Composite current collector and lithium battery

Abstract

The present application relates to a kind of composite current collector and lithium battery, the composite current collector includes the organic polymer layer and conductive layer of laminated arrangement, the organic polymer layer includes spherulite, in slice state, the maximum width of the spherulite is 2~20 μm, and the spherulite of maximum width 3~7 μm is first spherulite, the number of the first spherulite accounts for the number of all the spherulite ratio ≥40%.By accurately controlling spherulite size and the number of first spherulite ratio, the mechanical strength and heat resistance of composite current collector can be effectively improved.Suitable spherulite size distribution can avoid local thermal stress concentration, reduce the risk of organic polymer layer thermal deformation when battery heating, thereby enhancing the safety performance of battery, while ensuring that the conductive layer and organic polymer layer are combined firmly, guaranteeing smooth current conduction and ensuring reliable operation.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials, specifically designing a composite current collector and a lithium battery. Background Technology

[0002] Current collectors are an indispensable component of lithium-ion batteries. Their main functions include carrying electrode active materials and conducting electricity. Current collectors not only collect and output the current generated by electrochemical reactions, but also reduce the battery's internal resistance, improve coulombic efficiency, and enhance cycle stability. Common current collector materials include aluminum foil for the positive electrode and copper foil for the negative electrode. In recent years, the emergence of composite current collectors, which replace traditional metal foils with lightweight base films, has been able to improve battery energy density and reduce costs.

[0003] In traditional composite current collectors, the heat resistance of organic polymers is a significant issue. When the battery heats up during charging and discharging, organic polymers are prone to thermal deformation or even failure, leading to internal short circuits and thermal runaway, severely threatening battery safety. This problem limits the widespread application of lithium batteries in fields with extremely high safety requirements, such as electric vehicles and energy storage systems. Therefore, developing a technical solution that can effectively improve the heat resistance of composite current collectors and enhance battery safety is of significant practical importance and urgency. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite current collector and a lithium battery that can effectively improve the heat resistance of the composite current collector and enhance the working safety of the lithium battery.

[0005] The technical solution is as follows: A composite current collector, the composite current collector includes an organic polymer layer and a conductive layer stacked together, the organic polymer layer includes spherulites, in a sliced ​​state, the maximum width of the spherulites is 2~20μm, and the spherulites with a maximum width of 3~7μm are the first spherulites, the number of the first spherulites accounts for ≥40% of the total number of the spherulites.

[0006] The aforementioned composite current collector consists of a stacked organic polymer layer and a conductive layer. The spherulites within the organic polymer layer exhibit a specific size distribution in a sliced ​​state. The maximum width of the spherulites is limited to 2-20 μm, allowing for stable interactions with the organic polymer molecular chains. Specifically, the first spherulites, with a maximum width of 3-7 μm, account for ≥40% of the total number of spherulites. This size enhances the entanglement and constraint between molecular chains, improving the structural stability of the organic polymer layer. When used in lithium-ion batteries, precise control of the spherulite size and the proportion of the first spherulites effectively improves the mechanical strength and heat resistance of the composite current collector. A suitable spherulite size distribution avoids localized thermal stress concentration, reducing the risk of thermal deformation of the organic polymer layer during battery heating, thereby enhancing battery safety. Simultaneously, it ensures a stable bond between the conductive layer and the organic polymer layer, guaranteeing smooth current conduction and operational reliability.

[0007] In one embodiment, the spherulites in the organic polymer layer with a maximum width of 7~12μm are second spherulites, and the number of second spherulites accounts for ≥35% of the total number of spherulites.

[0008] In one embodiment, the crystallinity of the organic polymer layer is 40% to 75%.

[0009] In one embodiment, the standard deviation of the crystalline region distribution of the organic polymer layer is less than or equal to 5% of the mean crystallinity.

[0010] In one embodiment, the X-ray diffraction full width at half maximum (FWHM) of the organic polymer layer is between 0.5° and 2°.

[0011] In one embodiment, the ratio of the crystallinity to the enthalpy of melting of the organic polymer layer is 0.8 to 1.2.

[0012] In one embodiment, the organic polymer layer further includes lamellae. In the sliced ​​state, the lamellae have a maximum width of 50nm~1.2μm and a maximum thickness of 5~30nm. The lamellae with a maximum width of 100nm~0.5μm are the first lamellae, and the number of the first lamellae accounts for 25~40% of the total number of the lamellae.

[0013] In one embodiment, the total thickness of all the lamellar crystals accounts for 5 to 15% of the total thickness of the organic polymer layer.

[0014] In one embodiment, the ratio of the maximum length to the maximum thickness of the lamellar crystal ranges from 5 to 11.

[0015] A lithium battery comprising the composite current collector described in any one of the above.

[0016] In the aforementioned lithium-ion battery, the positive and negative electrode composite current collectors are composed of stacked organic polymer layers and conductive layers. The spherulites within the organic polymer layers exhibit a specific size distribution in a sliced ​​state. The maximum width of the spherulites is limited to 2-20 μm, and spherulites within this range can form stable interactions with the organic polymer molecular chains. Specifically, the proportion of the first spherulites with a maximum width of 3-7 μm is ≥40%. Spherulites of this size enhance the entanglement and constraint between molecular chains, improving the structural stability of the organic polymer layer. When this composite current collector is used in lithium-ion batteries, precise control of the spherulite size and the proportion of the first spherulites can effectively improve the mechanical strength and heat resistance of the composite current collector. A suitable spherulite size distribution avoids localized thermal stress concentration, reducing the risk of thermal deformation of the organic polymer layer when the battery heats up, thereby enhancing battery safety. Simultaneously, it ensures a stable bond between the conductive layer and the organic polymer layer, guaranteeing smooth current conduction and operational reliability. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall structure of the composite current collector described in one embodiment;

[0020] Figure 2 This is a schematic diagram of the overall structure of the composite current collector described in one embodiment;

[0021] Figure 3 This is a schematic diagram of the internal structure of the composite current collector described in one embodiment.

[0022] Explanation of reference numerals in the attached figures:

[0023] 100. Composite current collector; 110. Conductive layer; 120. Organic polymer layer; 121. Spherulite; 122. Lamellar. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" 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 invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0029] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0030] Please see Figure 1 and Figure 3 , Figure 1 This diagram shows the overall structure of the composite current collector 100 described above in one embodiment of the present invention. Figure 3 This is a schematic diagram of the internal structure of the composite current collector 100 described in one embodiment. An embodiment of the present invention provides a composite current collector 100 comprising a stacked organic polymer layer 120 and a conductive layer 110. The organic polymer layer 120 includes spherulites 121. In a sliced ​​state, the maximum width of the spherulites 121 is 2~20μm, and spherulites 121 with a maximum width of 3~7μm are designated as first spherulites 121. The number of first spherulites 121 accounts for ≥40% of the total number of spherulites 121.

[0031] The aforementioned composite current collector 100 is composed of a stacked organic polymer layer 120 and a conductive layer 110. The spherulites 121 within the organic polymer layer 120 exhibit a specific size distribution in a sliced ​​state. The maximum width of the spherulites 121 is limited to 2-20 μm; spherulites 121 within this range can form stable interactions with the organic polymer molecular chains. When the maximum width of the spherulites 121 is <2 μm, the excessively small spherulites 121 lead to an overly dense microstructure of the organic polymer layer 120, restricting the space for molecular chain movement, significantly reducing material flexibility, and making it prone to cracking during battery assembly or bending. Simultaneously, the heat conduction path is reduced, and localized heat accumulation is likely. When spherulites 121 exceeding 20 μm are present, the excessively large spherulites 121 cause uneven distribution of crystalline regions, increase the gaps between spherulites 121, reduce mechanical strength, and cause stress concentration within the large spherulites 121 at high temperatures, making structural collapse more likely and leading to a decrease in the heat distortion temperature of the organic polymer layer 120. In this composite current collector 100, the proportion of first spherulites 121 with a maximum width of 3~7μm is ≥40%. Spherulites 121 of this size enhance the entanglement and constraint between molecular chains, improving the structural stability of the organic polymer layer 120. When this composite current collector 100 is used in a lithium battery, precise control of the size of the spherulites 121 and the proportion of first spherulites 121 effectively improves the mechanical strength and heat resistance of the composite current collector 100. A suitable spherulite 121 size distribution avoids localized thermal stress concentration, reducing the risk of thermal deformation of the organic polymer layer 120 when the battery heats up, thereby enhancing battery safety. Simultaneously, it ensures a stable bond between the conductive layer 110 and the organic polymer layer 120, guaranteeing smooth current conduction and operational reliability.

[0032] Optionally, the conductive layer 110 can be made of copper, aluminum, gold, silver, nickel, chromium, iron, zinc, or other materials. Specifically, when the conductive layer 110 is aluminum foil, the composite current collector 100 can be applied to the positive electrode of a lithium-ion battery, and when the conductive layer 110 is copper foil, the composite current collector 100 can be applied to the negative electrode of a lithium-ion battery.

[0033] The conductive layer 110 may be disposed on one side of the organic polymer layer 120, or as follows: Figure 2 As shown, the two sides are respectively disposed on opposite sides of the organic polymer layer 120.

[0034] Optionally, the organic polymer layer 120 may be one or more of the following: polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polyphenylene sulfide (PPS), polyurethane, polyamide, polybenzimidazole, polycarbonate, polybutylene terephthalate, poly(p-phenylene terephthalamide), or other polymer materials.

[0035] Specifically, taking PET as an example, the methods for forming the first spherulites 121 of the aforementioned specific size and proportion include melt crystallization, nucleating agent-induced synthesis, or other synthetic methods. The melt crystallization method involves heating the PET raw material to a molten state at 280-300°C, then slowly cooling it to 180-200°C at a rate of 5-10°C / min, and holding it at this temperature for 30-60 minutes. During this process, the PET molecular chains have sufficient time to arrange themselves in an orderly manner to form spherulites 121. By controlling the cooling rate, the maximum width of the spherulites 121 can be controlled within 2-20 μm. Furthermore, a lower cooling rate is more conducive to forming larger spherulites 121, while appropriately increasing the cooling rate can increase the proportion of smaller spherulites 121, thereby ensuring that the number of first spherulites 121 with a maximum width of 3-7 μm accounts for ≥40%.

[0036] Furthermore, the synthesis method using the nucleating agent-induced method involves adding 0.1% to 0.5% of a nucleating agent, such as talc or organophosphate salts, to the PET raw material. The nucleating agent acts as the core for the growth of spherulites 121, promoting their formation. Optionally, selecting appropriate types and amounts of nucleating agents can effectively control the size distribution of the spherulites 121. For example, adding an appropriate amount of talc nucleating agent can increase the number of 3-7 μm spherulites 121, making their proportion reach over 40%, while ensuring that the maximum width of the spherulites 121 is within the range of 2-20 μm. This embodiment only provides a specific synthesis method for a particular organic polymer layer 120, but is not limited thereto.

[0037] In one embodiment, the spherulites 121 with a maximum width of 7-12 μm in the organic polymer layer 120 are designated as second spherulites 121, and the number of second spherulites 121 accounts for ≥35% of the total number of spherulites 121. The larger size of the second spherulites 121 improves the thermal conductivity of the organic polymer layer 120, complementing the first spherulites 121. The first spherulites 121 enhance local structural stability, while the second spherulites 121 promote uniform heat diffusion within the layer; their synergistic effect optimizes the overall performance of the organic polymer layer 120. Thus, the addition of the second spherulites 121 further improves the heat resistance of the composite current collector 100, reduces local overheating, and thereby enhances the battery's operational stability. If the proportion of second spherulites 121 is lower than the aforementioned percentage, the insufficient number of larger spherulites 121 will lead to reduced thermal conductivity, uneven heat distribution within the organic polymer layer 120, an increase in localized high-temperature areas, and an increased risk of thermal runaway. Simultaneously, the uniform size distribution of the spherulites 121 results in poor mechanical property balance in the organic polymer layer 120, making it difficult to balance strength and toughness. The appropriate ratio of the first spheroid 121 to the second spheroid 121 can achieve a balance between mechanical strength and thermal conductivity of the organic polymer layer 120, thereby improving the durability of the composite current collector 100 during battery charge-discharge cycles and extending battery life.

[0038] Specifically, the second spherulites 121 are formed using a stepped cooling method, which involves first cooling molten PET to 200-220°C at a cooling rate of 10-15°C / min and holding it at that temperature for 15-20 minutes to form a certain number of first spherulites 121; then cooling it to 160-180°C at a cooling rate of 2-5°C / min and holding it at that temperature for 20-30 minutes to promote the growth of the second spherulites 121. By adjusting the cooling rate and holding time in the two stages, the proportion of the second spherulites 121 can be ≥35%, forming a reasonable ratio with the first spherulites 121.

[0039] In one embodiment, the crystallinity of the organic polymer layer 120 is 40% to 75%. Crystallinity reflects the proportion of crystalline regions in the polymer. Crystallinity within this range allows the crystalline regions to form a framework structure, dispersed in the amorphous regions, enhancing the intermolecular forces, while retaining a certain amount of amorphous regions to prevent the organic polymer layer 120 from becoming brittle due to over-crystallization. Furthermore, a crystallinity of 40% to 75% gives the organic polymer layer 120 both good heat resistance and flexibility. Insufficient crystalline regions will result in insufficient heat resistance of the organic polymer layer 120, making it prone to molecular chain slippage at high temperatures, leading to deformation or even melting of the organic polymer layer 120. Simultaneously, its mechanical strength will be low, unable to withstand the expansion stress during battery charging and discharging. Over-crystallization, on the other hand, increases the material's brittleness and drastically reduces its flexibility, making it prone to breakage due to volume changes during battery cycling. Additionally, excessively dense crystalline regions will increase internal stress, making it prone to warping or cracking during processing. Higher crystallinity enhances the material's resistance to thermal deformation, while a certain amount of amorphous region ensures that the material has a certain degree of elasticity and toughness when subjected to mechanical stress, reducing the probability of damage to the composite current collector 100 during processing and use, thereby improving the overall quality of the composite current collector 100.

[0040] Specifically, taking PET film as an example, an annealing treatment method is used. By adjusting the annealing process, the formed PET film material is annealed at 120~200℃ for 30~120 minutes. By adjusting the annealing temperature and time, the crystallinity of PET is controlled within the above range.

[0041] In one embodiment, the standard deviation of the crystalline region distribution of the organic polymer layer 120 is less than or equal to 5% of the average crystallinity. This ensures a uniform distribution of crystalline regions within the layer, allowing for even stress transfer within the material and preventing stress concentration caused by localized dense or sparse crystals, while also guaranteeing uniform heat dissipation within the layer. The uniform distribution of crystalline regions significantly improves the tear resistance and heat resistance uniformity of the composite current collector 100. Uniform stress transfer reduces the likelihood of material fracture due to excessive localized stress, and uniform heat dissipation reduces the risk of thermal runaway caused by localized high temperatures, making the composite current collector 100 more stable and reliable. If the values ​​exceed these limits, uneven crystal distribution leads to significant anisotropy in material properties. Locally densely crystalline areas are prone to fracture due to stress concentration, while sparsely crystalline areas exhibit poor heat resistance and deform first at high temperatures, overall reducing the stability and reliability of the composite current collector 100.

[0042] Specifically, in the production process of the organic polymer layer 120, a temperature-increasing crystallization method is adopted, in which the PET is slowly heated from room temperature to the crystallization temperature at a rate of 1~3℃ / min, and then held at this temperature. The stepwise heating method can make the internal temperature distribution of PET uniform, avoid local overheating or undercooling, thereby ensuring that the crystallization area is evenly distributed and that the standard deviation of the crystallization area distribution is kept at a low level.

[0043] In one embodiment, the half-width at half-maximum (WHM) of the X-ray diffraction (XRD) of the organic polymer layer 120 is between 0.5° and 2°. The WHM reflects the degree of crystal structure perfection; a narrower WHM indicates a more regular crystal structure with fewer defects. The regular crystal structure in the organic polymer layer 120 results in tightly packed molecular chains and strong intermolecular forces, providing better resistance to heat and external forces. Studies have found that a WHM within the above range corresponds to a higher degree of crystal perfection, which significantly improves the heat resistance and mechanical strength of the organic polymer layer 120. This makes the material less prone to structural damage at high temperatures, and also enhances tensile strength and hardness, improving the overall quality and service life of the composite current collector 100. When the XRD WHM is < 0.5°, excessive crystal perfection leads to excessive rigidity and a lack of necessary flexibility, making the material prone to brittle fracture under impact or vibration. Furthermore, the crystallization process is too time-consuming, which is detrimental to industrial production. When the full width at half maximum (FWHM) of X-ray diffraction exceeds 2°, excessive crystal defects reduce the intermolecular forces, decrease the material's heat resistance, and make the crystal structure easily damaged at high temperatures. At the same time, the mechanical strength is reduced, and the material is prone to breakage at defects during stretching.

[0044] In one embodiment, the ratio of crystallinity to enthalpy of fusion of the organic polymer layer 120 is 0.8 to 1.2. Enthalpy of fusion reflects the energy required for crystal melting, and this ratio reflects the degree of matching between crystallinity and crystal quality. A suitable ratio indicates that the crystalline region of the organic polymer layer 120 has high quality, forming a good synergy with crystallinity, further optimizing material properties. Meeting the above ratio range in the organic polymer layer 120 helps ensure that the crystallinity and crystal quality of the organic polymer layer 120 are compatible, enabling the material to achieve a better state in terms of heat resistance and mechanical properties. Higher crystallinity enhances the thermal stability and structural strength of the material, improving the reliability of the composite current collector 100 under complex operating conditions. Outside the above range, a ratio that is too low indicates a mismatch between crystallinity and crystal quality, a loose crystal structure, and that heat resistance and mechanical properties cannot meet expectations, potentially leading to thermal deformation at lower temperatures. A ratio that is too high means that the crystal structure is too dense, restricting molecular chain movement, reducing material flexibility and processing performance, and making it prone to microcracks due to excessive internal stress.

[0045] In one embodiment, the organic polymer layer 120 further includes lamellar crystals 122. In the sliced ​​state, the maximum width of the lamellar crystals 122 is 50 nm to 1.2 μm, and the maximum thickness is 5 to 30 nm. Lamellar crystals 122 with a maximum width of 1 to 5 nm are designated as the first lamellar crystals 122, and the number of first lamellar crystals 122 accounts for 25% to 40% of the total number of lamellar crystals 122. The lamellar crystals 122 can fill the gaps between the spherulites 121, forming a denser microstructure. They synergistically enhance the connection and constraint between molecular chains with the spherulites 121, while the two-dimensional structure of the lamellar crystals 122 facilitates lateral heat conduction. Thus, the synergistic effect of the spherulites 121 and lamellar crystals 122 significantly improves the overall performance of the composite current collector 100. The addition of lamellar crystals 122 makes the organic polymer layer 120 structure denser, improving the material's strength and heat resistance. The reasonable proportion of the first lamellar crystals 122 can enhance performance while avoiding a decrease in material flexibility, ensuring that the composite current collector 100 possesses both high strength and good processability. If the lamellar crystals 122 are too narrow, they cannot effectively fill the gaps between the spherulites 121, resulting in limited reinforcement. If the width is too large, the lamellar crystals 122 will interfere with each other, disrupting the uniformity of the microstructure and reducing the material's toughness. If the lamellar crystals 122 are too thin, the structure has poor stability and is prone to decomposition at high temperatures. If the thickness is too large, it is difficult to manufacture, costly, and increases thermal resistance, which is not conducive to heat conduction, while also reducing the material's flexibility. If the proportion is too low, an effective reinforcing network cannot be formed, and the improvement in mechanical properties is not significant. If the proportion is too high, the material will be too rigid, its tear resistance will decrease, and it will be easily damaged during processing.

[0046] Specifically, the lamellar crystals 122 within the aforementioned size range can be formed by stretching-crystallization, solution crystallization, or other processing methods. Specifically, the stretching-crystallization synthesis method involves uniaxially or biaxially stretching the PET film above its glass transition temperature, with the stretching ratio controlled between 2 and 4 times. During stretching, the PET molecular chains align along the stretching direction, followed by heat setting at 120–160°C for 20–40 minutes. The oriented molecular chains form lamellar crystals 122 during the heat setting process. By controlling the stretching ratio and heat setting temperature, lamellar crystals 122 of the aforementioned size can be formed in the PET film.

[0047] The specific method of solution crystallization is as follows: PET is dissolved in a phenol-tetrachloroethane mixed solvent to prepare a solution with a mass fraction of 5% to 10%. The solution is then slowly cast onto a glass plate, allowing the solvent to evaporate naturally at room temperature to form a thin film. The film is then heat-treated at 100 to 140°C for 1 to 2 hours. During the solution evaporation and heat treatment processes, the PET molecular chains arrange themselves in an orderly manner to form lamellar crystals 122. By controlling the solution concentration and the heat treatment temperature, the size of the lamellar crystals 122 and the proportion of the first lamellar crystal 122 can be controlled.

[0048] In one embodiment, the total thickness of all lamellar crystals 122 accounts for 5-5% of the total thickness of the organic polymer layer 120. A proportion of 5-15% ensures that the lamellar crystals 122 effectively perform their reinforcing and thermal conductivity functions within the layer without excessively occupying space and affecting the overall structural balance of the organic polymer layer 120. An appropriate proportion of the total thickness of the lamellar crystals 122 allows their reinforcing and thermal conductivity functions to be fully utilized, while maintaining the flexibility and mechanical balance of the organic polymer layer 120. This avoids material embrittlement due to an excessively high proportion of lamellar crystals 122, or ineffective reinforcement due to an excessively low proportion, further optimizing the performance of the composite current collector 100. When the lamellar crystal thickness proportion is less than 15%, the contribution of the lamellar crystals 122 is insufficient, failing to effectively improve the material's heat resistance and mechanical properties, and its thermal conductivity and stress dispersion effects are limited. When the thickness of the lamellar crystal 122 is greater than 25%, it will encroach on the space of the organic polymer layer 120, disrupt the overall structural balance, increase the brittleness of the material, affect the bonding force with the conductive layer 110, and reduce the current conduction efficiency.

[0049] Specifically, a PET film is prepared using a multi-layer co-extrusion apparatus, which includes a functional layer containing a lamellar 122 structure and a regular PET layer. By adjusting the thickness of the functional layer, the proportion of the total thickness of all lamellar 122 to the thickness of the organic polymer layer 120 is adjusted.

[0050] In one embodiment, the ratio of the maximum length to the maximum thickness of the lamellar crystal 122 ranges from 5 to 11. This aspect ratio reflects the shape characteristics of the lamellar crystal 122. A suitable aspect ratio allows the lamellar crystal 122 to better disperse stress within the organic polymer layer 120, while also facilitating heat conduction along the length of the lamellar crystal 122. An aspect ratio of 5 to 11 enables the lamellar crystal 122 to effectively disperse stress under load, improving the material's tear resistance and tensile strength, while also promoting rapid heat conduction and reducing localized overheating. Optimizing the shape of the lamellar crystal 122 further enhances its synergistic effect with the spherulite 121, improving the overall performance of the composite current collector 100. When the aspect ratio is less than 5, the lamellar crystal 122 is nearly equiaxed, resulting in insufficient directionality in heat conduction and stress dispersion, failing to effectively improve the material's performance in specific directions, and offering limited improvement in heat resistance and mechanical properties. When the aspect ratio is greater than 11, the lamellar crystal 122 becomes too slender, reducing structural stability and making it prone to fracture under stress or high temperatures, thus becoming a weak point in the material and reducing overall performance.

[0051] An embodiment of the present invention also provides a lithium battery (not shown in the figure) including a composite current collector 100 of any one of the above.

[0052] In the aforementioned lithium battery, the positive and negative electrode composite current collector 100 is composed of a stacked organic polymer layer 120 and a conductive layer 110. The spherulites 121 within the organic polymer layer 120 exhibit a specific size distribution in a sliced ​​state. The maximum width of the spherulites 121 is limited to 2~20μm, and spherulites 121 within this range can form stable interactions with the organic polymer molecular chains. Specifically, the proportion of the first spherulites 121 with a maximum width of 3~7μm is ≥40%. Spherulites 121 of this size can enhance the intertwining and constraint between molecular chains, improving the structural stability of the organic polymer layer 120. When this composite current collector 100 is used in a lithium battery, by precisely controlling the size of the spherulites 121 and the proportion of the first spherulites 121, the mechanical strength and heat resistance of the composite current collector 100 can be effectively improved. A suitable spherulite 121 size distribution can avoid local thermal stress concentration, reduce the risk of thermal deformation of the organic polymer layer 120 when the battery heats up, thereby enhancing the safety performance of the battery. At the same time, it ensures that the conductive layer 110 and the organic polymer layer 120 are firmly bonded, ensuring smooth current conduction and guaranteeing operational reliability.

[0053] The beneficial effects of the present invention will be verified through specific embodiments and comparative examples below.

[0054] Example 1

[0055] Preparation Process: PET raw materials are prepared and placed in a vacuum drying oven at 120℃ for 4 hours to remove moisture and volatiles. Subsequently, the dried PET is fed into a twin-screw extruder, with the screw speed set to 120 r / min. The barrel temperature is set sequentially from the feeding section to the die head to 250℃, 260℃, 270℃, 280℃, and 285℃ to ensure complete melting and plasticization of the PET. Next, a compression molding process is used, injecting the molten PET into a mold preheated to 190℃, holding at a pressure of 10 MPa for 5 minutes, and then slowly cooling to room temperature at a rate of 7℃ / min. Demolding yields a PET organic polymer layer containing spherulites. Finally, a 50nm thick copper conductive layer is deposited on the surface of the organic polymer layer using magnetron sputtering technology at a sputtering power of 150W for 30 minutes. This is followed by electroplating to thicken the copper conductive layer to a 1.5μm thickness, thus producing the composite current collector.

[0056] The spherulite structure in the composite current collector was characterized by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the maximum width of the spherulites was 2~20μm, and the number of first spherulites with a maximum width of 3~7μm accounted for 42%.

[0057] Example 2

[0058] Preparation process: PET chips were vacuum dried at 110℃ for 5 hours, and then melt-blended using a twin-screw extruder with a barrel temperature range of 240~285℃ and a screw speed of 150 r / min to ensure complete melting of the PET. PET sheets were first obtained using a casting method, then heated to 210℃ and rapidly cooled and pre-crystallized in a tenter frame at a cooling rate of 12℃ / min. Secondary crystallization was then performed in a 170℃ oven for 25 minutes to form an organic polymer layer with a specific spherulitic structure. Copper conductive layers were deposited on both sides of the organic polymer layer using magnetron sputtering, followed by electroplating for thickening, the process being the same as in Example 1, to obtain a composite current collector.

[0059] The spherulite structure in the composite current collector was characterized and analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the first spherulite accounted for 43% of the total number of spherulites, and the second spherulite, with a maximum width of 7~12μm, accounted for 36%.

[0060] Example 3

[0061] Preparation process: PET granules were dried in a vacuum environment at 105℃ for 6 hours. They were then melt-extruded using a single-screw extruder at an extrusion temperature of 255~280℃ and a screw speed of 100 r / min. After extrusion, the granules were cast into a film using a T-die, with a film thickness controlled at 50 μm. The cast film was then melt-crystallized at 190℃ for 1 hour, followed by annealing in an annealing furnace at 160℃ for 60 minutes. A conductive layer was formed on the surface of the annealed organic polymer layer using chemical copper plating. The chemical copper plating solution contained 20 g / L copper sulfate, 40 g / L potassium sodium tartrate, 15 g / L sodium hydroxide, and 10 mL / L formaldehyde. The plating temperature was 55℃, and the plating time was 40 minutes, resulting in a composite current collector.

[0062] The spherulite structure in the composite current collector was characterized and analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the first spherulite accounted for 41% of the total number of spherulites. The crystallinity was 55% by calculating the ratio of the integrated area of ​​the crystallization peak to the total scattering area using X-ray diffraction (XRD).

[0063] Example 4

[0064] Preparation process: Same as in Example 1, combined with stretching-crystallization method, PET film is uniaxially stretched 3 times at 90°C, heat-set at 140°C for 30 minutes, corona discharge and adhesive coating on the surface, then laminated with electrolytic copper foil, and baked to obtain composite current collector material.

[0065] The spherulite structure in the composite current collector was characterized and analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the first spherulite accounted for 40% of the total number of spherulites; the first lamellar crystals, with a maximum width of 50 nm to 1.2 μm, a maximum thickness of 5 to 30 nm, and a maximum width of 100 nm to 0.5 μm, accounted for 30% of the total number of lamellae.

[0066] Example 5

[0067] Preparation process: PET chips are first vacuum dried at 115℃ for 4.5 hours. In a twin-screw extruder, they are melt-blended at 240-280℃ with a screw speed of 140 r / min. The blended melt is then extruded through a T-die and cooled to form a base film. The base film undergoes a stepped cooling crystallization process: first, it is cooled from 210℃ to 180℃ at a rate of 12℃ / min and held for 15 minutes; then, it is cooled to 160℃ at a rate of 3℃ / min and held for 20 minutes to form a specific spherulitic structure. Next, the base film is heated to 95℃ and biaxially stretched at a stretch ratio of 3×3, then heat-set at 145℃ for 25 minutes to promote lamellar formation. On the surface of the composite organic polymer layer, a conductive layer was formed using a combination of magnetron sputtering and electroplating. First, a 50 nm thick copper seed layer was magnetron sputtered at a power of 180 W for 25 minutes. Then, electroplating was performed in a copper sulfate solution at a temperature of 25°C, a current density of 2 A / dm², and a plating time of 30 minutes to thicken the layer. Finally, the composite current collector was annealed at 150°C for 30 minutes to optimize its crystal structure.

[0068] The spherulite structure in the composite current collector was characterized using optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis revealed the following: the first spherulite accounted for 42%, the second spherulite for 35%, the first lamellar crystal for 32%, the total lamellar thickness for 20%, and the aspect ratio of the lamellar crystals was 8. XRD analysis showed a crystallinity of 60%, a standard deviation of crystalline region distribution of 4% of the mean crystallinity, and a half-width at half-maximum (FWHM) of 1.2°. Combined with DSC data, the crystallinity-to-enthalpy ratio was calculated to be 1.0.

[0069] Comparative Example 1

[0070] Preparation process: PET is directly fed into a twin-screw extruder, the barrel temperature is set to 285℃, and after rapid melting, it is rapidly cooled to 150℃ at a cooling rate of 20℃ / min. The PET organic polymer layer is obtained by blow molding process, and then coated with adhesive and pressed with copper foil to form a conductive layer, thus obtaining a composite current collector.

[0071] The spherulite structure in the composite current collector was characterized and analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the maximum width of the spherulites was mostly above 20 μm, and the number of first spherulites accounted for 20%.

[0072] Comparative Example 2

[0073] Preparation process: Molten PET is cooled to 170°C at a single rate of 5°C / min, and then laminated with copper foil to obtain a composite current collector.

[0074] The spherulite structure in the composite current collector was characterized and analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the first type of spherulite accounted for 41% of the total number of spherulites, and the second type of spherulite accounted for 20%.

[0075] Comparative Example 3

[0076] Preparation process: Same as in Example 1, using melt crystallization method, without annealing treatment.

[0077] The spherulite structure in the composite current collector was characterized and analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Statistical analysis showed that the first spherulite accounted for 40% of the total number of spherulites.

[0078] The composite current collectors of the above embodiments and comparative examples were subjected to heat distortion temperature tests, tensile strength tests, and tear strength tests. The test methods are as follows:

[0079] Heat distortion temperature test: The test was conducted according to GB / T1634.2-2004 standard. A sample measuring 80mm × 10mm × 4mm was cut from the composite current collector, ensuring the sample surface was flat and free of defects such as cracks and bubbles. A static bending load of 0.45MPa was applied, and the sample was immersed in silicone oil. The temperature was increased at a rate of 120℃ / h, and the temperature at which the deformation at the midpoint of the sample reached 0.25mm was recorded as the heat distortion temperature. Each sample was tested three times, and the average value was taken as the final result.

[0080] Tensile strength test: The test was conducted according to GB / T1040.3-2006. The composite current collector was cut into rectangular specimens with a mark spacing of 25 mm, a width of 4 mm, and a thickness equal to the actual sample thickness. A universal testing machine was used, with the tensile speed set to 50 mm / min, and the test was conducted at room temperature (23℃±2℃). The maximum load at which the specimen broke was recorded. The tensile strength was calculated based on the original cross-sectional area of ​​the specimen using the formula: Tensile strength = Maximum load / Original cross-sectional area. Each sample was tested 5 times, and the average value was taken after removing outliers.

[0081] Tear strength test: The test was performed according to GB / T 16578.1-2008. The composite current collector was made into a trouser-shaped specimen with a leg length of 75 mm and a width of 25 mm. A 10 mm long slit was pre-made at the top of the specimen. A universal testing machine was used, with the tensile speed set to 100 mm / min, and the test was conducted at room temperature. The maximum force value during the tearing process was recorded. The tear strength was the ratio of the maximum force value to the specimen thickness. Each sample was tested 5 times, and the average value was taken as the test result.

[0082] The test results of the examples and comparative examples are shown in Table 1 below:

[0083] Table 1

[0084]

[0085] According to the performance measurements in the table above, the organic polymer layer obtained by the composite current collector using the technical solution of the above embodiment has high tensile strength and tear resistance, and the heat distortion temperature is significantly improved, which can effectively improve the safety of lithium battery use.

[0086] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite current collector, characterized in that, The composite current collector includes a stacked organic polymer layer and a conductive layer. The organic polymer layer includes spherulites. In a sliced ​​state, the maximum width of the spherulites is 2~20μm, and the spherulites with a maximum width of 3~7μm are the first spherulites, and the number of the first spherulites accounts for ≥40% of the total number of spherulites. The spherulites in the organic polymer layer with a maximum width of 7~12μm are the second spherulites, and the number of the second spherulites accounts for ≥35% of the total number of spherulites. The organic polymer layer further includes lamellae. In the sliced ​​state, the lamellae have a maximum width of 50nm~1.2μm and a maximum thickness of 5~30nm. The lamellae with a maximum width of 100nm~0.5μm are the first lamellae. The number of the first lamellae accounts for 25~40% of the total number of the lamellae. The crystallinity of the organic polymer layer is 40%~75%.

2. The composite current collector according to claim 1, characterized in that, The standard deviation of the crystalline region distribution of the organic polymer layer is less than or equal to 5% of the mean crystallinity.

3. The composite current collector according to claim 1, characterized in that, The X-ray diffraction half-width of the organic polymer layer is between 0.5° and 2°.

4. The composite current collector according to claim 1, characterized in that, The ratio of the crystallinity to the enthalpy of melting of the organic polymer layer is 0.8 to 1.

2.

5. The composite current collector according to claim 1, characterized in that, In the sliced ​​state, the ratio of the maximum length to the maximum thickness of the lamellae ranges from 5 to 11.

6. A lithium battery, characterized in that, The lithium battery includes the composite current collector as described in any one of claims 1 to 5.

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