(Invited) Enabling Fast Charging Li-ion Batteries through Three-dimensional Graphite Anode Design

Abstract

Current Li-ion battery technology is highly optimized for performance at relatively slow charging rates. However, significant challenges still present for fast-charge conditions with < 15-minute charge time.1 In state-of-the-art Li-ion batteries with high energy densities, thick electrodes (> 50 μm) are adopted, which leads to a tradeoff between energy density and high-power performance. Thicker electrodes with tortuous pathways limit Li-ion transport through the electrode thickness, resulting in large electrolyte concentration gradients during cycling. This causes large cell polarizations, which reduce the accessible capacity of the battery. In addition, the electrochemical potential of the graphite anode can become more negative than the thermodynamic potential of Li metal during fast charging, resulting in irreversible Li plating. Therefore, to simultaneously achieve fast charging and maintain energy density of Li-ion batteries, new approaches are required to address Li ionic transport limitations through the thick graphite anodes.In this work, we demonstrate a structural modification of conventional graphite anodes to improve their fast-charge capability. This is achieved by introducing laser-patterned vertical channels into post-calendered graphite anodes.2 This 3-D electrode architecture consists of a hexagonal close-packed array of vertical channels that serve as linear pathways for rapid ionic diffusion through the electrode thickness, allowing for a more homogeneous Li-ion flux throughout the volume of the electrode and decreased ionic concentration gradients. As a result, the accessible capacity of the electrode can be significantly improved and Li plating can be minimized during fast charging. Utilizing the 3-D electrode design, we demonstrate significant improvement in capacity fade at 4C (15-minute) and 6C (10-minute) charge rate with industrial-relevant electrode material and loading (> 3 mAh/cm2 electrode loading in > 2Ah pouch cells). This work thus demonstrates the viability of realizing high energy density Li-ion batteries with fast charge capability based on thick electrodes.Reference Ahmed, S. et al. Enabling fast charging e A battery technology gap assessment. 367, 250–262 (2017).Chen, K.-H; Namkoong, M.; Goel, V.; Yang, C.; Mazumder, J; Thornton, K.; Sakamoto, J; Dasgupta, N. P. Efficient Fast-Charging of Lithium-ion Batteries Enabled by Laser-Patterned Three-Dimensional Graphite Anode Architectures. J. Power Sources In Press (2020).