Purdue Examines Next-gen Solid-state Battery Concept
Researchers are working to adapt low-cost organic cathode materials and solid-state polymer electrolytes to create a safer next-generation battery design.
Lithium-ion batteries are expanding their reach, powering everything from cell phones and personal electronics to electric vehicles (EVs), and providing backup to electrical power grids. At the same time, these batteries are being developed and refined to reduce costs and improve performance and safety. One example is the development of an organic-based cathode (positive electrode) by researchers at Purdue University that can be used with a solid-sate polymer electrolyte to create a battery that doesn’t depend on expensive nickel and scarce cobalt to attain high power and energy density.
A new composite solid electrolyte battery cell developed at Purdue University undergoing testing to determine its stability when bent, cut, and punched. Image used courtesy of Purdue University/Sensen Zhang
Commercial lithium-ion batteries use a cathode made from nickel, cobalt, aluminum (NCA), or manganese (NCM). The cathode can also be made from slightly less expensive iron and phosphate (LFP) compounds, with a reduction in energy and power density. The anode (negative electrode) is composed of carbon graphite. It allows the insertion of lithium ions (a process called intercalation) during charging and the release of the lithium ions when the battery is discharged. The lithium ions travel between the cathode and anode through a liquid electrolyte made from organic solvents. These solvents are highly flammable and can catch fire if the battery cell is overcharged, discharged too deeply, or damaged or punctured.
Battery cross-section. Image used courtesy of Adobe Stock
Purdue’s research has centered on replacing the expensive nickel-based cathode with one made from organic materials. The use of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) as the organic cathode was chosen because it exhibits an ultra-long life. Unfortunately, this type of organic cathode is easily dissolved in traditional liquid electrolytes, so to make a viable battery, the Purdue team is working with a composite solid polymer electrolyte (hybrid polymer-LiTFSI-LLZTO, HLL) as the electrolyte. A foil of lithium metal replaces the graphite as the battery anode.
Solid electrolytes in lithium-ion batteries are not a new concept, and many consider them the Holy Grail of future battery development.
Solid electrolytes can be made from polymer or ceramic materials and are said to improve the safety of lithium-ion cells as they do not contain the highly flammable liquid electrolyte of traditional battery configurations. In addition, the solid electrolyte suppresses the uncontrolled growth of spikey dendritic crystals on the anode during charging. Suppressing this dendritic growth means that lithium metal foil can be used in place of the carbon graphite anode, increasing the cell’s energy density by a factor of 2 to 3.
Promising Battery Cell Results
The battery cell produced by Purdue appears promising. When tested at a high current density of 500 milliamps per gram (mA/g), a capacity retention of 91 percent was realized after 1,000 cycles. The battery cell was thermally stable at temperatures as high as 178°C (higher than liquid electrolyte cells) and generated less heat than a similar liquid electrolyte lithium-ion cell.
Perhaps even more significantly, the solid-sate battery was proven safe when subjected to abuse that included bending, cutting, and puncturing.
While not yet ready for primetime, using an organic cathode appears possible thanks to the application of Purdue’s solid-state electrolyte. With further development, it might result in future lithium-ion batteries that are both safer and less expensive to produce.