Anode for lithium secondary battery, lithium secondary battery including the same, and method for manufacturing anode for lithium secondary battery

Abstract

The present invention is based on SiO x The present invention relates to a negative electrode for a lithium secondary battery, the negative electrode comprising a silicon-based negative electrode active material containing (0≦x<2) and Si nanoparticles; a negative electrode conductive material; and a negative electrode active material layer comprising a negative electrode binder, wherein the silicon-based negative electrode active material is in an uncoated state with carbon, the Si nanoparticles have an average particle size (D50) of 1 nm or less, and at least one side of the negative electrode active material layer is prelithiated, a lithium secondary battery including the same, and a method for manufacturing a negative electrode for a lithium secondary battery.

Description

[Technical Field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2023-0129932 filed with the Korean Intellectual Property Office on September 27, 2023, and Korean Patent Application No. 10-2024-0130673 filed with the Korean Intellectual Property Office on September 26, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the same, and a method for producing a negative electrode for a lithium secondary battery. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched areas as part of this is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices continues to grow, demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and widely used. Furthermore, active research is being conducted on methods for fabricating high-density electrodes with even higher energy density per unit volume for such high-capacity lithium secondary batteries, and there is a trend toward higher loading to improve energy density. However, this also increases electrode resistance and cell resistance, making it difficult to achieve performance such as high output and rapid charging. To address this issue, attempts have been made to physically expand the reaction surface and reduce resistance by fabricating patterned electrodes. Patterned electrodes enable improved performance by inducing reactions not only on the surface but also in the depth direction of the electrode.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] Generally, carbon materials such as graphite are used for the negative electrode of lithium secondary batteries, but the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm 3 ) Therefore, in order to improve the energy density of the anode, silicon (Si), tin (Sn), and their oxides and alloys, which are alloyed with lithium, are being considered as anode materials. Among these, silicon-based materials are attracting attention because they are inexpensive and have a high capacity (4200mAh / g).

[0008] However, silicon-based materials have the problem that their mechanical stability is reduced due to volume changes (shrinkage or expansion) during the lithium ion insertion / extraction process, resulting in impaired cycle performance. Therefore, it is necessary to develop materials that have structural stability and can ensure excellent stability and cycle performance when used as an active material in electrochemical devices.

[0009] Furthermore, when silicon-based negative electrode active materials are used, the problem of high initial irreversible capacity arises. During the charge-discharge reaction of a lithium secondary battery, lithium is released from the positive electrode and inserted into the negative electrode during charging, and then released from the negative electrode and returned to the positive electrode during discharge. However, in the case of silicon-based negative electrode active materials, due to severe volume changes and surface side reactions, much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a problem of high initial irreversible capacity. This high initial irreversible capacity leads to a problem of a rapid decrease in the initial capacity and efficiency of the battery.

[0010] To solve the above problems, a method of prelithiating a silicon negative electrode containing a silicon-based negative electrode active material is known. Known prelithiating methods include a method of preparing an electrode after lithiating the silicon negative electrode by a physical / chemical method such as electroplating, lithium metal transfer, or lithium metal vapor deposition, and a method of electrochemically prelithiating the negative electrode. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2022-0103469 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention relates to a negative electrode for a lithium secondary battery that can improve the initial capacity, efficiency, and lifespan of the battery, a lithium secondary battery including the same, and a method for manufacturing the negative electrode for a lithium secondary battery. [Means for solving the problem]

[0013] One embodiment of the present invention is a SiO x(0≦x<2) and a silicon-based negative electrode active material including Si nanoparticles; a negative electrode conductive material; and a negative electrode active material layer including a negative electrode binder, the silicon-based negative electrode active material is in an uncoated carbon state, The average particle size (D50) of the Si nanoparticles is 1 nm or less, The present invention provides a negative electrode for a lithium secondary battery, wherein at least one surface of the negative electrode active material layer is prelithiated.

[0014] One embodiment of the present specification relates to a positive electrode for a lithium secondary battery; The aforementioned negative electrode for lithium secondary batteries; a separator disposed between the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery; and A lithium secondary battery is provided that includes an electrolyte.

[0015] Another embodiment of the present specification provides a battery module including the above-described lithium secondary battery.

[0016] Yet another embodiment of the present specification provides a battery pack including the above-described lithium secondary battery.

[0017] One embodiment of the present disclosure provides a battery pack including the above-described battery module.

[0018] Finally, one embodiment of the present specification provides a method for manufacturing a negative electrode comprising the steps of: providing a negative electrode active material layer; and prelithiating at least one surface of the negative electrode active material layer; The negative electrode active material layer is made of SiO x (0≦x<2) and a silicon-based negative electrode active material including Si nanoparticles; a negative electrode conductive material; and a negative electrode binder, the silicon-based negative electrode active material is in an uncoated carbon state, The method for producing a negative electrode for a lithium secondary battery is provided, wherein the average particle size (D50) of the Si nanoparticles is 1 nm or less. [Effects of the Invention]

[0019] The negative electrode for a lithium secondary battery according to one embodiment of the present specification maintains the size of Si nanoparticles in the silicon-based negative electrode active material small, thereby maintaining the initial battery capacity and efficiency and providing advantageous benefits in terms of battery life performance.

[0020] Furthermore, by carrying out a prelithiation process on the negative electrode for a lithium secondary battery according to the above-described embodiment, the low conductivity and initial efficiency of the silicon-based negative electrode active material can be improved, contributing to the development of the initial capacity of the battery and increasing the energy density. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present specification. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present specification. DETAILED DESCRIPTION OF THE INVENTION

[0022] Before describing the present invention, some terms will first be defined.

[0023] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0024] It should be understood that in this specification, terms such as "comprises," "provides," or "has" specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0025] As used herein, when a part such as a layer exists "on" or "above" another part, it refers not only to the part being "directly above" the other part, but also to the case where there is another part between them. In contrast, when a part exists "directly above" another part, it means that there is no other part between them. Furthermore, when a part exists "on" or "above" a reference part, it means that the part is located above or below the reference part, and does not necessarily mean that the part is located "above" or "above" the reference part in the opposite direction of gravity.

[0026] In this specification, when a certain component is provided on "both sides" of another component, it means that a component is provided on one side of the other component, and a component is provided on the other side corresponding to the one side. This includes not only the case where one side of a component is in direct contact with the other side of the other component, but also the case where another component is present between the two components.

[0027] In this specification, "p to q" means a range of "not less than p and not more than q."

[0028] In this specification, the terms "unit" and "device" refer to a unit that processes at least one function or operation.

[0029] In this specification, "Dn" refers to particle size distribution and refers to the particle size (average particle size) at the n% point of the cumulative particle number distribution according to particle size. That is, D50 is the particle size at the 50% point of the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size when the particles pass through a laser beam.

[0030] In this specification, the average particle size of Si nanoparticles can be confirmed by X-ray diffraction analysis, which can be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endeavor, manufacturer: Bruker). Specifically, XRD measurement can be performed by placing a powder sample in a holder and measuring with Cu K alpha X-rays. The size of Si nanoparticles can be calculated by fitting the XRD results using the Scherrer equation, and the nanoparticles can be measured based on Si(220) (2θ=47.5°-48.5°).

[0031] In one embodiment of the present specification, the particle size or particle size may refer to the average diameter or typical diameter of the individual particles that make up the metal powder.

[0032] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0033] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0034] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0035] The negative electrode for a lithium secondary battery according to one embodiment of the present specification is made of SiO x(0≦x<2) and a silicon-based negative electrode active material containing Si nanoparticles; a negative electrode conductive material; and a negative electrode active material layer containing a negative electrode binder, wherein the silicon-based negative electrode active material is in an uncoated state with carbon, the Si nanoparticles have an average particle size (D50) of 1 nm or less, and at least one surface of the negative electrode active material layer is prelithiated.

[0036] In the charge-discharge reaction of a lithium secondary battery, lithium is released from the positive electrode and inserted into the negative electrode during charging, and is released from the negative electrode and returned to the positive electrode during discharge. However, in the case of silicon-based negative electrode active materials, due to severe volume changes and surface side reactions, much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a problem of large initial irreversible capacity. This large initial irreversible capacity leads to problems such as a rapid decrease in battery capacity and cycle life.

[0037] In the case of the present invention, by performing a prelithiation pretreatment on at least one surface of the negative electrode active material layer according to one embodiment of the present specification, the problem of initial irreversible capacity is solved and the battery capacity and lifespan are improved. In particular, by containing small-sized Si nanoparticles, stress is not applied to surrounding materials in the negative electrode in the process of reacting with lithium and expanding in volume during charging of the lithium secondary battery, and the battery lifespan can be maintained well.

[0038] The negative electrode active material layer according to one embodiment of the present specification is made of SiO x (0≦x<2) and may include a silicon-based negative electrode active material including Si nanoparticles.

[0039] The SiO x (0≦x<2) may exist in an amorphous state and contain randomly dispersed nano-sized Si particles therein, and the randomly dispersed nano-sized Si particles are referred to as Si nanoparticles in this specification.

[0040] That is, SiO 2 according to one embodiment of the present specification x(0≦x<2) may be an amorphous phase with Si nanoparticles dispersed therein, which can be confirmed by TEM (Transmission Electron Microscopy) or XRD (X-ray diffraction) analysis.

[0041] The SiO x (0≦x<2) corresponds to the matrix of the amorphous phase in the silicon-based negative electrode active material. x (0≦x<2) may be in a form containing Si and SiO2 in part, and the Si may form a phase. That is, the x may be the SiO x (0≦x<2) corresponds to the ratio of O to Si. x When (0≦x<2) is included, the discharge capacity of the secondary battery can be improved.

[0042] The silicon-based negative electrode active material may be formed by heating and vaporizing a mixed powder of Si powder and SiO2 powder, and then depositing the vaporized mixed gas. Specifically, the mixed powder of Si powder and SiO2 powder may be heat-treated at 1400°C to 1800°C or 1400°C to 1600°C under vacuum.

[0043] In one embodiment of the present specification, the average particle size (D50) of the Si nanoparticles may be 1 nm or less, specifically 0.8 nm or less.

[0044] In one embodiment of the present specification, the average particle size (D50) of the Si nanoparticles may be 0.1 nm or more, specifically 0.3 nm or more.

[0045] At this time, the amorphous SiO x The average particle size (D50) of the Si nanoparticles dispersed in (0≦x<2) can be measured by X-ray diffraction analysis.

[0046] Originally, silicon-based negative electrode active materials undergo extremely complex crystalline changes during the electrochemical reaction of absorbing, storing, and releasing lithium atoms. As the reaction of electrochemically absorbing, storing, and releasing lithium atoms progresses, the composition and crystalline structure of the silicon particles change to Si (crystalline structure: Fd3m), LiSi (crystalline structure: I41 / a), Li2Si (crystalline structure: C2 / m), Li7Si2 (Pbam), Li 22 The silicon nanoparticles change to Si5(F23), etc., and the volume of the silicon particles expands by approximately four times due to the change in their complex crystal structure. As a result, repeated charge-discharge cycles can destroy the silicon particles and form bonds between lithium atoms and silicon particles, damaging the lithium atom insertion sites that the silicon particles initially had, which can significantly reduce cycle life. In particular, in the case of a negative electrode manufactured from a negative electrode active material in accordance with one embodiment of the present specification, in which the Si nanoparticles have an average particle size (D50) of more than 1 nm, the volume expands due to reaction with lithium during charge-discharge of a lithium secondary battery, causing stress to the surrounding materials in the negative electrode, resulting in reduced battery life and other battery performance degradation. Therefore, it is preferable that the Si nanoparticles satisfy the above average particle size (D50) range.

[0047] In addition, the silicon-based negative electrode active material according to one embodiment of the present specification may be in an uncoated state with carbon.

[0048] Conventionally, a carbon coating layer has been formed on the surface of a silicon-based negative electrode active material to improve the low conductivity of the silicon-based negative electrode active material and mitigate the volume expansion of the silicon-based active material during charge and discharge. However, during the additional heat treatment process to form the coating layer, Si nanoparticles in the silicon-based negative electrode active material grow to several tens of nanometers, causing them to react with lithium. This volume expansion, as mentioned above, significantly reduces the capacity and lifespan of the negative electrode.

[0049] Typically, an additional heat treatment process for carbon coating a silicon-based negative electrode active material is performed at a temperature of 700° C. to 1200° C. However, the negative electrode active material according to one embodiment of the present specification does not require an additional heat treatment at this temperature range, thereby satisfying the above-mentioned average particle size (D50) range of the Si nanoparticles, thereby preventing the problem of reduced battery life due to volume expansion of silicon.

[0050] Specifically, carbon-uncoated SiO x In order to control the average particle size (D50) of the Si nanoparticles dispersed in (0≦x<2), it is possible to apply a method of limiting the heat treatment temperature and time. For example, Si nanoparticles with an average particle size (D50) of 1 nm or less can be formed by heat treatment at a temperature of 1000°C or less for 30 minutes or less.

[0051] Therefore, the anode active material layer according to one embodiment of the present specification is characterized by including a silicon-based anode active material that is not coated with carbon, i.e., a silicon-based anode active material that is not coated with carbon. This allows the size of Si nanoparticles to be maintained small, which prevents stress from being imposed on surrounding materials in the anode as they react with lithium and expand in volume during charge and discharge. It also reduces the process costs and time required for carbon coating. Furthermore, the low conductivity due to the lack of carbon coating can be sufficiently overcome by performing prelithiation, as described below.

[0052] The presence or absence of the carbon coating on the silicon-based negative electrode active material layer can be confirmed by an image formed by transmitting an electron beam accelerated by a high voltage through the silicon-based negative electrode active material layer using a transmission electron microscope (TEM).

[0053] The negative electrode for a lithium secondary battery according to one embodiment of the present specification is a negative electrode active material layer containing 100 parts by weight of the SiO x(0≦x<2) may be contained in an amount of 60 parts by weight or more and 95 parts by weight or less, specifically 65 parts by weight or more and 90 parts by weight or less, more specifically 70 parts by weight or more and 85 parts by weight or less. x When the content of (0≦x<2) satisfies the above range, the capacity and energy density can be increased.

[0054] The silicon-based negative electrode active material according to one embodiment of the present specification may be coated with a material other than carbon, or may be SiO 2 without being coated with a material other than carbon. x (0≦x<2) may be in a form exposed to the negative electrode binder and the negative electrode conductive material.

[0055] The silicon-based negative electrode active material according to an embodiment of the present specification may contain metal impurities.

[0056] The metal impurities may be contained in silicon, and the content thereof may be in the range of 0.1 parts by weight or less based on 100 parts by weight of the total silicon-based active material.

[0057] Meanwhile, the average particle size (D50) of the silicon-based negative electrode active material according to one embodiment of the present specification may be 1 μm to 10 μm, specifically 3 μm to 8 μm. In this case, the average particle size (D50) is determined by the SiO x The average particle size (D50) of the final particles containing both (0≦x<2) and Si nanoparticles can be used as a criterion.

[0058] When the average particle size (D50) is within the above range, the specific surface area of ​​the particles is within a suitable range, thereby forming a negative electrode slurry with a suitable viscosity. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based negative electrode active material is equal to or greater than the lower limit of the above range, the contact area between the silicon-based negative electrode active material particles and the conductive material is improved by the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of maintaining a conductive network and improving capacity retention. Meanwhile, when the average particle size (D50) is within the above range, excessively large silicon-based negative electrode active material particles are eliminated, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0059] In one embodiment of the present specification, the silicon-based negative electrode active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based negative electrode active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0060] In addition, the negative electrode for a lithium secondary battery according to an embodiment of the present specification may contain 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more of the silicon-based negative electrode active material, based on 100 parts by weight of the negative electrode active material layer, and may contain 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

[0061] The negative electrode for a lithium secondary battery according to one embodiment of the present specification contains a high content of a silicon-based negative electrode active material having an extremely high capacity, thereby increasing the energy density. Furthermore, even when used at a high content, the negative electrode contains both a negative electrode conductive material and a negative electrode binder that can suppress the volume expansion rate during charge and discharge. This prevents a decrease in the performance of the negative electrode, and provides excellent output characteristics during charge and discharge.

[0062] In one embodiment of the present specification, at least one surface of the negative electrode active material layer may be pre-lithiated.

[0063] In one embodiment of the present specification, the negative electrode active material layer may be one in which one surface is prelithiated, or both surfaces thereof may be prelithiated.

[0064] Lithium secondary batteries begin to lose lithium during the first charge after battery fabrication, and the loss continues during subsequent charge-discharge cycles and high-temperature storage, resulting in battery degradation. To compensate for this lithium loss, additional lithium is added to the battery before operation, a process known as pre-lithiation. In an embodiment of the present specification, a negative electrode for a lithium secondary battery is pre-lithiated on at least one side of the negative electrode active material layer, thereby increasing the battery capacity and improving its lifespan.

[0065] In one embodiment of the present specification, the prelithiation may be performed by a lithium electroplating process; a lithium metal transfer process; a lithium metal vapor deposition process; or a stabilized lithium metal powder (SLMP) coating process. Specifically, the prelithiation may be performed by a method of injecting a compound containing excess lithium as an additive during battery fabrication; a process of laminating a lithium metal thin film on the surface of an electrode active material to fabricate an electrode assembly, and then injecting an electrolyte solution so that lithium diffuses into the negative electrode active material, thereby causing prelithiation; a process of directly contacting lithium metal with an electrode under dry room conditions, thereby causing a spontaneous prelithiation reaction; or a process of adding lithium in the form of stabilized metal powder to an electrode in an amount sufficient to be consumed during the first charge.

[0066] In one embodiment of the present specification, the pre-lithiation may be performed by a lithium metal transfer process. When the pre-lithiation is performed by a lithium metal transfer process, lithium loss can be minimized and the reaction rate is fast, making it applicable to mass production.

[0067] In this specification, whether or not the negative electrode has been prelithiated can be confirmed by checking whether the total weight of the prepared negative electrode increases due to the weight of lithium inserted into the negative electrode active material layer compared to before prelithiation. In this case, the weight increase due to lithium inserted into the negative electrode active material layer due to prelithiation may be about 5% or more. The weight of the negative electrode and lithium can be measured in a glove box or glove compartment filled with argon (Ar) gas using a scale capable of measuring from mg to μg.

[0068] Alternatively, whether or not the negative electrode is prelithiated is indirectly confirmed in this specification by determining whether the charge / discharge efficiency in the first charge / discharge cycle of the finally manufactured battery is increased to 85% or more. The charge / discharge efficiency can be confirmed by measuring the charge / discharge capacity of the battery and then calculating it according to the following formula A-1: [Formula A-1] Charge / discharge efficiency = (discharge capacity / charge capacity) x 100 (%)

[0069] Alternatively, in this specification, whether or not a negative electrode has been prelithiated can also be confirmed by a color change in the negative electrode active material layer. The negative electrode active material layer before prelithiation is black, whereas after prelithiation, a carbon-based negative electrode active material layer exhibits a gold color, and a silicon-based negative electrode active material layer exhibits a green or purple color. This color change is due to the generation of nitrogen oxides due to a side reaction.

[0070] The above description of prelithiation may be applied to the following description of the prelithiation step.

[0071] The negative electrode conductive material contained in the negative electrode active material layer according to one embodiment of the present specification may include one or more selected from the group consisting of dot-like conductive materials, sheet-like conductive materials, and linear conductive materials, and specifically, may include one or more selected from the group consisting of sheet-like conductive materials and linear conductive materials.

[0072] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also serve to prevent the disconnection of conductive paths due to volume expansion, and is used as a concept including bulk conductive materials and plate-like conductive materials.

[0073] In one embodiment of the present specification, the sheet-like conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0074] In one embodiment of the present invention, the sheet-shaped conductive material may have an average particle size (D50) of 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the average particle size satisfies the above range, the particle size is sufficient to prevent an excessive increase in viscosity of the negative electrode slurry and facilitate dispersion. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0075] In one embodiment of the present specification, the sheet-shaped conductive material may have a D10 of 0.5 μm or more and 1.7 μm or less, a D50 of 3.5 μm or more and 5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0076] In one embodiment of the present specification, the sheet-like conductive material may be a sheet-like conductive material having a high BET specific surface area; or a sheet-like conductive material having a low specific surface area.

[0077] In one embodiment of the present specification, the sheet-like conductive material can be a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area, without any restrictions. However, since dispersion of the sheet-like conductive material according to the present invention can have some effect on electrode performance, it is particularly preferable to use a sheet-like conductive material with a low specific surface area in which dispersion does not cause problems.

[0078] In one embodiment of the present specification, the sheet-shaped conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0079] In another embodiment, the sheet-shaped conductive material has a BET specific surface area of ​​5 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0080] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a high specific surface area, and a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0081] In yet another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a low specific surface area, and a BET specific surface area of ​​5 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0082] Examples of linear conductive materials include carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes, which may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with each other, in a bundle or rope-like configuration, with the longitudinal axes of the carbon nanotube units substantially aligned in the same direction. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the curved angle and structure of the graphite sheet, the carbon nanotube unit may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode. Furthermore, the bundled carbon nanotubes can suppress electrode distortion due to volume expansion of silicon-based negative electrode active materials, thereby maintaining the initial cycle characteristics of the battery.

[0083] In one embodiment of the present specification, the linear conductive material may include one or more selected from the group consisting of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0084] In one embodiment of the present specification, the linear conductive material has a BET specific surface area of ​​100 m 2 / g or more 10,000m 2 / g or less, specifically 500m 2 / g or more 5,000m 2 / g or less, more specifically 1,000m 2 / g or more 1,500m 2 / g or less.

[0085] Furthermore, in one embodiment of the present specification, the aspect ratio of the linear conductive material may be 500 or more, specifically 1,000 or more, more specifically 10,000 or more, or may be 1,000,000 or less, specifically 100,000 or less, more specifically 50,000 or less.

[0086] In one embodiment of the present specification, the negative electrode conductive material may further include a dot-like conductive material, which is usable to improve the conductivity of the negative electrode, does not cause chemical changes, and is conductive. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which achieves high conductivity and excellent dispersibility.

[0087] In one embodiment of the present specification, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0088] In one embodiment of the present specification, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0089] In one embodiment of the present specification, the negative electrode conductive material may be included in an amount of 1 part by weight to 40 parts by weight based on 100 parts by weight of the negative electrode active material layer.

[0090] In another embodiment, the negative electrode conductive material may be included in an amount of 1 part by weight to 40 parts by weight, preferably 5 parts by weight to 30 parts by weight, and more preferably 10 parts by weight to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0091] The negative electrode conductive material according to the present specification has a completely different structure from the conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present specification serves to form a contact between the negative electrode active material, which experiences a large volume expansion during charging and discharging, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and thus has a completely different structure and role from the negative electrode conductive material according to the present specification.

[0092] Furthermore, the negative electrode conductive material according to the present invention is applied to a silicon-based negative electrode active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based negative electrode active materials as in the present invention.

[0093] In one embodiment of the present specification, the sheet-like conductive material used as the negative electrode conductive material is a material having a sheet or plate shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but refers to a material that ensures a conductive path in a sheet shape inside the negative electrode active material layer.

[0094] That is, in this specification, the term "plate-shaped graphite is used as an anode conductive material" means that the graphite is processed into a sheet or plate shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the anode active material contained therein has high capacity characteristics for storing and releasing lithium, and serves to store and release all lithium ions transferred from the cathode.

[0095] The negative electrode binder included in the negative electrode active material layer according to one embodiment of the present specification may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylamide, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0096] The negative electrode binder according to one embodiment of the present specification plays a role in holding the negative electrode active material and the negative electrode conductive material together to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based negative electrode active material expands and relaxes. Any common negative electrode binder that fulfills this role may be used. Specifically, a water-based binder may be used, and more specifically, a polyacrylamide (PAM)-based binder may be used.

[0097] Silicon-based active materials as negative electrode active materials have a higher volume expansion than carbon-based active materials (especially graphite), which can lead to a decrease in the negative electrode conductive network during charge and discharge. Conventional SBR / CMC binders have low mechanical rigidity, which can lead to serious problems such as swelling and a decrease in cell performance during charge and discharge.

[0098] However, when a polyacrylamide-based binder is used in a silicon-based negative electrode active material as in the present invention, it has superior mechanical rigidity and conductive connectivity during charge and discharge compared to conventional binders, and can suppress swelling.

[0099] In one embodiment of the present specification, the polyacrylamide-based binder refers to a binder whose main component is a poly(meth)acrylamide-based monomer, and may further include other components such as poly(meth)acrylic acid (PAA), polyvinyl alcohol (PVA), and poly(meth)acrylonitrile (PAN).

[0100] As used herein, the anode binder containing a plurality of compounds having a specific proportion (expressed in parts by weight or weight ratio) may mean that each compound (e.g., acrylamide, acrylic acid, acrylonitrile) is contained as a monomer of the binder polymer.

[0101] In this specification, the negative electrode binder may contain a plurality of compounds as monomers, and the monomer with the highest content may be considered as a representative one and may be named a "monomer"-based compound.

[0102] As used herein, "(meth)acrylic..." can mean methacryl and / or acrylic.

[0103] In one embodiment of the present specification, when the polyacrylamide-based binder contains a minor component as an additional monomer to form a copolymer, the ratio of each monomer is not particularly limited as long as the copolymer belongs to the intended aqueous binder.

[0104] In one embodiment of the present specification, the negative electrode binder may be contained in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, or 1 part by weight or more, or 3 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer.

[0105] The negative electrode for a lithium secondary battery according to an embodiment of the present specification may include the above-described negative electrode active material layer.

[0106] Specifically, the negative electrode may include a negative electrode current collector layer and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector layer.

[0107] 1 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present specification. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. Although FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0108] In one embodiment of the present specification, the negative electrode current collector layer may generally have a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. Furthermore, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0109] In one embodiment of the present specification, the thickness of the negative electrode current collector layer may be from 1 μm to 100 μm, and the thickness of the negative electrode active material layer may be from 20 μm to 500 μm, but the thicknesses may vary depending on the type and application of the negative electrode used and are not limited thereto.

[0110] The negative electrode active material layer may be formed by coating a negative electrode slurry containing the above-described negative electrode active material, a negative electrode binder, a thickener, and / or a negative electrode conductive material on at least one surface of a current collector, followed by drying and rolling.

[0111] In one embodiment of the present specification, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0112] In one embodiment of the present specification, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0113] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, more preferably 10% to 30%.

[0114] The solid content of the negative electrode slurry refers to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and may refer to the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode slurry.

[0115] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is suitable, and particle aggregation of the negative electrode active material layer composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0116] In one embodiment of the present specification, the slurry solvent is not limited as long as it can dissolve the negative electrode active material layer composition, and specifically, distilled water may be used.

[0117] The negative electrode according to one embodiment of the present specification may be formed by coating the negative electrode slurry on a negative electrode current collector layer and drying it.

[0118] The drying step may allow the slurry solvent in the negative electrode slurry to be dried.

[0119] The above-described description of the negative electrode active material layer and the negative electrode may be applied to the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification below.

[0120] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification includes the steps of: preparing a negative electrode active material layer; and prelithiating at least one surface of the negative electrode active material layer, wherein the negative electrode active material layer is made of SiO x (0≦x<2) and a silicon-based negative electrode active material containing Si nanoparticles; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based negative electrode active material is in an uncoated carbon state, and the Si nanoparticles have an average particle size (D50) of 1 nm or less.

[0121] In one embodiment of the present specification, the step of preparing the negative electrode active material layer comprises forming a negative electrode active material layer on a substrate using SiO x (0≦x<2) and a silicon-based negative electrode active material including Si nanoparticles; a negative electrode conductive material; and a negative electrode binder; preparing a negative electrode slurry including the prepared negative electrode slurry on at least one surface of a negative electrode current collector; rolling the negative electrode current collector coated with the negative electrode slurry; and drying.

[0122] In this case, the step of preparing the negative electrode active material layer only includes a step of performing a heat treatment in a final drying step, and does not include a step of coating the silicon-based negative electrode active material with carbon. Therefore, an additional heat treatment process is not performed, which can inhibit the promotion of growth of Si nanoparticles according to the present invention, thereby solving the above-mentioned problem caused by the growth of Si nanoparticles.

[0123] In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present specification, the silicon-based negative electrode active material may be the same as that described above.

[0124] In the method for producing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, x (0≦x<2) is an amorphous phase, and may have Si nanoparticles dispersed therein.

[0125] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification includes prelithiating at least one surface of the negative electrode active material layer.

[0126] The prelithiation step according to one embodiment of the present specification may be a method for manufacturing a negative electrode for a lithium secondary battery, which may be performed by any one of a lithium electroplating process, a lithium metal transfer process, a lithium metal deposition process, and a stabilized lithium metal powder (SLMP) coating process, and is preferably performed by a lithium metal transfer process, which has low cell degradation and a fast reaction rate during battery operation.

[0127] In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present specification, the pre-lithiation step may include a step of transferring a lithium metal layer onto at least one surface of the negative electrode active material layer. In this case, the lithium metal layer is a layer containing lithium metal for pre-lithiating at least one surface of the negative electrode active material layer, and may be, but is not limited to, a commonly used Li metal foil.

[0128] In the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the pre-lithiation step may include a step of transferring a transfer laminate including a lithium metal layer and a substrate layer onto at least one surface of the negative electrode active material layer, specifically, a step of preparing a transfer laminate including a lithium metal layer and a substrate layer; a step of contacting the transfer laminate with at least one surface of the negative electrode active material layer so that the lithium metal layer faces the surface; and a step of separating the substrate layer from the lithium metal layer.

[0129] In the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the thickness of the transfer laminate may be 65 μm or less, specifically 35 μm or less, or may be 10 μm or more, specifically 11 μm or more.

[0130] When the thickness of the transfer laminate according to one embodiment of the present specification satisfies the above range, the amount of heat generated during prelithiation is low, heat is released well, and lithium loss and safety issues do not arise.

[0131] In the method for producing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the thickness of the lithium metal layer may be 1 μm or more and 10 μm or less, specifically 1 μm or more and 9 μm or less, and more specifically 3 μm or more and 6.5 μm or less.

[0132] When the thickness of the lithium metal layer according to one embodiment of the present specification is equal to or greater than the lower limit of the above range, prelithiation can be performed to a degree that solves the problem of electrode irreversibility and improves coulombic efficiency. When the thickness is equal to or less than the upper limit of the above range, the amount of heat generated during prelithiation is low, heat is released efficiently, and lithium loss and safety issues due to the generation of lithium by-products do not occur.

[0133] In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present specification, the substrate layer may be any material that can withstand process conditions, such as high temperatures, in the step of depositing a lithium metal layer and can prevent a problem of reverse peeling, in which the deposited lithium metal layer is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal layer.

[0134] Specifically, in the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the substrate layer may be one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0135] The thickness of the substrate layer according to one embodiment of the present specification may be in the range of 1 μm or more and 300 μm or less, specifically 5 μm or more and 200 μm or less, more specifically 10 μm or more and 100 μm or less.

[0136] When the thicknesses of the substrate layer and the lithium metal layer satisfy the above ranges, the lithium metal can be efficiently transferred to the negative electrode active material layer side, and reverse transfer can be prevented.

[0137] In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present specification, a deposition method for depositing the lithium metal layer on the substrate layer may be selected from physical vapor deposition (PDV) and chemical vapor deposition (CVD). Among the physical vapor deposition methods, thermal evaporation may be mainly used, but is not limited thereto, and various deposition methods used in the art may be used.

[0138] Alternatively, the structure may further include another layer between the lithium metal layer and the substrate layer to alleviate heat generated by prelithiation, or the substrate layer may cover part or all of the lithium metal layer or another layer located on the lithium metal layer, but the structure is not limited thereto.

[0139] In the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, in the step of preparing the transfer laminate, the transfer laminate may further include a release layer. Specifically, the release layer may be included between the lithium metal layer and the substrate layer. Coating the release layer between the lithium metal layer and the substrate layer can facilitate transfer.

[0140] In the step of preparing the transfer laminate according to one embodiment of the present specification, the transfer laminate may further include a release layer, and the step of separating the substrate layer from the lithium metal layer may include the step of separating the release layer.

[0141] In the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the release layer may be one or more selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), and polymethylmethacrylate (PMMA), but is not limited thereto, and a silicon-based or fluorine-based material may also be used.

[0142] The thickness of the release layer according to one embodiment of the present specification may be 0.2 μm or more and 3 μm or less, specifically 0.5 μm or more and 1 μm or less.

[0143] In the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, when the release layer satisfies the above thickness range, sufficient release force is ensured, and the release layer located on the surface after transfer of the lithium metal layer can prevent heat release, thereby preventing the acceleration of by-product formation.

[0144] The release layer according to one embodiment of the present specification may be formed by a coating method. For example, the coating method may be selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but is not limited thereto. Various coating methods available in the art for forming a coating layer may be used.

[0145] In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present specification, the step of contacting the transfer laminate may further include a step of applying pressure, and the transfer laminate may be contacted and pressed simultaneously.

[0146] The pressing step is a step for transferring the lithium metal layer to at least one surface of the electrode active material layer, and the pressing step promotes contact between lithium and the electrode active material, thereby allowing prelithiation to be performed more smoothly.

[0147] In the method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the pressurizing step may be performed with a load of more than 200 kgf and not more than 600 kgf, 250 kgf or more and not more than 500 kgf, 300 kgf or more and not more than 500 kgf, 350 kgf or more and not more than 450 kgf, or 400 kgf or more and not more than 450 kgf.

[0148] In one embodiment of the present specification, when pressure is applied with a load satisfying the above range, prelithiation by transfer can be more actively performed, and since prelithiation is performed within an appropriate range, residual lithium on the surface of the electrode can be minimized, minimizing the loss of the added lithium. In addition, the electrode can be formed thin despite having a high energy density.

[0149] That is, in the laminating step according to one embodiment of the present specification, the transfer laminate may be positioned so that the lithium metal layer is in contact with one or both sides of the electrode active material layer, and then the transfer may be performed by a roll pressing process while applying a load within the above range.

[0150] The method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present specification may include a step of separating the substrate layer from the lithium metal layer.

[0151] In one embodiment of the present specification, the prelithiation reaction between the electrode active material layer and the lithium metal layer may start from the time when the lithium metal layer comes into contact with at least one surface of the electrode active material layer, or may start within several seconds to several minutes from the time when the lithium metal layer comes into contact, or may start from the time when removal of the carrier film begins.

[0152] In one embodiment of the present specification, the prelithiation reaction may be completed within several days, within 24 hours, or within several minutes to several seconds from the time when the lithium metal layer comes into contact with at least one surface of the electrode active material layer.

[0153] During pre-lithiation of the negative electrode active material layer according to one embodiment of the present specification, the initial charge capacity of the negative electrode decreases due to the lithium introduced into the negative electrode, and the initial irreversible capacity of the negative electrode decreases, so that the energy density or life performance of the battery improves depending on the degree of pre-lithiation, which means that the battery performance is superior to that of a battery using a negative electrode that has not been pre-lithiated.

[0154] In addition, the pre-lithiation step according to one embodiment of the present specification may be a step of loading lithium ions to 30% to 40% of the negative electrode loading amount, in order to match the efficiency with the positive electrode.

[0155] The pre-lithiation step according to an embodiment of the present specification may be expressed as a step of filling the lithium secondary battery finally manufactured according to an embodiment of the present specification so that the charge / discharge efficiency of the lithium secondary battery is 90% or more.

[0156] A lithium secondary battery according to one embodiment of the present specification includes a positive electrode for a lithium secondary battery; the above-described negative electrode for a lithium secondary battery; a separator provided between the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery; and an electrolyte.

[0157] 2 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present disclosure. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are stacked with a separator 30 interposed therebetween.

[0158] The negative electrode for the lithium secondary battery is the same as the negative electrode described above, and therefore a detailed description thereof will be omitted.

[0159] The positive electrode for a lithium secondary battery may include a positive electrode current collector layer, and a positive electrode active material layer formed on at least one surface of the positive electrode current collector layer and containing the positive electrode active material.

[0160] The positive electrode current collector layer in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector layer may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector layer to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0161] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.5 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion.

[0162] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0163] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0164] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0165] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferred that the separator exhibit low resistance to ion migration in the electrolyte and have excellent electrolyte humidification capabilities. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0166] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0167] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0168] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0169] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared, and therefore these cyclic carbonates can be used even more preferably.

[0170] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3- , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0171] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0172] A battery module according to an embodiment of the present specification may include the lithium secondary battery described above.

[0173] A battery pack according to another embodiment of the present specification may include the above-described lithium secondary battery or a battery module including the above-described lithium secondary battery.

[0174] The lithium secondary battery according to the embodiments of the present specification stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, as well as portable devices such as mobile phones, laptops, and digital cameras. For example, the battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Example]

[0175] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0176] <Production example> <Production of negative electrodes> Example 1 94 g of powder of Si and SiO2 mixed at a 1:1 molar ratio was mixed in a reactor and then vacuum heated to a sublimation temperature of 1,400°C. The vaporized Si and SiO2 mixture was then reacted in a vacuum cooling zone at a cooling temperature of 800°C and solidified. The preliminary silicon-based negative electrode active material was pulverized in a ball mill for 3 hours to produce silicon-based particles with a size of 6.1 μm, which was used as the negative electrode active material of Example 1.

[0177] The silicon-based negative electrode active material (average particle size (D50): 6.1 μm), plate-shaped graphite-based conductive material, SWCNT, and polyacrylamide binder were mixed in a weight ratio of 80:9.6:0.4:10 to prepare a negative electrode active material layer composition. The mixture was added to distilled water as a solvent for forming a negative electrode slurry to produce a negative electrode slurry (solid concentration: 25 wt%).

[0178] The plate-shaped graphite conductive material has a BET specific surface area of ​​17m 2 / g, D10 is 1.7 μm, D50 is 3.5 μm, and D90 is 6.8 μm, and the SWCNTs have a BET specific surface area of ​​1,000 m 2 / g~1,500m 2 / g and the aspect ratio is 10,000 or more.

[0179] The mixing method was as follows: the conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0180] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector at 3.675 mAh / cm 2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer (thickness: 25 μm).

[0181] Lithium metal (thickness: 6.2 μm) was transferred onto the top of the negative electrode active material layer to perform prelithiation.

[0182] Comparative Example 1 The negative electrode was manufactured in the same manner as in Example 1, except that the negative electrode active material layer was not prelithiated.

[0183] Comparative Example 2 A prelithiated negative electrode was prepared using the same method as in Example 1, except that the negative electrode active material in Example 1 was a silicon-based negative electrode active material coated with carbon.

[0184] Specifically, 94 g of powder containing Si and SiO2 mixed at a molar ratio of 1:1 was mixed in a reactor and then vacuum heated to a sublimation temperature of 1,400°C. The vaporized Si and SiO2 mixture was then reacted in a vacuum cooling zone at a cooling temperature of 800°C and solidified. The preliminary silicon-based anode active material was pulverized using a ball mill for 3 hours to produce silicon-based particles of 6 μm in size. Then, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based anode active material was placed in the hot zone of a CVD apparatus, and methane was blown into the hot zone at 900°C using Ar as a carrier gas for 10 minutes. -1 The reaction was carried out at torr for 5 hours to form a carbon layer on the surface of the silicon-based negative electrode active material, thereby preparing the carbon-coated (carbon-coated) silicon-based negative electrode active material of Comparative Example 2.

[0185] Comparative Example 3 A negative electrode was prepared in the same manner as in Comparative Example 2, except that the negative electrode active material layer using the carbon-coated silicon-based negative electrode active material of Comparative Example 2 was not prelithiated.

[0186] Comparative Example 4 A negative electrode was prepared in the same manner as in Example 1, except that an additional heat treatment was performed to adjust the average particle size (D50) of the Si nanoparticles.

[0187] Specifically, 94 g of powder containing Si and SiO2 mixed at a 1:1 molar ratio was mixed in a reactor and then vacuum-heated to a sublimation temperature of 1,400°C. The vaporized Si and SiO2 mixture was then reacted in a vacuum cooling zone at a cooling temperature of 800°C and solidified. The preliminary silicon-based negative electrode active material was pulverized using a ball mill for 3 hours to produce silicon-based particles with a size of 6 μm. The silicon-based negative electrode active material was then placed in a hot zone at 900°C under an inert atmosphere with Ar gas flow and heat-treated for 5 hours to grow the average particle size (D50) of the Si nanoparticles in the silicon-based negative electrode active material to the 3 nm level.

[0188] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 4.6 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.2:1.8 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0189] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) as a positive electrode current collector at 3.5 mAh / cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 74µm), thereby preparing a positive electrode (thickness: 162µm).

[0190] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte was injected thereinto to produce the secondary battery of Example 1.

[0191] The electrolyte was prepared by adding LiPF6 as a lithium salt at a concentration of 1.0 M to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70.

[0192] Secondary batteries were fabricated in the same manner as above, except that the negative electrodes of the Examples and Comparative Examples were used.

[0193] Experimental example 1: Evaluation of life characteristics The surface of the silicon-based negative electrode active material used in the negative electrodes prepared in Example 1 and Comparative Examples 1 to 4 was checked using TEM to see if it was coated with carbon. The results are shown in Table 1 below, with O indicating that the material was coated with carbon and X indicating that the material was not coated with carbon.

[0194] In addition, the average particle size (D50) of the Si nanoparticles in the silicon-based negative electrode active material was calculated by fitting the XRD results using the Scherrer equation and is shown in Table 1 below. The nanoparticles were measured based on Si(220) (2θ=47.4° to 48.5°).

[0195] Furthermore, a life evaluation was performed using an electrochemical charger / discharger on the lithium secondary batteries including the negative electrodes produced in Example 1 and Comparative Examples 1 to 4, and the capacity retention rate after 500 cycles was evaluated. When measuring the initial charge / discharge capacity, the C-rate was 1.0 C, charging was performed under CCCV conditions with an upper limit voltage of 4.2 V and a cut-off current of 0.05 C, and discharging was performed under CC conditions with a lower limit voltage of 2.5 V at 0.5 C. The results are shown in Table 1 below.

[0196] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0197] [Table 1]

[0198] As can be seen from Table 1, the secondary battery of Example 1, which was pre-lithiated using a silicon-based negative electrode active material that was not coated with carbon, was found to have excellent initial capacity and lifespan characteristics.

[0199] Specifically, Comparative Example 1 showed a capacity retention rate similar to that of Example 1 by using a silicon-based negative electrode active material that was not coated with carbon. However, since prelithiation was not performed, it was confirmed that the initial capacity and discharge capacity were significantly lower than those of Example 1.

[0200] In Comparative Example 2, it was confirmed that the initial capacity and discharge capacity were as high as in Example 1 due to prelithiation. However, it was confirmed that the capacity retention rate was significantly lower than in Example 1 due to the growth of Si nanoparticles during the carbon coating process on the silicon-based negative electrode active material. It has been known that coating the surface of a silicon-based negative electrode active material with carbon improves the cycle performance of a battery by acting as a buffer during the volume expansion of the silicon. However, in accordance with the present invention, by not performing a carbon coating or application process on the surface of the silicon-based active material, the Si nanoparticles in the silicon-based active material remain small, preventing stress on the surrounding area within the negative electrode during charge and discharge. This reduces manufacturing costs and time and demonstrates better battery life characteristics.

[0201] In Comparative Example 3, since prelithiation was not performed, it was confirmed that the initial capacity and discharge capacity were low, and since a carbon-coated silicon-based negative electrode active material was used, it was also confirmed that the life characteristics were relatively reduced.

[0202] In Comparative Example 4, the additional heat treatment caused growth of Si nanoparticles in the silicon-based negative electrode active material that was not coated with carbon, and in this case, it was confirmed that the capacity retention rate was lower than that of Example 1. This confirmed that the main reason for the relatively low capacity retention rates in Comparative Examples 2 and 3 was the size of the Si nanoparticles in the silicon-based negative electrode active material.

[0203] Therefore, the negative electrode for a lithium secondary battery according to one embodiment of the present specification can improve low conductivity and initial efficiency by performing a prelithiation process, thereby contributing to the development of initial cell capacity. In particular, since an additional carbon coating process is not performed, the size of Si nanoparticles in the silicon-based negative electrode active material is kept small, thereby maintaining initial cell capacity and efficiency, and having advantageous advantages for cell life performance, and is characterized by being able to reduce the cost and time required to manufacture the negative electrode. [Explanation of symbols]

[0204] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30 Separator 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. SiO ｘ (0≦x<2) and a silicon-based negative electrode active material containing Si nanoparticles; a negative electrode conductive material; and a negative electrode active material layer containing a negative electrode binder, the silicon-based negative electrode active material is in an uncoated carbon state, The average particle size (D50) of the Si nanoparticles is 1 nm or less, The negative electrode for a lithium secondary battery, wherein at least one surface of the negative electrode active material layer is prelithiated.

2. The SiO ｘ 2. The negative electrode for a lithium secondary battery according to claim 1, wherein (0≦x<2) is an amorphous phase in which the Si nanoparticles are dispersed.

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based negative electrode active material has an average particle size (D50) of 1 μm or more and 10 μm or less.

4. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based negative electrode active material has an average particle size (D50) of 3 μm or more and 8 μm or less.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, comprising 60 parts by weight or more of the silicon-based negative electrode active material based on 100 parts by weight of the negative electrode active material layer.

6. Positive electrodes for lithium secondary batteries; The negative electrode for a lithium secondary battery according to any one of claims 1 to 5; a separator provided between the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery; and electrolyte A lithium secondary battery comprising:

7. A battery module comprising the lithium secondary battery according to claim 6.

8. A battery pack comprising the lithium secondary battery according to claim 6.

9. A battery pack comprising the battery module according to claim 7.

10. Preparing a negative electrode active material layer; and prelithiating at least one surface of the negative electrode active material layer; Including, The negative electrode active material layer is made of SiO ｘ (0≦x<2) and a silicon-based negative electrode active material including Si nanoparticles; a negative electrode conductive material; and a negative electrode binder, the silicon-based negative electrode active material is in an uncoated carbon state, The method for producing a negative electrode for a lithium secondary battery, wherein the Si nanoparticles have an average particle size (D50) of 1 nm or less.

11. The SiO ｘ 11. The method for producing a negative electrode for a lithium secondary battery according to claim 10, wherein (0≦x<2) is an amorphous phase in which the Si nanoparticles are dispersed.

12. 12. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10, wherein the pre-lithiation of at least one surface of the negative electrode active material layer is a step of filling lithium ions to an amount of 30% to 40% of a negative electrode loading amount.

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