Researchers have developed a modified copper current collector designed to improve lithium deposition and reduce capacity loss in anode-free lithium-metal batteries. The study combines nanoscale interface engineering with surface and materials analysis to examine how the design affects battery performance.
Anode-free batteries are assembled without lithium metal on the negative electrode. During the first charge, lithium moves from the cathode and deposits directly onto a copper current collector. Removing the conventional graphite anode could increase energy density and reduce cell weight, but it also creates technical challenges.
Lithium may deposit unevenly on copper, while repeated charging can produce an unstable solid-electrolyte interphase, or SEI. This interfacial layer forms when the electrolyte reacts with the deposited lithium. An irregular SEI can consume active lithium and electrolyte, reducing Coulombic efficiency and shortening battery life.
Researchers created a three-dimensional nanotubular copper current collector and coated the structure with an approximately 10-nanometer layer of Ti₃C₂Tₓ MXene, a two-dimensional titanium carbide material. The MXene coating was designed to interact with hexafluorophosphate anions in the electrolyte. According to the researchers, this interaction promoted more uniform lithium nucleation and encouraged formation of an inorganic, lithium fluoride-rich SEI across the nanotubular structure.
The team used ex situ X-ray photoelectron spectroscopy to characterize the chemical composition of the interface. Time-of-flight secondary ion mass spectrometry provided spatial information about surface species, while transmission electron microscopy examined the nanoscale structure. These analyses indicated that lithium fluoride nanoparticles preferentially formed along the MXene coating, producing a more uniform interfacial layer.
The researchers then tested lithium-free MXene-coated copper current collectors in coin-type full cells paired with nickel-rich NCM811 cathodes. Testing was conducted under lean-electrolyte conditions, which reduce the amount of electrolyte available and provide a more demanding assessment of lithium and electrolyte consumption.
At cycle 125, cells containing the modified current collector retained a specific capacity of 78.1 milliampere-hours per gram and recorded a Coulombic efficiency of 99.06 percent. Cells constructed with unmodified copper retained 44.9 milliampere-hours per gram and had an efficiency of 95.01 percent.
The findings connect the observed electrochemical performance with the composition and distribution of the SEI. They also demonstrate how XPS, ToF-SIMS, and electron microscopy can be combined to investigate battery interfaces that are difficult to characterize using electrochemical measurements alone.
Further testing in larger-format cells will be needed to assess manufacturing consistency, long-term cycling, safety, and performance under conditions relevant to electric vehicles and other commercial applications.
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