Researchers from Pune’s National Chemical Laboratory (NCL) and Indian Institute of Science Education and Research (IISER) have used a simple, cost-effective and quick process to convert sugarcane bagasse into anode-grade porous, conducting, activated carbon material for use in Li-ion batteries.
While making anode-grade carbon is currently very expensive and time-consuming, the Pune researchers were able to produce high-quality carbon within minutes by using a low power microwave system. The results of the study were published on July 5 in the journal Electrochimica Acta .
The quality of carbon used for electrodes depends on the choice of precursors and the process used for converting the precursors into carbon. Anode-grade carbon is generally produced through decomposition at nearly 1000 degree Celsius.
“By using a simple kitchen microwave oven we achieved local heating and combustion to realise high quality factory-grade carbon materials within a few minutes,” says Prof. Satishchandra Ogale, the corresponding author from the Centre for Energy Science at IISER, Pune and formerly Chief Scientist, NCL, Pune.
“The process time to get anode-grade carbon is cut down dramatically. The electrical energy input is also reduced substantially,” Prof. Ogale says. “The quality of carbon and battery performance using this carbon is quite good and competitive with carbon made through other complicated schemes and processes. We are able to get competitive value of energy density and power density using the carbon anode made in the lab.”
The performance in terms of stability has also been good for a large number of charging and discharging cycles, Dr. Ogale says.
The initial carbonisation was carried out overnight at room temperature by mixing bagasse with concentrated sulphuric acid.
“Except silica most of the inorganic impurities present in bagasse get dissolved by acid treatment,” says Anil Suryawanshi, one of the authors of the paper from NCL, Pune. This also helps in forming robust carbon double bond backbone structure.
The solid product is washed thoroughly, oven-dried at 70 degree C and mixed with potassium hydroxide to form slurry. The slurry is then heated in a microwave oven for a few minutes.
Though the mixture achieves a burning temperature for a few minutes, it is self-generated by microwave and not through external heating; the power consumed by the microwave oven is just 700-900 watts.
“Local heating causes graphitisation and pores are eventually formed when potassium hydroxide reacts with carbon,” says Mr. Suryawanshi. The process is repeated one more time after mixing with water to optimise porosity and conductivity.
Porosity is important as lithium ions come through liquid electrolyte and must reach different parts of the carbon anode. Optimum porosity is needed for accessibility of lithium ions.