Secondary battery

Abstract

The present disclosure relates to a secondary battery. The secondary battery has a configuration in which an excess of a point-type conductive material is applied to a negative electrode, and a ratio of an irreversible capacity of a positive electrode to an irreversible capacity of the negative electrode is adjusted to a predetermined ratio. With such a configuration, the secondary battery not only has excellent energy density and power output performance, but also has high safety because it has a significant effect of suppressing heating of the secondary battery during high-rate charging and discharging.

Description

Technical Field

[0001] This invention relates to a secondary battery with excellent power output characteristics.

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0169577, filed on November 25, 2024, and Korean Patent Application No. 10-2025-0176613, filed on November 20, 2025, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Lithium-ion batteries are widely used not only in small devices such as portable electronic devices, but also in medium and large devices such as battery packs for hybrid or electric vehicles and energy storage devices.

[0004] Recently, the demand for lithium-ion batteries has also been increasing as they are used as power sources for Urban Air Mobility (UAM), the next generation of transportation alongside electric vehicles and portable electronic devices. Urban Air Mobility (UAM) must provide aviation services in complex urban environments. Therefore, it should be designed to enable vertical takeoff and landing to minimize operational space and requires high safety to improve social acceptance for commercialization. Specifically, because various complex and variable factors affect the operation of Urban Air Mobility (UAM), such as collisions with tall buildings and structures, low-altitude turbulence, and weather variations such as precipitation, the lithium-ion batteries used as power sources should also be designed to handle emergencies deviating from normal flight conditions.

[0005] However, research on lithium-ion batteries to date has primarily focused on applications in electric vehicles, and therefore has not yet met the performance requirements of urban air mobility (UAM), specifically considering the power output conditions during emergency descents. Therefore, there is a need to develop lithium-ion battery technologies for UAM. Summary of the Invention

[0006] Technical issues

[0007] The purpose of this disclosure is to provide a secondary battery with excellent energy density and power output performance.

[0008] Technical solution

[0009] To solve the above problems,

[0010] This public disclosure provides:

[0011] A secondary battery includes a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0012] The positive electrode includes a positive electrode active layer located on the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material and a positive electrode additive.

[0013] The negative electrode includes a negative electrode active layer located on the negative electrode current collector, and the negative electrode active layer includes a negative electrode active material and a point-type conductive material; and

[0014] When charging and discharging at 22±5℃ and 5C rate, the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode satisfies the range of 0.8-1.2.

[0015] Specifically, when charged and discharged at 22±5℃ and 5C rate, the secondary battery can satisfy the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode to be in the range of 0.9-1.15.

[0016] In this case, the content of the point-type conductive material in the negative electrode can be in the range of 10% to 60% by weight, based on the total weight of the negative electrode active layer.

[0017] The point-type conductive material may include acetylene black, oil furnace black, channel black, lamp black, thermal cracking black, or mixtures thereof.

[0018] The average particle size (D) of the point-type conductive material 50 It can be in the range of 0.5 μm-20 μm.

[0019] The negative electrode active material may include natural graphite, artificial graphite, condensed graphite, pyrolytic carbon, carbon microbeads, mesophase pitch, graphitized coke, or mixtures thereof.

[0020] The negative electrode active material can be selected from silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q At least one silicon-based anode active material, wherein 0.8 ≤ q ≤ 2.5.

[0021] Additionally, the positive electrode active material may include at least one lithium metal oxide represented by the following chemical formulas 1 and 2:

[0022] [Chemical Formula 1]

[0023] Li a [Ni b Co 1-b-c M1 c O2

[0024] [Chemical Formula 2]

[0025] Li p [Mn 2-q M 2 q O4

[0026] (In chemical formula 1 and chemical formula 2,

[0027] M 1 It is at least one element selected from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B and Mo;

[0028] M 2 It is at least one element selected from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo; and

[0029] a, b, c, p, and q satisfy 1.0≤a≤1.30, 0≤b<1, 0≤c≤0.4, 1.0≤p≤1.30, and 0≤q≤1.0, respectively.

[0030] The positive electrode additive may include at least one compound represented by the following chemical formulas 3 to 5:

[0031] [Chemical Formula 3]

[0032] Li m M 3 (1-n) M 4 n O4

[0033] [Chemical Formula 4]

[0034] Li2M 5 (1-r) M 6 r O2

[0035] [Chemical Formula 5]

[0036] Li2R z

[0037] (In chemical formulas 3 to 5,

[0038] M 3 Is Fe, Co, Mn, Zn, Al or Ga,

[0039] M 4 is at least one metal selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, with the proviso that M 3 and M 4 comprise different metals from each other;

[0040] M 5 is Ni or Cu,

[0041] M 6 is at least one metal selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, with the proviso that M 5 and M 6 comprise different metals from each other;

[0042] R is O, S or Se, and

[0043] m, n, r and z respectively satisfy 4≤m≤7, 0≤n≤0.5, 0<r≤0.5 and 0.8≤z≤2.5).

[0044] For example, the positive electrode additive may comprise at least one compound selected from the group consisting of Li5FeO4, Li6MnO4, Li6CoO4, Li6ZnO4, Li5AlO4, Li5GaO4, Li2NiO2, Li2CuO2, Li2O, Li2O2, Li2S and Li2Se.

[0045] Based on the total weight of the positive electrode active layer, the content of the positive electrode additive may range from 0.1 wt% to 5 wt%.

[0046] Beneficial Effects

[0047] The secondary battery according to the present disclosure is not only excellent in energy density and power output performance, but also has high safety because it has a remarkable effect of suppressing heat generation of the secondary battery during high-rate discharge. Specific Embodiments

[0048] The present disclosure may have various modifications and various embodiments, and specific embodiments will be described in detail in the following detailed description.

[0049] As used herein, the terms “comprising,” “including,” and “having” mean the presence, or combination thereof, of the features, numbers, steps, actions, components, or elements described in the specification, and it should be understood that the possibility of the presence or addition of one or more other features, numbers, steps, actions, components, elements, or combinations thereof is not excluded in advance.

[0050] In this specification, "comprising as a major component" can mean that the defined component is included in an amount of 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more) based on the total weight of the carbon-based compound. For example, "comprising carbon atoms as a major component" can mean that the total weight of the carbon-based compound includes 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more carbon atoms. In some cases, it can also mean that the entire carbon-based compound consists of carbon atoms, including 100% by weight.

[0051] Furthermore, in this specification, "average particle size (D)" 50 The average particle size refers to the particle size at which the cumulative value in the particle size distribution reaches 50%, and is also called the median diameter. The average particle size can be measured using methods conventionally applied in the art. For example, it can be measured using a laser diffraction particle size analyzer or a centrifugal particle size analyzer. In this disclosure, it can be a value measured by an analytical instrument using a laser diffraction particle size distribution measurement method. For example, the average particle size can be measured by dispersing relevant particles in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S-3500), irradiating it with ultrasound at approximately 28 kHz with an output of 60 W; obtaining a volumetric cumulative particle size distribution curve, and determining the particle size at the location where the volumetric cumulative amount on the obtained volumetric cumulative particle size distribution curve reaches 50%.

[0052] In this disclosure, "primary grains" refer to grain units that do not exhibit obvious grain boundaries when observed using a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000x. From this perspective, "secondary grains" refer to grains formed by the aggregation of multiple primary grains, and one or more grain boundaries are clearly observed when observed using a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000x. A "grain boundary" refers to the interface present between grains (or single particles).

[0053] In this disclosure, "average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle size of at least 20 or more primary particles observed in a scanning electron microscope image. In this case, particle size refers to the diameter of the longest axis of the primary particle.

[0054] In this disclosure, a "secondary particle" is a particle formed by the aggregation of multiple primary particles. In order to distinguish it from a conventional secondary particle formed by the aggregation of tens to hundreds of primary particles, a secondary particle in which 30 or fewer primary particles are aggregated will be referred to as a quasi-monoparticle.

[0055] In this specification, "irreversible capacity" refers to the deviation between the charge and discharge of the active material, and "irreversible efficiency" can be expressed as (charge - discharge) / charge.

[0056] The contents of this disclosure will be described in more detail below.

[0057] Secondary batteries

[0058] This public disclosure provides:

[0059] A secondary battery includes a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0060] The positive electrode includes a positive electrode active layer located on the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material and a positive electrode additive.

[0061] The negative electrode includes a negative electrode active layer located on the negative electrode current collector, and the negative electrode active layer includes a negative electrode active material and a point-type conductive material; and

[0062] When charging and discharging at 22±5℃ and 5C rate, the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode satisfies the range of 0.8-1.2.

[0063] The secondary battery according to the present invention can be a lithium secondary battery. The secondary battery includes a positive electrode, a negative electrode, and a separator inserted between the positive and negative electrodes. More specifically, the secondary battery includes an electrode assembly comprising a positive and a negative electrode and a separator inserted therebetween, and the electrode assembly can be inserted into a battery casing together with an electrolyte composition and has a sealed form. In this case, the electrode assembly can be in a stacked form, a stacked and folded form, or a jelly-roll shape. Because this type of electrode assembly exhibits high energy density within a limited space, it has the advantage of high applicability in terms of energy density and power output in secondary batteries.

[0064] Furthermore, the positive electrode may have a structure in which a positive active layer comprising a positive active material and a positive additive is disposed on at least one surface of the positive current collector.

[0065] In this case, the positive electrode active material is a material capable of inducing an electrochemical reaction and may contain at least one lithium metal compound represented by the following chemical formulas 1 and 2, which allows for reversible insertion and extraction of lithium ions:

[0066] [Chemical Formula 1]

[0067] Li a [Ni b Co 1-b-c M 1 c O2

[0068] [Chemical Formula 2]

[0069] Li p [Mn 2-q M 2 q O4

[0070] In chemical formula 1 and chemical formula 2,

[0071] M 1 It is at least one element selected from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B and Mo;

[0072] M 2 It is at least one element selected from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo; and

[0073] a, b, c, p, and q satisfy 1.0≤a≤1.30, 0≤b<1, 0≤c≤0.4, 1.0≤p≤1.30, and 0≤q≤1.0, respectively.

[0074] Lithium metal oxides represented by Formula 1 have a layered crystal structure, readily store lithium ions, and exhibit high lithium ion diffusion rate, making them suitable as positive electrode active materials for high-capacity / high-output secondary batteries. Lithium metal oxides represented by Formula 1 are metal oxides containing nickel (Ni) and / or cobalt (Co) as well as lithium, and in some cases may be doped with another transition metal (M). 1 For example, metal oxides can contain forms selected from LiCoO2, LiNiO2, and Li(Ni)O2. 0.6 Co 0.1 Mn 0.3 O2, Li(Ni) 0.6 Co 0.2 Mn 0.2 O2, Li(Ni) 0.7 Co 0.15 Mn 0.15 O2, Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, Li(Ni) 0.9 Co 0.05 Mn 0.05 O2, Li(Ni) 0.6 Co 0.2 Mn 0.1 Zr 0.1 O2, Li(Ni) 0.6 Co 0.2 Mn 0.15 Zr 0.05 O2, Li(Ni) 0.7 Co 0.1 Mn 0.1 Zr 0.1 O2, Li(Ni) 0.6 Co 0.2 Al 0.2 O2, Li(Ni) 0.6 Co 0.2 Al 0.2 O2, Li(Ni) 0.7 Co 0.15 Al 0.15 O2, Li(Ni) 0.8 Co 0.1 Al 0.1 O2, Li(Ni) 0.9 Co 0.05 Al 0.05 O2, Li(Ni)0.6 Co 0.2 Al 0.1 Zr 0.1 O2, Li(Ni) 0.6 Co 0.2 Al 0.15 Zr 0.05 )O2 and Li(Ni 0.7 Co 0.1 Al 0.1 Zr 0.1 At least one of O2.

[0075] Furthermore, the lithium metal oxide represented by Formula 2 possesses a spinel crystal structure readily observable in general metal oxides. The spinel crystal structure contains various three-dimensional channels, which facilitates lithium-ion insertion and thus results in excellent power output characteristics. The lithium metal oxide represented by Formula 2 is a manganese (Mn)-containing metal oxide, and in some cases may be doped with another transition metal (Mn). 2 In the form of lithium metal oxides, for example, lithium metal oxides may contain materials selected from LiMn2O4, LiMn2O4, etc. 1.7 Al 0.3 O4 and LiMn 1.5 Al 0.5 At least one of O4.

[0076] The positive electrode active material can be in the form of primary particles and / or secondary particles. Specifically, the positive electrode active material can consist of primary particles, or it can be in the form of secondary particles, some of which are aggregated together, mixed with the primary particles in a predetermined proportion. In this case, the proportion of secondary particles in all positive electrode active material particles can be in the range of 0% or more and 50% or less, and specifically in the range of 1% to 50%, 1% to 30%, 1% to 20%, 1% to 10%, 5% to 50%, 10% to 50%, 20% to 50%, 30% to 50%, 5% to 20%, 10% to 30%, 20% to 40%, or 15% to 40%. The proportion can be calculated from images obtained during optical microscopy or scanning electron microscopy (SEM) analysis of the cross-section of the positive electrode active layer. For example, scanning electron microscopy (SEM) images of the cross-section of the positive electrode active layer can be obtained, and image analysis can be performed on the obtained images to distinguish between particles containing grain boundaries and those without grain boundaries. Then, the area ratio of each type of particle in the entire image can be calculated. That is, this ratio can refer to the area ratio calculated through image analysis.

[0077] Since a separate process for particle aggregation is not required during manufacturing, cathode active materials in the form of primary particles are economical. Furthermore, due to the absence of grain boundaries within the particles, stress concentration is low and the particles themselves have high structural strength, resulting in minimal particle breakage due to repeated charging and discharging. This contributes to increased cathode lifespan. Additionally, cathode active materials in the form of primary particles exhibit little or no grain boundary resistance generated at the grain boundaries during charging and discharging. Cathode active materials with low grain boundary resistance exhibit faster lithium-ion diffusion rates and thus offer the advantage of improved power output performance. Specifically, when the cathode active material represented by Formula 1 is in the form of secondary particles, the structural stability of the particles is lower during high-voltage or high-rate charging, which may lead to side reactions with the electrolyte. In this case, gas is generated due to side reactions, thus limiting the thermal safety of the secondary battery.

[0078] The positive electrode additive contained in the positive electrode active layer is a perlithiated compound with high irreversible capacity, thus playing a role in controlling the irreversible capacity of the positive electrode. Such a positive electrode additive may include one, two, or more of the compounds represented by chemical formulas 3 to 5:

[0079] [Chemical Formula 3]

[0080] Li m M 3 (1-n) M 4 n O4

[0081] [Chemical Formula 4]

[0082] Li2M 5 (1-r) M 6 r O2

[0083] [Chemical Formula 5]

[0084] Li2R z

[0085] In chemical formulas 3 to 5

[0086] M 3 Is Fe, Co, Mn, Zn, Al or Ga,

[0087] M 4 It is at least one metal selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, provided that M is a metal selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. 3 and M4 comprising different metals;

[0088] M 5 is Ni or Cu,

[0089] M 6 is at least one metal selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, with the proviso that M 5 and M 6 comprise different metals;

[0090] R is O, S or Se, and

[0091] m, n, r and z satisfy 4≤m≤7, 0≤n≤0.5, 0<r≤0.5 and 0.8≤z≤2.5, respectively.

[0092] The positive electrode additive contains excess lithium and can provide lithium to compensate for lithium consumption caused by irreversible chemical and physical reactions at the negative electrode during initial charging. Since the positive electrode has been supplied with lithium from the positive electrode additive, it has increased charging capacity and reduced irreversible capacity, thereby improving the life characteristics and power output characteristics of a secondary battery comprising the same.

[0093] The positive electrode additive may comprise at least one overlithiated compound represented by chemical formula 1 to 3. In this case, the compound represented by chemical formula 1 may include Li6CoO4, Li6Co 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3 O4, Li6Co 0.7 Zn 0.2 Al 0.1 O4, Li5FeO4, Li6MnO4, Li6ZnO4, Li5AlO4, Li5GaO4, etc. In addition, the compound represented by chemical formula 2 may include Li2NiO2, Li2CuO2, etc.; the compound represented by chemical formula 3 may include Li2O2, Li2O, Li2S, Li2Se, etc.

[0094] Generally, positive electrode active materials have specific charge and discharge potentials depending on their composition. Therefore, positive electrode additives can be selectively used from those within the charge and discharge potentials of the secondary battery, specifically within the charge and discharge potential range of the positive electrode active material, from which lithium can be released. For example, when the positive electrode active material contains a lithium metal oxide represented by Formula 1 with a charge potential of about 3.8V or greater, compounds represented by Formula 3, such as Li6CoO4 and Li6Co, can be used. 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3 O4, Li6Co 0.7 Zn 0.2 Al 0.1 O4 and other additives are used as positive electrode additives.

[0095] The irreversible capacity of the positive electrode can be determined by the content of the positive electrode additive and the average particle size (D). 50 It can be controlled by, but is not limited to, )

[0096] For example, based on the total weight of the positive electrode active layer, the content of the positive electrode additive can range from 0.1 wt% to 5 wt%. For example, based on the total weight of the positive electrode active layer, the content of the positive electrode additive can range from 0.1 wt% to 4 wt%, 0.1 wt% to 3 wt%, 0.1 wt% to 2 wt%, 0.1 wt% to 1 wt%, 1 wt% to 5 wt%, 2.5 wt% to 5 wt%, 1 wt% to 4 wt%, 1 wt% to 3 wt%, 0.5 wt% to 2 wt%, 2 wt% to 4 wt%, 0.5 wt% to 1.3 wt%, or 0.5 wt% to 0.9 wt%. By controlling the content of the positive electrode additive within the above ranges, this disclosure can prevent the reduction in charge / discharge capacity caused by insufficient replenishment of lithium-ion losses in irreversible reactions due to low content of positive electrode additives. Furthermore, it can prevent the generation of large amounts of oxygen in the secondary battery during charging and discharging due to excessive amount of positive electrode additives.

[0097] Considering the irreversible reactivity of the compound during the initial charging period, the cathode additive can have a predetermined average particle size (D). 50 Specifically, the cathode additive can have an average particle size (D) ranging from 0.5 μm to 20 μm. 50For example, the cathode additive may have an average particle size (D) in the range of 0.5 μm to 18 μm, 0.5 μm to 15 μm, 0.5 μm to 12 μm, 0.5 μm to 10 μm, 0.5 μm to 5 μm, 0.5 μm to 3 μm, 1 μm to 9 μm, 5 μm to 20 μm, 5 μm to 15 μm, 5 μm to 13 μm, 8 μm to 19 μm, 9 μm to 15 μm, 10 μm to 20 μm, 10 μm to 15 μm, 7 μm to 14 μm, or 8 μm to 12 μm. 50 ).

[0098] This invention can control the average particle size (D) of the positive electrode additive. 50 Within the aforementioned range, it is preferable to prevent a large amount of unreacted compounds from remaining after the initial charge and discharge / activation due to the average particle size exceeding the upper limit. Compounds remaining after the initial charge and discharge / activation can act as a factor in generating gas and releasing lithium ions during subsequent charge and discharge processes. The generated gas can increase the internal pressure of the secondary battery, thereby jeopardizing its safety. Therefore, it is preferable to control the average particle size (D...). 50 The particle size distribution is equal to or lower than the aforementioned upper limit, allowing all or most of the positive electrode additives to participate in the irreversible reactions during initial charging and discharging / activation. Furthermore, this invention can minimize dispersion during the positive electrode manufacturing process or due to the average particle size (D...). 50 The amount of positive electrode additive lost due to its uneven dispersion in the positive electrode active layer, which is less than the lower limit mentioned above.

[0099] Similar to the positive electrode, the negative electrode includes a negative electrode active layer located on at least one surface of the negative electrode current collector. The negative electrode active layer refers to the layer that enables the electrochemical activity of the negative electrode. Such a negative electrode active layer is manufactured by coating a negative electrode slurry containing a negative electrode active material onto at least one surface of the negative electrode current collector, and then drying and rolling the slurry. This negative electrode active material performs an electrochemical redox reaction during battery charging and discharging.

[0100] The negative electrode contains negative electrode active material as the main component of the negative electrode active layer. Specifically, based on total weight, the negative electrode active layer may contain 35% to 99.8% of negative electrode active material. For example, based on total weight, the negative electrode active layer may contain 35% or more, 45% or more, 50% or more, 60% or more, 70% or more, 80% or more, 95% or more, 98% or more, 84% to 99.8%, 90% to 99.8%, 94% to 99.8%, 88% to 96%, or 92% to 97.5% of negative electrode active material.

[0101] The negative electrode active material may include carbon-based negative electrode active materials and / or silicon-based negative electrode active materials as the main components.

[0102] Carbon-based anode active materials are materials containing carbon atoms as the main component, and may include natural graphite, artificial graphite, condensed graphite, pyrolytic carbon, carbon microbeads, mesophase carbon microbeads sintered carbon using tar and pitch as raw materials, and graphitized coke or mixtures thereof.

[0103] Carbon-based anode active materials can take the form of components in which multiple particles are granulated. Specifically, carbon-based anode active materials can take the form of secondary particles composed of multiple primary particles. In this case, a graphite component can be formed by assembling 2 to 100, preferably 3 to 20, graphite particles.

[0104] For example, carbon-based anode active materials can include natural graphite. Natural graphite has the advantages of excellent price competitiveness and outstanding lifetime characteristics when used as an anode.

[0105] Furthermore, the carbon-based negative electrode active material can include natural graphite and artificial graphite, and in this case, the artificial graphite can be in the form of a graphite assembly in which 10 to 30 particles are aggregated. Additionally, the mixing ratio of natural graphite to artificial graphite can be 50-95:5-50, 70-95:5-30, 5-50:50-95, or 5-30:70-95 by weight. By including the carbon-based negative electrode active material in the above-mentioned mixing ratio of natural graphite to artificial graphite, the adhesion between the negative electrode current collector and the negative electrode active layer can be firmly ensured, while achieving high power output performance of the negative electrode active layer.

[0106] Carbon-based anode active materials can have an average particle size within a predetermined range. Specifically, carbon-based anode active materials can have an average particle size (D) in the range of 0.5 μm to 20 μm. 50 For example, the average particle size (D) of carbon-based anode active materials. 50The particle size can range from 0.5 μm to 15 μm, 0.5 μm to 10 μm, 5 μm to 20 μm, 10 μm to 20 μm, 12 μm to 18 μm, 2 μm to 7 μm, 0.5 μm to 5 μm, or 11 μm to 15 μm. As the average particle size of the carbon-based anode active material decreases, the disorder of each particle in the expansion direction is maximized, thereby reducing the expansion of the anode active layer due to lithium-ion intercalation during charging. However, when the particle size of the carbon-based anode active material is less than 0.5 μm, a large amount of binder is required due to the increased number of particles per unit volume, thus potentially reducing the energy density of the anode. On the other hand, when the maximum particle size exceeds 20 μm, the expansion of the anode active layer during charging can become severe. In this case, with repeated charging and discharging of the secondary battery, the adhesion between particles in the anode active layer and the adhesion between particles and the current collector deteriorates, thus potentially significantly reducing the cycle characteristics of the secondary battery.

[0107] Silicon-based anode active materials are materials containing silicon (Si) as the main component and can improve the charge and discharge capacity of the anode. Examples of such silicon-based anode active materials include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO2), and these can be contained individually or in combination of two or more in the anode active layer. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as silicon-based anode active materials and contained in the anode active layer, they can be represented as silicon oxide (SiO2). q (where 0.8≤q≤2.5).

[0108] Furthermore, silicon-based anode active materials can be doped with Li, Mg, Al, Ca, or Ti, or alloyed with them. Additionally, when silicon-based anode active materials contain oxygen (O), a carbon coating can be applied to their surface, or they can be combined with carbon particles. The aim is to suppress volume expansion during charging and simultaneously improve the conductivity of the anode active material.

[0109] Since silicon-based anode active materials are anode active materials with large irreversible capacity, their content, average particle size, etc., can be appropriately controlled in order to adjust the ratio of the irreversible capacity of the positive electrode to the negative electrode to a predetermined range.

[0110] For example, based on the total weight of the negative electrode active layer, the silicon-based negative electrode active material can be included in the range of 0.1 wt% to 40 wt%. Specifically, based on the total weight of the negative electrode active layer, the silicon-based negative electrode active material can be included in the range of 0.5 to 20 wt%, 1 to 9 wt%, 5 to 15 wt%, 3 to 7 wt%, 11 to 19 wt%, 13 to 17 wt%, 15 to 20 wt%, 10 to 30 wt%, 20 to 40 wt%, 25 to 35 wt%, 15 to 25 wt%, or 9 to 22 wt%. This disclosure, by controlling the content ratio of silicon-based negative electrode active material contained in the negative electrode active layer within the above range, can improve the charging capacity per unit mass while reducing lithium consumption and irreversible capacity loss of the secondary battery during the initial charge and discharge period. Specifically, when the content ratio of silicon-based negative electrode active material exceeds the above upper limit, the following problems exist: the irreversible capacity of the negative electrode increases significantly, reducing the power output of the secondary battery, and increasing the heat generated during high-rate discharge. In addition, when the content ratio of silicon-based anode active material meets the above range, the volume change of the anode active layer caused by lithium ion insertion during secondary battery charging can be minimized, thereby extending the life of the secondary battery.

[0111] The negative electrode may include an excess of point-type conductive material in its active layer. Point-type conductive material refers to a conductive material with a sphericity of 0.7 or greater, where sphericity represents the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameters passing through the center of the conductive material particle in its two-dimensional projection. Specifically, point-type conductive materials may have a lower limit of 0.75 or greater, 0.8 or greater, 0.85 or greater, 0.9 or greater, or 0.95 or greater, and an upper limit of 1.0 or less, 0.95 or less, 0.9 or less, 0.85 or less, or 0.8 or less. For example, point-type conductive materials can have sphericity in the range of 0.7-1.0, 0.7-0.95, 0.7-0.9, 0.8-1.0, 0.85-1.0, 0.90-1.00, 0.90-0.99, 0.92-0.98, 0.95-0.99, 0.92-0.97, and 0.95-0.98, or greater than 0.90 and less than 1.0. When the sphericity is 1, the particles can have a spherical shape. Sphericity can be determined by measurement using a particle shape analyzer, or by measuring the particle shape using an optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy, etc., and then analyzing the results.

[0112] Generally, when linear conductive materials are used in the negative electrode active layer, the conductivity of the negative electrode can be increased by forming a conductive network between the linear conductive materials. However, in this case, the linear conductive materials impede the path of lithium ion movement and may instead degrade the power output performance and / or charging performance of the negative electrode. On the other hand, point-type conductive materials can reduce the resistance of the negative electrode active layer without hindering the movement of lithium ions and other particles within the negative electrode active layer.

[0113] In addition, point-type conductive materials can increase the power output of a secondary battery by participating in the insertion and extraction of lithium ions within the negative electrode active layer during charging and discharging, thereby assisting the power output of the negative electrode. Examples of such point-type conductive materials include carbon blacks such as acetylene black, furnace black, tank black, lamp black, thermal cracking black, or mixtures thereof.

[0114] Point-type conductive materials can have an average particle size (D) controlled within a predetermined range. 50 Specifically, the average particle size (D) of point-type conductive materials 50 The average particle size (D) of point-type conductive materials can range from 0.5 μm to 20 μm. 50 The particle size can be in the range of 1 μm to 20 μm, 5 μm to 20 μm, 10 μm to 20 μm, 11 μm to 19 μm, 8 μm to 15 μm, 15 μm to 20 μm, 13 μm to 19 μm, 14 μm to 17 μm, 5 μm to 8 μm, 0.5 μm to 15 μm, 0.5 μm to 10 μm, 0.5 μm to 8 μm, 0.5 μm to 5 μm, 0.5 μm to 3 μm, 0.5 μm to 1 μm, 5 μm to 10 μm, 1 μm to 5 μm, 0.5 μm to 4.5 μm, 0.5 μm to 3 μm, 1 μm to 4.5 μm, 1 μm to 3 μm, or 0.8 μm to 1.8 μm. This disclosure controls the average particle size (D) of the point-type conductive material. 50 Within the above range, the heat generation phenomenon generated by the secondary battery during high-rate discharge can be suppressed, and a high energy density of the negative electrode active layer can be achieved.

[0115] Furthermore, the negative electrode active layer may contain an excessive amount of dot-type conductive material. Specifically, based on the total weight of the negative electrode active layer, the dot-type conductive material may range from 10 wt% to 60 wt%. For example, based on the total weight of the negative electrode active layer, the dot-type conductive material may range from 15 wt% to 60 wt%, 20 wt% to 60 wt%, 25 wt% to 60 wt%, 30 wt% to 60 wt%, 35 wt% to 60 wt%, 40 wt% to 60 wt%, 45 wt% to 60 wt%, 10 wt% to 50 wt%, 10 wt% to 40 wt%, 10 wt% to 30 wt%, 10 wt% to 20 wt%, 20 wt% to 40 wt%, 30 wt% to 60 wt%, 50 wt% to 60 wt%, 11 wt% to 55 wt%, 11 wt% to 25 wt%, 21 wt% to 55 wt%, 21 wt% to 45 wt%, or 35 wt% to 55 wt%. This disclosure allows for the achievement of high energy density in secondary batteries by controlling the content of point-type conductive material within the aforementioned range. Furthermore, when the content of point-type conductive material in the negative electrode exceeds the upper limit, a significant increase in heat generation at the negative electrode during high-rate discharge of the secondary battery can be prevented. Additionally, a decrease in power output of the secondary battery when the content of point-type conductive material is below the lower limit can be prevented.

[0116] Meanwhile, in high-power secondary batteries, those used in urban air traffic (UAM) must possess the ability to provide high power output for a sustained period or longer at a low state of charge (SOC), ensuring safe landing of UAMs even in emergency situations. In this regard, as mentioned above, point-type conductive materials can reduce the resistance of the negative electrode active layer without hindering the movement of lithium ions within it. This reduced resistance compensates for the power output performance of the secondary battery under low SOC conditions. For example, discharging a secondary battery with a SOC of 35% at a constant power of approximately 900W for 15 seconds, and then discharging it to 0% at a constant power of approximately 1,000W, could take 10 seconds or more, 20 seconds or more, or 30 seconds or more. In this case, the upper limit voltage could be 4.2V and the lower limit voltage could be 2.5V.

[0117] The fact that the secondary battery can operate at an output power of 1000W or greater for more than 10 seconds with a state of charge (SOC) below 35% means that even when one of the batteries is depleted (BO, Battery Out), a landing time of 10 seconds or more can be guaranteed. Specifically, discharging to a 35% SOC refers to battery operation during the cruise process of Urban Air Traffic (UAM) before landing preparation (i.e., cruise before transition). Furthermore, a 15-second discharge process at a constant power of 900W refers to the transition process after cruise to landing mode. Finally, subsequent operation at an output power of 1000W or greater refers to the landing process. The ability to perform all these processes means that the minimum power output conditions required for landing during Urban Air Traffic (UAM) operations are met. Therefore, it can be seen that the secondary battery of this disclosure is suitable as a secondary battery for urban air traffic.

[0118] Furthermore, the positive and negative electrodes included in the secondary battery can meet a predetermined range for their irreversible capacity ratio. Specifically, when each of the positive and negative electrodes is charged and discharged at 22±5℃ and a 5C rate, the secondary battery can meet the requirement that the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode is in the range of 0.8-1.2. For example, when each of the positive and negative electrodes is charged and discharged under constant current conditions at 22±5℃ and a 5C rate, the secondary battery can meet the requirement that the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode is in the range of 0.8-1.15, 0.8-1.12, 0.8-1.1, 0.8-1.05, 0.85-1.2, 0.85-1.15, 0.85-1.12, 0.9-1.2, 0.9-1.15, or 0.9-1.12. The ratio of irreversible capacity of the negative and positive electrodes can be controlled by adjusting the components and / or content contained in each active layer of the negative and positive electrodes, but it is not limited to this.

[0119] An increase in irreversible capacity in the electrodes means a decrease in the discharge capacity used relative to the charge capacity of the electrodes, which in turn leads to a decrease in the power output of the secondary battery. Therefore, by controlling the ratio of the irreversible capacity of the negative electrode to the positive electrode within the aforementioned range, the present disclosure can achieve high energy density and power output characteristics of the secondary battery. Furthermore, a secondary battery in which the ratio of the irreversible capacity of the negative electrode to the positive electrode is controlled within the aforementioned range has the effect of suppressing heat generation during high-rate discharge. Therefore, the secondary battery according to the present disclosure is suitable for high-power secondary batteries requiring high energy density, high power output performance, and high thermal safety, such as those used in urban air traffic (UAM).

[0120] Meanwhile, the secondary battery according to this disclosure may include a positive electrode with high energy density, thus making it suitable for high-power secondary batteries such as those used in urban air traffic (UAM). For example, the positive electrode included in the secondary battery may have an energy density of 250 Wh / kg or greater, preferably 270 Wh / kg or greater, and more preferably 280 Wh / kg or greater. While a higher energy density of the positive electrode is preferred because it can exhibit higher energy at a lower weight, it may be 320 Wh / kg or less, considering the difficulty in meeting power output conditions as the positive electrode load increases to achieve high energy density, and the limitation on the proportion of the battery in the aircraft weight. In this case, the "energy density of the positive electrode" can be measured by placing an electrode assembly in which a 15 μm thick polyethylene-based separator is inserted between the positive electrode and lithium metal as the negative electrode in a battery casing, and then injecting an electrolyte solution into the casing to create a button-type half-cell, wherein the electrolyte solution is 1 M LiPF6 dissolved in an organic solvent of a mixture of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7. Specifically, the energy density of the positive electrode is recorded as a value obtained by charging the button half-cell at 25°C under constant current / constant voltage conditions from 0.33C to 4.25V, and then discharging it at a constant current of 0.33C until it reaches 3.0V; the initial discharge capacity (Ah) of the secondary battery obtained therefrom is multiplied by the average discharge voltage and then divided by the weight (kg) of the button half-cell.

[0121] Furthermore, the negative electrode active layer can have a thickness and / or loading within a predetermined range. Since the negative electrode active layer contains a negative electrode active material that exhibits electrochemical activity during the charging and discharging of the secondary battery, increasing the content of the negative electrode active material can increase the thickness of the negative electrode active layer, thereby increasing the charge / discharge capacity of the negative electrode. However, when the thickness of the negative electrode active layer becomes too thick, it becomes difficult to control the crystal orientation of the carbon-based negative electrode active material contained in the negative electrode active layer, and the increased volume change caused by lithium ion insertion and extraction during charging and discharging can significantly reduce the lifetime of the negative electrode. Therefore, the present disclosure allows for controllable average thickness of the negative electrode active layer within the range of 50 μm to 500 μm. For example, the average thickness of the negative electrode active layer can be controlled within the range of 50 μm to 450 μm, 50 μm to 300 μm, 100 μm to 450 μm, 100 μm to 400 μm, 100 μm to 350 μm, 100 μm to 300 μm, 100 μm to 250 μm, 100 μm to 200 μm, 150 μm to 400 μm, 200 μm to 450 μm, 300 μm to 500 μm, 150 μm to 300 μm, 150 μm to 250 μm, or 150 μm to 220 μm.

[0122] By controlling the average thickness of the negative electrode active layer within the aforementioned range, this disclosure can prevent a decrease in the charge / discharge capacity of the negative electrode due to the average thickness of the negative electrode active layer being lower than the lower limit of the aforementioned range. Furthermore, it can prevent a decrease in power output performance caused by an increase in the resistance of the pores contained within the negative electrode active layer due to the average thickness of the negative electrode active layer being greater than the upper limit of the aforementioned range.

[0123] Furthermore, this disclosure allows for control of the average loading of the negative electrode active layer at 250 mg / 25 cm⁻¹. 2 -700 mg / 25cm 2 Within a certain range. For example, the average loading of the negative electrode active layer can be 300 mg / 25 cm⁻¹. 2 -700 mg / 25cm 2 400 mg / 25cm 2 -700 mg / 25cm 2 500 mg / 25cm 2 -700 mg / 25cm 2 250 mg / 25cm 2 -500 mg / 25cm 2 250 mg / 25cm 2 -350 mg / 25cm 2 300 mg / 25cm2 -550 mg / 25cm 2 450 mg / 25cm 2 -650 mg / 25cm 2 300 mg / 25cm 2 -600 mg / 25cm 2 or 300 mg / 25cm 2 -450 mg / 25cm 2 This disclosure allows the average loading of the negative electrode active layer to be maintained at or above the aforementioned lower limit. In this case, since the energy density and power output performance of the negative electrode can reach a high level, it can be easily applied to devices requiring high power output, such as urban air mobility (UAM). Furthermore, by maintaining the loading of the negative electrode active layer at or below the aforementioned upper limit, this disclosure prevents a decrease in lithium-ion diffusion capacity and an increase in volume change due to lithium intercalation during the charging and discharging of the secondary battery.

[0124] In addition, each of the positive and negative electrodes may further include adhesives, conductive materials, other additives, etc., together with the active substances in each active layer (i.e., the positive active layer and the negative active layer).

[0125] For example, the positive and negative electrodes can contain an adhesive in each active layer to fix the individual components contained in each active layer and achieve adhesion to the current collector. The adhesive can be a substance with adhesive strength and electrochemical stability. Examples of such adhesives include styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene-butadiene-styrene block polymer (SBS), styrene-ethylene-butadiene block polymer (SEB), styrene-(styrene-butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene propylene diene monomer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-co-hexafluoropropylene, and polyvinylidene fluoride-co-trichloroethylene. Fluoride-co-trichloroethylene, polymethyl(meth)acrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene, polypropylene, polyethylene-co-vinyl acetate, polyethylene oxide, polypropylene oxide, polyarylate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, or combinations thereof.

[0126] The adhesive may be included in an amount of 0.1-5% by weight, based on the total weight of the positive or negative active layer. For example, the adhesive may be included in an amount of 0.1-4% by weight, 2-4% by weight, 1.5-5% by weight, 1-3% by weight, 0.1-2% by weight, or 0.1-1% by weight, based on the total weight of the positive or negative active layer.

[0127] Furthermore, in the case of the positive electrode, a separate conductive material can be included in the positive electrode active layer. Since lithium metal oxide, which is the main component of the positive electrode active layer, typically does not have high conductivity, a conductive material can be included in the positive electrode active layer to increase conductivity.

[0128] Conductive materials may include graphite; carbon blacks such as acetylene black, channel black, furnace black, lamp black, and thermal cracking black; carbon nanostructures such as carbon nanotubes and graphene; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorinated carbon, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. These can be used alone or in combination.

[0129] The amount of conductive material can account for 0.1-5% of the total weight of the positive electrode active layer. For example, the content of conductive material can be 0.1-4% of the total weight of the positive electrode active layer; 2-4% of the total weight; 1.5-5% of the total weight; 1-3% of the total weight; 0.1-2% of the total weight; or 0.1-1% of the total weight.

[0130] Each current collector for both the positive and negative electrodes can comprise a highly conductive metal, and there are no particular limitations, as long as the active layer of each electrode can easily adhere to it and the current collector is non-reactive within the battery's voltage range. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., can be used as the current collector. Furthermore, the thickness of the current collector can typically range from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion of the active material. For example, the composition can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0131] Furthermore, the separator inserted between the positive and negative electrodes of the secondary battery is an insulating film with high ion permeability and mechanical strength, and there are no particular limitations, as long as it is commonly used in the art. Specifically, the separator may comprise at least one polymer selected from chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymers. The separator may be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric comprising the aforementioned polymers, and in some cases may be in the form of a composite separator in which organic or inorganic particles are coated onto the porous polymer substrate with an organic adhesive. In addition, the separator may have an average pore size of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0132] Electrolyte compositions may include non-aqueous organic solvents, lithium salts, electrolyte additives, etc.

[0133] There are no particular limitations on the non-aqueous organic solvent used, as long as it is a solvent used in non-aqueous electrolytes in the art. For example, non-protic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate (EC), propylene carbonate (PC), propylene carbonate (PP), butenyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), γ-butyrolactone, 1,2-dimethoxyethane (DME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, ether, methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP) can be used as non-aqueous organic solvents.

[0134] Furthermore, the non-aqueous organic solvents used in this disclosure can be used alone or by mixing two or more types in any combination or ratio, depending on the intended use. Of particular preference, from the viewpoint of electrochemical stability regarding oxidation and reduction reactions and chemical stability regarding reactions with heat or solutes, mixtures of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate are preferred.

[0135] There are no particular limitations on the lithium salt, and it can be used as long as it is a lithium salt used in non-aqueous electrolytes in the art. Specifically, the lithium salt may include at least one selected from: LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi and (FSO2)2NLi.

[0136] The lower limit of the appropriate concentration range for the proper use of lithium salts is 0.5 mol / L or greater, specifically 0.7 mol / L or greater, and more specifically 0.9 mol / L or greater, and the upper limit is 2.5 mol / L or less, specifically 2.0 mol / L or less, and more specifically 1.5 mol / L or less. When the concentration of lithium salts is below 0.5 mol / L, there is a risk of degradation in the cycle characteristics and power output characteristics of the non-aqueous electrolyte battery due to decreased ionic conductivity. Furthermore, when the concentration of lithium salts exceeds 2.5 mol / L, the viscosity of the electrolyte solution in the non-aqueous electrolyte battery increases, which may reduce ionic conductivity and potentially degrade the cycle characteristics and power output characteristics of the non-aqueous electrolyte battery.

[0137] Furthermore, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the temperature of the electrolyte composition may rise due to the heat of lithium salt dissolution. When the temperature of the non-aqueous organic solvent rises significantly due to the heat of lithium salt dissolution in this manner, there is a risk that decomposition may be accelerated and hydrofluoric acid (HF) may be generated, especially in the case of fluorine-containing lithium salts. Hydrogen fluoride (HF) is undesirable because it degrades battery performance. Therefore, there is no particular limitation on the temperature at which lithium salts dissolve in non-aqueous organic solvents, but it can be controlled from -20°C to 80°C, specifically from 0°C to 60°C.

[0138] The secondary battery according to this disclosure has the above configuration, and therefore not only has excellent energy density and power output performance, but also has high safety due to its significant effect in suppressing secondary battery heating during high-rate charging and discharging.

[0139] The present disclosure will be described in more detail below through examples and comparative examples.

[0140] However, the following embodiments and comparative examples are only used to illustrate the present disclosure, and the content of the present disclosure is not limited to the following embodiments and comparative examples.

[0141] Examples 1 to 3 and Comparative Examples 1 to 10. Manufacturing of secondary batteries

[0142] Manufacturing of the positive electrode

[0143] Preparation of LiNi in primary particle form 0.8 Co 0.1 Mn 0.1O2 was used as the positive electrode active material and Li6CoO4 as the positive electrode additive, and carbon nanotubes (CNTs) and polyvinylidene fluoride (PVdF) were prepared as conductive materials and binders, respectively. A positive electrode slurry was prepared by mixing 97 wt% of the prepared positive electrode active material, 1.2 wt% of the conductive material, and 1.8 wt% of the binder with N-methylpyrrolidone at a solids content of 50%. The mixing of the positive electrode additive into the positive electrode slurry was controlled as shown in Table 1 below. In Table 1, "O" indicates the case where the positive electrode additive is mixed, and "X" indicates the case where the positive electrode additive is not mixed. Furthermore, when the positive electrode additive was mixed, the contents of the positive electrode active material and the positive electrode additive were controlled to be 94-96.5 wt% and 0.5-3 wt%, respectively.

[0144] The prepared positive electrode slurry is applied to an aluminum sheet (thickness: 12 μm) conveyed by a roller-to-roll (conveyor speed: 6 m / min) using a die coater, then dried with hot air and rolled at 50 to 60°C at a speed of 30 to 40 m / min to manufacture the positive electrode.

[0145] Manufacturing of negative electrode

[0146] By mixing natural graphite (average particle size (D)) at a weight ratio of 1:1 50 : Approximately 11 to 13 μm) and artificial graphite (average particle size (D 50 Mixed graphite (approximately 15 to 16 μm) was prepared as a carbon-based negative electrode active material. In addition, styrene-butadiene rubber (SBR) was prepared as a binder and carboxymethyl cellulose (CMC) as a thickener, and carbon black (Super-P, sphericity: approximately 0.88 ± 0.3) and carbon nanotubes (CNTs) were prepared as conductive materials.

[0147] Then, an anode slurry was prepared by mixing carbon-based anode active material, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and conductive material with water at a solids content of 50%. At this time, i) the type of conductive material was applied as shown in Table 1 below. Furthermore, in the anode slurry, the content of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) was fixed at 3.1% by weight of the total solids content, with the remainder filled with carbon-based anode active material and conductive material, and ii) the content of conductive material was controlled based on the total solids content as shown in Table 1 below.

[0148] The prepared negative electrode slurry was applied to a copper sheet (thickness: 6 μm) conveyed by a roller-to-roll conveyor (conveyor speed: 6 m / min) using a die coater. The applied negative electrode slurry was dried with hot air in the range of approximately 180 ± 10 °C and rolled using a roller press to form a negative electrode active layer on the negative electrode current collector, thereby manufacturing a negative electrode for secondary batteries (average loading: approximately 250 mg / 25 cm⁻¹). 2 -300 mg / 25cm 2 ).

[0149] Irreversible capacity measurement of positive and negative electrodes

[0150] The same process is used to manufacture the positive and negative electrodes respectively.

[0151] A positive electrode half-cell was fabricated using separately prepared positive electrode and lithium metal, and a negative electrode half-cell was fabricated in the same manner using the prepared negative electrode and lithium metal. A separator made of 14 μm polypropylene and an electrolyte solution prepared by dissolving LiPF6 at a concentration of 1 M in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a 1:1 volume ratio were used.

[0152] Each of the manufactured positive and negative half-cells was charged and discharged to measure its charge-discharge capacity. Charge and discharge were performed at 5.0C and 22±5℃ respectively, and the irreversible capacity (X) of the positive electrode and the irreversible capacity (Y) of the negative electrode were calculated based on the measured charge and discharge capacities. The irreversible capacity was then calculated based on the deviation between the charge and discharge capacities. The ratio (Y / X) of the irreversible capacity (Y) of the negative electrode to the irreversible capacity (X) of the positive electrode was calculated using the results. The results are shown in Table 1 below.

[0153] Assembly of secondary batteries

[0154] A separator made of 14 μm polypropylene is inserted between the pre-prepared positive and negative electrodes and inserted into the casing. Then, an electrolyte composition is injected to assemble a 1Ah-class secondary battery.

[0155] Here, as the electrolyte composition, a solution prepared by dissolving LiPF6 at a concentration of 1M in an organic solvent is used, the organic solvent comprising ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 3:4:3.

[0156] [Table 1]

[0157]

[0158] Examples 4-6. Manufacturing of Secondary Batteries

[0159] The secondary battery was manufactured in the same manner as in Example 2, except that the positive electrode active material used was LiNi. 0.8 Co 0.1 Mn 0.1 O2 is controlled to have the particle form shown in Table 2 below.

[0160] At this point, scanning electron microscopy (SEM) images (magnification: approximately 20,000×) of the cross-section of the manufactured positive electrode active layer are acquired, and image analysis is performed on the acquired images to identify particles without grain boundaries (i.e., primary particles) and particles containing grain boundaries (i.e., secondary particles), thereby confirming the particle form of the positive electrode active material. Then, the ratio of primary particles to secondary particles is confirmed by calculating the area ratio of each type of particle in the entire image.

[0161] [Table 2]

[0162]

[0163] Example 7 and Comparative Examples 11-12. Manufacturing of secondary batteries

[0164] The secondary battery was manufactured using the same method as in Example 2, except that, as shown in Table 3 below, natural graphite (with an average particle size of D) was mixed in a 1:1 weight ratio. 50 : Approximately 11–13 μm) and artificial graphite (average particle size (D 50 Mixed graphite (approximately 15–16 μm) and silicon dioxide (SiO₂) were prepared. q (where 0.8≤q≤2.5) is used as the negative electrode active material.

[0165] [Table 3]

[0166]

[0167] Experimental Example 1

[0168] The following experiments were conducted to evaluate the performance characteristics of the secondary battery according to this disclosure.

[0169] Evaluation of energy density and power output rate

[0170] The lithium secondary batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 12 were charged to 4.2V at 0.3C rate under CC-CV conditions at 25°C, and then discharged to 2.5V at 0.3C rate under CC conditions for activation.

[0171] Each activated lithium secondary battery was charged to 4.2V at 1.0C under CC-CV conditions at 25°C, and the discharge capacity was measured for the first time. Simultaneously, it was discharged to 2.5V at 0.33C under CC conditions. Subsequently, each discharged secondary battery was charged again to 4.2V at 1.0C under CC-CV conditions at 25°C, and the discharge capacity was measured a second time while discharging to 2.5V at 5.0C under CC conditions.

[0172] The ratio of the discharge capacity at 5.0C under CC conditions to the discharge capacity at 0.33C under CC conditions (DC) was calculated from each measured discharge capacity. 5.0C / DC 0.33C To obtain the 5C rate discharge efficiency of each secondary battery.

[0173] Furthermore, the ratio of the discharge efficiency of Comparative Example 1 to the discharge efficiency of each secondary battery was calculated based on the 5C rate discharge efficiency to determine the rate of increase or decrease in energy density of each secondary battery. The results are shown in Table 4 below.

[0174] Heating measurement during high-rate discharge

[0175] The lithium secondary batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 12 were charged to 4.2V at 0.3C rate under CC-CV conditions at 25°C, and then discharged to 2.5V at 0.3C rate under CC conditions for activation.

[0176] Each activated secondary battery underwent a total of 300 charge-discharge cycles, where one cycle was defined as charging to 4.2V at a rate of 1.0C under CC-CV conditions and discharging to 2.5V at a rate of 5.0C under CC conditions. During this time, a temperature sensor was installed on the outside of the casing of each secondary battery to measure the temperature of the secondary battery during discharge, thereby measuring the maximum heat generation temperature of the secondary battery. Based on the measured results, the deviation between the maximum heat generation temperature of each secondary battery and the maximum heat generation temperature of Comparative Example 1 was calculated, and the results are shown in Table 4 below.

[0177] [Table 4]

[0178]

[0179]

[0180] Referring to Table 4, it can be seen that the secondary battery disclosed in this invention not only has excellent energy density and power output performance, but also suppresses heat generation during high-rate discharge.

[0181] Specifically, it was found that the secondary battery manufactured in the examples had an energy density that was about 5% higher than that of the secondary battery in Comparative Example 1, wherein the positive electrode of Comparative Example 1 did not contain positive electrode additives and the negative electrode did not contain point-type conductive materials. Furthermore, it was confirmed that the secondary battery manufactured in the examples exhibited a high discharge efficiency of about 80% or more when discharged at a 5C rate, and that the secondary battery suppressed heat generation during high-rate discharge.

[0182] These results demonstrate that secondary batteries, including the negative electrode according to this disclosure, can be used as secondary batteries for urban air mobility (UAM) applications requiring high energy density, high power output performance, and high thermal safety.

[0183] Experiment Example 2

[0184] The following experiments were conducted to evaluate the power output performance of the secondary battery according to this disclosure at a low state of charge (SOC).

[0185] The lithium secondary batteries manufactured in Examples 1-7 and Comparative Examples 1-12 were charged to SOC 30% at a constant current of 0.1C at 25°C, activated, and then degassed.

[0186] Then, it was charged to 4.2V under constant current / constant voltage conditions of 0.33C, discharged to 35% state of charge (SOC) under constant power conditions of approximately 250W, and subsequently discharged for 18 seconds under constant power conditions of approximately 900W. The time required to reach the lower limit voltage of 2.5V was then measured during discharge at a constant power condition of approximately 1,100W. The results are shown in Table 5 below.

[0187] [Table 5]

[0188]

[0189] As shown in Table 5, it can be seen that the secondary battery according to this disclosure has excellent power output performance even at a low state of charge (SOC) of 35%.

[0190] Specifically, it was found that the secondary battery manufactured in the embodiment, at 35% state of charge (SOC), required 10 seconds or more, specifically 30 seconds or more, or 35 seconds or more, to reach 2.5V after discharging for 18 seconds at a constant power of approximately 900W, and then at a constant power of approximately 1,100W.

[0191] This means that even at a low state of charge (SOC), the secondary battery manufactured in the embodiment exhibits high power output performance.

[0192] These results demonstrate that secondary batteries, including the negative electrode according to this disclosure, can be used as secondary batteries for urban air mobility (UAM) applications requiring high energy density, high power output performance, and high thermal safety.

[0193] Although this disclosure has been described with reference to preferred embodiments, those skilled in the art will understand that various modifications and variations may be made therein without departing from the scope of this disclosure as defined by the appended claims. Therefore, the scope of this disclosure should not be limited by the specific description in the specification, but rather by the appended claims.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive active layer located on a positive current collector, and the positive active layer comprises a positive active material and a positive additive, wherein the negative electrode comprises a negative active layer located on a negative current collector, and the negative active layer comprises a negative active material and a point-type conductive material; and wherein when charging and discharging are performed at 22±5°C and 5C rate, the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode satisfies the range of 0.8 to 1.

2.

2. The secondary battery according to claim 1, wherein when charging and discharging are performed at 22±5°C and 5C rate, the ratio of the irreversible capacity of the negative electrode to the irreversible capacity of the positive electrode satisfies the range of 0.9 to 1.

15.

3. The secondary battery according to claim 1, wherein based on the total weight of the negative active layer, the content of the point-type conductive material is in the range of 10 wt% to 60 wt%.

4. The secondary battery according to claim 1, wherein the point-type conductive material comprises acetylene black, oil furnace carbon black, channel carbon black, lamp carbon black, thermal cracking carbon black, or a mixture thereof.

5. The secondary battery according to claim 1, wherein the average particle size (D) of the point-type conductive material is... 50 (In the range of 0.5 μm-20 μm) 6. The secondary battery according to claim 1, wherein the negative active material is a carbon-based negative active material comprising natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase pitch, graphitized coke, or a mixture thereof.

7. The secondary battery according to claim 1, wherein the negative electrode active material is at least one selected from silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q Silicon-based anode active materials, where 0.8≤q≤2.5).

8. The secondary battery according to claim 1, wherein the positive active material comprises at least one lithium metal oxide represented by the following Chemical Formula 1 and 2: [Chemical Formula 1] Li a [Ni b Co 1-b-c M 1 c ]O2 [Chemical Formula 2] Li p [Mn 2-q M 2 q ]O4 wherein in Chemical Formula 1 and Chemical Formula 2, M 1 It is at least one element selected from W, Cu, Fe, V, Cr, Mn, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B and Mo; M 2 It is at least one element selected from W, Cu, Fe, V, Cr, Ni, Al, Mg, Ca, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ce, Nb, B, and Mo, and a, b, c, p and q respectively satisfy 1.0≤a≤1.30, 0≤b<1, 0≤c≤0.4, 1.0≤p≤1.30 and 0≤q≤1.

0.

9. The secondary battery according to claim 1, wherein the positive active material comprises at least one of primary particles and secondary particles formed by agglomeration of the primary particles.

10. The secondary battery according to claim 1, wherein the positive additive comprises at least one compound represented by the following Chemical Formula 3 to Chemical Formula 5: [Chemical Formula 3] Li m M 3 (1-n) M 4 n O4 [Chemical Formula 4] Li2M 5 (1-r) M 6 r O2 [Chemical Formula 5] Li2R z wherein in Chemical Formula 3 to Chemical Formula 5, M 3 is Fe, Co, Mn, Zn, Al or Ga, M 4 It is at least one metal selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, provided that M is a metal selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. 3 and M 4 Including different metals; M 5 Is it Ni or Cu? M 6 It is at least one metal selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, provided that M is a metal selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. 5 and M 6 Including different metals; R is O, S or Se, and m, n, r and z respectively satisfy 4≤m≤7, 0≤n≤0.5, 0<r≤0.5 and 0.8≤z≤2.

5.

11. The secondary battery according to claim 10, wherein the positive electrode additive comprises at least one compound selected from Li5FeO4, Li6MnO4, Li6CoO4, Li6ZnO4, Li5AlO4, Li5GaO4, Li2NiO2, Li2CuO2, Li2O, Li2O2, Li2S and Li2Se.

12. The secondary battery according to claim 1, wherein the content of the positive electrode additive is in the range of 0.1% by weight to 5% by weight based on the total weight of the positive electrode active layer.

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