ORNL process for cleaner cathode material

Exploring new chemistries to reduce the necessity for critical metals needed for renewable energy, especially in the form of batteries, Oak Ridge National Laboratory has developed a method for producing lithium-ion batteries without the need for cobalt.

With the future expectantly being powered with batteries, all walks of studious life have been knuckling down to improve a nearly half-century-old technology that, until recently, was good enough – given the imperative need to reduce carbon emissions, good enough is far below the marker these days.

Used in products from the home appliances and smartphones we use every day to the electric vehicles that are the future of transportation, lithium-ion batteries are composed of a cathode and an anode with an electrolyte in between. Simple yet sophisticated, ions move from anode to cathode through the electrolyte in a reaction that converts chemical energy into electrical energy.

The drive toward decarbonization and the demand for electric mobility has increased the focus on sustainably producing energy-dense cathodes. However, traditional processing now presents modern challenges that we simply cannot settle on any longer.

The first obstacle has generally continued to be the reliance on cobalt, a relatively rare metal mined and refined overseas. Notwithstanding the dependence on foreign sources posing a risk to western manufacturing supply chains and transportation infrastructure, the sourcing also hosts a significant moral dilemma, with the main propagator being the Democratic Republic of Congo, accounting for roughly 70% of global production of cobalt.

Setting cobalt aside, the balance of other metals common in cathodes also makes the manufacturing process longer and more hazardous. For example, high nickel concentration has led to the widespread use of a chemical mixing method for cathode production that requires large quantities of ammonia as a corrosive reagent.

Using this toxic chemical not only increases costs but also heightens health and environmental concerns, especially in the form of water, as it is needed to reduce ammonia's acidity.

Published in the "Journal of Power Sources," ORNL researchers state they have developed a cleaner, cheaper, and more efficient method for making a new class of high-capacity cathode material – without cobalt.

Ethanol is the answer

Instead of continuously blending cathode materials with chemicals in a reactor, ORNL's hydrothermal synthesis approach crystallizes the cathode using metals dissolved in ethanol. As ethanol is vastly safer to store and handle than ammonia, not to mention it can be distilled and reused afterward, this approach has already proved worth exploring.

"This novel process offers the key advantage of moving the cathode industry to cleaner and more cost-competitive production while putting less burden on our environment," said Ilias Belharouak, principal investigator for the project at ORNL.

"The hydrothermal synthesis method is also much faster," said ORNL lead researcher Rachid Essehli, as the time required to make particles and prepare for the next cathode batch drops from as many as a few days to roughly 12 hours.

Additionally, the material produced results in a design structure that is more uniform and tightly packed, allowing for more efficient generation of energy and more condensation for capacity. Although the ORNL team had previously identified other cobalt-free combinations that work, the material developed through this study was overall better at maintaining stability throughout the battery charge cycle.

Because its properties are similar to those of today's cobalt-based cathodes, this new material can be seamlessly integrated into existing battery manufacturing processes.

Presently, a patent is pending on the technology, which is ultimately ready to be scaled up for commercial production by industry.

"This cathode material can give more energy and decrease the cost of electric car batteries," said Essehli.