Anode surface-stabilizing electrolyte additive for lithium metal battery using polarizable non-polar molecules

Abstract

Disclosed is an anode surface-stabilizing electrolyte additive for a lithium metal battery, using polarizable non-polar molecules. The electrolyte additive according to an embodiment comprises non-polar molecules, whereby lifetime characteristics of a lithium battery may be controlled based on the polarizability of the non-polar molecules, or comprises at least one of 3-mercapto-1-propanesulfonic acid sodium salt (MPS) and 1,3-propane disulfonate acid disodium salt (PDS).

Description

Electrolyte additive for stabilizing the negative electrode surface for lithium metal batteries using polarizable nonpolar molecules

[0001] The following description relates to an electrolyte additive for stabilizing the negative electrode surface for lithium metal batteries using a polarizable nonpolar molecule and an electrolyte additive for stabilizing the negative electrode surface for lithium metal batteries with a polyanion functional group control.

[0002] The most widely commercialized type of secondary battery today is the lithium-ion battery, which primarily uses graphite as its anode material. With secondary batteries being utilized in a variety of fields, led by the electric vehicle market, demand for high-energy-density secondary batteries is growing exponentially. However, graphite's low theoretical capacity limits its potential for improving energy density, making it unable to meet this growing demand. Consequently, the development of new anode materials that can replace graphite while simultaneously addressing diverse conditions is ongoing.

[0003] Among these, lithium metal (Li metal) anode materials possess the most superior performance characteristics, with high theoretical capacity and low electrode potential. Furthermore, the development of next-generation secondary batteries, such as lithium-sulfur batteries and lithium-air batteries, is based on the commercialization of lithium metal anode materials, making it a highly anticipated anode material. However, lithium metal has the problem of high reactivity of lithium itself, which causes severe side reactions with the electrolyte, and in particular, the rapid formation of dendrites on the surface of the metal material can lead to safety accidents such as fires and explosions.

[0004] A negative electrode surface stabilizing electrolyte additive for a lithium metal battery using a polarizable nonpolar molecule is provided.

[0005] A polyanion functional group-controlled electrolyte additive for stabilizing the surface of a negative electrode for a lithium metal battery is provided.

[0006] An electrolyte additive is provided, which comprises a non-polar molecule and is characterized in that the life characteristics of a lithium battery are controlled through the polarization value of the non-polar molecule.

[0007] According to one aspect, at least one of surface planarization and formation of a SEI (Solid-Electrolyte Interface) layer on a negative electrode of a lithium battery using an electrolyte including the electrolyte additive is controlled according to the polarization value based on the molecular size of the nonpolar molecule, thereby controlling the life characteristics of the lithium battery.

[0008] According to another aspect, the electrolyte additive including the non-polar molecule may be characterized by inducing horizontal growth of crystals of lithium metal included in the negative electrode.

[0009] According to another aspect, the nonpolar molecule may be characterized as containing anthracene.

[0010] An electrolyte is provided, which comprises an electrolyte additive including a nonpolar molecule, and is characterized in that the life characteristics of a lithium battery are controlled through the polarization value of the nonpolar molecule.

[0011] A lithium battery is provided, comprising: a positive electrode; a negative electrode; an electrolyte for transferring lithium ions between the positive electrode and the negative electrode; and an electrolyte additive included in the electrolyte and including a nonpolar molecule, wherein the lifespan characteristics are controlled through the polarization value of the nonpolar molecule.

[0012] An electrolyte additive comprising at least one of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) and PDS (1,3-Propane disulfonate acid disodium salt) is provided.

[0013] According to one aspect, as the charge / discharge cycle of a lithium battery using an electrolyte including the electrolyte additive progresses, the proportion of horizontal crystals of the negative electrode included in the lithium battery increases.

[0014] According to another aspect, it can be characterized by suppressing dendrite formation on the cathode and changing the chemical composition of the SEI (Solid-Electrolyte Interface) layer.

[0015] According to another aspect, it may be characterized by increasing the ratio of at least one of LiF and Li2S in the chemical composition of the SEI layer.

[0016] An electrolyte is provided comprising an electrolyte additive comprising at least one of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) and PDS (1,3-Propane disulfonate acid disodium salt).

[0017] According to one aspect, as the charge and discharge cycle of a lithium battery using the electrolyte progresses, the proportion of horizontal crystals of the negative electrode included in the lithium battery increases.

[0018] According to another aspect, it may be characterized by suppressing dendrite formation on the cathode, changing the chemical composition of the SEI (Solid-Electrolyte Interface) layer, and increasing the ratio of at least one of LiF and Li2S in the chemical composition of the SEI layer by the electrolyte additive.

[0019] A lithium battery is provided, characterized by comprising: a positive electrode; a negative electrode; an electrolyte for transferring lithium ions between the positive electrode and the negative electrode; and an electrolyte additive included in the electrolyte, the electrolyte additive including at least one of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) and PDS (1,3-Propane disulfonate acid disodium salt).

[0020] A negative electrode surface stabilizing electrolyte additive for a lithium metal battery using a polarizable nonpolar molecule can be provided.

[0021] A multi-anion functional group-controlled electrolyte additive can be provided for stabilizing the surface of a negative electrode for a lithium metal battery.

[0022] FIG. 1 is a drawing showing an example of a nonpolar molecule applied to stabilize a Li metal negative electrode in one embodiment of the present invention.

[0023] FIGS. 2 to 4 are drawings showing the results of Li-Li symmetric cell tests performed under various current density conditions in one embodiment of the present invention.

[0024] Figures 5 to 9 are drawings for explaining the influence of non-polar molecules in one embodiment of the present invention.

[0025] FIGS. 10 to 13 are drawings for explaining the electrochemical stabilization effect according to the difference in polarity of a non-polar additive in one embodiment of the present invention.

[0026] FIGS. 14 to 16 are drawings for explaining changes in the crystal structure of a Li metal negative electrode after charging and discharging in one embodiment of the present invention.

[0027] FIG. 17 is a diagram showing an example of calculation results for energy levels of a nonpolar additive and a solvent in one embodiment of the present invention.

[0028] FIGS. 18 to 21 are drawings showing examples of ex-situ XPS (X-ray Photoelectron Spectroscopy) measurement results for a Li metal negative electrode after 30 charge and discharge cycles in one embodiment of the present invention.

[0029] FIG. 22 is a drawing showing an example of components of an SEI layer in one embodiment of the present invention.

[0030] FIG. 23 is a drawing showing an example of the properties of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) as a sulfur-based copper plating accelerator in another embodiment of the present invention.

[0031] FIG. 24 is a drawing showing the flatness of a lithium metal surface according to an electrolyte additive in another embodiment of the present invention.

[0032] FIGS. 25 and 26 are drawings showing examples of Li-Li symmetric cell test results according to electrolyte additives in another embodiment of the present invention.

[0033] Figure 27 is a diagram showing resistance values ​​according to electrolyte additives in another embodiment of the present invention.

[0034] FIGS. 28 to 30 are drawings for explaining flattening of a lithium metal surface according to an electrolyte additive in another embodiment of the present invention.

[0035] Figures 31 to 33 are drawings showing XRD (X-ray diffraction) analysis results according to electrolyte additives in another embodiment of the present invention.

[0036] FIG. 34 is a diagram showing an example of calculation results for energy levels according to electrolyte additives in another embodiment of the present invention.

[0037] FIGS. 35 and 36 are drawings showing examples of XPS (X-ray Photoelectron Spectroscopy) measurement results for a lithium metal negative electrode in another embodiment of the present invention.

[0038] FIG. 37 is a drawing showing an example of a component of an SEI layer in another embodiment of the present invention.

[0039] The present invention can be modified in various ways and has various embodiments. Hereinafter, specific embodiments will be described in detail based on the attached drawings.

[0040] In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description is omitted.

[0041] With the goal of implementing high-energy, next-generation batteries, intensive research and strategies are actively being developed to stabilize the lithium metal anode in lithium metal batteries (LMBs). Uncontrolled growth of lithium dendrites in Li metal anodes poses a serious safety risk, leading to short circuits and battery fires.

[0042] The development of various next-generation batteries that surpass the existing lithium-ion battery (LIB) is actively underway. Among them, the lithium metal battery (LMB) has a very high theoretical capacity (3860 mAh g -1 ), low density (0.59 g cm -3) and the lowest electrochemical redox potential (-3.04 V vs. standard hydrogen electrode, SHE), making it promising for next-generation battery applications. Therefore, research is actively being conducted to realize the next-generation lithium metal battery. However, lithium metal anodes face various instability problems due to their high reactivity, which is an obstacle to commercialization. In particular, when lithium dendrites are formed on the lithium metal anode, significant problems such as short circuits and continuous electrolyte decomposition can occur due to the solid-electrolyte interface (SEI) layer that is continuously formed as the dendrites detach. Furthermore, as dendrites are repeatedly formed during charge and discharge reactions, 'dead lithium' is generated, which reduces battery efficiency.

[0043] To alleviate these problems, precise control of Li deposition and stripping behavior is crucial. Embodiments of the present invention provide electrolyte additives containing nonpolar molecules with various functionalities to achieve surface stabilization of Li metal anodes. The characteristics of the induced dipole formed by electrons within the nonpolar molecules are significantly correlated with high induced current density and a larger volume of the additive molecules. Adding a large volume of nonpolar molecules at high current densities can provide advantageous properties for Li metal anodes, such as surface planarization, control of Li metal crystal orientation, and formation of a stable solid electrolyte interface (SEI) layer.

[0044] Figure 1 is a diagram illustrating examples of nonpolar molecules applied to stabilize a Li metal anode in an embodiment of the present invention. The embodiment of Figure 1 explains the effect of nonpolar molecules on stabilizing a Li metal anode through examples of two nonpolar molecules, benzene and anthracene. Before introducing the two nonpolar additives, various calculations were performed using a Gaussian program to computationally evaluate their properties. The embodiment of Figure 1 shows the electrostatic potential map, dipole moment, polarizability, and molar volume for two molecules, benzene and anthracene. Both benzene and anthracene molecules used as additives were confirmed to be nonpolar with a dipole moment value of 0D. However, the two molecules each had a dipole moment of 88.9 cm 3 / mol and 143.3 cm 3 / mol, indicating different molecular sizes. Consequently, a significant difference in polarizability values ​​due to intramolecular electron distribution can be observed between the two molecules. The calculated polarizability values ​​are 66.508 au for benzene and 179.130 au for anthracene. The calculation results highlight the basis for investigating the lifetime of Li-Li symmetric cells by considering the change in polar properties when introducing nonpolar molecules as additives.

[0045] To electrochemically verify the stabilizing effect of a nonpolar additive as an electrolyte additive for Li metal anodes, Li-Li symmetric cell tests were performed. The electrolyte used was 1 M LiTFSI in TEGDME with or without 1 wt% benzene and anthracene. Li-Li symmetric cell tests revealed decomposition of the Li metal anode. As the cell operated, problems such as excessive electrolyte consumption, formation of a SEI layer at the interface, dendrite growth, and dead Li formation comprehensively contributed, resulting in increased overvoltage or a sudden voltage drop, which in turn led to a short circuit.

[0046] In one embodiment, the criterion for determining cell degradation over time is set based on an overpotential that increases to a threshold of 1 V. Figures 2 to 4 are diagrams illustrating the results of Li-Li symmetric cell tests performed under various current density conditions in one embodiment of the present invention. As shown in Figure 2, 1 mA cm -2 At a current density of 5 mA cm, the battery life was observed to be 146 hours without additive (w / o additive), 135 hours with benzene as an additive (w / Benzene), and 259 hours with anthracene as an additive (w / Anthracene). However, when the experiment was conducted under conditions of gradually increasing current density, contrasting life characteristics were observed for anthracene with high polarization and benzene with low polarization. As shown in Fig. 3, at 5 mA cm -2 In the absence of additives and with benzene, the lifetimes are 43 and 56 hours, respectively, while with anthracene, the lifetime is improved to 325 hours, surpassing the results under low current density conditions. This trend is observed at a current density of 10 mA cm -2 This becomes more pronounced with further increase in the amount of additive. As shown in Fig. 4, the lifetime was reduced to 35 hours and 26 hours when no additive was present and when benzene was used, respectively, whereas when anthracene was used, stable cycling was maintained for up to 675 hours without significant overpotential.

[0047] Figures 5 to 9 are drawings for explaining the influence of non-polar molecules in one embodiment of the present invention.

[0048] The graph in Figure 5 shows significant differences in the cycle life characteristics according to the additive effect (w / o additive, w / Benzene, w / Anthracene) under various current density conditions. It can be interpreted that the phenomenon of intramolecular electron localization with high polarizability values ​​is more prominent under high electric field conditions. Introducing molecular dipoles as electrolyte additives can improve the cycling performance of lithium metal anodes at higher current densities due to the increased polarizability value. Similarly, when introducing nonpolar additives, it can be seen that the molecular volume and polarizability value are closely related to the degree of stability they provide to the lithium metal anode.

[0049] Furthermore, Electrochemical Impedance Spectroscopy (EIS) analysis was performed using a Li-Li symmetric cell to investigate the charge transfer resistance between the Li metal cathode and the electrolyte and the SEI layer resistance. EIS analysis can determine not only the resistance (Rsol) caused by the movement of Li ions across the interfaces of the electrolyte, separator, and Li metal electrode, but also the charge transfer resistance (Rct) related to the diffusion of Li ions between the electrolyte / SEI layer and the SEI layer / Li metal electrode. Rsol, which is known to be most affected by the electrolyte, is commonly used as an indicator of electrolyte degradation. Typically, as the cycling process progresses, side reactions such as electrolyte decomposition occur, which impede the movement of Li ions and reduce Li ion conductivity, resulting in an increase in Rsol. Simultaneously, the charge transfer resistance (Rct) at the electrode-electrolyte interface also increases during the electrochemical reaction. Figure 6 shows the interfacial resistance of a Li-Li symmetric cell measured every 30 cycles when using an electrolyte without any additives. Figure 7 shows the interfacial resistance of a Li-Li symmetric cell measured every 30 cycles when using an electrolyte containing benzene, and Figure 8 shows the interfacial resistance of a Li-Li symmetric cell measured every 30 cycles when using an electrolyte containing anthracene. The data are shown only up to 120 cycles because the cell stopped operating before reaching 150 cycles in the absence of additive and in the presence of benzene. In both conditions, a rapid increase in interfacial resistance was observed as the cell was operated. In contrast, in the case of anthracene, the cell not only operated stably up to 150 cycles, but also maintained the interfacial resistance without a significant increase.

[0050] Figure 9 shows the overall resistance values ​​when using a pristine electrolyte (w / o additive) and an electrolyte containing a nonpolar additive (w / Benzene, w / Anthracene). The remarkably stable resistance when using anthracene suggests that the highly polarizable nature of the nonpolar molecule contributes to the enhanced electrochemical performance and interface stabilization of lithium metal batteries.

[0051] FIGS. 10 to 13 are drawings for explaining the electrochemical stabilization effect according to the difference in polarity of a non-polar additive in one embodiment of the present invention.

[0052] To investigate the electrochemical stabilization effect due to the difference in polarity of nonpolar additives, surface morphology analysis was performed with the goal of confirming surface planarization and interface stabilization. To confirm the morphological changes of the Li metal anode according to the introduction of various additives, a current density of 5 mA cm was used. -2 After cycling the cell 100 times, ex-situ scanning electron microscopy (SEM) characterization was performed. Figures 10a and d show the surface of the Li metal anode using the electrolyte without any additives. Excessive accumulation of side reaction products results in the formation of an extremely uneven and bumpy surface. Figures 10b and e show the case where benzene was introduced as an additive. In this case as well, the surface of the Li metal anode was observed to be similarly unstable. On the other hand, when highly polarizable anthracene was added as an additive, the surface of the Li metal anode was observed to be stable and smooth even after long-term charge and discharge, as shown in Figures 10c and f.

[0053] In addition, Fig. 11 shows the results of evaluating the surface roughness and cross-sectional height of the Li metal electrode after 100 cycles using ex-situ AFM (Atomic Force Microscopy) for the cases using three different electrolytes. Consistent with the SEM results, the Li metal electrodes cycled without additives and with benzene as an additive exhibited rough and uneven surfaces due to non-uniform Li deposition, as shown in Fig. 11g and h. In contrast, the Li electrode with anthracene, which has a high polarizability value, added as an additive exhibited a uniform and smooth surface, demonstrating uniform Li plating and peeling, as shown in Fig. 11i.

[0054] Figure 12 shows the vertical cross-sectional height analysis results of Li metal electrodes obtained after cycling. The surface roughness of the Li electrodes after cycling showed variation and changes in both the absence of additives and the presence of benzene. In contrast, the Li metal electrode with anthracene exhibited a stable height profile with minimal surface curvature.

[0055] In addition, as shown in Fig. 13, the surface roughness of the Li metal electrode cycled without additives was 60.939 nm, and in the case of benzene, it was 59.229 nm, but with the introduction of anthracene, the surface roughness was significantly reduced to 38.824 nm.

[0056] FIGS. 14 to 16 are diagrams illustrating changes in the crystal structure of a Li metal anode after charge and discharge in one embodiment of the present invention. To further investigate the changes in the crystal structure of the Li metal anode after charge and discharge, ex-situ XRD (X-ray diffraction) analysis was performed on the cycled electrode under various conditions, such as an electrolyte without an additive and an electrolyte containing benzene and anthracene. During the charge and discharge cycle, the crystallinity of the Li metal can form a plane represented by a face-centered cubic and hexagonal close-packed structure, as shown in FIG. 14a. It is known that the crystal orientation of the (110) plane formed by the Li metal anode induces a low overpotential, contributing to the formation of a stable Li metal anode. On the other hand, in FIGS. 15 and 16, when no electrolyte additive was used, it was observed that the crystallinity was not well maintained even after 100 charge and discharge cycles, leading to induced dendrite growth. On the other hand, when benzene and anthracene are added to the electrolyte as additives, the crystal strength is well maintained even after charge and discharge. However, the two additives differ in their crystal orientations. As shown in Figures 15 and 16, the introduction of benzene induces relatively vertical crystal growth toward the (200) plane, whereas the introduction of anthracene induces horizontal crystal growth toward the (110) plane. These results suggest that the introduction of anthracene, which has a significant polarizability value, leads to positive rearrangement of Li plating and stripping.

[0057] Figure 17 is a diagram illustrating an example of calculation results for the energy levels of a nonpolar additive and a solvent in one embodiment of the present invention. The electrolyte additive decomposes before the solvent and affects the formation of the SEI layer. To understand the effects observed in this process, calculations were performed for the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) energy levels of the nonpolar additive and the solvent TEGDME. The results in Figure 17 suggest that both benzene and anthracene have lower LUMO energy levels than the electrolyte solvent TEGDME, and thus can potentially contribute to faster reductive decomposition and SEI formation compared to the solvent. This not only affects the chemical composition change of the SEI layer, but also has the effect of suppressing unnecessary electrolyte decomposition during battery operation.

[0058] FIGS. 18 to 21 are diagrams showing examples of ex-situ XPS (X-ray photoelectron spectroscopy) measurement results for a Li metal anode after 30 charge and discharge cycles in an embodiment of the present invention. In this example, ex-situ XPS measurements were performed on a Li metal anode after 30 charge and discharge cycles to further analyze the interfacial structure of the solid electrolyte interface (SEI) layer containing an additive including a non-polar additive. As shown in the graph of FIG. 18, prominent CH and CO peaks corresponding to the decomposition reaction products of the TEGDME electrolyte were observed in the C 1s XPS spectra under all conditions. In addition, when anthracene was introduced as an additive, although in a trace amount, a CF3 peak was observed in the fluoride series. The combination of carbonate and fluorine components is known to form a stable and flexible structure of the SEI layer, suggesting that the introduction of the anthracene additive contributes to improving the structural stability of the SEI layer. Also, as shown in the graph of Fig. 19, the O 1s spectra show the main peaks of Li2CO3 and Li2O2 under all three conditions. However, in the absence of additives, an additional ROLi peak was observed. As shown in the graph of Fig. 20, the Li 1s spectra show significant chemical composition differences induced by the nonpolar additives. In the absence of additives, a strong LiOH peak was formed along with oxide components such as Li2O. In contrast, when benzene and anthracene additives were introduced, carbonate components such as Li2CO3 were mainly formed. Finally, as shown in the graph of Fig. 21, in the F 1s spectra, the LiF peak was dominant without additives, whereas when benzene and anthracene additives were added, the LiF peak was formed along with the CF peak. The CF component is known to positively contribute to LiF formation through further cycling.

[0059] FIG. 22 is a diagram illustrating examples of components of an SEI layer according to an embodiment of the present invention. The components of the oxide-rich SEI layer are relatively hard, which causes volume changes and mechanical stress during repeated charge and discharge cycles, resulting in continuous electrolyte consumption. On the other hand, the non-polar additive included in the electrolyte induces compositional changes in the SEI layer, thereby promoting the formation of a durable and flexible SEI layer, thereby enhancing structural stability. XPS analysis demonstrated that both benzene and anthracene have the effect of enhancing structural stability through changes in the composition of the SEI layer. This modified SEI layer can withstand volume changes of the lithium metal anode during charge and discharge, thereby preventing continuous electrolyte consumption and promoting Li ion diffusion through the components of the anode SEI layer.

[0060] As described above, the introduction of two nonpolar additives with different polarities as electrolyte additives can affect the stabilization of lithium metal anodes. Benzene and anthracene are both nonpolar additives with a dipole moment of 0D, but their polarizabilities vary depending on their molecular size. There is a close relationship between the polarizabilities of these nonpolar molecules and the evolving lifespan characteristics of lithium metal batteries. Nonpolar additives with high polarizabilities can effectively suppress the growth of lithium dendrites, resulting in a surface smoothing effect. Furthermore, they can induce horizontal growth of lithium crystallinity and flexible changes in the SEI layer composition during charge and discharge. On the other hand, nonpolar additives with low polarizabilities cannot effectively suppress the growth of lithium dendrites, resulting in persistent surface instability and vertical growth of lithium crystallinity. These results demonstrate the influence of the polarization characteristics of nonpolar additive molecules on the stabilization of lithium metal anodes. Thus, electrolyte additives containing nonpolar molecules according to embodiments of the present invention can improve the stability and lifespan of lithium metal batteries.

[0061] Additionally, other embodiments of the present invention promote lithium metal planarization and stabilization by adding a sulfur-based copper plating accelerator to the electrolyte. These electrolyte additives offer superior properties, including price competitiveness, process simplification, and compatibility with current industrial production lines, and thus can contribute to the growth of the electrochemical industry, including the development of next-generation batteries.

[0062] Figure 23 is a diagram illustrating an example of the properties of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) as a sulfur-based copper plating accelerator in another embodiment of the present invention. In the copper electroplating mechanism, thiols, which are functional groups of MPS, are Cu 2+ When present, it is oxidized to form disulfide, which can induce spontaneous reduction of Cu ions, which is the RDS (Rate-Determining Step) of copper electroplating.

[0063] Fig. 24 is a diagram showing the flatness of a lithium metal surface according to an electrolyte additive in another embodiment of the present invention. Fig. 24 is an example that confirms the performance of an additive according to a substituent and a dipole moment, and shows the change in the lithium metal surface for each of an electrolyte without an additive (Pristine), an electrolyte using DMP (1,3-Dimercaptopropane) as an additive, an electrolyte using PDS (1,3-Propane disulfonate acid disodium salt) as an additive, and an electrolyte using MPS as an additive. When Pristine or DMP is used, an uneven lithium surface is observed, lithium dendrites grow, and a SEI (solid electrolyte interface) layer with little LiF and Li2S is formed, whereas when PDS or MPS is used, a smooth lithium surface is observed, protrusion tips are suppressed, and an SEI layer rich in LiF and Li2S is formed. This may mean that in the case of electrolytes using PDS or MPS as additives, it is possible to improve electrochemical performance due to the implementation of a stable lithium metal surface and the acceleration effect.

[0064] Figures 25 and 26 are diagrams showing examples of Li-Li symmetric cell test results according to electrolyte additives in another embodiment of the present invention. As in the graph of Figure 25, 1 mA cm -2 At a current density of 5 mA cm, the battery life was observed to be 206 h for Pristine, 152 h for DMP, 812 h for PDS, and more than 1000 h for MPS. In addition, at a current density of 5 mA cm -2At a current density of , the battery life was observed to be 79 hours for Pristine, 68 hours for DMP, and over 400 hours for PDS and MPS. In addition, among the graphs in Fig. 26, the left graph shows the results of relatively slow charge / discharge cycles, and the right graph shows the results of fast charge / discharge cycles. In other words, Pristine and DMP show rapid cycling stability decline in both low-rate charge / discharge and high-rate charge / discharge, whereas PDS and MPS show stable charging voltages even after more than 1000 cycles in high-rate / rapid charge / discharge. In this way, the cycling stability at both low and high current densities was in the order of DMP < Pristine < PDS < MPS.

[0065] FIG. 27 is a graph showing resistance values ​​according to electrolyte additives in another embodiment of the present invention. Looking at the graphs of FIG. 27, DMP shows the lowest resistance value before cycling. However, as the cycling progresses, the resistance value of DMP increases, indicating that its cycle stability is lower than that of Pristine. On the other hand, PDS and MPS show lower resistance values ​​than Pristine even before cycling, and maintain low resistance values ​​even as the cycling progresses. Since the resistance value increases as a large amount of dead lithium is produced or a thick SEI layer is formed, the results of FIG. 27 indirectly indicate that PDS and MPS effectively control the production of dead lithium or the formation of dendrites. In particular, MPS shows the relatively smallest change in resistance value, which may indicate that the formed SEI layer is stable and that the lithium plating / stripping kinetics function is improved.

[0066] FIGS. 28 to 30 are drawings for explaining the flattening of a lithium metal surface according to an electrolyte additive in another embodiment of the present invention. FIG. 28 shows SEM (Scanning Electron Microscopy) images of a lithium metal surface, and FIG. 29 shows the AFM (Atomic Force Microscopy) results of a lithium metal surface. In addition, FIG. 30 shows the height (y-axis of the graph) of the lithium metal surface. When pristine and DMP were used as electrolyte additives, the lithium metal surface showed an uneven surface with needle-shaped dendrites, and when PDS was used as an electrolyte additive, the lithium metal surface showed a uniform surface with almost no unwanted byproducts. In addition, when MPS was used as an electrolyte additive, the lithium metal surface showed the flattest and shiniest surface. The color of lithium is silver, and in the case of PDS and MPS, the color of the lithium metal surface was well maintained. Meanwhile, the roughness shows MPS (23.801 nm) < PDS (53.226 nm) < Pristine (66.020 nm) < DMP (132.563 nm). As such, it can be seen that the flattening effect is the highest when MPS is used as an electrolyte additive.

[0067] FIGS. 31 to 33 are diagrams illustrating XRD (X-ray diffraction) analysis results according to electrolyte additives in another embodiment of the present invention. As charge and discharge progresses, the process of lithium melting and deposition may be repeated. Accordingly, the crystallization of lithium may change. It is known that the crystal direction of the (110) plane (horizontal crystal direction) formed by the Li metal negative electrode has a relatively high exchange current density, enabling uniform surface deposition, and contributing to the formation of a stable Li metal negative electrode. In other words, the crystallization that grows in the most flattened direction is known as the 110 surface. The results of FIGS. 32 and 33 show that Pristine and DMP are aligned in the 200 surface direction (vertical crystal direction), which is the worst for flattening. On the other hand, PDS and MPS show that the crystallization changes to the 110 surface. Although PDS shows an increase in 200 surfaces with increasing cycles, the proportion of 110 surfaces is still relatively high compared to Pristine and DMP. On the other hand, MPS shows an even higher proportion of 110 surfaces with increasing cycles. Thus, the MPS additive can improve the sustainability of the Li(110) plane even during cycling.

[0068] Figure 34 is a diagram illustrating an example of calculation results for energy levels according to electrolyte additives in another embodiment of the present invention. The electrolyte additive decomposes before the solvent and influences the formation of the SEI layer. To understand the effects observed in this process, calculations were performed for the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unemption Molecular Orbital) energy levels of the electrolyte additive and the solvent TEGDME. The results in Figure 34 suggest that both PDS and MPS have lower LUMO energy levels than the electrolyte solvent TEGDME, and thus can potentially contribute to faster reductive decomposition and SEI formation compared to the solvent. This not only affects the change in the chemical composition of the SEI layer, but also has the effect of suppressing unnecessary electrolyte decomposition during battery operation.

[0069] FIGS. 35 and 36 are diagrams showing examples of XPS (X-ray Photoelectron Spectroscopy) measurement results for a lithium metal anode according to another embodiment of the present invention, and FIG. 37 is a diagram showing examples of components of an SEI layer according to one embodiment of the present invention. FIGS. 35 and 36 show that in the case of Pristine and DMP, a fragile, low ion-conductivity SEI layer is formed that is deficient in LiF and Li2S due to the formation of Ch3Li, CH, LiOH, etc. through solvent reduction, and that in the case of Pristine and DMP, a LiF- and Li2S-rich, stable, and high ion-conductivity SEI layer is formed. The components of the oxide-rich SEI layer are relatively hard, which causes volume changes and mechanical stress during repeated charge and discharge cycles, resulting in continuous electrolyte consumption. In addition, the PDS or MPS additive included in the electrolyte induces a compositional change in the SEI layer, thereby promoting the formation of a durable and flexible SEI layer, thereby improving structural stability. XPS analysis demonstrated that both PDS and NPS enhanced structural stability by altering the SEI layer composition. This modified SEI layer can withstand volume changes in the lithium metal anode during charge and discharge, preventing continuous electrolyte consumption and promoting Li ion diffusion through the anode SEI layer components.

[0070] According to other embodiments of the present invention, a polyanion functional group-controlled electrolyte additive for stabilizing the surface of a negative electrode for a lithium metal battery can be provided.

[0071] Furthermore, although the above examples only describe examples of lithium metal batteries, lithium-ion batteries may also form dendrites on the surface when lithium is transferred from the positive electrode to the negative electrode during rapid charging, as lithium enters the graphite. In this case, an electrolyte additive containing non-polar molecules can prevent the formation of dendrites and thereby improve the performance of the lithium-ion battery. Furthermore, an electrolyte additive containing PDS and / or MPS can also prevent the formation of dendrites and thereby improve the performance of the lithium-ion battery.

[0072] The above description is merely an illustrative illustration of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are intended to illustrate, rather than limit, the technical idea of ​​the present invention, and the present invention is not limited to these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included within the scope of the rights of the present invention.

Claims

1. The life characteristics of a lithium battery are controlled through the polarization value of the nonpolar molecule, including nonpolar molecules, or Containing at least one of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) and PDS (1,3-Propane disulfonate acid disodium salt) Electrolyte additive characterized by .

2. In paragraph 1, An electrolyte additive characterized in that at least one of surface planarization and formation of a SEI (Solid-Electrolyte Interface) layer on a negative electrode of a lithium battery using an electrolyte containing the electrolyte additive is controlled according to the polarization value based on the molecular size of the nonpolar molecule, thereby controlling the life characteristics of the lithium battery.

3. In paragraph 2, An electrolyte additive comprising the non-polar molecule, characterized in that it induces horizontal growth of crystals of lithium metal contained in the negative electrode.

4. In paragraph 1, An electrolyte additive characterized in that the above nonpolar molecule contains anthracene.

5. In paragraph 1, An electrolyte additive characterized in that the proportion of horizontal crystals of a negative electrode included in a lithium battery increases as a charge / discharge cycle of the lithium battery using the electrolyte including the electrolyte additive including at least one of the MPS and PDS progresses.

6. In paragraph 5, An electrolyte additive characterized by suppressing dendrite formation on the cathode and changing the chemical composition of the SEI (Solid-Electrolyte Interface) layer.

7. In paragraph 6, An electrolyte additive characterized by increasing the ratio of at least one of LiF and Li2S in the chemical composition of the SEI layer.

8. An electrolyte additive including a non-polar molecule, the life characteristics of which are controlled through the polarization value of the non-polar molecule; or Electrolyte additive comprising at least one of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) and PDS (1,3-Propane disulfonate acid disodium salt) including An electrolyte characterized by .

9. In paragraph 8, At least one of surface planarization and formation of a SEI (Solid-Electrolyte Interface) layer on the negative electrode of the lithium battery including the electrolyte is controlled according to the polarization value based on the molecular size of the nonpolar molecule, thereby controlling the life characteristics of the lithium battery. An electrolyte characterized by .

10. In paragraph 9, The electrolyte additive containing the above nonpolar molecule induces horizontal growth of the lithium metal crystals contained in the above negative electrode. An electrolyte characterized by .

11. In paragraph 8, An electrolyte characterized in that the nonpolar molecule comprises anthracene.

12. In paragraph 8, As the charge and discharge cycle of a lithium battery using an electrolyte including an electrolyte additive including at least one of the MPS and PDS progresses, the proportion of horizontal crystals of the negative electrode included in the lithium battery increases. An electrolyte characterized by .

13. In paragraph 12, Suppressing dendrite formation on the above cathode and changing the chemical composition of the SEI (Solid-Electrolyte Interface) layer An electrolyte characterized by .

14. In paragraph 13, Increasing the ratio of at least one of LiF and Li2S in the chemical composition of the SEI layer by an electrolyte additive including at least one of the MPS and PDS An electrolyte characterized by .

15. Bipolar; cathode; An electrolyte that transfers lithium ions between the positive electrode and the negative electrode; and Electrolyte additive included in the above electrolyte Including, The electrolyte additive comprises a non-polar molecule, the life characteristics of which are controlled through the polarization value of the non-polar molecule, or comprises at least one of MPS (3-Mercapto-1-propanesulfonic acid sodium salt) and PDS (1,3-Propane disulfonate acid disodium salt). A lithium battery characterized by .

16. In paragraph 15, At least one of surface planarization and formation of a SEI (Solid-Electrolyte Interface) layer on the negative electrode of the lithium battery is controlled according to the polarization value based on the molecular size of the nonpolar molecule, thereby controlling the life characteristics. A lithium battery characterized by .

17. In paragraph 16, The electrolyte additive containing the above nonpolar molecule induces horizontal growth of the lithium metal crystals contained in the above negative electrode. A lithium battery characterized by .

18. In paragraph 15, By the electrolyte additive including at least one of the MPS and PDS, the ratio of horizontal crystals of the negative electrode increases as the charge and discharge cycle progresses. A lithium battery characterized by .

19. In paragraph 18, Suppressing dendrite formation on the above cathode and changing the chemical composition of the SEI (Solid-Electrolyte Interface) layer A lithium battery characterized by .

20. In paragraph 19, By the electrolyte additive including at least one of the MPS and PDS, the ratio of at least one of LiF and Li2S in the chemical composition of the SEI layer increases. A lithium battery characterized by .

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