Negative electrode composition, negative electrode for lithium secondary battery comprising negative electrode composition, and lithium secondary battery comprising same

Abstract

The present invention relates to a negative electrode composition, a negative electrode for a lithium secondary battery comprising the negative electrode composition, and a lithium secondary battery comprising same, whereby, by using a negative electrode active material including silicon oxide in which Si nanocrystals having an average particle diameter (D50) of 0.1 nm or more and 5 nm or less are included, in an appropriate composition combination with a negative electrode conductive material and a negative electrode aqueous binder, the energy density of a lithium secondary battery is enhanced, and by lowering the degree of degradation when driving the lithium secondary battery, the life characteristics can be further improved.

Description

Negative electrode composition, negative electrode for lithium secondary battery including negative electrode composition, and lithium secondary battery including same

[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] This 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.

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

[0004] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, active research is being conducted on methods for manufacturing high-density electrodes with even higher energy densities per unit volume as electrodes for such high-capacity lithium secondary batteries. The trend toward higher loading is driving increased energy density. However, this also increases electrode resistance and cell resistance, making it difficult to secure performance such as high output and rapid charging. To address this issue, attempts are being made to manufacture patterned electrodes to physically expand the reactive surface and induce resistance reduction. Patterned electrodes induce reactions not only on the electrode surface but also in the depth of the electrode, enabling improved performance.

[0006] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and deintercalates lithium ions from the positive electrode. Silicon particles with a high discharge capacity can be used as the negative electrode active material.

[0007] Graphite is mainly used as an anode active material in lithium secondary batteries. However, because graphite has a low capacity per unit mass of 372 mAh / g, it is difficult to increase the capacity of lithium secondary batteries. Accordingly, non-carbonaceous anode materials with higher energy density than graphite, such as silicon, tin, and their oxides, are being developed to increase the capacity of lithium secondary batteries. However, these non-carbonaceous anode materials have a problem in that, although they have a large capacity, they have low initial efficiency, which leads to a large lithium consumption during the initial charge and discharge, and a large irreversible capacity loss.

[0008] Furthermore, lithium secondary batteries have specific sizes required for their intended use, and thus must be designed within a limited space. While consumer demand for increased energy density and high-power performance is growing, the use of high-capacity cathode materials necessitates increased anode material content to meet these demands. This limits the ability to increase battery efficiency within a limited space. Consequently, the development of batteries with improved performance, including efficiency and lifespan, within a limited space is urgently needed.

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Korean Patent Publication No. 10-2023-0050258

[0012] The present invention relates to an anode composition capable of maximally improving the energy density and lifespan of a lithium secondary battery, an anode for a lithium secondary battery including the same, and a lithium secondary battery including the same.

[0013] One embodiment of the present invention is a negative electrode composition comprising a negative electrode active material including silicon oxide; a negative electrode conductive material; and a negative electrode aqueous binder,

[0014] Based on 100 parts by weight of the solid content of the above negative electrode composition, the negative electrode active material is included in an amount of 70 parts by weight or more, the negative electrode conductive material is included in an amount of 0.3 parts by weight or more, and the negative electrode aqueous binder is included in an amount of 9 parts by weight or more.

[0015] The above-mentioned negative electrode conductive material includes a linear conductive material in an amount of 0.3 parts by weight or more and 3 parts by weight or less based on 100 parts by weight of the solid content of the above-mentioned negative electrode composition,

[0016] The above silicon oxide comprises Si nanocrystals,

[0017] The above Si nanocrystals provide a cathode composition having an average particle diameter (D50) of 0.1 nm or more and 5 nm or less.

[0018] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, wherein a negative electrode active material layer including 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.

[0019] One embodiment of the present invention comprises: a positive electrode;

[0020] The aforementioned negative electrode for a lithium secondary battery;

[0021] A separator provided between the anode and the cathode; and

[0022] A lithium secondary battery including an electrolyte is provided.

[0023] Another embodiment of the present invention provides a battery module or battery pack including the aforementioned lithium secondary battery.

[0024] Finally, another embodiment of the present invention provides a battery pack including the battery module described above.

[0025] According to one embodiment of the present invention, a negative electrode composition can maximize the energy density and cycle performance of a lithium secondary battery by using silicon oxide having a high specific capacity in an appropriate composition combination with a linear conductive material and a negative electrode aqueous binder, and further improve the life characteristics by lowering the degree of degradation during operation of a lithium secondary battery by using silicon oxide including Si nanocrystals having a small average particle diameter (D50).

[0026] Figure 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.

[0027] Figure 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present invention.

[0028] Before explaining the present invention, some terms are first defined.

[0029] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0030] In this specification, when it is said that a member is located “on” another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0031] In this specification, ‘p to q’ means a range of ‘p or more and q or less.’

[0032] In this specification, "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan. That is, in this specification, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0033] In this specification, "Dn" means particle size distribution, and means particle diameter at the n% point of the cumulative distribution of particle numbers according to particle diameter. That is, D50 is the particle diameter (average particle diameter) at the 50% point of the cumulative distribution of particle numbers according to particle diameter, D90 is the particle diameter at the 90% point of the cumulative distribution of particle numbers according to particle diameter, and D10 is the particle diameter at the 10% point of the cumulative distribution of particle numbers according to particle diameter. Meanwhile, the average particle diameter can be measured using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0034] The above average particle size can be measured using a Microtrac device (manufacturer: Microtrac model number: S3500) using water and a triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured in the range of a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured under the condition of a refractive index of 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, the particles can be introduced into a commercially available laser diffraction particle size measuring device, irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then a volume cumulative particle size distribution graph can be obtained, and then the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0035] Alternatively, in one embodiment of the present specification, the average particle diameter (D50) of the Si nanocrystals can be confirmed through X-ray diffraction analysis, and the X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analysis device (product name: D4-endavor, manufacturer: Bruker). Specifically, the XRD measurement can be performed by sampling a powder-type sample into a holder and measuring it through 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 standard of the nanocrystals at this time can be measured based on Si (220). (2θ=47.5° to 48.5°)

[0036] In this specification, particle size or particle diameter may mean the average diameter or representative diameter of each grain forming the metal powder.

[0037] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0038] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0039] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0040] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0041] Hereinafter, preferred embodiments of the present invention will be described in detail. 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.

[0042] <Cathode composition>

[0043] According to one embodiment of the present specification, a negative electrode composition comprises a negative electrode active material; a negative electrode conductive material; and a negative electrode aqueous binder, wherein the negative electrode active material is included in an amount of 70 parts by weight or more, the negative electrode conductive material is included in an amount of 0.3 parts by weight or more, and the negative electrode aqueous binder is included in an amount of 9 parts by weight or more, based on 100 parts by weight of the solid content of the negative electrode composition, and the negative electrode conductive material includes a linear conductive material in an amount of 0.3 parts by weight or more and 3 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition, and the silicon oxide includes Si nanocrystals, and the Si nanocrystals have an average particle diameter (D50) of 0.1 nm or more and 5 nm or less.

[0044] Because silicon oxide inherently has high capacity, excessive use can make it difficult to balance capacity with the cathode active material. Furthermore, due to the material properties of silicon oxide, the larger the average particle diameter (D50) of the Si nanocrystals, the greater the amount of lithium (Li) remaining within the material, potentially leading to degradation of cycle performance and increased swelling.

[0045] Accordingly, the present invention is characterized in that it can secure energy density by including silicon oxide in excess as an anode active material, while also securing cycle performance by appropriately combining the contents of a cathode conductive agent and a cathode binder to suppress volume expansion during charge and discharge. In particular, by keeping the average particle diameter (D50) of Si nanocrystals dispersed in the silicon oxide of the present invention small, from 0.1 nm to 5 nm, the stress caused by volume expansion of the cathode active material particles during charge and discharge can be reduced, thereby preventing breakage of the particles, and thus further improving cycle characteristics and swelling.

[0046] The negative electrode composition according to one embodiment of the present specification may include 70 parts by weight or more of the negative electrode active material including the silicon oxide based on 100 parts by weight of the solid content of the negative electrode composition.

[0047] In this specification, the “solid content” means excluding solvents such as water included in the negative electrode composition.

[0048] In one embodiment of the present specification, the negative electrode active material including the silicon oxide may be included in an amount of 70 to 99 parts by weight, specifically 70 to 90 parts by weight, and more specifically 80 to 89.6 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode composition.

[0049] In one embodiment of the present specification, the negative active material may include the silicon oxide, and specifically, may be made of the silicon oxide.

[0050] That is, in one embodiment of the present specification, the silicon oxide may be included in an amount of 70 to 99 parts by weight, specifically 70 to 90 parts by weight, and more specifically 80 to 89.6 parts by weight, based on 100 parts by weight of the total solid content of the cathode composition.

[0051] In this specification, the above “silicon oxide” refers to SiOx (0) in an amorphous state. <x<2)를 포함하고, 그 내부에 랜덤하게 분산된 나노 크기의 Si 결정을 포함하는 것일 수 있으며, 랜덤하게 분산된 나노 크기의 Si 결정을 본 발명에 따른 "Si 나노결정 (nanograin)"으로 표현할 수 있다.

[0052] Originally, when silicon oxide is included in an excessive amount as an anode active material, there is a problem that the cycle characteristics of the battery are disadvantageous due to volume expansion during charge and discharge and a decrease in the relative contents of the anode conductive material and anode binder. However, the anode composition according to the present specification can maximize the energy density and life performance of the battery by deriving an optimal content appropriately combined with the anode conductive material and anode aqueous binder described below while improving the energy density of the electrode by including silicon oxide in an excessive amount.

[0053] According to one embodiment of the present specification, the silicon oxide is SiOx (0 <x<2)를 포함할 수 있다. 이 때, 상기 SiOx (0<x<2)는 상기 실리콘 산화물 입자 내에서 비정질상의 매트릭스 (matrix)에 해당한다. 상기 SiOx (0<x<2)는 Si 및 SiO2가 일부 포함된 형태일 수 있으며, 상기 Si는 상(phase)을 이루고 있을 수도 있다. 즉, 상기 x는 상기 SiOx (0<x<2) 내에 포함된 Si에 대한 O의 개수비에 해당한다. 상기 실리콘 산화물 입자가 상기 SiOx (0<x<2)를 포함하는 경우, 이차 전지의 방전 용량이 개선될 수 있다.

[0054] In one embodiment of the present specification, the silicon oxide includes Si nanocrystals, and the Si nanocrystals may have an average particle diameter (D50) of 0.1 nm or more and 5 nm or less. In one embodiment of the present specification, the average particle diameter (D50) of the Si nanocrystals of the silicon oxide may be 5 nm or less, and specifically, 3 nm or less.

[0055] In addition, in one embodiment of the present specification, the average particle diameter (D50) of Si nanocrystals included in the silicon oxide may be 0.1 nm or more, specifically 0.5 nm or more, and more specifically more than 1 nm.

[0056] When the average particle diameter (D50) of the Si nanocrystals satisfies the above range, Li ions are uniformly diffused inside the Si particles, which has the effect of stably maintaining the structure of the negative electrode active material particles during charge and discharge. On the other hand, when the average particle diameter (D50) of the Si nanocrystals exceeds the above range, cracks may be formed in the negative electrode active material particles due to stress generated by shrinkage / expansion of the Si nanocrystals during charge and discharge, and Li ions may not diffuse into the Si nanocrystals, which may cause reaction non-uniformity, and this may cause a problem in that the battery deteriorates rapidly, resulting in a reduction in its lifespan.

[0057] Originally, silicon oxide negative active materials undergo very complex crystallographic changes in the reaction of electrochemically absorbing, storing, and releasing lithium atoms. As the reaction of electrochemically absorbing, storing, and releasing lithium atoms progresses, the composition and crystal structure of Si particles change to Si (crystal structure: Fd3m), LiSi (crystal structure: I41 / a), Li2Si (crystal structure: C2 / m), Li7Si2(Pbam), and Li 22 As the Si nanocrystals change into Si5(F23), etc., the volume of the Si particles expands by about 4 times according to the change in the complex crystal structure. Accordingly, when the charge / discharge cycle is repeated, the Si particles are destroyed, and as the bond between the lithium atoms and the Si particles is formed, the insertion site of the lithium atoms that the Si particles initially had is damaged, so that the cycle life may be significantly reduced. That is, when the average particle diameter (D50) of the Si nanocrystals according to one embodiment of the present specification exceeds 5 nm, when the lithium secondary battery is charged and the volume expands due to reaction with lithium, stress is applied to the surrounding materials in the negative electrode, which causes a problem of lowering the performance of the battery, such as a reduction in the lifespan of the battery, so it is preferable that the Si nanocrystals satisfy the maximum average particle diameter (D50) range.

[0058] In addition, the minimum average particle diameter (D50) of the Si nanocrystals according to one embodiment of the present specification may be 0.1 nm. If the average particle diameter of the Si nanocrystals is less than 0.1 nm, a problem of a decrease in the energy density of the cathode may occur.

[0059] The negative electrode composition according to one embodiment of the present specification can sufficiently increase energy density and capacity by using a negative electrode active material including silicon oxide. However, silicon oxide has a limitation in that it rapidly expands in volume during the charge / discharge process, thereby damaging the conductive path formed within the negative electrode active material layer, thereby lowering the performance of the battery. Therefore, the type of negative electrode conductive material used together with the negative electrode active material is important.

[0060] The cathode composition according to one embodiment of the present specification may include 0.3 parts by weight or more of the cathode conductive material based on 100 parts by weight of the solid content of the cathode composition.

[0061] 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 or more and 11 parts by weight or less based on 100 parts by weight of the total solid content of the negative electrode composition, and more specifically, may be included in an amount of 0.4 parts by weight or more and 10 parts by weight or less.

[0062] When the negative electrode conductive material according to one embodiment of the present specification is included in an amount less than the lower limit of the content range, it may be difficult to control the distortion phenomenon of the electrode due to volume expansion of silicon oxide or it may be difficult to suppress the disconnection of the conductive path due to volume expansion, and when it is included in an amount exceeding the upper limit of the content range, the content of the negative electrode active material and the negative electrode binder may be relatively reduced, resulting 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 content range.

[0063] At this time, the content of the negative electrode conductive material may be the weight part of the negative electrode conductive material including only the linear conductive material and other solvents, or may be the content of the negative electrode conductive material including both the linear conductive material and additional planar or dot-shaped conductive material.

[0064] In one embodiment of the present specification, the negative electrode conductive material may include a linear conductive material in an amount of 0.3 parts by weight or more and 3 parts by weight or less based on 100 parts by weight of the solid content of the negative electrode composition.

[0065] In the present specification, the "linear conductive material" refers to a conductive material having a one-dimensional (1D) structure with a diameter in the nanometer scale and a high aspect ratio, or a conductive material having a fibrous structure such as a cylindrical type or a tube type. Examples of the linear conductive material include carbon nanotubes, and the carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, unless otherwise stated, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in parallel or entangled with the longitudinal axes of the carbon nanotube units. The carbon nanotube units have a cylindrical shape in which a graphite sheet has a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or semiconductor. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during the manufacture of the cathode, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0066] In addition, by necessarily including a linear conductive material as the negative electrode conductive material according to one embodiment of the present specification, the distortion phenomenon of the electrode due to volume expansion of the silicon oxide included in the negative electrode active material can be controlled to maintain the initial cycle characteristics of the battery. However, since it is difficult to maintain the cycle characteristics with only the linear conductive material according to one embodiment of the present specification during repeated charge / discharge processes of the battery, the above problem was attempted to be solved through an optimal content combination with the negative electrode aqueous binder to be described below.

[0067] In one embodiment of the present specification, the negative electrode conductive material may include a linear conductive material in an amount of 0.3 parts by weight or more and 3 parts by weight or less based on 100 parts by weight of the total solid content of the negative electrode composition, specifically, 0.4 parts by weight or more and 3 parts by weight or less, and more specifically, 0.4 parts by weight or more and 1 part by weight or less.

[0068] If the linear conductive material according to one embodiment of the present specification is included in an amount less than the lower limit of the content range, rapid capacity degradation may occur in the initial cycle of the battery, and if the linear conductive material is included in an amount exceeding the upper limit of the content range, the performance is not as good as if the linear conductive material is included in an excessive amount, and rather, there is a disadvantage in that only the manufacturing cost increases due to the use of an expensive linear conductive material.

[0069] 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 an excessive amount, the initial cycle characteristics are maintained, but rapid battery capacity degradation may occur after 200 cycles. Therefore, it is preferable to prevent battery degradation by including an appropriate content of the negative electrode aqueous binder described below.

[0070] In one embodiment of the present specification, the linear conductive material may include a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT), and specifically, may include a single-walled carbon nanotube (SWCNT).

[0071] In one embodiment of the present specification, the linear conductive material has a BET specific surface area of ​​100 m 2 / g or more than 100,000m 2 / g or less, specifically 500m 2 / g or more than 10,000m 2 / g or less, more specifically 1,000m 2 / g or more than 5,000m 2 / g can be less.

[0072] In addition, 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.

[0073] 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.

[0074] In one embodiment of the present specification, the cathode aqueous binder may be included in an amount of 9 parts by weight or more, specifically 9.4 parts by weight or more, and more specifically 10 parts by weight or more, based on 100 parts by weight of the total solid content of the cathode composition.

[0075] In addition, in one embodiment of the present specification, the cathode aqueous binder may include 20 parts by weight or less, specifically 18 parts by weight or less, and more specifically 15 parts by weight or less, based on 100 parts by weight of the total solid content of the cathode composition.

[0076] In one embodiment of the present specification, the negative electrode water-based binder may be included in an amount of 9 parts by weight or more and 20 parts by weight or less, specifically 9.4 parts by weight or more and 18 parts by weight or less, and more specifically 10 parts by weight or more and 15 parts by weight or less, based on 100 parts by weight of the total solid content of the negative electrode composition.

[0077] When the negative electrode aqueous binder according to one embodiment of the present specification satisfies the above content range, it can hold silicon oxide that undergoes a large volume expansion during the charge / discharge process, thereby improving the life performance of the battery. In particular, when the negative electrode aqueous binder according to the present invention is included in an amount less than the lower limit of the above range, even if the negative electrode conductive material according to the present invention, particularly the linear conductive material, is added in an amount of more than twice, the negative electrode conductive material can only temporarily suppress distortion of the electrode due to volume change of the silicon oxide active material only at the beginning of the cycle, and it is difficult for the negative electrode aqueous binder according to the present invention to perform the corresponding role throughout the cycle, so the performance of the battery does not return. In addition, when the negative electrode aqueous binder is included in an amount exceeding the upper limit of the above range, the contents of the negative electrode active material and the negative electrode conductive material become relatively small, which may result in a decrease in energy density or capacity degradation.

[0078] Therefore, since the negative electrode conductive material and negative electrode aqueous binder according to one embodiment of the present specification satisfy the content range described above, even if the negative electrode active material including silicon oxide according to the present invention is included in an excessive amount, the energy density of the electrode can be improved while maximizing the life performance.

[0079] The negative electrode aqueous binder according to one embodiment of the present specification serves to hold the negative electrode active material and the negative electrode conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon oxide active material expands and relaxes. Any general negative electrode aqueous binder satisfying the above-described role may be applied, but specifically, it may be a polyacrylamide (PAM) binder.

[0080] As the above-mentioned negative active material, silicon oxide has a high volume expansion compared to carbon-based active materials (especially graphite), which may cause the negative electrode conductive network to deteriorate during charge and discharge. In addition, as a binder, the existing SBR / CMC binder has low mechanical rigidity, which may aggravate problems such as swelling and deterioration of cell performance during charge and discharge.

[0081] On the other hand, when a PAM-based binder is applied to silicon oxide as in the present invention, the mechanical strength is superior to that of existing binders, so that the conductive connection during charge and discharge is excellent and swelling can be suppressed.

[0082] In one embodiment of the present specification, the PAM-based binder means a binder whose main component is composed of a poly(meth)acrylamide-based monomer, and may additionally include poly(meth)acrylic acid (PAA), polyvinyl alcohol (PVA), poly(meth)acrylonitrile (PAN), etc. as other components.

[0083] In this specification, a polymerization initiator is used for the production of the PAM-based binder, and ammonium persulfate can be used as an example of the polymerization initiator, but is not limited thereto.

[0084] In the present specification, the binder comprising a plurality of compounds having a specific ratio (expressed as parts by weight or weight ratio) may mean that each compound (e.g., acrylamide, acrylic acid, acrylonitrile) is included as a monomer of the binder polymer.

[0085] In this specification, the binder may include multiple compounds as monomers, and the monomer with the largest content may be considered as a representative, and may be named a “monomer” compound.

[0086] In this specification, “(meth)acrylic…” may mean methacrylic and / or acrylic.

[0087] In one embodiment of the present specification, when the PAM-based binder forms a copolymer by including an additional monomer as a secondary component, the ratio of each monomer is not particularly limited as long as it belongs to the intended aqueous binder.

[0088] In one embodiment of the present specification, the negative electrode composition may include the negative electrode active material in an amount of 70 parts by weight or more and 99 parts by weight or less, the negative electrode conductive material in an amount of 0.3 parts by weight or more and 11 parts by weight or less, and the negative electrode aqueous binder in an amount of 9 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0089] Specifically, the negative electrode composition may include the negative electrode active material in an amount of 70 parts by weight or more and 90 parts by weight or less, the negative electrode conductive material in an amount of 0.3 parts by weight or more and 11 parts by weight or less, and the negative electrode aqueous binder in an amount of 9 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0090] More specifically, the negative electrode composition may include the negative electrode active material in an amount of 80 parts by weight or more and 89.6 parts by weight or less, the negative electrode conductive material in an amount of 0.4 parts by weight or more and 10 parts by weight or less, and the negative electrode aqueous binder in an amount of 9.4 parts by weight or more and 18 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0091] In one embodiment of the present specification, the negative electrode composition may include the silicon oxide in an amount of 70 parts by weight or more and 99 parts by weight or less, the negative electrode conductive material in an amount of 0.3 parts by weight or more and 11 parts by weight or less, and the negative electrode aqueous binder in an amount of 9 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0092] Specifically, the negative electrode composition may include the silicon oxide in an amount of 70 parts by weight or more and 90 parts by weight or less, the negative electrode conductive material in an amount of 0.3 parts by weight or more and 11 parts by weight or less, and the negative electrode aqueous binder in an amount of 9 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

[0093] More specifically, the negative electrode composition may include 80 parts by weight or more and 89.6 parts by weight or less of the silicon oxide, 0.4 parts by weight or more and 10 parts by weight or less of the negative electrode conductive material, and 9.4 parts by weight or more and 18 parts by weight or less of the negative electrode aqueous binder, based on 100 parts by weight of the solid content of the negative electrode composition.

[0094] When the composition of the negative electrode composition according to one embodiment of the present specification satisfies the range of the above combination, the energy density and cycle performance of the lithium secondary battery can be maximized.

[0095] In addition to the above, the negative electrode composition according to one embodiment of the present specification may be applied with the following contents.

[0096] In the negative electrode composition according to one embodiment of the present specification, the Si nanocrystals included in the silicon oxide may be formed by performing heat treatment under conditions of 500°C or more and 1500°C or less during the manufacture of the negative electrode active material, specifically, may be formed by performing heat treatment under conditions of 600°C or more and 1300°C or less, and more specifically, 700°C or more and 1200°C or less. When the negative electrode active material is manufactured under temperature conditions outside the above range, the Si nanocrystals dispersed in the silicon oxide grow to exceed the average particle diameter (D50) range of the Si nanocrystals according to the present specification, which may cause the above-described problem, and when the temperature conditions are too low, it may be difficult to manufacture the desired negative electrode active material.

[0097] In one embodiment of the present specification, the silicon oxide may have a carbon layer on at least a portion of its surface. At this time, the carbon layer may be partially coated on at least a portion of the surface, that is, the surface of the silicon oxide, or may be coated on the entire surface of the silicon oxide. When the carbon layer is provided on at least a portion of the surface of the silicon oxide, conductivity is imparted to the negative electrode active material, and the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery may be improved.

[0098] In one embodiment of the present specification, the carbon layer may include amorphous carbon, and the carbon layer may additionally include crystalline carbon.

[0099] 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.

[0100] In one embodiment of the present specification, the amorphous carbon may be a carbonaceous 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 of chemical vapor deposition, and the amorphous carbon may appropriately maintain the strength of the carbon layer, thereby suppressing expansion of the silicon oxide.

[0101] In the present specification, the carbonized substance of the other organic substance may be a carbonized substance of an organic substance selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or kedohexose and combinations thereof.

[0102] In the present 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, or hexane, etc. 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, or phenanthrene, etc.

[0103] In one embodiment of the present specification, the carbon layer may be an amorphous carbon layer.

[0104] 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 total 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, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0105] In one embodiment of the present specification, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically 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, and the side reaction between the electrolyte and the negative electrode active material is suppressed, thereby improving the initial efficiency and / or lifespan of the battery.

[0106] In one embodiment of the present specification, the carbon layer may be formed by a chemical vapor deposition (CVD) method using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0107] In one embodiment of the present specification, the silicon oxide may further include a metal impurity. The metal impurity is an impurity that may be included in silicon, and its content may satisfy a range of 0.1 part by weight or less based on 100 parts by weight of the total silicon-based active material.

[0108] Meanwhile, in one embodiment of the present specification, the average particle diameter (D50) of the negative electrode active material including the silicon oxide may be 1 ㎛ to 15 ㎛, specifically 2 ㎛ to 12.5 ㎛, and more specifically 5 ㎛ to 10 ㎛. At this time, the average particle diameter (D50) of the negative electrode active material is SiOx (0 <x<2) 및 Si 나노결정을 모두 포함하는 최종 파티클(particle)의 평균 입경(D50)을 기준으로 한다.

[0109] When the average particle diameter (D50) of the negative electrode active material satisfies the above range, the viscosity of the negative electrode composition can be formed within an appropriate range as the specific surface area of ​​the particles is included within an appropriate range, thereby facilitating dispersion of the particles constituting the negative electrode composition. In addition, since the contact area between the silicon oxide and the negative electrode conductive material is improved by the complex composed of the negative electrode conductive material and the negative electrode binder within the negative electrode composition, the possibility of sustaining the conductive network increases, thereby increasing the capacity retention rate. In addition, excessively large silicon oxide particles are excluded, thereby enabling the surface of the negative electrode to be formed smoothly, thereby preventing the phenomenon of uneven current density during charge and discharge.

[0110] In a cathode composition according to one embodiment of the present specification, the cathode conductive material may further include at least one selected from the group consisting of a planar conductive material and a dot-shaped conductive material.

[0111] In one embodiment of the present specification, the cathode conductive material may further include a planar conductive material.

[0112] In the present specification, the "planar conductive material" refers to a conductive material having a two-dimensional (2D) structure in which atoms form a crystal structure on a plane with a thickness of a single atomic layer or multiple atomic layers of two or more layers. The planar conductive material refers to a material for securing a conductive path in a planar shape within the negative electrode active material layer, and at the same time, can play a role in suppressing disconnection of the conductive path due to volume expansion, and can be expressed as a plate-shaped conductive material or a bulk conductive material. Specifically, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0113] In one embodiment of the present specification, the average particle diameter (D50) of the planar 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 diameter (D50) of the planar conductive material satisfies the above range, dispersion is easy without causing excessive viscosity increase of the negative electrode slurry due to the sufficient particle size. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0114] In one embodiment of the present specification, the surface-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.

[0115] In one embodiment of the present specification, the planar conductive material may be a high-specific surface area planar conductive material having a high BET surface area; or a low-specific surface area planar conductive material.

[0116] In one embodiment of the present specification, a high surface area surface conductive material or a low surface area surface conductive material may be used without limitation as the surface conductive material, but in particular, since the surface conductive material according to the present specification may be affected to some extent by dispersion effects on electrode performance, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0117] In another embodiment of the present specification, the surface-shaped conductive material has a BET specific surface area of ​​5 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0118] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 / g can satisfy the range below.

[0119] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​5 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0120] In the case of the negative electrode conductive material according to one embodiment of the present specification, it has a completely separate composition from the conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material according to the present invention, it plays a role of securing the contact between the negative electrode active materials, which undergo a large volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material plays a role of providing some conductivity while acting as a buffer when rolled, and its composition and role are completely different from those of the negative electrode conductive material of the present invention.

[0121] In addition, 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 composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based negative electrode active material as in the present invention.

[0122] In one embodiment of the present specification, the cathode conductive material may further include a dot-shaped conductive material.

[0123] The negative electrode conductive material according to one embodiment of the present specification may include, without limitation, any commonly used dot-shaped conductive material. However, if the negative electrode conductive material does not include a linear conductive material but only a dot-shaped conductive material, the dot-shaped conductive material has lower conductivity and specific surface area than the linear conductive material or the planar conductive material, and thus, when used in the present invention, a conductive path (pass) in the negative electrode active material layer may not be formed, which may cause significant capacity degradation. If the negative electrode conductive material according to one embodiment of the present specification uses a dot-shaped conductive material together with the linear conductive material, changes in the physical properties of the negative electrode slurry and gas problems at high temperatures may occur.

[0124] In the negative electrode composition according to one embodiment of the present specification, the negative electrode binder may further include those known in the art to improve adhesion between negative electrode active material particles and adhesion between negative electrode active material particles and negative electrode current collector, and 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), fluoroelastomer, polyacrylic acid The present invention may further include at least one selected from the group consisting of substances in which hydrogen is substituted with Li, Na or Ca, etc., and may further include various copolymers thereof.

[0125] <Cathode>

[0126] A negative electrode for a lithium secondary battery according to one embodiment of the present specification may have a negative electrode active material layer including the above-described negative electrode composition or a cured product thereof on at least one surface of a negative electrode current collector layer.

[0127] Specifically, the negative electrode for the lithium secondary battery may include a negative electrode current collector and a negative electrode active material layer disposed on one or both sides 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.

[0128] At this time, in the present specification, including the “cured product” may mean a case where the cathode composition is cured by heat treatment or light treatment by a method known in the art.

[0129] FIG. 1 is a diagram showing a laminated structure of an anode for a lithium secondary battery according to one embodiment of the present specification. Specifically, a lithium secondary battery anode (100) including an anode active material layer (20) on one surface of an anode current collector layer (10) can be confirmed, and although FIG. 1 shows that the anode active material layer is formed on one surface of the anode current collector layer, it can be included on both surfaces of the anode current collector layer.

[0130] The above negative electrode active material layer can be formed by applying the negative electrode slurry containing the above-described negative electrode composition, a solvent for forming negative electrode slurry, and / or a thickener to at least one surface of the negative electrode current collector layer, and drying and rolling.

[0131] The above-described cathode slurry may include a solvent for forming the cathode slurry. Specifically, the solvent for forming the cathode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of the components.

[0132] The negative electrode current collector layer may be any material that is conductive and does not cause a chemical change in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that adsorbs carbon well, 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 thereto.

[0133] The above thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the present technical field may be appropriately employed.

[0134] In one embodiment of the present specification, the thickener may be included in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, and more specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0135] In one embodiment of the present specification, the solid content of the cathode 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 total cathode slurry.

[0136] Secondary battery

[0137] A lithium secondary battery according to one embodiment of the present specification may include a positive electrode; an anode for the lithium secondary battery described above; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0138] FIG. 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present specification. Specifically, a lithium secondary battery negative electrode (100) including a negative electrode active material layer (20) on one surface of a negative electrode current collector layer (10) can be confirmed, and a lithium secondary battery positive electrode (200) including a positive electrode active material layer (40) on one surface of a positive electrode current collector layer (50) can be confirmed, and it is shown that the lithium secondary battery negative electrode (100) and the lithium secondary battery positive electrode (200) are formed in a laminated structure with a separator (30) interposed therebetween.

[0139] A lithium secondary battery according to one embodiment of the present specification may particularly include the anode described above. Specifically, the secondary battery may include a cathode, a cathode, a separator interposed between the cathode and the anode, and an electrolyte, wherein the cathode is identical to the anode described above. Since the anode has been described above, a detailed description thereof will be omitted.

[0140] The above positive electrode is formed on the positive electrode current collector layer and the positive electrode current collector layer, and may include a positive electrode active material layer including a positive electrode active material.

[0141] In the above positive electrode, the positive electrode current collector layer is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector layer may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector layer to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0142] The above 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), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxide represented by O2 (wherein, 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 (wherein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0143] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0144] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, it can be used without special restrictions as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0145] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector layer. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0146] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0147] 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 the manufacture of lithium secondary batteries.

[0148] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0149] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0150] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0151] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 may be used.

[0152] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0153] 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.

[0154] In addition, another embodiment of the present specification provides a battery pack including the lithium secondary battery.

[0155] The lithium secondary battery according to the embodiments of the present specification stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as 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. For example, the battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0156] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0157]

[0158] <Manufacturing Example>

[0159] <Manufacturing of the cathode>

[0160] Example 1

[0161] Silicon oxide (average particle diameter (D50): 5.5 μm) containing Si nanocrystals with an average particle diameter (D50) of 3 nm as a negative active material, SWCNT (BET specific surface area: 1,000 m 2 / g to 1,500 m 2 / g, aspect ratio: 10,000 or more) and polyacrylamide binder were prepared 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 prepare a negative electrode slurry (solid content concentration: 28 wt%).

[0162] The average particle diameter (D50) of the above Si nanocrystals was calculated by fitting the XRD results using the Scherrer equation, and the nanocrystal standard at this time was measured based on Si (220). (2θ=47.4° to 48.5°)

[0163] As a mixing method, the above-mentioned conductive material, binder, and water were dispersed using a homo mixer at 2500 rpm for 30 min, and then the negative electrode active material was added and dispersed at 2500 rpm for 30 min to produce a negative electrode slurry.

[0164] The above negative electrode slurry was applied to both sides of a copper current collector (thickness: 15㎛) as a negative electrode current collector at a concentration of 3.675 mAh / cm 2 The coating was carried out with a loading amount of , rolled (roll pressed), and dried in a vacuum oven at 130°C for 10 hours to form a cathode (thickness: 57 μm).

[0165] Example 2

[0166] Silicon oxide (average particle diameter (D50): 5.5 μm) containing Si nanocrystals with an average particle diameter (D50) of 2.5 nm as a negative active material, SWCNT (BET specific surface area: 1,000 m 2 / g to 1,500 m 2 / g, aspect ratio: 10,000 or more), graphite as an additional planar conductive material (product name: SFG-6L, BET surface area 17 m 2 / g) and polyacrylamide binder were prepared in a weight ratio of 80.0:0.4:9.6:10.0, and a negative electrode was formed in the same manner as in the manufacturing example of Example 1.

[0167] Example 3

[0168] Silicon oxide (average particle diameter (D50): 5.5 ㎛) containing Si nanocrystals with an average particle diameter (D50) of 3 nm as a negative active material, SWCNT (BET specific surface area: 1,000 m 2 / g to 1,500 m 2 / g, aspect ratio: 10,000 or more) and polyacrylamide binder in a weight ratio of 88.5:1.2:10.3, and a negative electrode was formed in the same manner as in the manufacturing example of Example 1.

[0169] Example 4

[0170] Silicon oxide (average particle diameter (D50): 5.5 μm) containing Si nanocrystals with an average particle diameter (D50) of 2.5 nm as a negative active material, SWCNT (BET specific surface area: 1,000 m 2 / g to 1,500m 2 / g, aspect ratio: 10,000 or more), an additional dot-shaped conductive agent (carbon black) and a polyacrylamide binder were prepared in a weight ratio of 80.0:0.4:9.6:10.0, and a negative electrode was formed in the same manner as in the manufacturing example of Example 2.

[0171] Comparative Example 1

[0172] A negative electrode was formed in the same manner as in the manufacturing example of Example 1, except that the negative electrode composition was prepared using graphite (average particle diameter (D50): 5.5 μm) as a carbon-based negative electrode active material, SWCNT, and polyacrylamide binder in a weight ratio of 95.6:1.0:3.4.

[0173] Comparative Example 2

[0174] A negative electrode was formed in the same manner as in the manufacturing example of Example 1, except that the negative electrode composition was prepared by mixing silicon oxide (average particle diameter (D50): 5.5 μm) containing Si nanocrystals having an average particle diameter (D50) of 2.6 nm as a negative electrode active material, SWCNT, and polyacrylamide binder in a weight ratio of 93.8:0.47:5.73.

[0175] Comparative Example 3

[0176] A negative electrode was formed in the same manner as in the manufacturing example of Example 1, except that the negative electrode composition was prepared by mixing silicon oxide (average particle diameter (D50): 5.5 μm) containing Si nanocrystals having an average particle diameter (D50) of 2.8 nm as a negative electrode active material, SWCNT, and polyacrylamide binder in a weight ratio of 92.7:0.927:6.373.

[0177] Comparative Example 4

[0178] A negative electrode was formed in the same manner as the manufacturing example of Example 1, except that silicon oxide containing Si nanocrystals having an average particle diameter (D50) of 0.08 nm was included as the negative electrode active material.

[0179] Comparative Example 5

[0180] A negative electrode was formed in the same manner as the manufacturing example of Example 1, except that silicon oxide containing Si nanocrystals having an average particle diameter (D50) of 7 nm was included as the negative electrode active material.

[0181] Comparative Example 6

[0182] Silicon oxide (average particle diameter (D50): 5.5 ㎛) containing Si nanocrystals with an average particle diameter (D50) of 3 nm as a negative active material, SWCNT (BET specific surface area: 1,000 m 2 / g to 1,500m 2 / g, aspect ratio: 10,000 or more) and polyacrylamide binder in a weight ratio of 88.5:0.2:11.3, and a negative electrode was formed in the same manner as in the manufacturing example of Example 1.

[0183] Comparative Example 7

[0184] A negative electrode was formed in the same manner as in the manufacturing example of Example 1, except that the negative electrode composition was prepared by using silicon oxide (average particle diameter (D50): 5.5 μm) containing Si nanocrystals with an average particle diameter (D50) of 3 nm as a negative electrode active material, a dot-shaped conductive material (carbon black), and a polyacrylamide binder in a weight ratio of 88.5:0.44:11.06.

[0185] Comparative Example 8

[0186] Silicon oxide (average particle size (D50): 5.5 μm) containing Si nanocrystals with an average particle size (D50) of 2.5 nm as a negative active material, dot-shaped conductive material (carbon black), and additional planar conductive material (product name: SFG-6L, BET specific surface area 17 m 2 / g) and polyacrylamide binder were prepared in a weight ratio of 80.0:0.4:9.6:10.0, and a negative electrode was formed in the same manner as in the manufacturing example of Example 2.

[0187]

[0188] <Manufacturing of Lithium Secondary Batteries>

[0189] A cathode slurry was prepared by adding NCMA active material (average particle diameter (D50): 9.6 μm) as a cathode active material, carbon nanotubes as a cathode conductive material, and polyvinylidene fluoride (PVdF) as a cathode binder to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a cathode slurry at a weight ratio of 97.6:0.8:1.6.

[0190] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12㎛) as a positive electrode collector at a density of 3.5 mAh / cm. 2A positive electrode was manufactured by coating with a loading amount, rolling (roll pressing), and drying in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 75 μm) (positive electrode thickness: 162 μm, porosity 26%).

[0191] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte was injected to manufacture a full-cell lithium secondary battery of Example 1.

[0192] The above electrolyte is an organic solvent containing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) mixed in a volume ratio of 10:90, vinylene carbonate added at 0.5 wt% based on the total weight of the electrolyte, and LiPF6 and LiFSI added at 0.5 M and 1 M concentrations, respectively, as lithium salts.

[0193] Lithium secondary battery full-cells were manufactured in the same manner as above, except that the negative electrodes of Examples 2 to 4 and Comparative Examples 1 to 8 were used.

[0194]

[0195] Experimental Example 1: Evaluation of Energy Density and Lifetime Characteristics

[0196] The energy density (cell energy density) of lithium secondary batteries including the negative electrodes manufactured in Examples 1 to 4 and Comparative Examples 1 to 8 was measured, and the lifespan was evaluated using an electrochemical charger / discharger to evaluate the capacity retention rate at 300 cycles.

[0197] Specifically, when evaluating the life characteristics, the C-rate was set to 1.0C when measuring the initial charge capacity, and the charging was performed under the upper limit voltage of 4.2V, CCCV conditions, and cut-off current of 0.05C, and when measuring the initial discharge capacity, the C-rate was set to 0.5C, the lower limit voltage was 2.5V, and CC conditions.

[0198] Capacity retention rate (%) = {(charge / discharge capacity in the Nth cycle) / (charge / discharge capacity in the first cycle)} X 100

[0199] The results of the energy density and life characteristics evaluation are shown in Table 1 below.

[0200] Energy density E / D (Wh / L) Capacity retention (%) (@300 cycles) Example 1865.180.9 Example 2761.880.3 Example 3867.879.8 Example 4755.580.0 Comparative example Over 1629.195 Comparative example 2774.472.8 Comparative example 3772.377.8 Comparative example 4680.782 Comparative example Less than 5890.160 Comparative example 6854.268.1 Comparative example Less than 7862.560 Comparative example Less than 8759.560

[0201] Previously, to achieve high energy density in the cathode, the silicon content was simply increased, but this resulted in a decrease in cycle capacity retention (less than approximately 79%), or when adjusting the active material and other characteristics to secure capacity retention (more than approximately 79%), there was a problem in which energy density was not secured (less than 750 Wh / L).

[0202] Since the lithium secondary battery using the negative electrode composition according to the present specification aims to simultaneously satisfy high energy density and excellent life characteristics, it was determined that the energy density must be about 750 Wh / L or more and the capacity retention rate after 300 cycles must be about 79% or more to be usable as the lithium secondary battery according to the present invention.

[0203] As can be seen in Table 1 above, in the case of Examples 1 to 4 using the negative electrode composition according to the present specification, the energy density was 750 Wh / L or more, and at the same time, the capacity retention rate at 300 cycles was 79% or more, so that it could be used as a lithium secondary battery having high energy density and excellent life characteristics according to the present invention. This corresponds to the result of using a negative electrode active material in which the negative electrode active material is 70 parts by weight or more based on 100 parts by weight of the solid content of the negative electrode composition, the negative electrode conductive material is 0.3 parts by weight or more, particularly, the linear conductive material is included in an amount of 0.3 parts by weight or more and 3 parts by weight or less, and the negative electrode aqueous binder is 9 parts by weight or more, and each content is optimized, and the average particle diameter (D50) of the Si nanocrystals as silicon oxide is 0.1 nm or more and 5 nm or less.

[0204] However, in the case of Example 3, the energy density and cycle performance were similar to those of Example 1 when the content of SWCNT was increased by three times compared to Example 1, but there was no greater performance improvement due to the inclusion of a high content of SWCNT, and it was rather disadvantageous in terms of cost.

[0205] In addition, in the case of Example 4, carbon black (dot-shaped conductive material) was used as the second conductive material instead of the planar conductive material (SFG-6L) of Example 2, and although there was no significant difference in energy density and cycle performance compared to Example 2, it was confirmed in the preliminary evaluation (production of negative electrode slurry and analysis of gas generation) that the application of the dot-shaped conductive material caused changes in the properties of the negative electrode slurry and gas problems at high temperatures.

[0206] The lithium secondary battery of Comparative Example 1, which used graphite as the negative active material, did not use a negative active material containing silicon oxide, so there was no decrease in the cycle performance of the electrode due to volume expansion, but the energy density was significantly reduced, so it could not be used as a lithium secondary battery having high energy density and excellent lifespan characteristics according to the present invention.

[0207] Compared to the negative electrode composition of Example 1, the lithium secondary battery of Comparative Example 2, which contained half the content of the negative electrode aqueous binder, had a relatively high content of the negative electrode active material, satisfying an energy density of 750 Wh / L or more. However, as the content of the negative electrode aqueous binder was reduced, it became difficult to suppress warping of the electrode due to volume change of the silicon oxide active material throughout the cycle, and thus the capacity retention rate was only in the early 70%, so it could not be used as a lithium secondary battery with excellent performance according to the present invention.

[0208] The lithium secondary battery of Comparative Example 3, which contained half the content of the negative electrode aqueous binder compared to the negative electrode composition of Example 1, satisfied an energy density of 750 Wh / L or more, similar to Comparative Example 2. However, even though it contained more than twice the amount of the negative electrode linear conductive material compared to Example 1, the capacity retention rate did not reach 79%, and thus it could not be used as a lithium secondary battery with excellent performance according to the present invention. Through this, it was confirmed that it is difficult to maintain cycle characteristics during repeated charge / discharge processes of the battery even if only a large amount of the negative electrode linear conductive material is included without an appropriate composition combination of the negative electrode active material and the negative electrode aqueous binder according to the present invention.

[0209] The lithium secondary battery of Comparative Example 4, which used silicon oxide with significantly smaller Si nanocrystals as the negative electrode active material, satisfied a capacity retention rate of 79% or more with an appropriate combination of the negative electrode composition according to the present invention, but the size of the Si nanocrystals was too small, so the energy density was significantly lower than that of Example 1, and thus it could not be used as a lithium secondary battery with excellent performance according to the present invention.

[0210] The lithium secondary battery of Comparative Example 5, which used silicon oxide as an anode active material, having a size of Si nanocrystals larger than the size range of Si nanocrystals according to the present specification, was excellent in terms of energy density, but it was confirmed that cracks were formed in the anode active material as charge and discharge were repeated, and the Li ions could not diffuse into the nanocrystals, resulting in accelerated deterioration of the battery due to reaction non-uniformity, and the capacity retention rate was significantly reduced.

[0211] In the case of Comparative Example 6, it was confirmed that rapid capacity degradation occurred from the beginning of the cycle as the SWCNT content was reduced to half compared to Example 1. Specifically, as a result of measuring the initial cycle capacity, the initial cycle capacity of Example 1 was 88.2 mAh, the initial cycle capacity of Example 2 was 89.0 mAh, but the initial cycle capacity of Comparative Example 6 was significantly low at 86.8 mAh. As a result, it was confirmed that the capacity retention rate in Table 1 was also significantly low. At this time, the initial cycle capacity was measured by charging (4.2 V, current 5% cut) under CC-CV conditions at a rate of 0.33 C and discharging (2.5 V) under CC conditions at a rate of 0.33 C.

[0212] In Comparative Example 7, carbon black was used as a conductive material instead of the linear conductive material (SWCNT) of Example 1. Since carbon black has a small conductivity and specific surface area, it cannot form a conductive path (pass) within the negative electrode active material layer, resulting in a significant capacity degradation, and it was confirmed that the capacity retention rate was significantly lower than that of Example 1.

[0213] In the case of Comparative Example 8, carbon black was used as a conductive material instead of the linear conductive material (SWCNT) of Example 2, and it was confirmed that the capacity retention rate was significantly low as a conductive path (pass) was not formed within the negative electrode active material layer, resulting in significant capacity degradation.

Claims

1. A negative electrode composition comprising a negative electrode active material including silicon oxide; a negative electrode conductive material; and a negative electrode aqueous binder, Based on 100 parts by weight of the solid content of the above negative electrode composition, the negative electrode active material is included in an amount of 70 parts by weight or more, the negative electrode conductive material is included in an amount of 0.3 parts by weight or more, and the negative electrode aqueous binder is included in an amount of 9 parts by weight or more. The above-mentioned negative electrode conductive material includes a linear conductive material in an amount of 0.3 parts by weight or more and 3 parts by weight or less based on 100 parts by weight of the solid content of the above-mentioned negative electrode composition, The above silicon oxide comprises Si nanocrystals, The above Si nanocrystals are a cathode composition having an average particle diameter (D50) of 0.1 nm or more and 5 nm or less.

2. In claim 1, A cathode composition wherein the above cathode aqueous binder is a polyacrylamide-based binder.

3. In claim 1, The negative electrode composition comprises the negative electrode active material in an amount of 70 parts by weight or more and 90 parts by weight or less, the negative electrode conductive material in an amount of 0.3 parts by weight or more and 11 parts by weight or less, and the negative electrode aqueous binder in an amount of 9 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the solid content of the negative electrode composition.

4. In claim 1, The above silicon oxide is SiOx (0 <x<2)를 포함하는 것인 음극 조성물.

5. In claim 1, The above silicon oxide is amorphous SiOx (0 <x<2)를 포함하며, A cathode composition in which the Si nanocrystals are dispersed within the amorphous silicon oxide.

6. In claim 1, A negative electrode composition wherein the D50 of the above negative electrode active material is 5 μm or more and 10 μm or less.

7. A negative electrode for a lithium secondary battery, wherein a negative electrode active material layer comprising a negative electrode composition or a cured product thereof according to any one of claims 1 to 6 is provided on at least one surface of a negative electrode current collector layer.

8. Bipolar; A negative electrode for a lithium secondary battery according to claim 7; A separator provided between the anode and the cathode; and A lithium secondary battery containing an electrolyte.

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

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

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

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