Researchers at KAIST and partner institutions have developed a semiconductor manufacturing technique that extends the lifespan of anode-free batteries by using secondary sputtering lithography and an ultrathin MXene primer layer to promote uniform lithium deposition, potentially enabling smaller and lighter electric vehicles.
Overcoming the Lithium Dendrite Obstacle in Anode-Free Batteries
Electric vehicles rely heavily on the capacity and weight of their power sources. Next-generation anode-free batteries eliminate traditional anode materials like graphite entirely, depositing lithium directly onto a thin copper foil. By removing the heavy materials that normally store lithium during charging, this design packs significantly more energy into a smaller and lighter footprint.
Yet practical adoption has hit a stubborn wall. Repeated charging cycles cause lithium to deposit unevenly across the copper foil, growing into spike-like structures known as dendrites that degrade performance and shorten battery life. Previous attempts to fix this involved adding excess lithium or coating surfaces with thick protective films, which unfortunately added back the weight and volume that anode-free designs were meant to eliminate.
Applying Semiconductor Microfabrication to Battery Foils
To solve the dendrite problem without bulking up the battery, a joint research team turned to advanced microprocessing techniques traditionally reserved for semiconductor device manufacturing. Led by Professors Jinwoo Lee and Hee-Tae Jung from the Department of Chemical and Biomolecular Engineering at KAIST alongside researchers from Kyungpook National University and the National NanoFab Center, the project targeted the copper current collector itself.
The team utilized a process called secondary sputtering lithography (SSL) to create an array of microscopic tube structures directly onto the copper surface. Much like marking out tightly arranged parking spaces in a crowded lot, these microscopic features force lithium to spread out evenly instead of concentrating in vulnerable pockets.
The tubes measure roughly 300 nanometers in diameter and 150 nanometers in height. This precise geometry expands the available surface area for lithium deposition to about four times that of flat copper foil, directly mitigating localized, spike-like growth.
The Role of the MXene Primer Layer and Electrolyte Chemistry
Beyond physical etching, the researchers introduced a chemical primer to guide how the battery operates internally. They coated the modified copper foil with a roughly 10-nanometer-thick layer of MXene, a two-dimensional material forming a film thousands of times thinner than a human hair.
Rather than acting as a standalone protective shell, the MXene functions as a molecular primer that attracts the specific components needed to build one. When paired with the LiPF6-based electrolyte used in the study, the MXene surface prompts the creation of a robust, lithium fluoride-rich protective barrier during operation.
“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.”
Professor Jinwoo Lee, KAIST
Advanced Surface Analysis Confirms Uniform Protective Growth
To verify that the nanoscale protection actually formed as intended, the research team examined electrode surfaces and cross sections while strictly minimizing air exposure. Their investigation relied on an array of sophisticated material characterization methods, including X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and transmission electron microscopy.
These diagnostic techniques confirmed that the protective layer formed uniformly along the MXene framework, suppressing unwanted side reactions between the lithium and the electrolyte. Co-first authors Eunji Kim, Hyunju Jung, and Jinuk Kim participated alongside faculty leaders from KAIST and Kyungpook National University, establishing a foundational advance aimed at accelerating the commercial viability of high-energy electric vehicle batteries.
