Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. The negative electrode includes SiOx (where 0 < x < 2) and a carbon-based negative electrode active material. The positive electrode includes a positive electrode active material containing a lithium-rich manganese-based oxide in which the content of manganese exceeds 50 mol% among all metals other than lithium and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium exceeds 1. In a state of SOC 0%, the depth of use of SiOx defined by the following formula (1) is 1 to 15, preferably 3 to 15. Formula (1): Depth of use of SiOx = (Capacity of Li remaining in the negative electrode / Capacity of SiOx in the negative electrode) × 100

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0131947 filed on October 5, 2021 and Korean Patent Application No. 10-2022-0127247 filed on October 5, 2022, and all contents disclosed in the documents of said 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 that uses a layered perlithium manganese oxide as a positive electrode active material and a mixture of silicon oxide and a carbon-based negative electrode active material as a negative electrode active material. [Background technology]

[0003] Recently, lithium secondary batteries have been attracting attention as an energy source for electric vehicles. As the use of electric vehicles becomes more widespread, there is an increasing need for lithium secondary batteries that can travel longer distances on a single charge and can be quickly charged. This has led to a demand for the development of lithium secondary batteries that have high energy density and can be quickly charged.

[0004] Lithium secondary batteries are generally fabricated by forming an electrode assembly by interposing a separator between a positive electrode including a lithium-containing transition metal oxide positive electrode active material 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, which serves as a medium for transferring lithium ions, and sealing the battery case. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt.

[0005] 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, since such carbon-based negative electrode active materials have a small capacity, there is a limit to achieving high capacity in secondary batteries applying this material. Therefore, the development of lithium secondary batteries applying silicon-based negative electrode active materials, which have a theoretical capacity more than 10 times larger than that of carbon-based materials, has been attempted. In the case of silicon-based negative electrode active materials, there is an advantage that a higher capacity can be achieved compared to carbon-based materials. However, in the charging process, the volume rapidly expands, and damage to the negative electrode and disconnection of the conduction path may occur. Therefore, there is a problem that the battery performance rapidly deteriorates.

[0006] Therefore, the development of lithium secondary batteries applying silicon-based negative electrode active materials and having excellent life characteristics is required.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention is for solving the above problems, and by including SiOx and over-lithiated manganese-based oxide having excellent capacity characteristics as active materials, it aims to provide a lithium secondary battery having a high energy density and excellent life characteristics.

Means for Solving the Problems

[0008] In one aspect, the present invention includes a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. The negative electrode includes SiOx (where 0 < x < 2) and a carbon-based negative electrode active material. The positive electrode includes a positive electrode active material including an over-lithiated manganese-based oxide in which the content of manganese exceeds 50 mol% of the total metal other than lithium and the ratio (Li / Me) of the number of moles of lithium to the number of moles of the total metal other than lithium exceeds 1. The present invention provides a lithium secondary battery in which the SiOx utilization depth defined by the following formula (1) is 1 to 15, preferably 3 to 15, in the state of SOC 0%. Formula (1): SiOx utilization depth = (capacity of Li remaining in the negative electrode / capacity of SiOx in the negative electrode) × 100

[0009] On the one hand, the over-lithium manganese-based oxide can be represented by the following [Chemical Formula 1]. [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 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, 1.1 ≤ a ≤ 1.5, 0.1 ≤ b ≤ 0.4, 0 ≤ c ≤ 0.05, 0.5 ≤ d ≤ 0.80, 0 ≤ e ≤ 0.1.

[0010] On the other hand, the positive electrode active material is D 50 can be 2 μm to 10 μm, and the BET specific surface area can be 1 to 10 m 2 / g.

[0011] Also, the initial irreversible capacity of the positive electrode can be 5% to 70%, and the electrode density can be 2.5 to 3.8 g / cc.

[0012] The negative electrode can contain a SiOx: carbon-based negative electrode active material in a weight ratio of 1:99 to 50:50.

[0013] The degree of prelithiation of the negative electrode represented by the following formula (2) can be 1% to 30%. Formula (2): Degree of prelithiation (%) = {Capacity per unit area of Li inserted into the negative electrode by prelithiation / Negative electrode loading amount} × 100

[0014] The negative electrode further includes a conductive material and a binder, and the conductive material can include single-walled carbon nanotubes.

[0015] The negative electrode may include a lower negative electrode composite layer formed on a negative electrode current collector, and an upper negative electrode composite layer formed on the lower negative electrode composite layer.

[0016] The SiOx D 50 can be 3 μm to 8 μm.

[0017] The SiOx is M b Metal (where M b The metal can be doped with a Group 1 alkali metal element and / or a Group 2 alkaline earth metal element.

[0018] The lithium secondary battery may have an N / P ratio of 100% to 150%. [Effects of the Invention]

[0019] The lithium secondary battery of the present invention is designed so that the ratio of the remaining Li capacity to the SiOx capacity in the negative electrode in a fully discharged state (SOC=0) satisfies a specific range, thereby suppressing the expansion of SiOx during charge and discharge, and providing excellent safety and life characteristics.

[0020] In addition, the present invention uses a perlithium manganese-based oxide, which is a mixture of a rock-salt Li2MnO3 phase and a layered LiMO2 phase (where M is Ni, Co, or Mn), as the positive electrode active material, and a silicon-based negative electrode active material as the negative electrode active material. This allows the excess lithium generated from the LiMO2 phase during the activation process to compensate for the irreversible capacity of the silicon-based negative electrode active material. This minimizes the use of sacrificial positive electrode materials and prelithiation for negative electrode compensation, maximizing positive electrode capacity.

[0021] Furthermore, the perlithium manganese-based oxide can be stably driven at a relatively high voltage compared to conventionally used lithium nickel cobalt manganese-based oxides. Therefore, when a positive electrode active material containing the perlithium manganese-based oxide is used together with a silicon-based negative electrode active material, the driving voltage can be increased to achieve a high energy density.

[0022] Furthermore, the lithium secondary battery of the present invention has excellent energy density and rapid charging performance because it contains, as the negative electrode active material, a silicon-based negative electrode active material that is excellent in capacity and rate characteristics. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is an image showing the formation of a conductive path on the surface of a negative electrode active material when single-walled carbon nanotubes are used as a conductive material. [Figure 2] 1 is an image showing the formation of a conductive path on the surface of a negative electrode active material when multi-walled carbon nanotubes are used as a conductive material. DETAILED DESCRIPTION OF THE INVENTION

[0024] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best explain his or her invention.

[0025] In the present invention, the term "primary particles" refers to particle units that do not appear to have grain boundaries when observed under a scanning electron microscope at a magnification of 5,000 to 20,000. The term "average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed in a scanning electron microscope image.

[0026] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of a plurality of primary particles.

[0027] In the present invention, the "average particle size D 50 " means the particle diameter at 50% 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.). 50can be measured using the laser diffraction method. For example, a powder of the particles to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000). Ultrasound of approximately 28 kHz is irradiated at an output of 60 W, and a volume cumulative particle size distribution graph is obtained. Then, the particle diameter corresponding to 50% of the volume cumulative amount is determined.

[0028] In the present invention, the "N / P ratio" means the percentage of the negative electrode loading amount to the positive electrode loading amount, that is, (negative electrode loading amount / positive electrode loading amount) x 100.

[0029] In this specification, the term "positive electrode loading amount" refers to the discharge capacity per unit area of ​​the positive electrode (unit: mAh / cm 2 ), "negative electrode loading amount" is the discharge capacity per unit area of ​​the negative electrode (unit: mAh / cm 2 ) means

[0030] The present invention will be specifically described below.

[0031] As a result of extensive research into the development of a lithium secondary battery with excellent energy density and life characteristics, the inventors discovered that high energy density and excellent life characteristics can be achieved by using a perlithium manganese-based oxide with excellent capacity characteristics and SiOx as active materials, and by designing the battery so that the depth of use of SiOx in a fully discharged state (SOC=0) satisfies a specific range, thereby completing the present invention.

[0032] The lithium secondary battery according to the present invention includes a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. The negative electrode contains SiOx (where 0 < x < 2) and a carbon-based negative electrode active material as the negative electrode active material. The positive electrode contains a hyper-lithium manganese-based oxide in which the content of manganese exceeds 50 mol% among all metals other than lithium, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of all metals other than lithium exceeds 1. In the state of SOC 0%, the depth of use of SiOx defined by the following formula (1) satisfies 1 to 15. Formula (1): Depth of use of SiOx (%) = (Capacity of Li remaining in the negative electrode / Capacity of SiOx in the negative electrode) × 100

[0033] Hereinafter, each component of the lithium secondary battery according to the present invention will be specifically described.

[0034] negative electrode The negative electrode according to the present invention contains silicon oxide (i.e., SiOx (where 0 < x < 2)) and a carbon-based negative electrode active material as the negative electrode active material. For example, 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 contains SiOx (where 0 < x < 2) and a carbon-based negative electrode active material as the negative electrode active material.

[0035] SiOx (where 0 < x < 2) has a higher theoretical capacity than the carbon-based negative electrode active material and a faster reaction rate with lithium. Therefore, when SiOx is included as the negative electrode active material, the energy density and rapid charging performance are improved. However, SiOx has a large irreversible capacity and a large volume expansion during charge and discharge, so it is inferior in terms of life characteristics. In particular, when used in combination with a hyper-lithium manganese-based oxide in which an oxygen-redox reaction occurs, there is a problem that the deterioration of the life characteristics becomes more serious. Further, when SiOx and a carbon-based negative electrode active material are mixed and used, non-uniformity occurs in the negative electrode due to the difference in the reaction rate between the silicon-based negative electrode active material and the carbon-based negative electrode active material, resulting in deterioration of the negative electrode.

[0036] In order to solve the above problems, the present invention minimizes the volume expansion and non-uniformity of the reaction between the negative electrode active materials during charge and discharge by controlling the depth of SiOx used in the negative electrode within a specific range.

[0037] Specifically, the lithium secondary battery according to the present invention can have a usage depth of SiOx defined by the following formula (1) at an SOC of 0%, i.e., in a fully discharged state, of 1 to 15%, preferably 3 to 15%, and more preferably 5 to 15%.

[0038] Equation (1): SiOx usage depth (%) = (Li capacity remaining in negative electrode / SiOx capacity in negative electrode) × 100

[0039] Research by the inventors has shown that when the SiOx usage depth is less than 1% or more than 15% at an SOC of 0% (i.e., fully discharged), the life characteristics rapidly deteriorate. Specifically, when the SiOx usage depth is less than 1% at a fully discharged state, the volume of SiOx rapidly changes during the charge / discharge process, resulting in a deterioration in energy density and life characteristics. When the SiOx usage depth is more than 15% at a fully discharged state, the electrical connectivity of the electrode deteriorates, resulting in a deterioration in life characteristics.

[0040] The SiOx usage depth is affected by a combination of factors such as the ratio of the negative electrode loading amount to the positive electrode loading amount (N / P ratio), the composition of the negative electrode active material, the composition of the positive electrode active material, the degree of prelithiation of the negative electrode, and activation conditions, and the SiOx usage depth can be adjusted by appropriately controlling these factors.

[0041] On the other hand, the capacity of Li remaining in the negative electrode and the capacity of SiOx in the negative electrode when the SOC is 0% can be measured by the following method.

[0042] First, a lithium secondary battery is fully discharged and then disassembled to separate the negative electrode. A coin-half cell is then fabricated using the separated negative electrode and a Li metal counter electrode, and the cell is delithiated at 0.1 C to 1.0 V to measure the discharge capacity. Since the measured discharge capacity is the capacity generated by the Li remaining in the negative electrode, it can be evaluated as the capacity of Li remaining in the negative electrode.

[0043] Next, the capacity of SiOx in the negative electrode can be determined by obtaining a voltage-capacity graph while charging and discharging the coin-half cell at 0.1 C in a voltage range of 0.005 V to 1.0 V, and then using the voltage-capacity graph.

[0044] Specifically, the SiOx capacity in the negative electrode can be determined by the following method.

[0045] When measuring a voltage-capacity graph of a coin half-cell fabricated using a negative electrode containing a carbon-based negative electrode active material and SiOx, the slope of the voltage-capacity graph changes abruptly around 0.25 V. The capacity achieved at voltages below the point where the slope changes abruptly (e.g., 0.25 V) is the capacity attributable to the carbon-based negative electrode active material, while the capacity achieved at voltages above the point where the slope changes abruptly (e.g., 0.25 V) is the capacity attributable to SiOx. Therefore, if the capacity at the point where the slope changes abruptly in the capacity-voltage graph of the coin half-cell is A and the total discharge capacity of the coin half-cell is B, the capacity of SiOx in the negative electrode can be calculated as B A.

[0046] On the other hand, the SiOx may be, if necessary, b It can be doped with a metal, where M b The metal can be a Group 1 alkali metal element and / or a Group 2 alkaline earth metal element, such as Li, Mg, etc. bMetal-doped SiOx has high efficiency and can achieve high energy density, although the capacity of the active material is reduced by the doping element.

[0047] Furthermore, the SiOx may further include a carbon coating layer on the particle surface, if necessary. Here, the amount of carbon coating may be 20 wt% or less, preferably 0.1 to 20 wt%, based on the total weight of the SiOx active material. The application of the carbon coating improves the electrical conductivity of the SiOx surface, improves the uniformity of the SEI layer, and improves the initial efficiency and lifespan characteristics. Here, the carbon coating layer may be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).

[0048] On the other hand, the SiOx preferably has a capacity of 1000 to 4000 mAh / g, preferably 1000 to 3800 mAh / g, and more preferably 1200 to 3800 mAh / g. When SiOx satisfying the above capacity range is used, high capacity characteristics can be realized.

[0049] The SiOx may have an initial efficiency of 60 to 95%, 70 to 95%, and preferably 75 to 95%. Here, the initial efficiency of SiOx refers to the percentage of the discharge capacity relative to the charge capacity measured by fabricating a half-cell using a negative electrode containing 100% SiOx as the negative electrode active material and a Li metal counter electrode, and then charging and discharging the half-cell at a 0.1 C rate in a voltage range of 0.01 V to 1.5 V. When the initial efficiency of SiOx satisfies this range, lithium provided from the positive electrode can be reversibly used, thereby achieving excellent fast charging performance.

[0050] The SiOx has an average particle size D 50Dmin to Dmax can be 3 μm to 8 μm, preferably 4 μm to 7 μm, and Dmin to Dmax can be 0.01 μm to 30 μm, preferably 0.01 μm to 20 μm, and more preferably 0.5 μm to 15 μm. When the particle size of SiOx satisfies the above range, sufficient electrode density can be ensured when mixed with a carbon-based negative electrode active material.

[0051] Meanwhile, the carbon-based negative electrode active material may be any of various carbon-based negative electrode active materials used in the art, such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, or a combination thereof. Preferably, artificial graphite, natural graphite, or a combination thereof may be used.

[0052] The carbon-based negative electrode active material has an average particle size D 50 However, the particle size can be 2 μm to 30 μm, preferably 5 μm to 30 μm. When the particle size of the carbon-based negative electrode active material satisfies the above range, sufficient electrode density can be ensured when mixed with SiOx.

[0053] Meanwhile, the SiOx and carbon-based negative electrode active material may be contained in the negative electrode in a weight ratio (SiOx:carbon-based negative electrode active material) of 1:99 to 50:50, preferably 3:97 to 50:50, more preferably 5:95 to 50:50, and even more preferably 5:95 to 30:70. When the mixing ratio of SiOx and carbon-based negative electrode active material satisfies the above range, a secondary battery with excellent energy density, life characteristics, and rapid charge performance can be realized. If the SiOx ratio is too low, the improvement effects on energy density and rapid charge performance may be insufficient, and if the SiOx ratio is too high, the life characteristics may be reduced.

[0054] Meanwhile, the negative electrode active material layer may further include a conductive material and a binder, if necessary.

[0055] Examples of the conductive material include spherical or flake graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be included in an amount of 0.1 to 30 wt %, 0.1 to 20 wt %, or 0.1 to 10 wt % based on the total weight of the negative electrode active material layer.

[0056] Preferably, single-walled carbon nanotubes can be used as the conductive material. When carbon nanotubes are used as the conductive material, a wide conductive path is formed, which can increase durability and reduce resistance, thereby achieving excellent life characteristics.

[0057] Figure 1 shows an image illustrating the formation of conductive paths on the surface of a negative electrode active material when single-walled carbon nanotubes are used as the conductive material, and Figure 2 shows an image illustrating the formation of conductive paths on the surface of a negative electrode active material when multi-walled carbon nanotubes are used as the conductive material.

[0058] As shown in Figures 1 and 2, when single-walled carbon nanotubes are used as a conductive material, conductive paths are uniformly formed on the surface of the negative electrode active material, thereby improving cycle characteristics.

[0059] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 20 wt %, 2 to 20 wt %, or 2 to 10 wt % based on the total weight of the negative electrode active material layer.

[0060] Meanwhile, the negative electrode may have a single negative electrode active material layer or a multi-layer structure composed of two or more layers. For example, the negative electrode may include a first negative electrode active material layer formed on a negative electrode current collector and a second negative electrode active material layer formed on the first negative electrode active material layer.

[0061] When the negative electrode active material layer has a multi-layer structure composed of two or more layers, the layers may differ from each other in the type and / or content of the negative electrode active material, binder, and / or conductive material.

[0062] For example, the first negative electrode active material layer (lower layer) may have a higher carbon-based negative electrode active material content than the second negative electrode active material layer (upper layer), and the second negative electrode active material layer may have a higher silicon-based negative electrode active material content than the first negative electrode active material layer, or the second negative electrode active material layer (upper layer) may have a higher conductive material content than the first negative electrode active material layer (lower layer).

[0063] By forming the negative electrode active material layer in a multi-layer structure and varying the composition of each layer, the performance characteristics of the battery can be improved. For example, by forming the upper layer with a higher content of conductive material or silicon-based negative electrode active material than the lower layer, the effect of improving fast charging performance can be obtained.

[0064] On the other hand, in the present invention, the negative electrode may be a prelithiated negative electrode, if necessary.

[0065] The prelithiation of the negative electrode can be performed, for example, by a method of compressing or depositing lithium metal on a negative electrode active material layer, a method of inserting lithium into a negative electrode active material layer by an electrochemical method, a method of inserting excess lithium contained in a sacrificial positive electrode material contained in a positive electrode into the negative electrode by an activation process, or a method of adding excess lithium to the positive electrode by an electrochemical method or a method of compressing or depositing lithium metal, and then inserting the excess lithium added to the positive electrode by an activation process into the negative electrode, or two or more of the above methods can be combined.

[0066] When performing the prelithiation process, the SiOx use depth in a fully discharged state can be adjusted by adjusting the degree of prelithiation, and even when the SiOx content in the negative electrode is higher than when prelithiation is not performed, the SiOx use depth that satisfies the range of the present invention can be achieved. Since the energy density increases as the SiOx content in the negative electrode increases, the use of a prelithiated negative electrode can achieve a higher energy density than when a negative electrode that is not prelithiated is used. In other words, when a prelithiated negative electrode is used, the SiOx content in the negative electrode can be increased and the SiOx use depth can be adjusted within the range of the present invention, thereby further improving the energy density and life characteristics.

[0067] Preferably, the negative electrode of the present invention has a degree of prelithiation represented by the following formula (2) of 1 to 30%, preferably 1 to 20%, and more preferably 3 to 20%.

[0068] Formula (2): Degree of prelithiation (%) = {Capacity per unit area of ​​Li inserted into the negative electrode by prelithiation / negative electrode loading amount} × 100

[0069] When the degree of prelithiation of the negative electrode satisfies the above range, a lithium secondary battery having excellent energy density and life characteristics can be realized.

[0070] Meanwhile, the negative electrode active material layer may 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 property may be reduced, resulting in reduced lithium mobility, while if the porosity is too large, the energy density may be reduced.

[0071] positive electrode The positive electrode according to the present invention includes, as a positive electrode active material, a perlithium manganese-based oxide in which the manganese content of all metals other than lithium exceeds 50 mol % and the ratio of the number of moles of lithium to the number of moles of all metals other than lithium (Li / Me) exceeds 1. 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, and the positive electrode active material layer includes a perlithium manganese-based oxide in which the manganese content of all metals other than lithium exceeds 50 mol % and the ratio of the number of moles of lithium to the number of moles of all metals other than lithium (Li / Me) exceeds 1.

[0072] In the case of perlithium manganese oxides containing excess lithium, they have a structure that combines a layered phase (LiM'O2) and a rock salt phase (Li2MnO3), and the rock salt phase is activated during the initial activation process to generate excess lithium ions, achieving high capacity. In addition, because the lithium ions generated during the activation process compensate for the irreversible capacity of the anode, there is no need to add a separate compensating material such as a sacrificial cathode material, and the cathode capacity can be increased.

[0073] Preferably, the perlithium manganese-based oxide may be represented by Chemical Formula 1.

[0074] [Chemical Formula 1] Li a Ni b Co c Mn d M e O2

[0075] In Chemical Formula 1 above, 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.

[0076] On the other hand, a is the molar ratio of Li in the over-lithiated manganese-based oxide, and 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 SiOx can be sufficiently compensated, and high-capacity characteristics can be realized.

[0077] b is the molar ratio of Ni in the over-lithiated manganese-based oxide, and can be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0078] c is the molar ratio of Co in the over-lithiated manganese-based oxide, and 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 may become serious, resulting in a decrease in life characteristics.

[0079] d is the molar ratio of Mn in the over-lithiated manganese-based oxide, and 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 is excessively small, and the effects of negative electrode irreversible compensation and capacity improvement are not significant.

[0080] e is the molar ratio of the doping element M in the over-lithiated manganese-based oxide, and 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.

[0081] Meanwhile, in the perlithium manganese-based oxide represented by [Chemical Formula 1], the ratio of the number of moles of Li to the number of moles of all 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, excellent rate characteristics and capacity characteristics are achieved. If the Li / Me ratio is too high, electrical conductivity decreases and the rock salt phase (Li2MnO3) increases, which can lead to an increased rate of degradation. If the Li / Me ratio is too low, the effect of improving energy density is not significant.

[0082] Meanwhile, the composition of the perlithium manganese-based oxide can be expressed by the following [Chemical Formula 2].

[0083] [Chemical formula 2] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0084] In the formula 2, M may 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.

[0085] The X represents the ratio of the Li2MnO3 phase in the perlithium manganese-based oxide, and may be 0.2≦x≦0.5, 0.25≦x≦0.5, or 0.25≦x≦0.4. When the ratio of the Li2MnO3 phase in the perlithium manganese-based oxide satisfies this range, the irreversible capacity of the SiOx negative electrode active material can be sufficiently compensated for, and high capacity characteristics can be achieved.

[0086] The 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.

[0087] The z is the molar ratio of Co in the LiM'O2 phase and may be 0≦z≦0.1, 0≦z≦0.08, or 0≦z≦0.05. If z exceeds 0.1, gas generation and deterioration of the positive electrode active material may become severe, resulting in reduced life characteristics.

[0088] The 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.

[0089] Meanwhile, the positive electrode active material according to the present invention may further include a coating layer on the surface of the perlithium manganese-based oxide, if necessary. When the positive electrode active material includes the coating layer, the coating layer may prevent contact between the perlithium manganese-based oxide and the electrolyte, thereby reducing electrolyte side reactions and improving the lifespan characteristics.

[0090] The coating layer is made of a coating element M 1 The coating element M 1 For 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, and is preferably Al, Co, Nb, W, and combinations thereof, and more preferably Al, Co, and combinations thereof. 1 may contain two or more kinds, for example, Al and Co.

[0091] The coating elements are in the oxide form in the coating layer, i.e., M 1 It can exist as Oz (1≦z≦4).

[0092] The coating layer can be formed by dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. Among them, atomic layer deposition is preferred because it allows the coating layer to be formed over a large area.

[0093] The area on which the coating layer is formed can be 10 to 100%, preferably 30 to 100%, and more preferably 50 to 100% of the total surface area of ​​the perlithium manganese-based oxide particles. When the area on which the coating layer is formed satisfies the above range, the effect of improving the life characteristics is excellent.

[0094] Meanwhile, the cathode active material according to the present invention may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle diameter D 50 The thickness of the positive electrode active material can be 2 μm to 10 μm, preferably 2 μm to 8 μm, and more preferably 4 μm to 8 μm. 50 When the above range is satisfied, excellent electrode density can be achieved and the decrease in capacity and rate characteristics can be minimized.

[0095] The positive electrode active material has a BET specific surface area of ​​1 m 2 / g~10m 2 / g, 3-8m 2 / g or 4~6m 2 If the BET specific surface area of ​​the positive electrode active material is too low, the reaction area with the electrolyte is insufficient, making it difficult to achieve sufficient capacity, whereas if the specific surface area is too high, moisture absorption is rapid, accelerating side reactions with the electrolyte and making it difficult to ensure long life characteristics.

[0096] In addition, the positive electrode according to the present invention preferably has an initial irreversible capacity of about 5 to 70%, 5 to 50%, or 5 to 30%. The initial irreversible capacity of the positive electrode is a percentage of the discharge capacity when a half cell is manufactured using the positive electrode and a lithium counter electrode, and the half cell is charged at a high voltage of 4.6 V or higher, when the half cell is charged and discharged at a voltage range of 2.5 to 4.4 V, measured at 0.1 C. When the initial irreversible capacity of the positive electrode satisfies the above range, the irreversible capacity of the silicon-based negative electrode active material can be sufficiently compensated for without the use of a separate compensation material such as a sacrificial positive electrode material.

[0097] Meanwhile, the perlithium manganese-based oxide can be prepared by mixing a transition metal precursor and a lithium source material and then calcining the mixture.

[0098] Examples of the lithium source material include lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3), etc.), and chlorides (e.g., lithium chloride (LiCl)), and any of these may be used alone or in combination.

[0099] Meanwhile, the transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. When a carbonate precursor is used, it is more preferable in that a positive electrode active material having a relatively high specific surface area can be prepared.

[0100] The transition metal precursor can be prepared by a co-precipitation process. For example, the transition metal precursor can be prepared by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, and then mixing the metal solution with an ammonium cation complexing agent and a basic compound, followed by a co-precipitation reaction. If necessary, an oxidizing agent or oxygen gas can be further added during the co-precipitation reaction.

[0101] Here, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, etc.

[0102] The ammonium cation complexing agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0103] The basic compound may be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may vary 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.

[0104] Meanwhile, the transition metal precursor and the lithium source material may be mixed in amounts such that the molar ratio of the total transition metals (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.

[0105] The firing may be performed at a temperature of 600 to 1000°C or 700 to 950°C for a firing time of 5 to 30 hours or 5 to 20 hours. The firing atmosphere may be air or oxygen, for example, an atmosphere containing 20 to 100% by volume of oxygen.

[0106] Meanwhile, the positive electrode active material layer may further include a conductive material and a binder in addition to the positive electrode active material.

[0107] Examples of the conductive material include spherical or flake graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be included in an amount of 0.1 to 20 wt %, 1 to 20 wt %, or 1 to 10 wt % based on the total weight of the positive electrode active material layer.

[0108] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and these may be used alone or in combination. The binder may be included in an amount of 1 to 20 wt %, 2 to 20 wt %, or 2 to 10 wt % of the total weight of the negative electrode active material layer.

[0109] Meanwhile, the positive electrode according to the present invention may have an electrode density of about 2.5 to 3.8 g / cc, 2.5 to 3.5 g / cc, or 3.0 to 3.3 g / cc. When the electrode density of the positive electrode satisfies the above range, a high energy density can be achieved.

[0110] As described above, the lithium secondary battery of the present invention, which uses the perlithium manganese-based oxide represented by Chemical Formula 1 as a positive electrode active material, can stably operate and achieve high capacity characteristics even when the end-of-charge voltage is set as high as 4.3 V to 4.5 V during battery operation.

[0111] Separator In the lithium secondary battery of the present invention, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without particular limitation. In particular, a separator that exhibits low resistance to ion migration and excellent humidification ability for the electrolyte solution is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0112] electrolyte Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0113] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0114] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate solvents such as propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes.

[0115] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be 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 may be at least one 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, LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 5.0M.

[0116] The electrolyte may contain additives for the purpose of improving the life characteristics of the battery, suppressing capacity reduction, suppressing gas generation, etc. Examples of the additives 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 bis(oxalato)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium tetrafluorooxalatophosphate (LiTFOP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propane sultone (PS), propene sultone (PRS), succinonitrile (SN), adiponectin, and the like. Tolyl (AND), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyl di(prop-2-yn-1-yl)phosphate (EDP), 5-methyl-5 propargyloxylcarbonyl-1,3-dioxan-2-one (MPOD), a compound represented by the following chemical formula A (e.g., cyanoethyl polyvinyl alcohol, PVA-CN), a compound represented by the following chemical formula B (e.g., heptafluorobutyl cyanoethyl polyvinyl alcohol, PF-PVA-CN), a compound represented by the following chemical formula C (e.g., propargyl 1H-imidazole-1-carboxylate, PAC), and / or a compound represented by the following chemical formula D (e.g., arylimidazole such as CHN), may be used.

[0117] [ka]

[0118] In the above chemical formula A, n and m are each independently an integer of 1-100.

[0119] [ka]

[0120] [ka]

[0121] In the above chemical formula C, R 16 is a linear or non-linear alkylene group having 1 to 3 carbon atoms, and R 17 ~R 19 are each independently at least one selected from the group consisting of hydrogen, an alkyl group having 1 to 3 carbon atoms, and a cyano group (-CN), and D is CH or N.

[0122] [ka]

[0123] In the above chemical formula D, R1, R2, R3, and R4 can each independently represent hydrogen; or an alkyl group having 1 to 5 carbon atoms, 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).

[0124] Preferably, the additive may be a compound that acts as an oxygen scavenger. For example, phosphite-based substances (see Chemical Formula E) such as tristri(methylsilyl)phosphite (TMSPi), tristrimethylphosphite (TMPi), and tris(2,2,2-trifluoroethyl)phosphite (TTFP) are used; tristri(methylsilyl)phosphate (TMSPa); polyphosphate trimethylsilyl ester (PPSE); tris(pentafluorophenyl)borane (TPFPB); coumarin-3-carbonitrile (CMCN), 7-ethynylcoumarin (ECM), 3- Compounds containing a coumarin structure (see chemical formula F), such as acetylcoumarin (AcCM) and 3-[(trimethylsilyl)coumarin (TMSCM)); 3-[(trimethylsilyl)oxyl]-2H-1-benzopyran-2-one (TMSOCM), 3-(2-propyn-1-yloxyl)-2H-1-benzopyran-2-one (POCM), and 2-propyn-1-yl-2-iodo-2H-1-benzopyran-3-carboxylate (OBCM) can be used as oxygen scavengers.

[0125] [ka]

[0126] [ka]

[0127] In Chemical Formula E and Chemical Formula F, R1 to R6 can each independently include a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms and a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, 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).

[0128] On the other hand, the lithium secondary battery according to the present invention may have an N / P ratio of 100% to 150%, preferably 105% to 130%, and more preferably 105% to 120%. If the N / P ratio is less than the above range, lithium deposition may occur in the negative electrode if it is less than 100%, and it is difficult to achieve the depth of use of SiOx within the range of the present invention if it exceeds 150%.

[0129] On the other hand, the lithium secondary battery according to the present invention, containing SiOx, can realize excellent energy density and rapid charging performance, and exhibit excellent life characteristics. Specifically, the lithium secondary battery according to the present invention can achieve an 80% life cycle count of 510 or more, preferably 530 or more, and more preferably 550 or more, and can have an energy density of 460 Wh / L or more, preferably 470 Wh / L or more, and more preferably 480 Wh / L or more.

[0130] The present invention will be described in more detail below with reference to specific examples.

[0131] Example 1 <Production of positive electrodes> The positive electrode active material, conductive material, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 96:1:3 to prepare a positive electrode slurry. 1.143 [Ni 0.33 Mn 0.67 ] 0.857 O2 was used, and carbon nanotubes were used as the conductive material.

[0132] The positive electrode slurry was applied to an aluminum current collector sheet, dried, and then rolled to obtain a current collector with a loading of 4.30 mAh / cm. 2 A positive electrode was produced.

[0133] <Production of negative electrodes> Anode active material: conductive material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) was mixed in water in a weight ratio of 96.2:0.8:2:1 to prepare anode slurry. Here, the anode active material was SiOx: graphite (Gr) mixed in a weight ratio of 5.5:94.5, and the conductive material was single-walled carbon nanotubes.

[0134] The negative electrode slurry was applied to a copper current collector sheet, dried, and then rolled to obtain a loading of 4.95 mAh / cm. 2 A negative electrode having the formula:

[0135] <Lithium secondary battery manufacturing> A separator was interposed between the cathode and anode to prepare an electrode assembly, and the electrode assembly was inserted into a battery case and an electrolyte was injected to prepare a battery cell. The battery cell was then charged at a constant current of 0.1 C at 45° C. to 4.6 V, and then discharged at a constant current of 0.1 C to 2.0 V to activate the Li2MnO3 phase of the cathode active material, thereby preparing a lithium secondary battery.

[0136] Example 2 During the manufacturing of the negative electrode, the negative electrode loading was 4.52 mAh / cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the above-mentioned conditions were met.

[0137] Example 3 During the manufacturing of the positive electrode, Li was coated with 1500 ppm of Al as the positive electrode active material. 1.167 [Ni 0.25 Mn 0.75 ] 0.833 A lithium secondary battery was produced in the same manner as in Example 1, except that O2 was used.

[0138] Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the activation process was performed by charging at a constant current of 0.1 C at 45° C. to 4.7 V and then discharging at a constant current of 0.1 C to 2.0 V.

[0139] Examples 5 to 8 A lithium secondary battery was fabricated in the same manner as in Example 1, except that a mixture of SiOx and graphite in a weight ratio of 10:90 was used as the negative electrode active material when fabricating the negative electrode, and a prelithiation process was further performed by an electrochemical method after fabrication of the negative electrode so that the negative electrode had a prelithiation degree shown in Table 1 below.

[0140] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that SiOx:graphite was mixed in a weight ratio of 10:90 to use as the negative electrode active material when manufacturing the negative electrode.

[0141] Comparative Example 2 During negative electrode manufacturing, the negative electrode loading was 5.16 mAh / cm 2 A lithium secondary battery was produced in the same manner as in Example 1, except that the above-mentioned conditions were met.

[0142] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that after manufacturing the negative electrode, a prelithiation process was further performed by an electrochemical method so that the negative electrode had a prelithiation degree shown in Table 1 below.

[0143] Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the activation process was performed by charging at a constant current of 0.1 C at 45° C. to 4.3 V and then discharging at a constant current of 0.1 C to 2.0 V.

[0144] Comparative Example 5 During the manufacture of the positive electrode, Li[Ni 0.8 Co 0.1 Mn 0.1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the activation process was performed using 02 and charging at a constant current of 0.1 C to 4.2 V at 45° C., followed by discharging at a constant current of 0.1 C to 2.0 V.

[0145] [Table 1]

[0146] Experimental Example 1 The lithium secondary batteries of the Examples and Comparative Examples were fully discharged, and then disassembled to separate the negative electrodes. Coin-half cells were fabricated using the separated negative electrodes and Li metal counter electrodes. The coin-half cells were delithiated to 1.0 V at a constant current of 0.1 C, and the discharge capacity up to the point of full discharge was measured, which was determined as the capacity of Li remaining in the negative electrodes.

[0147] Next, the coin-half cell was charged and discharged at 25°C and 0.1C in the voltage range of 0.005V to 1.0V, and the discharge capacity of the negative electrode at 1V was measured. The capacity attributed to SiOx in the negative electrode was measured using the measured discharge capacity of the negative electrode.

[0148] The measured values ​​were substituted into the following formula (1) to calculate the depth of use of SiOx at SOC 0%.

[0149] Equation (1): SiOx usage depth = (Capacity of Li remaining in negative electrode / Capacity of SiOx in negative electrode) × 100

[0150] Experimental example 2: Number of times that 80% of the lifespan is reached The secondary batteries prepared in the examples and comparative examples were charged at 25°C at a constant current of 0.33 C to 4.35 V and then discharged at a constant current of 0.33 C to 2.5 V, which constituted one cycle. The number of cycles required for the discharge capacity to reach 80% of the initial discharge capacity was measured. The measurement results are shown in Table 2 below.

[0151] Experimental Example 3: Energy density (unit: Wh / L) The secondary batteries manufactured in the examples and comparative examples were measured for energy density per unit volume in the voltage range of 4.35 to 2.5 V. The measurement results are shown in Table 2 below.

[0152] [Table 2]

[0153] As shown in Table 2, the batteries of Examples 1 to 8, which use a perlithium manganese oxide as the positive electrode active material and have an SiOx depth of use within the range of the present invention in a fully discharged state, exhibit superior life characteristics compared to the batteries of Comparative Examples 1 to 4, whose SiOx depth of use is outside the range of the present invention. Furthermore, it was confirmed that Comparative Example 5, which uses NCM instead of a perlithium manganese oxide as the positive electrode active material, exhibited significantly lower life characteristics and energy density compared to the batteries of the Examples.

Claims

1. A lithium secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, the negative electrode comprises SiOx (where 0<x<2) and a carbon-based negative electrode active material, The positive electrode includes, as a positive electrode active material, a perlithium manganese-based oxide in which a manganese content of all metals other than lithium exceeds 50 mol % and a ratio of the number of moles of lithium to the number of moles of all metals other than lithium (Li / Me) exceeds 1; A lithium secondary battery having an SiOx usage depth defined by the following formula (1) of 1 to 15 when the SOC is 0%, where 0% SOC means a fully discharged state. Formula (1): SiOx usage depth = (capacity of Li remaining in negative electrode / capacity of SiOx in negative electrode) × 100

2. 2. The lithium secondary battery according to claim 1, wherein the SiOx usage depth defined by the formula (1) is 3 to 15 at an SOC of 0%.

3. 2. The lithium secondary battery of claim 1, wherein the perlithium manganese-based oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M ｅ O ２ In 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.

4. 4. The lithium secondary battery according to claim 3, wherein, in Chemical Formula 1, 1.1≦a≦1.5, 0.1≦b≦0.4, 0≦c≦0.05, 0.5≦d≦0.80, and 0≦e≦0.

1.

5. The positive electrode active material is D ５０ 2. The lithium secondary battery according to claim 1, wherein the average particle size is 2 μm to 10 μm.

6. The positive electrode active material has a BET specific surface area of ​​1 to 10 m ２ 2. The lithium secondary battery according to claim 1, wherein the SiO2 content is 0.15 wt %.

7. 2. The lithium secondary battery of claim 1, wherein the positive electrode has an initial irreversible capacity of 5% to 70%. The initial irreversible capacity of the positive electrode is a percentage of a discharge capacity measured at 0.1 C when a half cell is prepared using the positive electrode and a lithium counter electrode and then charged at a high voltage of 4.6 V or more, and the half cell is charged and discharged at a voltage range of 2.5 to 4.4 V.

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

9. 9. The lithium secondary battery according to claim 1, wherein the negative electrode contains SiOx:carbon-based negative electrode active material in a weight ratio of 1:99 to 50:

50.

10. 2. The lithium secondary battery according to claim 1, wherein the negative electrode has a degree of prelithiation represented by the following formula (2) of 1 to 30%: Formula (2): Degree of prelithiation (%) = {capacity per unit area of ​​Li inserted into the negative electrode by prelithiation / negative electrode loading amount} × 100

11. the negative electrode further comprises a conductive material and a binder; The lithium secondary battery according to claim 1 , wherein the conductive material comprises single-walled carbon nanotubes.

12. D of the SiOx ５０ 2. The lithium secondary battery according to claim 1, wherein the average particle size is 3 μm to 8 μm.

13. 2. The lithium secondary battery according to claim 1, wherein the negative electrode includes a lower negative electrode mixture layer formed on a negative electrode current collector, and an upper negative electrode mixture layer formed on the lower negative electrode mixture layer.

14. The SiOx is M ｂ Metal (where M ｂ 2. The lithium secondary battery according to claim 1, wherein the metal is doped with an alkali metal element of Group 1 and / or an alkaline earth metal element of Group 2.

15. 2. The lithium secondary battery according to claim 1, wherein the N / P ratio of the lithium secondary battery is 100% to 150%.

16. 2. The lithium secondary battery according to claim 1, wherein the number of times to reach 80% life is 510 or more, and the energy density is 460 Wh / L or more.

17. The positive electrode further includes a coating layer on the surface of the perlithium manganese-based oxide, The coating layer is a coating element M １ and the coating element 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.

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