KR20220105397A - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery including an electrode assembly including a positive electrode and a negative electrode alternately disposed, wherein the negative electrode is disposed at the outermost part of the electrode assembly, the outermost negative electrode includes: a negative electrode current collector; a first negative electrode active material layer formed on the inner surface of the negative electrode current collector; and a second negative electrode active material layer formed on the outer surface of the negative electrode current collector, and a loading ratio of the first negative electrode active material layer and the second negative electrode active material layer satisfies a predetermined range.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to a lithium secondary battery. More particularly, it relates to an electrode assembly including a positive electrode and a negative electrode, and a lithium secondary battery including a case accommodating the electrode assembly.

A secondary battery is a battery that can be repeatedly charged and discharged, and is widely applied as a power source for portable electronic devices such as mobile phones and notebook PCs.

For example, the secondary battery includes a lithium secondary battery, a nickel cadmium battery, and a nickel hydrogen battery. Among them, lithium secondary batteries are being actively developed and applied in that they have high operating voltage and energy density per unit weight, and are advantageous for charging speed and weight reduction.

A lithium secondary battery includes: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and an electrolyte impregnating the electrode assembly. In addition, the lithium secondary battery may further include a casing for accommodating the electrode assembly and the electrolyte.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The anode active material layer includes an anode active material, and the anode active material may affect charge/discharge capacity and lifespan characteristics of a lithium secondary battery.

For example, the negative active material is a material capable of intercalating and deintercalating lithium ions, and may include a carbon-based active material such as natural graphite or artificial graphite. Recently, in order to secure a high capacity of a lithium secondary battery, research and development of a silicon-based active material is active.

For example, Korean Patent Laid-Open No. 10-2015-0117316 discloses a negative electrode for a lithium secondary battery including a silicon-based active material.

Korean Patent Publication No. 10-2015-0117316

One object of the present invention is to provide a lithium secondary battery having a high capacity.

One object of the present invention is to provide a lithium secondary battery having excellent high-temperature life characteristics (eg, 45 ℃ capacity retention rate).

The present invention includes an electrode assembly including positive electrodes and negative electrodes arranged alternately, a negative electrode is disposed on the outermost side of at least one side of the electrode assembly, and the outermost negative electrode includes a negative electrode current collector; a first anode active material layer formed on the inner surface of the anode current collector; and a second negative active material layer formed on the outer surface of the negative electrode current collector, wherein the first negative active material layer and the second negative active material layer satisfy Equation 1 below.

[Equation 1]

1≤LW ₂ /LW ₁ <1.25

In Equation 1, LW ₁ is the loading amount of the first negative active material layer, and LW ₂ is the loading amount of the second negative active material layer.

In an embodiment, each of the first anode active material layer and the second anode active material layer may include a carbon-based active material.

In some embodiments, the first anode active material layer may further include a silicon-based active material.

In some embodiments, the second anode active material layer may not include a silicon-based active material.

In some embodiments, the second negative active material layer further includes a silicon-based active material, and the content of the Si element in the first negative active material layer is greater than or equal to ?t of the Si element in the second negative active material layer. can

In some embodiments, the content of the Si element in the first anode active material layer may be 1 to 15% by weight.

In some embodiments, the content of the Si element in the second anode active material layer may be greater than 0 and less than or equal to 5 wt%.

In an embodiment, the electrode assembly may include a plurality of negative electrodes, and the negative electrode active material layer included in the negative electrode other than the outermost negative electrode may have the same composition and loading amount as the first negative electrode active material layer.

In an embodiment, the electrode assembly may further include a separator disposed between the positive electrode and the negative electrode.

In some embodiments, the electrode assembly may further include a separator on the outer surface of the second negative active material layer.

In some embodiments, the lithium secondary battery includes a liquid electrolyte impregnating the electrode assembly; and a case accommodating the electrode assembly and the liquid electrolyte.

A lithium secondary battery according to an embodiment of the present invention includes an electrode assembly including positive electrodes and negative electrodes that are alternately disposed, a negative electrode is disposed on the outermost side of at least one side of the electrode assembly, and the outermost negative electrode is a negative electrode A current collector and a negative active material layer having a different application amount (ie, a loading amount) on one surface and the other surface of the negative electrode collector may be included. In this case, it is possible to suppress the distortion of the outermost negative electrode during charging and discharging of the lithium secondary battery. In addition, it is possible to prevent detachment of the anode active material layer formed on the inner surface of the outermost anode. Accordingly, the lithium secondary battery may implement excellent lifespan characteristics (eg, high temperature capacity retention rate, etc.).

1 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment of the present invention.

In this specification, the meaning that a component (eg, layer, etc.) is "formed or disposed on" another component means that a component is directly formed (or disposed on) another component, Alternatively, it may be interpreted as meaning that a third component may be formed (or disposed) between them.

Hereinafter, the lithium secondary battery of the present invention will be described.

A lithium secondary battery according to an embodiment of the present invention includes an electrode assembly including positive electrodes and negative electrodes that are alternately disposed, a negative electrode is disposed on the outermost side of at least one side of the electrode assembly, and the outermost negative electrode is a negative electrode current collector; a first anode active material layer formed on the inner surface of the anode current collector; and a second negative active material layer formed on the outer surface of the negative electrode current collector, wherein the first negative active material layer and the second negative active material layer may satisfy Equation 1 below.

[Equation 1]

1≤LW ₂ /LW ₁ <1.25

In Equation 1, LW ₁ is the loading amount of the first negative active material layer, and LW ₂ is the loading amount of the second negative active material layer.

According to an embodiment of the present invention, it is possible to suppress the distortion of the outermost negative electrode during charging and discharging, and it is possible to prevent the detachment of the first negative electrode active material layer. In addition, a lithium secondary battery having excellent lifespan characteristics (eg, high temperature capacity retention, etc.) may be implemented.

1 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment of the present invention.

Hereinafter, a lithium secondary battery according to an exemplary embodiment of the present invention will be described in more detail with reference to FIG. 1 .

Referring to FIG. 1 , a lithium secondary battery may include an electrode assembly 150 including positive electrodes 130 and negative electrodes 110 and 120 that are alternately disposed. For example, the positive electrode and the negative electrode may each be plural, and may be alternately and repeatedly disposed (eg, stacked).

In an embodiment, the cathode may be disposed on the outermost side of at least one side of the electrode assembly 150 . Alternatively, the cathode may be disposed on the outermost sides of both sides of the electrode assembly 150 .

Hereinafter, the outermost cathode 110 is referred to as an outermost cathode 110 , and a cathode 120 other than the outermost cathode 110 is referred to as an inner cathode 120 .

For example, the outermost negative electrode 110 may include a negative electrode current collector 115 , a first negative active material layer 112 formed on the inner surface of the negative current collector 115 , and a first negative electrode active material layer 112 formed on the outer surface of the negative electrode collector 115 . 2 may include a negative active material layer 114 . For example, the “inner surface” of the negative electrode current collector 115 may refer to a surface of both surfaces of the negative electrode current collector 115 in a direction toward the center of the electrode assembly 150 . In addition, the “outer side” of the negative electrode current collector 115 may mean a side facing the outside of the electrode assembly 150 among both surfaces of the negative electrode current collector 115 .

In an embodiment, the first negative active material layer 112 and the second negative active material layer 114 may satisfy Equation 1 below. When the following Equation 1 is satisfied, it is possible to suppress the distortion of the outermost negative electrode 110 during charging and discharging. In addition, detachment of the first anode active material layer 112 can be prevented, and a lithium secondary battery having excellent lifespan characteristics (eg, high temperature capacity retention rate, etc.) can be implemented.

[Equation 1]

1≤LW ₂ /LW ₁ <1.25

In Equation 1, LW ₁ is the loading amount (ie, application amount) of the first negative active material layer, and LW ₂ is the loading amount of the second negative active material layer.

In some embodiments, 1≤LW ₂ /LW ₁ ≤1.2, better, 1.1≤LW ₂ /LW ₁ ≤1.2. In this case, the above-described effect may be further improved.

In an embodiment, the outermost negative electrode 110 forms a first negative electrode active material layer on one surface (eg, a surface opposite to the positive electrode) of the negative electrode current collector 115, and the other surface (eg, It may be prepared by forming a second anode active material layer on the side not facing the cathode).

For example, the first anode active material layer 112 may include a first anode active material, if necessary, an anode binder and a conductive material. In addition, the second anode active material layer 114 may include a second anode active material, if necessary, an anode binder and a conductive material.

For example, the first negative electrode active material layer 112 is prepared by mixing and stirring the first negative electrode active material, the negative electrode binder, the conductive material, the dispersion medium, etc. It can be formed by coating, drying and rolling on one surface of (115). Similarly, the second anode active material layer 114 is prepared by mixing and stirring a second anode active material, a cathode binder, a conductive material, a dispersion medium, etc. to prepare a second anode slurry, and then applying the second anode slurry to the anode current collector 115 ) can be formed by coating, drying and rolling on the other surface. In order to satisfy Equation 1, the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry may be different.

In an embodiment, the outermost negative electrode 110 is coated with a first negative electrode slurry on one surface of the negative electrode current collector 115 and dried, and the second negative electrode slurry is applied on the other surface of the negative electrode current collector 115 . And after drying, it may be prepared by rolling at the same time. In order to satisfy Equation 1, the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry may be different.

For example, in a rolling process for forming the first anode active material layer 112 and the second anode active material layer 114 , the pressure magnitudes may be the same. For example, since the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry are different from each other, the first negative electrode active material layer 112 and the second negative electrode active material layer 114 may have different thicknesses. In this case, the distortion of the outermost anode 110 and the detachment of the first anode active material layer 112 can be further prevented.

For example, the negative electrode current collector 115 may include gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and more preferably, may include copper or a copper alloy.

For example, the first negative active material and the second negative active material may include a material capable of intercalating and deintercalating lithium ions.

In an embodiment, each of the first negative active material and the second negative active material may include a carbon-based active material. That is, each of the first anode active material layer 112 and the second anode active material layer 114 may include a carbon-based active material.

For example, the carbon-based active material may include at least one selected from amorphous carbon, crystalline carbon, carbon composite material, carbon fiber, and the like.

The amorphous carbon may be, for example, hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500° C. or lower, mesophase pitch-based carbon fiber (MPCF), etc. . The crystalline carbon may be, for example, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, or the like.

In some embodiments, the first negative active material may further include a silicon-based active material. That is, the first anode active material layer 112 may further include a silicon-based active material. In this case, a lithium secondary battery having a higher capacity may be implemented.

For example, the silicon-based active material may include Si, SiO _x (0<x<2), Si/C, SiO/C, Si-Metal, and the like.

In some embodiments, the second negative active material may not include a silicon-based active material. That is, the second anode active material layer 114 may not include a silicon-based active material.

In some embodiments, the second negative active material may further include a silicon-based active material. That is, the second anode active material layer 114 may further include a silicon-based active material.

In some embodiments, the content of the element Si in the first anode active material layer 112 may be greater than or equal to the content of the element Si in the second anode active material layer 114 . More preferably, the content of the Si element in the first anode active material layer 112 may be greater than the content of the Si element in the second anode active material layer 114 . In this case, a lithium secondary battery having better lifespan characteristics (eg, high-temperature capacity retention rate) may be implemented.

In some embodiments, the content of the Si element in the first anode active material layer 112 may be 1 to 15 wt%.

In some embodiments, the content of the Si element in the second anode active material layer 114 may be greater than 0 and less than or equal to 5 wt%.

For example, the negative electrode binder is, polyvinylidene fluoride (PVDF; polyvinylidenefluoride, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile (polyacrylonitrile), polymethyl methacrylic It may include an organic binder such as polymethylmethacrylate, an aqueous binder such as styrene-butadiene rubber (SBR), etc. Also, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, and carbon nanotubes; and a metal-based conductive material such as a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, or LaSrMnO3.

For example, the internal negative electrode 120 is a negative electrode current collector 125 (to be distinguished from the negative electrode current collector 115 , hereinafter referred to as an internal negative electrode current collector) and a negative electrode active material formed on both surfaces of the internal negative electrode current collector 125 . layer 122 (hereinafter, referred to as an internal anode active material layer to distinguish it from the first anode active material layer 112 and the second anode active material layer 114).

For example, the internal negative active material layer 122 may include at least one selected from a carbon-based negative active material, a silicon-based negative active material, and the like, as an anode active material. In addition, like the first anode active material layer 112 and the second anode active material layer 114 , if necessary, an anode binder and a conductive material may be included.

For example, the inner negative active material layer 122 and the first negative active material layer 112 may be substantially the same. That is, the internal negative active material layer 122 may be applied as it is with respect to the above-described first negative active material layer 112 . In this case, a lithium secondary battery having a higher capacity may be implemented.

For example, the positive electrode 130 may include a positive electrode current collector 135 and a positive electrode active material layer 132 on at least one surface of the positive electrode current collector 135 . For example, the positive electrode active material layer 132 may be formed on both surfaces of the positive electrode current collector 135 .

For example, the positive electrode active material layer 110 may include a positive electrode active material, if necessary, a positive electrode binder and a conductive material.

The positive electrode 100 is, for example, by mixing and stirring a positive electrode active material, a positive electrode binder, a conductive material, a dispersion medium, etc. to prepare a positive electrode slurry, and then coating, drying and rolling the positive electrode slurry on the positive electrode current collector 105 . can be manufactured.

The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and more preferably, may include aluminum or an aluminum alloy.

For example, the positive active material may be a material capable of reversible intercalation and deintercalation of lithium ions.

For example, the positive active material may include lithium metal oxide including at least one metal element selected from nickel, cobalt, manganese, aluminum, and the like.

In one embodiment, the lithium metal oxide includes nickel, and the content of nickel among all elements excluding lithium and oxygen may be 80 mol% or more.

In one embodiment, the positive active material may include a lithium metal oxide represented by the following formula (1).

[Formula 1]

Li _x Ni _a Co _b M _c O _y

In Formula 1, M is at least one of Al, Zr, Ti, B, Mg, Mn, Ba, Si, Y, W, and Sr, 0.9≤x≤1.1, 1.9≤y≤2.1, 0.8≤a≤1, 0≤c/(a+b)≤0.13 and 0≤c≤0.11.

In some embodiments, the lithium metal oxide particles may further include a coating element or a doping element. For example, the coating element or the doping element may be at least one selected from Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, La, and the like. In this case, the lithium secondary battery may secure stability against penetration of external objects and improved lifespan characteristics.

For example, the positive electrode binder and the conductive material may be substantially the same as or similar to the negative electrode binder and the conductive material.

In an embodiment, the electrode assembly 150 may further include a separator 140 disposed between the anode 130 and the cathodes 110 and 120 .

For example, the separator 140 includes a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, or an ethylene/methacrylate copolymer. can do.

The separator 140 may include a nonwoven fabric formed of a high melting point glass fiber, polyethylene terephthalate fiber, or the like.

In some embodiments, the electrode assembly 150 may further include a separator on the outer surface of the second negative active material layer 114 .

In an embodiment, the electrode assembly 150 may be formed by lamination, winding, or z-folding of the separator 140 .

For example, the negative electrode, the separator, and the positive electrode may be repeatedly stacked (eg, separator/cathode/separator/anode/separator/cathode) to form an electrode assembly.

For example, the separator is disposed so as to cover the outer surface of the outermost negative electrode on the other side of the electrode assembly by passing from the outer surface of the outermost negative electrode on one side of the electrode assembly to all positive electrodes and between all the negative electrodes in a zigzag pattern to form an electrode assembly. Can (Z-folding).

The electrode assembly 150 may be accommodated together with the liquid electrolyte in the case 160 to form a lithium secondary battery. For example, the liquid electrolyte may impregnate the electrode assembly 150 .

The liquid electrolyte may include, for example, a lithium salt and an organic solvent.

For example, the lithium salt may be expressed as Li ⁺ X ⁻ . The anion (X ^- ) of the lithium salt is, for example, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , ( CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- _, CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be any one selected from. In some embodiments, the lithium salt may include at least one of LiBF ₄ and LiPF ₆ .

For example, the organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). ethyl methyl carbonate), methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, etc. It may include any one or more selected.

For example, the electrode assembly 150 may include a solid electrolyte disposed between the positive electrode 130 and the negative electrode 110 and 120 .

For example, the solid electrolyte may be at least one selected from a gel-type polymer electrolyte, a dry polymer electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, and a phosphate-based solid electrolyte. Since the solid electrolytes are already known in the art, a detailed description thereof will be omitted herein.

The lithium secondary battery may be manufactured, for example, in a cylindrical shape, a prismatic shape, a pouch type, or a coin type.

Hereinafter, exemplary Examples and Comparative Examples of the present invention will be described. However, the following examples are only illustrative examples of the present invention and are not limited thereto.

[Example 1]

1. Preparation of anode

A negative active material, a CNT conductive material, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in which SiOx (O<X<2) and artificial graphite are mixed in a weight ratio of 6:94, and carboxymethyl cellulose (CMC) in a ratio of 97.3:0.5:1.2:1 By mixing in a weight ratio, a first negative electrode slurry was prepared.

Artificial graphite, SBR, and CMC were mixed in a weight ratio of 97.8:1.2:1 to prepare a second negative electrode slurry.

A copper foil having a thickness of 8 μm in which a protrusion (hereinafter, a negative electrode tab) is formed on one side was prepared. The first negative electrode slurry was applied and dried on one surface of the copper foil to form a first negative electrode active material layer. Next, the second negative electrode slurry was applied and dried on the other surface of the surface on which the first negative electrode active material layer was formed of the copper foil to form a second negative electrode active material layer. The first negative electrode slurry and the second negative electrode slurry were not applied on the protrusion of the copper foil.

At this time, the application amount (loading amount, LW ₁ ) of the first negative electrode slurry and the application amount (LW ₂ ) of the second negative electrode slurry were each adjusted to 10 mg/cm ² . That is, LW ₁ : LW ₂ was adjusted to 1:1.

Thereafter, the first negative active material layer and the second negative active material layer were rolled so that the average electrode density was 1.7 g/cc to prepare an anode.

2. Preparation of secondary battery

A positive electrode slurry was prepared by mixing a positive electrode active material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ), polyvinylidene fluoride (PVDF), and carbon black in a weight ratio of 96.5:1.5:2.

An aluminum foil having a thickness of 12 μm in which a protrusion (hereinafter, anode tab) is formed on one side was prepared. The positive electrode slurry was applied on both sides of the aluminum foil, dried and rolled to prepare a positive electrode. The positive electrode slurry was not applied on the protrusion of the aluminum foil.

An electrode assembly was prepared by interposing a 13 μm thick polyethylene separator between the positive electrode and the negative electrode. When disposing the negative electrode, the first negative active material layer was disposed to face the positive electrode.

A positive electrode lead and a negative electrode lead were respectively welded and connected to the positive electrode tab and the negative electrode tab.

The electrode assembly was accommodated in a pouch (case) so that some regions of the positive electrode lead and the negative electrode lead were exposed to the outside, and three surfaces except for the electrolyte injection part were sealed.

After injecting the electrolyte and sealing the electrolyte injection part, the lithium secondary battery sample was prepared by immersion for 12 hours.

As the electrolyte, a 1 M LiPF ₆ solution (a mixed solvent of EC/EMC/DEC at a volume ratio of 25:45:30) was prepared, and then, based on the total weight of the electrolyte, 2wt% of FEC (Fluoroethylene carbonate), PS (1, A mixture of 0.5 wt% of 3-propane sultone) and 0.5 wt% of PRS (Prop-1-ene-1,3-sultone) was used.

[Example 2]

The negative electrode was prepared in the same manner as in Example 1, except that the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry were set to 1:1.1.

[Example 3]

The negative electrode was prepared in the same manner as in Example 1, except that the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry were set to 1:1.2.

[Example 4]

SiOx (O<X<2) and artificial graphite mixed in a weight ratio of 3:97, a negative active material, CNT conductive material, SBR, and CMC were mixed in a weight ratio of 97.3:0.5:1.2:1 and used as a second negative electrode slurry. Except, it was carried out in the same manner as in Example 1.

[Example 5]

The negative electrode was prepared in the same manner as in Example 1, except that the first negative electrode slurry was applied instead of the second negative electrode slurry.

[Comparative Example 1]

The negative electrode was prepared in the same manner as in Example 1, except that the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry were set to 1:0.9.

[Comparative Example 2]

The negative electrode was prepared in the same manner as in Example 1, except that the application amount of the first negative electrode slurry and the application amount of the second negative electrode slurry were set to 1:1.3.

Experimental Example 1: Evaluation of high temperature life characteristics

(1) Initial discharge capacity measurement

CC/CV charging (0.1C 4.2V 0.05C CUT-OFF) and CC discharging (0.1C 2.5V CUT-OFF) were performed once for the secondary batteries of Examples and Comparative Examples to measure initial charging and discharging capacities Thus, it is described in Table 2 below.

(2) 45℃ capacity retention rate evaluation

CC/CV charging (0.33C 4.2V 0.05C CUT-OFF) and CC discharging (0.33C 2.5V CUT-OFF) at high temperature (45°C) for secondary batteries of Examples and Comparative Examples were repeated 300 times did.

The 45°C capacity retention rate was calculated as a percentage of the value obtained by dividing the discharge capacity measured at the 300th time by the initial discharge capacity measured in (1) of Experimental Example 1.

Capacity retention rate at 45°C = (300th discharge capacity/initial discharge capacity) × 100 (%)

The calculated 45°C capacity retention rate is shown in Table 1 below.

Experimental Example 2: Evaluation of detachment of the first anode active material layer

After the secondary batteries of Examples and Comparative Examples were repeatedly charged and discharged 300 times according to (2) of Experimental Example 1, the secondary batteries were disassembled.

Whether or not the first anode active material layer was detached from the anode at the edge or the tab portion was visually checked, and is shown in Table 1 below.

When the detachment of the first anode active material layer is not observed: ○

When detachment of the first anode active material layer is observed: ×

first anode active material layer Second cathode active material layer LW1: LW2 45℃
Volume
retention rate
(%) first anode active material layer
tally rating SiOx
content
(wt%) Application amount (mg/cm ² ) SiOx content
(wt%) Application amount (mg/cm ² ) Example 1 6 10 0 10 1:1 88.1 ○ Example 2 6 10 0 11 1:1.1 88.8 ○ Example 3 6 10 0 12 1:1.2 88.5 ○ Example 4 6 10 3 10 1:1 87.5 ○ Example 5 6 10 6 10 1:1 85.9 ○ Comparative Example 1 6 10 0 9 1:0.9 83.8 × Comparative Example 2 6 10 0 13 1:1.3 86 ×

In the secondary batteries of the Examples, no detachment of the first negative active material layer (ie, the negative active material layer on the surface opposite to the positive electrode) was observed during repeated charging and discharging at 45° C. for 300 times, and exhibited better capacity retention. On the other hand, in the secondary batteries of Comparative Examples 1 and 2, detachment of the first anode active material layer was observed, and the secondary batteries of Comparative Examples 1 and 2 exhibited a lower capacity retention rate.

The above-described difference is considered to be due to whether the distortion of the negative electrode occurs according to the ratio of the application amount (ie, the loading amount) of the first negative electrode active material layer and the second negative electrode active material layer. That is, in the secondary batteries of the embodiments, it is determined that the first negative active material layer and the second negative active material layer satisfy a predetermined application amount ratio, so that the distortion of the negative electrode and the detachment of the negative active material layer are prevented.

Comparing the secondary batteries of Examples 1, 4, and 5, when the Si content in the first anode active material layer is greater than the Si content in the second anode active material layer, it can be seen that a better capacity retention rate is exhibited.

110: outermost negative electrode 112: first negative electrode active material layer
114: second anode active material layer 115: anode current collector
120: internal negative electrode 122: internal negative electrode active material layer
125: internal negative electrode current collector 130: positive electrode
132: positive active material layer 140: separator
150: electrode assembly 160: case

Claims (11)

An electrode assembly comprising alternating positive and negative electrodes,
A cathode is disposed on the outermost side of at least one side of the electrode assembly,
The outermost negative electrode is a negative electrode current collector; a first anode active material layer formed on the inner surface of the anode current collector; and a second anode active material layer formed on the outer surface of the anode current collector;
The first anode active material layer and the second anode active material layer satisfy Equation 1 below, a lithium secondary battery:
[Equation 1]
1≤LW ₂ /LW ₁ <1.25
(In Equation 1, LW ₁ is a loading amount of the first anode active material layer, and LW ₂ is a loading amount of the second anode active material layer). The lithium secondary battery of claim 1, wherein each of the first anode active material layer and the second anode active material layer includes a carbon-based active material. The lithium secondary battery of claim 2, wherein the first anode active material layer further comprises a silicon-based active material. The lithium secondary battery of claim 3 , wherein the second anode active material layer does not include a silicon-based active material. The method according to claim 3, wherein the second negative active material layer further comprises a silicon-based active material, the content of the Si element in the first negative active material layer is greater than or equal to ?t of the Si element in the second negative active material layer, lithium secondary battery. The method according to claim 5, wherein the content of the Si element in the first negative active material layer is 1 to 15% by weight, the lithium secondary battery. The lithium secondary battery according to claim 5, wherein the content of the Si element in the second negative active material layer is greater than 0 and less than or equal to 5% by weight. The lithium secondary battery of claim 1, wherein the electrode assembly includes a plurality of negative electrodes, and the negative electrode active material layer included in the negative electrode other than the outermost negative electrode has the same composition and loading as the first negative electrode active material layer. The lithium secondary battery of claim 1, wherein the electrode assembly further comprises a separator disposed between the positive electrode and the negative electrode. The lithium secondary battery of claim 9 , wherein the electrode assembly further comprises a separator on an outer surface of the second anode active material layer. 10. The method of claim 9,
a liquid electrolyte impregnating the electrode assembly; and
The lithium secondary battery further comprising; a case accommodating the electrode assembly and the liquid electrolyte.

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