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; the positive electrode active material contains a perlithium manganese oxide represented by [Chemical Formula 1]; and the battery has a Si depth of charge represented by the following formula (1) of 30% to 60% and a Si depth of discharge represented by the following formula (2) of 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 priority rights under Korean Patent Application No. 10-2021-0131946 dated October 5, 2021, and Korean Patent Application No. 10-2022-0127249 dated October 5, 2022, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery in which silicon (Si) particles are used as the negative electrode active material. [Background technology]

[0003] Recently, lithium-ion batteries have been gaining attention as an energy source for electric vehicles. As the adoption of electric vehicles expands, there is a growing need for lithium-ion batteries that offer longer driving ranges on a single charge and shorter fast-charging times.

[0004] Lithium-ion batteries are generally manufactured by forming an electrode assembly with a separator in between a positive electrode containing a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode containing a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transferring lithium ions, and then sealing it. The non-aqueous electrolyte generally consists 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 negative electrode active materials for lithium-ion batteries. However, because these carbon-based negative electrode active materials have low capacity and a slow reaction rate with lithium, there are limitations in achieving high capacity and rapid charging performance in secondary batteries using them.

[0005] 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.

[0006] 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]

[0007] 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]

[0008] 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 positive electrode active material contains a perlithium manganese oxide represented by the following [Chemical Formula 1], 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. [Chemical formula 1] Li a Ni b Co c Mn d M e O2 In Chemical Formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 ≤ d < 1.0, 0 ≤ e ≤ 0.2, and M 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. Formula (1): Si Depth of Charge (%) = {(Positive Electrode Loading Amount + Pre-lithiation Capacity of Negative Electrode) / Negative Electrode Loading Amount} × 100 In the above Formula (1), the positive electrode loading amount is the capacity per unit area of the positive electrode (unit: mAh / cm 2 ), the negative electrode loading amount is the capacity per unit area of the negative electrode (unit: mAh / cm 2 ), and the pre-lithiation capacity of the negative electrode is the capacity per unit area of lithium (Li) inserted into the negative electrode by pre-lithiation (unit: mAh / cm 2 ). Formula (2): Si Depth of Discharge (%) = {(Positive Electrode Loading Amount + Pre-lithiation Capacity of Negative Electrode - Discharge Loading Amount) / Negative Electrode Loading Amount} × 100 In the above Formula (2), the positive electrode loading amount is the capacity per unit area of the positive electrode (unit: mAh / cm 2 ), the negative electrode loading amount is the capacity per unit area of the negative electrode (unit: mAh / cm 2 ), the pre-lithiation capacity of the negative electrode is the capacity per unit area of lithium (Li) inserted into the negative electrode by pre-lithiation (unit: mAh / cm 2 ), and the discharge loading amount is the value obtained by dividing the discharge capacity of the secondary battery at the discharge cut-off voltage by the positive electrode area.

Advantages of the Invention

[0009] The lithium secondary battery according to the present invention exhibits excellent lifespan characteristics despite using Si particles as the negative electrode active material, because the Si charging depth and Si discharging depth are designed to meet specific ranges. On the other hand, since Si particles have superior reactivity with lithium and capacity characteristics compared to carbon-based negative electrode active materials and / or SiOx-based negative electrode active materials, the lithium secondary battery according to the present invention, which incorporates these, can achieve excellent capacity characteristics and rapid charging performance. In other words, the lithium secondary battery according to the present invention is superior in capacity characteristics, lifespan characteristics, and rapid charging performance.

[0010] Furthermore, as in the present invention, when using a perlithium manganese oxide in which a rock salt-type structure Li2MnO3 phase and a layered structure LiMO2 phase (where M is Ni, Co, or Mn) are mixed as the positive electrode active material, the Si negative electrode can be pre-lithified with excess lithium generated from the LiMO2 phase by performing the activation process at a high voltage of 4.6V or higher, without using a sacrificial positive electrode material for negative electrode compensation or another process for pre-lithification. [Modes for carrying out the invention]

[0011] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0012] In this invention, "primary particle" refers to a particle unit that, when observed using a scanning electron microscope at a field of view of 5,000x to 20,000x, does not appear to have a grain boundary. "Average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle size of primary particles observed from scanning electron microscope images.

[0013] In this invention, "secondary particles" are particles formed by the aggregation of multiple primary particles.

[0014] In this invention, "average particle size D 50 " refers to the particle size at the 50% reference level of the volume cumulative particle size distribution of the measured particle powder (e.g., positive electrode active material powder, negative electrode active material powder, etc.). The average particle size D 50 This can be measured using the laser diffraction method. For example, the powder of the particles to be measured is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and after irradiating it with ultrasound at approximately 28 kHz with an output of 60 W, a volume cumulative particle size distribution graph is obtained, and the particle size corresponding to 50% of the volume cumulative amount is determined.

[0015] The present invention will be described in detail below.

[0016] Si exhibits superior capacity characteristics and lithium reactivity compared not only to carbon-based negative electrode active materials such as graphite, but also to silicon-based negative electrode active materials such as SiOx and SiC. Therefore, when Si is used as a negative electrode active material, improved energy density and rapid charging performance can be obtained. However, because Si undergoes significant volume changes during charging and discharging, and the negative electrode deteriorates rapidly during charging and discharging, 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, and 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.

[0017] Specifically, the lithium secondary battery according to the present invention is a lithium secondary battery including 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 positive electrode active material contains a lithium-rich manganese-based oxide represented by the following [Chemical Formula 1], 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 other types of negative electrode active materials and can consist only of silicon. [Chemical Formula 1] Li a Ni b Co c Mn d M e O2 In the above Chemical Formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 ≤ d < 1.0, 0 ≤ e ≤ 0.2, and M 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. Formula (1): Si charge depth (%) = {(positive electrode loading amount + prelithiation capacity of the negative electrode) / negative electrode loading amount} × 100 In the above formula (1), the positive electrode loading amount is the capacity per unit area of the positive electrode (unit: mAh / cm 2 ), the negative electrode loading amount 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 ). Here, the positive electrode loading amount means the capacity value per unit area of the positive electrode measured when the secondary battery is charged and discharged in a voltage range of 2.25 V to 4.45 V. Formula (2): Si discharge depth (%) = {(positive electrode loading amount + prelithiation capacity of the negative electrode - discharge loading amount) / negative electrode loading amount} × 100 In the above formula (2), the positive electrode loading amount is the capacity per unit area of the positive electrode (unit: mAh / cm 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 cutoff voltage.

[0018] 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 45% to 60%.

[0019] 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.

[0020] 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 30-60%, if the Si discharge depth is less than 10%, the life characteristics deteriorate rapidly. Preferably, the Si discharge depth can be 10-30%, more preferably 10-25%, even more preferably 15-25%, and even more preferably 17-25%.

[0021] 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 (charge / discharge cut-off voltage), and the degree of pre-lithification of the negative electrode. By appropriately controlling these factors, the Si discharge depth can be adjusted.

[0022] 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.

[0023] Equation (3): Si usage range (%) = Si charging depth - Si discharge depth

[0024] 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 significant, which may actually lead to a decrease in lifespan.

[0025] 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 can reach 80% lifespan 400 times or more, preferably 450 times or more, and more preferably 500 times or more.

[0026] Next, we will specifically describe each component of the lithium secondary battery according to the present invention.

[0027] [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 has superior capacity characteristics and lithium reactivity compared not only to carbon-based negative electrode active materials such as graphite, but also to silicon-based negative electrode active materials such as SiOx and SiC. Therefore, when Si is applied as the negative electrode active material, improved energy density and rapid charging performance can be obtained.

[0028] 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 5 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 uneven, 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.

[0029] 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 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area can be measured in accordance with DIN 66131 using nitrogen.

[0030] 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.

[0031] 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, and even more preferably 80% by weight or less, based on the total weight of the negative electrode active material layer.

[0032] On the other hand, the negative electrode according to the present invention can further contain other negative electrode active materials other than the silicon as necessary. The other negative electrode active materials can be SiOx (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.

[0033] 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.

[0034] On the other hand, the negative electrode active material layer can further contain a conductive material and a binder as necessary.

[0035] 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.

[0036] 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.

[0037] The point-like conductive material can be used to improve conductivity in 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.

[0038] 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.

[0039] 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%.

[0040] 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.

[0041] 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.

[0042] The aforementioned plate-shaped 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 described as a planar conductive material or a bulk conductive material.

[0043] 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.

[0044] 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 excellent.

[0045] 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 It can be less than or equal to / g.

[0046] 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.

[0047] 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.

[0048] 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 SiOx (where 0 <x<2)であることができる。

[0049] 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.

[0050] On the other hand, in the present invention, the negative electrode can be a pre-lithium-treated negative electrode.

[0051] For example, the pre-lithiumization of the negative electrode can be carried out by methods such as pressing or depositing lithium metal onto the negative electrode active material layer, inserting lithium into the negative electrode active material layer by an electrochemical method, 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 imparting excess lithium to the positive electrode by an electrochemical method or by pressing or depositing lithium metal, and then inserting the excess lithium imparted to the positive electrode into the negative electrode by an activation step. Two or more of the above methods can be combined to carry out the procedure.

[0052] More specifically, in the present invention, the pre-lithiumized negative electrode can be formed by performing an activation process at a high voltage of 4.6V or higher after assembling the cell, thereby activating the Li2MnO3 phase of the positive electrode active material and inserting the resulting lithium into the negative electrode. When the negative electrode is pre-lithiumized using this method, it is not necessary to perform another pre-lithiumization process, the use of sacrificial positive electrode material can be minimized, and the capacity of the positive electrode can be increased.

[0053] 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 the driving voltage of the lithium secondary battery can be set to a relatively wider range, and the usable state of charge (SOC) can be increased.

[0054] 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%.

[0055] 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

[0056] 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, it becomes necessary to adjust the depth of discharge to ensure lifespan characteristics, and in this case, it may be difficult to ensure sufficient energy density. On the other hand, 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.

[0057] [Positive electrode] The positive electrode according to the present invention includes a perlithium manganese oxide represented by chemical formula 1 as the positive electrode active material. Specifically, the positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer may include a positive electrode active material comprising a perlithium manganese oxide represented by the following chemical formula 1.

[0058] [Chemical formula 1] Li a Ni b Co c Mn d M e O2

[0059] In the above Chemical Formula 1, M 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.

[0060] On the other hand, a is the molar ratio of Li in the over-lithiated manganese-based oxide, and it can be 1 < a, 1.1 ≤ a ≤ 1.5, or 1.1 ≤ a ≤ 1.3. When a satisfies the above range, the irreversible capacity of the Si negative electrode active material can be sufficiently compensated, and high-capacity characteristics can be realized.

[0061] The above b is the molar ratio of Ni in the over-lithiated manganese-based oxide, and it can be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0062] The above c is the molar ratio of Co in the over-lithiated manganese-based oxide, and it can be 0 ≤ c ≤ 0.1, 0 ≤ c ≤ 0.08, or 0 ≤ c ≤ 0.05. When c exceeds 0.1, it is difficult to ensure high capacity, and the generation of gas and the deterioration of the positive electrode active material become severe due to the increase in the oxygen-redox reaction, and the life characteristics may decline.

[0063] The above d is the molar ratio of Mn in the over-lithiated manganese-based oxide, and it can be 0.5 ≤ d < 1.0, 0.50 ≤ d ≤ 0.80, or 0.50 ≤ d ≤ 0.70. When d is less than 0.5, the ratio of the rock salt phase becomes excessively small, and the effects of negative electrode irreversible compensation and capacity improvement are not significant.

[0064] The above e is the molar ratio of the doping element M in the over-lithiated manganese-based oxide, and it can be 0 ≤ e ≤ 0.2, 0 ≤ e ≤ 0.1, or 0 ≤ e ≤ 0.05. If the content of the doping element is too much, it may have an adverse effect on the active material capacity.

[0065] In the case of perlithium manganese oxides containing an excess of lithium, the structure consists of a mixed layer phase (LiM'O2) and a rock salt phase (Li2MnO3), and the rock salt phase is activated at a high voltage of 4.6V or higher, generating an excess of ions. Therefore, as in the present invention, by using a perlithium manganese oxide as the positive electrode active material, the excess lithium ions generated by the activation process at a high voltage of 4.6V or higher are inserted into the negative electrode, without the need for other compensating materials or a pre-lithification process, thereby obtaining a pre-lithification effect that compensates for the irreversible capacity of the negative electrode.

[0066] On the other hand, in the perlithium manganese oxide represented by [Chemical Formula 1], the ratio of moles of Li to the total number of moles of metal elements other than Li (Li / Me) can be 1.2 to 1.5, 1.25 to 1.5, or 1.25 to 1.4. When the Li / Me ratio satisfies the above range, the rate characteristics and capacity characteristics are excellent. If the Li / Me ratio is too high, the electrical conductivity decreases and the rock salt phase (Li2MnO3) increases, which can lead to a faster degradation rate. If it is too low, there is little effect in improving the energy density.

[0067] On the other hand, the composition of the perlithium manganese oxide can also be represented by the following [Chemical Formula 2].

[0068] [Chemical formula 2] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0069] In the above [Chemical Formula 2], M can be at least one selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0070] The aforementioned X represents the ratio of the Li2MnO3 phase within the perlithium manganese oxide, and can be 0.2 ≤ X ≤ 0.5, 0.25 ≤ X ≤ 0.5, or 0.25 ≤ X ≤ 0.4. When the ratio of the Li2MnO3 phase within the perlithium manganese oxide satisfies the above range, the irreversible capacity of the SiOx negative electrode active material can be sufficiently compensated, and high capacity characteristics can be achieved.

[0071] The aforementioned y is the molar ratio of Mn in the LiM'O2 layer phase, and can be 0.4 ≤ y < 1, 0.4 ≤ y ≤ 0.8, or 0.4 ≤ y ≤ 0.7.

[0072] The aforementioned z is the molar ratio of Co in the LiM'O2 layer phase, and can be 0 ≤ z ≤ 0.1, 0 ≤ z ≤ 0.08, or 0 ≤ z ≤ 0.05. If z exceeds 0.1, gas generation and degradation of the positive electrode active material may become severe, potentially reducing the lifetime characteristics.

[0073] The aforementioned w is the molar ratio of the doping element M in the LiM'O2 layer phase, and can be 0 ≤ w ≤ 0.2, 0 ≤ w ≤ 0.1, or 0 ≤ w ≤ 0.05.

[0074] On the other hand, the positive electrode active material according to the present invention may further include a coating layer on the surface of the perlithium manganese oxide, if necessary. When the positive electrode active material includes a coating layer, the coating layer suppresses contact between the perlithium manganese oxide and the electrolyte, reducing electrolyte side reactions, thereby improving the lifespan characteristics.

[0075] The aforementioned coating layer contains coating element M 1 It may include the coating element M 1For example, the coating element M 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, preferably at least one selected from the group consisting of Al, Co, Nb, W, and combinations thereof, and more preferably at least one selected from the group consisting of Al, Co, and combinations thereof. 1 It can contain two or more types, for example, Al and Co.

[0076] The aforementioned coating element exists in oxide form within the coating layer, i.e., M 1 It can exist as Oz(1≦z≦4).

[0077] The coating layer can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, atomic layer deposition is preferred because it allows for the formation of a large coating layer area.

[0078] The area of ​​the coating layer can be 10% to 100%, preferably 30% to 100%, and more preferably 50% to 100%, of the total surface area of ​​the perlithium manganese oxide particles. When the area of ​​the coating layer satisfies the above range, the effect of improving lifespan characteristics is excellent.

[0079] On the other hand, the positive electrode active material according to the present invention can be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle size D of the secondary particles 50 However, it can be 2 μm to 10 μm, preferably 2 μm to 8 μm, and more preferably 4 μm to 8 μm. D of the positive electrode active material 50 When the above range is satisfied, excellent electrode density can be achieved, and the degradation of capacity and rate characteristics can be minimized.

[0080] Furthermore, the positive electrode active material has a BET specific surface area of ​​1 m².2 / g~10m 2 / g, 3-8m 2 / g or 4-6m 2 It can be / g. If the specific surface area of ​​the positive electrode active material BET is too low, there is insufficient reaction area with the electrolyte, making it difficult to achieve sufficient capacity. If the specific surface area is too high, moisture absorption is rapid, accelerating side reactions with the electrolyte, making it difficult to ensure lifespan characteristics.

[0081] Furthermore, the positive electrode according to the present invention preferably has an initial irreversible capacity of approximately 5% to 70%, 5% to 50%, or 5% to 30%. The initial irreversible capacity of the positive electrode is the ratio of the high-voltage charging capacity when the half-cell is activated at a high voltage of 4.6V or higher after manufacturing the half-cell with the positive electrode and the lithium metal counter electrode, to the discharge capacity when the half-cell is charged and discharged in a voltage range of 2.5V to 4.4V, and is a value measured on a 0.1C basis.

[0082] When the initial irreversible capacitance of the positive electrode satisfies the aforementioned range, the irreversible capacitance of the Si negative electrode active material can be sufficiently compensated without using another compensating material such as a sacrificial positive electrode material.

[0083] On the other hand, the perlithium manganese oxide can be produced by mixing a transition metal precursor with a lithium raw material and then calcining it.

[0084] Examples of the lithium raw material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), and chlorides (e.g., lithium chloride (LiCl)). One of these can be used alone or a mixture of two or more.

[0085] On the other hand, the transition metal precursor can be in the form of a hydroxide, oxide, or carbonate. Using a carbonate precursor is more preferable because it allows for the production of a positive electrode active material with a relatively high specific surface area.

[0086] The transition metal precursor can be produced by a coprecipitation process. For example, the transition metal precursor can be produced by dissolving each transition metal-containing raw material in a solvent to produce a metal solution, then mixing the metal solution, an ammonium cation complex-forming agent, and a basic compound, and then carrying out a coprecipitation reaction. If necessary, an oxidizing agent or oxygen gas can be further added during the coprecipitation reaction.

[0087] Here, the transition metal-containing raw material can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material can be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, etc.

[0088] The ammonium cation complex-forming agent can be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0089] The basic compound can be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor can change depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. Furthermore, when a basic compound and an oxidizing agent are used together, an oxide-form precursor can be obtained.

[0090] On the other hand, the transition metal precursor and the lithium raw material can be mixed in such an amount that the overall molar ratio of the transition metal (Ni+Co+Mn):Li is 1:1.05 to 1:2, preferably 1:1.1 to 1:1.8, and more preferably 1:1.25 to 1:1.8.

[0091] On the other hand, the firing can be carried out at a temperature of 600°C to 1000°C or 700°C to 950°C, and the firing time can be 5 to 30 hours or 5 to 20 hours. The firing atmosphere can be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20% ​​to 100% by volume of oxygen.

[0092] On the other hand, the positive electrode active material layer may further include a conductive material and a binder in addition to the positive electrode active material.

[0093] 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.

[0094] 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 negative electrode active material layer.

[0095] On the other hand, the positive electrode according to the present invention can have an electrode density of approximately 2.5 g / cc to 3.8 g / cc, 2.5 g / cc to 3.5 g / cc, or 3.0 g / cc to 3.3 g / cc. When the electrode density of the positive electrode satisfies the above range, a high energy density can be achieved. [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.

[0096] [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.

[0097] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0098] 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.

[0099] 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 at least one selected from the group consisting of the following, and examples of lithium salts that can be used include 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. The concentration of the lithium salt is preferably in the range of 0.1 to 5.0 M.

[0100] 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.

[0101] [ka]

[0102] In the chemical formula A, m and n are each an integer between 1 and 100, independently of each other.

[0103] [ka]

[0104] [ka]

[0105] 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.

[0106] [ka]

[0107] 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).

[0108] 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-ethylenylcoumarin Compounds containing a coumarin structure, such as tylcoumarin (AcCM) and 3-[(trimethylsilyl)coumarin (TMSCM) (see chemical formula F); 3-[(trimethylsilyl)oxyl]-2H-1-benzopyran-2-one (TMSOCM), 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.

[0109] [ka]

[0110] [ka]

[0111] In the chemical formulas E and F, R1 to R6 can each independently include a substituted or unsubstituted C2-C20 alkenyl group and a substituted or unsubstituted C2-C20 alkynyl group, cyano group, fluoro group (F), ether group (COC), carboxyl group (OC=O), trimethylsilyl group (-TMS), isocyanate group (-NCO), and / or isothiocyanate group (-NCS).

[0112] Hereinafter, the present invention will be described more specifically by way of specific examples.

[0113] Production Example 1 <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 96:1:3 in N-methylpyrrolidone. Here, as the positive electrode active material, Li coated with 1500 ppm of Al 1.143 [Ni 0.35 Mn 0.65 0.857 O2 was used, and carbon nanotubes were used as the conductive material.

[0114] 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 3.50 mAh / cm 2 as described above.

[0115] <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, as the negative electrode active material, Si particles (manufactured by Waker) with an average particle size of 5 μm were used, and as the conductive material, carbon black, graphite, and CNT were mixed and used in a weight ratio of 9.8:10:0.52.

[0116] 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 7.36 mAh / cm 2 as described above.

[0117] <Production of Lithium Secondary Battery> An electrode assembly was produced with a separator interposed between the positive electrode and the negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolytic solution was injected to produce a lithium secondary battery A.

[0118] Production Examples 2 and 3 Lithium secondary batteries B and C were produced in the same manner as in Production Example 1, except that the loading amounts of the positive electrode and the negative electrode were changed as described in the following [Table 1].​

[0119] Production Example 4 <Manufacture of Positive Electrode> A positive electrode slurry was produced by mixing a positive electrode active material, a conductive material, and a PVDF binder at a weight ratio of 96:1:3 in N-methylpyrrolidone. Here, as the positive electrode active material, Li coated with 1500 ppm of Al 1.143 [Ni 0.35 Mn 0.65 0.857 O2 was used, and carbon nanotubes were used as the conductive material.

[0120] 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 as described above.

[0121] <Manufacture of Negative Electrode> A negative electrode slurry was produced by mixing a negative electrode active material, a conductive material, and an acrylic binder at a weight ratio of 70:20.3:9.7 in water. Here, as the negative electrode active material, Si particles (manufactured by Elkem) with an average particle diameter of 5 μm were used, and as the conductive material, carbon black, graphite, and CNT were mixed and used at a weight ratio of 9.8:10:0.52.

[0122] 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 11.90 mAh / cm 2 as described above.

[0123] <Manufacture of Lithium Secondary Battery> An electrode assembly was produced with a separator interposed between the positive electrode and the negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, an electrolyte was injected to produce a lithium secondary battery D.

[0124] Production Examples 5 to 7 Lithium secondary batteries E to G were produced in the same manner as in Production Example 4, except that the loading amounts of the positive electrode and the negative electrode were changed as described in the following [Table 1].

[0125] ​ Manufacturing Example 8 <Manufacturing of positive electrodes> A positive electrode slurry was prepared by mixing positive electrode active material, conductive material, and PVDF binder in a weight ratio of 96:1:3 in N-methylpyrrolidone. Here, the positive electrode active material was Li coated with 1500 ppm of Al. 1.143 [Ni 0.35 Mn 0.65 ] 0.857 O2 was used, and carbon nanotubes were used as the conductive material.

[0126] The positive electrode slurry is applied to an aluminum current collector sheet, dried, and then rolled to produce a load of 3.03 mAh / cm². 2 We manufactured the positive electrode.

[0127] <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.

[0128] The negative electrode slurry is applied to a copper current collector sheet, dried, and then rolled to produce a load of 7.75 mAh / cm². 2 We manufactured the negative electrode.

[0129] <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.

[0130] Subsequently, the lithium secondary battery was charged to 4.65V to activate the Li2MnO3 phase of the positive electrode active material, and the negative electrode was pre-lithified to produce lithium secondary battery H, where the degree of pre-lithification of the negative electrode was at a level of 5.4%.

[0131] Manufacturing examples 9-11 Lithium secondary batteries I to K were manufactured in the same manner as in Manufacturing Example 8, except that the loading amount of the positive electrode was changed as shown in Table 1 below. Here, the degree of negative electrode prelithiation of lithium secondary batteries I to K is as shown in Table 1 below.

[0132] The N / P ratio, Si charging depth, and pre-lithiumization degree of lithium secondary batteries A to K manufactured as described above are shown in Table 1 below.

[0133] [Table 1]

[0134] 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 K. Here, the charging and discharging were performed at 25°C, 1C / 0.5C, in CCCV mode. The charge cutoff voltage was set to 4.4V, and the discharge cutoff voltage was set so that the Si discharge depth had the values ​​shown in [Table 2] below. The measurement results are shown in [Table 2] below. Furthermore, the usable SOC for each lithium secondary battery within its charge / discharge voltage range is shown in Table 2.

[0135] [Table 2]

[0136] As shown in Table 1 above, in the case of lithium secondary batteries of Examples 1 to 8, where the Si charging depth is 30% to 60% or less and the Si discharge depth is 10% to 20%, the number of times 80% life is reached is high, at 450 or more, despite using Si as the negative electrode active material. 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 excellent cell energy density is observed, it can be confirmed that the number of times 80% life is reached 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, The positive electrode active material includes a perlithium manganese oxide represented by the following [Chemical Formula 1], 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. [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M ｅ O ２ In the above chemical formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.1, 0.5 ≤ d < 1.0, and 0 ≤ e ≤ 0.2, and M 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. Formula (1): Si charging depth (%) = {(positive electrode loading amount + negative electrode pre-lithium capacity) / negative electrode loading amount} × 100 In the formula (1), the positive electrode loading amount is the capacity per unit area of the positive electrode (unit: mAh / cm ２ ), the negative electrode loading amount 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 ), and Equation (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 the discharge capacity of the secondary battery at the discharge cutoff voltage is the value measured by performing charge / discharge under the conditions of 25°C, 1C / 0.5C, CCCV mode, and a charge cutoff voltage of 4.4V.

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 perlithium manganese oxide is represented by the following [Chemical Formula 2]. [Chemical formula 2] XLi ２ MnO ３ ・(1-^)L[Ni １－ｙ－ｚ－ｗ Mn ｙ Co ｚ M ｗ ]O ２ In the above [Chemical Formula 2], M is at least one element selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and satisfies 0.2 ≤ X ≤ 0.5, 0.4 ≤ y < 1, 0 ≤ z ≤ 0.1, and 0 ≤ w ≤ 0.

2.

11. The positive electrode active material is D ５０ The lithium secondary battery according to claim 1, wherein the diameter is 2 μm to 10 μm.

12. The positive electrode active material has a BET specific surface area of ​​1 m². ２ / g to 10m ２ A lithium secondary battery according to claim 1, wherein the value is / g.

13. The lithium secondary battery according to claim 1, wherein the positive electrode has an initial irreversible capacity of 5% to 70%.

14. The lithium secondary battery according to claim 1, wherein the positive electrode has an electrode density of 2.5 g / cc to 3.8 g / cc.

15. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a lifespan of 400 or more cycles of reaching 80% of its lifespan.

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