Molten-Salt Electrolysis Turns CO2 into Battery-Grade Graphite

Scientists from Lawrence Berkeley National Laboratory, the University of California Berkeley, and Estonia’s National Institute of Chemical Physics and Biophysics observed carbon dioxide being reduced to solid carbon in real time inside a molten-salt bath held at 500 °C (932 °F). Using molten-salt electrolysis, an electric current strips oxygen from CO2, depositing pure carbon onto a cathode. A custom reaction cell with heat-resistant lenses allowed continuous microscopy of the process despite the corrosive, high-temperature environment.

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The reaction proceeds in two steps regardless of the salt mixture or electrode material, but variations in those inputs change the physical structure of the deposited carbon. Different electrode surfaces and salt chemistries produce distinct geometric patterns, enabling control over the crystalline alignment required for battery-grade graphite. Uniform carbon layers are essential for electric-vehicle batteries, where ions must slide smoothly between evenly spaced graphene sheets.

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The current laboratory setup operates at 500 °C, demanding continuous energy to keep the salts liquid. Researchers highlight several engineering hurdles before industrial deployment: managing gas flow, ensuring uniform heat distribution, and maintaining consistent current density across larger electrodes. Optimizing combinations of molten salts, electrode materials, temperatures, and voltages will be necessary to produce graphite and other carbon materials at scale. If these hurdles are overcome, the method could generate synthetic graphite directly from captured industrial CO2 emissions.

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Mike Whittaker, a Berkeley Lab scientist involved in the work, described the achievement as a major step toward synthesizing critical materials with molten salts. He emphasized that lowering operating temperatures and using inexpensive salts could allow the process to be deployed widely and supply enough graphite for battery supply chains.

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• “This is a major win in a larger effort of synthesizing critical materials and battery materials using molten salts,” — Mike Whittaker, a Berkeley Lab scientist

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• “If you could run this process at low temperatures with really cheap salts, you could have it in a lot of places, and you could generate enough graphite that you could feed into battery supply chains,” — Whittaker. This

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