Using a technique called neutron scattering characterization on lithium vanadium oxide, scientists revealed that the material can rapidly charge and discharge energy. The material has a structure similar to table salt but with a more random atomic arrangement. Scientists call this a disordered rock salt structure. Lithium vanadium oxide charges and discharges without growing lithium metal "dendrites." These are rigid, tree-like structures that can cause dangerous short circuits. During testing, the material not only resisted dendrite growth. It also delivered more than 40 percent of its energy capacity in just 20 seconds. Research suggests the rapid charging and discharging occurs because the rock salt electrode can cycle two lithium ions in and out of vacant sites in its crystal structure.
It can take several hours to fully recharge a lithium-ion battery, even those used to power small devices such as mobile phones and laptops. The primary reason is that most devices and their chargers deliberately charge their batteries at slower, controlled rates. Slow charging helps prevent the dendrite growth that can pierce the battery's protective layers. Losing this protective layer can lead to severe reactions, such as fires. Safer, faster-charging batteries could reduce or eliminate one of the biggest factors slowing consumer adoption of electric vehicles powered by lithium-ion batteries.
A team of university and national laboratory scientists worked together to better understand energy storage and discharge in materials for next-generation lithium-ion batteries. They carried out operando neutron diffraction measurements at the VULCAN instrument at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS) on a new material--lithium vanadium oxide with a disordered rock salt crystal structure--as an anode in a lithium-ion battery. This research sought to understand how the rock salt's ions behave when the battery experiences charge/discharge cycles at various rates. Neutrons can easily track lithium ions and oxygen atoms inside the material, and the VULCAN instrument can precisely measure structural changes during the charge/discharge cycles. In addition to the neutron measurements, the researchers conducted X-ray studies at Argonne National Laboratory's Advanced Photon Source (APS), battery performance assessments, and theory and modeling at the National Energy Research Scientific Computing Center and University of California, San Diego computing capabilities. The new material demonstrated many desirable properties for energy storage, including very fast charge/discharge and high energy storage capacity needed for electric vehicles, power tools, electric scooters, and other applications. This research shows that materials with rock salt-structures could replace graphite, a common electrode material used in lithium-ion batteries. These batteries can store a lot of energy but can experience fires under some conditions. The new material could also replace lithium titanate, another commonly used electrode that can safely charge rapidly, but has a lower energy storage capacity. Disordered rock salt could be a "Goldilocks" solution because it offers just the right combination of fast charging/discharging, safety, long cycle life, and higher energy storage capacity.
This research used resources at SNS, APS, and CFN, all of which are DOE Office of Science user facilities. The research was sponsored by the DOE Office of Science, the DOE Office of Energy Efficiency and Renewable Energy, the National Science Foundation, National Sciences and Engineering Research Council of Canada, and the University of California San Diego.