A new polymer lithium ion battery fabrication process and process parameters effects on its performance

New polymer lithium ion (PLiON) battery technology is based on a hybrid, i.e., plasticized polymer, binder and separator system in which two high-solids-content electrodes and the separator comprise a polymer binder swollen with a liquid electrolyte. It combines the advantages of liquid-electrolyte Li-ion batteries that have high power rates, with those of polymer electrolytes, which offer leakproof cells with high shape versatility and large size scalability [1]. The technology exhibits performance similar to commercially proven liquid electrolyte Li ion cells, but with the difference that the liquid electrolyte is immobilized in an electrochemically intert polymer matrix. The polymer matrix, preferably a copolymer of poly(vinylidene fluoride) and hexafluoropropylene (PVDF-HFP), comprises a mixture of amorphous regions and crystalline domains. The amorphous domains entrain the liquid electrolyte, while the crystalline segments provide the mechanical integrity and strength for rugged battery electrodes. The crystalline domains also eliminate the need for chemical or radiation crosslinking which is often necessary in competitive technologies. In this technology process, the moisture sensitive lithium salt is introduced into the cell only at the end of the cell building process. Therefore, ordinary factory environments can be used for ninety percent of the cell assembly line. The free-standing electrode and separator films are prepared through solvent casting. Both electrodes and separator films contain the same copolymer, along with a plasticizer, preferably propylene carbonate (PC), as the processing aid ]2[. It residue in the cell is compatible with the liquid electrolytes used to activate the cells, it is non-toxic, inexpensive, and exhibits excellent plasticizing effect toward PVDF-HFP copolymer binders. As indicated by limited testing, the new cells exhibit efficient thermal shutdown at T 135 °C, and thus are expected to possess enhanced safety characteristics under abuse conditions, especially in the case of large-capacity cells. The electrode, separator and metal collector grids (Al for the positive and Cu for the negative) are laminated together using mild heat and pressure. The presence of the same copolymer and plasticizer in all three layers provides permanent adhesion with little chance for intefacial separation. After the cell is built, the plasticizer is extracted in a solvent extraction step. The remaining micropores and the polymer matrix are later refilled with liquid electrolyte during the cell activation step. The cells are then packaged, formed, degassed and finally vacuum-sealed. A light foil laminate package provides a hermetic seal.