Mixing a form of rust and water might help to make inexpensive battery electrodes with long cycle lives a real possibility. If they have much higher energy densities than more expensive “conventional” electrodes used in lithium batteries, so much the better.
Zhaolin Liu of the A*STAR (Agency for Science, Technology and Research) Institute of Materials Research and Engineering, Singapore; Aishui Yu of Fudan University, China, and co-workers have created an electrode material that’s not only inexpensive, but scalable to large-scale manufacturing.
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Normally, lithium batteries “shuttle” lithium ions between two electrodes connected in a circuit. According to A*STAR, “During charging, lithium ions escape from the cathode, which is made from materials such as lithium cobalt oxide. The ions migrate through a liquid electrolyte and into the anode, which is usually made of graphite riddled with tiny pores. When the battery discharges, the process runs in reverse, generating an electrical current between the electrodes.”
That norm for lithium batteries tends to reduce the energy storage available with each cycle. The hunt for longer-lasting and inexpensive ways of overcoming these shortcomings is a constant in battery research. A*STAR researchers note that, “Iron oxides have a much higher charging capacity than graphite, but the process is slow. Forcing lithium ions into the material also changes its volume, destroying the anode after just a few charging cycles.”
To avoid that self-destructive behavior, researchers tested the idea that an anode made from iron oxide nanoparticles would charge more quickly, because its pores would give ready access to lithium ions. The pores may also allow the material’s structure to change as the ions pack inside.
By heating iron nitrate in water, they made 5-nanometer-wide particles of an iron oxide known as α-Fe2O3, then mixed the particles with a dust called carbon black, bound them together with polyvinylidene fluoride and coated the mixture onto copper foil to make their anodes.
The first charge-discharge cycles showed a credible, but disappointing anode efficiency of 75 to 78 percent, “depending on the current density used.” Ten additional cycles raised the efficiency to 98 percent, near that of commercial lithium-ion batteries. Other researchers suggest that the first few cycles broke the iron-oxide particles down to a more efficient size.
Even better, the newly-sized α-Fe2O3/carbon-black mix retained its storage capacity after 230 more cycles, stabilizing at 1,009 milliamp hours per gram – almost three times greater than that for commercial graphite anodes, and according to researchers, “experienced none of the degradation problems that have plagued other iron oxide anodes.”
According to the Institute, “The team is now working to optimize the nanoparticle synthesis and increase the efficiency of the anode’s initial charging cycles.” The team’s findings are detailed in their paper in the April 2013 Electrochemical Communications.
Again, this research is devoted to one element of the complete battery, with the need to integrate this area of study with the work being done on electrolytes, alternative materials, cathodes and anodes to finally reach a battery that combines the best of all possible ingredients. Resources and intellect being given in abundance to this challenge gives hope for a successful breakthrough (or breakthroughs) that will lead to viable and delightful electric vehicles.