An alkaline electrochemical cell containing a neat multiphase thermoplastic polymer separator is disclosed. The microstructure and composition of the polymer are selected to provide a film that can physically endure the rigors of a cell assembly process and also provide adequate ionic conductivity to support a high rate discharge. In one embodiment, the ionic conductivity of the separator is improved upon contact with the cell's alkaline electrolyte. Processes that can be used to manufacture a cell of this invention are also described.