Method for manufacturing lithium silicon oxide composites

Abstract

The present invention relates to a method for producing lithium silicon oxide composites in which gas generation is suppressed when an aqueous slurry is applied, wherein silicon or silicon oxide (SiO₂) is added to a lithium compound-containing solution under an inert gas atmosphere. x , 0

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0075099 filed on June 12, 2023, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a method for producing a lithium silicon oxide composite in which gas generation is suppressed when an aqueous slurry is applied.

Background Art

[0003] Recently, as the application fields of lithium secondary batteries have rapidly expanded not only to power supply for electronic devices such as electric, electronic, communication, and computers but also to power storage and supply for large-scale devices such as automobiles and power storage devices, the need for high-capacity, high-output, and high-stability lithium secondary batteries has been increasing.

[0004] A lithium secondary battery is generally manufactured by applying a slurry in which a positive electrode material or a negative electrode material capable of inserting and desorbing lithium ions or a negative electrode material capable of occluding and releasing lithium ions, and optionally a binder and a conductive material, are mixed, to a positive electrode current collector and a negative electrode current collector respectively, removing the solvent by heat or the like to produce a positive electrode and a negative electrode, laminating these on both sides of a separator to form an electrode current collector of a predetermined shape, and then inserting this electrode current collector and a non-aqueous electrolyte into a battery case.

[0005] Graphite-based negative electrode materials, which are representative negative electrode materials, are excellent in structural stability even during insertion and desorption of lithium and show stable capacity retention characteristics even in long cycles, but their low theoretical capacity (350 mAh / g for LiC6) is not suitable as a high-capacity, high-output material currently required. Therefore, silicon-based negative electrode materials such as silicon and silicon oxide have a low reduction potential with lithium, a large abundance, and a theoretical capacity about 10 times higher than that of graphite (2700 to 4200 mAh / g for Li 4.4Because of its properties, silicon (Si) is attracting attention as a negative electrode material for next-generation lithium-ion batteries. However, despite these advantages, silicon-based negative electrode materials consume about three times more lithium than graphite-based negative electrode materials. When lithium-ion batteries using silicon-based negative electrode materials are charged and discharged, volume expansion and surface side reactions prevent a large amount of lithium inserted into the negative electrode from returning to the positive electrode during initial charging, resulting in a problem of large initial irreversible capacity.

[0006] Also, in particular, silicon oxide (SiO x In the case of particles, various methods have been attempted to improve initial efficiency by doping with Mg or prelithiating silicon oxide particles with Li, in order to solve the problem of initial efficiency due to irreversible reactions of Li ions. However, when using this to manufacture a negative electrode material slurry in an aqueous process, the Li2O generated inside the prelithiated silicon oxide particles reacts with H2O to produce LiOH byproducts. This reduces the viscosity of the slurry, generates hydrogen, and deteriorates the coating properties of the slurry. As a result, problems of reduced adhesion between the negative electrode material layer and the current collector and volume expansion still exist.

[0007] Therefore, there is a need to develop an anode material that exhibits excellent initial capacity and capacity retention, minimal viscosity changes during the manufacturing of the anode material slurry using an aqueous process, suppresses hydrogen generation, and exhibits suppressed volume expansion during charging and discharging of the anode using this material. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] KR10-2014-0091388A [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention is derived to solve the problems of the prior art, and provides a method for manufacturing a lithium silicon oxide composite useful as a negative electrode material, which has excellent initial capacity and capacity retention rate, has almost no change in viscosity during the production of slurry by an aqueous process, and suppresses the generation of hydrogen.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention provides a method for manufacturing a lithium silicon oxide composite.

[0011] (1) The present invention includes a step (S1) of adding silicon or silicon oxide (SiO x , 0 < x ≤ 2) to a lithium compound-containing solution and stirring in an inert gas atmosphere, and a step (S2) of separating the generated particles and then drying and firing. The concentration of the lithium compound-containing solution is more than 0.5 M and less than 1.0 M, and provides a method for manufacturing a lithium silicon oxide composite.

[0012] (2) In the above (1), the present invention provides a method for manufacturing a lithium silicon oxide composite, in which a polycyclic aromatic compound or a linear polyphenylene compound is added to an organic solvent in the lithium compound-containing solution, stirred to produce a polycyclic aromatic compound solution or a linear polyphenylene compound solution, and lithium particles are added to the polycyclic aromatic compound solution or the linear polyphenylene compound solution and reacted to produce.

[0013] (3) In the above (2), the present invention provides a method for manufacturing a lithium silicon oxide composite, in which the polycyclic aromatic compound is at least one selected from the group consisting of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene and chrysene.

[0014] (4) The present invention provides a method for producing a lithium silicon oxide composite in which, in (2) or (3) above, the linear polyphenylene compound is one or more selected from the group consisting of biphenyl and terphenyl.

[0015] (5) The present invention provides a method for producing a lithium silicon oxide composite in which the silicon and silicon oxide have a carbon coating layer on their surface, in any one of the above (1) to (4).

[0016] (6) The present invention provides a method for producing a lithium silicon oxide composite in any one of (1) to (5) above, wherein the silicon or silicon oxide is added in an amount greater than 0.131 parts by weight and less than 0.142 parts by weight based on 100 parts by weight of the lithium compound-containing solution.

[0017] (7) The present invention provides a method for producing a lithium silicon oxide composite in any one of the above (1) to (5), wherein the stirring in step (S1) is performed by primary stirring at a temperature range of 30°C to 90°C for 1 hour or more, followed by secondary stirring while cooling to room temperature, and the primary stirring and secondary stirring are performed for the same amount of time.

[0018] (8) The present invention provides a method for producing a lithium silicon oxide composite in any one of the above (1) to (6), wherein the firing in step (S2) is performed by heat treatment in an inert gas atmosphere at a temperature range of 850°C to 900°C for 1 to 2 hours. [Effects of the Invention]

[0019] The method for producing a lithium silicon oxide composite according to the present invention includes adding silicon or silicon oxide to a lithium compound-containing solution with a concentration exceeding 0.5 M and less than 1.0 M in which a lithium-containing compound is dissolved, stirring, and heat-treating for prelithiation. By doing so, even when produced with an aqueous negative electrode material slurry that does not contain crystalline lithium silicate (Li2SiO3) and SiO2, hydrogen generation is suppressed, and a lithium silicon oxide composite excellent in initial capacity and capacity retention rate can be produced.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, for the purpose of facilitating understanding of the present invention, the present invention will be described in more detail.

[0021] In the description of the present invention and the claims, terms and words used should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meanings and concepts consistent with the technical idea of the present invention, in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0022] Method for manufacturing lithium silicon oxide The present invention provides a method for producing a lithium silicon oxide composite useful as a negative electrode material, which is excellent in initial capacity and capacity retention rate, has almost no change in viscosity during the production of slurry by an aqueous process, and suppresses hydrogen generation.

[0023] The method for producing the lithium silicon oxide composite according to an embodiment of the present invention includes, under an inert gas atmosphere, adding silicon or silicon oxide (SiO x , 0 < x ≤ 2) to a lithium compound-containing solution and stirring (step S1), and after separating the generated particles, drying and firing (step S2). The concentration of the lithium compound-containing solution is characterized by exceeding 0.5 M and less than 1.0 M.

[0024] As a negative electrode material, graphite-based negative electrode materials are known. Graphite-based negative electrode materials exhibit excellent structural stability during lithium insertion and removal, and show stable capacity retention characteristics even during long cycles. However, due to their low theoretical capacity (350mAh / g for LiC6), they are not suitable as the high-capacity, high-power material currently required. Therefore, a theoretical capacity approximately 10 times higher than graphite (~4200mAh / g for LiC6) is needed. 4.4 Silicon and silicon oxides containing Si are attracting attention. However, silicon-based anode materials consume about three times more lithium than graphite-based anode materials, and have the problem of large irreversible capacity. To solve the problem of initial efficiency due to irreversible reactions of lithium ions, methods are being attempted to improve initial efficiency by prelithiation of Li.

[0025] Pre-lithified silicon-based anode materials offer advantages such as superior charge-discharge efficiency and favorable cycle characteristics, but they suffer from reduced capacity and gas generation during the manufacturing process. In particular, pre-lithified silicon-based anode materials are typically manufactured by heat-treating both lithium metal and silicon-based anode material. These materials generally consist of crystalline lithium silicate (Li4SiO4, Li2SiO3, Li2Si2O5) and crystalline silica (SiO2). Of the crystalline lithium silicates, Li4SiO4 and Li2SiO3 are highly soluble in water. When these pre-lithified silicon-based anode materials are used in the production of aqueous anode slurry, they dissolve in water. The internal silicon oxidizes upon contact with water, and the water, while reducing it, generates hydrogen gas, changing the viscosity of the slurry and degrading the slurry coating properties. This can lead to serious defects in the slurry coating, potentially resulting in fatal problems such as a rapid decrease in capacity due to electrical short circuits with the current collector. Furthermore, if silica remains in the pre-lithiumized silicon-based anode material, it can cause a problem of reduced initial efficiency by forming crystalline lithium silicate, an irreversible phase during the charging process, and consuming lithium.

[0026] However, in the method for producing a lithium silicon oxide composite according to an embodiment of the present invention, a silicon-based negative electrode material is added to a lithium compound-containing solution having a concentration of more than 0.5 M and less than 1.0 M in which the lithium compound is dissolved at a specific concentration in an organic solvent, and the mixture is stirred and heat-treated to produce a lithium silicon oxide composite in which Li is inserted and diffused inside the silicon-based negative electrode while an appropriate redox process occurs, thereby producing a lithium silicon oxide composite in which crystalline lithium silicate and silica do not remain.

[0027] Hereinafter, the method for producing a lithium silicon oxide composite according to an embodiment of the present invention will be described in more detail step by step.

[0028] (S1) Step The step (S1) is a step of pre-lithiating silicon or silicon oxide to generate lithium silicon oxide composite particles. In an inert gas atmosphere, silicon or silicon oxide (SiO x , 0 < x ≤ 2) is added and stirred. The lithium biphenyl compound-containing solution may have a concentration of more than 0.5 M and less than 1.0 M.

[0029] Here, the fact that the lithium compound-containing solution has a concentration of more than 0.5 M and less than 1.0 M means that more than 0.5 mol and less than 1.0 mol of the lithium compound are dissolved per liter of the solution.

[0030] In an embodiment of the present invention, the silicon and the silicon oxide may each have an amorphous structure. The silicon may have an average particle size (D 50 ) of 1 μm to 20 μm, and the silicon oxide may have an average particle size (D 50 ) of 5 nm to 1 μm.

[0031] Further, the silicon and the silicon oxide may include a carbon coating layer on the surface. Here, the thickness of the carbon coating layer may be 1 nm to 1 μm, or 100 nm to 1 μm.

[0032] The carbon coating layer comprises a carbon-based material, and the carbon-based material may include at least one of amorphous carbon and crystalline carbon.

[0033] The crystalline carbon can further improve the conductivity of the negative electrode material and may, for example, be one or more selected from the group consisting of fluorene, carbon nanotubes, and graphene.

[0034] Furthermore, the amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch and other organic materials as a source in chemical vapor deposition, in order to adequately maintain the strength of the carbon coating layer. The carbides of other organic materials may be carbides of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, or combinations thereof.

[0035] Furthermore, the hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon, and may include, for example, methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane or hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene or phenanthrene.

[0036] In one embodiment of the present invention, the silicon or silicon oxide can be added in an amount greater than 0.131 parts by weight and less than 0.142 parts by weight per 100 parts by weight of the lithium compound-containing solution.

[0037] Here, the lithium compound-containing solution can be produced by adding a polycyclic aromatic compound or a linear polyphenylene compound to an organic solvent, stirring, producing a polycyclic aromatic compound solution or a linear polyphenylene compound solution, and then adding lithium particles to the polycyclic aromatic compound solution or linear polyphenylene compound solution and reacting them.

[0038] Furthermore, the lithium particles react with the polycyclic aromatic compound or linear polyphenylene compound in a polycyclic aromatic compound solution or linear polyphenylene compound solution in a 1:1 mole ratio.

[0039] Furthermore, the polycyclic aromatic compound may be one or more selected from the group consisting of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene, fluorene, and 9,9-dimethylfluorene, and the linear polyphenylene compound may be one or more selected from the group consisting of biphenyl, terphenyl, and 4,4-dimethylbiphenyl. Specifically, the polycyclic aromatic compound may be any one selected from naphthalene, fluorene, and 9,9-dimethylfluorene, and the linear polyphenylene compound may be biphenyl or 4,4-dimethylbiphenyl.

[0040] Furthermore, the organic solvent can be an ether-based solvent, a ketone-based solvent, an ester-based solvent, an alcohol-based solvent, an amine-based solvent, or a mixture thereof. For example, the ether-based solvent can be diethyl ether, tert-butyl methyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or a mixture thereof. Among these, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, and 1,2-dimethoxyethane are preferred.

[0041] Furthermore, as the ketone solvent, acetone, acetophenone, etc., can be used, and as the ester solvent, methyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, or a mixture thereof can be used.

[0042] Furthermore, as alcohol-based solvents, methanol, ethanol, propanol, isopropyl alcohol, or mixtures thereof can be used, and as amine-based solvents, methylamine, ethylamine, ethylenediamine, or mixtures thereof can be used.

[0043] Furthermore, the reaction to obtain the lithium compound-containing solution can be carried out at a temperature range of 20°C to 90°C while stirring for 0.5 to 6.0 hours, and stirring at the above temperature for the above time allows for more effective formation of the lithium compound.

[0044] In step (S1) above, the stirring may be performed by primary stirring at a temperature range of 30°C to 90°C for 1 hour or more, and secondary stirring while cooling to room temperature, taking into consideration the adjustment of the lithium ion diffusion rate and appropriate pre-lithiation. The primary and secondary stirring may be performed for the same amount of time.

[0045] (S2) Step Step (S2) is a step for producing a lithium silicon oxide composite by separating, drying, and calcining the lithium silicon oxide composite particles generated in step (S1), and can be carried out by separating the particles generated in step (S1), followed by drying and calcining.

[0046] The generated particles can be separated from the solution by means of conventional methods in the industry, for example, by centrifuging the solution to separate the supernatant from the precipitate, which is the generated particles.

[0047] The drying can be carried out by conventional means in the art. For example, it can be carried out by allowing it to stand still at a temperature range of 70°C to 90°C, or at 75°C to 85°C for 2 hours or more.

[0048] Also, the firing can be carried out by heat treatment in an inert gas atmosphere at a temperature range of 850°C to 900°C for 1 hour to 2 hours.

[0049] On the other hand, in the method for producing the lithium silicon oxide composite according to an embodiment of the present invention, the inert gas may be argon, nitrogen, or a combination thereof.

[0050] Lithium silicon oxide composite The lithium silicon oxide composite produced by the method for producing a lithium silicon oxide composite according to the present invention contains no crystalline lithium silicate (Li2SiO3) or contains only a very small amount thereof. When producing a slurry by an aqueous process, the generation of hydrogen is prevented, there is no coating defect and no reduction in adhesive strength, and it can be excellent in initial capacity characteristics and capacity retention rate.

[0051] As another example, the lithium silicon oxide composite may contain silicon, silicon oxide, and a lithium silicon-based compound. The lithium silicon-based compound is a compound formed by doping lithium metal into silicon or silicon oxide while pre-lithiation of silicon or silicon oxide is performed by the above-described production method. Exemplarily, it may contain any one or more of lithium disilicate and lithium silicide. As still another example, the lithium silicon-based compound may further contain lithium silicate as appropriate, but in this case, the lithium silicate may be a small amount less than 5% by weight.

[0052] The lithium silicide can contain Li y Si(2 < y < 5). Exemplarily, Li 4.4 Si, Li 3.75 Si, Li 3.25 Si and Li2.33 It may be one or more elements selected from the group consisting of Si.

[0053] Furthermore, in the XRD pattern of the lithium silicon oxide composite according to one embodiment of the present invention, measured using unmonochromatic CuKα radiation, peaks are present at 2θ positions of 23.8±0.5°, 24.3±0.5°, and 24.7±0.5°, and no peak is present at 27.0±0.2°, satisfying the following mathematical equation 1.

[0054] [Mathematical formula 1] y sio2,max ≤0.4·y Si,111

[0055] In the above mathematical formula 1, y sio2,max This is the peak height of the highest SiO2 peak among those corresponding to the positions 2θ = 20.7 ± 0.5°, 21.6 ± 0.5°, and 26.5 ± 0.5° in the XRD pattern measured using unmonochromatic CuKα lines, and y Si,111 This corresponds to the Si peak height at the position 2θ = 28.5 ± 0.5° in the aforementioned XRD pattern.

[0056] Furthermore, the lithium silicon oxide according to one embodiment of the present invention is characterized in that it satisfies the following mathematical formula 2.

[0057] [Mathematical formula 2] I q,100 +I c,111 +I q,011 ≤0.3·I si,111

[0058] In the aforementioned mathematical formula 2, I q,100 , I c,111 and I q,011 These are XRD patterns measured using unmonochromatic CuKα lines, and represent the integrated intensities of the SiO2 peaks corresponding to the positions 2θ = 20.7±0.5°, 21.6±0.5°, and 26.5±0.5°, respectively. si,111This represents the integrated intensity of the Si peak corresponding to the position 2θ = 28.5 ± 0.5° in the aforementioned XRD pattern.

[0059] As yet another example, the lithium silicon oxide composite satisfies the presence or absence of peaks in a specific positional range in the XRD pattern, as well as mathematical formula 1 and mathematical formula 2.

[0060] As yet another example, the lithium silicon oxide composite is 29 Obtained by Si solid-state MAS (magic angle spinning) NMR measurement. 29 The Si NMR spectrum includes a first peak with a width of 0.2 to 2.0 ppm in the range of -88 to -99 ppm and a second peak with a width of 3 to 10 ppm, and the ratio of the integral value of the first peak to the integral value of the second peak (first peak / second peak) may be greater than 0.22 and less than or equal to 0.31.

[0061] As yet another example, the lithium silicon oxide composite is 29 Obtained by Si solid-state MAS (magic angle spinning) NMR measurement. 29 In the Si NMR spectrum, it is not necessary for there to be no peaks in the chemical shift range of -71 to -77 ppm.

[0062] Furthermore, the lithium silicon oxide composite according to one embodiment of the present invention may satisfy the following mathematical formula 3.

[0063] [Mathematical formula 3] 0.45 ≤ PX 512 / PX T

[0064] In the above mathematical formula 3, PX T This refers to the Raman mapping technique, where a 150 μm × 150 μm area of ​​lithium silicon oxide surface is evenly divided into 5 μm × 5 μm pixels, resulting in a total of 900 pixels, PX 512This is a Raman shift of 200 cm obtained by the Raman mapping technique for each of the 900 pixels mentioned above. -1 From 520cm -1 Of the Raman spectra up to 512 cm⁻¹, -1 More than 520cm -1 The following is the number of pixels with the maximum peak.

[0065] As yet another example, the lithium silicon oxide composite may satisfy the following mathematical formula 4.

[0066] [Mathematical formula 4] 5≦PX 512 / PX 500

[0067] In the aforementioned mathematical formula 4, PX 512 This involves using the Raman mapping technique to divide a 150 μm × 150 μm area of ​​the lithium silicon oxide composite surface into 900 pixels of equal size (5 μm × 5 μm), and then applying a Raman shift of 200 cm to each of these pixels. -1 From 520cm -1 Of the Raman spectra up to 512 cm⁻¹, -1 More than 520cm -1 The following is the number of pixels with the highest peak, PX 500 This is a Raman shift of 200 cm for each of the 900 pixels mentioned above. -1 From 520cm -1 Of the Raman spectra up to 490 cm² -1 More than 500cm -1 The following is the number of pixels with the maximum peak.

[0068] As yet another example, the lithium silicon oxide satisfies both mathematical formula 3 and mathematical formula 4.

[0069] On the other hand, in the Raman spectrum, crystalline Si has a Raman shift of 500 cm. -1 Super 520cm -1 The following peaks were observed, and amorphous Si has a Raman shift of 490 cm⁻¹.-1 More than 500cm -1 A peak is observed below. Therefore, in the Raman spectrum measured by the Raman mapping technique according to one embodiment of the present invention, at 512 cm⁻¹ -1 Pixels with the highest peak are those with a higher proportion of crystalline Si, at 500 cm². -1 Pixels with the highest peak indicate pixels with a higher proportion of amorphous Si.

[0070] negative electrode The present invention provides a negative electrode comprising the lithium silicon oxide composite.

[0071] The negative electrode according to one embodiment of the present invention comprises a conductive metal current collector and a negative electrode material layer provided on at least one surface of the current collector, wherein the negative electrode material layer comprises the lithium silicon oxide composite.

[0072] The anode according to the present invention includes an anode material layer containing a lithium silicon oxide composite, which provides excellent initial efficiency, suppresses volume expansion of the anode, and enables excellent capacity retention and long-term stability.

[0073] The conductive metal current collector contains a highly conductive metal, and there are no particular limitations on the conductive metal current collector as long as it is unreactive within the battery voltage range. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used. The current collector can also have a thickness of 3 μm to 500 μm.

[0074] On the other hand, the negative electrode can be manufactured by mixing an aqueous solvent, the lithium silicon oxide composite, a binder, and a conductive material to produce a negative electrode material slurry, applying the negative electrode material slurry to at least one surface of a conductive metal current collector, and drying it. Here, the aqueous solvent can be water.

[0075] Furthermore, the conductive material can be any material that does not cause chemical changes and has electronic conductivity, without any particular limitations. Specifically, the conductive material may include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these materials alone or a mixture of two or more materials can be used.

[0076] Furthermore, the binder can typically be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0077] Lithium-ion rechargeable battery The present invention provides a lithium secondary battery including the negative electrode.

[0078] According to one embodiment of the present invention, the lithium secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium secondary battery may also optionally further include a battery container for housing the electrode assembly of the negative electrode, positive electrode, and separator, and a sealing member for sealing the battery container.

[0079] According to one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode material layer located on the positive electrode current collector.

[0080] According to one embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The positive electrode current collector can also typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on its surface to strengthen the bonding force of the positive electrode material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0081] According to one embodiment of the present invention, the cathode material layer may selectively include a binder and a conductive material together with the cathode material.

[0082] According to one embodiment of the present invention, the cathode material may be LiCoO2, LiCoPO4, LiNiO2, Li x Ni a Co b M 1 c M 2 d O2(M 1 and M 2 Each is independently selected from the group consisting of Al, Mn, Cu, Fe, V, Cr, Mo, Ga, B, W, Mo, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y, and 0.9 ≤ x ≤ 1.1, 0 <a<1.0、0<b<1.0、0≦c<0.5、0≦d<0.5、a+b+c+d=1である。)、LiMnO2、LiMnO3、LiMn2O3、LiMn2O4、LiMn 2-e M 3 e O2(M 3( is one or more elements selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01 ≤ e ≤ 0.1. ), Li2Mn3M 4 O8(M 4 (This is one or more selected from the group consisting of Ci, Ni, Fe, Cu, and Zn.) It can also be one selected from the group consisting of LiFePO4, Li2CuO2, LiV3O8, V2O5, Cu2V2O7, and lithium metal.

[0083] According to one embodiment of the present invention, the binder is a component that helps to bond the conductive material, the positive electrode material, and the current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0084] According to one embodiment of the present invention, the conductive material in the positive electrode layer is a component for further improving the conductivity of the positive electrode material, and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the positive electrode layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0085] According to one embodiment of the present invention, the positive electrode can be manufactured by applying a slurry for forming a positive electrode material layer, which is prepared by dissolving or dispersing a positive electrode material and a binder and a conductive material selectively in a solvent, onto the positive electrode current collector and drying it, or by casting the slurry for forming a positive electrode material layer onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0086] According to one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator that is normally used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. In addition, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as a single-layer or multi-layer structure.

[0087] According to one embodiment of the present invention, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte, which can be used in the manufacture of lithium secondary batteries, and is not limited to these. Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0088] According to one embodiment of the present invention, the organic solvent can be used without particular limitations as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0089] According to one embodiment of the present invention, the lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt is F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - Or (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of the following, and the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0090] According to one embodiment of the present invention, the electrolyte may also contain, in addition to the electrolyte components, other components for improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), propane sultone (PS), 1,3-propane sultone (PRS), ethylene sulfate (Esa), succinonitrile (SN), adiponitrile (AN), hexane tricarbonitrile (HTCN), γ-butyrolactone, biphenyl (BP), cyclohexylbenzene (CHB), and t-amylbenzene (tert-amyl The mixture may further contain one or more additives selected from the group consisting of benzene, TAB, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. Here, the additives may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0091] The lithium secondary battery containing the negative electrode according to the present invention exhibits excellent capacity characteristics, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the electric vehicle field, including hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0092] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0093] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0094] Accordingly, according to one embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0095] According to one embodiment of the present invention, the battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0096] Examples Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0097] Example 1 2.77 g of biphenyl was added to 30 ml of 2-methyltetrahydrofuran and stirred for 10 minutes. When the solution turned transparent, 0.126 g of Li powder was added thereto, and the mixture was stirred for 6 hours to produce a dark green 0.6 M LiBP solution.

[0098] To the LiBP solution, 4 g of SiO 50 / C (0 < x ≦ 2) powder having a carbon coating layer on the surface with an average particle diameter (D x ) of 5 μm was added, and the mixture was stirred at 80°C for 1 hour. Next, it was further stirred for 1 hour while cooling to room temperature (25°C). Here, all processes were carried out under an argon atmosphere.

[0099] Next, the solution was centrifuged to separate only the powder particles, and the separated particles were dried at 80°C for 4 hours, heated to 900°C, and heat-treated under an argon atmosphere for 2 hours to produce a lithium silicon oxide composite.

[0100] Example 2 In Example 1 above, a 0.8 M LiBP solution was produced using 3.696 g of biphenyl and 0.168 g of Li powder, and a lithium silicon oxide composite was produced in the same manner as in Example 1 except for using this solution.

[0101] Comparative Example 1 In Example 1 above, a 0.3 M LiBP solution was produced using 1.386 g of biphenyl and 0.063 g of Li powder, and a lithium silicon oxide composite was produced in the same manner as in Example 1 except for using this solution.

[0102] Comparative Example 2 In Example 1 above, a 0.5 M LiBP solution was produced using 2.31 g of biphenyl and 0.105 g of Li powder, and a lithium silicon oxide composite was produced in the same manner as in Example 1 except for using this solution.

[0103] Comparative Example 3 In the above-mentioned Example 1, a 1.0 M LiBP solution was prepared using 4.62 g of biphenyl and 0.21 g of Li powder, and a lithium silicon oxide composite was produced in the same manner as in Example 1, except that this solution was used.

[0104] Experimental Example 1 XRD analysis was performed on each lithium silicon oxide composite produced in the examples and comparative examples to confirm the presence or absence of lithium silicate (Li2SiO3), lithium disilicate (Li2Si2O5), and silica (SiO2), and the results are shown in Table 1.

[0105] XRD analysis was performed using a Brucker D8 ADNAVCE powder x-ray diffractiometer (Bruker) with a current of 49kV, a voltage of 40mA CuKα, a Bragg angle (2θ) of 15° to 95°, and a scan speed of 0.02° / 0.20sec. The presence of lithium disilicate (Li2Si2O5) was confirmed by the presence or absence of peaks at 2θ = 23.5±0.5°, 24.0±0.5°, and 24.5±0.5° in the spectrum. The presence of lithium silicate (Li2SiO3) was confirmed by the presence or absence of a peak at 2θ = 27.0±0.5°. The presence of silica was confirmed by the presence or absence of peaks at 2θ = 20.7±0.5°, 21.6±0.5°, and 26.5±0.5°.

[0106] [Table 1]

[0107] As can be seen in Table 1 above, the lithium silicon oxide composites of Example 1 and Example 2 did not show lithium silicate peaks or silica peaks in their XRD patterns.

[0108] On the other hand, in the lithium silicon oxide composites of Comparative Examples 1 and 2, no lithium silicate peak was observed in the XRD pattern, but a silica peak was observed, while in Comparative Example 3, a lithium silicate peak was observed.

[0109] Experimental Example 2 Aqueous anode material slurries were prepared using the lithium silicon oxide composites manufactured in the examples and comparative examples, and the amount of gas generated was measured. The results are shown in Table 2 below.

[0110] A negative electrode material aqueous slurry was prepared by mixing each lithium silicon oxide composite, graphite, Super-C65 as a conductive material, and styrene-butadiene rubber binder and carboxymethyl cellulose as binders in an aqueous solvent in a weight ratio of 19.2:77:1:1.1:1.6. Next, 5 g of the negative electrode material aqueous slurry was placed in an aluminum pouch, sealed, and stored in an oven at 60°C, and the amount of gas generated was measured using a hydrometer.

[0111] [Table 2]

[0112] As can be seen from Table 2 above, the negative electrode material slurries containing lithium silicon oxide composites of Example 1 and Example 2 showed a reduced amount of gas generation compared to the negative electrode material slurry containing lithium silicon oxide composite of Comparative Example 3, in which a lithium silicate peak was observed.

[0113] On the other hand, the negative electrode slurry containing the lithium silicon oxide composite of Comparative Example 1, which, like the example, did not show a lithium silicate peak, exhibited a gas generation amount equivalent to that of the example. However, as can be seen from Experimental Example 3 described later, it showed a considerably inferior tendency in terms of initial capacity.

[0114] Furthermore, although no silica peak was observed in the XRD pattern of the lithium silicon oxide composite of Comparative Example 3, the initial efficiency decreased compared to the examples, as shown in Table 3 below. This is presumed to be due to residual biphenyl used during manufacturing, which carbonized during the heat treatment process and acted as a byproduct.

[0115] Experimental Example 3 Half-cells were manufactured using the lithium silicon oxides of the examples and comparative examples, and their battery characteristics were measured. The results are shown in Table 3 below.

[0116] Each lithium silicon oxide composite was mixed with the conductive material Super-C65 and the binder Li-PAA in a weight ratio of 70:15:15 to produce a negative electrode slurry. This slurry was then applied to copper foil, and the negative electrode was manufactured through drying, rolling, and punching processes.

[0117] After leaving the coin half-cell for 24 hours, it was charged to 0.005V with a constant current (CC) of 0.1C in the 0.005-1.5V vs. Li / Li+ range, then charged with a constant voltage (CV) until the charging current reached 0.02C, and finally discharged with a constant current (CC) of 0.1C until it reached 1.5V. The charge / discharge capacity and initial efficiency of the first cycle were then measured.

[0118] [Table 3]

[0119] As can be seen from Table 3 above, it can be confirmed that Examples 1 and 2 have superior initial efficiency compared to Comparative Examples 1 to 3.

Claims

1. Under an inert gas atmosphere, silicon or silicon oxide (SiO₂) is added to a lithium compound-containing solution. ｘ Step (S1) involves adding (0 < x ≤ 2) and stirring, The process includes the steps of separating the generated particles, drying and calcining (S2), A method for producing a lithium silicon oxide composite, wherein the concentration of the lithium compound-containing solution is greater than 0.5 M and less than 1.0 M.

2. The method for producing a lithium silicon oxide composite according to claim 1, wherein the lithium compound-containing solution is produced by adding a polycyclic aromatic compound or a linear polyphenylene compound to an organic solvent, stirring to produce a polycyclic aromatic compound solution or a linear polyphenylene compound solution, and then adding lithium particles to the polycyclic aromatic compound solution or linear polyphenylene compound solution and reacting them.

3. The method for producing a lithium silicon oxide composite according to claim 2, wherein the polycyclic aromatic compound is one or more selected from the group consisting of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene, fluorene, and 9,9-dimethylfluorene.

4. The method for producing a lithium silicon oxide composite according to claim 2, wherein the linear polyphenylene compound is one or more selected from the group consisting of biphenyl, terphenyl, and 4,4-dimethylbiphenyl.

5. The method for producing a lithium silicon oxide composite according to claim 1, wherein the silicon and silicon oxide include a carbon coating layer on their surfaces.

6. The method for producing a lithium silicon oxide composite according to claim 1, wherein the silicon or silicon oxide is added in an amount greater than 0.131 parts by weight and less than 0.142 parts by weight based on 100 parts by weight of the lithium compound-containing solution.

7. The stirring in step (S1) above is performed by primary stirring at a temperature range of 30°C to 90°C for 1 hour or more, followed by secondary stirring while cooling to room temperature. The method for producing a lithium silicon oxide composite according to claim 1, wherein the primary stirring and secondary stirring are performed for the same amount of time.

8. The method for producing a lithium silicon oxide composite according to claim 1, wherein the firing in step (S2) is carried out by heat treatment in an inert gas atmosphere at a temperature range of 850°C to 900°C for 1 to 2 hours.

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