Composition for positive electrode active material layer and lithium secondary battery

Abstract

The present invention relates to a composition for a positive electrode active material layer of a lithium secondary battery, the composition including a positive electrode active material containing a lithium composite transition metal compound that contains nickel, cobalt, and manganese and contains 80 mol % or more and less than 100 mol % of nickel among metals excluding lithium, and an additive represented by chemical formula A, and a positive electrode, a lithium secondary battery, a battery module, and a battery pack each containing the same.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0160762, filed with the Korean Intellectual Property Office on November 19, 2021, and all contents disclosed in the document of the Korean patent application are included herein.

[0002] This application relates to a composition for a positive electrode active material layer and a lithium secondary battery.

Background Art

[0003] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, electric vehicles, power tools, and vacuum cleaners, the demand for secondary batteries that are small and lightweight but relatively high-capacity and / or high-output has been rapidly increasing. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for electronic devices. For this reason, research and development efforts to improve the performance of lithium secondary batteries are being actively carried out.

[0004] A lithium secondary battery is a state in which an organic electrolyte or a polymer electrolyte is filled between a positive electrode and a negative electrode made of an active material capable of inserting (intercalations) and desorbing (deintercalation) lithium ions, and electrical energy is produced by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.

[0005] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMn2O4), lithium iron phosphate compound (LiFePO4), etc. are used. Among them, lithium cobalt oxide (LiCoO2) has the advantages of a high operating voltage and excellent capacity characteristics, so it is widely used and applied as a positive electrode active material for high voltage. However, due to the price increase and supply instability of cobalt (Co), there is a limit to its large-scale use as a power source in fields such as electric vehicles, and the need to develop a replaceable positive electrode active material has emerged.

[0006] As a result, nickel cobalt manganese-based lithium composite transition metal oxides (hereinafter simply referred to as "NCM-based lithium composite transition metal oxides") in which a part of cobalt (Co) is replaced with nickel (Ni) and manganese (Mn) have been developed. In recent years, research has been conducted to increase the Ni content in NCM-based lithium composite transition metal oxides to increase the capacity. However, in the case of high-concentration nickel (Ni-rich) positive electrode active materials with a high nickel content, there are disadvantages such as a decrease in thermal stability, an increase in resistance due to an increase in side reactions during the electrochemical reaction, and an increase in gas generation.

[0007] On the other hand, graphite is mainly used as the negative electrode active material of a lithium secondary battery. However, since the capacity per unit mass of graphite is as small as 372 mAh / g, it is difficult to increase the capacity of the lithium secondary battery. For this reason, as a non-carbon-based negative electrode material having a higher energy density than graphite for increasing the capacity of the lithium secondary battery, negative electrode materials such as silicon, tin, and their oxides have been developed. However, in the case of such non-carbon-based negative electrode materials, although the capacity is large, there are problems such as low initial efficiency, a large lithium consumption during the initial charge and discharge, and a large irreversible capacity loss. Summary of the Invention Problems to be Solved by the Invention

[0008] The inventors of the present application aim to provide a composition for a positive electrode active material layer of a lithium secondary battery, a positive electrode containing the same, a lithium secondary battery, a battery module, and a battery pack that can improve battery performance.

Means for Solving the Problems

[0009] One embodiment of the present application includes a positive electrode active material containing a lithium composite transition metal compound containing nickel, cobalt, and manganese, and containing 80 mol% or more and less than 100 mol% of nickel among the metals excluding lithium; and an additive represented by the following Chemical Formula A and provides a composition for a positive electrode active material layer of a lithium secondary battery: [Chemical Formula A] Li x Co (1-y-z-m) Zn y Al z M m O4 In the Chemical Formula A, M is Ti, Zr, Mn, or Ni, 5 ≤ x ≤ 7, 0 < y ≤ 0.5, 0 < z ≤ 0.5, 0 < y + z + m < 1, and 0 ≤ m ≤ 0.5.

[0010] A further embodiment of the present application provides a positive electrode for a lithium secondary battery including a positive electrode current collector; and a positive electrode active material layer provided on the positive electrode current collector and containing the composition according to the above-described embodiment.

[0011] A further embodiment of the present application is a lithium secondary battery including a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the positive electrode active material layer contains the composition according to the above-described embodiment, and provides a lithium secondary battery.

[0012] According to a further embodiment of the present application, the negative electrode active material layer of the foregoing embodiment contains 10 parts by weight or more of silicon-based oxide with respect to 100 parts by weight of the total negative electrode active material.

[0013] A further embodiment of the present application provides a battery module including the foregoing lithium secondary battery, and a battery pack including the battery module.

Advantages of the Invention

[0014] According to the embodiments described in this specification, it is possible to increase the energy density of a lithium secondary battery designed within a limited space, improve the high-output performance, and also improve the battery cycle performance.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. At this time, the terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0017] In this specification, terms such as "comprising", "providing", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0018] Also, when a certain part such as a layer is present "on" or "above" another part, this includes not only the case where it is present "directly above" the other part, but also the case where there are other parts in between. Conversely, when a certain part is present "directly above" another part, it means that there are no other parts in between. Also, being present "on" or "above" the reference part does not necessarily mean being located "above" or "upper" in the opposite direction of gravity, but rather being located above or below the reference part.

[0019] One embodiment of the present application is a positive electrode active material including a lithium composite transition metal compound containing nickel, cobalt, and manganese and containing 80 mol% or more and less than 100 mol% of nickel among metals excluding lithium; and an additive represented by the following Chemical Formula A to provide a composition for a positive electrode active material layer of a lithium secondary battery: [Chemical Formula A] Li x Co (1-y-z-m) Zn y Al z M m O4 In the above Chemical Formula A, M is Ti, Zr, Mn, or Ni, 5 ≦ x ≦ 7, 0 < y ≦ 0.5, 0 < z ≦ 0.5, 0 < y + z + m < 1, 0 ≦ m ≦ 0.5.

[0020] Lithium secondary batteries have sizes required according to their applications and must be designed within limited spaces accordingly. Although the demands of consumers for increased energy density and improved high-power performance are increasing, when using a cathode material with a high capacity, the content of the anode material must be increased to match it. Therefore, there are limitations in enhancing the efficiency of the battery within a limited space. Also, depending on the type of anode material, it is necessary to design a cathode material having an efficiency that matches the efficiency of the anode material.

[0021] The composition for a cathode active material layer according to the above-described embodiment of the present invention is useful when using a silicon-based oxide as the anode active material. Specifically, when using a silicon-based oxide as the anode active material, it is characterized in that a specific composition is used as the cathode material so as to match the efficiency of the anode active material. In particular, a lithium composite transition metal oxide containing nickel, cobalt, and manganese is used as the cathode active material. At this time, those in which the content of nickel among the metals excluding lithium is contained at 80 mol% or more and less than 100 mol% are used, and a specific type of additive is used together therewith.

[0022] The silicon-based oxide used as the anode active material has an efficiency, for example, the ratio of the discharge capacity to the charge capacity in the first cycle (charge 0.1C ~ 5mV, 0.005C cut-off, discharge 0.1C ~ 1.5V) is usually 70% to 90%, and the discharge capacity is at the level of 1,000 to 1,600 mAh / g. Thus, the silicon-based oxide has a high capacity and can be used for increasing the energy density of the battery and realizing high power. However, it has lower efficiency than graphite, and it is necessary to lower the efficiency of the cathode so as to match the efficiency of the anode.

[0023] Therefore, in the above-described embodiment, a silicon-based oxide is used as the anode active material, and a high-capacity material with a relatively high nickel content is used as the cathode active material. At this time, by using a specific type of additive, the efficiency of the cathode can be made to match the efficiency according to the type of the anode active material.

[0024] Specifically, it is characterized by using the material of Chemical Formula A described above as an additive. The additive of Chemical Formula A can provide a lithium-ion source or storage site to compensate for the irreversible capacity loss of the silicon-based oxide used as the negative electrode active material, while having the property of being less efficient compared to general positive electrode active materials. Also, compared to LiNiO2, the material of Chemical Formula A has a higher capacity and can be used by blending a relatively small amount. LiNiO2 is vulnerable to exposure to moisture in the air, resulting in gas generation in the battery, deterioration of thermal stability, and an increase in by-products in the slurry, which can cause gelation, such as the gelation problem of PVDF. In contrast, the material of Chemical Formula A can play a role in matching the capacity and efficiency of the positive electrode with the negative electrode even in a relatively small amount, and can ensure moisture stability and slurry stability compared to other materials such as LiNiO2.

[0025] According to a further embodiment of the present application, the lithium composite transition metal compound containing nickel, cobalt, and manganese and containing nickel in an amount of 80 mol% or more and less than 100 mol% among the metals excluding lithium may include one or more mixtures represented by the following Chemical Formula 1.

[0026] [Chemical Formula 1] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0027] In the above formula, Q is any one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, and 1 ≦ a ≦ 1.5, 0 < b ≦ 0.5, 0 < c ≦ 0.5, 0 ≦ d ≦ 0.1, 0 < b + c + d ≦ 0.2, -0.1 ≦ δ ≦ 1.0.

[0028] In the lithium composite transition metal oxide of Chemical Formula 1, Li may be contained in an amount corresponding to a, that is, 1 ≤ a ≤ 1.5. If a is less than 1, the capacity may decrease. If a exceeds 1.5, the particles may sinter in the firing process, making it difficult to manufacture the positive electrode active material. Considering the significance of the improvement effect of the capacity characteristics of the positive electrode active material by controlling the content of Li and the balance of the sinterability during the manufacture of the active material, the Li may more preferably be contained in an amount of 1.1 ≤ a ≤ 1.2.

[0029] In the lithium composite transition metal oxide of Chemical Formula 1, Ni may be contained in an amount corresponding to 1-(b + c + d), for example, 0.8 ≤ 1-(b + c + d) < 1. If the content of Ni in the lithium composite transition metal oxide of Chemical Formula 1 is 0.8 or more, a sufficient amount of Ni contributing to charge and discharge can be ensured, and high capacity can be achieved. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.8 or more, preferably 0.83 or more, and more preferably 0.85 or more. Preferably, 1-(b + c + d), which is the content of Ni, may be 0.99 or less, 0.96 or less.

[0030] In the lithium composite transition metal oxide of Chemical Formula 1, Co may be contained in an amount corresponding to b, that is, 0 < b ≤ 0.5. If the content of Co in the lithium composite transition metal oxide of Chemical Formula 1 exceeds 0.5, there is a risk of increased cost. Considering the significance of the improvement effect of the capacity characteristics by containing Co, the Co may more specifically be contained in an amount of 0.03 ≤ b ≤ 0.2, for example, 0.05 ≤ b ≤ 0.1.

[0031] In the lithium composite transition metal oxide of Chemical Formula 1, Mn may be contained in an amount corresponding to c, that is, 0 < c ≤ 0.5. If c in the lithium composite transition metal oxide of Chemical Formula 1 exceeds 0.5, there is a risk that the output characteristics and capacity characteristics of the battery may instead decrease. The Mn may more specifically be contained in an amount of 0.01 ≤ c ≤ 0.2, 0.02 ≤ c ≤ 0.06.

[0032] In the lithium composite transition metal oxide of the foregoing Chemical Formula 1, Q may be a doping element contained in the crystal structure of the lithium composite transition metal oxide, and Q may be contained in an amount corresponding to d, that is, 0 ≦ d ≦ 0.1, preferably 0.005 ≦ d ≦ 0.05. Q may be one or more selected from Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr. For example, Q may be Al.

[0033] The above-described lithium composite transition metal oxide may have the form of secondary particles. The secondary particles mean a form formed by aggregation of dozens to hundreds of primary particles, and can be distinguished from the concept of single particles composed of one primary particle or aggregated particles of 10 or fewer primary particles.

[0034] The particle size of the secondary particles is D 50 may be 1 μm to 20 μm, preferably 5 μm to 10 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0035] The secondary particles may include a first particle having a relatively large particle size and a second particle having a relatively small particle size, and the particle size distribution may be in a bi-modal state. At this time, based on 100 total parts by weight of the secondary particles, the content of the first particles may be larger than the content of the second particles. For example, based on 100 total parts by weight of the secondary particles, the first particles may be contained in an amount of 60 parts by weight or more and less than 100 parts by weight, 70 parts by weight or more and 90 parts by weight or less, and the second particles may be contained in an amount of more than 0 parts by weight and 40 parts by weight or less, 10 parts by weight or more and 30 parts by weight or less. The D 50 of the first particles may be 5 μm to 15 μm, preferably 8 μm to 10 μm, and the D 50It may be 1 μm to 8 μm, preferably 3 μm to 5 μm.

[0036] The first particles and the second particles may have the same composition of elements such as Ni, Co, Mn, and Al, or may be different from each other. For example, the Ni content of the first particles may be higher than the Ni content of the second particles. The first particles may contain Al as Q in Chemical Formula 1, and the second particles may have d, which is the content of Q, equal to 0.

[0037] In one embodiment of the present application, the additive represented by Chemical Formula A is represented by the following Chemical Formula A: [Chemical Formula A] Li x Co (1-y-z-m) Zn y Al z M m O4

[0038] In Chemical Formula A, M is Ti, Zr, Mn, or Ni, 5 ≤ x ≤ 7, 0 < y ≤ 0.5, 0 < z ≤ 0.5, 0 < y + z + m < 1, and 0 ≤ m ≤ 0.5.

[0039] In Chemical Formula A, when m is 0, it may be represented by the following Chemical Formula A-1.

[0040] [Chemical Formula A-1] Li x Co (1-y-z-m) Zn y Al z O4

[0041] When M is present, M may be Ti, Zr, Mn, or Ni, and for example, may be Zr.

[0042] In Chemical Formulas A and A-1, 5.5 ≤ x ≤ 6.5, 0.2 ≤ y ≤ 0.4, 0 < z ≤ 0.1, and 0 ≤ m ≤ 0.1 may also be satisfied.

[0043] In one embodiment of the present application, the additive represented by the chemical formula A may be contained in an amount of 0.5 parts by weight to 10 parts by weight, or may be contained in an amount of 1 part by weight to 5 parts by weight, based on 100 parts by weight of the above-described positive electrode active material.

[0044] The additive represented by the chemical formula A may be contained in an amount of 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight or more, 1.1 parts by weight or more, or 1.3 parts by weight or more, based on 100 parts by weight of the positive electrode active material. The additive represented by the chemical formula A may be contained in an amount of 10 parts by weight or less, 9 parts by weight or less, 8 parts by weight or less, 7 parts by weight or less, 6 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, 3 parts by weight or less, or 2 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0045] Using the content within such a range is advantageous for matching the efficiency of the positive electrode and the negative electrode by adding the additive represented by the chemical formula A. It is preferable that the efficiency of the positive electrode due to the combination of the single-particle positive electrode active material contained in the positive electrode and the additive represented by the chemical formula A is designed to be lower than the efficiency of the negative electrode due to the negative electrode active material containing a silicon-based oxide or a silicon-based oxide and a carbon-based active material. Therefore, the content of the additive represented by the chemical formula A can be determined according to the capacity and efficiency of the active materials of the positive electrode and the negative electrode, and in particular, can be determined according to the content of the silicon-based oxide.

[0046] According to a further embodiment of the present application, in the composition for a positive electrode active material layer according to the above-described embodiment, the lithium composite transition metal compound containing nickel in an amount of 80 mol% or more and less than 100 mol% among the metals containing nickel, cobalt, and manganese and excluding lithium may be 90 parts by weight to 100 parts by weight, for example, 100 parts by weight, based on 100 parts by weight of the total positive electrode active material.

[0047] According to a further embodiment of the present application, the composition for a positive electrode active material layer according to the above-described embodiment may further contain a positive electrode binder and a conductive material.

[0048] The positive electrode binder can play a role in improving the adhesion between positive electrode active material particles and the adhesive force between the positive electrode active material particles and the positive electrode current collector. As the positive electrode binder, any material well-known in the technical field can be used. Non-limiting examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0049] The positive electrode binder may be included in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the composition for the positive electrode active material layer. For example, preferably, it may be included in an amount of 0.3 part by weight or more and 35 parts by weight or less, more preferably 0.5 part by weight or more and 20 parts by weight or less.

[0050] The conductive material contained in the composition for the positive electrode active material layer is used to impart conductivity to the electrode, and any material having electron conductivity without causing a chemical change in the battery can be used without particular limitation. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0051] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The conductive material may be included in an amount of 0.1 parts by weight or more and 2 parts by weight or less based on 100 parts by weight of the composition for the positive electrode active material layer. For example, it may preferably be included in an amount of 0.3 parts by weight or more and 1.5 parts by weight or less, and more preferably 0.5 parts by weight or more and 1.2 parts by weight or less.

[0052] According to a further embodiment of the present application, the composition for the positive electrode active material layer has a viscosity of 10,000 cps or less when stored at 40 °C and RH 10% for 3 days. The viscosity may be the viscosity of the slurry when stored in an environment of 40 °C and RH 10% for 3 days after manufacturing the positive electrode slurry using the composition for the positive electrode active material layer.

[0053] The viscosity is a value measured using a Brookfield viscometer with a No. 64 spindle at 12 rpm, and the RH 10% means a humidity range.

[0054] The composition for the positive electrode active material layer may have a viscosity of 1000 cps or more, 2000 cps or more, 3000 cps or more, or 4000 cps or more when stored at 40 °C and RH 10% for 3 days. The composition for the positive electrode active material layer may have a viscosity of 10,000 cps or less, 9000 cps or less, or 8500 cps or less when stored at 40 °C and RH 10% for 3 days.

[0055] By including the additive represented by Chemical Formula A, the composition for the positive electrode active material layer can satisfy the above range, which is advantageous for ensuring moisture stability and slurry stability. Specifically, LiNiO2 is vulnerable to exposure to moisture in the air, resulting in an increase in by-products in the slurry and causing problems such as gelation, for example, gelation of PVDF. However, the additive represented by Chemical Formula A can play a role in matching the capacity and efficiency of the positive electrode with the negative electrode even in a relatively small amount, and can prevent gelation in the slurry and ensure slurry stability compared to other materials such as LiNiO2.

[0056] A further embodiment of the present application is a positive electrode current collector; and a positive electrode active material layer provided on the positive electrode current collector and containing the composition for the positive electrode active material layer according to the above-described embodiment and provides a positive electrode for a lithium secondary battery.

[0057] A further embodiment of the present application is a lithium secondary battery including a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the positive electrode active material layer contains the composition for the positive electrode active material layer according to the above-described embodiment, and provides a lithium secondary battery.

[0058] According to a further embodiment of the present application, in the lithium secondary battery according to the above-described embodiment, the silicon-based oxide is contained in an amount of 10 parts by weight or more with respect to 100 parts by weight of the negative electrode active material contained in the negative electrode active material layer.

[0059] The silicon-based oxide may be contained in an amount of 10 parts by weight or more and 70 parts by weight or less, preferably 10 parts by weight or more and 60 parts by weight or less, with respect to 100 parts by weight of the negative electrode active material contained in the negative electrode active material layer.

[0060] The silicon-based oxide may be contained in an amount of 15 parts by weight or more, 15.5 parts by weight or more, 16 parts by weight or more, 16.5 parts by weight or more, or 17 parts by weight or more with respect to 100 parts by weight of the negative electrode active material contained in the negative electrode active material layer. The silicon-based oxide may be contained in an amount of 70 parts by weight or less, 60 parts by weight or less, 30 parts by weight or less, 20 parts by weight or less, or less than 20 parts by weight with respect to 100 parts by weight of the negative electrode active material contained in the negative electrode active material layer.

[0061] Using a silicon-based oxide within the above range is advantageous for realizing high capacity and high output performance. For example, increasing the content of the silicon oxide is advantageous for realizing high capacity and high output. However, since the thickness of the negative electrode can be reduced, it is necessary to design an appropriate thickness range for realizing processability in a mass production line. By using the silicon-based oxide within the above range, it is possible to achieve high output performance and processability.

[0062] The silicon-based oxide contained in the negative electrode active material layer may be present in a particulate state and may contain SiO x (0 < x < 2). The SiO x (0 < x < 2) may correspond to a matrix within the silicon-based oxide particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based oxide particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0063] In a further embodiment of the present application, the silicon-based oxide may further contain a metal or a metal oxide. For example, the silicon-based oxide may further contain at least one of Li and Mg or a compound phase thereof.

[0064] When the silicon-based oxide contains Mg, the Mg may exist as a Mg compound phase. The Mg compound phase may contain, for example, at least any one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may contain at least any one of Mg2SiO4 and MgSiO3. The Mg silicide may contain Mg2Si. The Mg oxide may contain MgO.

[0065] When the silicon-based oxide contains Li, the Li may exist as a Li compound phase. The Li compound phase may exist in at least one form among lithium silicate, lithium silicide, and lithium oxide. The Li compound phase may be lithium silicate, for example, Li a Si b O c (where 2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and more specifically, it may contain one or more selected from the group consisting of Li2SiO3, Li2Si2O5, Li3SiO3, and Li4SiO4.

[0066] The Mg compound and / or Li compound may be distributed on the surface and / or inside of the silicon-based compound particles in a form doped into the particles of the silicon-based oxide. The Mg compound and / or Li compound is distributed on the surface and / or inside of the silicon-based oxide particles, and can control the expansion / contraction of the volume of the silicon-based oxide particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the Mg compound and / or the Li compound may be included in terms of reducing the proportion of the irreversible phase (for example, SiO2) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0067] The content of the Mg element or Li element can be confirmed by ICP analysis. For the ICP analysis, after accurately sampling a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300), at the wavelength specific to the Mg element or Li element, the intensity of the standard solution prepared using a standard solution (5 mg / kg) is measured to create a reference calibration curve. Then, the pretreated sample solution and the blank sample are introduced into the instrument, the intensity of each is measured to calculate the actual intensity, after calculating the concentration of each component with respect to the created calibration curve, it is converted so that the overall sum becomes the theoretical value, and the content of the Mg element of the manufactured negative electrode active material can be analyzed.

[0068] When Mg and / or Li are contained in the silicon-based oxide particles, the content of each of them may be contained in an amount of 0.1 atm% to 20 atm% with respect to 100 atm% of the Si element.

[0069] According to one embodiment, the silicon-based oxide particles may further include a carbon layer provided on at least a part of the surface.

[0070] The carbon layer may cover the entire surface of the silicon-based oxide particles, or may be in a state of covering only a part. The carbon layer imparts conductivity to the silicon-based oxide particles, and the volume change of the negative electrode active material including the silicon-based oxide particles can be effectively suppressed, and the life characteristics of the battery can be improved.

[0071] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0072] The crystalline carbon can further improve the conductivity of the silicon-based oxide particles. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0073] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based oxide particles. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based substance formed using a hydrocarbon as a source of chemical vapor deposition method.

[0074] The carbide of the other organic substances may be a carbide of an organic substance selected from the carbides of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose and combinations thereof.

[0075] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. Examples of the substituted or unsubstituted aromatic hydrocarbon as the aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0076] In one embodiment, the carbon layer may be contained in an amount of 1 wt% to 50 wt%, specifically 5 wt% to 45 wt%, more specifically 8 wt% to 40 wt%, based on 100 wt% of the total amount of the silicon-based oxide particles. When the above range is satisfied, the conductivity of the negative electrode active material can be improved, the volume change of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the life characteristics of the battery can be improved.

[0077] In one embodiment, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the above range is satisfied, the volume change of the negative electrode active material can be easily suppressed, the side reaction between the electrolyte and the negative electrode active material can be suppressed, and the life characteristics of the battery can be improved.

[0078] When the silicon-based oxide particles contain Mg and / or Li, this may be produced by a method including a step of doping the silicon-based oxide particles with Mg and / or Li.

[0079] For example, silicon-based oxide particles containing Mg can use the in-situ doping method. As an example, the step of manufacturing the silicon-based oxide particles containing Mg may be formed by a step of vaporizing Si powder and SiO2 powder and Mg respectively and then mixing them to form a mixed gas, and a step of heat-treating the mixed gas at 800 °C to 950 °C in a vacuum state. As another example, the step of manufacturing silicon-based oxide particles containing Mg may be formed by a step of mixing the powder of Si powder and SiO2 powder and Mg, then vaporizing all of them to form a mixed gas; and a step of heat-treating the mixed gas at 800 °C to 950 °C in a vacuum state.

[0080] The mixed powder of the Si powder and the SiO2 powder may be heat-treated and vaporized at 1,000 °C to 1,800 °C or 1,200 °C to 1,500 °C, and the Mg powder may be heat-treated and vaporized at 500 °C to 1,200 °C or 600 °C to 800 °C. By making the materials react in a gaseous state in this way, Mg can be uniformly distributed in the silicon-based oxide particles. In the silicon-based oxide particles, the Mg compound phase may include the aforementioned Mg silicate, Mg silicide, Mg oxide, etc. The silicon-based oxide particles containing Mg manufactured by the method as described above may have their particle size adjusted by a pulverization method such as the mechanical milling method as needed.

[0081] As a further example, the silicon-based oxide particles containing Li may be carried out by an ex-situ doping method. For example, the step of distributing Li in the silicon-based oxide particles may include a step of forming a carbon layer on the surface of the silicon-based oxide particles, and a step of distributing Li in the silicon-based oxide particles on which the carbon layer is formed.

[0082] The step of forming a carbon layer on the surface of the silicon-based oxide particles may be carried out by injecting a carbon-based raw material gas such as methane gas and performing heat treatment in a rotating tubular furnace. Specifically, the silicon-based oxide particles are charged into a rotating tubular furnace and heated at a rate of 3 °C / min to 10 °C / min, or at a rate of about 5 °C / min, to 800 °C to 1,150 °C, 900 °C to 1,050 °C, or 950 °C to 1,000 °C. While rotating the rotating tubular furnace, argon gas and a carbon-based material raw material gas are flowed, and heat treatment is performed for 30 minutes to 8 hours to form a carbon layer.

[0083] The step of distributing Li to the silicon-based oxide particles on which the carbon layer is formed may be carried out by mixing the silicon-based oxide particles on which the carbon layer is formed with lithium metal powder or a lithium precursor, for example, LiOH, Li2O, and performing heat treatment at 400 °C to 1,200 °C if necessary. Alternatively, the step may be carried out using an electrochemical method.

[0084] If necessary, both of the aforementioned in-situ doping of Mg and ex-situ doping of Li may be carried out to produce silicon-based oxide particles containing both Mg and Li.

[0085] As an example, the method may include a step of forming a carbon layer on at least a part of the surface of silicon oxide particles, and a step of doping Mg and Li into the silicon oxide particles on which the carbon layer is formed.

[0086] Before or after forming the carbon layer, the particle size of the silicon-based oxide particles may be adjusted by a pulverization method such as a mechanical milling method if necessary.

[0087] The step of forming a carbon layer on the surface of the silicon-based oxide particles may be performed, for example, by injecting a carbon-based raw material gas such as methane gas and performing heat treatment in a rotary tubular furnace. Specifically, the silicon-based oxide particles are charged into a rotary tubular furnace and heated at a rate of 3°C / min to 10°C / min, or at a rate of about 5°C / min, to 800°C to 1,150°C, 900°C to 1,050°C, or 950°C to 1,000°C. While rotating the rotary tubular furnace, argon gas and a carbon-based material raw material gas are passed through, and heat treatment may be performed for 30 minutes to 8 hours to form a carbon layer.

[0088] The step of doping Li and Mg into the silicon-based oxide particles having the carbon layer formed thereon may be performed by mixing the silicon-based oxide particles having the carbon layer formed thereon with a doping material, for example, magnesium metal powder or a magnesium precursor, for example, MgO; lithium metal powder or a lithium precursor, for example, LiOH, Li2O, and performing heat treatment at 400°C to 1,200°C if necessary. Alternatively, the step may be performed using an electrochemical method.

[0089] According to another embodiment of the present invention, the average particle diameter (D 50 ) of the silicon-based oxide particles may be 1 μm to 30 μm. Specifically, the average particle diameter (D 50 ) of the silicon-based oxide particles may be 3 μm to 20 μm, and more specifically, may be 5 μm to 10 μm. When the above range is satisfied, the side reaction between the negative electrode active material and the electrolyte can be controlled, and the discharge capacity and initial efficiency of the battery can be effectively realized. In this specification, the average particle diameter (D 50 ) can be defined as the particle diameter corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The average particle diameter (D 50 ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters in the range from the submicron region to about several mm, and can obtain highly reproducible and highly resolvable results.

[0090] According to another embodiment of the present invention, the BET specific surface area of the silicon-based oxide particles may be 0.01 m 2 / g to 150 m 2 / g. The BET specific surface area of the silicon-based oxide particles is preferably 0.1 m 2 / g to 100 m 2 / g, particularly preferably 0.2 m 2 / g to 80 m 2 / g, specifically 0.6 m 2 / g to 20 m 2 / g, and more specifically may be 0.8 m 2 / g to 15 m 2 / g. When the above range is satisfied, the side reaction between the electrolyte and the negative electrode active material during charging and discharging of the battery can be reduced, so that the life characteristics of the battery can be improved. The BET specific surface area can be measured by the BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by the BET six-point method by the nitrogen gas adsorption flow method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

[0091] According to another embodiment of the present invention, the silicon-based oxide particles may further contain Si crystal grains. The Si crystal grains may have a particle size of 1 nm to 15 nm.

[0092] According to a further embodiment of the present application, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material may further contain a carbon-based active material.

[0093] In one embodiment of the present application, the negative electrode active material may contain a carbon-based active material. Specifically, the carbon-based active material may be graphite. The graphite may be natural graphite, artificial graphite, or a mixture thereof. Based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the carbon-based active material may be contained in an amount exceeding 0 parts by weight and not exceeding 85 parts by weight.

[0094] According to a further embodiment of the present application, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material layer may further include a negative electrode binder in addition to the silicon-based oxide and the carbon-based active material.

[0095] The negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive force between the negative electrode active material particles and the negative electrode current collector. As the negative electrode binder, any material well-known in the art can be used. Non-limiting examples include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and at least any one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and various copolymers thereof may also be included.

[0096] The negative electrode binder may be included in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the negative electrode active material layer. For example, preferably 0.3 part by weight or more and 35 parts by weight or less, more preferably 0.5 part by weight or more and 20 parts by weight or less.

[0097] The negative electrode active material layer may further contain a conductive material. The conductive material contained in the negative electrode active material layer is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 to 30 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0098] In one embodiment of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0099] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive electrode current collector may usually have a thickness of 1 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven bodies.

[0100] In one embodiment of the present application, the negative electrode current collector may be any material that does not cause a chemical change in the battery and has conductivity, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0101] In one embodiment of the present application, the thickness of the positive electrode and the negative electrode active material layer may be 20 μm or more and 500 μm or less, for example, 50 μm or more and 200 μm or less. According to an example, the thickness of the positive electrode active material layer may be 90% to 110%, for example, 95% to 105% of the thickness of the negative electrode active material layer, and these thicknesses may be the same.

[0102] In one embodiment of the present application, the ratio (C / A) of the efficiency (C) of the positive electrode to the efficiency (A) of the negative electrode may be 1 or less, preferably less than 1. The ratio (C / A) may be 0.8 or more, preferably 0.9 or more, more preferably 0.95 or more, for example, 0.96 or more, or 0.97 or more. Also, in one embodiment of the present application, the difference between the efficiency (C) of the positive electrode and the efficiency (A) of the negative electrode may be 10% or less, for example, 5% or less, or 3% or less. Further, in one embodiment of the present application, the efficiency (C) of the positive electrode and the efficiency (A) of the negative electrode are preferably 80% or more, more preferably 83% or more, and even more preferably 85% or more, respectively. When the positive electrode and the negative electrode have the efficiencies as described above, the irreversible capacity of the positive electrode is further increased, and the capacity expression of the target high capacity is possible from the initial stage.

[0103] In one embodiment of the present application, the ratio (AA / BB) of the content (AA) of the additive represented by Chemical Formula A to 100 parts by weight of the positive electrode active material and the content (BB) of the silicon-based oxide to 100 parts by weight of the negative electrode active material may be 0.01 to 0.5, more preferably 0.05 to 0.5, and even more preferably 0.1 to 0.3.

[0104] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Generally, any separator that can be used in a secondary battery can be used without particular limitation. In particular, it is preferably low resistance to the ion migration of the electrolyte and excellent in the ability to hold the electrolyte solution. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Further, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single layer or a multilayer structure.

[0105] Examples of the electrolyte 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.

[0106] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0107] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate may be used.

[0108] In particular, ethylene carbonate and propylene carbonate which are cyclic carbonates among the carbonate-based organic solvents are preferably used as high-viscosity organic solvents because they have a high dielectric constant and can dissociate lithium salts well. When such cyclic carbonates are mixed and used in an appropriate ratio with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be produced, so they can be more preferably used.

[0109] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily soluble in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- 、(CF3SO2)2N - 、(FSO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - 、and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0110] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, and the like.

[0111] The lithium secondary battery according to an embodiment of the present invention may be a cylindrical battery. The cylindrical battery may mean that the shape of the battery itself including the assembly containing the positive electrode, negative electrode, separator, and electrolyte is cylindrical. Specifically, it may be composed of a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap. It is preferably used for a cylindrical battery that is more free in gas amount than a pouch, but is not limited thereto.

[0112] A further embodiment of the present invention provides a battery module including the above-described cylindrical battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0113] The lithium secondary battery according to an embodiment of the present invention can be used not only for portable devices such as mobile phones, notebook computers, and digital cameras but also as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems because it stably exhibits excellent discharge capacity, output characteristics, and cycle performance. For example, the battery module or the battery pack can be used as a power source for any one or more of medium to large-sized devices such as power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); or power storage systems.

[0114] Hereinafter, preferred examples are presented to assist in understanding the present invention. However, it is obvious to those skilled in the art that the following examples are merely illustrative of the description and various changes and modifications are possible within the scope of the description and the scope of the technical idea, and such variations and modifications naturally belong to the scope of the appended claims.

[0115] <Example 1> Based on 100 parts by weight of the positive electrode active material layer, a lithium composite transition metal compound in the form of secondary particles having a content of 88 mol% of Ni, 7 mol% of Co, 4 mol% of Mn, and 1.8 mol% of Al among metals excluding lithium as the positive electrode active material and Li6Co 0.7 Zn 0.25 Al 0.05An O4 additive (1.3 parts by weight based on 100 parts by weight of the positive electrode active material), 97.49 parts by weight, 1.85 parts by weight of PVDF as a binder, and 0.66 parts by weight of a CNT pre-dispersion liquid containing CNT and a dispersant as a conductive material were used to coat a positive electrode active material layer composition on an aluminum foil with a thickness of 30 μm so that the dry thickness became 80 μm, and then dried to produce a positive electrode.

[0116] Based on 100 parts by weight of the negative electrode active material layer, 98.10 parts by weight of artificial graphite and natural graphite (weight ratio of 7:3, 90 parts by weight based on 100 parts by weight of the negative electrode active material) and SiO which is a silicon-based oxide (10 parts by weight based on 100 parts by weight of the negative electrode active material), 1 part by weight of SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose) as a binder were included. In addition, a negative electrode active material layer forming composition containing 0.9 parts by weight of a CNT pre-dispersion liquid containing a dispersant and single-layer CNT was coated on a copper foil with a thickness of 15 μm so that the dry thickness became 80 μm, and then dried to produce a negative electrode.

[0117] A separator was interposed between the positive electrode and the negative electrode and laminated, and an electrolytic solution (1.3M LiPF6, VC2 / SN (succinonitrile) = 0.5%) was injected to fabricate a battery.

[0118] The content of the additive was set to 1.3 parts by weight based on 100 parts by weight of the positive electrode active material so that the efficiency of the positive electrode was about 87%. After producing a positive electrode slurry using the positive electrode active material layer composition containing this, the viscosity of the slurry was measured by storing it in an environment of 40°C and RH 10%, and the results are shown in Table 1.

[0119] <Example 2> A negative electrode was produced in the same manner as in Example 1, except that 5 parts by weight of SiO which is a silicon-based oxide was included based on 100 parts by weight of the negative electrode active material.

[0120] <Example 3> A negative electrode was manufactured in the same manner as in Example 1, except that 15 parts by weight of SiO, which is a silicon-based oxide, was included based on 100 parts by weight of the negative electrode active material.

[0121]

Table 1

[0122] Referring to Table 1, Example 1 contains 10 parts by weight of SiO, which is a silicon-based oxide, and 90 parts by weight of graphite based on 100 parts by weight of the negative electrode active material according to the present invention. Example 2 contains 5 parts by weight of SiO, which is a silicon-based oxide, and 95 parts by weight of graphite. Example 3 contains 15 parts by weight of SiO, which is a silicon-based oxide, and 85 parts by weight of graphite. It can be confirmed that the designed capacity of Example 2 decreases by 6% compared to Example 1. Thus, it can be seen that when the content of SiO, which is a silicon-based oxide, in the negative electrode active material is less than 10 parts by weight, the designed capacity of the lithium secondary battery decreases.

[0123] In addition, charge and discharge were performed at 25 °C on the batteries manufactured in Examples 1 to 3 to evaluate the energy retention rate (%), which is shown in FIG. 1.

[0124] Charging conditions: CCCV 4.2V 1C 1 / 20C cut-off (at 25 °C) / rest 30 min Discharging conditions: CC 1C 2.5V cut-off (at 25 °C) / rest 30 min

[0125] The energy retention rate (%) was derived by the following calculations respectively. Capacity retention rate (%) = (discharge capacity at the Nth time / discharge capacity at the first time) × 100 Energy retention rate (%) = capacity retention rate (%) × nominal voltage

[0126] FIG. 1 shows the cycle number (N)-energy retention rate (%) curve as a graph of the 25° C. cycle in which charging and discharging were performed at 25° C., and the energy retention rate when the cycle number advanced to 100 times was shown in Remark of Table 1 above.

[0127] In Examples 1 to 3, it was confirmed that the energy retention rate was maintained relatively high. In particular, in Example 1, it was confirmed that the energy retention rate was 80% or more and the capacity retention rate was maintained high when the 25° C. cycle advanced 100 times. From this, it can be seen that it is important to set an appropriate efficiency between the positive electrode and the negative electrode.

[0128] <Comparative Example 1> A positive electrode was manufactured in the same manner as in Example 1, except that the additive contained in the positive electrode active material layer was LiNiO2 (4.5 parts by weight based on 100 parts by weight of the positive electrode active material).

[0129] The content of LiNiO2 was set to 4.5 parts by weight based on 100 parts by weight of the positive electrode active material so that the efficiency of the positive electrode was about 87%, and the viscosity of the slurry was measured in the same manner as in Example 1, and the results are shown in Table 2.

[0130]

Table 2

[0131] Referring to Table 2, Example 1 contains the additive represented by Chemical Formula A according to the present invention. After manufacturing the positive electrode slurry using the composition for the positive electrode active material layer, the viscosity did not exceed 10,000 cps or gelate until the third day of storage in an environment of 40° C. and RH 10%, and maintained a viscosity range of 10,000 cps or less, which was confirmed to be advantageous for the stability of the slurry.

[0132] In contrast, Comparative Example 1 contains LiNiO2 which is not the additive represented by Chemical Formula A according to the present invention. After manufacturing the positive electrode slurry using the composition for forming the positive electrode active material layer, the viscosity on the first day of storage in an environment of 40°C and RH 10% was 9,000 cps, and it was confirmed that gelation occurred on the second day of storage. In the case of LiNiO2, it was confirmed that gelation occurred due to a rapid increase in viscosity, which may affect the processability during the manufacture of the electrode, and thus there is a problem that the stability of the slurry decreases.

[0133] <Comparative Example 2> A positive electrode was manufactured in the same manner as in Example 1, except that LiMn2O4 was included as the positive electrode active material.

[0134] Table 3 shows the contents of the positive electrode material and SiO, which is a silicon-based oxide, with respect to 100 parts by weight of the negative electrode active material for Example 1 and Comparative Example 2.

[0135]

Table 3

[0136] Referring to Table 3, Example 1 contains the positive electrode active material and additive according to the present invention, and Comparative Example 2 contains an LMO positive electrode material (LiMn2O4) which is not the positive electrode active material according to the present invention. It can be confirmed that the designed capacity of Comparative Example 2 decreases by 40% compared to Example 1, and thus it can be seen that when the positive electrode active material according to the present invention is not included, the designed capacity of the lithium secondary battery decreases.

[0137] Figure 2 is a graph showing the occurrence or non-occurrence of voltage drop during high-temperature (60°C) storage of the batteries manufactured in Example 1 and Comparative Example 2 and the increase in resistance due to high-temperature (60°C) storage.

[0138] Charging conditions: 0.25C 4.2V, 250 mA cut-off (at 25°C), stored at 60°C

[0139] Referring to FIG. 2, no voltage drop phenomenon should occur until about the 30th day during storage at the high temperature (60°C). However, in Comparative Example 2, a voltage drop phenomenon occurred on about the 20th day during storage at the high temperature (60°C), and it was confirmed that an increase in resistance due to storage at the high temperature (60°C) appeared. On the other hand, in Example 1, it was confirmed that the voltage was maintained almost constant even on about the 60th day, and the increase in resistance due to storage at the high temperature (60°C) was relatively small. This shows that the positive electrode active material according to the present invention is advantageous in terms of the designed capacity, voltage drop during storage at the high temperature (60°C), and increase in resistance due to storage at the high temperature (60°C).

Claims

1. A cylindrical lithium secondary battery comprising a positive electrode, a negative electrode, a separator provided between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the positive electrode active material layer includes a composition for a positive electrode active material layer of a lithium secondary battery, the composition for the positive electrode active material layer includes a positive electrode active material containing a lithium composite transition metal compound containing nickel, cobalt, and manganese and containing 80 mol% or more and less than 100 mol% of nickel among the metals excluding lithium; and an additive represented by the following Chemical Formula A A cylindrical lithium secondary battery comprising: [Chemical Formula A] Li ｘ Co （１－ｙ－ｚ－ｍ） Zn ｙ Al ｚ M ｍ O ４ In the Chemical Formula A, M is Ti, Zr, Mn, or Ni, 5 ≤ x ≤ 7, 0 < y ≤ 0.5, 0 < z ≤ 0.5, 0 < y + z + m < 1, and 0 ≤ m ≤ 0.

5.

2. The lithium secondary battery according to Claim 1, wherein the additive is contained in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the positive electrode active material.

3. The lithium secondary battery according to Claim 1, wherein the lithium composite transition metal compound containing nickel, cobalt, and manganese and containing 80 mol% or more and less than 100 mol% of nickel among the metals excluding lithium is contained in an amount of 90 parts by weight to 100 parts by weight based on 100 parts by weight of all the positive electrode active materials.

4. The lithium secondary battery according to Claim 1, further comprising a positive electrode binder and a conductive material.

5. The lithium secondary battery according to Claim 1, wherein the composition for the positive electrode active material layer has a viscosity of 10,000 cps or less when stored at 40°C and 10% RH for 3 days.

6. The lithium secondary battery according to Claim 1, wherein the negative electrode active material layer contains 10 parts by weight or more of a silicon-based oxide based on 100 parts by weight of all the negative electrode active materials.

7. The lithium secondary battery according to Claim 6, wherein the negative electrode active material layer further contains a carbon-based active material.

8. The lithium secondary battery according to Claim 6, wherein the silicon-based oxide contains at least one of Mg and Li.

9. The lithium secondary battery according to Claim 7, wherein the negative electrode active material layer further contains a negative electrode binder and a conductive material.

10. A battery module including the lithium secondary battery according to Claim 1.

11. A battery pack including the battery module according to Claim 10.

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