Photolithography & Wafer Processing

Our battery manufacturing process combines photolithography with standard solar-cell fabrication equipment to achieve high-volume, low-cost battery production through the following process. 1) A photolithographic mask and etch process is applied to a solar-grade silicon (SG-Si) wafe­­r. 2) The 100% silicon that remains after wet etching forms the anode and backbone of the interlaced cell structure. 3) A thin layer of metal is plated to the anode and backbone to form current collectors. 4) A ceramic separator is deposited around the anode current collectors, and 5) a cathode coating fills the remaining voids in the wafer die. The individual cells are laser sliced from the multiple-cell (full) wafer, die stack tabs are attached, the dies are baked, and 1-mm cells are stacked to the desired thickness and packaged in a pouch or case.

We leverage substantial investments and improvements made over the years in solar cell supply chains, production equipment technology, and process knowledge for our own low-cost battery production. For example, the average cost of solar photovoltaic wafer processing for top tier manufacturers declined an average of 20% per year between 2008 and 2013. Modeling the SunPower manufacturing technology and processes used in our production line demonstrates that the cost of volume production for our cells will be comparable with that of conventional Li-ion cells, but with significantly higher energy density and greatly improved safety.