Experimental and Simulation Investigations of Porosity Graded Cathodes in Mitigating Battery Degradation of High Voltage Lithium-Ion Batteries

Abstract

LiNi0.5Mn1.5O4 (LNMO) is one of the high potential cathodes for lithium-ion batteries due to high operating voltage (4.7 V vs. Li) and high specific energy (650 Wh·kg−1). However, severe accelerated performance degradation occurring especially at the interface between electrode and electrolyte, hinder the implementation of the LNMO. In this work, porosity-graded cathodes are designed to mitigate LNMO degradation. The LNMO is synthesized using the solid-state reaction. We confirm the crystalline phase and electrochemical performance of the synthesized LNMO via X-ray powder diffraction (XRD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Scanning electron microscope (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) are utilized. The porosities are measured by both 2-D imaging method (i.e., through ImageJ) and 3-D pore size analyzer in this study. Cycling tests show that porosity-graded cells reduce the capacity fade about 8.285% in full cell and 5.29% in half-cell, respectively. The porosity increase can improve the conductivity and diffusivity of lithium-ions through the electrode. Also, solid electrolyte interphase (SEI) formation can be varied and controlled when the porosity is different inside the electrode. Furthermore, we adopted Elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II) to demonstrate the porosity-grading as a strategy for mitigating battery degradation.