Voltage-triggered lithium-ion battery embedded safety device, control method and battery

Abstract

The application relates to the technical field of lithium ion battery safety, in particular to a lithium ion battery embedded safety device based on voltage triggering, a control method and a battery. The safety device is arranged in the battery and connected between the positive pole lug and the negative pole lug of the battery. The safety device comprises an MIT section, a first conductive section connected with the positive pole lug, a second conductive section connected with the negative pole lug and a first resistance section connected with the MIT section in series and connected between the first conductive section and the second conductive section to form a discharge loop. Based on the insulator-metal phase change characteristic of the MIT material, the MIT section automatically conducts the discharge loop when the battery is overcharged, the voltage continues to rise is inhibited, and the Joule heat generated by the first resistance section maintains the conduction to continuously consume energy after the phase change; the MIT section is cooled and reset to an insulating state after the overvoltage is eliminated, so that the self-recovery overcharge protection without external control is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery safety technology, specifically to a voltage-triggered embedded safety device, control method, and battery for lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, as a type of high-efficiency electrochemical energy storage device, are composed of key components such as current collectors, positive electrodes, negative electrodes, separators, electrolytes, and casings. Due to the inherent flammability of their materials, they pose a fundamental safety hazard. During thermal runaway, a chain of exothermic reactions occurs inside the battery, causing the temperature to rise continuously and potentially leading to combustion or explosion.

[0003] With the rapid development and large-scale application of the new energy industry and energy storage power stations, the safety of lithium-ion batteries has increasingly attracted widespread attention from all sectors of society. In particular, overcharging significantly increases the risk of thermal runaway during charging. Under overcharged conditions, energy accumulates continuously inside the battery, the electrochemical activity of the positive and negative electrodes increases, and side reactions intensify. Specifically, the negative electrode grows lithium dendrites because it cannot embed the excess lithium ions, which can easily puncture the separator and cause internal short circuits; the positive electrode releases active oxygen due to excessive delithiation, which reacts violently with the electrolyte and triggers thermal runaway. Such runaway can extend from the battery cell to the battery module and even the system level, causing serious safety accidents.

[0004] For the reasons mentioned above, the safety protection of lithium-ion batteries under overcharge conditions is particularly important. Although the battery management system (BMS) currently in use can regulate the charging and discharging process to a certain extent, it still has failure risks such as strategy limitations, signal interruption, and poor battery consistency, making it difficult to provide completely reliable overcharge protection. Summary of the Invention

[0005] To address the above technical problems, this invention provides a technical solution for a voltage-triggered embedded safety device, control method, and battery for lithium-ion batteries.

[0006] The technical problem solved by this invention can be achieved by the following technical solution: a voltage-triggered embedded safety device for lithium-ion batteries, comprising: the safety device being disposed inside the battery and connected between the positive and negative tabs of the battery; the safety device comprising: an MIT segment; a first conductive segment connected to the positive tab; a second conductive segment connected to the negative tab; and a first resistive segment connected in series with the MIT segment and jointly connected between the first conductive segment and the second conductive segment to form a discharge circuit.

[0007] Preferably, the MIT segment includes two conductive metal bodies and an MIT layer disposed between the two conductive metal bodies, for performing an insulator-metal phase transition under overcharge voltage triggering to conduct the discharge circuit, and automatically resetting to shut off the discharge circuit after the overcharge is released and the temperature is cooled below the phase transition temperature.

[0008] Preferably, the MIT layer is an electric field-induced insulator-metal phase change material used to establish an electric field between the two conductive metal bodies to induce a phase change.

[0009] Preferably, a second resistor segment is further connected in series in the discharge circuit, the second resistor segment being used to block the discharge circuit in a high-temperature environment when the discharge circuit is turned on.

[0010] Preferably, the second resistance segment is a polymer material with a positive temperature coefficient.

[0011] Preferably, the safety device further includes an encapsulation section for sealing and encapsulating the first resistor segment, the MIT segment, and the second resistor segment.

[0012] Preferably, the first resistor segment includes a plurality of resistor elements connected in parallel, used to limit current and convert electrical energy into heat energy when the discharge circuit is turned on in order to maintain the metal phase transition state of the MIT segment.

[0013] This invention also provides a control method for overcharging lithium-ion batteries, applied to the voltage-triggered embedded safety device for lithium-ion batteries as described above, comprising: step S1, real-time monitoring of battery voltage; when the battery voltage reaches a preset overcharge threshold, triggering an electric field-induced insulator-metal phase transition in the MIT segment of the safety device to automatically open the discharge circuit; step S2, the battery controllably discharges the overcharged charge through the discharge circuit to suppress the rise in battery voltage, and maintains the metal phase transition state of the MIT segment through Joule heating generated by the first resistor segment to keep the discharge circuit continuously open in the overcharged state; step S3, real-time monitoring of battery voltage; when the battery voltage falls below the preset overcharge threshold and the MIT cools below the phase transition temperature, the MIT segment automatically returns to the insulating state to shut off the discharge circuit.

[0014] Preferably, the overcharge threshold is set according to the material composition, thickness, and critical phase transition electric field strength of the MIT segment.

[0015] The present invention also provides a battery having a built-in voltage-triggered embedded safety device for lithium-ion batteries as described above.

[0016] Beneficial effects: This invention utilizes the insulator-metal phase transition characteristics of the MIT segment under overcharge high voltage to automatically open the discharge circuit, bypassing the overcharge current, thereby effectively suppressing the continuous rise in battery voltage and avoiding side reactions such as lithium dendrite growth and active oxygen release caused by overcharge. After the phase transition is completed, the conduction state is maintained by the Joule heat generated by the first resistive segment to ensure continuous energy dissipation. After the overvoltage is eliminated, the MIT segment gradually cools down until it is below the phase transition temperature, at which point it automatically resets to the insulating state, allowing the battery to return to normal operation. This achieves overcharge protection that can be automatically recovered without external control, improving the intrinsic safety level of lithium-ion batteries. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the dry cell structure of the embedded safety device of the present invention;

[0018] Figure 2a This is a schematic diagram showing the installation position of the safety device of the present invention in the dry cell;

[0019] Figure 2b This is a schematic diagram of the dry cell cross-section of the embedded safety device of the present invention;

[0020] Figure 3 This is a schematic diagram of the internal structure of the safety device of the present invention;

[0021] Figure 4 This is a schematic cross-sectional view of the packaged safety device of the present invention;

[0022] Figure 5 This is a schematic diagram of the battery structure of the embedded safety device of the present invention;

[0023] Figure 6 This is a schematic diagram of the battery cross-section of the embedded safety device of the present invention;

[0024] Figure 7 This is a schematic diagram of the battery cross-section of the external safety device of the present invention;

[0025] Figure 8 This is a flowchart of the control method of the present invention;

[0026] Figure 9 This is a graph showing the changes in voltage and temperature with state of charge (SOC) during the charging process of the lithium-ion battery of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0030] Reference Figure 1 , Figure 2b and Figure 3 This invention provides a voltage-triggered embedded safety device for lithium-ion batteries. The safety device 3 is disposed inside the battery and connected between the positive tab 11 and the negative tab 12 of the battery. The safety device 3 includes: an MIT segment 33; a first conductive segment 31 connected to the positive tab 11; a second conductive segment 35 connected to the negative tab 12; and a first resistive segment 32 connected in series with the MIT segment 33 and jointly connected between the first conductive segment 31 and the second conductive segment 35 to form a discharge circuit. The MIT segment 33 is used to perform an insulator-metal phase transition under overcharge voltage triggering to conduct the discharge circuit, and automatically resets to shut off the discharge circuit after the overcharge is released and the circuit is cooled below the phase transition temperature. The first resistive segment 32 is used to limit the current and convert electrical energy into heat energy when the discharge circuit is conducting to maintain the metal phase transition state of the MIT segment 33.

[0031] Specifically, in this embodiment of the invention, in response to the safety issue of thermal runaway that easily occurs under overcharge conditions of lithium-ion batteries, the present invention uses a built-in voltage-triggered discharge circuit formed by the MIT segment 33 and the first resistor segment 32 connected in series to automatically bypass the current and limit the voltage rise during overcharge, thereby avoiding the risks of side reactions such as lithium dendrite penetration of the separator and oxygen release from the positive electrode caused by continuous overcharge. This achieves intrinsic safety protection that can be automatically reset without external intervention, and significantly improves the intrinsic safety level of the battery system.

[0032] The MIT (Metal-Insulator Transition) segment 33 is a metal-insulator phase transition segment, a core component composed of a phase change material (such as vanadium dioxide VO2) with dual voltage and temperature sensitivity. Under normal battery voltage, the MIT segment 33 is in a high-resistance insulating state. When the overcharge voltage reaches its phase transition threshold, the MIT segment 33 undergoes an insulator-metal phase transition under the induction of a strong electric field, instantly opening the discharge circuit. After the circuit is opened, the Joule heat generated by the first resistive segment 32 will raise the temperature of the MIT material. Once the temperature reaches its thermally induced phase transition threshold (e.g., 68°C), even if external overcharging stops and the voltage is below the electrical trigger threshold, the phase transition state can still be spontaneously maintained by heat, thus continuing to discharge current and further reducing the battery voltage. Until the system cools down below the phase transition temperature, the MIT segment 33 returns to the insulating state, the discharge circuit is disconnected, and the battery voltage finally returns to and stabilizes in the normal range, achieving automatic reset.

[0033] Specifically, in practical applications, the safety device 3 is directly connected to the battery tabs through conductive segments (i.e., the first conductive segment 31 and the second conductive segment 35), enabling it to respond quickly in the early stages of battery overcharging. Once the voltage exceeds the set threshold, its MIT segment 33 rapidly undergoes a phase transition, changing from a high-resistance state to a low-resistance state, forming a stable discharge path. This continuously consumes the overcharged energy and dissipates it as heat, effectively preventing the battery voltage from rising further. Until charging stops or the voltage drops below the set threshold and the temperature is below the phase transition temperature, the safety device 3 automatically returns to the high-resistance state and cuts off the bypass current. The entire process requires no external control intervention, achieving embedded, self-recovering overcharge protection for individual batteries.

[0034] Accordingly, the first conductive segment 31 is made of aluminum or steel and is used to connect the safety device 3 to the positive electrode 11 of the battery; the second conductive segment 35 is made of nickel, copper, or steel and is used to connect the safety device 3 to the negative electrode 12 of the battery. Both the first conductive segment 31 and the second conductive segment 35 are directly embedded inside the battery's dry cell 2, and the connection is completed simultaneously during the welding of the current collector and the electrode tab via ultrasonic welding or laser welding. This embedded design not only allows the safety device 3 and the dry cell 2 to form a tight integrated structure, simplifying the integration process and enabling efficient compatibility with the manufacturing process of the dry cell 2, but also ensures low impedance and high reliability of the connection interface. This guarantees that the discharge circuit can quickly and stably conduct large currents when triggered, effectively improving the overall response performance and consistency of overcharge protection.

[0035] Among them, reference Figure 1 , Figure 2a and Figure 2bIn the lead-out areas of the positive tab 11 and negative tab 12 of the dry cell 2, tab adhesive 13 is provided to achieve insulation and sealing between the metal tabs and the aluminum-plastic film packaging. This insulating and sealing structure not only ensures the stability of the internal electrochemical environment of the battery, but also provides the necessary installation and insulation support for the embedded safety device 3.

[0036] In a preferred embodiment of the present invention, the first resistor segment 32 includes a plurality of resistor elements connected in parallel to distribute the power of the discharge circuit.

[0037] Specifically, in this embodiment of the invention, by adopting a topology of multiple resistors connected in parallel, the power carrying capacity and heat dissipation performance of this functional segment are effectively improved, ensuring its stability and reliability during continuous high-current discharge. Each resistor element in the parallel configuration has a rated power of not less than 1W (preferably 2W), and the total number of parallel resistors can be adjusted from 1 to 10 according to specific application requirements. The total resistance after parallel connection is designed to be between 0.5Ω and 10Ω. Furthermore, each resistor element preferably uses a 2512 package surface mount resistor, and a double-sided mounting method is adopted to optimize PCB space utilization and thermal management.

[0038] To be more specific, refer to Figures 1 to 3 The first resistor segment 32 is connected in series between the MIT segment 33 and the first conductive segment 31. This arrangement allows the overcharge current to flow sequentially through the first conductive segment 31, the first resistor segment 32, the MIT segment 33, and the second conductive segment 35 when the discharge circuit is triggered, ultimately forming a closed loop. The multi-resistor parallel structure of the first resistor segment 32 not only effectively disperses the current-induced thermal effect and avoids single-point overheating, but also ensures that the discharge current is within a safe and controllable range through its stable resistance characteristics. This provides a continuous and stable thermal environment for maintaining the phase transition state of the MIT segment 33, while ensuring the safety and durability of the entire discharge process.

[0039] In a preferred embodiment of the present invention, the MIT segment 33 includes two conductive metal bodies and an MIT layer disposed between the two conductive metal bodies; the MIT layer is made of an electric field-induced insulator-metal phase change material, which is used to establish an electric field between the two conductive metal bodies to induce a phase change.

[0040] Specifically, in this embodiment of the invention, the MIT segment 33 is composed of two conductive metal bodies with a flatness of ≤1μm on one side end face and an MIT layer sandwiched between them. The smooth end faces of the two conductive metal bodies are parallel to each other and electrically isolated by the MIT layer.

[0041] The conductive metal body can be selected from metals or alloys with good conductivity and stability, such as aluminum, nickel, copper, steel, titanium, silver, platinum, and gold. The thickness of the MIT layer is 1 to 10 μm, and the MIT layer can be prepared on the end face of the conductive metal body by deposition methods such as vacuum evaporation, magnetron sputtering, spraying, roller coating, or physical compaction.

[0042] When overcharging causes the battery voltage to exceed the threshold, the electric field strength on both sides of the MIT layer reaches a critical value, inducing the induced insulator-metal phase change material (i.e., MIT material) to undergo a phase transition from insulator to metallic state, forming a low-resistance path to achieve bypass discharge; during the subsequent continuous discharge process, the Joule heat generated by the loop current will keep the MIT material in a conductive state until the battery voltage drops below the safe range.

[0043] More specifically, in the embodiments of the present invention, the MIT material selected for the MIT layer covers a variety of types, mainly including transition metal oxides (e.g., VO2, WO3), perovskite oxides (e.g., SrCoO3), and various two-dimensional materials and their heterostructures.

[0044] This MIT layer can be prepared using various film-forming techniques such as physical vapor deposition, chemical vapor deposition, and sol-gel. By doping with metal ions (such as introducing elements like W, Mo, and Nb into VO2), constructing heterogeneous interfaces, or controlling the nanostructure, the critical electric field strength required for the phase transition can be precisely set to 0.45 × 10⁻⁶. 6 V / m to 2×10 6 Within the V / m range.

[0045] Correspondingly, taking VO2 material as an example, its phase transition temperature in its unmodified state is about 68°C. However, by introducing metal ions such as W, Mo, and Nb, the phase transition temperature can be reduced to around 60°C while improving the material's response to electric fields, making it more suitable for the actual requirements of response temperature and voltage threshold in lithium-ion battery overvoltage protection.

[0046] In a preferred embodiment of the present invention, a second resistor segment 34 is also connected in series in the discharge circuit. The second resistor segment 34 is used to block the discharge circuit in a high-temperature environment when the discharge circuit is turned on.

[0047] Specifically, to enhance the protection redundancy of safety device 3 under abnormally high current or high temperature conditions, and to prevent the risk of battery over-discharge and heat accumulation that may be caused by the continuous conduction of MIT segment 33 at high temperatures, in this embodiment of the invention, referring to... Figures 1 to 3The second resistor segment 34 is connected in series between the MIT segment 33 and the second conductive segment 35. Under normal conditions, it exhibits a low resistance state to ensure the normal triggering and current discharge function of the discharge circuit. When the circuit current rises abnormally or the ambient temperature exceeds its set threshold, the resistance value of this component will change by several orders of magnitude, thereby quickly limiting or even cutting off the bypass current, effectively preventing the battery from entering a new thermal runaway risk area due to continuous over-discharge, and providing a dual protection mechanism for battery safety.

[0048] In a preferred embodiment of the present invention, the second resistive segment 34 is a polymer positive temperature coefficient material.

[0049] Specifically, in this embodiment of the invention, the second resistor segment 34 is composed of a polymer resettable fuse (PPTC). The PPTC element is packaged in a standard surface mount package such as 1206 or 1812, and its holding current at room temperature (23°C) is not less than 3A, and its operating temperature is set to 85°C or above.

[0050] Under normal operating conditions, the resistance of this component is extremely low and can be regarded as a wire, ensuring that the impedance of the discharge circuit is small enough when triggered. When the discharge circuit causes the current to exceed 5A due to abnormal conditions or the ambient temperature to rise above 85°C, the polymer matrix inside the component rapidly undergoes volume expansion and crystal phase transformation, and the resistance increases sharply by more than three orders of magnitude, thereby effectively limiting the abnormal current and cutting off the potential dangerous energy path.

[0051] This design not only effectively suppresses the risks of overcurrent and overheating in the circuit, but more importantly, it blocks the conduction maintenance mechanism that may form in the MIT section under high temperature conditions, preventing the battery from falling into over-discharge or secondary thermal abuse state due to continuous discharge, and providing dual synergistic protection for lithium-ion batteries based on current and temperature triggering.

[0052] As a preferred embodiment of the present invention, the safety device 3 further includes an encapsulation section for sealing and encapsulating the first resistor segment 32, the MIT segment 33 and the second resistor segment 34.

[0053] Specifically, in order to prevent the electrolyte from corroding the device, causing short circuits, and interfering with its electrochemical performance, in this embodiment of the invention, reference is made to... Figure 4 The encapsulation section includes a lower encapsulation 36 and an upper encapsulation 37, which are joined together by a sealing process to form a sealed encapsulation body, which encloses the above-mentioned functional sections and achieves reliable physical isolation from the electrolyte inside the battery.

[0054] More specifically, the encapsulation material is preferably thermally conductive silicone. This material provides excellent electrical insulation and environmental sealing while possessing high thermal conductivity, enabling it to effectively dissipate the Joule heat generated by the first resistive section 32 and the second resistive section 34 during operation, thus preventing heat accumulation inside the device and ensuring the long-term stability and reliability of each functional section. The specific dimensions, sealing method, and heat dissipation capacity of this encapsulation unit can be tailored and adjusted according to the specific battery model, capacity, and available internal space, ensuring the wide applicability of this safety device in different types of lithium-ion batteries and the convenience of embedded integration.

[0055] As a preferred embodiment of the present invention, the fabrication steps of the safety device 3 include: Step 1, fabricating an electric field-induced insulator-metal phase transition (MIT) layer on a conductive substrate using a film-forming technique to obtain an MIT thin film; Step 2, encapsulating the MIT thin film between the smooth end faces of two conductive metal bodies to form an MIT chip, obtaining an MIT segment 33; Step 3, arranging multiple resistive elements in parallel to form a first resistive segment 32; Step 4, electrically connecting the MIT segment 33, the first resistive segment 32, and the second resistive segment 34; Step 5, ... Step six: Connect the positive terminal of the first resistive segment 32 to one side of the first conductive segment 31; Step seven: Connect the negative terminal of the second resistive segment 34 to one side of the second conductive segment 35; Step eight: Insulate and encapsulate the MIT segment 33, the first resistive segment 32, and the second resistive segment 34 to obtain the safety device 3; Step eight: Perform electrical performance testing on the encapsulated safety device 3, and weld the first conductive segment 31 and the second conductive segment 35 of the safety device 3 to the positive tab 11 and the negative tab 12 of the dry cell 2, respectively, to complete the integration of the safety device 3 inside the battery 1.

[0056] Specifically, in this embodiment of the invention, the above steps, through reasonable process selection and parameter control, ensure the performance and reliability of each functional segment of the safety device 3, and achieve efficient compatibility with the battery 1 manufacturing process.

[0057] Accordingly, the specific processes and preferred parameters for each of the above steps are as follows:

[0058] In step one, vacuum evaporation, magnetron sputtering, spraying, roller coating, physical compaction, sol-gel methods are preferred to prepare VO2 / MoO3 composite films on substrates such as aluminum, copper, steel, conductive glass, or graphite in an argon atmosphere. The total film thickness is controlled within the range of 1–10 μm, with 3 μm being preferred in practical applications to balance response speed and mechanical strength. Simultaneously, the critical electric field strength for inducing the phase transition is set to 0.45 × 10⁻⁶ through doping or microstructure control. 6 V / m ~2×10 6 Between V / m, 1.5×10 is typically used under typical operating conditions.6 V / m to achieve matching with common battery overvoltage thresholds.

[0059] In step two, one end face of the two selected conductive metal bodies needs to be precisely machined to a flatness of no more than 0.5μm. The preferred materials are copper, aluminum, nickel, or silver. During packaging, the highly flat end faces of the two metal bodies are placed opposite each other, and the MIT film is sandwiched between them to maintain close contact. The entire MIT chip can be made using standard packaging forms such as SMA, SMB, or DO-41 to ensure that it is in an insulating state under normal conditions.

[0060] In step three, the first resistor segment 32 is composed of multiple surface-mount resistors connected in parallel. The rated power of a single resistor element is not less than 1W, with a typical selection of 2W. The number of resistors connected in parallel can be flexibly configured between 1 and 10 according to application requirements, with 6 being the most common. The total resistance after parallel connection is designed to be between 0.5 and 10Ω, with a typical value of 2.25Ω. Each resistor is preferably in a 2512 package and is arranged on a PCB or other insulating substrate in a double-sided mounting manner to improve power capacity and heat dissipation performance.

[0061] In step four, when making electrical connections, connect the negative terminal of the first resistor segment 32 to one side pin of the MIT segment 33, and then connect the other side pin of the MIT segment 33 to the positive terminal of the second resistor segment 34.

[0062] In steps five and six, the first conductive section 31 is made of aluminum or steel, and the second conductive section 35 is made of nickel, copper or steel. The thickness of both is controlled between 0.05 and 0.3 mm, and the width is between 1 and 10 mm. A welding area of ​​2 to 30 mm needs to be reserved on one side of each conductive section for reliable connection with the battery tabs in the future.

[0063] More specifically, after the safety device 3 is integrated inside the battery 1, the battery 1 is further encapsulated, as shown in the following description. Figure 5 and Figure 6 The integrated dry cell 2 and the embedded safety device 3 are placed together in the casing of the battery 1, and subsequent operations such as casing sealing, liquid injection, formation and capacity testing are completed through conventional processes, finally forming a lithium-ion battery 1 with a complete structure and normal operation and embedded safety device 3.

[0064] In this structure, the safety device 3 is reliably electrically connected to the positive electrode 11 and the negative electrode 12 through its first conductive section 31 and second conductive section 35 respectively, and is located in the central area inside the battery 1, thereby ensuring that it can effectively monitor the status of the battery 1 and quickly trigger the protection action in case of overcharging.

[0065] Reference Figure 8The present invention also provides a control method for overcharging of lithium-ion batteries, applied to the voltage-triggered embedded safety device for lithium-ion batteries as described above, comprising: step S1, real-time monitoring of battery voltage, when the battery voltage reaches a preset overcharge threshold, triggering an electric field-induced insulator-metal phase transition in the MIT segment 33 of the safety device 3 to automatically open the discharge circuit; step S2, the battery controlsably discharges the overcharged charge through the discharge circuit to suppress the rise in battery voltage, and maintains the metal phase transition state of the MIT segment 33 through Joule heat generated by the first resistor segment 32 to keep the discharge circuit continuously open in the overcharged state; step S3, real-time monitoring of battery voltage, when the battery voltage falls below the preset overcharge threshold and the MIT cools below the phase transition temperature, the MIT segment 33 automatically returns to the insulating state to shut off the discharge circuit.

[0066] Specifically, in this embodiment of the invention, to address the safety challenge of thermal runaway caused by the continuous voltage rise during overcharging of lithium-ion batteries, a built-in voltage-triggered discharge circuit achieves rapid, automatic, and self-recoverable overcharge protection. This safety device 3 requires no external commands or complex control logic; it can trigger and complete the entire protection process solely based on the battery's own voltage.

[0067] Specifically, the overcharge threshold is set within the range of 4.2V to 4.8V, preferably 4.5V, based on the battery system and safety requirements. When the battery voltage reaches this threshold, the electric field strength established across the MIT segment 33 exceeds its critical phase transition electric field (preferably ≥1.5×10). 6 (V / m), inducing a transition from an insulator to a metallic state; after the discharge circuit is turned on, the overcharge flows through the first resistor section 32 and is converted into heat energy dissipation, suppressing the battery voltage from continuing to rise; at the same time, the Joule heat generated by the first resistor section 32 provides thermal maintenance for the MIT section 33, which in some cases allows it to remain in a low-resistance metallic state after the overcharge is released, forming a positive feedback loop of energy discharge-thermal maintenance until charging stops and the voltage drops to the normal range.

[0068] Based on the relative magnitudes of the discharge circuit current and the overcharge current, the safety device 3 can provide multi-level protection, as follows: When the overcharge current is less than the discharge circuit current of the safety device, the battery voltage begins to drop, thus effectively preventing overcharging; when the overcharge current is equal to the discharge circuit current of the safety device, the battery charging current and discharge current reach a balance, and the battery voltage remains stable and no longer rises; when the overcharge current is greater than the discharge circuit current of the safety device, the safety device 3 can significantly slow down the voltage rise rate, buying valuable time for the system to take other protective measures, which plays an important role in preventing battery thermal runaway; when overcharging stops, and the temperature of the MIT section 33 rises to the phase transition temperature threshold under the Joule heat generated by the first resistor section 32, the safety device 3 will continue to discharge current. As the voltage decreases, when the temperature of the MIT material drops below the phase transition temperature, the MIT section 33 becomes an insulator, cutting off the discharge circuit, thereby stabilizing the battery voltage within the normal range.

[0069] Reference Figure 9 The following details the battery overcharge process. When the battery is overcharged at 4.2V (horizontal axis: 100% SOC - 145% SOC), and the voltage reaches Vmax (approximately 5.5V), the battery temperature remains below 50℃, which is insufficient to trigger the temperature-dependent phase transition of the phase change material. As charging continues (horizontal axis: 145% SOC - 165% SOC), the battery temperature slowly increases, eventually leading to thermal runaway. The temperature increases rapidly and within a very short time; once the thermal runaway initiation point is reached, it becomes irreversible. Because the battery temperature change is small before thermal runaway occurs, the protection provided by temperature-induced phase transitions is limited. However, directly triggering the phase transition circuit through voltage can provide protection before the battery temperature rises and thermal runaway begins.

[0070] As a preferred embodiment of the present invention, the overcharge threshold is set according to the material composition, thickness and critical phase transition electric field strength of the MIT segment 33.

[0071] Specifically, in the embodiments of the present invention, the band structure and phase transition characteristics of the MIT material are adjusted by means of doping (such as doping VO2 with elements such as W, Mo, and Nb), heterojunction design, or nanostructure control, thereby precisely controlling its critical phase transition electric field at 0.45 × 10⁻⁶. 6 V / m to 2×10 6 Within the V / m range; further, by controlling the thickness of the MIT layer (preferably 1 to 10 μm), the voltage threshold for triggering phase transition can be adapted to different battery systems, enabling customizable design of overcharge protection trigger points in the voltage range of 4.2V to 4.8V or even higher.

[0072] Reference Figure 5 and Figure 6The present invention also provides a battery having a built-in voltage-triggered embedded safety device for lithium-ion batteries as described above.

[0073] Specifically, in this embodiment of the invention, the safety device 3 is embedded inside the battery 1 after encapsulation. Its first conductive segment 31 and second conductive segment 35 are reliably electrically connected to the positive electrode tab 11 and negative electrode tab 12 of the battery 1 by welding, respectively. The safety device 3 is located in the central region inside the dry cell 2, isolated from the positive and negative electrode plates, and insulated from and thermally managed by the encapsulation part and heat dissipation structure.

[0074] This built-in integration ensures that the safety device 3 can monitor the battery status in real time and quickly establish a discharge path when overcharging occurs, achieving accurate, fast, and non-intervention-required overcharge protection, which significantly improves the inherent safety of the battery under abuse conditions.

[0075] In summary, this invention integrates a voltage-triggered MIT functional material with a current-limiting resistor structure and embeds it inside battery 1 to construct an embedded intelligent protection device. This device utilizes the intrinsic electric field response characteristics of MIT material under overcharge high voltage to automatically achieve an insulator-metal phase transition and establish a low-resistance discharge path. It quickly bypasses the overcharge current and suppresses voltage rise without relying on external BMS commands. Through the resistive section in the discharge circuit, it converts electrical energy into heat energy and maintains the phase transition state, forming a self-sustaining energy dissipation mechanism. After the overcharge is released, it automatically returns to the insulating state, achieving zero-power standby and resettable protection.

[0076] Compared with traditional external protection solutions such as fuses or MOSFETs, this invention has many advantages, including fast response speed, automatic reset, built-in integration without taking up extra space, precise protection per cell, short discharge path with low impedance, and flexible customization of trigger voltage, which significantly improves the inherent safety and reliability of lithium-ion battery systems.

[0077] The following are several specific embodiments to illustrate the implementation of the present invention in detail:

[0078] Example 1:

[0079] 1) A MIT (Insulator-Metal Transition) material capable of undergoing an insulator-metal phase transition induced by an electric field was prepared by magnetron sputtering. The material was 3 μm thick and deposited on a 10 μm copper foil. The critical phase transition electric field strength was 1.5 × 10⁻⁶. 6 V / m corresponds to an operating voltage of 4.5V.

[0080] 2) The MIT material is SMA packaged with two square copper rods with a flatness of 0.1μm and a cross-sectional area of ​​2mm×2mm in the order of "copper rod-MIT-copper rod" to make an MIT chip, thus obtaining MIT segment 33.

[0081] 3) Select 6 surface mount resistors with a power of 2W and a resistance of 13.5Ω. Connect the 6 surface mount resistors in parallel to form the first resistor segment 32 with a resistance of 2.25Ω. Package it in 2512 and mount it on the PCB board on both sides.

[0082] 4) Prepare a PPTC chip, model MF-PSHT400 / 85-2, I_hold (23°C) = 4A, packaged in 1206 to obtain the second resistor segment 34.

[0083] 5) Install the MIT chip at the back end of the parallel resistor and connect the negative terminal of the parallel resistor to one pin (input terminal) of the MIT chip. Install the PPTC chip at the back end of the MIT chip and connect the other pin (output terminal) of the MIT chip to the PPTC (input terminal), thereby electrically connecting the first resistor segment 32, the MIT segment 33, and the second resistor segment 34 in sequence.

[0084] 6) Use 0.1mm thick and 4mm wide aluminum strip and nickel strip as the first conductive section 31 and the second conductive section 35 respectively. Connect one side of the first conductive section 31 to the positive terminal of the parallel resistor, and reserve an 8mm long soldering area on the other side; at the same time, connect one side of the second conductive section 35 to the negative terminal (output terminal) of the PPTC, and also reserve an 8mm long soldering area on the other side.

[0085] 7) Thermally conductive silicone is used to perform thermal insulation sealing on the first resistive segment 32, the MIT segment 33, and the second resistive segment 34. The encapsulation form, encapsulated size, and heat dissipation capacity can be adjusted according to the type, capacity, and structure of different batteries 1 to meet different needs. The fabrication of the embedded safety device 3 is thus completed.

[0086] 8) Perform insulation testing on safety device 3 to confirm that the device is normal and there is no short circuit.

[0087] 9) Prepare 2Ah stacked cells using conventional processes. The positive electrode uses lithium nickel cobalt manganese oxide (NCM) ternary material, and the negative electrode uses silicon carbon material. The working voltage is 2.5V to 4.2V. At the same time, prepare 0.1mm thick and 8mm wide aluminum and nickel tabs. Weld the first conductive section 31 and the second conductive section 35 to the positive and negative tabs of the cell by ultrasonic welding. The welding is completed simultaneously during the welding process between the current collector and the tabs, so that the safety device 3 is located in the middle of the positive and negative tabs of the cell and between the cell body and the tab adhesive 13.

[0088] 10) The battery 1 is packaged and the device is encapsulated inside the battery 1. The battery 1 is then subjected to processes such as liquid injection, formation, and capacity testing according to conventional process flow to complete the preparation of the battery 1.

[0089] Example 2:

[0090] The embedded safety device 3 and battery 1 are fabricated according to the method of Example 1, except that the thickness of the MIT material is 2.8 μm and its corresponding operating voltage is 4.2 V, the positive electrode material of the battery is lithium iron phosphate (LFP), and the operating voltage range is 2.5 V to 3.65 V.

[0091] Example 3:

[0092] The embedded safety device 3 and battery 1 are fabricated according to the method of Example 1, except that the thickness of the MIT material is 3.2 μm and its corresponding operating voltage is 4.8 V, and the positive electrode material of the battery is high-voltage lithium cobalt oxide (LCO) with an operating voltage range of 2.5 V to 4.5 V.

[0093] Example 4:

[0094] The safety device 3 and battery 1 were prepared according to the method of Example 1, referring to... Figure 7 The difference is that the safety device 3 is installed externally, which is suitable for retrofitting finished batteries without affecting the original structure and performance of the battery.

[0095] In addition, several comparative examples are provided to illustrate battery performance without the safety device 3 of the present invention:

[0096] Comparative Example 1: Battery 1 was prepared according to the method of Example 1, except that the embedded safety device 3 was not selected.

[0097] Comparative Example 2: Battery 1 was prepared according to the method of Example 3, except that the embedded safety device 3 was not selected.

[0098] Comparative Example 3: Battery 1 was prepared according to the method of Example 4, except that the embedded safety device 3 was not selected.

[0099] The specific testing process is as follows:

[0100] First, a 0.2C capacity test was conducted on battery 1 with a rated capacity of 2Ah in each embodiment and comparative example. Then, battery 1 was continuously charged at a current of 1C (2A) until battery 1 failed (e.g., discharge, smoke, fire, explosion) or the overcharge capacity reached 100% of the rated capacity. Specifically, overcharge tests were conducted on battery 1 in Example 1 under three current conditions: 0.5C (1A), 1C (2A), and 1.5C (3A) to simulate different operating conditions where the discharge current is greater than, equal to, and less than the overcharge current. The state of battery 1 was closely observed during the test, and the voltage and capacity of batteries that did not experience thermal runaway were measured after 24 hours. Specific test results are shown in Table 1.

[0101] Table 1 Battery overcharge test results

[0102]

[0103] The test results in the table above demonstrate that the embedded safety device 3 provided by this invention has a significant effect on suppressing continuous battery overcharging and preventing fires and explosions. The specific performance and analysis of each embodiment are as follows:

[0104] I. Example 1 (NCM ternary lithium battery): Multi-current overcharge test and mechanism analysis

[0105] In this embodiment 1, an NCM ternary lithium battery (normal operating voltage 2.5-4.2V) is used as the test object. The overcharge protection voltage is set to 4.5V, and overcharge tests are performed at 0.5C (1A), 1C (2A), and 1.5C (3A) to simulate three operating conditions: discharge current greater than, equal to, and less than the overcharge current.

[0106] 0.5C (1A) Overcharge (Discharge Current > Overcharge Current): When the battery voltage rises to 4.5V, a phase transition occurs in the MIT segment, and the discharge circuit is activated. Because the discharge current (approximately 2A) is greater than the charging current (1A), the battery voltage cannot be maintained at 4.5V, causing the MIT segment to be at the critical point of phase transition and to alternate between phase transitions. As the discharge progresses and the temperature rises, the MIT segment is heated and remains activated, and the continuous discharge current causes the voltage to drop. Eventually, the voltage drops to 4.157V (within the normal range), and the battery capacity does not decrease, achieving non-destructive protection.

[0107] 1C (2A) Overcharge (Discharge Current = Overcharge Current): The overcharge current and discharge current reach equilibrium, and the battery voltage stabilizes at around 4.5V. After charging stops, the MIT segment remains in a metallic state due to Joule heating and continues to discharge until the battery voltage drops to 3.934V and the temperature falls below the phase transition point, at which point the circuit is shut off. The battery is undamaged and its capacity is normal.

[0108] 1.5C (3A) Overcharge (Discharge Current < Overcharge Current): The device continues to discharge but cannot completely offset the overcharge energy, causing the battery voltage to rise slowly, triggering electrolyte decomposition and gas production (slight swelling). After charging stops, the MIT segment remains conductive due to high temperature, and the continued discharge causes the voltage to drop back to 3.853V. Although side reactions are not completely avoided in this situation, the thermal runaway process is significantly delayed, buying time for system intervention.

[0109] This embodiment 1 shows that the discharge circuit needs to be designed based on the maximum expected overcharge current in order to avoid insufficient current as much as possible; at the same time, the PPTC and heat sink in the device work together to control the temperature between 60 and 80°C to avoid the new thermal risks caused by exceeding 85°C.

[0110] II. Applicability Verification of Different Battery Systems

[0111] Example 2 (LFP lithium iron phosphate battery): The trigger threshold was set to 4.2V based on its operating voltage (2.5~3.65V). After testing, the battery showed no change in appearance or gas expansion, and the voltage was discharged to 3.277V (within the normal range), effectively avoiding thermal runaway and capacity decay.

[0112] Example 3 (High-voltage LCO lithium cobalt oxide battery): The protection voltage was set to 4.8V to account for its high-voltage characteristics (operating voltage 2.5–4.5V). The device triggered and discharged normally; the battery did not swell or run away from the system, and the voltage recovered to 4.125V, indicating that the device is suitable for high-voltage systems.

[0113] Example 4 (External Safety Device): The protection effect is the same as that of the built-in device when it is installed later, which verifies the effectiveness and flexibility of this solution under different integration methods.

[0114] III. Comparison of Results from Comparative Examples (Without Safety Devices)

[0115] Comparative Examples 1-3 (NCM, LFP, and LCO batteries without the device): Both NCM and LCO batteries experienced thermal runaway (fire and explosion), while the LFP battery, due to its better material thermal stability, only experienced discharge and smoke, but still posed a high risk of thermal runaway if overcharging continued. This stark contrast with the embodiments highlights the necessity and effectiveness of this safety device.

[0116] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A voltage trigger based lithium ion battery embedded safety device, characterized in that, The safety device (3) is arranged inside the battery and connected between the positive tab (11) and the negative tab (12) of the battery. The safety device (3) comprises: An MIT segment (33) for electric field-induced insulator-metal phase transition to turn on the discharge circuit under overcharge voltage trigger and automatically reset to turn off the discharge circuit after overcharge is removed and cooled below the phase transition temperature; A first conductive segment (31) connected with the positive tab (11); A second conductive segment (35) connected with the negative tab (12); A first resistance segment (32) connected in series with the MIT segment (33) and connected between the first conductive segment (31) and the second conductive segment (35) to form a discharge circuit; The first resistance segment (32) comprises a plurality of resistance elements arranged in parallel for current limiting and converting electrical energy into heat to maintain the metal phase of the MIT segment (33) when the discharge circuit is turned on; The discharge circuit further comprises a second resistance segment (34) connected in series for blocking the discharge circuit in high temperature environment when the discharge circuit is turned on.

2. The voltage trigger based lithium-ion battery embedded safety device of claim 1, wherein, The MIT layer adopts an electric field-induced insulator-metal phase transition material for establishing an electric field between the two conductive metal bodies to induce phase transition.

3. The voltage trigger based lithium-ion battery embedded safety device of claim 1, wherein, The second resistance segment (34) is a piece of polymer positive temperature coefficient material.

4. The voltage trigger based lithium-ion battery embedded safety device of claim 2, wherein, The safety device (3) further comprises a packaging part for sealing and packaging the first resistance segment (32), the MIT segment (33) and the second resistance segment (34).

5. A control method for overcharging of a lithium-ion battery, characterized by, The safety device (3) is applied to a voltage-triggered lithium ion battery embedded safety device as claimed in any one of claims 1-4, comprising: Step S1, real-time monitoring of the battery voltage, when the battery voltage reaches a preset overcharge threshold, triggering the MIT segment (33) in the safety device (3) to undergo electric field-induced insulator-metal phase transition to automatically turn on the discharge circuit; Step S2, the battery discharges the overcharged electrical energy through the discharge circuit to suppress the rise of the battery voltage, and the MIT segment (33) maintains the metal phase by the Joule heat generated by the first resistance segment (32) to keep the discharge circuit continuously turned on under overcharge; Step S3, real-time monitoring of the battery voltage, when the battery voltage falls below the preset overcharge threshold and the MIT is cooled below the phase transition temperature, the MIT segment (33) automatically returns to the insulating state to turn off the discharge circuit.

6. The control method for overcharging of a lithium-ion battery according to claim 5, characterized in that, The overcharge threshold is set according to the material composition, thickness and critical phase transition electric field strength of the MIT segment (33).

7. A battery, characterized by The safety device (3) is applied to a voltage-triggered lithium ion battery embedded safety device as claimed in any one of claims 1-4, comprising:

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