A University of California SD nanoengineering team has developed an energy-efficient cathode recycling process that could fully restore the storage and charging capabilities of spent lithium ion batteries.
Professor Zheng Chen and a team of scientists at University of California’s San Diego Department of NanoEngineering have been working towards solving the problem of effective Li-ion battery recycling, with their findings recently published in a paper in the Green Chemistry journal.
Aiming for a non-destructive approach, meaning the batteries are not simply stripped for metals but can be reusable, the team has developed a process whereby worn cathodes can be treated with a chemical solution and a heat/cooling method to return function. The process has been shown to restore the storage and charging capabilities of the cathodes to the original, pre-use, level and then integrated into a new battery.
Typically recycling involves a chemical ‘leaching’ process, which while economically beneficial is also complicated and damaging to the environment. Despite a recent report stating that the overall cost of Li-ion batteries is falling, the base metal costs have been increasing significantly. Chen argues that “recovering these expensive materials could lower battery costs”.
The news should be considered as a boon to the EV industry. Recently, the US Department of Energy’s Argonne National Laboratory developed a model designed specifically to gauge the impact of battery recycling. Preliminary findings found that a recycled cathode could cost up to 30% less than a brand new battery and it is hoped that the figures will help to steer the automotive industry towards “the development of a recycling infrastructure.”
Typically, less than 5% of Li-ion batteries are currently recycled, despite being labelled as hazardous waste. Chen added: “Think about the millions of tons of lithium ion battery waste in the future, especially with the rise of electric vehicles, and the depletion of precious resources like lithium and cobalt—mining more of these resources will contaminate our water and soil. If we can sustainably harvest and reuse materials from old batteries, we can potentially prevent such significant environmental damage and waste”.
How it works
The process can be used fairly widely, from recovering and restoring lithium cobalt oxide (used in smartphones and laptops) to nickel manganese cobalt oxide (NMC) which is used in electric vehicles. Initially, cathode particles are collected from used Li-ion batteries, and then the particles are then pressurised in a hot, alkaline, solution containing lithium salt.
Following this, the treated particles go through an ‘annealing’ process whereby they are heated to 800°C and then slowly cooled. The regenerated particles are then used to make new cathodes that, once integrated, show the same energy storage capacity, charging time, and life expectancy as an unspent battery.
Chen’s method allows the cathodes to be reused, by restoring the lithium concentration and atomic structure of the elements, rather than just mining the valuable metals. Additionally, the alkaline solution can be used again, to process more batches.
The team also considered the extra costs, in terms of energy usage, to recycle the cathodes. This new recycling process uses 5.9 megajoules of energy to restore one kilogram of cathode material; this amount is equivalent to the energy found in about three-quarters of a cup (approximately 175ml) of gasoline. According to the study, most other recycling processes use at least twice that.
The issue with many of these studies is when and how the innovative new process can be implemented on an industrial scale. However, Chen revealed that his team is already planning to work with battery companies in Asia. There is still some work to be done, particularly at the particle harvesting stage – they currently need to be picked out by hand – but researchers are working to simplify or automate this step. The process will also need to be refined and made available to all types of lithium ion cathode material – something Chen says is the team’s ultimate goal.
The news is promising given one of the main arguments presented against the EV industry is often concern over the environmental and earth resources cost to manufacturing batteries. It’s also important that the EV industry examines its own sustainability, and does not focus solely on reducing tailpipe emissions. Projects such as this prove that there are already viable solutions in the works, and should help to maximise the benefits batteries can bring.