An electrochemical resistor for discharging spent lithium-ion batteries: discharging mechanism and environmental impact analysis

Abstract

Discharging spent lithium-ion batteries (LIBs) is crucial to eliminating potential safety issues and hazards during battery recycling, but the contamination caused by this process has been neglected. Herein, we report an electrochemical resistor (ECR) to convert residual energy into heat in an electrochemical cell containing a reversible electrochemical redox couple (e.g., K₃[Fe(CN)₆]/K₄[Fe(CN)₆]). During the discharge process, battery energy is converted into heat and not chemicals. From an electrochemical perspective, the redox couple enables electron exchange at the electrode/electrolyte interface at a fast rate, making the electrons flow through the outer circuit, and [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ transformation happens back and forth in the electrolyte. In 135.5 min, over 98% of the energy of a 5.94 W h 18650-type LiFePO₄ battery could be converted into heat. Unlike the traditional salt-soaking method, the ECR method does not dissociate water, which generates H₂, O₂, or Cl₂, and corrodes battery shells, thereby releasing electrolytes into the salt solution. Based on the contamination caused by directly discharging batteries in salt solutions, life cycle assessment (LCA) analysis suggests that the environmental impact of ECR discharge has benefits for global warming, resource consumption, human health, and environmental/economic costs. Therefore, the ECR is a green and efficient way to discharge various types of spent batteries and harness residual battery energy as a heat resource.