Three-dimensional current collector, preparation method thereof and secondary battery

Abstract

The invention discloses a three-dimensional current collector, a preparation method thereof and a secondary battery, and relates to the technical field of secondary batteries. According to the three-dimensional current collector provided by the invention, the three-dimensional current collector with an electrolyte gradient and a conductive gradient is constructed by taking a metal net as a framework, taking a porous conductive metal microsphere as a current collector filler and taking a solid electrolyte and a conductive agent as additive fillers. The sodium metal can grow in the current collector, so that sufficient sodium metal deposition space is provided, the volume change of the battery is smaller, sodium dendrites are not easy to appear, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular, to a three-dimensional current collector, a preparation method thereof, and a secondary battery. Background Art

[0002] A non-aqueous anode battery is a battery that uses a layered oxide material, a Prussian blue analogue material, or a polyanion as the cathode, and a carbon-coated metal foil fluid as the anode. It mainly uses ethers as solvents, and adds metal salts (such as fluorides, borates, and perchlorates, etc.) electrolytes and various additives to form an electrolyte solution. Although non-aqueous anode batteries have advantages such as good low-temperature performance, low cost, and high energy density, their battery volume will change significantly (showing significant expansion and contraction), and gas generation and metal dendrites are serious.

[0003] In non-aqueous anode metal batteries with a relatively high energy density, the growth of dendrites is more violent, and there is a risk of rapid short-circuiting of the battery, which will seriously hinder the application of metal batteries. Among them, as a key component in the battery, the most common modification of the current collector is only to coat a conductive agent on the surface of aluminum foil / copper foil. Such a current collector cannot adapt to the characteristics of obvious volume change of non-aqueous anode metal batteries, and the growth of dendrites on the metal foil plane is also likely to pierce the separator and cause more side reactions, which greatly reduces the cycle life of the battery.

[0004] Therefore, there is an urgent need to improve the current collector at present to reduce the battery volume change, reduce the generation of sodium dendrites, and thereby improve the cycle life of the battery.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a three-dimensional current collector, a preparation method thereof, and a secondary battery, aiming to improve the cycle life of the battery by reducing the battery volume change and the generation of sodium dendrites.

[0007] The present invention is implemented as follows:

[0008] In a first aspect, the present invention provides a three-dimensional current collector, including a skeleton and a filler filled in the skeleton;

[0009] Among them, the skeleton is a metal mesh;

[0010] The filler includes a current collector filler and an additive filler. The current collector filler is a porous conductive metal microsphere, and the additive filler includes a solid electrolyte and a conductive agent.

[0011] In an optional embodiment, the porous conductive metal microsphere includes conductive carbon fibers, carbon nanotubes, and metal particles;

[0012] Preferably, the material of the metal particles is selected from at least one of pure aluminum, aluminum-copper alloy, pure copper, bronze, red copper, brass, and pure titanium;

[0013] Preferably, the porous conductive metal microspheres further include a first binder, a dispersant, and a liquid-retaining material. The first binder is selected from at least one of polyvinyl alcohol, polyvinyl butyral, and styrene-butadiene rubber; the dispersant is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, and sodium carboxymethylcellulose; the liquid-retaining material is selected from at least one of montmorillonite and hydrotalcite;

[0014] More preferably, in the porous conductive metal microspheres, the mass fraction of the conductive carbon fiber is 3%-5%, the mass fraction of the carbon nanotube is 1%-3%, the mass fraction of the metal particles is 80%-90%, the mass fraction of the first binder is 3%-5%, the mass fraction of the dispersant is 1%-3%, and the mass fraction of the liquid-retaining material is 2%-4%.

[0015] In an alternative embodiment, the mass ratio of the porous conductive metal microspheres in the three-dimensional current collector is 75%-85%, the mass ratio of the solid electrolyte in the three-dimensional current collector is 3%-5%, and the mass ratio of the conductive agent in the three-dimensional current collector is 3%-5%;

[0016] Preferably, the solid electrolyte is selected from at least one of oxides, polymers, and sulfides;

[0017] Preferably, the conductive agent is selected from at least one of conductive carbon black, Ketjen black, and acetylene black;

[0018] Preferably, the metal mesh is selected from at least one of aluminum mesh and copper mesh;

[0019] Preferably, the thickness of the three-dimensional current collector is 100 μm - 200 μm.

[0020] In a second aspect, the present invention provides a method for preparing a three-dimensional current collector according to any one of the foregoing embodiments, including: providing porous conductive metal microspheres;

[0021] Mixing a conductive agent, a solid electrolyte, porous conductive metal microspheres, and a second binder, and then pressing and molding with a metal mesh in a high-temperature kneader.

[0022] In an alternative embodiment, the preparation process of the porous conductive metal microspheres includes: mixing raw materials and water to obtain a mixed slurry, and then atomizing and drying the mixed slurry;

[0023] Preferably, drying is carried out in a drying tower, and the inlet temperature is controlled at 150°C - 300°C, and the outlet temperature is 80°C - 150°C.

[0024] In an alternative embodiment, the preparation process of the mixed slurry includes: mixing metal particles, conductive carbon fibers, carbon nanotubes, a first binder, a dispersant, a liquid-retaining material, and a pore-forming agent, and then mixing with water to form a homogeneous slurry to obtain the mixed slurry;

[0025] Preferably, the solid content of the mixed slurry is 50%-70%;

[0026] Preferably, the pore-forming agent is selected from at least one of copper carbonate and sodium bicarbonate;

[0027] Preferably, the mass ratio of the metal particles, conductive carbon fibers, carbon nanotubes, the first binder, the dispersant, the liquid-retaining material, and the pore-forming agent is 100:(4-6):(2-4):(4-6):(2-6):(3-5):(3-5);

[0028] Preferably, the metal particles are pretreated and pre-oxidized before preparing the mixed slurry; the pretreatment includes pickling to remove the oxide layer; the pre-oxidation is carried out in an oxygen-containing atmosphere, controlling the pre-oxidation temperature to be 200°C-500°C, and pre-oxidizing for 0.1h-1h.

[0029] In an alternative embodiment, the mass ratio of the metal mesh, porous conductive metal microspheres, conductive agent, solid electrolyte, and second binder is 100:(750-850):(30-50):(30-50):(30-50).

[0030] Preferably, the second binder is polytetrafluoroethylene.

[0031] In an alternative embodiment, the operating temperature of the high-temperature open mill is 40°C-70°C, the rolling pressure is 1T-50T, the mixing time is 5min-15min, and the number of open millings is 5-15 times.

[0032] In a third aspect, the present invention provides a secondary battery, which uses the three-dimensional current collector in any one of the foregoing embodiments or the three-dimensional current collector prepared by the preparation method in any one of the foregoing embodiments as the negative electrode, and is prepared by using a non-negative electrode battery process.

[0033] In an alternative embodiment, the secondary battery further includes an electrolyte, a positive electrode, and a separator;

[0034] Preferably, the electrolyte includes a solvent and an alkali metal salt, and the alkali metal salt is NaPF6 or LiPF6;

[0035] Preferably, the positive electrode is obtained by coating an active material on a carbon-coated aluminum foil current collector, and the active material is selected from at least one of ternary positive electrode materials, polyanion materials, layered oxide materials, and Prussian blue analogue materials;

[0036] Preferably, the separator is selected from at least one of polyethylene, polypropylene, and glass fiber.

[0037] The present invention has the following beneficial effects: The three-dimensional current collector provided by the present invention uses a metal mesh as the skeleton, porous conductive metal microspheres as the current collector filler, and solid electrolyte and conductive agent as the additive filler to construct a three-dimensional current collector with an electrolyte gradient and a conductivity gradient. Sodium metal can grow inside the current collector, so there is sufficient sodium metal deposition space, the volume change of the battery is smaller, and sodium dendrites are not likely to appear, which is beneficial to improving the cycle life of the battery.

[0038] It should be noted that the reason why the three-dimensional current collector provided by the present invention has an electrolyte gradient and a conductivity gradient is mainly due to the following reasons: Since the current collector has a large compaction density, less electrolyte is stored in the gaps of the current collector, while there are many pores and liquid-retaining materials in the metal microspheres, so there is more electrolyte in the metal microspheres. In addition, the gaps are filled with solid electrolyte, which also makes the conductivity on the surface and in the gaps of the current collector not good, while the conductivity of the metal microspheres is excellent. These make the surface and gaps of the current collector form a conductivity gradient and an electrolyte gradient with the internal metal microspheres, so that more metal ions will enter the metal microspheres inside the electrode through the solid electrolyte on the electrode surface. The porous structure and pores inside the metal microspheres provide space for metal deposition. Although the conductivity of the gaps in the current collector is not good, using a metal mesh to penetrate the entire current collector improves the conductivity of the current collector. In this way, there is sufficient sodium metal deposition space, the volume change of the battery is smaller, and sodium dendrites are not likely to appear. Specific embodiments

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0040] Glossary:

[0041] Dendrite: Chinese name is dendritic crystal, English name is dendritic crystal. The detailed explanation is that dendritic crystal (dendrite) is a crystal that develops in a typical multi-branched tree form. The growth of dendritic crystals is very common, which can be illustrated by the formation of snowflakes and frost patterns on the window. Dendritic crystallization forms a natural fractal pattern.

[0042] The embodiment of the present invention provides a preparation method for a three-dimensional current collector, and the steps are as follows:

[0043] S1. Pretreatment and pre-oxidation

[0044] Prepare metal particles and a metal mesh. The metal particles can be commercially available metal powders, and the metal mesh can be a commercially available metal mesh.

[0045] The material of the metal particles can be at least one of pure aluminum, aluminum-copper alloy, pure copper, bronze, red copper, brass, and pure titanium, and the material of the metal powder can be any one or several of the above. The metal mesh is selected from at least one of an aluminum mesh and a copper mesh, and the metal mesh can be any one or several of the above.

[0046] In some embodiments, the metal particles and the metal mesh are pre-treated and pre-oxidized before use. The pre-treatment includes pickling to remove the original uneven oxide layer on the surface through pickling; the pre-oxidation is treatment in an oxygen-containing atmosphere to form a thinner and more uniform oxide layer on the surface.

[0047] Further, during the pre-treatment process, before pickling, the surface can also be cleaned using acetone and pure water to remove surface impurities. Pickling can be soaking in dilute hydrochloric acid and then washing several times with pure water.

[0048] Further, the pre-oxidation process can be carried out in a tube furnace, introducing pure oxygen, controlling the pre-oxidation temperature to be 200°C - 500°C, such as 200°C, 300°C, 400°C, 500°C, etc.; the pre-oxidation time is 0.1h - 1h, such as 0.1h, 0.3h, 0.5h, 0.8h, 1.0h, etc. The surface of the metal powder is uniformly oxidized in an environment of pure O2, and a thinner and more uniform oxide layer is formed on the surface.

[0049] It should be noted that the pre-treatment and pre-oxidation are not necessary steps and are selectively operated according to the situation of the raw materials. If the metal particles and the metal mesh themselves have a relatively uniform oxide layer, there is no need for pre-treatment and pre-oxidation. After pickling and then pre-oxidation of the metal particles and the metal mesh, the oxide layer on the metal surface can be regulated by the acid value, time of pickling, time of pre-oxidation, etc.

[0050] S2. Prepare a mixed slurry

[0051] The preparation process of the mixed slurry includes: mixing the metal particles obtained in step S1 with conductive carbon fibers (high-conductivity agent CF), carbon nanotubes (CNT), a first binder, a dispersant, a liquid-retaining material, and a pore-forming agent evenly, and then mixing with water to form a homogeneous slurry to obtain a mixed slurry for standby. The metal particles contain conductive non-active metals such as pure aluminum / aluminum alloy / copper alloy, or contain conductive non-active metals such as pure copper / bronze / red copper / brass / pure titanium to improve the conductivity of the material. By introducing a mixed carbon fiber of conductive carbon fibers and carbon nanotubes, the high conductivity and high cross-linking property of the metal microspheres are increased, and the liquid-retaining material and the pore-forming agent provide electrolyte storage and metal space for the metal microspheres.

[0052] In some embodiments, the first binder is selected from at least one of polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and styrene-butadiene rubber (SBR). The first binder can be any one or several of the above; the dispersant is selected from at least one of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and sodium carboxymethyl cellulose (CMC). The dispersant can be any one or several of the above; the liquid-retaining material is selected from at least one of montmorillonite and hydrotalcite. The liquid-retaining material can be any one or several of the above. The pore-forming agent is selected from at least one of copper carbonate and sodium bicarbonate. The pore-forming agent can be any one or several of the above.

[0053] In the actual operation process, the metal particles can be mixed with conductive carbon fibers (highly conductive agent CF), carbon nanotubes (CNT), the first binder, the dispersant, the liquid-retaining material, and the pore-forming agent in a mixer for 3 h - 8 h, and then mixed with deionized water and homogenized by a homogenizer for 1 h - 3 h to obtain a uniform mixed slurry. By controlling the amount of water used, the solid content of the mixed slurry is made 50% - 70%.

[0054] In some embodiments, the mass ratio of the metal particles, conductive carbon fibers, carbon nanotubes, the first binder, the dispersant, the liquid-retaining material, and the pore-forming agent is 100:(4 - 6):(2 - 4):(4 - 6):(2 - 6):(3 - 5):(3 - 5), such as 100:4:2:4:2:3:3, 100:5:3:5:4:4:4, 100:6:4:6:6:5:5, etc. It is appropriate to control the mass of each raw material within the above range, so that the subsequent prepared porous conductive metal microspheres have sufficient sodium metal deposition space and make the volume change of the battery smaller.

[0055] S3. Atomization and drying;

[0056] The mixed slurry obtained in step S2 is atomized and then dried to form porous conductive metal microspheres.

[0057] Specifically, the mixed slurry is atomized by pressure atomization. The high-pressure slurry forms a liquid film through a nozzle and is broken into droplets. The droplets contact with hot air flow in a drying tower and are quickly dried to form particles. The following changes occur during this process: the solvent on the surface of the droplets quickly evaporates to form a porous or dense outer shell; the internal solvent diffuses to the surface through pores and further dries and shrinks; the binder cures to maintain the particle structure, and the surface tension causes the droplets to shrink into spherical shapes, forming metal microspheres constructed by metal powders. The drying efficiency and the particle movement trajectory need to match the atomization speed, and controlling the humidity in the drying tower can adjust the particle porosity.

[0058] In some embodiments, drying is carried out in a drying tower, and the inlet temperature is controlled to be 150°C - 300°C, such as 150°C, 200°C, 250°C, 300°C, etc.; the outlet temperature is 80°C - 150°C, such as 80°C, 100°C, 120°C, 150°C, etc.

[0059] S4. Compression molding by a high-temperature kneader

[0060] Mix the conductive agent, solid electrolyte, porous conductive metal microspheres and the second binder, and then press and mold them with a metal mesh in a high-temperature kneader to form a three-dimensional current collector. The second binder can be polytetrafluoroethylene (PTFE), but is not limited thereto. The PTFE kneading process is selected for the PTFE current collector molding, which results in fewer gaps in the current collector and less electrolyte storage during the working process.

[0061] It should be noted that the current collector prepared by using the PTFE kneading process has a very large compaction density, resulting in less electrolyte stored in the gaps of the current collector. There are many pores and liquid-retaining materials in the metal microspheres, so there is more electrolyte in the metal microspheres. In addition, the gaps are filled with solid electrolyte, which also makes the conductivity on the surface and in the gaps of the current collector not good. However, using a metal mesh to penetrate the entire current collector improves the conductivity of the current collector. These form an electric potential gradient and an electrolyte gradient between the surface and the gaps of the current collector and the internal metal microspheres, so that more metal ions will enter the metal microspheres inside the electrode through the solid electrolyte on the electrode surface. The porous structure and pores inside the metal microspheres provide space for metal deposition. Although the conductivity of the current collector gaps is not good, using a metal mesh to penetrate the entire current collector improves the conductivity of the current collector. In this way, there is sufficient space for sodium metal deposition, the volume change of the battery is smaller, and sodium dendrites are not likely to appear.

[0062] In some embodiments, the solid electrolyte can be a common lithium / sodium solid electrolyte. The lithium / sodium solid electrolyte provides an ion transport channel for the current collector and avoids the deposition of metal on the surface and in the gaps of the current collector. The solid electrolyte can specifically be selected from at least one of oxides, polymers, and sulfides, and can be any one or several of the above, such as sodium lanthanum zirconium oxide, sodium aluminum titanium phosphorus, sodium aluminum oxide, polyethylene oxide, polyacrylonitrile, Na3PS4, Na4P2S7, and 11 Sn2PS 12 at least one of them. The conductive agent is selected from at least one of conductive carbon black, Ketjen black, and acetylene black, and the conductive agent can be any one or several of the above.

[0063] In the actual operation process, the conductive agent, solid electrolyte, porous conductive metal microspheres, and the second binder can be first mixed in a mixer for 3h - 8h. The mixed powder enters a high-temperature open mill. After multiple open mills, it is pressed together with a metal mesh to obtain a dense three-dimensional collector of metal microspheres. The thickness of the three-dimensional collector is about 100μm - 200μm, such as 100μm, 130μm, 150μm, 180μm, 200μm, etc.

[0064] In some embodiments, the mass ratio of the metal mesh, porous conductive metal microspheres, conductive agent, solid electrolyte, and the second binder is 100:(750 - 850):(30 - 50):(30 - 50):(30 - 50), such as 100:750:30:30:30, 100:800:40:40:40, 100:850:50:50:50, etc. The dosage of each raw material is appropriate within the above range to prepare a three-dimensional collector with a relatively large compaction density, so that less electrolyte is stored in the gaps of the collector. There are many pores and liquid-retaining materials in the metal microspheres, so that more electrolyte is in the metal microspheres, constructing a three-dimensional collector of metal microspheres with an electrolyte gradient and a conductivity gradient.

[0065] Furthermore, the operating temperature of the high-temperature open mill is 40°C - 70°C (such as 40°C, 50°C, 60°C, 70°C, etc.), the calendering pressure is 1T - 50T (such as 1T, 10T, 20T, 30T, 40T, 50T, etc.), the mixing time is 5min - 15min (such as 5min, 8min, 10min, 13min, 15min, etc.), and the number of open mill times is 5 - 15 times (such as 5 times, 10 times, 15 times, etc.). By adjusting the operating parameters of the high-temperature open mill, a uniform three-dimensional collector can be prepared.

[0066] An embodiment of the present invention provides a three-dimensional collector, which includes a skeleton and fillers filled in the skeleton. Among them, the skeleton is a metal mesh; the fillers include collector fillers and additive fillers. The collector fillers are porous conductive metal microspheres, and the additive fillers include solid electrolytes and conductive agents.

[0067] It should be noted that this three-dimensional collector uses a metal mesh as the skeleton, porous conductive metal microspheres as the collector fillers, and solid electrolytes and conductive agents as the additive fillers to construct a three-dimensional collector with an electrolyte gradient and a conductivity gradient. Sodium metal can grow inside the collector, so there is sufficient sodium metal deposition space, the volume change of the battery is smaller, and sodium dendrites are not likely to appear, which is beneficial to improving the cycle life of the battery.

[0068] In some embodiments, the porous conductive metal microspheres include conductive carbon fibers, carbon nanotubes, and metal particles. The types of metal particles are referred to the above text of the specification. In a preferred embodiment, the porous conductive metal microspheres further include a first binder, a dispersant, and a liquid retention material. The types of the first binder, the dispersant, and the liquid retention material are referred to the above text of the specification. By introducing the liquid retention material, the sodium metal deposition space is further increased.

[0069] In a preferred embodiment, in the porous conductive metal microspheres, the mass fraction of the conductive carbon fibers is 3% - 5% (such as 3%, 4%, 5%, etc.), the mass fraction of the carbon nanotubes is 1% - 3% (such as 1%, 2%, 3%, etc.), the mass fraction of the metal particles is 80% - 90% (such as 80%, 85%, 90%, etc.), the mass fraction of the first binder is 3% - 5% (such as 3%, 4%, 5%, etc.), the mass fraction of the dispersant is 1% - 3% (such as 1%, 2%, 3%, etc.), and the mass fraction of the liquid retention material is 2% - 4% (such as 2%, 3%, 4%, etc.). By regulating the contents of the components in the porous conductive metal microspheres, the conductive performance of the metal microspheres is more suitable, and sufficient space for sodium metal deposition can be provided.

[0070] Furthermore, the mass ratio of the porous conductive metal microspheres in the three-dimensional current collector is 75% - 85% (such as 75%, 80%, 85%, etc.), the mass ratio of the solid electrolyte in the three-dimensional current collector is 3% - 5% (such as 3%, 4%, 5%, etc.), and the mass ratio of the conductive agent in the three-dimensional current collector is 3% - 5% (such as 3%, 4%, 5%, etc.). The above are the main components of the three-dimensional current collector, so the sum is not 100%. By regulating the contents of each part, on the basis of having good conductivity, the three-dimensional current collector has sufficient sodium metal deposition space inside, reducing the volume change of the battery and the generation of sodium dendrites.

[0071] The embodiment of the present invention provides a secondary battery, which uses the three-dimensional current collector provided by the embodiment of the present invention as the negative electrode and is prepared by using a non-negative electrode battery process. Through the improvement of the three-dimensional current collector, a metal microsphere three-dimensional current collector with an electrolyte gradient and a conductivity gradient is obtained. Applying it to a non-negative electrode battery can reduce the volume change of the battery and the generation of sodium dendrites.

[0072] It should be noted that in a common sodium metal-free battery, the aluminum foil current collector acts as the negative electrode, but there are still many problems. For example, the space for sodium metal deposition on the aluminum foil is limited and it can only deposit on the surface, which will lead to a large volume change of the battery and the easy generation of sodium dendrites, greatly reducing the cycle life of the battery. Therefore, in the embodiments of the present invention, a three-dimensional current collector is constructed using metal microspheres with an electrolyte gradient and a conductivity gradient. Most of the lithium / sodium metal tends to grow inside the metal microspheres, which can provide sufficient sodium metal deposition space, making the volume change of the battery smaller and sodium dendrites less likely to appear.

[0073] In some embodiments, the secondary battery further includes an electrolyte, a positive electrode, and a separator, and is made into an electrode core by a stacking process or a winding process, and then a complete battery structure is formed. The specific types of the electrolyte, the positive electrode, and the separator are not limited.

[0074] In some embodiments, the electrolyte includes a solvent and an alkali metal salt. The alkali metal salt is NaPF6 or LiPF6, the solvent can be diglyme, and the concentration of the alkali metal salt can be about 1M. The positive electrode is obtained by coating a lithium / sodium active material on a carbon-coated aluminum foil current collector. The active material is selected from at least one of a ternary positive electrode material, a polyanion material, a layered oxide material, and a Prussian blue analogue material. The lithium / sodium active material can be any one or several of the above. The separator is selected from at least one of polyethylene, polypropylene, and glass fiber, and the type of the separator can be any one or several of the above.

[0075] The features and properties of the present invention will be further described in detail below in conjunction with embodiments.

[0076] Example 1

[0077] This example provides a method for preparing a three-dimensional current collector, and the steps are as follows:

[0078] (1) Commercial metal powder (aluminum metal powder) and commercial metal mesh (aluminum mesh) are purchased, and the metal powder and the metal mesh are cleaned with acetone and pure water, and then soaked in dilute hydrochloric acid (concentration: 0.1 mol / L) for 0.5 h, and washed three times with pure water.

[0079] (2) The metal powder and the metal mesh treated in step (1) are respectively placed in a tubular furnace, pure O2 is introduced, and the pre-oxidation temperature is controlled at 350 °C and the pre-oxidation time is 0.5 h.

[0080] (3) Prepare highly conductive agents CF (vapor-grown carbon fiber with a length of 5 - 20 μm, purchased from Showa Denko K.K., Japan), carbon nanotubes CNT, the metal powder obtained in step (2), binder PVA, dispersant PVP, liquid-retaining material (montmorillonite), and pore-forming agent (copper carbonate). Mix the above materials in a mixer for 5 h, add deionized water, and homogenize with a homogenizer for 2 h to obtain a uniform mixed slurry. Among them, the mass ratio of the metal powder, conductive carbon fiber, carbon nanotubes, binder, dispersant, liquid-retaining material, and pore-forming agent is 100:5:3:5:4:4:4, and the solid content of the mixed slurry is 60%.

[0081] (4) Atomize the mixed slurry obtained in step (3) in a drying tower and contact it with hot air flow for rapid drying to form particles. Control the atomization pressure to be 10 MPa, the inlet temperature of the drying tower to be 250 °C, the outlet temperature to be 120 °C, and the residence time to be 15 s to obtain porous conductive metal microspheres.

[0082] (5) Prepare a conductive agent (SP), a solid-state electrolyte (polyethylene oxide), and a binder (polytetrafluoroethylene). Mix the porous conductive metal microspheres with the conductive agent, solid-state electrolyte, and binder in a mixer for 5 h. The mixed powder enters a high-temperature open mill and is kneaded with a metal mesh 10 times. The operating temperature of the high-temperature open mill is 60 °C, the rolling pressure is 10 T, and the kneading time is 10 min to obtain a dense three-dimensional metal microsphere current collector with a thickness of 200 μm. Among them, the mass ratio of the metal mesh, porous conductive metal microspheres, conductive agent, solid-state electrolyte, and the second binder is 100:850:30:30:30.

[0083] Example 2

[0084] The difference from Example 1 is only that: in step (3), the mass ratio of the metal powder, conductive carbon fiber, carbon nanotubes, binder, dispersant, liquid-retaining material, and pore-forming agent is 100:6:4:4:6:5:5.

[0085] Example 3

[0086] The difference from Example 1 is only that: in step (3), the mass ratio of the metal powder, conductive carbon fiber, carbon nanotubes, binder, dispersant, liquid-retaining material, and pore-forming agent is 100:4:2:4:2:3:3.

[0087] Example 4

[0088] The difference from Example 1 is only that: in step (5), the mass ratio of the metal mesh, porous conductive metal microspheres, conductive agent, solid-state electrolyte, and the second binder is 100:800:40:40:40.

[0089] Example 5

[0090] The difference from Example 1 is only that: in step (5), the mass ratio of the metal mesh, porous conductive metal microspheres, conductive agent, solid electrolyte, and second binder is 100:750:50:50:50.

[0091] Example 6

[0092] The difference from Example 1 is only that: in step (3), the liquid-retaining material is not added.

[0093] Example 7

[0094] The difference from Example 1 is only that: in step (3), the type of the liquid-retaining material is hydrotalcite.

[0095] Example 8

[0096] This example provides a method for preparing a three-dimensional current collector, and the steps are as follows:

[0097] (1) Purchase commercial metal powder (copper metal powder) and commercial metal mesh (copper mesh), clean the metal powder and metal mesh with acetone and pure water, then soak them in dilute hydrochloric acid (concentration: 0.1 mol / L) for 0.5 h, and wash them three times with pure water.

[0098] (2) Put the metal powder and metal mesh treated in step (1) into a tube furnace respectively, introduce pure O2, control the pre-oxidation temperature at 350 °C, and the pre-oxidation time at 0.5 h.

[0099] (3) Prepare a highly conductive agent CF (vapor-grown carbon fiber, with a length of 5-20 microns, purchased from Showa Denko K.K. of Japan), carbon nanotube CNT, the metal powder obtained in step (2), binder PVA, dispersant PVP, liquid-retaining material (montmorillonite), and pore-forming agent (copper carbonate), mix the above materials in a mixer for 5 h, add deionized water, and homogenize with a homogenizer for 2 h to obtain a uniform mixed slurry. Among them, the mass ratio of the metal powder, conductive carbon fiber, carbon nanotube, binder, dispersant, liquid-retaining material, and pore-forming agent is 100:5:3:5:4:4:4, and the solid content of the mixed slurry is 60%.

[0100] (4) Atomize the mixed slurry obtained in step (3) in a drying tower and contact it with hot air flow for rapid drying to form particles. Control the atomization pressure at 10 MPa, the inlet temperature of the drying tower at 250 °C, the outlet temperature at 120 °C, and the residence time at 15 s to obtain porous conductive metal microspheres.

[0101] (5) Prepare the conductive agent (SP), solid electrolyte (polyethylene oxide), and binder (polytetrafluoroethylene). Mix the porous conductive metal microspheres with the conductive agent, solid electrolyte, and binder in a mixer for 5 h. The mixed powder enters a high-temperature open mill and is kneaded with a metal mesh 10 times. The operating temperature of the high-temperature open mill is 60 °C, the rolling pressure is 10 T, and the kneading time is 10 min to obtain a dense three-dimensional current collector of metal microspheres with a thickness of 200 μm. Among them, the mass ratio of the metal mesh, porous conductive metal microspheres, conductive agent, solid electrolyte, and second binder is 100:850:30:30:30.

[0102] Comparative Example 1

[0103] This comparative example provides an aluminum foil current collector.

[0104] Comparative Example 2

[0105] This comparative example provides a current collector of carbon-coated aluminum foil.

[0106] Comparative Example 3

[0107] The difference from Example 1 is only that: in step (5), the porous conductive metal microspheres are not added.

[0108] Comparative Example 4

[0109] A current collector is a pure copper foil (with a thickness of 20 μm).

[0110] Test Example 1

[0111] Test the application effects of the current collectors provided in the examples and comparative examples in non-negative electrode batteries. The results are shown in Table 1.

[0112] Test method: Select the current collector provided in the example or comparative example as the negative electrode; the electrolyte is NaPF6 + diethylene glycol dimethyl ether, and the concentration of NaPF6 is 1 M; the positive electrode is a carbon-coated aluminum foil current collector coated with a sodium active material (sodium iron pyrophosphate phosphate); the separator is a polyethylene with a thickness of 20 μm; the battery core is made by the stacking process or winding process, and the battery is assembled using the non-negative electrode battery process. Among them, the preparation process of the positive electrode includes: uniformly mixing sodium iron pyrophosphate phosphate, conductive carbon black, PVDF, and PAA in a ratio of 95:2:2:1 and adding them to a solvent (NMP) to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of a carbon-coated aluminum foil current collector with a thickness of 10 μm, and the coating areal density is 40 mg / cm 3 , and then dried.

[0113] Test the rate performance, cycle performance, and cycle gas generation of the battery core at 25 °C, as shown in Table 1.

[0114] Table 1 Application effects of the current collectors provided in the examples and comparative examples in non-negative electrode batteries

[0115]

[0116] Test Example 2

[0117] An anode-free lithium-ion battery was prepared using the current collectors provided in Example 8 and Comparative Example 4 as the anode. Among them, the cathode sheet was prepared by uniformly mixing NCM811, conductive carbon black, PVDF, and PAA in a ratio of 95:2:2:1 and adding them to a solvent (NMP) to obtain a cathode slurry, and then coating the cathode slurry on the surface of carbon-coated aluminum foil to obtain the cathode sheet;

[0118] The electrolyte was: ethylene glycol dimethyl ether containing 1M LiFSI;

[0119] The separator was: a polyethylene separator.

[0120] An anode-free lithium-ion laminated battery was assembled in a glove box under an inert atmosphere according to the same preparation method.

[0121] The performances of the batteries prepared in Example 8 and Comparative Example 4 were respectively detected (including charge-discharge capacity, initial Coulomb efficiency, 5C capacity retention rate (compared with normal 0.5C cycling, the percentage of capacity compared to 0.5C cycling), capacity retention rate after 100 charge-discharge cycles at 0.1C / 0.1C, gas generation amount, capacity retention rate after 300 charge-discharge cycles at 0.5C / 1C), and the results are shown in Table 2.

[0122] Table 2 Application effects of the current collectors provided in Example 8 and Comparative Example 4 in anode-free batteries

[0123]

[0124] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A three-dimensional current collector, characterized in that, It includes a framework and a filler filled in the framework; Among them, the framework is a metal mesh; The filler includes a current collector filler and an additive filler. The current collector filler is a porous conductive metal microsphere, and the additive filler includes a solid electrolyte and a conductive agent.

2. The three-dimensional current collector according to claim 1, wherein The porous conductive metal microsphere includes conductive carbon fibers, carbon nanotubes and metal particles; Preferably, the material of the metal particles is selected from at least one of pure aluminum, aluminum-copper alloy, pure copper, bronze, red copper, brass and pure titanium; Preferably, the porous conductive metal microsphere further includes a first binder, a dispersant and a liquid retention material. The first binder is selected from at least one of polyvinyl alcohol, polyvinyl butyral and styrene-butadiene rubber; the dispersant is selected from at least one of polyvinylpyrrolidone, polyethylene glycol and sodium carboxymethylcellulose; the liquid retention material is selected from at least one of montmorillonite and hydrotalcite; More preferably, in the porous conductive metal microsphere, the mass fraction of conductive carbon fibers is 3%-5%, the mass fraction of carbon nanotubes is 1%-3%, the mass fraction of metal particles is 80%-90%, the mass fraction of the first binder is 3%-5%, the mass fraction of the dispersant is 1%-3%, and the mass fraction of the liquid retention material is 2%-4%.

3. The three-dimensional current collector according to claim 1 or 2, characterized in that, The mass proportion of the porous conductive metal microsphere in the three-dimensional current collector is 75%-85%, the mass proportion of the solid electrolyte in the three-dimensional current collector is 3%-5%, and the mass proportion of the conductive agent in the three-dimensional current collector is 3%-5%; Preferably, the solid electrolyte is selected from at least one of oxides, polymers and sulfides; Preferably, the conductive agent is selected from at least one of conductive carbon black, Ketjen black and acetylene black; Preferably, the metal mesh is selected from at least one of aluminum mesh and copper mesh; Preferably, the thickness of the three-dimensional current collector is 100μm-200μm.

4. The preparation method of the three-dimensional current collector according to any one of claims 1-3, characterized in that, It includes: Providing the porous conductive metal microsphere; Mixing the conductive agent, the solid electrolyte, the porous conductive metal microsphere and a second binder, and then pressing and molding with a metal mesh in a high-temperature kneader.

5. The preparation method according to claim 4, characterized in that, The preparation process of the porous conductive metal microsphere includes: mixing raw materials and water to obtain a mixed slurry, and then atomizing and drying the mixed slurry; Preferably, drying is carried out in a drying tower, controlling the inlet temperature to be 150℃-300℃ and the outlet temperature to be 80℃-150℃.

6. The preparation method according to claim 5, wherein The preparation process of the mixed slurry includes: mixing metal particles, conductive carbon fibers, carbon nanotubes, a first binder, a dispersant, a liquid retention material and a pore-forming agent, and then mixing and homogenizing with water to obtain a mixed slurry; Preferably, the solid content of the mixed slurry is 50%-70%; Preferably, the pore-forming agent is selected from at least one of copper carbonate and sodium bicarbonate; Preferably, the mass ratio of the metal particles, the conductive carbon fibers, the carbon nanotubes, the first binder, the dispersant, the liquid retention material and the pore-forming agent is 100:(4-6):(2-4):(4-6):(2-6):(3-5):(3-5); Preferably, the metal particles are pretreated and pre-oxidized before preparing the mixed slurry; the pretreatment includes pickling to remove the oxide layer; the pre-oxidation is carried out in an oxygen-containing atmosphere, controlling the pre-oxidation temperature at 200°C - 500°C, and pre-oxidizing for 0.1 h - 1 h.

7. The preparation method according to claim 4, characterized in that, The mass ratio of the metal mesh, the porous conductive metal microspheres, the conductive agent, the solid electrolyte, and the second binder is 100:(750 - 850):(30 - 50):(30 - 50):(30 - 50); Preferably, the second binder is polytetrafluoroethylene.

8. The preparation method according to claim 4, wherein The operating temperature of the high-temperature open mill is 40°C - 70°C, the rolling pressure is 1T - 50T, the mixing time is 5 min - 15 min, and the number of open millings is 5 - 15 times.

9. A secondary battery, characterized in that, The three-dimensional current collector prepared by the three-dimensional current collector according to any one of claims 1 - 3 or the preparation method according to any one of claims 4 - 8 is used as the negative electrode and is prepared by using a non-negative electrode battery process.

10. The secondary battery according to claim 9, characterized in that, The secondary battery further includes an electrolyte, a positive electrode, and a separator; Preferably, the electrolyte includes a solvent and an alkali metal salt, and the alkali metal salt is NaPF6 or LiPF6; Preferably, the positive electrode is obtained by coating an active material on a carbon-coated aluminum foil current collector, and the active material is selected from at least one of a ternary positive electrode material, a polyanion material, a layered oxide material, and a Prussian blue analogue material; Preferably, the separator is selected from at least one of polyethylene, polypropylene, and glass fiber.

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