A high-energy-density lithium-ion battery cathode and a method of making the same

Abstract

The application discloses a high-energy-density lithium ion battery positive electrode, which comprises a composite current collector and a positive active material coating, wherein the composite current collector comprises an aluminum foil layer and a composite foamed aluminum layer; the composite foamed aluminum layer comprises first foamed aluminum, second foamed aluminum and third foamed aluminum arranged in sequence from inside to outside; the density p1 of the first foamed aluminum, the density p2 of the second foamed aluminum and the density p3 of the third foamed aluminum satisfy the relationship p1 > p2 > p3; the porosity phi of the first foamed aluminum, the porosity phi of the second foamed aluminum and the porosity phi of the third foamed aluminum satisfy the relationship phi1 < phi2 < phi3; and the thickness h1 of the first foamed aluminum, the thickness h2 of the second foamed aluminum and the thickness h3 of the third foamed aluminum satisfy the relationship h1 < h2 < h3. The lithium ion battery positive electrode current collector provided by the application has high specific surface area, high electrical conductivity, high mechanical strength and high structural stability, and effectively meets the requirements of high energy density and long cycle stability of the positive electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a high-energy-density lithium ion battery positive electrode and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices, electric vehicles and energy storage systems due to their high energy density, long cycle life and environmental friendliness. However, with the continuous expansion of application fields and the increasing performance requirements, the existing lithium ion battery positive electrode materials and structural designs have been difficult to meet the demands of high energy density, high rate performance and long cycle stability.

[0003] In the lithium ion battery positive electrode, the current collector serves as the carrier of active materials and the electron transmission channel, and its performance has an important influence on the energy density, rate performance and cycle stability of the battery. Currently, aluminum foil is commonly used as the current collector material in commercial lithium ion battery positive electrodes. However, aluminum foil current collectors have low specific surface area and limited active material loading, making it difficult to further improve the energy density of the battery. To solve this problem, researchers have proposed a design scheme using foamed aluminum as the positive electrode current collector.

[0004] However, the existing foamed aluminum current collectors generally use a single layer of uniform porosity and density design, which sacrifices the mechanical strength and structural stability of the current collector while improving the specific surface area and conductivity. This easily leads to deformation or fracture of the current collector during battery assembly and charging and discharging, resulting in problems such as active material shedding and increased interface impedance, which seriously affect the performance and cycle life of the battery. In addition, the stress distribution of the single-layer foamed aluminum current collector is uneven, and damage is likely to occur in the stress concentration area, further reducing the mechanical stability and reliability of the current collector.

[0005] Therefore, how to design and prepare a current collector with high specific surface area, high conductivity, high mechanical strength and high structural stability, and further develop a lithium ion battery positive electrode with high energy density, high rate performance and long cycle life, is still a technical problem that needs to be solved in the field. SUMMARY

[0006] The main purpose of the present application is to provide a lithium ion battery positive electrode current collector with high specific surface area, high conductivity, high mechanical strength and high structural stability, in order to effectively improve the energy density, rate performance and cycle performance of the lithium ion battery positive electrode.

[0007] To achieve the above-mentioned purpose, the technical solutions adopted by the present application are as follows:

[0008] A high-energy-density lithium-ion battery cathode comprises a composite current collector and a cathode active material coating layer coated on at least one surface of the composite current collector, wherein the composite current collector comprises an aluminum foil layer and a composite aluminum foam layer arranged on the aluminum foil layer, and the composite aluminum foam layer is composed of three layers of aluminum foams with different densities, different porosities and different thicknesses.

[0009] The composite aluminum foam layer comprises a first aluminum foam, a second aluminum foam and a third aluminum foam arranged in sequence from inside to outside, wherein the density of the first aluminum foam ρ1, the density of the second aluminum foam ρ2 and the density of the third aluminum foam ρ3 satisfy the relationship ρ1>ρ2>ρ3; the porosity of the first aluminum foam φ1, the porosity of the second aluminum foam φ2 and the porosity of the third aluminum foam φ3 satisfy the relationship φ1<φ2<φ3; and the thickness of the first aluminum foam h1, the thickness of the second aluminum foam h2 and the thickness of the third aluminum foam h3 satisfy the relationship h1<h2<h3.

[0010] Preferably, the density of the first aluminum foam ρ1 is 0.5-0.9 g / cm3, the density of the second aluminum foam ρ2 is 0.3-0.5 g / cm3, and the density of the third aluminum foam ρ3 is 0.1-0.3 g / cm3.

[0011] Preferably, the porosity of the first aluminum foam φ1 is 50-70%, the porosity of the second aluminum foam φ2 is 70-85%, and the porosity of the third aluminum foam φ3 is 85-95%.

[0012] Preferably, the thickness of the first aluminum foam h1 is 0.5-1 μm, the thickness of the second aluminum foam h2 is 1-2 μm, and the thickness of the third aluminum foam h3 is 2-4 μm; the thickness of the aluminum foil layer h4 is 0.5-1 μm; and the total thickness of the composite current collector is 4-8 μm.

[0013] Preferably, the surface of the composite aluminum foam layer is further provided with a carbon nano coating layer, and the thickness of the carbon nano coating layer is 10-20 nm.

[0014] Preferably, the pore diameter of the first aluminum foam d1, the pore diameter of the second aluminum foam d2 and the pore diameter of the third aluminum foam d3 satisfy the relationship d1<d2<d3.

[0015] Preferably, the pore diameter of the first aluminum foam d1 is 1-5 μm, the pore diameter of the second aluminum foam d2 is 5-10 μm, and the pore diameter of the third aluminum foam d3 is 10-15 μm.

[0016] In addition, the present application also provides a preparation method of the high-energy-density lithium-ion battery cathode, comprising the following steps:

[0017] 1) preparing a first foamed aluminum layer slurry, a second foamed aluminum layer slurry and a third foamed aluminum layer slurry respectively;

[0018] The first foamed aluminum layer slurry is prepared by mixing aluminum powder, urea and polyvinylpyrrolidone in a mass ratio of 100:(15-25):1, adding anhydrous ethanol, and adjusting the solid content to 30-50wt%;

[0019] The second foamed aluminum layer slurry is prepared by mixing aluminum powder, urea and polyvinylpyrrolidone in a mass ratio of 100:(25-35):1, adding anhydrous ethanol, and adjusting the solid content to 15-30wt%;

[0020] The third foamed aluminum layer slurry is prepared by mixing aluminum powder, urea and polyvinylpyrrolidone in a mass ratio of 100:(45-55):1, adding anhydrous ethanol, and adjusting the solid content to 5-15wt%;

[0021] 2) Preheat the aluminum foil substrate, then coat the first foamed aluminum layer slurry, the second foamed aluminum layer slurry and the third foamed aluminum layer slurry on the aluminum foil substrate in turn, and spray a small amount of anhydrous ethanol on the surface of each layer of slurry during the coating process;

[0022] 3) Put the coated aluminum foil into a vacuum sintering furnace, heat to 650-750℃ at a heating rate of 2-5℃ / min under argon or nitrogen protection, and keep the temperature for 0.5-1h, so that the aluminum powder is sintered to form a gradient porous structure, and the urea decomposes to generate gas to form a gradient foamed aluminum layer;

[0023] 4) After cooling, a composite current collector is obtained, the composite current collector is ultrasonically cleaned in anhydrous ethanol for 3-5min to remove the surface residual urea decomposition products and impurities, and then the composite current collector is dried;

[0024] 5) Coating the positive active material coating slurry on at least one surface of the composite current collector, and drying, to obtain the lithium ion battery positive electrode.

[0025] Preferably, in step 4), the composite current collector obtained after cooling is further surface modified to deposit a carbon nano coating layer with a thickness of 10-20nm, and the surface modified composite current collector is hot rolled on a precision rolling mill at a rolling temperature of 100-150℃ and a rolling rate of 5-10%.

[0026] Preferably, in step 1), in the first foamed aluminum layer slurry, the particle size of the aluminum powder is 0.1-0.4μm, and the particle size of the urea is 0.2-0.5μm; in the second foamed aluminum layer slurry, the particle size of the aluminum powder is 0.2-0.8μm, and the particle size of the urea is 0.4-1μm; in the third foamed aluminum layer slurry, the particle size of the aluminum powder is 0.5-1.5μm, and the particle size of the urea is 0.8-1.8μm.

[0027] Compared with the prior art, the present application has at least the following beneficial effects:

[0028] 1) The positive electrode of the present application adopts a composite current collector of aluminum foil and composite aluminum foam, wherein the composite aluminum foam layer has a high specific surface area and a three-dimensional network structure, which is not only beneficial to the infiltration of electrolyte, but also can load more active materials and is beneficial to the uniform distribution of active materials, can shorten the transmission path of electrons and ions, reduce the interface resistance, and improve the energy density and rate performance of the battery.

[0029] 2) The composite aluminum foam with gradient density, porosity and thickness distribution adopted by the present application can realize layer-by-layer stress transmission and buffering, avoid stress concentration leading to local deformation, fracture or damage of the current collector, and improve the mechanical stability and reliability of the current collector.

[0030] 3) The composite aluminum foam with gradient density, porosity and thickness distribution adopted by the present application can not only significantly improve the specific surface area and conductivity of the current collector, but also can take into account the mechanical strength and structural stability, effectively solving the problem of easy deformation and fracture of the existing single-layer foam aluminum current collector.

[0031] 4) Among them, the second and third layers of low-density high-porosity aluminum foam can provide a larger specific surface area, which is beneficial to the loading of active materials and the infiltration of electrolyte, and improve the energy density and rate performance of the battery; while the first layer of aluminum foam has relatively high density and low porosity, which can provide sufficient mechanical support and anti-deformation ability, and ensure the structural integrity and stability of the composite current collector. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a structural schematic diagram of the positive electrode in an embodiment of the present application;

[0033] Figure 2 is a structural schematic diagram of the composite current collector of the positive electrode in an embodiment of the present application;

[0034] Figure 3 is a structural schematic diagram of the composite current collector of the positive electrode in another embodiment of the present application.

[0035] In the figure: 1, composite current collector; 11, aluminum foil layer; 12, composite aluminum foam layer; 121, first aluminum foam; 122, second aluminum foam; 123, third aluminum foam; 13, carbon nano coating; 2, positive active material coating. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0037] Please refer to the accompanying Figures 1-2 The present application provides a high-energy-density lithium-ion battery cathode, which comprises a composite current collector 1 and a cathode active material coating layer 2 coated on at least one surface of the composite current collector 1, the composite current collector 1 comprises an aluminum foil layer 11 and a composite foam aluminum layer 12 arranged on the aluminum foil layer 11, the composite foam aluminum layer 12 is composed of three layers of foam aluminum with different densities, different porosities and different thicknesses; the composite current collector 1 is connected with a cathode tab.

[0038] The composite foam aluminum layer 12 comprises a first foam aluminum 121, a second foam aluminum 122 and a third foam aluminum 123 arranged in sequence from inside to outside, the density p1 of the first foam aluminum 121, the density p2 of the second foam aluminum 122 and the density p3 of the third foam aluminum 123 satisfy the relationship: p1>p2>p3; the porosity f1 of the first foam aluminum 121, the porosity f2 of the second foam aluminum 122 and the porosity f3 of the third foam aluminum 123 satisfy the relationship: f1<f2<f3; and the thickness h1 of the first foam aluminum 121, the thickness h2 of the second foam aluminum 122 and the thickness h3 of the third foam aluminum 123 satisfy the relationship: h1<h2<h3.

[0039] Among them, the composite current collector 1 of the present application comprises an aluminum foil layer 11 and a composite foam aluminum layer 12, wherein the composite foam aluminum layer 12 is composed of three layers of foam aluminum with different densities, porosities and thicknesses, and is in gradient distribution, which has the following advantages:

[0040] 1) High specific surface area: the gradient-distributed composite foam aluminum layer 12 has high specific surface area and three-dimensional porous structure as a whole, the outer layer of foam aluminum with low density, high porosity and large thickness can load more active substances, improve the utilization rate of active materials and increase the capacity of the battery.

[0041] 2) High electrical conductivity: the outer layer of foam aluminum directly contacts with the active material, and the loose and porous structure is conducive to the infiltration of electrolyte and the rapid transmission of ions, thereby reducing the interface resistance; the inner layer of foam aluminum with high density and low porosity can provide an effective electron transmission channel to ensure the high electrical conductivity of the current collector.

[0042] 3) High mechanical strength: the inner layer of foam aluminum with high density, low porosity and thin thickness can provide sufficient mechanical support to ensure the structural integrity of the current collector; the middle layer with moderate density and porosity plays a transition and buffering role to improve the mechanical stability of the current collector.

[0043] 4) High structural stability: The gradient structure design can realize the layer-by-layer transmission and uniform distribution of stress. The outer layer of low-density high-porosity thick large-thickness foam aluminum can effectively absorb and buffer the stress generated during the charging and discharging process of the battery, avoid stress concentration leading to local deformation or fracture of the current collector, and prolong the cycle life of the battery.

[0044] In summary, the high-energy-density lithium-ion battery anode provided by the application adopts an innovative composite current collector 1 design, realizes the perfect balance of high specific surface area, high electrical conductivity, high mechanical strength and high structural stability through gradient density, porosity, thickness and pore size distribution, and can significantly improve the energy density, rate performance and cycle life of the lithium-ion battery.

[0045] In an embodiment according to the application, the density ρ1 of the first foam aluminum 121 is 0.5-0.9 g / cm³, the density ρ2 of the second foam aluminum 122 is 0.3-0.5 g / cm³, and the density ρ3 of the third foam aluminum 123 is 0.1-0.3 g / cm³. The mechanical strength and structural stability can be considered while ensuring high specific surface area and high electrical conductivity, and the optimal performance of the composite foam aluminum current collector is obtained.

[0046] In an embodiment according to the application, the porosity φ1 of the first foam aluminum 121 is 50-70%, the porosity φ2 of the second foam aluminum 122 is 70-85%, and the porosity φ3 of the third foam aluminum 123 is 85-95%. The mechanical strength and structural stability can be considered while ensuring high specific surface area and high electrical conductivity, and the optimal performance of the composite foam aluminum current collector is obtained.

[0047] In an embodiment according to the application, the thickness h1 of the first foamed aluminum 121 is 0.5-1 μm, the thickness h2 of the second foamed aluminum 122 is 1-2 μm, and the thickness h3 of the third foamed aluminum 123 is 2-4 μm; the thickness h4 of the aluminum foil layer 11 is 0.5-1 μm; and the total thickness of the composite current collector 1 is 4-8 μm. The mechanical strength and structural stability can be taken into account while ensuring high specific surface area and high electrical conductivity, and the composite foamed aluminum current collector with optimal performance can be obtained. In addition, the total thickness of the positive electrode composite current collector 1 according to the application is controlled in the ultra-thin range of 4-8 μm, compared with the conventional aluminum foil current collector, the thickness and mass of the current collector can be significantly reduced, and the energy density and specific power of the battery are further improved, which is beneficial to the miniaturization and lightweight design of the battery. In addition, the thickness of each foamed aluminum layer will also directly affect the performance of the battery; if the thickness of each foamed aluminum layer is insufficient, the active material particles may be squeezed out of the pores or damaged under pressure, which will reduce the overall performance of the electrode sheet, thereby leading to the decrease of the rate performance and cycle life of the battery; on the other hand, if the thickness of each foamed aluminum layer is too large, the proportion of non-active materials will increase, thereby reducing the energy density of the battery. Therefore, controlling the appropriate thickness of each foamed aluminum layer is crucial to optimize the performance of the lithium ion battery.

[0048] In an embodiment according to the application, the surface of the composite foamed aluminum layer 12 is further provided with a carbon nano coating layer 13, and the thickness of the carbon nano coating layer 13 is 10-20 nm. The electrical conductivity and corrosion resistance of the current collector can be further improved, and the interface compatibility between the current collector and the active material can be improved, and the interface impedance can be reduced. The appropriate thickness of the carbon nano coating layer 13 can avoid the pore blockage or the increase of the interface impedance caused by the too thick coating.

[0049] In an embodiment according to the application, the pore diameter d1 of the first foamed aluminum 121, the pore diameter d2 of the second foamed aluminum 122, and the pore diameter d3 of the third foamed aluminum 123 satisfy the relationship: d1 < d2 < d3. The gradient distribution of the pore diameter in the form of a horn can form a multi-stage porous structure which is beneficial to the diffusion of lithium ions and the embedding of active substances, the large pore diameter of the outer layer is beneficial to the rapid transmission of electrolyte and lithium ions, and the small pore diameter of the inner layer can inhibit the volume expansion of the active substance, maintain the stability of the electrode structure, and improve the rate performance and cycle stability of the battery.

[0050] In an embodiment according to the present application, the first foamed aluminum 121 has a pore size d1 of 1-5 μm, the second foamed aluminum 122 has a pore size d2 of 5-10 μm, and the third foamed aluminum 123 has a pore size d3 of 10-15 μm. The optimal performance of the composite foamed aluminum current collector can be achieved while ensuring high specific surface area and high electrical conductivity, and taking into account mechanical strength and structural stability. Moreover, the gradient pore structure is conducive to the uniform distribution and rapid penetration of electrolyte, and improves the ion transport efficiency of the battery. In addition, the size of the pore size has a decisive influence on the wettability of the slurry; if the pore size is too small, the slurry may not be able to effectively fill the pores due to the effect of the surface tension of the slurry, which will hinder the uniform distribution of the active material and affect the performance of the electrode sheet; on the contrary, if the pore size is too large, the slurry will easily overfill the pores, resulting in an increase in the area density, and during the drying process, this overfilling may cause the generation of local cracks, further affecting the rate performance of the battery. Therefore, the selection of the appropriate pore size is crucial to ensure the quality of the electrode sheet and the performance of the battery.

[0051] In addition, the present application also provides a preparation method of the above-mentioned high-energy-density lithium ion battery positive electrode, comprising the following steps:

[0052] 1) preparing a first foamed aluminum layer slurry, a second foamed aluminum layer slurry and a third foamed aluminum layer slurry, respectively;

[0053] The first foamed aluminum layer slurry is mixed by aluminum powder, urea and polyvinylpyrrolidone according to a mass ratio of 100:(15-25):1, and anhydrous ethanol is added, and the solid content is adjusted to 30-50 wt%;

[0054] The second foamed aluminum layer slurry is mixed by aluminum powder, urea and polyvinylpyrrolidone according to a mass ratio of 100:(25-35):1, and anhydrous ethanol is added, and the solid content is adjusted to 15-30 wt%;

[0055] The third foamed aluminum layer slurry is mixed by aluminum powder, urea and polyvinylpyrrolidone according to a mass ratio of 100:(45-55):1, and anhydrous ethanol is added, and the solid content is adjusted to 5-15 wt%;

[0056] 2) preheating the aluminum foil substrate, and then coating the first foamed aluminum layer slurry, the second foamed aluminum layer slurry and the third foamed aluminum layer slurry on the aluminum foil substrate in sequence, and spraying a small amount of anhydrous ethanol on the surface of each layer of slurry during the coating process to promote the bonding and fusion between the layers;

[0057] 3) placing the coated aluminum foil into a vacuum sintering furnace, and heating to 650-750℃ at a heating rate of 2-5℃ / min under the protection of argon or nitrogen, and holding for 0.5-1 h, so that the aluminum powder is sintered to form a gradient porous structure, and at the same time, the urea decomposes to generate gas to form a gradient foamed aluminum layer;

[0058] 4) cooling to obtain the composite current collector 1, ultrasonic cleaning the composite current collector 1 in anhydrous ethanol for 3-5 min to remove the surface residual urea decomposition products and impurities, and drying the composite current collector 1 again;

[0059] 5) coating the positive active material coating slurry on at least one surface of the composite current collector 1 and drying to obtain the lithium ion battery positive electrode.

[0060] The application provides a preparation method of a composite foam aluminum current collector and a lithium ion battery positive electrode.

[0061] In an embodiment according to the application, in step 4), the obtained composite current collector 1 after cooling is further surface modified, a carbon nano coating 13 with a thickness of 10-20 nm is deposited, and the surface modified composite current collector 1 is hot rolled on a precision rolling mill at a rolling temperature of 100-150 DEG C and a rolling rate of 5-10%. The introduction of the surface modification and hot rolling processes can further improve the electrical conductivity and bonding strength of the composite current collector 1 and improve the interface compatibility and mechanical properties between the current collector and the active material coating.

[0062] In an embodiment according to the application, in step 1), in the first foam aluminum layer slurry, the particle size of the aluminum powder is 0.1-0.4 μm, and the particle size of the urea is 0.2-0.5 μm; in the second foam aluminum layer slurry, the particle size of the aluminum powder is 0.2-0.8 μm, and the particle size of the urea is 0.4-1 μm; and in the third foam aluminum layer slurry, the particle size of the aluminum powder is 0.5-1.5 μm, and the particle size of the urea is 0.8-1.8 μm. The particle size of the aluminum powder and the urea pore-forming agent in different layers is preferably controlled, which can effectively control the pore size and porosity of the foam aluminum, ensure the formation of the gradient structure, and avoid problems such as incomplete sintering or pore collapse caused by excessively large or small particle sizes.

[0063] In an embodiment according to the present application, the positive electrode active material coating 2 comprises positive electrode active material, binder and conductive agent, wherein the types and amounts of the positive electrode active material, binder and conductive agent in the positive electrode active material coating 2, and the thickness of the positive electrode active material coating 2, etc. can be conventional choices in the art. For example, as some specific examples, the positive electrode active material in the positive electrode active material coating 2 can include but is not limited to lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium iron phosphate, etc., the binder can include but is not limited to polyvinylidene fluoride, butadiene rubber, polyvinyl alcohol, polyurethane, etc., and the conductive agent can include but is not limited to carbon nanofiber, carbon nanotube, conductive carbon black, graphene, etc. Among them, the areal density of the positive electrode active material coating 2 can be 10-12 mg / cm 2 .

[0064] In an embodiment according to the present application, the positive electrode active material coating 2 further comprises 1,3,5-tris(4-carboxyphenyl)benzene. By adding 1,3,5-tris(4-carboxyphenyl)benzene in the positive electrode active material coating, a coordination bond can be formed with the active material inside the pores of the aluminum foam, realizing the connection of the internal structure, which is conducive to the improvement of the conductive performance, and can also enhance the internal support structure of the aluminum foam and the bending resistance of the positive electrode sheet. At the same time, the binding effect of 1,3,5-tris(4-carboxyphenyl)benzene on the active material can also reduce the generation of free active material during the use of the battery, and improve the cycle performance of the battery.

[0065] Specifically, the addition of 1,3,5-tris(4-carboxyphenyl)benzene in the positive electrode active material coating has at least the following advantages:

[0066] 1) The center of 1,3,5-tris(4-carboxyphenyl)benzene is a benzene ring, and three 4-carboxyphenyl groups are uniformly modified at the 1,3,5 positions of the central benzene ring. This symmetrical three-dimensional space structure is conducive to the formation of a uniform and stable metal-organic framework; the three-dimensional structure of 1,3,5-tris(4-carboxyphenyl)benzene can provide more coordination sites and steric hindrance, forming a more three-dimensionally cross-linked network and enhancing the internal support of the aluminum foam.

[0067] 3) The three 4-carboxyphenyl groups of 1,3,5-tris(4-carboxyphenyl)benzene exhibit a unique spatial orientation, which can form an interlaced steric barrier structure within the pores of the aluminum foam after the formation of the metal-organic framework; this steric hindrance effect can increase the mechanical strength of the positive electrode material and improve the bending resistance on the one hand; on the other hand, it can effectively inhibit the shedding and dissolution of the active material during the battery cycle, reduce the generation of free active material, and improve the cycle stability of the battery.

[0068] 4) The central benzene ring of 1,3,5-tris(4-carboxyphenyl)benzene is connected to the three 4-carboxyphenyl groups by rigid σ bonds, and the overall molecular conformation is relatively stable; this rigid structure is conducive to maintaining the structural integrity of the metal-organic framework in the complex and porous internal environment of the aluminum foam, avoiding the collapse of the framework caused by the change in the conformation of the ligand; at the same time, the rigid structure can also buffer the volume change during the charging and discharging of the battery, maintaining the structural stability of the positive electrode material.

[0069] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are used only to explain the present application and cannot be understood as limiting the present application. The reagents or instruments used are not specified by the manufacturer, but are conventional products that can be obtained commercially.

[0070] Example 1

[0071] Preparation of the positive electrode sheet:

[0072] The positive electrode of the lithium ion battery of the present embodiment comprises a composite current collector 1 and a positive electrode active material coating layer 2 coated on one surface of the composite current collector 1, the composite current collector 1 comprises an aluminum foil layer 11 and a composite aluminum foam layer 12 disposed on the aluminum foil layer 11, the composite aluminum foam layer 12 is composed of three layers of aluminum foam with different densities, different porosities and different thicknesses; the composite current collector 1 is connected with a positive electrode tab;

[0073] The composite foam aluminum layer 12 comprises a first foam aluminum layer 121, a second foam aluminum layer 122 and a third foam aluminum layer 123 arranged in sequence from inside to outside, the density p1 of the first foam aluminum layer 121, the density p2 of the second foam aluminum layer 122 and the density p3 of the third foam aluminum layer 123 satisfy the relationship: p1>p2>p3; the porosity f1 of the first foam aluminum layer 121, the porosity f2 of the second foam aluminum layer 122 and the porosity f3 of the third foam aluminum layer 123 satisfy the relationship: f1<f2<f3; and the thickness h1 of the first foam aluminum layer 121, the thickness h2 of the second foam aluminum layer 122 and the thickness h3 of the third foam aluminum layer 123 satisfy the relationship: h1<h2<h3.

[0074] Specifically, in the embodiment, the density p1 of the first foam aluminum layer 121 is 0.7 g / cm3, the density p2 of the second foam aluminum layer 122 is 0.4 g / cm3, and the density p3 of the third foam aluminum layer 123 is 0.2 g / cm3. The porosity f1 of the first foam aluminum layer 121 is 60%, the porosity f2 of the second foam aluminum layer 122 is 80%, and the porosity f3 of the third foam aluminum layer 123 is 90%. The thickness h1 of the first foam aluminum layer 121 is 0.5 μm, the thickness h2 of the second foam aluminum layer 122 is 1.5 μm, and the thickness h3 of the third foam aluminum layer 123 is 3 μm. The thickness h4 of the aluminum foil layer 11 is 1 μm. The total thickness of the composite current collector 1 is 6 μm.

[0075] The preparation method of the positive electrode tab is as follows:

[0076] 1) Prepare a first foam aluminum layer slurry, a second foam aluminum layer slurry and a third foam aluminum layer slurry respectively;

[0077] The first foam aluminum layer slurry is mixed by aluminum powder, urea and polyvinylpyrrolidone according to a mass ratio of 100:20:1, anhydrous ethanol is added, and the solid content is adjusted to 40wt%;

[0078] The second foam aluminum layer slurry is mixed by aluminum powder, urea and polyvinylpyrrolidone according to a mass ratio of 100:30:1, anhydrous ethanol is added, and the solid content is adjusted to 25wt%;

[0079] The third foam aluminum layer slurry is mixed by aluminum powder, urea and polyvinylpyrrolidone according to a mass ratio of 100:50:1, anhydrous ethanol is added, and the solid content is adjusted to 10wt%;

[0080] 2) Preheat the aluminum foil substrate, then coat the first foam aluminum layer slurry, the second foam aluminum layer slurry and the third foam aluminum layer slurry on the aluminum foil substrate in sequence, and spray a small amount of anhydrous ethanol on the surface of each layer of slurry during the coating process to promote the bonding and fusion between the layers;

[0081] 3) Place the coated aluminum foil into a vacuum sintering furnace and heat it to 700°C at a heating rate of 4°C / min under the protection of argon atmosphere. Hold it at this temperature for 1 hour to sinter the aluminum powder into a gradient porous structure. At the same time, urea decomposes to produce gas and form a gradient foam aluminum layer.

[0082] 4) After cooling, the composite current collector is obtained. The composite current collector is ultrasonically cleaned in anhydrous ethanol for 3-5 minutes to remove residual urea decomposition products and impurities on the surface. Then the composite current collector is dried at 70℃ for 0.5 hours.

[0083] 5) The positive electrode active material lithium nickel cobalt manganese oxide, conductive agent conductive carbon black, and binder polyvinylidene fluoride are dispersed in the solvent NMP (N-methylpyrrolidone) at a mass ratio of 95:2:3. After stirring evenly, a positive electrode active material coating slurry is obtained. This slurry is coated on the surface of a composite current collector and dried to obtain the positive electrode sheet of a lithium-ion battery.

[0084] Preparation of negative electrode sheet:

[0085] Hard carbon, carbon black, and water-based carboxymethyl cellulose are dispersed in water at a mass ratio of 95:2:3 to form a uniformly dispersed slurry. The slurry is then uniformly coated onto the surface of the current collector copper foil and transferred to a vacuum drying oven for complete drying to obtain the negative electrode sheet.

[0086] Electrolyte preparation:

[0087] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1. Then, FEC (fluoroethylene carbonate) was added at a volume percentage of 5%. Next, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a concentration ratio of 1 mol / L to prepare the electrolyte.

[0088] Preparation of the separator: A PET / PP composite film with a thickness of 12 micrometers was selected.

[0089] The fabrication of lithium-ion batteries:

[0090] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrolyte is then added, and the battery is assembled using conventional processes.

[0091] Example 2

[0092] Unlike Example 1, as Figure 3 As shown, in this embodiment, the surface of the composite aluminum foam layer 12 in the composite current collector 1 of the positive electrode is also provided with a carbon nanotube coating 13, the thickness of which is 15nm.

[0093] In addition, in step 4) of the preparation method of the positive electrode plate, the composite current collector 1 obtained after cooling is further subjected to surface modification, a 15 nm thick carbon nano coating 13 is deposited, and the surface modified composite current collector 1 is subjected to hot rolling on a precision rolling mill, with a rolling temperature of 120°C and a rolling rate of 8%.

[0094] Other than the embodiment 1, which will not be repeated here.

[0095] Embodiment 3

[0096] Different from the embodiment 1, the pore diameter d1 of the first foamed aluminum 121, the pore diameter d2 of the second foamed aluminum 122 and the pore diameter d3 of the third foamed aluminum 123 in the composite current collector 1 of the positive electrode of the present embodiment satisfy the relationship: d1 < d2 < d3.

[0097] Specifically, in the present embodiment, the pore diameter d1 of the first foamed aluminum 121 is 4 pm, the pore diameter d2 of the second foamed aluminum 122 is 8 pm, and the pore diameter d3 of the third foamed aluminum 123 is 12 pm.

[0098] In addition, in step 1) of the preparation method of the positive electrode plate, in the first foamed aluminum layer slurry, the particle size of the aluminum powder is 0.1 pm, and the particle size of the urea is 0.3 pm; in the second foamed aluminum layer slurry, the particle size of the aluminum powder is 0.5 pm, and the particle size of the urea is 0.8 pm; in the third foamed aluminum layer slurry, the particle size of the aluminum powder is 1 pm, and the particle size of the urea is 1.5 pm.

[0099] Other than the embodiment 1, which will not be repeated here.

[0100] Embodiment 4

[0101] Different from the embodiment 1, the positive electrode active material coating 2 of the positive electrode of the present embodiment comprises positive electrode active material lithium nickel cobalt manganese oxide, conductive agent conductive carbon black, binder polyvinylidene fluoride and 1,3,5-tris(4-carboxyphenyl)benzene, wherein the mass ratio of lithium nickel cobalt manganese oxide, conductive carbon black, polyvinylidene fluoride and 1,3,5-tris(4-carboxyphenyl)benzene is 95:2:2:1.

[0102] Other than the embodiment 1, which will not be repeated here.

[0103] Comparative Example 1

[0104] Different from the embodiment 1, the current collector of the positive electrode of the present comparative example is an aluminum foil current collector with a thickness of 10 pm.

[0105] Other than the embodiment 1, which will not be repeated here.

[0106] Comparative Example 2

[0107] Different from example 1, the current collector of the positive electrode of the comparative example is a single layer of foam aluminum current collector, the density of the foam aluminum current collector is 0.5 g / cm3, the porosity is 90%, and the thickness is 10 μm.

[0108] Other than example 1, which will not be repeated here.

[0109] The positive electrode tabs of the above examples and comparative examples are respectively tested for ductility, stability and contact resistance, and the lithium ion batteries prepared from the positive electrode tabs are tested for energy density and 1000 cycle performance at room temperature, and the test results are shown in Table 1.

[0110] Ductility test: the positive electrode tabs prepared from the examples and comparative examples are rolled under the condition of keeping the same pressure (20 tons of pressure), and it is observed whether there is brittle fracture or cracking on the surface of the tab. If any of the above phenomena occurs, it means that the ductility is poor.

[0111] Stability test: 10 positive electrode tabs prepared from the examples and comparative examples are respectively subjected to 90 degree folding and twisting experiments, and the condition of the active material at the folding or twisting part is observed. If there is active material falling off or breaking, it means that the structural stability is poor.

[0112] Table 1

[0113]

[0114] As can be seen from the test results in Table 1, compared with the positive electrode prepared from the existing copper foil current collector or single layer of foam aluminum current collector, the positive electrode of the present application has good ductility, structural stability and low contact resistance. Because the active material of the positive electrode of the present application has penetrated into the three-dimensional structure of the composite foam aluminum, and the gradient density composite foam aluminum itself has good flexibility, it has better retention effect on the active material penetrated therein, thereby ensuring that the positive electrode prepared from the composite foam aluminum has better deformation resistance and structural stability during the processing process and the use process of the battery, can effectively prevent the positive electrode from brittle fracture or cracking, and effectively reduce the contact resistance, so that the lithium ion battery prepared from the positive electrode of the present application has higher energy density and cycle performance.

[0115] As can be seen from the comparison between comparative example 1 and example 2, when the surface of the composite foam aluminum layer of the positive electrode is further provided with a carbon nano coating for surface modification, and the composite current collector after surface modification is further subjected to hot rolling treatment, the conductivity of the tab can be further improved, the interface resistance can be reduced, which is beneficial to further improve the rate performance and cycle performance of the battery.

[0116] As can be seen from Comparative Example 1 and Example 3, when the composite foam aluminum layer of the positive electrode has a pore size gradient distribution, a multi-stage porous structure beneficial to lithium ion diffusion and active material intercalation can be formed, the large pore size of the outer layer is beneficial to the rapid transmission of electrolyte and lithium ions, and the small pore size of the inner layer can inhibit the volume expansion of the active material and maintain the stability of the electrode structure, so that the positive electrode has high specific surface area and high electrical conductivity, and meanwhile, the mechanical strength and structural stability are also considered, thereby further improving the energy density and cycle performance of the battery.

[0117] As can be seen from Comparative Example 1 and Example 4, when the positive electrode active material coating of the positive electrode further adds 1,3,5-tri(4-carboxylphenyl)benzene, the deformation resistance and structural stability of the positive electrode can be further improved, and the contact resistance of the electrode sheet is reduced, thereby improving the cycle performance of the battery. This is because 1,3,5-tri(4-carboxylphenyl)benzene can form a coordination bond with the active material in the pores of the foam aluminum, realizing the connection of the internal structure, which is beneficial to the improvement of the electrical conductivity and the enhancement of the internal support structure of the foam aluminum, thereby enhancing the bending resistance of the positive electrode sheet. Meanwhile, the binding effect of 1,3,5-tri(4-carboxylphenyl)benzene on the active material can also reduce the generation of free active material during the use of the battery, thereby improving the cycle performance of the battery.

[0118] In the description of the present specification, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0119] The preferred embodiments of the application disclosed above are only used to help explain the application. The preferred embodiments do not describe all the details and limit the application to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well understand and utilize the application. The application is limited only by the claims and their full scope and equivalents.

Claims

1. A high energy density lithium-ion battery cathode, characterized in that, A composite current collector including a composite current collector and a positive electrode active material coating layer coated on at least one surface of the composite current collector, a surface density of the positive electrode active material coating layer being ; the composite current collector including an aluminum foil layer and a composite foamed aluminum layer disposed on the aluminum foil layer, the composite foamed aluminum layer being composed of three layers of foamed aluminum having different densities, different porosities, and different thicknesses; The composite foam aluminum layer comprises a first foam aluminum, a second foam aluminum and a third foam aluminum arranged in sequence from inside to outside, the density of the first foam aluminum ρ1, the density of the second foam aluminum ρ2 and the density of the third foam aluminum ρ3 satisfy the relationship: ρ1>ρ2>ρ3; the porosity of the first foam aluminum φ1, the porosity of the second foam aluminum φ2 and the porosity of the third foam aluminum φ3 satisfy the relationship: φ1<φ2<φ3; and the thickness of the first foam aluminum h1, the thickness of the second foam aluminum h2 and the thickness of the third foam aluminum h3 satisfy the relationship: h1<h2<h3. The density of the first foam aluminum ρ1 is 0.5-0.9 g / cm3, the density of the second foam aluminum ρ2 is 0.3-0.5 g / cm3, and the density of the third foam aluminum ρ3 is 0.1-0.3 g / cm3. The porosity of the first foam aluminum φ1 is 50-70%, the porosity of the second foam aluminum φ2 is 70-85%, and the porosity of the third foam aluminum φ3 is 85-95%. The thickness of the first foam aluminum h1 is 0.5-1 μm, the thickness of the second foam aluminum h2 is 1-2 μm, and the thickness of the third foam aluminum h3 is 2-4 μm.

2. The high energy density lithium-ion battery cathode of claim 1, wherein: The thickness of the aluminum foil layer h4 is 0.5-1 μm; and the total thickness of the composite current collector is 4-8 μm.

3. The high energy density lithium-ion battery cathode of claim 1, wherein: The surface of the composite foam aluminum layer is further provided with a carbon nano coating, and the thickness of the carbon nano coating is 10-20 nm.

4. The high energy density lithium-ion battery cathode of claim 1, wherein: The pore diameter of the first foam aluminum d1, the pore diameter of the second foam aluminum d2 and the pore diameter of the third foam aluminum d3 satisfy the relationship: d1<d2<d3.

5. The high energy density lithium-ion battery cathode of claim 4, wherein: The pore diameter of the first foam aluminum d1 is 1-5 μm, the pore diameter of the second foam aluminum d2 is 5-10 μm, and the pore diameter of the third foam aluminum d3 is 10-15 μm.

6. A method of producing a high-energy-density positive electrode for a lithium-ion battery according to any one of claims 1 to 5, characterized by, The method comprises the following steps: 1) preparing a first foam aluminum layer slurry, a second foam aluminum layer slurry and a third foam aluminum layer slurry respectively; The first foam aluminum layer slurry is prepared by mixing aluminum powder, urea and polyvinylpyrrolidone in a mass ratio of 100:(15-25):1, adding anhydrous ethanol, and adjusting the solid content to 30-50 wt%; The second foam aluminum layer slurry is prepared by mixing aluminum powder, urea and polyvinylpyrrolidone in a mass ratio of 100:(25-35):1, adding anhydrous ethanol, and adjusting the solid content to 15-30 wt%; The third foam aluminum layer slurry is prepared by mixing aluminum powder, urea and polyvinylpyrrolidone in a mass ratio of 100:(45-55):1, adding anhydrous ethanol, and adjusting the solid content to 5-15 wt%; 2) preheating the aluminum foil substrate, and then coating the first foam aluminum layer slurry, the second foam aluminum layer slurry and the third foam aluminum layer slurry on the aluminum foil substrate in sequence, and spraying a small amount of anhydrous ethanol on the surface of each layer of slurry during the coating process; 3) placing the coated aluminum foil into a vacuum sintering furnace, heating to 650-750 ℃ at a heating rate of 2-5 ℃ / min under the protection of argon or nitrogen, and keeping the temperature for 0.5-1 h, so that the aluminum powder is sintered to form a gradient porous structure, and the urea is decomposed to generate gas to form a gradient foam aluminum layer. 4) After cooling, the composite current collector is obtained. The composite current collector is ultrasonically cleaned in anhydrous ethanol for 3-5 minutes to remove residual urea decomposition products and impurities on the surface, and then dried. 5) Coat at least one surface of the composite current collector with the positive electrode active material coating slurry, and dry it to obtain the lithium-ion battery positive electrode.

7. The method of claim 6, wherein the method further comprises: Step 4) further includes surface modification of the cooled composite current collector, depositing a 10-20 nm thick carbon nanotube coating, and hot rolling the surface-modified composite current collector on a precision rolling mill at a rolling temperature of 100-150 °C and a rolling rate of 5-10%.

8. The method of claim 6, wherein the method further comprises: In step 1), in the first aluminum foam layer slurry, the particle size of the aluminum powder is 0.1~0.4μm and the particle size of the urea is 0.2~0.5μm; in the second aluminum foam layer slurry, the particle size of the aluminum powder is 0.2~0.8μm and the particle size of the urea is 0.4~1μm; in the third aluminum foam layer slurry, the particle size of the aluminum powder is 0.5~1.5μm and the particle size of the urea is 0.8~1.8μm. ​

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