Modification method of negative electrode of lithium metal battery

Abstract

The invention discloses a lithium metal battery negative electrode modification method which comprises the following steps: preparing a ceramic diaphragm which comprises a base membrane and an aluminum oxide ceramic thin film, preparing an alloy coating on the surface of the aluminum oxide ceramic thin film by a magnetron sputtering method, and then carrying out degumming treatment on glue between the aluminum oxide ceramic thin film and the base membrane to obtain the lithium metal battery negative electrode. And then enabling the alloy coating to face the lithium foil, aligning the ceramic diaphragm and the lithium foil, synchronously feeding the ceramic diaphragm and the lithium foil into a micro rolling mill for transfer printing, and transferring the alloy coating and the aluminum oxide ceramic film onto the lithium foil to prepare the lithium metal battery negative electrode. According to the method, large-area and high-flux preparation of the lithium metal battery negative electrode can be realized, the unit cost is reduced, the prepared lithium metal battery negative electrode takes the alloy plating layer as a modified functional layer, the growth of lithium dendrites in the charging and discharging process of the lithium metal battery can be effectively inhibited, the uniform deposition of lithium ions is facilitated, the generation of side reaction is reduced, and the service life of the lithium metal battery is prolonged. The cycle performance and coulombic efficiency of the lithium metal battery are improved, and potential safety hazards are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of lithium metal batteries, and in particular relates to a method for modifying a negative electrode of a lithium metal battery. Background Art

[0002] Lithium metal as a negative electrode material has an ultra-high theoretical specific capacity (3860 mAh g -1 ) and the lowest redox potential (-3.04V vs. standard hydrogen electrode), it is considered an ideal choice for achieving high-energy-density energy storage systems. This characteristic of lithium metal enables lithium metal batteries to simultaneously possess the advantages of high specific capacity and high operating voltage. However, despite the significant theoretical advantages of lithium metal anodes, their practical application still faces three key challenges: First, the dynamic evolution of the solid electrolyte interphase (SEI). During cycling, the SEI film that continuously forms on the lithium metal surface is structurally fragile and compositionally heterogeneous, leading to a cumulative increase in interfacial impedance, significantly reducing coulombic efficiency and accelerating capacity decay. Second, there is the difficulty of controlling the lithium deposition morphology. Due to the uneven local current density distribution on the electrode surface and the limitations of mass transfer kinetics, lithium ions tend to preferentially deposit at specific sites. This uneven deposition behavior easily triggers dendritic lithium growth, which not only causes the accumulation of "dead lithium" and leads to irreversible loss of active materials, but more seriously, sharp dendrites can penetrate the separator, causing internal short circuits and posing safety risks such as thermal runaway. Third, there is the structural instability caused by volume effects. During the repeated lithium deposition / stripping process, metallic lithium undergoes drastic volume changes (theoretical volume expansion rate is about 300%). The resulting mechanical stress can cause the electrode structure to pulverize, destroy the electrode integrity and aggravate the interfacial side reactions.

[0003] In order to solve the problems faced, researchers have studied lithium dendrite inhibition methods from different angles and found that three-dimensional structures can inhibit the growth of dendrites. Huan et al. proposed to use an in-situ electrochemical method to prepare a lithium-philic binary lithium aluminum alloy layer with a three-dimensional porous structure to guide the uniform nucleation and growth of metallic lithium, thereby inhibiting the growth of lithium dendrites (see reference Huan Ye et al, Angewandte Chemie-International Edition, 2019, 58 (4): 1094-1099). Various 3D conductive supports have been developed, including silicon-coated porous carbon matrix, gas-phase grown carbon fiber coated glass fiber matrix, nitrogen-doped graphite carbon foam, 3D nickel foam body, 3D Cu-CuO-Ni hybrid structure, silver-plated carbon fiber support and 3D TiC / C core / shell nanowire skeleton. These 3D conductive supports provide good mechanical and chemical stability for the Li negative electrode during the cycle, help minimize the volume change of Li metal, provide a larger surface area for Li deposition, thereby reducing the local current density and the possibility of dendrite formation, and improving the long-term stability and electrochemical performance of lithium metal batteries. Although these 3D conductive scaffolds have achieved certain breakthroughs, they all have certain limitations, such as poor lithium affinity, which leads to the inability to induce uniform nucleation of lithium.

[0004] Patent CN202210465483.7 discloses a composite lithium metal anode material. This material is formed by mixing a skeleton material, nitrate, and molten lithium metal to form a skeleton material, lithium nitride, hydroxide, and the like. This composite lithium anode exhibits a stable interface and a dual conductive network with high ionic and electronic conductivity, enabling long-cycle stability in solid-state batteries. However, this solution involves high-temperature melting of lithium metal, which requires a relatively high processing temperature and correspondingly higher energy consumption. Furthermore, the secondary forming of the lithium metal after melting must also be considered.

[0005] Wan et al. proposed a method of directly rolling the modified material on the lithium negative electrode (reference Wan M, Kang S, Wang L, et al. Mechanical rolling formation of interpenetrated lithium metal / lithium tin alloy foil for ultrahigh-rate battery anode[J]. Nature Communications, 2020, 11(1): 829.), Li / Li 22The preparation of Sn5 foil is achieved by repeated folding and rolling methods and spontaneous reaction between metallic lithium and tin. First, a tin foil and two lithium foils with the same size and designed Li / Sn ratio are stacked to form a Li-Sn-Li "sandwich" and pressed together by mechanical rolling using a roller press in an Ar-filled glove box. The Li-Sn-Li "sandwich" is repeatedly folded and rolled, resulting in a gradual increase in the number of each metal layer and a gradual decrease in thickness. This process produces a large number of fresh Li / Sn interfaces, where metallic lithium and tin react spontaneously to form a three-dimensional Li 22 Sn5 skeleton. Although physical pressing simplifies the traditional chemical deposition process and reduces production costs, the uniform coverage of the modified layer effectively inhibits dendrite growth and improves cycle stability. However, this technology also has limitations: it is necessary to strictly screen modified materials with suitable flexibility and adhesion, otherwise interlayer peeling is likely to occur; the rolling process parameters (pressure, temperature) directly affect the thickness uniformity and structural density of the modified layer. Too thick will hinder ion transmission, and too thin will provide insufficient protection; at the same time, it may induce lithium metal lattice distortion. Material adaptability and process control are still technical difficulties; it needs to be operated in a glove box filled with protective gas, making it difficult to achieve large-scale preparation. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for modifying the negative electrode of a lithium metal battery in response to the shortcomings of the existing technology. The method can realize large-area and high-throughput preparation of the negative electrode of a lithium metal battery, reduce the unit cost of the negative electrode of a lithium metal battery, and the lithium metal battery negative electrode prepared by this method uses an alloy plating layer as a modified functional layer, which can effectively inhibit the growth of lithium dendrites during the charging and discharging process of the lithium metal battery, is conducive to the uniform deposition of lithium ions, reduces the generation of side reactions, improves the cycle performance and coulombic efficiency of the lithium metal battery, and reduces the safety hazards caused by the formation of lithium dendrites.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a method for modifying the negative electrode of a lithium metal battery, comprising the following steps: preparing a ceramic diaphragm, which includes a base membrane and an alumina ceramic film adhered to the surface of the base membrane by glue, and then preparing an alloy coating on the surface of the alumina ceramic film by a magnetron sputtering method, and then removing the glue between the alumina ceramic film and the base membrane, and then making the alloy coating face the lithium foil, aligning the ceramic diaphragm and the lithium foil and simultaneously feeding them into a micro-rolling mill with different roller gaps for transfer printing, separating the base membrane from the alumina ceramic film, and transferring the alloy coating and the alumina ceramic film to the lithium foil, thereby preparing the negative electrode of the lithium metal battery.

[0008] The method is based on a magnetron sputtering method combined with thin film transfer and rolling technology to modify and prepare the lithium metal battery negative electrode, the magnetron sputtering method has high deposition rate and repeatability, and can ensure the uniformity of the alloy coating thickness and composition; the thin film transfer and rolling technology transfers the alloy coating and the aluminum oxide ceramic film from the base film to the lithium foil, breaks through the limitation of the base film material in the traditional process, and expands the application scene. The method can realize large-area and high-throughput preparation of the lithium metal battery negative electrode, and reduce the unit cost of the lithium metal battery negative electrode. The lithium metal battery negative electrode prepared by the method takes the alloy coating as a modified functional layer, can effectively inhibit the growth of lithium dendrites in the charging and discharging process of the lithium metal battery, is beneficial to the uniform deposition of lithium ions, reduces the occurrence of side reactions, improves the cycle performance and coulomb efficiency of the lithium metal battery, and reduces the safety hidden danger caused by lithium dendrites.

[0009] In a preferred technical solution, the alloy coating is a Cu-Si alloy coating, and the thickness is 50-300 nm.

[0010] In another preferred technical solution, the alloy coating is a SiO x N y The thickness of the alloy coating is 10-200 nm.

[0011] The Cu-Si alloy coating exhibits multiple advantages by synergizing the high conductivity of copper and the high theoretical capacity of silicon: the three-dimensional porous structure can uniformly regulate the flow of lithium ions and inhibit dendrite growth, while the lithium storage property of silicon combined with the mechanical stability of copper can effectively alleviate the volume expansion and enhance the integrity of the electrode structure; the high thermal conductivity of the Cu-Si alloy coating can improve the heat diffusion capacity of the aluminum oxide ceramic film, reduce the risk of local overheating, and reduce the electrolyte side reaction combined with the chemically inert surface, thereby significantly improving the battery safety and cycle life, and adapting to the high-energy-density lithium metal battery system.

[0012] The SiO x N y The alloy coating exhibits the following significant advantages in the lithium metal battery: the high mechanical strength can physically block the penetration of lithium dendrites, greatly improving the safety; the excellent thermal stability (temperature resistance > 800℃) can effectively inhibit the risk of high-temperature thermal runaway, far exceeding the traditional polyolefin separator. The SiO x N y The alloy coating optimizes the ion transmission path by nitrogen doping, so that the lithium ion conductivity is improved to the order of 10 -4 S / cm, the interface impedance is reduced by more than 30%, and the rate performance is significantly enhanced. At the same time, the SiO x N y The alloy coating exhibits chemical inertness in a high-voltage (>4.5V) electrolyte environment, can inhibit side reactions, and has high capacity retention rate. The SiOx N y The thickness of the alloy coating is less than 100nm, which is a non-porous, dense, uniform nano-scale ultra-thin SiO x N y Alloy coating can effectively block lithium dendrites and maintain low interface impedance, and the nano-scale ultra-thin SiO x N y The alloy coating hardly increases the thickness of the alumina ceramic film, is compatible with high energy density design, and provides an innovative path for the next generation of high-safety, long-life batteries.

[0013] Preferably, the alloy coating is deposited on the surface of the alumina ceramic film using the magnetron sputtering method on a roll-to-roll magnetron sputtering apparatus. The roll-to-roll magnetron sputtering apparatus enables continuous coating, ensuring large-scale modification and efficient production of lithium metal battery negative electrodes.

[0014] Compared with existing technologies, the present invention has the following advantages: The method of the present invention is based on a magnetron sputtering method combined with thin film transfer and roller pressing technology, combining multiple materials to carry out large-scale modification and preparation of lithium metal battery negative electrodes. This can achieve large-area, high-throughput preparation of lithium metal battery negative electrodes, reducing the unit cost of lithium metal battery negative electrodes. The lithium metal battery negative electrode prepared by the method of the present invention uses an alloy coating as a modified functional layer, which can effectively inhibit the growth of lithium dendrites during the charge and discharge process of the lithium metal battery, promote the uniform deposition of lithium ions, reduce the generation of side reactions, improve the cycle performance and coulombic efficiency of the lithium metal battery, and reduce the safety risks caused by the formation of lithium dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the modification process of the negative electrode of the lithium metal battery in Example 1;

[0016] Figure 2-Figure 7 Performance test results of Li||NCM full cell, 100nm Cu-Si Li||NCM full cell and 150nm Cu-Si Li||NCM full cell;

[0017] Figures 8-10 For Li||NCM soft pack batteries and SiO x N y Performance test results of Li||NCM soft-pack batteries. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the accompanying drawings and embodiments. Raw materials, processes, equipment, etc. not limited in the present invention are all conventional techniques in the art.

[0019] Example 1: A method for modifying a negative electrode of a lithium metal battery, comprising the following steps: preparing different commercial ceramic diaphragms, wherein the commercial ceramic diaphragms comprise a base film and an alumina ceramic film adhered to the surface of the base film by glue; and then preparing a Cu-Si alloy coating on the surface of the alumina ceramic film by magnetron sputtering on a desktop DC magnetron sputtering apparatus, wherein the target material is a Cu-Si alloy target, and the vacuum chamber before sputtering is 9×10 -4 Pa, argon gas flow rate during sputtering is 40sccm, sputtering pressure is 0.2Pa, DC current power is 50W, and two Cu-Si alloy coatings of 100nm and 150nm are deposited on the commercial ceramic diaphragm according to different sputtering times; then the glue between the alumina ceramic film and the base film is removed, and then the Cu-Si alloy coating is faced to the lithium foil, the ceramic diaphragm and the lithium foil are aligned and simultaneously sent to a micro-rolling mill with different roller gaps for transfer printing, so that the base film is separated from the alumina ceramic film, and the Cu-Si alloy coating and the alumina ceramic film are transferred to the lithium foil, thus preparing the lithium metal battery negative electrode. The schematic diagram of the modification process of the above-mentioned lithium metal battery negative electrode is shown in Figure 1 .

[0020] The lithium metal battery negative electrode with a Cu-Si alloy coating thickness of 100 nm and 150 nm prepared in Example 1 and a high-load NCM6 positive electrode were assembled into full batteries (4.6 mAh), respectively. The unmodified ordinary lithium negative electrode and the high-load NCM6 positive electrode were assembled into a full battery (4.6 mAh). Three batteries were obtained, namely, a Li||NCM full battery, a 100 nm Cu-Si Li||NCM full battery, and a 150 nm Cu-Si Li||NCM full battery. The performance of these three batteries was tested at a rate of 0.33 C. The performance test results are shown in FIG. Figure 2-Figure 7 . Figure 2-Figure 7In the data, "Li," "100nm Cu-Si Li," and "150nm Cu-Si Li" represent Li||NCM full cells, 100nm Cu-Si Li||NCM full cells, and 150nm Cu-Si Li||NCM full cells, respectively. "th" represents the cycle, and the number before "th" represents the cycle number. Testing showed that the initial discharge capacities of the Li||NCM full cell, 100nm Cu-Si Li||NCM full cell, and 150nm Cu-Si Li||NCM full cell were 4.49mAh, 4.55mAh, and 4.45mAh, respectively. The 100nm Cu-SiLi||NCM full cell exhibited discharge capacities of 3.38mAh and 2.01mAh at the 20th and 40th cycles, respectively, with corresponding capacity retention rates of 74.2% and 44.2%, respectively. The 150nm Cu-Si Li||NCM full battery exhibited a discharge capacity of 3.87mAh and 2.58mAh at the 20th and 40th cycles, respectively, with corresponding capacity retention rates of 86.9% and 58.0%, respectively. Compared with the 67.2% and 37.8% capacity retention rates of the ordinary Li||NCM full battery at the 20th and 40th cycles, the capacity retention rates of the 100nm Cu-Si Li||NCM full battery and the 150nm Cu-Si Li||NCM full battery have been effectively improved. Figure 6 and Figure 7 It can also be clearly seen from the charge and discharge voltage curves at different cycle numbers that the 100nm Cu-Si Li||NCM full battery and the 150nm Cu-Si Li||NCM full battery can provide more capacity at the same operating voltage.

[0021] Example 2: A method for modifying a negative electrode of a lithium metal battery, comprising the following steps: preparing different commercial ceramic diaphragms, the commercial ceramic diaphragms comprising a base film and an alumina ceramic film adhered to the surface of the base film by glue; and then preparing a SiO2 film having a thickness of 70 nm on the surface of the alumina ceramic film by magnetron sputtering on a roll-to-roll magnetron sputtering apparatus. x N y Alloy coating, wherein the Si target is reactively sputtered in a nitrogen and oxygen atmosphere, and the vacuum chamber before sputtering is 9×10 -4 Pa, argon gas flow rate 300sccm, nitrogen gas flow rate 80sccm, oxygen gas flow rate 50sccm, sputtering pressure 0.4Pa, DC current power 5000W, depositing 70nm thick SiO on commercial ceramic diaphragm x N y Alloy coating; then the glue between the alumina ceramic film and the base film is removed, and then the SiO x N yThe alloy coating layer faces the lithium foil, and the ceramic diaphragm and lithium foil are aligned and simultaneously fed into a micro-rolling mill with different roller gaps for transfer printing, so that the base film is separated from the alumina ceramic film and the SiO x N y The alloy coating and alumina ceramic film are transferred to the lithium foil to prepare the lithium metal battery negative electrode. The modification process of the lithium metal battery negative electrode can be found in Figure 1 .

[0022] The SiO prepared in Example 2 x N y The alloy-plated lithium metal battery negative electrode and the high-load NCM6 positive electrode were assembled into full batteries (0.125Ah), namely SiO x N y Li||NCM soft pack battery, and the unmodified ordinary lithium negative electrode and high load NCM6 positive electrode were assembled into a full battery (4.6mAh), and two batteries were obtained, namely Li||NCM soft pack battery and SiO x N y Li||NCM soft pack battery, the performance of these two batteries was tested at a rate of 0.33C. The performance test results are shown in Figures 8-10 . Figures 8-10 In the figure, “Li” represents Li||NCM soft pack battery, “SiO x N y Li or SiON Li" represents SiO x N y Li||NCM soft pack battery, "th" represents the cycle, and the number before "th" represents the number of cycles. x N y The Li||NCM soft pack battery showed a slight capacity improvement in the first 100 cycles, and after 150 cycles, its capacity retention was significantly better than that of the unmodified Li||NCM soft pack battery. Specifically, the discharge capacity of the Li||NCM soft pack battery decreased significantly after 300 cycles and failed at the 420th cycle; in contrast, the SiO x N y Li||NCM soft pack batteries can operate stably for more than 500 cycles. In terms of capacity retention, SiO x N y The capacity retention rates of the Li||NCM soft-pack battery at the 300th and 400th cycles were 91.0% and 83.2%, respectively, which were significantly higher than the 83.1% and 66.2% of the Li||NCM soft-pack battery at the 300th and 400th cycles.

Claims

1. A method for modifying a negative electrode of a lithium metal battery, characterized in that: The method comprises the following steps: preparing a ceramic diaphragm, which comprises a base film and an alumina ceramic film adhered to the surface of the base film by glue; preparing an alloy coating on the surface of the alumina ceramic film by a magnetron sputtering method; then removing the glue between the alumina ceramic film and the base film; then making the alloy coating face the lithium foil; aligning the ceramic diaphragm and the lithium foil and simultaneously feeding them into a micro-rolling mill with different roller gaps for transfer printing, separating the base film from the alumina ceramic film; and transferring the alloy coating and the alumina ceramic film to the lithium foil, thereby preparing a negative electrode for a lithium metal battery.

2. The method for modifying a negative electrode of a lithium metal battery according to claim 1, wherein: The alloy plating layer is a Cu-Si alloy plating layer, and its thickness is 50-300nm.

3. The method for modifying a negative electrode of a lithium metal battery according to claim 1, wherein: The alloy coating is SiO x N y The alloy coating has a thickness of 10-200 nm.

4. The method for modifying a negative electrode of a lithium metal battery according to claim 1, wherein: An alloy coating is prepared on the surface of an alumina ceramic film by using the magnetron sputtering method on a roll-to-roll magnetron sputtering apparatus.

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