467 Wh/kg. That is the specific energy a pouch cell reached at the Hong Kong University of Science and Technology (HKUST), in an anode-free lithium metal battery, according to the study. The researchers say the figure is comparable to conventional commercial batteries. A full coin cell kept 90% of its capacity after 200 charge-discharge cycles.
Within weeks, a second group in South Korea reported its own fix for the same weak point. Both teams are chasing the dendrite problem.
What anode-free means
A normal lithium-ion cell stores lithium in a graphite anode. An anode-free cell skips it. Lithium plates straight onto a thin copper current collector during charging and strips off again on discharge. Dropping the graphite saves space and weight, so the same volume holds more energy. For electric vehicles, that points to smaller packs with the same range, or more cabin and cargo room.
The catch is deposition. Ordinary copper does not attract lithium evenly, and the metal builds up in sharp, branching dendrites that can pierce the separator and short the cell. The protective layer that forms on the electrode, the solid electrolyte interphase (SEI), is often unstable too.
KAIST: patterned copper and a thin coating
On September 22, KAIST announced its result, led by Professors Jinwoo Lee and Hee-Tae Jung of the Department of Chemical and Biomolecular Engineering. Kyungpook National University and the National NanoFab Center took part. The paper appeared online on September 1 in Advanced Functional Materials.
Earlier fixes added extra lithium or thicker coatings, which added weight and bulk and cut into the point of going anode-free. KAIST changed the copper itself instead. Using secondary sputtering lithography, a technique adapted from semiconductor manufacturing, the team etched an array of microscopic tubes into the foil. Each is about 300 nanometers wide and 150 nanometers tall. Together they give roughly four times the surface area of flat copper for lithium to settle on.
On top went a layer of MXene, a two-dimensional material, about 10 nanometers thick. In the electrolyte used, it steers the cell toward a protective layer rich in lithium fluoride, which limits unwanted reactions and holds back dendrite growth. The team checked the result with X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and transmission electron microscopy.
“This study shows how ultrafine fabrication techniques used in semiconductor manufacturing can create both uniform sites for lithium deposition and a stable protective layer without changing the bulk electrolyte formulation or adding excess lithium,” Lee said.
HKUST: a silver additive
The Hong Kong group, led by Professor Shao Minhua, went chemical. Its additive, called AMI, pairs silver ions with anions. Once the cell is assembled, the silver makes the copper more attractive to lithium, a property called lithiophilicity. It also anchors anion-derived species that build an SEI with an organic-rich inner layer and an inorganic-rich outer layer. The released anions set off polymerization in the electrolyte, producing a quasi-solid gel that keeps the interfaces in close contact.
“The key is not simply adding a silver salt or a polymerization initiator,” Shao said. “Our AMI releases multiple functions through a controlled process after cell assembly.” The result, she said, is highly reversible lithium plating and stripping. The study, published in Nature Communications, is titled “Highly stable quasi-solid-state initially-anode-free lithium metal batteries enabled by dynamic integrated interface engineering.” The 467 Wh/kg works out to 212 Wh/lb.
Still lab results
Neither result puts an anode-free car on the road. The KAIST team says further development and validation are needed on long-term cycling, different temperatures, fast charging and large-scale manufacturing. A coin cell holding 90% after 200 cycles is a long way from the thousands of cycles a vehicle battery has to survive.
Sources
- Anode-free battery
- Silver-based additive reconfigures interfaces in anode-free lithium metal
- HKUST advances anode-free lithium battery design – Best Magazine
- Silver additive helps new battery retain 90% capacity after 200 cycles
- KAIST Develops Anode-Free EV Battery to Boost Range
- Smaller EV batteries, longer range? Scientists may have found a way
Photo: Uploaded by Duk 08:45, 16 Feb 2005 (UTC) (Public domain)
