A thermal safety type functional current collector, a preparation method thereof, a pole piece and a battery

Abstract

This invention discloses a thermally safe functional current collector, its preparation method, an electrode, and a battery. The current collector includes a polymer base film layer and thermally safe functional layers disposed on both sides of the polymer base film layer. The thermally safe functional layers include a heat-shrinkable layer and a conductive layer. The polymer base film layer and the heat-shrinkable layer are adjacent. The heat-shrinkable layer contains a material with negative thermal expansion, and the conductive layer contains a metallic material. The functional current collector of this invention can promptly cut off power in high-temperature environments, improving the thermal safety of the current collector and reducing the risk of heat spread.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a thermally safe functional current collector and its preparation method, as well as an electrode and a battery. Background Technology

[0002] The functional current collector integrates the characteristics of a lightweight and thin current collector with high safety. Because its intermediate polymer layer can provide effective resistance to puncture and short circuit, it improves the battery's resistance to puncture and impact, and effectively reduces the risk of thermal runaway caused by external impact.

[0003] However, existing functional current collectors have not effectively improved the high temperature resistance. When a single battery has already experienced thermal runaway, the functional current collectors of adjacent batteries cannot cut off the power in time under high temperature conditions. Instead, the low thermal conductivity of the polymer layer can easily cause heat accumulation, triggering chain thermal runaway of adjacent batteries, which can lead to a chain reaction and heat spread, thus creating a high temperature safety hazard for the battery. Summary of the Invention

[0004] The purpose of this invention is to provide a thermally safe functional current collector, its preparation method, electrode, and battery, thereby improving the high-temperature resistance of the current collector and solving the high-temperature safety hazards of existing functional current collectors.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0006] The first aspect of this application provides a thermally safe functional current collector, including a polymer base film layer and thermally safe functional layers disposed on both sides of the polymer base film layer;

[0007] The thermal safety functional layer consists of a heat-shrinkable layer and a conductive layer; the polymer base film layer is adjacent to the heat-shrinkable layer.

[0008] The heat-shrinkable layer contains a negative thermal expansion material, and the conductive layer contains a metallic material.

[0009] To optimize the above technical solution, the specific limitations also include:

[0010] The thermal safety functional layer includes a heat-shrinkable layer and a conductive layer;

[0011] Alternatively, the thermal safety functional layer may include multiple heat-shrinkable layers and multiple conductive layers, with the heat-shrinkable layers and conductive layers alternately arranged.

[0012] Furthermore, the negative thermal expansion material has a negative thermal expansion coefficient < -1.0 × 10⁻⁶. -6 K -1 Ceramic materials with negative thermal expansion.

[0013] Furthermore, the heat shrinkable layer also contains a thermal conventional ceramic material with a coefficient of thermal expansion > 0; in the heat shrinkable layer containing thermal conventional ceramic material, the mass ratio of negative thermal expansion ceramic material to thermal conventional ceramic material ranges from 1 to 9: 9 to 1.

[0014] Furthermore, the lower limit of the negative thermal expansion temperature range of the heat shrinkable layer is 120℃~160℃, and the upper limit is 240℃~900℃; wherein the negative thermal expansion of the negative thermal expansion material is isotropic or anisotropic.

[0015] Furthermore, the negative thermal expansion ceramic material is selected from PbTiO3, BaTiO3, LiAlSiO4, and Mg2Al4Si5O. 12 NaZr2P3O 12 The material is selected from one or more of ZrW2O8, manganese nitride, and lanthanide compounds; the thermally conventional ceramic material is selected from one or more of alumina, aluminum nitride, aluminum carbide, calcium oxide, and calcium carbide.

[0016] Furthermore, the metal material is aluminum or copper; the thickness of each heat-shrinkable layer is 10–100 nm, and the thickness of each conductive layer is 0.8–1.2 micrometers.

[0017] The second aspect of this application provides a method for preparing a thermally safe functional current collector, comprising the following steps:

[0018] At least one heat-shrinkable layer and at least one conductive layer are prepared on both sides of the polymer base film layer;

[0019] When preparing multiple heat-shrinkable layers and multiple conductive layers on the surface of a polymer base film, the heat-shrinkable layer is prepared first, and then the conductive layer is prepared on the surface of the heat-shrinkable layer. This process is repeated to obtain multiple heat-shrinkable layers and multiple conductive layers that are interleaved on the outer side of the polymer base film.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] The functional current collector of this invention has a heat-shrinkable layer containing a negative thermal expansion material and a conductive layer containing a metallic material disposed on the outer side of the polymer base film layer. When an abnormal current occurs inside the battery, or when it is affected by the high temperature of external factors such as the environment or other thermal runaway batteries, the internal temperature of the battery gradually rises. The negative thermal expansion material of the heat-shrinkable layer shrinks due to heat, while the conductive layer containing the metallic material expands due to heat. At this time, a large stress difference will appear inside the heat-shrinkable layer and between the heat-shrinkable layer and the conductive layer. These stress differences cause the thinner conductive layer to break when it exceeds its tensile strength, causing a large number of cracks to be generated in the conductive layer of the current collector, thereby achieving the function of isolating the current. This design can quickly and extensively cut off the power inside the battery at high temperatures, preventing the temperature from rising further, thereby reducing the risk of thermal runaway of individual batteries and heat spread within the battery pack.

[0022] The heat shrinkable layer of the present invention is preferably made of a mixture of a ceramic material containing negative thermal expansion and a conventional ceramic material. When heated, the heat shrinkable layer will generate a greater stress difference due to the large difference in the expansion coefficients of the different materials, which is more conducive to the faster breakage of the conductive layer.

[0023] The conductive layer of this invention preferably uses a metallic aluminum conductive layer or a metallic copper conductive layer. This conductive layer serves both as a fracture-resistant layer providing a stress difference with the heat-shrinkable layer and as the basic conductive structure of the aluminum or copper functional current collector, forming a structure that utilizes the functional components of the positive electrode (corresponding to the aluminum-containing functional current collector) or the negative electrode (corresponding to the copper-containing functional current collector) to achieve thermal safety protection. Furthermore, the ceramic material in the heat-shrinkable layer of this invention can enhance the bonding strength between the polymer base film layer and the metallic conductive layer. In the functional current collector, the ceramic material can also isolate the polymer base film layer from the electrolyte, thereby extending the service life of the polymer base film layer.

[0024] The functional current collector of the present invention can cut off power in a timely manner in high-temperature environments, thereby improving the thermal safety of the functional current collector and reducing the risk of thermal propagation. Attached Figure Description

[0025] Figure 1 : A schematic diagram of the structure of a thermally safe functional current collector according to one embodiment of the present invention.

[0026] Figure 2 : A schematic diagram of the structure of a thermally safe functional current collector according to another embodiment of the present invention.

[0027] In the diagram: 1-Polymer base film layer, 2-Heat shrinkable layer, 3-Conductive layer. Detailed Implementation

[0028] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0030] For the sake of brevity, this article only discloses some numerical values ​​and the range of options. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range. Similarly, any upper limit can be combined with any other upper limit to form an unspecified range; the options in the range of options can also be combined arbitrarily.

[0031] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art.

[0032] The following is an explanation of some of the terms used in this invention:

[0033] Functional current collectors are a type of current collector with a "sandwich" structure. The inner layer is a polymer layer, such as PET, PP or PI film, and the two sides of the polymer layer are metal conductive layers, such as Al or Cu layers, which are aluminum functional current collectors and copper functional current collectors, respectively.

[0034] Negative thermal expansion materials are a type of material with negative thermal expansion properties. The thermal shrinkage rate of such materials after being heated is ≤0, which means that they have the opposite characteristic of "thermal contraction and cold expansion" to ordinary materials. The volume or length in a certain direction of negative thermal expansion materials will decrease as the temperature rises, and the negative thermal expansion phenomenon only occurs in a certain temperature range.

[0035] This invention provides a thermally safe functional current collector, comprising a polymer base film layer and thermally safe functional layers disposed on both sides of the polymer base film layer;

[0036] The thermal safety functional layer includes at least one heat-shrinkable layer and at least one conductive layer; the polymer base film layer is adjacent to the heat-shrinkable layer;

[0037] The heat-shrinkable layer includes a negative thermal expansion material, and the conductive layer includes a metallic material.

[0038] The thermal safety functional layer consists of a heat-shrinkable layer and a conductive layer; or, the thermal safety functional layer includes multiple heat-shrinkable layers and multiple conductive layers, with the heat-shrinkable layers and conductive layers alternating.

[0039] Non-limiting examples of the polymer base film layer in this application may be polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0040] The thickness of the polymer base film layer in this application can be 4 to 10 micrometers.

[0041] When an abnormal current occurs inside the battery, or when it is affected by high temperatures from external factors such as the environment or other thermal runaway batteries, the internal temperature of the battery gradually rises. The negative thermal expansion material of the heat shrink layer shrinks due to heat, while the conductive layer containing metallic materials expands due to heat. At this time, a large stress difference will occur inside the heat shrink layer and between the heat shrink layer and the conductive layer, causing the conductive layer to break when it exceeds its tensile strength, and the current collector conductive layer will generate a large number of cracks, thereby achieving the function of isolating the current.

[0042] Metallic materials generally have higher tensile strength than ceramics and possess better toughness. Therefore, compared to conductive layers, the stress difference within the thermal safety functional layer makes adjacent conductive layers more prone to fracture. Furthermore, due to the higher brittleness of ceramic materials, cracks extend further upon fracture, resulting in a faster power-off response. Additionally, ceramic materials can enhance the bonding strength between the polymer base film and the conductive layer. In functional current collectors, ceramic materials can also isolate the polymer base film from the electrolyte, thus extending the base film's lifespan.

[0043] The thermal safety functional layer of this application can be prepared by one or more of the following methods: physical vapor deposition, chemical vapor deposition, etc.; wherein physical vapor deposition can be vacuum evaporation and magnetron sputtering; chemical vapor deposition can be atmospheric pressure chemical vapor deposition and plasma-enhanced chemical vapor deposition.

[0044] In some embodiments, the negative thermal expansion material has a negative thermal expansion coefficient < -1.0 × 10⁻⁶. -6 K -1 Ceramic materials with negative thermal expansion.

[0045] The negative thermal expansion coefficient of the negative thermal expansion material of the present invention should not be too small. If it is too small, its deformation is insufficient, the stress difference generated is small, and it is not enough to tear the conductive layer.

[0046] In some embodiments, the heat shrinkable layer further includes a thermal conventional ceramic material with a coefficient of thermal expansion > 0; in the heat shrinkable layer containing thermal conventional ceramic material, the mass ratio of negative thermal expansion ceramic material to thermal conventional ceramic material ranges from 1 to 9: 9 to 1.

[0047] In some embodiments, the lower limit of the negative thermal expansion temperature range of the heat-shrinkable layer is 120°C to 160°C, and the upper limit is 240°C to 900°C, wherein the negative thermal expansion of the negative thermal expansion material is isotropic or anisotropic. The range of the negative thermal expansion temperature range can be adjusted by using different material compositions in the heat-shrinkable layer.

[0048] The negative thermal expansion temperature range of the heat-shrinkable layer of this invention needs to be set within a suitable range to function properly. Because the battery also generates heat during normal use cycles, but the heat is limited and will not cause the battery temperature to become too high. Therefore, it is necessary to avoid abnormal breakage of the current collector metal layer due to this normal heat generation. By setting a suitable lower limit of the expansion temperature range, the normal operation of the battery can be guaranteed. The upper limit of the expansion temperature range should also not be too large. If it is too large, it will exceed the temperature of battery thermal runaway, and the current collector will not be able to cut off the power in time, thus failing to play its role in controlling thermal runaway.

[0049] The negative thermal expansion of a material is preferably anisotropic. Anisotropy allows for different internal expansion coefficients, and larger differences in expansion coefficients make it easier to break.

[0050] In some embodiments, the negative thermal expansion ceramic material is selected from PbTiO3, BaTiO3, LiAlSiO4, Mg2Al4Si5O 12 NaZr2P3O 12 ZrW₂O₈, manganese nitrides such as Mn₃AN, and lanthanide compounds such as La(Fe,Si) 13 One or more of the following; in Mn3AN, A is Zn, Ga, or Cu; the conventional ceramic material is selected from one or more of alumina, aluminum nitride, aluminum carbide, calcium oxide, and calcium carbide.

[0051] In some embodiments, the metallic material is aluminum or copper; the metallic material may also include one or more of aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys.

[0052] The conductive layer of this application is mainly composed of conductive metal, and may also contain metal oxides or other doped materials.

[0053] In some embodiments, the thickness of each heat-shrinkable layer is 10–100 nm, and the thickness of each conductive layer is 0.8–1.2 μm.

[0054] This invention also provides a method for preparing a thermally safe functional current collector, comprising the following steps:

[0055] At least one heat-shrinkable layer and at least one conductive layer are prepared on both sides of the polymer base film layer;

[0056] When preparing multiple heat-shrinkable layers and multiple conductive layers on the surface of a polymer base film, the heat-shrinkable layer is prepared first, and then the conductive layer is prepared on the surface of the heat-shrinkable layer. This process is repeated to obtain multiple heat-shrinkable layers and multiple conductive layers that are interleaved on the outer side of the polymer base film.

[0057] The present invention also provides an electrode comprising the above-described thermally safe functional current collector.

[0058] The present invention also provides a battery comprising the above-described electrode.

[0059] The technical solution of the present invention will be further described in detail below with reference to specific embodiments:

[0060] Example 1

[0061] A thermally safe functional current collector, preparation method:

[0062] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0063] 1) The target arrangement is set with 16 LiAlSiO4 targets (all with a purity of 99.95%), and the magnetron sputtering power density is 60 W / cm³. 2 The vacuum degree was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, and the deposition time was 10 s. The resulting heat-shrinkable layer had a thickness of 30 nm. The negative thermal expansion temperature range of LiAlSiO4 was 140–330 °C, and the coefficient of thermal expansion was -8.6 × 10⁻⁶. -6 k -1 ;

[0064] 2) After the above steps, transfer to another magnetron sputtering machine, set the target arrangement to 24 copper targets (all with a purity of 99.95%), and the magnetron sputtering power density to 60 W / cm³. 2 The vacuum degree was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 6 s, and a copper seed layer of 16 nm was obtained.

[0065] 3) The copper layer is thickened by electroplating the thin film coated with LiAlSiO4 layer and copper seed layer. The thin film obtained above is completely immersed in copper sulfate electrolyte, which includes: copper sulfate with a concentration of 180 g / L, sulfuric acid with a concentration of 80 g / L, and chloride ions with a volume concentration of 40 ppm. The temperature of the copper sulfate electrolyte is 50°C, and the thickness of the electroplated copper layer is 1 micrometer.

[0066] 4) Complete the above steps on both sides of the current collector to obtain the finished copper functional current collector.

[0067] Example 2

[0068] A thermally safe functional current collector, preparation method:

[0069] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0070] 1) The target arrangement is set to 16 NaZr2P3O targets. 12 The target material (all with a purity of 99.95%) was used, and the magnetron sputtering power density was 60 W / cm². 2 The vacuum level was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 10 s, and the resulting heat-shrinkable layer had a thickness of 30 nm, a negative thermal expansion temperature range of 120–260 °C, and an expansion coefficient of -16.1 × 10⁻⁶. -6 k -1 ;

[0071] 2) After the above steps, transfer to a vacuum evaporation equipment and evacuate to a vacuum level of 5*10. -3 Pa, argon gas is introduced to maintain the vacuum level at 5*10. -2 Pa, start the winding carriage, control the belt speed at 300m / min, simultaneously heat the evaporation boat and feed aluminum wire at a speed of 350mm / min, so that an aluminum layer is formed on the surface of the base film, and control the thickness of the aluminum layer to be 1.1μm;

[0072] 3) Complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0073] Example 3

[0074] A thermally safe functional current collector, preparation method:

[0075] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0076] 1) Set the target arrangement to 16 Sc2W3O 12 The target material (all with a purity of 99.95%) was used, and the magnetron sputtering power density was 60 W / cm². 2 The vacuum degree was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 10 s, and the resulting heat-shrinkable layer had a thickness of 30 nm, a negative thermal expansion temperature range of 50–570 °C, and an expansion coefficient of -12.4 × 10⁻⁶. -6 k -1 ;

[0077] 2) After the above steps, transfer to a vacuum evaporation equipment and evacuate to a vacuum level of 5*10. -3Pa, argon gas is introduced to maintain the vacuum level at 5*10. -2 Pa, start the winding carriage, control the belt speed at 300m / min, simultaneously heat the evaporation boat and feed aluminum wire at a speed of 350mm / min, so that an aluminum layer is formed on the surface of the base film, and control the thickness of the aluminum layer to be 1.1μm;

[0078] 3) Complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0079] Example 4

[0080] A thermally safe functional current collector, preparation method:

[0081] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0082] 1) The target arrangement consists of 16 ZrVPO7-based targets (all with a purity of 99.95%), and the magnetron sputtering power density is 60 W / cm³. 2 The vacuum level was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 10 s, and the resulting heat-shrinkable layer had a thickness of 30 nm, a negative thermal expansion temperature range of 380–660 °C, and a thermal expansion coefficient of -19.6 × 10⁻⁶. -6 k -1 ;

[0083] 2) After the above steps, transfer to a vacuum evaporation equipment and evacuate to a vacuum level of 5*10. -3 Pa, argon gas is introduced to maintain the vacuum level at 5*10. -2 Pa, start the winding carriage, control the belt speed at 300m / min, simultaneously heat the evaporation boat and feed aluminum wire at a speed of 350mm / min, so that an aluminum layer is formed on the surface of the base film, and control the thickness of the aluminum layer to be 1.1μm;

[0084] 3) Complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0085] Example 5

[0086] A thermally safe functional current collector, preparation method:

[0087] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0088] 1) The target arrangement is set to two NaZr2P3O targets. 12The target material plus 16 aluminum targets (all with a purity of 99.95%), with the tape travel direction from NaZr2P3O 12 The target material is fed to the aluminum target, and the magnetron sputtering power density is 40 W / cm². 2 The vacuum level was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 15 s, and the resulting heat-shrinkable layer had a thickness of 5 nm, a negative thermal expansion temperature range of 120–260 °C, and an expansion coefficient of -16.1 × 10⁻⁶ K. -1 The aluminum layer thickness is 40nm;

[0089] 2) Repeat the above steps until the coating thickness on one side reaches 1.1 μm, then stop coating preparation;

[0090] 3) Complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0091] Example 6

[0092] A thermally safe functional current collector, preparation method:

[0093] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0094] 1) The target arrangement is set to 16 NaZr2P3O targets. 12 The target material (all with a purity of 99.95%) was used, and the magnetron sputtering power density was 60 W / cm². 2 The vacuum level was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 5 s, and the resulting heat-shrinkable layer had a thickness of 15 nm, a negative thermal expansion temperature range of 120–260 °C, and a thermal expansion coefficient of -16.1 × 10⁻⁶. -6 k -1 ;

[0095] 2) After the above steps, the target arrangement is set to 16 Al2O3 targets (all with a purity of 99.9%), and the magnetron sputtering power density is 50 W / cm³. 2 The vacuum level was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, and the deposition time was 5 s. The resulting thermally conventional ceramic underlayer had a thickness of 15 nm and an expansion coefficient of 6.5 × 10⁻⁶. -6 k -1 ;

[0096] 3) After the above steps, transfer to a vacuum evaporation equipment and evacuate to a vacuum level of 5*10. -3 Pa, argon gas is introduced to maintain the vacuum level at 5*10. -2Pa, start the winding carriage, control the belt speed at 300m / min, simultaneously heat the evaporation boat and feed aluminum wire at a speed of 350mm / min, so that an aluminum layer is formed on the surface of the base film, and control the thickness of the aluminum layer to be 1.1μm;

[0097] 4) Complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0098] Comparative Example 1

[0099] A functional current collector, preparation method:

[0100] A 6μm thick PET film was placed in a magnetron sputtering machine, and underlayer and conductive layers were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0101] The obtained base film is sequentially coated with an alumina coating and an aluminum layer; among them, after the winding trolley enters the evaporation chamber, a vacuum of 5*10 is applied. -3 Pa, start the winding carriage, control the speed at 280 m / min, simultaneously heat the evaporation boat and feed the aluminum wire at a speed of 320 mm / min, and simultaneously start the oxygen intake, controlling the vacuum degree at 5*10 -2 Pa was applied to form an alumina coating on the base film surface, with the thickness of the alumina coating controlled at 30 nm; then the vacuum was broken and evacuated to a vacuum level of 5*10. -3 Pa, argon gas is introduced to maintain the vacuum level at 5*10. -2 Pa, and then deposit another aluminum layer in the same way, with a thickness of 1μm; complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0102] Comparative Example 2

[0103] A functional current collector, preparation method:

[0104] A 6μm thick PET film was placed in a magnetron sputtering machine, and a heat-shrinkable layer and a conductive layer were prepared on both sides of the PET film in the thickness direction. The specific process conditions were as follows:

[0105] 1) Select vacuum evaporation equipment and evacuate to a vacuum level of 5*10. -3 Pa, argon gas is introduced to maintain the vacuum level at 5*10. -2 Pa, start the winding carriage, control the PET film conveyor belt speed at 300m / min, simultaneously heat the evaporation boat and feed aluminum wire at a speed of 350mm / min, so that an aluminum layer is formed on the surface of the base film, and control the thickness of the aluminum layer to 1.1μm;

[0106] 2) After the above steps, transfer to the magnetron sputtering equipment and set the target arrangement to 16 NaZr2P3O targets. 12 The target material (all with a purity of 99.95%) was used, and the magnetron sputtering power density was 60 W / cm². 2 The vacuum level was 0.1 Pa, the protective gas was argon with a flow rate of 50 mL / min, the deposition time was 10 s, and the resulting heat-shrinkable layer had a thickness of 30 nm, a negative thermal expansion temperature range of 120–260 °C, and an expansion coefficient of -16.1 × 10⁻⁶. -6 k -1 ;

[0107] 3) Complete the above steps on both sides of the current collector to obtain the finished aluminum functional current collector.

[0108] Experimental testing and verification:

[0109] The surface resistance thermal response and peel force of the functional current collectors prepared in all the above embodiments and comparative examples were tested. The specific test methods are as follows:

[0110] Surface sheet resistance: Sheet resistance is tested using a four-probe resistivity meter. The number of sheet resistance tests is determined based on the product's lateral width, with one test point every 100 mm. Other requirements are tested according to the methods specified in GB / T 22638.6-2016. The functional current collector sample is placed in a heating chamber for programmed temperature rise at a rate of 0.3℃ / s. The surface sheet resistance of the functional current collector is tested before heating, at 60℃, 80℃, 100℃, 120℃, 140℃, and 160℃. After each temperature rise to the target temperature, the sample is removed for surface sheet resistance testing, and the heating chamber is kept at a constant temperature. After each test, heating continues until the next target temperature is reached before testing again. The change in surface sheet resistance is used to evaluate the thermal cut-off response capability of the functional current collector.

[0111] Peel strength test: Cut the sample into 10*2cm pieces; test using an electronic peel tester; attach the cut sample to the stainless steel plate to be tested using 2cm wide 3M tape, and perform a 180° electrode peel test by peeling one end of the sample. Record the test parameters after the test.

[0112] 2. Test Results

[0113] The surface resistance thermal response test and peel force test results of the functional current collectors prepared in all the above embodiments and comparative examples are shown in Tables 1 and 2.

[0114] Table 1. Peel force test results of functional current collectors in the examples and comparative examples.

[0115]

[0116] Table 2. Test results of the surface resistance thermal response of the functional current collector in the embodiments and comparative examples.

[0117]

[0118] The functional current collector in this invention can promptly cut off power in high-temperature environments, improving battery thermal safety and reducing the risk of heat spread. The thermal safety functional layer of this invention can consist of a heat-shrinkable layer and a conductive layer, or it can be a multi-layer structure formed by alternating layers of heat-shrinkable and conductive layers.

[0119] Examples 1 and 2 of this application provide examples of preparing copper functional current collectors and aluminum functional current collectors, respectively. The conductive metal layer serves both as a fractured layer that provides a stress difference with the heat-shrinkable layer and as the basic conductive structure of the functional current collector, thus achieving the purpose of thermal safety protection by utilizing the functional composition of the electrode itself.

[0120] Examples 2-4 of this application provide examples of aluminum functional current collectors with different material compositions to form different negative thermal expansion temperature zones. In example 3, the lower limit of the negative thermal expansion temperature zone is too low, which will cause the current collector to lose power at the normal operating temperature of the battery, affecting its use. In example 4, the lower limit of the negative thermal expansion temperature zone is too high, which will cause the initial temperature of battery thermal runaway to fail to trigger power loss in time.

[0121] Example 5 of this application provides an example of preparing multiple alternating layers of heat-shrinkable layer and conductive metal layer. Compared with a single-layer heat-shrinkable layer and conductive layer, the bonding strength of the multi-layer structure is slightly worse, but its power-off response is faster.

[0122] Embodiment 6 of this application provides an example of using a heat-shrinkable layer containing both negative thermal expansion ceramic material and thermal conventional ceramic material. When heated, the heat-shrinkable layer will generate a greater stress difference due to the large difference in the expansion coefficients of the different materials, which is more conducive to the faster fracture of the conductive layer.

[0123] Based on the negative thermal expansion temperature range required for the thermal safety of the current collector, this application preferably uses NaZr2P3O. 12 As a negative thermal expansion ceramic material, the target material can also be prepared by combining several other negative thermal expansion ceramic materials to form a heat shrinkable layer containing mixed materials to achieve a similar effect and meet the negative thermal expansion temperature range required for the thermal safety of battery current collectors.

[0124] Comparative Example 1 of this application provides a conventional functional aluminum current collector without thermal power-off function. Comparing Example 2 of this application with this comparative example, it can be seen that Example 2 not only has thermal power-off response function, but its bonding strength can also reach a level comparable to that of conventional functional aluminum current collectors.

[0125] Comparative Example 2 of this application provides a scheme in which the conductive layer and the polymer base film layer are adjacent, so that the heat shrinkable layer is placed on the outside of the conductive layer. The test shows that this comparative example also has the function of thermal power failure response, but its bonding strength is very poor and the surface sheet resistance is very high, which cannot meet the battery application standards.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A thermally safe functional current collector, characterized in that: It includes a polymer base film layer and thermal safety functional layers disposed on both sides of the polymer base film layer; The thermal safety functional layer includes at least one heat-shrinkable layer and at least one conductive layer; the polymer base film layer is adjacent to the heat-shrinkable layer; The heat-shrinkable layer contains a negative thermal expansion material, and the conductive layer contains a metallic material. The aforementioned negative thermal expansion material has a negative thermal expansion coefficient of <-1.0×10⁻⁶. -6 K -1 Ceramic materials with negative thermal expansion; The lower limit of the negative thermal expansion temperature range of the heat-shrinkable layer is 120℃~160℃, and the upper limit is 240℃~900℃; the negative thermal expansion of the negative thermal expansion material is isotropic or anisotropic; the thermal safety functional layer consists of a heat-shrinkable layer and a conductive layer. Alternatively, the thermal safety functional layer may include multiple heat-shrinkable layers and multiple conductive layers, with the heat-shrinkable layers and conductive layers alternately arranged. The negative thermal expansion ceramic material is selected from PbTiO3, BaTiO3, LiAlSiO4, and Mg2Al4Si5O. 12 NaZr2P3O 12 One or more of ZrW2O8, manganese nitrides, and lanthanide compounds; The metal material is aluminum or copper; the thickness of each heat-shrinkable layer is 10~100nm, and the thickness of each conductive layer is 0.8~1.2μm.

2. The thermally safe functional current collector according to claim 1, characterized in that: The heat shrinkable layer also contains a thermal conventional ceramic material with a coefficient of thermal expansion > 0; in the heat shrinkable layer containing thermal conventional ceramic material, the mass ratio of negative thermal expansion ceramic material to thermal conventional ceramic material ranges from 1 to 9: 9 to 1.

3. The thermally safe functional current collector according to claim 2, characterized in that: The thermally conventional ceramic material is selected from one or more of alumina, aluminum nitride, aluminum carbide, calcium oxide, and calcium carbide.

4. A method for preparing a thermally safe functional current collector according to any one of claims 1-3, characterized in that, Includes the following steps: At least one heat-shrinkable layer and at least one conductive layer are prepared on both sides of the polymer base film layer; When preparing multiple heat-shrinkable layers and multiple conductive layers on the surface of a polymer base film, the heat-shrinkable layer is prepared first, and then the conductive layer is prepared on the surface of the heat-shrinkable layer. This process is repeated to obtain multiple heat-shrinkable layers and multiple conductive layers that are interleaved on the outer side of the polymer base film.

5. An electrode sheet, characterized in that: It includes the thermally safe functional current collector as described in any one of claims 1-3 or the thermally safe functional current collector prepared by the method described in claim 4.

6. A battery, characterized in that: It includes the electrode sheet as described in claim 5.

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