How a Battery Separator Is Used in Cell Fabrication

There are numerous other companies developing lithium-ion battery separators, such as Ultimate Membrane Technology, Advanced Membrane Systems, Aporous, Porous Power, Optodot, and so on. In addition, some battery developers are either making or modifying separators in-house. Technologies for making hthium-ion battery separators are discussed in Section 20.3. 

The requirements for a battery separator can best be understood in the context of how the separator is used. Currently there are two major designs spirally wound or stacked plate. There are two types of stacked-plate designs, one relying on stack pressure to maintain good interfacial contact between the electrodes and separators, and a second which uses an adhesive to bond the electrodes and separators. The manufacturing processes for both spiral and stack cell designs are reviewed by Brodd and Tagawa [7]. Both processes put stress on the separator. 

Once wound, the separator is cut and the loose end is taped to the spiral. The spiral is pushed off the winding pin and inserted into a can. The can is filled with electrolyte and the separator must be wetted quickly by the electrolyte so that the header (or cover) can be installed in the next processing step. Electrolyte filling becomes more problematic the larger the cell, so this presents an opportunity for separators that can wick electrolyte. 

Once in an operational battery, the separator should be physically and chemically stable to the electrochemical environment inside the cell. The separator should prevent migration of particles between electrodes, so the effective pore size should be less than 1 gm. 

1) C rate refers to the discharge rate of the battery (amperes) divided by its nominal 

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