UC Berkeley

Multivalent-ion batteries offer an alternative to Li-based technologies, with the potential for greater sustainability, improved safety, and higher energy density, primarily due to their rechargeable system featuring a passivating metal anode. Although a system based on the Ca2+/Ca couple is particularly attractive given the low electrochemical plating potential of calcium, the remaining challenge for a viable rechargeable Ca battery is to identify Ca cathodes with fast ion transport due to the sluggish kinetics that arise from stronger electrostatic interactions between the multivalent-ion and host lattice. In this dissertation, a high-throughput computational pipeline is adapted to (1) discover novel Ca cathodes in a largely unexplored space of “empty intercalation hosts” and (2) develop material design rules for Ca-ion mobility. Several new Ca cathode materials are investigated theoretically, and the zircon family alongside W2O3(PO4)2 are evaluated experimentally. A Nudged Elastic Band (NEB) migration barrier as low as 113 meV is computationally found in YVO4, which is the lowest Ca2+ barrier reported to date. Low barriers are confirmed across 18 zircon compositions, which are attributed to the low coordination change and reduced interstitial site preference of Ca2+ along the diffusion pathway. W2O3(PO4)2 also has a low NEB barrier of 168 meV within a one-dimensional (1D) ion percolation topology. Among the four zircon materials that are synthesized, characterized, and electrochemically cycled, the highest initial capacity of 81 mAh/g and the most reversible capacity of 65 mAh/g are achieved in YVO4 and BiVO4, respectively. Reversible Ca cycling is achieved with a capacity of 25 mA h/g in W2O3(PO4)2. To further accelerate the screening for promising Ca cathodes, machine learning (ML) Random Forest (RF) and Extreme Gradient Boosting (XGB) classification models are created with local environment descriptors based on a large, structurally and chemically-diverse dataset of minimum energy pathways that span over 5,000 Density Functional Theory (DFT) site energy calculations. Accuracies of 92% are achieved, material design metrics are quantified, ML force-fields are leveraged in another iteration of the screening, and a total of 27 novel Ca cathode materials are highlighted for further investigation.