Various embodiments of the invention describe nanoporous silicon (Si) network thin films with controllable porosity and thickness that are fabricated by a robust and scalable electrochemical process, and then released from Si wafers and transferred to flexible and conductive substrates. These nanoporous Si network thin films serve as high performance Li-ion battery electrodes, with an initial discharge capacity of 2570 mA h g.sup.-1, above 1000 mA h g.sup.-1 after 200 cycles without any electrolyte additives.
STATEMENT OF GOVERNMENTAL SUPPORT
 The invention described and claimed herein was made in part utilizing funds supplied by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 between the U.S. Department of Energy and the Regents of the University of California for the management and operation of the Lawrence Berkeley National Laboratory. The government has certain rights in this invention.