Lightweight composite negative electrode and preparation method thereof

Abstract

This invention discloses a lightweight composite anode and its preparation method, belonging to the field of electrochemical energy storage technology. The composite anode includes a conductive framework with at least two porous carbon layers along its thickness direction. The electronic conductivity of each porous carbon layer decreases sequentially from the inside out, forming an electronic conductivity gradient. Lithophilic materials are loaded into the pores of at least one porous carbon layer of the conductive framework. This invention, through the design of the electronic conductivity gradient, forces lithium ions to preferentially nucleate and deposit deep within the current collector, achieving uniform growth "from the inside out," effectively suppressing lithium dendrites and volume expansion. Combined with pre-deposited lithium to compensate for initial cycle lithium loss, and a surface protective layer to physically isolate electrolyte side reactions, it significantly improves the battery's initial coulombic efficiency, cycle stability, and safety. This invention also provides a preparation method for the composite anode, which is simple, cost-controllable, and suitable for high-energy-density lithium-ion batteries and lithium metal batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a lightweight composite anode and its preparation method. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic devices, and energy storage power stations, higher requirements are being placed on the energy density, cycle life, and safety of lithium-ion and lithium metal batteries. As a key component of the battery, the performance of the anode material directly affects the overall battery performance.

[0003] Traditional negative electrode current collectors often use copper or nickel foil, which, while offering good conductivity, have a high density, limiting further improvements in battery energy density. To address this issue, existing technologies have proposed lightweight current collector solutions using metal layers deposited on both sides of a polymer support film. However, the bonding strength between the polymer film and the metal or carbon layers is insufficient, making them prone to defects during battery processing and cycling.

[0004] In lithium metal anode systems, exposed lithium metal or the surface of traditional current collectors is lithium-repellent, resulting in a high lithium nucleation overpotential and uneven lithium deposition, which easily leads to the formation of lithium dendrites and "dead lithium". Introducing a three-dimensional framework (such as porous carbon) can alleviate this problem to some extent, but due to the limitations of mass transfer kinetics within the framework, lithium ions tend to deposit on the outside of the framework (closer to the separator side), forming "top deposition", which hinders the utilization of internal pores and still cannot fundamentally solve the dendrite problem.

[0005] Existing lithiophilic modification techniques often employ precious metals (such as Ag and Au) or complex melt-filling processes, which are costly and complex, and cannot precisely control the chemical composition of the lithiophilic layer. In addition, in lithium-free anode systems, the deposition of lithium to form an SEI film during the first charge consumes a large amount of active lithium, resulting in low initial coulombic efficiency and accelerating capacity decay in subsequent cycles.

[0006] Therefore, developing a composite anode that combines lightweight, high structural stability, excellent lithium deposition uniformity, and high first-time coulombic efficiency is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] This invention aims to provide a low-cost, high-structural-stability composite anode solution. Through innovative multi-level structural gradient design and in-situ chemical modification, it solves the problems of lithium dendrite growth, large volume expansion, low initial coulombic efficiency, and limited energy density in existing technologies.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A lightweight composite anode includes a conductive framework having at least two porous carbon layers along its thickness direction, wherein the electronic conductivity of each porous carbon layer decreases sequentially from the inside to the outside, forming an electronic conductivity gradient; and at least one porous carbon layer of the conductive framework is loaded with a lithiophilic material in its pores.

[0010] As a preferred technical solution, the conductive framework comprises an inner layer and an outer layer. The carbon material of the inner layer is selected from at least one of carbon nanofibers, carbon nanotubes, graphene, or conductive carbon black. The porous carbon material of the outer layer has a porosity of 50%–90%, a specific surface area of ​​100–2500 m² / g, and a pore size range of 1 nm–100 μm, preferably 0.1–5 μm. The lithiophilic material is loaded into the pores of the outer layer.

[0011] As a preferred technical solution, the lithiophilic material is selected from at least one of metal oxides or metal nitrides; the mass of the lithiophilic material is 0.1% to 10% of the mass of the outer porous carbon material.

[0012] As a preferred technical solution, the composite negative electrode further includes a composite current collector, and the conductive skeleton is disposed on the composite current collector; the composite current collector includes a polymer support film (such as (PET, PP or PI)) and a metal conductive layer disposed on at least one side surface of the polymer support film.

[0013] As a preferred technical solution, the surface of the metal conductive layer that contacts the conductive skeleton is provided with a micron-level pattern.

[0014] As a preferred technical solution, the composite negative electrode further includes pre-deposited lithium, which fills the internal pores of the conductive framework.

[0015] As a preferred technical solution, the composite negative electrode further includes a surface protective layer, which is disposed on the side of the conductive skeleton away from the composite current collector.

[0016] As a preferred technical solution, the surface protective layer is a carbon layer, which is selected from at least one of amorphous carbon, graphene or polymer-derived carbon, and its thickness is 1~10 μm.

[0017] This embodiment also discloses a method for preparing a lightweight composite anode, including the following steps:

[0018] (1) Provide a composite current collector; deposit an ultra-thin metal conductive layer (copper / nickel) on both sides of a polymer support film (PET, PP or PI) with a thickness of 2μm~10μm. The surface of the metal layer is pre-formed with periodically arranged micron-level patterns / grooves by laser etching and microimprinting to enhance the bonding force with the second layer.

[0019] (2) At least two carbon material slurries with different electronic conductivity are sequentially coated on the composite current collector to form a porous carbon skeleton coating with decreasing electronic conductivity from the inside to the outside, wherein at least one layer of carbon material slurry contains a lithiophilic material; gradient design (electronic conductivity): composed of at least two layers of porous carbon skeleton slurry with different components, the electronic conductivity gradually decreases from the inside to the outside, and the innermost layer closest to the current collector is made of highly conductive carbon material, which can be one or more of carbon nanofibers, carbon nanotubes, graphene, and conductive carbon black;

[0020] The outer layer, away from the current collector, is made of porous carbon material with high porosity and high specific surface area. The porosity is 50%–90%, the specific surface area is 100–2500 m² / g, and the pore size is 1 nm–100 μm, preferably 0.1–5 μm. This layer is used to accommodate lithium. A lithiophilic material is pre-composite to the pores of the porous carbon. The lithiophilic material is a metal oxide or nitride, preferably tin oxide, zinc oxide, silver oxide, aluminum oxide, silicon oxide, magnesium oxide, copper oxide, titanium oxide; aluminum nitride, indium nitride, gallium nitride, magnesium nitride, etc. The mass percentage of the lithiophilic material relative to the porous carbon is 0.1%–10%, preferably 0.5%–2%.

[0021] The two-layer framework coating is prepared using a slurry coating method. Carbon materials, a lithiophilic material (outer layer), a binder, and a solvent are mixed. The binder is (PVDF, PAA, etc.), and the organic solvent is (N-methylpyrrolidone, N-vinylpyrrolidone). After uniform mixing and stirring, a slurry is formed and sequentially coated onto the surface of the composite current collector layer. The mixture is dried at 60°C–100°C, the organic solvent is evaporated, and then vacuum dried to obtain a lithiophilic modified gradient porous carbon framework coating.

[0022] (3) Pre-deposit metallic lithium in the internal pores of the porous carbon framework coating; pre-deposit a portion of metallic lithium inside the lithium-affinity modified porous carbon framework using vacuum evaporation, magnetron sputtering, or surface melt casting: the mass fraction of pre-deposited lithium is 1% to 15% of the total mass of the active layer, ensuring that metallic lithium preferentially fills the active sites deep within the framework, rather than merely accumulating on the surface. This step can eliminate irreversible capacity loss caused by the formation of an SEI film during the first cycle of the secondary battery.

[0023] (4) A surface protective layer is formed on the surface of the porous carbon skeleton coating. A carbon layer with a thickness of 1~10μm is constructed on the surface of the skeleton after lithium replenishment. This layer can be made by vacuum evaporation, slurry coating or magnetron sputtering. This protective layer forms a dense interface, avoiding direct contact between metallic lithium and electrolyte, thereby suppressing continuous harmful side reactions and gas generation; by sealing the macroporous structure of the skeleton surface, the effective specific surface area of ​​the negative electrode is significantly reduced, reducing electrolyte consumption. The flexibility of the carbon layer physically inhibits lithium dendrite growth and acts as a stress buffer to alleviate volume fluctuations during charging and discharging, ensuring the cycle stability and safety performance of the battery.

[0024] Through this "inside-out" gradient design, the composite anode can significantly improve the first coulombic efficiency and extend the cycle life of the battery while maintaining high energy density.

[0025] The beneficial effects that the lightweight composite anode and its preparation method disclosed in this application may bring include, but are not limited to:

[0026] 1. Extremely high energy density and lightweight advantages: The composite current collector, which uses a polymer support film with ultra-thin metal layers deposited on both sides, is about 70% to 90% lighter than traditional pure copper foil of the same thickness. At the same time, the three-dimensional porous carbon skeleton design significantly reduces the mass ratio of inactive materials, thereby increasing the overall energy density of the battery by 10% to 25%.

[0027] 2. Guiding Uniform Lithium Deposition "From the Inside Out": By designing a gradient framework with decreasing electronic conductivity from the inside out (from the current collector to the separator), the inner layer near the current collector has the lowest potential. This potential gradient forces lithium ions to pass through the external pores and preferentially nucleate and deposit deep within the current collector, achieving a "from the inside out" growth mode. This completely solves the common "top deposition" problem in three-dimensional frameworks and effectively suppresses the formation of lithium dendrites.

[0028] 3. Improved cycle stability and safety: Micro-patterning enhances the physical bonding between the current collector and the carbon skeleton, preventing coating peeling caused by stress during cycling; the outermost carbon protective layer forms a dense physical barrier, effectively isolating the direct contact between metallic lithium and the electrolyte, minimizing electrolyte side reactions and gas production; the porous carbon layer with high porosity and large specific surface area serves as an active lithium host, providing ample lithium storage space and greatly suppressing volume changes during charging and discharging.

[0029] 4. Excellent first-cycle coulombic efficiency and enhanced electrochemical kinetics: The pre-deposition lithium step precisely compensates for the active lithium consumed in the formation of the SEI film during the first cycle, resulting in a significant improvement in the battery's first-cycle coulombic efficiency; the lithiophilic sites reduce the nucleation overpotential and increase the lithium-ion exchange current density at the interface; the lithiophilic material embedded in the outer layer is transformed in situ into fast ion conductors such as Li3N, establishing a three-dimensional fast lithium-ion channel, which significantly reduces the nucleation overpotential and improves rate performance. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the lightweight composite negative electrode of the present invention. Detailed Implementation

[0031] Various exemplary embodiments, features, and aspects of this application will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0032] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0033] Example 1

[0034] See Figure 1 A composite current collector was constructed using a 4.5 μm PET film with 2 μm copper layers deposited on both sides and laser-etched microgrooves. A 10 μm high-conductivity CNT paste layer was then sequentially coated onto this composite current collector, followed by an outer 20 μm porous carbon paste layer loaded with 1.5 wt% ZnO nanoparticles. This formed a porous carbon framework coating with decreasing electronic conductivity from the inside out, where ZnO was loaded as a lithiophilic material within the outer pores. The pore size of the outer porous carbon layer ranged from 1 nm. After coating and drying at 80°C, 10% of the total mass of lithium was pre-deposited into the internal pores of the porous carbon framework coating via vacuum evaporation as pre-deposited lithium. Finally, a 3 μm carbon layer was applied as a surface protective layer. The resulting sample exhibited an initial coulombic efficiency of 102.5%, a full-charge volume expansion rate of only 10.5%, and a capacity retention of 92.3% after 500 cycles.

[0035] Example 2

[0036] A composite current collector was created by depositing 2 μm nickel layers on both sides of a 5 μm PP film and then micro-imprinting it. A 15 μm graphene slurry as the inner layer and a porous carbon slurry loaded with 2 wt% AlN as the outer layer were sequentially coated onto this composite current collector, forming a porous carbon framework coating with decreasing electronic conductivity from the inside out. AlN was loaded as a lithiophilic material within the pores of the outer layer. The pore size of the outer porous carbon layer ranged from 2 μm. After coating and drying at 80°C, 8% lithium was pre-deposited into the internal pores of the porous carbon framework coating via magnetron sputtering as pre-deposited lithium. Fast ion channels were constructed using Li3N formed through in-situ conversion. Finally, a 2 μm carbon layer was coated as a surface protective layer. The resulting anode exhibited an initial coulombic efficiency of 105.1%, a volume expansion rate of 9.8%, and a capacity retention of 91.5% after 500 cycles.

[0037] Example 3

[0038] A composite current collector was constructed by depositing 1.5 μm copper layers on both sides of a 3 μm PI film. A 20 μm inner layer of carbon fiber slurry and an outer layer of porous carbon slurry loaded with 1 wt% Ag₂O nanoparticles were then sequentially coated onto this composite current collector, forming a porous carbon framework coating with decreasing electronic conductivity from the inside out. Ag₂O, acting as a lithiophilic material, was loaded into the pores of the outer layer. The pore size of the outer porous carbon layer ranged from 5 μm. After coating and drying at 80°C, 12% lithium was pre-deposited into the internal pores of the porous carbon framework coating using a surface melt casting method as pre-deposited lithium. Finally, a 5 μm carbon layer was applied as a surface protective layer. This battery exhibited an initial coulombic efficiency of 98.7%, a volume expansion rate controlled within 13.6%, and a capacity retention of 94.8% after 500 cycles.

[0039] Example 4

[0040] A composite current collector was constructed by depositing 1 μm copper layers on both sides of a 4.5 μm PET film. An inner 8 μm CNT paste and an outer porous carbon paste loaded with 2.5 wt% SnO2 nanoparticles were then sequentially coated onto this composite current collector, forming a porous carbon framework coating with decreasing electronic conductivity from the inside out. SnO2, acting as a lithiophilic material, was loaded into the pores of the outer layer. The pore size of the outer porous carbon layer ranged from 100 μm. After coating, the material was dried at 80°C, and then 5% lithium was pre-deposited into the internal pores of the porous carbon framework coating using vacuum evaporation. Finally, a 1 μm dense carbon film was sputtered as a surface protective layer. This anode exhibited an initial coulombic efficiency of 101.2%, a full-charge volume expansion rate of 15.3%, and a capacity retention of 89.7% during 500-cycle testing.

[0041] Comparative Example 1: Using a traditional 10μm standard pure copper foil as the negative electrode current collector, without setting a three-dimensional framework, pre-replenished lithium layer and protective layer, lithium metal is directly deposited on the surface. The initial coulombic efficiency of this battery is only 84.5%, and the volume expansion rate is as high as 213.5% when fully charged. After 76 cycles, the internal short circuit failure is caused by lithium dendrites piercing the separator.

[0042] Comparative Example 2: The same composite current collector as in Example 1 was used, but the negative electrode skeleton was a 30 μm thick single-layer uniform conductive carbon black coating. It lacked an electronic conductivity gradient design and had no surface protection layer. Since lithium tends to accumulate on the skeleton surface near the separator, the initial coulombic efficiency of this sample was only 88.2%, the volume expansion rate reached 107.6%, and the capacity dropped rapidly after 200 cycles, with a capacity retention of only 23.5%.

[0043] Comparison Table of Composite Anode Performance Data

[0044] Example 1 102.5% 10.5% 92.3% Example 2 105.1% 9.8% 91.5% Example 3 98.7% 13.6% 94.8% Example 4 101.2% 15.3% 89.7% Comparative Example 1 84.5% 213.5% 76-week short circuit failure Comparative Example 2 88.2% 107.6% 23.5% (200-week plunge)

[0045] The test results show that, compared with the traditional pure copper foil current collector (Comparative Example 1) and the single-layer carbon skeleton lacking gradient structure design (Comparative Example 2), the composite anodes prepared in Examples 1-4 of this invention show significant advantages in many key performance indicators.

[0046] First, regarding the initial coulombic efficiency, the initial coulombic efficiency of the embodiments of the present invention reaches 98.7%~105.1%, which is much higher than 84.5% of Comparative Example 1 and 88.2% of Comparative Example 2. This is mainly attributed to the introduction of pre-deposited lithium in the present invention, which accurately compensates for the active lithium consumed by the formation of the SEI film during the first cycle. The initial efficiency exceeding 100% in some embodiments further proves the effectiveness of the lithium replenishment strategy.

[0047] Secondly, regarding volume expansion control, the fully charged volume expansion rate of the embodiments of the present invention is only 9.8%~15.3%, while that of Comparative Example 1 is as high as 213.5%, and that of Comparative Example 2 is also as high as 107.6%. This significant difference verifies the key role of the electronic conductivity gradient framework design in the present invention: the conductivity decreasing from the inside to the outside forces lithium ions to preferentially nucleate and deposit in the deep layer of the current collector, realizing a uniform growth mode "from the inside out", which completely solves the "top deposition" problem common in traditional three-dimensional frameworks. At the same time, the porous carbon layer with high porosity provides sufficient lithium storage space and effectively buffers volume changes.

[0048] Furthermore, regarding cycle stability, the embodiments of the present invention all achieved a capacity retention rate of over 89.7% after 500 cycles, with a maximum of 94.8%, while Comparative Example 1 failed after only 76 cycles due to lithium dendrites piercing the separator and short-circuiting, and Comparative Example 2's capacity rapidly dropped to 23.5% after 200 cycles. This is mainly attributed to the multilayer synergistic design of the present invention: the micropatterned current collector enhances the interlayer bonding force, the surface protective layer physically isolates electrolyte side reactions, and the lithiophilic sites reduce the nucleation overpotential. The combined effect of these three factors achieves long-term cycle stability.

[0049] In summary, this invention, through a multi-layered composite structure design of "conductivity gradient guidance + spatial fixed-point nucleation + surface physical isolation," successfully solves the core problems that have long existed in lithium metal anode and lithium-free anode systems, such as lithium dendrite growth, large volume expansion, and low initial coulombic efficiency, achieving a balance between high energy density, long cycle life, and high safety.

[0050] Key points and mechanism of action of this invention

[0051] 1. Collaborative design of multi-layered functional structures

[0052] The most significant technical feature of this invention is the establishment of a gradient framework in which the electronic conductivity decreases from the inside to the outside (from the current collector to the diaphragm).

[0053] Forced potential induction: The conductivity difference generated by at least two layers of porous carbon with different compositions (such as an inner layer of highly conductive CNT / graphene and an outer layer of highly porous carbon) causes the lowest potential point to be located deep within the current collector.

[0054] Spatial deposition control: This design forces lithium ions to pass through external pores, preferentially nucleate at the lithiophilic sites at the bottom layer and grow upwards, fundamentally solving the problems of "top deposition" and dendrite piercing caused by the limitation of mass transfer kinetics in traditional 3D frameworks.

[0055] 2. The "host" protective function of porous carbon with high porosity / high specific surface area

[0056] By designing an active lithium host layer with high porosity and high specific surface area, the most critical volume expansion problem of anode-free batteries has been solved.

[0057] Volumetric stress relief: The three-dimensional network structure provides ample physical storage space for lithium, making the macroscopic volume change during charging and discharging approach zero.

[0058] Current density homogenization: The large specific surface area significantly reduces the local current density, which, together with the lithium-affinity sites, reduces the nucleation overpotential and induces uniform and dense in-plane growth of lithium ions.

[0059] 3. Surface "physical-chemical" dual-effect protective layer design

[0060] A surface functional protective layer is introduced on the outermost layer of the structure to serve as a "closed-door protection".

[0061] Interfacial chemical stability: By sealing the large pores on the surface of the framework, the effective specific surface area of ​​the negative electrode is significantly reduced, and direct contact between lithium and electrolyte is physically isolated, thereby suppressing continuous side reactions and gas production in the electrolyte.

[0062] Mechanically strong crystal suppression: Utilizing the flexibility of the carbon layer, additional mechanical constraints are provided to the negative electrode surface to suppress the cross-layer growth of lithium dendrites.

[0063] 4. Mechanical reinforcement of micro-patterned current collectors and interfaces

[0064] The periodic micron-scale patterns formed on the surface of the composite current collector by laser etching or microimprinting greatly enhance the adhesion between the polymer support layer and the carbon skeleton layer through the mechanical interlocking effect, preventing interlayer delamination after long-term cycling.

[0065] The protection focus of this invention is on "conductivity gradient guidance" + "spatial fixed-point nucleation" + "surface physical isolation". Through multi-layer composite and process coupling, a leapfrog improvement in the cycle stability, rate performance and safety of negative electrode-free batteries is achieved.

[0066] The above embodiments illustrate in detail the specific implementation of the technical solution of the present invention, the logical and connection relationships of each component, and the complete working process. Those skilled in the art will understand that various changes and modifications can be made to the above embodiments without departing from the principles and spirit of the present invention, and all such changes and modifications should fall within the protection scope of the appended claims.

Claims

1. A lightweight composite anode, characterized in that, The conductive framework includes at least two porous carbon layers along its thickness direction, and the electronic conductivity of each porous carbon layer decreases sequentially from the inside to the outside, forming an electronic conductivity gradient; the pores of at least one porous carbon layer of the conductive framework are loaded with a lithiophilic material.

2. The lightweight composite negative electrode according to claim 1, wherein The conductive framework comprises an inner layer and an outer layer. The carbon material of the inner layer is selected from at least one of carbon nanofibers, carbon nanotubes, graphene, or conductive carbon black. The porous carbon material of the outer layer has a porosity of 50% to 90%, a specific surface area of ​​100 to 2500 m² / g, and a pore size range of 1 nm to 100 μm. The lithiophilic material is loaded in the pores of the outer layer.

3. The lightweight composite anode according to claim 1, wherein The lithiophilic material is selected from at least one of metal oxides or metal nitrides; the mass of the lithiophilic material is 0.1% to 10% of the mass of the outer porous carbon material.

4. The lightweight composite anode according to claim 1, wherein It also includes a composite current collector, on which the conductive skeleton is disposed; the composite current collector includes a polymer support film and a metal conductive layer disposed on at least one side surface of the polymer support film.

5. The lightweight composite anode according to claim 4, wherein The surface of the metal conductive layer that contacts the conductive skeleton is provided with a micron-scale pattern.

6. The lightweight composite anode according to claim 1, wherein It also includes pre-deposited lithium, which fills the internal pores of the conductive framework.

7. The lightweight composite anode according to claim 1, wherein It also includes a surface protective layer disposed on the side of the conductive skeleton away from the composite current collector.

8. The lightweight composite anode according to claim 7, wherein The surface protective layer is a carbon layer, which is selected from at least one of amorphous carbon, graphene, or polymer-derived carbon, and has a thickness of 1 to 10 μm.

9. A method for preparing a lightweight composite anode according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Provide a composite current collector; (2) At least two carbon material slurries with different electronic conductivity are sequentially coated on the composite current collector to form a porous carbon skeleton coating with decreasing electronic conductivity from the inside to the outside, wherein at least one layer of carbon material slurry contains a lithium-loving material. (3) Pre-deposit metallic lithium in the internal pores of the porous carbon skeleton coating; (4) A surface protective layer is formed on the surface of the porous carbon skeleton coating.

10. The method of claim 9, wherein, In step (2), the carbon material slurry is prepared as follows: carbon material is mixed with lithiophilic material, binder and organic solvent, and the mixture is stirred evenly to form a slurry; after coating, the slurry is dried at 60°C to 100°C; in step (3), the mass of the pre-deposited lithium metal is 1% to 15% of the total mass of the porous carbon skeleton coating, and the method of pre-depositing lithium metal is selected from at least one of vacuum evaporation, magnetron sputtering or surface melting casting.

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