Electrode additive, and lithium metal electrode and lithium metal battery comprising same

Abstract

The present invention relates to an electrode additive, and an electrode and a lithium metal battery comprising same. The present invention can provide an electrode additive, and an electrode and a lithium metal battery comprising same, wherein the electrode additive can significantly mitigate the formation of dendrites and dead lithium inevitably generated during charging and discharging of the lithium metal battery, thereby improving lifespan and stability.

Description

Electrode additive, lithium metal electrode and lithium metal battery containing the same

[0001] The present invention relates to an electrode additive, a lithium metal electrode including the same, and a lithium metal battery.

[0002] With the advent of the Battery of Things (BoT) era, where everything from electric vehicles to wearable devices is connected to batteries, demand for energy storage devices with high energy density, long lifespan, and high safety standards is increasing. In particular, with the rapid growth of the electric vehicle market, lithium-ion batteries are increasingly being used. However, their low energy density limits their applications in high-energy devices.

[0003] To overcome these limitations of lithium-ion batteries, lithium metal batteries, which use lithium metal as an anode material with a theoretical energy density approximately 10 times higher (3,842 mAh / g) than graphite anode materials (372 mAh / g) and a low redox potential (-3.04 V vs. SHE), are attracting attention as a next-generation technology. These lithium metal batteries are expected to significantly increase the driving range and charging speed of electric vehicles by increasing their energy density per unit weight.

[0004] However, the electrochemical instability of conventional lithium metal electrodes and the imbalance of lithium ion concentration that occurs during the initial cycle are the main causes of uneven lithium electrodeposition. This is because the repeated deposition and peeling of lithium during repeated charge / discharge cycles leads to the formation of lithium dendrites and dead lithium, which continuously and significantly reduces the capacity of the electrode and ultimately leads to the possibility of electrode short-circuiting and explosion. Various efforts have been made to coat the electrodes of lithium metal batteries or form three-dimensional structures, but these efforts have not been sufficient to reduce lithium dendrites and dead lithium.

[0005] Accordingly, the inventors of the present invention have discovered that when an ionic compound composed of a zero-dimensional carbon nanoparticle anion and a lithium cation is used as an electrode additive for a lithium metal battery, not only is dendritic and dead lithium significantly reduced, but the life characteristics of the battery are also improved, thereby completing the present invention.

[0006] The present invention has been devised to solve the problems described above, and the purpose of the present invention is to provide an electrode additive capable of significantly improving the generation of dendrites and dead lithium that inevitably occur during the charge and discharge process of a lithium metal battery, thereby improving the lifespan and stability, a lithium metal electrode including the same, and a lithium metal battery.

[0007] One aspect of the present invention provides an electrode additive for a lithium metal battery comprising an ionic compound comprising a zero-dimensional carbon nanoparticle anion and a lithium cation.

[0008] Another aspect of the present invention provides an electrode for a lithium metal battery comprising the electrode additive for a lithium metal battery.

[0009] Another aspect of the present invention provides a lithium metal battery comprising the electrode for the metal battery.

[0010] Another aspect of the present invention provides a method for producing an electrode additive for a lithium metal battery, comprising: (A) a step of mixing and reacting a carbon material and an acidic solution to produce zero-dimensional carbon nanoparticles; and (B) a step of mixing and reacting the zero-dimensional carbon nanoparticles and a lithium precursor to produce an ionic compound.

[0011] Another aspect of the present invention provides a method for manufacturing a lithium metal electrode, comprising: (I) a step of applying the electrode additive for a lithium metal battery to one side of a lithium metal; (II) a step of folding the lithium metal to which the electrode additive has been applied so that the one side faces each other; (III) a step of stretching the folded lithium metal; and (IV) a step of obtaining a lithium metal electrode by repeating steps (I) to (III).

[0012] The additive for a lithium metal battery according to the present invention can significantly improve the lifespan and stability by significantly improving the generation of dendrites and dead lithium that inevitably occur during the charge and discharge process of a lithium metal battery.

[0013] Figure 1 is a drawing briefly showing the manufacturing method of Example 1 of the present invention.

[0014] Figure 2 shows a photographic image of a lithium metal electrode manufactured in Example 1 of the present invention.

[0015] Figure 3 shows the 1 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD), Comparative Example 1 (pristine), and Comparative Example 2 (pristine 2, fold-pristine) of the present invention. -2 and 0.5 mAhcm -2 This is a graph of voltage over time.

[0016] Figure 4 shows the 1 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD), Comparative Example 1 (pristine), and Comparative Example 2 (pristine 2, fold-pristine) of the present invention. -2 and 0.5 mAhcm -2 This is a graph of voltage according to the number of cycles.

[0017] Figure 5 shows the 1 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD) and Comparative Example 1 (pristine) of the present invention. -2 and 3 mAh cm -2 This is a graph of voltage over time.

[0018] Figure 6 shows the 3 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD) and Comparative Example 1 (pristine) of the present invention. -2 and 3 mAh cm -2 This is a graph of voltage over time.

[0019] Figure 7 shows the 1 mA cm of the electrodes of (ac) Comparative Example 1 and (df) Example 1 of the present invention. -2 / 3 mAhcm -2 This shows a cross-sectional scanning electron microscope (CP-SEM) image of the electrode surface after 50 cycles of symmetric cell testing under current density conditions.

[0020] Figure 8 shows the results of Example 1 (Li-GQD) and Comparative Example 1 (Pristine) of the present invention used as a cathode, and 5.4 mg / cm 2 This graph shows the discharge capacity according to the cycle of a full cell using NCM523 as the cathode.

[0021] Figure 9 shows the results of Example 1 (Li-GQD) and Comparative Example 1 (Pristine) of the present invention as cathodes, at 17 mg / cm 2 This graph shows the discharge capacity according to the cycle of a full cell using NCM523 as the cathode.

[0022] Figure 10 shows the results of Example 1 (Li-GQD) and Comparative Example 1 (Pristine) of the present invention as cathodes, at 13 mg / cm 2 This graph shows the discharge capacity according to the cycle of a full cell using NCM811 as the positive electrode.

[0023] Figure 11 shows a voltage graph at high current density of a lithium metal symmetric battery using the electrodes of Example 1 and Comparative Example 1 of the present invention.

[0024] Figure 12 shows a graph of discharge capacity according to cycle of a half-cell using Example 1 (Li-GQD) of the present invention and Comparative Example 1 (Pristine) as a negative electrode.

[0025] The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. These embodiments are provided solely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined solely by the scope of the claims.

[0026] In describing the present invention, if a detailed description of a related known technology is judged to unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When "comprises," "has," "consists of," etc. are used in this specification, other parts may be added unless "only" is used. In addition, terms such as "comprises" or "has" are intended to specify the presence of a feature, number, step, component, or combination thereof described in the specification, and should not be understood to exclude the presence or possibility of adding one or more other features, numbers, steps, components, or combinations thereof. In addition, when a component is expressed in the singular, it includes the case of including the plural unless specifically stated otherwise.

[0027] Hereinafter, the present invention will be described in more detail.

[0028] As described above, conventional lithium metal batteries have problems in that the electrode capacity continuously decreases due to dendrites and dead lithium formed during the charge / discharge process, and ultimately, the risk of electrode short-circuiting and explosion increases. Therefore, the present invention provides an electrode additive for a lithium metal battery that is included in the electrode for a lithium metal battery and can significantly reduce the formation of dendrites and dead lithium and improve the life characteristics.

[0029] More specifically, one aspect of the present invention provides an electrode additive for a lithium metal battery comprising an ionic compound comprising a zero-dimensional carbon nanoparticle anion; and a lithium cation.

[0030] The above ionic compound is a solid compound formed by the electrostatic bonding of lithium cations and zero-dimensional carbon nanoparticle anions, and can suppress dendrites on the surface of a lithium metal electrode without dissolving in a conventional liquid electrolyte and generating gas or corrosion, thereby improving the performance and safety of the battery.

[0031] The above zero-dimensional carbon nanoparticles refer to carbon nanoparticles having a size of less than 20 nm, and having an anionic group containing oxygen on the surface and / or edges. These zero-dimensional carbon nanoparticles have the characteristics of zero-dimensional carbon quantum dots, in which the fluorescence wavelength varies depending on the size.

[0032] The above ionic compound has low lattice energy and thus is easily ionized, and the anion is relatively fixed in position due to its large size, whereas the lithium cation is relatively small in size and can be easily moved, so that as the mobility of lithium increases, the phenomenon of uneven lithium deposition / desorption can be compensated for, thereby suppressing dendrites.

[0033] In addition, the ionic compound can form a uniform solid electrolyte interface (SEI) on the lithium metal surface and improve its conductivity.

[0034] The above zero-dimensional carbon nanoparticle anion may be manufactured from any one selected from the group consisting of carbon nanofibers, graphene, graphene oxide, carbon nanotubes, fullerenes, and carbon black, and preferably may be manufactured from carbon nanofibers. In particular, carbon nanofibers have the advantages of being easy to produce, low cost, and having a high specific surface area. In addition, since the starting material of the zero-dimensional carbon nanoparticle anion already has a core structure composed of sp2 bonded carbon composed solely of carbon, it is easier to synthesize zero-dimensional carbon nanoparticles of various sizes and shapes.

[0035] The above zero-dimensional carbon nanoparticle anion may include at least one anionic functional group selected from the group consisting of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group, and the lithium cation may be bound to the anionic functional group to exist as an ionic compound.

[0036] The above zero-dimensional carbon nanoparticle anion and the lithium cation may be in a molar ratio of 1:3 to 8, preferably 1:5 to 7, more preferably 1:5.3 to 6.7, and most preferably 1:5.5 to 6.5. If the molar ratio of lithium cation to 1 mol of zero-dimensional carbon nanoparticle anion is less than the lower limit, the efficacy as an electrode additive cannot be expected, and conversely, if it exceeds the upper limit, single-molecule impurity anions during the manufacturing process may be adsorbed to the zero-dimensional carbon nanoparticle, causing a side reaction in the electrode, which may result in a deterioration in performance.

[0037] Another aspect of the present invention provides an electrode for a lithium metal battery comprising the electrode additive for a lithium metal battery.

[0038] The above lithium metal battery electrode additive may be included in an amount of 3 to 25 wt%, preferably 5 to 20 wt%, more preferably 6 to 15 wt%, and most preferably 7 to 12 wt%. If the content of the lithium metal battery electrode additive is less than the lower limit, the resin improvement effect may not be sufficient, and conversely, if it exceeds the upper limit, the electrode additive may aggregate as the battery is charged and discharged.

[0039] Another aspect of the present invention provides a lithium metal battery comprising the electrode for the metal battery.

[0040] Another aspect of the present invention provides a method for producing an electrode additive for a lithium metal battery, comprising: (A) a step of mixing and reacting a carbon material and an acidic solution to produce zero-dimensional carbon nanoparticles; and (B) a step of mixing and reacting the zero-dimensional carbon nanoparticles and a lithium precursor to produce an ionic compound.

[0041] (A) A step of manufacturing zero-dimensional carbon nanoparticles by mixing and reacting carbon material and an acid solution.

[0042] The above carbon material may be at least one selected from the group consisting of carbon nanofibers, graphene, graphene oxide, carbon nanotubes, fullerene, and carbon black, and most preferably, carbon nanofibers.

[0043] The above acidic solution may be a mixture of a nitric acid solution having a concentration of 31 to 50 wt% and a sulfuric acid solution having a concentration of 90 to 99 wt% in a volume ratio of 1:2 to 4, preferably a mixture of a nitric acid solution having a concentration of 33 to 47 wt% and a sulfuric acid solution having a concentration of 91 to 99 wt% in a volume ratio of 1:2.1 to 3.8, more preferably a mixture of a nitric acid solution having a concentration of 35 to 45 wt% and a sulfuric acid solution having a concentration of 92 to 99 wt% in a volume ratio of 1:2.3 to 3.7, and most preferably a mixture of a nitric acid solution having a concentration of 36 to 43 wt% and a sulfuric acid solution having a concentration of 93 to 98 wt% in a volume ratio of 1:2.5 to 3.5.

[0044] For 5 g of the carbon material, the acidic solution may be mixed in an amount of 140 to 180 mL, preferably 147 to 177 mL, more preferably 150 to 170 mL, and most preferably 155 to 165 mL. If the acidic solution is mixed in an amount of less than 140 mL for 5 g of the carbon material, zero-dimensional carbon nanoparticles may not be produced, and conversely, if the acidic solution is mixed in an amount exceeding 180 mL, excessive time and cost may be required to remove the acidic solution thereafter.

[0045] The reaction of step (A) may be performed at 80 to 130°C for 18 to 30 hours, preferably at 85 to 120°C for 20 to 28 hours, more preferably at 90 to 110°C for 21 to 27 hours, and most preferably at 95 to 105°C for 22 to 26 hours. If at least one of the reaction temperature and time of step (A) is below the lower limit, zero-dimensional carbon nanoparticles may not be sufficiently produced, and conversely, if it exceeds the upper limit, the size of the produced carbon nanoparticles may increase, so that they may not exhibit characteristics as zero-dimensional quantum dots, or they may aggregate with each other, resulting in reduced dispersibility and making it difficult to expect an effect as an electrolyte additive.

[0046] The above zero-dimensional carbon nanoparticles may include at least one anionic functional group selected from the group consisting of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group.

[0047] (B) A step of producing an ionic compound by mixing and reacting the above zero-dimensional carbon nanoparticles and lithium precursor.

[0048] The lithium precursor may be at least one selected from the group consisting of lithium hydroxide, lithium fluoride and lithium carbonate, and most preferably lithium carbonate.

[0049] The above zero-dimensional carbon nanoparticles and the lithium precursor may be mixed so that the lithium to zero-dimensional carbon nanoparticle molar ratio is 1:3 to 8, preferably 1:5 to 7, more preferably 1:5.3 to 6.7, and most preferably 1:5.5 to 6.5.

[0050] The reaction of step (B) may be performed at 15 to 35°C for 18 to 30 hours, preferably at 18 to 32°C for 20 to 28 hours, more preferably at 20 to 30°C for 21 to 27 hours, and most preferably at 22 to 27°C for 22 to 26 hours. If at least one of the time and temperature of the reaction of step (B) is below the lower limit, the lithium cation content of the ionic compound produced may decrease, and conversely, if it exceeds the upper limit, the reaction rate may significantly decrease or the ionic compound yield may decrease.

[0051] According to a preferred embodiment of the present invention, ① the carbon material is carbon nanofibers, ② the acidic solution is a mixture of a nitric acid solution having a concentration of 36 to 43 wt% and a sulfuric acid solution having a concentration of 93 to 98 wt% in a volume ratio of 1:2.5 to 3.5, ③ the acidic solution is mixed in an amount of 155 to 165 mL for 5 g of the carbon material, ④ the reaction of step (A) is performed at 95 to 105° C. for 22 to 26 hours, ⑤ the zero-dimensional carbon nanoparticles include a hydroxyl group and a carboxyl group, ⑥ the lithium precursor is lithium carbonate, ⑦ the zero-dimensional carbon nanoparticles and the lithium precursor are mixed so that the lithium to the zero-dimensional carbon nanoparticles is in a molar ratio of 1:5.5 to 6.5, and ⑧ the reaction of step (B) is performed at 22 to 27° C. It may be performed for 22 to 26 hours. In the case of an electrode additive for a lithium metal battery manufactured by a method that satisfies all of the conditions ① to ⑧ above, it was confirmed that the thermal stability and chemical resistance of the lithium metal electrode can be significantly improved, and in particular, it is excellent.

[0052] Another aspect of the present invention provides a method for manufacturing a lithium metal electrode, comprising: (I) a step of applying the electrode additive to one side of a lithium metal; (II) a step of folding the lithium metal to which the electrode additive has been applied so that the one side faces each other; (III) a step of stretching the folded lithium metal; and (IV) a step of obtaining a lithium metal electrode by repeating steps (I) to (III).

[0053] The method for manufacturing a lithium metal electrode according to the present invention uses the electrode additive for a lithium metal battery and manufactures the electrode by a coating-folding-pressing method rather than a slurry method, thereby omitting the mixing, coating, and drying processes during the electrode manufacturing process, and simplifying the rolling process without damaging the existing process by adding the additive. In addition, the electrode additive for a lithium metal battery is non-reactive with a lithium metal thin film and can be added directly without pretreatment, thereby further simplifying the process.

[0054] Hereinafter, each step of the method for manufacturing a lithium metal electrode of the present invention will be described in more detail.

[0055] (Ⅰ) A step of applying the above lithium metal battery electrode additive to one side of the lithium metal.

[0056] The above step (Ⅰ) is a step of applying the electrode additive for the lithium metal battery to one surface of the lithium metal.

[0057] The above electrode additive may be manufactured according to the manufacturing method of the electrode additive for a lithium metal battery described above.

[0058] (Ⅱ) A step of folding the lithium metal coated with the above electrode additive so that the above one side faces each other.

[0059] The above step (Ⅱ) is a step of folding the lithium metal coated with the electrode additive so that one side of the lithium metal coated with the electrode additive faces the other side.

[0060] At this time, it is important to fold so that the side where the electrode additive is applied faces the surface. If, on the contrary, the side where the electrode additive is applied is folded so that it is exposed to the outside, a problem may occur in which the electrode additive is not uniformly mixed into the electrode and is lost in the later stage.

[0061] (Ⅲ) Step of stretching the folded lithium metal

[0062] The above step (Ⅲ) is a step of uniformly dispersing electrode additives while pressing the folded lithium to stretch the lithium metal. The stretching process can be performed by pressing the folded lithium metal.

[0063] The above pressurization may be performed by applying a pressure of 0.5 to 3 MPa, preferably 0.6 to 2 MPa, more preferably 0.7 to 1.5 MPa, and most preferably 0.9 to 1.1 MPa. If the pressurization is performed below the lower limit, the electrode additive may not be sufficiently dispersed and may cause agglomeration, and conversely, if the pressurization is performed at a pressure exceeding the upper limit, the lithium metal may be damaged and the mechanical properties of the electrode ultimately manufactured may deteriorate.

[0064] (Ⅳ) A step of obtaining a lithium metal electrode by repeating steps (Ⅰ) to (Ⅲ) above.

[0065] The above step (Ⅳ) is a step of manufacturing a homogeneous lithium metal electrode by repeating the above steps (Ⅰ) to (Ⅲ) multiple times.

[0066] The above step (Ⅳ) may be performed so that the area of ​​the lithium metal electrode is 1.2 to 6 times, preferably 1.5 to 4 times, more preferably 2 to 3.5 times, and most preferably 2.3 to 2.8 times the area of ​​the lithium metal in the above step (Ⅰ). If the finally obtained lithium metal electrode is stretched to an area less than 1.2 times the area of ​​the lithium metal in the above step (Ⅰ), the electrode additive may aggregate, and conversely, if the area is stretched to a greater extent than 6 times the area, the mechanical properties of the manufactured lithium metal electrode may deteriorate.

[0067] The above steps (Ⅰ) to (Ⅲ) may be repeated 10 to 50 times, preferably 12 to 35 times, more preferably 15 to 30 times, and most preferably 18 to 23 times. If the number of repetitions is less than the lower limit, the electrode additive may aggregate, and conversely, if it exceeds the upper limit, the mechanical properties of the lithium metal electrode produced may deteriorate.

[0068] The electrode additive for the lithium metal battery may be included in an amount of 3 to 25 wt%, preferably 5 to 20 wt%, more preferably 6 to 15 wt%, and most preferably 7 to 12 wt%. If the electrode additive for the lithium metal battery is less than the lower limit, the resin improvement effect may be minimal, and conversely, if it exceeds the upper limit, the electrode additive may be unevenly distributed.

[0069] According to the most preferred embodiment of the present invention, ① step (III) is performed by applying a pressure of 0.9 to 1.1 MPa to the folded lithium metal, ② step (IV) is performed so that the area of ​​the lithium metal electrode becomes 2.3 to 2.8 times the area of ​​the lithium metal in step (I), ③ steps (I) to (III) are repeated 18 to 23 times, and ④ the lithium metal battery electrode additive may be included in an amount of 7 to 12 wt% with respect to 100 wt% of the total lithium metal electrode.

[0070] In the method for manufacturing a lithium metal electrode of the present invention, when all of the conditions ① to ④ of the most preferred embodiment are satisfied, it was confirmed that the electrode additive maintains its ionic bond even after 1000 charge / discharge cycles of a battery using the same, and is uniformly distributed as in the beginning without being lost or aggregated, which is particularly superior.

[0071] Hereinafter, the present invention will be described in more detail through examples, etc., but the scope and content of the present invention cannot be interpreted as being reduced or limited by the examples, etc. below.

[0072] Example 1

[0073] Manufacturing of additives for electrodes

[0074] (1) Oxidation (cutting)

[0075] 5.0 g of carbon nanofibers, 40 mL of a 38 wt% nitric acid (HNO3) solution, and 120 mL of a 98 wt% sulfuric acid solution were mixed and refluxed at 100°C for 24 hours to produce 0.5 g of zero-dimensional carbon nanoparticles. The size of the produced zero-dimensional carbon nanoparticles was 6 nm, and hydroxyl and carboxyl functional groups were present on the surface.

[0076] (2) Lithition

[0077] Next, the refluxed mixture was cooled to room temperature, and 1.62 mol of lithium carbonate (Li2CO3) was added until the pH of the mixture became 11, and the condition was maintained at 24 °C for 24 hours. Then, twice the amount of ethanol of the mixture after 24 hours was added, and it was centrifuged at 10,000 rpm for 30 minutes. Centrifugation was repeated until no pellet was generated. Then, a suspended ionic compound (Li-GQD) was obtained from the supernatant, and the molar ratio of the zero-dimensional carbon nanoparticle anion:lithium cation of the ionic compound was 1:6.

[0078] (3) Post-processing

[0079] The Li-GQD obtained above was concentrated using a rotary evaporator at 40°C, and dried in a vacuum oven at 70°C to obtain Li-GQD powder.

[0080] Electrode manufacturing

[0081] Figure 1 is a drawing briefly showing the manufacturing method of Example 1 of the present invention.

[0082] Lithium metal measuring 2 cm x 4 cm x 0.1 cm was prepared, and the Li-GQD powder was uniformly applied to the surface of the lithium metal. Then, the lithium to which the Li-GQD powder was applied was folded so that the surfaces to which the powder was applied were in contact, and then stretched by applying a pressure of 1 MPa. Then, the Li-GQD powder was applied using the same application amount and method, and the folding and stretching process using the same method and pressure was repeated. In Example 1, the powder application-folding-stretching process was repeated a total of 20 times. The Li-GQD was included at 10 wt% with respect to 100 wt% of the resulting electrode, and the thickness of the electrode was 0.04 cm (Fig. 2).

[0083] Comparative Example 1. Pristine

[0084] Lithium metal measuring 2 cm x 4 cm x 0.1 cm was used.

[0085] Comparative Example 2. Pristine 2

[0086] After folding the lithium metal to form a 2 cm x 4 cm x 0.1 cm piece, a pressure of 1 MPa was applied to stretch it to the same size as the initial area. The folding-stretching process was then repeated a total of 20 times.

[0087] Experimental Example 1. Symmetric Cell Performance Evaluation

[0088] A symmetrical cell was manufactured using the electrodes manufactured in the above examples and comparative examples and 1 M LiPF6in EC / EMC (3:7 v / v) electrolyte, and the voltage graph over time was shown in FIGS. 3 to 5 by operating the cell while changing the current density.

[0089] Figure 3 shows the 1 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD), Comparative Example 1 (pristine), and Comparative Example 2 (pristine 2, fold-pristine) of the present invention. -2 and 0.5 mAhcm -2 This is a graph of voltage over time.

[0090] Figure 4 shows the 1 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD), Comparative Example 1 (pristine), and Comparative Example 2 (pristine 2, fold-pristine) of the present invention. -2 and 0.5 mAhcm -2 This is a graph of voltage according to the number of cycles.

[0091] Referring to FIGS. 3 and 4, it can be seen that Comparative Examples 1 and 2, which did not use the electrode additive according to the present invention, exhibited unstable operation from 300 cycles onwards, resulting in a significant decrease in cycle stability. On the other hand, Example 1 exhibited slightly unstable behavior only after approximately 900 hours, confirming excellent cycle stability.

[0092] Classification Example 1 Comparative Example 1 (Li bare cathode) Stability for lithium electrode (Li / Li symmetric cell test) Stable up to 1,280 cycles, unstable operation after 580 cycles, short circuit after 630 cycles

[0093] In addition, as shown in Table 1 above, in the operating voltage range of a typical battery (less than 0.3 V), the electrode of Example 1 was stable up to 1,280 cycles, but the operation of Comparative Example 1 began to become unstable from the 580th cycle and was short-circuited after the 630th cycle.

[0094] Figure 5 shows the 1 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD) and Comparative Example 1 (pristine) of the present invention. -2 and 3 mAh cm -2 This is a graph of voltage over time.

[0095] Figure 6 shows the 3 mA cm of a symmetric cell using the electrodes of Example 1 (Li-GQD) and Comparative Example 1 (pristine) of the present invention. -2 and 3 mAh cm -2 It is a graph of voltage over time in . Specifically, the above figure 6 shows 1 mA cm -2 / 3 mAh cm -2 10 cycles and 2 mA cm under conditions -2 / 3 mAh cm -2 After 10 cycles under the condition of 3 mA cm -2 / 3 mAh cm -2 This is a graph obtained by conducting a symmetric cell test with conditions.

[0096] Referring to FIGS. 5 and 6, it can be confirmed that the life characteristics of the electrode of Example 1 (Li-GQD) of the present invention are significantly improved compared to the electrode of Comparative Example 1 (pristine) even under high current density conditions. In particular, referring to FIG. 6, in the case of Comparative Example 1, operation became very unstable after 100 hours, but in the case of Example 1, slight instability was confirmed from 200 hours, and it can be confirmed that the cycle stability of Example 1 increased by about 2 times even under high current density conditions.

[0097] Experimental Example 2. Electrode Surface Analysis

[0098] A symmetrical cell using the electrodes of the above examples and comparative examples was used at 1 mA cm -2 / 3 mAhcm -2 After conducting a 50-cycle symmetrical cell test under current density conditions, the cross-section of the electrode was photographed using a cross-section polisher-scanning electron microscope (CP-SEM), and the results are shown in Fig. 7.

[0099] Figure 7 shows the 1 mAcm of the electrodes of (ac) Comparative Example 1 and (df) Example 1 of the present invention. -2 / 3 mAh cm -2 This shows a cross-sectional scanning electron microscope (CP-SEM) image of the electrode surface after 50 cycles of symmetric cell testing under current density conditions.

[0100] Referring to the above FIGS. 7 (a) and (d), the thickness of the entire electrode expressed in red was 246 μm for Comparative Example 1 and 439 μm for Example 1. In addition, the thickness of the lithium metal expressed in dark color was 81 μm for Comparative Example 1 and 296 μm for Example 1. During the battery charging and discharging process, Li metal is used and consumed, and considering that Example 1 and Comparative Example 1 used lithium metal of the same size, it can be confirmed that the thickness of the lithium metal of Example 1 is thicker and therefore less lithium metal is consumed.

[0101] In addition, in the above Fig. 7, the bright layer appearing over the relatively dark Li metal layer is an SEI layer generated during the battery charging and discharging process. It was confirmed that the SEI layer was formed in a denser and relatively softer shape in Example 1 (Fig. 7 (ef)) compared to Comparative Example 1 (Fig. 7 (bc)), thereby improving the life characteristics.

[0102] Through this, it can be confirmed that SEI was uniformly formed and the consumption of Li metal was reduced during the battery charge / discharge process in the electrode of Example 1 to which Li-GQD was added.

[0103] Experimental Example 3. Full Cell Performance Evaluation

[0104] NCM523: Super P: PVDF = 90:5:5 ratio cathode material was manufactured under the condition of 10 mil (0.254 mm) thickness, and the final loading level was 5.4 mg / cm 2NCM523 was used as a cathode. Then, a full cell was manufactured using Example 1 or Comparative Example 1 as a cathode, NCM523 as a cathode, and an electrolyte of 1.0 M LiPF6in EC / EMC 3:7, and discharged to 3 V and charged to 4.3 V. Then, a stable SEI formation environment was created through a formation cycle at 0.1 C for 2 cycles, and a test was performed at 1 C. The results are shown in Fig. 8.

[0105] Figure 8 shows the results of Example 1 (Li-GQD) and Comparative Example 1 (Pristine) of the present invention as cathodes, with 5.4 mg / cm 2 This graph shows the discharge capacity according to the cycle of a full cell using NCM523 as the cathode.

[0106] Referring to the above Figure 8, when the life of the battery is defined as the point at which 70% of the initial discharge capacity is reached, it was confirmed that the life of Comparative Example 1 (Pristine) was 130 cycles, and that of Example 1 (LiGQD) was 250 cycles, which is about twice the life of Example 1 of the present invention.

[0107] Full cells were manufactured in the same manner as described above, but with a loading level of 5.4 mg / cm 2 Instead of NCM523 cathode, cathode material of NCM523: Super P: PVDF = 90:5:5 ratio was manufactured with 10 mil (0.254 mm) thickness condition, and final loading level was 17 mg / cm 2 For the full cell manufactured using the positive electrode, a stable SEI formation environment was created through a formation cycle for two cycles at 0.1 C, and then a test was performed by discharging to 3 V and charging to 4.3 V at 1 C, and the results are shown in Fig. 9.

[0108] Figure 9 shows the results of Example 1 (Li-GQD) and Comparative Example 1 (Pristine) of the present invention as cathodes, at 17 mg / cm 2 This graph shows the discharge capacity according to the cycle of a full cell using NCM523 as the cathode.

[0109] Referring to the above Figure 9, the initial discharge capacity started at 135 mAh / g, Comparative Example 1 (pristine) reached 70% of the initial discharge capacity in 38 cycles, and Example 1 (Li-GQD) reached 70% of the initial discharge capacity in 65 cycles, confirming that the electrode of Example 1 of the present invention showed an increase in life characteristics by about 1.7 times even at a high loading level.

[0110] In addition, in order to verify the life characteristics at high capacity, the cathode material of NCM811: Super P: PVDF = 90:5:5 ratio was manufactured under the condition of 10 mil (0.254 mm) thickness, and the final loading level was 13 mg / cm 2 A full cell was manufactured in the same manner as described above, except that an NCM811 cathode was manufactured and used instead of NCM 523, and a stable SEI formation environment was created through a formation cycle at 0.1 C for 2 cycles, and then a test was performed by discharging to 3 V and charging to 4.3 V at 1 C, and the results are shown in Fig. 10.

[0111] Figure 10 shows the results of Example 1 (Li-GQD) and Comparative Example 1 (Pristine) of the present invention as cathodes, at 13 mg / cm 2 This graph shows the discharge capacity according to the cycle of a full cell using NCM811 as the cathode.

[0112] Referring to the above Figure 10, the initial discharge capacity was 179 mAh / g, and in the case of Comparative Example 1 (Pristine), it became 125 mAh / g, which is 70% of the initial discharge capacity, in the 85th cycle, and in the case of Example 1 (Li-GQD), it became 70% of the initial discharge capacity in the 121st cycle, and the life characteristics increased by about 1.4 times in Example 1 (Li-GQD), confirming that the degree of improvement in life characteristics is excellent even at a high loading level.

[0113] Experimental Example 4. High Current Density Conditions

[0114] A lithium metal symmetric battery was manufactured using the electrodes of Example 1 and Comparative Example 1 and a 1 M LiPF6in EC / EMC (3:7 v / v) electrolyte, and the voltage graph according to the cycle is shown in Fig. 11 and Table 2.

[0115] Figure 11 shows a voltage graph at high current density of a lithium metal symmetric battery using the electrodes of Example 1 and Comparative Example 1 of the present invention.

[0116] Example 1 Comparative Example 1 (Li bare cathode) Stability for lithium electrode (Li / Li symmetric cell test) Stable up to 200 cycles 3 mA cm -2 , 3 mAh cm -2 Unstable from 90 cycles after starting operation under conditions, short circuit after 128 cycles

[0117]

[0118] As shown in the above Figure 11 and Table 2, the electrode of Comparative Example 1 began to become unstable from the 90th cycle and short-circuited after the 128th cycle, but it was confirmed that the battery using the electrode of Example 1 was stable up to the 200th cycle, showing a significantly improved lifespan characteristic.

[0119] Experimental Example 5. Half-cell Evaluation

[0120] NCM523: Super P: PVDF = 90:5:5 ratio cathode material was manufactured under the condition of 10 mil (0.254 mm) thickness, and the final loading level was 5.4 mg / cm 2 NCM523 was used as a cathode. Then, a half-cell was manufactured using Example 1 or Comparative Example 1 as a cathode, NCM523 as a cathode, and an electrolyte of 1.0 M LiPF6in EC / EMC 3:7, and discharged to 3 V and charged to 4.3 V. Then, a stable SEI formation environment was created through a formation cycle at 0.1 C for 2 cycles, and then a test was performed at 1 C. The results are shown in Fig. 12 and Table 3.

[0121] Figure 12 shows a graph of discharge capacity according to cycle of a half-cell using Example 1 (Li-GQD) of the present invention and Comparative Example 1 (Pristine) as a negative electrode.

[0122] Distinction Example 1 Comparative Example 1 (Li bare cathode) Capacity retention rate (Li / NCM523 half cell) (at 70% retention) 281 cycles 132 cycles

[0123] As shown in the above Figure 12 and Table 3, the point at which the capacity retention rate reaches 70% is 281 and 132 cycles for Example 1 and Comparative Example 1, respectively, and it can be seen that the life characteristics of the present invention have increased by 2.13 times.

Claims

1. 0-dimensional carbon nanoparticle anion; and An electrode additive for a lithium metal battery comprising an ionic compound composed of lithium cations.

2. An electrode additive for a lithium metal battery, characterized in that in paragraph 1, the zero-dimensional carbon nanoparticle anion is prepared from any one selected from the group consisting of carbon nanofibers, graphene, graphene oxide, carbon nanotubes, fullerene, and carbon black.

3. An electrode additive for a lithium metal battery, characterized in that in the first paragraph, the zero-dimensional carbon nanoparticle anion comprises at least one anionic functional group selected from the group consisting of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group.

4. An electrode additive for a lithium metal battery, characterized in that the zero-dimensional carbon nanoparticle anion and the lithium cation in the first paragraph have a molar ratio of 1:3 to 8.

5. A lithium metal battery electrode comprising an electrode additive for a lithium metal battery according to any one of claims 1 to 4.

6. A lithium metal battery electrode, characterized in that the lithium metal battery electrode additive in the fifth paragraph is contained in an amount of 3 to 25 wt%.

7. A lithium metal battery comprising an electrode for a lithium metal battery according to any one of claims 5 to 6. 8.(A) A step of manufacturing zero-dimensional carbon nanoparticles by mixing and reacting carbon material and an acid solution; and (B) A method for producing an electrode additive for a lithium metal battery, comprising the step of mixing and reacting the above zero-dimensional carbon nanoparticles and a lithium precursor to produce an ionic compound.

9. A method for producing an electrode additive for a lithium metal battery, characterized in that in paragraph 8, the acid solution is 140 to 180 mL for 5 g of the carbon material.

10. A method for producing an electrode additive for a lithium metal battery, characterized in that in the 8th paragraph, the reaction of step (A) is performed at 80 to 130°C for 18 to 30 hours.

11. A method for producing an electrode additive for a lithium metal battery, characterized in that in paragraph 8, the zero-dimensional carbon nanoparticles and the lithium precursor have a molar ratio of lithium to the zero-dimensional carbon nanoparticles of 1:3 to 8.

12. A method for producing an electrode additive for a lithium metal battery, characterized in that in the 8th paragraph, the reaction of step (B) is performed at 15 to 35°C for 18 to 30 hours. 13.(Ⅰ) A step of applying an electrode additive for a lithium metal battery according to any one of paragraphs 1 to 4 to one surface of a lithium metal; (Ⅱ) A step of folding the lithium metal coated with the electrode additive so that the one side faces each other; (Ⅲ) a step of stretching the folded lithium metal; and (Ⅳ) A method for producing a lithium metal electrode, comprising: a step of obtaining a lithium metal electrode by repeating steps (Ⅰ) to (Ⅲ).

14. A method for manufacturing a lithium metal electrode, characterized in that in the 13th paragraph, the step (Ⅲ) is performed by applying a pressure of 0.5 to 3 MPa to the folded lithium metal.

15. A method for manufacturing a lithium metal electrode, characterized in that in the 13th paragraph, the step (Ⅳ) is performed so that the area of ​​the lithium metal electrode is 1.2 to 6 times the area of ​​the lithium metal in the step (Ⅰ).

16. A method for manufacturing a lithium metal electrode, characterized in that steps (Ⅰ) to (Ⅲ) in paragraph 13 are repeated 10 to 50 times.

17. A method for manufacturing a lithium metal electrode, characterized in that, in the 13th paragraph, the lithium metal battery electrode additive is included in an amount of 3 to 25 wt% with respect to 100 wt% of the total lithium metal electrode.

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