Raising temperatures and limiting load and voltage could all help prolong the life of lithium-ion batteries, according to results of a three-year research effort.
The European Union-funded ABattRelife project also singled out damage to negative graphite electrodes as a factor that leads to a sharp drop in battery performance.
“The project showed that it was possible to delay aging by reducing loading capacities, limiting voltage and raising temperatures, ideally to around 35°C,” wrote officials from Germany’s Fraunhofer Institute for Silicate Research ISC, where the results were revealed.
Researchers with the ABattRelife project also found that it was predominantly the negative electrodes of lithium-ion batteries that cause end-of-life performance losses.
“Shortly before the extreme bend of performance, small areas showed significant changes, so-called lithium plating,” wrote Fraunhofer in a press release. “The scientists at the Fraunhofer ISC discovered that the conductor compressed these areas [more intensely] than the rest of the battery. This indicates that pressure produces a local overload, which leads to massive loss of lithium and completely destroys this part of the battery.”
ABattRelife was set up in 2012 to create a knowledge base pertaining to high-voltage traction battery deterioration, a safe management structure for electric-vehicle battery recycling and strategies, and technologies for battery reuse.
The research push brought together 10 institutions, including PSA Peugeot Citroën, BMW and DNV KEMA, from across France, Germany and the Netherlands.
One team, led by the German project developer Beck Automation, put together a storage system “made of readily available components” and used BMW car batteries, said Fraunhofer.
Another developed a recycling method to recover up to 50 percent of the raw materials in electric-vehicle batteries, although the process appears to have had mixed results.
“During the development, it became clear that the process had to be adapted to the different types of battery and that the effort depends highly on the different components,” Fraunhofer reported. “The recycling process has already been optimized in order to use it on a pilot scale. The question remains whether greater effort is justified from the economical point of view.”
It is not clear how the research will be used now that the ABattRelife initiative has finished. For now, battery life remains a critical issue for electric vehicles, stationary energy storage and consumer electronics devices.
Last month, for example, Samsung created a stir when it announced a breakthrough that could double the lifespan of lithium-ion batteries. Media attention focused on the implications for batteries used in Samsung’s leading Galaxy smartphone brand.
However, the discovery, which appears to center on the electrode problems identified by ABattRelife, could be extended to the automotive and stationary energy-storage battery systems sold through Samsung SDI.
“Some of the best electrochemists in academia and industry are working on the battery ageing problem,” stated Mike Fife, chief technology officer at the storage system developer Demand Energy.
“Demand Energy is focused downstream on modeling aging parametrically for a wide range of operational profiles. When we incorporate these models into our real-time controls, aging becomes a part of the cost function that we optimize on a minute-by-minute basis," said Fife.
Being able to manage battery lifespan helps to significantly improve the cost of projects, he said. “For most of our applications, battery cost is still dominant in the overall cost of a storage system, so proper real-time consideration and treatment of aging can dramatically reduce the levelized cost of electricity.”
Until long-life battery chemistries make it to the mainstream, most energy-storage system developers will continue to focus on active system management to extend the useful lifespan of batteries.
Much of this effort already appears focused on the problem areas identified by ABattRelife.
“We believe that environmental control and monitoring is essential to optimizing lifetime,” said Doug Staker, vice president of global sales at Demand Energy. “For both lithium and lead-acid, keeping temperatures under control is mandatory. One element that we see for both designs is that the physical mass of a battery tank helps keep the system stable, and we don’t see a lot of internal heating effects during operation.”
Furthermore, said Staker: “Keeping voltage and temperature within a manufacturer’s specification, and being able to track and demonstrate that the system has not exceeded these limits, is a key point to a storage system’s software.”