Achieving Long Life Time Batteries: Understanding and Controlling Non-Faradaic Reactions

Abstract

Characterization of electrochemical properties determines the energy content for new materials and possible viability for a potential application. Equally critical yet more challenging is determining the non-Faradaic parasitic reactions of the active materials in a battery environment and their relationship to useful battery life. In order to be successful in long calendar life battery applications, only very low levels of parasitic reactions can be tolerated. For example, calendar life is a particularly important consideration for implantable medical batteries, especially for devices powering essential life functions such as cardiac rhythm management devices. Determining stability by direct systems level testing is slow and expensive as it can require many years and many batteries to affirm. The dissolution of cathode materials including manganese, cobalt and vanadium oxides in battery systems has been identified as a specific battery failure mechanism. However, dissolution studies including kinetic analysis of the dissolution of active battery materials in non-aqueous electrolytes are largely absent from the literature. We developed a quantitative approach to assess battery materials for their solubility and then validated the approach with battery testing. In this study, a series of vanadium oxide and vanadium phosphate based cathode materials were studied relative to their dissolution in battery electrolyte. Kinetic analysis of the results provided a quantitative approach for understanding the impact of structure and composition on the dissolution of active materials. Negative electrode surfaces from cells using cathodes displaying different levels of solubility were analyzed. A conceptual model of the negative electrode surface electrolyte interphase was developed to rationalize the observed cell impedance and performance. Implications for lifetime prediction for these and other battery systems will be discussed.