Performance of cells with a garnet electrolyte at low temperatures is of critical importance to deployment of solid-state cells in electric vehicles (EV). Though numerous attempts have been made to develop catholytes with low-temperature performance capabilities, the compatibility between catholytes and garnet under low-temperature conditions has not been explored. Realizing low temperature capable catholytes for solid-state cells is essential for deployment of solid-state technologies for EV applications so that solid-state cells may remain fast-charging and long lasting even in adverse conditions. To maximize cell performance and energy density, ION is developing a hybrid cell which is based upon a garnet-type solid state electrolyte formed into a bilayer structure which enables no applied pressure or cell heating for cell operation (a critical factor for ease of integration into EV battery packs). The bilayer is composed of a dense layer that acts as a separator and a porous layer that acts as a host structure for an energy-dense lithium metal anode. The proposed project will aim to develop a drop-in catholyte integrated into solid-state cells which meet USABC low-temperature capability guidelines. The catholyte is expected to demonstrate >70% useable energy at a C/3 discharge rate at -20°C, operation at -30°C, and survival up to -40°C. This catholyte will be compatible with LLZO type solid-state electrolytes and stability will be analyzed under a range of voltages (0.0 V to 6.0 V vs. Li+/Li) and temperatures (-40 °C to 66 °C) to demonstrate catholyte feasibility in full cells. ION will engage strong industrial partners who manufacture electrolyte substituents from R&D- to Gigafactory-level scales. This approach is critical to technology deployment because there is a direct path to scale-up supply and setting of cost targets necessary for EV deployment. In Phase I, the proposed project will develop a catholyte and hybrid cell that meet USABCs targets for low-temperature conditioning. The project is designed to incrementally demonstrate performance in low temperatures from 0°C to -30°C, with cell form factor scaling from an initial research-level single electrode pair (dimensions 1x1 cm) to large-scale 4-electrode pair (dimensions 4x4 cm) stacked cell with =200 mAh capacity. Cell survival will be examined at -40°C. Key performance and evaluation metrics include ex situ garnet compatibility, low-temperature performance, flammability, and manufacturability. While low temperature performance is the focus of this Phase I project, it is important to note that the overarching objective is to provide a catholyte for a battery compliant with all USABC metrics, including at elevated temperatures. High-temperature testing will be conducted at 52°C for operation and at 66°C for survival. Success in the development of a low-temperature capable catholyte for solid-state applications in Phase I will have a direct impact on the extent to which the rate and total deployment of EV cells is achieved. Future Phase II and III projects will lead to the further optimization, scaling, and commercialization of the catholyte formulation for a host of cell applications. Several groups would benefit from the development and access to this type of catholyte. This technology will lend itself to additional development from cell makers or licensees, lowered cell costs for automotive OEMs building U.S. factories, increased manufacturing jobs for the American public, and improved supply chain security.
