Composite current collector and preparation method and application thereof

Abstract

The invention relates to a composite current collector and a preparation method and application thereof. The composite current collector comprises a base film, conductive layers arranged on the two faces of the base film in the thickness direction, and metal layers arranged on the faces, away from the base film, of the conductive layers. The conductive layer comprises a WS2-C3N4 / PANI composite nanofiber material, and the WS2-C3N4 / PANI composite nanofiber material comprises a WS2-C3N4 nanofiber and a polyaniline coating layer, and the surface of the WS2-C3N4 nanofiber is coated with the polyaniline coating layer. The conductive layer containing the WS2-C3N4 / PANI composite nanofiber material is introduced between the base film and the metal layer of the composite current collector, so that on one hand, a W-N bond is formed at a WS2-C3N4 interface in the conductive layer to accelerate electron transfer, and on the other hand, the PANI with good cohesiveness can effectively improve the cohesive force between multiple layers of structures; therefore, the conductivity and the structural stability of the composite current collector are effectively improved, and the secondary battery comprising the composite current collector has better rate capability and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a composite current collector and a preparation method and application thereof. Background Art

[0002] The current collector is a crucial component of lithium-ion batteries. Its primary function is to concentrate the current within the battery, enabling more stable and efficient power output. Currently, the current collectors used in lithium-ion batteries are primarily metal foils, such as copper and aluminum foils. With the advancement of new energy lithium-ion battery technology, traditional current collectors (pure copper and aluminum foils) are reaching their limits in terms of energy density and safety, making them inadequate for the further development and application of lithium-ion battery technology.

[0003] Composite current collectors have attracted attention due to their high safety and high energy density. Currently, the main structure of composite current collectors is a "sandwich structure", consisting of a metal layer-polymer layer-metal layer. The polymer layer produces small burrs when punctured by a needle, and has high safety. In addition, due to the low density of the polymer layer, it is lightweight when used as a current collector, which can increase energy density. However, the middle polymer layer is insulating and has poor conductivity, resulting in high resistance, which reduces the battery's rate performance and cycle performance; the adhesion between the polymer layer and the metal layer is poor, and the thermal expansion coefficients of the two are very different. When the battery is charged and discharged or the temperature changes, stress is easily generated at the interface, causing the metal layer to fall off.

[0004] Based on this, there is an urgent need for a composite current collector with high conductivity and excellent structural stability to further optimize the battery's rate performance and cycle stability while meeting the high energy density and safety requirements of secondary batteries. Summary of the Invention

[0005] To solve the above problems, the present invention provides a composite current collector and its preparation method and application. By introducing a conductive layer comprising WS2-C3N4 / PANI composite nanofiber material between the base film and the metal layer of the composite current collector, on the one hand, the WN bond formed at the WS2-C3N4 interface in the conductive layer is utilized to accelerate electron transfer. At the same time, PANI with good adhesion can effectively improve the adhesion between the multilayer structure, thereby improving the conductivity and structural stability of the composite current collector, so that the secondary battery containing the above composite current collector has better rate performance and cycle performance.

[0006] Specifically, the following technical solutions are provided:

[0007] A first aspect of the present invention provides a composite current collector, comprising a base film, a conductive layer disposed on both sides of the base film along the thickness direction, and a metal layer disposed on a side of the conductive layer away from the base film;

[0008] The conductive layer comprises a WS2-C3N4 / PANI composite nanofiber material, wherein the WS2-C3N4 / PANI composite nanofiber material comprises WS2-C3N4 nanofibers and a polyaniline (PANI) coating layer coated on the surface of the WS2-C3N4 nanofibers.

[0009] Furthermore, the thickness of the base film is preferably 2-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., including but not limited to the thickness values ​​listed above; the material of the base film can be selected from one or more of polyethylene terephthalate, polypropylene, polyethylene, polyimide, and polyvinylidene fluoride.

[0010] Furthermore, the thickness of the conductive layer is preferably 2-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., including but not limited to the thickness values ​​listed above.

[0011] Furthermore, the length of the WS2-C3N4 / PANI composite nanofiber material is preferably 20-35 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, etc., and the diameter is preferably 2-10 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc.

[0012] Furthermore, the thickness of the polyaniline coating layer is preferably 1-5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc., including but not limited to the thickness values ​​listed above.

[0013] Furthermore, the thickness of the metal layer is preferably 1-2 μm, for example, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, etc., including but not limited to the thickness values ​​listed above; the material of the metal layer is preferably aluminum or copper.

[0014] Furthermore, the base film is provided with one or more through holes along the thickness direction, and the conductive layers arranged on both sides of the base film along the thickness direction form an interconnected structure through the through holes; preferably, the aperture of the through holes is 50-100 μm; the total area of ​​the through holes accounts for 10%-20% of the single-side area of ​​the base film along the thickness direction.

[0015] The second aspect of the present invention provides a method for preparing the composite current collector according to the first aspect, comprising the following steps:

[0016] S1, dispersing WS2-C3N4 nanomaterials in an inorganic acid solution containing aniline, adding an initiator and a stabilizer for reaction, and obtaining a WS2-C3N4 / PANI composite nanofiber material after washing and drying;

[0017] S2, uniformly sputtering the WS2-C3N4 / PANI composite nanofiber material on the upper and lower surfaces of the base film by magnetron sputtering to form a conductive layer;

[0018] S3. Use magnetron sputtering to uniformly sputter metal on the side of the conductive layer away from the base film to form a metal layer, thereby obtaining the composite current collector.

[0019] Furthermore, in step S1, the mass ratio of the WS2-C3N4 nanomaterial to the aniline is preferably (1-5):1, such as 1:1, 2:1, 3:1, 4:1, 5:1, etc., including but not limited to the mass ratios listed above.

[0020] Furthermore, in step S1, the inorganic acid can be selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and other conventional inorganic acids in the art can also be used.

[0021] Furthermore, in step S1, the initiator is selected from one or more of ammonium persulfate, potassium persulfate, and ferric chloride; and the stabilizer is selected from one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and polyacrylic acid.

[0022] Furthermore, in step S1, the reaction temperature is preferably 0-15°C, for example 5°C.

[0023] Furthermore, in step S1, an initiator is first added and stirred for 0.5-1 h, and then a stabilizer is added and the stirring reaction is continued for 24-48 h.

[0024] Furthermore, in step S1, the washing solvent is water and / or an alcohol solvent, and the alcohol solvent includes but is not limited to ethanol.

[0025] Furthermore, in step S2, the base film is first laser-drilled to obtain one or more through holes penetrating the base film, and then the WS2-C3N4 / PANI composite nanofiber material is uniformly sputtered on the upper and lower surfaces of the base film by magnetron sputtering, so that the conductive layers formed on the upper and lower surfaces of the base film can form an interconnected structure through the through holes.

[0026] A third aspect of the present invention provides a pole piece comprising the composite current collector described in the first aspect or the composite current collector prepared by the preparation method described in the second aspect.

[0027] A fourth aspect of the present invention provides a secondary battery comprising the electrode described in the third aspect.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention provides a composite current collector. A conductive layer comprising a WS2-C3N4 / PANI composite nanofiber material is introduced between the base film and the metal layer of a traditional composite current collector. The WN bond formed at the interface between WS2 and C3N4 in the conductive layer can accelerate electron transfer and improve the conductivity of the current collector. At the same time, the PANI coating layer coated on the surface of the composite nanofiber material can form hydrogen bonds or π-π stacking with C3N4 through aniline groups, and the protonated amino groups contained therein can electrostatically adsorb with the sulfur edge sites of WS2 to form a three-dimensional interconnected network, which is not only conducive to further improving the conductive and ion-conducting properties of the conductive layer, but also can cooperate with the adhesion of PANI to effectively improve the adhesion between the conductive layer and the base film and the metal layer, thereby improving the structural stability of the composite current collector.

[0030] 2. The present invention forms WS2-C3N4 / PANI composite nanofibers with a specific one-dimensional structure by in-situ polymerization of aniline monomers on the surface of WS2-C3N4 layered materials under the synergistic effect of molecular self-assembly and heterojunction interface; in the WS2-C3N4 / PANI composite nanofibers prepared by the above method, the WS2-C3N4 nanomaterial and PANI are more tightly combined, and the heterojunction is more evenly dispersed. The conductive layer prepared on the surface of the base film by magnetron sputtering can not only effectively improve the conductivity of the composite current collector, but also help to improve the adhesion between the layers.

[0031] 3. The lithium-ion battery constructed with the positive and negative electrode sheets prepared from the above composite current collector not only has a high energy density, but also has a low AC internal resistance, showing better rate performance and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Transmission electron microscopy (TEM) image of the WS2-C3N4 / PANI composite nanofiber material prepared in Example 1;

[0033] Figure 2 Schematic diagram of the structure of the composite current collector prepared in Example 1;

[0034] Figure 3 Schematic diagram of the partial structure of the composite current collector prepared in Example 1;

[0035] In the figure: 01 is the base film, 02 is the conductive layer, 03 is the metal layer, and 011 is the through hole. DETAILED DESCRIPTION

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The terms "including" or "comprising" as used herein may also be replaced by the enclosed form "being" or "consisting of."

[0037] As described in the background technology, the use of composite current collectors in lithium batteries is beneficial to improving the safety and energy density of the battery. However, the composite current collector composed of a metal layer-polymer layer-metal layer has poor conductivity and structural stability due to the insulation of the polymer layer and poor adhesion between the polymer layer and the metal layer, which affects the rate performance and cycle stability of the battery.

[0038] To solve the above problems, the embodiments of the present invention provide a composite current collector, which includes a base film, a conductive layer arranged on both sides of the base film along the thickness direction, and a metal layer arranged on the side of the conductive layer away from the base film; the conductive layer contains WS2-C3N4 / PANI composite nanofiber material, and the WS2-C3N4 / PANI composite nanofiber material includes WS2-C3N4 nanofibers and a polyaniline (PANI) coating layer coated on the surface of the WS2-C3N4 nanofibers.

[0039] Based on the problems of poor conductivity and poor structural stability of the current composite current collector composed of metal layer-polymer layer-metal layer, the present invention introduces a conductive layer containing WS2-C3N4 / PANI composite nanofiber material between the base film (polymer layer) and the metal layer. The conduction band (-0.2eVvs.SHE) of WS2 in the conductive layer and the valence band (+1.4eV) of C3N4 will form a type II heterojunction, thereby forming a WN bond at the interface between the two. The formed WN bond acts as a bridge to accelerate the transmission of electrons and ions at the interface, thereby improving the conductivity of the composite current collector. In addition, the conductive layer is coated with the composite nanofiber. The PANI on the surface of the material contains aniline groups that can be combined with the aromatic ring of C3N4 through hydrogen bonds or π-π stacking. At the same time, its protonated amino group can undergo electrostatic adsorption with the sulfur edge sites of WS2 to form a three-dimensional interconnected network, which is beneficial to further improve the transfer of electrons and ions in the conductive layer. The conductive layer with a three-dimensional network structure formed cooperates with the adhesion of PANI to effectively improve the adhesion between the conductive layer and the base film and the metal layer, thereby improving the structural stability of the composite current collector, so that the secondary battery constructed by the above-mentioned composite current collector has high energy density while having excellent rate performance and cycle performance.

[0040] In the present invention, the thickness of the base film is preferably 2-10μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., including but not limited to the thickness values ​​listed above; in addition, the material of the base film can be selected from one or more of polyethylene terephthalate, polypropylene, polyethylene, polyimide, and polyvinylidene fluoride, and other materials that can be used as composite current collector base films in this field can also be used.

[0041] In the present invention, the thickness of the conductive layer magnetron sputtering will affect the rate of lithium ion diffusion. When the thickness is moderate, the diffusion path of lithium ions will not be increased while electrons and ions flow rapidly. If the thickness is too large, the diffusion path of electrons will be increased, resulting in slow lithium ion diffusion kinetics. If the thickness is too small, the conduction effect is not obvious. Preferably, the thickness of the conductive layer is controlled in the range of 2-10μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., including but not limited to the thickness values ​​listed above; more preferably, the thickness of the conductive layer is 4μm.

[0042] In the present invention, the length of the WS2-C3N4 / PANI composite nanofiber material in the conductive layer is 20-35 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, etc., and the diameter is 2-10 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc., including but not limited to the lengths or diameters listed above.

[0043] In the present invention, the thickness of the polyaniline coating layer is preferably 1-5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc., including but not limited to the thickness values ​​listed above.

[0044] In the present invention, the thickness of the metal layer is preferably 1-2 μm, for example, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, etc., including but not limited to the thickness values ​​listed above; the material of the metal layer is preferably aluminum or copper. When the material of the metal layer is aluminum, the prepared composite current collector is used in the positive electrode sheet. When the material of the metal layer is copper, the prepared composite current collector is used in the negative electrode sheet.

[0045] In the present invention, the base film is provided with one or more through holes along the thickness direction, and the conductive layers arranged on both sides of the base film along the thickness direction form an interconnected structure through the through holes; the above-mentioned structure allows the base film and the conductive layer to communicate with each other, which is not only beneficial to improving the structural stability between the base film and the conductive layer, but also can further improve the conductivity of the composite current collector, promote lithium ion diffusion, and is beneficial to reducing the AC internal resistance of the battery cell.

[0046] In the present invention, the aperture size and total area ratio of the through hole will affect the electron transmission effect and energy density. If the aperture is too small and the area ratio is too low, the contact area between the base film and the conductive layer is too small, and the effect on electron transmission is not obvious; if the aperture is too large and the area ratio is too high, the fusing effect of the base film will be worse when encountering a short circuit, and the battery energy density and cycle stability will be reduced; in some preferred embodiments of the present invention, the aperture of the through hole is 50-100μm, for example, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, etc.; the total area of ​​the through hole accounts for 10%-20% of the single-side area of ​​the base film along the thickness direction, for example, 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0047] The present invention also provides a method for preparing the composite current collector, which comprises the following steps:

[0048] S1, dispersing WS2-C3N4 nanomaterials in an inorganic acid solution containing aniline, adding an initiator and a stabilizer for reaction, and obtaining a WS2-C3N4 / PANI composite nanofiber material after washing and drying;

[0049] S2, uniformly sputtering the WS2-C3N4 / PANI composite nanofiber material on the upper and lower surfaces of the base film by magnetron sputtering to form a conductive layer;

[0050] S3. Use magnetron sputtering to uniformly sputter metal on the side of the conductive layer away from the base film to form a metal layer, thereby obtaining the composite current collector.

[0051] The present invention disperses WS2-C3N4 nanomaterials with a layered nanosheet structure in an acid solution containing aniline monomers, and in the presence of an initiator and a stabilizer, the aniline monomers are in situ polymerized on the surface of the WS2-C3N4 nanomaterials to form PANI, and under the synergistic effect of molecular self-assembly driving and heterojunction interface, WS2-C3N4 / PANI composite nanofibers with a specific one-dimensional structure can be formed; in the WS2-C3N4 / PANI composite nanofibers prepared by this method, PANI can be combined with WS2-C3N4 through covalent bonds, which is advantageous. In terms of enhancing the interfacial bonding strength, compared with the composite materials prepared by physically mixing WS2-C3N4 nanomaterials with PANI (the interfacial bonding strength formed in the composite materials prepared by physical mixing is weak, and the dispersion is uneven, and agglomeration is prone to occur. In addition, the interface of the composite materials prepared by physical mixing lacks a continuous conductive path, which leads to an aggravated energy band mismatch and cannot effectively improve electron transmission), the heterojunctions in the composite nanofibers prepared by the above method are more evenly dispersed, and the three-dimensional conductive network constructed by the one-dimensional composite nanofibers in the conductive layer can effectively improve the conductivity of the conductive layer.

[0052] In step S1 of the present invention, the mass ratio of the WS2-C3N4 nanomaterial to the aniline needs to be controlled. If the content of the WS2-C3N4 nanomaterial is too high, the reaction will be incomplete, and the remaining WS2-C3N4 will not have time to react, making the conductive layer prepared by the composite nanofiber uneven, affecting the effect of electron transfer, resulting in an increase in internal resistance, and thus affecting the rate and cycle performance of the battery; if the content of WS2-C3N4 is too low, the WN bond formation in the conductive layer will be unstable, affecting the conductive effect, and then affecting the transmission of electrons, and then affecting the rate and cycle performance of the battery; preferably, the mass ratio of the WS2-C3N4 nanomaterial to the aniline is controlled in the range of (1-5):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, etc., including but not limited to the mass ratios listed above, so that the battery has better rate performance and cycle performance.

[0053] In some preferred embodiments of the present invention, in step S1, the inorganic acid can be selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and other conventional inorganic acids in the art can also be used.

[0054] In some preferred embodiments of the present invention, in step S1, the initiator can be selected from one or more of ammonium persulfate, potassium persulfate, and ferric chloride; the stabilizer can be selected from one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and polyacrylic acid.

[0055] In some preferred embodiments of the present invention, in step S1, the reaction temperature is preferably 0-15°C, for example 5°C.

[0056] More preferably, in step S1, the initiator is first added and stirred for 0.5-1 h, and then the stabilizer is added and the stirring reaction is continued for 24-48 h.

[0057] In some preferred embodiments of the present invention, in step S1, the washing solvent is water and / or an alcohol solvent, and the alcohol solvent includes but is not limited to ethanol.

[0058] In some preferred embodiments of the present invention, in step S2, the base film is first laser-drilled to obtain one or more through holes penetrating the base film, and then the WS2-C3N4 / PANI composite nanofiber material is uniformly sputtered on the upper and lower surfaces of the base film by magnetron sputtering, so that the conductive layers formed on the upper and lower surfaces of the base film can form an interconnected structure through the through holes.

[0059] The embodiments of the present invention further provide a pole piece comprising a composite current collector prepared by the above preparation method.

[0060] In addition, the embodiments of the present invention also provide a secondary battery comprising the above-mentioned electrode sheets; the electrode sheets include positive electrode sheets and / or negative electrode sheets. The secondary battery constructed by the above-mentioned electrode sheets not only has high energy density, but also has excellent rate performance and cycle stability.

[0061] The present invention will be further described below with reference to specific embodiments and accompanying drawings so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention.

[0062] Example 1

[0063] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets, which specifically includes the following steps:

[0064] (1) Preparation of WS2-C3N4 / PANI composite nanofiber material: Weigh 50mL of hydrochloric acid (0.5mol / L) and add 0.5mmol of aniline to it and stir to dissolve it. Add 0.138g of WS2-C3N4 nanomaterial (Anqiyue Biotechnology Co., Ltd., QL-WS2CN) to the above solution, mix the two and then ultrasonically treat to achieve a good dispersion effect. After the mixture is cooled to 5℃, 0.25g of ammonium persulfate is added. After stirring for 0.5h, 30mg of PVP is added to the mixed solution, and the above mixture is placed on a magnetic stirrer to react for 30h, then washed with water and ethanol respectively, and finally dried in a vacuum oven at 50℃ for 25h to obtain WS2-C3N4 / PANI composite nanofiber material. Its TEM image is shown as follows Figure 1 As shown, PANI is uniformly coated on WS2-C3N4, the PANI coating thickness is 2 nm, and the WS2-C3N4 / PANI nanoparticle size is 30 nm.

[0065] (2) Preparation of a composite current collector for the positive electrode: A 4 μm polypropylene base film was laser-drilled to a pore size of 80 μm, with the pore area accounting for 14% of the total area. The WS2-C3N4 / PANI material prepared in step (1) was then uniformly sputtered on the upper and lower surfaces of the base film using magnetron sputtering. After drying, aluminum was sputtered on the upper and lower surfaces of the conductive layer. After drying, a composite current collector was obtained. The thickness of the single-layer WS2-C3N4 / PANI conductive layer was 4 μm, and the thickness of the single-layer aluminum layer was 1 μm.

[0066] Preparation of a composite current collector for a negative electrode: A 4 μm polypropylene base film is laser-drilled to a pore size of 80 μm, with the pore area accounting for 14% of the total area. The WS2-C3N4 / PANI material prepared in step (1) is then uniformly sputtered on the upper and lower surfaces of the base film using magnetron sputtering. After drying, metallic copper is sputtered on the upper and lower surfaces of the conductive layer. After drying, a composite current collector is obtained, wherein the thickness of a single WS2-C3N4 / PANI conductive layer is 4 μm, and the thickness of a single metallic copper layer is 1 μm.

[0067] Example 2

[0068] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that the thicknesses of the conductive layer and the metal layer in the composite current collectors for the positive / negative electrode sheets are different. Specifically, the thickness of the single-layer conductive layer is 2 μm, and the thickness of the single-layer metal aluminum / copper layer is 2 μm. The remaining operations are the same, and the corresponding composite current collectors for the positive / negative electrode sheets are prepared.

[0069] Example 3

[0070] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that the thicknesses of the conductive layer and the metal layer in the composite current collectors for the positive / negative electrode sheets are different. Specifically, the thickness of the single-layer conductive layer is 10 μm, and the thickness of the single-layer metal aluminum / copper layer is 2 μm. The remaining operations are the same, and the corresponding composite current collectors for the positive / negative electrode sheets are prepared.

[0071] Example 4

[0072] This embodiment relates to the preparation of a composite current collector for positive and negative electrode sheets. The only difference from Example 1 is that: in step (1), the amount of WS2-C3N4 nanomaterial added is 0.046 g, the amount of PVP added is 10 mg, and the PANI coating thickness of the prepared WS2-C3N4 / PANI composite nanofiber material is 1 nm; the remaining operations are the same, and the corresponding composite current collector for positive / negative electrode sheets is prepared.

[0073] Example 5

[0074] This embodiment relates to the preparation of a composite current collector for positive and negative electrode sheets. The only difference from Example 1 is that in step (1), the amount of WS2-C3N4 nanomaterial added is 0.26 g, the amount of PVP added is 50 mg, and the PANI coating thickness of the prepared WS2-C3N4 / PANI composite nanofiber material is 5 nm; the remaining operations are the same, and the corresponding composite current collector for positive / negative electrode sheets is prepared.

[0075] Example 6

[0076] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that the pore size in step (2) is 50 μm, and the pore area accounts for 10% of the total area; the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0077] Example 7

[0078] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that the pore diameter in step (2) is 100 μm, and the pore area accounts for 20% of the total area; the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0079] Example 8

[0080] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that the polypropylene base film is not laser punched in step (2); the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0081] Example 9

[0082] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that in step (2), a polyethylene-based film of equal thickness is used instead of a polypropylene-based film; the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0083] Example 10

[0084] This embodiment relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that in step (2), a polyethylene terephthalate base film of equal thickness is used instead of a polypropylene base film; the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0085] Comparative Example 1

[0086] This comparative example involves the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that in step (2), WS2-C3N4 nanomaterials are uniformly sputtered on the upper and lower surfaces of the base film by magnetron sputtering; the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0087] Comparative Example 2

[0088] This comparative example relates to the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that in step (2), an equal amount of WS2-C3N4 / PANI composite material is used to replace the WS2-C3N4 / PANI composite nanofiber material. The preparation of the WS2-C3N4 / PANI composite material is as follows:

[0089] 296 mg of WS2-C3N4 material and 100 mg of PANI were weighed and mixed, NMP was used as the solvent, and the mixture was stirred at 2000 rpm for 2 hours to ensure that WS2-C3N4 and PANI were fully in contact. The mixture was centrifuged at 10000 rpm for 20 minutes and finally dried in an oven at 50°C. The remaining steps were the same as in Example 1 to obtain a WS2-C3N4 / / PANI composite material.

[0090] The remaining operations are the same to prepare the corresponding composite current collector for the positive / negative electrode sheets.

[0091] Comparative Example 3

[0092] This comparative example involves the preparation of composite current collectors for positive and negative electrode sheets. The only difference from Example 1 is that in step (1), an equal amount of WSe2-MoSi2N4 nanomaterial is used instead of WS2-C3N4 nanomaterial; the remaining operations are the same, and the corresponding composite current collectors for positive / negative electrode sheets are prepared.

[0093] Application and performance testing

[0094] The positive and negative electrode sheets prepared in the above examples and comparative examples are used to prepare lithium-ion batteries, and the specific operations are as follows:

[0095] Preparation of the positive electrode sheet: The positive electrode active material (ternary nickel cobalt lithium manganese oxide material), the conductive agent (conductive carbon black) and the binder (PVDF) are mixed in a mass ratio of 96:3:1 to obtain a mixed material, and the mixed material is fully stirred at a high speed in NMP to obtain a positive electrode slurry, which is respectively coated on the composite current collector prepared in the above embodiment and comparative example, and dried to obtain a positive electrode sheet.

[0096] Preparation of the negative electrode sheet: Graphite, a conductive agent (conductive carbon black) and a binder (CMC) are mixed in a mass ratio of 75:2:23 to obtain a mixed material, the mixed material is fully stirred at a high speed in deionized water to obtain a negative electrode slurry, which is coated on the composite current collector prepared in the above embodiment and comparative example, and dried to obtain a negative electrode sheet.

[0097] Electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0098] Isolation membrane: PP porous polymer film is used as the isolation membrane.

[0099] Battery assembly: Assemble the above-mentioned positive electrode sheet, separator, negative electrode sheet, and electrolyte in a glove box filled with high-purity argon to obtain the corresponding lithium-ion battery.

[0100] The following electrochemical performance tests were performed on the lithium-ion batteries constructed with different composite current collectors:

[0101] Internal resistance test: The internal resistance of different groups of batteries is obtained through a battery internal resistance meter.

[0102] Battery energy density test: First weigh the battery and record its weight as m. Then, at 25°C, charge the battery at a constant current of 0.33C to 4.2V. Then, charge it at a constant voltage of 4.2V to a current ≤ 0.05C. After standing for 5 minutes, discharge it at a constant current of 0.33C to 2.8V. The discharge energy Q is obtained. The battery energy density is calculated as Q / m.

[0103] Coulombic efficiency test: At 25°C, the battery was charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage of 4.2V to a current of I≤0.05C, and the battery charging capacity was recorded as C0. After standing for 5 minutes, the battery was discharged at a constant current of 0.33C to 2.8V, and the battery discharge capacity was recorded as C1. The coulombic efficiency was calculated as C1 / C0×100%.

[0104] Battery cycle performance test: At 25°C, charge the battery at a constant current of 0.33C to a voltage of 4.2V, then charge at a constant voltage to a current of 0.05C. After 5 minutes of rest, discharge the battery at a constant current of 0.33C to 2.8V. Record the discharge capacity at this point, which is the discharge capacity of the first cycle, C0. Follow this cycle test and record the capacity at the 300th cycle, denoted as C. Use the formula C / C0 × 100% to calculate the capacity retention rate after 300 cycles.

[0105] The test results are shown in Table 1 below:

[0106] Table 1

[0107]

[0108] As can be seen from Table 1, the lithium-ion batteries constructed using the composite current collectors prepared in Examples 1-10 have high energy density, low battery cross-linking internal resistance, and exhibit better rate performance and cycle stability.

[0109] As shown in Examples 1-3, the thickness of the magnetron sputtered conductive layer affects the rate of lithium ion diffusion. When the thickness is too large (Example 3), the diffusion path of electrons is increased, resulting in slow lithium ion diffusion kinetics. When the thickness is too small (Example 2), the diversion effect is not obvious. When the thickness is moderate, while electrons and ions flow rapidly, the diffusion path of lithium ions is not increased. Experiments show that when the conductive layer is 4μm, the AC internal resistance of the battery cell is minimized, the lithium ion diffusion rate kinetics are optimized, and the cycling performance is also the best.

[0110] In addition, it can be seen from Examples 1, 4, 5 and Comparative Example 1 that the electrochemical performance of the lithium ion battery constructed by preparing the composite current collector using WS2-C3N4 / PANI composite nanofibers is better than that of the composite current collector prepared by using only WS2-C3N4 nanomaterials to prepare the conductive layer (Comparative Example 1); and it can be seen from Examples 1, 4, and 5 that the content ratio of WS2-C3N4 to PANI in the nanomaterials used to prepare the conductive layer will affect the battery performance. If the content of WS2-C3N4 is too large (Example 5), the reaction will be incomplete, and the remaining WS2-C3N4 will not have time to react, making the conductive layer uneven, affecting the effect of electron transfer, resulting in an increase in internal resistance, and thus affecting the rate and cycle performance of the battery; if the content of WS2-C3N4 is too small (Example 4), the WN bond formation in the conductive layer will be unstable, affecting the conductive effect, thereby affecting the transmission of electrons, and thus affecting the rate and cycle performance of the battery. Experiments show that when the mass ratio of WS2-C3N4 nanomaterial to aniline is 3:1 when preparing WS2-C3N4 / PANI composite nanofibers, the lithium-ion battery constructed with the prepared composite current collector has better performance.

[0111] It can be seen from Examples 1 and 6-8 that setting through holes on the surface of the base film is beneficial to improving the battery energy density, coulomb efficiency and cycle stability, etc., and the aperture size and area ratio of the through hole will affect the electron transmission effect and energy density. If the aperture is too small and the area ratio is too low (Example 6), the contact area between the conductive layer is too small, and the electron transmission effect is not obvious; if the aperture is too large and the area ratio is too high (Example 7), the base film will cause the fuse effect to deteriorate when encountering a short circuit, and will reduce the battery energy density and cycle stability. Preferably, when the aperture size is 80μm and the aperture ratio is 14%, it has the best effect on improving conductivity and better battery cycle performance.

[0112] In addition, compared with Example 1, in Comparative Example 2, the conductive layer of the composite current collector is prepared by using a WS2-C3N4 / PANI composite material prepared by physical mixing. The energy density of the lithium-ion battery prepared by the composite current collector is significantly reduced, and the cross-linking internal resistance increases, and the coulombic efficiency and cycle performance of the battery are significantly reduced. This is because the interface bonding force formed in the WS2-C3N4 / PANI composite material prepared by physical mixing is weak, and the dispersion is uneven, which is prone to agglomeration. In addition, the interface lacks a continuous conductive path, resulting in an aggravated energy band mismatch and an inability to effectively improve electron transmission. In Comparative Example 3, WSe2-MoSi2N4 nanomaterial is used to replace WS2-C3N4 nanomaterial to prepare WSe2-MoSi2N4 / PANI composite nanomaterial, which is used to prepare the conductive layer of the composite current collector by magnetron sputtering. The lithium-ion battery constructed by the composite current collector prepared by it not only has a low energy density, but also has poor rate performance and cycle stability.

[0113] The above-described embodiments are merely preferred examples for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A composite current collector, characterized in that: The composite current collector includes a base film, a conductive layer provided on both sides of the base film along the thickness direction, and a metal layer provided on a side of the conductive layer away from the base film; The conductive layer comprises a WS2-C3N4 / PANI composite nanofiber material, and the WS2-C3N4 / PANI composite nanofiber material comprises WS2-C3N4 nanofibers and a polyaniline coating layer coated on the surface of the WS2-C3N4 nanofibers.

2. The composite current collector according to claim 1, characterized in that The thickness of the base film is 2-10 μm; The material of the base film is selected from one or more of polyethylene terephthalate, polypropylene, polyethylene, polyimide, and polyvinylidene fluoride.

3. The composite current collector according to claim 1, wherein: Contain at least one of the following characteristics: (1) The thickness of the conductive layer is 2-10 μm; (2) The WS2-C3N4 / PANI composite nanofiber material has a length of 20-35 nm and a diameter of 2-10 nm; (3) The thickness of the polyaniline coating layer is 1-5 nm.

4. The composite current collector according to claim 1, characterized in that The thickness of the metal layer is 1-2 μm; The material of the metal layer is aluminum or copper.

5. The composite current collector according to claim 1, characterized in that The base film is provided with one or more through holes along the thickness direction, and the conductive layers provided on both sides of the base film along the thickness direction form an interconnection structure through the through holes; The through hole has a pore diameter of 50-100 μm; The total area of ​​the through holes accounts for 10%-20% of the area of ​​a single surface of the base film along the thickness direction.

6. A method for preparing the composite current collector according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, dispersing WS2-C3N4 nanomaterials in an inorganic acid solution containing aniline, adding an initiator and a stabilizer for reaction, and obtaining a WS2-C3N4 / PANI composite nanofiber material after washing and drying; S2, uniformly sputtering the WS2-C3N4 / PANI composite nanofiber material on the upper and lower surfaces of the base film by magnetron sputtering to form a conductive layer; S3. Use magnetron sputtering to uniformly sputter metal on the side of the conductive layer away from the base film to form a metal layer, thereby obtaining the composite current collector.

7. The preparation method according to claim 6, characterized in that In step S1, at least one of the following features is included: (1) The mass ratio of the WS2-C3N4 nanomaterial to the aniline is (1-5):1; (2) The inorganic acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; (3) The initiator is selected from one or more of ammonium persulfate, potassium persulfate, and ferric chloride; (4) The stabilizer is selected from one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and polyacrylic acid; (5) The reaction temperature is 0-15°C; (6) First add the initiator and stir for 0.5-1h, then add the stabilizer and continue stirring and reacting for 24-48h; (7) The washing solvent is water and / or an alcohol solvent.

8. The preparation method according to claim 6, characterized in that In step S2, the base film is first laser-drilled to obtain one or more through holes penetrating the base film, and then the WS2-C3N4 / PANI composite nanofiber material is uniformly sputtered on the upper and lower surfaces of the base film by magnetron sputtering, so that the conductive layers formed on the upper and lower surfaces of the base film can form an interconnected structure through the through holes.

9. A pole piece, characterized in that: The composite current collector comprises the composite current collector according to any one of claims 1 to 5 or the composite current collector prepared by the preparation method according to any one of claims 6 to 8.

10. A secondary battery, characterized in that: Comprising the pole piece according to claim 9.

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