Microstructural Study of Cathode Materials for Li-Ion Batteries to Improve Ion Diffusion and Volumetric Capacity

Abstract

The need for the development of secondary lithium-ion batteries (LIB) with high power and high energy density is imperative for the advancement of portable devices, electric vehicles (EV), and integrated renewable energy system. LIB designed for high power density suffers from low energy density and vice versa. In this regard, optimizing both power and energy density simultaneously is at the forefront of current energy research. Both experimental and computational studies have demonstrated that designing novel microstructure of LIB electrodes to facilitate ionic and electronic transport is the key aspect to balance between power and energy density (1, 2). Our research involves investigating how to improve Li-ion diffusion through 3D porous electrodes via optimization of microstructural features such as particle size, porosity and tortuosity and electrode thickness. Report shows that with decreasing particle size, surface area increases leading to formation of thick layer of solid-electrolyte interface (SEI) (3). This obstructs the diffusion of Li+ and results large irreversible capacity. Additionally, significant decrease in particle size yields a very low tap density. This translates into low volumetric energy density (4). On the other hand, large particle size increases the diffusion length (3, 5). Thus, effects the power performance by increasing the characteristic time constant for Li+ to transport within the particles. Our research goal is to investigate the optimal particle size to balance both power and energy densities. In this presentation, we will be reporting the fabrication of lithium nickel manganese cobalt oxide (NMC) cathode materials with particle size less than 0.5µm through a scalable suspension atomization and spray deposition technique. Additionally, microstructural parameters – porosity and tortuosity – are investigated using FIB-SEM tomography and simulation (6) respectively. Chun Huang (Ann) NY. A two layer electrode structure for improved Li ion diffusion and volumetric capacity in Li ion batteries. Nano Energy. 2017;31:377-85. Chen YH, Wang CW, Zhang X, Sastry AM. Porous cathode optimization for lithium cells: Ionic and electronic conductivity, capacity, and selection of materials. Journal of Power Sources. 2010;195(9):2851-62. Arrebola JC, Caballero A, Hernan L, Morales J. PMMA-assisted synthesis of Li1-xNi0.5Mn1.5O4-delta for high-voltage lithium batteries with expanded rate capability at high cycling temperatures. Journal of Power Sources. 2008;180(2):852-8. Oh SW, Myung ST, Bang HJ, Yoon CS, Amine K, Sun YK. Nanoporous Structured LiFePO4 with Spherical Microscale Particles Having High Volumetric Capacity for Lithium Batteries. Electrochem Solid St. 2009;12(9):A181-A5. Jo M, Hong YS, Choo J, Cho J. Effect of LiCoO2 Cathode Nanoparticle Size on High Rate Performance for Li-Ion Batteries. Journal of the Electrochemical Society. 2009;156(6):A430-A4. Cooper SJ, Berteia A, Shearing PR, Kilner JA, Brandon NP. TauFactor: An open-source application for calculating tortuosity factors from tomographic data. SoftwareX. 2016:203-10.