KR102172154B1 - Positive electrode for secondary battery and secondary battery comprising the same - Google Patents

Abstract

In the present invention, in a positive electrode for a secondary battery including a positive electrode current collector and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector, the positive electrode current collector exhibits an elongation of 1.6% to 3.0%, and the positive electrode active material layer Silver contains at least 50% by weight of a fine positive electrode active material with an average particle diameter (D ₅₀ ) of 3㎛ to 6㎛ based on the total weight of the positive electrode active material, and has a porosity of 17% to 32%, so battery safety, especially when penetrating the needle There is provided a positive electrode for a secondary battery and a secondary battery including the same, which can greatly improve.

Description

A positive electrode for a secondary battery and a secondary battery including the same {POSITIVE ELECTRODE FOR SECONDARY BATTERY AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a positive electrode for a secondary battery capable of improving the safety of a battery by controlling an internal short-circuit mode between the needle bed and an electrode in the battery when penetrating the battery by the needle bed, and a secondary battery including the same.

Lithium secondary batteries are small, lightweight, and large-capacity batteries that have been widely used as power sources for portable devices since their appearance in 1991. In recent years, with the rapid development of the electronics, communication, and computer industries, camcorders, mobile phones, notebook PCs, etc. have emerged and are undergoing remarkable development, and the demand for lithium secondary batteries as a power source to drive these portable electronic information and communication devices is increasing day by day. Are doing.

Lithium secondary batteries include an electrode assembly consisting of a positive electrode, a negative electrode, and a separator, and may be classified into a jelly-roll (winding type), a stack type (stacking type), and a stack/folding type according to the structure of the electrode assembly.

On the other hand, when the electrode assembly in the lithium secondary battery is penetrated by a sharp needle-shaped conductor having electrical conductivity such as a nail, a short circuit occurs locally between the positive electrode and the negative electrode. At this time, excessive current flows locally, and heat generation occurs due to this current. When the temperature of the electrode assembly rises above a critical value due to the heat generated at this time, a thermal runaway phenomenon occurs, which may act as a major cause of ignition or explosion of the electrode assembly and the secondary battery. In addition, when the electrode active material layer bent by the acicular conductor or the current collector contacts the opposite electrodes facing each other, the thermal runaway phenomenon can be further accelerated. Such a phenomenon may occur more seriously in a bicell including a plurality of electrodes and an electrode assembly including the same.

In addition, when heat is generated inside the battery, the separator shrinks, causing an additional short circuit between the positive and negative electrodes, and the short circuit section increases due to repeated heat generation and shrinkage of the separator, causing thermal runaway or constituting the inside of the battery. The positive electrode, the negative electrode, and the electrolyte react or burn with each other. This reaction is a very exothermic reaction, and thus the battery is ignited or exploded. This risk becomes more important as the energy density increases as the lithium secondary battery becomes higher in capacity.

Various methods have been studied to secure the safety of such needle penetration, most of which are to mount an element outside the cell or use a material inside the cell. However, these methods have problems such as deterioration of battery performance due to generation of by-products during the formation of the passivation film, or reduction of the capacity of the battery due to the large volume occupied inside the battery. It was not enough.

WO2012-060558 (published on May 10, 2012)

The first technical problem to be solved by the present invention is to provide a positive electrode for a secondary battery capable of improving safety by controlling an internal short-circuit mode between the bed and the electrode inside the battery when penetrating the bed.

A second technical problem to be solved by the present invention is to provide a lithium secondary battery, including the positive electrode, showing improved safety.

In order to solve the above problems, according to an embodiment of the present invention, a positive electrode current collector; And a positive electrode active material layer positioned on at least one side of the positive electrode current collector, wherein the positive electrode current collector exhibits an elongation of 1.6% to 3.0%, and the positive electrode active material layer has an average particle diameter (D ₅₀ ) of 3 μm to 6 It provides a positive electrode for a secondary battery containing at least 50% by weight of a fine positive electrode active material of ㎛ based on the total weight of the positive electrode active material, and having a porosity of 17% to 32%.

In addition, according to another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

The positive electrode according to the present invention greatly enhances safety along with output characteristics and energy density of the battery by controlling the internal short circuit mode between the needle bed and the electrode inside the battery when penetrating the needle through the structure of the positive electrode active material layer and the elongation control of the positive electrode current collector. Can be improved.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The positive electrode for a secondary battery according to an embodiment of the present invention,

Positive electrode current collector; And

And a positive electrode active material layer positioned on at least one surface of the positive electrode current collector,

The positive electrode current collector has an elongation of 1.6% to 3.0%,

The positive electrode active material layer contains at least 50% by weight of a fine positive electrode active material having an average particle diameter (D ₅₀ ) of 3 μm to 6 μm based on the total weight of the positive electrode active material, and has a porosity of 17% to 32%.

Specifically, in the positive electrode for a secondary battery according to an embodiment of the present invention, the positive electrode active material layer contains a particulate positive electrode active material having an average particle diameter (D ₅₀ ) of 3 μm to 6 μm in an amount of 50% by weight or more based on the total weight of the positive electrode active material. do. By including the fine-grained positive electrode active material having an optimized particle size as described above, the positive electrode active material layer is structured to control the internal short-circuit mode between the needle and the positive electrode inside the battery when penetrating the needle. If the content of the fine positive electrode active material in the positive electrode active material layer is less than 50% by weight, or the particle size of the fine positive electrode active material is out of the above range, it is not easy to control the internal short circuit mode between the bed and the positive electrode inside the battery. As a result, battery safety can be greatly degraded.

In addition, when considering the remarkable effect of improving the safety of the battery during the penetration test according to the inclusion of such a fine positive electrode active material, the positive electrode active material layer in the positive electrode for a secondary battery according to an embodiment of the present invention is based on the total weight of the positive electrode active material. With respect to the average particle diameter (D ₅₀ ) of 3㎛ to 6㎛ 50% by weight or more and less than 100% by weight of the particulate positive electrode active material; And an average particle diameter (D ₅₀ ) of more than 6 μm and 20 μm or less of a granulated positive electrode active material of more than 0% by weight to 50% by weight, and more specifically, an average particle diameter (D ₅₀ ) of the total weight of the positive electrode active material 50% to 90% by weight of a fine positive electrode active material of 3 μm to 6 μm; And an average particle diameter (D ₅₀ ) of 10% to 50% by weight of an assembled positive electrode active material having an average particle diameter of more than 6 μm and 20 μm or less.

In addition, the fine and granulated positive electrode active material is a ratio of the average particle diameter (D ₅₀ ) of the fine positive electrode active material to the average particle diameter (D ₅₀ ) of the granulated positive electrode active material under conditions satisfying the above average particle diameter range (=fine particles less than D D ₅₀ of 0.15 or more and ₅₀ / assembling the positive electrode active material 1 of the positive electrode active material, more specifically from 0.2 to be 0.55 days. positive electrode active material intra-layer satisfy the particulate and the positive electrode active material average particle ratio of the above conditions the diameter of the assembly which includes In this case, it is possible to exhibit an excellent effect of improving battery characteristics without fear of deteriorating cell performance due to unbalanced mixing of active materials in the electrode.

In addition, in the positive electrode for a secondary battery according to an embodiment of the present invention, the positive electrode active material, specifically, the fine-grained and granulated positive electrode active material may each independently consist of a single particle of the primary particle, or a plurality of primary particles It may also consist of agglomerated secondary particles. At this time, the primary particles may be uniform or non-uniform. The positive electrode active material is a primary particle composed of a single particle; Or secondary particles days when the average particle diameter (D ₅₀₎ is the case of the average particle diameter (D ₅₀₎ to the 3㎛ 6㎛ particulate positive electrode active material, in the case of assembling the positive electrode active material average particle diameter (D ₅₀₎ exceeds the 6㎛ It may be 20 μm or less. In addition, when the fine and granulated positive electrode active materials are each independently secondary particles, the primary particles constituting the secondary particles are average particle diameters (D ₅₀ ) under conditions that satisfy the average particle diameter range of the secondary particles. This may be 30nm to 2㎛. When the average particle diameter of the primary particles is less than 30 nm, the dispersibility is deteriorated due to aggregation between particles, and when the average particle diameter exceeds 2 μm, the capacity characteristics of the electrode may decrease due to a decrease in packing density. More specifically, the primary particles may have an average particle diameter (D ₅₀ ) of 50 nm to 1 μm.

In the present invention, the average particle diameter (D ₅₀ ) of the positive electrode active material may be defined as a particle diameter based on 50% of the particle diameter distribution. The average particle diameter (D ₅₀ ) of the positive electrode active material particles according to an embodiment of the present invention may be measured using, for example, a laser diffraction method. Specifically, the average particle diameter (D ₅₀ ) of the positive electrode active material is, after dispersing the particles of the positive electrode active material in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) to output an ultrasonic wave of about 28 kHz. After irradiation at 60 W, the average particle diameter (D ₅₀ ) in the standard of 50% of the particle diameter distribution in the measuring device can be calculated.

In the present invention, the fine and granulated positive electrode active materials are classified based on the average particle diameter, and the materials constituting each may be the same or different. Specifically, in the positive electrode for a secondary battery according to an embodiment of the present invention, the fine and granulated positive electrode active materials included in the positive electrode active material layer are each independently a compound capable of reversible intercalation and deintercalation of lithium ( Lithiated intercalation compound), specifically, a substance having a hexagonal layered rock salt structure (eg, LiCoO ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , or LiNiO _2, etc.), Materials having an olivine structure (eg, LiFePO ₄ ), spinel materials having a cubic structure (eg, LiMn ₂ O _4, etc.), in addition to V ₂ O ₅ , vanadium oxides such as TiS or MoS, etc. It may be a chalcocene compound.

More specifically, the positive electrode active material may be a lithium composite metal oxide including any one or two or more selected from the group consisting of cobalt, manganese, nickel, and aluminum together with lithium. Specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O Etc.), lithium-cobalt-based oxides (e.g., LiCoO ₂ etc.), lithium-nickel-based oxides (e.g., LiNiO ₂ etc.), lithium-nickel-manganese oxides (e.g., LiNi _{1 - a} Mn _a O ₂ (here, a is the atomic fraction of Mn, 0<a<1) or LiMn _{2 - b} Ni _b O ₄ (here, b is the atomic fraction of Ni, 0<b<2), etc.) , Lithium-nickel-cobalt-based oxide (e.g., LiNi _1-d Co _d O ₂ (here, d is the atomic fraction of Co, 0<d<1), etc.), lithium-manganese-cobalt-based oxide ( For example, LiCo _{1 - e} Mn _e O ₂ (here, e is the atomic fraction of Mn, 0<e<1), LiMn _{2 -f} Co _f O ₄ (here, f is the atomic fraction of Co , 0<f<2), etc.), lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni _g Co _h Mn _i )O ₂ (here, g, h and j are each of independent elements). As an atomic fraction, 0<g<1, 0<h<1, 0<j<1, g+h+j=1) or Li(Ni _k Co _l Mn _m )O ₄ (here, k, l and m is the atomic fraction of each independent element, 0<k<2, 0<l<2, 0<m<2, k+l+m=2), etc.), lithium-nickel cobalt-aluminum oxide (e.g. For example, Li(Ni _n Co _p Al _q )O ₂ (here, n, p and q are atomic fractions of each independent element, 0<n<1, 0<p<1, 0<q<1 , n+p+q=2), etc.) or lithium-nickel-cobalt-manganese-metal (Me) oxide (e.g., Li(Ni _r Co _s Mn _t Me _u ) O ₂ (wherein Me is Al , Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Nb, Mg, B, W and Mo include any one or two or more selected from the group consisting of, r, s, t and u are each As the atomic fraction of independent elements, 0<r<1, 0<s<1, 0<t<1, 0<u<1, r+s+t+u=1), etc.) , A combination of any one or two or more of these Water may be included.

In addition, in the lithium composite metal oxide, at least one of the metal elements other than lithium is Al, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc , Gd, Sm, Ca, Ce, Nb, Mg, B, W and Mo may be doped with any one or two or more elements selected from the group consisting of. In this way, when the above-described metal element is further doped on the lithium-defective lithium composite metal oxide, the structural stability of the positive electrode active material is improved, and as a result, the output characteristics of the battery may be improved. In this case, the content of the doping element contained in the lithium composite metal oxide may be appropriately adjusted within a range not deteriorating the characteristics of the positive electrode active material, and specifically, may be 0.02 atomic% or less.

In addition, when the cathode active material is doped, the lithium composite metal oxide doped with the doping element may be uniformly distributed in the cathode active material, or a concentration gradient in which the content distribution from the center of the cathode active material to the surface increases or decreases. And may be present, or may be present only on the surface side of the positive electrode active material. As described above, when the doping element is distributed at a high concentration on the surface side of the active material particle and includes a concentration gradient in which the concentration decreases toward the center of the particle, it is possible to prevent a decrease in capacity while exhibiting thermal stability.

In the present invention, the concentration gradient structure and concentration of the doping element in the positive electrode active material particles are electron probe micro analyzer (EPMA), inductively coupled plasma-atomic emission spectroscopy (Inductively Coupled Plasma-Atomic Emission Spectrometer, ICP- AES), or a time of flight secondary ion mass spectrometer (Time of Flight Secondary Ion Mass S pectrometry, ToF-SIMS). Specifically, EPMA can be used from the center of the cathode active material to the surface. As it moves, it is possible to measure the atomic ratio of each metal.

In addition, in the present invention, the'surface side' of the lithium composite metal oxide particle refers to a region close to the surface excluding the center of the particle, and specifically, the distance from the surface to the center of the lithium composite metal oxide particle, that is, the lithium composite For the half diameter of the metal oxide, a region corresponding to a distance of 0% or more and less than 100% from the particle surface, more specifically 0% to 50% from the particle surface, and even more specifically 0% to 30% from the particle surface. it means.

In the positive electrode according to an embodiment of the present invention, when considering the effect of stabilizing the structure in the positive electrode active material layer by controlling the particle size of the positive electrode active material, and improving the output characteristics and energy density of the battery, more specifically The positive electrode active material may each independently contain a lithium composite metal oxide represented by Formula 1:

[Formula 1]

Li _α Ni _x1 Co _y1 M1 _z1 M2 _w1 O ₂

In Formula 1

M1 is at least one selected from the group consisting of Mn and Al,

M2 is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, And any one or two or more doping elements selected from the group consisting of Mo,

α, x1, y1, z1 and w1 are the atomic fractions of independent elements, respectively, 0.95≤α≤1.05, 0<x1<1, 0<y1<1, 0<z1<1, x1+y1+z1=1 , 0≤w1≤0.02, and more specifically 0.95≤α≤1.05, 0.6≤x1<1, 0<y1≤0.4, 0<z1≤0.4, x1+y1+z1=1, 0≤w1≤ Is 0.02. In this case, α is a value when not charged, and the composition of Formula 1 is an average value.

More specifically, the compound of Formula 1 is LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , LiNi _{0 . 6} Co _{0 . 2 Mn 0 .2 W 0. 02 O} 2 or LiNi _{0. 85} Co _{0 . 09} Mn _{0 . 045} Al _{0 .015} and the like, and any one or a mixture of two or more of them may be used.

According to another embodiment of the present invention, the fine-grained and granulated positive electrode active material may each independently contain at least one or two or more intercalation compounds of the following formulas 2a, 2b, and 3 Can be:
[Formula 2a]
LiNi _1-x4 Ti _a4 Mg _b4 O ₂
(In Formula 2a, X4=a4+b4, x4 is greater than 0 and less than 0.5, a4 is almost the same as b4, and more specifically b4 is not less than a4)
[Formula 2b]
LiCo _1-x5 Ti _a5 Mg _b5 O ₂
(In Formula 2b, X5=a5+b5, x5 is greater than 0 and less than 0.5, a5 is almost the same as b5, more specifically b5 is not less than a5)

[Formula 3]

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LiNi _1-x3 Co _y3 M5 _z3 M6 _w3 O ₂

(In Formula 3, M5 includes any one or two or more selected from the group consisting of Ti and Zr, and M6 includes any one or two or more selected from the group consisting of Mg, Ca, Sr and Ba, and , x3=y3+z3+w3, x3 is greater than 0 and less than 0.5, y3 is greater than 0 and less than 0.5, z3 is greater than 0 and less than 0.15, w3 is greater than 0 and less than 0.15).

For example, the compound of Formula 2a is LiNi _0.9 Ti _0.05 Mg _0.05 O ₂ , LiNi _0.8 Ti _0.1 Mg _0.1 O ₂ , LiNi _0.75 Ti _0.125 Mg _0.125 O ₂ , LiNi _0.7 Ti _0.15 Mg _0.15 O ₂ , LiNi _0.75 Ti _0.15 Mg _0.10 O ₂ and the like may be mentioned, and any one or a mixture of two or more of them may be used.

The intercalation compound of Formula 2a as described above has a large specific capacity when used as a positive electrode active material, and exhibits stable and good cycle characteristics compared to conventional LiNiO ₂ .

When Ti and Mg are used at the same time, overcharge protection is imparted to the intercalation compound, and safety may be further improved along with excellent cycling characteristics at a large capacity.

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In addition, the intercalation compound of Formula 3 may specifically be a compound of Formula 3a. The intercalation compounds of Formula 3 above may exhibit remarkably improved effects in terms of irreversible capacity and cycle characteristics.

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[Formula 3a]

LiNi _1-x4 Co _y4 Ti _z4 Mg _w4 O ₂

(In Formula 3a, x4=y4+z4+w4, 0<x4≤0.5, 0.1≤y4≤0.3, 0<z4≤0.15, 0<w4≤0.15, and z4 is almost the same as w4, and more specifically, w4 is less than z4. not)

More specifically, the intercalation compound of Formula 3 is LiNi _0.7 Co _0.1 Ti _0.1 Mg _0.1 O ₂ , LiNi _{0 . 75} Co _{0 . 15} Ti _{0 . 05} Mg _{0 . 05} O ₂ or LiNi _{0 . 7} Co _{0 . 2} Ti _{0 . 05} Mg _{0 . 05} O ₂ or the like, and any one or a mixture of two or more of them may be used.

In addition, in the positive electrode for a secondary battery according to an embodiment of the present invention, the positive electrode active material layer contains the positive electrode active material in an amount of 80% to 99% by weight, more specifically 85% to 98% by weight, based on the total weight of the positive electrode active material layer. It may be included in an amount of weight %. When included in the above content range, excellent capacity characteristics may be exhibited.

Meanwhile, in the positive electrode for a secondary battery according to an embodiment of the present invention, the positive electrode active material layer may further include at least one of a conductive material and a binder in addition to the positive electrode active material.

The binder serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC ), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used. The binder may be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black, carbon nanotubes, or carbon fibers; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskers such as fluorocarbon, zinc oxide, or potassium titanate; Conductive metal oxides such as titanium oxide; Or a conductive polymer such as a polyphenylene derivative may be used, and any one or a mixture of two or more of them may be used. The conductive material may be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode active material layer in the positive electrode according to an embodiment of the present invention as described above may include fine particles; Alternatively, it includes a plurality of voids (or pores) formed between particulate and granular positive electrode active materials and particulate constituents. At this time, the size and ratio of the voids formed in the positive electrode active material layer may be adjusted through control of processing conditions during the manufacturing process of the positive electrode, for example, rolling conditions during a rolling process, and drying conditions during drying.

Along with the particle size and content ratio of the positive electrode active material of fine particles and granules in the positive electrode active material layer, and the elongation of the positive electrode current collector, the porosity in the positive electrode active material layer affects the elongation of the positive electrode, and as a result, the safety of the battery when penetrating the needle Affects When considering the elongation control of the positive electrode according to such a combination configuration, the positive electrode active material layer in the positive electrode for a secondary battery according to an embodiment of the present invention may have a porosity of 17% to 32%. If the positive electrode active material layer does not satisfy the porosity condition described above, the elongation rate condition of the positive electrode is not satisfied, and as a result, battery safety may be significantly deteriorated when penetrating the needle. More specifically, the positive electrode active material layer may have a porosity of 20% to 30%.

Meanwhile, in the present invention, the porosity of the positive electrode active material layer refers to the ratio of the volume occupied by the voids (or pores) with respect to the volume of the positive electrode active material layer, and the unit is %. In addition, the pore volume can be measured using a porosimeter such as a mercury intrusion method or a pore distribution measurement method such as a gas adsorption method such as BET, and in the present invention, it is a value measured using a mercury intrusion porosimeter. .

In addition, the positive electrode active material layer having the above configuration may be formed on one or both surfaces of the positive electrode current collector, and the thickness thereof may be appropriately determined in consideration of the positive electrode elongation. Specifically, the thickness of a single positive electrode active material layer formed on one or both surfaces of the positive electrode current collector may be 20 μm to 100 μm.

Meanwhile, in the positive electrode according to an embodiment of the present invention, the positive electrode current collector may have an elongation of 1.6% to 3.0% as measured by the method of ISO 527-3.

In the tensile test of the object, the elongation refers to a percentage value obtained by calculating the deformation rate of the object until fracture during the test based on the state before the test, and the length change of the positive electrode current collector in the case of the present invention. By having the above-described elongation, the length that increases as the electrode bends when penetrating the needle is reduced, so that the contact area between the acicular conductor and the electrode and the contact area between the anode and the cathode can be reduced. If the elongation exceeds 3.0%, the elongation is too large to control stress on the positive electrode current collector.

The elongation rate of the positive electrode current collector may be controlled by the metal composition and thickness of the positive electrode current collector. Specifically, the positive electrode current collector in the positive electrode for a secondary battery according to an embodiment of the present invention may include an Al-Si-Fe-Cu-based aluminum alloy.

Since problems such as breakage occurring during application of the positive electrode active material or breakage occurring at the bent portion during winding generally exist, high strength is required as a positive electrode current collector. In particular, if the strength is low after applying and drying the active material, elongation is likely to occur in the positive electrode current collector during rolling. As a result, winding wrinkles occur during winding, the adhesion between the positive electrode active material and the positive electrode current collector decreases, and fracture is likely to occur during slit. In particular, when the adhesion between the positive electrode active material and the surface of the positive electrode current collector decreases, there is a problem that the capacity of the battery decreases due to peeling during repeated charge and discharge.

In addition, high conductivity is required for a positive electrode current collector used for a positive electrode of a lithium secondary battery. In particular, lithium secondary batteries used in automobiles or power tools are required to have greater output characteristics than lithium secondary batteries used in mobile phones or notebook computers. However, when the electrical conductivity of the positive electrode current collector is low, the internal resistance of the battery increases when a large current flows, and as a result, there is a problem that the output voltage of the battery decreases. Accordingly, a high-purity aluminum alloy has been mainly used as a positive electrode current collector for a secondary battery that requires high conductivity. However, since the high-purity aluminum alloy-based positive electrode current collector does not contain solid solution elements or fine precipitates capable of suppressing the transfer of electric charges, the strength decreases during heat treatment.

On the other hand, since the positive electrode current collector used in the present invention contains an Al-Si-Fe-Cu-based aluminum alloy, the strength characteristics, particularly the strength after heating in the drying process, are high while maintaining high electrical conductivity. In addition, since the positive electrode current collector having the above composition has an optimized elongation, it is possible to exhibit a better internal short-circuit control effect when the positive electrode active material layer is combined with the structured positive electrode active material layer so as to control the internal short-circuit mode during needle penetration.

Specifically, the aluminum alloy in the positive electrode current collector includes Si, Fe, and Cu together with 99% by weight or more of aluminum, and may optionally further include at least one of Mn and Zn. More specifically, the aluminum alloy includes Si 0.1% to 0.8% by weight, Fe 0.1% to 0.8% by weight, Cu 0.05% to 0.2% by weight and the balance of aluminum, the total amount of Si and Fe It may be 0.2% to 1.0% by weight based on the total weight of the aluminum alloy. In addition, the Al alloy may optionally further include at least one of 0.05% by weight or less of Mn and 0.1% by weight or less of Zn, if necessary.

In the aluminum alloy, Fe, Si, and Cu may be contained in a solid solution in the aluminum alloy. When the solid solution is dissolved in this way, the transfer of electric charges is suppressed, so that higher strength can be achieved, and the work hardenability is also improved by increasing the solid solution, so that the strength of the positive electrode current collector can be increased.

Among them, Si and Fe are elements that improve strength, and Si and Fe may each independently be included in 0.1% to 0.8% by weight based on the total weight of the aluminum alloy, but the total amount of the two elements is 0.2 based on the total weight of the aluminum alloy. It may be in the range of wt% to 1.0% by weight. When the total amount of the two elements is less than 0.2% by weight, there is a concern of lowering the strength, and when the Si content exceeds 1.0% by weight, it is difficult to maintain a high electric conductivity.

In addition, in the aluminum alloy, Cu is also an element that improves strength together with Si and Fe, and is included in an amount of 0.05% to 0.2% by weight based on the total weight of the aluminum alloy. If the Cu content is less than 0.05% by weight, there is a concern of a decrease in strength, and if the Cu content exceeds 0.2% by weight, it is difficult to maintain a high electric conductivity.

In addition, the aluminum alloy may further include at least one of Mn and Zn.

When Mn is further included, it may be further included in an amount of 0.05% by weight or less based on the total weight of the alloy. However, since Mn is dissolved in the Al alloy to significantly lower the conductivity, the aluminum alloy may not contain Mn more specifically.

On the other hand, Zn suppresses the transfer of electric charges due to an increase in the solid solution capacity in the Al alloy, and as a result, strength and work hardenability can be further improved. Accordingly, when Zn is further included, it may be further included in an amount of 0.1% by weight or less, more specifically 0.01 to 0.1% by weight, based on the total weight of the alloy.

In addition, the aluminum alloy may further contain unavoidable impurities such as Ti, Cr, Ni, Mg, B, V, and Zr, and the content may be specifically 0.15% by weight or less.

The positive electrode current collector including the aluminum alloy having the above composition may have a thickness of 5 μm to 20 μm under conditions satisfying the elongation condition described above. If the thickness of the positive electrode current collector is less than 5 μm, a pinhole is likely to occur in the positive electrode current collector, or a fracture shape is likely to occur during processing. If the thickness exceeds 20 μm, the elongation is high, so that electrodes and electrodes when penetrating the needle. There is a concern that the needle penetration safety may be deteriorated by increasing the contact area with the needle-shaped conductor. In addition, the volume and weight of the positive electrode current collector increases, and the volume and weight of the positive electrode active material layer are relatively reduced, thereby deteriorating the capacity characteristics of the battery. More specifically, the positive electrode current collector may have a thickness of 8 μm to 15 μm. Furthermore, the positive electrode current collector may have a thickness ratio of 0.08 to 0.75 to the thickness of the positive electrode active material layer under conditions satisfying the above-described thickness range.

In addition, the positive electrode current collector may have various forms, such as a film, sheet, foil, net, porous material, foam, and non-woven fabric, and may further include fine irregularities on the surface in terms of improving adhesion to the positive electrode active material.

Meanwhile, the positive electrode for a secondary battery according to an exemplary embodiment of the present invention including the positive electrode current collector and the positive electrode active material layer may be manufactured using a conventional method for manufacturing a positive electrode. Specifically, a composition for forming a positive electrode active material layer is prepared by dissolving or dispersing at least one of a binder and a conductive material in a solvent together with the positive electrode active material, and the composition is applied to at least one surface of the positive electrode current collector, and then dried. And rolling. At this time, the positive electrode active material, the binder, the type and content of the conductive material, and the positive electrode current collector are as described above.

The solvent usable for preparing the composition for forming the positive electrode active material layer may be a solvent generally used in the art, and may be dimethyl sulfoxide (DMSO), isopropyl alcohol, and N-methylpi. Rolidone (NMP), acetone, water, and the like, and one of them alone or a mixture of two or more may be used. The amount of the solvent used may be determined within a range to have an appropriate viscosity in consideration of the coating properties of the composition for forming the positive electrode active material layer and the uniformity of the thickness of the formed positive electrode active material layer.

In addition, the application process of the composition for forming the positive electrode active material layer to the positive electrode current collector may be performed using various conventional application methods such as dip coating, roll coating, bar coating, immersion or spraying, and the final positive electrode active material The application amount may be determined according to the thickness of the layer.

In addition, the drying process after application of the composition for forming the positive electrode active material layer may be performed by evaporating and removing the solvent by applying a temperature equal to or higher than the boiling point of the solvent contained in the composition using a conventional drying method such as hot air drying or heat drying.

In addition, the rolling process for the coating film of the composition for forming the positive electrode active material layer formed after the drying process is performed by applying a pressure such that the porosity in the positive electrode active material layer finally manufactured using a conventional rolling method such as roll press meets the above range. Can be done.

In addition, after the rolling process, in order to remove the solvent remaining in the positive electrode active material layer and control the structure in the positive electrode active material layer, a drying process under a temperature of 120 to 180° C. under vacuum may be further selectively performed.

Alternatively, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling from the support on at least one surface of the positive electrode current collector.

In the present invention, the positive electrode including the current collector and the positive electrode active material layer may have an elongation of 0.6% to 1.1% as measured by the method of ISO 527-3. By having the above elongation, the positive electrode according to the present invention minimizes the contact area between the needle-shaped conductor and the electrodes of the electrode assembly, while the positive-electrode current collector is stretched by the frictional force with the needle-shaped conductor when the needle-shaped conductor penetrates the electrode assembly. And, as a result, it is possible to prevent excessive current from flowing through the acicular conductor.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, or the like, or aluminum-cadmium alloy may be used. In addition, the negative electrode current collector may have a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, microscopic irregularities may be formed on the surface of the negative electrode current collector to enhance the bonding strength with the negative electrode active material. In addition, the negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

In addition, the negative active material layer optionally further includes at least one of a binder and a conductive material together with the negative active material.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; Metal oxides capable of doping and undoping lithium, such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a composite including the metal compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more of them may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. Further, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are typical, and high crystalline carbon is amorphous, plate-like, scale-like, spherical or fibrous natural or artificial graphite, Kish graphite (Kish). graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes) is representative.

In addition, the binder and the conductive material may be the same as described above for the positive electrode.

The negative electrode active material layer may be dried after applying a negative electrode forming composition prepared by dissolving or dispersing at least one of a negative electrode active material and optionally a binder and a conductive material in a solvent on at least one surface of the negative electrode current collector; Alternatively, it may be prepared by casting the composition for forming the negative electrode on a separate support and then laminating a film obtained by peeling from the support on at least one surface of the negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions, and it may be preferable that the separator has low resistance to ion movement of the electrolyte and has excellent electrolyte-moisture ability. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A stacked structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT), PB(Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ ( Inorganic particles such as PMN-PT), HfO ₂ , lithium phosphate (Li ₃ PO ₄ ), lithium germanium thiophosphate, and lithium nitride; Alternatively, it may be an organic/inorganic composite porous SRS (Safety-Reinforcing Separators) coated with a polymer material such as polyolefin, and may be optionally used in a single layer or multilayer structure. The SRS separator may have a uniform pore structure formed by an interstitial volume between inorganic particles, which is an active layer component, as well as a pore structure included in the separator substrate itself, and the pores can prevent external impacts applied to the electrode assembly. Not only can the mitigation considerably, but also the smooth movement of lithium ions through the pores is achieved, and a large amount of electrolyte is filled to show a high impregnation rate, so that the performance of the battery can be improved together.

In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used in the manufacture of a lithium secondary battery, limited to these. It does not become.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of a battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate-based solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group and may contain a double bonded aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes or the like may be used. Among them, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (e.g., ethylene carbonate or propylene carbonate, etc.), which can increase the charging/discharging performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to 9, the electrolyte may exhibit excellent performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can effectively move.

In addition to the electrolyte constituents, the electrolyte includes, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery; Or pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N -One or more additives such as substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

As described above, since the positive electrode active material composition according to the present invention or a lithium secondary battery including a positive electrode manufactured using the same stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, such as mobile phones, notebook computers, digital cameras, etc. Portable devices; And electric vehicle (EV), hybrid electric vehicle (HEV), or plug-in hybrid electric vehicle (PHEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack may include a power tool; Electric vehicles, including electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles; Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a power storage system.

Hereinafter, examples will be described in detail to illustrate the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

Example 1: Preparation of positive electrode

94% by weight of the positive electrode active material shown in Table 1 below, 3% by weight of carbon black as a conductive material, and 3% by weight of polyvinylidene fluoride (PVdF) as a binder N-methyl-2-pyrrolidone It was added to (NMP) to prepare a composition for forming a positive electrode active material layer (viscosity: 1500 cps). The composition for forming a positive electrode active material layer was applied to both sides of the aluminum alloy-based positive electrode current collector shown in Table 1 below to have the same thickness, and then dried. The resulting coating film of the composition for forming a positive electrode active material layer was uniformly compressed by applying pressure to have the porosity shown in Table 1 using a roll press, and vacuum dried in a vacuum oven at 130°C for 12 hours. A positive electrode was prepared.

Example 2-8 and Comparative example 1-5: Preparation of anode

A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode active material and the positive electrode current collector described in Table 1 were used.

Comparative Example 6: Preparation of positive electrode

A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode active material and the positive electrode current collector described in Table 1 were used. However, the positive electrode current collector used in Comparative Example 6 had an excessively low elongation and fracture occurred during the rolling process for manufacturing the positive electrode, so that the positive electrode could not be manufactured.

Comparative Example 7: Preparation of positive electrode

A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode active material and the positive electrode current collector described in Table 1 were used, and the rolling process was not performed.

Comparative Example 8: Preparation of positive electrode

It was carried out in the same manner as in Example 1, except that the positive electrode active material and the positive electrode current collector described in Table 1 were used, and overpressure was applied so that the porosity in the positive electrode active material layer was 10% or less during the rolling process. However, it was not possible to manufacture a positive electrode because fracture occurred during the rolling process.

Fine cathode active material
Assembly cathode active material Particulate: Weight ratio of assembled positive electrode Porosity of cathode active material layer*
(%) Positive electrode active material layer thickness**
(㎛) Positive electrode current collector Kinds D ₅₀
(㎛) Kinds D ₅₀
(㎛) Kinds thickness
(㎛) Elongation
(%) Example 1 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 100:0 25 45 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Example 2 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 70:30 24 44 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Example 3 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 50:50 23 43 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Example 4 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 4.5 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 12 70:30 24 55 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Example 5 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 4.5 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 12 50:50 23 53 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Example 6 LiNi _0.85 Co _0.09 Mn _0.045 Al _0.015 O ₂ 4 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 15 70:30 28 46 Al-Si-Fe-Cu-Mn-Zn alloy ^{2 )} 12 2.4 Example 7 LiNi _0.75 Ti _0.125 Mg _0.125 O ₂ 5 LiNi _{0 . 75} Ti _{0 .125} Mg _0.125 O ₂ 18 70:30 23 63 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Example 8 LiNi _0.7 Co _0.2 Ti _0.05 Mg _0.05 O ₂ 5 LiNi _{0 . 7 Co 0 .2 Ti 0.05 Mg 0.05} O 2 18 70:30 23 63 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Comparative Example 1 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 0:100 25 48 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Comparative Example 2 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 30:70 24 47 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Comparative Example 3 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 4.5 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 12 30:70 24 55 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Comparative Example 4 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 4.5 LiNi _{0 . 6} Co _{0 .2} Mn _0.2 O ₂ 12 70:30 25 55 Al-Si-Fe-Cu alloy ^{1 )} 25 3.6 Comparative Example 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 70:30 24 44 Al-Si-Fe-Cu-Mn alloy ³⁾ 12 3.2 Comparative Example 6 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 70:30 24
(The electrode breaks during rolling, making it impossible to manufacture) 44 Al-Si-Fe-Cu alloy ^{1 )} 4 0.7 Comparative Example 7 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 70:30 40
58 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4 Comparative Example 8 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 5 LiNi _{0 . 8} Co _{0 .1} Mn _0.1 O ₂ 18 70:30 10
(The electrode breaks during rolling, making it impossible to manufacture) 45 Al-Si-Fe-Cu alloy ^{1 )} 12 2.4

In Table 1, the porosity and thickness of the positive electrode active material layers of * and ** are values obtained by measuring the porosity and thickness of any one positive electrode active material layer under the condition that the two positive electrode active material layers formed on both sides of the current collector are the same. to be.

In addition, in Table 1, the porosity of the positive electrode active material layer is the ratio of the volume occupied by the pores to the total volume of the positive electrode active material layer, and was measured using a mercury intrusion porosimeter, and the elongation was measured using the method of ISO 527-3. Thus, the change in length of the current collector was measured.

In addition, the current collector composition of 1) to 3) is as follows:

1) Composition of Al-Si-Fe-Cu-based alloy: Al=99.2% by weight, Si=0.3% by weight, Fe=0.4% by weight, Cu=0.1% by weight

2) Composition of Al-Si-Fe-Cu-Mn-Zn-based alloy: Al=99.2% by weight, Si=0.3% by weight, Fe=0.4% by weight, Cu=0.05% by weight, Mn=0.03% by weight, Zn= 0.02% by weight

3) Composition of Al-Si-Fe-Cu-Mn-based alloy: Al=98% by weight, Si=0.3% by weight, Fe=0.35% by weight, Cu=0.35% by weight, Mn=1% by weight

Manufacturing Example: Manufacturing of lithium secondary battery

96.3% by weight of graphite powder as a negative active material, 1.0% by weight of super-p as a conductive material, 1.5% by weight and 1.2% by weight of styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) as a binder, respectively, and in NMP as a solvent Added to prepare a composition for forming an anode active material layer. The prepared composition for forming a negative electrode active material layer was applied to a thin film of copper (Cu) which is a negative electrode current collector having a thickness of about 10 μm, dried, and then roll pressed to prepare a negative electrode.

LiPF ₆ was added to a non-aqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate as an electrolyte at a volume ratio of 30:70 to prepare a 1 M LiPF ₆ non-aqueous electrolyte.

A cell was manufactured by interposing a separator of porous polyethylene between the positive electrode prepared in Examples and Comparative Examples and the negative electrode prepared above, and injecting the prepared non-aqueous electrolyte solution.

Experimental Example 1

For the positive electrodes prepared in Examples 1 to 7 and Comparative Examples 1 to 5 and 7, the elongation was measured by the method of ISO 527-3, and the results are shown in Table 2 below.

Anode elongation (%) Example 1 0.78 Example 2 0.87 Example 3 0.90 Example 4 0.82 Example 5 0.90 Example 6 0.87 Example 7 0.92 Example 8 0.88 Comparative Example 1 1.28 Comparative Example 2 1.26 Comparative Example 3 1.23 Comparative Example 4 1.52 Comparative Example 5 1.45 Comparative Example 7 2.2

Experimental example 2

A nail-penetrating experiment was performed for lithium secondary batteries including the positive electrodes prepared in Examples 1 to 8 and Comparative Examples 1 to 5 and 7.

Specifically, each lithium secondary battery was completely charged to 4.2V, and the center of the battery was penetrated at a speed of 25 mm/s using a nail having a diameter of 5 mm and a tip angle of 45 degrees at 25°C. Hazard level and ignition were observed, and the results are shown in Table 3 below.

[Risk Assessment]

1: No effect. No loss of function

2: defects and damage occurred

-No leakage, no venting, no ignition or flame, no rupture and explosion, no exothermic reaction or thermal runaway. Irreversible battery damage occurs. Need repair

3: Leakage and mass change of less than 50% occur

-No branching, ignition or flame. No burst and explosion. Less than 50% weight loss of electrolyte (solvent + salt)

4: Branching and more than 50% mass change

-No ignition or flame. No burst and explosion. Weight loss of 50% or more of the weight of the electrolyte (solvent + salt) occurs

5: Ignite or spark

-No rupture and explosion (no flying parts)

6: rupture occurs

There is no explosion, but there is a flying part of the active mass

7: explosion occurred

Explosion (battery collapse)

Risk level Maximum temperature (℃) Fire or not Example 1 2 36 Unfired Example 2 2 38 Unfired Example 3 2 43 Unfired Example 4 2 41 Unfired Example 5 2 42 Unfired Example 6 2 51 Unfired Example 7 2 44 Unfired Example 8 2 46 Unfired Comparative Example 1 5 - Ignition Comparative Example 2 5 - Ignition Comparative Example 3 5 - Ignition Comparative Example 4 5 - Ignition Comparative Example 5 5 - Ignition Comparative Example 7 5 - Ignition

As a result of the experiment, all of the lithium secondary batteries including the positive electrodes prepared in Examples 1 to 8 and Comparative Examples 1 to 5 and 7 were completely penetrated. However, in the batteries of Examples 1 to 8, the internal short-circuit due to needle penetration hardly occurred, so that the increase in cell temperature was small, and as a result, no ignition occurred, whereas the batteries of Comparative Examples 1 to 5 and 7 had large internal short circuits. As a result, the temperature of the cell increased and eventually fired.

Claims (13)

Positive electrode current collector; And
And a positive electrode active material layer positioned on at least one surface of the positive electrode current collector,
The positive electrode current collector has an elongation of 1.6% to 3.0%,
The positive electrode active material layer includes at least 50% by weight of a particulate positive electrode active material having an average particle diameter (D ₅₀ ) of 3 μm to 6 μm based on the total weight of the positive electrode active material, and has a porosity of 17% to 32%.
The method of claim 1,
The positive electrode active material layer has an average particle diameter (D ₅₀ ) of 3 μm to 6 μm, 50% to 90% by weight, and an average particle diameter (D ₅₀ ) of more than 6 μm and 20 μm or less based on the total weight of the positive electrode active material. A positive electrode for a secondary battery containing 10% to 50% by weight of an assembled positive electrode active material.
The method of claim 2,
The fine and granulated positive electrode active material each independently comprises a lithium composite metal oxide represented by the following formula (1) A positive electrode for a secondary battery:
[Formula 1]
Li _α Ni _x1 Co _y1 M1 _z1 M2 _w1 O ₂
In Formula 1
M1 is at least one selected from the group consisting of Mn and Al,
M2 is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, And any one or two or more doping elements selected from the group consisting of Mo,
α, x1, y1, z1 and w1 are 0.95≤α≤1.05, 0.6≤x1<1, 0<y1≤0.4, 0<z1≤0.4, x1+y1+z1=1 and 0≤w1≤0.02.
The method of claim 1,
The positive electrode current collector has a thickness of 5 μm to 20 μm.
The method of claim 1,
The positive electrode current collector is a positive electrode for a secondary battery comprising an aluminum-based alloy.
The method of claim 5,
The aluminum-based alloy contains 0.1 to 0.8% by weight of Si, 0.1 to 0.8% by weight of Fe, 0.05 to 0.2% by weight of Cu, and the balance of aluminum, wherein the total amount of Si and Fe is 0.2 to 1.0% by weight based on the total weight of the alloy. % Of the positive electrode for secondary batteries.
The method of claim 5,
The aluminum-based alloy further comprises at least one metal element selected from the group consisting of Mn and Zn.
The method of claim 1,
The positive electrode for a secondary battery that the elongation of the positive electrode is 0.6% to 1.1%.
The method of claim 1,
The fine positive electrode active material is a positive electrode for a secondary battery comprising any one or two or more intercalation compounds of the compounds of Formulas 2a, 2b and 3 below:
[Formula 2a]
LiNi _1-x4 Ti _a4 Mg _b4 O ₂
(In Formula 2a, x4=a4+b4, and x4 is greater than 0 and less than 0.5)
[Formula 2b]
LiCo _1-x5 Ti _a5 Mg _b5 O ₂
(In Formula 2b, x5=a5+b5, and x5 is greater than 0 and less than 0.5)
[Formula 3]
LiNi _1-x3 Co _y3 M5 _z3 M6 _w3 O ₂
(In Formula 3, M5 includes any one or two or more selected from the group consisting of Ti and Zr, and M6 includes any one or two or more selected from the group consisting of Mg, Ca, Sr and Ba, and , x3=y3+z3+w3, x3 is greater than 0 and less than 0.5, y3 is greater than 0 and less than 0.5, z3 is greater than 0 and less than 0.15, w3 is greater than 0 and less than 0.15).
The method of claim 9,
The positive electrode for a secondary battery that the elongation of the positive electrode is 0.6% to 1.1%.
The method of claim 9,
The compound of Formula 2a is LiNi _0.9 Ti _0.05 Mg _0.05 O ₂ , LiNi _0.8 Ti _0.1 Mg _0.1 O ₂ , LiNi _0.75 Ti _0.125 Mg _0.125 O ₂ , LiNi _0.7 Ti _0.15 Mg _0.15 O ₂ and LiNi _0.75 Ti _0.15 Mg _0.10 O ₂ A cathode for a secondary battery that is selected from the group consisting of.
The method of claim 9,
The compound of Formula 3 is selected from the group consisting of LiNi _0.7 Co _0.1 Ti _0.1 Mg _0.1 O ₂ , LiNi _0.75 Co _0.15 Ti _0.05 Mg _0.05 O ₂ and LiNi _0.7 Co _0.2 Ti _0.05 Mg _0.05 O _{2 A} cathode for a secondary battery.
A lithium secondary battery comprising the positive electrode according to any one of claims 1 to 12.