Membranes for Solid State Lithium Batteries

The use of a solid polymer electrolyte instead of the conventional liquid or gel electrolyte can drastically improve the safety aspects of Li-ion batteries. However, existing solid electrolytes based on poly(ethylene oxide) (PEO) do not meet the functional performance requirements. At low temperatures, the conductivity is poor due to the presence of crystalline PEO segments, which restrict lithium ion mobility. This restriction limits the useful operating temperature of Li-ion polymer batteries to between 70oC and 100oC, which excludes the use of solid polymer based batteries in room temperature commercial applications. This project will investigate the use of a novel nanocomposite organic/inorganic hybrid material as a potential solid polymer electrolyte system that can exhibit high Li-ion conductivity at room temperature and below, along with good mechanical properties. The presence of inorganic moieties in the material will inhibit the crystallization of PEO chains, leading to increased low temperature ionic conductivity and an increased lithium transference number. Phase I involved the synthesis of a composite material in which the PEO component remained amorphous, resulting in an order-of-magnitude higher Li-ion conductivity at room temperature and below, and almost twice the lithium transference number compared to conventional PEO/Li-salt membranes. In Phase II, the structure of the new material will be optimized, electrolyte membranes will be produced via an economical processing method, and both Li-metal and Li-ion cells will be fabricated and tested. Commercial Applications and other Benefits as described by the awardee: Although rechargeable lithium-ion batteries are ubiquitous in the commercial marketplace, existing Li-ion batteries contain flammable liquid electrolytes, which compromises safety. The proposed solid polymer electrolyte should enable the development of safer lithium batteries, particularly those that can be used in large format batteries for electric and hybrid electric vehicles, telecommunications, and electric utility applications.