3D anode composite material, preparation method and application thereof

Abstract

This invention discloses a 3D anode composite material, its preparation method, and its applications. The anode composite material has a carbon nanotube aerogel membrane as the main framework, filled with a lithium-aluminum alloy or a lithium-lithium-aluminum alloy. The lithium-aluminum alloy is uniformly attached to the surface of the carbon nanotubes to construct a continuous porous 3D secondary framework. Unalloyed free lithium metal is uniformly filled inside the composite three-dimensional framework, together forming the 3D anode composite material. It can be used as a battery negative electrode without the need for a traditional current collector substrate. The preparation method is as follows: In an argon-filled glove box, a lithium-aluminum mixture is cast into a graphite mold containing a carbon nanotube aerogel membrane. After cooling and solidification, the anode composite material is obtained. The anode composite material prepared by this invention can be assembled with any positive electrode material for the fabrication of lithium-ion batteries and all-solid-state lithium batteries. The prepared batteries have high capacity, high initial coulombic efficiency, and good cycle performance. The preparation process of this invention is simple, the product consistency is good, and the operation is highly operable.

Description

Technical Field

[0001] This invention belongs to the field of battery material processing technology, specifically relating to a 3D anode composite material, its preparation method and application. Background Technology

[0002] Lithium-ion rechargeable batteries are a type of green new energy battery that primarily relies on the movement of lithium ions between the positive and negative electrodes to function. Currently, the widely used commercial lithium-ion battery negative electrode material is mainly graphite, with a theoretical capacity of 372 mAh·g. -1 Lithium plating easily occurs during high-current charge and discharge, which cannot adequately meet the demands of high-performance lithium-ion batteries. Therefore, to achieve high specific energy of batteries, it is essential to research and develop high-capacity anode materials.

[0003] Lithium metal has a high theoretical specific capacity (3860 mAh·g). -1 With its low redox potential (-3.04V vs. standard hydrogen electrode), lithium metal is considered an ideal anode material for high-energy-density batteries such as lithium-sulfur and lithium-oxygen batteries. However, highly reactive lithium metal is susceptible to attack by most non-aqueous electrolytes, leading to the formation of a solid electrolyte interphase (SEI). The brittle SEI layer cannot adapt to changes in lithium volume, resulting in the exposure of fresh lithium metal beneath the SEI layer. The continuous reaction between fresh lithium metal and the electrolyte increases the thickness of the SEI layer and the resistance of the lithium / electrolyte interface. Furthermore, lithium dendrites gradually form on the lithium anode surface due to non-uniform lithium-ion diffusion flux and electric field. These lithium dendrites either detach from the lithium anode during lithium dissolution, leading to poor lithium metal cycle stability and reduced coulombic efficiency, or penetrate the separator during lithium deposition, causing battery short circuits and serious safety issues. Therefore, uncontrolled lithium dendrite nucleation and growth during electroplating / stripping is a major limitation to the commercial application of lithium metal anodes. Various methods have been explored to overcome the aforementioned problems of lithium metal anodes. Lithium can form alloys with a variety of metals at room temperature, with tin, silicon, and aluminum being the most studied, and their theoretical capacities being 994 mAh / g (Li). 4.4 Sn), 4200mAh / g (Li 4.4 The values ​​are 2234 mAh / g (Si) and 2234 mAh / g (Al4Li9). Among these, there have been a few reports on the use of metallic aluminum and its alloys as anode materials. Figure 1 As shown in the Al-Li binary phase diagram, aluminum and lithium can form three alloys: AlLi, Al2Li3, and Al4Li9. Even with AlLi, the theoretical capacity can reach 993 mAh / g, comparable to that of tin-based anode materials. Furthermore, its lithium intercalation potential is 0.2V vs. Li... +With a lithium content around 0.96%, it effectively avoids the formation of lithium dendrites, improving safety performance. Furthermore, the lithium insertion / extraction process of aluminum has a flat electrochemical reaction platform, providing a very stable operating voltage. Therefore, it has the potential to become a novel high-capacity lithium-ion battery anode material.

[0004] Currently, there is an increasing number of literature reports on the application of aluminum in battery anode materials, and the preparation processes are also diverse. However, most anode materials suffer from three main problems: 1. Low battery capacity; 2. Unsatisfactory cycle performance; 3. Failure to fully utilize the potential of the active materials in the electrode. These are also three important indicators for evaluating the performance of electrode materials. Without solving these three problems, the practical application of metallic aluminum in lithium-ion battery anode materials cannot be realized.

[0005] The present invention is made to address the aforementioned problems existing in the prior art. Summary of the Invention

[0006] To address at least one of the aforementioned technical problems, this invention provides a 3D anode composite material, its preparation method, and its application. The preparation method first prepares a three-dimensional porous carbon nanotube aerogel framework, then fills it with a lithium-aluminum mixture, cools and solidifies it, and obtains a three-dimensional anode composite material with stable structure, high toughness, good conductivity, and high efficiency in transporting and storing lithium metal.

[0007] The technical solution of this invention is as follows:

[0008] This invention relates to a 3D anode composite material, with a carbon nanotube aerogel membrane as the main framework, filled with a lithium-aluminum alloy or a lithium-lithium-aluminum alloy. The lithium-aluminum alloy is uniformly attached to the surface of the carbon nanotubes to form a continuous porous 3D secondary framework, and unalloyed free lithium metal is uniformly filled in the pores inside the composite three-dimensional framework, together constituting the 3D anode composite material. The composite three-dimensional framework consists of a main framework and a porous 3D secondary framework. This composite material does not contain a traditional current collector substrate and can be directly used as a battery negative electrode.

[0009] Carbon nanotube aerogel, with carbon nanotubes as the main material, is an excellent ionic and electronic conductor. The anode composite material eliminates the need for liquid electrolyte infiltration. The framework material effectively guides the uniform electroplating of metallic lithium along the carbon nanotube direction and ensures effective bonding with aluminum, preventing random nucleation and growth of the metal on the negative electrode surface. During lithium stripping, the lithium-lithium-aluminum alloy within the anode material can achieve "3D stripping" through rapid balancing of the electric field, forming a continuous porous 3D lithium-aluminum framework attached between the carbon nanotube aerogel framework. This creates a unique porous three-dimensional composite framework that simultaneously provides lithium-ion transport channels. Especially under high current, this composite porous three-dimensional framework exhibits advantages in lithium-ion dissolution kinetics. The three-dimensional lithium-aluminum framework formed after lithium stripping maintains its original shape and stability, with no significant changes in the thickness and volume of the composite material, effectively ensuring the structural stability of the SEI film on the anode surface. During electroplating, the composite porous three-dimensional framework structure provides a larger specific surface area than bare lithium, effectively reducing local current density and regulating the electric field distribution. The large specific surface area also provides more nucleation sites and lithium-ion transport channels, which is beneficial for improving the stability of the anode composite material at high rates. Furthermore, the excellent nucleophilic interaction between lithium and aluminum induces lithium ions to uniformly fill the pores of the three-dimensional framework structure, effectively avoiding volume changes and lithium dendrite formation in the lithium metal electrode. Therefore, lower hysteresis is achieved during repeated cycling, resulting in good stability in long-term cycling of symmetric and full-cell batteries. In contrast, the stripping / electroplating process of bare lithium anodes only occurs on the surface of metallic lithium. Repeated stripping / electroplating on the electrode surface easily leads to lithium dendrite formation, causing volume expansion or the formation of "dead lithium," thereby damaging the SEI film.

[0010] The present invention also relates to a method for preparing a 3D anode composite material, wherein a uniformly mixed lithium-aluminum mixture is poured into a graphite mold containing a carbon nanotube aerogel film in an argon-filled glove box, and after cooling and solidification, a 3D anode composite material is obtained.

[0011] Preferably, one method for preparing the carbon nanotube aerogel membrane is as follows: first, a carbon nanotube dispersion is prepared, then the carbon nanotube dispersion is coated on the surface of the current collector, and after freeze-drying / supercritical drying, it is peeled off to obtain the carbon nanotube aerogel membrane.

[0012] Preferably, the second method for preparing the carbon nanotube aerogel membrane is as follows: first, a carbon nanotube dispersion is prepared; then, the carbon nanotube dispersion is passed through a micro-nano foaming machine to form uniform micro-nano bubbles inside; then, the foamed carbon nanotube dispersion is coated on the surface of the current collector substrate, dried quickly, and peeled off to obtain the carbon nanotube aerogel membrane.

[0013] Preferably, the current collector substrate is one of copper foil, aluminum foil, copper mesh, and aluminum mesh.

[0014] Preferably, a carbon nanotube dispersion is prepared by uniformly mixing a solvent, carbon nanotubes, a binder, and a stabilizer in a certain proportion. The specific preparation process is as follows: carbon nanotubes are dispersed in a solvent, a certain amount of binder and stabilizer are added, and the mixture is continuously stirred at a rate of 200-300 rpm for 20-30 minutes to ensure thorough and uniform mixing, thereby obtaining the carbon nanotube dispersion. More preferably, the solvent is at least one selected from deionized water, alcohol, ethylene glycol, propanol, isopropanol, acetone, and N-methylpyrrolidone; the binder is at least one selected from polyvinylpyrrolidone, polyvinyl alcohol, polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, perfluorosulfonic acid polymers, lithium alginate, and lithium pectate; the stabilizer is sodium carboxymethyl cellulose (CMC); and the carbon nanotubes are multi-walled carbon nanotubes with a purity greater than 99%, a diameter of 10-200 nm, and a length of 5-20 μm.

[0015] Preferably, the mass concentration of carbon nanotubes in the nanotube dispersion is 9% to 15%, and the mass ratio of carbon nanotubes to binder and stabilizer is 20 to 10:0.7:0.3.

[0016] Preferably, the method for preparing the lithium-aluminum mixture is as follows: in an argon-filled glove box (O2<0.1ppm, H2O<0.1ppm), the lithium metal source and the aluminum metal source are placed in a stainless steel crucible, heated to 300℃~550℃, and continuously stirred to ensure that the lithium and aluminum metals are completely melted to form a uniform mixture.

[0017] Preferably, the lithium metal source is lithium foil or lithium powder, and the aluminum metal source is aluminum foil or nano-aluminum powder.

[0018] Preferably, the lithium-aluminum mixture contains between 20% and 90% lithium by mass.

[0019] This invention also relates to the application of the above-mentioned 3D anode composite material in the manufacture of lithium-ion batteries and all-solid-state lithium batteries. The 3D anode composite material can be assembled with any positive electrode material as a negative electrode to manufacture lithium-ion batteries and all-solid-state lithium batteries. The prepared batteries have high capacity, high initial coulombic efficiency, and good cycle performance.

[0020] The beneficial effects of this invention are:

[0021] 1) The anode composite material prepared by this invention can be used with lithium-free cathode materials such as MnO2, S, V2O5, and Li. 1+xIt can be matched with V3O8 and other materials to form batteries, or it can be matched with lithium-containing cathode materials such as lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide to form batteries; it can be used to assemble both lithium-ion batteries with electrolyte and all-solid-state lithium batteries. The anode composite material prepared by this invention has good conductivity and high efficiency in storing and transporting lithium metal when used as a battery negative electrode. The batteries prepared by this invention have the advantages of high capacity, high initial efficiency, good rate performance and cycle performance.

[0022] 2) During lithium stripping, the lithium-aluminum alloy within the anode material can achieve "3D stripping" through a rapidly equilibrated electric field, forming a continuous porous 3D lithium-aluminum framework attached between the carbon nanotube aerogel framework. This creates a unique porous three-dimensional composite framework that simultaneously provides lithium-ion transport channels. Especially under high current, this composite porous three-dimensional framework exhibits advantages in lithium-ion dissolution kinetics. The three-dimensional lithium-aluminum framework formed after lithium stripping maintains its original shape and stability, with no significant changes in the thickness and volume of the composite material, effectively ensuring the structural stability of the SEI film on the anode surface.

[0023] 3) During electroplating, the composite porous three-dimensional framework structure provides a larger specific surface area than bare lithium, effectively reducing local current density and regulating the electric field distribution. The large specific surface area also provides more nucleation sites and lithium-ion transport channels, which is beneficial for improving the stability of the anode composite material at high rates. The excellent nucleophilic interaction between lithium and aluminum induces lithium ions to uniformly fill the pores of the three-dimensional framework structure, effectively avoiding volume changes and lithium dendrite formation in the lithium metal electrode. Therefore, lower hysteresis is achieved during repeated cycling, resulting in good stability in long-term cycling of symmetrical and full-cell batteries.

[0024] 4) The preparation method of this invention is simple, the product has good consistency, strong operability, and has broad commercial application prospects. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0026] Figure 1 The aluminum-lithium binary phase diagram;

[0027] Figure 2 The anode composite material prepared in Example 1 of this invention has a peel strength of 20 mAh·cm⁻¹. -2 After lithium plating, a step-by-step lithium plating process is performed, and the surface is shown in SEM images under different conditions.

[0028] In the figure: (a) stripping 20 mAh·cm -2 The anode surface states after lithium deposition, (b, c, d) represent the re-plating of 5mAh·cm⁻¹, respectively. -2 15mAh·cm-2 20mAh·cm -2 The anodic surface state of lithium. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0030] Example 1

[0031] 10 kg of carbon nanotubes were added to 90 kg of 50% alcohol solution and ultrasonically treated. Then, 7 kg of 10% polyvinyl alcohol solution and 3 kg of 10% sodium carboxymethyl cellulose solution were added to the mixture. The mixture was stirred continuously at 200 rpm for 30 min to ensure thorough mixing and uniformity, thus obtaining a carbon nanotube dispersion. The carbon nanotube dispersion was coated onto the surface of an aluminum mesh and fed into a liquid ammonia cryogenic dehydration tank via a conveyor. The mesh was then placed in a -10℃ low-temperature drying chamber and dried before being peeled off to obtain a carbon nanotube aerogel film.

[0032] In an argon-filled glove box (O2 < 0.1 ppm, H2O < 0.1 ppm), lithium foil and aluminum foil with a mass ratio of lithium:aluminum = 1:1 were placed in a stainless steel crucible and heated to 350°C on a heating plate with continuous stirring until the metals were completely melted to form a homogeneous mixture. This mixture was then cast into a graphite mold containing a carbon nanotube aerogel film and allowed to cool and solidify to obtain the anode composite material.

[0033] CR2032 coin cells were assembled in an argon-filled glove box using lithium metal as the counter electrode, Cellgard 2400 as the separator, and 1M LiPF6 (EC / DMC = 1:1 volume ratio) as the electrolyte. After stabilizing the assembled cells for 6 hours, constant current charge-discharge performance tests were conducted on the LAND battery testing system, with a charge-discharge range of 1.5V to 4.8V. The cells achieved 100% initial efficiency at 20mA·g. -1 After 100 cycles at the current density, the capacity still remains at 1963.6 mAh·g. -1 The material can also maintain excellent capacity retention during the cycling process.

[0034] The prepared anode composite material was exfoliated at 20 mAh·cm -2 After lithium plating, a stepwise lithium plating process was performed, and SEM images of the surface under different conditions were observed, such as... Figure 2 As shown. Among them, (a) represents the peeling of 20 mAh·cm³. -2The anode surface states after lithium deposition, (b, c, d) represent the re-plating of 5mAh·cm⁻¹, respectively. -2 15mAh·cm -2 20mAh·cm -2 The anode surface state of lithium. (From...) Figure 2 As can be seen, the three-dimensional lithium-aluminum framework formed after lithium stripping attaches to the carbon nanotube main framework and completely encapsulates it, maintaining its original shape stability. Measurements show that the thickness and volume of the composite material do not change significantly. Figure 2 From b to 2d, it was observed that as the lithium plating amount increased, the porous structure of the 3D anode gradually decreased. When lithium returned to the anode and was electroplated on the anode surface, it tended to return to the three-dimensional pores rather than re-nucleating and forming lithium dendrites on the anode surface. When the lithium plating capacity increased to 20 mAh·cm⁻¹, the porous structure of the 3D anode gradually decreased. -2 At this time, most of the pore structure is covered by lithium, the anode surface is smooth and flat, no lithium dendrites are formed, and it exhibits good reversibility.

[0035] Example 2

[0036] The carbon nanotube dispersion was prepared in the same manner as in Example 1. The prepared carbon nanotube dispersion was circulated 5 times through a micro-nano foaming machine with a dispersion flow rate of 300 L / h and an air flow rate of 150 L / h to obtain a foamed carbon nanotube dispersion. The foamed carbon nanotube dispersion was coated on the surface of aluminum foil and fed into a rapid drying chamber via a conveyor. After drying, it was peeled off to obtain a nano-carbon aerogel film.

[0037] In an argon-filled glove box (O2 < 0.1 ppm, H2O < 0.1 ppm), lithium foil and nano-aluminum powder (mass ratio of lithium:aluminum = 1:4) were placed in a stainless steel crucible and heated to 500°C on a heating plate with continuous stirring until the metals were completely melted to form a homogeneous mixture. This mixture was then cast into a graphite mold containing a carbon nanotube aerogel film and allowed to cool and solidify to obtain the desired anode composite material.

[0038] A positive electrode sheet was prepared using lithium iron phosphate (LFP) as the positive electrode material. 53 parts by mass of N-methylpyrrolidone were added to LFP in a mass ratio of 94:3:3. After thorough mixing, the mixture was coated, baked, and rolled to obtain the positive electrode sheet.

[0039] Using the obtained positive electrode as the counter electrode, Cellgard 2400 as the separator, and 1M LiPF6 (EC / DMC = 1:1 volume ratio) as the electrolyte, the battery was assembled in an argon-filled glove box. The charge / discharge range was 2.0V–4.2V. The initial coulombic efficiency was 100%. After 100 cycles at 0.5C and 2C, the capacity retention rates were 99.9% and 99.6%, respectively, and after 400 cycles, the capacity retention rates were 99.5% and 99.1%, respectively.

[0040] In contrast, the corresponding battery assembled with pure lithium foil as the anode experienced rapid capacity degradation in less than 100 cycles.

[0041] Example 3

[0042] 10 kg of carbon nanotubes were added to 90 kg of 40% ethanol solution and sonicated. Then, 7 kg of 10% polyvinyl alcohol solution and 3 kg of 10% sodium carboxymethyl cellulose solution were added to the mixture. The mixture was stirred continuously at 200 rpm for 30 minutes to ensure thorough mixing, thus obtaining a carbon nanotube dispersion. The prepared carbon nanotube dispersion was circulated three times through a micro / nano foaming machine with a dispersion flow rate of 300 L / h and an air flow rate of 150 L / h to obtain a foamed carbon nanotube dispersion. This foamed carbon nanotube dispersion was coated onto the surface of aluminum foil and fed into a rapid drying chamber via a conveyor. After drying, it was peeled off to obtain a nano-carbon aerogel film.

[0043] In an argon-filled glove box (O2 < 0.1 ppm, H2O < 0.1 ppm), lithium foil and aluminum foil with a mass ratio of lithium:aluminum = 9:1 were placed in a stainless steel crucible and heated to 300°C on a heating plate with continuous stirring until the metals were completely melted to form a homogeneous mixture. This mixture was then cast into a graphite mold containing a carbon nanotube aerogel film and allowed to cool and solidify to obtain the desired anode composite material.

[0044] 150 mg of Li6PS5Cl solid electrolyte powder was cold-pressed at 180 MPa; cathode material was prepared by manually mixing lithium cobalt oxide and Li6PS5Cl solid electrolyte powder in a mass ratio of 7:3; then, the solid electrolyte and cathode material were sequentially laid on the anode composite material, and then pressed under 90 MPa pressure to obtain an all-solid-state battery. The charge / discharge range is 3.0–4.2 V, the initial coulombic efficiency is 100%, and the capacity retention rate is still greater than 90% (90.4%) after 300 cycles at 0.1C.

[0045] In contrast, all-solid-state batteries prepared using pure lithium foil as the anode only retain 46.5% of their capacity after 300 cycles at 0.1C.

[0046] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A 3D anodic composite material, characterized in that, The carbon nanotube aerogel membrane serves as the main framework, filled with lithium-aluminum alloy or lithium-lithium-aluminum alloy. The lithium-aluminum alloy is uniformly attached to the surface of the carbon nanotube to form a continuous porous 3D secondary framework, while unalloyed free lithium metal is uniformly filled in the pores inside the composite three-dimensional framework, together forming a 3D anode composite material. The carbon nanotube aerogel membrane is prepared by method one or two. Method 1 involves uniformly mixing solvent, carbon nanotubes, binder, and stabilizer in a certain proportion to prepare a carbon nanotube dispersion. The carbon nanotube dispersion is then coated onto the surface of the current collector, freeze-dried / supercritically dried, and then peeled off to obtain the carbon nanotube aerogel film. Method 2 is as follows: The solvent, carbon nanotubes, binder and stabilizer are mixed uniformly in a certain proportion to prepare a carbon nanotube dispersion. Then, the carbon nanotube dispersion is passed through a micro-nano foaming machine to form uniform micro-nano bubbles inside. The foamed carbon nanotube dispersion is then coated on the surface of the current collector substrate, dried quickly and then peeled off to obtain the carbon nanotube aerogel film. The preparation method of the 3D anode composite material is as follows: In a glove box filled with argon gas, a uniformly mixed lithium-aluminum mixture is poured into a graphite mold containing a carbon nanotube aerogel membrane. After cooling and solidification, the 3D anode composite material is obtained. The lithium-aluminum mixture contains lithium with a mass percentage between 20% and 90%. The 3D anode composite material has no current collector substrate and can be directly used as the negative electrode of the battery.

2. A method for preparing the 3D anodic composite material according to claim 1, characterized in that, In an argon-filled glove box, a uniformly mixed lithium-aluminum liquid is poured into a graphite mold containing a carbon nanotube aerogel membrane. After cooling and solidification, a 3D anode composite material is obtained.

3. The preparation method according to claim 2, characterized in that, The carbon nanotube aerogel membrane is prepared by uniformly mixing solvent, carbon nanotubes, binder and stabilizer in a certain proportion to prepare carbon nanotube dispersion, then coating the carbon nanotube dispersion onto the surface of the current collector, freeze-drying / supercritical drying and then peeling off to obtain the carbon nanotube aerogel membrane.

4. The preparation method according to claim 2, characterized in that, The preparation method of the carbon nanotube aerogel film is as follows: solvent, carbon nanotubes, binder and stabilizer are uniformly mixed in a certain proportion to prepare carbon nanotube dispersion. Then, the carbon nanotube dispersion is passed through a micro-nano foaming machine to form uniform micro-nano bubbles inside. The foamed carbon nanotube dispersion is then coated on the surface of the current collector substrate, dried quickly and then peeled off to obtain the carbon nanotube aerogel film.

5. The preparation method according to claim 2, characterized in that, The method for preparing the lithium-aluminum mixture is as follows: In an argon-filled glove box, the lithium metal source and the aluminum metal source are placed in a crucible, heated to 300℃~550℃, and continuously stirred to ensure that the lithium and aluminum metals are completely melted to form a uniform mixture.

6. The preparation method according to claim 5, characterized in that, The lithium metal source is lithium foil or lithium powder, and the aluminum metal source is aluminum foil or nano-aluminum powder.

7. The preparation method according to claim 2 or 5, characterized in that, The lithium-aluminum mixture contains lithium at a mass percentage between 20% and 90%.

8. The application of the 3D anode composite material according to claim 1 in the manufacture of lithium-ion batteries and all-solid-state lithium batteries.

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