A method for preparing a composite current collector film

Abstract

The application discloses a preparation method of a composite current collector film. The composite current collector film comprises a polymer substrate, a metal plating layer on the front surface and the back surface of the polymer substrate, and a through hole in the polymer substrate. The through hole is filled with the metal plating layer material, and the metal plating layers on the front surface and the back surface are connected. The preparation method comprises the following steps: flattening and fixing the polymer substrate; performing laser drilling along the normal direction of the polymer substrate to obtain a polymer substrate with a through hole; the aperture of the through hole is 0.5-5 microns; performing surface modification treatment on the inner wall of the through hole to make the inner wall of the through hole have gradient hydrophobicity; preparing the metal plating layer on the front surface and the back surface of the polymer substrate with the gradient hydrophobic through hole by using the metal plating layer material respectively, and filling the through hole with the metal plating layer material, the filling degree of the metal plating layer material in the through hole is more than 99.7%; and welding a tab to any one of the metal plating layers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a preparation method of a composite current collector film. BACKGROUND

[0002] However, the key component of the current lithium ion battery, the current collector, accounts for a large proportion of the volume and weight of the battery, which limits the further improvement of the actual energy density of the lithium ion battery. Therefore, the light and thin current collector has become a trend in the industry. There is a demand for reducing the weight of the current collector.

[0003] In order to solve the demand for light and thin current collector weight reduction, the related technology discloses a preparation method of a composite current collector, which adopts a light and thin, insulating polymer intermediate layer, and a copper or aluminum conductive metal plating layer with a thickness of about 1 μm or more is prepared on the two sides of the polymer intermediate layer, that is, the front and back surfaces, to form a sandwich type composite current collector with a structure similar to a sandwich. Since the polymer intermediate layer is relatively light and thin, the area density and thickness of the composite current collector are reduced compared with the traditional copper and aluminum foil, the proportion of auxiliary materials in the battery is reduced, and the energy density of the battery is improved.

[0004] In order to improve the purity and conductivity of the metal plating layer, a vacuum plating method is generally used to prepare the metal plating layer in the composite current collector, but it takes a long time to prepare a metal plating layer with a thickness of 1 μm or more, which causes difficulties in the industrialization of the composite current collector technology. In addition, since the metal plating layers on both sides of the intermediate layer are not conductive to each other, it is necessary to weld the tabs on both sides of the metal plating layer, which affects the yield of the tab welding process. In addition, the thick metal plating layer causes inherent bottlenecks in the further lightening and thinning of the current collector. SUMMARY

[0005] To have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not a general review, nor is it intended to determine key / important elements or delineate the scope of protection of these embodiments, but as a prelude to the detailed description below.

[0006] The present application provides a preparation method of a composite current collector film, to prepare a composite current collector that is lighter and thinner than the prior art, thereby improving the energy density of the lithium ion battery.

[0007] The composite current collector film disclosed by the present application comprises a polymer substrate and a metal plating layer. The polymer substrate comprises a front surface and a back surface, and a plurality of through holes are arranged along the direction from the front surface to the back surface. The metal plating layer is arranged on the front surface and the back surface respectively, and the metal plating layer material fills the through holes to make the metal plating layers on the front surface and the back surface communicate.

[0008] Optionally, the kind of the polymer substrate is one selected from polyethylene terephthalate, polypropylene, polycarbonate, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polyethylene and polytetrafluoroethylene. In a preferred embodiment, the kind of the polymer substrate is polyethylene terephthalate or polycarbonate.

[0009] Optionally, the thickness of the polymer substrate is 0.5-4.5 μm. Specifically, the thickness of the polymer substrate is 0.5-3.5 μm. More specifically, the thickness of the polymer substrate is 0.5-1.5 μm.

[0010] Optionally, the component of the metal plating layer is one or more selected from copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotube, ketjen black, acetylene black, graphite powder and carbon fiber. In a preferred embodiment, the component of the metal plating layer is copper or aluminum.

[0011] Optionally, the thickness of the metal plating layer on the polymer substrate is 0.3-1 μm. Specifically, the thickness of the metal plating layer is 0.5-0.8 μm. More specifically, the thickness of the metal plating layer is 0.5 μm.

[0012] Optionally, the pore size of the through hole is 0.5-5 μm. It is to be noted that the pore size of the through hole should not be too large or too small. In the case that the pore size of the through hole is greater than 5 μm, the volume to be filled in the through hole is too large, and thus the thickness of the deposited metal plating layer needs to be further increased, resulting in a lower battery energy density. In the case that the pore size of the through hole is less than 0.5 μm, the interconnected area of the metal plating layers on the front and back surfaces of the polymer substrate is small, resulting in a lower conductivity of the composite current collector film. Therefore, the pore size of the through hole is set to the above range, so as to make the composite current collector film more lightweight while improving the conductivity of the composite current collector film and the battery energy density.

[0013] Optionally, the porosity of the through hole is 1-10%. Specifically, the porosity of the through hole is 2-8%.

[0014] Optionally, the through hole comprises a first region and a second region. The first region is arranged close to the front surface of the polymer substrate, and the first region comprises a first conical surface and a second conical surface. The through hole diameter corresponding to the first conical surface decreases from 1.3 μm to 5 μm at the end surface of the through hole to 0.8 μm to 2 μm at the middle part of the through hole. The second conical surface is connected with the first conical surface, and the corresponding through hole diameter decreases from 0.8 μm to 2 μm to 0.5 μm to 1 μm. The second region is arranged close to the back surface of the polymer substrate, and the second region is the same size and symmetrical shape as the first region. The second region comprises a third conical surface arranged symmetrically with the first conical surface, and a fourth conical surface arranged symmetrically with the second conical surface. The second conical surface and the fourth conical surface meet to form a throat of the through hole, and the throat diameter is 0.5 μm to 1 μm. The through hole diameter corresponding to the first region and the second region gradually decreases from both ends of the through hole to the throat. The junctions of the first conical surface and the second conical surface and the junctions of the third conical surface and the fourth conical surface each have one protruding shoulder.

[0015] Optionally, the first conical surface forms a first angle of 45° to 90° with the normal of the polymer substrate. The second conical surface forms a second angle of 17° to 64° with the normal of the polymer substrate. The first angle is greater than the second angle.

[0016] Optionally, the through hole depth corresponding to the region of the first conical surface is a first depth. The through hole depth corresponding to the region of the second conical surface is a second depth. The first depth is less than the second depth.

[0017] Optionally, the surface of the inner wall of the through hole has gradient hydrophobicity. The hydrophobicity of the inner wall corresponding to the first region gradually decreases from the first conical surface to the second conical surface. The hydrophobicity of the inner wall corresponding to the second region is symmetrical to the first region, that is, the hydrophobicity gradually decreases from the third conical surface to the fourth conical surface. Therefore, the hydrophobicity of the inner wall corresponding to the throat of the through hole is the weakest, and the inner wall of the throat has relatively weak hydrophobicity.

[0018] In this embodiment, the ratio a of the oxygen and carbon element compositions of the surface of the inner wall of the through hole represents the hydrophobicity. The ratio a of the oxygen and carbon element compositions of the surface of the inner wall of the through hole is controlled by surface modification treatment to make the inner wall of the through hole have gradient hydrophobicity.

[0019] Optionally, the ratio a of the O (oxygen) element composition to the C (carbon) element composition of the surface of the inner wall of the through hole with gradient hydrophobicity is in the range of 10% to 40%, and the ratio a gradually increases from the inner wall corresponding to both ends of the through hole to the inner wall corresponding to the throat of the through hole (i.e., gradually decreases from the throat to the end of the through hole). The a value of the inner wall close to the end of the through hole is in the range of 10% to 25%, the a value of the inner wall of the throat is in the range of 25% to 40%, and the a value of the inner wall of the throat is 10% to 20% higher than the a value of the inner wall close to the end of the through hole.

[0020] Optionally, the ratio a of the O element composition to the C element composition of the inner wall surface of the through hole with gradient hydrophobicity is less than the ratio of the O element composition to the C element composition of the polymer substrate surface. In the present application, the throat aperture is 0.5-1 μm, and too small throat aperture will limit the smooth and effective communication between the front and back metal coatings of the polymer substrate, and too large throat aperture will make the atomic groups of the metal coating material not easy to form good filling in the throat during the filling process.

[0021] The present application provides a preparation method of a composite current collector film, comprising:

[0022] S1: flattening and fixing the polymer substrate;

[0023] S2: laser drilling along the normal direction of the polymer substrate to obtain a polymer substrate with a through hole with a pore size of 0.5-5 μm;

[0024] S3: surface modification treatment is performed on the inner wall of the through hole to make the inner wall of the through hole have gradient hydrophobicity;

[0025] S4: using a metal coating material to prepare a metal coating on the front and back of the polymer substrate respectively, and the metal coating material fills the through hole, wherein the filling degree of the metal coating material in the through hole is more than 99.7%.

[0026] S5: welding the tab to any one of the metal coatings to conduct the active materials on the upper and lower surfaces of the composite current collector film.

[0027] In the present application, the through hole is prepared on the normal direction of the polymer substrate by laser drilling process, and the inner wall of the through hole is surface modified to have gradient hydrophobicity, so that the metal coating can completely and densely fill the through hole by interatomic collision and accumulation during deposition. In this way, while realizing a more lightweight current collector, the conductivity of the current collector is also improved. The present application finds that the filling degree of the metal coating material in the through hole affects the degree of improvement of the conductivity of the composite current collector and the degree of improvement of the performance of the battery, and further affects the stability and safety of the battery. If the metal coating material in the through hole is not completely filled, i.e. there are gaps in the through hole, due to capillary principle, the electrolyte will accumulate in the unfilled gaps in the through hole, causing the coating to corrode and break, the electrolyte to be unevenly distributed, and the electrode to fail. Therefore, in the composite current collector film in the present application, the through hole needs to be completely filled with the metal coating material. By completely filling the metal coating material in the through hole of the polymer substrate, the phenomena of coating corrosion and breakage, uneven distribution of electrolyte, and electrode failure are avoided, the conductivity performance of the composite current collector film is improved, and the adhesion between the polymer substrate and the metal coating is improved, thereby improving the energy density of the battery using the composite current collector film and the cycle life of the battery.

[0028] The present application finds that the surface characteristics of the inner wall of the through hole affect the filling effect in the through hole when simulating the filling process of the through hole on the polymer substrate by vacuum plating. When the inner wall of the through hole is neutral or hydrophilic, the plated material atoms of vacuum plating are easy to deposit and adhere on the inner wall at the contact position with the through hole and form filling, which will block the further filling of the plated material atoms to the area below the formed filling area; or the plated material atoms reaching the inner wall of the through hole will tend to adhere to the inner wall of the through hole, and when the plated material atoms further expand radially on this basis, microscopically, the radially expanded plated material atoms will still be subjected to the pulling force tending to the inner wall of the through hole, and this pulling between the micro particles will cause micro defects such as micro pores and micro bridges in the filling. Although the plated material atoms have filled the through hole well from the surface, microscopic structure analysis will find that there are a certain proportion of micro defects in the filling that are not easy to detect, and although the proportion of such micro defects is small, they will still affect the conductivity of the composite current collector, affect the bonding force between the metal plating layer and the polymer substrate, and in the long-term battery charging and discharging cycle, there is a risk of electrolyte penetration, which is easy to cause electrode failure, affect the cycle life of the battery, and make the battery have safety hazards.

[0029] In the present application, the inner wall of the through hole is provided with gradient hydrophobicity by surface modification treatment, that is, the hydrophobicity of the inner wall corresponding to the first region gradually weakens from the first conical surface to the second conical surface, the hydrophobicity of the inner wall corresponding to the second region is symmetrical to the first region, that is, the hydrophobicity gradually weakens from the third conical surface to the fourth conical surface, and the inner wall of the throat portion has relatively weak hydrophobicity. The control of the gradient hydrophobicity degree of the inner wall of the through hole is realized by controlling the ratio of oxygen and carbon element components of the inner wall of the through hole by surface modification, thereby realizing the outstanding technical effect of completely filling the through hole with the metal plating layer material. The gradient hydrophobicity of the inner wall of the through hole with the oxygen and carbon element component ratio distribution characteristics as described above provides a suitable downward driving tendency for the plating material atoms incident on the inner wall of the through hole. To cooperate with the gradient hydrophobicity of the inner wall of the through hole, the through hole of the present application includes the first region and the second region with the aforementioned structural and shape characteristics, and the complete filling process of the metal plating layer in the through hole is illustrated by taking the first region as an example. Since the first conical surface is relatively open, a large number of metal plating layer atoms can enter the inside of the through hole and be incident on the surface of the first conical surface or the second conical surface. When the atoms of the metal plating layer are incident on the inclined surface of the first conical surface or the third conical surface, the atoms will generate a component velocity tending to the direction of the throat portion of the through hole and move toward the direction of the throat portion of the through hole. At the same time, due to the gradient hydrophobicity of the inner wall of the through hole, the atoms will generate a downward driving tendency instead of staying in place. The metal plating layer atoms with a large initial speed incident on the first conical surface are slightly accelerated by the gradient hydrophobicity of the surface, and have a large speed when reaching the edge portion of the junction between the first conical surface and the second conical surface, so that such atoms fly out of the space in the second conical surface when passing through the edge portion and away from the inner wall of the through hole. Since the initial speeds of the metal plating layer atoms when being incident are different, the lengths of the slightly accelerated paths of such atoms on the first conical surface are also different, so that the flight paths and distances of such atoms flying out of the space corresponding to the second conical surface are also diversified. When the metal plating layer atoms with a small initial speed are incident on the first conical surface, although they are also driven by the gradient hydrophobicity to reach the edge portion along the first conical surface, their speed is not enough to fly out of the inner wall of the through hole, and they still move toward the throat portion along the second conical surface. The flying metal plating layer atoms collide and contact each other to form atom groups, and in the subsequent flight process, the atoms and atom groups collide and contact each other, gradually contact and adhere to larger atom groups in the process of moving toward the throat portion. The larger atom groups continue to move toward the throat portion in the form of flight or movement along the inner wall of the through hole, and with the decrease of the flight speed of the larger atom groups or with the gradual weakening of the hydrophobicity of the inner wall of the through hole, the movement tendency of the larger atom groups also slows down.When the large atom group moves to the throat, due to the weakest or nearly neutral hydrophobicity of the throat, and the smallest aperture of the throat, multiple large atom groups directly stay in the throat and generate support and extrusion, forming filling, and subsequent atoms or atom groups coming along the inner wall of the through hole or flying form a self-down-to-up layer-by-layer deposition filling on the basis of the throat filling. In the process of deposition filling (including throat filling), due to the hydrophobicity of the inner wall of the through hole at the deposition position, the inner wall will continuously push the atom group to the middle, and then extrude and compact in the middle first, remove the pores, and then gradually expand and grow outward along the radial direction, until a gapless filling is formed between the inner wall. This process enables the metal coating material to form a gapless, complete and dense filling effect in the through hole, with a filling degree of more than 99.7%, greatly avoiding the existence of micro-pores or micro-bridges and other micro-defects in the filling. In this embodiment, setting the surface of the inner wall of the through hole to have gradient hydrophobicity can produce better filling effect, which is exactly opposite to the research direction of the prior art and breaks through the industry prejudice.

[0030] Optionally, in S2, the polymer substrate passes through a punching process area. The punching process area includes a front punching process section and a rear punching process section. When the polymer substrate passes through the front punching process section, the front surface is laser punched by a first laser beam. When the polymer substrate passes through the rear punching process section, the rear surface is laser punched by a second laser beam. In the laser punching process, the spot diameters of the first laser beam and the second laser beam both have a decreasing trend, so that the aperture of the through hole gradually decreases from both ends of the through hole to the middle of the through hole, and the through hole converges into a throat in the middle of the through hole.

[0031] Optionally, the decreasing trend includes a first decreasing trend and a second decreasing trend. The spot diameter of the first decreasing trend decreases from 1.3 μm-5 μm to 0.8 μm-2 μm to form a first conical surface and a third conical surface, the normal of the through hole inner wall of the corresponding area and the polymer substrate forms a first included angle of 45°-90°, and the through hole depth of the corresponding area is a first depth. The spot diameter of the second decreasing trend decreases from 0.8 μm-2 μm to 0.5 μm-1 μm to form a second conical surface and a fourth conical surface, the normal of the through hole inner wall of the corresponding area and the polymer substrate forms a second included angle of 17°-64°, and the through hole depth of the corresponding area is a second depth. The spot diameter at the end of the first decreasing trend is the spot diameter at the beginning of the second decreasing trend. Optionally, the first included angle is greater than the second included angle, and the first depth is less than the second depth.

[0032] Optionally, the sizes of the spot diameters of the first laser beam and the second laser beam are realized by the cooperation of a dynamic lens system and / or a laser cavity length. By controlling the size of the spot diameter, the shape of the through hole is changed to realize the preparation of a through hole including different conical surfaces.

[0033] Optionally, in S2, the wavelength of the first laser beam and the second laser beam is between 230 nm and 270 nm.

[0034] The present application finds that, in the process of laser drilling of the polymer substrate with a wavelength of 230-270 nm, a non-thermal etching photochemical reaction is utilized, that is, the chemical bonds in the polymer are broken by high-energy photons to achieve "non-contact" to achieve the purpose of removing the irradiated part from the substrate. On the one hand, this process is different from the traditional thermal etching principle of laser drilling, which will not cause the ablation expansion area on the basis of the designed aperture, affecting the accurate preparation of the aperture, on the other hand, the laser drilling process in this wavelength range will not change the chemical composition of the through-hole wall, which lays the foundation for the subsequent construction of the gradient hydrophobicity of the through-hole wall surface modification treatment (the gradient hydrophobicity of the through-hole wall is controlled by controlling the oxygen-carbon element ratio of the through-hole wall through surface modification treatment), in addition, the polymer substrate after drilling will not produce wrinkles caused by the thermal etching process, ensuring the flatness of the composite current collector film, and then realizing the stability of the electrode sheet and improving the cycle life of the battery.

[0035] In this embodiment, the front surface and the back surface of the polymer substrate are double drilled by the laser drilling process, and the spot diameter of the laser beam is adjusted to form a structure with a first conical surface-second conical surface-fourth conical surface-third conical surface. Realize in physical structure, guide the atoms of metal plating layer to fill in the middle part of the through hole, improve the filling degree of the through hole.

[0036] Optionally, the first laser beam and the second laser beam are the same.

[0037] Optionally, the first laser beam and the second laser beam are perpendicular to the front surface and the back surface, respectively.

[0038] Optionally, in S3, the surface modification treatment includes:

[0039] The polymer substrate passes through the modification process area, and the modification process area includes a front modification process section and a rear modification process section. The front modification process section and the rear modification process section each include a group of nozzle assemblies, and the nozzle assemblies include first nozzles, second nozzles, and third nozzles arranged concentrically and from inside to outside. When the polymer substrate passes through the front modification process section, the inner wall of the through hole from the end of the through hole located on the front surface to the throat is surface modified by the nozzle assembly; when the polymer substrate passes through the rear modification process section, the inner wall of the through hole from the end of the through hole located on the back surface to the throat is surface modified by the nozzle assembly, so that the hydrophobicity of the inner wall of the through hole gradually weakens from the area corresponding to the first decreasing trend to the area corresponding to the second decreasing trend, forming a through hole inner wall with gradient hydrophobicity; the hydrophobicity of the inner wall corresponding to the throat of the through hole is the weakest, and the inner wall of the throat has relatively weak hydrophobicity.

[0040] The surface modification specifically includes:

[0041] The first nozzle sprays a support gas column, and the diameter of the support gas column is less than or equal to the diameter of the through-hole throat;

[0042] The second nozzle sprays annular process gas, and the inner ring diameter of the process gas is equal to the diameter of the support gas column, and the outer ring diameter of the process gas is equal to the hole diameter of the two ends of the through-hole. The support gas column mainly plays a "positioning" role, controls the radial thickness of the process gas in the through-hole, and determines the degree of hydrophobic reaction; the radial thickness of the process gas in the through-hole is squeezed by the support gas column to control the degree of hydrophobic reaction of the inner wall surface. Taking the former modification process section as an example, since the hole diameter of the through-hole gradually decreases from the two ends of the through-hole to the through-hole throat, the radial thickness of the area formed by the process gas entering the through-hole also gradually decreases, so that the process gas in the area corresponding to the first conical surface is relatively more, which can carry away relatively more oxygen elements; the process gas in the area corresponding to the second conical surface is relatively less, which can carry away relatively less oxygen elements; the process gas at the position corresponding to the through-hole throat is the least, which can carry away the least oxygen elements. The process of the latter modification process section is the same as that of the former modification process section. Through the chemical reaction between the process gas and the inner wall of the through-hole, the through-hole from the two ends to the through-hole throat presents a gradient hydrophobicity.

[0043] The third nozzle sprays annular positioning gas towards the surface of the polymer substrate, and the inner ring diameter of the positioning gas is equal to the hole diameter of the two ends of the through-hole, and the outer ring diameter of the positioning gas is greater than the hole diameter of the two ends of the through-hole, and the outer ring diameter of the positioning gas gradually decreases during spraying, which can play a "directional" role. The directional gas spraying direction is straight to the surface of the polymer substrate close to the through-hole, and tends to the inside of the through-hole, so as to prevent the process gas sprayed by the second nozzle from spreading in the vacuum chamber.

[0044] The support gas column and the positioning gas respectively limit the process gas in the reaction area between the inner wall of the through-hole and the support gas column from the inside and the outside, which can accurately make the process gas react with the inner wall of the through-hole to form a through-hole inner wall with gradient hydrophobicity.

[0045] In this embodiment, by adopting the cooperation of "support gas column-process gas-positioning gas", the reaction degree of the inner wall of the through-hole with the process gas is controlled, and the gradient hydrophobicity of the inner wall of the through-hole in chemical composition is realized. The improvement of the physical structure of the through-hole cooperates with the atomic collision and accumulation of the metal coating to the through-hole throat, which drives and guides the metal coating, so as to facilitate the complete filling of the through-hole in the subsequent metal coating deposition process.

[0046] Optionally, the temperature of the process gas is 60-120℃. In this temperature range, the process gas is more likely to react with the polymer substrate of the through-hole wall. At the same time, the temperature of the process gas is limited to below the thermal deformation temperature of the polymer, so as to prevent the thermal deformation of the polymer substrate.

[0047] Optionally, the process gas is one or more selected from CO, NO, SO, CH4, H2S, PH3, SiH4, HI, HBr. The process gas can react with the polymer substrate on the inner wall of the through hole and take away oxygen in the polymer substrate corresponding to the inner wall, so as to reduce the oxygen-carbon element ratio.

[0048] Optionally, the gas pressure of the process gas entering the area formed inside the through hole is less than the gas pressure of the support gas column entering the area formed inside the through hole. In this way, the support gas column can be prevented from being penetrated by the process gas, so as to achieve the effect of extruding the process gas in the through hole in the radial direction.

[0049] Optionally, the temperature of the gas of the support gas column and the positioning gas is room temperature, and the gas of the support gas column and the positioning gas is one or more selected from N2, Ar, He, Ne, Kr, Xe.

[0050] Optionally, the first nozzle, the second nozzle and the third nozzle spray gas to the polymer substrate at the same jet frequency to complete the preparation of the gradient hydrophobicity of the same through hole. Optionally, the through holes obtained by laser drilling on the polymer substrate are arranged in an array, and the laser drilling frequency of the first laser beam and the second laser beam and the jet frequency of the first nozzle, the second nozzle and the third nozzle are matched and corresponded to the interval between the adjacent two rows of through holes along the film moving direction and the roller speed of the coating machine, so as to accurately realize the laser drilling and the gradient hydrophobicity reaction on the inner wall of the through hole.

[0051] Optionally, the recovery device is further included in the front modification process section and the rear modification process section respectively, for recovering the residual gas after surface modification. When the polymer substrate passes through the front modification process section, the recovery device recovers the residual gas after surface modification flowing out of the through hole on the reverse side. When the polymer substrate passes through the rear modification process section, the recovery device recovers the residual gas after surface modification flowing out of the through hole on the front side. In this way, the gas sprayed by the nozzle assembly can be prevented from flowing out and spreading in the vacuum chamber after reaction in the through hole.

[0052] Optionally, in S4, the metal plating layer of the polymer substrate is prepared by a vacuum coating method; and the vacuum coating method is any one selected from magnetron sputtering, vacuum evaporation and ion plating.

[0053] Optionally, the preparation of the metal plating layer of the polymer substrate by the vacuum coating method specifically includes: when the magnetron sputtering is used, the power is 20-35kw, the base vacuum degree is less than or equal to 5x10 -2 Pa, and the roller speed of the coating main roller is 1-20m / min.

[0054] Optionally, the metal plating layer of the polymer substrate is prepared by vacuum plating, which specifically includes: when vacuum evaporation is used, the evaporation boat is heated to 600-1700 DEG C, the background vacuum degree is less than or equal to 5*10 -2 Pa, and the roller speed is 60-200 m / min.

[0055] Optionally, the metal plating layer of the polymer substrate is prepared by vacuum plating, which specifically includes: when ion plating is used, the background vacuum degree is less than or equal to 5*10 -3 Pa, the bias voltage is 50-300 V, and the arc current is 50-150 A.

[0056] Optionally, the metal plating layer on the front surface and the back surface is the same in composition.

[0057] Optionally, the deposition of the metal plating layer of the polymer substrate and the filling of the through hole are carried out simultaneously.

[0058] Optionally, the first area and the second area of the through hole are both plated by vacuum plating to completely fill the metal plating layer of the polymer substrate, thereby improving the filling degree of the through hole. Meanwhile, the surface of the polymer substrate after vacuum plating is flat on the corresponding metal plating layer surface above and below the area with the through hole and the area without the through hole.

[0059] The present application utilizes a laser beam with a set wavelength and a set spot diameter to prepare a through hole structure with a controlled atomic directional movement function of the metal plating layer, and simultaneously realizes the formation of the front surface and the back surface of the polymer substrate and the dense and complete filling of the through hole. Specifically, a short wavelength laser is used to control the spot diameter to prepare a through hole structure of "first conical surface-second conical surface-fourth conical surface-third conical surface", and through the degree of hydrophobic reaction between the process gas and the surface of the through hole, the preparation of the gradient hydrophobicity of the inner wall of the through hole is realized, the atoms of the metal plating layer are guided and driven to preferentially deposit, accumulate and grow at the throat of the through hole, so as to realize the vacuum plating filling of the through hole, and the filling degree of the through hole is more than 99.7%.

[0060] The preparation method of the composite current collector film provided by the present application can realize the following technical effects:

[0061] (1) By adopting the cooperation of "supporting air column-process gas-positioning gas", the reaction degree of the inner wall of the via hole and the process gas is controlled, the gradient hydrophobicity of the inner wall of the via hole in chemical composition is realized by the modification process, and the improvement of the physical structure of the via hole cooperates to drive and guide the atomic collision and accumulation of the metal plating layer to the via hole throat, so that the via hole is completely filled in the subsequent metal plating layer deposition process, the filling degree is greater than 99.7%, the metal plating layer on the front and back surfaces of the polymer substrate is tightly connected as a whole, the bonding force between the polymer substrate and the metal plating layer is greatly improved, the adhesion of the metal plating layer and the polymer substrate is inhibited, the stability of the electrode sheet in the electrolyte is improved, and the cycle life of the battery is prolonged. The metal plating layers on the front and back surfaces are interconnected, thereby reducing the thickness of the metal plating layer and further improving the energy density of the battery.

[0062] (2) The filling material in the via hole is consistent with the surface metal plating layer of the polymer substrate, there is no electronic transfer interface resistance, and the front and back surfaces of the polymer substrate can realize the same electrical interconnection as the traditional metal foil current collector. The metal plating layer filled in the via hole provides tension and strengthens the adhesion of the metal plating layer on the surface of the polymer substrate, so as to avoid the separation of the metal plating layers on the front and back surfaces of the polymer.

[0063] (3) The interconnection of the metal plating layers on the front and back surfaces of the polymer substrate can ensure the consistency of the electronic transfer between the composite current collector film double-sided electrode material layer and the composite current collector film, balance the voltage and current, continue the single-sided tab welding process of the copper and aluminum foil current collector, and solve the equipment upgrading problem caused by the traditional composite current collector. In addition, the electronic transmission cross-sectional area is increased, the electronic transmission resistance is further reduced, the fast charging performance of the battery can be improved if the thickness of the metal plating layer remains unchanged, and the thickness of the metal plating layer can be reduced if the resistance of the metal plating layer remains unchanged.

[0064] (4) The preparation method of the present application is an industrialized technology suitable for mass production of composite current collectors, which is conducive to reducing the manufacturing cost of composite current collectors, promoting the commercial application of composite current collectors in the field of lithium batteries, and further improving the energy density of the battery.

[0065] The above general description and the following description are only exemplary and explanatory, and are not used to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0066] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitation on the embodiments, elements with the same reference numerals in the drawings show similar elements, and the drawings do not constitute proportional limitation.

[0067] Figure 1 The structure of the composite current collector film involved in the present application is shown in the schematic diagram.

[0068] Figure 2is a schematic diagram of the cross-sectional structure of the through hole in the application;

[0069] Figure 3 is a schematic diagram of the spot diameters of the first laser beam and the second laser beam in the application showing a decreasing trend during the laser drilling process;

[0070] Figure 4 is a schematic diagram of the nozzle assembly performing surface modification treatment on the inner wall of the through hole in the application. DETAILED DESCRIPTION

[0071] In order to enable a more detailed understanding of the features and technical content of the application, the implementation of the application will be described in detail below in conjunction with the accompanying drawings, which are for reference only and do not limit the application. In the following technical description, for the convenience of explanation, a plurality of details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be simplified to facilitate the drawings.

[0072] The terms "first", "second", "front", "back", etc. in the specification and claims of the application and the above-mentioned drawings are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances to implement the embodiments of the application described herein.

[0073] The term "and / or" is a description of the association relationship of the object, which means that there can be three relationships. For example, A and / or B, which means that there are three relationships of A or B, or A and B.

[0074] The term "corresponding" can refer to an association or binding relationship, and A corresponds to B means that there is an association or binding relationship between A and B.

[0075] Figure 1 is a schematic diagram of the structure of the composite current collector film involved in the application. As shown in Figure 1 The composite current collector film includes a polymer substrate 1 and a metal plating layer 2 and a metal plating layer 3. The polymer substrate 1 includes a front surface and a back surface, and a through hole 4 is provided in the front-to-back direction. The metal plating layer 2 and the metal plating layer 3 are respectively located on the front surface and the back surface, and the through hole is filled with metal plating material to make the metal plating layers on the front surface and the back surface communicate. The aperture of the through hole is 0.5-5 μm.

[0076] The polymer substrate is selected from polyethylene terephthalate, polypropylene, polycarbonate, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polyethylene, and polytetrafluoroethylene. The metal coating is selected from one or more of copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotubes, Ketjen black, acetylene black, graphite powder, and carbon fiber.

[0077] The thickness of the polymer substrate is 0.5μm-4.5μm. The thickness of the metal coating is 0.3μm-1μm.

[0078] Optionally, the porosity of the through-hole is 1%-10%. Specifically, the porosity of the through-hole is 2%-8%.

[0079] Figure 2 This is a schematic diagram of the cross-sectional structure of the through hole in this invention, as shown below. Figure 2 As shown, the through-hole 4 includes a first region and a second region. The first region is located near the front side of the polymer substrate 1 and includes a first conical surface 5 and a second conical surface 6. The diameter of the through-hole corresponding to the first conical surface 5 decreases from 1.3μm-5μm from the end face of the through-hole to 0.8μm-2μm from the middle face. The second conical surface 6 is connected to the first conical surface 5, and the diameter of the corresponding through-hole decreases from 0.8μm-2μm to 0.5μm-1μm. The second region is located near the reverse side of the polymer substrate 1 and is the same size and symmetrical in shape as the first region. The second region includes a third conical surface 7 symmetrically arranged with respect to the first conical surface 5 and a fourth conical surface 8 symmetrically arranged with respect to the second conical surface 6. The second conical surface 6 and the fourth conical surface 8 intersect to form the throat 9 of the through-hole, and the diameter of the throat 9 is 0.5μm-1μm. The diameter of the through-hole corresponding to the first and second regions gradually decreases from both ends of the through-hole to the throat. The junction of the first conical surface 5 and the second conical surface 6, as well as the junction of the third conical surface 7 and the fourth conical surface 8, have protruding edges 10 and 11, respectively.

[0080] The first conical surface forms a first angle of 45°-90° with the normal of the polymer substrate. The second conical surface forms a second angle of 17°-64° with the normal of the polymer substrate. The first angle is greater than the second angle. The through-hole depth in the region corresponding to the first conical surface 5 is a first depth b. The through-hole depth in the region corresponding to the second conical surface 6 is a second depth c. The first depth b is less than the second depth c.

[0081] The inner wall of the through-hole exhibits gradient hydrophobicity. Specifically, the hydrophobicity of the inner wall corresponding to the first region gradually decreases from the first conical surface to the second conical surface. The hydrophobicity of the inner wall corresponding to the second region is symmetrical to that of the first region, i.e., the hydrophobicity gradually decreases from the third conical surface to the fourth conical surface. The hydrophobicity of the inner wall corresponding to the throat of the through-hole is the weakest, and the inner wall of the throat also exhibits relatively weak hydrophobicity.

[0082] The ratio a of oxygen-carbon element composition of the inner wall surface of the through hole with gradient hydrophobicity is in the range of 10-40%, and the ratio a gradually increases from the inner wall corresponding to the two ends of the through hole to the inner wall corresponding to the throat of the through hole. The a value of the inner wall near the end of the through hole is in the range of 10-25%, the a value of the inner wall of the throat is in the range of 25-40%, and the a value of the inner wall of the throat is 10-20% higher than the a value of the inner wall near the end of the through hole.

[0083] Optionally, the ratio of oxygen-carbon element composition of the inner wall surface of the through hole with gradient hydrophobicity is less than the ratio of oxygen-carbon element composition of the surface of the polymer substrate.

[0084] In this embodiment, the ratio a of oxygen-carbon element composition of the inner wall surface of the through hole characterizes the hydrophobicity, and the gradient hydrophobicity of the inner wall of the through hole is realized by controlling the ratio of oxygen-carbon element composition of the inner wall surface of the through hole through surface modification treatment.

[0085] In the present application, a preparation method of the composite current collector film is provided, and the preparation method comprises:

[0086] S1: flattening and fixing the polymer substrate;

[0087] S2: laser drilling along the normal direction of the polymer substrate to obtain a polymer substrate with through holes with a pore size of 0.5-5 μm;

[0088] S3: surface modification treatment is performed on the inner wall of the through hole to make the inner wall of the through hole have gradient hydrophobicity;

[0089] S4: a metal plating layer is prepared on the front surface and the back surface of the polymer substrate with through holes with gradient hydrophobicity respectively by using a metal plating material, and the metal plating material fills the through holes, wherein the filling degree of the metal plating material in the through holes is more than 99.7%;

[0090] S5: the tab is welded to any one of the metal plating layers to make the upper and lower active materials of the composite current collector film conductive.

[0091] Optionally, in S2, the polymer substrate passes through a drilling process area. The drilling process area includes a front drilling process section and a rear drilling process section. When the polymer substrate passes through the front drilling process section, the front surface is laser drilled by a first laser beam. When the polymer substrate passes through the rear drilling process section, the back surface is laser drilled by a second laser beam. In the laser drilling process, the spot diameters of the first laser beam and the second laser beam both show a decreasing trend, so that the pore size of the formed through holes gradually decreases from the two ends of the through holes to the middle of the through holes, and the middle of the through holes converges into a throat.

[0092] Figure 3This is a schematic diagram showing that the spot diameters of the first and second laser beams in this invention decrease during the laser drilling process. The spot diameters 22 of the first and second laser beams emitted by laser 12 have the following characteristics during the drilling process: Figure 3 The decreasing trend shown includes a first decreasing trend 13 and a second decreasing trend 14. In the first decreasing trend 13, the spot diameter decreases from 1.3 μm-5 μm to 0.8 μm-2 μm to form a first conical surface 5 and a third conical surface 7 of a through-hole. The inner wall of the through-hole in the corresponding region forms a first angle of 45°-90° with the normal to the polymer substrate, and the through-hole depth in the corresponding region is a first depth. In the second decreasing trend 14, the spot diameter decreases from 0.8 μm-2 μm to 0.5 μm-1 μm to form a second conical surface 6 and a fourth conical surface 8. The inner wall of the through-hole in the corresponding region forms a second angle of 17°-64° with the normal to the polymer substrate, and the through-hole depth in the corresponding region is a second depth. The spot diameter at the end of the first decreasing trend is the same as the spot diameter at the beginning of the second decreasing trend. Optionally, the first angle is greater than the second angle, and the first depth is less than the second depth.

[0093] Optionally, the spot diameters of both the first and second laser beams are achieved through a dynamic lens system and / or by coordinating the laser cavity length. By controlling the spot diameter, the shape of the through-hole can be changed, enabling the fabrication of through-holes with different conical surfaces.

[0094] Optionally, in S2, the wavelengths of both the first and second laser beams are between 230nm and 270nm.

[0095] In this embodiment, the front and back sides of the polymer substrate are drilled by laser drilling process in different drilling process stages, and the spot diameter of the laser beam is adjusted so that the through hole forms a structure with a first conical surface - a second conical surface - a fourth conical surface - a third conical surface.

[0096] Optionally, the first laser beam and the second laser beam are identical. The first laser beam and the second laser beam are incident perpendicularly on the front and back surfaces, respectively.

[0097] In S3, surface modification treatment includes:

[0098] The polymer substrate passes through a modification process zone, the modification process zone including a front modification process section and a rear modification process section, the front modification process section and the rear modification process section each including a set of nozzle assemblies. When the polymer substrate passes through the front modification process section, the inner wall of the through hole from the through hole end located at the front side to the throat is surface modified by the nozzle assemblies. When the polymer substrate passes through the rear modification process section, the inner wall of the through hole from the through hole end located at the rear side to the throat is surface modified by the nozzle assemblies, so that the hydrophobicity of the inner wall of the through hole gradually weakens from the region corresponding to the first decreasing trend to the region corresponding to the second decreasing trend, forming a through hole inner wall with gradient hydrophobicity. Figure 4 is a schematic diagram of the nozzle assembly in the present application for surface modification of the inner wall of the through hole, as Figure 4 shown, the nozzle assembly includes first nozzles 15, second nozzles 16 and third nozzles 17 arranged concentrically from inside to outside.

[0099] The surface modification specifically includes:

[0100] The first nozzles 15 spray support gas columns 18, and the diameter of the support gas columns 18 is less than or equal to the diameter of the throat 9 of the through hole;

[0101] The second nozzles 16 spray annular process gas 19, and the inner ring diameter of the process gas 19 is equal to the diameter of the support gas columns 18, and the outer ring diameter of the process gas 19 is equal to the hole diameter of the two ends of the through hole 4. The radial thickness of the process gas 19 in the through hole is controlled by the support gas columns 18, so as to control the reaction degree of the surface hydrophobicity of the inner wall. Taking the front modification process section as an example, since the hole diameter of the through hole gradually decreases from the two ends of the through hole to the throat of the through hole, the radial thickness of the region formed by the process gas entering the through hole also gradually decreases, so that the process gas in the region corresponding to the first conical surface is relatively more, which can carry away relatively more oxygen elements; the process gas in the region corresponding to the second conical surface is relatively less, which can carry away relatively less oxygen elements; and the process gas at the position corresponding to the throat of the through hole is the least, which can carry away the least oxygen elements. The process of the rear modification process section is the same as that of the front modification process section. Through the chemical reaction between the process gas and the inner wall of the through hole, the through hole from the two ends to the throat presents gradient hydrophobicity.

[0102] The third nozzles 17 are directed towards the surface of the polymer substrate 1 and spray annular positioning gas 20, the inner ring diameter of the positioning gas 20 is equal to the hole diameter of the two ends of the through hole 4, the outer ring diameter of the positioning gas 20 is greater than the hole diameter of the two ends of the through hole 4, and the outer ring diameter of the positioning gas 20 gradually decreases in the process of spraying, which can play a "directional" role. The direction of the directional gas is straightly close to the surface of the polymer substrate 1 of the through hole, and tends to the inside of the through hole, so as to prevent the process gas sprayed by the second nozzles from spreading in the vacuum chamber.

[0103] Optionally, the temperature of the process gas is 60-120℃. The process gas is one or more selected from CO, NO, SO, CH4, H2S, PH3, SiH4, HI, HBr.

[0104] Optionally, the gas pressure of the process gas entering the area formed inside the through hole is less than the gas pressure of the supporting gas column entering the area formed inside the through hole, which has the effect of extruding the process gas in the through hole to control the radial thickness of the process gas.

[0105] Optionally, the temperature of the supporting gas column and the positioning gas is room temperature, and the supporting gas column and the positioning gas are one or more selected from N2, Ar, He, Ne, Kr, Xe.

[0106] Optionally, the first nozzle, the second nozzle and the third nozzle spray gas to the polymer substrate at the same jet frequency to complete the preparation of the gradient hydrophobicity of the same through hole. The through holes obtained by laser drilling on the polymer substrate are arranged in an array, and the laser drilling frequency of the first laser beam and the second laser beam, and the jet frequency of the first nozzle, the second nozzle and the third nozzle are matched with the pitch between the adjacent two rows of through holes along the film moving direction and the roller speed (film moving speed) of the coating machine.

[0107] Optionally, the front modification process section and the rear modification process section further comprise a recovery device 21 respectively for recovering the residual gas after surface modification. When the polymer substrate passes through the front modification process section, the recovery device 21 is used to recover the residual gas after surface modification flowing out of the through hole on the reverse side. When the polymer substrate passes through the rear modification process section, the recovery device is used to recover the residual gas after surface modification flowing out of the through hole on the front side. In this way, the gas sprayed by the nozzle assembly can be prevented from flowing out and spreading in the vacuum chamber after reacting in the through hole.

[0108] In S4, the metal coating layer of the polymer substrate is prepared by a vacuum coating method. The vacuum coating method is one selected from magnetron sputtering, vacuum evaporation and ion plating. The preparation of the metal coating layer of the polymer substrate by the vacuum coating method specifically includes:

[0109] When the magnetron sputtering is used, the power is 20-35kw, the base vacuum degree is less than or equal to 5×10 -2 Pa, and the roller speed of the coating main roller is 1-20m / min. When the vacuum evaporation is used, the evaporation boat is heated to 600-1700℃, the base vacuum degree is less than or equal to 5×10 -2 Pa, and the roller speed is 60-200m / min. When the ion plating is used, the base vacuum degree is less than or equal to 5×10 -3 Pa, the bias voltage is 50-300V, and the arc current is 50-150A.

[0110] Optionally, the metal plating layer on the front side and the back side has the same composition.

[0111] Optionally, the metal plating layer of the polymer substrate is deposited simultaneously with the filling of the through hole to fill the through hole.

[0112] Optionally, the first area and the second area of the through hole are both filled with the metal plating layer of the polymer substrate by vacuum plating, thereby improving the filling degree of the through hole. Meanwhile, the surface of the polymer substrate after vacuum plating is flat in the area with the through hole and the area without the through hole.

[0113] The composite current collector film in the embodiment is an overall conductive composite current collector film. The active material on the front side and the back side of the composite current collector film can be connected by welding the tab to any layer of the metal plating layer. If the polymer substrate does not have a through hole, the metal plating layers on the front side and the back side are not connected to each other, so the tabs need to be welded on the front side and the back side of the composite current collector, respectively. However, the welding process of the tabs on both sides reduces the yield of the welding process of the tabs, and the yield of the welding process of the tabs on both sides can only reach about 93%. In addition, the welding process of the tabs on both sides also brings pressure to the welding process and equipment of the single-sided welding process of the current copper and aluminum foil current collector industrialization process. The yield of the welding process of the tabs on one side of the composite current collector film in the present application can reach a high level of about 99%, and the welding process and equipment of the single-sided welding process of the current copper and aluminum foil current collector industrialization process can still be used, which is beneficial to simplifying the process and matching the existing production line.

[0114] Hereinafter, the present application will be described through specific examples. In addition, these examples are used to illustrate the present application, and do not limit the scope of the present application.

[0115] Example 1

[0116] A composite current collector film is prepared by the following steps:

[0117] S1: Select polyethylene terephthalate (PET) with a thickness of 1 μm as a polymer substrate, and fix the polymer substrate by flattening through a winding system;

[0118] S2: In the drilling process area, laser drilling is performed along the normal direction of the polymer substrate using a first laser beam and a second laser beam. In the front drilling process section, during laser drilling of the front surface using the first laser beam, the wavelength of the first laser beam is controlled to be 240-260 nm, and the first laser beam spot diameter is controlled to decrease from 3 μm to 1.4 μm when the first conical surface is constructed. Then, when the second conical surface is constructed, the first laser beam spot diameter is controlled to decrease from 1.4 μm to 1 μm, and a "first conical surface-second conical surface" through-hole structure is formed in the first region. In the rear drilling process section, during laser drilling of the back surface using the second laser beam which is the same as the first laser beam, the wavelength of the second laser beam is controlled to be 240-260 nm, and the first laser beam spot diameter is controlled to decrease from 3 μm to 1.4 μm when the third conical surface is constructed. Then, when the fourth conical surface is constructed, the first laser beam spot diameter is controlled to decrease from 1.4 μm to 1 μm, and a "third conical surface-fourth conical surface" through-hole structure symmetric to the first region is formed in the second region. The depths of the first conical surface and the third conical surface are both 0.2 μm, and the depths of the second conical surface and the fourth conical surface are both 0.3 μm. The first conical surface and the third conical surface each form a first included angle of 76° with the normal direction of the polymer substrate. The second conical surface and the fourth conical surface each form a second included angle of 34° with the normal direction of the polymer substrate. The porosity of the through-hole on the polymer substrate is 5%.

[0119] S3: In the modification process area, the inner wall of the through-hole is subjected to surface modification treatment using a nozzle assembly and a recovery device, so that the inner wall of the through-hole has gradient hydrophobicity. In the front modification process section, during surface modification treatment of the front surface using the nozzle assembly, the first nozzle sprays an N2 support gas column with a column diameter of 1 μm; the second nozzle sprays CO process gas at a temperature of 95°C; the third nozzle sprays N2 positioning gas, and the recovery device corresponding to the nozzle assembly collects residual gas flowing out of the through-hole on the back surface. In the rear modification process section, the back surface is subjected to similar surface modification treatment using the nozzle assembly.

[0120] S4: In a vacuum evaporation manner, a metal aluminum layer with a thickness of 0.5 μm is prepared on the front surface and the back surface of the polymer substrate obtained in step S3, and the through-hole filling is simultaneously completed. The evaporation boat is heated to 1300°C, the background vacuum degree is 5×10 -2 Pa, and the roller speed is 100 m / min.

[0121] S5: The tab is welded to any one of the metal aluminum layers in step S4 to connect the active materials on the upper and lower surfaces of the composite current collector film.

[0122] Example 2

[0123] A composite current collector film was prepared using substantially the same process steps as in Example 1, but wherein the parameters of the through-hole structure obtained were different from those in Example 1, as shown in Table 1.

[0124] Comparative Example 1

[0125] A composite current collector film was prepared using substantially the same process steps as in Example 1. However, the S3 step in which the inner wall of the through-hole was made to have gradient hydrophobicity by surface modification treatment was not included, and instead the inner wall of the through-hole was treated to have hydrophilicity.

[0126] Comparative Example 2

[0127] A composite current collector film was prepared using substantially the same process steps as in Example 1. However, the S3 step in which the inner wall of the through-hole was made to have gradient hydrophobicity by surface modification treatment was not included, i.e. the inner wall of the through-hole was not treated to have hydrophobicity or hydrophilicity.

[0128] Comparative Example 3

[0129] A comparative composite current collector film was prepared by the following steps:

[0130] S1: A polyethylene terephthalate (PET) with a thickness of 1 pm was selected as the polymer substrate, and the polymer substrate was flattened and fixed by a winding system.

[0131] S2: In the punching process area, a laser beam was used to perform laser punching along the normal direction of the polymer substrate. The wavelength of the laser beam was 240-260 nm, and the spot diameter of the laser beam was 1 pm, forming vertical cylindrical through-holes with a uniform aperture of 1 pm.

[0132] The subsequent steps were the same as the corresponding steps in Example 1.

[0133] Comparative Example 4

[0134] A comparative composite current collector film was prepared by the following steps:

[0135] S1: A polyethylene terephthalate (PET) with a thickness of 1 pm was selected as the polymer substrate, and the polymer substrate was flattened and fixed by a winding system.

[0136] S2: A metal aluminum layer with a thickness of 0.8 pm was prepared on the front and back surfaces of the polymer substrate by vacuum evaporation. The evaporation boat was heated to 1300°C, and the background vacuum degree was 5x10 -2 Pa, and the roller speed was 100 m / min.

[0137] That is, the composite current collector film in Comparative Example 4 does not include through-holes on the polymer substrate.

[0138] The characteristics of the composite current collector films in the above examples and comparative examples are shown in Table 1.

[0139] Table 1. Comparison of characteristics of the composite current collector films in the examples and comparative examples

[0140]

[0141] The composite current collector films prepared in the examples and comparative examples were used as the positive electrode current collector, 6 μm copper foil was used as the negative electrode current collector, the active material was graphite, the active material was lithium cobaltate, the electrolyte was carbonate solution containing 1 M LiPF6, and Celgard 2400 was used as the separator to assemble a 2000 mAh soft pack battery.

[0142] The batteries assembled using the above composite current collector films and corresponding electrode sheets were tested, and the test results are shown in Table 2.

[0143] Table 2. Comparison of the performance of the composite current collector films and the cycle life performance of the corresponding batteries in the examples and comparative examples

[0144]

[0145] As can be seen from the test data in Table 2, the composite current collector films in Examples 1 and 2 were prepared using the preparation method of the present application, and the through holes were completely filled with the metal plating layer material. Through microscopic analysis of the through hole filling condition, it was found that the metal plating layer material completely filled the through holes without any gap, and the through hole filling degree reached 99.8 and 99.9%, respectively.

[0146] The metal plating material filled in the through holes of the polymer substrate in Example 1 and Example 2 connects the metal plating layers on the front and back surfaces of the polymer substrate into one body, which expands the lateral electron transmission path of the composite current collector film compared with the composite current collector film in Comparative Example 4, and the metal plating material completely fills the through holes. Therefore, although the thickness of the metal plating layer in Example 1 and 2 is only 0.5 μm, which is about 63% of the thickness of the metal plating layer in Comparative Example 4, the average conductivity of the composite current collector film is significantly higher than that of Comparative Example 4, and has approached the theoretical conductivity of the aluminum foil. The thickness of the composite current collector film prepared in Example 1 and 2 is reduced by about 25% compared with Comparative Example 4, and the energy density of the battery is also improved. In the composite current collector film prepared in Example 1 and 2, the metal plating material filled in the through holes tightly connects the polymer substrate and the metal plating layers on the front and back surfaces into one body, which greatly improves the bonding force between the polymer substrate and the metal plating layer, and the peel strength reaches 1145 N / m and 1152 N / m, which is much higher than that of Comparative Example 4. Therefore, the 1C cycle capacity retention performance of the battery made of the composite current collector film prepared in Example 1 and 2 is also much higher than that of Comparative Example 4, and the stability of the electrode sheet in the electrolyte and the cycle life of the battery are obviously improved.

[0147] Although the composite current collector films of Comparative Example 1 and Comparative Example 2 also have through holes filled with metal plating material, the filling density is obviously reduced due to the lack of the gradient hydrophobicity of the inner wall of the through holes in Example 1 and 2. Although the filling of the through holes in Comparative Example 1 and 2 appears to be good from the appearance, the cross-sectional microscopic detection of the filling of the through holes shows that the plating material does not completely fill the inside of the through holes, and there are a certain proportion of defects such as micropores or micro-bridge defects in the filling inside of Comparative Example 1, and the proportion of defects in the filling inside of Comparative Example 2 is larger. These factors affect the communication effect between the metal plating layers on the front and back surfaces, so the conductivity is higher than that of Comparative Example 4, but there is still a significant gap compared with Example 1 and 2. Because there are different proportions of defects (micropores or micro-bridge defects, etc.) in the filling inside of the through holes of Comparative Example 1 and 2, the bonding force between the polymer substrate and the metal plating layer is affected, so the 1C cycle capacity retention performance of the battery is higher than that of Comparative Example 4, but there is still a large gap compared with Example 1 and 2, which affects the stability of the electrode sheet in the electrolyte and the cycle life of the battery.

[0148] In Comparative Example 3, the polymer substrate of the composite current collector film lacks the two-stage conical structure of Examples 1 and 2. Metal plating atoms reaching the inner wall surface of the via cannot migrate, collide, accumulate, or support the via throat. Consequently, the filling degree of the metal plating atoms inside the via is the worst, with a filling degree of only 30.4%. Therefore, the metal plating on both sides cannot achieve good connectivity, resulting in very low conductivity. Similarly, the bonding force between the polymer substrate and the metal plating is also very low. Consequently, the battery performance with the lowest 1C cycle life after 1000 cycles is among the lowest for composite current collector films with vias on a polymer substrate, leading to poor cycle life performance.

[0149] The foregoing description and accompanying drawings fully illustrate embodiments of this disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments.

[0150] Furthermore, the terminology used in this application is for descriptive purposes only and is not intended to limit the claims. As used in the description of the embodiments and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Similarly, the term “and / or” as used in this application refers to any and all possible combinations of one or more of the associated listed terms.

[0151] The methods and products disclosed in the embodiments herein (including but not limited to apparatus, devices, etc.) may be implemented in other ways.

[0152] The embodiments disclosed herein are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from their scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method of making a composite current collector film, characterized by, The composite current collector film comprises a polymer substrate including a front surface and a back surface, a plurality of through holes being provided along a direction from the front surface to the back surface, and metal plating layers respectively located on the front surface and the back surface, wherein the through holes are filled with a metal plating material to make the metal plating layers on the front surface and the back surface communicate with each other, and a preparation method comprises: S1: flattening and fixing the polymer substrate; S2: laser drilling along a normal direction of the polymer substrate to obtain a polymer substrate with through holes, wherein the aperture of the through holes is 0.5-5 μm, and the porosity of the through holes is 1-10%; during the laser drilling, the spot diameter of the laser beam presents a decreasing trend, so that the aperture of the through holes gradually decreases from both ends of the through holes to the middle part of the through holes, and the middle part of the through holes converges into a throat part; the decreasing trend comprises a first decreasing trend and a second decreasing trend; the spot diameter of the first decreasing trend decreases from 1.3-5 μm to 0.8-2 μm, and the spot diameter of the second decreasing trend decreases from 0.8-2 μm to 0.5-1 μm; S3: performing surface modification treatment on the inner wall of the through holes to make the inner wall of the through holes have gradient hydrophobicity; through the surface modification treatment, the hydrophobicity of the inner wall of the through holes gradually weakens from the region corresponding to the first decreasing trend to the region corresponding to the second decreasing trend, so that the inner wall of the through holes has gradient hydrophobicity; S4: using a metal plating material to prepare the metal plating layers on the front surface and the back surface of the polymer substrate respectively, and making the metal plating material fill the through holes; the filling degree of the metal plating material in the through holes is more than 99.7%; S5: welding a tab to any one of the metal plating layers to make the upper and lower active materials of the composite current collector film conductive.

2. The preparation method of the composite current collector film according to claim 1, wherein in S2, the polymer substrate passes through a drilling process area; the drilling process area comprises a front drilling process section and a rear drilling process section; when the polymer substrate passes through the front drilling process section, the front surface is laser drilled by a first laser beam; when the polymer substrate passes through the rear drilling process section, the back surface is laser drilled by a second laser beam; wherein during the laser drilling, the spot diameters of the first laser beam and the second laser beam both present a decreasing trend.

3. The preparation method of the composite current collector film according to claim 2, wherein the inner wall of the through holes in the region corresponding to the first decreasing trend forms a first included angle of 45-90° with the normal direction of the polymer substrate, and the depth of the through holes in the region corresponding to the first decreasing trend is a first depth; the inner wall of the through holes in the region corresponding to the second decreasing trend forms a second included angle of 17-64° with the normal direction of the polymer substrate, and the depth of the through holes in the region corresponding to the second decreasing trend is a second depth; wherein the first included angle is greater than the second included angle, the first depth is less than the second depth, and the spot diameter at the end of the first decreasing trend is the spot diameter at the beginning of the second decreasing trend.

4. The preparation method of the composite current collector film according to claim 2, wherein in S2, the wavelengths of the first laser beam and the second laser beam are both between 230 nm and 270 nm. ​ ​ ​ 5. The method of claim 3, wherein, In S3, the surface modification treatment comprises: The polymer substrate passes through a modification process zone, which comprises a front modification process section and a rear modification process section, and each of the front modification process section and the rear modification process section comprises a set of nozzle assemblies, and each nozzle assembly comprises first, second and third nozzles arranged concentrically from inside to outside; When the polymer substrate passes through the front modification process section, the inner wall of the through hole from the through hole end on the front side to the throat is surface-modified by the nozzle assembly; the surface modification specifically comprises: the first nozzle sprays a support gas column, and the diameter of the support gas column is less than or equal to the diameter of the throat; the second nozzle sprays annular process gas; and the third nozzle sprays annular positioning gas, the inner ring diameter of the positioning gas is equal to the aperture of the two ends of the through hole, and the outer ring diameter of the positioning gas is greater than the aperture of the two ends of the through hole; The support gas column and the positioning gas respectively limit the process gas in the reaction region between the inner wall of the through hole and the support gas column from the inside and the outside, so that the process gas and the inner wall of the through hole undergo a hydrophobic reaction to form the inner wall of the through hole with gradient hydrophobicity; When the polymer substrate passes through the rear modification process section, the inner wall of the through hole from the through hole end on the rear side to the throat is surface-modified by the nozzle assembly.

6. The method of claim 5, wherein, In the front modification process section and the rear modification process section, a recovery device is further included respectively for recovering residual gas after surface modification.

7. The method of claim 5, wherein, The ratio a of the O element composition to the C element composition of the inner wall surface of the through hole with gradient hydrophobicity is 10-40%, and the ratio a gradually decreases from the throat to the direction of the through hole end; the a value of the inner wall close to the through hole end is within the range of 10-25%, the a value of the inner wall of the throat is within the range of 25-40%, and the a value of the inner wall of the throat is 10-20% higher than the a value of the inner wall close to the through hole end.

8. The method of claim 5, wherein, The temperature of the process gas is 60-120°C, and the process gas is one or more selected from CO, NO, SO, CH4, H2S, PH3, SiH4, HI and HBr; The temperatures of the support gas column and the positioning gas are both room temperature, and the support gas column and the positioning gas are respectively one or more selected from N2, Ar, He, Ne, Kr and Xe.

9. The method of claim 1, wherein, In S4, the metal coating layer of the polymer substrate is prepared by a vacuum coating method; the vacuum coating method is any one selected from magnetron sputtering, vacuum evaporation and ion plating; The thickness of the metal coating layer on the polymer substrate is 0.3-1 μm; the deposition of the metal coating layer and the filling of the through hole are carried out simultaneously.

10. The method of claim 1, wherein, The kind of the polymer substrate is one selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polyethylene, and polytetrafluoroethylene; The thickness of the polymer substrate is 0.5 μm to 1.5 μm.

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