Lithium-ion rechargeable battery

Abstract

The present invention relates to a lithium secondary battery comprising: a negative electrode containing a negative electrode active material; a positive electrode containing a positive electrode active material; a separator interposed between the negative electrode and the positive electrode; and an electrolyte, wherein the negative electrode active material contains silicon particles, and the Si depth of charge represented by the following formula (1) is 30% to 60%, and the Si depth of discharge represented by the following formula (2) is 10% or more. Formula (1): Si charge depth (%) = {(positive electrode loading amount + negative electrode pre-lithiation capacity) / negative electrode loading amount} × 100 Equation (2): Si discharge depth (%) = {(positive electrode loading amount + negative electrode pre-lithiation capacity - discharge loading amount) / negative electrode loading amount} × 100 In the above formulas (1) and (2), the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm 2 ), and the negative electrode loading is the capacity per unit area of ​​the negative electrode (unit: mAh / cm 2 ), and the prelithiation capacity of the negative electrode is the capacity per unit area of ​​lithium (Li) inserted into the negative electrode by prelithiation (unit: mAh / cm 2 The discharge loading amount is a value obtained by dividing the discharge capacity of the secondary battery at the discharge cut-off voltage by the positive electrode area.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0131946 filed on October 5, 2021, and Korean Patent Application No. 10-2022-0127248 filed on October 5, 2022, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery applying silicon (Si) particles as an anode active material.

Background Art

[0003] Recently, lithium secondary batteries have been in the spotlight as an energy source for electric vehicles.

[0004] As the popularity of electric vehicles expands, the need for lithium secondary batteries that can travel a longer distance per charge and shorten the rapid charging time is increasing.

[0005] A lithium secondary battery is generally manufactured by forming an electrode assembly with a separator interposed between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte serving as a medium for transmitting lithium ions, and then sealing it. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Conventionally, carbon-based materials such as natural graphite and artificial graphite have been mainly used as the negative electrode active material of lithium secondary batteries. However, such carbon-based negative electrode active materials have a small capacity and a slow reaction rate with lithium, so there is a limit to achieving high capacity and rapid charging performance in secondary batteries applying them.

[0006] Therefore, attempts are being made to develop lithium secondary batteries using silicon-based negative electrode active materials, which have a theoretical capacity more than 10 times greater than carbon-based materials. Silicon-based negative electrode active materials have advantages over carbon-based materials, such as a higher theoretical capacity, a faster reaction rate with lithium, and the ability to improve capacity characteristics and rapid charging performance. However, during the charging process, their volume expands rapidly, which can cause damage to the negative electrode and disruption of the conductive path, resulting in a problem of rapid deterioration of battery performance.

[0007] Therefore, there is a need to develop lithium-ion secondary batteries that utilize silicon-based negative electrode active materials and possess excellent lifespan characteristics. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to solve the above-mentioned problems and to provide a lithium secondary battery that achieves high capacity characteristics and excellent lifespan characteristics by applying silicon (Si) particles as the negative electrode active material. [Means for solving the problem]

[0009] In one aspect, the present invention provides a lithium secondary battery comprising a negative electrode containing a negative electrode active material, a positive electrode containing a positive electrode active material, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode active material contains silicon particles, the Si charge depth represented by the following formula (1) is 30% to 60%, and the Si discharge depth represented by the following formula (2) is 10% or more. Equation (1): Si charging depth (%) = {(positive electrode loading amount + negative electrode pre-lithium capacity) / negative electrode loading amount} × 100 In equation (1) above, the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm²). 2 ), the negative electrode loading amount is the capacity per unit area of ​​the negative electrode (unit: mAh / cm²). 2 The pre-lithium capacity of the negative electrode is the capacity per unit area of ​​lithium (Li) inserted into the negative electrode by pre-lithiumization (unit: mAh / cm²).2 ) Equation (2): Si discharge depth (%) = {(positive electrode loading amount + negative electrode pre-lithiumization capacity - discharge loading amount) / negative electrode loading amount} × 100 In equation (2) above, the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm²). 2 ), the negative electrode loading amount is the capacity per unit area of ​​the negative electrode (unit: mAh / cm²). 2 The pre-lithium capacity of the negative electrode is the capacity per unit area of ​​lithium (Li) inserted into the negative electrode by pre-lithiumization (unit: mAh / cm²). 2 The discharge loading amount is the value obtained by dividing the discharge capacity of the secondary battery by the positive electrode area at the discharge cut-off voltage. [Effects of the Invention]

[0010] The lithium secondary battery according to the present invention exhibits excellent lifetime characteristics despite using Si particles as the negative electrode active material, by designing the Si charge depth and Si discharge depth to satisfy specific ranges. On the other hand, Si particles are used as carbon-based negative electrode active materials and / or SiO x Because it exhibits superior reactivity with lithium and capacity characteristics compared to conventional negative electrode active materials, the lithium secondary battery of the present invention, to which this material is applied, can achieve excellent capacity characteristics and rapid charging performance. In other words, the lithium secondary battery of the present invention is superior in capacity characteristics, life characteristics, and rapid charging performance.

[0011] Furthermore, the lithium secondary battery according to the present invention can use, for example, a lithium nickel-based oxide with a Ni content of 60 mol% or more as the positive electrode active material, and in particular, the capacity characteristics can be further improved when the Ni content is 80 mol% or more. [Modes for carrying out the invention]

[0012] In the present specification and claims, terms and words used should not be construed in a limited sense of their ordinary or dictionary meanings. In accordance with the principle that inventors can appropriately define the concepts of terms in order to explain their inventions in the best way, they should be construed in meanings and concepts consistent with the technical idea of the present invention.

[0013] In the present invention, "primary particle" means a particle unit in which no grain boundaries are present in appearance when observed at a magnification of 5000 to 20000 times using a scanning electron microscope. "Average particle size of primary particles" means the arithmetic mean value calculated after measuring the particle sizes of primary particles observed from a scanning electron microscope image.

[0014] In the present invention, "secondary particle" is a particle formed by aggregation of a plurality of primary particles.

[0015] In the present invention, "average particle size D 50 " means the particle diameter at the 50% criterion of the volume cumulative particle size distribution of the particle powder to be measured (for example, positive electrode active material powder, negative electrode active material powder, etc.). The average particle size D 50 can be measured using the laser diffraction method. For example, after dispersing the powder of the particles to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and after obtaining a volume cumulative particle size distribution graph, it can be measured by obtaining the particle diameter corresponding to 50% of the volume cumulative amount.

[0016] Hereinafter, the present invention will be specifically described.

[0017] Si is not only a carbon-based negative electrode active material such as graphite, but also SiO xCompared to silicon-based negative electrode active materials such as SiC, Si exhibits superior capacity characteristics and lithium reactivity. Therefore, when Si is used as a negative electrode active material, improved energy density and rapid charging performance can be obtained. However, Si undergoes significant volume changes during charging and discharging, and the negative electrode deteriorates rapidly during charging and discharging. As a result, it has been difficult to achieve satisfactory life characteristics when Si is used as a negative electrode active material. The inventors of this invention have diligently conducted research to improve the life characteristics of lithium secondary batteries using Si as a negative electrode active material. They have found that by designing the battery so that the Si charging depth and Si discharging depth meet specific ranges, it is possible to use Si as a negative electrode active material while achieving excellent life characteristics, thus completing the present invention.

[0018] Specifically, the lithium secondary battery according to the present invention is a lithium secondary battery comprising a negative electrode containing a negative electrode active material, a positive electrode containing a positive electrode active material, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode active material contains silicon (Si), the Si charge depth represented by the following formula (1) is 30% to 60%, and the Si discharge depth represented by the following formula (2) is 10% or more. Preferably, the negative electrode active material does not contain any other type of negative electrode active material and consists only of silicon.

[0019] Equation (1): Si charging depth (%) = {(positive electrode loading amount + negative electrode pre-lithium capacity) / negative electrode loading amount} × 100

[0020] In equation (1) above, the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm²). 2 ), the negative electrode loading amount is the capacity per unit area of ​​the negative electrode (unit: mAh / cm²). 2 The pre-lithium capacity of the negative electrode is the capacity per unit area of ​​lithium (Li) inserted into the negative electrode by pre-lithiumization (unit: mAh / cm²). 2 )

[0021] Equation (2): Si discharge depth (%) = {(positive electrode loading amount + negative electrode pre-lithiumization capacity - discharge loading amount) / negative electrode loading amount} × 100

[0022] In equation (2) above, the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm²). 2 ), the negative electrode loading amount is the capacity per unit area of ​​the negative electrode (unit: mAh / cm²). 2 The pre-lithium capacity of the negative electrode is the capacity per unit area of ​​lithium (Li) inserted into the negative electrode by pre-lithiumization (unit: mAh / cm²). 2 The discharge loading amount is the value obtained by dividing the discharge capacity of the secondary battery by the positive electrode area at the discharge cut-off voltage.

[0023] The Si charging depth is a value that indicates the degree of bonding between Si and Li in a fully charged state (i.e., SOC=100). According to the inventors' research, it has been shown that if the Si charging depth exceeds 60% or is less than 30%, the lifetime characteristics deteriorate rapidly. Specifically, if the Si charging depth exceeds 60%, a rapid volume expansion of Si occurs, resulting in a decrease in energy density and lifetime characteristics. If the Si charging depth is less than 30%, severe reaction heterogeneity occurs, leading to a decrease in lifetime characteristics. Preferably, the Si charging depth can be 40% to 60%, and more preferably 50% to 60%.

[0024] The Si charging depth can be adjusted by controlling the positive electrode loading amount, the negative electrode loading amount, and / or the degree of pre-lithiation of the negative electrode, and the positive electrode loading amount and / or negative electrode loading amount can be set taking into consideration the type and content of the active material used, the porosity of the active material layer, and / or the thickness of the active material layer.

[0025] On the other hand, the Si discharge depth indicates the capacity of lithium remaining on the negative electrode at the discharge cut-off voltage. Our research has shown that even if the Si charge depth is 30% to 60%, if the Si discharge depth is less than 10%, the life characteristics deteriorate rapidly. Preferably, the Si discharge depth can be 10% to 30%, more preferably 10% to 25%, even more preferably 15% to 25%, and even more preferably 17% to 25%.

[0026] The Si discharge depth is influenced by a combination of factors, including the ratio of the negative electrode capacity to the positive electrode capacity (N / P ratio), the battery's operating voltage range, and the degree of pre-lithification of the negative electrode. By appropriately controlling these factors, the Si discharge depth can be adjusted.

[0027] On the other hand, the lithium secondary battery of the present invention can be designed so that the Si usage range is 10% to 50%, preferably 20% to 40%, and more preferably 30% to 40%. The Si usage range represents the difference between the Si charging depth and the Si discharging depth, as shown in formula (3) below. If the Si usage range is large, the energy density increases, but the lifespan characteristics deteriorate significantly, and if the Si usage range is too small, the energy density decreases.

[0028] Equation (3): Si usage range (%) = Si charging depth - Si discharge depth

[0029] On the other hand, the lithium secondary battery according to the present invention can have an N / P ratio, which is the percentage of the negative electrode loading amount to the positive electrode loading amount, of 150% to 300%, preferably 180% to 300%, and more preferably 190% to 300%. If the N / P ratio, which is the percentage of the negative electrode loading amount to the positive electrode loading amount, is less than the above range, the Si charging depth may increase, leading to a decrease in lifespan. If it exceeds the above range, the non-uniformity of the Si reaction on the electrode surface becomes severe, which may actually lead to a decrease in lifespan.

[0030] The lithium secondary battery according to the present invention, designed to satisfy the above-mentioned conditions, uses Si particles to achieve excellent energy density and rapid charging performance, and also exhibits excellent lifespan characteristics. Specifically, the lithium secondary battery according to the present invention has an energy density of 500 Wh / L or more, preferably 550 Wh / L or more, more preferably 600 Wh / L or more, and even more preferably 650 Wh / L or more, and the number of times it reaches 80% life can be 450 or more, preferably 480 or more, more preferably 500 or more, even more preferably 600 or more, and even more preferably 700 or more.

[0031] For example, the lithium secondary battery according to the present invention may have a cell energy density of 500 Wh / L or more and reach 80% lifespan 450 times or more, or a cell energy density of 550 Wh / L or more and reach 80% lifespan 480 times or more, or a cell energy density of 650 Wh / L or more and reach 80% lifespan 480 times or more, or a cell energy density of 550 Wh / L to 600 Wh / L and reach 80% lifespan 700 times or more.

[0032] Next, we will specifically describe each component of the lithium secondary battery according to the present invention.

[0033] negative electrode The negative electrode according to the present invention may contain silicon (Si) as the negative electrode active material, and preferably, 100% silicon (Si) can be used as the negative electrode active material. The silicon used in the present invention may be pure silicon (Pure Si) that does not bond with other metals or oxygen. Specifically, the negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, and the negative electrode active material layer may contain silicon (Si) as the negative electrode active material. Si can be not only carbon-based negative electrode active materials such as graphite, but also SiO2 xFurthermore, it possesses superior capacity characteristics and lithium reactivity compared to silicon-based anode active materials such as SiC. Therefore, when Si is used as the anode active material, improved energy density and rapid charging performance can be obtained.

[0034] The average particle size of the aforementioned silicon (D 50 The average particle size can be between 1 μm and 10 μm, specifically between 2 μm and 8 μm, and more specifically between 3 μm and 7 μm. If the average particle size is less than 1 μm, the specific surface area of ​​the particles increases excessively, causing the viscosity of the negative electrode slurry to rise excessively. As a result, the particles constituting the negative electrode slurry are not dispersed smoothly. Also, if the size of the silicon particles is too small, the contact area between the silicon particles and the conductive material decreases due to the composite of the conductive material and 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 is greater than 10 μm, there will be silicon particles that are too large, making the surface of the negative electrode less smooth, and thus causing non-uniform 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. Consequently, the capacity retention rate of the battery decreases.

[0035] On the other hand, the BET specific surface area of ​​the silicon 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. The BET surface area can be measured using nitrogen in accordance with DIN 66131.

[0036] Also, the silicon can be present in crystalline or amorphous form and is preferably not porous. The silicon particles can be spherical or flaky particles, but are not limited thereto, and can also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0037] Always, the silicon can be contained in an amount of 50% by weight or more, 60% by weight or more, preferably 65% by weight or more, more preferably 70% by weight or more, and can be contained in an amount of 99% by weight or less, preferably 95% by weight or less, more preferably 90% by weight or less, still more preferably 80% by weight or less, based on the total weight of the negative electrode active material layer.

[0038] On the other hand, the negative electrode according to the present invention can further contain other negative electrode active materials other than the silicon, if necessary. The other negative electrode active materials can be, for example, SiO x (where 0 < x < 2), carbon-based negative electrode active materials, etc. Here, the carbon-based negative electrode active materials can be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., but are not limited thereto.

[0039] The other negative electrode active materials can be contained in an amount of 50% by weight or less, preferably 45% by weight or less, more preferably 30% by weight or less, based on the total weight of the negative electrode active material layer.

[0040] On the other hand, the negative electrode active material layer can further contain a conductive material and a binder, if necessary.

[0041] Examples of the conductive material include spherical or flaky graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-wall carbon nanotubes, and multi-wall carbon nanotubes; 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 can be used. The conductive material can be included in an amount of 0.1% to 40% by weight, 1% to 30% by weight, or 5% to 30% by weight relative to the total weight of the negative electrode active material layer.

[0042] Preferably, the negative electrode active material layer according to the present invention may contain two or more conductive materials, in which case the conductive materials may include point-shaped conductive materials and plate-shaped conductive materials.

[0043] The point-like conductive material can be used to improve the conductivity of the negative electrode, and is preferably conductive without causing chemical changes. Specifically, the conductive material can 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 fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black in terms of achieving high conductivity and excellent dispersibility.

[0044] The aforementioned point-shaped conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It can be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It can be less than or equal to / g.

[0045] The aforementioned point-shaped conductive material can satisfy the functional group content (volatile matter) of 0.01% to 0.05%, preferably 0.01% to 0.04%, and more preferably 0.01% to 0.03%.

[0046] The functional group content can be adjusted according to the degree of heat treatment of the point-shaped conductive material. That is, in the production of a point-shaped conductive material, a high functional group content means that there are many foreign substances, and a low functional group content means that more heat treatment processing has been performed. The point-shaped conductive material according to this application is characterized in that a predetermined partial heat treatment is applied to the point-shaped conductive material to satisfy the functional group content within the range described above.

[0047] The particle size of the point-like conductive material can be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm. The plate-like conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode and suppress the disruption of the conductive path due to volume expansion, and can be expressed as a planar conductive material or a bulk conductive material.

[0048] The plate-shaped conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and is preferably plate-shaped graphite.

[0049] The average particle size (D) of the plate-shaped conductive material 50 The particle size can be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is met, the sufficient particle size prevents excessive viscosity increase of the negative electrode slurry and facilitates dispersion. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is superior.

[0050] The aforementioned plate-shaped conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It can be less than or equal to / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 300m 2 It can be less than or equal to / g.

[0051] Next, examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more can be used. The binder may be present in an amount of 1% to 20% by weight, 2% to 20% by weight, or 2% to 10% by weight relative to the total weight of the negative electrode active material layer.

[0052] On the other hand, the negative electrode can have a multilayer structure in which the negative electrode active material layer is composed of a single layer or two or more layers. In the case of a multilayer structure in which the negative electrode active material layer is composed of two or more layers, each layer may have different types and / or contents of negative electrode active material, binder, and / or conductive material.

[0053] For example, the negative electrode according to the present invention can have a two-layer structure, and the type of negative electrode active material in the layer adjacent to the current collector (hereinafter referred to as the lower layer) and the upper layer formed on the lower layer can be different from each other. Specifically, in a two-layer negative electrode, the negative electrode active material of the lower layer is silicon, and the negative electrode active material of the upper layer is SiO x (Here, 0 <x<2)であることができる。

[0054] On the other hand, the negative electrode active material layer can have a porosity of 20% to 70% or 20% to 50%. If the porosity of the negative electrode active material layer is too small, the electrolyte impregnation may decrease and lithium mobility may decrease, and if the porosity is too large, the energy density may decrease.

[0055] On the other hand, in the present invention, the negative electrode may be a pre-lithified negative electrode in which lithium has been inserted before charging and discharging. Pre-lithification of the negative electrode can be carried out by a method of pre-lithification of a negative electrode that is well known in the art. For example, the pre-lithification of the negative electrode can be carried out by a method of pressing or depositing lithium metal onto the negative electrode active material layer, a method of inserting lithium into the negative electrode active material layer by an electrochemical method, a method of inserting excess lithium contained in the sacrificial cathode material or cathode active material contained in the positive electrode into the negative electrode by an activation step, or a method of imparting excess lithium to the positive electrode by an electrochemical method or a method of pressing or depositing lithium metal, and then inserting the excess lithium imparted to the positive electrode into the negative electrode by an activation step, and two or more of the above methods can be combined to carry out the procedure.

[0056] As described above, when using a pre-lithium-treated negative electrode, the degradation of life characteristics is less even when discharged to a relatively lower cut-off voltage compared to a non-pre-lithium-treated negative electrode. Therefore, the range of drive voltage for the lithium secondary battery can be set to a relatively wider range, and the usable state of charge (SOC) can be increased.

[0057] Preferably, the negative electrode of the present invention may have a pre-lithification degree represented by the following formula (4) of 5% to 50%, preferably 5% to 30%, and more preferably 10% to 20%.

[0058] Formula (4): Pre-lithification degree (%) = {Capacity of Li per unit area inserted into the negative electrode by pre-lithification / Capacity of Si per unit area} × 100

[0059] When the degree of pre-lithiation of the negative electrode satisfies the aforementioned range, a lithium secondary battery with excellent capacity and lifespan characteristics can be realized. Specifically, if the degree of pre-lithiation of the negative electrode is too low, the lifespan characteristics may deteriorate. While the lifespan characteristics can be improved by controlling the depth of discharge, in this case, it is difficult to ensure cell energy density. Also, if the degree of pre-lithiation of the negative electrode is too high, the degradation of silicon particles in the electrode accelerates, which may reduce capacity characteristics.

[0060] positive electrode The positive electrode according to the present invention includes a positive electrode active material layer. Specifically, the positive electrode according to the present invention may include a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector.

[0061] The positive electrode active material layer comprises a positive electrode active material and may further comprise a conductive material and / or a binder, if necessary.

[0062] As the positive electrode active material, various positive electrode active materials known in the art, lithium nickel oxides, lithium manganese oxides, lithium cobalt oxides, etc., can be used. Preferably, the positive electrode active material of the present invention may contain a lithium nickel oxide in which the molar ratio of nickel to the total metals other than lithium is 60 mol% or more, preferably 80 mol% or more, more preferably 83 mol% or more, and even more preferably 85 mol% or more. Since lithium nickel oxides containing 60 mol% or more Ni have high capacity, when a lithium nickel oxide containing 60 mol% or more Ni is used as the positive electrode active material and Si is used as the negative electrode active material, a lithium secondary battery with significantly better capacity characteristics than conventional batteries can be manufactured.

[0063] The lithium nickel oxide can be represented, for example, by the following chemical formula 1.

[0064] [Chemical formula 1] Li 1+x1 [Ni a1 Co b1 Mn c1 M 1 d1 ]O2

[0065] In the above chemical formula 1, the above M 1 This can be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0066] On the other hand, 1+x1 represents the molar ratio of lithium in the lithium nickel oxide, and can be -0.2≦x1≦0.2 or 0≦x1≦0.1.

[0067] The a1 in the lithium nickel oxide represents the molar ratio of nickel to the total metals other than lithium, and can be 0.6≦a1<1, 0.8≦a1<1, 0.8≦a1≦0.98, 0.82≦a1≦0.98, 0.83≦a1≦0.98, 0.85≦a1≦0.98, 0.88≦a1≦0.98, or 0.90≦a1≦0.98.

[0068] The above b1 represents the molar ratio of cobalt to the total metals other than lithium in lithium nickel oxide, and 0 <b1<0.4、0<b1<0.2、0<b1<0.18、0.01≦b1<0.18、0.01≦b1<0.17、0.01≦b1<0.15、0.01≦b1<0.12、または0.01≦b1<0.10であることができる。

[0069] The aforementioned c1 represents the molar ratio of manganese to the total metals other than lithium in lithium nickel oxide, and 0 <c1<0.4、0<c1<0.2、0<c1<0.18、0.01≦c1<0.18、0.01≦c1<0.17、0.01≦c1<0.15、0.01≦c1<0.12、または0.01≦c1<0.10であることができる。

[0070] The aforementioned d1 is M of the total metals other than lithium in lithium nickel oxides. 1 This represents the molar ratio, and can be 0≦d1<0.2, 0≦d1<0.18, 0≦d1<0.17, 0≦d1<0.15, 0≦d1<0.12, or 0≦d1<0.10.

[0071] On the other hand, the positive electrode active material may, if necessary, further include a coating layer on the surface of the lithium nickel oxide.

[0072] The aforementioned coating layer contains coating element M 2 It may include the coating element M 2For example, the coating layer can be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. The coating layer can be formed by various coating methods well known in the art, such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).

[0073] The form of the positive electrode active material is not particularly limited and can be, for example, a secondary particle form in which tens to hundreds of primary particles are aggregated, a single particle form composed of 10 or fewer primary particles, or a combination thereof. When the positive electrode active material is in a secondary particle form, the average particle size of the primary particles can be 0.05 μm to 4 μm, specifically, the average particle size of the primary particles can be 0.05 μm or more, 0.1 μm or more, and the average particle size of the primary particles can be 4 μm or less, 3 μm or less, or 2 μm or less. If the average particle size of the primary particles is too large, a rock salt phase may be formed, which may reduce the resistance characteristics and lifetime characteristics, and if the average particle size of the primary particles is too small, the contact area with the electrolyte may increase, which may cause rapid degradation. Furthermore, the average particle size of the secondary particles can be 2 μm to 25 μm, specifically, it can be 2 μm or more, 3 μm or more, or 4 μm or more, and it can be 25 μm or less, 20 μm or less, or 18 μm or less. When the average particle size of the secondary particles satisfies the above range, it is possible to prevent the positive electrode active material particles from being destroyed during the rolling process or the processability from deteriorating during slurry production. On the other hand, when the positive electrode active material is in the form of single particles, the average particle size D of the single particles 50 The average particle size D of the single particle can be 2 μm to 10 μm. Specifically, the average particle size D of the single particle 50 The average particle size D of a single particle can be 2 μm or larger, 3 μm or larger, 4 μm or larger, 5 μm or larger, or 6 μm or larger, and can be 10 μm or smaller, 9 μm or smaller, 8 μm or smaller, or 7 μm or smaller. 50If the particle size is too large, the lithium transfer path becomes longer, increasing resistance and potentially degrading the output characteristics. If it is too small, the specific surface area increases, potentially increasing side reactions with the electrolyte. Furthermore, the average particle size of the primary particles constituting the single particle can be 0.5 μm to 4 μm, specifically, it can be 0.5 μm or more, 0.7 μm or more, 1 μm or more, or 1.5 μm or more, and 4 μm or less, 3.5 μm or less, or 3 μm or less. If the average particle size of the primary particles constituting the single particle is too large, the lithium transfer path becomes longer, increasing resistance and potentially degrading the output characteristics. If it is too small, the specific surface area increases, potentially increasing side reactions with the electrolyte.

[0074] On the other hand, examples of the conductive material include spherical or flaky graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-wall carbon nanotubes, and multi-wall carbon nanotubes; 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. Of these, one or more can be used. The conductive material can be included in an amount of 0.1% to 20% by weight, 1% to 20% by weight, or 1% to 10% by weight relative to the total weight of the positive electrode active material layer.

[0075] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these can be used alone or a mixture of two or more. The binder may be present in an amount of 1% to 20% by weight, 2% to 20% by weight, or 2% to 10% by weight relative to the total weight of the positive electrode active material layer.

[0076] Separator In the lithium secondary battery of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator commonly used in lithium secondary batteries, but it is especially preferable to use one that has low resistance to ion movement of the electrolyte and excellent moisture-absorbing capacity for the electrolyte. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can 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 separators containing ceramic components or polymeric substances may be used, and they can be selectively used as single-layer or multi-layer structures.

[0077] electrolyte Furthermore, the electrolytes used in the present invention 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.

[0078] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0079] The organic solvent can be used without particular limitations as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a hydrocarbon group with 2 to 20 carbon atoms in a linear, branched, or cyclic structure, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used.

[0080] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - The lithium salt can be selected from the group consisting of LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used in the range of 0.1M to 5.0M.

[0081] Furthermore, the electrolyte may contain additives for the purpose of improving the battery's lifespan characteristics, suppressing capacity reduction, and suppressing gas generation. These additives may include various additives used in the art, such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (ESa), lithium difluorophosphate (LiPO2F2), lithium bisoxalate borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium difluorobisoxalate phosphate (LiDFBP), lithium tetrafluorooxalate phosphate (LiTFOP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propane sultone (PS), propensultone (PRS), succinonitrile (SN), and adiponyl nitrile. Tolyl (AND), 1,3,6-hexanetricarbonitrate (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyldi(pro-2-i-1-yl)phosphate (EDP), 5-methyl-5-propargyloxylcarbonyl-1,3-dioxan-2-one (MPOD), compounds represented by the following chemical formula A (e.g., cyanoethyl polyvinyl alcohol, PVA-CN), compounds represented by the following chemical formula B (e.g., heptafluorobutylcyanoethyl polyvinyl alcohol, PF-PVA-CN), compounds represented by the following chemical formula C (e.g., propargyl 1H-imidazole-1-carboxylate, PAC), and / or compounds represented by the following chemical formula D (e.g., arylimidazoles such as C6H8N2), etc., can be used.

[0082] [ka]

[0083] In the chemical formula A, m and n are each an integer between 1 and 100, independently of each other.

[0084] [ka]

[0085] [ka]

[0086] In the above chemical formula C, R 16 R is a linear or nonlinear alkylene group having 1 to 3 carbon atoms, 17 ~R 19 Each of these is independently at least one selected from the group consisting of hydrogen, an alkyl group having 1 to 3 carbon atoms, and -CN, and D is CH or N.

[0087] [ka]

[0088] In the aforementioned chemical formula D, R1, R2, R3, and R4 can each independently contain hydrogen; or a C1-C5 alkyl group, a cyano group (CN), an allyl group, a propargyl group, an amine group, a phosphate group, an ether group, a benzene group, a cyclohexyl group, a silyl group, an isocyanate group (-NCO), or a fluoro group (-F).

[0089] Preferably, the additive can be a compound that acts as an oxygen scavenger. Phosphite-type substances such as tristri(methylsilyl) phosphite (TMSPi), tristrimethylphosphite (TMPi), and tris(2,2,2-trifluoroethyl) phosphite (TTFP) (see chemical formula E); tristri(methylsilyl) phosphate (TMSPa); trimethylsilyl polyphosphate (PPSE); tris(pentafluorophenyl)borane (TPFPB); coumarin-3-carbonitride (CMCN), 7-ethynylcoumarin (ECM), 3-A Compounds containing a coumarin structure, such as cetylcoumarin (AcCM), 3-[(trimethylsilyl)oxyl]-2H-1-benzopyran-2-one (TMSOCM), and 3-(trimethylsilyl)coumarin (TMSCM) (see chemical formula F); and compounds such as 3-(2-propyne-1-nyloxyl)-2H-1-benzopyran-2-one (POCM) and 2-propyne-1-nyl-2-iodo-2H-1-benzopyran-3-carboxylate (OBCM) can be used as oxygen absorbers.

[0090] [ka]

[0091] [ka]

[0092] In the chemical formulas E and F, R1 to R6 can each independently include a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a cyano group (-CN), a fluoro group (F), an ether group (COC), a carboxyl group (OC=O), a trimethylsilyl group (-TMS), an isocyanate group (-NCO), and / or an isothiocyanate group (-NCS).

[0093] The present invention will be described in more detail below with reference to specific examples.

[0094] Manufacturing Example 1 <Manufacturing of positive electrodes> A positive electrode slurry was prepared by mixing positive electrode active material, conductive material, and PVDF binder in N-methylpyrrolidone in a weight ratio of 97.7:0.9:1.4. Here, LiNi was used as the positive electrode active material. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 was used, and carbon nanotubes (CNTs) were used as the conductive material.

[0095] The positive electrode slurry is applied to an aluminum current collector sheet, dried, and then rolled to produce a load of 4.52 mAh / cm². 2 We manufactured the positive electrode.

[0096] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by mixing a negative electrode active material, conductive material, and acrylic binder in water in a weight ratio of 70:20.3:9.7. Here, the negative electrode active material used was Si particles (manufactured by Elkem) with an average particle size of 5 μm, and the conductive material was a mixture of carbon black, graphite, and CNTs in a weight ratio of 9.8:10:0.52.

[0097] The negative electrode slurry is applied to a copper current collector sheet, dried, and then rolled to produce a load of 8.73 mAh / cm². 2 We manufactured the negative electrode.

[0098] <Manufacturing of lithium-ion secondary batteries> An electrode assembly was manufactured by interposing a separator between the positive electrode and negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolyte solution was injected to manufacture a lithium secondary battery A.

[0099] Manufacturing Example 2 <Manufacturing of positive electrodes> A positive electrode slurry was prepared by mixing positive electrode active material, conductive material, and PVDF binder in N-methylpyrrolidone in a weight ratio of 96.25:1.5:2.25. Here, LiNi was used as the positive electrode active material. 0.83 Co 0.11 Mn 0.06 O2 was used, and Denka Black was used as the conductive material.

[0100] The positive electrode slurry is applied to an aluminum current collector sheet, dried, and then rolled to produce a load of 3.50 mAh / cm². 2 We manufactured the positive electrode.

[0101] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by mixing a negative electrode active material, conductive material, and acrylic binder in water in a weight ratio of 70:20.3:9.7. Here, Si particles with an average particle size of 5 μm (manufactured by Walker) were used as the negative electrode active material, and carbon black, graphite, and CNTs were mixed in a weight ratio of 9.8:10:0.52 as the conductive material.

[0102] The negative electrode slurry is applied to a copper current collector sheet, dried, and then rolled to produce a load of 7.36 mAh / cm². 2 We manufactured the negative electrode.

[0103] <Manufacturing of lithium-ion secondary batteries> An electrode assembly was manufactured by interposing a separator between the positive electrode and negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolyte solution was injected to manufacture a lithium secondary battery B.

[0104] Manufacturing Example 3 Lithium secondary battery C was manufactured using the same method as in Manufacturing Example 2, except that the loading amounts of the positive and negative electrodes were changed as shown in [Table 1] below.

[0105] Manufacturing Examples 4-6 Lithium secondary batteries D to F were manufactured using the same method as in Manufacturing Example 1, except that the loading amounts of the positive and negative electrodes were changed as shown in [Table 1] below.

[0106] Production Example 7 A lithium secondary battery G was manufactured in the same manner as in Production Example 2, except that the loading amounts of the positive and negative electrodes were changed as described in [Table 1] below.

[0107] Production Example 8 <Production of Positive Electrode> A positive electrode slurry was produced by mixing a positive electrode active material, a conductive material, and a PVDF binder in a weight ratio of 97.7:0.9:1.4 in N-methylpyrrolidone. Here, LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 was used, and CNT was used as the conductive material.

[0108] The positive electrode slurry was applied onto an aluminum current collector sheet, dried, and then rolled to produce a positive electrode with a loading amount of 3.03 mAh / cm 2 .

[0109] <Production of Negative Electrode> A negative electrode slurry was produced by mixing a negative electrode active material, a conductive material, and an acrylic binder in a weight ratio of 70:20.3:9.7 in water. Here, Si particles (manufactured by Elkem) with an average particle size of 5 μm were used as the negative electrode active material, and carbon black, graphite, and CNT were mixed and used as the conductive material in a weight ratio of 9.8:10:0.52.

[0110] The negative electrode slurry was applied onto a copper current collector sheet, dried, and then rolled to produce a negative electrode with a loading amount of 7.75 mAh / cm 2 .

[0111] Lithium metal was pressure-bonded onto the negative electrode for prelithiation, and at this time, the degree of prelithiation was 7.38%.

[0112] <Production of Lithium Secondary Battery> An electrode assembly was manufactured by interposing a separator between the positive electrode and the pre-lithiumized negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolyte solution was injected to manufacture a lithium secondary battery H.

[0113] Manufacturing Examples 9-11 Lithium secondary batteries I to K were manufactured using the same method as in Manufacturing Example 8, except that the loading amount of the positive electrode was changed as shown in [Table 1] below.

[0114] Manufacturing Example 12 Lithium secondary battery L was manufactured using the same method as in manufacturing example 8, except that the pre-lithiation of the negative electrode was performed so that the degree of pre-lithiation (%) was 16.5%.

[0115] The N / P ratio and Si charging depth of lithium secondary batteries A to L manufactured as described above are shown in Table 1 below.

[0116] [Table 1]

[0117] Examples and Comparative Examples The number of cycles required to reach 80% capacity retention (number of cycles to reach 80% lifespan) and the cell energy density were measured while charging and discharging lithium secondary batteries A to L. Here, the charging and discharging was performed at 25°C, 1C / 0.5C, CCCV mode, with a charge cutoff voltage of 4.2V and a discharge cutoff voltage set so that the Si discharge depth was the value shown in [Table 2] below. The measurement results are shown in [Table 2] below. The usable SOC for each lithium secondary battery within the charge / discharge voltage range is also shown in Table 2.

[0118] [Table 2]

[0119] As shown in Table 1 above, in the case of lithium secondary batteries of Examples 1 to 9, where the Si charging depth is 30% to 60% and the Si discharge depth is 10% to 20%, the number of cycles to reach 80% life is high at 480 or more, despite using Si as the negative electrode active material. Furthermore, the cell energy density is good at 500 Wh / L or more. In contrast, in the case of Comparative Examples 1 to 12, where either the Si charging depth or Si discharge depth deviates from the scope of the present invention, although the capacity characteristics are excellent, it can be confirmed that the number of cycles to reach 80% life is significantly reduced.

Claims

1. A lithium secondary battery comprising a negative electrode containing a negative electrode active material, a positive electrode containing a positive electrode active material, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, The negative electrode active material contains silicon particles, A lithium secondary battery in which the Si charge depth, represented by the following formula (1), is 30% to 60%, and the Si discharge depth, represented by the following formula (2), is 10% or more. Formula (1): Si charging depth (%) = {(positive electrode loading amount + negative electrode pre-lithium capacity) / negative electrode loading amount} × 100 In formula (1) above, the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm²). ２ ), the negative electrode loading amount is the capacity per unit area of ​​the negative electrode (unit: mAh / cm²). ２ The pre-lithiumization capacity of the negative electrode is the capacity per unit area (unit: mAh / cm²) of lithium (Li) inserted into the negative electrode by pre-lithiumization. ２ ) and Formula (2): Si discharge depth (%) = {(Positive electrode loading amount + Negative electrode pre-lithiumization capacity - Discharge loading amount) / Negative electrode loading amount} × 100 In formula (2) above, the positive electrode loading amount is the capacity per unit area of ​​the positive electrode (unit: mAh / cm²). ２ ), the negative electrode loading amount is the capacity per unit area of ​​the negative electrode (unit: mAh / cm²). ２ The pre-lithiumization capacity of the negative electrode is the capacity per unit area (unit: mAh / cm²) of lithium (Li) inserted into the negative electrode by pre-lithiumization. ２ The discharge loading amount is the value obtained by dividing the discharge capacity of the secondary battery at the discharge cutoff voltage by the positive electrode area, and is measured with charging / discharging performed at 25°C, 1C / 0.5C, CCCV mode, and the charge cutoff voltage set to 4.2V.

2. The lithium secondary battery according to claim 1, wherein the negative electrode active material consists of silicon particles.

3. The lithium secondary battery according to claim 1, wherein the Si charging depth is 40% to 60%.

4. The lithium secondary battery according to claim 1, wherein the Si discharge depth is 10% to 30%.

5. The lithium secondary battery according to claim 1, wherein the Si usage range represented by the following formula (3) is 10% to 50%. Equation (3): Si usage range (%) = Si charging depth - Si discharge depth

6. The lithium secondary battery according to claim 1, wherein the N / P ratio, which is the percentage of the negative electrode loading amount to the positive electrode loading amount, is 150% to 300%.

7. The lithium secondary battery according to claim 1, wherein the N / P ratio, which is the percentage of the negative electrode loading amount to the positive electrode loading amount, is 180% to 300%.

8. The lithium secondary battery according to any one of claims 1 to 7, wherein the negative electrode is a pre-lithiumized negative electrode, and the degree of pre-lithiumization represented by the following formula (4) is 5% to 50%. Formula (4): Pre-lithification degree (%) = {Capacity of Li per unit area inserted into the negative electrode by pre-lithification / Capacity of Si per unit area} × 100

9. The lithium secondary battery according to claim 8, wherein the degree of pre-lithiumization is 5% to 30%.

10. The lithium secondary battery according to claim 1, wherein the positive electrode active material includes a lithium nickel-based oxide in which the nickel content among the total metals other than lithium is 60 mol% or more.

11. The lithium nickel oxide is represented by the following chemical formula 1, as described in claim 10, for the lithium secondary battery. [Chemical formula 1] Li １＋ｘ１ [Ni ａ１ Co ｂ１ Mn ｃ１ M １ ｄ１ ]O ２ In the above chemical formula 1, -0.2 ≤ x1 ≤ 0.2, 0.6 ≤ a1 < 1, 0 < b1 < 0.4, 0 < c1 < 0.4, 0 ≤ d1 < 0.2, M １ is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

12. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a cell energy density of 500 Wh / L or more and has reached 80% life 450 times or more.

13. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a cell energy density of 650 Wh / L or more and has reached 80% life 480 times or more.

14. The lithium secondary battery according to claim 1, wherein the cell energy density is 550 Wh / L to 600 Wh / L and the number of times it reaches 80% life is 700 or more.

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