Electrochemical lithium recovery from waste secondary batteries by direct electrolysis in molten lithium carbonate

초록

The depletion of primary Li resources and growing demand for Li due to the increasing popularity of Li-ion batteries used to power electric vehicles and portable electronics necessitate the development of methods for extracting Li from secondary resources, e.g., spent batteries. However, the state-of-the-art Li extraction methods suffer from volatilization-induced Li loss, generation of hazardous waste, high carbon footprints, and other drawbacks. To address the need for efficient and ecofriendly Li recovery methods, we herein pyrometallurgical recovered Li from the cathodes of waste secondary Li-ion batteries (compressed and sintered LiNiCoMnO2) as highly pure (99%) crystalline Li2CO3 via continuous electrolysis in the highly conductive molten Li2CO3. The Li2O produced upon LiNiCoMnO2 reduction reacted with the carbonate ions in the electrolyte to form Li2CO3, which was captured within the melt. The electrochemical behavior was kinetically evaluated based on variations in electrode potential and current density during electrolysis, revealing that the reduction of lithium oxide commenced at potentials above 1.3 V. Under constant potential and current conditions, the average current and cell voltage were recorded as 2.4 A and 3.01 V, respectively. The lithium recovery yield was strongly dependent on the applied potential to the LiNiCoMnO2 electrode, reaching 95-98% under optimal conditions. Unlike conventional commercial processes, this method enables direct lithium recovery without any wet leaching or washing steps, thereby offering a promising pathway for realizing a closed-loop battery economy at industrial scale.

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