A dual temperature protection method for lithium battery

Abstract

The application relates to the technical field of lithium battery safety management, and discloses a double-temperature protection method for a lithium battery, which comprises a first-stage protection module and a second-stage protection module. The first-stage protection module comprises a thermistor connected to the temperature protection circuit, the temperature signal of a battery pack is detected through the thermistor, and the over-temperature protection of the battery during charging and discharging is carried out according to the temperature signal detected by the thermistor. The second-stage protection module comprises a metal normally-closed temperature control switch connected in series between the B-end of a battery protection board and the B-end of a battery cell, and the on-off of the circuit is controlled through the deformation of the metal normally-closed temperature control switch at different temperatures. According to the technical scheme, the hardware control and the physical closing are cooperated, the circuit is cut off through the physical action of the temperature control switch when the electronic protection fails, the technical scheme of single dependence on the electronic protection is optimized, and the reliability of the temperature protection is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery safety management technology, and in particular to a dual temperature protection method for lithium batteries. Background Technology

[0002] As lithium batteries are used more and more widely, the safety protection of lithium batteries is becoming increasingly important.

[0003] Existing temperature protection solutions for lithium battery protection boards rely solely on NTC thermistors for temperature detection, which presents the following problems: 1. Relying solely on electronic protection, the protection mechanism completely fails when the sensor or control chip malfunctions; weak anti-interference capability: 2. The analog signal of the NTC is susceptible to interference from circuit noise, changes in contact resistance, or fluctuations in ambient temperature, which may lead to misjudgments, such as false triggering of protection or failure to report real danger; lack of thorough physical isolation: 3. Traditional solutions only shut down the MOSFET, but in extreme cases, leakage current still poses a risk of temperature rise; lack of redundancy design: 4. Single detection point without backup, once the NTC is damaged or the connection is abnormal, the temperature protection function completely fails, and the system risk increases sharply. Summary of the Invention

[0004] To address the problems in the prior art, this invention provides a dual temperature protection method for lithium batteries. By combining hardware control and physical shutdown, the circuit is physically cut off by a temperature control switch when electronic protection fails. This optimizes the technical solution that relies solely on electronic protection and improves the reliability of temperature protection.

[0005] This invention provides a dual temperature protection method for lithium batteries, comprising: The first-level protection module includes an external thermistor in the temperature protection circuit. The thermistor detects the temperature signal of the battery pack and performs over-temperature protection for charging and discharging the battery based on the temperature signal detected by the thermistor. The second-level protection module includes a normally closed metal temperature control switch connected in series between the B-terminal of the battery protection board and the B-terminal of the battery cell. The circuit is switched on and off by the deformation of the normally closed metal temperature control switch at different temperatures.

[0006] Optionally, the first-level protection module further includes: The external resistors in the temperature protection circuit are RDOT for the high temperature detection pin during discharge, RCOT for the high temperature detection pin during charging, and RUT for the low temperature detection pin during charging and discharging. The resistors RDOT, RCOT, and RUT share a single thermistor.

[0007] Optionally, the first-level protection module sets the discharge high-temperature protection threshold and the charging high-temperature protection threshold by adjusting the external resistors RDOT and RCOT, respectively.

[0008] Optionally, when the battery is discharging, if the thermistor detects that the temperature of the battery pack is higher than the high-temperature protection threshold for discharge and the duration of the state is greater than or equal to 4 times the fixed duration, the voltage of the DHC pin in the temperature protection circuit will be changed to a low level and the CHC pin will be changed to a high-resistance state, thus entering the over-temperature protection state for discharge.

[0009] Optionally, during charging, if the battery pack temperature detected by the thermistor is higher than the charging high temperature protection threshold and the duration of the state is greater than or equal to 8 times the fixed duration, the CHC pin in the temperature protection circuit will become high resistance and enter the charging over-temperature protection state.

[0010] Optional, also includes: In the over-temperature protection state during charging, if the battery pack temperature continues to rise above the high-temperature protection threshold during discharge and the state time is greater than or equal to 4 times the fixed duration, the voltage of the DHC pin in the temperature protection circuit will become low.

[0011] Optional, also includes: In the over-temperature protection state, if the load is connected and the DCS pin voltage is higher than the discharge detection voltage, the temperature protection circuit will turn on the charging MOS Q1. If the load is removed before the overheating condition is resolved, the temperature protection circuit will shut down the charging MOSQ1.

[0012] This invention provides a dual temperature protection mechanism for lithium batteries that combines hardware control and physical shutdown. The first level of protection is achieved through an external thermistor in the temperature protection circuit, while the second level is achieved through a normally closed metal temperature control switch connected in series between the B-terminal of the battery protection board and the B-terminal of the battery cell. The second and first levels of protection work together as a hardware-level backup. When the first level of protection fails (e.g., MOSFET breakdown), the main circuit is directly cut off to prevent thermal runaway. This mechanism is often used as a "last line of defense" in lithium battery systems, improving the reliability of lithium battery temperature protection. Attached Figure Description

[0013] Figure 1 A circuit diagram of a temperature protection circuit provided in an embodiment of the present invention; Figure 2 A circuit diagram of a temperature protection peripheral circuit provided in an embodiment of the present invention; Figure 3 This is a structural diagram of a second-level protection module provided in an embodiment of the present invention. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures. Example

[0015] This invention provides a dual temperature protection method for lithium batteries. This method provides a dual temperature protection mechanism that combines hardware control and physical shutdown. When electronic protection fails, the circuit is physically cut off by a temperature control switch, thus optimizing the reliability of relying solely on electronic protection.

[0016] Specifically, the method includes: The first-level protection module includes an external thermistor connected in the temperature protection circuit. The thermistor detects the temperature signal of the battery pack and performs over-temperature protection for charging and discharging the battery based on the temperature signal detected by the thermistor.

[0017] The second-level protection module includes a normally closed metal temperature control switch connected in series between the B-terminal of the battery protection board and the B-terminal of the battery cell. The circuit is switched on and off by the deformation of the normally closed metal temperature control switch at different temperatures.

[0018] See Figure 1 and Figure 2 , Figure 1 This is a circuit diagram of a temperature protection circuit provided in an embodiment of the present invention. Figure 2 A circuit diagram of a temperature protection peripheral circuit provided for an embodiment of the present invention.

[0019] In this embodiment, the temperature protection peripheral circuit of the first-level protection module can be implemented by using an external resistor RT for the discharge high temperature detection pin DOTS, an external resistor RCOT for the charging high temperature detection pin COTS, and an external resistor RUT for the charging and discharging low temperature detection pin UTS.

[0020] As a preferred option, the recommended thermistor is the AT103 type NTC thermistor with a B value of 3435. This thermistor has the advantages of high precision, fast response, good thermal cycling resistance and good stability.

[0021] In this embodiment, the high-temperature protection threshold for discharge can be adjusted by changing the resistor RDOT, and the high-temperature protection threshold for charging can be adjusted by changing the resistor RCOT.

[0022] When the battery is discharging, if the thermistor detects that the temperature of the battery pack is higher than the discharge high temperature protection threshold TDOTP and the state time lasts for 4 times the fixed duration tTDET or longer, the DHC (Discharge High Current Control) pin voltage becomes low and the CHC (Charge High Current Control) pin of the HTL6024 becomes high impedance, entering the discharge over-temperature protection state.

[0023] Furthermore, during charging, if the battery pack temperature detected by the thermistor is higher than the charging high temperature protection threshold TCOTP and lasts for 8 times the fixed duration tTDET or longer, the CHC pin of the HTL6024 becomes high-resistance and enters the charging over-temperature protection state.

[0024] During the over-temperature protection state, the battery pack temperature continues to be monitored. If the battery pack temperature continues to rise above the discharge high temperature protection threshold TDOTP and the state time lasts for 4 times the fixed duration tTDET or longer, the DHC pin voltage goes low.

[0025] In the over-temperature protection state, if a load is connected (at which point the charging state changes to the discharging state) and the DCS pin voltage is higher than the discharge detection voltage VIN_DSG, the HTL6024 will immediately turn on MOS Q1. If the load is removed before the over-temperature protection state is lifted, the charging MOS Q1 will be turned off again.

[0026] See further Figure 3 In this embodiment, the function of the second-level protection module is to physically shut down the circuit. This module is a normally closed metal temperature control switch (such as the BH02-BB8D series, with an operating temperature of 85℃±5℃) connected in series between the B- of the battery protection board and the B- of the battery cell.

[0027] The core structure and materials of the normally closed metal temperature control switch in this embodiment include: Bimetallic sheet: It is made of two metals with different coefficients of thermal expansion laminated together.

[0028] High expansion layer: expands significantly when heated.

[0029] Low expansion layer: expands only slightly when heated.

[0030] Contacts: Typically made of silver alloy material to ensure low contact resistance and high conductivity.

[0031] Outer shell: Encapsulated with insulating material, resistant to high temperature and dust and moisture.

[0032] The working principle of the normally closed metal temperature control switch in this embodiment includes: (1) Normal temperature state (closed) When the temperature is below the set temperature (e.g., 85°C), the bimetallic strip remains flat, the moving contact and the stationary contact are in close contact, and the circuit is conductive.

[0033] (2) Temperature rises to the threshold (disconnect) When the ambient temperature reaches a set threshold, the bimetallic sheet bends and deforms due to the difference in thermal expansion between the two layers: High expansion layer: It expands significantly when heated and bends towards the low expansion layer.

[0034] Bending direction: determined by the fixed end of the bimetallic strip, usually bending towards the side with lower expansion.

[0035] The bending of the bimetallic strip pushes the moving contact to separate from the stationary contact, breaking the circuit, cutting off the load power supply, and realizing over-temperature protection.

[0036] (3) Temperature drops (reset) When the temperature drops to the reset temperature (usually 60°C below the trigger temperature), the bimetallic strip returns to its flat position, the contacts close again, and the circuit is turned on.

[0037] In this embodiment, the normally closed metal temperature control switch is automatically reset, requiring no manual intervention, and automatically recovers after the temperature drops.

[0038] This invention provides a dual temperature protection mechanism for lithium batteries that combines hardware control and physical shutdown. By coordinating the second-level protection with the first-level protection as a hardware-level backup, the main circuit is directly cut off when the first-level protection fails (such as MOSFET breakdown), preventing thermal runaway. This mechanism is often used as the "last line of defense" in lithium battery systems, thus improving the reliability of lithium battery temperature protection.

[0039] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for dual temperature protection of a lithium battery, characterized in that, include: The first-level protection module includes an external thermistor in the temperature protection circuit. The thermistor detects the temperature signal of the battery pack and performs over-temperature protection for charging and discharging the battery based on the temperature signal detected by the thermistor. The second-level protection module includes a normally closed metal temperature control switch connected in series between the B-terminal of the battery protection board and the B-terminal of the battery cell. The circuit is switched on and off by the deformation of the normally closed metal temperature control switch at different temperatures.

2. The method according to claim 1, characterized in that, The first-level protection module also includes: The external resistors in the temperature protection circuit are RDOT for the high temperature detection pin during discharge, RCOT for the high temperature detection pin during charging, and RUT for the low temperature detection pin during charging and discharging. The resistors RDOT, RCOT, and RUT share a single thermistor.

3. The method according to claim 2, characterized in that, The first-level protection module sets the discharge high temperature protection threshold and the charging high temperature protection threshold by adjusting the external resistors RDOT and RCOT, respectively.

4. The method according to claim 1, characterized in that, When the battery is discharging, if the thermistor detects that the temperature of the battery pack is higher than the high-temperature protection threshold for discharge and the duration of the state is greater than or equal to 4 times the fixed time, the voltage of the DHC pin in the temperature protection circuit will go low and the CHC pin will go to a high-resistance state, thus entering the over-temperature protection state for discharge.

5. The method according to claim 1, characterized in that, During charging, if the battery pack temperature detected by the thermistor is higher than the charging high temperature protection threshold and the duration of the state is greater than or equal to 8 times the fixed duration, the CHC pin in the temperature protection circuit will become high resistance and enter the charging over-temperature protection state.

6. The method according to claim 5, characterized in that, Also includes: In the over-temperature protection state during charging, if the battery pack temperature continues to rise above the high-temperature protection threshold during discharge and the state time is greater than or equal to 4 times the fixed duration, the voltage of the DHC pin in the temperature protection circuit will become low.

7. The method according to claim 5, characterized in that, Also includes: In the over-temperature protection state, if the load is connected and the DCS pin voltage is higher than the discharge detection voltage, the temperature protection circuit will turn on the charging MOS Q1. If the load is removed before the overheating condition is resolved, the temperature protection circuit controls the shutdown of charging MOS Q1.

Images