TECHNOLOGY FOCUS - CERAMICS AND GLASS - Preferred Material: The ceramic PTC thermistor is made of barium titanate-based oxide.    TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Component: The head of the electrode terminal has the shape of a square pole, and the terminal groove has the shape of a square. The protective device groove has an insulation layer formed on its inner surface. The rechargeable battery includes a safety vent formed below the protective device groove. The second protective device is a positive temperature coefficient (PTC) thermistor, a thermal fuse, and a thermo-breaker.The PTC thermistor is a complex system thermistor having:(i) upper and lower plates made of metal; and(ii) a thin film of a composite material formed by mixing resin and carbon powder bonded between the plates.The thermo-breaker comprises:(a) a bimetal;(b) a terminal lead wire that has an end connected to the electrode terminal and another end in contact with the bimetal; and(c) a case having a closed space into which the bimetal and the terminal lead wire are inserted from its both lateral surfaces.The bimetal is formed by laminating a metal that has a larger expansion coefficient and another metal that has a smaller expansion coefficient. The thermo-breaker has a conductive plate positioned on top of the bimetal. The thermo-breaker has a thin plate-type ceramic PTC thermistor positioned below or on top of the bimetal. The case comprises a box-type case body with an open bottom and having a bimetal hole and a terminal lead wire hole formed on the top of both respective lateral surfaces so that the bimetal and the terminal lead wire penetrate them; and a cover for sealing the bottom of the case body. The terminal groove is integrated with the protective device groove. It has a terminal through-hole formed on its side into which the electrode terminal is inserted. The second protective device is seated on the other side of the terminal groove. The two electrode plates are configured as negative and positive electrode plates, respectively. The electrode terminal is configured as a negative terminal.Preferred Parameter: The bimetal is 0.1-l mm thick.Preferred Condition: The thermal fuse is actuated at 90-100degreesC.    TECHNOLOGY FOCUS - METALLURGY - Preferred Material: The thermal fuse is made of tin alloy. The metal of larger expansion coefficient is made of an alloy of copper and zinc, nickel and manganese or iron, nickel, chromium, iron, or alloy of nickel, manganese and copper. The another metal having smaller expansion coefficient is made of an alloy of nickel and iron. The conductive plate is made copper, nickel, aluminum, or silver.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The thermal fuse includes a polyethylene or polyurethane insulation film formed on its surface.