Cycle Life Sensor for Rechargeable Lithium Batteries

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Rechargeable power sources which provide high energy densities at high rates have been under active investigation for the past twenty-five years. While many effective rechargeable positive electrode materials (the cathode) have evolved over the past 10 years, progress in developing a practical secondary Li negative (the anode) has been slow. The principal reason for the slow evolution of this technology resides in the inability to cycle the Li electrode at high capacities with high efficiency over a long period of time. This is because aprotic organic solvents and supporting electrolyte salts are intrinsically reactive with Li. Thus, the relative rates of a host of competing reactions ultimately determine cell cycle life. The goal of this research is two-fold: to ascertain which chemical degradation products ultimately influence cell safety and cycle life; and to develop a commercial in situ electroanalytical sensor which specifies the state of a cell at any point along its cycle life. In battery configurations, a single cycle-life or voltage limited cell will unbalance the system causing premature failure. A state of cell sensor would enable the end user to simply replace a single bad cell rather than the entire battery unit. The PIs plan to use computer-controlled square wave voltammetry (SWV) at two or more microelectrodes to obtain information regarding homogeneous and heterogeneous cell chemistries. Ni microelectrodes, embedded in the cell package, will be used to directly sense the nature and degree of Li/electrolyte reactivity as a function of cycling history. They are well qualified to complete this work and their facilities are adequate. A Phase I SBIR grant is recommended.