A new study suggests that the carbon-based waste material given off by burning candles could be suitable for use in larger, more powerful lithium ion batteries such as those used in electric cars. Two researchers from the Indian Institute of Technology found that as an anode material, candle soot compares favorably to existing commercial options because of its low cost of production and fractal-like nanoparticle structure.
The researchers, Chandra Sharma and Manohar Kakunuri, looked into the electrochemical properties of candle soot after reasoning that since it's made of carbon, which has electric potential, it might have potential as an electrode.
They collected soot from the tip and the middle of a candle flame and compared and tested these samples. Soot from the tip of the flame, which has a temperature in the vicinity of 1,400 degrees Celsius (2,600 F), had fewer impurities such as wax, and as a result it fared better in electrical conduction.
In both cases, the researchers found that the process of burning a candle produces an interconnected network of carbon nanoparticles. Normally carbon (usually in the form of graphite) is ill-suited for use in the more powerful batteries used by things like electric cars because its crystalline structure cannot produce a high enough current density. But the shape and size – the nanoparticles measure 30 to 40 nanometers across – of these nanoparticles in soot lend them the higher density required.
The researchers tested the soot as a conducting material in a battery, using a technique called cyclic charge-discharge, or CCD. It basically involves repetitively charging and discharging the battery. Ideally it will retain most of its initial capacity after hundreds or thousands of cycles.
Sharma and Kakunuri tried several different C-rates – this is the name given to the charge and discharge current, equivalent at 1C to the battery's maximum capacity (so a 1,000mAh battery provides 1000mA for an hour if discharged at a 1C rate). Candle soot performed best under high charge conditions (i.e. for powerful batteries with higher C-rates). At 0.1C, for instance, its efficiency after 100 cycles was 91.6 percent and its capacity retention just 24.7 percent, while at 10C it had efficiency of 98.1 percent and capacity retention of 46.6 percent, and the numbers were similar after 1,000 cycles.
The researchers take this as a very positive indication that candle soot could become a future choice for electric car battery anodes. Not only does it perform well, but it's scalable and cheap to produce.
They plan to test hybrid materials that contain candle soot to see if they can improve its performance, and also to develop batteries to test the technology further. Then, no doubt, to compare it more closely with existing lithium ion battery anodes and with other emerging solutions.
A paper describing the study was published in the journal Electrochimica Acta.