Anode composition, anode for lithium secondary battery including the anode composition, and lithium secondary battery including the same

Abstract

The present invention relates to a negative electrode composition that can improve the energy density of a lithium secondary battery, reduce the degree of deterioration during operation of the lithium secondary battery, and further improve the life characteristics by using a negative electrode active material containing silicon oxide containing Si nanocrystals having an average particle size (D50) of 0.1 nm or more and 5 nm or less in combination with a negative electrode conductive material and a negative electrode aqueous binder in an appropriate composition; a negative electrode for a lithium secondary battery containing the negative electrode composition; and a lithium secondary battery containing the same.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the negative electrode composition, and a lithium secondary battery including the same.

[0002] The present invention claims the benefit of Korean Patent Application No. 10-2023-0114515 filed with the Korean Intellectual Property Office on August 30, 2023, and Korean Patent Application No. 10-2024-0116069 filed with the Korean Intellectual Property Office on August 28, 2024, the entire contents of which are incorporated herein by reference. [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] Graphite is the primary negative electrode active material for lithium secondary batteries. However, its low capacity per unit mass (372 mAh / g) makes it difficult to increase the capacity of lithium secondary batteries. Therefore, to increase the capacity of lithium secondary batteries, non-carbon-based negative electrode materials such as silicon, tin, and their oxides have been developed as materials with higher energy densities than graphite. However, while these non-carbon-based negative electrode materials offer high capacity, they suffer from low initial efficiency, high lithium consumption during initial charging and discharging, and large irreversible capacity loss.

[0008] In addition, lithium secondary batteries have a required size depending on the application, and must be designed accordingly within a limited space. While consumer demands for increased energy density and high output performance are increasing, the use of high-capacity cathode materials requires an increased content of anode materials to match, limiting the efficiency of the battery within a limited space. Therefore, there is a need to develop batteries with improved performance, such as efficiency and lifespan, within a limited space. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2023-0050258 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention relates to a negative electrode composition capable of maximizing the energy density and lifespan of a lithium secondary battery, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0011] One embodiment of the present invention is a negative electrode composition comprising: a negative electrode active material containing silicon oxide; a negative electrode conductive material; and a negative electrode aqueous binder, The negative electrode composition contains 70 parts by weight or more of the negative electrode active material, 0.3 parts by weight or more of the negative electrode conductive material, and 9 parts by weight or more of the negative electrode aqueous binder, based on 100 parts by weight of the solid content of the negative electrode composition, the negative electrode conductive material includes 0.3 parts by weight or more and 3 parts by weight or less of a linear conductive material based on 100 parts by weight of the solid content of the negative electrode composition, the silicon oxide includes Si nanocrystals; The negative electrode composition provides the Si nanocrystals having an average particle size (D50) of 0.1 nm or more and 5 nm or less.

[0012] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, in which a negative electrode active material layer containing the above-described negative electrode composition or a cured product thereof is provided on at least one surface of a negative electrode current collector layer.

[0013] One embodiment of the present invention comprises a positive electrode; The aforementioned negative electrode for lithium secondary batteries; a separator disposed between the positive electrode and the negative electrode; and A lithium secondary battery is provided that includes an electrolyte.

[0014] Another embodiment of the present invention provides a battery module or a battery pack including the above-described lithium secondary battery.

[0015] Finally, another embodiment of the present invention provides a battery pack including the above-described battery module. [Effects of the Invention]

[0016] The negative electrode composition according to one embodiment of the present invention uses a silicon oxide having a high specific capacity in an appropriate compositional combination with a linear conductive material and a negative electrode aqueous binder, thereby maximizing the energy density and cycle performance of a lithium secondary battery. Furthermore, the use of a silicon oxide containing Si nanocrystals with a small average particle size (D50) reduces the degree of degradation during operation of the lithium secondary battery, further improving its life characteristics. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present invention. [Figure 2] 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Before describing the present invention, some terms will first be defined.

[0019] 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.

[0020] In this specification, when a member is positioned "on" another member, it does not only mean that the member is in contact with the other member, but also that another member exists between the two members.

[0021] In this specification, "p to q" means a range of "not less than p and not more than q."

[0022] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in this specification, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0023] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0024] The average particle size can be measured using a Microtrac device (manufacturer: Microtrac, model name: S3500) with water and Triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured at a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured at a refractive index of 1.97 or 2.42. For example, the particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer, and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. A volume cumulative particle size distribution graph can then be obtained, and the particle size corresponding to 50% of the volume cumulative amount can be determined.

[0025] Alternatively, in one embodiment of the present specification, the average particle size (D50) of the Si nanocrystals can be determined by X-ray diffraction analysis, which can be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: Bruker). Specifically, XRD measurement can be performed by placing a powder sample in a holder and measuring it using a Cu K alpha X-ray. The size of the Si nanocrystals can be calculated by fitting the XRD results using the Scherrer equation, and the nanocrystals can be measured based on Si(220) (2θ=47.5° to 48.5°).

[0026] In this 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.

[0027] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, it is interpreted in the same way as when a polymer contains the monomer as a monomer unit.

[0028] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0029] 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.

[0030] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0031] 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.

[0032] <Negative electrode composition> A negative electrode composition according to one embodiment of the present specification comprises a negative electrode active material; a negative electrode conductive material; and a negative electrode aqueous binder, the negative electrode composition comprising 70 parts by weight or more of the negative electrode active material, 0.3 parts by weight or more of the negative electrode conductive material, and 9 parts by weight or more of the negative electrode aqueous binder, based on 100 parts by weight of the solid content of the negative electrode composition, the negative electrode conductive material comprising 0.3 parts by weight or more and 3 parts by weight or less of a linear conductive material, based on 100 parts by weight of the solid content of the negative electrode composition, the silicon oxide comprising Si nanocrystals, and the Si nanocrystals having an average particle size (D50) of 0.1 nm or more and 5 nm or less.

[0033] Silicon oxide has a high capacity, so when used excessively, it is difficult to balance the capacity with the positive electrode active material. Also, due to the material properties of silicon oxide, the larger the average particle size (D50) of the Si nanocrystals, the more lithium (Li) remains in the material, which can cause problems such as deterioration of cycle performance and severe swelling.

[0034] Therefore, the present invention is characterized by the fact that the energy density is ensured by including an excess amount of silicon oxide as the negative electrode active material, and the cycle performance is also ensured by appropriately combining the contents of the negative electrode conductive material and the negative electrode binder to suppress volume expansion during charge and discharge. In particular, by maintaining the average particle size (D50) of the Si nanocrystals dispersed in the silicon oxide of the present invention small, between 0.1 nm and 5 nm, stress due to volume expansion of the negative electrode active material particles during charge and discharge can be reduced and particle cracking can be prevented, thereby further improving cycle performance and swelling.

[0035] The negative electrode composition according to one embodiment of the present specification may contain 70 parts by weight or more of the negative electrode active material containing the silicon oxide, based on 100 parts by weight of the solid content of the negative electrode composition.

[0036] In this specification, the term "solid content" refers to the content excluding solvents such as water contained in the negative electrode composition.

[0037] In one embodiment of the present specification, the negative electrode active material containing silicon oxide may be included in an amount of 70 parts by weight to 99 parts by weight, specifically 70 parts by weight to 90 parts by weight, and more specifically 80 parts by weight to 89.6 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0038] In one embodiment of the present specification, the negative electrode active material may contain the silicon oxide, and specifically may consist of the silicon oxide.

[0039] That is, in one embodiment of the present specification, the silicon oxide may be contained in an amount of 70 parts by weight to 99 parts by weight, specifically 70 parts by weight to 90 parts by weight, and more specifically 80 parts by weight to 89.6 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0040] As used herein, the "silicon oxide" includes amorphous SiOx (0 < x < 2) and may contain nano-sized Si crystals randomly dispersed therein. The randomly dispersed nano-sized Si crystals can be referred to as "Si nanograins" according to the present invention.

[0041] Originally, when the silicon oxide is excessively contained as the anode active material, there is a problem that the cycle characteristics of the battery are disadvantageously affected by the volume expansion during charge and discharge and the relative content reduction of the anode conductive material and the anode binder. However, the anode composition according to the present specification can improve the energy density of the electrode by excessively containing the silicon oxide, and can maximize the energy density and life performance of the battery by deriving an optimal content appropriately combined with the anode conductive material and the aqueous anode binder described below.

[0042] According to one embodiment of the present specification, the silicon oxide may contain SiOx (0 < x < 2). At this time, the SiOx (0 < x < 2) corresponds to an amorphous-phase matrix within the silicon oxide particles. The SiOx (0 < x < 2) may be in a form containing a part of Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiOx (0 < x < 2). When the silicon oxide particles contain the SiOx (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0043] In one embodiment of the present specification, the silicon oxide contains Si nanocrystals, and the Si nanocrystals may have an average particle size (D50) of 0.1 nm or more and 5 nm or less. In one embodiment of the present specification, the average particle size (D50) of the Si nanocrystals of the silicon oxide may be 5 nm or less, specifically, 3 nm or less.

[0044] In one embodiment of the present specification, the average particle size (D50) of the Si nanocrystals contained in the silicon oxide may be 0.1 nm or more, specifically 0.5 nm or more, and more specifically more than 1 nm.

[0045] When the average particle size (D50) of the Si nanocrystals is within this range, Li ions are uniformly diffused within the Si particles, thereby maintaining the stable structure of the negative electrode active material particles during charge and discharge. On the other hand, when the average particle size (D50) of the Si nanocrystals is beyond this range, stress occurs due to the contraction / expansion of the Si nanocrystals during charge and discharge, causing cracks to form in the negative electrode active material particles, preventing Li ions from diffusing into the Si nanocrystals and resulting in non-uniform reactions, which can accelerate battery degradation and shorten the lifespan.

[0046] Silicon oxide negative electrode active materials inherently undergo extremely complex crystal 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 crystal structure of the Si particles change to Si (crystal structure: Fd3m), LiSi (crystal structure: I41 / a), Li2Si (crystal structure: C2 / m), Li7Si2 (Pbam), Li 22 The Si nanocrystals change to Si5(F23), etc., and the volume of the Si particles expands by about four times due to changes in their complex crystal structure. As a result, when charge / discharge cycles are repeated, the Si particles are broken and lithium atoms form bonds with the Si particles, damaging the lithium atom insertion sites that the Si particles initially had, which can significantly reduce cycle life. That is, if the average particle size (D50) of the Si nanocrystals according to one embodiment of the present specification exceeds 5 nm, stress is applied to the surrounding materials in the anode during the reaction with lithium during charging of a lithium secondary battery, resulting in problems such as reduced battery life and reduced battery performance. Therefore, it is preferable that the Si nanocrystals satisfy the maximum average particle size (D50) range.

[0047] Furthermore, the minimum average particle size (D50) of the Si nanocrystals according to one embodiment of the present specification may be 0.1 nm. If the average particle size of the Si nanocrystals is less than 0.1 nm, the energy density of the negative electrode may decrease.

[0048] The negative electrode composition according to an embodiment of the present specification can sufficiently increase the energy density and capacity by using a negative electrode active material containing silicon oxide. However, silicon oxide has a limitation in that its volume rapidly expands during charge / discharge processes, damaging the conductive pathway formed in the negative electrode active material layer and thereby degrading the performance of the battery. Therefore, the type of negative electrode conductive material used together with the negative electrode active material is important.

[0049] The negative electrode composition according to one embodiment of the present specification may include 0.3 parts by weight or more of the negative electrode conductive material based on 100 parts by weight of the solid content of the negative electrode composition.

[0050] Specifically, in one embodiment of the present specification, the negative electrode conductive material may be included in an amount of 0.3 parts by weight to 11 parts by weight, more specifically, 0.4 parts by weight to 10 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0051] If the negative electrode conductive material according to one embodiment of the present specification is contained in an amount less than the lower limit of the above range, it may be difficult to control electrode distortion due to volume expansion of silicon oxide or to prevent disconnection of the conductive path due to volume expansion, while if the negative electrode conductive material is contained in an amount exceeding the upper limit of the above range, the content of the negative electrode active material and the negative electrode binder may be relatively low, which may result in a decrease in energy density or capacity degradation. Therefore, it is preferable that the negative electrode conductive material according to one embodiment of the present specification satisfies the above range.

[0052] In this case, the content of the negative electrode conductive material may be the part by weight of the negative electrode conductive material including only the linear conductive material and other solvent, or may be the content of the negative electrode conductive material including both the linear conductive material and additional sheet-like or dot-like conductive material.

[0053] In one embodiment of the present specification, the negative electrode conductive material may include 0.3 parts by weight or more and 3 parts by weight or less of linear conductive material based on 100 parts by weight of the solid content of the negative electrode composition.

[0054] In this specification, the term "linear conductive material" refers to a conductive material with a one-dimensional (1D) structure having a nanometer-level diameter and a high aspect ratio, or a conductive material with a fibrous structure such as a cylindrical or tubular structure. Examples of the linear conductive material include carbon nanotubes, which may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a bundle- or rope-like secondary shape in which a plurality of carbon nanotube units are arranged side by side or intertwined with the longitudinal axes of the carbon nanotube units in substantially the same orientation. The carbon nanotube units are formed by a graphite sheet having a cylindrical shape with a nanometer-sized diameter, and a sp 2 The bundled carbon nanotubes have a bonded structure. Depending on the angle and structure of the graphite sheets, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0055] In addition, by including a linear conductive material as the negative electrode conductive material according to an embodiment of the present disclosure, it is possible to control the distortion of the electrode caused by the volume expansion of silicon oxide contained in the negative electrode active material, thereby maintaining the initial cycle characteristics of the battery. However, since it is difficult to maintain the cycle characteristics during repeated battery charge and discharge using only the linear conductive material according to an embodiment of the present disclosure, it is intended to solve this problem by combining the linear conductive material according to an embodiment of the present disclosure with an aqueous negative electrode binder, which will be described later, in an optimal amount.

[0056] In one embodiment of the present specification, the negative electrode conductive material may include 0.3 parts by weight or more and 3 parts by weight or less of a linear conductive material, specifically 0.4 parts by weight or more and 3 parts by weight or less, more specifically 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0057] If the linear conductive material according to one embodiment of the present specification is contained in an amount less than the lower limit of the content range, rapid capacity degradation may occur in the initial cycle of the battery. If the linear conductive material is contained in an amount exceeding the upper limit of the content range, the excessive amount of the linear conductive material does not necessarily improve performance, but rather increases manufacturing costs due to the use of expensive linear conductive material.

[0058] Therefore, it is preferable that the content of the linear conductive material according to one embodiment of the present specification satisfies the above range. However, if the content of the negative electrode binder is reduced and the negative electrode conductive material is included in excess, the initial cycle characteristics may be maintained, but a rapid deterioration in battery capacity may occur after 200 cycles. Therefore, it is preferable to prevent battery deterioration by including an appropriate content of the negative electrode aqueous binder described below.

[0059] In one embodiment of the present specification, the linear conductive material may include a single-walled carbon nanotube (SWCNT, Single-Walled Carbon Nano Tube) or a multi-walled carbon nanotube (MWCNT, Multi-Walled Carbon Nano Tube), and specifically, may include a single-walled carbon nanotube (SWCNT, Single-Walled Carbon Nano Tube).

[0060] In one embodiment of the present specification, the linear conductive material has a BET specific surface area of ​​100 m 2 / g or more 100,000m 2 / g or less, specifically 500m 2 / g or more 10,000m 2 / g or less, more specifically 1,000m 2 / g or more 5,000m 2 / g or less.

[0061] 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, and may be 1,000,000 or less, specifically 100,000 or less.

[0062] The negative electrode composition according to one embodiment of the present specification may include 9 parts by weight or more of the negative electrode aqueous binder based on 100 parts by weight of the solid content of the negative electrode composition.

[0063] In one embodiment of the present specification, the negative electrode aqueous binder may be included in an amount of 9 parts by weight or more, specifically 9.4 parts by weight or more, more specifically 10 parts by weight or more, based on 100 parts by weight of the solid content of the negative electrode composition.

[0064] In one embodiment of the present specification, the negative electrode aqueous binder may be included in an amount of 20 parts by weight or less, specifically 18 parts by weight or less, more specifically 15 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0065] In one embodiment of the present specification, the negative electrode aqueous binder may be included in an amount of 9 parts by weight to 20 parts by weight, specifically 9.4 parts by weight to 18 parts by weight, and more specifically 10 parts by weight to 15 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0066] When the anode aqueous binder according to one embodiment of the present disclosure satisfies the above content range, it can retain silicon oxide, which undergoes significant volume expansion during charge and discharge, thereby improving the battery's lifespan. In particular, when the anode aqueous binder according to the present disclosure is included in an amount less than the lower limit of the above range, even if the anode conductive material according to the present disclosure, particularly the linear conductive material, is added in an amount more than twice as large, the anode conductive material can only temporarily suppress electrode distortion due to volume changes of the silicon oxide active material only at the beginning of cycling. It is difficult for the anode aqueous binder according to the present disclosure to perform this function throughout the entire cycle, as is the case with the anode aqueous binder according to the present disclosure, and battery performance is therefore not restored. Furthermore, when the anode aqueous binder is included in an amount greater than the upper limit of the above range, the content of the anode active material and the anode conductive material is relatively low, which may result in a decrease in energy density or capacity degradation.

[0067] Therefore, when the negative electrode conductive material and the negative electrode aqueous binder according to an embodiment of the present specification satisfy the above-mentioned content ranges, the energy density of the electrode can be improved and the life performance can be maximized even if the negative electrode active material containing the silicon oxide according to the present invention is contained in excess.

[0068] The negative electrode aqueous 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 deformation of the negative electrode structure when the volume of the silicon oxide active material expands and relaxes. Any common negative electrode aqueous binder that fulfills the above role can be used, and specifically, a polyacrylamide (PAM)-based binder may be used.

[0069] Silicon oxide as the negative electrode active material has a greater volume expansion than carbon-based active materials (especially graphite), which can cause the conductive network of the negative electrode to deteriorate during charging and discharging. In addition, conventional SBR / CMC binders have low mechanical rigidity, which can lead to serious problems such as swelling and deterioration of cell performance during charging and discharging.

[0070] In contrast, when a PAM-based binder is applied to silicon oxide as in the present invention, it is possible to achieve superior mechanical rigidity, superior conductive connectivity during charge and discharge, and suppress swelling compared to conventional binders.

[0071] In one embodiment of the present specification, the PAM-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).

[0072] In the present specification, a polymerization initiator is used to prepare the PAM-based binder, and an example of the polymerization initiator may be ammonium persulfate, but is not limited thereto.

[0073] As used herein, the 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.

[0074] In this specification, the binder may contain a plurality of compounds as monomers, and the monomer with the largest content may be considered as a representative and may be named a "monomer" compound.

[0075] As used herein, "(meth)acrylic..." can mean methacryl and / or acrylic.

[0076] In one embodiment of the present specification, when the PAM-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 it belongs to the intended aqueous binder.

[0077] In one embodiment of the present specification, the negative electrode composition may include, based on 100 parts by weight of a solid content of the negative electrode composition, 70 parts by weight or more and 99 parts by weight or less of the negative electrode active material, 0.3 parts by weight or more and 11 parts by weight or less of the negative electrode conductive material, and 9 parts by weight or more and 20 parts by weight or less of the negative electrode aqueous binder.

[0078] Specifically, the negative electrode composition may include, based on 100 parts by weight of the solid content of the negative electrode composition, 70 parts by weight to 90 parts by weight of the negative electrode active material, 0.3 parts by weight to 11 parts by weight of the negative electrode conductive material, and 9 parts by weight to 20 parts by weight of the negative electrode aqueous binder.

[0079] More specifically, the negative electrode composition may include, based on 100 parts by weight of the solid content of the negative electrode composition, 80 parts by weight to 89.6 parts by weight of the negative electrode active material, 0.4 parts by weight to 10 parts by weight of the negative electrode conductive material, and 9.4 parts by weight to 18 parts by weight of the negative electrode aqueous binder.

[0080] In one embodiment of the present specification, the negative electrode composition may include, based on 100 parts by weight of a solid content of the negative electrode composition, 70 parts by weight or more and 99 parts by weight or less of the silicon oxide, 0.3 parts by weight or more and 11 parts by weight or less of the negative electrode conductive material, and 9 parts by weight or more and 20 parts by weight or less of the negative electrode aqueous binder.

[0081] Specifically, the negative electrode composition may include, based on 100 parts by weight of the solid content of the negative electrode composition, 70 parts by weight to 90 parts by weight of the silicon oxide, 0.3 parts by weight to 11 parts by weight of the negative electrode conductive material, and 9 parts by weight to 20 parts by weight of the negative electrode aqueous binder.

[0082] More specifically, the negative electrode composition may include, based on 100 parts by weight of the solid content of the negative electrode composition, 80 parts by weight to 89.6 parts by weight of the silicon oxide, 0.4 parts by weight to 10 parts by weight of the negative electrode conductive material, and 9.4 parts by weight to 18 parts by weight of the negative electrode aqueous binder.

[0083] When the composition of the negative electrode composition according to one embodiment of the present specification satisfies the above-mentioned combined range, the energy density and cycle performance of the lithium secondary battery can be improved to the maximum.

[0084] In addition, the negative electrode composition according to an embodiment of the present specification may be applied with the following features.

[0085] In an anode composition according to one embodiment of the present specification, the Si nanocrystals contained in the silicon oxide may be formed by heat treatment at 500° C. to 1500° C., specifically 600° C. to 1300° C., more specifically 700° C. to 1200° C., during preparation of the anode active material. If the anode active material is prepared at a temperature outside this range, the Si nanocrystals dispersed in the silicon oxide may grow and exceed the average particle size (D50) range of the Si nanocrystals according to the present specification, resulting in the above-mentioned problems. If the temperature is too low, it may be difficult to prepare the desired anode active material.

[0086] In one embodiment of the present specification, the silicon oxide may have a carbon layer formed on at least a portion of its surface. In this case, the carbon layer may be formed on at least a portion of the surface, i.e., the surface of the silicon oxide, or may be formed on the entire surface of the silicon oxide. When a carbon layer is formed on at least a portion of the surface of the silicon oxide, conductivity is imparted to the negative electrode active material, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0087] In one embodiment of the present specification, the carbon layer may include amorphous carbon, and the carbon layer may further include crystalline carbon.

[0088] In one embodiment of the present specification, the crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene, and the crystalline carbon may further improve the conductivity of the negative electrode active material.

[0089] In one embodiment of the present specification, the amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic substances as a source in a chemical vapor deposition process, and the amorphous carbon may appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon oxide.

[0090] In this specification, the carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0091] In this specification, the hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, or the like. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.

[0092] In one embodiment of the present specification, the carbon layer may be an amorphous carbon layer.

[0093] In one embodiment of the present specification, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on 100 parts by weight of the silicon oxide. More specifically, it may be included in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the content of the carbon layer satisfies the above range, it is possible to prevent a decrease in the capacity and efficiency of the negative electrode active material.

[0094] In one embodiment of the present specification, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically may be 5 nm to 300 nm. When the thickness of the carbon layer satisfies the above range, the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or life of the battery are improved.

[0095] In one embodiment of the present specification, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0096] In one embodiment of the present specification, the silicon oxide may further contain metal impurities. The metal impurities are impurities contained in silicon, and the content thereof may satisfy the range of 0.1 part by weight or less based on 100 parts by weight of all silicon-based active materials.

[0097] On the other hand, in one embodiment of the present specification, the average particle size (D50) of the negative electrode active material containing the silicon oxide may be 1 μm to 15 μm, specifically 2 μm to 12.5 μm, and more specifically 5 μm to 10 μm. At this time, the average particle size (D50) of the negative electrode active material is based on the average particle size (D50) of the final particles (particles) containing both SiOx (0 < x < 2) and Si nanocrystals.

[0098] When the average particle size (D50) of the negative electrode active material satisfies the above range, the specific surface area of ​​the particles falls within a suitable range, allowing the viscosity of the negative electrode composition to be formed within an appropriate range, thereby facilitating the dispersion of particles constituting the negative electrode composition. Furthermore, the composite of the negative electrode conductive material and the negative electrode binder in the negative electrode composition provides an excellent contact area between the silicon oxide and the negative electrode conductive material, increasing the likelihood of maintaining a conductive network and improving capacity retention. Furthermore, the removal of excessively large silicon oxide particles allows the formation of a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0099] In the negative electrode composition according to one embodiment of the present specification, the negative electrode conductive material may further include one or more selected from the group consisting of a sheet-like conductive material and a dot-like conductive material.

[0100] In one embodiment of the present specification, the negative electrode conductive material may further include a sheet-shaped conductive material.

[0101] In this specification, the term "sheet-like conductive material" refers to a two-dimensional (2D) conductive material in which atoms have a thickness of a single atomic layer or two or more atomic layers and form a planar crystalline structure. The sheet-like conductive material refers to a material that ensures a conductive path in a sheet form within the negative electrode active material layer and simultaneously serves to prevent the conductive path from being broken due to volume expansion. It can be referred to as a plate-like conductive material or a bulk-like conductive material. Specifically, the sheet-like conductive material may include at least one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and is preferably plate-like graphite.

[0102] In one embodiment of the present specification, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size (D50) of the sheet-like conductive material satisfies the above range, the sufficient particle size does not cause an excessive increase in viscosity of the negative electrode slurry and dispersion is easy. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0103] In one embodiment of the present specification, the sheet-shaped conductive material may have a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0104] 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.

[0105] 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 the dispersion of the sheet-like conductive material according to the present specification can have a certain degree of influence on the 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.

[0106] In another embodiment of the present specification, 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.

[0107] 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.

[0108] 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.

[0109] The negative electrode conductive material according to one embodiment of 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 invention 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 acts as a buffer during rolling and also provides some conductivity, and thus has a completely different structure and role from the negative electrode conductive material of the present invention.

[0110] Furthermore, the negative electrode conductive material according to one embodiment of the present specification 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.

[0111] In one embodiment of the present specification, the negative electrode conductive material may further include dot-like conductive material.

[0112] The negative electrode conductive material according to one embodiment of the present specification may include any commonly used point-like conductive material, but if the negative electrode conductive material does not include linear conductive materials and only includes point-like conductive materials, the point-like conductive materials have lower conductivity and specific surface area than the linear conductive materials or sheet-like conductive materials, and therefore, when used in the present invention, they are unable to form conductive paths in the negative electrode active material layer, which can result in significant capacity degradation.If the negative electrode conductive material according to one embodiment of the present specification uses point-like conductive materials together with the linear conductive materials, changes in the physical properties of the negative electrode slurry and gas problems at high temperatures can occur.

[0113] In the negative electrode composition according to one embodiment of the present specification, the negative electrode binder may further include a binder known in the art for improving adhesion between negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. Non-limiting examples thereof include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid. The polymer may further include at least one selected from the group consisting of: a carboxylic acid, and substances in which hydrogen atoms of the carboxylic acid are substituted with Li, Na, Ca, or the like, and may further include various copolymers thereof.

[0114] <Negative electrode> In the negative electrode for a lithium secondary battery according to an embodiment of the present specification, a negative electrode active material layer including the above-described negative electrode composition or a cured product thereof may be provided on at least one surface of a negative electrode current collector layer.

[0115] Specifically, the negative electrode for a lithium secondary battery may include a negative electrode current collector and a negative electrode active material layer disposed on one or both surfaces of the negative electrode current collector, and the negative electrode active material layer may include the above-described negative electrode composition or a cured product thereof.

[0116] In this specification, the term "cured product" may refer to the negative electrode composition cured by heat treatment or light treatment using a method well known in the art.

[0117] 1 is a diagram showing a 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, including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side of the negative electrode current collector layer, it may be formed on both sides of the negative electrode current collector layer.

[0118] The negative electrode active material layer may be formed by applying a negative electrode slurry containing the above-described negative electrode composition, a solvent for forming a negative electrode slurry, and / or a thickener to at least one surface of the negative electrode current collector layer, followed by drying and rolling.

[0119] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0120] The negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the negative electrode current collector layer may be 6 μm to 20 μm, but the thickness of the current collector is not limited to this.

[0121] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the technical field may be appropriately adopted.

[0122] In one embodiment of the present specification, the thickener may be included in an amount of 0.5 parts by weight to 25 parts by weight, specifically 0.5 parts by weight to 20 parts by weight, more specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode slurry.

[0123] In one embodiment of the present specification, the solid content of the negative electrode slurry may be 10 parts by weight to 99 parts by weight, specifically 20 parts by weight to 80 parts by weight, based on 100 parts by weight of the negative electrode slurry.

[0124] <Secondary battery> A lithium secondary battery according to an embodiment of the present specification may include a positive electrode; the above-described negative electrode for a lithium secondary battery; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0125] 2 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present disclosure. Specifically, a negative electrode 100 for a lithium secondary battery including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10 can be seen, and a positive electrode 200 for a lithium secondary battery including a positive electrode active material layer 40 on one side of a positive electrode current collector layer 50 can be seen, and the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are stacked with a separator 30 interposed therebetween.

[0126] A lithium secondary battery according to an embodiment of the present specification may include, in particular, the negative electrode described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0127] The positive electrode may include a positive electrode current collector layer, and a positive electrode active material layer formed on the positive electrode current collector layer and containing a positive electrode active material.

[0128] 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.

[0129] 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≦0.3 is satisfied); 2-c3 M c3Examples of suitable lithium manganese composite oxides 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 satisfying 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. The positive electrode may be Li metal.

[0130] 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.

[0131] 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.

[0132] 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 layer. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, 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.

[0133] 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 preferable that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. 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 laminated 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 separator coated with a ceramic component or a polymeric material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0134] 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.

[0135] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0136] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl 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.

[0137] 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 having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0138] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. 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:

[0139] 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.

[0140] One embodiment of the present specification provides a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0141] Another embodiment of the present specification provides a battery pack including the lithium secondary battery.

[0142] 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]

[0143] 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.

[0144] <Production example> <Production of negative electrodes> Example 1 The negative electrode active material was silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50): 3 nm, SWCNT (BET specific surface area: 1,000 m 2 / g~1,500m 2 / g, aspect ratio: 10,000 or more) and polyacrylamide binder in a weight ratio of 88.5:0.44:11.06 to prepare a negative electrode composition. This was added to distilled water as a solvent for forming a negative electrode slurry to produce a negative electrode slurry (solid concentration: 28 wt%).

[0145] The average particle size (D50) of the Si nanocrystals was calculated by fitting the XRD results using the Scherrer equation, and the nanocrystals were measured based on Si(220) (2θ=47.4°-48.5°).

[0146] The conductive material, binder and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the negative electrode active material was added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0147] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 15 μm) as a negative electrode current collector at 3.675 mAh / cm 2 The coated film was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode (thickness: 57 µm).

[0148] Example 2 The negative electrode active material was silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50) of 2.5 nm, SWCNT (BET specific surface area: 1,000 m 2 / g~1,500m 2 / g, aspect ratio: 10,000 or more), and graphite (product name: SFG-6L, BET specific surface area: 17m) as an additional sheet-type conductive material. 2 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that a negative electrode composition was prepared using the same weight ratio of 80.0:0.4:9.6:10.0 as the weight ratio of the polyacrylamide binder and the polyimide binder.

[0149] Example 3 The negative electrode active material was silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50): 3 nm, SWCNT (BET specific surface area: 1,000 m 2 / g~1,500m 2A negative electrode was formed in the same manner as in the preparation example of Example 1, except that a negative electrode composition was prepared using the same SiO2 / SiO2 (SiO2 / g, aspect ratio: 10,000 or more) and a polyacrylamide binder in a weight ratio of 88.5:1.2:10.3.

[0150] Example 4 The negative electrode active material was silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50) of 2.5 nm, SWCNT (BET specific surface area: 1,000 m 2 / g~1,500m 2 A negative electrode was formed in the same manner as in the preparation example of Example 2, except that a negative electrode composition was prepared by mixing the conductive material (carbon black) and the polyacrylamide binder in a weight ratio of 80.0:0.4:9.6:10.0.

[0151] Comparative Example 1 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that a negative electrode composition was prepared using graphite (average particle size (D50): 5.5 μm) as a carbon-based negative electrode active material, SWCNTs, and a polyacrylamide binder in a weight ratio of 95.6:1.0:3.4.

[0152] Comparative Example 2 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that a negative electrode composition was prepared using silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50) of 2.6 nm as the negative electrode active material, SWCNTs, and a polyacrylamide binder in a weight ratio of 93.8:0.47:5.73.

[0153] Comparative Example 3 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that a negative electrode composition was prepared using silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50) of 2.8 nm as the negative electrode active material, SWCNTs, and a polyacrylamide binder in a weight ratio of 92.7:0.927:6.373.

[0154] Comparative Example 4 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that silicon oxide containing Si nanocrystals with an average particle size (D50) of 0.08 nm was used as the negative electrode active material.

[0155] Comparative Example 5 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that silicon oxide containing Si nanocrystals with an average particle size (D50) of 7 nm was used as the negative electrode active material.

[0156] Comparative Example 6 The negative electrode active material was silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50): 3 nm, SWCNT (BET specific surface area: 1,000 m 2 / g~1,500m 2 A negative electrode was formed in the same manner as in the preparation example of Example 1, except that a negative electrode composition was prepared using the same SiO2 / SiO2 (SiO2 / g, aspect ratio: 10,000 or more) and a polyacrylamide binder in a weight ratio of 88.5:0.2:11.3.

[0157] Comparative Example 7 A negative electrode was formed in the same manner as in the manufacturing example of Example 1, except that a negative electrode composition was prepared using silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50) of 3 nm as the negative electrode active material, a dot-like conductive material (carbon black), and a polyacrylamide binder in a weight ratio of 88.5:0.44:11.06.

[0158] Comparative Example 8 The negative electrode active material consisted of silicon oxide containing Si nanocrystals with an average particle size (D50) of 2.5 nm (average particle size (D50): 5.5 μm), a dot-shaped conductive material (carbon black), and an additional sheet-shaped conductive material (product name: SFG-6L, BET specific surface area: 17 m). 2 A negative electrode was formed in the same manner as in the preparation example of Example 2, except that a negative electrode composition was prepared using the same weight ratio of 80.0:0.4:9.6:10.0 as the weight ratio of the polyacrylamide binder and the polyimide binder.

[0159] <Manufacturing lithium secondary batteries> A positive electrode slurry was prepared by adding NCMA active material (average particle size (D50): 9.6 μm) as a positive electrode active material, carbon nanotubes as a positive electrode conductive material, and polyvinylidene fluoride (PVdF) as a positive electrode binder in a weight ratio of 97.6:0.8:1.6 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry.

[0160] 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: 75 μm) to prepare a positive electrode (thickness: 162 μm, porosity: 26%).

[0161] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte solution was injected into the separator, thereby preparing a full-cell lithium secondary battery of Example 1.

[0162] The electrolyte solution was prepared by adding 0.5 wt % of vinylene carbonate (based on the total weight of the electrolyte) to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and adding 0.5 M of LiPF6 and 1 M of LiFSI as lithium salts.

[0163] Lithium secondary battery full-cells were fabricated in the same manner as above, except that the negative electrodes of Examples 2 to 4 and Comparative Examples 1 to 8 were used.

[0164] [Experimental Example 1: Evaluation of energy density and life characteristics] The cell energy density of the lithium secondary batteries including the negative electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 8 was measured, and a lifespan evaluation was performed using an electrochemical charger / discharger to evaluate the capacity retention rate after 300 cycles.

[0165] Specifically, in the evaluation of the life characteristics, when measuring the initial charge 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 when measuring the initial discharge capacity, the C-rate was 0.5 C, and charging was performed under CC conditions with a lower limit voltage of 2.5 V.

[0166] Capacity retention rate (%) = {(charge / discharge capacity at Nth cycle) / (charge / discharge capacity at first cycle)} × 100

[0167] The evaluation results of energy density and life characteristics are shown in Table 1 below.

[0168] [Table 1]

[0169] Previously, the silicon content was simply increased to achieve high energy density in the negative electrode, but this resulted in a decrease in cycle capacity retention (less than about 79%), or when adjusting the active material and other characteristics to ensure capacity retention (more than about 79%), the energy density could not be secured (less than 750Wh / L).

[0170] The lithium secondary battery using the negative electrode composition according to the present specification is intended to simultaneously satisfy the requirements of high energy density and excellent life characteristics. Therefore, it was determined based on the criteria that the battery can be used as a lithium secondary battery according to the present invention when it has an energy density of about 750 Wh / L or more and a capacity retention rate at 300 cycles of about 79% or more.

[0171] As can be seen from Table 1, in Examples 1 to 4 using the negative electrode composition according to the present invention, the energy density was 750 Wh / L or more and the capacity retention rate at 300 cycles was 79% or more, so that the lithium secondary battery according to the present invention could be used with high energy density and excellent life characteristics. This corresponds to the result of optimizing the content of each component to 70 parts by weight or more of the negative electrode active material, 0.3 parts by weight or more of the negative electrode conductive material, particularly 0.3 to 3 parts by weight of the linear conductive material, and 9 parts by weight or more of the negative electrode aqueous binder, based on 100 parts by weight of the solid content of the negative electrode composition, and using a negative electrode active material in which the average particle size (D50) of Si nanocrystals as silicon oxide is 0.1 to 5 nm.

[0172] However, in the case of Example 3, the SWCNT content was increased to three times that of Example 1, and the energy density and cycle performance were similar to those of Example 1, but there was no significant improvement in performance due to the inclusion of a high SWCNT content, and it was actually disadvantageous in terms of cost.

[0173] In addition, in the case of Example 4, carbon black (dot-like conductive material) was used as the second conductive material instead of the sheet-like conductive material (SFG-6L) used in Example 2. In this case, no significant differences in energy density and cycle performance were observed compared to Example 2. However, in a preliminary evaluation (negative electrode slurry preparation and gas generation analysis), it was confirmed that the use of the dot-like conductive material caused changes in the physical properties of the negative electrode slurry and gas generation problems at high temperatures.

[0174] The lithium secondary battery of Comparative Example 1, which used graphite as the negative electrode active material, did not use a negative electrode active material containing silicon oxide, and therefore did not experience a decrease in electrode cycle performance due to volume expansion. However, the energy density was significantly reduced, and the battery could not be used as a lithium secondary battery having high energy density and excellent life characteristics according to the present invention.

[0175] The lithium secondary battery of Comparative Example 2, in which the content of the negative electrode aqueous binder was reduced by half compared to the negative electrode composition of Example 1, had a relatively higher content of negative electrode active material and an energy density of 750 Wh / L or more. However, since the content of the negative electrode aqueous binder was reduced, it was difficult to suppress electrode distortion due to volume change of the silicon oxide active material throughout the cycles, and the capacity retention rate was only in the low 70% range, so it could not be used as a lithium secondary battery with excellent performance according to the present invention.

[0176] The lithium secondary battery of Comparative Example 3, in which the content of the negative electrode aqueous binder was reduced by half compared to the negative electrode composition of Example 1, achieved an energy density of 750 Wh / L or more, similar to Comparative Example 2. However, despite containing more than twice the amount of negative electrode linear conductive material compared to Example 1, the capacity retention rate did not reach 79%, and the battery could not be used as a lithium secondary battery with excellent performance according to the present invention. This confirms that, in the absence of an appropriate compositional combination of the negative electrode active material and negative electrode aqueous binder according to the present invention, even if a large amount of negative electrode linear conductive material is contained alone, it is difficult to maintain cycle characteristics during repeated battery charge and discharge.

[0177] The lithium secondary battery of Comparative Example 4, which used silicon oxide with extremely small Si nanocrystal size as the negative electrode active material, achieved a capacity retention rate of 79% or more due to the appropriate combination of the negative electrode composition of the present invention. However, because the Si nanocrystal size was excessively small, the energy density was significantly reduced compared to Example 1, and the battery could not be used as a lithium secondary battery with excellent performance according to the present invention.

[0178] The lithium secondary battery of Comparative Example 5, which used a silicon oxide negative electrode active material whose Si nanocrystal size was larger than the Si nanocrystal size range specified in this specification, had excellent energy density. However, it was confirmed that cracks formed in the negative electrode active material after repeated charge and discharge, preventing Li ions from diffusing into the nanocrystals. This resulted in non-uniform reactions, accelerating battery degradation, and significantly reducing the capacity retention rate.

[0179] In Comparative Example 6, the SWCNT content was reduced to half that of Example 1, which resulted in a rapid capacity degradation from the beginning of cycling. Specifically, the initial cycle capacity was measured. The initial cycle capacity of Example 1 was 88.2 mAh, and that of Example 2 was 89.0 mAh. However, the initial cycle capacity of Comparative Example 6 was significantly lower at 86.8 mAh. This confirmed that the capacity retention rate in Table 1 was also significantly lower. The initial cycle capacity was measured by charging (4.2 V, current cutoff 5%) under CC-CV conditions at 0.33 C-rate and discharging (2.5 V) under CC conditions at 0.33 C-rate.

[0180] In Comparative Example 7, carbon black was used as the conductive material instead of the linear conductive material (SWCNT) used in Example 1. Carbon black has low conductivity and specific surface area, and is therefore unable to form a conductive path in the negative electrode active material layer, resulting in significant capacity degradation. As a result, it was confirmed that the capacity retention rate was significantly lower than that of Example 1.

[0181] In Comparative Example 8, carbon black was used as the conductive material instead of the linear conductive material (SWCNT) used in Example 2. In this case, it was confirmed that a conductive path could not be formed in the negative electrode active material layer, causing significant capacity degradation and resulting in a significantly low capacity retention rate.

Claims

1. A negative electrode composition comprising: a negative electrode active material containing silicon oxide; a negative electrode conductive material; and a negative electrode aqueous binder, The negative electrode composition contains 70 parts by weight or more of the negative electrode active material, 0.3 parts by weight or more of the negative electrode conductive material, and 9 parts by weight or more of the negative electrode aqueous binder, based on 100 parts by weight of the solid content of the negative electrode composition, the negative electrode conductive material includes 0.3 parts by weight or more and 3 parts by weight or less of a linear conductive material based on 100 parts by weight of a solid content of the negative electrode composition, the silicon oxide includes Si nanocrystals; The negative electrode composition, wherein the Si nanocrystals have an average particle size (D50) of 0.1 nm or more and 5 nm or less.

2. The negative electrode composition according to claim 1 , wherein the negative electrode aqueous binder is a polyacrylamide-based binder.

3. 2. The negative electrode composition according to claim 1, wherein the negative electrode composition contains, based on 100 parts by weight of a solid content of the negative electrode composition, 70 parts by weight to 90 parts by weight of the negative electrode active material, 0.3 parts by weight to 11 parts by weight of the negative electrode conductive material, and 9 parts by weight to 20 parts by weight of the negative electrode aqueous binder.

4. 2. The negative electrode composition of claim 1, wherein the silicon oxide comprises SiOx (0<x<2).

5. The silicon oxide includes amorphous SiOx (0<x<2), The negative electrode composition according to claim 1 , wherein the Si nanocrystals are dispersed within the amorphous silicon oxide.

6. The negative electrode composition according to claim 1 , wherein the negative electrode active material has a D50 of 5 μm or more and 10 μm or less.

7. 10. A negative electrode for a lithium secondary battery, comprising a negative electrode active material layer comprising the negative electrode composition according to claim 1 or a cured product thereof, provided on at least one surface of a negative electrode current collector layer.

8. positive electrode; The negative electrode for a lithium secondary battery according to claim 7; a separator disposed between the positive electrode and the negative electrode; and electrolyte A lithium secondary battery comprising:

9. A battery module comprising the lithium secondary battery according to claim 8.

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

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

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