Development of new safe electrode for lithium rechargeable battery

A new concept cathode was proposed to improve die safety of lithium rechargeable batteries. The cathode contains a positive temperature coefficient (PTC) compound that can drastically increase resistivity at more than a specified temperature (PTC properties). A PTC cathode containing the PTC compound was fabricated and its resistivity was evaluated. The resistivity of PTC cathodes increased by several tens at 130-140 degrees C, which is the melting point of polyethylene. In lithium rechargeable batteries using these cathodes (PTC cell), a level nearly reaching the designed capacity is obtained at less than 1C rate. The discharge capacity of PTC cells became high as the content of PTC compound increases. Moreover, under 3C discharge condition, the voltage of PTC cell dropped at 138 degrees C where the resistivity of the PTC cathode drastically increased. Additionally, on the external short circuit test at 145 degrees C, the short circuit current of the PTC cell was almost 0 A. These results indicate that PTC cathodes will improve the battery safety. (c) 2005 Elsevier B.V. All rights reserved.