Lithium-ion rechargeable battery

Abstract

The present invention relates to a lithium secondary battery that includes a positive electrode containing a perlithium manganese-based oxide as a positive electrode active material, 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, a negative electrode containing a silicon-based negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and satisfies the following formula (1): 0.25A≦B≦0.6A. In the formula (1), A is the area of ​​the discharge curve in the voltage region of 2.0V to 4.6V of a dQ / dV graph obtained by differentiating a graph of the voltage V after one cycle measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C and measuring the battery discharge capacity Q, and B is the area of ​​the discharge curve in the voltage region of 2.0V to 3.5V of the dQ / dV graph.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2021-0131945 dated October 5, 2021, and Korean Patent Application No. 10-2022-0127208 dated October 5, 2022, and all content disclosed in the documents of the 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 comprising a perlithium manganese oxide as the positive electrode active material and a silicon-based negative electrode active material as the negative electrode active material. [Background technology]

[0003] Recently, interest in energy storage technologies has been steadily increasing, and as its applications expand to include mobile phones, camcorders and laptop computers, and even electric vehicles, efforts to research and develop electrochemical devices are becoming increasingly concrete.

[0004] Among electrochemical devices, there is growing interest in the development of rechargeable secondary batteries, and lithium-ion batteries, developed in the early 1990s, are attracting particular attention due to their advantages such as high operating voltage and much higher energy density.

[0005] Lithium secondary 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 acts 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.

[0006] Recently, with the increasing demand for secondary batteries having a high energy density such as electric vehicle batteries, the development of high-voltage secondary batteries driven at a high voltage has been actively carried out.

[0007] Conventionally developed lithium secondary batteries for automobiles mainly use lithium nickel-based oxides as the positive electrode active material and carbon-based negative electrode active materials such as graphite as the negative electrode active material. However, when lithium nickel-based oxides are driven at a high voltage, problems such as the collapse of the structure of the positive electrode active material, the elution of transition metals, and the generation of gas occur, and therefore, there is a problem that the life characteristics of the battery deteriorate. In addition, since carbon-based negative electrode active materials have a small capacity and a slow reaction rate with lithium, there is a limit to achieving a high energy density in secondary batteries applying the same.

[0008] Therefore, there is a need to develop a lithium secondary battery having a higher energy density and better life characteristics than conventional ones.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention is for solving the above problems, and includes a positive electrode containing a hyperlithium manganese-based oxide as the positive electrode active material, a negative electrode containing a silicon-based negative electrode active material, and is designed to have specific behavior during charge / discharge, and aims to provide a lithium secondary battery excellent in energy density and life characteristics.

Means for Solving the Problems

[0010] On one side, the present invention provides a lithium secondary battery including a positive electrode containing a hyperlithium manganese-based oxide in which the content of manganese exceeds 50 mol% of the total metals other than lithium and the ratio (Li / Me) of the number of moles of lithium to the number of moles of the total metals other than lithium exceeds 1 as the positive electrode active material, a negative electrode containing a silicon-based negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and satisfying the following formula (1). Formula (1): 0.25A ≦ B ≦ 0.6A In equation (1) above, A is the discharge curve area (in Ah) in the 2.0V to 4.6V voltage region of the dQ / dV graph obtained by differentiating the graph of the voltage V and battery discharge capacity Q after one cycle, measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C, and B is the discharge curve area (in Ah) in the 2.0V to 3.5V voltage region of the dQ / dV graph. [Effects of the Invention]

[0011] The lithium secondary battery according to the present invention contains a perlithium manganese oxide as the positive electrode active material and a silicon-based negative electrode active material as the negative electrode active material. The perlithium manganese oxide can be driven at a relatively higher voltage than lithium nickel oxide and has excellent capacity characteristics. Furthermore, the silicon-based negative electrode active material has a theoretical capacity more than 10 times larger than that of carbon-based negative electrode active materials and has a fast reaction rate with lithium ions, so when applied, the capacity characteristics and rate characteristics of the lithium secondary battery can be improved. Therefore, the lithium secondary battery of the present invention, which contains a perlithium manganese oxide and a silicon-based negative electrode active material, can achieve excellent energy density and rapid charging performance.

[0012] Furthermore, as in the present invention, when using a perlithium manganese oxide and a silicon-based negative electrode active material, the excess lithium generated from the Li2MnO3 phase during the activation process can compensate for the irreversible capacity of the silicon-based negative electrode active material. Therefore, the lithium secondary battery of the present invention can minimize the use of sacrificial anode material for negative electrode compensation and pre-lithiation, maximize the capacity of the positive electrode, and suppress the volume expansion of the silicon-based negative electrode active material during the charge / discharge process, thereby suppressing the degradation of the negative electrode.

[0013] However, in the case of perlithium manganese oxides, an oxygen redox reaction occurs during the charge / discharge process. If this reaction occurs excessively, a large amount of gas is generated, leading to the collapse of the active material crystal structure and internal cracking, resulting in severe positive electrode degradation and potentially reducing the battery's lifespan. Therefore, in this invention, the lithium secondary battery is designed to satisfy specific discharge behavior during charge / discharge (i.e., the discharge curve area B in the 2.0V to 3.5V voltage range on the dQ / dV graph is 0.25 to 0.6 times the discharge curve area A in the 2.0V to 4.6V voltage range), thereby minimizing the reduction in lifespan due to the oxygen redox reaction. [Brief explanation of the drawing]

[0014] [Figure 1] This is a dQ / dV graph showing the voltage-capacity relationship during charging and discharging of a lithium secondary battery using a perlithium manganese oxide. [Figure 2] This image illustrates the formation of conductive pathways on the surface of the negative electrode active material when single-walled carbon nanotubes are used as the conductive material. [Figure 3] This image illustrates the formation of conductive pathways on the surface of the negative electrode active material when multi-walled carbon nanotubes are used as the conductive material. [Modes for carrying out the invention]

[0015] The terms and words used herein and in the claims shall not be interpreted to be limited to their ordinary or dictionary meanings, but rather to be interpreted in a way that is 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.

[0016] 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 sizes of primary particles observed from scanning electron microscope images.

[0017] In the present invention, "secondary particles" are particles formed by the aggregation of multiple primary particles.

[0018] 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.

[0019] In this invention, the "N / P ratio" means the percentage of the negative electrode loading amount relative to the positive electrode loading amount, i.e., (negative electrode loading amount / positive electrode loading amount) × 100.

[0020] In this specification, "positive electrode loading amount" refers to the discharge capacity per unit area of ​​the positive electrode (unit: mAh / cm²). 2 ), "negative electrode loading amount" is the discharge capacity per unit area of ​​the negative electrode (unit: mAh / cm²). 2 ) means.

[0021] The present invention will be described in detail below.

[0022] The lithium secondary battery according to the present invention is characterized by comprising a positive electrode containing a perlithium manganese oxide as a positive electrode active material, wherein the manganese content of the total metals other than lithium exceeds 50 mol%, and the ratio of the number of moles of lithium to the total number of moles of metals other than lithium (Li / Me) exceeds 1; a negative electrode containing a silicon-based negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, satisfying the following formula (1).

[0023] Formula (1): 0.25A≦B≦0.6A

[0024] In equation (1) above, A is the discharge curve area (in Ah) in the 2.0V to 4.6V voltage region of the dQ / dV graph obtained by differentiating the graph of the voltage V and battery discharge capacity Q after one cycle, measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C, and B is the discharge curve area (in Ah) in the 2.0V to 3.5V voltage region of the dQ / dV graph.

[0025] Perlithium manganese oxides in which the manganese content exceeds 50 mol% of the total metals other than lithium, and the ratio of the number of moles of lithium to the total number of moles of metals other than lithium (Li / Me) exceeds 1, are substances that have a structure in which a layered phase (LiM'O2) and a rock salt structure phase (Li2MnO3) are present.

[0026] In lithium secondary batteries using the aforementioned perlithium manganese oxide, it is known that capacity is achieved through transition metal oxidation and oxygen redox reactions during the charge / discharge process. Figure 1 shows a dQ / dV graph illustrating the voltage-capacity relationship during charge / discharge of a lithium secondary battery using a perlithium manganese oxide. As shown in Figure 1, lithium secondary batteries using perlithium manganese oxide achieve higher capacity compared to lithium nickel oxides, which achieve capacity solely through transition metal oxidation, because capacity is further realized through oxygen redox reactions in addition to capacity achieved through transition metal oxidation reactions during discharge. However, if the oxygen redox reaction is excessive, gas generation due to oxygen desorption and collapse of the positive electrode active material structure occur, leading to a rapid decrease in lifespan characteristics. Therefore, in the present invention, a lithium secondary battery is designed to achieve both excellent lifespan characteristics and high energy density by using a perlithium manganese oxide as the positive electrode active material and ensuring that oxygen redox reactions are appropriately performed during the charge / discharge process.

[0027] Specifically, the lithium secondary battery according to the present invention is designed to have a discharge behavior that satisfies the following formula (1).

[0028] Formula (1): 0.25A≦B≦0.6A

[0029] In equation (1) above, A is the discharge curve area in the 2.0V to 4.6V voltage region of the dQ / dV graph obtained by differentiating the graph of voltage V and battery discharge capacity Q after one cycle, measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C, and B is the discharge curve area in the 2.0V to 3.5V voltage region of the dQ / dV graph, where the lithium secondary battery is a battery that has completed the activation process.

[0030] As shown in Figure 1, during the discharge of a lithium secondary battery, the capacity due to the oxygen-oxidation-reduction reaction is represented in the voltage range of 2.0 to 3.5 V. Therefore, the degree of oxygen-oxidation-reduction reaction can be indicated by the ratio of the discharge capacity in the 2.0 to 3.5 V voltage range to the discharge capacity in the overall voltage range of the lithium secondary battery (2.0 V to 4.6 V). This can be represented by the ratio of the discharge curve area in the 2.0 to 3.5 V voltage range (B) to the overall discharge curve area (A) of the dQ / dV graph of the lithium secondary battery.

[0031] According to our research, lithium secondary batteries exhibit superior lifetime characteristics and energy density when they have discharge behavior satisfying equation (1), that is, when the discharge curve area B in the 2.0 to 3.5V voltage range on the dQ / dV graph is between 0.25A and 0.6A. Specifically, it has been shown that when B exceeds 0.6A, the oxygen-oxidation-reduction reaction occurs excessively, causing a rapid decline in lifetime characteristics, and when it is less than 0.25A, both energy density and lifetime characteristics decline.

[0032] Preferably, the lithium secondary battery can be designed to satisfy the following equation (1-1). When the discharge behavior of the lithium secondary battery satisfies the following equation (1-1), better life characteristics and energy density can be achieved.

[0033] Formula (1-1): 0.3A≦B≦0.5A

[0034] In equation (1-1) above, A and B are as defined in equation (1).

[0035] On the other hand, the discharge behavior of the lithium secondary battery, that is, the shape of the discharge curve in the dQ / dV graph, can be affected by the N / P ratio, negative electrode composition, positive electrode composition, activation process conditions, and other factors. Therefore, by appropriately adjusting these factors and designing the battery, it is possible to manufacture a lithium secondary battery with desired discharge behavior.

[0036] On the other hand, silicon-based negative electrode active materials have a theoretical capacity more than 10 times greater than carbon-based negative electrode active materials and react faster with lithium ions, so when applied, the capacity characteristics and rate characteristics of lithium secondary batteries can be improved. However, in the case of silicon-based negative electrode active materials, the irreversible capacity is large, so compensation for the irreversible capacity of the negative electrode is necessary to balance the positive and negative electrodes. Conventionally, to compensate for the irreversible capacity of silicon-based negative electrode active materials, methods such as performing a pre-lithification process after the manufacture of the negative electrode or including a sacrificial anode material in the positive electrode to compensate for the irreversible capacity of the negative electrode have been mainly used. On the other hand, when perlithium manganese oxide undergoes an initial activation process at a high voltage of 4.6V or higher, the rock salt structure phase contained in the perlithium manganese oxide is activated and an excess amount of lithium ions are generated, and the lithium ions generated in the activation process can be used to compensate for the irreversible capacity of the negative electrode. Therefore, as in the present invention, when the positive electrode active material contains a perlithium manganese oxide and the negative electrode active material contains a silicon-based negative electrode active material, a high-voltage activation process of 4.6V or higher can be performed to minimize the need for other compensating materials such as sacrificial anode materials or pre-lithiation processes, thereby achieving a balance with the negative electrode containing the silicon-based negative electrode active material.

[0037] Furthermore, as in the present invention, when a positive electrode active material containing a perlithium manganese oxide and a silicon-based negative electrode active material are used together, it is possible to operate at a high voltage of 4.3V or higher, and a high energy density can be achieved.

[0038] The lithium secondary battery according to the present invention exhibits excellent energy density and lifespan characteristics. Specifically, the lithium secondary battery according to the present invention can reach 80% lifespan 560 times or more, preferably 590 times or more, and more preferably 600 times or more, and its energy density can be 450 Wh / L or more, preferably 470 Wh / L or more, and more preferably 500 Wh / L or more.

[0039] The following describes in detail each component of the lithium secondary battery according to the present invention.

[0040] positive electrode The positive electrode according to the present invention includes, as a positive electrode active material, a lithium-rich manganese-based oxide in which the content of manganese exceeds 50 mol% of the total amount of metals other than lithium, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of the total amount of metals other than lithium exceeds 1. Specifically, the positive electrode of 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 contains a lithium-rich manganese-based oxide in which the content of manganese exceeds 50 mol% of the total amount of metals other than lithium, and the ratio (Li / Me) of the number of moles of lithium to the number of moles of the total amount of metals other than lithium exceeds 1.

[0041] In the case of a lithium-rich manganese-based oxide containing an excess of lithium, it has a structure in which a layered phase (LiM’O2) and a rock salt structure phase (Li2MnO3) coexist. During the initial activation process, the rock salt structure phase is activated to generate an excess of lithium ions, enabling the realization of a high capacity. Further, since the irreversible capacity of the negative electrode is compensated by the lithium ions generated during the activation process, there is no need to add another compensation substance such as a sacrificial anode material, and the capacity of the positive electrode can be increased.

[0042] Preferably, the lithium-rich manganese-based oxide can be represented by Chemical Formula 1.

[0043] [Chemical Formula 1] Li a Ni b Co c Mn d M e O2

[0044] In 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.

[0045] On the one 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.

[0046] Said 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.

[0047] Said 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 gas generation and deterioration of the positive electrode active material may become severe, resulting in a decrease in life characteristics.

[0048] Said 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 structure phase becomes excessively small, and the effects of negative electrode irreversible compensation and capacity improvement are not significant.

[0049] Said 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 high, it may have an adverse effect on the active material capacity.

[0050] On the other hand, in the over-lithiated manganese-based oxide, the ratio of the molar number of Li to the total molar number of metals other than Li (Li / Me) can be 1.2 - 1.5, 1.25 - 1.5, or 1.25 - 1.4. When the Li / Me ratio satisfies the above range, excellent rate characteristics and capacity characteristics are shown. If the Li / Me ratio is too high, the electrical conductivity decreases, the rock salt structure phase (Li2MnO3) increases, and the deterioration rate may increase. If it is too low, the effect of improving the energy density is not significant.

[0051] On the other hand, the composition of the perlithium manganese oxide can also be represented by the following [Chemical Formula 2].

[0052] [Chemical formula 2] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0053] 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.

[0054] 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 silicon-based anode active material can be sufficiently compensated, and high capacity characteristics can be achieved.

[0055] 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.

[0056] 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 worsen, potentially reducing the lifetime characteristics.

[0057] 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.

[0058] 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.

[0059] The aforementioned coating layer contains coating element M 1 It may include the coating element M 1 The coating element M can be, for example, 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 Al, Co, Nb, W, and combinations thereof, and more preferably Al, Co, and combinations thereof. 1 It can contain two or more types, for example, Al and Co.

[0060] The aforementioned coating element exists in oxide form within the coating layer, i.e., M 1 It can exist as Oz(1≦z≦4).

[0061] 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.

[0062] 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 the lifespan characteristics is excellent.

[0063] 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.

[0064] 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 BET specific surface area of ​​the positive electrode active material is too low, there will be insufficient reaction area with the electrolyte, making it difficult to achieve sufficient capacity. If the specific surface area is too high, moisture absorption will be rapid, accelerating side reactions with the electrolyte, making it difficult to ensure lifespan characteristics.

[0065] Furthermore, the positive electrode according to the present invention preferably has an initial irreversible capacity of approximately 5-70%, 5-50%, or 5-30%. The initial irreversible capacity of the positive electrode is the percentage of the discharge capacity when the half-cell is charged and discharged in a voltage range of 2.5-4.4V to the charge capacity when the half-cell is charged at a high voltage of 4.6V or higher after manufacturing a half-cell with the positive electrode and lithium counter electrode, and is a value measured on a 0.1C basis. 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 without using another compensating material such as a sacrificial anode material.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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, Mn3O4MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, etc.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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 fibers, single-walled carbon nanotubes, and multi-walled 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 may 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.

[0077] 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), 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 1-20% by weight, 2-20% by weight, or 2-10% by weight relative to the total weight of the negative electrode active material layer.

[0078] On the other hand, the positive electrode according to the present invention can have an electrode density of approximately 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.

[0079] As described above, the lithium secondary battery of the present invention using a lithium-rich manganese-based oxide as the positive electrode active material can stably drive the cell even when the charge termination voltage is set high to the level of 4.3 V to 4.5 V during the driving of the battery, and can achieve high-capacity characteristics.

[0080] Negative electrode The negative electrode according to the present invention includes a silicon-based negative electrode active material as the negative electrode active material. 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 can include a silicon-based negative electrode active material as the negative electrode active material.

[0081] Since the silicon-based negative electrode active material has a higher theoretical capacity and a faster reaction rate with lithium than the carbon-based negative electrode active material, when the negative electrode includes the silicon-based negative electrode active material, the energy density and rapid charging performance are improved. However, the silicon-based negative electrode active material 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 lithium-rich manganese-based oxide in which an oxygen-redox reaction occurs, there is a problem that the degradation of the life characteristics becomes more severe. However, as described above, when the discharge behavior of the lithium secondary battery satisfies Equation (1), it is possible to minimize the degradation of the life characteristics due to the oxygen-redox reaction and to achieve excellent energy density and rapid charging performance.

[0082] The silicon-based negative electrode active material is, for example, Si, SiOw (where 0 < w ≦ 2), Si-C composite, Si-M a Alloy (M a is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, Ni) or a combination thereof.

[0083] On the other hand, the silicon-based negative electrode active material can be doped with M b metal as needed, where the M bThe metal can be a Group 1 alkali metal element and / or a Group 2 alkaline earth metal element, and can be, for example, Li, Mg, etc. Specifically, the silicon negative electrode active material is M b Si doped with metal, SiOw (where 0 < w ≦ 2), Si-C composite, etc. can be used. In the case of a metal-doped silicon-based negative electrode active material, although the active material capacity decreases due to the doping element, it has high efficiency, so a high energy density can be realized.

[0084] In addition, the silicon-based negative electrode active material can further include a carbon coating layer on the surface of the particles as needed. Here, the carbon coating amount can be 20% by weight or less, preferably 0.1 to 20% by weight, based on the total weight of the silicon-based negative electrode active material. When the carbon coating is applied, the electrical conductivity of the silicon surface is improved, the SEI layer uniformity is improved, and the initial efficiency and life characteristics are improved.

[0085] The carbon coating layer can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc.

[0086] On the other hand, the silicon-based negative electrode active material preferably has a capacity of 1000 to 4000 mAh / g, preferably 1000 to 3800 mAh / g, more preferably 1200 to 3800 mAh / g. When a silicon-based negative electrode active material satisfying the above capacity range is used, high capacity characteristics can be realized.

[0087] Furthermore, the silicon-based anode active material can have an initial efficiency of 60-95%, 70-95%, preferably 75-95%. The initial efficiency of the silicon-based anode active material refers to the percentage of the discharge capacity to the charge capacity measured by charging and discharging between 0.01V and 1.5V at a 0.1C rate after manufacturing a half-cell with a negative electrode using 100% silicon-based anode active material and a lithium counter electrode. When the initial efficiency of the silicon-based anode active material satisfies the above range, the lithium supplied from the positive electrode can be used reversibly, and excellent rapid charging performance can be achieved.

[0088] Furthermore, the particle size of the silicon-based negative electrode active material is D 50 The size is 3 μm to 8 μm, preferably 4 μm to 7 μm, and D min ~D max The particle size 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 the silicon-based anode active material satisfies the above range, sufficient electrode density can be ensured by mixing it with the carbon-based anode or by using it alone.

[0089] Furthermore, the negative electrode may, if necessary, further contain a carbon-based negative electrode active material. The carbon-based negative electrode active material may, but is not limited to, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, or hard carbon.

[0090] On the other hand, the silicon-based anode active material can be included in an amount of 1 to 100% by weight, 1 to 50% by weight, 1 to 30% by weight, 1 to 15% by weight, 10 to 70% by weight, or 10 to 50% by weight relative to the total weight of the anode active material.

[0091] The carbon-based anode active material may be included in an amount of 0-99% by weight, 50-99% by weight, 70-99% by weight, 85-99% by weight, 30-90% by weight, or 50-90% by weight, relative to the total weight of the anode active material.

[0092] On the other hand, it is preferable that the lithium secondary battery of the present invention is configured to have a different N / P ratio, which is the percentage of the negative electrode loading amount to the positive electrode loading amount, depending on the type of negative electrode active material used.

[0093] For example, when using a mixture of SiOw and a carbon-based negative electrode active material as the negative electrode active material, the N / P ratio can be 100% to 150%, preferably 100% to 140%, and more preferably 100% to 120%. If the negative electrode discharge capacity deviates from the above range relative to the positive electrode discharge capacity, the balance between the positive and negative electrodes will be disrupted, leading to a decrease in lifespan characteristics or the occurrence of lithium deposition.

[0094] Furthermore, when 100% Si is used as the negative electrode active material, the N / P ratio can be 150% to 300%, preferably 160% to 300%, and more preferably 180% to 300%. If the negative electrode discharge capacity deviates from the above range relative to the positive electrode discharge capacity, the balance between the positive and negative electrodes will be disrupted, leading to a decrease in lifespan characteristics or the occurrence of lithium deposition.

[0095] On the other hand, the negative electrode active material layer may further include a conductive material and a binder, if necessary.

[0096] 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-walled carbon nanotubes, and multi-walled 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 may be included in an amount of 0.1 to 30% by weight, 0.1 to 20% by weight, or 0.1 to 10% by weight relative to the total weight of the negative electrode active material layer.

[0097] 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, increasing durability and reducing resistance, thereby achieving excellent lifespan characteristics.

[0098] Figure 2 illustrates the formation of conductive pathways on the surface of the negative electrode active material when single-walled carbon nanotubes are used as the conductive material, and Figure 3 illustrates the formation of conductive pathways on the surface of the negative electrode active material when multi-walled carbon nanotubes are used as the conductive material.

[0099] As illustrated in Figures 2 and 3, when single-walled carbon nanotubes are used as a conductive material, conductive pathways are uniformly formed on the surface of the negative electrode active material, thereby improving the cycle characteristics.

[0100] 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), 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 can be included in an amount of 1-20% by weight, 2-20% by weight, or 2-10% by weight relative to the total weight of the negative electrode active material layer.

[0101] 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. 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.

[0102] In the case of a multilayer structure in which the negative electrode active material layer consists of two or more layers, each layer may have different types and / or contents of negative electrode active material, binder, and / or conductive material.

[0103] For example, in the first negative electrode active material layer (lower layer), the content of carbon-based negative electrode active material among the total negative electrode active material can be made higher than in the second negative electrode active material layer (upper layer), and in the second negative electrode active material layer, the content of silicon-based negative electrode active material among the total negative electrode active material can be made higher than in the first negative electrode active material layer, or the conductive material content of the second negative electrode active material layer (upper layer) can be made higher than in the first negative electrode active material layer (upper layer).

[0104] In this way, by forming the negative electrode active material layer in a multilayer structure and varying the composition of each layer, the performance characteristics of the battery can be improved. For example, if the upper layer contains a higher content of conductive material or silicon-based negative electrode active material than the lower layer, an improvement in rapid charging performance can be obtained.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0109] The aforementioned 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 aforementioned 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 linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, 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.

[0110] 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 the lithium salt can be LiPF6, LiN(FSO2)2, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 5.0 M.

[0111] Furthermore, the electrolyte may contain additives for the purpose of improving the battery's lifespan characteristics, suppressing capacity reduction, and suppressing gas generation. Examples of such 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 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 adiponitrile (AND). ,1,3,6-hexanetricarbonite (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 (Chemical Formula 1) (e.g., cyanoethyl polyvinyl alcohol, PVA-CN), compounds represented by the following chemical formula B (Chemical Formula 2) (e.g., heptafluorobutylcyanoethyl polyvinyl alcohol, PF-PVA-CN), compounds represented by the following chemical formula C (Chemical Formula 3) (e.g., propargyl 1H-imidazole-1-carboxylate, PAC), and / or compounds represented by the following chemical formula D (Chemical Formula 4) (e.g., arylimidazoles such as C6H8N2) can be used.

[0112] [ka]

[0113] In the chemical formula A, n and m are each an integer between 1 and 100, independently of each other.

[0114] [ka]

[0115] [ka]

[0116] 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, a C1-C3 alkyl group, and a cyano group (-CN), and D is CH or N.

[0117] [ka]

[0118] In the chemical formula D, R1, R2, R3, and R4 can each independently be 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).

[0119] Preferably, the additive can be a compound that acts as an oxygen scavenger. For example, phosphite-based substances such as tristri(methylsilyl) phosphite (TMSPi), tristrimethylphosphite (TMPi), and tris(2,2,2-trifluoroethyl) phosphite (TTFP) (see chemical formula E (Chemical Formula 5)); tristri(methylsilyl) phosphate (TMSPa); trimethylsilyl polyphosphate (PPSE); tris(pentafluorophenyl)borane (TPFPB); coumarin-3-carbonitride (CMCN), 7-ethynylcoumarin (ECM), 3- Compounds containing a coumarin structure, such as acetylcoumarin (AcCM) and 3-[(trimethylsilyl)coumarin (TMSCM) (see chemical formula F (Chemical Formula 6)); 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.

[0120] [ka]

[0121] [ka]

[0122] In the chemical formulas E and F, R1 to R6 can each independently include a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a cyano group (-CN), a fluoro group (F), an ether group (COC), a carboxyl group (OC=O), a trimethylsilyl group (-TMS), an isocyanate group (-NCO), and / or an isothiocyanate group (-NCS).

[0123] The present invention will be described in more detail below with reference to specific examples.

[0124] Example 1 <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.

[0125] The positive electrode slurry is applied to an aluminum current collector sheet, dried, and then rolled to achieve a loading capacity of 5.0 mAh / cm². 2 We manufactured the positive electrode.

[0126] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by mixing a negative electrode active material, conductive material, styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 96.2:0.8:2:1. In this preparation, SiOx and graphite (Gr) were mixed in a weight ratio of 5.5:94.5 as the negative electrode active material, and single-walled carbon nanotubes were used as the conductive material.

[0127] The negative electrode slurry is applied to a copper current collector sheet, dried, and then rolled to achieve a loading volume of 5.5 mAh / cm². 2 We manufactured the negative electrode.

[0128] <Manufacturing of lithium-ion secondary batteries> An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes produced as described above. After inserting the electrode assembly into a battery case, an electrolyte solution was injected to manufacture a battery cell. Subsequently, the battery cell was charged at 45°C with a constant current of 0.1C until it reached 4.6V, and then discharged to 2.0V with a constant current of 0.1C to activate the Li2MnO3 phase of the positive electrode active material and manufacture a lithium secondary battery.

[0129] Example 2 During the manufacturing of the negative electrode, the negative electrode loading amount was 6.0 mAh / cm². 2 A lithium secondary battery was manufactured using the same method as in Example 1, except that it was modified to achieve the desired result.

[0130] Example 3 A lithium secondary battery was manufactured using the same method as in Example 1, except that SiOx:graphite was mixed in a weight ratio of 10:90 as the negative electrode active material during the manufacturing of the negative electrode.

[0131] Example 4 During the manufacturing of the positive electrode, 1500 ppm of Al is coated onto the lithium as the positive electrode active material. 1.167 [Ni 0.25 Mn 0.75 ] 0.833 A lithium secondary battery was manufactured using the same method as in Example 1, except that O2 was used.

[0132] Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the battery cell was charged at 45°C with a constant current of 0.1C until it reached 4.7V, and then discharged to 2.0V with a constant current of 0.1C to activate the Li2MnO3 phase of the positive electrode active material.

[0133] Comparative Example 1 During the manufacturing of the negative electrode, the negative electrode loading amount was 7.5 mAh / cm². 2 A lithium secondary battery was manufactured using the same method as in Example 1, except that it was modified to achieve the desired result.

[0134] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the battery cell was charged at 45°C with a constant current of 0.1C until it reached 4.9V, and then discharged with a constant current of 0.1C until it reached 2.0V to activate the Li2MnO3 phase of the positive electrode active material.

[0135] Comparative Example 3 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 15:85 as the negative electrode active material during the manufacturing of the negative electrode.

[0136] [Table 1]

[0137] Experimental Example 1 The secondary batteries manufactured in the examples and comparative examples were charged at 25°C with a constant current of 0.1C until the voltage reached 4.60V, and then discharged with a constant current of 0.1C until the voltage reached 2.0V. The voltage-discharge capacity graph was measured, and the dQ / dV graph was obtained by differentiating the voltage-discharge capacity graph. Subsequently, the discharge curve area A in the 2.0V to 4.6V voltage range and the discharge curve area B in the 2.0V to 3.5V voltage range were measured from the dQ / dV graph. The measurement results are shown in Table 2 below.

[0138] Experimental Example 2: Number of times reaching 80% of lifespan The secondary batteries manufactured in the above examples and comparative examples were charged at 25°C with a constant current of 0.33C until the voltage reached 4.35V, and then discharged with a constant current of 0.33C until the voltage reached 2.5V. This process was repeated as one cycle, and the number of cycles required for the discharge capacity after the cycle to reach 80% of the initial discharge capacity was measured. The measurement results are shown in Table 2 below.

[0139] Experimental Example 3: Energy Density (Unit: Wh / L) The secondary batteries manufactured in the above examples and comparative examples were charged and discharged at 25°C and 0.1C within a voltage range of 4.35V to 2.5V, and their energy density was measured. Here, the energy density was calculated by multiplying the discharge capacity by the average voltage and then dividing by the unit volume of the secondary battery. The average voltage was the integral value of the capacity-voltage profile curve divided by the capacity. The measurement results are shown in Table 2 below.

[0140] [Table 2]

[0141] As shown in Table 2 above, the lithium secondary batteries of Examples 1 to 5, in which the discharge curve area B in the 2.0V to 3.5V voltage range of the dQ / dV graph is 0.25 to 0.6 times the discharge curve area A in the 2.0V to 4.6V voltage range, achieve an energy density of 450 Wh / L or more and exhibit excellent performance with 80% lifespan reached after 590 cycles or more. In contrast, in the case of the lithium secondary batteries of Comparative Examples 1 to 3, in which the discharge curve area B in the 2.0V to 3.5V voltage range of the dQ / dV graph deviates from the scope of the present invention, it can be confirmed that the number of cycles to reach 80% lifespan is significantly reduced compared to Examples 1 to 5.

Claims

1. The positive electrode active material includes a perlithium manganese oxide in which the manganese content exceeds 50 mol% of the total metals other than lithium, and the ratio of the number of moles of lithium to the total number of moles of metals other than lithium (Li / Me) is 1.25 to 1.

4. A negative electrode comprising a negative electrode active material layer containing a silicon-based negative electrode active material, A separator interposed between the positive electrode and the negative electrode, It contains electrolytes, A lithium secondary battery that satisfies the following formula (1), Formula (1): 0.25A≦B≦0.6A In equation (1) above, A is the discharge curve area in the 2.0V to 4.6V voltage region of the dQ / dV graph obtained by differentiating the graph of the voltage V and battery discharge capacity Q after one cycle, measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C, and B is the discharge curve area in the 2.0V to 3.5V voltage region of the dQ / dV graph. The aforementioned perlithium manganese oxide is represented by the following chemical formula 1, [Chemical formula 1] Li ａ Ni ｂ Mn ｄ M ｅ O ２ In the above chemical formula 1, 1 < a, 0 ≤ b ≤ 0.5, 0.5 ≤ d < 1.0, and 0 ≤ e ≤ 0.05, and M is at least one selected from the group consisting of Al, B, W, Co, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. D of the positive electrode active material ５０ A lithium secondary battery with a diameter of 2 μm to 10 μm.

2. The aforementioned lithium secondary battery satisfies the following equation (1-1): Formula (1-1): 0.3A≦B≦0.5A In formula (1-1), A is the discharge curve area in the 2.0V to 4.6V voltage region of the dQ / dV graph obtained by differentiating the graph of the voltage V and battery discharge capacity Q after one cycle, measured while charging the lithium secondary battery to 4.6V at 0.1C and then discharging it to 2.0V at 0.1C, and B is the discharge curve area in the 2.0V to 3.5V voltage region of the dQ / dV graph, as described in claim 1.

3. A lithium secondary battery according to claim 1 or 2, wherein in the chemical formula 1, 1.1 ≤ a ≤ 1.5, 0.1 ≤ b ≤ 0.4, 0.5 ≤ d ≤ 0.80, and e = 0.

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

5. The lithium secondary battery according to claim 1 or 2, wherein the initial irreversible capacity of the positive electrode is 5% to 70%.

6. The lithium secondary battery according to claim 1 or 2, wherein the electrode density of the positive electrode is 2.5 to 3.8 g / cc.

7. The lithium secondary battery according to claim 1 or 2, wherein the initial efficiency of the silicon-based negative electrode active material is 60% to 95%.

8. The negative electrode active material layer further comprises a conductive material and a binder. The lithium secondary battery according to claim 1 or 2, wherein the conductive material includes single-walled carbon nanotubes.

9. The silicon-based negative electrode active material D ５０ A lithium secondary battery according to claim 1 or 2, wherein the diameter is 3 μm to 8 μm.

10. The lithium secondary battery according to claim 1 or 2, wherein the porosity of the negative electrode active material layer is 20% to 70%.

11. The aforementioned silicon-based anode active material is a mixture of silicon oxide and a carbon-based anode active material. The lithium secondary battery according to claim 1 or 2, wherein the N / P ratio of the lithium secondary battery is 100% to 120%.

12. The lithium secondary battery according to claim 11, wherein the negative electrode has a multilayer structure including two or more negative electrode composite layers.

13. The lithium secondary battery according to claim 1 or 2, wherein the number of times the lithium secondary battery reaches 80% life is 560 times or more, and the energy density of the lithium secondary battery is 450 Wh / L or more.

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