POSTECH: heat-treated copper collector extends anode-free lithium metal cell life more than fivefold
Heat-treating copper foil at about 850 °C ordered its grain boundaries. Lithium then plated flat, and laboratory anode-free cells lasted more than five times longer.
A research team at POSTECH has shown that the evenness of lithium growth in anode-free lithium metal batteries depends on grain boundaries in the copper current collector, and has developed a way to control them. The university announced this on the 11th, as reported by kpinews.kr kpinews.kr
kpinews.krkpinews.krOpen source ↗. The group includes Professors Minah Lee and Jihyun Hong of the Department of Battery Engineering, together with Professor Dong-Yeon Kim's group at the Department of Chemistry, Jeonbuk National University. The work was published online in ACS Energy Letters.
Why the copper foil matters
An anode-free cell has no anode material: lithium is deposited directly on thin copper foil, which reduces weight and volume. With repeated charging and discharging, however, the lithium accumulates unevenly, loses electrical contact, and the cell's life falls quickly. Earlier work focused on coatings and structures added on top of the foil, treating the copper as little more than a conductive path.
Under magnification, copper foil consists of small grains, each with atoms stacked in one orientation, fitted together like mosaic tiles. Where grains meet, the atomic arrangement is disrupted. The team found that uniform lithium growth is governed not by grain orientation but by how many boundaries there are and how well they fit together.
Heat treatment and results
The researchers heat-treated copper foil to tune grain size. A higher temperature gave larger grains and fewer boundaries, and the remaining boundaries became better aligned. Turning the whole foil into a single crystal was not necessary; a temperature near 850 °C was the practical optimum kpinews.kr
kpinews.krkpinews.krOpen source ↗.
In plating tests, lithium on foil with disordered boundaries clustered in places and grew in branch-like shapes. On foil with ordered boundaries it formed a flat, dense layer across the surface. Atomistic simulations showed that disordered boundaries act like high speed bumps that trap lithium, while ordered boundaries present lower barriers and let lithium spread widely. Anode-free cells made with this copper had a service life more than five times longer. The approach relies on heat treatment alone, without a demanding single-crystal process.
