Thermal safety type functional current collector, preparation method thereof, pole piece and battery

Abstract

The invention discloses a thermal safety type functional current collector and a preparation method thereof, a pole piece and a battery. The thermal safety type functional current collector comprises a macromolecule base membrane layer and thermal safety functional layers arranged on the surfaces of the two sides of the macromolecule base membrane layer; the thermal safety functional layer comprises a thermal shrinkage layer and a conductive layer; the macromolecular base film layer is adjacent to the thermal shrinkage layer; wherein the thermal shrinkage layer contains a negative thermal expansion material, and the conductive layer contains a metal material. The functional current collector can be powered off in time in a high-temperature environment, the thermal safety of the functional current collector is improved, and the risk of heat spreading is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a thermally safe functional current collector, a preparation method thereof, a pole piece and a battery. Background Art

[0002] The functional current collector integrates the characteristics of a thin and light, highly safe current collector. Since the polymer layer in the middle layer can provide effective puncture and short-circuit resistance, the puncture and impact resistance of the battery are improved, and the risk of thermal runaway caused by external force impact on the battery is effectively reduced.

[0003] However, the existing functional current collectors do not effectively improve the high-temperature resistance. When a single battery has a thermal runaway, the functional current collectors of adjacent batteries cannot cut off the power supply in a timely manner in a high-temperature environment. Instead, due to the low thermal conductivity of the polymer layer, heat accumulation is likely to occur, leading to chain thermal runaway of adjacent batteries, and thus a chain reaction causes thermal spread, posing a high-temperature safety hazard to the battery. Summary of the Invention

[0004] The purpose of the present invention is to provide a thermally safe functional current collector, a preparation method thereof, a pole piece and a battery, so as to improve the high-temperature resistance of the current collector and solve the high-temperature safety hazard problem of the existing functional current collectors.

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

[0006] The first aspect of the present application provides a thermally safe functional current collector, which includes a polymer base film layer and thermally safe functional layers provided on both surface sides of the polymer base film layer;

[0007] The thermally safe functional layer is composed of a thermal shrinkage layer and a conductive layer; the polymer base film layer is adjacent to the thermal shrinkage layer;

[0008] Among them, the thermal shrinkage layer contains a negative thermal expansion material, and the conductive layer contains a metal material.

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

[0010] The thermally safe functional layer includes a thermal shrinkage layer and a conductive layer;

[0011] Or, the thermally safe functional layer includes multiple thermal shrinkage layers and multiple conductive layers, and the thermal shrinkage layers and the conductive layers are alternately arranged.

[0012] Further, the negative thermal expansion material is a negative thermal expansion ceramic material with a negative thermal expansion coefficient < -1.0×10 -6 K -1

[0013] Further, the thermal shrinkage layer further contains a thermal conventional ceramic material with a coefficient of thermal expansion > 0; in the thermal shrinkage layer containing the thermal conventional ceramic material, the mass ratio range of the negative thermal expansion ceramic material to the thermal conventional ceramic material is 1-9:9-1.

[0014] Further, the lower limit value of the negative thermal expansion temperature range of the thermal shrinkage layer is in the range of 120 °C to 160 °C, and the upper limit value is in the range of 240 °C to 900 °C; the negative thermal expansion of the negative thermal expansion material is isotropic or anisotropic.

[0015] Further, the negative thermal expansion ceramic material is selected from one or more of PbTiO3, BaTiO3, LiAlSiO4, Mg2Al4Si5O 12 , NaZr2P3O 12 , ZrW2O8, manganese nitride, lanthanum-based compounds; the thermal conventional ceramic material is selected from one or more of alumina, aluminum nitride, aluminum carbide, calcium oxide, calcium carbide.

[0016] Further, the metal material is aluminum metal or copper metal; the thickness of each thermal shrinkage layer is 10-100 nm, and the thickness of each conductive layer is 0.8-1.2 microns.

[0017] The second aspect of the present application provides a preparation method of a thermally safe functional current collector, including the following steps:

[0018] At least one thermal shrinkage layer and at least one conductive layer are respectively prepared on both surfaces of the polymer base film layer;

[0019] When multiple thermal shrinkage layers and multiple conductive layers are prepared on the surface of the polymer base film layer, the thermal shrinkage layer is first prepared, and then the conductive layer is prepared on the surface of the thermal shrinkage layer, and this step is cycled to obtain multiple alternating thermal shrinkage layers and multiple conductive layers on the outside of the polymer base film layer.

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

[0021] The functional current collector of the present invention is provided with a heat shrinkage layer containing a negative thermal expansion material and a conductive layer containing a metal material on the outside of the polymer base film layer; when an abnormal current occurs inside the battery, or when the battery is affected by high temperature of the external environment or other thermal runaway batteries, the internal temperature of the battery gradually rises, and the negative thermal expansion material of the heat shrinkage layer shrinks due to the heat, while the conductive layer containing the metal material expands due to the heat. At this time, a large stress difference will appear inside the heat shrinkage layer and between the heat shrinkage layer and the conductive layer. These stress differences cause the thinner conductive layer to break when it breaks through its own tensile strength, causing a large number of cracks in the current collector conductive layer, thereby achieving the effect of isolating the current; this design can enable the battery to quickly and extensively complete power-off at high temperatures, avoiding further temperature increases, thereby reducing the risk of thermal runaway of a single battery and heat spread in the battery pack.

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

[0023] The conductive layer of the present invention preferably adopts a metal aluminum conductive layer or a metal copper conductive layer. The conductive layer serves as a breakable layer that can provide a stress difference with the heat shrinkable layer, and at the same time serves as a basic conductive structure of the aluminum functional current collector or the copper functional current collector, forming a functional composition that can utilize the positive electrode sheet (corresponding to the aluminum-containing functional current collector) or the negative electrode sheet (corresponding to the copper-containing functional current collector) itself to achieve the purpose of thermal safety protection. In addition, the ceramic material in the heat shrinkable layer of the present invention can also improve the bonding strength between the polymer base film layer and the metal conductive layer. The ceramic material in the functional current collector can also play a role in isolating the polymer base film layer from the electrolyte, thereby improving the service life of the polymer base film layer.

[0024] The functional current collector of the present invention can be powered off in a timely manner in a high temperature environment, thereby improving the thermal safety of the functional current collector and reducing the risk of heat spread of the functional current collector. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0027] In the figure: 1-polymer base film layer, 2-heat shrinkage layer, 3-conductive layer. DETAILED DESCRIPTION

[0028] The above content of the present invention will be further described in detail below in the form of specific embodiments. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following embodiments. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention.

[0029] The test methods used in the following embodiments are all conventional methods unless otherwise specified. The reagents, methods, and equipment used are all conventional reagents, methods, and equipment in the technical field unless otherwise specified.

[0030] For the sake of brevity, only some numerical values and optional ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recited; the options in the optional range can also be combined arbitrarily.

[0031] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various common measurement methods in the art.

[0032] Some of the noun explanations in the present invention are described as follows:

[0033] Functional current collector: It is a current collector with a "sandwich" structure. The inner layer is a polymer high molecular layer, such as PET, PP or PI film. Both sides of the polymer high molecular 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 material: It is a type of material with negative thermal expansion performance. The thermal shrinkage rate of this material after heating is ≤0, that is, it has the characteristic of "shrinking when heated and expanding when cooled" opposite to that of general materials. The volume or the length in a certain direction of the negative thermal expansion material will decrease with the increase of temperature, and the negative thermal expansion phenomenon only appears in a certain temperature range.

[0035] The present invention provides a thermally safe functional current collector, which includes a polymer base film layer and thermally safe functional layers provided on both surface sides of the polymer base film layer;

[0036] The thermally safe functional layer includes at least one thermal shrinkage layer and at least one conductive layer; the polymer base film layer is adjacent to the thermal shrinkage layer;

[0037] Among them, the thermal shrinkage layer includes a negative thermal expansion material, and the conductive layer includes a metal material.

[0038] The thermally safe functional layer is composed of one thermal shrinkage layer and one conductive layer; or, the thermally safe functional layer includes multiple thermal shrinkage layers and multiple conductive layers, and the thermal shrinkage layers and the conductive layers are arranged alternately.

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

[0040] The thickness of the polymer-based film layer of the present application can be 4 to 10 micrometers.

[0041] When there is an abnormal current inside the battery or it is affected by external high temperatures such as the environment or other thermally runaway batteries, the internal temperature of the battery gradually rises. The negative thermal expansion material of the thermal shrinkage layer is heated and shrinks, while the conductive layer containing the metal material expands due to heating. At this time, a large stress difference will appear inside the thermal shrinkage layer and between the thermal shrinkage layer and the conductive layer, causing the conductive layer to break when it exceeds its own tensile strength, and a large number of cracks will occur in the current collector conductive layer, thus achieving the function of isolating the current.

[0042] The tensile strength of the metal material is generally greater than that of ceramics, and it has better toughness. Therefore, compared with the conductive layer, the stress difference inside the thermal safety functional layer makes the adjacent conductive layer more likely to break; and because the ceramic material has a higher brittleness, the crack extends longer when it breaks, and the power-off response is faster; and the ceramic material can improve the bonding strength between the polymer-based film layer and the conductive layer, and the ceramic material can also play a role in isolating the polymer-based film layer and the electrolyte in the functional current collector, improving the life of the base film.

[0043] The preparation method of the thermal safety functional layer of the present application can adopt one or more of physical vapor deposition, chemical vapor deposition, etc.; among them, the physical vapor deposition method can be vacuum evaporation and magnetron sputtering; the 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 is a negative thermal expansion ceramic material with a negative thermal expansion coefficient < -1.0×10 -6 K -1

[0045] The negative thermal expansion coefficient of the negative thermal expansion material of the present invention cannot be too small. If it is too small, the deformation amount is insufficient, the generated stress difference is small, and the conductive layer cannot be torn.

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

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

[0048] The negative thermal expansion temperature range of the heat shrinkable layer of the present invention needs to be set within a suitable range to be able 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 be too high, so it is necessary to avoid abnormal fracture 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 is ensured; the upper limit of the expansion temperature range should not be too large either. If it is too large and exceeds the temperature of battery thermal runaway, the current collector cannot cut off the power in time and cannot play a role in controlling thermal runaway.

[0049] The negative thermal expansion of the negative thermal expansion material is preferably anisotropic. Anisotropy can make the internal expansion coefficients different, and a larger difference in expansion coefficients is more likely to cause fracture.

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

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

[0052] The conductive layer of the present application is mainly composed of conductive metal and may also contain metal oxides or other doping materials.

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

[0054] The present invention also provides a preparation method of a thermally safe functional current collector, including the following steps:

[0055] Prepare at least one heat shrinkable layer and at least one conductive layer on both surface sides of the polymer-based film layer;

[0056] When preparing a multi-layer thermal shrinkage layer and a multi-layer conductive layer on the surface of a polymer base film layer, the thermal shrinkage layer is prepared first, and then the conductive layer is prepared on the surface of the thermal shrinkage layer. This step is repeated to obtain the multi-layer thermal shrinkage layer and the multi-layer conductive layer that are alternately arranged on the outer side of the polymer base film layer.

[0057] The present invention also provides a pole piece, which includes the above-mentioned thermally safe functional current collector.

[0058] The present invention also provides a battery, which includes the above-mentioned pole piece.

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

[0060] Example 1

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

[0062] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare the thermal shrinkage layer and the conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

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

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

[0065] 3) Thicken the copper layer of the film plated with the LiAlSiO4 layer and the copper seed layer by electroplating with water. Immerse the above-obtained film completely in the copper sulfate electrolyte. The electrolyte 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 μm;

[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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare a thermal shrinkage layer and a conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

[0070] 1) Set the target arrangement to 16 NaZr2P3O 12 Targets (with a purity of 99.95% for all), the magnetron sputtering power density is 60 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, the deposition time is 10 s, obtaining a thermal shrinkage layer with a thickness of 30 nm, a negative thermal expansion temperature range of 120 - 260 °C, and a thermal expansion coefficient of -16.1×10 -6 k -1 ;

[0071] 2) After the above steps, transfer to a vacuum evaporation equipment, evacuate to a vacuum degree of 5*10 -3 Pa, introduce argon to control the vacuum degree at 5*10 -2 Pa, start the winding trolley, control the tape running speed at 300 m / min, and at the same time heat the evaporation boat and feed the aluminum wire, with a wire feeding speed of 350 mm / min, so as to form an aluminum layer on the surface of the base film, and control the thickness of the aluminum layer to be 1.1 μm;

[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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare a thermal shrinkage layer and a conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

[0076] 1) Set the target arrangement to 16 Sc2W3O 12 Targets (with a purity of 99.95% for all), the magnetron sputtering power density is 60 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, the deposition time is 10 s, obtaining a thermal shrinkage layer with a thickness of 30 nm, a negative thermal expansion temperature range of 50 - 570 °C, and a thermal expansion coefficient of -12.4×10 -6 k -1 ;

[0077] 2) After the above steps, transfer to a vacuum evaporation equipment, evacuate to a vacuum degree of 5*10 -3Pa, introduce argon gas to maintain the vacuum degree at 5*10 -2 Pa, start the winding trolley, control the tape running speed at 300 m / min, simultaneously heat the evaporation boat and feed the aluminum wire, with the wire feeding speed of 350 mm / min, so as to form an aluminum layer on the surface of the base film, and control the thickness of the aluminum layer to be 1.1 μm;

[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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare a thermal shrinkage layer and a conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

[0082] 1) Set the target arrangement mode as 16 ZrVPO7-based targets (with a purity of 99.95% for all), the magnetron sputtering power density is 60 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, and the deposition time is 10 s, to obtain a thermal shrinkage layer with 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 k -1 ;

[0083] 2) After the above steps, transfer to a vacuum evaporation device, evacuate to a vacuum degree of 5*10 -3 Pa, introduce argon gas to maintain the vacuum degree at 5*10 -2 Pa, start the winding trolley, control the tape running speed at 300 m / min, simultaneously heat the evaporation boat and feed the aluminum wire, with the wire feeding speed of 350 mm / min, so as to form an aluminum layer on the surface of the base film, and control the thickness of the aluminum layer to be 1.1 μm;

[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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare a thermal shrinkage layer and a conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

[0088] 1) Set the target arrangement mode as 2 NaZr2P3O 12Target + 16 aluminum targets (with a purity of 99.95% each), and the tape running direction is from the NaZr2P3O 12 target to the aluminum targets. The magnetron sputtering power density is 40 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, the deposition time is 15 s, the thickness of the thermal shrinkage layer obtained is 5 nm, the negative thermal expansion temperature range is 120 - 260 °C, and the expansion coefficient is -16.1×10-6k -1 , and the thickness of the aluminum layer is 40 nm;

[0089] 2) Repeat the above steps until the thickness of the single-sided coating reaches 1.1 μm, and then stop the preparation of the coating;

[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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare the thermal shrinkage layer and the conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are:

[0094] 1) Set the target arrangement method as 16 NaZr2P3O 12 targets (with a purity of 99.95% each), the magnetron sputtering power density is 60 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, the deposition time is 5 s, the thickness of the thermal shrinkage layer obtained is 15 nm, the negative thermal expansion temperature range is 120 - 260 °C, and the expansion coefficient is -16.1×10 -6 k -1 ;

[0095] 2) After the above steps, set the target arrangement method as 16 Al2O3 targets (with a purity of 99.9% each), the magnetron sputtering power density is 50 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, the deposition time is 5 s, the thickness of the thermally conventional ceramic underlayer obtained is 15 nm, and the expansion coefficient is 6.5×10 -6 k -1 ;

[0096] 3) After the above steps, transfer to a vacuum evaporation equipment, evacuate to a vacuum degree of 5*10 -3 Pa, introduce argon gas to protect and control the vacuum degree at 5*10 -2Pa, start the winding trolley, control the tape running speed at 300 m / min, simultaneously heat the evaporation boat and feed the aluminum wire, with the wire feeding speed at 350 mm / min, so as to form an aluminum layer on the surface of the base film, and control the thickness of the aluminum layer to be 1.1 μm;

[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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare a primer layer and a conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

[0101] Successively coat the obtained base film with an alumina coating and an aluminum layer; among them, after the winding trolley enters the evaporation chamber, evacuate to 5×10 -3 Pa, start the winding trolley, control the speed at 280 m / min, simultaneously heat the evaporation boat and feed the aluminum wire, with the wire feeding speed at 320 mm / min, and simultaneously start the oxygen intake, control the vacuum degree at 5×10 -2 Pa, so as to form an alumina coating on the surface of the base film, and control the thickness of the alumina coating to be 30 nm; then break the vacuum, evacuate to a vacuum degree of 5×10 -3 Pa, introduce argon to protect and control the vacuum degree at 5×10 -2 Pa, continue to coat an aluminum layer in the same way, and the thickness of the aluminum layer is 1 μm; 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] Place a PET film with a thickness of 6 μm in a magnetron sputtering machine, and prepare a heat shrinkable layer and a conductive layer on both sides in the thickness direction of the PET film. The specific process conditions are as follows:

[0105] 1) Select a vacuum evaporation device, evacuate to a vacuum degree of 5×10 -3 Pa, introduce argon to protect and control the vacuum degree at 5×10 -2 Pa, start the winding trolley, control the tape running speed of the PET film at 300 m / min, simultaneously heat the evaporation boat and feed the aluminum wire, with the wire feeding speed at 350 mm / min, so as to form an aluminum layer on the surface of the base film, and control the thickness of the aluminum layer to be 1.1 μm;

[0106] 2) After the above steps, transfer to a magnetron sputtering equipment, and set the target arrangement as 16 NaZr2P3O 12 targets (with a purity of 99.95% for all), the magnetron sputtering power density is 60 W / cm 2 , the vacuum degree is 0.1 Pa, the protective gas is argon, the flow rate is 50 mL / min, the deposition time is 10 s, obtaining a thermal shrinkage layer with a thickness of 30 nm, a negative thermal expansion temperature range of 120 - 260 °C, and a thermal expansion coefficient of -16.1×10 -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] Test and verification:

[0109] Perform surface sheet resistance thermal response tests and peel strength tests on the functional current collectors prepared in all the above examples and comparative examples. The specific test methods are as follows:

[0110] Surface sheet resistance: The sheet resistance is measured using a four-probe resistivity tester. Determine the number of sheet resistance tests according to the lateral width of the product, with one test point for every 100 mm. Other requirements are tested according to the method specified in GB / T 22638.6 - 2016. Place the functional current collector sample in a heating chamber for programmed temperature rise heating, with a heating rate of 0.3 °C / s. Measure the surface sheet resistance of the functional current collector before heating, at 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, and 160 °C respectively. After each heating temperature rise reaches the target temperature, take out the sample for surface sheet resistance measurement, keep the heating chamber at a constant temperature, and continue heating to the next target temperature for measurement after the test. Evaluate the thermal power-off response ability of the functional current collector based on the change in surface sheet resistance.

[0111] Peel strength test: Cut the sample into a size of 10 * 2 cm; use an electronic peel tester for testing; paste the cut sample onto the test stainless steel plate with a 2-cm-wide 3M tape, and perform a 180° pole piece peel test by peeling one end of the sample. After the test, record the test parameters.

[0112] 2. Test results

[0113] Perform surface sheet resistance thermal response tests and peel strength tests on the functional current collectors prepared in all the above examples and comparative examples. The test results are shown in Tables 1 and 2.

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

[0115]

[0116] Table 2 Test Results of Sheet Resistance Thermal Response Test of Functional Set Fluids in Examples and Comparative Examples

[0117]

[0118] The functional set fluid of the embodiment of the present invention can cut off the power supply in time under high-temperature environments, improve the thermal safety of the battery, and reduce the risk of thermal propagation. The thermal safety functional layer of the present invention can be composed of a thermal shrinkage layer and a conductive layer, or can be a multi-layer structure formed by multiple thermal shrinkage layers and multiple conductive layers arranged alternately.

[0119] Examples 1 and 2 of the present application respectively give examples of preparing copper functional current collectors and aluminum functional current collectors. The conductive metal layer serves both as a breakable layer that can provide a stress difference with the thermal shrinkage layer and at the same time as the basic conductive structure of the functional current collector, achieving the purpose of thermal safety protection by utilizing the functional composition of the electrode itself.

[0120] Examples 2-4 of the present application respectively give examples of aluminum functional current collectors with different material compositions and different negative thermal expansion temperature ranges; among them, the lower limit of the negative thermal expansion temperature range in Example 3 is too low, which will cause the current collector to cut off power during the normal operating temperature of the battery, affecting the use; the lower limit of the negative thermal expansion temperature range in Example 4 is too high, which will cause the initial temperature of the battery thermal runaway to not trigger power-off in time.

[0121] Example 5 of the present application provides an example of preparing a multi-layer structure with alternately arranged thermal shrinkage layers and conductive metal layers. Compared with the single-layer structure of the thermal shrinkage layer and the conductive layer, the bonding strength of the multi-layer structure is slightly worse, but its power-off response is faster.

[0122] Example 6 of the present application provides an example of using a thermal shrinkage layer containing both negative thermal expansion ceramic materials and thermal conventional ceramic materials. When heated, a greater stress difference will be generated inside the thermal shrinkage layer due to the large difference in the expansion coefficients of different materials, which is more conducive to the faster fracture of the conductive layer.

[0123] According to the range of the negative thermal expansion temperature range required for the thermal safety of the current collector, the present application preferably uses NaZr2P3O 12 target as the negative thermal expansion ceramic material, or other several different combinations of negative thermal expansion ceramic materials can also be selected to prepare a thermal shrinkage layer containing a mixed material to achieve a similar effect and meet the range of the negative thermal expansion temperature range required for the thermal safety of the battery current collector.

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

[0125] Comparative Example 2 of the present application provides a solution in which the conductive layer is adjacent to the polymer base film layer, and the heat shrinkable layer is disposed outside the conductive layer. Tests show that this comparative example also has the function of thermal power-off response, but its bonding strength is very poor and the surface sheet resistance is very high, which cannot meet the battery application standard.

[0126] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiments, etc., 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 a thermal safety functional layer arranged on both sides of the polymer base film layer; The thermal safety functional layer comprises at least one heat shrinkable layer and at least one conductive layer; the polymer base film layer is adjacent to the heat shrinkable layer; Wherein, the heat shrinkable layer contains negative thermal expansion material, and the conductive layer contains metal material.

2. The thermally safe functional current collector according to claim 1, characterized in that: The thermal safety functional layer is composed of a heat shrinkable layer and a conductive layer; Alternatively, the thermal safety functional layer includes multiple heat shrinkable layers and multiple conductive layers, and the heat shrinkable layers and the conductive layers are alternately arranged.

3. The thermally safe functional current collector according to claim 1, characterized in that: The negative thermal expansion material has a negative thermal expansion coefficient of <-1.0×10 -6 K -1 Negative thermal expansion ceramic material.

4. The thermally safe functional current collector according to claim 3, characterized in that: The heat shrink layer also contains a thermally conventional ceramic material with a thermal expansion coefficient greater than 0; in the heat shrink layer containing the thermally conventional ceramic material, the mass ratio of the negative thermal expansion ceramic material to the thermally conventional ceramic material is in the range of 1-9:9-1.

5. The thermally safe functional current collector according to claim 1, characterized in that: The lower limit of the negative thermal expansion temperature zone of the heat shrinkable layer is in the range of 120°C to 160°C, and the upper limit is in the range of 240°C to 900°C; wherein the negative thermal expansion of the negative thermal expansion material is isotropic or anisotropic.

6. The thermally safe functional current collector according to claim 4, characterized in that: The negative thermal expansion ceramic material is selected from PbTiO3, BaTiO3, LiAlSiO4, Mg2Al4Si5O 12 、NaZr2P3O 12 , ZrW2O8, manganese nitride, one or more of lanthanum-based compounds; the thermal conventional ceramic material is selected from one or more of aluminum oxide, aluminum nitride, aluminum carbide, calcium oxide, and calcium carbide.

7. The thermally safe functional current collector according to claim 1, characterized in that: The metal material is metal aluminum or metal copper; the thickness of each heat shrinkable layer is 10-100 nm, and the thickness of each conductive layer is 0.8-1.2 microns.

8. A thermally safe functional current collector and a method for preparing the same, characterized in that: The following steps are involved: At least one heat shrinkable layer and at least one conductive layer are respectively 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 layer, the heat shrinkable layer is prepared first, and then the conductive layer is prepared on the surface of the heat shrinkable layer. This step is repeated to obtain multiple heat shrinkable layers and multiple conductive layers alternately arranged on the outside of the polymer base film layer.

9. A pole piece, characterized in that: A thermally safe functional current collector comprising the method described in any one of claims 1 to 7 or prepared by the method described in claim 8.

10. A battery, characterized in that: A pole piece comprising the pole piece as claimed in claim 9.

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