Three-dimensional batteries with compressible cathodes

A method of formation of a secondary battery for cycling between a charged and a discharged state, the secondary battery comprising a battery enclosure, an electrode assembly, and carrier ions within the battery enclosure,

• the electrode assembly having a population of anode structures, a population of cathode structures, and electrically insulating separators electrically separating members of the anode and compressible cathode structure populations, wherein members of the anode and cathode structure populations are arranged in an alternating sequence in a longitudinal direction, and wherein members of the population of anode structures comprise anode active material layers that expand in cross-sectional area A upon charging of the secondary battery, members of the population of cathode structures comprise compressible cathode active material layers having a cross-sectional area C, the cross-sectional areas being measured in a first longitudinal plane that is parallel to the longitudinal direction,
• the electrode assembly further comprises a set of electrode constraints that at least partially restrains growth of the electrode assembly in the longitudinal direction during charging of the secondary battery, and
• the compressible cathode active material layers of members of the population of cathode structures comprise filler particles that are compressible and elastic, the method comprising:
• in an initial formation step, charging the secondary battery such that expansion of the anode active material layers in the members of the population of anode structures compresses the electrically insulating separators against the compressible cathode active material layers of the cathode structures at a pressure that contracts the cross-sectional area C of the compressible cathode active material layers, while also at least partially adhering the electrically insulating separators to the compressible cathode active material layers of the cathode structures and the anode active material layers of the anode structures;
• wherein, upon discharge of the secondary battery and contraction in the cross-sectional area A of the anode active material layers, the at least partial adhesion of the electrically insulating separators to the compressible cathode active material layers and the anode active material layers causes expansion in the cross-sectional area C of the compressible cathode active material layers.