KR20230047555A - Secondary battery improved safety - Google Patents

Abstract

The present invention relates to a secondary battery. The secondary battery has a structure in which a plurality of unit cells are stacked and when the unit cells are stacked, an average particle size or/and sphericity of a negative electrode active material included in a negative electrode are controlled to have a constant gradient so as to realize a heat radiation effect at the same time while minimizing heat generation without lowering performance of a battery in case of charging/discharging of the battery.

Description

Secondary battery with improved safety {SECONDARY BATTERY IMPROVED SAFETY}

The present invention relates to a secondary battery with improved safety by controlling the average particle size and/or sphericity of an anode active material contained in an anode when unit cells are stacked.

Recently, secondary batteries have been widely applied not only to small devices such as portable electronic devices, but also to medium and large devices such as battery packs or power storage devices of hybrid vehicles and electric vehicles.

Such a secondary battery has advantages such as high operating voltage and high energy density, but since it uses an organic electrolyte, overcharging of the lithium secondary battery causes overcurrent and overheating, and in severe cases, a fire due to explosion or ignition may occur.

As an example, a pouch-type battery including a stacked/folding type electrode assembly may swell due to gas generation when left at a high temperature, so that the electrode and separator cannot be firmly fixed, and in particular, due to shrinkage of the outer separator Safety problems become serious when the anode and cathode are short-circuited. In addition, heat generation occurs due to resistance during charging and discharging of the pouch-type battery, and heat is more severe because heat transfer is not easily achieved in the electrode of the unit cell disposed in the central layer than in the unit cell disposed in the outer layer. Therefore, there is a problem in that the electrodes of the unit cells disposed in the center layer are degraded due to high heat more quickly than the electrodes of other unit cells in the vicinity, and in the long term, the battery performance deteriorates due to the difference in capacity and resistance between the electrode layers.

Therefore, there is a need for a method for solving the problem of battery performance deterioration and safety due to high heat generated during charging and discharging of the battery.

Republic of Korea Patent Publication No. 10-2013-0091067 Republic of Korea Patent Publication No. 10-2019-0094921

Accordingly, an object of the present invention is to improve the deterioration of performance due to deterioration of the battery due to the temperature rise generated during charging and discharging of the battery, and to provide a secondary battery with improved battery safety.

In order to solve the above problems,

In one embodiment, the present invention

It includes a plurality of unit cells having an anode, a cathode, and a separator interposed between the anode and the cathode,

The negative electrode has a structure in which a negative electrode composite layer containing an negative electrode active material is provided on a negative electrode current collector,

The plurality of unit cells have a stacked structure in the thickness direction,

Provided is a secondary battery in which the average particle size of an anode active material included in each unit cell increases as the unit cell disposed in the center is stacked to the unit cell disposed on the outermost part.

At this time, the negative electrode active material included in each unit cell may have an average particle size of 1 μm to 50 μm.

In addition, the negative active material included in each unit cell may have an average particle size deviation of 0.1 to 6 μm from the negative active material of an adjacent unit cell.

In addition, the negative electrode active material included in each unit cell has a degree of sphericity of 0.5 to 1.0, and the degree of sphericity of the negative electrode active material tends to decrease as it progresses from the centrally disposed unit cell to the outermost unit cell. there is.

At this time, the negative electrode active material included in each unit cell may have a deviation in sphericity of 0.01 to 0.1 from the negative electrode active material of the adjacent unit cell.

In addition, the negative electrode active material included in each unit cell may include at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and Ketjen black.

In addition, the negative electrode mixture layer of the negative electrode provided in each unit cell has an average thickness of 50 μm to 200 μm, and the average thickness of the negative electrode mixture layer progresses from the central unit cell to the outermost unit cell. can increase

In addition, the separator interposed between the positive electrode and the negative electrode of the secondary battery may include at least one polymer among polyethylene, polypropylene, and polyethylene-propylene copolymer.

In addition, the secondary battery may further include an auxiliary separator between unit cells, and the auxiliary separator may include a polymer substrate in which inorganic particles or glass fibers are dispersed.

Also, the number of unit cells included in the secondary battery may be 3 to 50.

Furthermore, the present invention, in one embodiment,

Provided is a secondary battery module including the secondary battery according to the present invention described above.

The secondary battery according to the present invention has a structure in which a plurality of unit cells are stacked, and when the unit cells are stacked, the average particle size and/or sphericity of the negative electrode active material contained in the negative electrode is controlled to have a constant gradient, so that the battery is charged and discharged. Since heat generation can be minimized and a heat dissipation effect can be implemented at the same time without deterioration of battery performance, there is an advantage in preventing battery deterioration and improving safety.

Since the present invention can have various changes and various embodiments, specific embodiments will be described in detail in the detailed description.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

In the present invention, the term "comprises" or "has" is intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features s, number, step, action, component, part or It should be understood that it does not preclude the possibility of existence or addition of combinations thereof.

Further, in the present invention, when a part such as a layer, film, region, plate, etc. is described as being “on” another part, this includes not only the case where it is “directly on” the other part, but also the case where another part is present in the middle thereof. . Conversely, when a part such as a layer, film, region, plate, or the like is described as being “under” another part, this includes not only being “directly under” the other part, but also the case where there is another part in the middle. In addition, in the present application, being disposed "on" may include the case of being disposed not only on the upper part but also on the lower part.

Hereinafter, the present invention will be described in more detail.

secondary battery

In one embodiment, the present invention

It includes a plurality of unit cells having an anode, a cathode, and a separator interposed between the anode and the cathode,

The negative electrode has a structure in which a negative electrode composite layer containing an negative electrode active material is provided on a negative electrode current collector,

The plurality of unit cells have a stacked structure in the thickness direction,

Provided is a secondary battery in which the average particle size of an anode active material included in each unit cell increases as the unit cell disposed in the center is stacked to the unit cell disposed on the outermost part.

The secondary battery according to the present invention has a structure in which a plurality of unit cells are stacked in the thickness direction of the unit cell, and the average particle size of the negative electrode active material contained in each unit cell is stacked on the outermost layer based on the unit cell disposed in the center. has a configuration in which increases with a constant gradient.

Accordingly, since the secondary battery can more dissipate heat generated inside the cell during charging and discharging, heat accumulation inside the secondary battery can be improved, and battery deterioration can be suppressed and safety can be improved.

Specifically, the secondary battery according to the present invention has a structure in which a plurality of unit cells including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are stacked in a thickness direction.

In this case, the positive electrode includes a positive electrode composite material layer prepared by applying, drying, and pressing a positive electrode active material on a positive electrode current collector, and may optionally further include a conductive material, a binder, and other additives, if necessary.

The cathode active material may include one commonly applied to a lithium secondary battery, but preferably may include a lithium metal composite oxide containing three or more elements selected from the group consisting of nickel, cobalt, manganese, and aluminum, In some cases, the lithium metal composite oxide may have a form doped with another transition metal (M ¹ ). For example, the cathode active material may be a lithium metal composite oxide represented by Formula 1 capable of reversible intercalation and deintercalation:

[Formula 1]

Lix[NiyCozMnwM ^1v ]Ou

In Formula 1,

M ¹ is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and At least one element selected from the group consisting of Mo,

x, y, z, w, v and u are 1.0≤x≤1.30, 0.1≤y<0.95, 0.01<z≤0.5, 0≤w≤0.5, 0≤v≤0.2, 1.5≤u≤4.5, respectively.

As an example, the cathode active material is LiNi1/3Co1/3Mn1/3O2, LiNi0.8Co0.1Mn0.1O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.9Co0.05Mn0.05O2, LiNi0.6Co0.2Mn0.1Al0.1O2 , LiNi0.6Co0.2Mn0.15Al0.05O2 and LiNi0.7Co0.1Mn0.1Al0.1O2.

In addition, as the positive electrode current collector, one having high conductivity without causing chemical change in the battery may be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and aluminum or stainless steel may be surface-treated with carbon, nickel, titanium, silver, or the like.

In addition, the positive electrode current collector may form fine irregularities on the surface to increase the adhesiveness of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics are possible. In addition, the average thickness of the current collector may be appropriately applied in the range of 3 to 500 μm in consideration of the conductivity and total thickness of the anode to be manufactured.

In addition, the negative electrode, like the positive electrode, includes a negative electrode mixture layer prepared by applying, drying, and pressing a negative electrode active material on a negative electrode current collector, and may optionally further include a conductive material, a binder, and other additives as needed. there is.

The anode active material may include, for example, a carbon material. Specifically, the carbon material refers to a material containing carbon atoms as a main component, and the carbon material is selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black It may include one or more species that are.

In addition, the negative electrode active material may have a configuration in which the average particle size of the negative electrode active material included in each unit cell increases with a constant gradient as the negative electrode active material is stacked from the central unit cell to the outermost unit cell. That is, the average particle size of the negative electrode active material of the unit cell disposed in the center is smaller than the average particle size of the negative electrode active material of the unit cell disposed on the outermost edge, and the average particle size of the negative electrode active material is such that the position of the stacked unit cells is from the center to the outermost edge. As it progresses, it may have a constant increasing slope.

At this time, the negative electrode active material may have an average particle size of 1 μm to 50 μm, specifically 1 μm to 40 μm; 1 μm to 30 μm; 1 μm to 20 μm; 5 μm to 30 μm; 10 μm to 30 μm; It may be 8 μm to 25 μm or 9 μm to 18 μm. Here, the "average particle size" means the average size of negative electrode active material particles. The average particle size may be obtained by measuring the particle size of minimum particles distinguished as one lump when observing a cross section of the negative electrode active material through a scanning electron microscope (SEM), and calculating an arithmetic average value thereof. Alternatively, the average particle size may be a value measured using a particle size analyzer. In this case, the average particle size at a point corresponding to D50, that is, a point at which 50% of the cumulative volume distribution of the negative electrode active material measured using the particle size analyzer is obtained. It can be used as granularity.

In addition, the negative electrode active material included in each unit cell may have an average particle size gradient due to a particle size deviation of a certain range from the negative electrode active material included in the adjacent unit cell. Specifically, the negative electrode active material may have a particle size deviation of 0.1 μm to 6 μm and the negative electrode active material included in the adjacent unit cell, 0.1 μm to 5 μm; 0.1 μm to 4 μm; 0.1 μm to 3 μm; 0.1 μm to 2 μm; 0.1 μm to 1 μm; 0.1 μm to 0.8 μm; 0.5 μm to 2.5 μm; 0.5 μm to 5 μm; 1 μm to 4 μm; 2 μm to 5 μm; Alternatively, it may have a particle size deviation of 0.1 μm to 0.6 μm.

As described above, the secondary battery of the present invention controls the average particle size of the negative electrode active material contained in each unit cell, so that the average particle size gradient can be implemented so that the average particle size of the negative electrode active material increases as it progresses from the center to the outermost layer of the stacked unit cells. Through this, there is an advantage in that heat generated during charging and discharging of the secondary battery can be more effectively dissipated to prevent heat storage inside the battery.

In addition, the average particle size and sphericity of the negative electrode active material may be controlled according to the location of the stacked unit cells. Specifically, the negative electrode active material may have a degree of sphericity of 0.5 to 1.0, more specifically 0.5 to 0.9; 0.5 to 0.7; 0.6 to 0.8; Or it may have a sphericity of 0.8 to 1.0. Here, the term "sphericity" may mean the ratio of the major axis to the minor axis of the particle. The degree of sphericity may be measured through a particle shape analyzer. Specifically, after deriving the cumulative distribution of the sphericity of the negative electrode active material particles through the particle shape analyzer, the sphericity of which the distribution ratio from the particles having a large sphericity is 50% is determined as the sphericity of the negative electrode active material particles. can

In addition, as the negative electrode active material progresses from a central unit cell to an outermost unit cell, the sphericity of the negative electrode active material may decrease.

As an example, the negative electrode active material included in each unit cell may have a sphericity deviation of 0.01 to 0.1 from the negative electrode active material included in the adjacent unit cell, specifically 0.01 to 0.09; 0.01 to 0.05; 0.01 to 0.04; 0.03 to 0.09; Alternatively, it may have a sphericity deviation of 0.05 to 0.1.

As described above, the present invention has a sphericity and sphericity deviation of the negative electrode active material included in each unit cell, so that the sphericity of the negative electrode active material decreases as it progresses from the center to the outermost layer of the stacked unit cells, thereby forming a constant sphericity gradient Through this, it is possible to prevent battery performance deterioration by lowering resistance inside the battery during charging and discharging of the secondary battery, and it is possible to prevent heat storage inside the battery by implementing a heat dissipation effect generated.

Furthermore, the negative electrode mixture layer of the negative electrode provided in each unit cell may have an average thickness of 50 μm to 200 μm, specifically 80 μm to 200 μm; 100 μm to 200 μm; 120 μm to 200 μm; 150 μm to 200 μm; 80 μm to 190 μm; 90 μm to 170 μm; 130 μm to 170 μm; 160 μm to 190 μm; Or it may be 110 μm to 160 μm.

In addition, the average thickness of the negative electrode mixture layer may increase as it progresses from a central unit cell to an outermost unit cell.

The present invention increases the average thickness of the negative electrode mixture layer provided in each unit cell as the unit cells progress from the center to the outermost layer of the stacked structure, thereby increasing the density and / or the density of the negative electrode active material included in the center of the stacked unit cells Since the loading amount can be lowered, the amount of heat generated inside the cell during charging and discharging of the secondary battery can be reduced.

On the other hand, the separator interposed between the anode and cathode of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the art, but is specifically chemical-resistant and hydrophobic polypropylene. ; polyethylene; Polyethylene-propylene copolymers containing at least one polymer may be used. The separator may have the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above-described polymer, and in some cases may have the form of a composite separator coated with organic or inorganic particles on the porous polymer substrate with an organic binder. may be In addition, the separator may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

In addition, the secondary battery according to the present invention may further include an auxiliary separator between unit cells in addition to the separator provided inside each unit cell. The auxiliary separator may be disposed between unit cells to separate unit cells in order to prevent an internal short circuit due to contact of each electrode provided in the unit cell, similar to a separator provided inside the unit cell.

This auxiliary separator is chemically resistant and hydrophobic polypropylene; polyethylene; It may have a structure in which inorganic particles or glass fibers are dispersed in a porous polymer substrate composed of at least one polymer of polyethylene-propylene copolymer, and may be inserted between unit cells by an alternating lamination process of unit cells and unit cells. there is.

Furthermore, in the secondary battery, although the number of stacked unit cells may be appropriately controlled depending on the purpose for which the battery is used, specifically, it may include 3 to 50 unit cells, and more specifically, 3 to 40 unit cells. dog; 3 to 30; 3 to 20; 5 to 10; 8 to 25; 15 to 30; 20 to 40; 30 to 50; Alternatively, it may include 10 to 40 unit cells.

According to the present invention, by controlling the number of unit cells included in the secondary battery within the above range, desired battery output and capacity can be realized while minimizing degradation in battery performance due to heat generated during charging and discharging of the battery.

As described above, the secondary battery according to the present invention has a structure in which a plurality of unit cells are stacked, but when the unit cells are stacked, the average particle size and / or sphericity of the negative electrode active material contained in the negative electrode is controlled to have a certain gradient, Since heat generation of the battery can be minimized during charging and discharging of the battery and at the same time a heat dissipation effect can be implemented, there is an advantage in preventing battery deterioration and improving safety.

Secondary battery module

In addition, in one embodiment of the present invention,

Provided is a secondary battery module including the secondary battery according to the present invention described above.

The secondary battery module according to the present invention includes the above-described secondary battery of the present invention, and since the heat dissipation effect of the secondary battery is excellent during charging and discharging of the module, heat storage of the secondary battery can be prevented. There is an advantage that deterioration can be suppressed and safety can be improved.

Since the secondary battery module according to the present invention has a configuration including the secondary battery of the present invention and has excellent safety when exposed to high temperatures, it can be used as a power source for medium or large-sized devices requiring high temperature safety, long cycle characteristics, and high rate characteristics. . Specific examples of these medium-large devices include a power tool powered by an omniscient motor and moving; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); electric golf carts; A power storage system may be mentioned, and more specifically, a hybrid electric vehicle (HEV) may be cited, but is not limited thereto.

Hereinafter, the present invention will be described in more detail by examples and experimental examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the contents of the present invention are not limited to the following Examples and Experimental Examples.

Examples 1 to 4 and Comparative Examples 1 to 3. Manufacturing of secondary batteries

N-methylpyrrolidone was injected into a homo mixer, and 97.8 parts by weight of LiNi0.6Co0.2Mn0.2O2 as a cathode active material was added to 100 parts by weight of the solid content of the cathode slurry; 0.7 parts by weight of carbon black as a conductive material; 1.5 parts by weight of PVdF as a binder was weighed and added, and mixed at 2,000 rpm for 60 minutes to prepare a cathode slurry for a lithium secondary battery. The prepared positive electrode slurry was applied to both sides of an aluminum thin plate, dried, and then rolled to prepare a positive electrode.

Separately, water was injected into a homomixer, and 97.5 parts by weight of artificial graphite as an anode active material was added to 100 parts by weight of the solid content of the anode slurry; 2 parts by weight of styrene butadiene rubber (SBR) as a binder; A negative electrode slurry for a lithium secondary battery was prepared by weighing and adding 0.5 parts by weight of carboxylmethyl cellulose (CMC) as a thickener, and mixing at 2,000 rpm for 60 minutes. The prepared negative electrode slurry was applied to both sides of a thin copper plate, dried, and then rolled to prepare a negative electrode.

A unit cell was manufactured by interposing a porous polyethylene (PE) film (average thickness: 20 μm) between the prepared positive electrode and negative electrode. Five manufactured unit cells were stacked in the thickness direction of the unit cells with an auxiliary separator therebetween to make an electrode assembly, which was inserted into a cell pouch, and an electrolyte was injected to prepare a secondary battery.

At this time, the auxiliary separator used a porous polyethylene (PE) film (average thickness: 20 μm) in which glass fibers were dispersed, and the electrolyte solution injected into the cell pouch had EC (Ethylene Carbonate) and EMC (Ethyl Methyl Carbonate) in a ratio of 3:7. A liquid electrolyte in which LiPF ₆ was added as a lithium salt to an organic solvent mixed in a volume ratio of , was used.

In addition, the average thickness of the negative electrode mixture layer provided in each unit cell, the average particle size and sphericity of each layer of the negative electrode active material contained in the negative electrode mixture layer are shown in Table 1 below for each layer 1 / 2 / 3 / 4 / 5 Adjusted as indicated.

negative active material
Average particle size per layer
[Unit: ㎛] negative active material
Sphericity by layer of the cathode composite layer
Average thickness per layer
[Unit: ㎛] Example 1 16/13/11/13/16 0.8/0.8/0.8/0.8/0.8 120/120/120/120/120 Example 2 16/13/11/13/16 0.6/0.8/1.0/0.8/0.6 120/120/120/120/120 Example 3 16/13/11/13/16 0.8/0.8/0.8/0.8/0.8 140/120/80/120/140 Example 4 16/13/11/13/16 0.6/0.8/1.0/0.8/0.6 140/120/80/120/140 Comparative Example 1 13/13/13/13/13 0.8/0.8/0.8/0.8/0.8 120/120/120/120/120 Comparative Example 2 13/13/13/13/13 0.6/0.8/1.0/0.8/0.6 120/120/120/120/120 Comparative Example 3 13/13/13/13/13 0.8/0.8/0.8/0.8/0.8 140/120/80/120/140

experimental example.

In order to evaluate the performance of the secondary battery according to the present invention, the following experiments were performed.

A) Evaluation of battery heat during charging and discharging

Overcharging was performed on the secondary batteries fabricated in Examples and Comparative Examples, and surface and internal temperatures of the overcharged secondary batteries were measured. Specifically, a thermal sensor was installed inside the case of each target secondary battery, and after charging at 4.2V, the charged battery was overcharged until it reached 10V with a constant current of 1A. Then, a constant voltage of 10 V was maintained for 6 hours. After 6 hours, the internal temperature of the battery was measured with a thermal sensor installed on each secondary battery. It was measured as the surface temperature of the battery at time. The measured results are shown in Table 2 below.

B) Evaluation of secondary battery resistance after overcharging

The secondary batteries prepared in Examples and Comparative Examples were overcharged, and the resistance of the overcharged secondary batteries was measured to evaluate the degree of deterioration of each battery. Specifically, target secondary batteries were fully charged at 4.2V, and DC resistance of the fully charged secondary batteries was measured. Then, the charged battery was overcharged with a constant current of 1A until it reached 10V, and then the constant voltage of 10V was maintained for 6 hours. After 6 hours had elapsed, the DC resistance of each secondary battery was measured to confirm the degree of change before and after overcharging.

At this time, the DC resistance measurement was performed through CV measurement, and the measurement potential of the CV measurement started from 3V, and was performed at a measurement rate of 5 mV/cm 2 and a potential measurement range of 3 to 5.5 V. The measured results are shown in Table 2 below.

Battery temperature when overcharged Change in DC resistance of the battery surface interior Example 1 37±1℃ 46±1℃ 3.2Ω Example 2 34±1℃ 43±1℃ 2.1Ω Example 3 34±1℃ 44±1℃ 2.5Ω Example 4 30±1℃ 41±1℃ 2.0Ω Comparative Example 1 52±1℃ 61±1℃ 17.0Ω Comparative Example 2 50±1℃ 59±1℃ 9.7Ω Comparative Example 3 49±1℃ 58±1℃ 11.6Ω

As shown in Table 2, it can be seen that the secondary battery according to the present invention has an excellent dissipation effect while minimizing an increase in internal and surface temperatures without deteriorating battery performance during overcharging.

Specifically, the secondary batteries of the above embodiment have a structure in which a plurality of unit cells are stacked, but have a particle size gradient so that the average particle size of the negative electrode active material contained in the negative electrode increases as the stacking position of the unit cells progresses from the center to the outermost layer As a result, it was confirmed that the exothermic temperature of the battery was as low as less than 50° C. during overcharging, and the change in DC resistance of the battery was remarkably low due to delayed deterioration of the battery.

From these results, the secondary battery according to the present invention has a structure in which a plurality of unit cells are stacked, and as the unit cells are stacked from the center to the outermost layer, the average particle size of the negative electrode active material contained in the unit cell is By having a particle size gradient that increases from the center to the outermost part, it is possible to minimize heat generation by realizing the heat dissipation effect of the battery during charging and discharging, especially during overcharging, thereby suppressing battery deterioration and improving safety. there is.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art or those having ordinary knowledge in the art do not deviate from the spirit and technical scope of the present invention described in the claims to be described later. It will be understood that various modifications and changes can be made to the present invention within the scope.

Therefore, the technical scope of the present invention is not limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims (12)

It includes a plurality of unit cells having an anode, a cathode, and a separator interposed between the anode and the cathode,
The negative electrode has a structure in which a negative electrode composite layer containing an negative electrode active material is provided on a negative electrode current collector,
The plurality of unit cells have a stacked structure in the thickness direction of the unit cells,
A secondary battery in which the average particle size of the negative electrode active material included in each unit cell increases as the unit cell disposed in the center is stacked from the unit cell disposed in the outermost part.
According to claim 1,
A secondary battery in which the negative electrode active material included in each unit cell has an average particle size of 1 μm to 50 μm.
According to claim 1,
A secondary battery in which the negative electrode active material included in each unit cell has an average particle size deviation of 0.1 to 6 μm from the negative electrode active material of an adjacent unit cell.
According to claim 1,
The negative electrode active material included in each unit cell has a degree of sphericity of 0.5 to 1.0,
A secondary battery in which the degree of sphericity of an anode active material decreases as it progresses from a central unit cell to an outermost unit cell.
According to claim 4,
A secondary battery in which the negative electrode active material included in each unit cell has a sphericity deviation of 0.01 to 0.1 from the negative electrode active material of an adjacent unit cell.
According to claim 1,
A secondary battery comprising an anode active material included in each unit cell including at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and ketjen black.
According to claim 1,
The negative electrode mixture layer provided in each unit cell has an average thickness of 50 μm to 200 μm,
A secondary battery in which the average thickness of the negative electrode mixture layer increases as it progresses from a central unit cell to an outermost unit cell.
According to claim 1,
A secondary battery in which the separator includes at least one polymer selected from among polyethylene, polypropylene, and polyethylene-propylene copolymers.
According to claim 1,
The secondary battery further includes an auxiliary separator between unit cells.
According to claim 9,
The auxiliary separator is a secondary battery including a polymer substrate in which inorganic particles or glass fibers are dispersed.
According to claim 1,
A secondary battery including 3 to 50 unit cells.
A secondary battery module comprising the secondary battery according to claim 1 .