Why do batteries fail?
Why batteries go bad Rechargeable batteries are found in a range of everyday devices, from shavers and laptops to cars and airplanes. Over time, these batteries can fail, either through a gradual loss of charge or through the inability to work under tough environmental conditions, leading to more catastrophic failures that cause fires or explosions. Palacin and de Guibert review such failures and suggest that, although often chemistry specific, common causes can be found. They also look at ways to enhance battery lifetime, such as through improved battery management systems, which are needed for advanced rechargeable batteries. Science, this issue p. 10.1126/science.1253292 BACKGROUND We are all familiar with the importance of mobile power sources (automobile batteries, cell phone batteries, etc. and their seeming tendency to malfunction at just the wrong moment. All batteries show performance losses during their service lives that involve a progressive decrease in capacity (loss of autonomy) and increase in internal resistance, leading to voltage decay and loss of power. Battery aging phenomena evolve at substantially different rates depending on storage or usage conditions (temperature, charge/discharge rates, and voltage operation limits) and are specific to each battery chemistry. The study of the origin of such processes is important for battery calendar life predictions, but this research is complex to carry out because it involves field trials as well as extrapolation from accelerated tests using suitable models. ADVANCES Electrification of automotive transportation and renewable energy integration constitute two imperative pathways toward reduction of gas emissions and global warming. These incur challenges in terms of energy storage technologies, for which batteries emerge as a versatile and efficient option. Durability is critical per se in such large scale applications and also has a direct impact in terms of cost. As a result, efforts toward understanding the mechanisms of battery degradation have intensified in recent years. Aging and failure mechanisms result from various interrelated processes taking place at diverse time scales, hence their complete elucidation is a very challenging target. Battery operation upon each charge/discharge cycle should ideally only involve changes in the phases present at both electrodes and modification of their physical properties. However, all battery components can interact with one another to some extent, contributing to a convoluted system of interrelated physicochemical processes in which the influences of temperature and charge/discharge rate are decisive. Although interactions between the active materials and the electrolyte are largely responsible for aging upon storage, cycling generally damages electrode active materials' reversibility because of the mechanical stresses induced by the structural changes taking place. Although both mechanisms are often considered as additive, interactions may occur and some additional factors (such as temperature) have an impact on both. Moreover, the variety of possible parasitic reactions is enhanced by the number of chemical elements present in the cell; this number is lowest for Pb/acid batteries (redox processes involve lead at both electrodes and current collectors are also made of lead) and highest for lithium ion batteries, which can also comprise a larger variety of subtechnologies depending on the active materials used. Overall, the current available knowledge on these matters results from a vast combination of experimental and modeling approaches and has greatly benefited from the progressive improvement of available materials science characterization tools. OUTLOOK The requirements for battery long term stability are extremely stringent, and hence the advent of batteries with optimized calendar and cycle life will only be triggered by a full understanding of the ways in which the different systems fail. Thorough studies involving both testing and monitoring of real or model cells under different environments and/or postmortem studies using a wide range of experimental techniques coupled to modeling approaches are crucial to the complete elucidation of aging and failure mechanisms. Such knowledge is vital to developing reliable, realistic operation models, which in turn will synergistically contribute to the development of batteries with optimized calendar life. This is currently a research priority in the field that is expected to yield substantial progress in the years to come. Performance degradation is common to all battery technologies. Failure and gradual performance degradation (aging) are the result of complex interrelated phenomena that depend on battery chemistry, design, environment (temperature) and actual operation conditions (discharge rate, charge protocol, depth of discharge, etc. Knowledge of such processes is crucial for the widespread deployment of large scale battery applications such as transportation and the electric grid. Battery failure and gradual performance degradation (aging) are the result of complex interrelated phenomena that depend on battery chemistry, design, environment, and the actual operation conditions. The current available knowledge on these matters results from a vast combination of experimental and modeling approaches. We explore the state of the art with respect to materials as well as usage (temperature, charge/discharge rate, etc. for lead acid, nickel cadmium, nickel metal hydride, and lithium ion chemistries. Battery diagnosis strategies and plausible developments related to large scale battery applications are also discussed.
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