UC Berkeley

To combat the effects of global warming, renewable energy sources are desirable but produce power intermittently, greatly limiting their ability to fulfill electricity demand on the grid. Storing energy produced for the grid and dispensing it at a later time would remove a major obstacle in the adoption of renewable energy sources. However, grid scale energy storage must be inexpensive to be cost-competitive with existing energy sources such as coal and natural gas. Batteries have been widely considered due to their energy storage capabilities, but existing technologies are too expensive, often limited by raw material cost and difficulty scaling to high capacity installations. Flow batteries are designed for scaling to high capacities, but existing materials remain too costly for widespread adoption.

Semi solid flow batteries (SSFB) are developed by forming suspensions of electrochemically active and conductive particles for use as an anolyte or catholyte in a flow battery. By utilizing micron-scale powders from mature battery chemistries in a flowable suspension, the benefits of energy-dense intercalation chemistries with the scalability of flow battery architectures can be combined for low cost electrochemical storage. Presently, a narrow set of materials has been explored, focusing on chemistries with a lithium anode. In this work, a magnesium SSFB with an optimized MoS2 cathodic slurry is demonstrated as a low cost and high material abundance alternative to lithium-based chemistries.

In this work, a mixed ionic-electronic conductive network is designed around a dual-ion (Mg2+, Li+) electrolyte, by combining the all-phenyl complex electrolyte (APC) with LiCl. MoS2 and Ketjenblack (KB) are dispersed in the APC+LiCl electrolyte to form the cathodic slurry. The rheological, electrical, and electrochemical properties of APC-MoS2-KB slurries with varying compositions have been measured. Full cells, with a Mg foil anode and MoS2 slurry cathode, are shown to cycle reversibly in a non-flowing and flowing configuration, reaching 225mAh/g discharge capacity. LiCl concentration and KB concentration are identified as critical to high capacity slurry cathodes. The relative impacts of Mg2+ and Li+ are quantitatively analyzed, showing that both ions are active and reversible during cycling. The rate capability of the optimized slurry is characterized and discussed, and long term cycling tests are presented, showing non-flowing and flowing slurry batteries for 135 cycles. This work provides experimental data and insight into how existing low cost material sets can be utilized in a semi solid flow battery architecture.