Secondary battery having reduced gas generation

Abstract

A secondary battery according to the present invention can generate a reduced amount of gas while including a manganese-rich oxide as a positive electrode active material.

Description

Secondary battery with reduced gas generation

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2025-0002631 dated January 8, 2025, and all contents disclosed in the literature of said Korean patent applications are incorporated herein as part of this specification.

[0002] The present invention relates to a secondary battery that includes a manganese-rich (Mn-rich) oxide as a positive electrode active material while reducing gas generation.

[0003] Lithium-ion batteries are utilized as various energy storage media through reversible electrochemical reactions. A field of active research in lithium-ion batteries is the increasing of energy density. Among these, one method receiving attention is the use of cathode active materials known as manganese-rich (Mn-rich), lithium-rich (Li-rich), and / or lithium-manganese-rich oxides.

[0004] These manganese-rich cathode active materials have a high theoretical reversible capacity of over 250 mAh / g through the participation of oxygen in anionic redox as well as the redox reaction of transition metals. In addition, the above manganese-rich cathode active materials have characteristics such as being cobalt-free and / or having a low nickel content, and are being studied as alternatives to existing NCM-based cathode active materials in terms of energy density, development sustainability, and price competitiveness.

[0005] For example, manganese-rich (Mn-rich) cathode active materials have a problem in that electrochemical interfacial reactions between the electrolyte and the cathode material are induced by manganese redox, resulting in a higher amount of gas generation compared to other cathode materials.

[0006] Therefore, there is a need for a technology that can reduce gas generation while utilizing the above-mentioned manganese-rich cathode active material, etc.

[0007] Accordingly, the present invention aims to provide a secondary battery that includes a manganese-rich (Mn-rich) oxide as a positive electrode active material while reducing gas generation.

[0008] To solve the problem described above, in one embodiment, a secondary battery according to the present invention comprises: a positive electrode comprising a lithium oxide as a positive active material that contains 50 mol% or more of Mn among all metals excluding lithium, or has a molar ratio of lithium to transition metals exceeding 1; and a negative electrode comprising a carbon-based active material. In one example, the carbon-based active material comprises one or more of natural graphite and artificial graphite, wherein the proportion of natural graphite is greater than 50 wt% based on the total weight of the carbon-based active material.

[0009] In one embodiment, the lithium oxide is represented by Chemical Formula 1.

[0010] [Chemical Formula 1]

[0011] Li x M (1-y-z) Mn y M 1 z O2

[0012] In the above chemical formula 1,

[0013] M is one or more of Ni, Co, and Fe, and

[0014] M 1 It is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0015] x, y, and z are respectively 0.8≤x≤2, 0.5≤y<1, and 0≤z≤0.1, where y+z=1.

[0016] Specifically, in the above chemical formula 1, x is in the range of 1.2 to 1.5.

[0017] In a specific example, the lithium oxide can be represented by Chemical Formula 2.

[0018] [Chemical Formula 2]

[0019] Li x M (1-y) Mn y O2

[0020] In the above chemical formula 2,

[0021] M is one or more of Ni and Co, and

[0022] x and y are 1.01≤x≤2 and 0.5≤y<0.9, respectively.

[0023] In one embodiment, the carbon-based active material has a natural graphite content in the range of 75 wt% to 100 wt%. In a specific example, the carbon-based active material has a natural graphite content in the range of 70 wt% to 90 wt%.

[0024] In another embodiment, the carbon-based active material has an orientation index according to Formula 1 below of an average of 15 or less, specifically in the range of an average of 0.1 to 15.

[0025] [Equation 1]

[0026] OI= I 004 / I 110

[0027] In the above Equation 1

[0028] I 110 represents the intensity of the peak indicating the (110) crystal plane of the carbon-based active material when measured by X-ray diffraction spectroscopy (XRD), and

[0029] I 004 represents the intensity of the peak indicating the (004) crystal plane of the carbon-based active material during X-ray diffraction spectroscopy (XRD) measurement.

[0030] In one embodiment, the cathode further comprises a silicon-based active material as an active material. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt% based on the total weight of the cathode active material. For example, the silicon-based active material is silicon (Si), silicon carbide (SiC), a composite of carbon and silicon (Si / C), and silicon oxide (SiO₂). q , provided that it includes at least one of 0.8≤q≤2.5).

[0031] In addition, the above secondary battery is a pouch-type secondary battery. As another example, the above secondary battery is a cylindrical or prismatic secondary battery.

[0032] In addition, the secondary battery according to the present invention is, for example, a battery for automobiles or an Energy Storage System (ESS).

[0033] The secondary battery according to the present invention includes a manganese-rich (Mn-rich) oxide as a positive electrode active material and can reduce the amount of gas generated.

[0034] Figure 1 is a graph showing the results of analyzing the gas generated at 45°C and 300 cycles for secondary batteries according to the examples and comparative examples.

[0035] FIG. 2 is a graph analyzing the capacity by voltage for secondary batteries according to the examples to comparative examples under conditions of 45°C and 300 cycles.

[0036] Figure 3 is a graph showing the results of analyzing the gas generated when stored at 60°C and for 8 weeks for secondary batteries according to the examples and comparative examples.

[0037] Figure 4 is a graph analyzing the capacity by voltage for secondary batteries according to the examples to comparative examples under conditions of 60°C and 300 cycles.

[0038] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description.

[0039] However, this is not intended to limit the invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0040] In the present invention, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0041]

[0042] The present invention will be described in more detail below.

[0043]

[0044] In one embodiment, the secondary battery according to the present invention comprises: a positive electrode comprising a lithium oxide as a positive active material that contains 50 mol% or more of Mn among all metals excluding lithium, or has a molar ratio of lithium to transition metals exceeding 1; and a negative electrode comprising a carbon-based active material. In addition, the carbon-based active material comprises one or more of natural graphite and artificial graphite, wherein the proportion of natural graphite exceeds 50 wt% based on the total weight of the carbon-based active material.

[0045] The present invention applies, as a positive electrode active material, (i) an oxide containing 50 mol% or more of Mn among all metals excluding lithium (hereinafter referred to as "manganese-rich oxide"), (ii) an oxide in which the molar ratio of lithium to transition metals exceeds 1 (hereinafter referred to as "over-lithium oxide"), and / or (iii) an oxide in which Mn among all metals excluding lithium is 50 mol% or more and the molar ratio of lithium to transition metals exceeds 1 (hereinafter referred to as "over-lithium manganese-rich oxide"). In the present invention, the oxides for positive electrode active materials of (i) to (iii) mentioned above are collectively referred to as "manganese-rich oxides." Specifically, the positive electrode active material used in the present invention is a manganese-rich oxide or an over-lithium manganese-rich oxide. For example, the positive electrode active material is an over-lithium manganese-rich oxide.

[0046] In one embodiment, the lithium oxide applied as the positive electrode active material can be represented by Chemical Formula 1.

[0047] [Chemical Formula 1]

[0048] Li x M (1-y-z) Mn y M 1 z O2

[0049] In the above chemical formula 1,

[0050] M is one or more of Ni, Co, and Fe, and

[0051] M 1 It is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0052] x, y, and z are respectively 0.8≤x≤2, 0.5≤y<1, and 0≤z≤0.1, where y+z=1.

[0053] For example, in the above chemical formula 1, x is in the range of 1.2 to 1.5.

[0054] In one more specific embodiment, the lithium oxide can be represented by Chemical Formula 2.

[0055] [Chemical Formula 2]

[0056] Li x M (1-y) Mn y O2

[0057] In the above chemical formula 2,

[0058] M is one or more of Ni and Co, and

[0059] x and y are 1.01≤x≤2 and 0.5≤y<0.9, respectively.

[0060] In a lithium secondary battery containing the aforementioned positive electrode active materials, a peak appears in the dQ / dV graph at 3.5V or lower during discharge. This peak is understood to appear as manganese ions (Mn ions) are reduced during the activation process. The present invention, for example, controls the compositional ratio of natural graphite and artificial graphite among the negative electrode active materials and suppresses the utilization rate of the Li2MnO3 phase.

[0061] In addition, the present invention can reduce oxygen desorption within the crystal structure of the positive electrode active material and reduce cation mixing of manganese ions. Typically, as cation mixing increases, the resistance of the battery or positive electrode increases. By controlling the composition ratio of natural graphite and artificial graphite in the negative electrode, the present invention can reduce cation mixing and thereby reduce the amount of gas generated during cycling and / or storage in a manganese-rich cell.

[0062] The present invention controls the composition and content of a cathode active material included in a cathode. Specifically, the present invention includes a carbon-based active material as the cathode active material. The carbon-based active material includes one or more of natural graphite and artificial graphite, wherein the proportion of natural graphite exceeds 50 wt% based on the total weight of the carbon-based active material. Specifically, the proportion of natural graphite in the carbon-based active material is in the range of more than 50 wt% to less than 100 wt%, or in the range of 75 wt% to 100 wt%. Alternatively, the proportion of natural graphite is 100 wt%, which means that only natural graphite is included among the carbon-based active materials. More specifically, the proportion of natural graphite in the carbon-based active material is in the range of 70 wt% to 90 wt% or in the range of 75 wt% to 85 wt%.

[0063] In one embodiment, the cathode active material layer comprises a carbon-based active material as the active material. Specifically, the carbon-based active material comprises one or more of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon made from tar and pitch, and graphitized coke. For example, the carbon-based active material may include graphite. The graphite may include one or more of natural graphite and artificial graphite. For example, the carbon-based active material may include natural graphite alone, or in some cases, may include a mixture of natural graphite and artificial graphite.

[0064] If the content ratio of artificial graphite in the cathode active material increases excessively, the amount of gas generated during charging, discharging, or storage and the rate of expression of a capacity of 3.5V or less increase. The present invention derived the above composition ratio by considering these characteristics, the reduction of manufacturing costs due to the use of natural graphite, and the increase in electrode capacity due to the use of artificial graphite.

[0065] In another embodiment, the carbon-based active material has an orientation index according to Formula 1 below of an average of 15 or less.

[0066] [Equation 1]

[0067] OI= I 004 / I 110

[0068] In the above Equation 1

[0069] I 110 represents the intensity of the peak indicating the (110) crystal plane of the carbon-based active material when measured by X-ray diffraction spectroscopy (XRD), and

[0070] I 004 represents the intensity of the peak indicating the (004) crystal plane of the carbon-based active material during X-ray diffraction spectroscopy (XRD) measurement.

[0071] Specifically, the orientation degree of the carbon-based active material represented by Equation 1 above is in the range of 0.1 to 15, 1 to 15, 1 to 10, 3 to 8, or 6 to 7. In the present invention, when manufacturing a negative electrode, a magnetic field is applied before drying the negative electrode active material layer to orient the carbon-based active material in a direction perpendicular to the current collector. By orienting the active material contained in the negative electrode active material layer, the mobility of lithium ions is increased, and consequently, rapid charge / discharge efficiency can be improved.

[0072] In the present invention, "carbon-based active material is oriented" or "carbon-based active material is aligned" means that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) representing the two-dimensional planar structure of the carbon-based active material constituting the active material particles is arranged to have a predetermined inclination with respect to the surface of the current collector, which may differ from the carbon-based active material particles themselves being arranged to have a specific direction within the negative electrode active material layer.

[0073] In the present invention, having a small value for "orientation degree (OI)" may mean that the crystal planes of the carbon-based active material contained in the negative electrode active material layer are arranged at a high angle (e.g., an angle close to vertical, 45° or more; specifically 60° or more) with respect to the surface of the current collector. Additionally, having a large value for "orientation degree (OI)" may mean that specific crystal planes representing the two-dimensional planar structure of the carbon-based active material contained in the negative electrode active material layer (e.g., the ab-axis crystal plane of graphite) are arranged at a low angle (e.g., less than 45°) with respect to the surface of the current collector or are non-oriented.

[0074] Furthermore, in the present invention, "crystal plane of a carbon-based active material" refers to a plane in which atoms of the carbon-based active material form the outer shape of the crystal, and may mean a crystal plane including a plane of the carbon-based active material, or a crystal plane including the a-axis / b-axis / ab-axis of the carbon-based active material crystal.

[0075] In addition, the method for controlling the orientation of the carbon-based active material described above according to Equation 1 below is as follows. In the process of manufacturing a cathode, a cathode slurry is applied onto a current collector, and a magnetic field is applied to the surface of the applied cathode slurry, and then the cathode slurry is dried, thereby manufacturing a cathode in which the crystal characteristics of the active material are controlled.

[0076] Here, the step of applying the cathode slurry is a step of coating the surface of a moving current collector by discharging the cathode slurry. The above step can be applied without particular limitation as long as it is a method commonly applied in the industry, but preferably, a die coating method may be used. The die coating method may be performed through a slot die equipped with a shim for controlling the discharge conditions of the cathode slurry. In this case, by controlling the shape of the shim, the loading amount and coating thickness of the cathode slurry applied on the cathode current collector can be easily controlled.

[0077] Meanwhile, the step of applying the magnetic field may be a step of controlling the crystal characteristics of the active material contained in the cathode slurry. Specifically, this step aligns the ab-axis crystal planes of the carbon-based active material contained in each cathode slurry to have a high angle with respect to the current collector by applying a magnetic field to the surface of the cathode slurry coated on the current collector.

[0078] At this time, the magnetic field may be applied by magnetic parts positioned at the top and bottom of a current collector that is moved with a negative electrode slurry applied to its surface. In addition, the polarities of the magnetic parts positioned at the top and bottom may be different from each other.

[0079] In addition, the alignment degree (OI) of the carbon-based active material contained in the cathode slurry can be controlled by the strength of the applied magnetic field, and accordingly, the step of applying the magnetic field can be performed under a predetermined magnetic field strength condition.

[0080] Specifically, the step of applying the magnetic field may apply a magnetic field in the range of 1,000 to 20,000 G (Gauss), and specifically, a magnetic field may be applied with a strength of 1,500 G to 9,000 G; 2,000 G to 6,500 G; 5,500 G to 8,500 G; or 2,500 G to 3,500 G.

[0081] Additionally, the step of applying the magnetic field may be performed for 1 second to 20 seconds, specifically for 1 second to 15 seconds; 1 second to 10 seconds; 5 seconds to 20 seconds; 10 seconds to 20 seconds; 11 seconds to 18 seconds; 1 second to 5 seconds; 4 seconds to 9 seconds; or 6 seconds to 11 seconds.

[0082] As an example, in the step of applying the magnetic field, a magnetic field of 3,000 ± 50 G may be applied to the cathode slurry for 1 second to 30 seconds.

[0083] Furthermore, the step of applying the magnetic field is performed by a magnetic part introduced at the top and bottom of the coated cathode slurry as previously mentioned, and the size of the magnetic part may be adjusted to be larger than the size of the coated cathode slurry so that the magnetic field applied to the cathode slurry can be applied uniformly across the entire surface of the cathode slurry. For example, the magnetic part may have a length ratio of 105% to 200% based on the width direction length of the cathode slurry, and specifically, may have a length ratio of 110% to 180%; 110% to 160%; 110% to 140%; 110% to 130%; 130% to 150%; or 105% to 120% based on the width direction length of the cathode slurry.

[0084] The present invention includes, after the step of applying the magnetic field, a step of drying the cathode and a step of rolling. The step of drying the cathode involves drying the cathode slurry to which the magnetic field has been applied at a high temperature to form a cathode active material layer on a current collector. The step of drying the cathode can be performed, for example, by applying hot air at a temperature of 160°C to 250°C. The step of rolling can be performed by applying pressure to the cathode that has undergone the drying process on one or both sides. The method of applying pressure can be performed using a roll press or a plate press, etc. For example, the step of rolling is performed by rolling with a roll press so that the rolling porosity of the cathode active material layer becomes 25±5%.

[0085] In one embodiment, the cathode further comprises a silicon-based active material as an active material. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt% based on the total weight of the active material in the cathode active material layer. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt%, 1 wt% to 30 wt%, 1 wt% to 10 wt%, 0.1 wt% to 5 wt%, 5 wt% to 30 wt%, or 6 wt% to 20 wt% based on the total weight of the active material contained in the cathode active material layer. The silicon-based active material has the advantage of increasing the cathode capacity compared to carbon-based active materials. On the other hand, the silicon-based active material has the problem of causing volume changes during the charging and discharging process. Therefore, it is desirable to control the content of the silicon-based active material by considering the application field or form of the secondary battery.

[0086] Specifically, the silicon-based active material is silicon (Si), silicon carbide (SiC), a carbon-silicon composite (Si / C), and silicon oxide (SiO₂). q ..., provided that it includes one or more of the following: , provided that 0.8≤q≤2.5). As one example, the active material may include graphite and silicon (Si)-containing particles together, and the graphite may include one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure. The silicon (Si)-containing particles may include silicon (Si) particles as a main component as a metal component, silicon (Si) particles, silicon oxide (SiO, SiO2) particles, or a mixture of silicon (Si) particles and silicon oxide (SiO, SiO2) particles.

[0087] In addition, the silicon-based active material may be doped with Li, Mg, Al, Ca, or Ti, or form an alloy. Furthermore, the silicon-based active material may be surface-treated with a carbon coating layer or the like for the purpose of suppressing volume expansion during charging or improving electrical conductivity.

[0088] Specifically, the secondary battery is a pouch-type secondary battery. As another example, the secondary battery is a cylindrical or prismatic secondary battery.

[0089]

[0090] secondary battery

[0091] In one example according to the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-type secondary battery. For example, the secondary battery is a pouch-type secondary battery. The pouch-type secondary battery includes an electrode assembly in which a unit structure in which a positive electrode, a separator, and a negative electrode are stacked is repeated.

[0092] The above secondary battery includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes, and a case surrounding the electrode assembly.

[0093] The secondary battery according to the present invention includes an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately arranged and a separator is located between them. The lithium secondary battery is equipped with the negative electrode of the present invention described above, and has the advantage of having excellent rapid charging performance by improving lithium ion diffusion ability, as well as high energy density.

[0094] At this time, since the cathode active material included in the above cathode has the same composition as described above, a detailed description is omitted. The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector and containing a cathode active material. Specifically, the above cathode is manufactured by coating, drying, and rolling a cathode active material on a cathode current collector, and may optionally further include a conductive material, an organic binder polymer, a filler, etc., as needed.

[0095] In this case, the negative electrode active material may include one or more of natural graphite and artificial graphite. Additionally, the negative electrode active material may further include a silicon-based active material.

[0096] The above conductive material may include one or more types of carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and thermal black; graphene; carbon nanotubes and carbon fibers, but is not limited thereto.

[0097] As an example, the above-mentioned cathode active material layer may contain carbon black, carbon nanotubes, carbon fibers, etc., as a conductive material, either alone or in combination.

[0098] At this time, the content of the conductive material may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active material layer. Specifically, the conductive material may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight per 100 parts by weight of the entire negative electrode active material layer. By controlling the content of the conductive material within the above range, the present invention can prevent the decrease in charging capacity caused by an increase in the resistance of the negative electrode due to a low content of the conductive material. Furthermore, the present invention can prevent problems such as a decrease in charging capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of conductive material exceeding the above range, or an increase in electrical resistance due to an increase in the loading amount of the negative electrode active material layer.

[0099] In addition, the binder is a component that assists in the bonding of the cathode active material and the conductive material, and the bonding to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the cathode. For example, the binder may include one or more of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0100] The content of the binder may be 0.1 to 10 parts by weight per 100 parts by weight of the entire negative electrode active material layer. Specifically, the binder may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight per 100 parts by weight of the entire negative electrode active material layer. By controlling the content of the binder contained in the negative electrode active material layer to the above range, the present invention can prevent the adhesion of the active material layer from being reduced due to a low content of binder or the electrical properties of the negative electrode from being reduced due to an excessive amount of binder.

[0101] In addition, the cathode active material layer may have an average thickness of 100㎛ to 800㎛, and specifically, may have an average thickness of 100㎛ to 780㎛; 100㎛ to 550㎛; 120㎛ to 500㎛; 140㎛ to 200㎛ or 140㎛ to 160㎛.

[0102] In addition, the above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used.

[0103] In addition, the above-mentioned negative current collector, like the positive current collector, may form fine irregularities on its surface to strengthen the bonding force with the negative active material, and can take various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics. Furthermore, the average thickness of the above-mentioned negative current collector can be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0104] In addition, the anode comprises an anode active material layer containing an anode active material on an anode current collector, and the anode active material layer may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0105] The above-mentioned positive active material is a material capable of causing an electrochemical reaction on the positive current collector. The description of the positive active material is as previously mentioned.

[0106] In addition, the above-mentioned positive active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the total positive active material layer. Specifically, the above-mentioned positive active material may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more based on 100 parts by weight of the total positive active material layer.

[0107] In addition, the above-mentioned positive active material layer may further include a conductive material, a binder, other additives, etc., along with the positive active material.

[0108] At this time, the conductive material is used to improve the electrical performance of the anode, and while commonly used in the industry may be applied, specifically, it may include one or more of natural graphite; artificial graphite; carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and thermal black; graphene; and carbon nanotubes.

[0109] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of each positive active material layer. Specifically, the conductive material may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 1 to 3 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight based on 100 parts by weight of each positive active material layer.

[0110] In addition, the binder serves to bind the positive active material, the positive additive, and the conductive material together, and any binder having this function can be used without particular limitation. Specifically, the binder may include one or more resins selected from polyvinylidenefluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidenefluoride.

[0111] In addition, the binder may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of each positive electrode active material layer. Specifically, the binder may be included in an amount of 2 to 8 parts by weight or 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

[0112] The total thickness of the above positive active material layer is not particularly limited, but specifically may be in the range of 50㎛ to 800㎛, and more specifically may be in the range of 100㎛ to 800㎛; 80㎛ to 150㎛; 120㎛ to 170㎛; 150㎛ to 300㎛; 200㎛ to 600㎛; or 150㎛ to 390㎛.

[0113] In addition, the anode may be used as an anode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, surface-treated materials such as carbon, nickel, titanium, silver, etc. may be used. Furthermore, the average thickness of the current collector may be appropriately applied from 3㎛ to 500㎛, taking into consideration the conductivity and total thickness of the anode being manufactured.

[0114] In addition, the separator interposed between the positive and negative electrodes of the lithium secondary battery is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is one commonly used in the industry. Specifically, the separator may be one comprising one or more polymers selected from chemically resistant and hydrophobic polypropylene; polyethylene; and polyethylene-propylene copolymer. The separator may have the form of a porous polymer substrate, such as a sheet or nonwoven fabric, containing the aforementioned polymer, and in some cases, may have the form of a composite separator in which organic or inorganic particles are coated on the porous polymer substrate by an organic binder. Furthermore, the separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0115] Meanwhile, the secondary battery according to the present invention is not particularly limited, but may be a secondary battery of a form that includes a stack type; a zigzag type; or a zigzag-stack type electrode assembly.

[0116] In addition, the secondary battery according to the present invention may include a lithium salt-containing electrolyte. The lithium salt-containing electrolyte may consist of an electrolyte and a lithium salt, and the electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0117] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0118] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0119] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., may be used.

[0120] The above lithium salt is a substance that dissolves well in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronicate, imide, etc. may be used.

[0121] In addition, for the purpose of improving charge / discharge characteristics and flame retardancy, the electrolyte may be further enriched with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further enriched, carbon dioxide gas may be further enriched to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc.

[0122] Meanwhile, in one embodiment, the present invention provides a module including the secondary battery described above to a battery pack including the module.

[0123] The above battery pack can be used as a power source for medium-to-large devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. Specific examples of such medium-to-large devices include power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems. More specifically, hybrid electric vehicles (HEVs) can be cited, but are not limited thereto.

[0124] Furthermore, the above-mentioned positive and negative electrodes may be wound into a jelly roll shape and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or stored in a pouch-type battery in a folding or stack-and-folding form. For example, the secondary battery according to the present invention may be a pouch-type battery.

[0125] As described above, the secondary battery according to the present invention can be used in a battery module or battery pack comprising a plurality of unit cells. Specifically, it is useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0126] The present invention will be explained in more detail below through examples and the like. However, the rights of the present invention are not limited thereto.

[0127]

[0128] Examples and Comparative Examples: Manufacturing of Secondary Batteries

[0129] Cathode active material (Li 1.35 [Ni 0.360 Co 0.005 Mn 0.635 An anode slurry (solid content 65 wt%) was prepared by adding a conductive material (carbon nanotube) and a binder (polyvinylidene fluoride) in a weight ratio of 96.0:1.5:2.5 to the solvent N-methyl-2-pyrrolidone (NMP). The anode slurry was applied to one surface of an anode current collector (Al thin film) with a thickness of 12 μm, and an anode was manufactured by drying and rolling.

[0130]

[0131] A cathode slurry (solid content 50 wt%) was prepared by adding a cathode active material (mixture of artificial graphite and natural graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber) to distilled water, which is a solvent, in a weight ratio of 96.7:1.0:2.3. The cathode slurry was applied to one surface of a cathode current collector (Cu thin film) with a thickness of 8 μm, and a cathode was manufactured by drying and rolling. Here, the mixing ratio of artificial graphite and natural graphite constituting the cathode active material is as shown in Table 1 below.

[0132]

[0133] A secondary battery was manufactured by interposing a polyethylene porous film separator between the anode and cathode manufactured above in a dry room, and then injecting the non-aqueous electrolyte manufactured above.

[0134] Classification Graphite composition ratio (wt%) in cathode Natural Graphite Artificial Graphite Example 1 1000 Example 2 8020 Example 3 7030 Example 4 6040 Example 5 5545 Comparative Example 1 5050 Comparative Example 2 4555

[0135] Experimental Example 1: Calculation of Gas Generation Amount and Capacity Change Rate by Voltage During Charging and Discharging

[0136] For the secondary batteries prepared in the examples and comparative examples, the amount of gas generated during charging and discharging was detected. Specifically, each secondary battery was charged and discharged at 45°C, 300 times, and 1°C. At the time the charging and discharging were completed, the amount of gas generated and the rate of change in capacity by voltage were analyzed. The amount of gas generated for each secondary battery is shown in Table 2 below. In addition, the type and amount of gas generated from the secondary batteries according to Examples 1 and 2 and Comparative Example 2 were analyzed using gas chromatography, and the results are shown in Figure 1.

[0137] In addition, the capacity of 3.5V or less and the capacity exceeding 3.5V were distinguished for each secondary battery. The rate of change of the capacity of 3.5V or less after 300 charge-discharge cycles is shown in Table 2 below. Furthermore, the rate of change of capacity by voltage during charge-discharge is shown in Figure 2.

[0138] Classification Gas Generation Amount (ml) 3.5V or less Capacity (%) Example 1 120.6 115.9 Example 2 141.7 117.8 Example 3 148.5 118.2 Example 4 152.9 118.6 Example 5 158.3 119.0 Comparative Example 1 172.7 120.4 Comparative Example 2 185.2 122.6

[0139] First, referring to Table 2, when lithium-rich manganese oxide is applied as the positive electrode active material, it can be observed that the amount of gas generated tends to increase to a certain level as the artificial graphite content in the negative electrode increases. Specifically, it can be seen that the amount of gas generated by the secondary batteries according to Examples 1 to 5 is less than 160 ml. In particular, the amount of gas generated by the secondary battery according to Example 1 is confirmed to be the smallest at 120.6 ml. The amount of gas generated by the secondary batteries according to Comparative Examples 1 and 2 was calculated to be 172.7 ml and 185.2 ml, respectively. It was confirmed that the amount of gas generated increases rapidly when the content of artificial graphite in the negative electrode active material is 50 wt% or more. Referring to Figure 1, the types and amounts of gas generated in the secondary batteries according to Examples 1 and 2 and Comparative Example 2 can be confirmed. Through Figure 1, it can be seen that the amount of gas generated increases as the content of artificial graphite increases, and in particular, the amount of CO2 gas generated increases rapidly. The present invention can reduce the amount of gas generated by controlling the content of artificial graphite in the cathode active material to less than 50 wt%, and in particular, significantly reduce the generation of CO2 gas.

[0140] In addition, referring to Table 2 and Figure 2, it can be seen that in a battery containing lithium-rich manganese oxide as the positive electrode active material, the capacity development rate of 3.5V or lower increases as the content of artificial graphite in the negative electrode increases. However, the secondary batteries according to Examples 1 to 5 effectively suppress the capacity development rate of 3.5V or lower despite the increase in the content of artificial graphite. In contrast, it was confirmed that the secondary batteries according to Comparatives 1 and 2 exceeded 120% of the capacity development rate of 3.5V or lower. In particular, when comparing the secondary batteries according to Examples 1 and 2 and Comparative Example 2 in Figure 2, it can be seen that the capacity exceeding 3.5V does not show a significant difference as charging and discharging progresses. In this regard, it can be seen that the capacity of 3.5V or lower is effectively suppressed in the secondary batteries according to Examples 1 and 2.

[0141]

[0142] Experimental Example 2: Calculation of Gas Generation Amount and Capacity Change Rate by Voltage During High-Temperature Storage

[0143] For the secondary batteries prepared in Examples 1 and 2 and Comparative Example 1, respectively, the amount of gas generated during high-temperature storage was detected. Specifically, after storing each secondary battery at 60°C for 8 weeks, the amount of gas generated and the rate of change in capacity by voltage during that period were analyzed. The amount of gas generated for each secondary battery is shown in Table 3 below. In addition, the type and amount of gas generated from each secondary battery were analyzed using gas chromatography, and the results are shown in Figure 3.

[0144] In addition, the capacity of 3.5V or less and the capacity exceeding 3.5V were distinguished for each secondary battery. The rate of change in capacity when stored for 8 weeks under 60℃ conditions is shown in Table 3 below. Furthermore, the rate of change in capacity according to voltage by period during high-temperature storage is shown in Figure 4.

[0145] Classification Gas Generation Amount (ml) 3.5V or less Capacity (%) Example 1 138.5 108.7 Example 2 145.0 108.9 Comparative Example 1 154.2 109.7

[0146] First, referring to Table 3 and Figure 3, it was confirmed that compared to the secondary batteries according to Examples 1 and 2, the secondary battery according to Comparative Example 1 showed a significant increase in gas generation amount and the rate of capacity development below 3.5V. Additionally, referring to Figure 4, when comparing the secondary batteries according to Examples 1 and 2 and Comparative Example 2, it can be seen that there is no significant difference in capacity exceeding 3.5V during high-temperature storage. In this regard, it can be seen that the secondary batteries according to Examples 1 and 2 effectively suppress the development of capacity below 3.5V.

[0147]

[0148] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0149] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. A cathode comprising, as a positive active material, a lithium oxide containing 50 mol% or more of Mn among all metals excluding lithium, or having a molar ratio of lithium to transition metals exceeding 1; and It includes a cathode containing a carbon-based active material, and The above carbon-based active material comprises one or more of natural graphite and artificial graphite, and is a secondary battery in which the proportion of natural graphite exceeds 50 wt% based on the total weight of the carbon-based active material.

2. In Paragraph 1, A secondary battery characterized by the above lithium oxide being represented by Chemical Formula 1: [Chemical Formula 1] Li x M (1-y-z) Mn y M 1 z O2 In the above chemical formula 1, M is one or more of Ni, Co, and Fe, and M 1 It is one or more elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, and z are respectively 0.8≤x≤2, 0.5≤y<1, and 0≤z≤0.1, where y+z=1.

3. In Paragraph 1, A secondary battery characterized in that, in the above chemical formula 1, x is in the range of 1.2 to 1.

5.

4. In Paragraph 1, A secondary battery characterized by the above lithium oxide being represented by Chemical Formula 2: [Chemical Formula 2] Li x M (1-y) Mn y O2 In the above chemical formula 2, M is one or more of Ni and Co, and x and y are 1.01≤x≤2 and 0.5≤y<0.9, respectively.

5. In Paragraph 1, The above carbon-based active material is a secondary battery in which the proportion of natural graphite is in the range of 75 wt% to 100 wt%.

6. In Paragraph 1, The above carbon-based active material is a secondary battery in which the proportion of natural graphite is in the range of 70 wt% to 90 wt%.

7. In Paragraph 1, The above carbon-based active material is a secondary battery having an average orientation index of 15 or less according to Formula 1 below: [Equation 1] OI= I 004 / I 110 In the above Equation 1 I 110 represents the intensity of the peak indicating the (110) crystal plane of the carbon-based active material when measured by X-ray diffraction spectroscopy (XRD), and I 004 represents the intensity of the peak indicating the (004) crystal plane of the carbon-based active material during X-ray diffraction spectroscopy (XRD) measurement.

8. In Paragraph 1, The above cathode further comprises a silicon-based active material as an active material, and A secondary battery in which the content of the silicon-based active material is in the range of 0.1% to 30% by weight based on the total weight of the negative electrode active material.

9. In Paragraph 8, The above silicon-based active material is silicon (Si), silicon carbide (SiC), a composite of carbon and silicon (Si / C), and silicon oxide (SiO₂). q A secondary battery comprising at least one of the following: , provided that 0.8≤q≤2.5).

10. In Paragraph 1, The above secondary battery is characterized as being a pouch-type secondary battery.

11. In Paragraph 1, The above secondary battery is characterized by being a cylindrical or prismatic secondary battery.

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