Battery Lab Q&A VOL.001: Why is copper foil used for the negative electrode and aluminum foil for the positive electrode in lithium batteries?
Release time：2025-07-18
Why lithium batteries?
The negative electrode uses copper foil,
and the positive electrode uses aluminum foil?
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If lithium-ion batteries were reversed ——If the negative electrode used aluminum foil instead of copper foil, and the positive electrode used copper foil instead of aluminum foil, the battery might fail after only three cycles.
The negative electrode operates at a low potential, approximately 0.01V vs Li/Li⁺, If aluminum foil were used! Lithium would penetrate the aluminum lattice , forming a Li-Al alloy. After three charges and discharges, the originally smooth aluminum foil would be "eaten away" into powder, causing the battery to swell and leak. Therefore, it definitely cannot be used.
Copper is well-behaved ——It is stable with lithium in the 0-3V range, does not undergo an alloying reaction, has good conductivity, can be made to a thickness of 6-8μm, is lightweight, and saves costs.
The positive electrode operates at a high potential, and using copper foil is even more problematic . Ternary or lithium iron phosphate positive electrodes operate at potentials between 3.2-4.2V. At high potentials, copper foil is oxidized by the electrolyte, forming a loose layer of copper salt on the surface. Not only does the conductivity plummet, but the dissolved copper ions also migrate to the negative electrode, depositing on the lithium surface like scale. Finally, the battery internal resistance soars to hundreds of ohms, and the charged electricity is all converted into heat loss.
Aluminum comes in handy —— At high potentials, a dense oxide film Al₂O₃ forms on the aluminum surface , protecting itself from corrosion by the electrolyte, and exhibiting excellent stability. Furthermore, aluminum is lighter than copper and significantly cheaper, making it cost-effective for use as a positive electrode current collector.
This is why the industry has consistently used copper foil and aluminum foil for the negative and positive electrodes, respectively, for decades.
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Lithium battery R&D technology,Battery laboratory equipment,Fundamentals of electrochemistry,Introduction to Renewable Energy Research and Development,Lithium battery basic technology
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