A temperature sensitive current limited self-closing current collector

Abstract

This invention discloses a temperature-sensitive, current-limiting, self-shutting current collector for lithium-ion batteries, addressing the issues of response delay and insufficient safety redundancy inherent in existing BMS (Battery Management System) protection technologies. It comprises a metal current collector, a temperature-sensitive current-limiting layer positioned along the current direction, and an electrode active material layer. The temperature-sensitive current-limiting layer uses a positive temperature coefficient material, exhibiting at least a 102-fold increase in volume resistivity within a narrow temperature range of 90-130°C, and also possessing a high specific heat capacity. Under normal conditions, the temperature-sensitive current-limiting layer exhibits low resistance, allowing for normal charging and discharging of the battery cell. At high temperatures, its resistance increases sharply, limiting or cutting off the current and mitigating heat generation. Upon triggering, this current collector is identified by the existing BMS through internal resistance and current anomalies, forming dual internal and external protection. This requires no modification to the existing system, offers high manufacturability, and significantly improves the safety and reliability of energy storage systems.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery safety technology, and in particular to a temperature-sensitive, current-limiting, self-closing current collector. Background Technology

[0002] With the widespread application of lithium-ion batteries in portable energy storage, residential energy storage, and industrial and commercial energy storage, the safety of battery packs has become an increasingly important concern. Especially under conditions of high-rate discharge, thermal buildup, or internal short circuits, the internal temperature of a single battery cell can rise rapidly, leading to decomposition of active materials, electrolyte decomposition, or even thermal runaway accidents.

[0003] Currently, the safety management of battery packs mainly relies on the Battery Management System (BMS), which monitors voltage, current, temperature, and estimates parameters such as internal resistance and SOC / SOH to determine whether a single cell is abnormal. BMS typically uses constant current control, voltage equalization strategies, or alarm processing to protect the pack. However, existing technologies have the following drawbacks: when the internal temperature of the cell rises rapidly, the sampling and control cycle of the BMS through current, voltage, and external temperature sensors may not be able to prevent thermal runaway in time; BMS mainly relies on external current control or voltage equalization, lacking an intrinsic physical current-limiting mechanism within the cell; and existing technologies cannot provide an independent physical disconnection mechanism within the cell in cases of BMS sampling delays, sensor failures, or control malfunctions, lacking independent intrinsic safety redundancy.

[0004] Therefore, there is an urgent need for a self-protection mechanism triggered by the internal temperature of the battery cell, which can directly limit or cut off the current when the internal temperature is abnormal, while being compatible with the existing BMS system to achieve dual safety protection. Summary of the Invention

[0005] To address the issues of response delay, lack of internal physical current limiting mechanism, and insufficient safety redundancy in existing lithium-ion battery protection technologies that rely on BMS systems, this invention provides a temperature-sensitive current-limiting self-closing current collector. This collector achieves intrinsic protection triggered by temperature through an internal temperature-sensitive current-limiting structure within the battery cell, limiting or cutting off current without relying on an external control system, thereby improving the safety and reliability of the energy storage system.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a temperature-sensitive, current-limiting, self-closing current collector, applied to a single lithium-ion battery cell, comprising: Metal current collectors serve as the main conductive channels in the battery cell; A temperature-sensitive current-limiting layer is disposed along the current direction of the metal current collector and is tightly bonded to the metal current collector; An electrode active material layer is disposed on one side of the metal current collector and is electrically connected to the metal current collector; The temperature-sensitive current-limiting layer is made of a positive temperature coefficient temperature-sensitive material with a resistance change temperature range of 90-130℃. When the temperature exceeds the change temperature, the volume resistivity increases by at least 102 times in the narrow temperature range, and the positive temperature coefficient temperature-sensitive material has a large specific heat capacity.

[0007] Preferably, the metal current collector is a copper foil or an aluminum foil with a thickness of 3-20 μm.

[0008] Preferably, the thickness of the temperature-sensitive current-limiting layer is 5-50 μm.

[0009] Preferably, the structure of the temperature-sensitive current-limiting layer is one of the following two: Structure 1: Includes a micropore or microgroove structure in the temperature-sensitive current limiting module substrate, and a positive temperature coefficient temperature-sensitive material unit filled in the micropore or microgroove structure; Structure 2: A planar coating formed by a positive temperature coefficient thermosensitive material.

[0010] Preferably, the positive temperature coefficient thermosensitive material is selected from at least one of barium titanate-based semiconductor ceramic materials, polymer-based conductive composite positive temperature coefficient materials, and conductive composite materials with crystalline phase transition properties.

[0011] Preferably, the polymer-based conductive composite positive temperature coefficient material uses polyethylene, polypropylene, or polyvinyl chloride as the matrix and is doped with carbon black, graphite, or metal powder as conductive filler.

[0012] Preferably, the resistance change temperature is set below the critical temperature for thermal runaway of the battery cell.

[0013] Preferably, the specific heat capacity of the positive temperature coefficient thermosensitive material is not less than 1.2 J / (g·℃).

[0014] Preferably, the thickness of the temperature-sensitive current-limiting layer is 5-50 μm.

[0015] Preferably, the pore diameter or groove width of the micropore or microgroove structure is 10-100 μm, and the porosity or groove ratio is 20%-50%.

[0016] Another object of the present invention is to provide a lithium-ion battery comprising the above-mentioned temperature-sensitive current-limiting self-closing current collector.

[0017] The working principle of this invention is as follows: Normal operating condition: When the cell temperature is lower than the temperature change temperature of the temperature-sensitive material, the temperature-sensitive current-limiting layer is in a low resistance state (volume resistivity ≤10⁻²Ω·cm). The current is mainly transmitted through the metal current collector and the temperature-sensitive current-limiting layer. The cell is charged and discharged normally, and the charging and discharging efficiency is basically the same as that of existing ordinary cells. High temperature triggering state: When the temperature inside the cell rises abnormally due to high-rate discharge, heat accumulation or internal short circuit and exceeds the sudden change temperature of the temperature-sensitive material, the volume resistivity of the temperature-sensitive current limiting layer increases rapidly, the overall equivalent internal resistance of the current collector increases significantly, the current flowing through the cell is restricted or tends to be interrupted, the electrochemical reaction rate inside the cell decreases, the heating rate decreases, and thermal runaway is delayed or avoided. Coordination mechanism with BMS system: When the temperature-sensitive current limiting layer is triggered, the cell will show an increase in internal resistance, a decrease in current or an abnormal terminal voltage. The BMS will quickly identify the abnormal state through the existing monitoring mechanism and further execute control strategies such as current limiting, voltage equalization, disconnection or alarm, forming a dual redundancy of "internal physical protection + external system protection".

[0018] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The temperature-sensitive current-limiting self-closing current collector disclosed in this invention realizes "bidirectional collaborative redundancy" between the intrinsic physical protection inside the battery cell and the existing BMS system, breaking the industry's conventional understanding that "independent protection mechanisms are difficult to be compatible with external control systems." Existing technologies either rely on the external monitoring and control of the BMS (which has a response delay) or only attempt a single internal protection structure (which is difficult to be recognized by the system). However, this invention, through the characteristics of sudden increase in internal resistance and sudden drop in current after the temperature-sensitive current-limiting layer is triggered, naturally forms an abnormal signal that the BMS can accurately capture. It does not require modification of the existing control logic of the BMS, and can independently play the role of current limiting and interruption when the BMS is delayed or fails, thus constructing a dual guarantee of "internal physical first line of defense + external system second line of defense". It completely solves the core pain point of insufficient safety redundancy in existing technologies, and its collaborative protection effect far exceeds the expectation of simply superimposing two protection mechanisms.

[0019] (2) The temperature-sensitive current-limiting self-closing current collector disclosed in this invention has a temperature-sensitive material design that brings the dual effect of "current limiting + temperature control", breaking through the functional limitation of traditional temperature-sensitive components that "only focus on resistance changes". Current-limiting materials in the prior art mostly pursue resistance change characteristics, but ignore the active intervention during the temperature rise process. The positive temperature coefficient material selected in this invention can not only achieve a resistivity jump of at least 102 times in a narrow temperature range of 90-130℃, but also quickly cut off the current path to help buffer the local transient temperature rise rate during the resistance change process. This design provides a critical time window for the BMS system response and thermal management system intervention, avoiding the potential risk of "temperature continuing to soar after current limiting", and realizing the dual protection of "cutting off current" and "delaying thermal runaway", which far exceeds the single functional expectation of conventional temperature-sensitive current-limiting structures.

[0020] (3) The temperature-sensitive current-limiting self-closing current collector disclosed in this invention achieves a unity of "high-performance protection and large-scale adaptation" in its structural design, solving the industry problem that "safety upgrades inevitably require changes to the production process." In the prior art, current collectors with special protection functions often require changes to the core structure of the battery cell or the addition of complex processing steps, resulting in great difficulty in industrialization. However, the two temperature-sensitive current-limiting layer structures provided by this invention, namely micropore / microgroove filling and planar coating, can be tightly combined with conventional metal current collectors such as copper foil and aluminum foil to form good thermal coupling and electrical connection. Moreover, the processing technology is compatible with the existing battery cell coating, rolling, and assembly processes, without the need for additional production equipment. This design not only ensures that the temperature-sensitive material can truly reflect the internal temperature changes of the battery cell and ensure the accuracy of protection triggering, but also achieves seamless docking with the existing energy storage battery cell production line, making the large-scale application of high-performance safety components possible. Its balance between structural compatibility and manufacturability far exceeds the industry's conventional expectations for "new safety current collectors." Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the temperature-sensitive, current-limiting, self-closing current collector of the present invention. Detailed Implementation

[0022] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0023] Example 1: Thermosensitive Current-Limiting Current Collector of Barium Titanate-Doped Semiconductor Ceramic Material 1. Preparation of metal current collector: 12μm thick copper foil is selected, cleaned and dried for later use; 2. Preparation of temperature-sensitive current-limiting layer (structure 1): A microporous structure with a pore size of 30 μm and a porosity of 30% is formed on the surface of copper foil by laser drilling; barium titanate is used as the matrix, and 5 mol% of lanthanum oxide is doped and mixed by ball milling to form a slurry; the slurry is fixed in the current collector microporous structure by a low-temperature assisted densification process, wherein the densification process includes at least one of low-melting-point glass phase assisted sintering, in-situ conversion of chemical precursors or polymer-based composite molding, and the processing temperature is not higher than 800℃; 3. Preparation of electrode active material layer: NCM811 positive electrode active material, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 95:3:2, N-methylpyrrolidone is added to make a slurry, which is coated on the metal current collector side. After drying and rolling, an electrode active material layer with a thickness of 100μm is formed. 4. Cell assembly: The prepared current collector, negative electrode, separator, and electrolyte are assembled into an 18650 lithium-ion battery with a capacity of 2.5Ah.

[0024] Example 2: Polymer-based conductive composite positive temperature coefficient material temperature-sensitive current collector 1. Preparation of metal current collector: 15μm thick aluminum foil is selected, cleaned and dried for later use; 2. Preparation of temperature-sensitive current limiting layer (structure 2): Using polypropylene as the matrix, 30wt% carbon black conductive filler is added, and after mixing, toluene solvent is added and stirred to form a uniform slurry; the slurry is coated on the surface of aluminum foil and dried at 80℃ for 1h to form a planar coating-like temperature-sensitive current limiting layer with a thickness of 15μm; 3. Preparation of electrode active material layer: Lithium iron phosphate positive electrode active material, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone is added to make a slurry, which is coated on one side of aluminum foil, and after drying and rolling, an electrode active material layer with a thickness of 120μm is formed. 4. Cell assembly: Assemble into a 21700 type lithium-ion battery with a capacity of 4.0Ah.

[0025] Example 3: Conductive composite material temperature-sensitive current collector with crystalline phase transition properties 1. Preparation of metal current collector: 10μm thick copper foil is selected, cleaned and dried for later use; 2. Preparation of temperature-sensitive current limiting layer (structure 2): Using polyethylene oxide as the matrix, 15wt% lithium carbonate and 25wt% graphite conductive particles are added, mixed, and then acetone solvent is added and stirred to form a slurry; coated on the surface of copper foil and dried at 60℃ for 2h to form a temperature-sensitive current limiting layer with a thickness of 25μm; 3. Preparation of electrode active material layer: Same as in Example 1, assemble into an 18650 type lithium-ion battery with a capacity of 2.5Ah.

[0026] Control group: Ordinary current collector cells The same copper foil of the same specifications as in Example 1 (without a temperature-sensitive current-limiting layer) was selected, and the rest of the structure and preparation process were the same as in Example 1. The resulting 18650 lithium-ion battery was assembled as a control group.

[0027] Experimental Data and Analysis To verify the technical effects of the present invention, the following performance tests were conducted on the battery cells of Examples 1-3 and the control group: Test 1: Resistance-Temperature Characteristic Test Test method: The current collector sample was placed in a temperature control chamber, and the volume resistivity at different temperatures was measured using the four-probe method. The heating rate was 5℃ / min, and the test range was 25-150℃.

[0028] The test results are shown in Table 1 below: Table 1. Results of volume resistivity tests at different temperatures Analysis: The volume resistivity of the temperature-sensitive current-limiting current collectors in Examples 1–3 increased by 10 °C at the set abrupt change temperature (102–110 °C). 4 The resistivity of the current-limiting layer of this invention is more than 10 times that of the control group, far exceeding the preset requirement of 102 times. In contrast, the resistivity of the ordinary current collector in the control group changes very little throughout the temperature range, with no obvious abrupt change characteristics, which proves that the temperature-sensitive current-limiting layer of this invention has excellent resistance jump effect.

[0029] Test 2: Simulated Thermal Runaway Current Limitation Test Test Method: The battery cell was placed in an adiabatic environment, and an internal short-circuit scenario was simulated by an external short circuit (equivalent short-circuit resistance not exceeding 0.1Ω). The changes in cell temperature and current over time were recorded until the cell experienced thermal runaway (temperature surge exceeding 200℃) or stabilized. The test results are shown in Table 2 below: Table 2. Simulated thermal runaway current limiting test results Analysis: The control group cells experienced thermal runaway within 30 seconds after a short circuit, with a maximum temperature of 320°C; while the cells in Examples 1-3 experienced a current drop below 1A within 8-12 seconds after a short circuit, effectively limiting the heating rate. No thermal runaway occurred during the 210-second test, and the maximum temperature was below 180°C. This demonstrates that the current collector of the present invention can quickly trigger current limiting and effectively suppress the occurrence of thermal runaway.

[0030] Test 3: BMS Compatibility Test Test method: Connect the battery cell of Example 1 to an existing Pack-level BMS system to simulate a thermal accumulation scenario (heat the battery cell temperature to 105°C by heating), and record the BMS's recognition time and response action to abnormal signals of the battery cell.

[0031] Test results: When the cell temperature rises to 105℃, the temperature-sensitive current limiting layer is triggered, the cell internal resistance rises from the initial 25mΩ to 1500mΩ, and the terminal voltage fluctuates by more than 0.3V; the BMS identifies the abnormal internal resistance and voltage within 2 seconds and immediately performs a protection action to limit the current to 0.5A without any misjudgment or delay, proving that the current collector of the present invention has good compatibility with the existing BMS system.

[0032] Test 4: Cyclic Stability Test Test method: The battery cell of Example 1 was subjected to 1000 charge-discharge cycles (0.5C charge / 1C discharge). After the cycle, the resistance-temperature characteristics and the effect of simulating thermal runaway current limiting were repeatedly tested.

[0033] Test results: After 1000 cycles, the current collector abruptly temperature in Example 1 remained at 103–107 °C, and the resistivity increase factor was 1.2 × 10⁻⁶. 5The current drops below 1A in 9 seconds, and the thermal runaway trigger time is 175 seconds, which is basically consistent with the performance before cycling, proving that the current collector of the present invention has good cycling stability and service life.

[0034] As can be seen, the temperature-sensitive current-limiting self-shutting current collector of this invention achieves intrinsic physical current limiting and interruption protection triggered by temperature through reasonable structural design and material selection. Experimental data shows that this current collector has significant resistance jump characteristics in the range of 90–130℃, with resistivity increasing by more than 102 times. It can quickly limit the current in short-circuit or thermal accumulation scenarios, delaying or even preventing thermal runaway. At the same time, it is highly compatible with existing BMS systems, forming a dual safety guarantee, and has excellent cycle stability and manufacturability, making it suitable for large-scale application in various energy storage lithium-ion batteries, effectively improving the safety and reliability of energy storage systems.

[0035] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A temperature-sensitive, current-limiting, self-closing current collector, applied to a single lithium-ion battery cell, characterized in that, include: Metal current collectors serve as the main conductive channels in the battery cell; A temperature-sensitive current-limiting layer is disposed along the current direction of the metal current collector and is tightly bonded to the metal current collector; An electrode active material layer is disposed on one side of the metal current collector and is electrically connected to the metal current collector; The temperature-sensitive current-limiting layer is made of a positive temperature coefficient temperature-sensitive material with a resistance change temperature range of 90-130℃. When the temperature exceeds the change temperature, the volume resistivity increases by at least 102 times in the narrow temperature range, and the positive temperature coefficient temperature-sensitive material has a large specific heat capacity.

2. The temperature-sensitive, current-limiting, self-closing current collector according to claim 1, characterized in that, The metal current collector is a copper foil or an aluminum foil with a thickness of 3-20 μm.

3. The temperature-sensitive, current-limiting, self-closing current collector according to claim 1, characterized in that, The thickness of the temperature-sensitive current-limiting layer is 5-50 μm.

4. The temperature-sensitive, current-limiting, self-closing current collector according to claim 1, characterized in that, The temperature-sensitive current-limiting layer has one of the following two structures: Structure 1: Includes a micropore or microgroove structure in the temperature-sensitive current limiting module substrate, and a positive temperature coefficient temperature-sensitive material unit filled in the micropore or microgroove structure; Structure 2: A planar coating formed by a positive temperature coefficient thermosensitive material.

5. The temperature-sensitive, current-limiting, self-closing current collector according to claim 1, characterized in that, The positive temperature coefficient thermosensitive material is selected from at least one of barium titanate-based semiconductor ceramic materials, polymer-based conductive composite positive temperature coefficient materials, and conductive composite materials with crystalline phase transition properties.

6. The temperature-sensitive, current-limiting, self-closing current collector according to claim 5, characterized in that, The polymer-based conductive composite positive temperature coefficient material uses polyethylene, polypropylene, or polyvinyl chloride as the matrix and is doped with carbon black, graphite, or metal powder as conductive fillers.

7. The temperature-sensitive, current-limiting, self-closing current collector according to claim 1, characterized in that, The resistance mutation temperature is set below the critical temperature for thermal runaway of the battery cell.

8. The temperature-sensitive, current-limiting, self-closing current collector according to claim 1, characterized in that, The specific heat capacity of the positive temperature coefficient thermosensitive material is not less than 1.2 J / (g·℃); the thickness of the thermosensitive current-limiting layer is 5-50 μm.

9. The temperature-sensitive, current-limiting, self-closing current collector according to claim 4, characterized in that, The pore diameter or groove width of the micropore or microgroove structure is 10-100μm, and the porosity or groove ratio is 20%-50%.

10. A lithium-ion battery comprising a temperature-sensitive, current-limiting, self-closing current collector as described in any one of claims 1-9.

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