# US 7,745,040 B2 · Safety device for preventing overcharge of secondary batteries and secondary batteries therewith > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,745,040 B2 - Document ID: US7745040B2 - Status: Granted - Kind: B2 - Application number: 11/209,462 - Filed: 2005-08-23 - Published: 2006-03-02 - Granted: 2010-06-29 - Earliest claimed: 2004-08-24 - Assignees: LG Chem, Ltd. - Inventors: Sung Kyun Chang; Jae Hyun Lee; Joon Hwan Lee; Soo Hyun Ha; Jeong Ju Cho - Web page: https://patentgrep.com/patent/US7745040B2 ## CPC - H01M 10/637: characterised by the use of reversible temperature-sensitive devices, e.g. NTC, PTC or bimetal devices; characterised by control of the internal current flowing through the cells, e.g. by switching (means for preventing undesired use or discharge H01M50/572) - H01M 10/48: Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte (constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569) - H01M 10/613: Cooling or keeping cold - H01M 50/572: Means for preventing undesired use or discharge - H02J 7/64: against overvoltage - H02J 7/65: against overtemperature - H01M 2200/10: Temperature sensitive devices - H02J 7/61: against overcharge - Y02E 60/10: Energy storage using batteries - H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract An object of the present invention is to provide the device for protecting a secondary battery safely from overvoltage and overheating caused by the overcharge by using simple safety device, which provides a contacted safety device which connects between a constant voltage element showing a discharge characteristic in the state of overvoltage and a MIT (metal insulator transition) element showing a discharge characteristic in the state of overheating. Each of the constant voltage element and the MIT element are connected in parallel between a cathode lead and an anode lead of the secondary battery. The contacted safety device has a characteristic combining a discharge/heat dissipation characteristic of the constant voltage element and a discharge characteristic of the MIT element which immediately responds to the heat dissipation of the constant voltage element, resulting in effect of preventing overcharge advantageously since the contacted safety device makes discharge in terms of 2 factors of voltage and temperature in case of overcharge. ## Claims ### Claim 1 A contacted safety device having a constant voltage element and a metal insulator transition (MIT) element combined, said constant voltage element having discharge/heat dissipation characteristic at more than a predetermined voltage, said MIT element having charge emitting characteristic at more than a predetermined temperature, said MIT element having an insulator-to-metal transition characteristic so that resistance of said MIT element decreases by a factor of about 1000 over a 20° C. change in temperature staffing at the predetermined temperature, wherein a critical temperature of said MIT element is equal to and above 50° C. and below 80° C. ### Claim 2 (depends on 1) The contacted safety device as claimed in claim 1, wherein said constant voltage element is a Zener diode or a varistor. ### Claim 3 (depends on 1) The contacted safety device as claimed in claim 1, wherein said constant voltage element has a low capacity. ### Claim 4 (depends on 1) The contacted safety device as claimed in claim 1, further comprising an electrical contact formed on a contact surface in a horizontal direction between said constant voltage element and said MIT element of the contacted safety device. ### Claim 5 (depends on 4) The contacted safety device as claimed in claim 4, further comprising an electrical contact formed on both end surfaces in a longitudinal direction of the contacted safety device. ### Claim 6 (depends on 4) The contacted safety device as claimed in claim 4, further comprising an electrical contact formed on an opposing surface in the horizontal direction, which is faced against the contact surface in the horizontal direction of the contacted safety device. ### Claim 7 (depends on 1) The secondary battery wherein the constant voltage element and the MIT element are connected between a cathode lead and an anode lead of the battery via a respective metal line in the contacted safety device according to claim 1. ### Claim 8 (depends on 5) The secondary battery wherein a cathode lead and an anode lead is respectively connected to both of the end surfaces of the contacted safety device according to claim 5 via a common metal line. ### Claim 9 (depends on 6) The secondary battery wherein, in the contacted safety device of claim 6, a cathode terminal of the battery is connected to a battery contact formed on the contact surface between the constant voltage element and the MIT element a common metal line and an anode terminal of the battery is connected to the electrical contact formed respectively on an opposing surface which is faced against the contact surface between the constant voltage element and the MIT element via a respective metal line. ### Claim 10 (depends on 1) The secondary battery wherein the safety contact device according to claim 1 is connected between a cathode lead and an anode lead of the secondary battery inside the secondary cell. ### Claim 11 (depends on 1) The secondary battery wherein the safety contact device according to claim 1 is connected between a cathode lead and an anode lead of the secondary battery outside the secondary cell.