Lithium-ion rechargeable battery

Abstract

This application relates to a lithium secondary battery.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0183766, filed with the Korean Intellectual Property Office on December 23, 2022, and all of its content is incorporated herein.

[0002] This application relates to a lithium secondary battery.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy has been increasing, and as part of this, the fields of power generation and power storage using electrochemical reactions are the most actively studied.

[0004] Currently, as a representative example of an electrochemical device using such electrochemical energy, a secondary battery can be cited, and its usage area is showing a trend of increasing more and more.

[0005] With the development of technologies related to mobile devices and the increase in demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, regarding electrodes for such high-capacity lithium secondary batteries, research on methods for manufacturing high-density electrodes with a higher energy density per unit volume has been actively conducted.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode. Although carbon-based materials such as graphite as a negative electrode material are excellent in stability and reversibility, they have limitations in terms of capacity, and in fields aiming for high capacity, attempts to use Si-based materials with a high theoretical capacity as a negative electrode material are increasing.

[0007] In other words, lithium secondary batteries are typically manufactured using a compound with lithium inserted, such as LiCoO2 or LiMn2O4, for the positive electrode, and a material without lithium inserted, such as a carbon-based or silicon-based material, for the negative electrode. During charging, lithium ions inserted in the positive electrode move to the negative electrode via the electrolyte, and during discharging, lithium ions move again from the negative electrode to the positive electrode. During the charging reaction, the lithium moving from the positive electrode to the negative electrode reacts with the electrolyte to form a type of protective film (passivation film) called a solid electrolyte interface (SEI) on the surface of the negative electrode. This SEI stabilizes the structure of the negative electrode by suppressing the movement of electrons required for the reaction between the negative electrode and the electrolyte, thereby preventing the decomposition reaction of the electrolyte. However, because it is an irreversible reaction, it leads to the consumption of lithium ions. That is, the lithium consumed in the formation of the SEI cannot return to the positive electrode during the subsequent discharge process, reducing the battery capacity.

[0008] On the other hand, efforts to improve the performance of lithium-ion secondary batteries require the development of technologies to increase charging speed. For lithium-ion secondary batteries to be charged rapidly, the lithium ion movement rate must be fast during the process of lithium ions being inserted into the negative electrode. Therefore, battery designs are being developed that reduce internal resistance and achieve high output by forming the negative electrode active material layer to a thin film thickness to reduce the diffusion distance of lithium, and by forming a carbon coating layer on its surface to increase conductivity.

[0009] However, it is difficult to achieve high capacity with a negative electrode equipped with such a thin-film negative electrode active material layer. Furthermore, it is difficult to achieve rapid charging with a negative electrode that achieves high capacity. In addition, when using a silicon-based negative electrode, the Si content of the negative electrode is increased to increase the energy density, which causes a rapid expansion of volume during the charging process, disrupting the conductive path and degrading the battery characteristics, resulting in a decrease in capacity from the start. Moreover, when silicon-based negative electrodes undergo repeated charge and discharge cycles, lithium ion charging does not occur uniformly in the depth direction of the negative electrode, and the reaction proceeds at the surface, accelerating surface degeneration, thus requiring performance improvement in terms of battery cycles.

[0010] Therefore, in order to overcome the aforementioned problems when using silicon-based compounds, which have excellent rapid charging performance, as negative electrode active materials on their own, various methods are being discussed, such as methods to adjust the driving potential, additionally, methods to further coat a thin film on the active material layer, methods to suppress volume expansion itself such as adjusting the particle size of the silicon-based compound, or the development of a binder that controls the volume expansion of the silicon-based compound to prevent the conduction path from being interrupted.

[0011] However, the aforementioned approach has limitations in its application, as it can actually degrade battery performance. There are still limitations to the regular production of negative electrode batteries with a high content of silicon-based compounds that offer superior rapid charging performance. As the proportion of silicon-based active material in the silicon-based active material layer increases, prelithiation concentrates on the surface of the negative electrode, which can actually damage the silicon-based active material on the surface and result in uneven prelithiation, thus hindering improvements in lifespan characteristics.

[0012] Therefore, research is needed on lithium secondary batteries that use a silicon-based active material in the negative electrode for high capacity while also improving cycle performance. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Published Patent No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0014] As a result of research into the aforementioned problems, we found that when using a silicon-based anode (especially a Pure Si anode) as the anode to ensure capacity characteristics, the range in which a silicon-based anode can be used can be limited by adjusting the NP ratio and incorporating a pre-lithiation process. Our research confirmed that this ensures the lifespan characteristics.

[0015] Therefore, this application relates to a lithium secondary battery including a silicon-based anode. [Means for solving the problem]

[0016] One embodiment of this specification provides a lithium secondary battery comprising a silicon-based negative electrode, a positive electrode, a separator membrane, and an electrolyte, wherein the positive electrode or the silicon-based negative electrode is a pre-lithified electrode, the silicon discharge capacity usage range of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, and the upper end of the silicon discharge capacity of the silicon-based negative electrode is 57% or less and the lower end is 13% or more. [Effects of the Invention]

[0017] The lithium secondary battery described in this application is characterized by applying a pre-lithiation process to the silicon-based negative electrode or positive electrode, thereby limiting the usable range of the overall discharge capacity when using a silicon-based negative electrode, and specifically controlling the upper and lower limits of the discharge capacity.

[0018] This makes it possible to produce batteries that achieve the advantages of using silicon-based negative electrodes, namely high capacity and high energy density, and also solves the problem of deterioration in lifespan performance due to volume expansion during repeated cycles, which was a problem with conventional batteries.

[0019] In other words, the lithium secondary battery described in this application is primarily characterized by ensuring the lifespan performance of the lithium secondary battery by limiting the area of ​​silicon used in the negative electrode. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows a lithium secondary battery related to this application. [Modes for carrying out the invention]

[0021] Before describing the present invention, let us first define some terms.

[0022] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0023] In this specification, "p~q" means "greater than or equal to p and less than or equal to q".

[0024] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area can mean the specific surface area measured by the above measurement method.

[0025] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. Alternatively, the particle size distribution may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0026] In this specification, the statement that a polymer contains a monomer as a monomer unit means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted as being equivalent to the polymer containing a monomer as a monomer unit.

[0027] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise explicitly stated as "homopolymer."

[0028] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0029] The present invention will be described in detail below with reference to the drawings so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0030] One embodiment of this specification provides a lithium secondary battery comprising a silicon-based negative electrode, a positive electrode, a separator membrane, and an electrolyte, wherein the positive electrode or the silicon-based negative electrode is a pre-lithified electrode, the silicon discharge capacity usage range of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, and the upper end of the silicon discharge capacity of the silicon-based negative electrode is 57% or less and the lower end is 13% or more.

[0031] This application has the advantage of producing a battery that can achieve high capacity and high energy density, which are advantages when using a silicon-based negative electrode, and also solves the problem of deterioration in lifespan performance due to volume expansion during repeated cycles, which is a problem with conventional batteries. In other words, the lithium secondary battery according to this application is mainly characterized by ensuring the lifespan performance of the lithium secondary battery by limiting the area of ​​silicon used in the negative electrode.

[0032] Figure 1 shows a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 containing a negative electrode active material layer 20 can be seen on one side of a negative electrode current collector layer 10, and a positive electrode 200 containing a positive electrode active material layer 40 can be seen on one side of a positive electrode current collector layer 50, showing that the negative electrode 100 and the positive electrode 200 for the lithium secondary battery are formed in a laminated structure with a separation film 30 in between.

[0033] In one embodiment of this application, a lithium secondary battery is provided in which the silicon discharge capacity usage range of the silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity, and the upper limit of the silicon discharge capacity of the silicon-based negative electrode is 57% or less, and the lower limit is 13% or more.

[0034] In one embodiment of this application, a lithium secondary battery is provided in which the NP ratio of the lithium secondary battery is 170% or more and 280% or less.

[0035] In one embodiment of this application, the NP ratio can satisfy the following formula A.

[0036] [Formula A] N / P ratio = Discharge capacity per unit area of ​​the negative electrode / Discharge capacity per unit area of ​​the positive electrode.

[0037] In the present invention, the "discharge capacity per unit area" refers to the discharge capacity per unit area in the first cycle of the negative electrode or positive electrode.

[0038] The discharge capacity per unit area of ​​the negative electrode can be obtained by the following method. Specifically, a half-cell is manufactured using a negative electrode sample containing negative electrode active material and a counter electrode (for example, a lithium metal electrode) facing the negative electrode sample. The discharge capacity measured by charging and discharging the half-cell is divided by the weight of the negative electrode active material to obtain the "discharge capacity of the negative electrode sample per unit weight of negative electrode active material". A secondary battery is manufactured using a negative electrode containing the same negative electrode active material as used in the half-cell and a positive electrode containing positive electrode active material. The "discharge capacity of the negative electrode sample per unit weight of negative electrode active material" is multiplied by the weight of the negative electrode active material contained in the secondary battery, and this is divided by the area of ​​the negative electrode contained in the secondary battery to obtain the discharge capacity per unit area of ​​the negative electrode.

[0039] The discharge capacity per unit area of ​​the positive electrode can be obtained by the following method. Specifically, a half-cell is manufactured using a positive electrode sample containing positive electrode active material and a counter electrode (for example, a lithium metal electrode) facing the positive electrode sample. The discharge capacity measured by charging and discharging the half-cell is divided by the weight of the positive electrode active material to obtain the "discharge capacity of the positive electrode sample per unit weight of positive electrode active material". A secondary battery is manufactured using a positive electrode containing the same positive electrode active material as used in the half-cell and a negative electrode containing negative electrode active material. The discharge capacity per unit area of ​​the positive electrode can be obtained by multiplying the "discharge capacity of the positive electrode sample per unit weight of positive electrode active material" by the weight of the positive electrode active material contained in the secondary battery and dividing this by the area of ​​the positive electrode contained in the secondary battery.

[0040] The lithium secondary battery according to this application is characterized by introducing a pre-lithiation process to the positive or negative electrode and adjusting the NP ratio to limit the USOC of the negative electrode.

[0041] In this application, the upper and lower limits of the discharge capacity refer to the values ​​obtained by calculating the upper and lower limits of the discharge reference active Li based on the total load of the negative electrode as percentages, with USOC as the reference value. These values ​​may also be calculated from the load of the positive electrode and its initial efficiency, as well as the initial efficiency of the negative electrode.

[0042] In one embodiment of this application, a lithium secondary battery is provided in which the upper end of the silicon discharge capacity of the silicon-based negative electrode is 45% or more and 57% or less, and the lower end of the silicon discharge capacity of the silicon-based negative electrode is 13% or more and 28% or less.

[0043] In another embodiment, the upper end of the silicon discharge capacity of the silicon-based negative electrode may be 45% or more and 57% or less, preferably 46% or more and 53% or less, and more preferably 48% or more and 52% or less.

[0044] In another embodiment, the lower end of the silicon discharge capacity of the silicon-based negative electrode may satisfy 13% to 28%, preferably 14% to 25%, and more preferably 16% to 24.5%.

[0045] In one embodiment of this application, a lithium secondary battery is provided in which the difference between the upper and lower limits of the silicon discharge capacity is less than 35%.

[0046] In other words, the difference between the upper and lower limits of the silicon discharge capacitance may be represented by △Si, which may represent the capacitance range used in silicon-based negative electrodes.

[0047] In another embodiment, the difference between the upper and lower ends of the silicon discharge capacity may be less than 35%, preferably 34.8% or less, more preferably 34.5% or less, and may be 20% or more, preferably 25% or more.

[0048] In other words, as mentioned above, the usable range of the negative electrode can be adjusted by changing the N / P ratio and pre-lithiumization, thereby ensuring lifespan characteristics while retaining the characteristics of a silicon-based negative electrode.

[0049] In one embodiment of this application, the silicon-based negative or positive electrode may be a pre-lithified electrode. Pre-lithification involves pre-supplying lithium to the electrode, and all methods used in the industry, such as transfer processes, electrochemical processes, and SLMP processes, can be applied.

[0050] The following sections will explain the positive electrode, negative electrode, electrolyte, and separator membrane included in lithium secondary batteries.

[0051] The silicon-based negative electrode according to this application may include a negative electrode active material layer comprising a negative electrode current collector layer and a negative electrode active material layer composition provided on one or both sides of the negative electrode current collector layer.

[0052] The negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0053] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited to this.

[0054] In one embodiment of this application, the negative electrode active material layer comprises a negative electrode active material layer composition, and the negative electrode active material layer composition may also contain a silicon-based active material.

[0055] In one embodiment of the present application, the negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition may contain one or more selected from the group consisting of a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0056] In one embodiment of the present application, the negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition may contain a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0057] In one embodiment of the present application, the silicon-based active material may contain one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0058] In one embodiment of the present application, the silicon-based active material contains one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and metal impurities, and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more.

[0059] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0060] In one embodiment of the present application, particularly pure silicon (Si) may be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, as described above, when the silicon-based active material is based on 100 parts by weight in total, it contains pure Si particles (SiOx (x = 0)) that are not combined with other particles or elements within the above range.

[0061] On the other hand, the average particle size (D50) of the silicon-based active material in the present invention may be 5 μm to 10 μm, more specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. If the average particle size is less than 5 μm, the specific surface area of ​​the particles increases too much, causing the viscosity of the negative electrode slurry to increase too much. As a result, the dispersion of the particles constituting the negative electrode slurry does not become smooth. Also, if the size of the silicon-based active material is too small, the contact area between the silicon particles and the conductive material decreases due to the composite consisting of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of the conductive network being interrupted and reducing the capacity retention rate. On the other hand, if the average particle size exceeds 10 μm, there will be silicon particles that are too large, resulting in an uneven surface on the negative electrode and uneven current density during charging and discharging. Also, if the silicon particles are too large, the phase stability of the negative electrode slurry becomes unstable, reducing processability. This reduces the capacity retention rate of the battery.

[0062] In one embodiment of this application, the silicon-based active material typically has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m². 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. BET surface area is measured according to DIN 66131 (using nitrogen).

[0063] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure or exist in the form of a silicon-containing film or coating, but these are less preferred.

[0064] In one embodiment of the present application, the negative electrode active material may be contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0065] In one embodiment of the present application, the silicon-based active material may be contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0066] In another embodiment, the silicon-based active material may be contained in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be contained in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0067] The negative electrode active material layer composition according to the present application uses a silicon-based active material having a significantly high capacity within the above range, and uses a negative electrode conductive material and a negative electrode binder capable of controlling the volume expansion rate during the charge and discharge process, so that even if the above range is included, the performance of the negative electrode is not deteriorated, and it has the characteristic of excellent output characteristics during charging and discharging.

[0068] In one embodiment of the present application, the silicon-based active material may have a non-spherical form, and its sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0069] In the present application, the sphericity is determined by the following formula 1, where A is the area and P is the boundary line.

[0070] [Formula 1] 4πA / P 2

[0071] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have a limitation: their volume expands rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer and actually degrading the battery's performance.

[0072] Therefore, in one embodiment of this application, the negative electrode active material layer composition may include a negative electrode conductive material and a negative electrode binder. That is, the negative electrode conductive material plays a role in securing conductive paths, and the binder plays a role in controlling such negative electrode conductive material during charging and discharging.

[0073] In one embodiment of this application, the negative electrode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0074] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity in the negative electrode and forms conductivity without inducing a chemical change, and means a conductive material whose form is circular or point-shaped. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably contains carbon black in terms of embodying high conductivity and having excellent dispersibility.

[0075] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more comfortably, 50m2 / g or more 60m 2 It may be less than / g.

[0076] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0077] In one embodiment of this application, the negative electrode conductive material may include a planar conductive material.

[0078] The planar conductive material refers to a conductive material that improves conductivity by increasing surface contact between silicon particles within the negative electrode, while simultaneously suppressing the disruption of the conductive path due to volume expansion. The planar conductive material may also be expressed as a plate-type conductive material or a bulk-type conductive material.

[0079] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate-type graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-type graphite.

[0080] In one embodiment of this application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is satisfied, the particle size is sufficient, so the viscosity of the negative electrode slurry does not increase excessively, and dispersion becomes easy. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is superior.

[0081] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0082] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0083] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material or a low specific surface area planar conductive material without limitation. In particular, the planar conductive material according to this application may be affected to some extent by the dispersion effect on electrode performance, and it is especially preferable to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0084] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0085] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0086] In another embodiment, the planar conductive material is a high specific surface area planar conductive material with a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 Less than / g, more comfortably, 100m 2 / g or more 250m 2 The range of / g or less may also be satisfied.

[0087] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, with a BET specific surface area of ​​1 m². 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 The range of / g or less may also be satisfied.

[0088] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, here, "bundle type" refers to a secondary shape in the form of a bundle or rope, where multiple carbon nanotube units are arranged parallel to each other with substantially the same orientation in the longitudinal direction of the carbon nanotube units, or are intertwined. The carbon nanotube units have a graphite sheet with a nanoscale diameter in a cylindrical shape and an sp2 bond structure. In this case, depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. The bundle-type carbon nanotubes can be dispersed more uniformly during the manufacture of the negative electrode compared to entangled type carbon nanotubes, and a conductive network can be smoothly formed within the negative electrode, thereby improving the conductivity of the negative electrode.

[0089] In one embodiment of this application, the negative electrode conductive material includes a linear conductive material, which may be a carbon nanotube.

[0090] In one embodiment of this application, the carbon nanotubes may be SWCNTs and / or MWCNTs. When the linear conductive material is SWCNTs, the length of the SWCNTs may be 0.5 μm to 100 μm, preferably 1 μm to 80 μm.

[0091] In one embodiment of this application, the negative electrode conductive material may contain 5 to 40 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0092] In another embodiment, the negative electrode conductive material may contain 5 to 40 parts by weight, preferably 5 to 30 parts by weight, and more preferably 5 to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0093] In one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, and the ratio of the planar conductive material to the linear conductive material can satisfy 1:0.001 to 1:0.3.

[0094] In one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each satisfying the aforementioned composition and ratio, thereby increasing the number of points where charging and discharging are possible without significantly affecting the life characteristics of a conventional lithium secondary battery, and providing excellent output characteristics at a high C-rate.

[0095] The negative electrode conductive material of this application has a completely different structure from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application plays a role in controlling the contact points between silicon-based active materials, which experience very large volume expansion during charging and discharging. The positive electrode conductive material, on the other hand, acts as a buffer during rolling while partially imparting conductivity, and its structure and role are completely different from those of the negative electrode conductive material of this invention.

[0096] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity. Thus, their structure and role are completely different from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0097] In one embodiment of this application, the plate-shaped conductive material used as the negative electrode conductive material has a structure and role different from that of carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0098] On the other hand, plate-type conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be represented as plate-type graphite. In other words, they are substances included to maintain conductive paths within the negative electrode active material layer, and do not play a role in lithium storage or release, but rather substances that secure conductive paths in a planar form within the negative electrode active material layer.

[0099] In other words, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped form and used as a material to secure a conductive path that does not serve the role of storing or releasing lithium. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0100] On the other hand, in this application, the use of a carbon-based active material as the active material means that it was processed into a point-like or spherical shape and used as a substance that plays a role in storing or releasing lithium.

[0101] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0102] The negative electrode binder according to one embodiment of this application plays a role in controlling the silicon-based active material and the negative electrode conductive material in order to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any ordinary negative electrode binder can be applied as long as it fulfills the above role. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0103] In one embodiment of this application, the negative electrode binder may be included in a quantity of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition, and may also be included in a quantity of 5 parts by weight or more, or 8 parts by weight or more.

[0104] Compared to conventional carbon-based anodes, when using a Si-based anode, a water-based binder may be applied in the aforementioned weight amounts, and a point-type conductive material with a low active group content may be used. Due to these characteristics, the point-type conductive material becomes hydrophobic and exhibits excellent bonding strength with the conductive material / binder.

[0105] In one embodiment of this application, the silicon-based negative electrode may be formed by coating one or both sides of a negative electrode current collector layer with a negative electrode slurry containing the negative electrode active material layer composition.

[0106] In one embodiment of this application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0107] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0108] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0109] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0110] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0111] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the clumping phenomenon of the negative electrode composition particles and enabling efficient formation of the negative electrode active material layer.

[0112] In one embodiment of this application, the slurry solvent may be any solvent that can disperse the negative electrode composition, but specifically, water or NMP may be used.

[0113] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0114] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0115] The aforementioned porosity is determined by the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to this application are included in specific compositions and content portions to satisfy the aforementioned range, thereby ensuring that the electrical conductivity and resistance of the electrode are within an appropriate range.

[0116] In one embodiment of this application, the positive electrode includes a positive electrode active material layer comprising a positive electrode current collector layer and a positive electrode active material layer composition provided on one or both sides of the positive electrode current collector layer.

[0117] In one embodiment of this application, the positive electrode active material layer comprises a positive electrode active material layer composition, which may comprise one or more selected from the group consisting of a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0118] In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., may be used. The positive electrode current collector layer may also have a thickness of 1 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector layer to increase adhesion to the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0119] In one embodiment of this application, a lithium secondary battery is provided in which the thickness of the positive electrode and negative electrode current collector layers is 1 μm or more and 100 μm or less, and the thickness of the positive electrode and negative electrode active material layers is 20 μm or more and 500 μm or less.

[0120] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be LiNi x Co y Mn z O2(x+y+z=1);LiNi a Co b Mn c Al d O2(a+b+c+d=1);LiMn2O4;LiNi 0.5 Mn 1.5 O2 and LiM x Fe y The cathode active material may include one or more elements selected from the group consisting of PO4 (M: Transition metal, x+y=1). However, the cathode active material is not limited to these elements alone.

[0121] Specifically, the positive electrode active material may be NCM or NCMA, which are commonly used.

[0122] Generally, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; 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 Ni-site type lithium nickel oxide represented as Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.6); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be Li-metal.

[0123] In one embodiment of this application, the positive electrode active material comprises a lithium composite transition metal containing nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium composite transition metal comprises single particles or secondary particles, and the average particle size (D50) of the single particles may be 1 μm or more.

[0124] For example, the average particle size (D50) of the single particle may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, greater than 1 μm and 12 μm or less, greater than 1 μm and 8 μm or less, or greater than 1 μm and 6 μm.

[0125] Even when the single particle is formed with a small particle size (average particle size (D50) of 1 μm or more and 12 μm or less), its particle strength may be excellent. For example, the single particle may have a strength of 650 kgf / cm². 2 When rolled with this force, the particle strength can be 100 MPa to 300 MPa. This allows the single particle to have a strength of 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increased fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0126] The single particle can be produced by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particle may be produced by a different method than that of the single particle, and its composition may be the same as or different from that of the single particle.

[0127] The method for forming the single particles is not particularly limited, but generally, they may be formed by increasing the firing temperature and over-firing, or they may be produced by using additives such as particle growth accelerators that are useful for over-firing, or by changing the starting material.

[0128] For example, the firing is carried out at a temperature that can form a single particle. To form this, firing must be performed at a higher temperature than when secondary particles are produced. For example, if the composition of the precursor is the same, firing must be performed at a temperature about 30°C to 100°C higher than when secondary particles are produced. The firing temperature for forming the single particle may vary depending on the metal composition in the precursor. For example, when trying to form a single particle of a high-nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, the firing temperature may be 700°C to 1000°C, preferably 800°C to 950°C. When the firing temperature is within the above range, a positive electrode active material containing a single particle with excellent electrochemical properties can be produced. If the firing temperature is below 790°C, a positive electrode active material containing a lithium composite transition metal in the form of secondary particles can be produced. If it exceeds 950°C, the firing may be excessive, preventing the proper formation of a layered crystal structure and potentially degrading the electrochemical properties.

[0129] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the aggregation of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and an aggregate of 30 or fewer primary particles, known as an analogous-single particle form.

[0130] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in an analogous-single particle form, and a secondary particle may be in a form in which several hundred primary particles are aggregated.

[0131] In one embodiment of this application, the lithium composite transition metal, which is the positive electrode active material, further contains secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0132] In the present invention, a single particle may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in an analogous-single particle form, and a secondary particle may be in a form in which several hundred primary particles are aggregated.

[0133] The lithium composite transition metals described above may further contain secondary particles. Secondary particles refer to forms formed by the aggregation of primary particles and can be distinguished from the concept of a single particle, which includes a single primary particle, a single particle, or an analogous-single-particle form that is an aggregate of 30 or fewer primary particles.

[0134] The particle size (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles is 0.05 m². 2 / g~10m 2 It may be / g, preferably 0.1m 2 / g~1m 2 It may be / g, and more preferably 0.3m 2 / g~0.8m 2 / g is also acceptable.

[0135] In additional embodiments of this application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0136] When the average particle size (D50) of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of aggregated primary particles forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially degrading the output characteristics.

[0137] According to an additional embodiment of this application, the average particle size (D50) of the single particle is smaller than the average particle size (D50) of the secondary particle. As a result, even if the single particle is formed with a small particle size, it may have excellent particle strength, thereby mitigating the phenomenon of increased fine particles in the electrode due to particle cracking, and improving the battery life characteristics.

[0138] In one embodiment of this application, the average particle size (D50) of the single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particle.

[0139] For example, the average particle size (D50) of the single particle may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particle.

[0140] When the average particle size (D50) of a single particle is smaller than the average particle size (D50) of secondary particles, for example, when the above range is satisfied, even if the single particle is formed with a small particle size, its particle strength is excellent, thereby mitigating the phenomenon of increased fine particles in the electrode due to particle cracking, resulting in improved battery life characteristics and improved energy density.

[0141] According to additional embodiments of this application, the single particle is included in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material. The single particle may also be included in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight per 100 parts by weight of the positive electrode active material.

[0142] For example, the single particle may be present in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the positive electrode active material. The single particle may be present in an amount of 100 parts by weight or less, per 100 parts by weight of the positive electrode active material.

[0143] When a single particle within the aforementioned range is included, it can be combined with the aforementioned negative electrode material to exhibit excellent battery characteristics. In particular, when the single particle is 15 parts by weight or more, the phenomenon of increasing fine particles within the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery's lifespan characteristics.

[0144] In one embodiment of this application, the lithium composite transition metal compound may further contain secondary particles, the amount of which may be 85 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 0 parts by weight or more per 100 parts by weight of the positive electrode active material.

[0145] When the above range is satisfied, the aforementioned effect due to the presence of single-particle positive electrode active material can be maximized. When secondary-particle positive electrode active material is included, its components may be the same as those exemplified in the single-particle positive electrode active material described above, or they may be different, and may represent a form in which single-particle forms are aggregated.

[0146] In one embodiment of this application, the positive electrode active material in 100 parts by weight of the positive electrode active material layer may be 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0147] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0148] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it has electronic conductivity in the battery without causing chemical changes. 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, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0149] Furthermore, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0150] The separation membrane, which separates the negative and positive electrodes and provides a pathway for lithium ions to move, can be used without particular limitations as long as it is one that is normally used as a separation membrane in secondary batteries. Particularly preferred is one that has low resistance to electrolyte ion movement while having excellent electrolyte moisture retention capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and they may be selectively used in single-layer or multi-layer structures.

[0151] In this application, the electrolyte can be, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0152] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0153] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0154] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, electrolytes with high electrical conductivity can be produced, making them even more suitable for use.

[0155] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble 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 - You may use one or more selected from the group consisting of the following:

[0156] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0157] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0158] [Examples] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept, and such variations and modifications naturally fall within the scope of the claims. [Manufacturing example]

[0159] (1) Manufacturing of the negative electrode Manufacturing of the negative electrode active material layer As silicon-based active materials, a negative electrode active material layer composition was prepared using Si (average particle size (D50): 5 μm) as a first conductive material and a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10. A negative electrode slurry was produced by adding these materials to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 28% by weight).

[0160] The first conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material is carbon nanotubes, with a particle size of 3.5 μm (average particle size D50) per g.

[0161] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed in a homo mixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for another 30 minutes to produce a slurry.

[0162] As the negative electrode current collector, a copper current collector (thickness: 15 μm) is coated with the negative electrode slurry at a rate of 3.00 mg / cm³ on both sides. 2 The material was coated with the specified load and rolled (roll press), then dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 23 μm).

[0163] (2) Manufacturing of the positive electrode LiNi 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as the conductive material, and polyvinylidene fluoride as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent for forming the positive electrode slurry at a weight ratio of 97:1.5:1.5 to produce a positive electrode slurry (solid content concentration 78 wt%).

[0164] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as the positive electrode current collector at a loading of 537 mg / 25 cm 2 and rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to produce a positive electrode (positive electrode thickness: 77 μm, porosity 26%).

[0165] An electrolyte was injected with a polyethylene separator interposed between the positive electrode and the negative electrode to produce a lithium secondary battery shown in Table 1 below.

[0166]

Table 1

[0167] The method for manufacturing the pre-lithiated applicable electrode in Table 1 above was as follows.

[0168] <Transfer method pre-lithiation> Lithium metal was vapor-deposited on the upper part of the PET substrate by PVD method at the thickness (pre-lithiation dosage) of the level shown in Table 1 on the upper part of the PET (PET with a release layer coating on one side, ionefilm, thickness 20 μm to 50 μm) layer with the release layer coated to produce a transfer laminate, and the lithium metal layer was transferred onto the electrode shown in Table 1 to perform pre-lithiation.

[0169] Experimental Example 1: Life performance evaluation The lithium secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries were subjected to cycle tests at 4.2-3.2V and 1C / 0.5C, and the number of cycles required to achieve an 80% capacity retention rate was measured and is shown in Table 2 below.

[0170] Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0171] Experimental Example 2: Measurement and Evaluation of Resistance Increase Rate In the test described in Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0172] For the measurement and evaluation of the resistance increase rate mentioned above, data was calculated for each 600 cycles, and the results are shown in Table 2 below.

[0173] [Table 2]

[0174] As can be seen in Tables 1 and 2 above, the lithium secondary battery according to the embodiment was found to be primarily characterized by limiting the usable range of the total discharge capacity, specifically by controlling the upper and lower limits of the discharge capacity, when a silicon-based negative electrode is used by pre-lithifying a specific amount in the positive or negative electrode.

[0175] This allows us to produce batteries that achieve the advantages of using silicon-based negative electrodes, namely high capacity and high energy density, while also resolving the conventional problems of deterioration in lifespan due to volume expansion during repeated cycles and increased resistance.

[0176] In other words, the lithium secondary battery described in this application is primarily characterized by ensuring the lifespan performance of the lithium secondary battery by limiting the area of ​​silicon used in the negative electrode.

[0177] In Comparative Example 1, when pre-lithiation was not applied to the positive or negative electrode, the NP ratio range was also formed to be low, and it was confirmed that the degradation of lithium life performance due to charging and discharging became serious when the entire upper and lower end was used to its full depth, and that the rate of increase in resistance was high.

[0178] In Comparative Examples 2 and 3, pre-lithiation was performed, but to such an extent that the upper and lower capacity limits of the present invention were not satisfied. Specifically, in Comparative Example 3, the upper limit range of the negative electrode capacity exceeded the range specified in this application, and in Comparative Example 4, the lower limit range of the negative electrode capacity was less than the range specified in this application. In these cases, although the performance was not as degraded as in Comparative Example 1, it was confirmed that the life performance due to negative electrode volume expansion was reduced compared to Examples 1 to 3. [Explanation of symbols]

[0179] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 ···Positive electrode current collector layer 100...Negative electrode 200...Positive electrode

Claims

1. A lithium secondary battery comprising a silicon-based negative electrode; a positive electrode; a separator membrane; and an electrolyte, The positive electrode is a pre-lithified electrode. The usable range of the silicon discharge capacity of the aforementioned silicon-based negative electrode is 35% or less of the total negative electrode discharge capacity. The silicon discharge capacity of the silicon-based negative electrode is 57% or less at the upper limit and 13% or more at the lower limit. A lithium secondary battery in which the difference between the upper and lower limits of the silicon discharge capacity is less than 35%.

2. The lithium secondary battery according to claim 1, wherein the NP ratio of the lithium secondary battery is 170% or more and 280% or less.

3. The upper limit of the silicon discharge capacity of the silicon-based negative electrode is 45% or more and 57% or less. The lithium secondary battery according to claim 1, wherein the lower end of the silicon discharge capacity of the silicon-based negative electrode is 13% or more and 28% or less.

4. The silicon-based negative electrode includes a negative electrode current collector layer and a negative electrode active material layer comprising a negative electrode active material layer composition provided on one or both sides of the negative electrode current collector layer. The positive electrode includes a positive electrode current collector layer and a positive electrode active material layer comprising a positive electrode active material layer composition provided on one or both sides of the positive electrode current collector layer. The negative electrode active material layer composition comprises a silicon-based active material, a negative electrode conductive material, and a negative electrode binder. The lithium secondary battery according to any one of claims 1 to 3, wherein the silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0), SiOx (0 < x < 2), and metal impurities, and contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

5. The lithium secondary battery according to claim 4, wherein the silicon-based active material is present in an amount of 60 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition.

6. The positive electrode active material layer composition comprises a positive electrode active material, The positive electrode active material is LiNi ｙ , ４ Co ｙ Mn ｚ O ２ (x + y + z = 1); LiNi ａ Co ｂ Mn ｃ Al ｄ O ２ (a + b + c + d = 1); LiMnO ２ O ４ ; LiNi ０．５ Mn １．５ O ２ ; and LiM ｘ Fe ｙ PO ４ (M: Transition metal, x + y = 1), the lithium secondary battery according to claim 4, comprising one or more selected from the group consisting of.

7. The thickness of the positive electrode and negative electrode current collector layers is 1 μm or more and 100 μm or less. The lithium secondary battery according to claim 4, wherein the thickness of the positive electrode and negative electrode active material layers is 20 μm or more and 500 μm or less.

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