Novel high-stability lithium-free negative electrode current collector and preparation method thereof

Abstract

The invention discloses a novel high-stability lithium-free negative electrode current collector and a preparation method thereof.The preparation method of the novel high-stability lithium-free negative electrode current collector comprises the steps that a metal zinc layer is deposited on the surface of a nickel material current collector through vacuum thermal evaporation, and then in-situ alloying treatment is conducted under argon protection to form a zinc-nickel alloy layer; and obtaining the zinc nickel-nickel composite current collector with the vertical nano array structure. The zinc-nickel nano-particles uniformly distributed on the surface of the current collector show excellent lithium-loving characteristics, have a strong adsorption effect on electrolyte anions, and synergistically promote formation of an interface layer rich in lithium fluoride. The capacity retention rate of a lithium-free total battery assembled by pairing the current collector and a high-nickel ternary positive electrode reaches 89.6% after 100 cycles, and the energy density breaks through 400 Wh kg <-1 >. The problem of cyclic pulverization of a traditional lithium-loving metal layer is effectively solved through a surface alloying strategy, and a key technical support is provided for practicability of a high-energy-density lithium metal battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium metal battery, and particularly relates to a novel high-stability lithium-free negative electrode current collector and a preparation method thereof. BACKGROUND

[0002] In recent years, with the rapid development of electric vehicles, smart grids and portable electronic devices, the market demand for high-energy-density energy storage systems has shown explosive growth. Among various battery technologies, lithium-free negative electrode lithium metal batteries are considered as one of the core development directions of next-generation battery technologies because they can theoretically achieve an extremely high energy density of more than 400 Wh kg -1 However, the industrialization process of this technology has been long limited by the key bottleneck of insufficient stability of the current collector interface. The traditional lithium-free negative electrode system usually uses copper foil as the current collector, which has an essential defect of strong lithium-phobicity on the surface of the material. This property causes lithium ions to be difficult to nucleate uniformly at the initial stage of deposition, leading to rapid growth of lithium dendrites and local electric field distortion. More seriously, the volume change (up to 300%) of lithium metal during repeated charging and discharging will continuously tear the newly formed solid electrolyte interface (SEI), causing continuous irreversible consumption of active lithium and electrolyte. Data shows that the coulombic efficiency of a half-cell assembled with a conventional copper foil current collector decays to below 90% after 50 cycles at a current density of 1 mA cm-2, which cannot meet the actual application requirements.

[0003] To improve the lithiumophilic property of the current collector, various technical routes such as metal nano-coating, three-dimensional porous structure and surface chemical modification have been developed. Among them, silver, zinc and other lithiumophilic metal coatings can reduce the nucleation overpotential by more than 80% due to their alloying effect with lithium, showing significant advantages at the initial stage. However, this type of modified layer has serious defects in long-term cycling: the volume expansion caused by the metal-lithium alloying reaction will generate a large internal stress, leading to the pulverization and peeling of the coating particles from the substrate.

[0004] Under this background, it is an urgent need in the industry to develop a new type of current collector that has high lithiumophilic property, structural stability and interface regulation capability. SUMMARY

[0005] The present application aims to at least solve one of the problems in the prior art.

[0006] To this end, the present application proposes a novel high-stability lithium-free negative electrode current collector and a preparation method thereof. The preparation method of the novel high-stability lithium-free negative electrode current collector has high stability and lithiumophilic property, which can promote the uniform epitaxial deposition of metal lithium and realize the in-situ construction of a stable SEI layer.

[0007] The novel high-stability lithium-free negative electrode current collector and the preparation method thereof according to the embodiment of the present application, comprising: preparing a zinc-nickel alloy nanolayer on the surface of the current collector to obtain the lithium-free negative electrode current collector.

[0008] According to an embodiment of the present application, the current collector is one of a nickel foil, a nickel mesh and a nickel foam.

[0009] According to an embodiment of the present application, the surface roughness of the nickel substrate is less than or equal to 0.2 μm, and the purity is greater than or equal to 99.9%.

[0010] According to an embodiment of the present application, the zinc-nickel alloy nanolayer is prepared on the surface of the current collector by using a vacuum thermal evaporation technology.

[0011] According to an embodiment of the present application, the zinc-nickel alloy nanolayer is prepared on the surface of the current collector by using an in-situ alloying method under argon protection.

[0012] According to an embodiment of the present application, the surface of the substrate is pretreated before the zinc-nickel alloy layer is prepared to remove the oxide layer and contaminants on the surface.

[0013] According to an embodiment of the present application, the vacuum degree when the metal zinc is thermally evaporated is less than or equal to 5 x 10 -3 Pa.

[0014] According to an embodiment of the present application, the evaporation rate when the metal zinc is thermally evaporated is 0.5-1.2 Å / s.

[0015] According to an embodiment of the present application, the deposition thickness of the metal zinc layer which is thermally evaporated is controlled to be 0.8-1.2 μm.

[0016] According to an embodiment of the present application, the temperature of the in-situ alloying reaction under argon protection is 420-480 ℃.

[0017] According to an embodiment of the present application, the temperature rising rate of the in-situ alloying reaction under argon protection is 2-5 ℃ / min.

[0018] According to an embodiment of the present application, the holding time of the in-situ alloying reaction under argon protection is 30-120 min.

[0019] According to an embodiment of the present application, the thickness of the zinc-nickel alloy layer formed is 0.8-1.5 μm, the surface nanoparticles are in a prismatic structure, and the particle size distribution is in the range of 50 nm-1 μm.

[0020] A novel high-stability lithium-free negative electrode current collector is prepared by using the preparation method of the novel high-stability lithium-free negative electrode current collector according to any one of the above embodiments.

[0021] The beneficial effects of the present application are that the present application adopts a zinc-nickel alloy coating to exhibit higher chemical stability and structural stability in the cycle process. The traditional silver-lithium and zinc-lithium alloy have obvious volume expansion and phase change behavior in the repeated deposition / peeling process, which is easy to cause the coating particles to be pulverized, cracked and finally peeled off, so that the lithiumophilic layer is rapidly deactivated. The zinc-nickel alloy has higher mechanical strength and is chemically inert to metallic lithium, and does not have serious pulverization and peeling phenomenon, thereby significantly improving the service life and interface stability of the lithiumophilic layer. This excellent cycle stability helps to maintain a low nucleation overpotential for a long time, and continuously induces uniform deposition of metallic lithium.

[0022] Compared with the traditional magnetron sputtering or wet chemical plating process, the "thermal evaporation deposition and in-situ alloying" technical route has the advantages of simple equipment, lower cost, mild process conditions and precise thickness control. The zinc layer deposited by thermal evaporation is uniform in vacuum environment, and the deposition rate and film thickness can be precisely adjusted by evaporation current and time, so that the final zinc-nickel alloy layer has highly controllable film thickness and morphology. The subsequent in-situ alloying reaction in an inert atmosphere can make zinc and the substrate nickel fully diffuse and form a uniform zinc-nickel alloy nanolayer, avoiding the thickness non-uniformity problem caused by the mismatch of sputtering rates of different targets in multi-target magnetron sputtering. The overall process route is simple, scalable and highly reproducible, and is extremely suitable for large-area manufacturing in the battery industry.

[0023] Another key advantage of this technical route is the ability to flexibly adjust the alloying ratio of zinc and nickel. By precisely controlling the evaporation amount (thickness) of the zinc layer and the subsequent alloying temperature and heat treatment time, zinc-nickel alloy layers with different composition gradients can be obtained, so that the nucleation overpotential, adsorption energy and interface mechanical properties of the lithiumophilic layer can be adjusted as needed. However, in traditional magnetron sputtering alloy preparation, due to the influence of factors such as target condition, plasma density, target interference and other factors, it is difficult to achieve stable, precise and repeatable zinc / nickel ratio, resulting in frequent composition drift of the material. The composition controllability of the present application makes the obtained alloy layer not only more uniform in chemical properties, but also can optimize its lithiumophilic ability, interface stability and mechanical matching according to the actual battery system requirements, thereby further improving the overall cycle life and safety of the aluminum lithium negative electrode.

[0024] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application.

[0025] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the following preferred embodiments are specifically described below, and the accompanying drawings are referred to. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings of which: Figure 1 Coulomb efficiency plot for half-cell cycling of Example 1 and Comparative Example 1; Figure 2 Surface Young's modulus distribution plot after 50 cycles of half-cell cycling of Example 1 and Comparative Example 1; Figure 3 Coulomb efficiency plot for half-cell cycling of Example 2 and Comparative Example 2; Figure 4 Cycle performance comparison of lithium-free full cells of Example 3 and Comparative Example 3; DETAILED DESCRIPTION Embodiments of the present application are described in detail below with reference to several examples illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments described below are examples of implementations only, and merely intended to explain the present application, and are not to be construed as limiting the present application.

[0027] In the description of the present application, it is to be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are merely intended to facilitate the description of the present application and simplify the description, and are not intended to indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be construed as limiting the present application. In addition, features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified and limited, the term "a plurality of" means two or more. In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixedly connected, or detachably connected, or integrally connected; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] The novel high-stability lithium-free negative electrode current collector and the preparation method thereof according to the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0029] Example 1 Preparation of the new high-stability lithium-free negative electrode current collector: Under the condition of 1 x 10 -3 Pa, a layer of metal zinc with a thickness of 1 μm was deposited on the surface of the nickel foil by thermal evaporation at an evaporation rate of 1 Å / s. Then, in-situ zinc-nickel alloying reaction was carried out under the protection of argon atmosphere, with an alloying temperature of 450 degrees and a reaction time of 1 h. The final zinc-nickel alloy layer had a thickness of about 1 μm, and the surface nanoparticles had a prismatic structure with a particle size distribution in the range of 50 nm-1 μm.

[0030] Assembly of the half-cell: The half-cell used metal lithium as the counter electrode and reference electrode, and the new high-stability lithium-free negative electrode current collector as the working electrode. The electrolyte was 1 M LiTFSI dissolved in DOL / DME (volume ratio of 1:1), with the addition of 2% LiNO3 additive by mass.

[0031] Comparative Example 1 Assembly of the half-cell: The half-cell used metal lithium as the counter electrode and reference electrode, and pure nickel foil as the working electrode. The electrolyte was 1 M LiTFSI dissolved in DOL / DME (volume ratio of 1:1), with the addition of 2% LiNO3 additive by mass.

[0032] The detection method for the cycle performance of the half-cell was constant current charge-discharge cycling, with a selected current density of 1 mA cm -2 , a metal lithium deposition capacity of 1 mAh cm -2 , and a charging cutoff voltage of 1 V. The coulombic efficiency was the ratio of the charging capacity to the discharging capacity in each cycle of charge-discharge cycling.

[0033] Example 2 Preparation of the new high-stability lithium-free negative electrode current collector: Under the condition of 1 x 10 -3 Pa, a layer of metal zinc with a thickness of 1 μm was deposited on the surface of the nickel foil by thermal evaporation at an evaporation rate of 1 Å / s. Then, in-situ zinc-nickel alloying reaction was carried out under the protection of argon atmosphere, with an alloying temperature of 450 degrees and a reaction time of 1 h. The final zinc-nickel alloy layer had a thickness of about 1 μm, and the surface nanoparticles had a prismatic structure with a particle size distribution in the range of 50 nm-1 μm.

[0034] Assembly of the half-cell: The half-cell used metal lithium as the counter electrode and reference electrode, and the new high-stability lithium-free negative electrode current collector as the working electrode. The electrolyte was 1 M LiTFSI dissolved in DOL / DME (volume ratio of 1:1), with the addition of 2% LiNO3 additive by mass.

[0035] Comparative Example 2 Assembly of the half-cell: The half-cell uses lithium metal as the counter electrode and reference electrode, pure nickel foil as the working electrode, and 1 M LiTFSI dissolved in DOL / DME (volume ratio of 1:1) as the electrolyte, with 2% LiNO3 additive added by mass.

[0036] The half-cell cycle performance was tested using the constant current charge-discharge cycle method, with a selected current density of 3 mA cm⁻¹. -2 The capacity of lithium metal deposition is 6 mAh cm⁻¹. -2 The charging cutoff voltage is 1 V. Coulomb efficiency is the ratio of charging capacity to discharging capacity per charge-discharge cycle.

[0037] Example 3 Preparation of a novel high-stability lithium-free anode current collector: Thermal evaporation technology was employed at a vacuum degree of 1×10⁻⁶. -3 Under Pa conditions, a layer of metallic zinc with a thickness of 1 μm was thermally evaporated and deposited on the surface of nickel foil at an evaporation rate of 1 Å / s. Subsequently, an in-situ zinc-nickel alloying reaction was carried out under an argon atmosphere at an alloying temperature of 450 °C for 1 h. The final zinc-nickel alloy layer was approximately 1 μm thick, with surface nanoparticles exhibiting a prismatic structure and a particle size distribution ranging from 50 nm to 1 μm.

[0038] Full cell assembly: The full cell uses commercially available high-nickel ternary material as the positive electrode (theoretical areal capacity 3.5 mAh cm⁻¹). -2 The novel high-stability lithium-free negative electrode current collector is used as the negative electrode, and the electrolyte is 1M LiPF6 + 0.02 M LiDFOB dissolved in FEC:FEMC:HFE (mass ratio of 1:3:1).

[0039] Comparative Example 3 Full cell assembly: The full cell uses commercially available high-nickel ternary material as the positive electrode (theoretical areal capacity 3.5 mAh cm⁻¹). -2 The negative electrode is a pure nickel foil current collector, and the electrolyte is 1M LiPF6 + 0.02M LiDFOB dissolved in FEC:FEMC:HFE (mass ratio 1:3:1).

[0040] The full battery cycle performance was tested using the constant current charge-discharge cycle method. The first cycle consisted of a charge-then-discharge program with a voltage range of 2.8 V to 4.3 V and a current density of 0.7 mA cm⁻¹. -2 .

[0041] Figure 1This diagram shows the coulombic efficiency of half-cell cycling for Example 1 and Comparative Example 1 of the present invention. The zinc-nickel alloy-modified current collector remained stable during 800 half-cell cycles, achieving an average coulombic efficiency of 99.21%. In contrast, the coulombic efficiency of the pure nickel foil decreased rapidly after approximately 200 cycles, attributed to electrolyte consumption and short circuits caused by lithium dendrite growth. This result demonstrates that the zinc-nickel alloy exhibits good lithiophilicity, promoting stable and uniform lithium deposition and improving the cycling performance of the half-cell.

[0042] Figure 2 This is a distribution diagram of the Young's modulus on the electrode surface after 50 cycles of the half-cells of Example 1 and Comparative Example 1 of the present invention. The diagram shows that the lithium metal deposited on the zinc-nickel alloy surface has a higher interfacial Young's modulus, which is attributed to the formation of a LiF-rich SEI layer induced by the zinc-nickel alloy, effectively suppressing lithium dendrite growth and improving the cycle performance of the battery.

[0043] Figure 3 This is a coulombic efficiency graph for half-cell cycling in Example 2 and Comparative Example 2 of this invention. Even under higher current density and deposition capacity conditions, the zinc-nickel alloy can still induce stable lithium deposition, remaining stable over 250 cycles with an average coulombic efficiency of 99.40%. This further demonstrates the good lithium affinity and high stability of the zinc-nickel alloy interface.

[0044] Figure 4 The figures show the long-cycle performance of the lithium-free full cells in Example 3 and Comparative Example 3 of this invention. Due to the good lithium affinity of the zinc-nickel alloy and its contribution to improving the mechanical properties of the SEI layer, the full cell assembled with the novel high-stability lithium-free anode current collector retains 89.6% of its capacity after 100 cycles, with an energy density greater than 400 Wh / kg. -1 In contrast, full cells assembled with nickel foil have a capacity close to zero after 40 cycles.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a novel high-stability lithium-free negative electrode current collector, characterized in that, include: A zinc-nickel alloy nanolayer was prepared on the surface of the current collector to obtain a lithium-free negative electrode current collector.

2. The preparation method of the novel high-stability lithium-free negative electrode current collector according to claim 1, characterized in that, The current collector is one of nickel foil, nickel mesh, or nickel foam.

3. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 1, characterized in that, The surface roughness of the nickel substrate is ≤0.2μm, and the purity is ≥99.9%.

4. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 1, characterized in that, A zinc nanolayer was prepared on the surface of a current collector using vacuum thermal evaporation technology, and a zinc-nickel alloy nanolayer was prepared on the surface of the current collector using an in-situ alloying method under argon protection.

5. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 4, characterized in that, The vacuum degree during thermal evaporation of metallic zinc is less than or equal to 5 × 10⁻⁶. -3 The evaporation rate of zinc during thermal evaporation is 0.5-1.2 Å / s.

6. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 4, characterized in that, The deposition thickness of the thermally evaporated zinc layer was controlled between 0.8 and 1.2 μm.

7. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 5, characterized in that, The in-situ alloying reaction under argon protection takes place at a temperature of 420-480℃.

8. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 5, characterized in that, The heating rate of the in-situ alloying reaction under argon protection is 2-5℃ / min, and the holding time of the in-situ alloying reaction is 30-120 minutes.

9. The method for preparing the novel high-stability lithium-free negative electrode current collector according to claim 1, characterized in that, The formed zinc-nickel alloy layer has a thickness of 0.8-1.5 μm, and the surface nanoparticles have a prismatic structure with a particle size distribution in the range of 50 nm-1 μm.

10. A novel high-stability lithium-free negative electrode current collector, characterized in that, It is prepared by any one of the methods for preparing novel lithium-free negative electrode current collectors according to claims 1-9.

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