Heating could offer longer-lasting batteries

Although a range of factors can affect the life span of batteries at high temperatures, researchers at the California Institute of Technology have shown that further heating could really help to prolong their longevity. Using a combination of a new experimental setup and computer simulation, they demonstrated that heat could extend the life of rechargeable batteries by breaking down the damaging structures called dendrites that can grow inside them, as well as help to predict their inherent structural characteristics, especially important with the surge in demand for energy storage devices.

Over time and many recharging cycles, the electrodes used in rechargeable battery cells can grow small, branch-like filaments called dendrites that can lead to short-circuiting, cell overheating and possible ignition, damaging the battery irreparably. The dendrites can also break off from the anode entirely and move around in the electrolyte, reducing the ability of the battery to store energy.

Although this critical problem is general to all rechargeable batteries, pure lithium has very high propensity to grow dendrites during consecutive recharging periods. In their experiment, as reported in The Journal of Chemical Physics [Aryanfar et al. J. Chem. Phys (2015) DOI: 10.1063/1.4930014], the team measured the temperature-dependent reduction of the lithium dendrites using a novel design and method. They grew lithium dendrites on a test battery before heating them over a couple of days, finding that temperatures of up to 55^oC managed to reduce the representative dendrites by up to 36%.

In this way, they demonstrated that higher temperatures triggered the atoms in the dendrites to move around in a couple of ways. Atoms at the tip of the pyramid structure would drop to lower levels, while atoms at a lower level would move off and leave a vacant area that is then taken by another atom, a reorganization that generated enough motion to topple the dendrite. If you know how much energy is required to change the dendrite’s structure, then it is possible to better understand its structural characteristics.

As team leader Asghar Aryanfar points out, “the results are useful for hindering the growth of destructive microstructures that cause hazard and capacity fade in rechargeable batteries, therefore leading to longer-lasting rechargeable batteries.” The work could lead to improved cyclic thermal treatment of dendrites to avoid the eventual short-circuiting of the cell during operation, and the team are also now looking to focus on preventing the nucleation of dendrites rather than preventing their growth.

"The results are useful for hindering the growth of destructive microstructures that cause hazard and capacity fade in rechargeable batteries, therefore leading to longer-lasting rechargeable batteries.”Asghar Aryanfar