Composite high-thermal-conductivity film, battery cell packaging structure and lithium ion battery
By adding a composite high thermal conductivity film in the middle of the battery cell, the high thermal conductivity of graphene solves the problem of heat accumulation inside fast-charging batteries, improves the cycle performance and temperature uniformity of the battery cell, and reduces the cost of cooling equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-20
- Publication Date
- 2026-04-07
AI Technical Summary
During the charging process, fast-charging batteries accumulate significant heat inside the cells, resulting in large temperature gradients that affect the long-term cycle performance of the cells. Existing technologies address this by adjusting the cell size, but this leads to a decrease in energy density and issues with process consistency.
A composite high thermal conductivity film is added in the middle of the battery cell core, including a graphene layer sandwiched between the first and second polyimide films. The high thermal conductivity of graphene is used to quickly conduct heat and reduce the temperature at the center of the battery cell.
It improves the fast-charging cycle performance of the battery cells, reduces temperature differences, saves on cooling equipment costs, and has a simple structure and low cost.
Smart Images
Figure CN224096750U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of new energy battery technology, specifically relating to a composite high thermal conductivity film, a cell packaging structure, and a lithium-ion battery. Background Technology
[0002] With the booming development of the new energy market, the demand for fast charging capabilities of power batteries is increasing. From the initial 1-1.5C fast charging to the currently prevalent 2-3C fast charging batteries, and even the latest CATL Kirin batteries with 4C charging capabilities, fast charging batteries need to withstand a large current during charging. Unlike the low charging rate requirements of traditional energy storage cells, this leads to severe heat generation during the overall charging process. High heat generation in the short term results in a significant temperature gradient inside the cell, with the center temperature potentially exceeding 50°C, which seriously affects the long-term cycle performance. Against this backdrop, how to quickly dissipate heat from inside the cell to the outside has become a key focus for fast charging cells. Currently, the thermal management strategies for fast / supercharged batteries in various research projects are mainly based on adjusting the cell size (using thinner, wider cells) to reduce internal heat accumulation and ensure long-term cycle performance. However, this approach suffers from two drawbacks: firstly, reduced casing thickness leads to a decrease in cell energy density; secondly, wider cells (similar to blade batteries) cause process inconsistencies.
[0003] In view of the above, this utility model is hereby proposed. Utility Model Content
[0004] To address the shortcomings and defects of existing technologies, this utility model aims to provide a composite high thermal conductivity film, a cell packaging structure, and a lithium-ion battery. By placing the designed composite high thermal conductivity film (composite high thermal conductivity insulating film) in the middle of the cell package, the heat dissipation area and thermal conductivity at the center of the cell are increased, thereby reducing the problem of excessively rapid temperature rise at the center of the cell under high-current fast charging.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] In a first aspect, the present invention provides a composite high thermal conductivity film, comprising a first polyimide film and a second polyimide film, wherein a graphene layer is sandwiched between the first polyimide film and the second polyimide film.
[0007] Furthermore, the first polyimide film and the second polyimide film have the same thickness.
[0008] Furthermore, the thickness of the first polyimide film and the second polyimide film is 0.01~0.1mm.
[0009] Furthermore, the thickness of the graphene layer is 0.01~0.2 mm.
[0010] Secondly, this utility model provides a battery cell packaging structure, including a composite high thermal conductivity film disposed between any two core packages in the battery cell, wherein the composite high thermal conductivity film includes a first polyimide film and a second polyimide film, and a graphene layer is sandwiched between the first polyimide film and the second polyimide film.
[0011] Furthermore, the first polyimide film and the second polyimide film have the same thickness.
[0012] Furthermore, the thickness of the first polyimide film and the second polyimide film is 0.01~0.1mm.
[0013] Furthermore, the thickness of the graphene layer is 0.01~0.2 mm.
[0014] Furthermore, the core package is a wound core or a stacked core;
[0015] And / or, the core package and the composite high thermal conductivity film are externally covered by a shell.
[0016] Thirdly, this utility model provides a lithium-ion battery, which includes the composite high thermal conductivity film described in the first aspect or the cell packaging structure described in the second aspect.
[0017] This invention designs and synthesizes a composite high thermal conductivity thin film and incorporates it into the center of the battery cell core. Utilizing its high thermal conductivity, it improves the heat dissipation problem at the core, thereby significantly reducing the risk of fast-charging cycle failure and enhancing the cell's cycle performance. Compared with existing technologies, it has the following advantages:
[0018] 1. It facilitates heat dissipation after heat generation inside the battery cell (especially fast charging cells), reduces the temperature difference inside the battery cell, and improves the long-term cycle performance of the battery cell;
[0019] 2. Saves on the overall cost of the battery pack. Because individual battery cells dissipate heat faster and more evenly, it can save on the operating costs of group cooling equipment.
[0020] 3. The structure is simple, highly feasible, has little impact on the internal design of the battery cell, and is inexpensive. Attached Figure Description
[0021] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0022] Figure 1 This is a schematic diagram of a composite high thermal conductivity film structure according to the present invention;
[0023] Figure 2 This is a schematic diagram of the structure of a composite high thermal conductivity film in a battery cell according to the present invention;
[0024] Figure 3 The above are SOC-temperature curves at the center of the 4C-level charging cell at an average temperature of 25°C for both the example and comparative examples.
[0025] Figure 4 The graph shows the capacity retention rate of the cells at 25°C during 4C-stage charge / 1C cycles for both the example and comparative models.
[0026] Icons: 1-First polyimide film; 2-Second polyimide film; 3-Graphene layer; 4-Core package; 5-Shell. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this utility model clearer, the following description, in conjunction with embodiments, further illustrates this utility model. The embodiments of this utility model are implemented based on the technical solutions of this utility model, providing detailed implementation methods and processes. Those skilled in the art should understand that the embodiments are merely illustrative and should not be considered as specific limitations on this utility model. Furthermore, the scope of protection of this utility model is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.
[0028] In the description of this utility model, the terms "opposite," "vertical," "upper," "lower," and "parallel," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this utility model and do not require that this utility model be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. The terms "connected," "linked," and "set up" used in this utility model should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components; they can refer to a wired electrical connection, a radio connection, or a wireless communication signal connection. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.
[0029] Process parameters not specifically specified in the embodiments of this utility model are generally performed under conventional conditions. Unless otherwise specified and / or stated, all numerical values involving component amounts are "weight or mass values or ratios" throughout. Unless otherwise stated, all raw materials used in this utility model are available from commercially available products.
[0030] In this invention, the endpoints of the disclosed ranges and any values 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 endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.
[0031] This invention addresses the issue of heat dissipation within the battery cell by adding a thin, highly thermally conductive film to the cell, thereby improving central heat dissipation and enhancing fast charging performance. Specifically, in a first aspect, this invention provides a composite highly thermally conductive film comprising a first polyimide film and a second polyimide film, wherein a graphene layer is sandwiched between the first and second polyimide films.
[0032] The composite high thermal conductivity film of this invention includes a polyimide film that mainly serves as structural support and provides insulation and corrosion protection; and a graphene layer that utilizes the high thermal conductivity of graphene to quickly transfer heat from the core to the outside, thereby reducing the core temperature.
[0033] In this invention, the composition and preparation method of the polyimide film and graphene layer are existing technologies. The technical effect of this application is mainly achieved through a structural design of two polyimide films sandwiching a graphene layer between them, rather than an improvement on the materials themselves. Specifically, the polyimide film and graphene layer are bonded together using existing technologies such as adhesives. The adhesive can be in the form of an adhesive layer, adhesive dots, adhesive lines, etc., to bond the polyimide film and graphene layer. The thickness of the composite high thermal conductivity film occupied by the adhesive or other substances that bond the polyimide film and graphene layer is negligible. Commonly used adhesives for PI films include latex glue, epoxy resin glue, or polyurethane glue, with environmentally friendly polyurethane glue being preferred.
[0034] As an optional embodiment of the composite high thermal conductivity film of this utility model, the thickness of the first polyimide film and the second polyimide film are equal, and / or the thickness of the first polyimide film and the second polyimide film is 0.01~0.1mm.
[0035] In the above technical solution, the thickness of the polyimide film monolayer is typically, but not limited to, 0.02mm, 0.03mm, 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, or 0.09mm, which provides excellent structural support. The first and second polyimide films on both sides of the graphene layer have equal thickness because, generally, the core packages in a multi-core battery cell have identical design properties, thus the core packages separating them on both sides are identical.
[0036] As an optional embodiment of the composite high thermal conductivity film of this utility model, the thickness of the graphene layer is 0.01~0.2mm.
[0037] The composite high thermal conductivity film is located at the center of the battery cell core. The thickness of the graphene layer is typically, but not limited to, 0.02 mm, 0.04 mm, 0.06 mm, 0.08 mm, 0.10 mm, 0.12 mm, 0.14 mm, 0.16 mm, and 0.18 mm. By limiting the thickness of each layer of the composite high thermal conductivity film, the total thickness of the composite high thermal conductivity film is controlled within a certain range, giving it good thermal conductivity while also ensuring safety and stability.
[0038] In a second aspect, a battery cell packaging structure includes a composite high thermal conductivity film disposed between any two core packages in the battery cell, wherein the composite high thermal conductivity film includes a first polyimide film and a second polyimide film, and a graphene layer is sandwiched between the first polyimide film and the second polyimide film, that is, the composite high thermal conductivity film is the composite high thermal conductivity film described in the first aspect.
[0039] Compared to traditional thermally conductive designs, this novel battery cell packaging structure addresses the heat accumulation problem caused by high heat generation and slow heat dissipation at the center of two adjacent core packages by adding a composite high thermal conductivity film. Simultaneously, the thinner film minimizes internal space loss. Furthermore, the composite high thermal conductivity film, located at the center of the core package, has a simple structure and does not affect the overall battery cell design. Moreover, the film is inexpensive and does not significantly impact the battery cell cost. Preferably, the polyimide film, primarily serving structural support and insulation / corrosion protection, has a thickness of 0.01~0.1mm, and the graphene layer has a thickness of 0.01~0.2mm. The high thermal conductivity of graphene is utilized to rapidly transfer heat from the core package center to the outside, thereby reducing the center temperature. By limiting the thickness of each layer of the composite high thermal conductivity film, the total thickness is controlled within a certain range, ensuring good thermal conductivity while maintaining safety and stability.
[0040] In this invention, the core package is the smallest constituent unit inside the battery cell, as illustrated in the diagram. Figure 2 The image shows a wound dual-cell battery. Furthermore, the composite high thermal conductivity film in this patent is primarily intended for the current mainstream multi-cell battery system, as it is impossible to add an additional thermally conductive film to a single-cell battery.
[0041] As an optional embodiment of the battery cell packaging structure of this utility model, the core package is a wound core or a stacked core.
[0042] As an optional embodiment of the battery cell packaging structure of this utility model, the core package and the composite high thermal conductivity film are covered by a shell. Further, the shell can be an aluminum shell, an iron shell, a plastic shell, a steel shell, or an aluminum-plastic film, etc.
[0043] Thirdly, a lithium-ion battery includes the composite high thermal conductivity film described in the first aspect or the cell packaging structure described in the second aspect.
[0044] This novel lithium-ion battery, due to its composite high thermal conductivity film, can significantly reduce the risk of cell failure during fast charging cycles and improve cell cycle performance.
[0045] The present invention will now be described in further detail with reference to specific embodiments.
[0046] Example
[0047] A composite high thermal conductivity film, such as Figure 1As shown, it includes a first polyimide film 1 and a second polyimide film 2, with a graphene layer 3 sandwiched between the first polyimide film 1 and the second polyimide film 2. Specifically, an adhesive (polyurethane glue) is applied to the maximum specific surface area of the graphene layer 3, and then the first polyimide film 1 and the second polyimide film 2 are pressed onto both sides of the graphene layer 3, and the graphene layer 3 is sandwiched between the first polyimide film 1 and the second polyimide film 2 by the adhesive.
[0048] Specifically, the first polyimide film 1 and the second polyimide film 2 have the same thickness, which is 0.05 mm. The graphene layer 3 has a thickness of 0.01 mm.
[0049] Applications and Test Cases
[0050] The positive and negative electrode active materials are processed through homogenization, coating, rolling, die-cutting, slitting, and winding to produce cores of specified dimensions (single core thickness 24mm, width 190mm, height 103mm). The positive electrode material (lithium iron phosphate), binder (polyvinylidene fluoride PVDF), and conductive agent (Super P) are combined at a ratio of 97wt%:2wt%:1wt%, coated onto a 13μm thick aluminum foil, with a single-sided areal density of 200 g / cm³. 3 The negative electrode material is composed of artificial graphite, conductive agent Super P, dispersant CMC, and binder SBR, with a composition of 95wt%:1.5wt%:1.5wt%:2.0wt%, coated on a 5 μm thick copper foil. The surface density on one side is 93 g / cm³. 3 .
[0051] Next, two identical winding cores were inserted into a cell housing with a double-winding core structure. Simultaneously, a temperature-sensing wire was embedded in the center of the large contact surface between the two cores to detect the temperature at the center of the battery. The embedded wire positions were consistent between the comparative example (sample 1) and the embodiment (sample 2). For example, in sample 2... Figure 2 As shown, the difference between it and sample 1 is that a composite high thermal conductivity film is first added between the two cores before the wire is buried, and the temperature at the center of the battery is also detected.
[0052] Subsequently, aluminum-cased cells with a dual-cell structure are prepared through processes such as encapsulation, liquid injection, and formation. Three cycles are performed under a high-rate charging condition of 25℃ and 4C SC / 1C. The temperature change of the sensing wire embedded at the center of the cell pack during the third charging cycle is monitored. Here, SC is an abbreviation for Step charge, referring to stepped charging. The fast-charging range specified in this patent is 10%-80% SOC. Stepped fast charging refers to achieving an average 4C charge (10-80% SOC charging time ≤ 10.5 min) by adjusting the charging current corresponding to different SOCs within the 10%-80% SOC fast-charging range. Specifically, the aluminum-cased cells prepared above are subjected to fast-charging temperature rise testing according to the following method:
[0053] The battery cell is discharged to 2.5V at 0.33C.
[0054] After resting for 30 minutes, charge the battery to 10% SOC using a 1C current, then charge the cell to 80% SOC using an average 4C step charging method (maximum current 700A), and finally charge to 3.65V using a 1C constant current method, and then charge to 0.05C using a 3.65V constant voltage method to bring the battery to 100% SOC.
[0055] Let it stand for 1.5 hours, then discharge the battery with a 1C current to 2.5V, reaching 0% SOC;
[0056] Steps 2)-4) are repeated twice, and the temperature of the sensing wire at the center of the core pack is recorded using a multi-channel tester during the third charging cycle.
[0057] The test results are shown in the table below. Figure 3 As shown:
[0058]
[0059] By comparing the charging temperatures at the center of the battery cells of Sample 1 and Sample 2 under the same conditions, it can be seen that the highest temperature at the center of the battery cell in Sample 1 without the composite high thermal conductivity film reached 53.8℃ during charging, with a maximum temperature rise of 24.5℃. In contrast, the highest temperature at the center of the battery cell in Sample 2 with the composite high thermal conductivity film was reduced to 46.6℃, with a maximum temperature rise of only 17.6℃. The highest temperature decreased by 7.2℃, and the temperature rise decreased by 6.9℃. The experiment demonstrates that the composite high thermal conductivity film of this invention can significantly reduce the temperature at the center of the battery pack.
[0060] The aluminum-cased battery cells prepared above were subjected to fast-charging cycle tests according to the following method:
[0061] The battery cell is discharged to 2.5V at 0.33C.
[0062] After resting for 30 minutes, charge the battery to 10% SOC using a 1C current, then charge the cell to 80% SOC using an average 4C step charging method (maximum current 700A), and finally charge to 3.65V using a 1C constant current method, and then charge to 0.05C using a 3.65V constant voltage method to bring the battery to 100% SOC.
[0063] Let it stand for 1.5 hours, then discharge the battery with a 1C current to 2.5V, reaching 0% SOC;
[0064] Steps 2)-4) are repeated 2500 times, and the discharge capacity of each charge test is recorded. When the battery capacity is less than 80% of the discharge capacity of the first cycle, the battery is considered to be in failure and the test ends.
[0065] Specific test results are as follows: Figure 4 And as shown in the table below:
[0066]
[0067] Comparing the 4C stage charge / 1C fast charge cycles of Sample 1 and Sample 2, it can be seen that Sample 1, without the composite high thermal conductivity film, has a capacity retention rate of 87.8% after 910 cycles, and is predicted to have approximately 1600 cycles at 80% EOL. In contrast, Sample 2, with the composite high thermal conductivity film, has a capacity retention rate of 93.5% after 910 cycles, and is predicted to have approximately 2900 cycles at 80% EOL. It is evident that the addition of the composite high thermal conductivity film significantly improves the cell's cycle life. This is because the cell has better internal heat dissipation, more uniform temperature, and fewer SEI damage and side reactions during cycling.
[0068] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model shall be within the scope of protection of the pending claims of the present utility model.
Claims
1. A composite high thermal conductivity film, characterized in that, It includes a first polyimide film (1) and a second polyimide film (2), with a graphene layer (3) sandwiched between the first polyimide film (1) and the second polyimide film (2); an adhesive is applied to the maximum specific surface area of the graphene layer (3), and the graphene layer (3) is sandwiched between the first polyimide film (1) and the second polyimide film (2) by the adhesive; The first polyimide film (1) and the second polyimide film (2) have the same thickness; The thickness of the first polyimide film (1) and the second polyimide film (2) is 0.01~0.05mm; The thickness of the graphene layer (3) is 0.01 mm.
2. A battery cell packaging structure, characterized in that, The method includes a composite high thermal conductivity film disposed between any two core packages (4) in the battery cell, wherein the composite high thermal conductivity film comprises a first polyimide film (1) and a second polyimide film (2), and a graphene layer (3) is sandwiched between the first polyimide film (1) and the second polyimide film (2); an adhesive is applied to the maximum specific surface area of the graphene layer (3), and the graphene layer (3) is sandwiched between the first polyimide film (1) and the second polyimide film (2) by the adhesive; The first polyimide film (1) and the second polyimide film (2) have the same thickness; The thickness of the first polyimide film (1) and the second polyimide film (2) is 0.01~0.05mm; The thickness of the graphene layer (3) is 0.01 mm.
3. The cell packaging structure as described in claim 2, characterized in that, The core package (4) is a wound core or a stacked core; And / or, the core package (4) and the composite high thermal conductivity film are externally covered by a shell (5).
4. A lithium-ion battery, characterized in that, The lithium-ion battery includes the composite high thermal conductivity film of claim 1 or the cell packaging structure of any one of claims 2-3.