Citric Acid + Ethylene Glycol = Battery Recycling - Harmful Waste

Efficient recycling of lithium-ion batteries provides many benefits to future development from both economic and environmental considerations. It holds the potential to markedly alleviate the scarcity of essential natural resources needed for battery production while also diminishing the harmful repercussions of disposing of batteries at the end of their life cycle.

 

Electric vehicle batteries awaiting recycling. Image used courtesy of Adobe Stock

 

The rapid advancement of electric vehicles and electronic devices has created a continuous surge in the demand for lithium-ion batteries. Consequently, the accumulation of end-of-life batteries is expected to increase steadily.

A research team from Oak Ridge National Laboratory (ORNL) seeks to alleviate battery demand and turnover concerns by improving the process of cathode recycling.

 

Complex Battery Recycling Methods

Recycling spent lithium-ion batteries through hydrometallurgy is one of the most promising methods for material recovery.

Conventional hydrometallurgy dissolves metals in acidic solutions, allowing recovery via precipitation, extraction, or electrodeposition. In this process, inorganic acids like sulfuric acid, hydrochloric acid, nitric acid, and hydrogen peroxide are typically used as reducing agents for cathode leaching. 

 

Hydrometallurgy is one of three common methods used for battery recycling. Image used courtesy of EPA

 

Although this method shows high leaching efficiency (>95 percent), the large amount of inorganic acid creates harmful byproducts—sulfur trioxide, chlorine, and nitrogen oxides—that cause environmental contamination. 

The presence of these impurities complicates the separation and recovery process. Recovering valuable metals involves adjusting the solution's pH using sodium hydroxide and ammonium hydroxide. 

Additional chemicals like sodium hydroxide and sodium carbonate are added for precipitation, increasing process complexity, cost, and hazardous risks.

Numerous research studies have explored using organic acids and reductants during the leaching process to prevent extra impurities and reduce environmental harm, with a similar leaching efficiency to the above method. However, there are still several hurdles to overcome to enhance the process for commercial use. Experiments are typically conducted at temperatures below 100°C, leading to longer reaction times due to the limitations posed by the water's boiling point in an aqueous medium.

Ultimately, these standard processes are proving to be too costly and environmentally hazardous to continue using to recycle batteries. This is why the ORNL team has presented an enhanced method that involves dissolving the battery in a liquid solution with a polyol-metallurgical method; this aims to minimize the quantity of hazardous materials and increase reusable output. 

 

Polyol-Metallurgical Battery Recycling

The uncomplicated, effective, and eco-friendly solution devised by ORNL researchers successfully tackles the primary challenges of earlier methods.

This method uses organic citric acid alongside ethylene glycol to substitute the conventional inorganic acid in an aqueous solvent. Sustainably sourced citric acid is notably safer to handle compared to inorganic acids. 

 

Citric acid. Image used courtesy of Wikimedia

 

This blend acts as a dual-purpose solution and an exceptionally efficient method for separating and recovering metals from the positively charged cathode of the battery.

The novel approach is expected to reduce the cost of batteries long term. As the cathode contains essential materials, it is the costliest component in batteries, at around 30 percent of the total cost. The recycling method managed to leach nearly 100 percent of the cobalt and lithium from the cathode without introducing impurities.

Most importantly, it accomplished a secondary role by quickly recovering more than 96 percent of the cobalt within a few hours, bypassing the usual need for additional chemicals in the careful process of manually balancing acid levels. 

This represents a far greater efficiency than the conventional methods and without the environmental hazard.

 

Recovering Critical Materials

While the leaching capabilities of citric acid and ethylene glycol have been investigated previously, this method requires a lesser quantity of acid and proves more effective. For the first time, a single solution system has successfully encompassed both leaching and recovery functions. 

Eliminating additional chemicals in the recovery process can reduce costs and avoid the generation of byproducts or secondary wastes.