Environmentally friendly and efficient: recycling lithium-ion batteries in neutral solution
A new strategy for recycling spent lithium-ion batteries is
based on a hydrometallurgical process in neutral solution. This allows
for the extraction of lithium and other valuable metals in an
environmentally friendly, highly efficient, and inexpensive way, as a
Chinese research team reports in the journal Angewandte Chemie.
The leaching efficiency is improved by a solid-solid reduction
mechanism, known as the battery effect, as well as the addition of the
amino acid glycine.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Lithium-ion batteries not only power our mobile phones,
tablets, and electric vehicles, they are also increasingly important as
storage for volatile renewable energy. As they become more widely used,
the number of spent batteries keeps increasing. Their recycling is
promising, having the potential to reduce environmental impact while
extracting raw materials such as lithium, cobalt, nickel, and manganese
for the production of new rechargeable batteries. Current
hydrometallurgical methods for the reprocessing of spent lithium-ion
batteries are based on acid or ammonia leaching processes. However,
excessive and repeated use of acids and bases increases the
environmental impact and safety hazards. A pH neutral process would be
safer and more environmentally friendly.
To come up with a neutral approach, the team led by Lei
Ming and Xing Ou at Central South University in Changsha, Zhen Yao at
Guizhou Normal University, and Jiexi Wong at the National Engineering
Research Central of Advanced Energy Storage Materials had to reach deep
into their bag of tricks because the aggressive reagents required for
classical leaching processes are not easy to replace.
The first trick: They constructed “micro batteries” in
situ. These help to break up the spent cathode material from the
batteries—lithium-coated nickel cobalt manganese oxide (NCM). The NCM
particles are mixed with an iron(II) salt, sodium oxalate, and the amino
acid glycine in a neutral liquid. This results in the deposition of a
thin, solid layer of iron(II) oxalate on the particles. This “shell”
acts as an anode while the NCM cores act as the cathode (battery
effect). This direct contact allows for easy electron transfer. The
coating also hinders deposition of undesired byproducts on the
particles. The battery effect drives an electrochemical reaction in
which the iron(II) ions are oxidized to iron(III) ions and oxygen ions
from the oxidic NCM particles are reduced to OH– ions
with water. This breaks up the NCM layers, releasing the lithium,
nickel, cobalt, and manganese ions they contain into the solution. In
the second trick, these ions are “trapped” in complexes by the glycine.
Glycine also has an additional task: it buffers the pH value of the
solution, maintaining a neutral range. Within 15 minutes, it was
possible to leach 99.99 % of the lithium, 96.8 % of the nickel, 92.35 %
of the cobalt, and 90.59 % of the manganese out of spent cathodes.
This efficient leaching in neutral solution could open new
pathways to the realization of large-scale, environmentally friendly
recycling of spent batteries. Barely any harmful gases are produced, and
the glycine effluent is suitable for use as a fertilizer. This process
uses significantly less energy and costs less than conventional methods.
(3404 characters)
About the Author
Dr. Xing Ou is a Professor at the School of Metallurgy and
Environment, Central South University. His primary research focuses on
advanced materials for energy storage and environmental applications,
with a particular emphasis on the development of sustainable
technologies for resource recovery and pollution control. He has been
actively involved in numerous national and international research
projects, contributing significantly to the field of environmental
metallurgy.