs. In addition, internal battery states, such as the individual electrode potentials and concentrations, can be obtained from the model at applied currents. Several key challenges in both electrodes and the electrolyte are herein unraveled, and useful design considerations to improve the performance of SIBs are highlighted.
Highlights
Several research groups and startups have recently shown great interest in developing sodium-ion batteries (SIBs) [1]
The EMF potentials for both the hard carbon (HC) and NVPF electrodes were experimentally determined as described in an accompanying publication [27]
An accurate physics-based model is, the only way to account for the various kinetic and mass transport effects at different rates
Summary
Several research groups and startups have recently shown great interest in developing sodium-ion batteries (SIBs) [1]. P2D models are widely accepted and demonstrate unparalleled accuracy and reliability, there remain practical challenges to parametrize new chemistries and integrate the models in BMS microcontrollers [16] This is because the models are based on systems of coupled partial differential equations (PDEs), which are computationally expensive and potentially non-convergent during execution [17]. The development of physics-based models remains an important undertaking to understand internal battery dynamics and provide a link with experimentally derived parameters. Analyses of the model results reveal mass transport limitations in the 1 kmol m−3 NaPF6 EC0.5 : PC0.5 (w/w) electrolyte and in the HC and NVPF active particles This can further guide the design of SIB systems, which are expected to operate at high-power demanding applications
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