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LITHIUM-ION BATTERIES GIVING NEW MEANING TO WASTE SILICON

- Jun 28, 2018 -

Researchers have developed a way to use discarded silicon to make flexible components for rechargeable lithium-ion batteries.

Study shows Silicon is a material that can absorb 10 times more lithium than the carbon used in Lithium-ion batteries but because of its expandable properties as the battery charges and discharges, it breaks down quickly.


Researchers came up with a technique to insert in an anode arrayed nanowires which are encased in electrically conducting copper and ion-conducting polymer electrolyte. The use of the nanowires in this case is better as the material gives the nanowires enough space to grow and shrink as needed and at the same time, the electrolyte is defined as a spacer between the anode and cathode.


The team of researchers define the transformation of waste into batteries as a scalable process which if well done could enable lithium-ion powered devices to be flexible, efficient and cheap with the batteries being able to be shaped however the device require.

 

The researchers based the experiment on a verified process which is called colloidal nanosphere lithography, by spreading polystyrene beads suspended in liquid onto a silicon wafer which make a silicon corrosion mask.


When shrunken chemically, the beads which were self-assembled into a hexagonal grid on the wafer stayed put. Before the polystyrene was removed, a thin layer of gold was sprayed which left a gold mask on top of the wafer.


The gold mask was then used in a metal assisted chemical etching, in which the silicon dissolved where it touched the metal. Over time in a chemical bath, the metal catalyst would sink into the silicon and leave millions of evenly spaced nanowires, 50 to 70 microns long, poking through the holes.


The researchers deposited a thin layer of copper on the nanowires to improve their ability to absorb lithium and then infused the array with an electrolyte that not only transported ions to the nanowires but also served as a separator between the anode and a later-applied cathode.
This method of application on battery is new even though etching is not a new process; which requires to take nanowires of the silicon wafer because pure, free-standing nanowires quickly crumble. The electrolyte engulfs the nanowire array in a flexible matrix and facilitates its easy removal. Just touch it with the razor blade and it peels right off. The mask is left on the unperturbed wafer to etch a new anode.


When combined with a spray-on current collector on one side and a cathode and current collector on the other, the resulting battery showed promise as it delivered 150 milliamp hours per gram with little decay over 50 charge/discharge cycles. Researchers are working to enhance those qualities and testing the anodes in standard battery configurations.