Electrode additive, negative electrode for lithium secondary battery containing the same, and method for manufacturing a negative electrode for lithium secondary battery

Abstract

The present invention relates to an electrode additive, a negative electrode for a lithium secondary battery containing the same, and a method for manufacturing a negative electrode for a lithium secondary battery. The electrode additive of the present invention can mitigate damage caused by volume changes in the negative electrode active material and improve the phenomenon of energy density reduction in the battery without a decrease in electrode density. Furthermore, it can dissociate into alkaline cations and carbon-based anions in the electrolyte like an ionic compound, replenish the loss of cations in the electrolyte, and significantly improve capacity maintenance performance.

Description

Technical Field

[0001] The present invention relates to an electrode additive, a negative electrode for a lithium secondary battery containing the same, and a method for manufacturing a negative electrode for a lithium secondary battery.

Background Art

[0002] Lithium secondary batteries have an application range such as existing small electronic devices such as smartphones, new renewable energy storage systems, and energy storage sources that can drive electric vehicles, and their market is gradually expanding. In particular, in order to solve energy and environmental problems, research is actively being conducted to use electric vehicles and renewable energy sources such as solar heat, sunlight, and wind energy, so there is a demand for larger-sized batteries for use in these.

[0003] As a battery that can drive this, a lithium ion secondary battery is the most promising. However, in the case of a lithium ion battery that currently commercially uses graphite as the main negative electrode material of a lithium secondary battery, due to its low theoretical capacity, it should be improved in many aspects in order to satisfy the performance required by the market in the future. In particular, in the case of an electric vehicle that replaces an internal combustion engine vehicle, the distance that can be traveled when the current level of battery is charged once is not satisfactory compared to an internal combustion engine vehicle, so a negative electrode having high energy density and high life performance is required. Therefore, negative electrode active material materials such as silicon (Si), tin (Sn), and germanium (Ge) that can be alloyed with lithium during charging of the battery and dealloyed during discharging, and can exhibit high capacity, have received great attention.

[0004] In particular, while graphite stores one lithium ion for every six carbon atoms, silicon can store 4.4 lithium ions per silicon atom. Therefore, silicon dramatically improves energy density (more than 10 times the capacity of graphite), which is advantageous not only for increasing the driving range of electric vehicles but also for designing rapid battery charging. Furthermore, silicon is an economical and environmentally friendly material. For this reason, silicon is attracting attention as a next-generation anode material that can replace graphite anode materials that have reached their capacity limits and break away from absolute dependence on China for graphite. In fact, it is being used in the form of an additive of about 5% by weight in graphite anode materials.

[0005] However, silicon has the disadvantage of poor lifetime characteristics because its volume repeatedly expands and contracts due to alloying and dealloying during charging and discharging, causing particle cracking and fracture as charging and discharging continue, and the capacity gradually decreases. To solve this problem, research has been conducted on methods such as manufacturing electrodes using the active material oxide, suppressing volume changes through structural improvements of the active material or coating with the active material, and improving the performance of the electrode binder, but these have had little effect.

[0006] Therefore, the present inventors discovered that when a composite of a carbon material containing oxygen-containing functional groups and lithium is introduced into the negative electrode of a lithium secondary battery, it dissociates like an ionic compound, can replenish lithium losses, significantly improves delamination or cracking phenomena due to volume changes of the active material, and improves the electrochemical performance of the lithium secondary battery, thus completing the present invention. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to provide an electrode additive comprising a composite of a carbon material containing an oxygen-containing functional group and lithium, which can be dissociated in the electrolyte, replenish the loss of cations, improve the mechanical strength of the electrode by bonding with a binder, and significantly improve damage due to volume expansion of the negative electrode active material, as well as a negative electrode for a lithium secondary battery comprising the same. [Means for solving the problem]

[0008] One aspect of the present invention provides an electrode additive comprising a composite of a carbon material containing an oxygen-containing functional group and lithium.

[0009] Another aspect of the present invention provides a negative electrode for a lithium secondary battery comprising the electrode additive; and a negative electrode active material.

[0010] Another aspect of the present invention provides a lithium secondary battery including the negative electrode.

[0011] Yet another aspect of the present invention is to provide a capacitor including the negative electrode.

[0012] A further aspect of the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising the steps of (I) mixing a carbon material containing an oxygen-containing functional group with a lithium precursor to produce an electrode additive; (II) adding the electrode additive obtained in step (I) and a negative electrode active material to a solvent to produce a negative electrode slurry; and (III) coating and drying the negative electrode slurry. [Effects of the Invention]

[0013] The electrode additive of the present invention comprises a composite of a carbon material containing oxygen-containing functional groups and lithium, and can significantly improve the phenomenon of electrode density reduction and battery energy density reduction. Furthermore, the composite can be dissociated into alkaline cations and carbon-based anions in the electrolyte, the cations can replenish lithium consumed in the electrolyte, especially at the interface, and can improve capacity and capacity maintenance performance, and the carbon-based anions can improve the dispersion of the binder by binding with the binder, increase the mechanical strength of the electrode, and can significantly improve delamination or cracking phenomena due to silicon volume expansion.

[0014] Furthermore, the electrode additive of the present invention can regulate the segmental mobility of the binder chain and provide sufficient flexibility to withstand volume changes of the silicon electrode during cycling.

[0015] Furthermore, the electrode additive of the present invention can improve the adhesion between components of a silicon-based electrode containing copper foil by forming hydrogen bonds through interaction with the polar groups (-COOH) of the binder using the abundant polar functional groups at its edges. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows a scanning electron microscope (SEM) image of the electrode additive manufactured in Example 1 of the present invention.

[0017] [Figure 2] This figure shows a transmission electron microscope (TEM) image of the electrode additive manufactured in Example 1 of the present invention.

[0018] [Figure 3] This figure shows a scanning electron microscope (SEM) image of Comparative Example 1 (SiO) of the present invention.

[0019] [Figure 4] This figure shows a scanning electron microscope (SEM) image of Comparative Example 2 (Si) of the present invention.

[0020] [Figure 5] It is a diagram showing the charge-discharge curves of the (a) first and (b) third cycles, and (c) long-term life characteristics of the electrode manufactured in Example 1 of the present invention.

[0021] [Figure 6] It is a diagram showing the charge-discharge curves of the (a) first and (b) third cycles, and (c) long-term life characteristics of the electrode manufactured in Example 2 of the present invention.

[0022] [Figure 7] It is a diagram showing the charge-discharge curves of the (a) first and (b) third cycles, and (c) long-term life characteristics of the electrode manufactured in Comparative Example 1 of the present invention.

[0023] [Figure 8] It is a diagram showing the (a) charge-discharge capacity and (b) long-term life characteristics of the electrode manufactured in Example 3 of the present invention.

[0024] [Figure 9] It is a diagram showing the (a) charge-discharge capacity and (b) long-term life characteristics of the electrode manufactured in Comparative Example 2 of the present invention.

[0025] [Figure 10] It is a diagram showing the specific capacity and cross-sectional scanning electron microscope (SEM) image by the cycle of the half-cell using the electrodes of Example 5 and Comparative Example 3 of the present invention.

[0026] [Figure 11] It is a graph showing the specific capacity by the cycle of the half-cell using the electrodes of Examples 6 to ⑦ and Comparative Example 4 of the present invention.

[0027] [Figure 12] It is a graph showing the specific capacity and Coulomb efficiency by the cycle of the half-cell using the electrodes of Example 8 and Comparative Example 5 of the present invention.

[0028] [Figure 13] This figure shows a scanning electron microscope (SEM) image of the electrode manufactured in Example 8 of the present invention.

[0029] [Figure 14] This graph shows (a) lifetime characteristics and (b) rate-limiting characteristics of half-cells using the electrodes of Examples 9 to 10 and Comparative Example 6 of the present invention.

[0030] [Figure 15] (a, c) are photographic images of the binder (PAA 70 wt% + additive 30 wt%) containing 100 wt% PAA and (b, d) the electrode additive produced in Example 1 of the present invention, after which (a, b) and (c, d) are images of the binder after bending.

[0031] [Figure 16] This figure shows the tensile test results and photographic images of the process for a binder (PAA 70 wt% + additive 30 wt%) containing 100 wt% PAA and the electrode additive manufactured in Example 1 of the present invention.

[0032] [Modes for carrying out the invention]

[0033] When describing the present invention, if a specific description of related known technology is deemed to obscure the gist of the invention, such detailed description will be omitted. Where "includes," "has," "constitutes," etc., as used herein, other parts may be added unless "only" is used. Furthermore, terms such as "includes" or "has" are intended to specify the existence of features, numbers, stages, components, or combinations thereof described in the specification, and should not be understood as excluding the existence or possibility of adding one or more other features, numbers, stages, components, or combinations thereof. Also, when a component is expressed singularly, it may include multiple components unless otherwise explicitly stated.

[0034] The present invention will be described in more detail below with reference to the accompanying drawings and examples.

[0035] The present invention provides an electrode additive comprising a composite of a carbon material containing an oxygen-containing functional group and lithium.

[0036] Generally, electrodes incorporating carbon materials were used to improve electrical conductivity. However, carbon materials reduced the density of the electrodes, leading to a decrease in the energy density of the batteries containing them. Furthermore, the volume change of the negative electrode active material during charging and discharging damaged the electron transport pathway, rendering the battery inoperable.

[0037] Therefore, in this invention, an electrode additive comprising a composite of a carbon material containing oxygen-containing functional groups and lithium has been manufactured. The electrode additive of this invention can be applied to electrodes and can significantly improve the phenomenon of energy density reduction in batteries containing it without reducing the density of the electrodes, and can effectively mitigate volume changes due to charging and discharging when mixed with the negative electrode active material. Furthermore, the electrode additive of this invention has the advantages of excellent mechanical strength and conductivity and a high specific surface area.

[0038] The lithium may bond with the oxygen-containing functional group. More specifically, the oxygen-containing functional group may exist as an anionic functional group and thus can bond with lithium cations, which are ions of lithium. Through this, the electrode additive of the present invention can dissociate into lithium cations and carbon-based anions in the electrolyte like an ionic compound. The lithium cations increase the cation flux between the electrode and the electrolyte interface, promote smooth electrochemical reactions of the electrode, and replenish the loss of cations in the electrolyte due to the formation of a surface film. Therefore, electrodes containing these cations can significantly improve the capacity maintenance performance of the battery.

[0039] The oxygen-containing functional group may be one or more of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group, and more preferably one or more of a hydroxyl group, a carboxyl group, and an ether group.

[0040] The carbon material may be one or more of graphene quantum dots, graphene, graphene oxide, carbon black, carbon nanotubes, graphite, fullerene, and carbon nanofibers, more preferably one or more of graphene quantum dots, graphene oxide, and carbon nanofibers, and most preferably graphene quantum dots.

[0041] In particular, the carbon material may be graphene quantum dots, which, unlike other carbon materials, have the advantage of excellent conductivity and the ability to improve the mechanical properties between electrochemical evaluations of electrodes.

[0042] The lithium may be present in an amount of 8% to 20% by weight, preferably 13% to 18% by weight, relative to 100% by weight of the entire electrode additive. If the lithium content is below the lower limit, it is difficult to expect an increase in the capacity maintenance performance of the battery containing it. On the other hand, if the lithium content exceeds the upper limit, the reliability of the electrode additive may decrease due to residual impurities in the additive during the synthesis process, which may hinder the effect of improving electrical conductivity.

[0043] The size of the carbon material may be 12 nm or less. If the size of the carbon material exceeds 12 nm, it may increase the π-π interaction between the carbon materials, which is undesirable because it can lead to aggregation between the carbon materials and reduce the reliability of the device. The lower limit of the size of the carbon material is not greatly restricted, but it may be 2 nm because when it is less than 2 nm, not only does the number of cations moving in the carbon material decrease, but the lattice energy also decreases, which can lead to a decrease in ionic conductivity.

[0044] Another aspect of the present invention provides a negative electrode for a lithium secondary battery including the electrode additive; and a negative electrode active material.

[0045] The negative electrode active material may include silicon (Si), tin (Sn), germanium (Ge), their oxides, their alloys, or combinations thereof.

[0046] The oxides of silicon (Si), tin (Sn), and germanium (Ge) may mean silicon oxides (SiOx, 0 < x ≤ 2), tin oxides (SnOy, 0 < y ≤ 2), and germanium oxides (GeOz, 0 < z ≤ 2). <00,00193> The alloys of silicon (Si), tin (Sn), and germanium (Ge) may mean silicon alloys (Si-A), tin alloys (Sn-B), and germanium alloys (Ge-C). At this time, A, B, and C may each be one or more of metals and metalloids. For example, they may be two or more metalloids, two or more metals, one metal, one metalloid, or one or more metals and one or more metalloids.

[0048] In the silicon alloy (Si-A), A may be any one or more of alkali metals, alkaline earth metals, transition metals, post-transition metals, and metalloids excluding silicon.

[0049] In the tin alloy (Sn-B), B may be any one or more of alkali metals, alkaline earth metals, transition metals, metalloids, and post-transition metals excluding tin.

[0050] In the germanium alloy (Ge-C), C may be any one or more of alkali metals, alkaline earth metals, transition metals, post-transition metals, and metalloids excluding germanium.

[0051] The weight ratio of the negative electrode active material to the electrode additive may be 100:1 to 8, preferably 100:2 to 5. If the electrode additive is less than the lower limit relative to 100 units of weight of the negative electrode active material, the effect of suppressing electrode volume change and improving capacity maintenance performance cannot be expected. On the other hand, if the electrode additive is included in an amount exceeding the upper limit, the amount dissociated will not increase further, thus reducing the energy density. Furthermore, since the electrode additive is not uniformly distributed within the negative electrode, aggregation within the electrode may occur, which can increase resistance during the intercalation and deintercalation processes of lithium ions in the battery.

[0052] The negative electrode for the lithium secondary battery may further contain a binder. The binder can be any polymer binder used in the industry, such as polyvinylidene fluoride, polyethylene oxide, polyacrylic acid, polyaniline, polystyrene, or mixtures thereof.

[0053] Generally, binders were introduced into electrodes to improve the phenomenon where capacity decreases with repeated charging and discharging due to the physical degradation of the material caused by rapid volume changes of the active material during charging and discharging, and the electrical degradation of the electrodes. However, conventional binders have low electrical conductivity, which reduces the electrical conductivity of the electrodes and leads to a decrease in energy density. Furthermore, their lack of mechanical strength and flexibility makes it difficult to fully accommodate large volume changes in silicon.

[0054] When the negative electrode for lithium secondary batteries of the present invention further contains a binder, the binder can bind to carbon-based anions formed by the dissociation of the electrode additive in the electrolyte. The binder's dispersion is improved by binding with carbon-based anions, which not only improves the mechanical strength of the electrode containing it but also improves its electrical conductivity. This significantly improves the electron transport pathway, which is damaged or lost due to the expansion and contraction of the negative electrode active material during charging and discharging, compared to when the binder is used alone.

[0055] The binder may be present in an amount of 5% to 20% by weight relative to 100% by weight of the entire negative electrode for the lithium secondary battery. If the binder content is below the lower limit, it is difficult to expect a buffering effect on the rapid volume change of the active material due to the addition of the binder. On the other hand, if the binder content exceeds the upper limit, the carbon-based anions will not bind sufficiently, and dispersion may decrease.

[0056] The negative electrode for the lithium secondary battery may further contain a conductive material. The conductive material is used to impart conductivity to the electrode and can be any electronically conductive material that does not cause a chemical change in the battery in which it is constructed. Examples of such materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, and carbon fibers; metallic materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0057] The conductive material may be included in an amount of 5% to 15% by weight relative to 100% by weight of the entire negative electrode for the lithium secondary battery. If the content of the conductive material is below the lower limit, it is difficult to expect an increase in conductivity due to the addition of the conductive material, while if the content of the conductive material exceeds the upper limit, the content of the negative electrode active material will relatively decrease, which may reduce the capacity of the lithium secondary battery.

[0058] Another aspect of the present invention provides a lithium secondary battery including the negative electrode.

[0059] Yet another aspect of the present invention is to provide a capacitor including the negative electrode.

[0060] A further aspect of the present invention is that an apparatus including the negative electrode can be provided, which may be any one of communication equipment, an energy storage system (ESS), and a means of transport.

[0061] A further aspect of the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, comprising the steps of (I) mixing a carbon material containing an oxygen-containing functional group with a lithium precursor to produce an electrode additive; (II) adding the electrode additive obtained in step (I) and a negative electrode active material to a solvent to produce a negative electrode slurry; and (III) coating and drying the negative electrode slurry.

[0062] The present invention's method for manufacturing a negative electrode for lithium secondary batteries uses the above-mentioned electrode additive, resulting in excellent dispersion capabilities in aqueous solutions. This allows for the direct use of conventional negative electrode material processes and enables a reduction in the number of steps involved.

[0063] The following describes in more detail each step of the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention.

[0064] (I) A step of mixing a carbon material containing oxygen-containing functional groups with a lithium precursor to produce an electrode additive.

[0065] First, a carbon material containing oxygen-containing functional groups is mixed with a lithium precursor to produce a composite of carbon material and lithium.

[0066] The oxygen-containing functional group may be one or more of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group, and more preferably one or more of a hydroxyl group, a carboxyl group, and an ether group.

[0067] The carbon material may be one or more of graphene quantum dots, graphene, graphene oxide, carbon black, carbon nanotubes, graphite, fullerene, and carbon nanofibers, and more preferably one or more of graphene quantum dots, graphene oxide, and carbon nanofibers.

[0068] When the carbon material is a graphene quantum dot, the graphene quantum dot may be produced by a method including: (a) mixing a carbon material and an acid solution to produce a mixed solution; and (b) hydrothermally synthesizing the mixed solution at 80°C to 120°C for 5 to 36 hours.

[0069] The carbon material may be any one or more of graphene, graphene oxide, carbon black, carbon nanotubes, graphite, fullerenes, and carbon nanofibers.

[0070] The size of the carbon material may be 12 nm or less.

[0071] The lithium precursor may be any one or more of lithium hydroxide, lithium carbonate, lithium sulfate, lithium oxide, and lithium chloride.

[0072] Based on 100% by weight of the whole electrode additive, the lithium may be contained in an amount of 8% to 20% by weight, preferably 13% to 18% by weight.

[0073] (II) A step of adding the electrode additive obtained in the step (I) and the negative electrode active material to a solvent to produce a negative electrode slurry

[0074] The solvent may be ethanol, toluene, heptane, butyrate, xylene, hexane, or a combination thereof, but is not greatly limited thereto.

[0075] The negative electrode active material may include silicon (Si), tin (Sn), germanium (Ge), their oxides, their alloys, or a combination thereof.

[0076] The oxides of silicon (Si), tin (Sn), and germanium (Ge) may mean silicon oxide (SiOx, 0 < x ≤ 2), tin oxide (SnOy, 0 < y ≤ 2), and germanium oxide (GeOz, 0 < z ≤ 2).

[0077] The aforementioned alloys of silicon (Si), tin (Sn), and germanium (Ge) may refer to silicon alloys (Si-A), tin alloys (Sn-B), and germanium alloys (Ge-C). In this case, A, B, and C may each be one or more of metals and quasimetallic materials, for example, two or more quasimetallic materials, two or more metals, one metal, one quasimetallic material, or one or more metals and one or more quasimetallic materials.

[0078] The weight ratio of the negative electrode active material to the electrode additive may be 100:1 to 8, preferably 100:2 to 5.

[0079] The negative electrode slurry may further contain a binder. The binder may be one or more of polyvinylidene fluoride, polyethylene oxide, polyacrylic acid, polyaniline, and polystyrene.

[0080] The binder may be included in an amount of 5% to 20% by weight relative to 100% by weight of the entire negative electrode for the lithium secondary battery.

[0081] The negative electrode slurry may further contain a conductive material. The conductive material may be one or more of the following: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, and carbon fibers; metallic materials such as metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials comprising mixtures thereof.

[0082] The conductive material may be included in an amount of 5% to 15% by weight relative to 100% by weight of the entire negative electrode for the lithium secondary battery.

[0083] (III) Step of applying and drying the negative electrode slurry.

[0084] Next, the negative electrode slurry is applied to the current collector and dried to manufacture the negative electrode.

[0085] The drying may be carried out at 80°C to 200°C for 30 minutes to 5 hours, preferably at 100°C to 150°C for 1 hour to 3 hours. If the drying temperature and time are below the lower limit, the solvent will not evaporate sufficiently, which may lead to a decrease in electrode performance or the occurrence of side reactions. On the other hand, if the drying temperature and time exceed the upper limit, the rapid drying of the organic solvent may result in a non-uniform morphology of the manufactured electrode.

[0086] According to the most preferred embodiment of the present invention, the carbon material is graphene quantum dots containing hydroxyl and carboxyl groups, the lithium precursor is lithium hydroxide, the lithium is present in an amount of 13% to 18% by weight relative to 100% by weight of the total electrode additive, the size of the carbon material is 12 nm or less, the negative electrode active material is silicon monoxide (SiO), the negative electrode active material and the electrode additive are mixed in a weight ratio of 100:2 to 5, the drying is carried out at 100°C to 150°C for 1 to 3 hours, and polyacrylic acid may be present as a polymer binder in an amount of 5% to 20% by weight relative to 100% by weight of the total negative electrode for lithium secondary battery.

[0087] When all the conditions of the most preferred embodiment described above are satisfied, the capacity of the battery using the manufactured negative electrode is maintained at an excellent level during 300 charge-discharge cycles, and it also exhibits excellent mechanical strength and stability.

[0088] However, if any of the above conditions are not met, it was observed that the capacity of the battery using the manufactured negative electrode decreases after 100 charge-discharge cycles, and a portion of the negative electrode deteriorates after 300 charge-discharge cycles. [Examples]

[0089] The present invention will be described in detail below with reference to specific examples. However, each example of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to each example described below. Each example of this specification is provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0090] <Example 1. SiO-3wt%>

[0091] (1) Manufacturing of electrode additives

[0092] Graphene oxide (GO) containing hydroxyl and carboxyl groups was dispersed in a mixed solution of nitric acid and sulfuric acid in a 1:3 volume ratio. The mixture was heated at 100°C and stirred for a certain period of time, and graphene quantum dots with a size of 12 nm or less were produced by hydrothermal synthesis over 24 hours. 1 M lithium hydroxide was added to the solution after the above reaction was completed to produce an ionic compound (carbon material-lithium composite) composed of carbon-based anions and lithium cations. Ethanol was mixed to remove impurities, and repeated centrifugation was performed to remove the precipitate. The supernatant of the solution from which the precipitate had been removed was dried to obtain electrode additive powder. At this time, lithium was present at 16% by weight relative to 100% by weight of the total electrode additive powder.

[0093] (2) Manufacturing of electrodes

[0094] 0.4 g of silicon oxide (SiO) powder was dry-mixed as the negative electrode active material to homogenize the particle size of the negative electrode active material. 0.05 g of carbon black powder was added to the dry-mixed powder and dry-mixed again. Dry mixing was performed using a mortar and pestle or a paint shaker.

[0095] A binder solution prepared by dissolving 0.05 g of polyacrylic acid in distilled water is mixed with 0.015 g of the obtained electrode additive, and then mixed with the dry-mixed active material and conductive material powder mixture. After adjusting the viscosity of the negative electrode slurry through the solvent of the binder solution used, the electrode slurry is placed on a copper foil and cast through a doctor blade. The cast copper foil is dried in an air atmosphere at 80°C and then rolled. The rolled copper foil is vacuum-dried at 120°C for more than 2 hours to produce the negative electrode.

[0096] <Example 2. SiO-1.5wt%>

[0097] The negative electrode was manufactured in the same manner as in Example 1, except that an electrode additive equivalent to 1.5 wt% of the electrode's weight was used.

[0098] <Example 3. Si-3wt%>

[0099] The negative electrode was manufactured using the same method as in Example 1, except that silicon (Si) was used as the negative electrode active material.

[0100] Table 1 below shows the content of the negative electrodes produced in Examples 1 to 3.

[0101] [Table 1]

[0102] <Example 4>

[0103] A negative electrode was prepared by mixing a C-SiO active material (micro-size, intermediate particle size = 7 μm), a conductive material (carbon black), a binder (PAA), and the electrode additive produced in Example 1 in a weight ratio of 80:10:7.7:2.3. At this time, the electrode loading level was 1.5 mg / cm². 2 That was the case.

[0104] <Example 5. micro C-SiO>

[0105] The negative electrode was manufactured in the same manner as in Example 1, and the loading level was set to 1.7 mg / cm². 2 I did.

[0106] <Example 6. micro Si>

[0107] The negative electrode was manufactured by mixing the active material Si (micro-size), conductive material (carbon black), binder (PAA), and the electrode additive produced in Example 1 in a weight ratio of 80:10:7.7:2.3.

[0108] <Example 7. micro Si>

[0109] The negative electrode was manufactured by mixing the active material Si (micro-size), conductive material (carbon black), binder (PAA), and the electrode additive produced in Example 1 in a weight ratio of 80:10:8.7:1.3.

[0110] <Example 8>

[0111] A negative electrode was manufactured by mixing a C-SiO active material (micro-size, intermediate particle size = 13 μm), a conductive material (carbon black), a binder (CMC), and the electrode additive produced in Example 1 in a weight ratio of 75:10:12.5:2.5.

[0112] <Example 9>

[0113] A negative electrode was manufactured by mixing the active material Si (submicro-size, intermediate particle size = 800 nm), conductive material (carbon black), binder (PAA), and the electrode additive manufactured in Example 1 in a weight ratio of 60:20:17:3.

[0114] <Example 10>

[0115] A negative electrode was manufactured by mixing the active material Si (submicro-size, intermediate particle size = 800 nm), conductive material (carbon black), binder (PAA), and the electrode additive produced in Example 1 in a weight ratio of 60:20:18.5:1.5.

[0116] <Comparative example 1.SiO>

[0117] The electrodes were manufactured in the same manner as in Example 1, except that no electrode additives were used.

[0118] <Comparative Example 2.Si>

[0119] The electrode was manufactured using the same method as in Comparative Example 1, except that silicon powder was used as the negative electrode active material.

[0120] <Comparative Example 3>

[0121] A negative electrode was manufactured by mixing a C-SiO active material (micro-size, intermediate particle size = 7 μm), a conductive material (carbon black), and a binder (PAA) in a weight ratio of 80:10:10.

[0122] <Comparative example 4.micro Si>

[0123] The negative electrode was manufactured by mixing the active material Si (micro-sized), conductive material (carbon black), and binder (PAA) in a weight ratio of 80:10:10.

[0124] <Comparative Example 5>

[0125] A negative electrode was manufactured by mixing a C-SiO active material (micro-size, intermediate particle size = 13 μm), a conductive material (carbon black), and a binder (CMC) in a weight ratio of 75:10:15.

[0126] <Comparative Example 6>

[0127] A negative electrode was manufactured by mixing Si active material (submicro-size, intermediate particle size = 800 nm), conductive material (carbon black), and binder (PAA) in a weight ratio of 60:20:20.

[0128] <Experimental Example 1: Analysis of Electrode Morphology>

[0129] Figure 1 shows a scanning electron microscope (SEM) image of the electrode additive manufactured in Example 1 of the present invention.

[0130] Figure 2 shows a transmission electron microscope (TEM) image of the electrode additive manufactured in Example 1 of the present invention.

[0131] Figure 3 shows a scanning electron microscope (SEM) image of Comparative Example 1 (SiO) of the present invention.

[0132] Figure 4 shows a scanning electron microscope (SEM) image of Comparative Example 2 (Si) of the present invention.

[0133] Referring to Figures 1 and 2 above, it can be seen that in the electrode additive produced in Example 1 of the present invention, the carbon material consists of particles at the 10 nm level. On the other hand, referring to Figures 3 and 4 above, it can be seen that the size of the silicon oxide in Comparative Example 1 is 5 μm to 10 μm, and the average size of the silicon powder in Comparative Example 2 is 5 μm to 7 μm.

[0134] <Experimental Example 2. Analysis of Capacity and Lifetime Characteristics>

[0135] The secondary batteries using electrodes manufactured in Examples 1 to 2 and Comparative Examples 1 to 2 underwent a chemical conversion process during a constant voltage charging process with a constant current of 65 mA and a current of 13 mA at 0.01 V. This was followed by two cycles of a discharge process with a constant current of 65 mA, and then a constant voltage charging process with a constant current of 650 mA and a current of 13 mA at 0.01 V, and finally a discharge process with a constant current of 650 mA. The charge-discharge characteristics were then analyzed, and the results are shown in Figures 5 to 7.

[0136] Figure 5 shows (a) the charge-discharge curves for the first and third cycles, and (c) the long-term life characteristics of the electrode manufactured in Example 1 of the present invention.

[0137] Figure 6 shows (a) the charge-discharge curves for the first and third cycles, and (c) the long-term life characteristics of the electrode manufactured in Example 2 of the present invention.

[0138] Figure 7 shows (a) the charge-discharge curves for the first and third cycles, and (c) the long-term life characteristics of the electrode manufactured in Comparative Example 1 of the present invention.

[0139] Referring to Figure 7(a) above, it can be seen that the charging capacity of the electrode manufactured in Comparative Example 1, which uses only silicon oxide powder, is 2229 mAh / g and the discharge capacity is 1645.4 mAh / g. On the other hand, referring to Figures 5(a) and 6(a) above, the charging capacity / discharge capacity of the electrodes manufactured in Example 1 and Example 2 are 2121.2 mAh / g, respectively. -1 / 1571.3mAhg -1 and 2166.6mAhg -1 / 1633.1mAhg -1 This shows that the charge and discharge efficiency is even higher compared to Comparative Example 1.

[0140] Furthermore, referring to Figures 5(b), 6(b), and 7(b) above, it can be seen that in the third charge-discharge curve, the charge-discharge efficiency in Example 1 (96.6%) and Example 2 (96.0%) of the present invention is significantly higher compared to the charge-discharge efficiency of Comparative Example 1 (83.9%).

[0141] Compared to the first cycle, the charge-discharge efficiency of the negative electrode of the present invention is confirmed to be even better in the third cycle. This is because, in the case of the silicon oxide used as the negative electrode active material in the above examples and comparative examples, carbon-coated silicon oxide was used, and the improvement in electrode conductivity due to the addition of the electrode additive of the present invention is directly reflected in the third cycle, which is performed at a relatively higher current than the conversion stage where charge-discharge is performed at a low current.

[0142] Referring to Figure 7(c) above, it can be seen that in the electrode of Comparative Example 1, which used only silicon oxide powder, the capacity rapidly decreased to less than half after 100 cycling cycles. This is because the rapid volume change of the silicon oxide powder caused delamination and pulverization within the electrode, which resulted in the collapse of conductive pathways within the electrode and a decrease in capacity. On the other hand, referring to Figures 5(c) and 6(c) above, it can be confirmed that the capacity of the electrodes manufactured in Examples 1 and 2 was maintained over a long period of cycling. Through this, it was confirmed that the electrode additive of the present invention can effectively buffer the rapid volume change of silicon oxide and maintain capacity over a long period of cycling by acting as a sustained electron transport pathway.

[0143] For batteries using electrodes manufactured in Examples 1 to 2 and Comparative Examples 1 to 2, a chemical conversion process was performed using a constant voltage charging process with a constant current of 125 mA and a current of 25 mA at 0.01 V. This was followed by two cycles of a discharge process with a constant current of 125 mA, and then a constant voltage charging process with a constant current of 500 mA and a current of 25 mA at 0.01 V, and a discharge process with a constant current of 500 mA. The results are shown in Figures 8 to 9.

[0144] Figure 8 shows (a) the charge / discharge capacity and (b) the long-term life characteristics of the electrode manufactured in Example 3 of the present invention.

[0145] Figure 9 shows (a) the charge / discharge capacity and (b) the long-term life characteristics of the electrode manufactured in Comparative Example 2 of the present invention.

[0146] Referring to Figures 8(a) and 9(a), it can be seen that the charging capacities of the electrodes produced in Example 3, which contained the electrode additive of the present invention, and Comparative Example 2, which contained only silicon powder, were 3692.2 mAh / g and 3453.8 mAh / g, respectively, and the discharging capacities were 3326.4 mAh / g and 2724.2 mAh / g, respectively. Through this, it can be confirmed that the electrode additive of the present invention can significantly improve the capacity and charge / discharge efficiency of the electrode.

[0147] Referring to Figures 8(b) and 9(b), it can be seen that in the electrode of Comparative Example 2, which contains only silicon powder, the capacity decreases to half of its initial value after 100 cycling cycles, indicating a decline in capacity retention characteristics. On the other hand, in the electrode of Example 3, which contains the electrode additive of the present invention, the capacity is maintained at an excellent level even after 100 cycling cycles.

[0148] Through this, it can be seen that the electrode additive of the present invention has excellent conductivity, effectively mitigates volume changes of silicon active material, improves capacity maintenance characteristics, and has the property of dissociating like an ionic compound in the electrolyte, thereby improving capacity and charge / discharge efficiency.

[0149] <Experimental Example 3>

[0150] The capacity retention rate of batteries using electrodes manufactured in Example 4 and Comparative Example 3 was measured, and the results are shown in Table 3 below. In both the electrodes manufactured in Example 4 and Comparative Example 3, the first cycle capacity began to appear at 1,600 mAh / g or higher, and in the electrode of Example 4, the capacity stabilized after 15 to 17 cycles.

[0151] [Table 2]

[0152] As shown in Table 2 above, the battery using the electrodes of Example 4 of the present invention has a capacity of 1,200 mAh after 100 cycles. / g The above specific capacity (1,000mAh at 400 cycles) / g In contrast to Comparative Example 3, the system did not operate any further, and an immediate decrease in capacity was observed.

[0153] <Experimental Example 4>

[0154] Half cells using 1M LiPF6in EC:EMC:DEC (2:2:5, v / v / v) + 10 wt% FEC as the electrolyte were driven at a speed of 0.5C using the electrodes of Example 5 and Comparative Example 3, respectively. Figure 10 shows the specific capacity and cross-sectional scanning electron microscope (SEM) images obtained by the cycle.

[0155] Figure 10 shows scanning electron microscope (SEM) images of the specific capacitance and cross-section of a half-cell cycle using the electrodes of Example 5 and Comparative Example 3 of the present invention.

[0156] As shown in Figure 10 above, in the electrode of Comparative Example 3, the specific capacity decreased rapidly as the number of cycles increased, dendrites formed on the electrode, and it exhibited a non-uniform surface, resulting in very poor lifetime characteristics. However, in the electrode of Example 5, even as the number of cycles increased, the specific capacity was maintained within an excellent range, and the electrode layer was maintained uniformly at the same level as the initial state.

[0157]

[0158] Half cells using 1M LiPF6in EC:EMC:DEC (2:2:5, v / v / v) + 10 wt% FEC as the electrolyte were driven at a speed of 0.5C using the electrodes of Examples 6 and 7 and Comparative Example 4, respectively. The specific capacity by cycle is shown in Figure 11 and Table 3 below.

[0159] Figure 11 is a graph showing the specific capacitance of half-cells cycled using the electrodes of Examples 6 to 7 and Comparative Example 4 of the present invention.

[0160] [Table 3]

[0161] As shown in Figure 11 and Table 3 above, in the electrode of Comparative Example 4, the specific capacity decreased sharply as the number of cycles increased, and the lifespan characteristics were very poor. However, in the electrodes of Examples 6 and 7, the specific capacity was maintained within an excellent range even when the number of cycles increased, and it was confirmed that the lifespan characteristics were very good. Furthermore, among Examples 6 and 7, Example 7, which had an additive ratio of 1.3%, showed even better lifespan characteristics.

[0162] <Experimental Example 5>

[0163] Half cells using 1M LiPF6in EC:EMC:DEC (2:2:5, v / v / v) + 10 wt% FEC as the electrolyte were driven at a speed of 0.5C using the electrodes of Example 8 and Comparative Example 5, respectively. The specific capacity and scanning electron microscope (SEM) images of the cross-section after cycling are shown in Figures 12 and 13.

[0164] Figure 12 is a graph showing the specific capacity and Coulomb efficiency of half-cells cycled using the electrodes of Example 8 and Comparative Example 5 of the present invention.

[0165] Figure 13 shows a scanning electron microscope (SEM) image of the electrode manufactured in Example 8 of the present invention.

[0166] [Table 4]

[0167] As shown in Figures 12 to 13 and Table 5 above, even in electrochemical evaluation using an active material with a relatively large particle size, where the intermediate particle size of the silicon anode material is 13 μm (micro-size), it was confirmed that the lifetime characteristics in Example 8 were excellent.

[0168] <Experimental Example 6>

[0169] Half cells using 1M LiPF6in EC:EMC:DEC (2:2:5, v / v / v) + 10 wt% FEC as the electrolyte were driven at a speed of 0.5C using the electrodes of Examples 9 to 10 and Comparative Example 6, respectively. The specific capacity by cycle is shown in Figure 14 and Table 6 below.

[0170] Figure 14 is a graph showing (a) lifetime characteristics and (b) rate-limiting characteristics of half-cells using the electrodes of Examples 9 to 10 and Comparative Example 6 of the present invention.

[0171] [Table 5]

[0172] As shown in Figure 14 and Table 6 above, the lifetime characteristics of Example 10 were confirmed to be more than 1.75 times better than those of Comparative Example 6. Furthermore, electrochemical evaluations were performed at two different charge-discharge rates of 0.5 and 1 c-rate, and it was confirmed that the discharge ratio capacity of Example 10 was far superior under both conditions.

[0173] <Example of experiment> 7 >

[0174] To confirm whether the electrode additive of the present invention can impart flexibility to the binder, the electrode additive manufactured in Example 1 was mixed with PAA, a conventional binder, in a weight ratio of 70:30, and the flexibility was compared and analyzed with that when only PAA was used. The results are shown in Figures 15 and 16.

[0175] Figure 15 shows photographic images of (a, b) and (c, d) the binder after bending, after manufacturing (a, c) 100 wt% PAA and (b, d) an electrode additive manufactured in Example 1 of the present invention (PAA 70 wt% + additive 30 wt%).

[0176] As shown in Figure 15 above, when PAA alone is used as a binder, it breaks immediately when bent, and no flexibility is exhibited at all. However, when the electrode additive of the present invention is introduced into the binder, it does not break even when bent, maintaining its original shape, and it was confirmed that the flexibility has been significantly improved.

[0177] Figure 16 shows the tensile test results and photographic images of the process for a binder (PAA 70 wt% + additive 30 wt%) containing 100 wt% PAA and the electrode additive produced in Example 1 of the present invention.

[0178] As shown in Figure 16 above, the tensile strength was evaluated under the same conditions for PAA alone and PAA with the electrode additive of the present invention. When PAA was used alone, the tensile deformation rate was 1%, and it broke early, so no flexibility was observed at all. However, in the case of the binder with the electrode additive of the present invention, the tensile deformation rate was 400%. Through this, it was confirmed that the electrode additive of the present invention can adjust the segmental mobility of the binder chain and provide sufficient flexibility to withstand volume changes of the silicon electrode during cycling.

Claims

1. An electrode additive comprising a composite of a carbon material containing oxygen-containing functional groups and lithium.

2. The electrode additive according to claim 1, characterized in that the lithium is bonded to the oxygen-containing functional group.

3. The electrode additive according to claim 1, characterized in that the oxygen-containing functional group is one or more of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group.

4. The electrode additive according to claim 1, characterized in that the carbon material is one or more of graphene quantum dots, graphene, graphene oxide, carbon black, carbon nanotubes, graphite, fullerene, and carbon nanofibers.

5. The electrode additive according to claim 1, characterized in that the lithium is contained in an amount of 8% to 20% by weight relative to 100% by weight of the entire electrode additive.

6. The electrode additive according to claim 1, characterized in that the size of the carbon material is 12 nm or less.

7. A negative electrode for a lithium secondary battery comprising an electrode additive according to any one of claims 1 to 6; and a negative electrode active material.

8. The negative electrode for a lithium secondary battery according to claim 7, characterized in that the negative electrode active material contains one or more of silicon (Si), tin (Sn), germanium (Ge), oxides thereof, alloys thereof, and combinations thereof.

9. The negative electrode for a lithium secondary battery according to claim 7, characterized in that the weight ratio of the negative electrode active material and the electrode additive is 100:1 to 8.

10. The negative electrode for a lithium secondary battery according to claim 7, further comprising a binder.

11. The negative electrode for a lithium secondary battery according to claim 7, further comprising a conductive material.

12. A lithium secondary battery comprising a negative electrode according to any one of claims 7 to 11.

13. A capacitor including a negative electrode according to any one of claims 7 to 11.

14. (I) A step of mixing a carbon material containing oxygen-containing functional groups with a lithium precursor to produce an electrode additive; (II) A step of adding the electrode additive and negative electrode active material obtained in step (I) to the solvent to produce a negative electrode slurry; and (III) A method for manufacturing a negative electrode for a lithium secondary battery, comprising the step of applying and drying the negative electrode slurry.

15. The method for producing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the oxygen-containing functional group is one or more of a hydroxyl group, an ether group, an aldehyde group, an epoxy group, an amide group, a carboxyl group, and a ketone group.

16. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the carbon material is one or more of graphene quantum dots, graphene, graphene oxide, carbon black, carbon nanotubes, graphite, fullerene, and carbon nanofibers.

17. The method for producing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the lithium precursor is one or more of lithium hydroxide, lithium carbonate, lithium sulfate, lithium oxide, and lithium chloride.

18. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the lithium is contained in an amount of 8% to 20% by weight relative to 100% by weight of the total electrode additive.

19. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the weight ratio of the negative electrode active material and the electrode additive is 100:1 to 8.

20. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the negative electrode slurry further comprises a binder.

21. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the negative electrode slurry further contains a conductive material.

22. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 14, characterized in that the drying is carried out at 80°C to 200°C for 30 minutes to 5 hours.

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