Corrosion of lithiuim-ion battery current collectors

The primary current-collector materials being used in lithium-ion cells are susceptible to environmental degradation: aluminum to pitting corrosion an d copper to environmentally assisted cracking. Localized corrosion occurred on bare aluminum electrodes during simulated ambient-temperature cycling i n an excess of electrolyte. The highly oxidizing potential associated with the positive-electrode charge condition was the primary factor. The corrosi on mechanism differed from the pitting typically observed in aqueous electr olytes because each site was filled with a mixed metal/metal-oxide product, forming surface mounds or nodules. Electrochemical impedance spectroscopy was shown to be an effective analytical tool for characterizing the corrosi on behavior of aluminum under these conditions. Eased on X-ray photoelectro n spectroscopy analyses, little difference existed in the composition of th e surface film on aluminum and copper after immersion or cycling in LiPF6 e lectrolytes made with two different solvent formulations, Although Li and P were the predominant adsorbed surface species. the corrosion resistance of aluminum may simply be due to its native oxide; Finally, copper was shown to be susceptible to environmental cracking at or near the lithium potentia l when specific metallurgical conditions existed (work hardening and large grain size). (C) 1999 The Electrochemical Society. S0013-4651(98)04-099-3. All rights reserved.