Lithium metal secondary batteries containing electrolyte-swellable polymer thin films.

Abstract

The present invention relates to a lithium metal secondary battery including an electrolyte-swellable polymer thin film that forms a special polymer film that can swell in a liquid electrolyte to utilize the high reactivity of lithium metal, thereby suppressing the formation of lithium dendrites and dead lithium, thereby improving the cycle life of lithium metal symmetric batteries and secondary batteries.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0022353, filed February 20, 2023, and Korean Patent Application No. 10-2024-0024293, filed February 20, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] This specification discloses a lithium metal secondary battery that includes an electrolyte-swellable polymer thin film. [Background technology]

[0003] Lithium metal has a high theoretical specific capacity (3860 mAh g -1 ) and low redox potential (-3.040 V vs. the standard hydrogen electrode), it has been recognized as a negative electrode material for high-energy lithium batteries. However, despite over 100 years of lithium battery development history, lithium metal anodes have not been easily applied to actual battery systems because their unstable surface chemistry induces the formation of dendrites during charge / discharge processes. Metallic Li itself has a high hydration enthalpy (-520 kJ mol -1 ), which is a strong reducing agent and can easily react with the electrolyte to form a solid-electrolyte interface (SEI) layer without the application of an electric potential. However, the SEI layer has the disadvantage of being mechanically weak due to heterogeneous polycrystalline grain boundaries that are prone to cracking due to volume changes in the lithium metal anode. As the lithium grows, the cracks expose it to the electrolyte, and an additional SEI layer spontaneously forms on the surface, depleting the liquid electrolyte (Figure 6). As the lithium metal and electrolyte are depleted by dead lithium and lithium dendrites grow over subsequent cycles, lithium metal batteries have long-term low coulombic efficiency, short battery cycle life, and safety issues due to the risk of lithium metal explosion.

[0004] One approach to addressing these issues is to introduce an "artificial SEI layer" that stabilizes the electrochemical reaction by modifying the lithium surface through a functional outer layer. For example, Li metal surfaces can be coated with a variety of materials, such as etched polymer layers, organic / inorganic frameworks, and nanosheets, which facilitate lithium ion transport while blocking lithium dendrites. Another approach involves treating the outermost lithium surface with liquid and gas chemicals to create a lithium-based composite film that stabilizes the lithium surface. However, this approach results in the preferential growth of the native SEI layer between the Li surface and the artificial SEI layer. This is because the native SEI layer has low interfacial resistance with the Li surface, while the artificial SEI layer, which has poor contact with the Li surface, exhibits high resistance. These issues have limited the methods for introducing artificial SEI layers.

[0005] Meanwhile, a method for directly modifying the native SEI layer using electrolytes decomposed by reacting with electrode materials has also been proposed. By adjusting the electrolyte composition with additives or by adjusting cycling conditions, the native SEI layer can be modified to promote or inhibit electrochemical reactions between the positive and negative electrodes. While this method improves contact between the SEI layer and the lithium surface, the directly modified SEI layer has polycrystalline properties, with randomly distributed particles and different elemental compositions. These structural characteristics weaken its mechanical stability, making it particularly susceptible to cracking. Furthermore, the native SEI layer is vulnerable to swelling caused by various electrolytes, resulting in reduced mechanical strength. Therefore, a solution that can promote the formation of a structurally strengthened native SEI layer is needed. Summary of the Invention [Means for solving the problem]

[0006] Lithium (Li) metal anodes suffer from instability and reactivity with electrolytes, leading to the formation of a non-uniformly distributed, easily collapsible SEI layer, ultimately resulting in the formation of Li dendrites and reduced battery life. Therefore, in embodiments of the present invention, to strengthen the SEI layer and stabilize the interface, an electrolyte-swellable polymer nanolayer can be monolithically deposited using initiator-assisted chemical vapor deposition (iCVD) to passivate the lithium metal. For example, a 100 nm-thick iCVD poly(dimethylaminomethylstyrene) (pDMAMS) layer can be swollen by approximately 264% in carbonate electrolyte to create an electrolyte-filled soft scaffold for lithium ion transport. This provides a uniform, Li2O-free, Li2CO3-rich native SEI layer.

[0007] This paper describes novel functional polymer scaffolds that can structurally accommodate and reinforce the SEI layer, improving mechanical properties and stabilizing electrochemical reactions. Specifically, the functional polymer scaffold must have the following properties: 1) be able to transport lithium ions and electrolytes through the matrix, 2) be compatible and miscible with the native SEI layer to integrate the lithium ions and electrolyte into the matrix, 3) provide sufficient mechanical strength, and 4) not be structurally damaged during electrochemical degradation. Ideally, a functional polymer layer that can swell with the electrolyte present in the battery system while fully accommodating the native SEI layer within its ample free space would meet these criteria. Therefore, in embodiments of the present invention, a protective thin polymer layer containing an electrolyte-swellable polymer is applied (Figure 1A).

[0008] Meanwhile, initiated chemical vapor deposition (iCVD), a method for coating functional polymer layers on lithium metal surfaces, can precisely fabricate uniform polymer layers with thicknesses of less than 10 nm, making it particularly useful for minimizing cell resistance, improving lithium ion diffusion, and investigating interfacial phenomena (Figure 1B). In particular, the iCVD method can modify the lithium surface without solvents or high-temperature processes, allowing for the direct application of various types of high-purity functional polymers while preventing potential damage to the lithium. Furthermore, the iCVD method allows for the control of the composition of copolymers with opposite chemical properties (e.g., hydrophilic-hydrophobic).

[0009] In one embodiment of the present invention, there is provided an electrode for a lithium metal battery, comprising: a negative electrode current collector; a lithium metal layer formed on the negative electrode current collector; and a polymer protective thin film layer formed on the lithium metal layer, wherein the polymer protective thin film layer comprises an electrolyte-swellable polymer, and the electrolyte-swellable polymer has a swelling ratio (%) represented by the following Equation 1 of 15% or more.

number

[0010] where d pristine is the thickness of the polymer protective thin film layer before swelling, d swollen is the thickness of the polymer protective thin film layer after swelling.

[0011] In an exemplary embodiment, the lithium metal layer can have a thickness of 1 to 200 μm.

[0012] In an exemplary embodiment, the electrolyte-swellable polymer may be a polymer including one or more monomers selected from the group consisting of dimethylaminomethyl styrene, ethylene glycol dimethacrylate, acrylic acid, 2-(perfluorohexyl)ethyl acrylate, and divinylbenzene.

[0013] For example, the electrolyte-swellable polymer may include one or more polymers selected from the group consisting of pDMAMS (poly(dimethylaminomethyl styrene)), pDVB (polydivinylbenzene), pC6FA (poly{2-(perfluorohexyl)ethyl acrylate}), pEGDMA (poly(ethylene glycol dimethacrylate)), and pAA (poly(acrylic acid)).

[0014] On the other hand, we selected amine-rich poly(dimethylaminomethylstyrene) (pDMAMS), fluorine-rich poly[2-(perfluorohexyl)ethyl acrylate] (pC6FA), oxygen-rich poly(ethylene glycol dimethacrylate) (pEGDMA), anionic poly(acrylic acid) (pAA), and aromatic polydivinylbenzene (pDVB) to confirm their interaction with the electrolyte (Figure 1C). These polymers have been widely studied as additives and binders for lithium-ion batteries due to their compatibility with the electrolyte, high LUMO energy levels, and excellent electrical insulation. In particular, iCVD technology, which is completely unaffected by oxygen and moisture, allows these polymers to be directly coated onto lithium metal with uniform and controlled thicknesses. Specifically, a surface-growth polymerization process can be performed, which promotes stable and sustained adsorption of vaporized monomers and radicals onto lithium metal (Table S1). For example, the cross-sectional SEM image in Figure 1D shows that a uniform 100 nm pDMAMS coating was formed on the Li metal surface (Figure 1D). -1 ~12nm / min -1 ), deposition time can be easily adjusted to obtain precise nanolayer thicknesses (Figure 7). This one-step surface treatment process, performed at a relatively low processing temperature of less than 40°C, protects the core functional groups of each monomer, which can be confirmed by in situ Fourier transform infrared (FT-IR) analysis (Figure 8).

[0015] [Table 1]

[0016] Table 1 shows the iCVD process conditions and composition of poly(DMAMS-co-C6FA), where a) the TBPO flow rate in the copolymerization was 0.59 sccm, and b) the composition ratio of DMAMS to C6FA present in the polymer film.

[0017] In an exemplary embodiment, the polymer protective thin film layer may be provided to completely or partially cover the contact surface between the negative electrode current collector and the lithium metal layer. Specifically, iCVD technology is particularly useful for producing conformal coatings on rough surfaces, as vaporized monomers and initiators can easily access even the deep recesses of the surface. As a result, the pDMAMS-coated lithium surface exhibited a topology nearly identical to that of the bare lithium surface (Figures 1E and 1F). This smooth contact and sufficient adhesion between the polymer nanolayer and the Li surface are crucial for stabilizing the interface to withstand mechanical stress during cell fabrication and electrochemical cell operation. In particular, when the coating thickness is less than 100 nm, the iCVD-treated surface can be effectively planarized, as evidenced by the reduction of sharp corners (Figure 1F) and the flattening of the upper boundary (Figure 7b) compared to the untreated region at the bottom. This planarization effect guides the electric field uniformly throughout the cell for uniform lithium ion transport and electrochemical reaction.

[0018] In an exemplary embodiment, the electrolyte-swellable polymer can swell in an electrolyte solution to form a solid-electrolyte layer composite.

[0019] Specifically, the polymer protective thin film layer must be highly permeable to the battery electrolyte to ensure high lithium-ion conductivity. Lithium ion permeability can be achieved by diffusion through the open polymer network via a hopping mechanism or through an expanded polymer network swollen by the electrolyte solution. As a reference, all polymer candidate materials in their unswollen state essentially consist of several open channels that allow the passage of oxygen molecules (0.35 nm diameter) and water vapor (0.26 nm diameter), as evidenced by the oxidation of polymer-coated lithium when exposed to ambient air (Figure 9). Nevertheless, the pores of the scaffold must be larger (diameter ≈0.9 nm) to ensure that the free space within the polymer protective thin film layer is completely filled with battery electrolyte, facilitating lithium ion migration. Therefore, we comprehensively evaluated the surface and swelling properties of the predicted polymer layer using an electrolyte solvent (a mixture of EC:DEC = 30:70, v / v). Contact angle measurements revealed that pEGDMA (3.52°) had the best interfacial affinity with the electrolyte solvent, followed by pDMAMS (11.89°), pDVB (13.30°), pAA (27.69°), and pC6FA (43.72°) (Figure 1G). Based on the measured contact angle values, pEGDMA, pDMAMS, and pDVB can be identified as electrolytic hydrophiles that facilitate interfacial transport of electrolytes.

[0020] These swelling characteristics were confirmed by ellipsometry analysis, comparing the thickness change of the iCVD films before and after immersion in the electrolyte solution. Contrary to the trend of the interfacial properties, the amine-rich pDMAMS layer exhibited the greatest swelling capacity with a remarkable swelling ratio of 164%, followed by pAA (16%), pC6FA (12%), pDVB (6%), and pEGDMA (2%) (Figures 1H, 1I, and 10). Such unusually fast (<3 min) swelling behavior of pDMAMS in carbonate solvents is likely due to the abundance of amine functional groups in the side chains, which is attributed to the high DEC (20.2 MPa). 1 / 2 ) and dimethylaminomethyl-containing polymer (20.4 MPa 1 / 2~21.0MPa 1 / 2 This is confirmed by the similar Hansen solubility parameters of pC6FA and pC6FA. Furthermore, the electrolyte-swollen pDMAMS layer maintained its thickness even after 3 minutes, exhibiting resistance to further dissolution and the absence of structural defects. This is all due to the high level of entanglement of the pDMAMS polymer chains. Furthermore, the multi-ionic amines bind to lithium ions, kinetically stabilizing the structure and providing strong adhesion to the lithium surface even at a highly swollen state of 164%. In contrast, the cross-linked molecular structure of pEGDMA did not contribute to the swelling properties, as in the case of pDVB. pC6FA had the poorest interfacial contact with the battery electrolyte solvent and its swelling properties were subpar. Although pC6FA appears to be swelling due to the solvent, the subtle changes in refractive index indicate that the thickness change is actually initiated by partial rearrangement of the ethyl groups in pC6FA. In particular, pDMAMS exhibits the best swelling performance among other iCVD polymers, thereby demonstrating high lithium ion transport properties.

[0021] We also evaluated the lithium ion transport properties of the iCVD polymer layer by lithium peeling / plating measurements in a symmetric lithium-lithium coin cell. Figure 2A shows the high current density (1 mA cm) at each discharge / charge cycle. -2 Actual lithium capacity (1mAh cm) -2 ) over time. The bare lithium cell lasted for 120 hours, with a high cell polarization of 150 mV occurring, primarily due to the formation of lithium dendrites, dead lithium debris, and depleted electrolyte, each of which is identified by a voltage fluctuation.

[0022] In contrast, iCVD polymer-coated lithium batteries exhibit very different electrochemical performance depending on the type of polymer used, due to their different chemical structures (Figure 2A). As predicted from the swelling test results, pDMAMS-Li, which allows electrolyte swelling, exhibited a low polarization of 50 mV for 820 h and a capacity of 410 mAh cm. -2pAA-Li showed the longest cycling performance with a cumulative capacity of 1000 sq ft, followed by pAA-Li (430 h), pDVB-Li (270 h), pEGDMA-Li (130 h), and pC6FA-Li (20 h). All iCVD polymer-Li cells exhibited high cell polarization in the initial cycles (<50 h), which subsequently decreased due to the formation of a low-impedance SEI layer. However, pC6FA only lasted for 14 h with a rapidly increasing cell polarization, indicating that the electrolyte-phobic, fluorine-rich polymer was insulating to lithium ions. For the other polymers, the cycle life was dependent on the mass-transfer-controlled potential (μ mtc , Figure 2B), which indicates that lithium ion transport through the polymer layer is difficult without swelling. pDMAMS-Li has the lowest μmtc and tip potential (μ tip、begin , μ tip、end ), which correlates with the formation of Li dendrites and dead Li, respectively. The low polarization degree of the pDMAMS-Li cell may be due to the uniform and close adhesion of pDMAMS to the Li metal, which greatly reduces the interfacial resistance and induces a uniform lithium ion flux of 1 mA cm. -2 After the 1st, 10th, and 100th cycles at 100 Hz, the pDMAMS-Li cells showed a significant reduction in the formation of Li dendrites and dead Li, as evidenced by comparative analysis of photographs and SEM images of pDMAMS-Li and bare Li cells after the 1st, 10th, and 100th cycles, respectively (Figures 2A and 11). In particular, the bare Li cells showed irregular, mossy dendrites within several cycles, which gradually transformed into isolated, dead Li cells, resulting in reduced battery life. In contrast, the pDMAMS-Li anode showed a tightly packed, well-preserved topology without dendrites, even after 100 cycles (200 h), indicating uniform Li transport through the layers (Figure 11).

[0023] In an exemplary embodiment, the electrolyte may have a lithium ion conductance (tLi+) in the range of 0.2 to 1 as measured by the Bruce-Vincent method.

[0024] Specifically, the Bruce-Vincent method was used to measure the lithium ion transition number (tLi; the contribution of cations to the overall ionic conduction performance) of bare-Li and pDMAMS-Li cells (Figures 2C, 2D, and 12). Compared with an existing organic liquid electrolyte (LiPF6 EC / DEC = 3:7 (v / v), tLi ≈ 0.4), pDMAMS-Li exhibited a tLi+ value of 0.95, which is the highest value reported to date for all known types of electrolyte additives, artificial SEIs, or solid electrolytes. This high tLi+ value indicates that the electrolyte-swollen pDMAMS matrix provides a favorable diffusion path for lithium ions without a dissolved layer, and that the coordination complex between lithium and the polymeric polydisaccharide amine contributes to the lithium ion selectivity. Furthermore, a 100 nm pDMAMS layer exhibited a tLi+ value of 6.54 mS cm, thanks to the electrolyte-swollen pDMAMS matrix. -1 It exhibits excellent ionic conductivity (Figure 13).

[0025] To separate the contributions of interfacial effects and the swelling phenomenon of pDMAMS-Li to the electrochemical reaction stability, we fabricated poly(DMAMS-co-C6FA)-Li with different ratios of electrolyte-swellable DMAMS and electrolyte-phobic C6FA moieties (Figures 1G and 2E). To this end, we prepared three copolymer nanolayer samples with various ratios of DMAMS and C6FA by adjusting the flow rates of each monomer during the iCVD process. The blending ratios were confirmed by FT-IR and X-ray photoelectron spectroscopy (XPS) analysis (Figures 2F, 14, and 15; Table S1). We found that the cycle life of poly(DMAMS-co-C6FA)-Li was proportional to the DMAMS / C6FA ratio (Figure 2G). By incorporating C6FA moieties, we can tune three properties of the polymer-Li layer: the degree of electrolyte swelling, adhesion, and mechanical robustness between the lithium surface and the poly(DMAMS-co-C6FA) layer. The μmtc values ​​of poly(DMAMS-co-C6FA)-Li cells were positively correlated with the C6FA content, but were lower than those of bare lithium cells. Considering that μmtc values ​​(44 mV–54 mV) were fairly similar across all types of pDMAMS-containing polymers evaluated (Figure 2H), the incorporation of C6FA moieties appears to have little effect on lithium ion transport. This is because the electrolyte-swollen DMAMS domains allow lithium ions to bypass the electrolyte-phobic C6FA domains (Figures 1H and 1I). Furthermore, the two peaks in the initial (dendritic formation) and terminal (dead Li formation) sections of the voltage profile of C6FA-containing polymers became stronger with increasing C6FA content (Figure 2H), indicating that C6FA weakens the interfacial contact and adhesion with lithium (Figure 16). The C6FA domains at the poly(DMAMS-co-C6FA)-Li interface act as impurities, favoring the growth of lithium dendrites and dead lithium (Figure 17). Finally, a higher C6FA content weakens the mechanical robustness of poly(DMAMS-co-C6FA) due to the reduced number of DMAMS moieties with rigid aromatic rings. Additionally, the long fluoroalkyl chains of C6FA promote chain mobility and expand the free volume in the copolymer network.Therefore, the C6FA domains are vulnerable to lithium dendritic growth, and the cycle life of poly(DMAMS-co-C6FA) is inversely proportional to the C6FA content (Figures 2G and 17a). Overall, we were able to confirm that adequate adhesion between the 3S layer and the lithium surface is as important as adequate lithium ion transport to promote stable electrochemical reactions.

[0026] In addition, poly(DMAMS-co-C6FA)-Li anode and LiNi 0.6 Mn 0.2 Co 0.2 We investigated the electrochemical performance of full cells assembled with an O2 (NMC-622) anode. Previously, symmetric lithium battery performance was not fully reflected in the evaluation of the entire battery due to the different operating voltage windows, especially for high-voltage anodes operating above 4.2 V. Therefore, before evaluating battery performance, we performed electrochemical floating experiments on the iCVD layers to determine the voltage window where electrochemical decomposition could be completely avoided. Compared to bare lithium, most iCVD polymer layers, with the exception of pC6FA, were electrochemically stable below 4.8 V (Figure 18). In particular, the leakage current of the pDMAMS-Li cell at 4.8 V was 0.5 μA lower than that of bare Li. Furthermore, cyclic voltage measurement data collected within the entire cell voltage window (3.0 V–4.2 V) confirmed that the other iCVD polymers, with the exception of pC6FA, did not undergo electrochemical decomposition in the operating cell (Figure 19). Thanks to such excellent electrochemical stability, the 3S layer can be applied to NMC-622 full cells using a high voltage of 4.2 V (Figure 3A). It can be used for over 650 cycles at 20 °C without capacity loss (0.08% per cycle) at 1 °C (2 mA cm). -2 ) at 159mAh g -1The NMC anode maintained a discharge capacity of 0.29% per cycle, whereas bare lithium experienced a severe fade of 0.29% per cycle (Figures 3B and 3C). Additionally, galvanostatic intermittent titration (GITT) and in situ XPS data confirmed the fact that the pDMAMS coating of lithium metal did not have any detrimental side effects on the anode, but instead slightly improved lithium ion diffusivity in the NMC anode compared to bare lithium (Figure 20).

[0027] To analyze the interfacial behavior of pDMAMS-Li without the influence of the negative electrode, we performed impedance spectroscopy of a Li-Li symmetric cell (Figures 3D, 3E, and 21; Table 2). Under non-cycling conditions, the interfacial resistance of pDMAMS-Li (~190 Ω) was two times lower than that of bare Li (~440 Ω) and other artificial SEI layers (Table S3). Interestingly, the addition of an insulating polymer layer reduced the interfacial resistance to less than half that of bare Li. This indicates that the bare Li / electrolyte interface has inherent electrochemical instability, which can be dramatically improved by reducing the interfacial resistance with the electrolyte-swollen polymer layer. Furthermore, with cell cycling, the interfacial resistance of pDMAMS-Li further decreased to 60 Ω with the formation of a low-impedance SEI layer, but this value was similar to that of bare Li (55 Ω) (Figures 3D and 3E). This difference in interfacial resistance implies that the SEI layer configurations with and without the pDMAMS layer are distinctly different, suggesting that a more resistive SEI layer may be more advantageous for stabilizing cell performance.

[0028] [Table 2]

[0029] Table 2 shows the fitting parameters for bare lithium and pDMAMS-Li (100 nm) cells obtained by fitting the impedance data of FIGS. 3D and 3E to the equivalent circuit model of FIG.

[0030] [Table 3]

[0031] Table 3 shows the measured resistance of a symmetric cell and the Nyquist plot for an embodiment of the present invention compared to previous studies.

[0032] Generally, bare Li forms an additional SEI layer on the surface, so a single semicircle in the electrical impedance spectroscopy (EIS) data splits into two parts for analysis after the first cycle. Notably, pDMAMS-Li maintains the initial two interfaces (i.e., two semicircles for Li and pDMAMS, respectively) after cycling, proving that the native SEI layer formed by the LiPF carbonate electrolyte is interchangeable with the pDMAMS layer. This is possible because the native SEI layer evolves within the electrolyte-swollen structure to form a single thermodynamic phase that is electrochemically indistinguishable. The unique interfacial design according to embodiments of the present invention, which accommodates the native SEI layer, opens up other chemically transformable routes toward practical lithium metal anodes.

[0033] After 10 cycles, the pDMAMS-Li in the NMC-622 whole cell was examined and found to maintain a much more luminous surface compared to the bare Li and pC6FA-Li samples (Figure 3F). Of the poly(DMAMS-co-C6FA)-Li samples, the pure pDMAMS-Li cell achieved a 130 mAh g at a rate of 2 °C. -1 The pDMAMS solvogel showed the highest capacity (70% of the capacity at a rate of 0.1 °C) and demonstrated reasonable rate capability (Figure 3G). Symmetric cell tests showed that the critical current density of the pDMAMS solvogel was approximately 2 mA cm. -2After this, the capacity and cycle life began to decline (Figure 22). Lithium dendrites only begin to appear above the critical current density because supersaturated lithium ions accumulate at the pDMAMS / Li interface, providing space for dendrite growth. Thanks to the flexibility of the expanded pDMAMS layer, the additional growth of Li dendrites is effectively mitigated even in whole cells operated at 2°C (Figure 3H). Overall, the overall performance of the pDMAMS-Li full cell was far superior to that of other types of iCVD thin film layers and bare lithium (Figure 23).

[0034] To clarify the chemical composition of the 3S / SEI layer, we analyzed the pDMAMS-Li anode before and after lithiation (i.e., after the first cycle with the NMC anode in the whole cell) using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and XPS with depth profiling. In TOF-SIMS analysis, pDMAMS was found to be a C released from the backbone. 12 H 16 + and amine-containing C3H8N fragments well preserved in pDMAMS-Li + and C8H7N + The composite is characterized by its characteristic structure (Figures 4A, 4B, and 24). Because pDMAMS is swollen and accommodated by the SEI layer and electrolyte, the intensity of the ionized pDMAMS species decreased after one lithiation cycle compared to that of uncycled pDMAMS-Li. This decreased intensity appears to have been replaced by the native SEI layer (Figures 4B and 4C). The coexistence of the native SEI layer components and the pDMAMS structure confirms the compatibility and compatibility of the two structures, and is consistent with the EIS data analysis (Figure 3E). Furthermore, the composite exhibited improved mechanical stability, similar to that of reinforced concrete (Figure 3H) (where pDMAMS corresponds to the "rebar" and the native SEI layer corresponds to the "concrete body"; Figure 4G). While native SEI layers typically have a multi-granular structure with an inorganic layer adjacent to the electrode and an organic-rich layer toward the outside, the SEI layer formed with the pDMAMS structure is more homogeneous, with the outer layers being CH2Li. + and other inorganic species instead of organic components, i.e., LiF+ and PF2 + was found to be more abundant.

[0035] We further investigated the structural composition of the SEI layer using XPS in depth profiling mode. The results showed that the native SEI layer in bare lithium exhibited a typical composition of an organic outer layer and an inorganic inner layer with a prominently LiO-rich layer (Figures 4D, 4H, and 25). However, the organic and inorganic components of the composite layer composed of native SEI and pDMAMS were largely homogenized, due to the excellent miscibility between pDMAMS and the native SEI layer (Figures 4E, 4F, 4I, 26, 27, and 28).

[0036] Notably, the LiO component was completely eliminated from the SEI layer formed in the pDMAMS structure. This LiO formation was inhibited because pDMAMS and LiO are poorly miscible, and pDMAMS prevents the further decomposition of lithium carbonate into LiO and LiF (Figure 4I). Another mechanism is that some tertiary amine groups on the branch ends of the pDMAMS polymer react electrochemically with DEC to form quaternary ammonium cations and carbonate ions (Figures 27, 28, and 29). The resulting quaternary ammonium cation polymer (poly(vinylbenzyltrimethylammonium carbonate), pVBTMAC) with side-chain functional groups constitutes an important precursor for the synthesis of selective ion-exchange polymers, which can effectively trap and preserve carbonate anions and other valuable SEI components. Furthermore, the partially tetramerized poly(DMAMS-co-VBTMAC) layer exhibits a high tLi+ value (0.95) because it selectively filters lithium ions from the dissolved electrolyte, allowing only the 3S layer to pass through. It should be noted that the quaternization reaction always involves an electrochemical reaction (Figure 30). The slightly higher interfacial resistance of pDMAMS-Li (60 Ω) than bare-Li (55 Ω, Figures 3D and 3E) is due to the fact that Li2CO3 is more insulating than LiF and Li2O. This is also consistent with the Li2CO3-rich composition of the SEI layer formed around the pDMAMS layer. This result also suggests that inorganic and crystalline Li2O may be the main factor in reducing the mechanical and chemical stability of the SEI layer by creating a heterogeneous multicomponent character with rich grain boundaries, which is different from the role of Li2O in the previously known SEI layer. The homogeneous, Li2O-free pDMAMS-SEI composite layer provides flexibility and durability to the Li / SEI interface, allowing it to withstand large volume changes due to Li metal and dendrite formation (Figure 3H). Furthermore, the homogeneous SEI layer without Li2O improves the adhesion between the Li surface and the pDMAMS layer, improving the mechanical properties and electrochemical stability of the Li / SEI / pDMAMS interface.The SEI layer structurally reinforces the 3S layer, similar to the way steel bars reinforce concrete, and physically suppresses the expansion of the SEI layer. This strengthening mechanism explains the principles of low polarization in lithium-lithium symmetric cells, low interfacial resistance in the entire cell, and extended battery life.

[0037] In an exemplary embodiment, the polymer protective thin film layer can have a thickness ranging from 10 nm to 500 nm. While we have confirmed that the 3S layer is permeable to lithium ions, its thickness must be optimized for practical purposes. An excessively thick layer reduces lithium flux, while an excessively thin layer increases the likelihood of physical damage (e.g., tears, punctures, wrinkles, etc.). Therefore, we evaluated cells fabricated with symmetric and full pDMAMS-Li layers ranging from 10 nm to 500 nm, and found that a 100 nm 3S layer provided optimal cycling performance (Figures 5A, 5B, and 5C). With thinner 3S layers (less than 50 nm), the pDMAMS layer was unable to fully accommodate the native SEI layer and was unable to resist the formation of Li dendrites and dead Li, as evidenced by the reduced double-peak potential compared to bare Li (Figure 5C). In contrast, when the 3S layer was much thicker than 100 nm, the interfacial resistance increased and the initial specific capacity decreased (Figures 5B, 5D, 5E, and 5F). Furthermore, the thicker the layer, the more difficult it is to achieve complete swelling. This results in unswelled regions at the bottom of the layer, resulting in reduced utilization of the 3S layer (Figures 5C and 31). This increases the overall cell resistance and reduces cell performance. Furthermore, the transition number for 300 nm pDMAMS-Li (0.63) is significantly lower than that for 100 nm pDMAMS-Li (0.95), indicating that the pDMAMS layer must be completely swollen to provide a high lithium ion flux (Figure 32).

[0038] In conclusion, we report a novel 3S nanolayer directly formed on a Li metal anode by iCVD. The 3S layer fabricated with pDMAMS exhibits satisfactory swelling behavior in the presence of carbonate electrolyte. The formed electrolyte solvogel has a homogeneous swollen structure and can host a native SEI layer without LiO, providing low DC ionic conductivity (Figure 5G, Table 4). Strong interfacial adhesion provides high lithium ion transport values ​​with low interfacial resistance, thus demonstrating mechanical stability and stable electrochemical behavior. In particular, the optimal thickness of 100 nm for pDMAMS-Li showed a 550% increase in cycle life in symmetric cells and a 600% increase in cycle life in full cells using a highly loaded NMC anode compared to bare lithium metal. Table S4 summarizes the ionic conductivity, lithium transfer number, and cycling performance data.

[0039] Based on our research results, we established ideal criteria for a swollen soft scaffold layer (Figure 5H). First, the 3S layer must provide sufficient free volume to allow adequate swelling by the battery electrolyte and facilitate lithium ion transfer. Second, the electrolyte solvogel must be thermodynamically miscible with the native SEI layer. Third, the thickness of the 3S layer must be approximately 100 nm to minimize cell resistance and fully accommodate the native SEI layer. Fourth, the 3S layer must be chemically and electrochemically inert over the large voltage range of a high-voltage negative electrode battery. Fifth, the layer must be flexible and mechanically strong enough to withstand the large volume changes of lithium metal. Finally, the adhesion of the 3S layer to the Li surface must be strong enough to suppress the formation of Li dendrites or dead Li. In particular, the 3S layer and Li must maintain tight adhesion, so complete stripping of Li metal down to copper is undesirable. The 3S layer formation method using iCVD is broadly applicable to other metal battery systems (e.g., sodium, potassium, zinc, magnesium, aluminum, etc.), particularly as it supports roll-to-roll processes that support commercial-scale production.

[0040] In another embodiment of the present invention, there is provided a secondary battery including: a negative electrode which is the above-described lithium metal battery electrode; a positive electrode; and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein the negative electrode includes a solid electrolyte interphase formed on its surface.

[0041] In an exemplary embodiment, the solid-electrolyte interfacial layer may be a LiO-free SEI layer. Here, the LiO-free SEI layer may be substantially free of LiO. For example, when the electrolyte-swellable polymer is pDMAMS, the miscibility between pDMAMS and LiO is low, and pDMAMS prevents further decomposition of lithium carbonate into LiO and LiF, resulting in the formation of a LiO-free SEI layer. The absence of LiO in the SEI layer provides flexibility and durability against volume changes due to dendrite formation. Meanwhile, in the lithium secondary battery of the other embodiment, the positive electrode can be manufactured by dispersing and mixing the positive electrode active material, binder, conductive material, etc. in a dispersion medium (solvent) to form a slurry, applying the slurry to a positive electrode current collector, and then drying and rolling the slurry. In this case, the dispersion medium may be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or a mixture thereof.

[0042] The positive electrode active material is not particularly limited as long as it is a material that allows reversible insertion and desorption of lithium ions, and can include, for example, a lithium metal composite oxide containing one or more metal elements selected from the group consisting of Co, Mn, Ni, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, and Mo.

[0043] More specifically, the positive electrode active material may be a compound represented by any one of the following chemical formulas: Li a A 1-b R b D2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b R b O 2-c D c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b R b O 4-c D c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b R c D α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co b R c O 2-α Z α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Co b R c O 2-α Z2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b R c D α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b R c O 2-α Z α (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b Rc O 2-α Z2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8 and 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; and Li (3-f) J2(PO4)3(0≦f≦2).

[0044] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, V, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; Z is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; T is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0045] In addition to the above-described positive electrode active material, the positive electrode may further include a binder and a conductive material. The binder is a component that aids in bonding the positive electrode active material to the conductive material and the current collector, and may be, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof, but is not limited thereto.

[0046] The binder can be used in an amount of 1 to 50 parts by weight, or 3 to 15 parts by weight, per 100 parts by weight of the total weight of the positive electrode, thereby maintaining excellent adhesive strength between the positive electrode active material and the current collector and excellent capacity characteristics of the secondary battery.

[0047] The conductive material contained in the positive electrode is not particularly limited as long as it has excellent electrical conductivity without inducing side reactions in the internal environment of the lithium secondary battery or chemical changes to the battery. Representative examples include graphite or conductive carbon, and include, but are not limited to, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, and lamp black; carbon-based materials having a graphene or graphite crystal structure; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives.

[0048] The conductive material can be used in an amount of 0.5 to 50 parts by weight, or 1 to 30 parts by weight, per 100 parts by weight of the total weight of the positive electrode, which allows the positive electrode and the lithium secondary battery to maintain excellent electrochemical properties such as conductivity and capacity.

[0049] A filler can be selectively added to the positive electrode as a component for suppressing the expansion of the electrode. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without inducing chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; etc. can be used.

[0050] The positive electrode current collector may be, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In-doped SnO), FTO (F-doped SnO), alloys thereof, or aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be in the form of a foil, film, sheet, punched, porous, foam, or the like.

[0051] Meanwhile, the liquid electrolyte contained in the electrolyte layer may contain a non-aqueous organic solvent and a lithium salt. The type of non-aqueous organic solvent that can be used is not particularly limited, and any organic solvent that has been known to be applicable to electrolytes for lithium-ion batteries may be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents.

[0052] More specifically, examples of the carbonate solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, and methyl (2,2,2-trifluoroethyl) carbonate. Examples of the phosphate solvent include trimethyl phosphate, triethyl phosphate, and 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide.

[0053] The ether solvent may be dibutyl ether, tetraglyme, diglyme, dimethoxyethane, or a tetrahydrofuran derivative such as 2-methyltetrahydrofuran, and the nitrile solvent may be succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile.The sulfone solvent may be dimethyl sulfone, ethyl methyl sulfone, or sulforane.

[0054] In an exemplary embodiment, the electrolyte may be a liquid electrolyte or a solid electrolyte. For example, the liquid electrolyte may include, as a non-aqueous electrolyte, one or a mixture of two or more selected from the group consisting of cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC), and linear carbonate compounds such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. Furthermore, the solid electrolyte may include Li 10 GeP2S 12 (LGPS), Li2SiP2S5Cl(LSPSCl), LPS, LiLaTiO4(LLTO), Li7La3Zr2O 12 (LLZO), Li 2+2x Zn 1-x GeO4(LISICON), Na1+x Zr2Si x P 3-x O 12 (NASICON, 0 < x < 3), and combinations thereof can be included.

[0055] However, from the perspective of better mechanical properties and safety of the composite electrolyte membrane, etc., as the organic solvent, at least a part of it can be cured together with the crosslinked polymer and can exhibit flame retardancy. It is preferable to use carbonate solvents, sulfone solvents, phosphate solvents, etc. Also, as the organic solvent, it is more preferable to use a solvent that exhibits low volatility under the curing conditions for forming the crosslinked polymer, for example, heat curing conditions of 60°C to 80°C.

[0056] On the other hand, as the lithium salt dissolved or dispersed in the organic solvent, any lithium salt known to be applicable to the electrolyte of a lithium secondary battery, for example, LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiCl, LiBr, LiI, LiClO4, LiBF4, LiPF6, LiB 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (C2F5SO2)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylic acids having 4 or less carbon atoms, lithium 4-phenylborate, and one or more selected from the group consisting of lithium imide, etc. can be used.

[0057] Such lithium salts may be contained in the organic solvent of the liquid electrolyte at a concentration of 0.8M to 4.0M, or 1.0M to 2.0M, whereby the composite electrolyte membrane of one embodiment can exhibit excellent thermal stability and ionic conductivity.

[0058] Meanwhile, in the lithium secondary battery of another embodiment, an electrolyte layer may be interposed between the positive electrode and the negative electrode, for example, in the form of a layered membrane or film. In this case, the electrolyte layer may also serve as a separator (i.e., electrically insulating the negative electrode from the positive electrode while allowing lithium ions to pass through). In this case, the electrolyte layer may be included in the secondary battery by being coated and attached in the form of a thin film on one surface of the positive electrode or the negative electrode. Alternatively, the electrolyte layer may be independently interposed between the positive electrode and the negative electrode. The lithium secondary battery of another embodiment may also be a semi-solid battery that uses both a liquid electrolyte and a solid electrolyte.

[0059] In addition, when a porous separator is added to the electrolyte layer in the lithium secondary battery, the separator can be made of an olefin polymer such as polyethylene or polypropylene, glass fiber, or the like, and can be used in the form of a sheet, multilayer, microporous film, woven fabric, or nonwoven fabric, but is not necessarily limited thereto. However, porous polyethylene or porous glass fiber nonwoven fabric is preferred, and porous glass fiber nonwoven fabric is even more preferred. The separator can be a thin insulating film with high ion permeability and mechanical strength, and the pore size of the separator can be generally 0.01 μm to 10 μm, and the thickness can be generally 5 μm to 300 μm, but is not limited thereto.

[0060] Meanwhile, the lithium secondary battery of the other embodiment can be manufactured by a conventional method in the art, for example, by forming a composite electrolyte membrane between a positive electrode and a negative electrode and optionally adding a porous separator.

[0061] Such lithium secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit batteries in battery modules that serve as power sources for medium- to large-sized devices.

[0062] In another embodiment of the present invention, there is provided a method for manufacturing the aforementioned lithium metal battery electrode, the method comprising forming a polymer protective thin film layer on a negative electrode current collector by an initiated chemical vapor deposition (iCVD) process using an initiator, the polymer protective thin film layer comprising an electrolyte-swellable polymer, the electrolyte-swellable polymer being formed from one or more monomers selected from the group consisting of dimethylaminomethyl styrene, ethylene glycol dimethacrylate, acrylic acid, 2-(perfluorohexyl)ethyl acrylate, and divinylbenzene.

[0063] In an exemplary embodiment, the initiator-assisted chemical vapor deposition process may be carried out using an initiator comprising tert-butyl peroxide (TBPO).

[0064] In an exemplary embodiment, the initiator-based chemical vapor deposition process is performed at a rate of 2 nm / min. -1 ~14nm / min -1 For example, the deposition rate may be 2 to 12 nm / min. -1 may be in the range of [Brief explanation of the drawings]

[0065] [Figure 1A] FIG. 1 shows a schematic of an electrolyte-expandable iCVD polymer nanolayer formed on Li metal, forming an expandable-soft scaffold on a Li metal anode for strengthening the SEI layer. [Figure 1B] FIG. 1 shows a schematic of an electrolyte-expandable iCVD polymer nanolayer formed on Li metal, where the iCVD polymer nanolayer was formed directly on Li metal. [Figure 1C]The chemical structures of pDMAMS, pC6FA, pDVB, pAA, and pEGDMA are shown. [Figure 1D] A cross-sectional focused ion beam scanning electron microscope (FIB-SEM) image of Li metal coated with a 100 nm thick layer of pDMAMS is shown (scale bar is 500 nm). [Figure 1E] Shown is an SEM image of bare Li. [Figure 1F] An SEM image of 100 nm pDMAMS-Li is shown. [Figure 1G] Figure 1 shows the contact angle of a sample coated with iCVD polymer on a Si substrate with a mixture of EC:DEC (3:7, v / v). [Figure 1H] Ellipsometry analysis of 100 nm pDMAMS-Si swollen in an electrolyte solvent (where the refractive index (n) of the EC:DEC mixture is 1.39) is shown. [Figure 1I] The difference in refractive index and swelling ratio of iCVD polymer films before and after swelling with an electrolyte solvent are shown. [Figure 2A] Voltage profiles of symmetric bare-Li and 100 nm iCVD polymer-Li symmetric cells are shown. Inset images are of the Li anode after the 10th and 50th cycles of pDMAMS-Li. [Figure 2B] The voltage profiles of the 2nd, 10th, 100th and 200th cycles in FIG. 2A are shown enlarged. [Figure 2C] The steady-state current measurement results of a symmetric bare Li cell under 10 mV polarization for 1 hour in one cycle are shown. [Figure 2D] The steady-state current measurements of a pDMAMS-Li (100 nm) cell under 10 mV polarization for 1 hour in one cycle are shown. [Figure 2E] The molecular structure of poly(DMAMS-co-C6FA) is shown. [Figure 2F] The content ratio (DMAMS:C6FA) of the poly(DMAMS-co-C6FA)-Li sample is shown. [Figure 2G]Figure 1 shows the voltage profile of a symmetric poly(DMAMS-co-C6FA)-Li(100 nm) cell. [Figure 2H] The voltage profile of the 10th cycle is shown enlarged in Figure 2g. [Figure 3A] The electrochemical behavior of 3S-Li||NMC batteries is shown, along with the cycling performance and coulombic efficiency of 100 nm poly(DMAMS-co-C6FA)-Li||NMC batteries with different DMAMS / C6FA ratios (charge and discharge current densities fixed at 2 mA cm-2 after the formation cycle of 0.1 mA cm-2 at 20 °C). [Figure 3B] Figure 1 shows the charge / discharge profiles of bare lithium pDMAMS-Li||NMC batteries from the 1st to 100th cycles. [Figure 3C] Figure 1 shows the charge / discharge profiles of a 100 nm pDMAMS-Li||NMC battery from the 1st to 100th cycles. [Figure 3D] 1 shows the Nyquist plot of a symmetric bare lithium cell from cycle 0 to cycle 100. [Figure 3E] Nyquist plots of a 100 nm pDMAMS-Li cell from 0 to 100 cycles are shown. [Figure 3F] Images of bare lithium, pC6FA-Li, and pDMAMS-Li after the 10th cycle are shown. [Figure 3G] Figure 1 C = 2 mA cm-2) showing the rate performance of a 100 nm poly(DMAMS-co-C6FA)-Li||NMC battery. [Figure 3H] SEM image of pDMAMS layer showing inhibition of Li dendrite propagation (scale bar, 50 μm). [Figure 4A] 1 shows the results of TOF-SIMS analysis of uncirculated 100 nm pDMAMS-Li. [Figure 4B] The results of TOF-SIMS analysis of re-sourced 100 nm pDMAMS-Li are shown. [Figure 4C]1 shows the TOF-SIMS analysis results for a resourced bare Li anode with depth profiling. [Figure 4D] 1 shows the XPS analysis results of uncirculated 100 nm pDMAMS-Li with depth profiling applied. [Figure 4E] The results of XPS analysis of lithiated 100 nm pDMAMS-Li are shown. [Figure 4F] 1 shows the results of XPS analysis of a lithiated bare Li negative electrode. [Figure 4G] Schematic of a native SEI layer accommodated in a swollen pDMAMS layer. [Figure 4H] Figure 1 shows XPS spectra for C1s and O1s data of bare lithiated Li with depth profiling applied. [Figure 4I] 1 shows the XPS spectrum for C1s and O1s data of 100 nm pDMAMS-Li. [Figure 5A] Electrochemical performance of 3S-Li batteries with different layer thicknesses. Voltage profiles of symmetric pDMAMS-Li batteries with pDMAMS layers ranging from 10 nm to 500 nm are shown. [Figure 5B] Figure 1 shows the cycling performance and coulombic efficiency of pDMAMS-Li||NMC batteries with different layer thicknesses (charge and discharge current densities were fixed at 2 mA cm-2 after the formation cycle at 0.1 mA cm-2). [Figure 5C] The voltage profile of FIG. 5A is shown enlarged. [Figure 5D] Figure 1 shows the initial charge / discharge profiles of bare-Li and pDMAMS-Li||NMC batteries with different pDMAMS layer thicknesses. [Figure 5E] Figure 1 shows Nyquist plots of pDMAMS-Li||NMC batteries at different thicknesses during the initial cycles. [Figure 5F] Figure 1 shows Nyquist plots of pDMAMS-Li||NMC batteries at the 50th cycle with different thicknesses. [Figure 5G]We compare and summarize the number of lithium ion transitions and ionic conductivity in recent studies. [Figure 5H] A schematic diagram of the 3S strategy is shown below. [Figure 6] Figure 1 shows a schematic representation of the lithium metal anode challenges: a) shows a schematic illustrating the general interfacial issues of lithium metal anodes; b) shows a schematic illustrating the limitations of the artificial SEI layer approach. [Figure 7] Cross-sectional focused ion beam scanning electron microscopy (FIB-SEM) analysis results: a) FIB-SEM images of Li foils each coated with a 50 nm layer of poly(dimethylaminomethylstyrene) (pDMAMS) (scale bar, 500 nm). b) FIB-SEM images of Li foils each coated with a 200 nm layer of pDMAMS (scale bar, 500 nm). [Figure 8] 1 shows Fourier transform infrared (FT-IR) spectroscopy results of a monomer and an iCVD-polymer according to an embodiment of the present invention. [Figure 9] Images of iCVD polymer-coated lithium metal exposed to ambient air at 25 °C and 20% to 35% relative humidity (RH) for 0, 1, 2, and 24 hours are shown. [Figure 10] Ellipsometry analysis results of pAA-Si, pEGDMA-Si, pDVB-Si, and pC6FA-Si swollen by battery electrolyte solvent are shown (a)–d), respectively. [Figure 11] Topology of bare and iCVD-coated lithium anodes after cycling: a) SEM images of bare lithium after 1, 10, and 100 cycles; b) SEM images of pDMAMS-Li after 1, 10, and 100 cycles. [Figure 12]a) Steady-state current of a symmetric bare lithium cell measured under 10 mV polarization for 1 hour at the 50th cycle. b) Steady-state current of a symmetric pDMAMS-Li(100 nm) cell measured under 10 mV polarization for 1 hour at the 50th cycle. c) Electrochemical impedance spectroscopy (EIS) of a symmetric bare Li cell measured at an open circuit voltage ranging from 100 mHz to 1 MHz with an amplitude of 10 mV. d) EIS of a symmetric pDMAMS-Li(100 nm) cell measured at an open circuit voltage ranging from 100 mHz to 1 MHz with an amplitude of 10 mV. [Figure 13] Ionic conductivity of iCVD polymer nanolayers: a) EIS data for various 100 nm iCVD polymer layers compared. b) EIS data for a stainless steel / iCVD polymer / stainless steel cell assembly. [Figure 14] a) FT-IR spectroscopy results, b) X-ray photoelectron spectroscopy (XPS) radiation spectra, and c) high-resolution (N1s) XPS spectra of pDMAMS, poly(DMAMS-co-C6FA), and pC6FA according to embodiments of the present invention. [Figure 15] Topology of pDMAMS and pC6FA homopolymers and poly(DMAMS-co-pC6FA) copolymers. SEM images of pDMAMS-Li, pD2F1-Li, and pC6FA-Li are compared (a)–c, respectively; scale bar, 50 μm). [Figure 16] A FIB-SEM image of pC6FA-Li is shown (scale bar, 400 nm). [Figure 17] Topological evaluation of pD2F1 after cycling. SEM images of pD2F1-Li after the 1st, 10th, and 100th cycles are shown (a) to c), respectively; scale bar, 50 μm). [Figure 18]a)-f) Electrochemical floating experiments of bare-Li, pC6FA-Li, pEGDMA-Li, pDVB-Li, pAA-Li, and pDMAMS-Li full cells with LiNi0.6Mn0.2Co0.2O2 (NMC-622) anodes (cells were charged to 4.0 V at 0.2 °C, then held at increasingly higher voltages up to 4.9 V for 10 h). [Figure 19] Cyclic voltammogram experiments of bare lithium, pC6FA-Li, pEGDMA-Li, pDVB-Li, pAA-Li, and pDMAMS-Li cells at scan rates of 0.1, 0.2, 0.3, 0.5, and 1.0 mV s are shown (a)–f), respectively. [Figure 20] Galvanostatic intermittent titration (GITT) and in situ XPS analysis of NMC anodes. ab) Typical GITT plots of bare lithium and pDMAMS-Li (100 nm) whole cells with NMC622, respectively. cd) Reactive resistances of bare lithium and pDMAMS-Li (100 nm) cells in a) and b), respectively. e) High-resolution N1s XPS spectra of NMC anodes assembled with bare lithium and pDMAMS-Li anodes. [Figure 21] The equivalent circuit for EIS analysis is shown. [Figure 22] Rate capacity of symmetric cells. a) Voltage profiles of symmetric bare lithium cells at various current densities of 1, 2, 5, and 10 mA cm (1 mAh cm). b) Voltage profiles of symmetric pDMAMS-Li (100 nm) cells at various current densities of 1, 2, 5, and 10 mA cm (1 mAh cm). [Figure 23]Whole-cell performance of iCVD polymers with NMC cathodes. a) Cycling performance and coulombic efficiency of 100 nm pC6FA-Li, pEGDMA-Li, pDVB-Li, pAA-Li, and pDMAMS-Li whole cells with NMC622 cathodes (charge and discharge current densities were fixed at 0.1 mA cm-2 and 2 mA cm-2 after the formation cycle at 25 °C). b)-d) Charge / discharge profiles of 100 nm pAA-Li, pEGDMA-Li, and pDVB-Li full cells with NMC at cycles 1-100. e)-h) Charge / discharge profiles of 100 nm pC6FA-Li and poly(DMAMS-co-C6FA)-Li full cells with NMC cathodes at cycles 1-100. [Figure 24] Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of a) uncirculated 300 nm pDMAMS-Li and b) circulated 300 nm pDMAMS-Li. [Figure 25] 1 shows XPS analysis results of a non-cycled bare lithium anode with depth profiling. [Figure 26] 1 shows XPS analysis results of pDMAMS-Li anodes subjected to depth profiling, including a) an uncycled 300 nm pDMAMS-Li anode subjected to depth profiling, and b) a cycled 300 nm pDMAMS-Li anode subjected to depth profiling. [Figure 27] Figure 1 shows the N1s XPS spectra of depth-profiling-applied pDMAMS-Li. The XPS spectra of N1s data for depth-profiling-applied bare lithiated, lithiated pDMAMS-Li, and non-circulated pDMAMS-Li are shown (a)-c), respectively. [Figure 28]N1s XPS spectra of pDMAMS-Li with depth profiling: a) illumination XPS spectrum of 100 nm pDMAMS-Li; b) high-resolution N1s XPS spectrum of 100 nm pDMAMS-Li; c) high-resolution C1s XPS spectrum of 100 nm pDMAMS-Li; d) N1s XPS spectrum of pDMAMS-Li after 50 cycles; e) C1s XPS spectrum of pDMAMS-Li after 50 cycles. [Figure 29] A schematic diagram of the proposed quaternization reaction of pDMAMS and diethyl carbonate (DEC) to form poly(DMAMS-co-VBTMAC) is shown. [Figure 30] NMR analysis results of pDMAMS cultivated in various solvents. a) NMR analysis results of pDMAMS cultivated in pDMAMS, DEC, and DEC solvents are shown. b) NMR analysis results showing pDMAMS cultivated in pDMAMS, DEC, and DEC solvents at 3.0 ppm to 3.5 ppm and 2.0 ppm to 2.5 ppm. c) FT-IR analysis results for pDMAMS cultivated in pDMAMS, DEC, ethylene carbonate (EC):DEC (3:7, v / v), and solvents are shown (*: tertiary amine (2764 cm-1), **: CN(CH3)3 (930 cm-1 to 920 cm-1). [Figure 31] a) Ellipsometry analysis of 300 nm pDMAMS-Li swollen by electrolyte solvent. b) Nyquist plot of 300 nm pDMAMS-Li||NMC battery during 50 cycles. c) Nyquist plot of 500 nm pDMAMS-Li||NMC battery during 50 cycles. [Figure 32]Transition number of thick pDMAMS layers. a) Steady-state current measurements of a symmetric 300 nm pDMAMS-Li cell under 10 mV polarization for 1 hour for 1 cycle. b) Steady-state current measurements of a symmetric 300 nm pDMAMS-Li cell under 10 mV polarization for 1 hour for 50 cycles. c) EIS measurements of a symmetric 300 nm (10 nm) cell in the range of 100 mHz to 1 MHz at an open circuit voltage amplitude of 10 mV. DETAILED DESCRIPTION OF THE INVENTION

[0066] Analysis method FT-IR characterization The monomers and polymers synthesized by iCVD were characterized by Fourier transform infrared (FT-IR) spectroscopy. -1 ~1627cm -1 The peaks in the blue region of Figure 14a are derived only from the vinyl moieties of each monomer, and the peak intensities of the iCVD polymers are reduced compared to the peak intensities of the monomers. The reduction in the vinyl peaks in the spectra indicates successful polymerization through the iCVD process. In contrast, the peak at 2764 cm in the red region of Figure 14a -1 The tertiary amino-methyl peak and the green region at 1735 cm -1 The copolymerization of DMAMS and C6FA was confirmed by the carbonyl peak of . As the DMAMS content in poly(DMAMS-co-C6FA) increased, the peak intensity in the red region gradually strengthened, while the peak intensity in the green region weakened. The composition of each copolymer could be appropriately controlled by precisely adjusting the flow rate of the monomers injected into the iCVD chamber (Table S1).

[0067] XPS peak deconvolution The SEI components of the pDMAMS layer were investigated by X-ray photoelectron spectroscopy (XPS) depth profiling using an Ar cluster gun (10 keV). For the deposited bare Li and pDMAMS-Li, C1, O1, and N1, high-resolution spectra were obtained at various depths by Ar sputtering. For more accurate XPS deconvolution of the electrolyte-swollen pDMAMS layer, irradiation scans and high-resolution XPS were performed on flat Si substrates. As can be seen in Figures 28a, 28b, and 28c, the peak at 399.25 eV in the N1s spectrum corresponds to C-N, and the peaks at 285.6 eV and 284.7 eV in the C1s spectrum correspond to C-N and C-C / C=C, respectively. After deposition with bare lithium, the C1s spectrum resolves into the organic components in the electrolyte, particularly ethylene carbonate (EC), such as Li2CO3 (290 eV), COC (288.5 eV), CO (286.8 eV), CC (284.8 eV), and lithium carbide (R-Li) (283.5 eV) (left side of Figure 4H). In contrast, the O1s spectrum shows peaks related to COC, such as R-CO2Li (533.5 eV), Li2CO3 (532 eV), and LiOR (531.5 eV), which are associated with the carbonate electrolyte, and the inorganic component Li2O (528 eV) from the LiPF6 salt (right side of Figure 4H). As the etching time increases, the organic SEI components rapidly disappear, while the intensity of the inorganic SEI components increases. In the case of the deposited pDMAMS-Li, Figure 4I shows peaks of pDMAMS and organic electrolyte, except for the EC-reduced R-Li and salt LiO. Furthermore, despite the gradual surface etching, the deposited pDMAMS-Li exhibited a uniform organic SEI component, with no significant decrease in the intensity of existing peaks or the formation of other inorganic peaks. After the 50th cycle, the quaternized pDMAMS in the N1s spectrum was characterized by the presence of a quaternary ammonium salt (CN). + A characteristic peak at 402.5 eV corresponding to (CH3)3) appeared (Fig. 28d).

[0068] NMR characterization To confirm the reaction between pDMAMS and the electrolyte, H nuclear magnetic resonance (NMR) spectra were recorded at T = 298 K using a Bruker Avance Neo Nanobay 400 MHz NMR spectrometer and analyzed using TopSpin 4.1.3 software on CentOS. For NMR sampling, the pDMAMS film deposited on the substrate was separated using a razor blade and collected in a vial. Deuterated chloroform (CDCl) containing 0.03% tetramethylsilane (TMS) was used as the NMR solvent. The ratio of pDMAMS to electrolyte was adjusted to 1:10, and an NMR solution was prepared at a ratio of 5 mg of the mixture per 1 mL of CDCl. Approximately 0.6 mL of the solution was transferred to a 5 mm NMR tube.

[0069] Experimental Method material Dimethylaminomethylstyrene (DMAMS, 90%, Acros, Belgium), 2-(perfluorohexyl)ethyl acrylate (C6FA, 98%, Shanghai Chuanbai Chemical, China), ethylene glycol dimethacrylate (EGDMA, 98%, Sigma-Aldrich, USA), divinylbenzene (DVB, 80%, Sigma-Aldrich, USA), and acrylic acid (AA, 99%, TCI, Japan) were used as monomers, respectively, and butyl peroxide (TBPO, 98%, Sigma-Aldrich, USA) was used as a thermal initiator.

[0070] Preparation of iCVD polymer-Li For iCVD polymer-Li, Li metal foil was punched and then functionalized using a separate iCVD reactor installed in a glove box under Ar atmosphere. Poly(dimethylaminomethylstyrene) (pDMAMS), poly[2-(perfluorohexyl)ethyl acrylate] (pC6FA), poly(ethylene glycol dimethacrylate) (pEGDMA), polydivinylbenzene (pDVB), and poly(acrylic acid) (pAA) were synthesized and conformally coated onto a Li metal anode via iCVD. The monomers, DMAMS, C6FA, EGDMA, DVB, and AA, and the initiator TBPO were vaporized by heating at 50°C, 50°C, 65°C, 45°C, 35°C, and 25°C, respectively, and then loaded into the iCVD reactor. For polymerizations using a single monomer via iCVD, the flow rates of DMAMS, C6FA, EGDMA, DVB, and AA were fixed at 0.82 sccm, 0.55 sccm, 0.33 sccm, 2.50 sccm, and 1.43 sccm, respectively, and TBPO was fixed at 0.59 sccm, 0.30 sccm, 0.44 sccm, 0.89 sccm, and 0.74 sccm, respectively. The substrate temperature was changed from 30°C to 40°C, and the chamber pressure was adjusted from 100 mTorr to 300 mTorr to prevent excessive adsorption of reactants, such as condensation on the lithium metal surface. The deposition rates of pDMAMS, pC6FA, pEGDMA, pDVB, and pAA were each 2.4 nm / min. -1 , 12.5nm / min -1 , 4.0nm / min -1 , 6.1nm / min -1 and 8.0 nm / min -1 For the copolymerization of poly(DMAMS-co-C6FA), the Pm / Psat and surface concentrations of each comonomer were controlled by the flow rates of DMAMS and C6FA at fixed chamber pressure and substrate temperature. In all iCVD processes, the filament temperature was maintained at 140 °C to initiate vapor-phase polymerization.

[0071] Characterization of iCVD polymer films and SEI layers The polymerization of each monomer was chemically confirmed by Fourier transform infrared (FT-IR) spectroscopy (ALPHA FT-IR, Bruker Optics) in absorbance mode. The structural composition, including the ratio of DMAMS to C6FA copolymers, was obtained by multipurpose X-ray photoelectron spectroscopy (Sigma Probe, Thermo VG Scientific) using a microfocus monochromated Al source (1486.7 eV). The electrolyte contact angle of the iCVD-coated polymer was measured using a contact angle analyzer (Phoenix150, SEO). A high-resolution focused ion beam (FIB, Helios G4 FX, Thermo Fisher Scientific) was used to obtain cross-sectional images of the iCVD-coated polymer on lithium metal. The surface morphology of the lithium metal, including the dendrites and SEI layer, was observed using an ultra-high-resolution field emission scanning electron microscope (UHR FE-SEM, SU8230, Hitachi). Optical images of the iCVD polymer film coated on the Si wafer and the lithium metal oxidation process were taken using a digital camera (ILCE-7M3, SONY). Images were taken every hour for the first 6 hours of lithium metal oxidation, and then every 6 hours until the first day after air exposure. To confirm the pDMAMS-SEI layer, depth profiling was performed using in-situ X-ray photoelectron spectroscopy (In-situ XPS, Axis-Supra, Kratos) and time-of-flight secondary ion mass spectrometry (TOF-SIMS, TOF.SIMS5, ION-TOF). In-situ XPS was performed using an Al Kα radiation source operating at 15 kV, with a 1 × 10 -9 The components and bonding state of the SEI layer were investigated at 5×10 torr. XPS depth profiling was performed by etching with an Ar cluster (10 keV). -9 To analyze the chemical composition of the SEI layer, TOF-SIMS was performed in a vacuum chamber at 1000 mbar. The etched area of ​​300 μm × 300 μm and the analyzed area of ​​100 μm × 100 μm were irradiated with Ar cluster (5 keV) and Bi3 +It was sputtered and profiled with a (60 keV) ion beam. To prevent oxidation by air, before all property analyses, it was sealed in an aluminum pouch welded in a glove box filled with Ar with lithium metal.

[0072] Ellipsometric characterization of iCVD polymer films The refractive index (n) and thickness (d) of all iCVD polymer films on the Si substrate were obtained by spectroscopic ellipsometry (M2000U equipped with an automatic angle ESM-300 base, J.A. Woollam). The swelling ratio of the polymer film in the organic electrolyte was measured with a liquid cell (5 mL Heated Liquid Cell TM , J.A. Woollam), which is an optical attachment of the ellipsometer, at a constant temperature of 25 °C, and d pristine and d swollen are the thicknesses before and after injecting the electrolyte into the liquid cell, respectively.

Number

[0073] Specifically, spectroscopic ellipsometry started by aligning at the air / membrane interface with a nominal angle of 75°, and then measured the thickness and refractive index of the deposited film in ambient air at an optical wavelength of 400 nm to 800 nm. All profile data were fitted by the Cauchy model. The dispersion of the refractive index is a function of wavelength and is described as follows.

Number

[0074] Here, λ is the wavelength of the beam, and A, B, and C are optical constants derived by data fitting. To ensure that it does not physically deviate from the fitting, the range of the constants was set to A > 0, 0 < B < 2, and C = 0.

[0075] To observe the swelling behavior, a liquid-surrounding model at the liquid / solid interface was confirmed using a 25 nm SiO2 calibration Si wafer fixed in an electrolyte-charged cell. The optical constants of the EC:DEC (3:7, v / v) electrolyte were consistent with previously reported literature values. After the electrolyte was infiltrated into the thin film, it was assumed that the refractive index gradient would occur perpendicular to the plane of the polymer thin film when the film swelled. The graded layer was analyzed by dividing it into five layers, each with its own refractive index. All model fits were performed using CompleteEASE6 software (JA Woollam) within an MSE (mean square error) of 5 or less.

[0076] Electrochemical measurements For all electrochemical tests, a 2032-type coin cell containing 675 μL of 1.0 M LiPF in EC:DEC (3:7, v / v) electrolyte (Panax Etec) was used. The amount of electrolyte required to swell the entire electrolyte was less than 1.2% (less than 700 nm of pDMAMS), which is insignificant for cell operation and falls within the experimental error margin. The separator was polypropylene-polyethylene-polypropylene (25 μm, Celgard). High-purity Li foil (200 μm, 99.95% (Shinhyung E&T)), LiNi 0.6 Mn 0.2 Co 0.2 O2 (NMC622) sheet (94% active material, Welcos) 1cm 2 The Li-Li symmetric cell was punched at 1 mA cm and used as a bare Li symmetric cell and a bare Li NMC whole cell. Galvanostatic cycling measurements of the Li-Li symmetric cell were performed at 1 mA cm. -2 (1mAh cm -2 ) current density. After the first activation cycle at C / 20 charge / discharge, the Li||NMC whole cell was charged at 1 C (2 mA cm) within the voltage window of 3.0 V to 4.2 V. -2 , 177mAg -1) were cycled. Electrical impedance spectroscopy (EIS) measurements were performed using a ZIVE MP1 system. Impedance data for the lithium electrode were calculated using ZIVE's ZMAN software by fitting a Nyquist plot to an equivalent circuit consisting of a resistor (R) and a constant phase element (CPE). Cycling tests for the symmetric cell and the whole cell were performed in a Wonatech battery system with an environmental chamber. EIS measurements were performed at an amplitude of 10 mV over a frequency range of 100 mHz to 1 MHz. The ionic conductivity of the iCVD-coated polymer film was measured using the same apparatus by assembling a stainless steel / iCVD-coated polymer film / stainless steel cell. The ionic conductivity was calculated from the Nyquist plot using the following equation:

number

[0077] where σ is the ionic conductivity, t is the thickness, R is the resistance, and A is the area of ​​the iCVD-coated polymer film. For the transition number measurement, a 10 mV constant voltage bias was applied to the lithium symmetric cell for 1 hour, and the lithium ion transition number (tLi+) was calculated using the Bruce-Vincent-Evans equation:

number

[0078] Here, I s and I0 are the steady-state current and the initial current, respectively, ΔV is the applied potential, and R s and R0 are the steady-state resistance and the initial resistance before and after polarization, respectively.

[0079] In addition, to confirm the stability of the NMC positive electrode and the interface between the lithium metal negative electrode and the deposited polymer, cyclic voltammetry, constant current intermittent titration (GITT), and floating experiments were performed. The cyclic voltage measurement test was performed for three cycles within the voltage range of 0.1 mV to 1 V. In the GITT experiment, the entire cell was repeatedly discharged and charged at C / 2 for 5 minutes, followed by a 1-hour rest period within the window voltage. The Wechner-Huggins method was used to measure lithium ion diffusion, taking into account the planar shape of the electrode. For the floating test, the entire cell was charged to 4.0 V at 0.05°C, and then applied up to 4.9 V for 10 hours.

[0080] Example 1: 100 nm pDMAMS The positive electrode was made by mixing 94% NMC-based positive electrode active material, 3% conductive material, and 3% binder by weight and applying it to an aluminum current collector (2 mAhcm -2) A 2032-type coin cell was fabricated as a lithium metal secondary battery by inserting a 25-μm-thick separator (Celgard 2325) between a 200-μm-thick lithium metal cathode, which was protected by a 100-nm-thick layer of pDMAMS [poly(dimethylaminomethyl styrene)] polymer using an iCVD process. The electrolyte was a solution of 1M LiPF6 salt and an organic solvent consisting of EC:DEC in a 3:7 volume ratio. A 2032-type coin cell fabricated using the same lithium metal anode instead of the NMC-based cathode was used as a symmetric lithium metal battery. Specifically, a pDMAMS polymer thin film was fabricated using the iCVD process. The substrate was placed in an iCVD chamber and the substrate temperature was maintained at 40°C. Next, dimethylaminomethyl styrene (DMAMS) and the initiator tert-butyl peroxide (TBPO) were vaporized at rates of 0.82 sccm and 0.59 sccm, respectively, and transferred to a chemical vapor deposition chamber. The chamber pressure was maintained at a vacuum of 200 mTorr, and the filament was heated to 140°C to radically polymerize the monomer adsorbed on the substrate to produce pDMAMS homopolymer. The desired polymer thin film thickness was achieved at a deposition rate of 2.4 nm / min.

[0081] Example 2: 10 nm pDMAMS A coin cell was fabricated in the same manner as in Example 1, except that the thickness of the pDMAMS polymer protective layer in the negative electrode of Example 1 was about 10 nm.

[0082] Example 3: pDMAMS at 500 nm A coin cell was fabricated in the same manner as in Example 1, except that the thickness of the pDMAMS polymer protective layer in the negative electrode of Example 1 was 500 nm.

[0083] Example 4: 100 nm pDVB A coin cell was fabricated in the same manner as in Example 1, except that the thickness of the pDVB (polydivinylbenzene) polymer protective layer in the anode was approximately 100 nm. Specifically, the pDVB polymer thin film was fabricated using an iCVD process. A substrate was placed in an iCVD chamber and maintained at 30°C. Divinylbenzene and the initiator tert-butyl peroxide (TBPO) were vaporized at 2.50 sccm and 0.89 sccm, respectively, and transferred to a chemical vapor deposition chamber. The chamber pressure was maintained at a vacuum of 300 mTorr. Simultaneously, the filament was heated to 140°C to radically polymerize the monomer adsorbed on the substrate to produce pDVB homopolymer. The desired polymer thin film thickness was achieved at a deposition rate of 6.1 nm / min.

[0084] Example 5: 100 nm of pC6FA A coin cell was fabricated in the same manner as in Example 1, except that the thickness of the pC6FA [poly{2-(perfluorohexyl)ethyl acrylate}] polymer protective layer in the anode was approximately 100 nm. Specifically, the pC6FA polymer thin film was fabricated using an iCVD process. A substrate was placed in an iCVD chamber and maintained at 30°C. 2-perfluorohexylethyl acrylate [C6FA] and the initiator tert-butyl peroxide (TBPO) were vaporized at rates of 0.55 sccm and 0.30 sccm, respectively, and transferred to a chemical vapor deposition chamber. The chamber pressure was maintained at a vacuum of 100 mTorr, and the filament was heated to 140°C to radically polymerize the monomer adsorbed on the substrate to produce pC6FA homopolymer. The desired polymer thin film thickness was achieved at a deposition rate of 12.5 nm / min.

[0085] Example 6: 100 nm pEGDMA A coin cell was fabricated in the same manner as in Example 1, except that the thickness of the pEGDMA [poly(ethylene glycol dimethacrylate)] polymer in the anode was approximately 100 nm. Specifically, the pEGDMA polymer thin film was fabricated using an iCVD process. A substrate was placed in an iCVD chamber, and the substrate temperature was maintained at 30°C. Ethylene glycol dimethacrylate (EGDMA) and the initiator tert-butyl peroxide (TBPO) were vaporized at rates of 0.33 sccm and 0.44 sccm, respectively, and transferred to a chemical vapor deposition chamber. The chamber pressure was maintained at a vacuum of 150 mTorr, and the filament was heated to 140°C to radically polymerize the monomer adsorbed on the substrate to produce pEGDMA homopolymer. The desired polymer thin film thickness was achieved at a deposition rate of 4.0 nm / min.

[0086] Example 7: 100 nm pAA A coin cell was fabricated in the same manner as in Example 1, except that the thickness of the pAA polymer in the anode was approximately 100 nm. Specifically, a pAA [poly(acrylic acid)] polymer thin film was fabricated using an iCVD process. A substrate was placed in an iCVD chamber and the substrate temperature was maintained at 30°C. Acrylic acid and the initiator tert-butyl peroxide (TBPO) were vaporized at rates of 1.43 sccm and 0.74 sccm, respectively, and transferred to a chemical vapor deposition chamber. The chamber pressure was maintained at a vacuum of 200 mTorr, and the filament was heated to 140°C to radically polymerize the monomer adsorbed on the substrate to produce a pAA homopolymer. The desired polymer thin film thickness was achieved at a deposition rate of 8.0 nm / min.

[0087] Comparative Example 1: 200 μm pure lithium metal A 2032-type coin cell of the same size as in Example 1 was fabricated using pure lithium metal with a thickness of about 200 μm without being covered with a polymer protective film.

[0088] Experimental Example 1: Analysis of refractive index and swelling ratio The refractive index and swelling ratio of the polymer thin film obtained in the ellipsometer liquid cell according to the present invention were measured. A polymer thin film deposited to a thickness of 100 nm on a silicon wafer (Si wafer) was placed in the liquid cell, and the changes in the refractive index and swelling ratio of the polymer thin film before and after injecting electrolyte into the liquid cell were recorded in Table 4.

[0089] [Table 4]

[0090] Experimental example 2: Cycle life The lithium metal symmetric batteries manufactured in Examples 1 to 7 and Comparative Example 1 were charged to 1 mAcm -2 The number of cycles at which an overvoltage of 5 V or more occurred was recorded in Table 5.

[0091] [Table 5]

[0092] It was confirmed that the number of cycles of the lithium symmetric battery of Example 1 protected with the pDMAMS polymer thin film was significantly improved compared to the lithium symmetric battery without the polymer thin film of Comparative Example 1. Furthermore, in Examples 7 and 1, which had swelling ratios of 15% or more, a significant improvement in cycle life was confirmed compared to the comparative examples.

[0093] Experimental example 3: Charge / discharge test The lithium metal secondary batteries prepared in Examples 1 to 7 and Comparative Example 1 were evaluated by the following charge / discharge test. In the first cycle of the charge / discharge test, the secondary battery was charged at a constant current of 0.5 C until the voltage reached 4.2 V, and then discharged at a constant current of 0.5 C until the voltage reached 3.0 V. Thereafter, the lithium metal secondary battery was charged at 1 C, 4.2 V under CC / CV conditions, and then discharged at 1 C, CC 3 V under the charge / discharge test. The number of cycles at which the initial specific capacity reached 80% was recorded in Table 6 below.

[0094] [Table 6]

[0095] The cycle life of the lithium metal secondary battery of Example 1 was significantly improved compared to that of the lithium metal secondary battery of Comparative Example 1, indicating that the pDMAMS polymer thin film suppresses the formation of lithium metal dendrites and dead lithium. Furthermore, in Examples 7 and 1, which had swelling ratios of 15% or more, a significant improvement in cycle life was confirmed compared to the comparative examples.

Claims

1. Negative electrode current collector; a lithium metal layer formed on the negative electrode current collector; and a polymer protective thin film layer formed on the lithium metal layer; The polymer protective thin film layer includes an electrolyte-swellable polymer, and the electrolyte-swellable polymer has a swelling ratio (%) of 15% or more, as expressed by the following Equation 1: [Equation 1] Here, d ｐｒｉｓｔｉｎｅ is the thickness of the polymer protective thin film layer before swelling, d ｓｗｏｌｌｅｎ is the thickness of the polymer protective thin film layer after swelling.

2. 2. The electrode for a lithium metal battery of claim 1, wherein the electrolyte-swellable polymer is a polymer containing one or more monomers selected from the group consisting of dimethylaminomethylstyrene, ethylene glycol dimethacrylate, acrylic acid, 2-(perfluorohexyl)ethyl acrylate, and divinylbenzene.

3. 2. The electrode for a lithium metal battery of claim 1, wherein the electrolyte-swellable polymer comprises one or more polymers selected from the group consisting of polydimethylaminomethylstyrene (pDMAMS), polydivinylbenzene (pDVB), poly(2-(perfluorohexyl)ethyl acrylate) (pC6FA), polyethylene glycol dimethacrylate (pEGDMA), and polyacrylic acid (pAA).

4. The electrode for a lithium metal battery according to claim 1 , wherein the polymer protective thin film layer is provided to cover all or part of the contact surface between the negative electrode current collector and the lithium metal layer.

5. 2. The electrode for a lithium metal battery according to claim 1, wherein the polymer protective thin film layer has a thickness in the range of 10 nm to 500 nm.

6. 2. The electrode for a lithium metal battery of claim 1, wherein the polymer protective thin film layer is formed based on an iCVD process using an initiator, and the initiator includes tert-butyl peroxide (TBPO).

7. 2. The electrode for a lithium metal battery according to claim 1, wherein the electrolyte-swellable polymer swells in an electrolyte solution to form a solid-electrolyte layer composite.

8. 8. The electrode for a lithium metal battery according to claim 7, wherein the electrolyte has a lithium ion conductance (tLi+) in the range of 0.2 to 1 as measured by the Bruce-Vincent method.

9. 2. The electrode for a lithium metal battery according to claim 1, wherein the lithium metal layer has a thickness of 1 μm to 200 μm.

10. A lithium metal battery electrode according to any one of claims 1 to 9, comprising: a negative electrode which is the electrode for a lithium metal battery according to any one of claims 1 to 9; a positive electrode; and an electrolyte layer interposed between the positive electrode and the negative electrode, The negative electrode includes a solid electrolyte interphase formed on the surface thereof.

11. The solid-electrolyte interface layer is Li ２ The secondary battery according to claim 10, which is an O-free SEI layer.

12. A method for producing an electrode for a lithium metal battery according to any one of claims 1 to 9, forming a polymer protective thin film layer on a negative electrode current collector by an initiated chemical vapor deposition (iCVD) process; The method for manufacturing an electrode for a lithium metal battery includes the polymer protective thin film layer including an electrolyte-swellable polymer, the electrolyte-swellable polymer being formed from one or more monomers selected from the group consisting of dimethylaminomethylstyrene, ethylene glycol dimethacrylate, acrylic acid, 2-(perfluorohexyl)ethyl acrylate, and divinylbenzene.

13. 13. The method of claim 12, wherein the chemical vapor deposition process using an initiator is performed using an initiator including tert-butyl peroxide (TBPO).

14. The chemical vapor deposition process using the initiator is carried out at a rate of 2 nm / min. －１ ~14 nm / min －１ The method for producing an electrode for a lithium metal battery according to claim 12, wherein the deposition rate is

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