Solid-state lithium-ion battery, made up of only solid components, has become more attractive to scientists. They offer a combination of greater safety and higher energy density. This is the energy a battery can store for a given volume.
Canadian researchers from the University of Waterloo have found a solid electrolyte with several significant advantages. They are part of the Joint Center for Energy Storage Research, located at the U.S. Department of Energy (DOE) ArgonneNational Laboratory.
The electrolyte is made up of lithium, scandium and indium. It conducts lithium ions well but electrons poorly. This combination is crucial to create an all-solid-state battery that can function without losing much capacity for more than 100 cycles at high voltage (above 4.5 volts) or thousands of cycles at medium voltage. Its stability at operating voltages above 4 volts is due to the electrolyte’s chloride nature. This makes it suitable for common cathode materials, which are the foundation of modern lithium-ion batteries.
Linda Nazar, a Distinguished Professor of Chemistry at UWaterloo, said that the main draw of solid-state electrolytes is their inability to catch fire and allows for efficient placement within the battery cells. She also noted that her team demonstrated stable high-voltage operation. Linda Nazar has been a JCESR member for a long.
Solid-state electrolytes currently focus heavily on sulfides. These oxidize and decay above 2.5 volts. They require an insulating layer around the cathode material operating above 4 volts. This reduces electrons’ and lithium ions’ ability to move from electrolyte to cathode.
Nazar stated that sulfide electrolytes present a problem. You want to electronic isolate the electrolyte from the cathode so that it doesn’t oxidize, but you still need electronic conductivity in the cathode material.
Although Nazar’s group was not the first to develop a chloride electrolyte from chloride, their decision to replace half the indium with scandium based upon previous work proved to have been a winner in terms of electronic and ionic conductivity. Nazar stated that chloride electrolytes are becoming more attractive as they do not oxidize at high voltages and can be chemically compatible with our best cathodes. Although there have been some reports of them recently, we created one that has distinct advantages.
The material’s 3D, crisscrossing structure called a spinel was the key chemical ingredient to its ionic conductivity. Researchers had to balance two competing goals: load the spinel as much charge-carrying as possible and allow ions to flow through the sites. Nazar explained that it was like hosting a dance party. You want people to attend, but not too many.
Nazar stated that a perfect situation would be for half of the spinel structures to be lithium-occupied and the other half to remain open. However, she said that it is difficult to create that scenario.
Nazar and her coworkers had to maintain lithium’s ionic conductivity. She said, “Imagine playing hopscotch.” Even if you are only trying to hop from one square to another, you can make it more difficult for electrons to jump over if you create a wall.
Nazar stated that although it isn’t clear why electronic conductivity is lower than other reported chloride electrolytes, it helps to establish a clean interface with the cathode material, which is responsible for the stability of the cathode even when there are high levels of active material.
The January 3rd online edition of Nature Energy published a paper on the research “High areal potential, long cycle life, 4 V ceramic all solid-state lithium-ion batteries enabling by chloride solid electrolytes.”