Researchers at Rensselaer have developed a new technique using heat to enable self-healing lithium-metal anodes to eliminate dangerous dendrite buildup, paving the way for higher energy density battery technologies.

Despite their extremely high energy density, lithium (Li) metal electrodes are not currently deployable in commercial rechargeable batteries because electrochemical plating and stripping invariably leads to growth of dendrites that reduce coulombic efficiency and eventually short the battery. Numerous approaches have been proposed to eliminate dendrite formation.

Now, a team from Rensselaer Polytechnic Institute (RPI) is taking essentially the opposite approach. The researchers ramped up the current density (charge-discharge rate) of the battery, thereby triggering extensive self-heating of the resulting dendrites, resulting in the surface diffusion of lithium—in other words, spreading the dendrites into an even layer. A paper on their work is published in the journal Science.

Image shows the temperature driven merging and fusing of lithium dendrites into a uniform (smooth) surface, which eliminates the risk of electrical shorting in lithium-ion batteries. Click to enlarge.

It is generally accepted that the dendrite problem is exacerbated at high current densities. Here, we report a regime for dendrite evolution in which the reverse is true. In our experiments, we found that when the plating and stripping current density is raised above ~9 milliamperes per square centimeter, there is substantial self-heating of the dendrites, which triggers extensive surface migration of Li. This surface diffusion heals the dendrites and smoothens the Li metal surface. We show that repeated doses of high-current-density healing treatment enables the safe cycling of Li-sulfur batteries with high coulombic efficiency.

—Li et al.

We have found that lithium metal dendrites can be healed in situ by the self-heating of the dendritic particles.

—Nikhil Koratkar, the John A. Clark and Edward T. Crossan Professor of Engineering at Rensselaer and corresponding author

The Rensselaer researchers’ proposed solution takes advantage of the battery’s internal resistive heating. Resistive heating (also known as Joule heating) is a process in which a metallic material resists current flow and, as a result, produces heat. This “self-heating” occurs through the charging and discharging process.

The RPI researchers first demonstrated this smoothening (healing) of the dendrites in a lithium-lithium symmetrical cell. They then showed the process with the same results in a proof-of-concept demonstration using a lithium-sulfur battery.

Dendrite healing in a Li-S battery. (A) Cycle stability and CE (highlighted in yellow) of Li-S batteries with and without periodic doses of healing treatment. Blue data points indi-cate performance of the baseline Li-S cell cycled at ~0.75 mA cm−2 without healing treatment. The red data points are for intermittent healing treatment (at current density of ~9 mA cm−2) applied between the 21 and 50th, 151st and 180th, and 311th and 360th cycles. For the remaining cycles, a current density of ~0.75 mA cm−2 was applied, which is identical to the baseline cell without healing. (B) Comparison of average CE of the Li-S battery when operated at a current density of ~0.75 mA cm-2 with and without the healing treatment. (C) Digital photo of membrane separator in the cycled Li-S batteries after 250 cycles of charge-discharge at a current density of ~0.75 mA cm−2 without the healing treatment. The dashed circle indicates the presence of dendritic Li particles that are impregnated in the separator. (D) Corresponding photo of the membrane separator taken after 360 cycles of charge-discharge with the healing treatment. (E) Morphology of the Li metal electrode surface after the third healing stage [after the 360th charge-discharge cycle indicated in (A) by the dashed circle]. Credit: AAAS, Li et al. Click to enlarge.

Dendrite healing would be carried out by battery management system software, which would provide doses of “self-healing” treatment by running a few cycles at a high rate of charge and discharge when an electronic device is not in use.

A limited amount of cycles at high current density would occur to heal the dendrites, and then normal operations can be resumed. Self-healing would occur as a maintenance strategy, long before the dendrites become a safety hazard.

—Nikhil Koratkar

Resources

• Lu Li, Swastik Basu, Yiping Wang, Zhizhong Chen, Prateek Hundekar, Baiwei Wang, Jian Shi, Yunfeng Shi, Shankar Narayanan, Nikhil Koratkar (2018) “Self-heating–induced healing of lithium dendrites” Science Vol. 359, Issue 6383, pp. 1513-1516 doi: 10.1126/science.aap8787