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Two materials, titanium oxide and alginate, could lead to safer lithium-ion batteries that store more energy in a smaller package, if research projects at Oak Ridge National Laboratory and the Georgia Institute of Technology pan out.
At Oak Ridge, a team of scientists discovered that replacing the traditional material in graphite electrodes with a new form of titanium dioxide lets the battery recharge faster. For example, in tests, a lithium-ion battery with TiO2 electrodes recharged to 50% of full capacity in 6 min while a traditional Li battery used the same current and time to pick up a 10% charge. The titanium-based material also has more load-carrying capacity — 256 instead of 164 mA/gm. The research team theorizes that the material, mesoporous TiO2 microspheres, gets it capabilities from the many small channels and pores in the spheres that let ions flow through unimpeded. The relatively inexpensive material also gives electrodes a sloping discharge voltage, which is helpful in controlling states of charge. And like other oxides, the material is safe and long lasting.
Meanwhile, researchers at Georgia Tech are trying to replace the polyvinylidene fluoride used as a binder in lithium-ion-battery electrodes with alginate, a material derived from brown algae. The binder suspends the graphite particles that interact with the electrolyte. Making the polyvinyl material currently used requires a potentially toxic solvent, so the new material should be more environmentally friendly. In tests, anodes made using alginate binders had a reversible capacity eight times that of today’s best graphite anodes. The anode also had a coulombic efficiency of nearly 100% and has survived over 1,000 charge-discharge cycles without a failure.
The research team began exploring low-cost alginate because it comes from a plant that lives in saltwater, which has a high concentration of ions. “Because battery electrodes are immersed in a liquid electrolyte, we felt aquatic plants, particularly those growing in an aggressive environment like saltwater, would be excellent candidates for binders,” says Igor Luzinov, a professor of material science. Still, the researchers do not know why the material works so well in electrodes.