Silicon composite anode material for lithium secondary battery, comprising lithium silicate matrix, preparation method therefor, and anode for lithium secondary battery, comprising same

Abstract

A composite anode material for a lithium secondary battery, comprising a lithium silicate matrix, is disclosed. Specifically, the present invention provides a composite anode material for a lithium secondary battery, comprising a lithium silicate matrix and silicon, and large volume expansion of silicon, which occurs during charging / discharging, can be suppressed by the lithium silicate matrix, and thus a lithium secondary battery having improved performance can be provided.

Description

Silicon composite anode material for lithium secondary batteries including a lithium silicate matrix, a method for producing the same, and a cathode for lithium secondary batteries including the same

[0001] The present invention relates to a composite negative electrode material for a lithium secondary battery including a lithium silicate matrix, a method for producing the same, and a lithium secondary battery including the same.

[0002] With technological developments and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which utilize the intercalation mechanism of lithium ions within the crystal structure of the cathode or anode materials, have been commercialized and are widely used, boasting high energy density, high voltage, and long cycle life.

[0003] A lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode to separate them, and an electrolyte that electrochemically communicates with the positive electrode and the negative electrode.

[0004] These lithium secondary batteries are typically manufactured using lithium-intercalated compounds such as LiCoO2 and LiMn2O4 for the anode, and non-lithium-intercalated materials such as carbon-based or Si-based for the anode. When charging, lithium ions intercalated into the anode move to the anode through the electrolyte, and when discharging, lithium ions move again from the anode to the anode. The lithium that moves from the anode to the anode during the charging reaction reacts with the electrolyte to form a passivation film, a solid electrolyte interface (SEI) layer, on the surface of the anode. This SEI layer stabilizes the structure of the anode and minimizes electrolyte consumption by reducing direct contact between the anode and the electrolyte, thereby preventing additional electrolyte decomposition reactions after the SEI layer is formed. However, because the SEI layer formation reaction is irreversible, it causes consumption of electrolyte additives and lithium ions during activation or the early stages of the cycle. In addition, there are regions in the active material itself where lithium can be irreversibly consumed depending on the structure, and in these regions, lithium ions are not released again after charging, resulting in lithium ion consumption. That is, the lithium consumed by the reaction at the cathode during the initial activation process does not return to the cathode during the subsequent discharge process, reducing the capacity of the battery. This phenomenon is called irreversible capacity.

[0005] Carbon-based materials such as graphite, while excellent in stability and reversibility as anode materials, have limitations in terms of capacity. Therefore, in fields targeting high capacity, Si-based materials with high theoretical capacity are used as anode materials. However, Si-based materials undergo rapid volume expansion due to changes in their crystal structure as lithium ions are inserted and released during charge and discharge. Si-based materials with volume expansion have high initial irreversible capacity, which leads to severe lithium depletion and low initial efficiency. In addition, with repeated charge and discharge, additional SEI reactions on the newly exposed active material surface deteriorate cycle characteristics.

[0006] For example, referring to the charge profile of a lithium secondary battery including a Si-based negative electrode, lithium ions are inserted into the Si-based material during charging. 12 Si7, Li2Si, Li 21 Si8, Li 15 Si4 and Li 22 Li such as Si5 x It forms a compound of Si, but among these, Li2Si or Li 21 Only Si8 shows reversible charge-discharge behavior, while the others do not.

[0007] Therefore, Li2Si or Li2Si2 exhibits reversible charge-discharge behavior on Si-based cathodes. 21 When charging occurs beyond the Si8 region, volume expansion significantly increases the thickness change rate of the anode, resulting in deterioration of the conductive network within the anode. This, in turn, leads to electrical short-circuiting and ultimately deteriorates charge-discharge characteristics. If this phenomenon accumulates, cracks can develop on the surface of the anode active material, leading to a rapid increase in electrolyte consumption.

[0008] Accordingly, pre-lithiation, a technology for suppressing the initial irreversible capacity or volume expansion of the negative electrode, that is, a method of improving the capacity and electrochemical performance of the battery by performing the irreversible reaction of the negative electrode in advance before manufacturing the battery or charging the negative electrode with lithium in advance to secure the initial reversibility, is being attempted. However, there are cases where the discharge capacity or life performance deteriorates, and when lithium metal is directly used for pre-lithiation, there are problems in that handling is difficult and there is a high risk of fire and explosion because lithium itself is unstable in the air and easily reacts with oxygen, nitrogen, and carbon dioxide.

[0009] Accordingly, the present invention is intended to solve the above problems, and the purpose of the present invention is to provide a composite anode material for a lithium secondary battery capable of maintaining an excellent conductive network even when a volume of a Si-based anode expands, a method for manufacturing the composite anode material for a lithium secondary battery, and a lithium secondary battery anode comprising the same.

[0010] The present invention uses gaseous lithium, obtained by vaporizing a lithium-containing compound (e.g., lithium metal, lithium oxide, lithium hydroxide, lithium alloy) as a reducing agent, to introduce lithium into the negative electrode in a manner different from the conventional method, thereby safely introducing lithium into the negative electrode, and thereby providing an effect of suppressing irreversibility and volume expansion of the negative electrode.

[0011] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof described in the specification.

[0012] According to a first aspect of the present invention for achieving the above object, a composite negative electrode material for a lithium secondary battery is provided, comprising a lithium silicate matrix and silicon.

[0013] According to a second aspect of the present invention, the lithium silicate matrix may include at least one compound selected from the group consisting of lithium orthosilicate (Li4SiO4), lithium metasilicate (Li2Si2O5), and lithium disilicate (Li2SiO3).

[0014] According to a third aspect of the present invention, in a composite negative electrode material of a lithium secondary battery including the lithium silicate matrix and silicon, based on the total weight of three compounds of lithium orthosilicate, lithium metasilicate, and lithium disilicate excluding silicon, lithium orthosilicate may be included in an amount of 15 wt% to 55 wt%, lithium metasilicate in an amount of 45 wt% to 90 wt%, and lithium disilicate in an amount of 0.01 wt% to 0.5 wt%.

[0015] According to a fourth aspect of the present invention, when the content of silicon in the lithium silicate matrix is ​​maintained at 40 wt% to 45 wt% based on the total weight of the lithium silicate matrix and silicon particles, lithium orthosilicate may be included at 5 wt% to 35 wt%, lithium metasilicate at 30 wt% to 60 wt%, and lithium disilicate at 0.01 wt% to 0.4 wt%.

[0016] According to the fifth aspect of the present invention, the average particle diameter of the composite negative electrode material of the lithium secondary battery including the lithium silicate matrix and silicon may be 1 to 20 μm.

[0017] According to the sixth aspect of the present invention, the negative electrode composite for a lithium secondary battery may further include a carbon material.

[0018] According to the seventh aspect of the present invention, the carbon material may be one or more compounds selected from the group consisting of graphene, carbon nanotubes (CNTs), carbon fibers, crystalline carbon, and amorphous carbon.

[0019] According to the eighth aspect of the present invention, a negative electrode for a lithium secondary battery can be provided, including the composite negative electrode material for a lithium secondary battery.

[0020] According to the ninth aspect of the present invention, the electrode density of the negative electrode for the lithium secondary battery is 1.2 g / cm -3 It could be as follows:

[0021] According to the tenth aspect of the present invention, (S1) Si and SiO2 are mixed to form silicon (SiO x, 0 <x<2) 혼합물을 준비하는 단계; (S2) 상기 실리콘 혼합물에 리튬 화합물을 첨가하여 실리콘-리튬 혼합물을 제조하는 단계; 및 (S3) 상기 실리콘-리튬 혼합물을 가열하는 단계;를 포함하는, 복합 음극재 제조방법을 제공할 수 있다.

[0022] According to the eleventh aspect of the present invention, in the step (S1), Si and SiO2 may be mixed in a mole ratio of 1:0.7 to 1:1.5.

[0023] According to the twelfth aspect of the present invention, in the step (S2), the silicon mixture and the lithium compound may be further included in a molar ratio of 1:1 to 1:1.5.

[0024] According to the 13th aspect of the present invention, the lithium compound of the step (S2) may be at least one compound selected from the group consisting of lithium metal, lithium oxide, lithium carbonate, lithium hydroxide, and lithium alloy.

[0025] According to the fourteenth aspect of the present invention, the step of heating the silicon-lithium mixture in the step (S3) may be a step of heating at 500°C to 1,500°C for 2 to 7 hours.

[0026] According to the fifteenth aspect of the present invention, a method for manufacturing a composite negative electrode material can be provided, further comprising a step of introducing a carbon material into the composite negative electrode material (S4).

[0027] According to the sixteenth aspect of the present invention, a negative electrode for a lithium secondary battery is provided, comprising the composite negative electrode material.

[0028] According to the 17th aspect of the present invention, the negative electrode for the lithium secondary battery has a tap density of 1.0 to 1.6 g / cm 3 It could be.

[0029] The solutions to the above problems do not enumerate all the features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the detailed description below.

[0030] According to one aspect of the present invention, the composite negative electrode material of the present invention can maintain a conductive network even when volume expands due to charge and discharge, thereby providing a negative electrode for a lithium secondary battery capable of implementing excellent electrochemical performance.

[0031] In addition to the aforementioned effects, the specific effects of the present invention are described below along with the specific details for implementing the invention. Furthermore, the effects of the present invention are not limited to the effects described above and can be readily achieved by the means and combinations thereof described in the specification.

[0032] Figure 1 is a schematic diagram showing a method for manufacturing a composite negative electrode material according to one embodiment of the present invention.

[0033] FIG. 2 shows an XRD (X-ray diffraction) pattern of a composite negative electrode material manufactured according to one embodiment of the present invention.

[0034] FIG. 3 shows the results of observation by applying HIGH ANGLE ANNULAR DARK FIELD IMAE (HADDF)-TEM, ENERGY-DISPERSIVE X-RAY SPECTROSCOPY (EDX), and ELECTRON ENERGY LOSS SPECTROSCOPY (EELS) techniques to a composite cathode material manufactured according to one embodiment of the present invention.

[0035] Figure 4 shows the results of measuring the speed characteristics of a composite negative electrode material manufactured according to one embodiment of the present invention.

[0036] Figure 5 shows the results of measuring the life characteristics of a composite negative electrode material manufactured according to one embodiment of the present invention.

[0037] Figure 6 shows the results of a charge / discharge experiment according to the tap density of a composite negative electrode material manufactured according to one embodiment of the present invention.

[0038] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0039] When multiple problem-solving means are described in this specification, the effects of the present invention may be defined to include not only the operational effects derived from each problem-solving means itself, but also the effects resulting from the organic combination of each problem-solving means. For example, even if problem-solving means 1 and 2 are described independently in this specification, unless the context clearly indicates otherwise, the effects resulting from the organic combination of problem-solving means 1 and 2 may also be included in the effects of the present invention.

[0040] The numerical range indicated by the term "to" in this specification refers to a numerical range that includes the values ​​described before and after the term as the lower limit and the upper limit, respectively. When multiple numerical values ​​are disclosed as the upper and lower limits of an arbitrary numerical range, the numerical range disclosed in this specification can be understood as any numerical range that has any one of the multiple lower limit values ​​and any one of the multiple upper limit values ​​as the lower limit and the upper limit, respectively. For example, when a to b, or c to d is described in the specification, it can be understood that a or more and b or less, a or more and d or less, c or more and d or less, or c or more and b or less is described.

[0041] As used herein, terms such as "about" or "substantially" mean a reasonable amount of variation from the term that does not significantly alter the final result. These terms may be interpreted to include a variation of at least ±5% or at least ±10%, provided that such variation does not alter the meaning of the term and render it invalid.

[0042] According to one aspect of the present invention, the present invention provides a lithium silicate (Li x Si y O z ) provides a composite anode material for a lithium secondary battery, including a matrix and silicon particles, and a method for manufacturing the composite anode material (wherein, 2≤x≤4, 1≤y≤2, 3≤z≤5).

[0043] As mentioned above, graphite-based anode materials are widely known as anode materials for lithium secondary batteries, and graphite-based anode materials have excellent structural stability even during insertion and removal of lithium, and show stable capacity retention characteristics even during long-term cycles. However, due to their low theoretical capacity (approximately 350 mAh / g), they are not suitable as high-capacity, high-output materials currently required. Therefore, graphite-based anode materials, which have a theoretical capacity about 10 times higher than that of graphite (~4,200 mAh / g for Li), are used. 4.4 Si or SiO having Si)x Si-based cathode materials including are attracting attention.

[0044] However, Si-based anode materials consume about three times more lithium than graphite-based anode materials, and have the problem of increased irreversible capacity. In order to solve the initial efficiency problem caused by the irreversible reaction of lithium ions, a method of improving the initial efficiency by pre-lithiating Li is being attempted. However, when manufacturing anode material slurry using a pre-lithiated Si-based anode material, the lithium compound generated by pre-lithiation reacts with H2O to produce LiOH byproducts, which increases hydrogen generation, changes the slurry viscosity, and deteriorates the slurry coating characteristics, causing serious defects in the slurry coating, and as a result, fatal problems such as rapid capacity decrease due to electrical short circuit with the current collector may occur.

[0045] Accordingly, the inventors of the present invention have discovered lithium silicate (Li x Si y O z ) found that a composite negative electrode material for a lithium secondary battery including a matrix and silicon particles can solve the above-described problems, and thus the present invention was achieved.

[0046] Hereinafter, the composite negative electrode material according to the present invention will be described in detail.

[0047]

[0048] 1. Composite cathode material

[0049] The present invention can provide a composite negative electrode material for a lithium secondary battery comprising a lithium silicate matrix and silicon particles.

[0050] In one embodiment of the present invention, the lithium silicate matrix may include at least one compound selected from the group consisting of lithium orthosilicate (Li4SiO4), lithium metasilicate (Li2Si2O5), and lithium disilicate (Li2SiO3).

[0051] In the composite negative electrode material for lithium secondary batteries provided in the present invention, the silicon is directly combined with lithium to form an amorphous lithium silicate (c-Si+xLi*a-Li) from crystalline silicon (c-Si). x Si y ) and after delithiation, it changes into amorphous silicon (a-Si). Here, as the crystalline silicon changes into the amorphous lithium silicate, a large volume expansion may occur, and at this time, the lithium silicate matrix can play a role in suppressing the volume expansion of the silicon.

[0052] In one embodiment of the present invention, the silicon particles may be present in a lithium silicate matrix, and the silicon particles in the lithium silicate matrix may be Si or SiO. x (0 <x<2)일 수 있다.

[0053] In one embodiment of the present invention, the average particle diameter of the silicon particles may be 5 to 100 nm or 1 to 10 μm.

[0054] In one embodiment of the present invention, the composite anode material for a lithium secondary battery may contain 20 to 80 parts by weight, preferably 20 to 70 parts by weight, of the silicon particles based on 100 parts by weight of the composite anode material. In this case, if the silicon particle ratio is too high, a large volume expansion occurs during charging / discharging, making it difficult to control the volume change of the electrode, and if the silicon particle ratio is low, the absolute charge / discharge capacity may decrease, which is not preferable.

[0055] The lithium silicate matrix forming the composite negative electrode material of the present invention is Li x Si y O z A compound having a general formula, lithium orthosilicate, lithium metasilicate, and lithium disilicate form a network and matrix (see Fig. 1). The lithium silicate matrix can mitigate the significant expansion of silicon particles during charge and discharge, thereby reducing the irreversible capacity of the battery and improving the electrochemical performance of the battery.

[0056] In one embodiment of the present invention, in the composite negative electrode material of a lithium secondary battery including the lithium silicate matrix and silicon, based on the total weight of three compounds of lithium orthosilicate, lithium metasilicate, and lithium disilicate excluding silicon, lithium orthosilicate may be included in an amount of 15 wt% to 55 wt%, preferably 16 wt% to 51 wt%, lithium metasilicate in an amount of 45 wt% to 90 wt%, preferably 49 wt% to 84 wt%, and lithium disilicate in an amount of 0.01 wt% to 0.5 wt%, preferably 0.01 wt% to 0.31 wt%.

[0057] Meanwhile, the weight ratios of the three compounds of lithium orthosilicate, lithium metasilicate, and lithium disilicate may be set differently while maintaining the silicon weight constant within the lithium silicate matrix. In one embodiment of the present invention, the silicon content within the lithium silicate matrix may be maintained at 40 wt% to 45 wt% based on the total weight of the lithium silicate matrix and silicon particles, while the contents of lithium orthosilicate, lithium metasilicate, and lithium disilicate may be configured differently. At this time, lithium orthosilicate may be included at 5 wt% to 35 wt%, preferably 10 wt% to 32 wt%, lithium metasilicate at 30 wt% to 60 wt%, preferably 31 wt% to 55 wt%, and lithium disilicate at 0.01 wt% to 0.4 wt%, preferably 0.01 wt% to 0.2 wt%.

[0058] In one embodiment of the present invention, the average particle diameter of the composite negative electrode material including the lithium silicate matrix and silicon may be 1 µm to 20 µm, preferably 1 µm to 15 µm.

[0059] Meanwhile, the composite negative electrode material for a lithium secondary battery according to the present invention may further include a carbon material.

[0060] The carbon material helps to maintain the lithium silicate matrix within the composite anode material more firmly. The composite anode material of the present invention can use an aqueous binder with excellent binding force due to the large volume change during charge and discharge. At this time, lithium silicate can react with water, which is the solvent of the aqueous binder, and decompose into LiOH and SiO2, but the carbon material can maintain the lithium silicate matrix firmly, thereby reducing the possibility of a reaction between water and lithium silicate.

[0061] In one embodiment of the present invention, the carbon material may be present in the form of a lithium silicate matrix coating within the composite negative electrode material. Since the carbon material is present in the form of a lithium silicate matrix coating, the reaction between lithium silicate and water can be effectively blocked.

[0062] In one embodiment of the present invention, the carbon material may be one or more compounds selected from the group consisting of graphene, carbon nanotubes (CNTs), carbon fibers, crystalline carbon, and amorphous carbon, and graphene is most preferable in terms of electrical conductivity and mitigating volume change during charge and discharge.

[0063] At this time, the crystalline carbon may be graphite such as natural graphite or artificial graphite in the form of an amorphous, plate-like, flake-like, spherical or fiber-like form, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, or a mixture thereof.

[0064] At this time, the crystalline carbon or amorphous carbon or graphene, carbon nanotube is subjected to additional heat treatment. D / I G You can adjust the ratio, I D / I G The lower the value is, the more desirable it is. (I D / I G is the relative intensity ratio of the D band peak and the G band peak in the Raman spectrum, obtained by Raman spectroscopy using a laser with a wavelength of 532 nm, which is 1,360±50 cm -1 The maximum peak intensity of the D band in (I D ) for 1,580±50cm -1 The maximum peak intensity of the G band in (I G ) means rain.)

[0065] In one embodiment of the present invention, the average particle diameter of the carbon material may be 10 nm to 500 nm, preferably 20 nm to 300 nm, and more preferably 5 nm to 50 nm.

[0066] According to one embodiment of the present invention, D of the composite negative electrode material for the lithium secondary battery 50 The silver may be 3㎛ to 10㎛.

[0067] According to one embodiment of the present invention, the specific surface area of ​​the composite negative electrode material for the lithium secondary battery is 1 to 10 m 2 g -1 It could be.

[0068] Meanwhile, the present invention can provide a method for manufacturing the composite anode material. In the present invention, the composite anode material can be manufactured by lithiothermic reduction reaction (LTRR). Specifically, the present invention

[0069] (S1) Mix Si and SiO2 in a mole ratio of 1:0.7 to 1:1.5 to form silicon (SiO x, 0 <x<2) 혼합물을 준비하는 단계;

[0070] (S2) A step of mixing the silicon mixture and the lithium compound in a molar ratio of 1:1 to 1:1.5 to prepare a silicon-lithium mixture;

[0071] (S3) A method for manufacturing a composite negative electrode material is provided, including a step of heating the silicon-lithium mixture.

[0072] The inventors of the present invention have confirmed that when a composite negative electrode material including lithium is manufactured using the above-described Lithiothermic reduction reaction (LTRR) manufacturing method, particularly lithium in a gaseous state, lithium orthosilicate, lithium metasilicate, and lithium disilicate can be effectively incorporated into a matrix.

[0073] Meanwhile, the present invention may further include a step of introducing a carbon material into the composite anode material (S4). The method for introducing the carbon material may use a known method, and for example, the carbon material may be introduced into the composite anode material through chemical vapor deposition (CVD) or simple mixing.

[0074] In one embodiment of the present invention, the molar ratio of Si and SiO2 in the step (S1) may preferably be 1:0.7 to 1:1.5. At this time, mixing SiO2 in a content of 100 mol% or less of Si in the step (S1) is not preferable because the final product, Li2Si2O5, may not be produced.

[0075] In one embodiment of the present invention, the molar ratio of the silicon mixture to the lithium mixture in step (S2) may preferably be 1:1 to 1:1.5. In this case, if the molar ratio of the lithium mixture to the silicon mixture in step (S2) is outside the above range, unreacted SiO2 may be present, which is undesirable.

[0076] In one embodiment of the present invention, the lithium compound of the step (S2) may be one or more compounds selected from the group consisting of lithium metal, lithium oxide, lithium hydroxide, and lithium alloy, and lithium metal is most preferred in terms of generating gaseous state lithium.

[0077] In one embodiment of the present invention, the heating step in the step (S3) may be a step of heating at 500°C to 1,500°C, preferably 500°C to 1,000°C, for 2 to 7 hours.

[0078] The above heating temperature is a temperature at which Si and SiO2 can exist simultaneously in a solid state, and at which lithium exists in a gaseous state. Since the lithiothermic reduction reaction (LTRR) is a reaction that proceeds using gaseous lithium Li(g), the above heating temperature range is an essential temperature range for implementing the manufacturing method of the present invention.

[0079]

[0080] 2. Cathode

[0081] In another embodiment of the present invention, a lithium secondary battery can be provided, including a negative electrode including the composite negative electrode material; a positive electrode; a separator; and an electrolyte.

[0082] Specifically, the lithium secondary battery of the present invention can be manufactured by injecting an electrolyte into an electrode structure comprising a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. At this time, the positive electrode, negative electrode, and separator forming the electrode structure can all be those conventionally used in the manufacture of lithium secondary batteries.

[0083] First, the negative electrode can be manufactured by forming a negative electrode composite layer on a negative electrode current collector. The negative electrode composite layer can be formed by coating a slurry containing a composite negative electrode material, a binder, a conductive material, a solvent, etc. on a negative electrode current collector, followed by drying and rolling.

[0084] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy, preferably copper.

[0085] The above negative electrode current collector may typically have a thickness of 3 to 500 μm.

[0086] The above-described negative electrode collector may have fine irregularities formed on its surface to enhance bonding strength with the composite negative electrode material. For example, the above-described negative electrode collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0087] A slurry containing a composite negative electrode material is applied onto the negative electrode current collector. The slurry may be applied, rolled, and dried onto the negative electrode current collector to form a composite negative electrode material layer.

[0088] The above slurry may be applied to one or both sides of the negative electrode current collector. When the above slurry is applied to both sides of the negative electrode current collector, a composite negative electrode material layer may be formed on both sides of the negative electrode current collector.

[0089] In order to sufficiently implement the high capacity of silicon in a secondary battery while minimizing the impact of volume expansion / contraction of silicon on the battery, the composite negative electrode material may be included in the negative electrode slurry at 50 wt% to 85 wt%, preferably 65 wt% to 80 wt%, based on the solid content of the negative electrode slurry.

[0090] The above slurry may further include a negative electrode conductive material and / or a negative electrode binder together with the above composite negative electrode material. The negative electrode binder may be used to improve the adhesion between the Si-based material and the negative electrode current collector, or to improve the bonding between Si-based materials. Specifically, the negative electrode binder may include at least one selected from the group consisting of styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluoro rubber, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacryl amide (PAM), in that it can further improve electrode adhesion and provide sufficient resistance to volume expansion / contraction of the Si-based active material.

[0091] The above-mentioned negative electrode binder may be included in the negative electrode slurry at 5 wt% to 30 wt%, preferably 10 wt% to 25 wt%, based on the solid content of the negative electrode slurry. When the amount is within the above range, silicon can be better bound, minimizing the problem of volume expansion of the active material, and at the same time, when preparing a slurry for forming a composite negative electrode material layer, facilitating dispersion of the negative electrode binder and improving the coatability and phase stability of the slurry.

[0092] The above-described negative conductive material may be used to assist and improve conductivity, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the above-described negative conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably, in order to realize high conductivity, the negative conductive material may include carbon black.

[0093] The above negative electrode conductive material facilitates the dispersion of the negative electrode conductive material during the preparation of slurry for forming a composite negative electrode material layer, and in terms of further improving the electrical conductivity, the specific surface area of ​​the negative electrode conductive material is 80 m 2 / g to 200m 2 / g, preferably 100m 2 / g to 150m 2 / g may be.

[0094] The above-mentioned negative electrode conductive material may be included in the negative electrode slurry in an amount of 5 wt% to 20 wt%, preferably 7 wt% to 15 wt%, based on the solid content of the negative electrode slurry, and is preferable in that it can form an excellent conductive network while alleviating the increase in resistance due to the negative electrode binder when included in the above range.

[0095] Meanwhile, according to one embodiment of the present invention, in addition to the carbon-based material described above, a material containing a metal element (e.g., metal powder) may be used as a conductive material. The material containing the metal element may be a material containing one or more elements selected from the group consisting of silver (Ag), gold (Au), tin (Sn), copper (Cu), nickel (Ni), and zinc (Zn), and preferably may be in the form of an alloy. In addition, a metal capable of forming an alloy with lithium may also be used as a conductive material.

[0096] Here, the metal that can be alloyed with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth element, or a combination thereof, and is not Si), Sn-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth element, or a combination thereof, and is not Sn).

[0097] The above element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, or Te.

[0098] Additionally, the material containing the metal element may have a spherical particle or wire shape.

[0099] The above-described negative electrode slurry may further include a solvent for forming a negative electrode slurry for mixing and dispersing the composite negative electrode material, the negative electrode binder and / or the negative electrode conductive material. The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of NMP (N-methyl-2-pyrrolidone), distilled water, ethanol, methanol and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the composite negative electrode material, the negative electrode binder and / or the negative electrode conductive material.

[0100] The solid content of the above cathode slurry may be 20 wt% to 35 wt%, preferably 23 wt% to 30 wt%, and when within the above range, the viscosity is lowered to an appropriate level, which is advantageous for coating a low-loading composite cathode material layer.

[0101]

[0102] 3. Bipolar

[0103] In one embodiment of the present invention, the positive electrode combined with the negative electrode including the composite negative electrode material may include a current collector and a positive electrode mixture layer formed on the current collector. The positive electrode mixture layer may be formed by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material, a solvent, etc. on a positive electrode current collector, followed by drying and rolling.

[0104] The above positive electrode active material is a compound capable of reversible lithiation and de-lithiation of lithium, and specifically may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O 4　 etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn YO2 (here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(wherein, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1)), and one or more compounds of these may be included.

[0105] Among these, the lithium composite metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2)O2,Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) etc.

[0106] The above positive electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the solid content in the positive electrode slurry.

[0107] The above binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0108] The above-mentioned conductive agent is typically added in an amount of 1 to 30 wt% based on the total weight of the solid content in the positive electrode slurry.

[0109] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include: graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, and nickel powders; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive agents include acetylene black series (Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company), Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

[0110] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desirable viscosity when including the positive electrode active material and optionally a binder and a conductive material. For example, the solvent may be included so that the solid concentration in the slurry including the positive electrode active material and optionally a binder and a conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0111]

[0112] 4. Membrane

[0113] In addition, the separator serves to block internal short circuits of both electrodes and impregnate the electrolyte. The separator composition may be prepared by mixing a polymer resin, a filler, and a solvent, and then the separator composition may be directly coated and dried on the top of the electrode to form a separator film, or the separator composition may be cast on a support and dried, and then the separator film peeled from the support may be laminated on the top of the electrode.

[0114] The above separator may be a porous polymer film that is commonly used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, which may be used alone or in a laminated manner, or a porous nonwoven fabric that is commonly used, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is not limited thereto.

[0115] At this time, the pore diameter of the porous separation membrane may generally be 0.01 to 50 μm, and the porosity may be 5 to 95%. In addition, the thickness of the porous separation membrane may generally be in the range of 5 to 300 μm.

[0116] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0117] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited by the following contents.

[0118]

[0119] [Manufacturing Preparation Example 1: Si / Li x Si y Oz Manufacturing of composite cathode materials]

[0120] In manufacturing the composite cathode material of the present invention, the lithiothermic reduction reaction (LTRR) method was used. Specifically, Si powder and SiO2 powder were mixed in a molar ratio of 1:0.7 to 1.5 and ball-milled to produce silicon (SiO x, 0 <x<2) 혼합물을 준비하였다. 이후 상기 실리콘 혼합물과 리튬 메탈을 1:1.3~1.4의 몰 비로 혼합한 뒤, 아르곤이 채워진 스테인리스 스틸 튜브에 투입하고 3 시간 동안 1,500℃에서 가열하여 기상 리튬 Li(g)와 실리콘 혼합물을 반응시켜 복합 음극재 Si / Li x Si y O z was manufactured.

[0121]

[0122] [Manufacturing Preparation Example 2: Electrode Manufacturing]

[0123] Example 1: Composite cathode material Si / Li x Si y O z Electrode containing / C

[0124] Composite cathode material Si / Li manufactured in Manufacturing Preparation Example 1 based on the total weight of the composite cathode material x Si y O z After mixing 60 wt% of PVdF, 20 wt% of Super-P (conductive material Timcal), and 20 wt% of NMP solvent, an electrode slurry was prepared using a centrifugal mixer. After that, the electrode slurry was coated on a copper foil using a doctor blade and dried in a vacuum oven at 110°C for 12 hours to prepare an electrode.

[0125]

[0126] Example 2: Composite cathode material Si / Li x Si y Oz Electrode containing @Gr / C

[0127] Si / Li as a composite cathode material x Si y O z Instead, Si / Li x Si y O z and graphite mixed (Si / Li) x Si y O z An electrode was manufactured in the same manner as in Example 1, except for @Gr / C. Based on the total weight of the composite anode material, the graphite was included in an amount of 72 wt%, and the conductive material, Super P, was included in an amount of 2 wt%.

[0128]

[0129] Example 3: Composite cathode material Si / Li x Si y O z Electrode containing @Gr / C

[0130] An electrode was manufactured in the same manner as in Example 2, except that 5 wt% of Super P, which corresponds to a conductive material, was used.

[0131]

[0132] Active material (Si / Li) x Si y O z Graphite (Gr) Binder (PVdF) Conductive (Super P) Example 160 wt% -20 wt% 20 wt% Example 220 wt% 72 wt% 6 wt% 2 wt% Example 320 wt% 72 wt% 3 wt% 5 wt%

[0133]

[0134] Comparative Example 1: Electrode containing pure Si / C

[0135] Si / Li x Si y O z An electrode was manufactured in the same manner as in Example 1, except that pure Si (manufactured by Alpha Aesar) was used instead.

[0136]

[0137] [Experimental Example 1: X-Ray Diffraction]

[0138] Si / Li synthesized in the above manufacturing preparation example 1 using XRD (X-Ray diffraction) x Si y O z The crystal structure was confirmed, and the results are shown in Fig. 2.

[0139] Referring to Figure 2, it can be confirmed that the lithium silicate and lithium disilicate structures are well developed in addition to pure Si. That is, it can be confirmed that the LTRR reaction has progressed through the presence of lithium silicate and lithium disilicate, rather than the Si and SiO2 peaks initially introduced into the reaction.

[0140]

[0141] [Experimental Example 2: TEM]

[0142] The distribution of atoms in the composite cathode material was observed using HIGH ANGLE ANNULAR DARK FIELD IMAE (HADDF)-TEM, ENERGY-DISPERSIVE X-RAY SPECTROSCOPY (EDX), and ELECTRON ENERGY LOSS SPECTROSCOPY (EELS) techniques, and the results are shown in Fig. 3.

[0143] Referring to Figure 3, silicon and lithium silicate (Li x Si y O z ) is coated with a carbon layer, and it can be confirmed that the elements forming the composite negative electrode material for lithium secondary batteries are uniformly distributed.

[0144]

[0145] [Experimental Example 3: Electrochemical Performance Evaluation]

[0146] Battery manufacturing

[0147] 2032 coin cells were manufactured using the electrodes manufactured in the above examples and comparative examples and lithium metal (Honjo Metal Co., Ltd.) as a counter electrode. Cellgard 2400 (Asahi Kasei Co., Ltd.) was used as a separator, and 1.0 M LiPF6 salt and 10 vol% FEC (fluoro-ethylene carbonate) as an additive were dissolved in a solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 (v / v) ratio and used as an electrolyte.

[0148]

[0149] Speed ​​characteristic evaluation

[0150] The capacity of the coin cells manufactured using the electrodes of Example 2 and Comparative Example 1 was measured while changing the current from 0.05 C to 1.6 C, and the results are shown in Fig. 4. As can be seen in Fig. 4, it can be confirmed that the coin cell using the electrode manufactured in Example 2 has a higher capacity than the coin cell using the electrode manufactured in Comparative Example 1 even when a higher current is applied.

[0151]

[0152] Life Characteristics Assessment

[0153] The capacity per cycle was measured while charging / discharging at 0.1 C for coin cells manufactured using the electrodes of Examples 2 and 3 and Comparative Example 1, and the results are shown in Fig. 5. As can be seen in Fig. 5, it can be confirmed that the coin cells using the electrodes manufactured in Examples 2 and 3 exhibit superior life performance than the coin cells using the electrodes manufactured in Comparative Example 1.

[0154]

[0155] Initial Coulomb Efficiency Evaluation

[0156] The initial coulombic efficiency of the coin cell manufactured using the electrode of Example 1 was measured by charging / discharging at 0.1 C, and the results are shown in Fig. 6. At this time, pressure was applied to the electrode to adjust the tap density of the electrode to 0.75 to 1.4 gcm. -3 As can be seen in Fig. 6a and Fig. 6b, the tap density of the electrode of Example 1 was 0.78 gcm -3 Despite the low tap density, it exhibited a high Coulombic efficiency of 83.5%, and it was confirmed that as the tap density of the electrode increased, the initial Coulombic efficiency decreased due to the exposure of the electrolyte on the surface of the active material particles. In other words, the composite negative electrode material of the present invention is significant in that it can exhibit a high initial Coulombic efficiency even at a low tap density.

[0157] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. Lithium silicate (Li x Si y O z ) containing a matrix and silicon particles, Composite cathode material for lithium secondary batteries. (Here, 2≤x≤4, 1≤y≤2, 3≤z≤5).

2. In paragraph 1, The above lithium silicate matrix A composite negative electrode material for a lithium secondary battery, comprising at least one compound selected from the group consisting of lithium orthosilicate, lithium metasilicate, and lithium disilicate.

3. In paragraph 2, A composite anode material for a lithium secondary battery, wherein, based on the total weight of three compounds of lithium orthosilicate, lithium metasilicate, and lithium disilicate excluding silicon in the composite anode material of a lithium secondary battery including the lithium silicate matrix and silicon, the lithium orthosilicate is contained in an amount of 15 to 55 wt%, the lithium metasilicate is contained in an amount of 45 to 90 wt%, and the lithium disilicate is contained in an amount of 0.01 to 0.5 wt%.

4. In paragraph 2, A composite anode material for a lithium secondary battery, wherein when the content of silicon in the lithium silicate matrix is ​​maintained at 40 wt% to 45 wt% based on the total weight of the lithium silicate matrix and silicon particles, lithium orthosilicate is contained at 5 wt% to 35 wt%, lithium metasilicate is contained at 30 wt% to 60 wt%, and lithium disilicate is contained at 0.01 wt% to 0.4 wt%.

5. In paragraph 1, A composite negative electrode material for a lithium secondary battery, wherein the average particle diameter of the lithium silicate matrix including the silicon particles is 1 to 20 μm.

6. In paragraph 1, A composite anode material for a lithium secondary battery, wherein the composite anode material for a lithium secondary battery further contains a carbon material.

7. In paragraph 6, A composite anode material for a lithium secondary battery, wherein the carbon material is at least one compound selected from the group consisting of graphene, carbon nanotubes (CNTs), carbon fibers, crystalline carbon, and amorphous carbon.

8. In paragraph 6, The above crystalline carbon or amorphous carbon or graphene, carbon nanotubes are I through additional heat treatment. D / I G You can adjust the ratio, I D / I G A negative electrode composite for a lithium secondary battery characterized in that the ratio is 1.0 or less 9. A negative electrode for a lithium secondary battery, comprising the composite negative electrode material for a lithium secondary battery of paragraph 1.

10. In the 8th paragraph, the electrode density of the negative electrode for the lithium secondary battery is 1.2 g / cm -3 A negative electrode for a lithium secondary battery, comprising a composite negative electrode material for a lithium secondary battery. 11.(S1) Si and SiO 2 Mixing silicon (SiO) x, 0 <x<2) 혼합물을 준비하는 단계; (S2) a step of preparing a silicon-lithium mixture by further adding a lithium compound to the silicon mixture; and (S3) A method for manufacturing a composite negative electrode material, comprising: a step of heating the silicon-lithium mixture.

12. In paragraph 10, Si and SiO in the above step (S1) 2 A method for manufacturing a composite cathode material, wherein the mixture is mixed at a mole ratio of 1:0.7 to 1:1.

5.

13. In paragraph 10, A method for manufacturing a composite negative electrode material, wherein in the step (S2), the lithium compound further includes Si and a lithium compound in a molar ratio of 1:1 to 1:1.

5.

14. In paragraph 10, A method for manufacturing a composite negative electrode material, wherein the lithium compound of the step (S2) is at least one compound selected from the group consisting of lithium metal, lithium oxide, lithium hydroxide, and lithium alloy.

15. In paragraph 10, A method for manufacturing a composite negative electrode material, wherein the step of heating the silicon-lithium mixture in the above step (S3) is a step of heating at 500°C to 1,500°C for 2 to 7 hours.

16. In paragraph 10, (S4) A method for manufacturing a composite cathode material, further comprising a step of introducing a carbon material into the composite cathode material.

17. A negative electrode for a lithium secondary battery, comprising the composite negative electrode material of clause 1.

18. In paragraph 16, The above negative electrode for a lithium secondary battery has an electrode tap density of 0.7 to 1.6 g / cm 3 A cathode for a lithium secondary battery.

Images