2018-04-12 | Editor:et_editor 571 pageviews

With Self-heating Effect, Li Metal Anode's Dendrites Will Become Smooth

Lithium (Li) metal anode battery's energy density is far higher than that of graphite anode's Li-ion battery. However, Li-metal anode battery's severe dendrite issue makes it hard to commercialize in a huge scale. However, scientists discovered, if repeating the charge-discharge cycles of high current density, dendrites with substantial self-heating effect will be smoothened out on the surface of Li metal anode.

Why does this new discovery matter? Because rechargeable lithium-ion battery is the mainstream battery of consumer electronics products. Li-ion battery is gaining ground on electric vehicle and storage of electricity grid segments.

Typically, a rechargeable lithium-ion battery's cathode is Li-metal oxides, and its anode is graphite.

In a graphite anode battery, there is no Li dendrite issue, so graphite anode battery is the best choice for now. However, in the near future, graphite anode battery might not satisfy the demand of increasing battery capacity.

Thus, scientists are seeking technologies for higher-energy-density Li-metal anode battery.

Researchers in Rensselaer Polytechnic Institute found a way to use heat inside the battery to merge dendrites on the surface of Li metal anode. Thus, the surface of the Li electrode becomes smoother. In the words of Professor Nikhil Koratkar, the research team leader in the Department of Mechanical, Aerospace, and Nuclear Engineering, dendrites can be "healed" via self-heating effect. This team's research paper was published in the journal of Science.

Let's explain this team's research in a simple way. A battery basically consists of cathode, anode, electrolyte and membrane separator. In particular, membrane separator is located in between the cathode and anode, in order to prevent the shorting of battery.

When a battery is discharged, Li+ is transported from anode to cathode. This is how electricity current is generated. When the battery is charged, Li+ flows from cathode to anode. During charge-discharge cycles, Li metal anode battery's surface of anode tends to accumulate Li dendrites.

These dendrites are problematic. Because they will pile up to a point that the sharp dendritic projections will puncture the separator and lead to a short circuit. In other words, the battery will catch fire.

To make higher energy density Li metal anode battery feasible, these researchers use resistive heating inside the battery, so that dendrites will become smoother. Resistive heating is also called Joule heating. Joule heating is a process where the metal material resists the electric current and heat is generated. The self-heating effect can take place during the charge-discharge cycles.

The increased current densities of a battery which results from the accelerated charge-discharge cycles will allow the self-heating effect to be enhanced. This process can smoothen and diffuse the dendrites. The research team names the diffusion process "healing."

The research seems to be promising because increasing higher current densities during the cycles of charge-discharge can smoothen with dendrites and prevent an electrical short circuit from happening. The battery will be safer with higher energy density.

However, can this method prevent battery capacity from rapid decay? Perhaps the team will need to research more.

(Image credit: Rensselaer Polytechnic Institute)

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