Active materials comprising secondary active-material structures for high rate battery applications and methods of fabricating such active materials

Described herein are active materials for use in negative electrodes of lithium-ion electrochemical cells as well methods of forming such active materials. In some examples, an active material comprises secondary active-material structures, each formed by physical or chemical attachment of multiple primary active-material structures. These primary active-material structures can comprise one of silicon, silicon oxide, tin, tin oxides, germanium, metal, and silicide, and each structure can have a size of between 5 nanometers and 30 micrometers. The small size of the primary active-material structures helps to maintain the mechanical stability of these structures as well as of the secondary active-material structures during battery cycling. Furthermore, these specific arrangements of the primary active-material structures support high charge-discharge rates. Some of the secondary active-material structures can be joined with other such structures, e.g., forming a network of the structures. An active material can be a powder and incorporated into slurries.