Lithium Ion Cell Development for Photovoltaic Energy Storage Applications

The overall project goal is to reduce the cost of home and neighborhood photovoltaic storage systems by reducing the single largest cost component – the energy storage cells. Solar power is accepted as an environmentally advantaged renewable power source. Its deployment in small communities and integrated into the grid, requires a safe, reliable and low cost energy storage system. The incumbent technology of lead acid cells is large, toxic to produce and dispose of, and offer limited life even with significant maintenance. The ideal PV storage battery would have the safety and low cost of lead acid but the performance of lithium ion chemistry. Present lithium ion batteries have the desired performance but cost and safety remain the two key implementation barriers. The purpose of this project is to develop new lithium ion cells that can meet PVES cost and safety requirements using A123Systems phosphate-based cathode chemistries in commercial PHEV cell formats. The cost target is a cell design for a home or neighborhood scale at <$25/kWh. This DOE program is the continuation and expansion of an initial MPSC (Michigan Public Service Commission) program towards this goal. This program further pushes the initial limits of some aspects of the original program – even lower cost anode and cathode actives implemented at even higher electrode loadings, and as well explores new avenues of cost reduction via new materials – specifically our higher voltage cathode. The challenge in our materials development is to achieve parity in the performance metrics of cycle life and high temperature storage, and to produce quality materials at the production scale. Our new cathode material, M1X, has a higher voltage and so requires electrolyte reformulation to meet the high temperature storage requirements. The challenge of thick electrode systems is to maintain adequate adhesion and cycle life. The composite separator has been proven in systems having standard loading electrodes; the challenge with this material will be to maintain proven performance when this composite is coated onto a thicker electrode; as well the high temperature storage must meet application requirements. One continuing program challenge was the lack of specific performance variables for this PV application and so the low power requirements of PHEV/EV transportation markets were again used