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Making a better battery
A flexible, plastic membrane developed at DOE's Idaho National Engineering and Environmental Laboratory advances the state-of-the-art of lithium rechargeable batteries. The INEEL solid polymer electrolyte promises safer, more versatile and longer-lasting rechargeables. Lithium batteries made with the experimental electrolyte last about 50 percent longer than with competing electrolytes. The electrolyte is safer and more environmentally friendly to produce than others-the waste products are essentially glass, phosphate and nitrogen compounds, which can be converted to fertilizer. According to team leader Mason K. Harrup, their initial target is for batteries to be used in space or heart pacemakers-situations where a low-power battery needs to last a long time or work in very cold conditions. The team is pursuing development collaborations with the space and satellite industry. Electrolytes are the key to creating a battery's electrical current. They separate the positive and negative electrodes. Positive ions such as lithium can move through the electrolyte, but negatively charged electrons can't, so electrons travel out of the battery and through the device being. Conventional electrolytes are made of toxic salt solutions within a liquid or gel base, such as a car battery's water-based electrolyte. The INEEL solid electrolyte is a mix of a liquid polymer known as polyphosphazene and a ceramic powder that turn into a clear, non-toxic flexible membrane when properly blended. The chemists needed the polymer to hold shape without interfering with its ability to transport lithium ions. They discovered that the ceramic creates a stable scaffold and the liquid polymers weave through it like ribbons. Most importantly, this particular way of stabilizing the polymer interferes with lithium transport 20 times less than a more common stabilization method developed at other research institutions. In addition, the researchers analyzed the electrolyte to determine how lithium ions traveled within the composite and if they would interact with the ceramic, a problem that could reduce ion movement. Using analytical chemistry methods, they determined that the lithium ions travel along the highly conductive polymer and virtually ignore the scaffold. The electrolyte structure does have its drawbacks, Harrup explained. The ponderous routes that the polymers take through the ceramic scaffold slow the travel time for lithium ions. Also, the ions are limited to traveling single-file along the polymer paths, unlike in a liquid where ions simultaneously move across the electrolyte at once, like an army marching over a field. These limitations make the electrolytes optimal for low-power, slow-release. For its potential impact on consumers' lives, the lithium battery solid polymer electrolyte being developed at INEEL topped a list of over 100 technologies nominated by the DOE laboratories nationwide for two special awards in the Energy 100 awards program. Submitted by DOE's Idaho National Engineering and Environmental Laboratory |
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