Light illuminates faster battery charging

Researchers at the US Department of Energy's (DOE) Argonne National Laboratory have reported a new mechanism to speed up the charging of lithium-ion batteries for electric vehicles. They found that simply exposing the cathode in the battery to a beam of concentrated light – for example, the white light from a xenon lamp – lowers the charging time by a remarkable factor of two or more. If commercialized, such technology could be a game changer for electric vehicles. The researchers report their findings in a paper in Nature Communications.

Owners of electric vehicles are well aware of ‘range anxiety’ as the charge level runs low or the location of the closest charging station seems too distant. Fast charging remains a critical challenge if such vehicles are ever to capture a large segment of the transportation market. Charging an electric car on empty typically takes about eight hours.

Special supercharging stations now exist that achieve ultrafast charging of electric vehicles by delivering a much higher current to the battery. Passing too much current over too short a time, however, can degrade battery performance. Typically, lithium-ion batteries for vehicles are slowly charged to obtain a complete electrochemical reaction, which involves removing lithium ions from the metal oxide cathode and inserting them into the graphite anode.

"We wanted to greatly shorten this charge reaction without damaging the electrodes from the resulting higher current flow," explained Christopher Johnson, group leader in Argonne’s Chemical Sciences and Engineering division.

Today's lithium-ion batteries work in a dark state, with the electrodes housed in a case. In contrast, Argonne's light-assisted technology would use a transparent container that allows concentrated light to illuminate the battery electrodes during charging.

To probe the charge process, the research team crafted small lithium-ion cells, known as coin cells, with transparent quartz windows. They then tested these cells with and without white light shining through the window onto the cathode.

"We hypothesized that, during charging, white light would interact favorably with the typical cathode material, and that proved to be the case in our cell tests," Johnson said. That cathode material was lithium manganese oxide (LMO; LiMn₂O₄).

The key ingredient in this favorable reaction is the interplay of light with LMO, a semiconducting material known to have optical properties. In response to the LMO absorbing the photons in the light during charging, the manganese in the LMO changes its charge state from trivalent to tetravalent (Mn³⁺ to Mn⁴⁺). This, in turn, results in lithium ions being ejected faster from the cathode than would occur without the photon-excitation process.

This condition drives the battery reaction faster. The team found that this faster reaction resulted in faster charging without degrading battery performance or cycle life. "Our cell tests showed a factor of two decrease in charging time with the light turned on," Johnson said.

The research team performed this work as part of the Center for Electrochemical Energy Science (CEES), a DOE Energy Frontier Research Center (EFRC) led by Argonne. "This research is a great example of how CEES's goal of understanding the electrode processes in lithium-ion batteries is enabling pivotal advances that are influencing technology," said Paul Fenter, CEES director and senior physicist in the Chemical Sciences and Engineering division. "This is emblematic of the transformational impacts that the EFRC program can achieve."

"This finding is the first of its kind whereby light and battery technologies are merged, and this intersection bodes well for the future of innovative charging concepts for batteries," Johnson added.

This story is adapted from material from Argonne National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.