Lithium-polymer batteries are the fourth most likely type of battery to be commercialized for EV applications. The discovery of nonmetallic solids capable of conducting ions has allowed for the development of these batteries. Lithium-polymer batteries have anodes made of either lithium or carbon intercalated with lithium. One candidate cathode under evaluation contains vanadium oxide. This particular battery chemistry has one of the greatest potentials for the highest specific energy and power. Unfortunately, design challenges associated with kinetics of the battery electrodes, the ability of the cathode and anode to absorb and release lithium ions, has resulted in lower specific power and limited cycle life for lithium-polymer batteries.
The current collector for lithium-polymer batteries is typically made of either copper or aluminum foil surrounded by a low thermal conductivity material such as polyurethane. The battery case is made of polypropylene, reinforced polypropylene, or polystyrene. Lithium-polymer batteries are considered solid-state batteries since their electrolyte is a solid. The most common polymer electrolyte is polyethylene oxide complexed with an appropriate electrolyte salt. The polymers can conduct ions at temperatures above about 60°C (140°F), allowing for the replacement of flammable liquid electrolytes by polymers of high molecular weight. Since the conductivity of these polymers is low, the batteries must be constructed in thin films ranging from 50 to 200mm thick. There is, however, a great safety advantage to this type of battery construction. Because the battery is solid-state by design, the materials will not flow together and electrolyte will not leak out in case there is a rupture in the battery case during an EV accident. Because the lithium is intercalated into carbon anodes, the lithium is in ionic form and is less reactive than pure lithium metal. Another major advantage of this type of battery construction is that a lithium-polymer battery can be formed in any size or shape, allowing vehicle manufacturers considerable flexibility in the manner in which the battery is incorporated into future vehicle designs.
The current collector for lithium-polymer batteries is typically made of either copper or aluminum foil surrounded by a low thermal conductivity material such as polyurethane. The battery case is made of polypropylene, reinforced polypropylene, or polystyrene. Lithium-polymer batteries are considered solid-state batteries since their electrolyte is a solid. The most common polymer electrolyte is polyethylene oxide complexed with an appropriate electrolyte salt. The polymers can conduct ions at temperatures above about 60°C (140°F), allowing for the replacement of flammable liquid electrolytes by polymers of high molecular weight. Since the conductivity of these polymers is low, the batteries must be constructed in thin films ranging from 50 to 200mm thick. There is, however, a great safety advantage to this type of battery construction. Because the battery is solid-state by design, the materials will not flow together and electrolyte will not leak out in case there is a rupture in the battery case during an EV accident. Because the lithium is intercalated into carbon anodes, the lithium is in ionic form and is less reactive than pure lithium metal. Another major advantage of this type of battery construction is that a lithium-polymer battery can be formed in any size or shape, allowing vehicle manufacturers considerable flexibility in the manner in which the battery is incorporated into future vehicle designs.
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