Heat conduction structure, preparation method thereof and battery system comprising heat conduction structure

Abstract

The invention relates to a heat conduction structure, a preparation method thereof and a battery system comprising the heat conduction structure, the heat conduction structure comprises a composite heat conduction layer and an outer cladding, and the heat conduction coefficient of the composite heat conduction layer is positively correlated with the temperature; the composite heat conduction layer is wrapped by the outer wrapping layer, and due to the fact that the heat conductivity coefficient of the composite heat conduction layer is in positive correlation with the temperature, when the temperature of the surrounding environment is increased, the heat conductivity coefficient of the composite heat conduction layer is increased; when the heat conduction structure is applied to a battery system, a large temperature difference exists among a plurality of battery monomers in a battery module, so that the heat conduction structure can be attached to a position between the battery module and a heat dissipation structure, and the part, close to the battery monomers with higher temperature, of the heat conduction structure is high in heat conduction coefficient and higher in heat exchange efficiency; therefore, the temperature difference among the plurality of battery monomers is effectively balanced, and the cycle life and the safety of the battery system are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of battery heat dissipation technology, and more particularly to a heat-conducting structure and its preparation method, and a battery system comprising the same. Background Technology

[0002] Most existing battery systems employ thermal management devices to control battery temperature. Battery thermal management is a core technology for ensuring its safety, performance, and lifespan. It is far more than just "heat dissipation"; its core objective is to maintain the battery temperature within an optimal range and ensure temperature uniformity within the battery pack.

[0003] Currently, batteries can be cooled using methods such as air cooling and liquid cooling. However, within a battery module, there are temperature differences between different individual battery cells, and neither air-cooled nor liquid-cooled thermal management devices can effectively balance these temperature differences. Summary of the Invention

[0004] In view of this, it is necessary to provide a thermally conductive structure and its preparation method, and a battery system including the same, to solve the problem that it is impossible to effectively balance the temperature difference between multiple battery cells in a battery module in a battery system.

[0005] In a first aspect, embodiments of the present invention provide a thermally conductive structure, including a composite thermally conductive layer and an outer cladding layer, wherein the thermal conductivity of the composite thermally conductive layer is positively correlated with temperature; and the outer cladding layer is disposed to enclose the composite thermally conductive layer.

[0006] Furthermore, the composite thermally conductive layer includes paraffin wax and multiple thermally conductive filler particles. The paraffin wax has solid, semi-solid, and liquid states depending on the temperature. The multiple thermally conductive filler particles are embedded in the paraffin wax, and a thermally conductive network is formed between the multiple thermally conductive filler particles. When the paraffin wax is solid, the thermally conductive network is disconnected; when the paraffin wax is semi-solid, the thermally conductive network is partially connected; and when the paraffin wax is liquid, the thermally conductive network is fully connected.

[0007] Furthermore, the paraffin wax includes low-melting-point paraffin wax and high-melting-point paraffin wax.

[0008] Furthermore, the thermally conductive filler particles are sheet-like graphene particles and / or filamentous carbon fiber particles.

[0009] Furthermore, the outer layer includes a PET film, which encapsulates the composite thermally conductive layer.

[0010] Furthermore, the outer layer also includes a thermally conductive silicone layer, which fills the space between the PET film and the composite thermally conductive layer.

[0011] In a second aspect, embodiments of the present invention also provide a method for preparing a thermally conductive structure, which is used to prepare the thermally conductive structure as described above, comprising the following steps: preparing a composite thermally conductive layer and encapsulating the composite thermally conductive layer with an outer cladding layer.

[0012] Furthermore, the method for preparing the composite thermally conductive layer is as follows: Paraffin solution is prepared by melting paraffin wax; Graphene particles, carbon fiber particles, glass fiber particles and ethyl acetate were added to a mixing tank, stirred and ultrasonically dispersed to obtain a filler dispersion. A filler dispersion was added to the epoxy resin and stirred to obtain a premix; Pour the paraffin solution into the premixed liquid, heat and stir to form a slurry, coat the slurry onto the template, and after cooling, form a composite thermally conductive layer.

[0013] In a third aspect, embodiments of the present invention also provide a battery system, including the heat-conducting structure as described above, and further including a housing and a battery module, wherein the battery module is fixedly disposed on the inner bottom wall of the housing, and the composite heat-conducting layer is disposed in the gap between the housing and the battery module.

[0014] Furthermore, a flow channel is formed at the bottom of the outer shell, the flow channel is positioned directly opposite the composite heat-conducting layer, and the side wall of the outer shell is provided with an inlet and an outlet respectively connecting the two ends of the flow channel.

[0015] Compared with existing technologies, the thermal conductivity of the composite thermal conductive layer is positively correlated with temperature. Therefore, its thermal conductivity increases as the ambient temperature rises. When applied to battery systems, there are situations where there are large temperature differences between multiple battery cells in a battery module. To address this, the thermal conductive structure can be attached between the battery module and the heat dissipation structure. The part of the thermal conductive structure closer to the hotter battery cells has a higher thermal conductivity and higher heat exchange efficiency, thereby effectively balancing the temperature differences between multiple battery cells and greatly improving the cycle life and safety of the battery system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the heat-conducting structure provided in the embodiment of the present invention; Figure 2 An exploded view of the battery system provided in an embodiment of the present invention; Figure 3 for Figure 2 A schematic diagram of liquid flow within the central channel; Figure 4 for Figure 2 A schematic diagram of the overall assembly. Detailed Implementation

[0017] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0018] like Figure 1 As shown, in a first aspect, embodiments of the present invention provide a thermally conductive structure, including a composite thermally conductive layer 110 and an outer cladding layer 120, wherein the thermal conductivity of the composite thermally conductive layer 110 is positively correlated with temperature; and the outer cladding layer 120 is disposed to enclose the composite thermally conductive layer 110.

[0019] Since the thermal conductivity of the composite thermal conductive layer 110 is positively correlated with temperature, its thermal conductivity increases as the ambient temperature rises. When applied to a battery system, there is a large temperature difference between multiple battery cells in the battery module 300. Therefore, the thermal conductive structure 100 can be attached to the position between the battery module 300 and the heat dissipation structure. The part of the thermal conductive structure 100 closer to the battery cell with a higher temperature has a higher thermal conductivity and a higher heat exchange efficiency, thereby effectively balancing the temperature difference between multiple battery cells and greatly improving the cycle life and safety of the battery system.

[0020] The composite thermally conductive layer 110 in this embodiment includes paraffin wax and multiple thermally conductive filler particles. The paraffin wax has solid, semi-solid, and liquid states depending on the temperature. The multiple thermally conductive filler particles are embedded in the paraffin wax, and a thermally conductive network is formed between the multiple thermally conductive filler particles. When the paraffin wax is solid, the thermally conductive network is disconnected; when the paraffin wax is semi-solid, the thermally conductive network is partially connected; and when the paraffin wax is liquid, the thermally conductive network is completely connected.

[0021] In one embodiment, the paraffin wax includes low-melting-point paraffin wax and high-melting-point paraffin wax.

[0022] In one embodiment, the thermally conductive filler particles are sheet-like graphene particles and / or filamentous carbon fiber particles.

[0023] The composite thermally conductive layer 110 is made of a composite ratio of paraffin wax, graphene, and carbon fiber. Its thermal conductivity increases gradually with temperature from 25℃ to 30℃ to 35℃. The core principle is "gradual change in the state of the paraffin wax matrix + gradual opening of the thermally conductive network of the thermally conductive filler". The two work together to achieve a smooth improvement in thermal conductivity, rather than an abrupt change. The following is a breakdown of the principle in stages.

[0024] It is understandable that the essence of thermal conduction is "heat transfer through molecular / particle collisions," and the thermal conductivity of the composite thermally conductive layer 110 is determined by two key factors: 1. Thermal conductivity of the matrix: The thermal conductivity of paraffin (0.2~0.3W / (m·K)) is much lower than that of thermally conductive fillers (graphene ~500W / (m·K), carbon fiber ~150W / (m·K)). However, the state of paraffin (solid, semi-solid, liquid) will affect the contact efficiency of the filler. 2. Connectivity of the thermally conductive network: The thermally conductive filler (graphene + carbon fiber) needs to form a continuous thermally conductive network to allow heat to be transferred quickly (discrete fillers can only conduct heat "locally", while continuous networks can achieve "through" heat conduction).

[0025] This composite thermally conductive layer 110 achieves a gradual increase in thermal conductivity by transforming the filler from a "discrete and dispersed" structure to a "continuous network" through "wide-temperature-range softening of compounded paraffin".

[0026] To ensure that the composite thermally conductive layer 110 maintains a certain shape during the process of state change, in one embodiment, the outer layer 120 includes a PET film 121, which wraps around the composite thermally conductive layer 110.

[0027] To improve heat conduction efficiency, in this embodiment, the outer layer 120 further includes a thermally conductive silicone layer 122, which is filled between the PET film 121 and the composite thermally conductive layer 110.

[0028] Example 1: Low temperature range (≤25℃, solid paraffin): thermal conductivity ≈2W / (m·K) (low and stable). Paraffin wax state: Both low-melting-point paraffin wax (28℃) and high-melting-point paraffin wax (33℃) are solid. The paraffin wax matrix has high hardness (Shore D40~50) and dense structure. Filler state: Graphene particles (sheet-like) and carbon fiber particles (filament-like) are dispersed in the paraffin matrix, and can only make local contact, and cannot form a continuous heat conduction path; Heat conduction path: Heat is mainly transferred through "paraffin matrix + local filler contact transfer". However, paraffin itself has poor thermal conductivity and the thermal network formed by the thermally conductive filler is not connected, resulting in low overall thermal conductivity and a thermal conductivity coefficient that is stable at around 2W / (m·K).

[0029] Example 2: Medium temperature range (25~30℃, initial stage of semi-solid paraffin): thermal conductivity increases to ≈5W / (m·K) (rapid increase); Paraffin wax state: Low melting point paraffin wax (28℃) first softens (from solid to semi-solid), expands slightly in volume (expansion rate ≈ 1.5%), decreases matrix hardness (Shore A 30~40), and increases fluidity; Filler state: The softened paraffin no longer "fixes" the filler, but acts as a "carrier" to allow graphene and carbon fibers to undergo slight displacement, that is, the sheet-like graphene overlaps with each other, and the filamentous carbon fibers are interwoven to form a "local continuous network" (similar to "preliminary interweaving of branches"). Heat conduction path: Heat is mainly transferred through "local filler network + paraffin matrix auxiliary transfer". The connectivity ratio of the filler network is increased from ≤30% to ≈60%, the heat conduction efficiency is greatly improved, and the thermal conductivity is increased to 5W / (m·K).

[0030] Example 3: Medium-high temperature range (30~35℃, late stage of paraffin semi-solid): thermal conductivity increases to ≈8W / (m·K) (gradually ending). Paraffin wax state: High melting point paraffin wax (33℃) begins to soften partially, and the overall paraffin wax becomes "mainly semi-solid with local semi-liquid state", and the volume further expands (total expansion rate ≈3%). The matrix hardness drops to Shore A20~30, and the fluidity is better. Filler condition: The full softening of paraffin allows the filler to overlap completely—graphene sheets form a "planar interconnected layer," and carbon fiber filaments interweave between the layers to form a "three-dimensional continuous thermally conductive network" (similar to "tree branches completely interwoven into a net"), with a connectivity ratio ≥90%; Heat conduction path: Heat is transferred through the "through-filling network" (accounting for more than 90% of the total heat conduction). Paraffin only serves as a "filling medium" to eliminate air in the gaps between the fillers (air has a thermal conductivity of only 0.023 W / (m·K), which would greatly increase thermal resistance). The overall thermal conductivity efficiency is close to the thermal conductivity level of the filler itself, and the thermal conductivity rises to 8 W / (m·K).

[0031] Example 4: High temperature range (≥35℃, semi-liquid paraffin): thermal conductivity stabilizes at 8~8.5W / (m·K) (tends to level off); Paraffin wax state: Low melting point paraffin wax is completely softened, high melting point paraffin wax is partially softened, the whole is semi-liquid, the volume is stable, and the matrix hardness remains Shore A20~30; Packing condition: The three-dimensional heat-conducting network has been fully formed, the contact area between the packings has reached its maximum value, the network connectivity ratio is ≈95%, and it no longer changes significantly with the increase of temperature; Heat conduction path: Heat transfer depends entirely on the filler network. The state changes of paraffin have a negligible effect on heat conduction. Therefore, the thermal conductivity tends to be stable, only slightly increasing to 8~8.5 W / (m·K) due to the decrease in paraffin viscosity.

[0032] In a second aspect, embodiments of the present invention also provide a method for preparing a thermally conductive structure 100, which is used to prepare the thermally conductive structure 100 as described above, comprising the following steps: preparing a composite thermally conductive layer 110, and having an outer cladding layer 120 encapsulate the composite thermally conductive layer 110.

[0033] The method for preparing the composite thermally conductive layer 110 is as follows: Paraffin solution is prepared by melting paraffin wax; Graphene particles, carbon fiber particles, glass fiber particles and ethyl acetate were added to a mixing tank, stirred and ultrasonically dispersed to obtain a filler dispersion. A filler dispersion was added to the epoxy resin and stirred to obtain a premix; The paraffin solution is poured into the premixed liquid, heated and stirred to form a slurry. The slurry is then coated onto the template and cooled to form a composite thermally conductive layer 110.

[0034] Example: Taking a thermally conductive structure 100 with dimensions of 640×150×1mm as an example; Step S1: Raw material pretreatment (adapted to thin coating dispersion requirements).

[0035] Step S11, Paraffin compounding and melting: 60.5g of low-melting-point paraffin and 40.7g of high-melting-point paraffin are heated and stirred in a 60L stirred tank at a heating temperature of 65℃ and a stirring speed of 600r / min for 40min. Then, 2.2g of polyetheramine is added and stirring is continued for 15min (the uniformity of paraffin is less important for thin coatings, so the stirring time is shortened) to obtain a paraffin solution.

[0036] Step S12, Filler dispersion: 9.9g graphene + 6.6g chopped carbon fiber + 2.2g chopped glass fiber, add 22g ethyl acetate, stir at high speed (1200r / min) for 25min, and ultrasonically disperse for 45min (to reduce the risk of agglomeration of the thin coating, shorten the ultrasonic time) to obtain the filler dispersion.

[0037] Step S13, binder dissolution: Add filler dispersion to 7.7g of epoxy resin and stir at 900r / min for 25min (the binder is reduced and dissolution is faster) to obtain a premixed solution.

[0038] Step S2: Preparation of coating slurry; Pour the paraffin melt (103.4g) into (48.4g of premixed liquid), heat to 65℃, and stir at 700r / min for 50min to obtain the slurry (wherein, the viscosity of the thin coating slurry is controlled at 800~1000mPa·s, which is lower than that of the thick coating).

[0039] Step S3: Large-size single-layer coating; Step S31, Substrate preparation: Vacuum adsorption fixation of the lower PET film 121 to prevent displacement; Step S32, Single-layer coating: 500μm blade gap (directly matches 0.5mm thickness, no layering required), coating speed 25mm / s (faster than the 0.7mm solution, thin coating is easy to uniform), precise control of coating area 640mm×150mm (excluding edge sealing); Step S33, Curing process: ① Low temperature solvent removal: 40℃ for 60 min (thin coating has less solvent, shortening the removal time); ② Medium temperature crosslinking: 60℃ for 60 min (thin coating crosslinks faster); ③ Room temperature curing: 25℃ for 18 h (shorter than thick coating, avoiding over-curing and embrittlement); final intermediate layer thickness 500 μm (error ±5 μm).

[0040] Step S4: Apply thermally conductive silicone transition layer (maintaining the advantages of a thick silicone layer). Step S41, Coating parameters: Use a large-size micro-coating machine, coating thickness 200μm, speed 20mm / s (thin intermediate layer does not affect silicone coating); Step S42, Drying time: Dry at 30℃ for 25 minutes (the thickness of the silicone layer remains unchanged, and the drying time is slightly shorter than that of the thick intermediate layer solution).

[0041] Step S5: Composite packaging (adapting the thermo-pressing parameters of the thin intermediate layer). Step S51, Layer Alignment: Same as the previous scheme, align the upper PET film 121 + middle layer (with silicone) + lower PET film 121 (with silicone), with a deviation ≤0.5mm; Step S52: Hot-press edge sealing optimization.

[0042] The parameters are as follows: Temperature: 115℃ (the thin interlayer is more sensitive to high temperatures, so the temperature is slightly lowered to avoid excessive softening of the paraffin); Pressure: 0.2MPa (lower than the 0.7mm solution to prevent the thin interlayer from being over-compressed); Time: 50s (heat conduction is faster at the edges of the thin interlayer, shortening the sealing time); Sealing area: 2mm at the edges, no pressure applied to the middle area.

[0043] Step S6, Post-processing (Simplified large-size shaping); Step S61, trimming and cutting: Same as the previous method, cut to 640mm×150mm, with no burrs on the edges; Step S62, Leveling treatment: Keep warm at 40℃ and 0.08MPa pressure for 20 minutes (the thin intermediate layer has a low risk of warping, shortening the leveling time). Step S63, Storage: Store flat (thin middle layer has better resistance to compression, no need for rolls), humidity ≤30%.

[0044] Step S7, Performance Testing (Focusing on verifying the thermal conductivity of the thin coating). Step S71: Basic performance testing; Step S71, Total thickness detection: 1.0±0.02mm (9-point measurement, error ≤0.02mm); Step S71, Thermal conductivity test: 25℃≥1.9W / (m·K) (thin coating filler network is easier to continue, slightly higher than thick coating), 30℃≥4.8W / (m·K), 35℃≥7.8W / (m·K); Step S71, Leakage prevention test: No leakage at 40℃ / 24h; Step S71, Thin Coating Specific Inspection; Step S71, Thermal conductivity uniformity test: Surface temperature difference ≤ 0.4℃ at 35℃ (thin coatings provide more uniform heat transfer); Step S71, Puncture resistance test: No puncture under 1N force (mechanical strength needs to be verified for thin intermediate layer). Step S71, Adhesion test: Contact rate ≥96% under 1MPa pressure (thin intermediate layer + thick silicone layer, better adhesion).

[0045] like Figure 2 and Figure 4 As shown, in a third aspect, embodiments of the present invention also provide a battery system, including the heat-conducting structure 100 as described above, and further including a housing 200 and a battery module 300, wherein the battery module 300 is fixedly disposed on the inner bottom wall of the housing 200, and the composite heat-conducting layer 110 is disposed in the gap between the housing 200 and the battery module 300.

[0046] like Figure 2-3 As shown, a flow channel 21a is formed at the bottom of the outer shell 200, and the flow channel 21a is positioned directly opposite the composite heat-conducting layer 110. The side wall of the outer shell 200 is provided with an inlet 211 and an outlet 212 that are respectively connected to the two ends of the flow channel 21a.

[0047] In one embodiment, the outer casing 200 includes a lower casing 210, an upper casing 220, and a sealing gasket 230. The lower casing 210 and the upper casing 220 are connected by screws, and the sealing gasket 230 is disposed at the mating portion between the lower casing 210 and the upper casing 220. The lower casing 210 has a flow channel 21a formed inside, and an inlet 210 and an outlet 220 connected to the flow channel 21a are provided on one side, so that the water pump and the cooler can continuously send cooling circulating water into the flow channel 21a.

[0048] Of course, in other embodiments, the battery module 300 may also adopt other cooling solutions such as air cooling, immersion cooling, and direct refrigerant cooling, which will not be elaborated or explained in detail here.

[0049] In one embodiment, the battery module 300 includes multiple battery cells (i.e., battery management system 310), high and low voltage connectors 320, copper busbars 330, and other structures, which are structures that can be conceived by those skilled in the art and will not be described or explained here.

[0050] Compared with existing technologies: Since the thermal conductivity of the composite thermal conductive layer 110 is positively correlated with temperature, its thermal conductivity increases as the ambient temperature rises. When applied to a battery system, there is a large temperature difference between multiple battery cells in the battery module 300. Therefore, the thermal conductive structure 100 can be attached to the position between the battery module 300 and the heat dissipation structure. The part of the thermal conductive structure 100 near the battery cell with higher temperature has a higher thermal conductivity and higher heat exchange efficiency, thereby effectively balancing the temperature difference between multiple battery cells and greatly improving the cycle life and safety of the battery system.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A thermally conductive structure, characterized in that, include: The composite thermally conductive layer has a thermal conductivity that is positively correlated with temperature. An outer layer is provided that encloses the composite thermally conductive layer.

2. The thermally conductive structure according to claim 1, characterized in that, The composite thermally conductive layer includes paraffin wax and multiple thermally conductive filler particles. The paraffin wax has solid, semi-solid, and liquid states depending on the temperature. The multiple thermally conductive filler particles are embedded in the paraffin wax and form a thermally conductive network between the multiple thermally conductive filler particles. When the paraffin wax is solid, the thermally conductive network is disconnected. When the paraffin wax is semi-solid, the thermally conductive network is partially connected. When the paraffin wax is liquid, the thermally conductive network is completely connected.

3. The thermally conductive structure according to claim 2, characterized in that, The paraffin wax includes low-melting-point paraffin wax and high-melting-point paraffin wax.

4. The thermally conductive structure according to claim 2, characterized in that, The thermally conductive filler particles are sheet-like graphene particles and / or filamentous carbon fiber particles.

5. The thermally conductive structure according to claim 1, characterized in that, The outer layer includes a PET film, which wraps around the composite thermally conductive layer.

6. The thermally conductive structure according to claim 5, characterized in that, The outer layer also includes a thermally conductive silicone layer, which fills the space between the PET film and the composite thermally conductive layer.

7. A method for preparing a thermally conductive structure, characterized in that, The method for preparing the thermally conductive structure as described in any one of claims 1-6 includes the following steps: preparing a composite thermally conductive layer and encapsulating the composite thermally conductive layer with an outer cladding layer.

8. The method for preparing the thermally conductive structure according to claim 7, characterized in that, The method for preparing the composite thermally conductive layer is as follows: Paraffin solution is prepared by melting paraffin wax; Graphene particles, carbon fiber particles, glass fiber particles and ethyl acetate were added to a mixing tank, stirred and ultrasonically dispersed to obtain a filler dispersion. A filler dispersion was added to the epoxy resin and stirred to obtain a premix; Pour the paraffin solution into the premixed liquid, heat and stir to form a slurry, coat the slurry onto the template, and after cooling, form a composite thermally conductive layer.

9. A battery system comprising the thermally conductive structure as described in any one of claims 1-6, characterized in that, It also includes a housing and a battery module, the battery module being fixedly disposed on the inner bottom wall of the housing, and the composite thermal conductive layer being disposed in the gap between the housing and the battery module.

10. The battery system according to claim 9, characterized in that, A flow channel is formed at the bottom of the outer shell, and the flow channel is positioned directly opposite the composite heat-conducting layer. The side wall of the outer shell is provided with an inlet and an outlet that are respectively connected to the two ends of the flow channel.

Images