Multi-Layer Anodes for Fast Charging of Li-Ion Batteries

Abstract

Li-ion batteries in automotive applications are expected to offer high energy and power density for proper range and charging time, respectively. Although a thicker electrode can improve energy density, fast charging of these cells remains a challenge. Restricted ion transport in high-density electrodes impedes fast charging and causes lithium plating, which degrades cell capacity quickly. Lithium plating happens mostly at low temperatures, high state of charge (SOC), and high charge rates.In this work, we present a combination of pouch-cell experiments and computational modeling of a two-layer anode structure designed by EnPower compared with a single-layer homogeneous baseline (Fig. 1). The multi-layer anode architecture consists of different materials and formulations in the layers near the current collector and separator, resulting in a high-energy electrode design with low tortuosity. The single-layer homogeneous baseline comprises identical materials in identical overall mass fractions, representing industry-standard electrode architectures. 6.4 Ah pouch cells were assembled and tested to quantify ohmic resistance (DCIR), discharge rate capability, fast-charging capability, and fast-charging cycle life. Electrode-level characterizations were performed as inputs to a computational model. MacMullin numbers for both the multi-layer and single-layer electrodes were determined by the blocking electrolyte method with symmetric pouch cells [1]. Image analysis of cross-sectioned micrographs was performed to quantify electrode porosity as a function of thickness. A pseudo-two-dimensional (Newman-type) electrochemical-thermal model was designed to better represent the performance of the multi-layer electrodes.Simulations show superior ion transport and lithiation behavior in the multi-layer anode (MLA) compared to the conventional homogenous single-layer anode (SLA), which supports the experimental data. Pouch cell testing results show multi-layer anodes have reduced DCIR, higher discharge capacity retention at elevated rates, increased tolerance for aggressive fast-charging results, and improved cycle life under high duty-cycle fast-charge cycling. This means MLA structures can reliably be employed in cell designs capable of delivering both high power and energy density.[1] Pouraghajan, Fezzeh, et al. Journal of the Electrochemical Society 165.11 (2018): A2644. Figure 1