NASA’s Jet Propulsion Laboratory has developed an advanced energy-storage device to accommodate portable devices, minimize emissions from automobiles, and enable more challenging space missions. The use of silicon for the anode of lithium ion (Li-ion) batteries is attractive because silicon has the highest theoretical charge capacity of any material when used as an anode in a Li-ion battery. Conventional silicon anodes undergo large-volume expansions and contractions with the absorption and desorption of Li-ions, however, and this results in pulverization of the anode after several charge and discharge cycles. JPL’s innovative Li-ion battery anodes are made of micro-textured silicon, which is able to accommodate the stress of expansion and contraction during the charging cycle. These robust silicon anodes make high-capacity, rapid-charge-rate Li-ion batteries practical.
JPL’s method of cryogenic etching using inductively coupled plasma rapidly and repeatedly produces a micro-scale and/or nano-scale textured silicon substrate known as black silicon over a relatively large area and in a cost-effective manner. Texturing the surface greatly increases the surface area, which increases the kinetic rates and therefore the charging rates of Li-ion batteries. The black silicon needle-like structures are able to accommodate the stresses of charging due to radial expansion and contraction of Li ions during the absorption and desorption of the charging cycle, and the micro-scale texturing avoids the generation of excess solid electrolyte interphase, which until now has inhibited the production of a practical (>2.5 V) battery employing silicon anodes.
A textured silicon anode has been demonstrated having needle-like structures with a depth of about 120 microns and a width of about 10 microns at the widest part. The textured substrate was produced using a two-step etch. The first step created a high-density stubble of black silicon across the surface, while the second step employed a higher forward power, a greater percentage of SF6, and less O2 to increase the depth of the etch. Textured silicon anodes allow for Li-ion batteries capable of over 200 Wh/kg.
Potential applications include use in Li-ion batteries, high specific energy batteries for portable electronic devices, plug-in hybrid and electric vehicles, and spacecraft.
Refer to NPO-47300-2.