This summer I was fortunate to be able to participate in the research experience for teachers (RET) program at the University of Notre Dame through the Center for Sustainable Energy at Notre Dame (cSEND). This is my fifth summer working with the RET program, and the first of the three year grant cycle for the NSF funded cSEND program.
My summer research focused on lithium-ion battery technologies; specifically the development of semi-porous solid state ceramics that served as the electrolyte barrier between cathode and anode in traditional Li-ion cells. The attraction to solid state electrolytes is strong; using a solid state electrolyte makes the batteries safer (less prone to short circuit) while also allowing for dramatically smaller cells to be fabricated.
Fabrication of the conductive ceramic was quite traditional. We used the Pechini method (a sol-gel process) to synthesize ceramic nanoparticles typically 30nm in size. This ceramic was then sintered in a kiln to allow for proper grain boundary growth. Depending upon the sample, materials would be mixed within the ceramic that would then burn off during sintering to increase the porosity of the ceramic.
Why porosity? Making the ceramic porous allows for intimate contact between the ceramic and the cathode material, and also defines quite a bit in regards to the performance of the cell. The ideal situation strikes a balance between porosity and conductivity. A more porous cell allows for a greater quantity of cathode material; while a more dense cell is more conductive in regards to the passage of lithium ions through the electrolyte.
I think a picture would help to illustrate what I have been describing. Here’s a SEM image of a ceramic electrolyte pellet that has been broken in half to show the porous and dense layers.
Once the ceramic has been sintered, the porous layer would be loaded with cathode material and then placed in a glovebox filled with argon to add the lithium metal to the dense side of the ceramic. The ceramic “sandwich” is then placed into a coin-cell battery case and coated with a wax to prevent oxidation of the lithium metal. Metal leads are added and the cell is cycled for roughly 20 days to determine the performance of the cell.
Got questions about lithium ion batteries or the research described? Fire off a comment or shoot me an email ( pcook [at] nd.edu ).