Composite adhesive tape as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of new energy batteries, and particularly relates to a composite adhesive tape and a preparation method and application thereof.The composite adhesive tape comprises a heat conduction layer and a substrate layer which are connected through a bonding layer, and a heat conduction material in the heat conduction layer is copper-diamond composite material powder and a carbon nanotube array vapor deposited on the copper-diamond composite material powder. The composite adhesive tape can be uniformly adhered to the inner wall of a lithium ion battery shell after the exposed bonding layer of the substrate layer is removed in a use mode similar to a double-sided adhesive tape, so that heat accumulation in a battery cell in a rapid charging and discharging process can be greatly guided out, the central temperature of a cell package is reduced, the use performance of the battery cell is optimized, and the long-term service life of the battery cell is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and in particular relates to a composite adhesive tape and a preparation method and application thereof. Background Art

[0002] With the vigorous development of the current new energy market, the market demand for fast charging capabilities of power batteries is getting higher and higher. Fast charging batteries have also evolved from the initial 1-1.5C fast charging to the current 2-3C fast charging that is common in the market. The latest Kirin battery even has a 4C charging capability. Unlike the 0.5P charging rate requirement of traditional energy storage cells, on-board fast charging batteries must use a very large current to charge the cells because they require rapid energy charging in a short period of time. In this process, serious heat is generated. On the one hand, the rapid intercalation and deintercalation of lithium ions between the positive and negative electrodes inside the cell must overcome the ohmic impedance and polarization impedance, which will generate a lot of heat. On the other hand, the ohmic heat generated by structural parts, especially the joints, will also become very huge. This requires that the development of fast charging cells must fully consider the thermal management of the charging and discharging process inside the cell.

[0003] Battery thermal management, from a broad perspective, can be divided into two main areas: 1. Reducing battery heat generation, such as reducing ohmic and polarization internal resistance through the selection and design of primary and auxiliary materials; 2. Increasing battery heat dissipation, such as increasing heat exchange through external air or liquid cooling. Currently, methods for reducing internal resistance and thus battery heat generation through material replacement and other design methods have reached their theoretical limits in existing lithium-ion battery systems. Therefore, increasing heat dissipation during battery operation has become a key breakthrough in power battery thermal management.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: how to increase the heat dissipation during the use of the battery. In order to solve the aforementioned technical problems, the present invention provides a high thermal conductivity composite tape and its preparation method and application. The thermal conductive material in the composite tape is a copper-diamond composite material powder and a carbon nanotube array vapor-deposited thereon. The copper powder and the subsequent in-situ generated carbon nanotube array are sequentially filled in the gaps between the diamond particles, which together play a good connecting role and form a complete heat conduction path. The composite tape can be removed from the base layer to expose the adhesive layer in a manner similar to double-sided tape and evenly attached to the inner wall of the lithium-ion battery shell, thereby greatly guiding the heat accumulation inside the battery cell during rapid charging and discharging, thereby reducing the core package center temperature, optimizing the battery cell performance, and improving the long-term service life of the battery cell.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, a composite tape comprises a heat-conducting layer and a base layer connected by an adhesive layer, wherein the heat-conducting material in the heat-conducting layer is copper-diamond composite material powder and a carbon nanotube array vapor-deposited thereon.

[0008] Furthermore, in the copper-diamond composite material powder, the mass ratio of copper to diamond is 0.5 to 2:1;

[0009] And / or, in the thermally conductive material, the mass fraction of carbon nanotubes is 2-5%;

[0010] And / or, the heat conductive layer further contains a bonding dispersant.

[0011] Furthermore, the bonding dispersant is polyvinylidene fluoride; and / or the mass ratio of the bonding dispersant to the copper-diamond composite material powder is 1:8-10.

[0012] Furthermore, the adhesive layer has a thickness of 0.02 to 0.07 mm and is formed by drying the polyurethane glue;

[0013] and / or, the thickness of the heat-conducting layer is not less than 0.25 mm;

[0014] And / or, the base layer has a thickness of 0.05 to 0.15 mm and is selected from release paper.

[0015] Furthermore, the preparation of the thermal conductive material includes the following steps:

[0016] S1, adding diamond nanopowder and nano-copper powder in a certain mass ratio, ball milling, stirring and dispersing, and hot pressing to obtain a copper-diamond composite material;

[0017] S2. The powder of the prepared copper-diamond composite material is heated in a reducing gas atmosphere, and then a gas for vapor-depositing carbon nanotubes is introduced to vapor-deposit carbon nanotubes to obtain a thermal conductive material.

[0018] Furthermore, the particle size of the diamond nanopowder is 200 to 500 nm, and the particle size of the nano-copper powder is 50 to 100 nm;

[0019] And / or, the hot pressing time is 30±10 min, the temperature is 800±10° C., and the pressure is 10±1 MPa;

[0020] and / or, the reducing gas is H2;

[0021] And / or, the heating rate is controlled at 5±1°C / s;

[0022] And / or, the gas used for vapor deposition of carbon nanotubes is C2H2, and the C2H2 flow rate is 20±5 sccm;

[0023] And / or, the temperature of the vapor deposition is 800±50° C. and the time is 8±1 h.

[0024] In a second aspect, a method for preparing the composite tape of the first aspect comprises: coating the glue for forming the bonding layer on the base layer, coating the slurry of the thermal conductive layer on the bonding layer after drying, and obtaining the composite tape after drying.

[0025] Furthermore, the preparation of the slurry includes: adding the powder of the thermal conductive material and the adhesive dispersant, stirring and dispersing them, and then adding a certain amount of solvent and mixing them evenly to obtain the slurry.

[0026] Furthermore, the stirring and dispersing is performed at a speed of 5±1 rpm and a time of 30±5 min;

[0027] and / or, the solvent is N-methylpyrrolidone;

[0028] And / or, the mixing speed is 12±1 rpm and the mixing time is 2±1 h.

[0029] In a third aspect, a lithium-ion battery comprises the composite tape described in the first aspect, or the composite tape prepared by the preparation method described in the second aspect, wherein the composite tape is located between the shell and the battery cell.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] The composite tape of the present invention has high thermal conductivity. When it is arranged between the battery housing and the battery core, it is beneficial to the heat diffusion after the heat is generated inside the battery core (especially the fast charging core). The thermal conductive material in the high thermal conductivity composite tape maximizes the material advantages through structural advantages. Compared with simple carbon nanotubes (CNTs), the thermal conductive material can be oriented to grow into an array due to CNT vapor deposition, which will have stronger thermal conductivity. At the same time, since CNTs are directly vapor-deposited on the copper-diamond composite material powder, the composite structure has better stability, which makes the composite structure meet the needs of long-term use inside the battery without falling off and failing. Compared with simple diamonds, due to the low density characteristics of diamonds, their actual compacted density is very low, and the gaps between the particles are large, thereby greatly reducing the actual thermal conductivity efficiency of diamonds. However, in the thermal conductive material of the present invention, the array CNT and copper powder play a good connecting role, which can fill the gaps between the diamond particles and form a complete thermal conduction path, which greatly improves the overall thermal conductivity effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1Schematic diagram of the structure of the composite tape of the present invention; wherein, 1-CNT; 2-nano copper powder; 3-diamond nanopowder; 4-adhesive layer; 5-base layer;

[0033] Figure 2 Schematic diagram of the use of the composite tape of the present invention in lithium-ion batteries Figure 1 ; Among them, 1- composite tape; 2- lithium ion battery shell; 3- temperature sensing wire;

[0034] Figure 3 Schematic diagram of the use of the composite tape of the present invention in lithium-ion batteries Figure 2 ; Among them, 1-composite tape; 2-lithium-ion battery shell. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0036] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0037] In a first aspect, the present invention provides a composite tape comprising a heat-conducting layer and a base layer connected by an adhesive layer, wherein the heat-conducting material in the heat-conducting layer is copper-diamond composite material powder and a carbon nanotube array vapor-deposited thereon.

[0038] The composite tape of the present invention has high thermal conductivity. After being arranged between the battery housing and the battery core, it is beneficial to the heat diffusion after the heat is generated inside the battery core (especially the fast charging core). The thermal conductive material in the high thermal conductivity composite tape maximizes the material advantages through structural advantages. Compared with simple CNTs, the thermal conductive material can have stronger thermal conductivity because of the orientation growth of CNT vapor deposition. At the same time, since CNTs are directly vapor-deposited on the copper-diamond composite material powder, the composite structure has better stability, which makes the composite structure meet the needs of long-term use inside the battery without falling off and failing. Compared with simple diamonds, due to the low density characteristics of diamonds, their actual compacted density is very low, and the gaps between the particles are large, thereby greatly reducing the actual thermal conductivity efficiency of diamonds. However, in the thermal conductive material of the present invention, the array CNT and copper powder play a good connecting role, which can fill the gaps between the diamond particles and form a complete thermal conduction path, which greatly improves the overall thermal conductivity effect.

[0039] Specifically, the use of vapor-deposited carbon nanotube arrays in thermal conductive materials allows CNTs to grow vertically along the spherical surface of the copper powder through vapor deposition until they grow and contact the diamond surface, performing oriented growth into an array. Compared with the method of directly mixing and adding CNTs, on the one hand, this optimizes the heat diffusion path (inside the battery cell - CNTs - copper - CNTs - diamonds - battery shell), and on the other hand, improves the thermal conductivity of the material. Heat conduction along the CNT growth direction allows the material to exhibit the highest thermal conductivity, greatly reducing the additional thermal management cost. At the same time, since CNTs are directly vapor-deposited on the copper-diamond composite material powder, the resulting composite structure has better stability, which is beneficial to improving the long-term service life of the battery cell. Compared with directly adding CNTs, or forming a composite powder of carbon nanotubes and copper and then mixing it with diamonds, the steric hindrance formed by CNTs will make it difficult for copper to fill the gaps between the diamond particles, and the CNT structure may be destroyed during the mixing process, ultimately resulting in an unstable structure and weak bonding of the composite material composed of diamond, copper and carbon nanotubes. The thermally conductive material of the present invention is a composite of copper and diamond followed by vapor deposition of carbon nanotubes. Specifically, nano-copper powder and diamond nano-powder are first compounded to form a copper-diamond composite material in which copper powder fills the gaps between diamonds. Then, an array of CNTs is grown in situ on the copper and connected to the diamonds through vapor deposition. This process avoids the steric hindrance of the CNTs and the possibility of structural damage during the CNT mixing process, resulting in a stable and firmly bonded composite material.

[0040] The thermal conductivity of the ordered array of CNTs in the thermally conductive layer of the composite tape of the present invention is approximately 3000 W / (m*k), a significant advantage over the aluminum shells currently used in square battery cells (with a thermal conductivity of approximately 204 W / (m*k)). Diamond is the primary thermal conductive material in the system. Diamond also has excellent thermal conductivity, with a thermal conductivity of approximately 2000 W / (m*k), and serves as an auxiliary heat conductor in the system. Its low thermal expansion coefficient and high mechanical strength also provide structural support. Copper provides active sites for the directional growth of CNTs and also assists in thermal conductivity.

[0041] The composite tape of the present invention boasts a simple structure, high feasibility, minimal impact on the internal design of the battery cell, and low cost. It has broad applicability and can meet the heat dissipation needs of batteries of all sizes. Specifically, by affixing it to the interior of the battery cell casing, the CNT and diamond array design significantly improves the heat dissipation problem at the center of the core pack. This significantly mitigates the inherently slow heat dissipation of lithium-ion battery structures, reducing the difficulty of battery thermal management from a design perspective. Furthermore, it can reduce the overall cost of the battery pack, as individual cells dissipate heat more quickly and evenly, saving operating costs for group cooling equipment.

[0042] As an optional embodiment of the composite tape of the present invention, in the copper-diamond composite material powder, the mass ratio of copper to diamond is 0.5 to 2:1 (such as 0.6:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, etc.);

[0043] And / or, in the thermally conductive material, the mass fraction of carbon nanotubes is 2-5% (e.g., 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, etc.);

[0044] And / or, the thermal conductive layer further contains a bonding dispersant, and further, the mass ratio of the bonding dispersant to the copper-diamond composite material powder is 1:8-10 (such as 1:8.1, 1:8.3, 1:8.5, 1:8.7, 1:8.9, 1:9.1, 1:9.3, 1:9.5, 1:9.7, 1:9.9, etc.).

[0045] In the above technical solution, the copper-to-diamond mass ratio is controlled at 0.5 to 2:1, allowing the hot-pressed nano-copper powder to be sufficiently and evenly dispersed and mixed with the diamond nanopowder. Consequently, during vapor deposition, CNTs can only grow vertically along the spherical surface of the copper powder until they contact the diamond surface, forming a CNT array and a good heat conduction path (cell interior - CNT - copper - CNT - diamond - battery casing). Furthermore, a bonding dispersant is used to ensure uniform and stable dispersion of the copper-diamond composite powder of the vapor-deposited carbon nanotube array in the thermal conductive layer, while also ensuring that the slurry system used before coating and drying the thermal conductive layer has an appropriate viscosity for uniform coating.

[0046] Considering the compatibility of use in the battery system, polyvinylidene fluoride (PVDF) can be selected as the main adhesive and dispersing material in the thermal conductive layer. Since PVDF is the current mainstream battery cell adhesive, its safety and stability in the battery system have been fully verified. If there is a similar adhesive dispersant, it can be replaced with other materials without affecting the actual use adaptability of the composite tape in the battery cell.

[0047] As an optional embodiment of the composite tape of the present invention, the adhesive layer has a thickness of 0.02 to 0.07 mm (such as 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, etc.), and is formed by drying the polyurethane glue;

[0048] And / or, the thickness of the thermal conductive layer is not less than 0.25 mm, further 0.25-0.35 mm (such as 0.26 mm, 0.27 mm, 0.28 mm, 0.29 mm, 0.3 mm, 0.31 mm, 0.32 mm, 0.33 mm, 0.34 mm, etc.);

[0049] And / or, the base layer has a thickness of 0.05 to 0.15 mm (such as 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, etc.), and is selected from release paper.

[0050] In the above technical solution, polyurethane glue is preferably used as the raw material for the adhesive layer, which primarily serves to bond the base layer and the thermally conductive layer for ease of use. Release paper is used as the base material for the composite tape, preventing contamination of the adhesive layer and ensuring its adhesion. This allows the composite tape to be used similarly to double-sided tape, with the base layer removed to expose the adhesive layer, allowing it to adhere to the inner wall of the battery casing together with the thermally conductive layer. Furthermore, the tape can be designed in different sizes to accommodate different cell sizes, making it easy to cut.

[0051] Other materials that can bond with the base layer, thermal conductive layer, and shell can also be used as raw materials for the bonding layer. Polyurethane is chosen here because of its good compatibility in the battery system and its easy availability.

[0052] Since composite tape is mainly used for heat dissipation of battery cells, if its thickness after removing the base layer is thicker, such as more than 0.5mm, it will affect the actual internal space of the battery cell. If it is thinner, it will not achieve a good bonding and heat dissipation effect, it will not be easy to maintain a good layered bonding structure, and it will be even more difficult to achieve the needs of good heat dissipation.

[0053] In a second aspect, the present invention provides a method for preparing the above-mentioned composite tape, comprising: coating the glue for forming the bonding layer on the base layer, coating the slurry of the thermal conductive layer on the bonding layer after drying, and obtaining the composite tape after drying.

[0054] As an optional embodiment of the preparation method of the present invention, the preparation of the slurry, including the preparation of the thermal conductive material, is as follows:

[0055] S1, adding diamond nanopowder and nano-copper powder in a certain mass ratio, ball milling, stirring and dispersing, and hot pressing to obtain a copper-diamond composite material in which the nano-copper powder fills the gaps between the diamond nanopowders;

[0056] S2. The powder of the prepared copper-diamond composite material is heated in a reducing gas atmosphere, and then a gas for vapor-depositing carbon nanotubes is introduced to vapor-deposit carbon nanotubes to obtain a thermal conductive material.

[0057] In the above technical solution, when both nano-copper powder and diamond nano-powder are in a solid state, the two nanomaterials are mixed and interspersed by hot pressing to obtain a copper-diamond composite material powder with a structure in which nano-copper powder fills the gaps between diamond nano-powders. The nano-copper powder is dispersed in the gaps between the diamond nano-powders, and copper is used as an active site for vapor deposition of a CNT array. This avoids the direct addition of CNTs or the formation of a composite powder of carbon nanotubes and copper and then mixing it with diamonds. Due to the steric hindrance of CNTs, it is difficult for copper to fill the gaps between diamond particles and the possibility of structural destruction during the CNT mixing process. To ensure the formation of carbon nanotubes, the system must first be placed in a reducing gas environment to avoid the presence of oxidizing gases such as oxygen that affect the formation of CNTs. Specifically, H2 (e.g., H2 at a flow rate of 200 sccm for 30 minutes) can be introduced.

[0058] As an optional embodiment of the preparation method of the present invention, the particle size of the diamond nanopowder is 200-500 nm, and the particle size of the nano-copper powder is 50-100 nm;

[0059] And / or, the hot pressing time is 30±10 min, the temperature is 800±10° C., and the pressure is 10±1 MPa;

[0060] and / or, the reducing gas is H2;

[0061] And / or, the heating rate is controlled at 5±1°C / s;

[0062] And / or, the gas for vapor deposition of carbon nanotubes is C2H2 gas path, and the C2H2 flow rate is 20±5sccm (such as 15sccm, 18sccm, 20sccm, 22sccm, 25sccm, etc.);

[0063] And / or, the temperature of the vapor deposition is 800±50℃ (such as 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, etc.), and the time is 8±1h (such as 7h, 7.5h, 8h, 8.5h, 9h, etc.).

[0064] In the above technical solution, the particle size of the diamond nanopowder is controlled to be 200-500 nm, and the particle size of the nano-copper powder is 50-100 nm; and / or the hot pressing time is controlled to be 30±10 min (such as 20 min, 25 min, 30 min, 35 min, 40 min, etc.), the temperature is 800±10° C. (such as 790° C., 795° C., 800° C., 805° C., 810° C., etc.), and the pressure is 10±1 MPa (such as 9 MPa, 9.5 MPa, 10 MPa, 10.5 MPa, 11 MPa, etc.), so that the nano-copper powder is well interspersed and dispersed in the diamond nanopowder to form a copper-diamond composite material.

[0065] As an optional embodiment of the preparation method of the present invention, the preparation of the slurry further comprises: S3, adding the powders of the thermal conductive material and the adhesive dispersant, stirring and dispersing them, and then adding a certain amount of solvent and mixing them evenly to obtain the slurry.

[0066] As an optional embodiment of the preparation method of the present invention, the stirring and dispersing speed is 5±1 rpm and the time is 30 min;

[0067] and / or, the solvent is N-methylpyrrolidone;

[0068] And / or, the mixing is carried out at a rotation speed of 12±1 rpm and for 2 hours.

[0069] In a third aspect, the present invention provides a lithium-ion battery, comprising the above-mentioned composite tape, wherein the composite tape is located between the shell and the battery cell.

[0070] The technical solution of the present invention is described in detail below with reference to specific embodiments and comparative examples.

[0071] Example 1

[0072] Provided is a high thermal conductivity composite tape and its preparation, specifically as follows:

[0073] Prepare release paper, polyurethane glue, NMP (N-methylpyrrolidone), PVDF powder, diamond nanopowder (particle size 200-500nm), nano-copper powder (50-100nm), hydrogen, and acetylene gas. The mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 45%: 45%.

[0074] Diamond nanopowder and nanocopper powder were added to a high-speed ball mill according to the aforementioned mass ratio and dispersed by stirring for 30 minutes at 20 rpm. After ball milling, the mixed powder was placed in a hot press and hot-pressed at 800°C and 10 MPa for 30 minutes to produce a copper-diamond composite material.

[0075] The powder of the prepared copper-diamond composite material is evenly spread in a high-temperature porcelain boat, and the high-temperature porcelain boat is placed in a tubular furnace. The tubular furnace is connected to the H2 gas line, the ventilation time is 30 minutes, the H2 flow rate is 200 sccm, and the entire tubular furnace is ensured to be in a reducing gas atmosphere. The tubular furnace is heated, and the heating rate is controlled at 5±1℃ / s and the temperature is 800℃. After reaching the temperature, the tubular furnace is connected to the C2H2 gas line, and the C2H2 flow rate is controlled to 20 sccm. The time is 8 hours to prepare a copper-diamond composite material (thermal conductive material) with array CNT deposition. The mass fraction of carbon nanotubes in the thermal conductive material is about 3-4%, and the length of the carbon nanotubes is less than 10nm.

[0076] The prepared copper-diamond composite material with CNT array deposition and the pre-prepared PVDF powder were sequentially added to a double planetary mixer for stirring and dispersion for 30 minutes at a speed of 5±1 rpm. Then, 45%-50% of NMP, which accounts for 45% to 50% of the total powder mass, was added to the double planetary mixer and stirred and dispersed for 2 hours at a speed of 12±1 rpm. After the stirring, a slurry for the thermal conductive layer was obtained. The solid content of the slurry was 50%-55% and the viscosity was 3000-6000 mPa.s.

[0077] Apply polyurethane glue evenly on release paper (thickness 0.1mm) and form a 0.05mm thick adhesive layer after drying; then apply thermal conductive layer slurry evenly on the adhesive layer and form a 0.25mm thick thermal conductive layer coating after drying at 80℃. After all the steps are completed, a high thermal conductive composite tape is obtained, the structure of which is as follows: Figure 1 shown.

[0078] Example 2

[0079] The only difference from Example 1 is that the mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 40%: 50%.

[0080] The rest of the settings are the same as those in Example 1.

[0081] Example 3

[0082] The only difference from Example 1 is that the mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 35%: 55%.

[0083] The rest of the settings are the same as those in Example 1.

[0084] Example 4

[0085] The only difference from Example 1 is that the mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 30%: 60%.

[0086] The rest of the settings are the same as those in Example 1.

[0087] Example 5

[0088] The only difference from Example 1 is that the mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 50%: 40%.

[0089] The rest of the settings are the same as those in Example 1.

[0090] Example 6

[0091] The only difference from Example 1 is that the mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 55%: 35%.

[0092] The rest of the settings are the same as those in Example 1.

[0093] Example 7

[0094] The only difference from Example 1 is that the mass ratio of PVDF: diamond nanopowder: nano-copper powder is 10%: 60%: 30%.

[0095] The rest of the settings are the same as those in Example 1.

[0096] Example 8

[0097] The only difference from Example 7 is that the coating thickness of the thermal conductive layer of the composite tape is 0.30 mm.

[0098] The rest of the settings are the same as those in Example 7.

[0099] Example 9

[0100] The only difference from Example 7 is that the coating thickness of the thermal conductive layer of the composite tape is 0.35 mm.

[0101] The rest of the settings are the same as those in Example 7.

[0102] Comparative Example 1

[0103] The only difference from Example 7 is that the coating thickness of the thermal conductive layer of the composite tape is 0.20 mm.

[0104] The rest of the settings are the same as those in Example 7.

[0105] Comparative Example 2

[0106] The only difference from Example 7 is that the coating thickness of the thermal conductive layer of the composite tape is 0.15 mm.

[0107] The rest of the settings are the same as those in Example 7.

[0108] Application test case

[0109] The composite tapes obtained in the examples and comparative examples were applied to secondary batteries. To further compare the effects of the composite tapes, blank controls (i.e., batteries without the composite tape and remaining in their original condition) were used. All samples were assembled using the same winding core, ensuring that all structures and materials, except for the thermally conductive layer in the battery housing, were identical. This included the identical bonding position of the tape on the battery housing and the placement of the temperature sensor.

[0110] Specifically, the positive and negative active materials are respectively made into a core of specified size (single core thickness 24mm, width 190mm, height 103mm) through the processes of homogenization, coating, rolling, die cutting, slitting and winding. Among them, the positive electrode material lithium iron phosphate: binder polyvinylidene fluoride PVDF: conductive agent Super P = 97wt%: 2wt%: 1wt%, coated on 13μm thick aluminum foil, with a single-side surface density of 200g / cm 3 Negative electrode material: artificial graphite: conductive agent SuperP: dispersant CMC: binder SBR = 95wt%: 1.5wt%: 1.5wt%: 2.0wt%, coated on 5μm thick copper foil, single surface density is 93g / cm 3 .

[0111] At the same time, the composite tape obtained in the embodiment and comparative example is cut into four suitable rectangles according to the size of the shell (two rectangles of 190mm*110mm and 48mm*110mm respectively), the release paper is torn off and the adhesive layer of the composite tape is pasted to the inside of the large surface of the aluminum shell (thickness 0.7±0.2mm), and after pasting, it is left to stand for 30 minutes to ensure that the adhesive layer of the composite tape is well adhered to the shell. Afterwards, two identical cores are installed in the aluminum shell with a double core structure, and a temperature sensor is embedded in the center of the large surface where the two cores are in contact to detect the temperature change of the core package center during the charging and discharging process, as shown in the figure. Figure 2 、 3 shown.

[0112] After all samples are assembled, the cells are baked, filled, formed, aged, and then taken offline normally. The cells are cycled for three weeks at 25°C at a high rate of 4C SC / 1C. SC stands for Step Charge, which means step charging. Step fast charging means adjusting the charging current corresponding to different SOCs within the 10%-80% SOC fast charging range to achieve an average 4C charge (10-80% SOC charging time ≤ 10.5min). The fast charge temperature rise test is conducted as follows:

[0113] 1) Discharge the battery to 2.5V at 0.33C.

[0114] 2) After standing for 30 minutes, charge the battery to 10% SOC with a 1C current, then charge the battery to 80% SOC using an average 4C step charge method (maximum current 700A). Finally, charge the battery to 3.65V with a 1C constant current method, and charge the battery to 100% SOC with a 3.65V constant voltage method at 0.05C.

[0115] 3) After standing for 1.5 hours, discharge the battery with a current of 1C to 2.5V, reaching 0% SOC;

[0116] 4) Steps 2) to 4) were repeated twice. The temperature change of the temperature sensing wire during the third charging cycle was detected using a temperature sensing wire embedded in the center of the core package. The results are shown in Table 1.

[0117] Table 1 Temperature changes of the temperature sensing wire of different samples during the third week of charging

[0118]

[0119] According to the test results in Table 1, it can be seen from the charging temperature at the center of the battery cell under the same conditions in the embodiment and the blank control that in the blank control without adding the high thermal conductivity tape, the maximum temperature at the center of the battery cell during charging of the battery cell reaches 54.2°C, and the maximum charging temperature rise reaches 24.4°C; while in the embodiment, after using the high thermal conductivity tape at the center of the battery cell, the maximum temperature can be reduced to 47.4°C, the maximum charging temperature rise can be reduced to 17.5°C, the maximum temperature can be reduced by 6.8°C, and the temperature rise can be reduced by 6.9°C. It can be seen that the reasonable use of the high thermal conductivity composite tape of the present invention on the lithium ion battery can significantly increase the thermal conductivity of the battery cell, thereby reducing the temperature at the center of the battery cell.

[0120] Furthermore, by comparing the test results of Examples 1-7, it can be seen that when the nano-copper powder content in the thermal conductive layer formula of the high thermal conductive tape changes from 30% to 60%, the temperature rise at the center of the battery cell under the same charging conditions first decreases and then increases, but the overall maximum temperature rise does not exceed 20°C, which is lower than the maximum charging temperature rise of 24.4°C of the blank control; among them, when the nano-copper powder content is 45%, the minimum temperature rise inside the battery cell is 17.5°C. This is mainly because the nano-copper powder content directly affects the quality of CNTs generated by the vapor deposition method. Since CNTs need to rely on copper as active sites for growth, a low nano-copper powder content will result in a low amount of CNTs generated and cannot achieve a high thermal conductivity effect; when the nano-copper powder content is high, the CNTs cannot grow in a directional arrangement, and curling and entanglement will occur, which in turn leads to a longer heat dissipation path and cannot achieve a high thermal conductivity effect.

[0121] Comparing the test results of Examples 7-9 and Comparative Examples 1-2 reveals that, under the same charging conditions, the temperature rise at the center of the battery cell first decreases and then increases when the coating thickness of the thermally conductive layer in the composite tape varies from 0.2mm to 0.35mm. However, the overall maximum temperature rise in Examples 7-9 does not exceed 20°C, while the overall maximum temperature rise in Comparative Examples 1 and 2 is above 20°C. This is primarily because when the coating thickness is small, the CNT distribution is less dense and the total amount is low, resulting in insufficient heat dissipation in the battery cell. When the coating thickness is large, the diamonds are overly densely packed, and the heat diffusion path through the thermally conductive layer is increased, resulting in lower overall heat dissipation.

[0122] In summary, the composite tape of the present invention, with a controlled copper-to-diamond mass ratio of 0.5 to 2:1 in the thermally conductive layer and a thickness of no less than 0.25 mm, effectively conducts and dissipates heat from the battery cells when used in lithium-ion batteries. In particular, when the thermally conductive layer's formula ratio is 10% PVDF: diamond nanopowder: nano-copper powder (by mass): 45%: 45%, and the thermally conductive layer coating has a thickness of 0.25 mm, optimal thermal conductivity is achieved when used in lithium-ion batteries, significantly reducing temperature buildup within the battery cells during fast charging.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite tape, characterized in that: The invention comprises a heat-conducting layer and a base layer connected by an adhesive layer, wherein the heat-conducting material in the heat-conducting layer is copper-diamond composite material powder and a carbon nanotube array vapor-deposited thereon.

2. The composite tape according to claim 1, wherein: In the copper-diamond composite material powder, the mass ratio of copper to diamond is 0.5 to 2:1; And / or, in the thermally conductive material, the mass fraction of carbon nanotubes is 2-5%; And / or, the heat conductive layer further contains a bonding dispersant.

3. The composite tape according to claim 2, wherein: The bonding dispersant is polyvinylidene fluoride; and / or the mass ratio of the bonding dispersant to the copper-diamond composite material powder is 1:8-10.

4. The composite tape according to claim 1, wherein: The thickness of the adhesive layer is 0.02 to 0.07 mm and is formed by drying the polyurethane glue; and / or, the thickness of the heat-conducting layer is not less than 0.25 mm; And / or, the base layer has a thickness of 0.05 to 0.15 mm and is selected from release paper.

5. The composite tape according to claim 1, wherein: The preparation of the thermal conductive material comprises the following steps: S1, adding diamond nanopowder and nano-copper powder in a certain mass ratio, ball milling, stirring and dispersing, and hot pressing to obtain a copper-diamond composite material; S2. The powder of the prepared copper-diamond composite material is heated in a reducing gas atmosphere, and then a gas for vapor-depositing carbon nanotubes is introduced to vapor-deposit carbon nanotubes to obtain a thermal conductive material.

6. The composite tape according to claim 5, wherein: The particle size of the diamond nanopowder is 200-500 nm, and the particle size of the nano-copper powder is 50-100 nm; And / or, the hot pressing time is 30±10 min, the temperature is 800±10° C., and the pressure is 10±1 MPa; and / or, the reducing gas is H2; And / or, the heating rate is controlled at 5±1°C / s; And / or, the gas used for vapor deposition of carbon nanotubes is C2H2, and the C2H2 flow rate is 20±5 sccm; And / or, the temperature of the vapor deposition is 800±50° C. and the time is 8±1 h.

7. A method for preparing the composite tape according to any one of claims 1 to 6, characterized in that: include: The glue for forming the bonding layer is coated on the base layer, and after drying, the slurry of the heat-conducting layer is coated on the bonding layer, and after drying, the composite tape is obtained.

8. The preparation method according to claim 7, wherein: The preparation of the slurry includes: adding the powder of the thermal conductive material and the adhesive dispersant, stirring and dispersing them, and then adding a certain amount of solvent and mixing them evenly to obtain the slurry.

9. The preparation method according to claim 8, wherein: The stirring and dispersing process was performed at a speed of 5±1 rpm and a time of 30±5 min; and / or, the solvent is N-methylpyrrolidone; And / or, the mixing speed is 12±1 rpm and the mixing time is 2±1 h.

10. A lithium-ion battery, characterized in that: The invention comprises the composite tape according to any one of claims 1 to 6, or the composite tape prepared by the preparation method according to any one of claims 7 to 9, wherein the composite tape is located between the shell and the battery cell.

Images