Composite current collector and preparation method thereof, pole piece and battery

Abstract

The embodiment of the invention relates to a composite current collector and a preparation method thereof, a pole piece and a battery. The composite current collector comprises a conductive substrate, and a first coating and a second coating which are sequentially laminated on the surface of at least one side of the conductive substrate, the first coating comprises hollow carbon spheres; the second coating comprises hollow carbon spheres, an inorganic solid electrolyte and an additive, and the additive comprises hydroxyl. Therefore, the ion conduction performance, the conductivity and the peel strength of the composite current collector can be improved, the pole piece resistance is reduced, the internal resistance of the battery is reduced, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a composite current collector, a preparation method thereof, a pole piece and a battery. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the advantages of high energy density, good cycling performance, green and pollution-free, etc., and have been widely used in multiple fields.

[0003] The current collector is a key component inside the secondary battery, and its main function is to collect and conduct current. The electrical conductivity, ion conduction performance and structural stability of the current collector not only affect the charge and discharge internal resistance of the battery, but also are related to the cycling performance and safety of the battery. Currently, aluminum foil is usually used as the positive current collector. In order to improve the current collection ability of the positive current collector, in the prior art, a conductive material coating (such as a carbon coating) is coated on the aluminum foil to improve the performance of the current collector.

[0004] However, the existing current collectors with coatings still have problems such as poor structural stability, high resistance and poor cycling stability during the charge and discharge process of the battery, which limits the improvement of the overall performance of the battery. Therefore, how to further improve the performance of the current collector has become a technical problem that needs to be solved urgently at present. Summary of the Invention

[0005] In view of this, embodiments of the present application provide a composite current collector, a preparation method thereof, a pole piece and a battery to solve at least one problem in the background art.

[0006] In a first aspect, embodiments of the present application provide a composite current collector, including a conductive substrate and a first coating and a second coating sequentially stacked on at least one surface of the conductive substrate;

[0007] The first coating includes hollow carbon spheres; the second coating includes hollow carbon spheres, an inorganic solid electrolyte and an additive, and the additive includes hydroxyl groups.

[0008] Combined with the first aspect of the present application, in an optional embodiment, the composite current collector satisfies at least one of the following characteristics:

[0009] (1) The inorganic solid electrolyte includes an oxide solid electrolyte; optionally, the oxide solid electrolyte includes at least one of a perovskite-type solid electrolyte, a garnet-type solid electrolyte, a fast ion conductor, an anti-perovskite-type solid electrolyte, and an amorphous solid electrolyte;

[0010] (2) The particle size of the inorganic solid electrolyte is 5 nm to 20 nm;

[0011] (3) The mass of the inorganic solid electrolyte is 40% to 60% of the mass of the hollow carbon spheres in the second coating;

[0012] (4) The particle size of the hollow carbon spheres is 20 nm to 40 nm;

[0013] (5) The additive includes alcohol compounds; optionally, the additive includes at least one of butanol, pentanol, n-propanol, and n-hexanol;

[0014] (6) The mass of the additive is 5% to 8% of the mass of the hollow carbon spheres in the second coating;

[0015] (7) The first coating further includes a first binder; optionally, the mass of the first binder is 70% to 100% of the mass of the hollow carbon spheres in the first coating; optionally, the first binder includes a polymer binder; further optionally, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate;

[0016] (8) The second coating further includes a second binder; optionally, the mass of the second binder is 70% to 100% of the mass of the hollow carbon spheres in the second coating; optionally, the second binder includes a polymer binder; further optionally, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate;

[0017] (9) The thickness of the first coating is 0.5 μm to 0.8 μm;

[0018] (10) The thickness of the second coating is 0.5 μm to 0.8 μm.

[0019] In a second aspect, an embodiment of the present application provides a method for preparing a composite current collector, the method including the following steps:

[0020] Adding hollow carbon spheres and a first binder to a first solvent, and stirring evenly to obtain a first slurry;

[0021] Adding hollow carbon spheres, an inorganic solid electrolyte, an additive, and a second binder to a second solvent, and stirring evenly to obtain a second slurry; the additive includes a hydroxyl group;

[0022] Coating the first slurry on at least one side surface of a conductive substrate, and drying to form a first coating;

[0023] Coating the second slurry on the first coating, and drying to form a second coating, thereby obtaining the composite current collector.

[0024] Combined with the second aspect of the present application, in an alternative embodiment, the preparation steps of the first slurry satisfy at least one of the following characteristics:

[0025] (1) The first binder includes a polymer binder; optionally, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate;

[0026] (2) The first solvent includes at least one of water, methanol, ethanol, isopropanol, and N-methylpyrrolidone;

[0027] (3) The mass of the first binder is 70% to 100% of the mass of the hollow carbon spheres;

[0028] (4) The solid content of the first slurry is 10% to 15%;

[0029] (5) The viscosity of the first slurry is 200 mPa·s to 300 mPa·s.

[0030] Combined with the second aspect of the present application, in an alternative embodiment, the preparation steps of the second slurry satisfy at least one of the following characteristics:

[0031] (1) The inorganic solid electrolyte includes an oxide solid electrolyte; optionally, the oxide solid electrolyte includes at least one of perovskite-type solid electrolytes, garnet-type solid electrolytes, fast ion conductors, inverse perovskite-type solid electrolytes, and amorphous solid electrolytes;

[0032] (2) The mass of the inorganic solid electrolyte is 40% to 60% of the mass of the hollow carbon spheres;

[0033] (3) The particle size of the inorganic solid electrolyte is 5 nm to 20 nm;

[0034] (4) The additive includes an alcohol compound; optionally, the additive includes at least one of butanol, pentanol, n-propanol, and n-hexanol;

[0035] (5) The second binder includes a polymer binder; optionally, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate;

[0036] (6) The second solvent includes at least one of water, methanol, ethanol, isopropanol, and N-methylpyrrolidone;

[0037] (7) The mass of the second binder is 70% to 100% of the mass of the hollow carbon spheres;

[0038] (8) The mass of the additive is 5% to 8% of the mass of the hollow carbon spheres;

[0039] (9) The solid content of the second slurry is 10% to 15%;

[0040] (10) The viscosity of the second slurry is 200 mPa·s to 300 mPa·s.

[0041] Combined with the second aspect of the present application, in an alternative embodiment, the steps of forming the first coating and the second coating satisfy at least one of the following features:

[0042] (1) The thickness of the first coating is 0.5 μm to 0.8 μm;

[0043] (2) The thickness of the second coating is 0.5 μm to 0.8 μm;

[0044] (3) The coating method of the first slurry and / or the second slurry includes at least one of roll coating, spraying, and knife coating.

[0045] Combined with the second aspect of the present application, in an alternative embodiment, the preparation method of the hollow carbon spheres includes the following steps:

[0046] Add an organosilicon source and an alkali solution to a third solvent, stir evenly to obtain a first mixed solution;

[0047] Add a phenolic compound and a formalin solution to the first mixed solution, stir to react, and obtain a precursor of resin-coated silica through centrifugation, washing, and drying;

[0048] Under a protective gas atmosphere, perform carbonization treatment on the precursor of resin-coated silica to obtain carbon-coated silica spheres;

[0049] Place the carbon-coated silica spheres in an acid solution for etching, and obtain the hollow carbon spheres through washing and drying.

[0050] Combined with the second aspect of the present application, in an alternative embodiment, the preparation method of the hollow carbon spheres satisfies at least one of the following features:

[0051] (1) The mass of the organosilicon source is 4% to 6% of the mass of the third solvent; optionally, the organosilicon source includes at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and silicon tetrachloride;

[0052] (2) The third solvent includes a mixed solution of an alcohol solution and water; optionally, the alcohol solution includes at least one of anhydrous methanol, anhydrous ethanol, and anhydrous isopropanol; optionally, the volume ratio of the alcohol solution to water is (5 to 8):1;

[0053] (3) The volume of the alkali solution is 3% - 5% of the volume of the third solvent; optionally, the mass fraction of the alkali solution is 20% - 30%; optionally, the alkali solution includes at least one of ammonia water, ammonium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution;

[0054] (4) The mass of the phenolic compound is 10% - 20% of the mass of the organosilicon source; optionally, the phenolic compound includes at least one of phenol, cresol, xylenol, polyphenol, and nuclear phenol;

[0055] (5) The mass of the formalin solution is 10% - 20% of the mass of the organosilicon source; optionally, the mass fraction of formaldehyde in the formalin solution is 35% - 40%;

[0056] (6) The temperature of the carbonization treatment is 700°C - 900°C;

[0057] (7) The heating rate of the carbonization treatment is 2°C / min - 5°C / min;

[0058] (8) The time of the carbonization treatment is 4h - 6h;

[0059] (9) The volume of the acid solution is 3 - 5 times the volume of the carbon-coated silica spheres; optionally, the mass fraction of the acid solution is 10% - 15%; optionally, the acid solution includes at least one of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid;

[0060] (10) The time of the etching treatment is 20h - 30h.

[0061] In a third aspect, an electrode provided by an embodiment of the present application includes the composite current collector according to any one of the first aspect or a composite current collector prepared by the preparation method of the composite current collector according to any one of the second aspect.

[0062] In a fourth aspect, an embodiment of the present application provides a battery including the electrode according to the third aspect.

[0063] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0064] The composite current collector provided by the embodiment of the present application, its preparation method, the electrode sheet and the battery. The composite current collector includes a conductive substrate, and a first coating and a second coating sequentially laminated on at least one surface of the conductive substrate; the first coating includes hollow carbon spheres; the second coating includes hollow carbon spheres, an inorganic solid electrolyte and an additive, and the additive includes hydroxyl groups. In the composite current collector provided by the embodiment of the present application, the first coating and the second coating include hollow carbon spheres. During the battery cycling process, the hollow carbon spheres can better maintain the structural integrity, reduce the damage of the conductive network, maintain a good electron conduction path, reduce the electron transport distance inside the material, and moreover, the carbon material itself has high conductivity, which can reduce the resistance. In addition, the hollow structure of the hollow carbon spheres is beneficial to the penetration of the electrolyte and can promote the rapid transport of active ions. Therefore, the conductive performance of the composite current collector can be improved, and further the high-temperature electrical performance and thermal safety performance of the battery can be improved; the second coating includes hollow carbon spheres, an inorganic solid electrolyte and an additive, and has good interfacial properties with the first coating. Hydrogen bonds can be formed between the hydroxyl groups in the additive and both the hollow carbon spheres and the inorganic solid electrolyte. Therefore, the uniformity and stability of the dispersion of the hollow carbon spheres and the inorganic solid electrolyte can be improved, as well as the adhesion between the first coating and the second coating, thereby improving the ion conduction performance, conductive performance and peel strength of the composite current collector, reducing the electrode sheet resistance, further reducing the battery internal resistance, and improving the cycle performance of the battery.

[0065] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present application. Brief Description of the Drawings

[0066] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0067] Figure 1 It is a schematic flow chart of a preparation method of a composite current collector provided by an embodiment of the present application;

[0068] Figure 2 It is a scanning electron microscope image of the hollow carbon spheres prepared in Example 1;

[0069] Figure 3 It is a transmission electron microscope image of the hollow carbon spheres prepared in Example 1;

[0070] Figure 4 It is an EDS element distribution map of the surface of the composite current collector prepared in Example 1. Detailed Embodiments

[0071] To make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following provides a detailed description by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions noted in the following embodiments, they are generally in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0072] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known to the art are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0073] The purpose of the terms used herein is only to describe specific embodiments and not to limit the present application. When used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, determine the presence of the described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0074] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows. However, in addition to these detailed descriptions, the present application may also have other embodiments.

[0075] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those in the technical and scientific fields to which the present application belongs.

[0076] For those not specifying specific techniques or conditions in the following embodiments, they are generally in accordance with the conventional techniques or conditions described in the literature in the art, or in accordance with the conditions recommended in the product specifications and by the manufacturers. The numerical ranges in the following embodiments all include the end point values.

[0077] An embodiment of the present application provides a composite current collector, which includes a conductive substrate and a first coating and a second coating sequentially stacked on at least one surface of the conductive substrate; the first coating includes hollow carbon spheres; the second coating includes hollow carbon spheres, an inorganic solid electrolyte and an additive, and the additive includes hydroxyl groups.

[0078] In the composite current collector provided by the embodiments of the present application, the first coating and the second coating include hollow carbon spheres. During the battery cycling process, the hollow carbon spheres can better maintain the structural integrity, reduce the damage of the conductive network, maintain a good electron conduction path, reduce the electron transport distance inside the material, and moreover, the carbon material itself has high conductivity, which can reduce the resistance. In addition, the hollow structure of the hollow carbon spheres is beneficial to the penetration of the electrolyte, which can promote the rapid transport of active ions. Therefore, the conductive performance of the composite current collector can be improved, the material can have a lower conductivity coefficient, and further, the high-temperature electrical performance and thermal safety performance of the battery can be improved; the second coating includes hollow carbon spheres, inorganic solid electrolytes and additives. Since both the first coating and the second coating contain hollow carbon spheres, the interface between the first coating and the second coating is good. The oxygen atom in the hydroxyl group of the additive has a relatively strong electronegativity, which can attract and retain a partial positive charge on the hydrogen atom, making the hydrogen atom carry a certain degree of positive charge, so that the hydroxyl group can form non-covalent hydrogen bonds with the inorganic solid electrolyte with good electronegativity and the hollow carbon spheres (the conductive carbon has a certain electronegativity, and the electronegativity is about 2.5). Therefore, the uniformity and stability of the dispersion of the hollow carbon spheres and the inorganic solid electrolyte can be improved, and the adhesion between the first coating and the second coating can be improved, so as to improve the ion conduction performance, conductive performance and peel strength of the composite current collector, reduce the electrode sheet resistance, and further reduce the battery internal resistance, and improve the cycle performance of the battery.

[0079] The present application places no particular restrictions on the material of the conductive substrate, as long as it can conduct electricity to achieve the collection and conduction of current. Exemplarily, the material of the conductive substrate may include at least one of aluminum, copper, nickel, titanium, stainless steel, etc.

[0080] The inorganic solid electrolytes in the embodiments of the present application may include, for example, oxide solid electrolytes, sulfide solid electrolytes, etc. These solid electrolytes can improve the ion conduction performance of the composite current collector and the safety of the battery. In some specific embodiments, the inorganic solid electrolyte may include an oxide solid electrolyte. Because oxygen has a relatively high electronegativity (about 3.5), the oxide solid electrolyte usually has a relatively high electronegativity. The oxide solid electrolyte with good electronegativity is beneficial to form more active sites of non-covalent hydrogen bonds, and further, the inorganic solid electrolyte and the hollow carbon spheres in the second coating can be more uniformly dispersed, thereby further improving the uniformity and stability of the coating. Further, the oxide solid electrolyte may include at least one of perovskite-type solid electrolytes (such as LLTO), garnet-type solid electrolytes (such as LLZO), fast ion conductors (such as LISICON, NASICON), inverse perovskite-type solid electrolytes, and amorphous solid electrolytes (such as LiPON type).

[0081] Generally, the electrical conductivity of inorganic solid electrolytes is relatively poor. When the mass proportion of the inorganic solid electrolyte in the second coating is too large, it will affect the electrical conductivity of the composite current collector; when the mass proportion of the inorganic solid electrolyte in the second coating is too small, the improvement of the ion-conducting performance of the composite current collector is relatively limited. Therefore, in some specific embodiments, the mass of the inorganic solid electrolyte can be 40% to 60% of the mass of the hollow carbon spheres in the second coating, for example, it can be 40%, 45%, 50%, 55%, 60% or any value between any two of the above numerical ranges.

[0082] In some embodiments, the particle size of the inorganic solid electrolyte can be 5 nm to 20 nm, for example, it can be 5 nm, 10 nm, 15 nm, 20 nm or any value between any two of the above numerical ranges. This can further improve the ion-conducting performance of the composite current collector.

[0083] In some embodiments, the particle size of the hollow carbon spheres can be 20 nm to 40 nm, for example, it can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm or any value between any two of the above numerical ranges. This can further improve the structural stability and peel strength of the composite current collector, thereby further improving the cycle stability of the battery.

[0084] In some embodiments, the additive can include alcohol compounds. Specifically, the additive can include alcohols with relatively poor volatility, such as at least one of butanol, pentanol, n-propanol, and n-hexanol.

[0085] It can be understood that when the mass proportion of the additive in the second coating is too small, it is not conducive to forming hydrogen bonds with the inorganic solid electrolyte and the hollow carbon spheres, and thus is not conducive to improving the uniformity and stability of the dispersion of the hollow carbon spheres and the inorganic solid electrolyte and the adhesion between the first coating and the second coating; when the mass proportion of the additive in the second coating is too large, it will cause a decrease in the content of the hollow carbon spheres and the inorganic solid electrolyte, which is not conducive to improving the electrical conductivity and ion-conducting performance of the composite current collector. Therefore, in some specific embodiments, the mass of the additive can be 5% to 8% of the mass of the hollow carbon spheres in the second coating, for example, it can be 5%, 6%, 7%, 8% or any value between any two of the above numerical ranges. This can better improve the electrical conductivity, ion-conducting performance and peel strength of the composite current collector.

[0086] In some embodiments, the first coating further includes a first binder. Specifically, the mass of the first binder can be 70% to 100% of the mass of the hollow carbon spheres in the first coating, for example, it can be 70%, 80%, 90%, 100%, or any value between any two of the above numerical ranges. In this way, the hollow carbon spheres can be tightly bonded to the conductive substrate through the first binder, ensuring the peel strength of the composite current collector, while avoiding excessive addition of the first binder, which reduces the proportion of the hollow carbon spheres and thus affects the performance of the composite current collector.

[0087] Exemplarily, the first binder can include a polymer binder. Further, the first binder can include, for example, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate.

[0088] In some embodiments, the second coating further includes a second binder. Specifically, the mass of the second binder can be 70% to 100% of the mass of the hollow carbon spheres in the second coating, for example, it can be 70%, 80%, 90%, 100%, or any value between any two of the above numerical ranges. In this way, the hollow carbon spheres, inorganic solid electrolyte, and additive can be tightly bonded to the first coating through the second binder, ensuring the peel strength of the composite current collector, while avoiding excessive addition of the second binder, which reduces the proportion of the hollow carbon spheres, inorganic solid electrolyte, and additive and thus affects the performance of the composite current collector.

[0089] Exemplarily, the second binder can include a polymer binder. Further, the second binder can include, for example, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate.

[0090] It can be understood that when the thicknesses of the first coating and the second coating are small, it is difficult to effectively improve the electrical conductivity, ion conductivity, and peel strength of the composite current collector; when the thicknesses of the first coating and the second coating are large, it is easy to cause a decrease in the quality of the coating and an extension of the active ion transport path, which will in turn affect the performance of the composite current collector and the battery. Therefore, in some embodiments, the thickness of the first coating can be 0.5 μm to 0.8 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any value between any two of the above numerical ranges. The thickness of the second coating can be 0.5 μm to 0.8 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any value between any two of the above numerical ranges.

[0091] Controlling the thicknesses of the first coating and the second coating within the above ranges can effectively improve the electrical conductivity, ion conduction performance, and peel strength of the composite current collector. Among them, the thicknesses of the first coating and the second coating can be different or the same. In a specific embodiment, the thicknesses of the first coating and the second coating can be the same, so that the performance of the composite current collector can be better improved through the combination of the first coating and the second coating.

[0092] The embodiments of the present application also provide a method for preparing a composite current collector. Please refer to Figure 1 , the method for preparing a composite current collector provided by the embodiments of the present application includes the following steps:

[0093] S1: Add hollow carbon spheres and a first binder to a first solvent, and stir evenly to obtain a first slurry;

[0094] S2: Add hollow carbon spheres, an inorganic solid electrolyte, an additive, and a second binder to a second solvent, and stir evenly to obtain a second slurry; the additive includes a hydroxyl group;

[0095] S3: Coat the first slurry on at least one surface of the conductive substrate, and dry to form a first coating;

[0096] S4: Coat the second slurry on the first coating, and dry to form a second coating to obtain a composite current collector.

[0097] In the embodiments of the present application, a composite current collector is obtained by forming a first coating on at least one surface of the conductive substrate and forming a second coating on the first coating. The first coating and the second coating include hollow carbon spheres. During the battery cycling process, the hollow carbon spheres can better maintain the structural integrity, reduce the damage of the conductive network, maintain a good electron conduction path, reduce the electron transport distance inside the material, and moreover, the carbon material itself has high electrical conductivity, which can reduce the resistance. In addition, the hollow structure of the hollow carbon spheres is beneficial to the penetration of the electrolyte, which can promote the rapid transport of active ions. Therefore, the electrical conductivity of the composite current collector can be improved, and further the high-temperature electrical performance and thermal safety performance of the battery can be improved; the second coating includes hollow carbon spheres, an inorganic solid electrolyte, and an additive, and has good interfacial properties with the first coating. The hydroxyl group in the additive can form hydrogen bonds with both the hollow carbon spheres and the inorganic solid electrolyte. Therefore, the uniformity and stability of the dispersion of the hollow carbon spheres and the inorganic solid electrolyte can be improved, as well as the adhesion between the first coating and the second coating, thereby improving the ion conduction performance, electrical conductivity, and peel strength of the composite current collector, reducing the resistance of the electrode sheet, and further reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0098] It should be understood that although the various steps in the above process flow diagram are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Moreover, at least a part of the steps in the above process flow diagram may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, nor are they necessarily carried out in sequence.

[0099] In step S1, the first binder used to prepare the first slurry may include a polymer binder. Specifically, the first binder may include, for example, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate.

[0100] In some specific embodiments, in step S1, the mass of the first binder may be 70% to 100% of the mass of the hollow carbon spheres, for example, it may be 70%, 80%, 90%, 100%, or any value between any two of the above numerical ranges. In this way, the hollow carbon spheres can be tightly bonded to the conductive substrate through the first binder, ensuring the peel strength of the composite current collector, while avoiding excessive addition of the first binder resulting in a reduced proportion of the hollow carbon spheres, thereby affecting the performance of the composite current collector.

[0101] There is no particular limitation on the first solvent in step S1. Exemplarily, the first solvent may include at least one of water, methanol, ethanol, isopropanol, and N-methylpyrrolidone.

[0102] In some embodiments, the solid content of the first slurry may be 10% to 15%, for example, it may be 10%, 11%, 12%, 13%, 14%, 15%, or any value between any two of the above numerical ranges. In this way, it is convenient to obtain a first coating with higher quality from the first slurry in the subsequent steps.

[0103] In some embodiments, the viscosity of the first slurry may be 200 mPa·s to 300 mPa·s, for example, it may be 200 mPa·s, 220 mPa·s, 240 mPa·s, 260 mPa·s, 280 mPa·s, 300 mPa·s, or any value between any two of the above numerical ranges. In this way, it is more convenient to uniformly coat the first slurry on the conductive substrate in the subsequent steps, thereby further improving the quality of the obtained first coating.

[0104] In step S2, the inorganic solid electrolyte used to prepare the second slurry may include an oxide solid electrolyte. Further, the oxide solid electrolyte includes at least one of perovskite-type solid electrolytes, garnet-type solid electrolytes, fast ion conductors, inverse perovskite-type solid electrolytes, and amorphous solid electrolytes.

[0105] In some embodiments, in step S2, the mass of the inorganic solid electrolyte can be 40% to 60% of the mass of the hollow carbon spheres, for example, it can be 40%, 45%, 50%, 55%, 60% or any value between any two of the above numerical ranges. This can further improve the performance of the prepared composite current collector.

[0106] In some embodiments, the particle size of the inorganic solid electrolyte can be 5 nm to 20 nm, for example, it can be 5 nm, 10 nm, 15 nm, 20 nm or any value between any two of the above numerical ranges. This can further improve the ion conduction performance of the composite current collector.

[0107] In step S2, the additive used to prepare the second slurry can include alcohol compounds. Specifically, the additive can include alcohols with relatively poor volatility, such as at least one of butanol, pentanol, n-propanol, and n-hexanol.

[0108] In some embodiments, in step S2, the mass of the additive can be 5% to 8% of the mass of the hollow carbon spheres, for example, it can be 5%, 6%, 7%, 8% or any value between any two of the above numerical ranges. This can better improve the electrical conductivity, ion conduction performance, and peel strength of the composite current collector.

[0109] In step S2, the second binder used to prepare the second slurry can include a polymer binder. Specifically, the second binder can include, for example, at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate.

[0110] In some embodiments, in step S2, the mass of the second binder can be 70% to 100% of the mass of the hollow carbon spheres, for example, it can be 70%, 80%, 90%, 100% or any value between any two of the above numerical ranges. This can tightly bond the hollow carbon spheres, inorganic solid electrolyte, and additive to the first coating through the second binder, ensuring the peel strength of the composite current collector, while avoiding excessive addition of the second binder, which may reduce the proportion of the hollow carbon spheres, inorganic solid electrolyte, and additive, thereby affecting the performance of the composite current collector.

[0111] There is no particular limitation on the second solvent in step S2. Exemplarily, the second solvent can include at least one of water, methanol, ethanol, isopropanol, and N-methylpyrrolidone.

[0112] In some embodiments, the solid content of the second slurry can be 10% to 15%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15% or any value between any two of the above numerical ranges. This facilitates the subsequent preparation of a second coating with high quality from the second slurry.

[0113] In some embodiments, the viscosity of the second slurry can be 200 mPa·s to 300 mPa·s. For example, it can be 200 mPa·s, 220 mPa·s, 240 mPa·s, 260 mPa·s, 280 mPa·s, 300 mPa·s, or any value between any two of the above numerical ranges. In this way, it is more convenient to uniformly coat the second slurry on the conductive substrate in subsequent steps, thereby further improving the quality of the obtained second coating.

[0114] In step S3, the coating method of the first slurry can include at least one of roll coating, spraying, and knife coating.

[0115] In some embodiments, the thickness of the first coating formed in step S3 can be 0.5 μm to 0.8 μm. For example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any value between any two of the above numerical ranges.

[0116] In step S4, the coating method of the second slurry can include at least one of roll coating, spraying, and knife coating.

[0117] In some embodiments, the thickness of the second coating formed in step S4 can be 0.5 μm to 0.8 μm. For example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any value between any two of the above numerical ranges.

[0118] Controlling the thickness of the first coating and the second coating within the above ranges can effectively improve the electrical conductivity, ion conductivity, and peel strength of the composite current collector. Among them, the thicknesses of the first coating and the second coating can be different or the same. In a specific embodiment, the thicknesses of the first coating and the second coating can be the same, so that the performance of the composite current collector can be better improved through the combination of the first coating and the second coating.

[0119] The preparation method of the hollow carbon spheres used in the above steps S1 and S2 can include the following steps:

[0120] Step (1): Add the organosilicon source and the alkali solution to the third solvent, stir evenly to obtain the first mixed solution.

[0121] In the above steps, the third solvent can include a mixed solution of an alcohol solution and water. Further, the volume ratio of the alcohol solution to water can be (5 - 8):1. Exemplarily, the alcohol solution can include at least one of anhydrous methanol, anhydrous ethanol, and anhydrous isopropyl alcohol.

[0122] In the above steps, the volume of the alkali solution can be 3% to 5% of the volume of the third solvent. Further, the mass fraction of the alkali solution can be 20% to 30%. Exemplarily, the alkali solution can include at least one of ammonia water, ammonium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution.

[0123] In the actual preparation process, the organosilicon source and the alkali solution can be added to the mixed solution of alcohol and water, and stirred evenly at room temperature to obtain the first mixed solution. Exemplarily, the organosilicon source can include at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and silicon tetrachloride. The organosilicon source can undergo a hydrolysis reaction in the mixed solution to generate a hydroxy-silicon compound, and the hydroxy-silicon compound further dehydrates to form silicon dioxide. The addition amount of the organosilicon source is related to the particle size of the subsequent formed hollow carbon spheres. In some specific embodiments, the mass of the organosilicon source can be 4% to 6% of the mass of the third solvent, which is beneficial to obtaining hollow carbon spheres with appropriate particle sizes subsequently.

[0124] Step (2): Add a phenolic compound and a formalin solution to the first mixed solution, stir to react, and after centrifugation, washing, and drying, obtain a precursor of resin-coated silicon dioxide (silicon dioxide@carbon precursor).

[0125] The phenolic compound and the formalin solution react to generate a phenolic resin, which uniformly coats the silicon dioxide formed in step (1). Further, the mass of the phenolic compound can be 10% to 20% of the mass of the organosilicon source. The mass of the formalin solution can be 10% to 20% of the mass of the organosilicon source; this is beneficial for a more sufficient reaction between the phenolic compound and the formalin solution, enabling the formed resin to better coat the silicon dioxide, thereby improving the quality of the finally obtained hollow carbon spheres. Exemplarily, the mass fraction of formaldehyde in the formalin solution can be 35% to 40%. The phenolic compound can include at least one of phenol, cresol, xylenol, polyphenol, and nuclear phenol.

[0126] Step (3): Under a protective gas atmosphere, carbonize the precursor of resin-coated silicon dioxide to obtain a carbon-coated silicon dioxide sphere.

[0127] In the actual preparation process, the precursor of resin-coated silicon dioxide can be placed in a porcelain boat and put into a high-temperature tube furnace for high-temperature carbonization. Among them, the protective gas can include at least one of nitrogen, argon, helium, and neon. Specifically, the temperature of the carbonization treatment can be 700°C to 900°C; the heating rate of the carbonization treatment can be 2°C / min to 5°C / min; the time of the carbonization treatment can be 4h to 6h. This can more fully carbonize the resin coated on the surface of the silicon dioxide, form a carbon coating layer with higher quality on the surface of the silicon dioxide, and thereby improve the quality of the finally obtained hollow carbon spheres.

[0128] Step (4): Place the carbon-coated silica spheres in an acid solution for etching, wash and dry them to obtain hollow carbon spheres.

[0129] In the actual preparation process, the carbon-coated silica spheres can be placed in a strongly corrosive acid to etch away the silica. Among them, the amount of the acid solution and the etching time are based on being able to completely remove the silica. Specifically, the etching time can be, for example, 20 h to 30 h. The volume of the acid solution can be, for example, 3 to 5 times the volume of the carbon-coated silica spheres. Further, the mass fraction of the acid solution can be 10% to 15%; exemplarily, the acid solution can include at least one of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid.

[0130] In the embodiments of the present application, first, a phenolic chemical substance and formalin solution are used to react to generate a low-order phenolic resin, and resin-coated silica is formed by hydrogen bonding in an organosilicon source solution. Secondly, a carbon shell is formed on the surface of the silica by high-temperature carbonization. Furthermore, a hollow spherical conductive carbon material (hollow carbon spheres) is formed after removing the silica by etching with a strongly corrosive acid. The hollow carbon spheres with excellent performance are prepared by the self-assembly method and the template method, and the preparation method is simple and easy to implement.

[0131] The embodiments of the present application also provide an electrode sheet, which includes the composite current collector described in any one of the above embodiments or a composite current collector prepared by the preparation method of the composite current collector described in any one of the above embodiments.

[0132] It should be understood that all the features and advantages of the composite current collector described in the above embodiments or the composite current collector prepared by the preparation method of the composite current collector also apply to the electrode sheet in the embodiments of the present application, and will not be elaborated herein one by one.

[0133] In some embodiments, the electrode sheet may include the composite current collector described in any one of the above embodiments and an active material layer disposed on at least one surface of the composite current collector. As an example, the composite current collector has two surfaces opposite to each other in its own thickness direction, and the active material layer is disposed on any one or both of the two opposite surfaces of the current collector. The present application does not particularly limit the preparation method of the electrode sheet, and any well-known preparation method in the art can be selected as long as the purpose of the present application can be achieved.

[0134] It should be noted that the composite current collector in the present application can be used as a positive current collector or a negative current collector. Considering that the negative active material can include a carbon material, therefore, the composite current collector in the present application is more suitable for use as a positive current collector.

[0135] The embodiments of the present application also provide a battery, which includes the electrode sheet described in the above embodiments.

[0136] It should be understood that since the battery in the embodiments of the present application includes the electrode sheets described in the above embodiments, that is, it includes the composite current collector described in any of the above embodiments or the composite current collector prepared by the preparation method of the composite current collector described in any of the above embodiments, the battery thus has a lower internal resistance, higher high-temperature electrical performance, thermal safety performance and cycling performance.

[0137] In some embodiments, the battery may be a secondary battery, and the secondary battery may be, for example, a lithium-ion battery or a sodium-ion battery, etc. Generally, the secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charging and discharging process of the battery, active ions (lithium ions or sodium ions) are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting sodium ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through.

[0138] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples.

[0139] Example 1

[0140] The preparation of the composite current collector in this embodiment includes the following steps:

[0141] Step S101: First, 26.8 mL of tetraethyl orthosilicate (organic silicon source) and 20 mL of ammonia water solution with a mass concentration of 25% (alkali solution) are added to a 500 mL mixed solution of ethanol and water (third solvent), and stirred at room temperature for 30 min to obtain a silicon solution (first mixed solution); Next, 2 g of phenol (phenolic compound) and 5 mL of formalin solution are added to the above silicon solution, and stirred and reacted for 24 h; Next, the reaction product is obtained by centrifugation, and washed three times with deionized water and anhydrous ethanol respectively, and then dried in an oven at 60 °C to obtain a silicon@carbon precursor (precursor of resin-coated silica); Next, the prepared silicon@carbon precursor is placed in a porcelain boat and put into a high-temperature tube furnace for high-temperature carbonization treatment. Under the protection of nitrogen (protective gas), it is carbonized at 800 °C for 5 h, and the heating rate is 5 °C / min; Next, the powder sample after high-temperature carbonization (carbon-coated silica spheres) is etched in 100 mL of hydrofluoric acid (mass fraction of 12 wt%) for 20 h to remove silica; Then it is washed three times with deionized water and dried in an oven at 60 °C to obtain a hollow spherical conductive carbon material (hollow carbon spheres);

[0142] Step S102: Take 49 g of the hollow spherical conductive carbon material prepared in Step S101 and 39 g of polyvinylidene fluoride (first binder) and add them to 500 mL of water solvent (first solvent) for high-speed stirring to obtain a first slurry;

[0143] Step S103: Take 37.3 g of the hollow spherical conductive carbon material prepared in Step S101, 18.6 g of lithium titanium aluminum phosphate solid electrolyte (inorganic solid electrolyte), 29.8 g of polyvinylidene fluoride (second binder), and 2.3 g of butanol (additive), and add them to 500 mL of water solvent (second solvent) for high-speed stirring to obtain a second slurry;

[0144] Step S104: First, spray a layer of the first slurry with a thickness of 1.2 μm on both the front and back sides of an aluminum foil material with a Dyn value of 0.15 or more and a thickness of 10 μm, and then, at 60 °C, blow-dry for 30 min to form a first coating with a thickness of 0.6 μm;

[0145] Step S105: Spray a layer of the second slurry with a thickness of 1.2 μm on the first coating, and then, at 60 °C, blow-dry for 30 min to form a second coating with a thickness of 0.6 μm. The first coating and the second coating are the composite coatings of the positive current collector, and finally, a composite current collector is obtained.

[0146] Example 2

[0147] The preparation steps of the composite current collector in this example are basically the same as those in Example 1, except that:

[0148] In Step S101: The organosilicon source is replaced with methyl orthosilicate, and the addition amount of methyl orthosilicate is 20 mL; the mass concentration of the ammonia water solution is 20%.

[0149] Example 3

[0150] The preparation steps of the composite current collector in this example are basically the same as those in Example 1, except that:

[0151] In Step S101: The phenolic compound is replaced with resorcinol, and the addition amount of resorcinol is 2.2 g; the addition amount of the formalin solution is 5.4 mL; the temperature of the carbonization treatment is 700 °C.

[0152] Example 4

[0153] The preparation steps of the composite current collector in this example are basically the same as those in Example 1, except that:

[0154] In Step S101: The protective gas is replaced with argon; the temperature of the carbonization treatment is 700 °C, and the time of the carbonization treatment is 4 h;

[0155] In Step S103: The additive is replaced with n-propanol.

[0156] Example 5

[0157] The preparation steps of the composite current collector in this example are basically the same as those in Example 1, except that:

[0158] In step S102: The addition amount of the hollow spherical conductive carbon material is 45 g, and the addition amount of polyvinylidene fluoride is 43 g;

[0159] In step S103: The additive is replaced with n-propanol.

[0160] Example 6

[0161] In this example, the preparation steps of the composite current collector are basically the same as those in Example 1, except that:

[0162] In step S102: The addition amount of the hollow spherical conductive carbon material is 45 g, and the addition amount of polyvinylidene fluoride is 43 g;

[0163] In step S103: The addition amount of the hollow spherical conductive carbon material is 40.9 g; the addition amount of lithium titanium aluminum phosphate solid electrolyte is 16.4 g; the addition amount of polyvinylidene fluoride is 28.7 g; the additive is replaced with n-propanol, and the addition amount of n-propanol is 2.1 g.

[0164] Comparative Example 1

[0165] In this comparative example, the preparation steps of the composite current collector are basically the same as those in Example 1, except that:

[0166] In step S101: The addition amount of tetraethyl orthosilicate is 80 mL.

[0167] Comparative Example 2

[0168] In this comparative example, the preparation steps of the composite current collector are basically the same as those in Example 1, except that:

[0169] In step S103, n-butanol is not added, that is, the additive is omitted when preparing the second slurry.

[0170] Comparative Example 3

[0171] The preparation steps of the composite current collector in this comparative example are as follows:

[0172] Step S201: Take 49 g of the hollow spherical conductive carbon material and 39 g of polyvinylidene fluoride and add them to 500 mL of an aqueous solvent for high-speed stirring to obtain a mixed slurry;

[0173] Step S202: Spray a layer of the mixed slurry prepared in step S201 with a thickness of 1.2 μm on both sides of an aluminum foil material with a dyn value of 0.15 or more and a thickness of 10 μm, and then dry it in a blast at 60 °C for 30 min to form a 0.6-μm hollow spherical conductive carbon coating.

[0174] It should be noted that the hollow spherical conductive carbon material used in step S201 is prepared by the preparation method of the hollow spherical conductive carbon material in step S101 of the above-mentioned embodiment 1, so it is not repeated here.

[0175] Comparative Example 4

[0176] The preparation steps of the composite current collector in this comparative example are as follows:

[0177] Step S301: Take 49 g of conductive carbon black (super-P, SP) and 39 g of polyvinylidene fluoride and add them to 500 mL of water solvent for high-speed stirring to obtain a mixed slurry.

[0178] Step S302: Spray a layer of the mixed slurry prepared in step S301 with a thickness of 1.2 μm on the front and back of an aluminum foil material with a surface energy value of 0.15 or more and a thickness of 10 μm, and then dry it in a blast dryer at 60 °C for 30 min to form a 0.6 μm conductive carbon black coating.

[0179] Test the performance of the composite current collectors obtained in the above examples and comparative examples. The specific tests are as follows:

[0180] (1) Peel strength test of the composite current collector: Cut the composite current collector into strips with a width of 25 mm and a length of 30 cm, fix the cut composite current collector in the fixture of a universal tensile machine, so that the peeling direction is perpendicular or reverse to the sample surface. Then, load the sample at a rate of 50 mm / min until the coating on its surface is completely separated from the aluminum foil. According to the universal tensile machine recording the peeling force and peeling width during the loading process, obtain the peeling force and peeling strength between the coating and the aluminum foil, where the peeling strength = peeling force / peeling width.

[0181] (2) Film resistance test of the composite current collector: Cut the rolled composite current collector into rectangular samples with dimensions of 5 cm × 10 cm, and use a film resistance meter for testing. Place the prepared samples between the two electrodes of the film resistance meter to ensure good contact between the electrodes and the samples, and set the required pressure (25 MPa) and pressure holding time (10 s) for the test; after starting the test, measure the resistance of the samples; randomly select 10 positions for each sample for testing, and take the average of the 10 measured data as the film resistance of the composite current collector.

[0182] (3) Peel strength and film resistance test of the positive electrode sheet: First, prepare a positive electrode active material layer (the positive electrode active material is lithium nickel cobalt manganese oxide) with the same material and thickness on the composite current collectors prepared in the above examples and comparative examples to obtain positive electrode sheets; then, measure the peel strength and film resistance of the positive electrode sheets respectively with reference to the peel strength test method and film resistance test method of the above composite current collectors.

[0183] The above test results are shown in Table 1.

[0184] (4) Internal resistance and cycle performance test of the battery:

[0185] The preparation steps of the battery are as follows: First, a positive electrode active material layer (the positive electrode active material is lithium nickel cobalt manganese oxide) with the same material and thickness is prepared on the composite current collectors obtained in the above-mentioned examples and comparative examples to obtain a positive electrode sheet; Next, a negative electrode sheet with graphite as the active material, a PE separator, and the positive electrode sheet are stacked in sequence, wound to obtain a bare battery cell, after welding the electrode tabs, the bare battery cell is placed into a battery aluminum shell / soft package aluminum-plastic film, and after injection of electrolyte, side top sealing, drying, formation, constant volume, and exhaust sealing, a lithium-ion battery is obtained.

[0186] Internal resistance test of the battery: Use a charge and discharge test cabinet to test the charging resistance and discharging resistance of each lithium-ion battery at 50% SOC (State of Charge) and 20% SOC to determine the internal resistance of the battery under different SOCs. The test results are shown in Table 2.

[0187] Cycle performance test (capacity retention rate test) of the battery: At 25°C or 45°C, charge at a rate of 1C to 4.25V, then charge at a constant voltage of 4.25V until the current decreases to 0.05C, discharge at a rate of 0.1C to 2.8V, record the discharge capacity at this time as the first-cycle discharge capacity, repeat the above charge and discharge cycle, record the discharge capacity of the battery at the 300th and 600th charge and discharge cycles, and the capacity retention rate = (discharge capacity of the nth cycle / first-cycle discharge capacity) * 100% (n = 300, 600). The test results are shown in Table 3.

[0188] Figure 2 and Figure 3 are the scanning electron microscope image and transmission electron microscope image of the hollow carbon spheres prepared in Example 1, respectively. From Figure 2 and Figure 3 it can be seen that conductive carbon spheres with a hollow structure are successfully prepared in this application, and the morphology is uniform. From Figure 3 it can be seen that the particle size of the hollow carbon spheres is basically in the range of 20nm to 40nm. Figure 4 is the EDS element distribution map on the surface of the composite current collector prepared in Example 1. From Figure 4 it can be seen that the main elements in the second coating of the composite current collector (C in the hollow carbon spheres and P, Ti, and Al in the lithium titanium aluminum phosphate solid electrolyte) are uniformly distributed on the entire surface, and the slurry is uniformly coated on the empty aluminum foil without foil leakage.

[0189] Table 1

[0190]

[0191] As can be seen from the data in Table 1, the peel strengths of the composite current collectors prepared in Examples 1 to 6 are higher than those of the composite current collectors prepared in Comparative Examples 1 to 4, and the peel strengths of the positive electrode sheets containing the composite current collectors prepared in Examples 1 to 6 are also higher than those of the positive electrode sheets containing the composite current collectors prepared in Comparative Examples 1 to 4. This indicates that the interface between the first coating and the second coating in the composite current collector prepared in this application is good, the adhesion between the first coating and the conductive substrate is high, and the additive can improve the uniformity and stability of the dispersion of the hollow carbon spheres and the inorganic solid electrolyte and improve the adhesion between the first coating and the second coating, thereby improving the peel strength of the composite current collector. In addition, the composite current collector prepared in this application can effectively improve the adhesion of the coating and improve the peel strength between the active material layer and the composite current collector, so that the corresponding positive electrode sheet has a high peel strength.

[0192] As can be seen from the data in Table 1, compared with Comparative Examples 2 and 4, the film resistances of the composite current collectors prepared in Examples 1 to 6 and the film resistances of the corresponding positive electrode sheets are lower. This indicates that both the first coating and the second coating in the composite current collector prepared in this application include hollow carbon spheres, which can maintain a good electron conduction path, reduce the electron transport distance inside the material, and since the carbon material itself has high conductivity, the resistance of the composite current collector can be reduced. The coatings in the composite current collectors prepared in Comparative Examples 1 and 3 also include hollow carbon spheres, so the film resistances of the composite current collectors and the corresponding positive electrode sheets are also at a relatively low level.

[0193] In addition, in Comparative Example 1, the addition amount of the organosilicon source is relatively large compared with Example 1, and the particle size of the prepared hollow carbon spheres is relatively large. Therefore, it is not conducive to maintaining the structural integrity of the hollow carbon spheres, which will affect the structural stability of the composite current collector and thus affect the peel strength of the coating. Therefore, the peel strengths of the composite current collector and the corresponding positive electrode sheet are relatively low. It can be seen from this that in this application, a particle size of 20 nm to 40 nm for the hollow carbon spheres is a more preferred range.

[0194] As can be seen from the data in Table 2, compared with Comparative Examples 1 to 4, the charging resistance and discharging resistance of the batteries containing the composite current collectors prepared in Examples 1 to 6 are generally at a relatively low level at 50% SOC and 20% SOC. As can be seen from the data in Table 3, compared with Comparative Examples 1 to 4, the cycle performance of the batteries containing the composite current collectors prepared in Examples 1 to 6 is significantly higher at 25°C and 45°C. This indicates that in the composite current collector prepared in the present application, during the battery cycle, the hollow carbon spheres in the first coating and the second coating can better maintain the structural integrity, reduce the damage to the conductive network, maintain a good electron conduction path, reduce the electron transport distance inside the material. Moreover, the carbon material itself has high conductivity, which can reduce the resistance. In addition, the hollow structure of the hollow carbon spheres is beneficial to the penetration of the electrolyte, which can promote the rapid transport of active ions. Therefore, it can improve the conductive performance of the composite current collector, make the material have a lower conductivity coefficient. In addition, the additive can improve the uniformity and stability of the dispersion of the hollow carbon spheres and the inorganic solid electrolyte and improve the adhesion between the first coating and the second coating, thereby improving the ion conduction performance, conductive performance and peel strength of the composite current collector, reducing the resistance of the electrode sheet, and further effectively reducing the internal resistance of the battery and improving the high-temperature electrical performance, thermal safety performance and cycle performance of the battery.

[0195] Table 2

[0196]

[0197] Table 3

[0198]

[0199]

[0200] Compared with Example 1, the second coating of the composite current collector prepared in Comparative Example 2 does not contain an additive. Therefore, the hollow carbon spheres and the inorganic solid electrolyte in the second coating are unevenly dispersed, resulting in poor conductivity of the coating, a large film resistance of the composite current collector, and a large charge-discharge internal resistance of the corresponding battery. This indicates that the second coating containing hollow carbon spheres, inorganic solid electrolyte and additive at the same time can ensure that the composite current collector has excellent ion conduction performance, conductive performance and peel strength, and further effectively improve the cycle performance of the battery.

[0201] In Comparative Example 3, a composite current collector was prepared by directly coating a hollow spherical conductive carbon coating on an aluminum foil. It can be seen from the test results in Tables 1 to 3 that, compared with Example 1, although the film resistance of the composite current collector and the corresponding positive electrode sheet prepared in Comparative Example 3 is smaller, the charge resistance and discharge resistance of the corresponding battery are both larger, that is, the internal resistance of the battery is larger, which is not conducive to the transmission of active ions. Therefore, the cycle performance of the corresponding battery is poor. In Comparative Example 4, a composite current collector was prepared by directly coating conductive carbon black on an aluminum foil. It can be seen from the test results in Tables 1 to 3 that, compared with Example 1, both the film resistance of the composite current collector and the corresponding positive electrode sheet are larger, the internal resistance of the battery is larger, and the cycle performance is poor. This shows that it is difficult to effectively improve the performance of the composite current collector by coating a single-layer carbon-containing coating on the aluminum foil.

[0202] In this application, a hollow spherical conductive carbon material with excellent performance, that is, hollow carbon spheres, is prepared by the self-assembly method and the template method. Combining an inorganic solid electrolyte and an additive, a double coating is constructed on a conductive substrate to obtain a composite current collector. Compared with traditional current collectors, the composite current collector in this application has excellent electrical conductivity, ion conduction ability and higher peel strength, with high structural stability. The battery assembled by coating active substances using this composite current collector has lower charge and discharge resistance, better high-temperature electrical performance, and better cycle stability, which is beneficial to improving the short-term and long-term performance of the battery. In addition, the preparation method of the composite current collector provided in this application has a wide range of raw materials and good feasibility, and has the potential for industrialization.

[0203] It should be noted that the composite current collector embodiments, the preparation method embodiments of the composite current collector, the electrode sheet embodiments and the battery embodiments provided in this application belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.

[0204] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners. Without departing from the scope of the present disclosure, various deformations and changes can be made based on the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present invention that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A composite current collector, characterized in that: It comprises a conductive substrate and a first coating layer and a second coating layer sequentially stacked on at least one side surface of the conductive substrate; The first coating layer includes hollow carbon spheres; the second coating layer includes hollow carbon spheres, an inorganic solid electrolyte and an additive, wherein the additive includes a hydroxyl group.

2. The composite current collector according to claim 1, characterized in that: The composite current collector satisfies at least one of the following characteristics: (1) The inorganic solid electrolyte includes an oxide solid electrolyte; optionally, the oxide solid electrolyte includes at least one of a perovskite solid electrolyte, a garnet solid electrolyte, a fast ion conductor, an antiperovskite solid electrolyte, and an amorphous solid electrolyte; (2) The particle size of the inorganic solid electrolyte is 5 nm to 20 nm; (3) The mass of the inorganic solid electrolyte is 40% to 60% of the mass of the hollow carbon spheres in the second coating layer; (4) The particle size of the hollow carbon sphere is 20 nm to 40 nm; (5) The additive includes an alcohol compound; optionally, the additive includes at least one of butanol, pentanol, n-propanol, and n-hexanol; (6) The mass of the additive is 5% to 8% of the mass of the hollow carbon spheres in the second coating layer; (7) The first coating layer further includes a first binder; optionally, the mass of the first binder is 70% to 100% of the mass of the hollow carbon spheres in the first coating layer; optionally, the first binder includes a polymer binder; further optionally, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate; (8) The second coating layer further includes a second binder; optionally, the mass of the second binder is 70% to 100% of the mass of the hollow carbon spheres in the second coating layer; optionally, the second binder includes a polymer binder; further optionally, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate; (9) The thickness of the first coating is 0.5 μm to 0.8 μm; (10) The thickness of the second coating layer is 0.5 μm to 0.8 μm.

3. A method for preparing a composite current collector, characterized in that: The method comprises the following steps: Adding the hollow carbon spheres and the first binder into the first solvent and stirring evenly to obtain a first slurry; Adding hollow carbon spheres, inorganic solid electrolyte, additives and second binder into a second solvent and stirring evenly to obtain a second slurry; wherein the additive includes a hydroxyl group; Applying the first slurry on at least one side of the conductive substrate and drying to form a first coating; The second slurry is coated on the first coating layer, and dried to form a second coating layer, thereby obtaining the composite current collector.

4. The method for preparing a composite current collector according to claim 3, characterized in that: The step of preparing the first slurry satisfies at least one of the following characteristics: (1) The first binder includes a polymer binder; optionally, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate; (2) the first solvent includes at least one of water, methanol, ethanol, isopropanol, and N-methylpyrrolidone; (3) The mass of the first binder is 70% to 100% of the mass of the hollow carbon sphere; (4) The solid content of the first slurry is 10% to 15%; (5) The viscosity of the first slurry is 200 mPa·s to 300 mPa·s.

5. The method for preparing a composite current collector according to claim 3, characterized in that: The step of preparing the second slurry satisfies at least one of the following characteristics: (1) The inorganic solid electrolyte includes an oxide solid electrolyte; optionally, the oxide solid electrolyte includes at least one of a perovskite solid electrolyte, a garnet solid electrolyte, a fast ion conductor, an antiperovskite solid electrolyte, and an amorphous solid electrolyte; (2) The mass of the inorganic solid electrolyte is 40% to 60% of the mass of the hollow carbon sphere; (3) The particle size of the inorganic solid electrolyte is 5 nm to 20 nm; (4) The additive includes an alcohol compound; optionally, the additive includes at least one of butanol, pentanol, n-propanol, and n-hexanol; (5) The second binder includes a polymer binder; optionally, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, sodium alginate, and polyacrylate; (6) The second solvent includes at least one of water, methanol, ethanol, isopropanol, and N-methylpyrrolidone; (7) The mass of the second binder is 70% to 100% of the mass of the hollow carbon sphere; (8) The mass of the additive is 5% to 8% of the mass of the hollow carbon sphere; (9) The solid content of the second slurry is 10% to 15%; (10) The viscosity of the second slurry is 200 mPa·s to 300 mPa·s.

6. The method for preparing a composite current collector according to claim 3, characterized in that: The steps of forming the first coating layer and the second coating layer satisfy at least one of the following features: (1) The thickness of the first coating is 0.5 μm to 0.8 μm; (2) The thickness of the second coating is 0.5 μm to 0.8 μm; (3) The coating method of the first slurry and / or the second slurry includes at least one of roller coating, spray coating, and scraper coating.

7. The method for preparing a composite current collector according to any one of claims 3 to 6, characterized in that: The preparation method of the hollow carbon sphere comprises the following steps: Adding the organosilicon source and the alkaline solution into the third solvent and stirring evenly to obtain a first mixed solution; Adding a phenolic compound and a formalin solution to the first mixed solution, stirring to react, and centrifuging, washing and drying to obtain a precursor of resin-coated silica; Under a protective gas atmosphere, carbonizing the precursor of the resin-coated silica to obtain carbon-coated silica balls; The carbon-coated silica spheres are placed in an acid solution for etching, and then washed and dried to obtain the hollow carbon spheres.

8. The method for preparing a composite current collector according to claim 7, characterized in that: The method for preparing the hollow carbon spheres satisfies at least one of the following characteristics: (1) The mass of the organic silicon source is 4% to 6% of the mass of the third solvent; optionally, the organic silicon source includes at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and silicon tetrachloride; (2) The third solvent comprises a mixture of an alcohol solution and water; optionally, the alcohol solution comprises at least one of anhydrous methanol, anhydrous ethanol, and anhydrous isopropanol; optionally, the volume ratio of the alcohol solution to water is (5-8):1; (3) The volume of the alkaline solution is 3% to 5% of the volume of the third solvent; optionally, the mass fraction of the alkaline solution is 20% to 30%; optionally, the alkaline solution includes at least one of ammonia water, ammonium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution; (4) The mass of the phenolic compound is 10% to 20% of the mass of the organosilicon source; Optionally, the phenolic compound includes at least one of phenol, cresol, xylenol, polyphenol, and nitrophenol; (5) The mass of the formalin solution is 10% to 20% of the mass of the organosilicon source; optionally, the mass fraction of formaldehyde in the formalin solution is 35% to 40%; (6) The temperature of the carbonization treatment is 700° C. to 900° C.; (7) The heating rate of the carbonization treatment is 2°C / min to 5°C / min; (8) The carbonization treatment time is 4h to 6h; (9) The volume of the acid solution is 3 to 5 times the volume of the carbon-coated silica spheres; optionally, the mass fraction of the acid solution is 10% to 15%; optionally, the acid solution includes at least one of hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid; (10) The etching process takes 20 hours to 30 hours.

9. A pole piece, characterized in that: A composite current collector comprising the composite current collector according to claim 1 or 2 or a composite current collector prepared by the preparation method of the composite current collector according to any one of claims 3 to 8.

10. A battery, characterized in that: Including the pole piece as claimed in claim 9.

Images