A method of growing electrochemically active materials in situ within a dispersed conductive matrix to yield nanocomposite cathodes or anodes for electrochemical devices, such as lithium-ion batteries. The method involves an in situ formation of a precursor of the electrochemically active materials within the dispersed conductive matrix followed by a chemical reaction to subsequently produce the nanocomposite cathodes or anodes, wherein: the electrochemically active materials comprise nanocrystalline or microcrystalline electrochemically active metal oxides, metal phosphates or other electrochemically active materials; the dispersed conductive matrix forms an interconnected percolation network of electrically conductive filaments or particles, such as carbon nanotubes; and the nanocomposite cathodes or anodes comprise a homogeneous distribution of the electrochemically active materials within the dispersed conductive matrix.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
 This invention was made with Government support under the following grants:
 Grant No. W911NF-09-D-0001, awarded by Army Research Office via the Institute for Collaborative Biotechnologies (ICB), having as its principal investigator Daniel E. Morse;
 Grant No. DEFG02-02ER46006, awarded by the U.S. Dept. of Energy under "Biological and Biomimetic Low-Temperature Routes to Materials for Energy Applications", having as its principal investigator Daniel E. Morse; and
 Grant No. DE-SC0001009, awarded by the U.S. Dept. of Energy via the Center for Energy Efficient Materials (CEEM), having as its principal investigator Daniel E. Morse.
 The Government has certain rights in this invention.