Enabling Fast Charging Lithium-Ion Batteries through the Rational Design of 3-D Anode Architectures

Today’s Li-ion technology is highly optimized for performance at relatively slow charging operation. However, significant challenges still present for fast charging conditions (> 4C). These challenges include large kinetic polarizations, concentration gradients, heat generation, and Li metal plating on the surface. In state-of-the-art Li-ion batteries with high energy densities, the electrodes are relatively thick (> 100 μm), which leads to a tradeoff between energy density and high-power performance. This is because thicker electrodes with a tortuous pathway naturally limit Li-ion transport through the electrode thickness, resulting in large electrolyte concentration gradients during cycling. This leads to large cell polarization, which reduces the accessible capacity of the battery under fast-charging conditions. In addition, the electrochemical potential of the anode can easily become more negative than the thermodynamic potential of Li metal during fast charging, resulting in 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 negative electrodes. 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-calendared electrodes.[1] The patterned anode architecture consists of a hexagonal close-packed array of vertical channels that serve as linear pathways for rapid ionic diffusion through the electrode thickness. This allows for a more homogeneous flux of Li throughout the volume of the electrode and decreased ionic concentration gradients, in comparison to slow/tortuous diffusion paths in the conventional anode, thus improving the accessible capacity of the electrode during fast charging. Through rationally designing and tuning the channel pore diameter and spacing, an optimal geometry can be determined to achieve optimal high-rate cycling performance for a given anode loading and porosity. In addition, we develop an electrochemical dynamics simulation framework to capture the experimentally-observed voltage changes during charge/discharge in both conventional and patterned electrodes. Through accounting for the anode physical properties and structural details, our simulation tool can predict/provide valuable information such as concentration profile and electrode polarization during fast charging. This further helps us pinpoint the design rules and tradeoffs associated with the patterned anode architecture. Utilizing the model-informed design of 3-D hierarchical anode structures, we demonstrate significant improvements (> 100%) on the accessible capacity and minimal capacity fade during fast charging (up to 6C) with anode loading of > 3 mAh/cm2. This work thus demonstrates the viability of realizing high energy density Li-ion batteries with fast charge capability based on thick electrodes. [1] Y. Kim, A. Drews, R. Chandrasekaran, T. Miller, J. Sakamoto, Ionics 24, 2935 (2018).